diff mbox series

[01/20] futex: Move to kernel/futex/

Message ID 20210915141524.674661678@infradead.org
State Not Applicable
Headers show
Series futex: splitup and waitv syscall | expand

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dj/TryBot-apply_patch fail Patch failed to apply to master at the time it was sent

Commit Message

Peter Zijlstra Sept. 15, 2021, 2:07 p.m. UTC
In preparation for splitup..

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 MAINTAINERS           |    2 
 kernel/Makefile       |    2 
 kernel/futex.c        | 4272 --------------------------------------------------
 kernel/futex/Makefile |    3 
 kernel/futex/core.c   | 4272 ++++++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 4277 insertions(+), 4274 deletions(-)
diff mbox series

Patch

--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -7720,7 +7720,7 @@  F:	Documentation/locking/*futex*
 F:	include/asm-generic/futex.h
 F:	include/linux/futex.h
 F:	include/uapi/linux/futex.h
-F:	kernel/futex.c
+F:	kernel/futex/*
 F:	tools/perf/bench/futex*
 F:	tools/testing/selftests/futex/
 
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -59,7 +59,7 @@  obj-$(CONFIG_FREEZER) += freezer.o
 obj-$(CONFIG_PROFILING) += profile.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
 obj-y += time/
-obj-$(CONFIG_FUTEX) += futex.o
+obj-$(CONFIG_FUTEX) += futex/
 obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
 obj-$(CONFIG_SMP) += smp.o
 ifneq ($(CONFIG_SMP),y)
--- a/kernel/futex.c
+++ /dev/null
@@ -1,4272 +0,0 @@ 
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- *  Fast Userspace Mutexes (which I call "Futexes!").
- *  (C) Rusty Russell, IBM 2002
- *
- *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
- *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
- *
- *  Removed page pinning, fix privately mapped COW pages and other cleanups
- *  (C) Copyright 2003, 2004 Jamie Lokier
- *
- *  Robust futex support started by Ingo Molnar
- *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
- *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
- *
- *  PI-futex support started by Ingo Molnar and Thomas Gleixner
- *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
- *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
- *
- *  PRIVATE futexes by Eric Dumazet
- *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
- *
- *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
- *  Copyright (C) IBM Corporation, 2009
- *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
- *
- *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
- *  enough at me, Linus for the original (flawed) idea, Matthew
- *  Kirkwood for proof-of-concept implementation.
- *
- *  "The futexes are also cursed."
- *  "But they come in a choice of three flavours!"
- */
-#include <linux/compat.h>
-#include <linux/jhash.h>
-#include <linux/pagemap.h>
-#include <linux/syscalls.h>
-#include <linux/freezer.h>
-#include <linux/memblock.h>
-#include <linux/fault-inject.h>
-#include <linux/time_namespace.h>
-
-#include <asm/futex.h>
-
-#include "locking/rtmutex_common.h"
-
-/*
- * READ this before attempting to hack on futexes!
- *
- * Basic futex operation and ordering guarantees
- * =============================================
- *
- * The waiter reads the futex value in user space and calls
- * futex_wait(). This function computes the hash bucket and acquires
- * the hash bucket lock. After that it reads the futex user space value
- * again and verifies that the data has not changed. If it has not changed
- * it enqueues itself into the hash bucket, releases the hash bucket lock
- * and schedules.
- *
- * The waker side modifies the user space value of the futex and calls
- * futex_wake(). This function computes the hash bucket and acquires the
- * hash bucket lock. Then it looks for waiters on that futex in the hash
- * bucket and wakes them.
- *
- * In futex wake up scenarios where no tasks are blocked on a futex, taking
- * the hb spinlock can be avoided and simply return. In order for this
- * optimization to work, ordering guarantees must exist so that the waiter
- * being added to the list is acknowledged when the list is concurrently being
- * checked by the waker, avoiding scenarios like the following:
- *
- * CPU 0                               CPU 1
- * val = *futex;
- * sys_futex(WAIT, futex, val);
- *   futex_wait(futex, val);
- *   uval = *futex;
- *                                     *futex = newval;
- *                                     sys_futex(WAKE, futex);
- *                                       futex_wake(futex);
- *                                       if (queue_empty())
- *                                         return;
- *   if (uval == val)
- *      lock(hash_bucket(futex));
- *      queue();
- *     unlock(hash_bucket(futex));
- *     schedule();
- *
- * This would cause the waiter on CPU 0 to wait forever because it
- * missed the transition of the user space value from val to newval
- * and the waker did not find the waiter in the hash bucket queue.
- *
- * The correct serialization ensures that a waiter either observes
- * the changed user space value before blocking or is woken by a
- * concurrent waker:
- *
- * CPU 0                                 CPU 1
- * val = *futex;
- * sys_futex(WAIT, futex, val);
- *   futex_wait(futex, val);
- *
- *   waiters++; (a)
- *   smp_mb(); (A) <-- paired with -.
- *                                  |
- *   lock(hash_bucket(futex));      |
- *                                  |
- *   uval = *futex;                 |
- *                                  |        *futex = newval;
- *                                  |        sys_futex(WAKE, futex);
- *                                  |          futex_wake(futex);
- *                                  |
- *                                  `--------> smp_mb(); (B)
- *   if (uval == val)
- *     queue();
- *     unlock(hash_bucket(futex));
- *     schedule();                         if (waiters)
- *                                           lock(hash_bucket(futex));
- *   else                                    wake_waiters(futex);
- *     waiters--; (b)                        unlock(hash_bucket(futex));
- *
- * Where (A) orders the waiters increment and the futex value read through
- * atomic operations (see hb_waiters_inc) and where (B) orders the write
- * to futex and the waiters read (see hb_waiters_pending()).
- *
- * This yields the following case (where X:=waiters, Y:=futex):
- *
- *	X = Y = 0
- *
- *	w[X]=1		w[Y]=1
- *	MB		MB
- *	r[Y]=y		r[X]=x
- *
- * Which guarantees that x==0 && y==0 is impossible; which translates back into
- * the guarantee that we cannot both miss the futex variable change and the
- * enqueue.
- *
- * Note that a new waiter is accounted for in (a) even when it is possible that
- * the wait call can return error, in which case we backtrack from it in (b).
- * Refer to the comment in queue_lock().
- *
- * Similarly, in order to account for waiters being requeued on another
- * address we always increment the waiters for the destination bucket before
- * acquiring the lock. It then decrements them again  after releasing it -
- * the code that actually moves the futex(es) between hash buckets (requeue_futex)
- * will do the additional required waiter count housekeeping. This is done for
- * double_lock_hb() and double_unlock_hb(), respectively.
- */
-
-#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
-#define futex_cmpxchg_enabled 1
-#else
-static int  __read_mostly futex_cmpxchg_enabled;
-#endif
-
-/*
- * Futex flags used to encode options to functions and preserve them across
- * restarts.
- */
-#ifdef CONFIG_MMU
-# define FLAGS_SHARED		0x01
-#else
-/*
- * NOMMU does not have per process address space. Let the compiler optimize
- * code away.
- */
-# define FLAGS_SHARED		0x00
-#endif
-#define FLAGS_CLOCKRT		0x02
-#define FLAGS_HAS_TIMEOUT	0x04
-
-/*
- * Priority Inheritance state:
- */
-struct futex_pi_state {
-	/*
-	 * list of 'owned' pi_state instances - these have to be
-	 * cleaned up in do_exit() if the task exits prematurely:
-	 */
-	struct list_head list;
-
-	/*
-	 * The PI object:
-	 */
-	struct rt_mutex_base pi_mutex;
-
-	struct task_struct *owner;
-	refcount_t refcount;
-
-	union futex_key key;
-} __randomize_layout;
-
-/**
- * struct futex_q - The hashed futex queue entry, one per waiting task
- * @list:		priority-sorted list of tasks waiting on this futex
- * @task:		the task waiting on the futex
- * @lock_ptr:		the hash bucket lock
- * @key:		the key the futex is hashed on
- * @pi_state:		optional priority inheritance state
- * @rt_waiter:		rt_waiter storage for use with requeue_pi
- * @requeue_pi_key:	the requeue_pi target futex key
- * @bitset:		bitset for the optional bitmasked wakeup
- * @requeue_state:	State field for futex_requeue_pi()
- * @requeue_wait:	RCU wait for futex_requeue_pi() (RT only)
- *
- * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
- * we can wake only the relevant ones (hashed queues may be shared).
- *
- * A futex_q has a woken state, just like tasks have TASK_RUNNING.
- * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
- * The order of wakeup is always to make the first condition true, then
- * the second.
- *
- * PI futexes are typically woken before they are removed from the hash list via
- * the rt_mutex code. See unqueue_me_pi().
- */
-struct futex_q {
-	struct plist_node list;
-
-	struct task_struct *task;
-	spinlock_t *lock_ptr;
-	union futex_key key;
-	struct futex_pi_state *pi_state;
-	struct rt_mutex_waiter *rt_waiter;
-	union futex_key *requeue_pi_key;
-	u32 bitset;
-	atomic_t requeue_state;
-#ifdef CONFIG_PREEMPT_RT
-	struct rcuwait requeue_wait;
-#endif
-} __randomize_layout;
-
-/*
- * On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
- * underlying rtmutex. The task which is about to be requeued could have
- * just woken up (timeout, signal). After the wake up the task has to
- * acquire hash bucket lock, which is held by the requeue code.  As a task
- * can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking
- * and the hash bucket lock blocking would collide and corrupt state.
- *
- * On !PREEMPT_RT this is not a problem and everything could be serialized
- * on hash bucket lock, but aside of having the benefit of common code,
- * this allows to avoid doing the requeue when the task is already on the
- * way out and taking the hash bucket lock of the original uaddr1 when the
- * requeue has been completed.
- *
- * The following state transitions are valid:
- *
- * On the waiter side:
- *   Q_REQUEUE_PI_NONE		-> Q_REQUEUE_PI_IGNORE
- *   Q_REQUEUE_PI_IN_PROGRESS	-> Q_REQUEUE_PI_WAIT
- *
- * On the requeue side:
- *   Q_REQUEUE_PI_NONE		-> Q_REQUEUE_PI_INPROGRESS
- *   Q_REQUEUE_PI_IN_PROGRESS	-> Q_REQUEUE_PI_DONE/LOCKED
- *   Q_REQUEUE_PI_IN_PROGRESS	-> Q_REQUEUE_PI_NONE (requeue failed)
- *   Q_REQUEUE_PI_WAIT		-> Q_REQUEUE_PI_DONE/LOCKED
- *   Q_REQUEUE_PI_WAIT		-> Q_REQUEUE_PI_IGNORE (requeue failed)
- *
- * The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this
- * signals that the waiter is already on the way out. It also means that
- * the waiter is still on the 'wait' futex, i.e. uaddr1.
- *
- * The waiter side signals early wakeup to the requeue side either through
- * setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending
- * on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately
- * proceed to take the hash bucket lock of uaddr1. If it set state to WAIT,
- * which means the wakeup is interleaving with a requeue in progress it has
- * to wait for the requeue side to change the state. Either to DONE/LOCKED
- * or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex
- * and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by
- * the requeue side when the requeue attempt failed via deadlock detection
- * and therefore the waiter q is still on the uaddr1 futex.
- */
-enum {
-	Q_REQUEUE_PI_NONE		=  0,
-	Q_REQUEUE_PI_IGNORE,
-	Q_REQUEUE_PI_IN_PROGRESS,
-	Q_REQUEUE_PI_WAIT,
-	Q_REQUEUE_PI_DONE,
-	Q_REQUEUE_PI_LOCKED,
-};
-
-static const struct futex_q futex_q_init = {
-	/* list gets initialized in queue_me()*/
-	.key		= FUTEX_KEY_INIT,
-	.bitset		= FUTEX_BITSET_MATCH_ANY,
-	.requeue_state	= ATOMIC_INIT(Q_REQUEUE_PI_NONE),
-};
-
-/*
- * Hash buckets are shared by all the futex_keys that hash to the same
- * location.  Each key may have multiple futex_q structures, one for each task
- * waiting on a futex.
- */
-struct futex_hash_bucket {
-	atomic_t waiters;
-	spinlock_t lock;
-	struct plist_head chain;
-} ____cacheline_aligned_in_smp;
-
-/*
- * The base of the bucket array and its size are always used together
- * (after initialization only in hash_futex()), so ensure that they
- * reside in the same cacheline.
- */
-static struct {
-	struct futex_hash_bucket *queues;
-	unsigned long            hashsize;
-} __futex_data __read_mostly __aligned(2*sizeof(long));
-#define futex_queues   (__futex_data.queues)
-#define futex_hashsize (__futex_data.hashsize)
-
-
-/*
- * Fault injections for futexes.
- */
-#ifdef CONFIG_FAIL_FUTEX
-
-static struct {
-	struct fault_attr attr;
-
-	bool ignore_private;
-} fail_futex = {
-	.attr = FAULT_ATTR_INITIALIZER,
-	.ignore_private = false,
-};
-
-static int __init setup_fail_futex(char *str)
-{
-	return setup_fault_attr(&fail_futex.attr, str);
-}
-__setup("fail_futex=", setup_fail_futex);
-
-static bool should_fail_futex(bool fshared)
-{
-	if (fail_futex.ignore_private && !fshared)
-		return false;
-
-	return should_fail(&fail_futex.attr, 1);
-}
-
-#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
-
-static int __init fail_futex_debugfs(void)
-{
-	umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
-	struct dentry *dir;
-
-	dir = fault_create_debugfs_attr("fail_futex", NULL,
-					&fail_futex.attr);
-	if (IS_ERR(dir))
-		return PTR_ERR(dir);
-
-	debugfs_create_bool("ignore-private", mode, dir,
-			    &fail_futex.ignore_private);
-	return 0;
-}
-
-late_initcall(fail_futex_debugfs);
-
-#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
-
-#else
-static inline bool should_fail_futex(bool fshared)
-{
-	return false;
-}
-#endif /* CONFIG_FAIL_FUTEX */
-
-#ifdef CONFIG_COMPAT
-static void compat_exit_robust_list(struct task_struct *curr);
-#endif
-
-/*
- * Reflects a new waiter being added to the waitqueue.
- */
-static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
-	atomic_inc(&hb->waiters);
-	/*
-	 * Full barrier (A), see the ordering comment above.
-	 */
-	smp_mb__after_atomic();
-#endif
-}
-
-/*
- * Reflects a waiter being removed from the waitqueue by wakeup
- * paths.
- */
-static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
-	atomic_dec(&hb->waiters);
-#endif
-}
-
-static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
-{
-#ifdef CONFIG_SMP
-	/*
-	 * Full barrier (B), see the ordering comment above.
-	 */
-	smp_mb();
-	return atomic_read(&hb->waiters);
-#else
-	return 1;
-#endif
-}
-
-/**
- * hash_futex - Return the hash bucket in the global hash
- * @key:	Pointer to the futex key for which the hash is calculated
- *
- * We hash on the keys returned from get_futex_key (see below) and return the
- * corresponding hash bucket in the global hash.
- */
-static struct futex_hash_bucket *hash_futex(union futex_key *key)
-{
-	u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
-			  key->both.offset);
-
-	return &futex_queues[hash & (futex_hashsize - 1)];
-}
-
-
-/**
- * match_futex - Check whether two futex keys are equal
- * @key1:	Pointer to key1
- * @key2:	Pointer to key2
- *
- * Return 1 if two futex_keys are equal, 0 otherwise.
- */
-static inline int match_futex(union futex_key *key1, union futex_key *key2)
-{
-	return (key1 && key2
-		&& key1->both.word == key2->both.word
-		&& key1->both.ptr == key2->both.ptr
-		&& key1->both.offset == key2->both.offset);
-}
-
-enum futex_access {
-	FUTEX_READ,
-	FUTEX_WRITE
-};
-
-/**
- * futex_setup_timer - set up the sleeping hrtimer.
- * @time:	ptr to the given timeout value
- * @timeout:	the hrtimer_sleeper structure to be set up
- * @flags:	futex flags
- * @range_ns:	optional range in ns
- *
- * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
- *	   value given
- */
-static inline struct hrtimer_sleeper *
-futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
-		  int flags, u64 range_ns)
-{
-	if (!time)
-		return NULL;
-
-	hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
-				      CLOCK_REALTIME : CLOCK_MONOTONIC,
-				      HRTIMER_MODE_ABS);
-	/*
-	 * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
-	 * effectively the same as calling hrtimer_set_expires().
-	 */
-	hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
-
-	return timeout;
-}
-
-/*
- * Generate a machine wide unique identifier for this inode.
- *
- * This relies on u64 not wrapping in the life-time of the machine; which with
- * 1ns resolution means almost 585 years.
- *
- * This further relies on the fact that a well formed program will not unmap
- * the file while it has a (shared) futex waiting on it. This mapping will have
- * a file reference which pins the mount and inode.
- *
- * If for some reason an inode gets evicted and read back in again, it will get
- * a new sequence number and will _NOT_ match, even though it is the exact same
- * file.
- *
- * It is important that match_futex() will never have a false-positive, esp.
- * for PI futexes that can mess up the state. The above argues that false-negatives
- * are only possible for malformed programs.
- */
-static u64 get_inode_sequence_number(struct inode *inode)
-{
-	static atomic64_t i_seq;
-	u64 old;
-
-	/* Does the inode already have a sequence number? */
-	old = atomic64_read(&inode->i_sequence);
-	if (likely(old))
-		return old;
-
-	for (;;) {
-		u64 new = atomic64_add_return(1, &i_seq);
-		if (WARN_ON_ONCE(!new))
-			continue;
-
-		old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
-		if (old)
-			return old;
-		return new;
-	}
-}
-
-/**
- * get_futex_key() - Get parameters which are the keys for a futex
- * @uaddr:	virtual address of the futex
- * @fshared:	false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
- * @key:	address where result is stored.
- * @rw:		mapping needs to be read/write (values: FUTEX_READ,
- *              FUTEX_WRITE)
- *
- * Return: a negative error code or 0
- *
- * The key words are stored in @key on success.
- *
- * For shared mappings (when @fshared), the key is:
- *
- *   ( inode->i_sequence, page->index, offset_within_page )
- *
- * [ also see get_inode_sequence_number() ]
- *
- * For private mappings (or when !@fshared), the key is:
- *
- *   ( current->mm, address, 0 )
- *
- * This allows (cross process, where applicable) identification of the futex
- * without keeping the page pinned for the duration of the FUTEX_WAIT.
- *
- * lock_page() might sleep, the caller should not hold a spinlock.
- */
-static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
-			 enum futex_access rw)
-{
-	unsigned long address = (unsigned long)uaddr;
-	struct mm_struct *mm = current->mm;
-	struct page *page, *tail;
-	struct address_space *mapping;
-	int err, ro = 0;
-
-	/*
-	 * The futex address must be "naturally" aligned.
-	 */
-	key->both.offset = address % PAGE_SIZE;
-	if (unlikely((address % sizeof(u32)) != 0))
-		return -EINVAL;
-	address -= key->both.offset;
-
-	if (unlikely(!access_ok(uaddr, sizeof(u32))))
-		return -EFAULT;
-
-	if (unlikely(should_fail_futex(fshared)))
-		return -EFAULT;
-
-	/*
-	 * PROCESS_PRIVATE futexes are fast.
-	 * As the mm cannot disappear under us and the 'key' only needs
-	 * virtual address, we dont even have to find the underlying vma.
-	 * Note : We do have to check 'uaddr' is a valid user address,
-	 *        but access_ok() should be faster than find_vma()
-	 */
-	if (!fshared) {
-		key->private.mm = mm;
-		key->private.address = address;
-		return 0;
-	}
-
-again:
-	/* Ignore any VERIFY_READ mapping (futex common case) */
-	if (unlikely(should_fail_futex(true)))
-		return -EFAULT;
-
-	err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
-	/*
-	 * If write access is not required (eg. FUTEX_WAIT), try
-	 * and get read-only access.
-	 */
-	if (err == -EFAULT && rw == FUTEX_READ) {
-		err = get_user_pages_fast(address, 1, 0, &page);
-		ro = 1;
-	}
-	if (err < 0)
-		return err;
-	else
-		err = 0;
-
-	/*
-	 * The treatment of mapping from this point on is critical. The page
-	 * lock protects many things but in this context the page lock
-	 * stabilizes mapping, prevents inode freeing in the shared
-	 * file-backed region case and guards against movement to swap cache.
-	 *
-	 * Strictly speaking the page lock is not needed in all cases being
-	 * considered here and page lock forces unnecessarily serialization
-	 * From this point on, mapping will be re-verified if necessary and
-	 * page lock will be acquired only if it is unavoidable
-	 *
-	 * Mapping checks require the head page for any compound page so the
-	 * head page and mapping is looked up now. For anonymous pages, it
-	 * does not matter if the page splits in the future as the key is
-	 * based on the address. For filesystem-backed pages, the tail is
-	 * required as the index of the page determines the key. For
-	 * base pages, there is no tail page and tail == page.
-	 */
-	tail = page;
-	page = compound_head(page);
-	mapping = READ_ONCE(page->mapping);
-
-	/*
-	 * If page->mapping is NULL, then it cannot be a PageAnon
-	 * page; but it might be the ZERO_PAGE or in the gate area or
-	 * in a special mapping (all cases which we are happy to fail);
-	 * or it may have been a good file page when get_user_pages_fast
-	 * found it, but truncated or holepunched or subjected to
-	 * invalidate_complete_page2 before we got the page lock (also
-	 * cases which we are happy to fail).  And we hold a reference,
-	 * so refcount care in invalidate_complete_page's remove_mapping
-	 * prevents drop_caches from setting mapping to NULL beneath us.
-	 *
-	 * The case we do have to guard against is when memory pressure made
-	 * shmem_writepage move it from filecache to swapcache beneath us:
-	 * an unlikely race, but we do need to retry for page->mapping.
-	 */
-	if (unlikely(!mapping)) {
-		int shmem_swizzled;
-
-		/*
-		 * Page lock is required to identify which special case above
-		 * applies. If this is really a shmem page then the page lock
-		 * will prevent unexpected transitions.
-		 */
-		lock_page(page);
-		shmem_swizzled = PageSwapCache(page) || page->mapping;
-		unlock_page(page);
-		put_page(page);
-
-		if (shmem_swizzled)
-			goto again;
-
-		return -EFAULT;
-	}
-
-	/*
-	 * Private mappings are handled in a simple way.
-	 *
-	 * If the futex key is stored on an anonymous page, then the associated
-	 * object is the mm which is implicitly pinned by the calling process.
-	 *
-	 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
-	 * it's a read-only handle, it's expected that futexes attach to
-	 * the object not the particular process.
-	 */
-	if (PageAnon(page)) {
-		/*
-		 * A RO anonymous page will never change and thus doesn't make
-		 * sense for futex operations.
-		 */
-		if (unlikely(should_fail_futex(true)) || ro) {
-			err = -EFAULT;
-			goto out;
-		}
-
-		key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
-		key->private.mm = mm;
-		key->private.address = address;
-
-	} else {
-		struct inode *inode;
-
-		/*
-		 * The associated futex object in this case is the inode and
-		 * the page->mapping must be traversed. Ordinarily this should
-		 * be stabilised under page lock but it's not strictly
-		 * necessary in this case as we just want to pin the inode, not
-		 * update the radix tree or anything like that.
-		 *
-		 * The RCU read lock is taken as the inode is finally freed
-		 * under RCU. If the mapping still matches expectations then the
-		 * mapping->host can be safely accessed as being a valid inode.
-		 */
-		rcu_read_lock();
-
-		if (READ_ONCE(page->mapping) != mapping) {
-			rcu_read_unlock();
-			put_page(page);
-
-			goto again;
-		}
-
-		inode = READ_ONCE(mapping->host);
-		if (!inode) {
-			rcu_read_unlock();
-			put_page(page);
-
-			goto again;
-		}
-
-		key->both.offset |= FUT_OFF_INODE; /* inode-based key */
-		key->shared.i_seq = get_inode_sequence_number(inode);
-		key->shared.pgoff = page_to_pgoff(tail);
-		rcu_read_unlock();
-	}
-
-out:
-	put_page(page);
-	return err;
-}
-
-/**
- * fault_in_user_writeable() - Fault in user address and verify RW access
- * @uaddr:	pointer to faulting user space address
- *
- * Slow path to fixup the fault we just took in the atomic write
- * access to @uaddr.
- *
- * We have no generic implementation of a non-destructive write to the
- * user address. We know that we faulted in the atomic pagefault
- * disabled section so we can as well avoid the #PF overhead by
- * calling get_user_pages() right away.
- */
-static int fault_in_user_writeable(u32 __user *uaddr)
-{
-	struct mm_struct *mm = current->mm;
-	int ret;
-
-	mmap_read_lock(mm);
-	ret = fixup_user_fault(mm, (unsigned long)uaddr,
-			       FAULT_FLAG_WRITE, NULL);
-	mmap_read_unlock(mm);
-
-	return ret < 0 ? ret : 0;
-}
-
-/**
- * futex_top_waiter() - Return the highest priority waiter on a futex
- * @hb:		the hash bucket the futex_q's reside in
- * @key:	the futex key (to distinguish it from other futex futex_q's)
- *
- * Must be called with the hb lock held.
- */
-static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
-					union futex_key *key)
-{
-	struct futex_q *this;
-
-	plist_for_each_entry(this, &hb->chain, list) {
-		if (match_futex(&this->key, key))
-			return this;
-	}
-	return NULL;
-}
-
-static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
-				      u32 uval, u32 newval)
-{
-	int ret;
-
-	pagefault_disable();
-	ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
-	pagefault_enable();
-
-	return ret;
-}
-
-static int get_futex_value_locked(u32 *dest, u32 __user *from)
-{
-	int ret;
-
-	pagefault_disable();
-	ret = __get_user(*dest, from);
-	pagefault_enable();
-
-	return ret ? -EFAULT : 0;
-}
-
-
-/*
- * PI code:
- */
-static int refill_pi_state_cache(void)
-{
-	struct futex_pi_state *pi_state;
-
-	if (likely(current->pi_state_cache))
-		return 0;
-
-	pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
-
-	if (!pi_state)
-		return -ENOMEM;
-
-	INIT_LIST_HEAD(&pi_state->list);
-	/* pi_mutex gets initialized later */
-	pi_state->owner = NULL;
-	refcount_set(&pi_state->refcount, 1);
-	pi_state->key = FUTEX_KEY_INIT;
-
-	current->pi_state_cache = pi_state;
-
-	return 0;
-}
-
-static struct futex_pi_state *alloc_pi_state(void)
-{
-	struct futex_pi_state *pi_state = current->pi_state_cache;
-
-	WARN_ON(!pi_state);
-	current->pi_state_cache = NULL;
-
-	return pi_state;
-}
-
-static void pi_state_update_owner(struct futex_pi_state *pi_state,
-				  struct task_struct *new_owner)
-{
-	struct task_struct *old_owner = pi_state->owner;
-
-	lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
-
-	if (old_owner) {
-		raw_spin_lock(&old_owner->pi_lock);
-		WARN_ON(list_empty(&pi_state->list));
-		list_del_init(&pi_state->list);
-		raw_spin_unlock(&old_owner->pi_lock);
-	}
-
-	if (new_owner) {
-		raw_spin_lock(&new_owner->pi_lock);
-		WARN_ON(!list_empty(&pi_state->list));
-		list_add(&pi_state->list, &new_owner->pi_state_list);
-		pi_state->owner = new_owner;
-		raw_spin_unlock(&new_owner->pi_lock);
-	}
-}
-
-static void get_pi_state(struct futex_pi_state *pi_state)
-{
-	WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
-}
-
-/*
- * Drops a reference to the pi_state object and frees or caches it
- * when the last reference is gone.
- */
-static void put_pi_state(struct futex_pi_state *pi_state)
-{
-	if (!pi_state)
-		return;
-
-	if (!refcount_dec_and_test(&pi_state->refcount))
-		return;
-
-	/*
-	 * If pi_state->owner is NULL, the owner is most probably dying
-	 * and has cleaned up the pi_state already
-	 */
-	if (pi_state->owner) {
-		unsigned long flags;
-
-		raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
-		pi_state_update_owner(pi_state, NULL);
-		rt_mutex_proxy_unlock(&pi_state->pi_mutex);
-		raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
-	}
-
-	if (current->pi_state_cache) {
-		kfree(pi_state);
-	} else {
-		/*
-		 * pi_state->list is already empty.
-		 * clear pi_state->owner.
-		 * refcount is at 0 - put it back to 1.
-		 */
-		pi_state->owner = NULL;
-		refcount_set(&pi_state->refcount, 1);
-		current->pi_state_cache = pi_state;
-	}
-}
-
-#ifdef CONFIG_FUTEX_PI
-
-/*
- * This task is holding PI mutexes at exit time => bad.
- * Kernel cleans up PI-state, but userspace is likely hosed.
- * (Robust-futex cleanup is separate and might save the day for userspace.)
- */
-static void exit_pi_state_list(struct task_struct *curr)
-{
-	struct list_head *next, *head = &curr->pi_state_list;
-	struct futex_pi_state *pi_state;
-	struct futex_hash_bucket *hb;
-	union futex_key key = FUTEX_KEY_INIT;
-
-	if (!futex_cmpxchg_enabled)
-		return;
-	/*
-	 * We are a ZOMBIE and nobody can enqueue itself on
-	 * pi_state_list anymore, but we have to be careful
-	 * versus waiters unqueueing themselves:
-	 */
-	raw_spin_lock_irq(&curr->pi_lock);
-	while (!list_empty(head)) {
-		next = head->next;
-		pi_state = list_entry(next, struct futex_pi_state, list);
-		key = pi_state->key;
-		hb = hash_futex(&key);
-
-		/*
-		 * We can race against put_pi_state() removing itself from the
-		 * list (a waiter going away). put_pi_state() will first
-		 * decrement the reference count and then modify the list, so
-		 * its possible to see the list entry but fail this reference
-		 * acquire.
-		 *
-		 * In that case; drop the locks to let put_pi_state() make
-		 * progress and retry the loop.
-		 */
-		if (!refcount_inc_not_zero(&pi_state->refcount)) {
-			raw_spin_unlock_irq(&curr->pi_lock);
-			cpu_relax();
-			raw_spin_lock_irq(&curr->pi_lock);
-			continue;
-		}
-		raw_spin_unlock_irq(&curr->pi_lock);
-
-		spin_lock(&hb->lock);
-		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-		raw_spin_lock(&curr->pi_lock);
-		/*
-		 * We dropped the pi-lock, so re-check whether this
-		 * task still owns the PI-state:
-		 */
-		if (head->next != next) {
-			/* retain curr->pi_lock for the loop invariant */
-			raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
-			spin_unlock(&hb->lock);
-			put_pi_state(pi_state);
-			continue;
-		}
-
-		WARN_ON(pi_state->owner != curr);
-		WARN_ON(list_empty(&pi_state->list));
-		list_del_init(&pi_state->list);
-		pi_state->owner = NULL;
-
-		raw_spin_unlock(&curr->pi_lock);
-		raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-		spin_unlock(&hb->lock);
-
-		rt_mutex_futex_unlock(&pi_state->pi_mutex);
-		put_pi_state(pi_state);
-
-		raw_spin_lock_irq(&curr->pi_lock);
-	}
-	raw_spin_unlock_irq(&curr->pi_lock);
-}
-#else
-static inline void exit_pi_state_list(struct task_struct *curr) { }
-#endif
-
-/*
- * We need to check the following states:
- *
- *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
- *
- * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
- * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
- *
- * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
- *
- * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
- * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
- *
- * [6]  Found  | Found    | task      | 0         | 1      | Valid
- *
- * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
- *
- * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
- * [9]  Found  | Found    | task      | 0         | 0      | Invalid
- * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
- *
- * [1]	Indicates that the kernel can acquire the futex atomically. We
- *	came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
- *
- * [2]	Valid, if TID does not belong to a kernel thread. If no matching
- *      thread is found then it indicates that the owner TID has died.
- *
- * [3]	Invalid. The waiter is queued on a non PI futex
- *
- * [4]	Valid state after exit_robust_list(), which sets the user space
- *	value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
- *
- * [5]	The user space value got manipulated between exit_robust_list()
- *	and exit_pi_state_list()
- *
- * [6]	Valid state after exit_pi_state_list() which sets the new owner in
- *	the pi_state but cannot access the user space value.
- *
- * [7]	pi_state->owner can only be NULL when the OWNER_DIED bit is set.
- *
- * [8]	Owner and user space value match
- *
- * [9]	There is no transient state which sets the user space TID to 0
- *	except exit_robust_list(), but this is indicated by the
- *	FUTEX_OWNER_DIED bit. See [4]
- *
- * [10] There is no transient state which leaves owner and user space
- *	TID out of sync. Except one error case where the kernel is denied
- *	write access to the user address, see fixup_pi_state_owner().
- *
- *
- * Serialization and lifetime rules:
- *
- * hb->lock:
- *
- *	hb -> futex_q, relation
- *	futex_q -> pi_state, relation
- *
- *	(cannot be raw because hb can contain arbitrary amount
- *	 of futex_q's)
- *
- * pi_mutex->wait_lock:
- *
- *	{uval, pi_state}
- *
- *	(and pi_mutex 'obviously')
- *
- * p->pi_lock:
- *
- *	p->pi_state_list -> pi_state->list, relation
- *	pi_mutex->owner -> pi_state->owner, relation
- *
- * pi_state->refcount:
- *
- *	pi_state lifetime
- *
- *
- * Lock order:
- *
- *   hb->lock
- *     pi_mutex->wait_lock
- *       p->pi_lock
- *
- */
-
-/*
- * Validate that the existing waiter has a pi_state and sanity check
- * the pi_state against the user space value. If correct, attach to
- * it.
- */
-static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
-			      struct futex_pi_state *pi_state,
-			      struct futex_pi_state **ps)
-{
-	pid_t pid = uval & FUTEX_TID_MASK;
-	u32 uval2;
-	int ret;
-
-	/*
-	 * Userspace might have messed up non-PI and PI futexes [3]
-	 */
-	if (unlikely(!pi_state))
-		return -EINVAL;
-
-	/*
-	 * We get here with hb->lock held, and having found a
-	 * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
-	 * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
-	 * which in turn means that futex_lock_pi() still has a reference on
-	 * our pi_state.
-	 *
-	 * The waiter holding a reference on @pi_state also protects against
-	 * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
-	 * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
-	 * free pi_state before we can take a reference ourselves.
-	 */
-	WARN_ON(!refcount_read(&pi_state->refcount));
-
-	/*
-	 * Now that we have a pi_state, we can acquire wait_lock
-	 * and do the state validation.
-	 */
-	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
-	/*
-	 * Since {uval, pi_state} is serialized by wait_lock, and our current
-	 * uval was read without holding it, it can have changed. Verify it
-	 * still is what we expect it to be, otherwise retry the entire
-	 * operation.
-	 */
-	if (get_futex_value_locked(&uval2, uaddr))
-		goto out_efault;
-
-	if (uval != uval2)
-		goto out_eagain;
-
-	/*
-	 * Handle the owner died case:
-	 */
-	if (uval & FUTEX_OWNER_DIED) {
-		/*
-		 * exit_pi_state_list sets owner to NULL and wakes the
-		 * topmost waiter. The task which acquires the
-		 * pi_state->rt_mutex will fixup owner.
-		 */
-		if (!pi_state->owner) {
-			/*
-			 * No pi state owner, but the user space TID
-			 * is not 0. Inconsistent state. [5]
-			 */
-			if (pid)
-				goto out_einval;
-			/*
-			 * Take a ref on the state and return success. [4]
-			 */
-			goto out_attach;
-		}
-
-		/*
-		 * If TID is 0, then either the dying owner has not
-		 * yet executed exit_pi_state_list() or some waiter
-		 * acquired the rtmutex in the pi state, but did not
-		 * yet fixup the TID in user space.
-		 *
-		 * Take a ref on the state and return success. [6]
-		 */
-		if (!pid)
-			goto out_attach;
-	} else {
-		/*
-		 * If the owner died bit is not set, then the pi_state
-		 * must have an owner. [7]
-		 */
-		if (!pi_state->owner)
-			goto out_einval;
-	}
-
-	/*
-	 * Bail out if user space manipulated the futex value. If pi
-	 * state exists then the owner TID must be the same as the
-	 * user space TID. [9/10]
-	 */
-	if (pid != task_pid_vnr(pi_state->owner))
-		goto out_einval;
-
-out_attach:
-	get_pi_state(pi_state);
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-	*ps = pi_state;
-	return 0;
-
-out_einval:
-	ret = -EINVAL;
-	goto out_error;
-
-out_eagain:
-	ret = -EAGAIN;
-	goto out_error;
-
-out_efault:
-	ret = -EFAULT;
-	goto out_error;
-
-out_error:
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-	return ret;
-}
-
-/**
- * wait_for_owner_exiting - Block until the owner has exited
- * @ret: owner's current futex lock status
- * @exiting:	Pointer to the exiting task
- *
- * Caller must hold a refcount on @exiting.
- */
-static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
-{
-	if (ret != -EBUSY) {
-		WARN_ON_ONCE(exiting);
-		return;
-	}
-
-	if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
-		return;
-
-	mutex_lock(&exiting->futex_exit_mutex);
-	/*
-	 * No point in doing state checking here. If the waiter got here
-	 * while the task was in exec()->exec_futex_release() then it can
-	 * have any FUTEX_STATE_* value when the waiter has acquired the
-	 * mutex. OK, if running, EXITING or DEAD if it reached exit()
-	 * already. Highly unlikely and not a problem. Just one more round
-	 * through the futex maze.
-	 */
-	mutex_unlock(&exiting->futex_exit_mutex);
-
-	put_task_struct(exiting);
-}
-
-static int handle_exit_race(u32 __user *uaddr, u32 uval,
-			    struct task_struct *tsk)
-{
-	u32 uval2;
-
-	/*
-	 * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
-	 * caller that the alleged owner is busy.
-	 */
-	if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
-		return -EBUSY;
-
-	/*
-	 * Reread the user space value to handle the following situation:
-	 *
-	 * CPU0				CPU1
-	 *
-	 * sys_exit()			sys_futex()
-	 *  do_exit()			 futex_lock_pi()
-	 *                                futex_lock_pi_atomic()
-	 *   exit_signals(tsk)		    No waiters:
-	 *    tsk->flags |= PF_EXITING;	    *uaddr == 0x00000PID
-	 *  mm_release(tsk)		    Set waiter bit
-	 *   exit_robust_list(tsk) {	    *uaddr = 0x80000PID;
-	 *      Set owner died		    attach_to_pi_owner() {
-	 *    *uaddr = 0xC0000000;	     tsk = get_task(PID);
-	 *   }				     if (!tsk->flags & PF_EXITING) {
-	 *  ...				       attach();
-	 *  tsk->futex_state =               } else {
-	 *	FUTEX_STATE_DEAD;              if (tsk->futex_state !=
-	 *					  FUTEX_STATE_DEAD)
-	 *				         return -EAGAIN;
-	 *				       return -ESRCH; <--- FAIL
-	 *				     }
-	 *
-	 * Returning ESRCH unconditionally is wrong here because the
-	 * user space value has been changed by the exiting task.
-	 *
-	 * The same logic applies to the case where the exiting task is
-	 * already gone.
-	 */
-	if (get_futex_value_locked(&uval2, uaddr))
-		return -EFAULT;
-
-	/* If the user space value has changed, try again. */
-	if (uval2 != uval)
-		return -EAGAIN;
-
-	/*
-	 * The exiting task did not have a robust list, the robust list was
-	 * corrupted or the user space value in *uaddr is simply bogus.
-	 * Give up and tell user space.
-	 */
-	return -ESRCH;
-}
-
-static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
-				 struct futex_pi_state **ps)
-{
-	/*
-	 * No existing pi state. First waiter. [2]
-	 *
-	 * This creates pi_state, we have hb->lock held, this means nothing can
-	 * observe this state, wait_lock is irrelevant.
-	 */
-	struct futex_pi_state *pi_state = alloc_pi_state();
-
-	/*
-	 * Initialize the pi_mutex in locked state and make @p
-	 * the owner of it:
-	 */
-	rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
-
-	/* Store the key for possible exit cleanups: */
-	pi_state->key = *key;
-
-	WARN_ON(!list_empty(&pi_state->list));
-	list_add(&pi_state->list, &p->pi_state_list);
-	/*
-	 * Assignment without holding pi_state->pi_mutex.wait_lock is safe
-	 * because there is no concurrency as the object is not published yet.
-	 */
-	pi_state->owner = p;
-
-	*ps = pi_state;
-}
-/*
- * Lookup the task for the TID provided from user space and attach to
- * it after doing proper sanity checks.
- */
-static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
-			      struct futex_pi_state **ps,
-			      struct task_struct **exiting)
-{
-	pid_t pid = uval & FUTEX_TID_MASK;
-	struct task_struct *p;
-
-	/*
-	 * We are the first waiter - try to look up the real owner and attach
-	 * the new pi_state to it, but bail out when TID = 0 [1]
-	 *
-	 * The !pid check is paranoid. None of the call sites should end up
-	 * with pid == 0, but better safe than sorry. Let the caller retry
-	 */
-	if (!pid)
-		return -EAGAIN;
-	p = find_get_task_by_vpid(pid);
-	if (!p)
-		return handle_exit_race(uaddr, uval, NULL);
-
-	if (unlikely(p->flags & PF_KTHREAD)) {
-		put_task_struct(p);
-		return -EPERM;
-	}
-
-	/*
-	 * We need to look at the task state to figure out, whether the
-	 * task is exiting. To protect against the change of the task state
-	 * in futex_exit_release(), we do this protected by p->pi_lock:
-	 */
-	raw_spin_lock_irq(&p->pi_lock);
-	if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
-		/*
-		 * The task is on the way out. When the futex state is
-		 * FUTEX_STATE_DEAD, we know that the task has finished
-		 * the cleanup:
-		 */
-		int ret = handle_exit_race(uaddr, uval, p);
-
-		raw_spin_unlock_irq(&p->pi_lock);
-		/*
-		 * If the owner task is between FUTEX_STATE_EXITING and
-		 * FUTEX_STATE_DEAD then store the task pointer and keep
-		 * the reference on the task struct. The calling code will
-		 * drop all locks, wait for the task to reach
-		 * FUTEX_STATE_DEAD and then drop the refcount. This is
-		 * required to prevent a live lock when the current task
-		 * preempted the exiting task between the two states.
-		 */
-		if (ret == -EBUSY)
-			*exiting = p;
-		else
-			put_task_struct(p);
-		return ret;
-	}
-
-	__attach_to_pi_owner(p, key, ps);
-	raw_spin_unlock_irq(&p->pi_lock);
-
-	put_task_struct(p);
-
-	return 0;
-}
-
-static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
-{
-	int err;
-	u32 curval;
-
-	if (unlikely(should_fail_futex(true)))
-		return -EFAULT;
-
-	err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
-	if (unlikely(err))
-		return err;
-
-	/* If user space value changed, let the caller retry */
-	return curval != uval ? -EAGAIN : 0;
-}
-
-/**
- * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
- * @uaddr:		the pi futex user address
- * @hb:			the pi futex hash bucket
- * @key:		the futex key associated with uaddr and hb
- * @ps:			the pi_state pointer where we store the result of the
- *			lookup
- * @task:		the task to perform the atomic lock work for.  This will
- *			be "current" except in the case of requeue pi.
- * @exiting:		Pointer to store the task pointer of the owner task
- *			which is in the middle of exiting
- * @set_waiters:	force setting the FUTEX_WAITERS bit (1) or not (0)
- *
- * Return:
- *  -  0 - ready to wait;
- *  -  1 - acquired the lock;
- *  - <0 - error
- *
- * The hb->lock must be held by the caller.
- *
- * @exiting is only set when the return value is -EBUSY. If so, this holds
- * a refcount on the exiting task on return and the caller needs to drop it
- * after waiting for the exit to complete.
- */
-static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
-				union futex_key *key,
-				struct futex_pi_state **ps,
-				struct task_struct *task,
-				struct task_struct **exiting,
-				int set_waiters)
-{
-	u32 uval, newval, vpid = task_pid_vnr(task);
-	struct futex_q *top_waiter;
-	int ret;
-
-	/*
-	 * Read the user space value first so we can validate a few
-	 * things before proceeding further.
-	 */
-	if (get_futex_value_locked(&uval, uaddr))
-		return -EFAULT;
-
-	if (unlikely(should_fail_futex(true)))
-		return -EFAULT;
-
-	/*
-	 * Detect deadlocks.
-	 */
-	if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
-		return -EDEADLK;
-
-	if ((unlikely(should_fail_futex(true))))
-		return -EDEADLK;
-
-	/*
-	 * Lookup existing state first. If it exists, try to attach to
-	 * its pi_state.
-	 */
-	top_waiter = futex_top_waiter(hb, key);
-	if (top_waiter)
-		return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
-
-	/*
-	 * No waiter and user TID is 0. We are here because the
-	 * waiters or the owner died bit is set or called from
-	 * requeue_cmp_pi or for whatever reason something took the
-	 * syscall.
-	 */
-	if (!(uval & FUTEX_TID_MASK)) {
-		/*
-		 * We take over the futex. No other waiters and the user space
-		 * TID is 0. We preserve the owner died bit.
-		 */
-		newval = uval & FUTEX_OWNER_DIED;
-		newval |= vpid;
-
-		/* The futex requeue_pi code can enforce the waiters bit */
-		if (set_waiters)
-			newval |= FUTEX_WAITERS;
-
-		ret = lock_pi_update_atomic(uaddr, uval, newval);
-		if (ret)
-			return ret;
-
-		/*
-		 * If the waiter bit was requested the caller also needs PI
-		 * state attached to the new owner of the user space futex.
-		 *
-		 * @task is guaranteed to be alive and it cannot be exiting
-		 * because it is either sleeping or waiting in
-		 * futex_requeue_pi_wakeup_sync().
-		 *
-		 * No need to do the full attach_to_pi_owner() exercise
-		 * because @task is known and valid.
-		 */
-		if (set_waiters) {
-			raw_spin_lock_irq(&task->pi_lock);
-			__attach_to_pi_owner(task, key, ps);
-			raw_spin_unlock_irq(&task->pi_lock);
-		}
-		return 1;
-	}
-
-	/*
-	 * First waiter. Set the waiters bit before attaching ourself to
-	 * the owner. If owner tries to unlock, it will be forced into
-	 * the kernel and blocked on hb->lock.
-	 */
-	newval = uval | FUTEX_WAITERS;
-	ret = lock_pi_update_atomic(uaddr, uval, newval);
-	if (ret)
-		return ret;
-	/*
-	 * If the update of the user space value succeeded, we try to
-	 * attach to the owner. If that fails, no harm done, we only
-	 * set the FUTEX_WAITERS bit in the user space variable.
-	 */
-	return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
-}
-
-/**
- * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
- * @q:	The futex_q to unqueue
- *
- * The q->lock_ptr must not be NULL and must be held by the caller.
- */
-static void __unqueue_futex(struct futex_q *q)
-{
-	struct futex_hash_bucket *hb;
-
-	if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
-		return;
-	lockdep_assert_held(q->lock_ptr);
-
-	hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
-	plist_del(&q->list, &hb->chain);
-	hb_waiters_dec(hb);
-}
-
-/*
- * The hash bucket lock must be held when this is called.
- * Afterwards, the futex_q must not be accessed. Callers
- * must ensure to later call wake_up_q() for the actual
- * wakeups to occur.
- */
-static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
-{
-	struct task_struct *p = q->task;
-
-	if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
-		return;
-
-	get_task_struct(p);
-	__unqueue_futex(q);
-	/*
-	 * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
-	 * is written, without taking any locks. This is possible in the event
-	 * of a spurious wakeup, for example. A memory barrier is required here
-	 * to prevent the following store to lock_ptr from getting ahead of the
-	 * plist_del in __unqueue_futex().
-	 */
-	smp_store_release(&q->lock_ptr, NULL);
-
-	/*
-	 * Queue the task for later wakeup for after we've released
-	 * the hb->lock.
-	 */
-	wake_q_add_safe(wake_q, p);
-}
-
-/*
- * Caller must hold a reference on @pi_state.
- */
-static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
-{
-	struct rt_mutex_waiter *top_waiter;
-	struct task_struct *new_owner;
-	bool postunlock = false;
-	DEFINE_RT_WAKE_Q(wqh);
-	u32 curval, newval;
-	int ret = 0;
-
-	top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
-	if (WARN_ON_ONCE(!top_waiter)) {
-		/*
-		 * As per the comment in futex_unlock_pi() this should not happen.
-		 *
-		 * When this happens, give up our locks and try again, giving
-		 * the futex_lock_pi() instance time to complete, either by
-		 * waiting on the rtmutex or removing itself from the futex
-		 * queue.
-		 */
-		ret = -EAGAIN;
-		goto out_unlock;
-	}
-
-	new_owner = top_waiter->task;
-
-	/*
-	 * We pass it to the next owner. The WAITERS bit is always kept
-	 * enabled while there is PI state around. We cleanup the owner
-	 * died bit, because we are the owner.
-	 */
-	newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
-
-	if (unlikely(should_fail_futex(true))) {
-		ret = -EFAULT;
-		goto out_unlock;
-	}
-
-	ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
-	if (!ret && (curval != uval)) {
-		/*
-		 * If a unconditional UNLOCK_PI operation (user space did not
-		 * try the TID->0 transition) raced with a waiter setting the
-		 * FUTEX_WAITERS flag between get_user() and locking the hash
-		 * bucket lock, retry the operation.
-		 */
-		if ((FUTEX_TID_MASK & curval) == uval)
-			ret = -EAGAIN;
-		else
-			ret = -EINVAL;
-	}
-
-	if (!ret) {
-		/*
-		 * This is a point of no return; once we modified the uval
-		 * there is no going back and subsequent operations must
-		 * not fail.
-		 */
-		pi_state_update_owner(pi_state, new_owner);
-		postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
-	}
-
-out_unlock:
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-
-	if (postunlock)
-		rt_mutex_postunlock(&wqh);
-
-	return ret;
-}
-
-/*
- * Express the locking dependencies for lockdep:
- */
-static inline void
-double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
-{
-	if (hb1 <= hb2) {
-		spin_lock(&hb1->lock);
-		if (hb1 < hb2)
-			spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
-	} else { /* hb1 > hb2 */
-		spin_lock(&hb2->lock);
-		spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
-	}
-}
-
-static inline void
-double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
-{
-	spin_unlock(&hb1->lock);
-	if (hb1 != hb2)
-		spin_unlock(&hb2->lock);
-}
-
-/*
- * Wake up waiters matching bitset queued on this futex (uaddr).
- */
-static int
-futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
-{
-	struct futex_hash_bucket *hb;
-	struct futex_q *this, *next;
-	union futex_key key = FUTEX_KEY_INIT;
-	int ret;
-	DEFINE_WAKE_Q(wake_q);
-
-	if (!bitset)
-		return -EINVAL;
-
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
-	if (unlikely(ret != 0))
-		return ret;
-
-	hb = hash_futex(&key);
-
-	/* Make sure we really have tasks to wakeup */
-	if (!hb_waiters_pending(hb))
-		return ret;
-
-	spin_lock(&hb->lock);
-
-	plist_for_each_entry_safe(this, next, &hb->chain, list) {
-		if (match_futex (&this->key, &key)) {
-			if (this->pi_state || this->rt_waiter) {
-				ret = -EINVAL;
-				break;
-			}
-
-			/* Check if one of the bits is set in both bitsets */
-			if (!(this->bitset & bitset))
-				continue;
-
-			mark_wake_futex(&wake_q, this);
-			if (++ret >= nr_wake)
-				break;
-		}
-	}
-
-	spin_unlock(&hb->lock);
-	wake_up_q(&wake_q);
-	return ret;
-}
-
-static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
-{
-	unsigned int op =	  (encoded_op & 0x70000000) >> 28;
-	unsigned int cmp =	  (encoded_op & 0x0f000000) >> 24;
-	int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
-	int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
-	int oldval, ret;
-
-	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
-		if (oparg < 0 || oparg > 31) {
-			char comm[sizeof(current->comm)];
-			/*
-			 * kill this print and return -EINVAL when userspace
-			 * is sane again
-			 */
-			pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
-					get_task_comm(comm, current), oparg);
-			oparg &= 31;
-		}
-		oparg = 1 << oparg;
-	}
-
-	pagefault_disable();
-	ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
-	pagefault_enable();
-	if (ret)
-		return ret;
-
-	switch (cmp) {
-	case FUTEX_OP_CMP_EQ:
-		return oldval == cmparg;
-	case FUTEX_OP_CMP_NE:
-		return oldval != cmparg;
-	case FUTEX_OP_CMP_LT:
-		return oldval < cmparg;
-	case FUTEX_OP_CMP_GE:
-		return oldval >= cmparg;
-	case FUTEX_OP_CMP_LE:
-		return oldval <= cmparg;
-	case FUTEX_OP_CMP_GT:
-		return oldval > cmparg;
-	default:
-		return -ENOSYS;
-	}
-}
-
-/*
- * Wake up all waiters hashed on the physical page that is mapped
- * to this virtual address:
- */
-static int
-futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
-	      int nr_wake, int nr_wake2, int op)
-{
-	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
-	struct futex_hash_bucket *hb1, *hb2;
-	struct futex_q *this, *next;
-	int ret, op_ret;
-	DEFINE_WAKE_Q(wake_q);
-
-retry:
-	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
-	if (unlikely(ret != 0))
-		return ret;
-	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
-	if (unlikely(ret != 0))
-		return ret;
-
-	hb1 = hash_futex(&key1);
-	hb2 = hash_futex(&key2);
-
-retry_private:
-	double_lock_hb(hb1, hb2);
-	op_ret = futex_atomic_op_inuser(op, uaddr2);
-	if (unlikely(op_ret < 0)) {
-		double_unlock_hb(hb1, hb2);
-
-		if (!IS_ENABLED(CONFIG_MMU) ||
-		    unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
-			/*
-			 * we don't get EFAULT from MMU faults if we don't have
-			 * an MMU, but we might get them from range checking
-			 */
-			ret = op_ret;
-			return ret;
-		}
-
-		if (op_ret == -EFAULT) {
-			ret = fault_in_user_writeable(uaddr2);
-			if (ret)
-				return ret;
-		}
-
-		cond_resched();
-		if (!(flags & FLAGS_SHARED))
-			goto retry_private;
-		goto retry;
-	}
-
-	plist_for_each_entry_safe(this, next, &hb1->chain, list) {
-		if (match_futex (&this->key, &key1)) {
-			if (this->pi_state || this->rt_waiter) {
-				ret = -EINVAL;
-				goto out_unlock;
-			}
-			mark_wake_futex(&wake_q, this);
-			if (++ret >= nr_wake)
-				break;
-		}
-	}
-
-	if (op_ret > 0) {
-		op_ret = 0;
-		plist_for_each_entry_safe(this, next, &hb2->chain, list) {
-			if (match_futex (&this->key, &key2)) {
-				if (this->pi_state || this->rt_waiter) {
-					ret = -EINVAL;
-					goto out_unlock;
-				}
-				mark_wake_futex(&wake_q, this);
-				if (++op_ret >= nr_wake2)
-					break;
-			}
-		}
-		ret += op_ret;
-	}
-
-out_unlock:
-	double_unlock_hb(hb1, hb2);
-	wake_up_q(&wake_q);
-	return ret;
-}
-
-/**
- * requeue_futex() - Requeue a futex_q from one hb to another
- * @q:		the futex_q to requeue
- * @hb1:	the source hash_bucket
- * @hb2:	the target hash_bucket
- * @key2:	the new key for the requeued futex_q
- */
-static inline
-void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
-		   struct futex_hash_bucket *hb2, union futex_key *key2)
-{
-
-	/*
-	 * If key1 and key2 hash to the same bucket, no need to
-	 * requeue.
-	 */
-	if (likely(&hb1->chain != &hb2->chain)) {
-		plist_del(&q->list, &hb1->chain);
-		hb_waiters_dec(hb1);
-		hb_waiters_inc(hb2);
-		plist_add(&q->list, &hb2->chain);
-		q->lock_ptr = &hb2->lock;
-	}
-	q->key = *key2;
-}
-
-static inline bool futex_requeue_pi_prepare(struct futex_q *q,
-					    struct futex_pi_state *pi_state)
-{
-	int old, new;
-
-	/*
-	 * Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has
-	 * already set Q_REQUEUE_PI_IGNORE to signal that requeue should
-	 * ignore the waiter.
-	 */
-	old = atomic_read_acquire(&q->requeue_state);
-	do {
-		if (old == Q_REQUEUE_PI_IGNORE)
-			return false;
-
-		/*
-		 * futex_proxy_trylock_atomic() might have set it to
-		 * IN_PROGRESS and a interleaved early wake to WAIT.
-		 *
-		 * It was considered to have an extra state for that
-		 * trylock, but that would just add more conditionals
-		 * all over the place for a dubious value.
-		 */
-		if (old != Q_REQUEUE_PI_NONE)
-			break;
-
-		new = Q_REQUEUE_PI_IN_PROGRESS;
-	} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
-
-	q->pi_state = pi_state;
-	return true;
-}
-
-static inline void futex_requeue_pi_complete(struct futex_q *q, int locked)
-{
-	int old, new;
-
-	old = atomic_read_acquire(&q->requeue_state);
-	do {
-		if (old == Q_REQUEUE_PI_IGNORE)
-			return;
-
-		if (locked >= 0) {
-			/* Requeue succeeded. Set DONE or LOCKED */
-			WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS &&
-				     old != Q_REQUEUE_PI_WAIT);
-			new = Q_REQUEUE_PI_DONE + locked;
-		} else if (old == Q_REQUEUE_PI_IN_PROGRESS) {
-			/* Deadlock, no early wakeup interleave */
-			new = Q_REQUEUE_PI_NONE;
-		} else {
-			/* Deadlock, early wakeup interleave. */
-			WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT);
-			new = Q_REQUEUE_PI_IGNORE;
-		}
-	} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
-
-#ifdef CONFIG_PREEMPT_RT
-	/* If the waiter interleaved with the requeue let it know */
-	if (unlikely(old == Q_REQUEUE_PI_WAIT))
-		rcuwait_wake_up(&q->requeue_wait);
-#endif
-}
-
-static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
-{
-	int old, new;
-
-	old = atomic_read_acquire(&q->requeue_state);
-	do {
-		/* Is requeue done already? */
-		if (old >= Q_REQUEUE_PI_DONE)
-			return old;
-
-		/*
-		 * If not done, then tell the requeue code to either ignore
-		 * the waiter or to wake it up once the requeue is done.
-		 */
-		new = Q_REQUEUE_PI_WAIT;
-		if (old == Q_REQUEUE_PI_NONE)
-			new = Q_REQUEUE_PI_IGNORE;
-	} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
-
-	/* If the requeue was in progress, wait for it to complete */
-	if (old == Q_REQUEUE_PI_IN_PROGRESS) {
-#ifdef CONFIG_PREEMPT_RT
-		rcuwait_wait_event(&q->requeue_wait,
-				   atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT,
-				   TASK_UNINTERRUPTIBLE);
-#else
-		(void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT);
-#endif
-	}
-
-	/*
-	 * Requeue is now either prohibited or complete. Reread state
-	 * because during the wait above it might have changed. Nothing
-	 * will modify q->requeue_state after this point.
-	 */
-	return atomic_read(&q->requeue_state);
-}
-
-/**
- * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
- * @q:		the futex_q
- * @key:	the key of the requeue target futex
- * @hb:		the hash_bucket of the requeue target futex
- *
- * During futex_requeue, with requeue_pi=1, it is possible to acquire the
- * target futex if it is uncontended or via a lock steal.
- *
- * 1) Set @q::key to the requeue target futex key so the waiter can detect
- *    the wakeup on the right futex.
- *
- * 2) Dequeue @q from the hash bucket.
- *
- * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock
- *    acquisition.
- *
- * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that
- *    the waiter has to fixup the pi state.
- *
- * 5) Complete the requeue state so the waiter can make progress. After
- *    this point the waiter task can return from the syscall immediately in
- *    case that the pi state does not have to be fixed up.
- *
- * 6) Wake the waiter task.
- *
- * Must be called with both q->lock_ptr and hb->lock held.
- */
-static inline
-void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
-			   struct futex_hash_bucket *hb)
-{
-	q->key = *key;
-
-	__unqueue_futex(q);
-
-	WARN_ON(!q->rt_waiter);
-	q->rt_waiter = NULL;
-
-	q->lock_ptr = &hb->lock;
-
-	/* Signal locked state to the waiter */
-	futex_requeue_pi_complete(q, 1);
-	wake_up_state(q->task, TASK_NORMAL);
-}
-
-/**
- * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
- * @pifutex:		the user address of the to futex
- * @hb1:		the from futex hash bucket, must be locked by the caller
- * @hb2:		the to futex hash bucket, must be locked by the caller
- * @key1:		the from futex key
- * @key2:		the to futex key
- * @ps:			address to store the pi_state pointer
- * @exiting:		Pointer to store the task pointer of the owner task
- *			which is in the middle of exiting
- * @set_waiters:	force setting the FUTEX_WAITERS bit (1) or not (0)
- *
- * Try and get the lock on behalf of the top waiter if we can do it atomically.
- * Wake the top waiter if we succeed.  If the caller specified set_waiters,
- * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
- * hb1 and hb2 must be held by the caller.
- *
- * @exiting is only set when the return value is -EBUSY. If so, this holds
- * a refcount on the exiting task on return and the caller needs to drop it
- * after waiting for the exit to complete.
- *
- * Return:
- *  -  0 - failed to acquire the lock atomically;
- *  - >0 - acquired the lock, return value is vpid of the top_waiter
- *  - <0 - error
- */
-static int
-futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
-			   struct futex_hash_bucket *hb2, union futex_key *key1,
-			   union futex_key *key2, struct futex_pi_state **ps,
-			   struct task_struct **exiting, int set_waiters)
-{
-	struct futex_q *top_waiter = NULL;
-	u32 curval;
-	int ret;
-
-	if (get_futex_value_locked(&curval, pifutex))
-		return -EFAULT;
-
-	if (unlikely(should_fail_futex(true)))
-		return -EFAULT;
-
-	/*
-	 * Find the top_waiter and determine if there are additional waiters.
-	 * If the caller intends to requeue more than 1 waiter to pifutex,
-	 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
-	 * as we have means to handle the possible fault.  If not, don't set
-	 * the bit unnecessarily as it will force the subsequent unlock to enter
-	 * the kernel.
-	 */
-	top_waiter = futex_top_waiter(hb1, key1);
-
-	/* There are no waiters, nothing for us to do. */
-	if (!top_waiter)
-		return 0;
-
-	/*
-	 * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
-	 * and waiting on the 'waitqueue' futex which is always !PI.
-	 */
-	if (!top_waiter->rt_waiter || top_waiter->pi_state)
-		return -EINVAL;
-
-	/* Ensure we requeue to the expected futex. */
-	if (!match_futex(top_waiter->requeue_pi_key, key2))
-		return -EINVAL;
-
-	/* Ensure that this does not race against an early wakeup */
-	if (!futex_requeue_pi_prepare(top_waiter, NULL))
-		return -EAGAIN;
-
-	/*
-	 * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
-	 * in the contended case or if @set_waiters is true.
-	 *
-	 * In the contended case PI state is attached to the lock owner. If
-	 * the user space lock can be acquired then PI state is attached to
-	 * the new owner (@top_waiter->task) when @set_waiters is true.
-	 */
-	ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
-				   exiting, set_waiters);
-	if (ret == 1) {
-		/*
-		 * Lock was acquired in user space and PI state was
-		 * attached to @top_waiter->task. That means state is fully
-		 * consistent and the waiter can return to user space
-		 * immediately after the wakeup.
-		 */
-		requeue_pi_wake_futex(top_waiter, key2, hb2);
-	} else if (ret < 0) {
-		/* Rewind top_waiter::requeue_state */
-		futex_requeue_pi_complete(top_waiter, ret);
-	} else {
-		/*
-		 * futex_lock_pi_atomic() did not acquire the user space
-		 * futex, but managed to establish the proxy lock and pi
-		 * state. top_waiter::requeue_state cannot be fixed up here
-		 * because the waiter is not enqueued on the rtmutex
-		 * yet. This is handled at the callsite depending on the
-		 * result of rt_mutex_start_proxy_lock() which is
-		 * guaranteed to be reached with this function returning 0.
-		 */
-	}
-	return ret;
-}
-
-/**
- * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
- * @uaddr1:	source futex user address
- * @flags:	futex flags (FLAGS_SHARED, etc.)
- * @uaddr2:	target futex user address
- * @nr_wake:	number of waiters to wake (must be 1 for requeue_pi)
- * @nr_requeue:	number of waiters to requeue (0-INT_MAX)
- * @cmpval:	@uaddr1 expected value (or %NULL)
- * @requeue_pi:	if we are attempting to requeue from a non-pi futex to a
- *		pi futex (pi to pi requeue is not supported)
- *
- * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
- * uaddr2 atomically on behalf of the top waiter.
- *
- * Return:
- *  - >=0 - on success, the number of tasks requeued or woken;
- *  -  <0 - on error
- */
-static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
-			 u32 __user *uaddr2, int nr_wake, int nr_requeue,
-			 u32 *cmpval, int requeue_pi)
-{
-	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
-	int task_count = 0, ret;
-	struct futex_pi_state *pi_state = NULL;
-	struct futex_hash_bucket *hb1, *hb2;
-	struct futex_q *this, *next;
-	DEFINE_WAKE_Q(wake_q);
-
-	if (nr_wake < 0 || nr_requeue < 0)
-		return -EINVAL;
-
-	/*
-	 * When PI not supported: return -ENOSYS if requeue_pi is true,
-	 * consequently the compiler knows requeue_pi is always false past
-	 * this point which will optimize away all the conditional code
-	 * further down.
-	 */
-	if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
-		return -ENOSYS;
-
-	if (requeue_pi) {
-		/*
-		 * Requeue PI only works on two distinct uaddrs. This
-		 * check is only valid for private futexes. See below.
-		 */
-		if (uaddr1 == uaddr2)
-			return -EINVAL;
-
-		/*
-		 * futex_requeue() allows the caller to define the number
-		 * of waiters to wake up via the @nr_wake argument. With
-		 * REQUEUE_PI, waking up more than one waiter is creating
-		 * more problems than it solves. Waking up a waiter makes
-		 * only sense if the PI futex @uaddr2 is uncontended as
-		 * this allows the requeue code to acquire the futex
-		 * @uaddr2 before waking the waiter. The waiter can then
-		 * return to user space without further action. A secondary
-		 * wakeup would just make the futex_wait_requeue_pi()
-		 * handling more complex, because that code would have to
-		 * look up pi_state and do more or less all the handling
-		 * which the requeue code has to do for the to be requeued
-		 * waiters. So restrict the number of waiters to wake to
-		 * one, and only wake it up when the PI futex is
-		 * uncontended. Otherwise requeue it and let the unlock of
-		 * the PI futex handle the wakeup.
-		 *
-		 * All REQUEUE_PI users, e.g. pthread_cond_signal() and
-		 * pthread_cond_broadcast() must use nr_wake=1.
-		 */
-		if (nr_wake != 1)
-			return -EINVAL;
-
-		/*
-		 * requeue_pi requires a pi_state, try to allocate it now
-		 * without any locks in case it fails.
-		 */
-		if (refill_pi_state_cache())
-			return -ENOMEM;
-	}
-
-retry:
-	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
-	if (unlikely(ret != 0))
-		return ret;
-	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
-			    requeue_pi ? FUTEX_WRITE : FUTEX_READ);
-	if (unlikely(ret != 0))
-		return ret;
-
-	/*
-	 * The check above which compares uaddrs is not sufficient for
-	 * shared futexes. We need to compare the keys:
-	 */
-	if (requeue_pi && match_futex(&key1, &key2))
-		return -EINVAL;
-
-	hb1 = hash_futex(&key1);
-	hb2 = hash_futex(&key2);
-
-retry_private:
-	hb_waiters_inc(hb2);
-	double_lock_hb(hb1, hb2);
-
-	if (likely(cmpval != NULL)) {
-		u32 curval;
-
-		ret = get_futex_value_locked(&curval, uaddr1);
-
-		if (unlikely(ret)) {
-			double_unlock_hb(hb1, hb2);
-			hb_waiters_dec(hb2);
-
-			ret = get_user(curval, uaddr1);
-			if (ret)
-				return ret;
-
-			if (!(flags & FLAGS_SHARED))
-				goto retry_private;
-
-			goto retry;
-		}
-		if (curval != *cmpval) {
-			ret = -EAGAIN;
-			goto out_unlock;
-		}
-	}
-
-	if (requeue_pi) {
-		struct task_struct *exiting = NULL;
-
-		/*
-		 * Attempt to acquire uaddr2 and wake the top waiter. If we
-		 * intend to requeue waiters, force setting the FUTEX_WAITERS
-		 * bit.  We force this here where we are able to easily handle
-		 * faults rather in the requeue loop below.
-		 *
-		 * Updates topwaiter::requeue_state if a top waiter exists.
-		 */
-		ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
-						 &key2, &pi_state,
-						 &exiting, nr_requeue);
-
-		/*
-		 * At this point the top_waiter has either taken uaddr2 or
-		 * is waiting on it. In both cases pi_state has been
-		 * established and an initial refcount on it. In case of an
-		 * error there's nothing.
-		 *
-		 * The top waiter's requeue_state is up to date:
-		 *
-		 *  - If the lock was acquired atomically (ret == 1), then
-		 *    the state is Q_REQUEUE_PI_LOCKED.
-		 *
-		 *    The top waiter has been dequeued and woken up and can
-		 *    return to user space immediately. The kernel/user
-		 *    space state is consistent. In case that there must be
-		 *    more waiters requeued the WAITERS bit in the user
-		 *    space futex is set so the top waiter task has to go
-		 *    into the syscall slowpath to unlock the futex. This
-		 *    will block until this requeue operation has been
-		 *    completed and the hash bucket locks have been
-		 *    dropped.
-		 *
-		 *  - If the trylock failed with an error (ret < 0) then
-		 *    the state is either Q_REQUEUE_PI_NONE, i.e. "nothing
-		 *    happened", or Q_REQUEUE_PI_IGNORE when there was an
-		 *    interleaved early wakeup.
-		 *
-		 *  - If the trylock did not succeed (ret == 0) then the
-		 *    state is either Q_REQUEUE_PI_IN_PROGRESS or
-		 *    Q_REQUEUE_PI_WAIT if an early wakeup interleaved.
-		 *    This will be cleaned up in the loop below, which
-		 *    cannot fail because futex_proxy_trylock_atomic() did
-		 *    the same sanity checks for requeue_pi as the loop
-		 *    below does.
-		 */
-		switch (ret) {
-		case 0:
-			/* We hold a reference on the pi state. */
-			break;
-
-		case 1:
-			/*
-			 * futex_proxy_trylock_atomic() acquired the user space
-			 * futex. Adjust task_count.
-			 */
-			task_count++;
-			ret = 0;
-			break;
-
-		/*
-		 * If the above failed, then pi_state is NULL and
-		 * waiter::requeue_state is correct.
-		 */
-		case -EFAULT:
-			double_unlock_hb(hb1, hb2);
-			hb_waiters_dec(hb2);
-			ret = fault_in_user_writeable(uaddr2);
-			if (!ret)
-				goto retry;
-			return ret;
-		case -EBUSY:
-		case -EAGAIN:
-			/*
-			 * Two reasons for this:
-			 * - EBUSY: Owner is exiting and we just wait for the
-			 *   exit to complete.
-			 * - EAGAIN: The user space value changed.
-			 */
-			double_unlock_hb(hb1, hb2);
-			hb_waiters_dec(hb2);
-			/*
-			 * Handle the case where the owner is in the middle of
-			 * exiting. Wait for the exit to complete otherwise
-			 * this task might loop forever, aka. live lock.
-			 */
-			wait_for_owner_exiting(ret, exiting);
-			cond_resched();
-			goto retry;
-		default:
-			goto out_unlock;
-		}
-	}
-
-	plist_for_each_entry_safe(this, next, &hb1->chain, list) {
-		if (task_count - nr_wake >= nr_requeue)
-			break;
-
-		if (!match_futex(&this->key, &key1))
-			continue;
-
-		/*
-		 * FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always
-		 * be paired with each other and no other futex ops.
-		 *
-		 * We should never be requeueing a futex_q with a pi_state,
-		 * which is awaiting a futex_unlock_pi().
-		 */
-		if ((requeue_pi && !this->rt_waiter) ||
-		    (!requeue_pi && this->rt_waiter) ||
-		    this->pi_state) {
-			ret = -EINVAL;
-			break;
-		}
-
-		/* Plain futexes just wake or requeue and are done */
-		if (!requeue_pi) {
-			if (++task_count <= nr_wake)
-				mark_wake_futex(&wake_q, this);
-			else
-				requeue_futex(this, hb1, hb2, &key2);
-			continue;
-		}
-
-		/* Ensure we requeue to the expected futex for requeue_pi. */
-		if (!match_futex(this->requeue_pi_key, &key2)) {
-			ret = -EINVAL;
-			break;
-		}
-
-		/*
-		 * Requeue nr_requeue waiters and possibly one more in the case
-		 * of requeue_pi if we couldn't acquire the lock atomically.
-		 *
-		 * Prepare the waiter to take the rt_mutex. Take a refcount
-		 * on the pi_state and store the pointer in the futex_q
-		 * object of the waiter.
-		 */
-		get_pi_state(pi_state);
-
-		/* Don't requeue when the waiter is already on the way out. */
-		if (!futex_requeue_pi_prepare(this, pi_state)) {
-			/*
-			 * Early woken waiter signaled that it is on the
-			 * way out. Drop the pi_state reference and try the
-			 * next waiter. @this->pi_state is still NULL.
-			 */
-			put_pi_state(pi_state);
-			continue;
-		}
-
-		ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
-						this->rt_waiter,
-						this->task);
-
-		if (ret == 1) {
-			/*
-			 * We got the lock. We do neither drop the refcount
-			 * on pi_state nor clear this->pi_state because the
-			 * waiter needs the pi_state for cleaning up the
-			 * user space value. It will drop the refcount
-			 * after doing so. this::requeue_state is updated
-			 * in the wakeup as well.
-			 */
-			requeue_pi_wake_futex(this, &key2, hb2);
-			task_count++;
-		} else if (!ret) {
-			/* Waiter is queued, move it to hb2 */
-			requeue_futex(this, hb1, hb2, &key2);
-			futex_requeue_pi_complete(this, 0);
-			task_count++;
-		} else {
-			/*
-			 * rt_mutex_start_proxy_lock() detected a potential
-			 * deadlock when we tried to queue that waiter.
-			 * Drop the pi_state reference which we took above
-			 * and remove the pointer to the state from the
-			 * waiters futex_q object.
-			 */
-			this->pi_state = NULL;
-			put_pi_state(pi_state);
-			futex_requeue_pi_complete(this, ret);
-			/*
-			 * We stop queueing more waiters and let user space
-			 * deal with the mess.
-			 */
-			break;
-		}
-	}
-
-	/*
-	 * We took an extra initial reference to the pi_state in
-	 * futex_proxy_trylock_atomic(). We need to drop it here again.
-	 */
-	put_pi_state(pi_state);
-
-out_unlock:
-	double_unlock_hb(hb1, hb2);
-	wake_up_q(&wake_q);
-	hb_waiters_dec(hb2);
-	return ret ? ret : task_count;
-}
-
-/* The key must be already stored in q->key. */
-static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
-	__acquires(&hb->lock)
-{
-	struct futex_hash_bucket *hb;
-
-	hb = hash_futex(&q->key);
-
-	/*
-	 * Increment the counter before taking the lock so that
-	 * a potential waker won't miss a to-be-slept task that is
-	 * waiting for the spinlock. This is safe as all queue_lock()
-	 * users end up calling queue_me(). Similarly, for housekeeping,
-	 * decrement the counter at queue_unlock() when some error has
-	 * occurred and we don't end up adding the task to the list.
-	 */
-	hb_waiters_inc(hb); /* implies smp_mb(); (A) */
-
-	q->lock_ptr = &hb->lock;
-
-	spin_lock(&hb->lock);
-	return hb;
-}
-
-static inline void
-queue_unlock(struct futex_hash_bucket *hb)
-	__releases(&hb->lock)
-{
-	spin_unlock(&hb->lock);
-	hb_waiters_dec(hb);
-}
-
-static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
-{
-	int prio;
-
-	/*
-	 * The priority used to register this element is
-	 * - either the real thread-priority for the real-time threads
-	 * (i.e. threads with a priority lower than MAX_RT_PRIO)
-	 * - or MAX_RT_PRIO for non-RT threads.
-	 * Thus, all RT-threads are woken first in priority order, and
-	 * the others are woken last, in FIFO order.
-	 */
-	prio = min(current->normal_prio, MAX_RT_PRIO);
-
-	plist_node_init(&q->list, prio);
-	plist_add(&q->list, &hb->chain);
-	q->task = current;
-}
-
-/**
- * queue_me() - Enqueue the futex_q on the futex_hash_bucket
- * @q:	The futex_q to enqueue
- * @hb:	The destination hash bucket
- *
- * The hb->lock must be held by the caller, and is released here. A call to
- * queue_me() is typically paired with exactly one call to unqueue_me().  The
- * exceptions involve the PI related operations, which may use unqueue_me_pi()
- * or nothing if the unqueue is done as part of the wake process and the unqueue
- * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
- * an example).
- */
-static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
-	__releases(&hb->lock)
-{
-	__queue_me(q, hb);
-	spin_unlock(&hb->lock);
-}
-
-/**
- * unqueue_me() - Remove the futex_q from its futex_hash_bucket
- * @q:	The futex_q to unqueue
- *
- * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
- * be paired with exactly one earlier call to queue_me().
- *
- * Return:
- *  - 1 - if the futex_q was still queued (and we removed unqueued it);
- *  - 0 - if the futex_q was already removed by the waking thread
- */
-static int unqueue_me(struct futex_q *q)
-{
-	spinlock_t *lock_ptr;
-	int ret = 0;
-
-	/* In the common case we don't take the spinlock, which is nice. */
-retry:
-	/*
-	 * q->lock_ptr can change between this read and the following spin_lock.
-	 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
-	 * optimizing lock_ptr out of the logic below.
-	 */
-	lock_ptr = READ_ONCE(q->lock_ptr);
-	if (lock_ptr != NULL) {
-		spin_lock(lock_ptr);
-		/*
-		 * q->lock_ptr can change between reading it and
-		 * spin_lock(), causing us to take the wrong lock.  This
-		 * corrects the race condition.
-		 *
-		 * Reasoning goes like this: if we have the wrong lock,
-		 * q->lock_ptr must have changed (maybe several times)
-		 * between reading it and the spin_lock().  It can
-		 * change again after the spin_lock() but only if it was
-		 * already changed before the spin_lock().  It cannot,
-		 * however, change back to the original value.  Therefore
-		 * we can detect whether we acquired the correct lock.
-		 */
-		if (unlikely(lock_ptr != q->lock_ptr)) {
-			spin_unlock(lock_ptr);
-			goto retry;
-		}
-		__unqueue_futex(q);
-
-		BUG_ON(q->pi_state);
-
-		spin_unlock(lock_ptr);
-		ret = 1;
-	}
-
-	return ret;
-}
-
-/*
- * PI futexes can not be requeued and must remove themselves from the
- * hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
- */
-static void unqueue_me_pi(struct futex_q *q)
-{
-	__unqueue_futex(q);
-
-	BUG_ON(!q->pi_state);
-	put_pi_state(q->pi_state);
-	q->pi_state = NULL;
-}
-
-static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
-				  struct task_struct *argowner)
-{
-	struct futex_pi_state *pi_state = q->pi_state;
-	struct task_struct *oldowner, *newowner;
-	u32 uval, curval, newval, newtid;
-	int err = 0;
-
-	oldowner = pi_state->owner;
-
-	/*
-	 * We are here because either:
-	 *
-	 *  - we stole the lock and pi_state->owner needs updating to reflect
-	 *    that (@argowner == current),
-	 *
-	 * or:
-	 *
-	 *  - someone stole our lock and we need to fix things to point to the
-	 *    new owner (@argowner == NULL).
-	 *
-	 * Either way, we have to replace the TID in the user space variable.
-	 * This must be atomic as we have to preserve the owner died bit here.
-	 *
-	 * Note: We write the user space value _before_ changing the pi_state
-	 * because we can fault here. Imagine swapped out pages or a fork
-	 * that marked all the anonymous memory readonly for cow.
-	 *
-	 * Modifying pi_state _before_ the user space value would leave the
-	 * pi_state in an inconsistent state when we fault here, because we
-	 * need to drop the locks to handle the fault. This might be observed
-	 * in the PID checks when attaching to PI state .
-	 */
-retry:
-	if (!argowner) {
-		if (oldowner != current) {
-			/*
-			 * We raced against a concurrent self; things are
-			 * already fixed up. Nothing to do.
-			 */
-			return 0;
-		}
-
-		if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
-			/* We got the lock. pi_state is correct. Tell caller. */
-			return 1;
-		}
-
-		/*
-		 * The trylock just failed, so either there is an owner or
-		 * there is a higher priority waiter than this one.
-		 */
-		newowner = rt_mutex_owner(&pi_state->pi_mutex);
-		/*
-		 * If the higher priority waiter has not yet taken over the
-		 * rtmutex then newowner is NULL. We can't return here with
-		 * that state because it's inconsistent vs. the user space
-		 * state. So drop the locks and try again. It's a valid
-		 * situation and not any different from the other retry
-		 * conditions.
-		 */
-		if (unlikely(!newowner)) {
-			err = -EAGAIN;
-			goto handle_err;
-		}
-	} else {
-		WARN_ON_ONCE(argowner != current);
-		if (oldowner == current) {
-			/*
-			 * We raced against a concurrent self; things are
-			 * already fixed up. Nothing to do.
-			 */
-			return 1;
-		}
-		newowner = argowner;
-	}
-
-	newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
-	/* Owner died? */
-	if (!pi_state->owner)
-		newtid |= FUTEX_OWNER_DIED;
-
-	err = get_futex_value_locked(&uval, uaddr);
-	if (err)
-		goto handle_err;
-
-	for (;;) {
-		newval = (uval & FUTEX_OWNER_DIED) | newtid;
-
-		err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
-		if (err)
-			goto handle_err;
-
-		if (curval == uval)
-			break;
-		uval = curval;
-	}
-
-	/*
-	 * We fixed up user space. Now we need to fix the pi_state
-	 * itself.
-	 */
-	pi_state_update_owner(pi_state, newowner);
-
-	return argowner == current;
-
-	/*
-	 * In order to reschedule or handle a page fault, we need to drop the
-	 * locks here. In the case of a fault, this gives the other task
-	 * (either the highest priority waiter itself or the task which stole
-	 * the rtmutex) the chance to try the fixup of the pi_state. So once we
-	 * are back from handling the fault we need to check the pi_state after
-	 * reacquiring the locks and before trying to do another fixup. When
-	 * the fixup has been done already we simply return.
-	 *
-	 * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
-	 * drop hb->lock since the caller owns the hb -> futex_q relation.
-	 * Dropping the pi_mutex->wait_lock requires the state revalidate.
-	 */
-handle_err:
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-	spin_unlock(q->lock_ptr);
-
-	switch (err) {
-	case -EFAULT:
-		err = fault_in_user_writeable(uaddr);
-		break;
-
-	case -EAGAIN:
-		cond_resched();
-		err = 0;
-		break;
-
-	default:
-		WARN_ON_ONCE(1);
-		break;
-	}
-
-	spin_lock(q->lock_ptr);
-	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-
-	/*
-	 * Check if someone else fixed it for us:
-	 */
-	if (pi_state->owner != oldowner)
-		return argowner == current;
-
-	/* Retry if err was -EAGAIN or the fault in succeeded */
-	if (!err)
-		goto retry;
-
-	/*
-	 * fault_in_user_writeable() failed so user state is immutable. At
-	 * best we can make the kernel state consistent but user state will
-	 * be most likely hosed and any subsequent unlock operation will be
-	 * rejected due to PI futex rule [10].
-	 *
-	 * Ensure that the rtmutex owner is also the pi_state owner despite
-	 * the user space value claiming something different. There is no
-	 * point in unlocking the rtmutex if current is the owner as it
-	 * would need to wait until the next waiter has taken the rtmutex
-	 * to guarantee consistent state. Keep it simple. Userspace asked
-	 * for this wreckaged state.
-	 *
-	 * The rtmutex has an owner - either current or some other
-	 * task. See the EAGAIN loop above.
-	 */
-	pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
-
-	return err;
-}
-
-static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
-				struct task_struct *argowner)
-{
-	struct futex_pi_state *pi_state = q->pi_state;
-	int ret;
-
-	lockdep_assert_held(q->lock_ptr);
-
-	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-	ret = __fixup_pi_state_owner(uaddr, q, argowner);
-	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
-	return ret;
-}
-
-static long futex_wait_restart(struct restart_block *restart);
-
-/**
- * fixup_owner() - Post lock pi_state and corner case management
- * @uaddr:	user address of the futex
- * @q:		futex_q (contains pi_state and access to the rt_mutex)
- * @locked:	if the attempt to take the rt_mutex succeeded (1) or not (0)
- *
- * After attempting to lock an rt_mutex, this function is called to cleanup
- * the pi_state owner as well as handle race conditions that may allow us to
- * acquire the lock. Must be called with the hb lock held.
- *
- * Return:
- *  -  1 - success, lock taken;
- *  -  0 - success, lock not taken;
- *  - <0 - on error (-EFAULT)
- */
-static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
-{
-	if (locked) {
-		/*
-		 * Got the lock. We might not be the anticipated owner if we
-		 * did a lock-steal - fix up the PI-state in that case:
-		 *
-		 * Speculative pi_state->owner read (we don't hold wait_lock);
-		 * since we own the lock pi_state->owner == current is the
-		 * stable state, anything else needs more attention.
-		 */
-		if (q->pi_state->owner != current)
-			return fixup_pi_state_owner(uaddr, q, current);
-		return 1;
-	}
-
-	/*
-	 * If we didn't get the lock; check if anybody stole it from us. In
-	 * that case, we need to fix up the uval to point to them instead of
-	 * us, otherwise bad things happen. [10]
-	 *
-	 * Another speculative read; pi_state->owner == current is unstable
-	 * but needs our attention.
-	 */
-	if (q->pi_state->owner == current)
-		return fixup_pi_state_owner(uaddr, q, NULL);
-
-	/*
-	 * Paranoia check. If we did not take the lock, then we should not be
-	 * the owner of the rt_mutex. Warn and establish consistent state.
-	 */
-	if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
-		return fixup_pi_state_owner(uaddr, q, current);
-
-	return 0;
-}
-
-/**
- * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
- * @hb:		the futex hash bucket, must be locked by the caller
- * @q:		the futex_q to queue up on
- * @timeout:	the prepared hrtimer_sleeper, or null for no timeout
- */
-static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
-				struct hrtimer_sleeper *timeout)
-{
-	/*
-	 * The task state is guaranteed to be set before another task can
-	 * wake it. set_current_state() is implemented using smp_store_mb() and
-	 * queue_me() calls spin_unlock() upon completion, both serializing
-	 * access to the hash list and forcing another memory barrier.
-	 */
-	set_current_state(TASK_INTERRUPTIBLE);
-	queue_me(q, hb);
-
-	/* Arm the timer */
-	if (timeout)
-		hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
-
-	/*
-	 * If we have been removed from the hash list, then another task
-	 * has tried to wake us, and we can skip the call to schedule().
-	 */
-	if (likely(!plist_node_empty(&q->list))) {
-		/*
-		 * If the timer has already expired, current will already be
-		 * flagged for rescheduling. Only call schedule if there
-		 * is no timeout, or if it has yet to expire.
-		 */
-		if (!timeout || timeout->task)
-			freezable_schedule();
-	}
-	__set_current_state(TASK_RUNNING);
-}
-
-/**
- * futex_wait_setup() - Prepare to wait on a futex
- * @uaddr:	the futex userspace address
- * @val:	the expected value
- * @flags:	futex flags (FLAGS_SHARED, etc.)
- * @q:		the associated futex_q
- * @hb:		storage for hash_bucket pointer to be returned to caller
- *
- * Setup the futex_q and locate the hash_bucket.  Get the futex value and
- * compare it with the expected value.  Handle atomic faults internally.
- * Return with the hb lock held on success, and unlocked on failure.
- *
- * Return:
- *  -  0 - uaddr contains val and hb has been locked;
- *  - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
- */
-static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
-			   struct futex_q *q, struct futex_hash_bucket **hb)
-{
-	u32 uval;
-	int ret;
-
-	/*
-	 * Access the page AFTER the hash-bucket is locked.
-	 * Order is important:
-	 *
-	 *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
-	 *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
-	 *
-	 * The basic logical guarantee of a futex is that it blocks ONLY
-	 * if cond(var) is known to be true at the time of blocking, for
-	 * any cond.  If we locked the hash-bucket after testing *uaddr, that
-	 * would open a race condition where we could block indefinitely with
-	 * cond(var) false, which would violate the guarantee.
-	 *
-	 * On the other hand, we insert q and release the hash-bucket only
-	 * after testing *uaddr.  This guarantees that futex_wait() will NOT
-	 * absorb a wakeup if *uaddr does not match the desired values
-	 * while the syscall executes.
-	 */
-retry:
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
-	if (unlikely(ret != 0))
-		return ret;
-
-retry_private:
-	*hb = queue_lock(q);
-
-	ret = get_futex_value_locked(&uval, uaddr);
-
-	if (ret) {
-		queue_unlock(*hb);
-
-		ret = get_user(uval, uaddr);
-		if (ret)
-			return ret;
-
-		if (!(flags & FLAGS_SHARED))
-			goto retry_private;
-
-		goto retry;
-	}
-
-	if (uval != val) {
-		queue_unlock(*hb);
-		ret = -EWOULDBLOCK;
-	}
-
-	return ret;
-}
-
-static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
-		      ktime_t *abs_time, u32 bitset)
-{
-	struct hrtimer_sleeper timeout, *to;
-	struct restart_block *restart;
-	struct futex_hash_bucket *hb;
-	struct futex_q q = futex_q_init;
-	int ret;
-
-	if (!bitset)
-		return -EINVAL;
-	q.bitset = bitset;
-
-	to = futex_setup_timer(abs_time, &timeout, flags,
-			       current->timer_slack_ns);
-retry:
-	/*
-	 * Prepare to wait on uaddr. On success, it holds hb->lock and q
-	 * is initialized.
-	 */
-	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
-	if (ret)
-		goto out;
-
-	/* queue_me and wait for wakeup, timeout, or a signal. */
-	futex_wait_queue_me(hb, &q, to);
-
-	/* If we were woken (and unqueued), we succeeded, whatever. */
-	ret = 0;
-	if (!unqueue_me(&q))
-		goto out;
-	ret = -ETIMEDOUT;
-	if (to && !to->task)
-		goto out;
-
-	/*
-	 * We expect signal_pending(current), but we might be the
-	 * victim of a spurious wakeup as well.
-	 */
-	if (!signal_pending(current))
-		goto retry;
-
-	ret = -ERESTARTSYS;
-	if (!abs_time)
-		goto out;
-
-	restart = &current->restart_block;
-	restart->futex.uaddr = uaddr;
-	restart->futex.val = val;
-	restart->futex.time = *abs_time;
-	restart->futex.bitset = bitset;
-	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
-
-	ret = set_restart_fn(restart, futex_wait_restart);
-
-out:
-	if (to) {
-		hrtimer_cancel(&to->timer);
-		destroy_hrtimer_on_stack(&to->timer);
-	}
-	return ret;
-}
-
-
-static long futex_wait_restart(struct restart_block *restart)
-{
-	u32 __user *uaddr = restart->futex.uaddr;
-	ktime_t t, *tp = NULL;
-
-	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
-		t = restart->futex.time;
-		tp = &t;
-	}
-	restart->fn = do_no_restart_syscall;
-
-	return (long)futex_wait(uaddr, restart->futex.flags,
-				restart->futex.val, tp, restart->futex.bitset);
-}
-
-
-/*
- * Userspace tried a 0 -> TID atomic transition of the futex value
- * and failed. The kernel side here does the whole locking operation:
- * if there are waiters then it will block as a consequence of relying
- * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
- * a 0 value of the futex too.).
- *
- * Also serves as futex trylock_pi()'ing, and due semantics.
- */
-static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
-			 ktime_t *time, int trylock)
-{
-	struct hrtimer_sleeper timeout, *to;
-	struct task_struct *exiting = NULL;
-	struct rt_mutex_waiter rt_waiter;
-	struct futex_hash_bucket *hb;
-	struct futex_q q = futex_q_init;
-	int res, ret;
-
-	if (!IS_ENABLED(CONFIG_FUTEX_PI))
-		return -ENOSYS;
-
-	if (refill_pi_state_cache())
-		return -ENOMEM;
-
-	to = futex_setup_timer(time, &timeout, flags, 0);
-
-retry:
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
-	if (unlikely(ret != 0))
-		goto out;
-
-retry_private:
-	hb = queue_lock(&q);
-
-	ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
-				   &exiting, 0);
-	if (unlikely(ret)) {
-		/*
-		 * Atomic work succeeded and we got the lock,
-		 * or failed. Either way, we do _not_ block.
-		 */
-		switch (ret) {
-		case 1:
-			/* We got the lock. */
-			ret = 0;
-			goto out_unlock_put_key;
-		case -EFAULT:
-			goto uaddr_faulted;
-		case -EBUSY:
-		case -EAGAIN:
-			/*
-			 * Two reasons for this:
-			 * - EBUSY: Task is exiting and we just wait for the
-			 *   exit to complete.
-			 * - EAGAIN: The user space value changed.
-			 */
-			queue_unlock(hb);
-			/*
-			 * Handle the case where the owner is in the middle of
-			 * exiting. Wait for the exit to complete otherwise
-			 * this task might loop forever, aka. live lock.
-			 */
-			wait_for_owner_exiting(ret, exiting);
-			cond_resched();
-			goto retry;
-		default:
-			goto out_unlock_put_key;
-		}
-	}
-
-	WARN_ON(!q.pi_state);
-
-	/*
-	 * Only actually queue now that the atomic ops are done:
-	 */
-	__queue_me(&q, hb);
-
-	if (trylock) {
-		ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
-		/* Fixup the trylock return value: */
-		ret = ret ? 0 : -EWOULDBLOCK;
-		goto no_block;
-	}
-
-	rt_mutex_init_waiter(&rt_waiter);
-
-	/*
-	 * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
-	 * hold it while doing rt_mutex_start_proxy(), because then it will
-	 * include hb->lock in the blocking chain, even through we'll not in
-	 * fact hold it while blocking. This will lead it to report -EDEADLK
-	 * and BUG when futex_unlock_pi() interleaves with this.
-	 *
-	 * Therefore acquire wait_lock while holding hb->lock, but drop the
-	 * latter before calling __rt_mutex_start_proxy_lock(). This
-	 * interleaves with futex_unlock_pi() -- which does a similar lock
-	 * handoff -- such that the latter can observe the futex_q::pi_state
-	 * before __rt_mutex_start_proxy_lock() is done.
-	 */
-	raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
-	spin_unlock(q.lock_ptr);
-	/*
-	 * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
-	 * such that futex_unlock_pi() is guaranteed to observe the waiter when
-	 * it sees the futex_q::pi_state.
-	 */
-	ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
-	raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
-
-	if (ret) {
-		if (ret == 1)
-			ret = 0;
-		goto cleanup;
-	}
-
-	if (unlikely(to))
-		hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
-
-	ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
-
-cleanup:
-	spin_lock(q.lock_ptr);
-	/*
-	 * If we failed to acquire the lock (deadlock/signal/timeout), we must
-	 * first acquire the hb->lock before removing the lock from the
-	 * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
-	 * lists consistent.
-	 *
-	 * In particular; it is important that futex_unlock_pi() can not
-	 * observe this inconsistency.
-	 */
-	if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
-		ret = 0;
-
-no_block:
-	/*
-	 * Fixup the pi_state owner and possibly acquire the lock if we
-	 * haven't already.
-	 */
-	res = fixup_owner(uaddr, &q, !ret);
-	/*
-	 * If fixup_owner() returned an error, propagate that.  If it acquired
-	 * the lock, clear our -ETIMEDOUT or -EINTR.
-	 */
-	if (res)
-		ret = (res < 0) ? res : 0;
-
-	unqueue_me_pi(&q);
-	spin_unlock(q.lock_ptr);
-	goto out;
-
-out_unlock_put_key:
-	queue_unlock(hb);
-
-out:
-	if (to) {
-		hrtimer_cancel(&to->timer);
-		destroy_hrtimer_on_stack(&to->timer);
-	}
-	return ret != -EINTR ? ret : -ERESTARTNOINTR;
-
-uaddr_faulted:
-	queue_unlock(hb);
-
-	ret = fault_in_user_writeable(uaddr);
-	if (ret)
-		goto out;
-
-	if (!(flags & FLAGS_SHARED))
-		goto retry_private;
-
-	goto retry;
-}
-
-/*
- * Userspace attempted a TID -> 0 atomic transition, and failed.
- * This is the in-kernel slowpath: we look up the PI state (if any),
- * and do the rt-mutex unlock.
- */
-static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
-{
-	u32 curval, uval, vpid = task_pid_vnr(current);
-	union futex_key key = FUTEX_KEY_INIT;
-	struct futex_hash_bucket *hb;
-	struct futex_q *top_waiter;
-	int ret;
-
-	if (!IS_ENABLED(CONFIG_FUTEX_PI))
-		return -ENOSYS;
-
-retry:
-	if (get_user(uval, uaddr))
-		return -EFAULT;
-	/*
-	 * We release only a lock we actually own:
-	 */
-	if ((uval & FUTEX_TID_MASK) != vpid)
-		return -EPERM;
-
-	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
-	if (ret)
-		return ret;
-
-	hb = hash_futex(&key);
-	spin_lock(&hb->lock);
-
-	/*
-	 * Check waiters first. We do not trust user space values at
-	 * all and we at least want to know if user space fiddled
-	 * with the futex value instead of blindly unlocking.
-	 */
-	top_waiter = futex_top_waiter(hb, &key);
-	if (top_waiter) {
-		struct futex_pi_state *pi_state = top_waiter->pi_state;
-
-		ret = -EINVAL;
-		if (!pi_state)
-			goto out_unlock;
-
-		/*
-		 * If current does not own the pi_state then the futex is
-		 * inconsistent and user space fiddled with the futex value.
-		 */
-		if (pi_state->owner != current)
-			goto out_unlock;
-
-		get_pi_state(pi_state);
-		/*
-		 * By taking wait_lock while still holding hb->lock, we ensure
-		 * there is no point where we hold neither; and therefore
-		 * wake_futex_pi() must observe a state consistent with what we
-		 * observed.
-		 *
-		 * In particular; this forces __rt_mutex_start_proxy() to
-		 * complete such that we're guaranteed to observe the
-		 * rt_waiter. Also see the WARN in wake_futex_pi().
-		 */
-		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
-		spin_unlock(&hb->lock);
-
-		/* drops pi_state->pi_mutex.wait_lock */
-		ret = wake_futex_pi(uaddr, uval, pi_state);
-
-		put_pi_state(pi_state);
-
-		/*
-		 * Success, we're done! No tricky corner cases.
-		 */
-		if (!ret)
-			return ret;
-		/*
-		 * The atomic access to the futex value generated a
-		 * pagefault, so retry the user-access and the wakeup:
-		 */
-		if (ret == -EFAULT)
-			goto pi_faulted;
-		/*
-		 * A unconditional UNLOCK_PI op raced against a waiter
-		 * setting the FUTEX_WAITERS bit. Try again.
-		 */
-		if (ret == -EAGAIN)
-			goto pi_retry;
-		/*
-		 * wake_futex_pi has detected invalid state. Tell user
-		 * space.
-		 */
-		return ret;
-	}
-
-	/*
-	 * We have no kernel internal state, i.e. no waiters in the
-	 * kernel. Waiters which are about to queue themselves are stuck
-	 * on hb->lock. So we can safely ignore them. We do neither
-	 * preserve the WAITERS bit not the OWNER_DIED one. We are the
-	 * owner.
-	 */
-	if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
-		spin_unlock(&hb->lock);
-		switch (ret) {
-		case -EFAULT:
-			goto pi_faulted;
-
-		case -EAGAIN:
-			goto pi_retry;
-
-		default:
-			WARN_ON_ONCE(1);
-			return ret;
-		}
-	}
-
-	/*
-	 * If uval has changed, let user space handle it.
-	 */
-	ret = (curval == uval) ? 0 : -EAGAIN;
-
-out_unlock:
-	spin_unlock(&hb->lock);
-	return ret;
-
-pi_retry:
-	cond_resched();
-	goto retry;
-
-pi_faulted:
-
-	ret = fault_in_user_writeable(uaddr);
-	if (!ret)
-		goto retry;
-
-	return ret;
-}
-
-/**
- * handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
- * @hb:		the hash_bucket futex_q was original enqueued on
- * @q:		the futex_q woken while waiting to be requeued
- * @timeout:	the timeout associated with the wait (NULL if none)
- *
- * Determine the cause for the early wakeup.
- *
- * Return:
- *  -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR
- */
-static inline
-int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
-				   struct futex_q *q,
-				   struct hrtimer_sleeper *timeout)
-{
-	int ret;
-
-	/*
-	 * With the hb lock held, we avoid races while we process the wakeup.
-	 * We only need to hold hb (and not hb2) to ensure atomicity as the
-	 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
-	 * It can't be requeued from uaddr2 to something else since we don't
-	 * support a PI aware source futex for requeue.
-	 */
-	WARN_ON_ONCE(&hb->lock != q->lock_ptr);
-
-	/*
-	 * We were woken prior to requeue by a timeout or a signal.
-	 * Unqueue the futex_q and determine which it was.
-	 */
-	plist_del(&q->list, &hb->chain);
-	hb_waiters_dec(hb);
-
-	/* Handle spurious wakeups gracefully */
-	ret = -EWOULDBLOCK;
-	if (timeout && !timeout->task)
-		ret = -ETIMEDOUT;
-	else if (signal_pending(current))
-		ret = -ERESTARTNOINTR;
-	return ret;
-}
-
-/**
- * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
- * @uaddr:	the futex we initially wait on (non-pi)
- * @flags:	futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
- *		the same type, no requeueing from private to shared, etc.
- * @val:	the expected value of uaddr
- * @abs_time:	absolute timeout
- * @bitset:	32 bit wakeup bitset set by userspace, defaults to all
- * @uaddr2:	the pi futex we will take prior to returning to user-space
- *
- * The caller will wait on uaddr and will be requeued by futex_requeue() to
- * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
- * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
- * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
- * without one, the pi logic would not know which task to boost/deboost, if
- * there was a need to.
- *
- * We call schedule in futex_wait_queue_me() when we enqueue and return there
- * via the following--
- * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
- * 2) wakeup on uaddr2 after a requeue
- * 3) signal
- * 4) timeout
- *
- * If 3, cleanup and return -ERESTARTNOINTR.
- *
- * If 2, we may then block on trying to take the rt_mutex and return via:
- * 5) successful lock
- * 6) signal
- * 7) timeout
- * 8) other lock acquisition failure
- *
- * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
- *
- * If 4 or 7, we cleanup and return with -ETIMEDOUT.
- *
- * Return:
- *  -  0 - On success;
- *  - <0 - On error
- */
-static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
-				 u32 val, ktime_t *abs_time, u32 bitset,
-				 u32 __user *uaddr2)
-{
-	struct hrtimer_sleeper timeout, *to;
-	struct rt_mutex_waiter rt_waiter;
-	struct futex_hash_bucket *hb;
-	union futex_key key2 = FUTEX_KEY_INIT;
-	struct futex_q q = futex_q_init;
-	struct rt_mutex_base *pi_mutex;
-	int res, ret;
-
-	if (!IS_ENABLED(CONFIG_FUTEX_PI))
-		return -ENOSYS;
-
-	if (uaddr == uaddr2)
-		return -EINVAL;
-
-	if (!bitset)
-		return -EINVAL;
-
-	to = futex_setup_timer(abs_time, &timeout, flags,
-			       current->timer_slack_ns);
-
-	/*
-	 * The waiter is allocated on our stack, manipulated by the requeue
-	 * code while we sleep on uaddr.
-	 */
-	rt_mutex_init_waiter(&rt_waiter);
-
-	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
-	if (unlikely(ret != 0))
-		goto out;
-
-	q.bitset = bitset;
-	q.rt_waiter = &rt_waiter;
-	q.requeue_pi_key = &key2;
-
-	/*
-	 * Prepare to wait on uaddr. On success, it holds hb->lock and q
-	 * is initialized.
-	 */
-	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
-	if (ret)
-		goto out;
-
-	/*
-	 * The check above which compares uaddrs is not sufficient for
-	 * shared futexes. We need to compare the keys:
-	 */
-	if (match_futex(&q.key, &key2)) {
-		queue_unlock(hb);
-		ret = -EINVAL;
-		goto out;
-	}
-
-	/* Queue the futex_q, drop the hb lock, wait for wakeup. */
-	futex_wait_queue_me(hb, &q, to);
-
-	switch (futex_requeue_pi_wakeup_sync(&q)) {
-	case Q_REQUEUE_PI_IGNORE:
-		/* The waiter is still on uaddr1 */
-		spin_lock(&hb->lock);
-		ret = handle_early_requeue_pi_wakeup(hb, &q, to);
-		spin_unlock(&hb->lock);
-		break;
-
-	case Q_REQUEUE_PI_LOCKED:
-		/* The requeue acquired the lock */
-		if (q.pi_state && (q.pi_state->owner != current)) {
-			spin_lock(q.lock_ptr);
-			ret = fixup_owner(uaddr2, &q, true);
-			/*
-			 * Drop the reference to the pi state which the
-			 * requeue_pi() code acquired for us.
-			 */
-			put_pi_state(q.pi_state);
-			spin_unlock(q.lock_ptr);
-			/*
-			 * Adjust the return value. It's either -EFAULT or
-			 * success (1) but the caller expects 0 for success.
-			 */
-			ret = ret < 0 ? ret : 0;
-		}
-		break;
-
-	case Q_REQUEUE_PI_DONE:
-		/* Requeue completed. Current is 'pi_blocked_on' the rtmutex */
-		pi_mutex = &q.pi_state->pi_mutex;
-		ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
-
-		/* Current is not longer pi_blocked_on */
-		spin_lock(q.lock_ptr);
-		if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
-			ret = 0;
-
-		debug_rt_mutex_free_waiter(&rt_waiter);
-		/*
-		 * Fixup the pi_state owner and possibly acquire the lock if we
-		 * haven't already.
-		 */
-		res = fixup_owner(uaddr2, &q, !ret);
-		/*
-		 * If fixup_owner() returned an error, propagate that.  If it
-		 * acquired the lock, clear -ETIMEDOUT or -EINTR.
-		 */
-		if (res)
-			ret = (res < 0) ? res : 0;
-
-		unqueue_me_pi(&q);
-		spin_unlock(q.lock_ptr);
-
-		if (ret == -EINTR) {
-			/*
-			 * We've already been requeued, but cannot restart
-			 * by calling futex_lock_pi() directly. We could
-			 * restart this syscall, but it would detect that
-			 * the user space "val" changed and return
-			 * -EWOULDBLOCK.  Save the overhead of the restart
-			 * and return -EWOULDBLOCK directly.
-			 */
-			ret = -EWOULDBLOCK;
-		}
-		break;
-	default:
-		BUG();
-	}
-
-out:
-	if (to) {
-		hrtimer_cancel(&to->timer);
-		destroy_hrtimer_on_stack(&to->timer);
-	}
-	return ret;
-}
-
-/*
- * Support for robust futexes: the kernel cleans up held futexes at
- * thread exit time.
- *
- * Implementation: user-space maintains a per-thread list of locks it
- * is holding. Upon do_exit(), the kernel carefully walks this list,
- * and marks all locks that are owned by this thread with the
- * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
- * always manipulated with the lock held, so the list is private and
- * per-thread. Userspace also maintains a per-thread 'list_op_pending'
- * field, to allow the kernel to clean up if the thread dies after
- * acquiring the lock, but just before it could have added itself to
- * the list. There can only be one such pending lock.
- */
-
-/**
- * sys_set_robust_list() - Set the robust-futex list head of a task
- * @head:	pointer to the list-head
- * @len:	length of the list-head, as userspace expects
- */
-SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
-		size_t, len)
-{
-	if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
-	/*
-	 * The kernel knows only one size for now:
-	 */
-	if (unlikely(len != sizeof(*head)))
-		return -EINVAL;
-
-	current->robust_list = head;
-
-	return 0;
-}
-
-/**
- * sys_get_robust_list() - Get the robust-futex list head of a task
- * @pid:	pid of the process [zero for current task]
- * @head_ptr:	pointer to a list-head pointer, the kernel fills it in
- * @len_ptr:	pointer to a length field, the kernel fills in the header size
- */
-SYSCALL_DEFINE3(get_robust_list, int, pid,
-		struct robust_list_head __user * __user *, head_ptr,
-		size_t __user *, len_ptr)
-{
-	struct robust_list_head __user *head;
-	unsigned long ret;
-	struct task_struct *p;
-
-	if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
-
-	rcu_read_lock();
-
-	ret = -ESRCH;
-	if (!pid)
-		p = current;
-	else {
-		p = find_task_by_vpid(pid);
-		if (!p)
-			goto err_unlock;
-	}
-
-	ret = -EPERM;
-	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
-		goto err_unlock;
-
-	head = p->robust_list;
-	rcu_read_unlock();
-
-	if (put_user(sizeof(*head), len_ptr))
-		return -EFAULT;
-	return put_user(head, head_ptr);
-
-err_unlock:
-	rcu_read_unlock();
-
-	return ret;
-}
-
-/* Constants for the pending_op argument of handle_futex_death */
-#define HANDLE_DEATH_PENDING	true
-#define HANDLE_DEATH_LIST	false
-
-/*
- * Process a futex-list entry, check whether it's owned by the
- * dying task, and do notification if so:
- */
-static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
-			      bool pi, bool pending_op)
-{
-	u32 uval, nval, mval;
-	int err;
-
-	/* Futex address must be 32bit aligned */
-	if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
-		return -1;
-
-retry:
-	if (get_user(uval, uaddr))
-		return -1;
-
-	/*
-	 * Special case for regular (non PI) futexes. The unlock path in
-	 * user space has two race scenarios:
-	 *
-	 * 1. The unlock path releases the user space futex value and
-	 *    before it can execute the futex() syscall to wake up
-	 *    waiters it is killed.
-	 *
-	 * 2. A woken up waiter is killed before it can acquire the
-	 *    futex in user space.
-	 *
-	 * In both cases the TID validation below prevents a wakeup of
-	 * potential waiters which can cause these waiters to block
-	 * forever.
-	 *
-	 * In both cases the following conditions are met:
-	 *
-	 *	1) task->robust_list->list_op_pending != NULL
-	 *	   @pending_op == true
-	 *	2) User space futex value == 0
-	 *	3) Regular futex: @pi == false
-	 *
-	 * If these conditions are met, it is safe to attempt waking up a
-	 * potential waiter without touching the user space futex value and
-	 * trying to set the OWNER_DIED bit. The user space futex value is
-	 * uncontended and the rest of the user space mutex state is
-	 * consistent, so a woken waiter will just take over the
-	 * uncontended futex. Setting the OWNER_DIED bit would create
-	 * inconsistent state and malfunction of the user space owner died
-	 * handling.
-	 */
-	if (pending_op && !pi && !uval) {
-		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
-		return 0;
-	}
-
-	if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
-		return 0;
-
-	/*
-	 * Ok, this dying thread is truly holding a futex
-	 * of interest. Set the OWNER_DIED bit atomically
-	 * via cmpxchg, and if the value had FUTEX_WAITERS
-	 * set, wake up a waiter (if any). (We have to do a
-	 * futex_wake() even if OWNER_DIED is already set -
-	 * to handle the rare but possible case of recursive
-	 * thread-death.) The rest of the cleanup is done in
-	 * userspace.
-	 */
-	mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
-
-	/*
-	 * We are not holding a lock here, but we want to have
-	 * the pagefault_disable/enable() protection because
-	 * we want to handle the fault gracefully. If the
-	 * access fails we try to fault in the futex with R/W
-	 * verification via get_user_pages. get_user() above
-	 * does not guarantee R/W access. If that fails we
-	 * give up and leave the futex locked.
-	 */
-	if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
-		switch (err) {
-		case -EFAULT:
-			if (fault_in_user_writeable(uaddr))
-				return -1;
-			goto retry;
-
-		case -EAGAIN:
-			cond_resched();
-			goto retry;
-
-		default:
-			WARN_ON_ONCE(1);
-			return err;
-		}
-	}
-
-	if (nval != uval)
-		goto retry;
-
-	/*
-	 * Wake robust non-PI futexes here. The wakeup of
-	 * PI futexes happens in exit_pi_state():
-	 */
-	if (!pi && (uval & FUTEX_WAITERS))
-		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
-
-	return 0;
-}
-
-/*
- * Fetch a robust-list pointer. Bit 0 signals PI futexes:
- */
-static inline int fetch_robust_entry(struct robust_list __user **entry,
-				     struct robust_list __user * __user *head,
-				     unsigned int *pi)
-{
-	unsigned long uentry;
-
-	if (get_user(uentry, (unsigned long __user *)head))
-		return -EFAULT;
-
-	*entry = (void __user *)(uentry & ~1UL);
-	*pi = uentry & 1;
-
-	return 0;
-}
-
-/*
- * Walk curr->robust_list (very carefully, it's a userspace list!)
- * and mark any locks found there dead, and notify any waiters.
- *
- * We silently return on any sign of list-walking problem.
- */
-static void exit_robust_list(struct task_struct *curr)
-{
-	struct robust_list_head __user *head = curr->robust_list;
-	struct robust_list __user *entry, *next_entry, *pending;
-	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
-	unsigned int next_pi;
-	unsigned long futex_offset;
-	int rc;
-
-	if (!futex_cmpxchg_enabled)
-		return;
-
-	/*
-	 * Fetch the list head (which was registered earlier, via
-	 * sys_set_robust_list()):
-	 */
-	if (fetch_robust_entry(&entry, &head->list.next, &pi))
-		return;
-	/*
-	 * Fetch the relative futex offset:
-	 */
-	if (get_user(futex_offset, &head->futex_offset))
-		return;
-	/*
-	 * Fetch any possibly pending lock-add first, and handle it
-	 * if it exists:
-	 */
-	if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
-		return;
-
-	next_entry = NULL;	/* avoid warning with gcc */
-	while (entry != &head->list) {
-		/*
-		 * Fetch the next entry in the list before calling
-		 * handle_futex_death:
-		 */
-		rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
-		/*
-		 * A pending lock might already be on the list, so
-		 * don't process it twice:
-		 */
-		if (entry != pending) {
-			if (handle_futex_death((void __user *)entry + futex_offset,
-						curr, pi, HANDLE_DEATH_LIST))
-				return;
-		}
-		if (rc)
-			return;
-		entry = next_entry;
-		pi = next_pi;
-		/*
-		 * Avoid excessively long or circular lists:
-		 */
-		if (!--limit)
-			break;
-
-		cond_resched();
-	}
-
-	if (pending) {
-		handle_futex_death((void __user *)pending + futex_offset,
-				   curr, pip, HANDLE_DEATH_PENDING);
-	}
-}
-
-static void futex_cleanup(struct task_struct *tsk)
-{
-	if (unlikely(tsk->robust_list)) {
-		exit_robust_list(tsk);
-		tsk->robust_list = NULL;
-	}
-
-#ifdef CONFIG_COMPAT
-	if (unlikely(tsk->compat_robust_list)) {
-		compat_exit_robust_list(tsk);
-		tsk->compat_robust_list = NULL;
-	}
-#endif
-
-	if (unlikely(!list_empty(&tsk->pi_state_list)))
-		exit_pi_state_list(tsk);
-}
-
-/**
- * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
- * @tsk:	task to set the state on
- *
- * Set the futex exit state of the task lockless. The futex waiter code
- * observes that state when a task is exiting and loops until the task has
- * actually finished the futex cleanup. The worst case for this is that the
- * waiter runs through the wait loop until the state becomes visible.
- *
- * This is called from the recursive fault handling path in do_exit().
- *
- * This is best effort. Either the futex exit code has run already or
- * not. If the OWNER_DIED bit has been set on the futex then the waiter can
- * take it over. If not, the problem is pushed back to user space. If the
- * futex exit code did not run yet, then an already queued waiter might
- * block forever, but there is nothing which can be done about that.
- */
-void futex_exit_recursive(struct task_struct *tsk)
-{
-	/* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
-	if (tsk->futex_state == FUTEX_STATE_EXITING)
-		mutex_unlock(&tsk->futex_exit_mutex);
-	tsk->futex_state = FUTEX_STATE_DEAD;
-}
-
-static void futex_cleanup_begin(struct task_struct *tsk)
-{
-	/*
-	 * Prevent various race issues against a concurrent incoming waiter
-	 * including live locks by forcing the waiter to block on
-	 * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
-	 * attach_to_pi_owner().
-	 */
-	mutex_lock(&tsk->futex_exit_mutex);
-
-	/*
-	 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
-	 *
-	 * This ensures that all subsequent checks of tsk->futex_state in
-	 * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
-	 * tsk->pi_lock held.
-	 *
-	 * It guarantees also that a pi_state which was queued right before
-	 * the state change under tsk->pi_lock by a concurrent waiter must
-	 * be observed in exit_pi_state_list().
-	 */
-	raw_spin_lock_irq(&tsk->pi_lock);
-	tsk->futex_state = FUTEX_STATE_EXITING;
-	raw_spin_unlock_irq(&tsk->pi_lock);
-}
-
-static void futex_cleanup_end(struct task_struct *tsk, int state)
-{
-	/*
-	 * Lockless store. The only side effect is that an observer might
-	 * take another loop until it becomes visible.
-	 */
-	tsk->futex_state = state;
-	/*
-	 * Drop the exit protection. This unblocks waiters which observed
-	 * FUTEX_STATE_EXITING to reevaluate the state.
-	 */
-	mutex_unlock(&tsk->futex_exit_mutex);
-}
-
-void futex_exec_release(struct task_struct *tsk)
-{
-	/*
-	 * The state handling is done for consistency, but in the case of
-	 * exec() there is no way to prevent further damage as the PID stays
-	 * the same. But for the unlikely and arguably buggy case that a
-	 * futex is held on exec(), this provides at least as much state
-	 * consistency protection which is possible.
-	 */
-	futex_cleanup_begin(tsk);
-	futex_cleanup(tsk);
-	/*
-	 * Reset the state to FUTEX_STATE_OK. The task is alive and about
-	 * exec a new binary.
-	 */
-	futex_cleanup_end(tsk, FUTEX_STATE_OK);
-}
-
-void futex_exit_release(struct task_struct *tsk)
-{
-	futex_cleanup_begin(tsk);
-	futex_cleanup(tsk);
-	futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
-}
-
-long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
-		u32 __user *uaddr2, u32 val2, u32 val3)
-{
-	int cmd = op & FUTEX_CMD_MASK;
-	unsigned int flags = 0;
-
-	if (!(op & FUTEX_PRIVATE_FLAG))
-		flags |= FLAGS_SHARED;
-
-	if (op & FUTEX_CLOCK_REALTIME) {
-		flags |= FLAGS_CLOCKRT;
-		if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
-		    cmd != FUTEX_LOCK_PI2)
-			return -ENOSYS;
-	}
-
-	switch (cmd) {
-	case FUTEX_LOCK_PI:
-	case FUTEX_LOCK_PI2:
-	case FUTEX_UNLOCK_PI:
-	case FUTEX_TRYLOCK_PI:
-	case FUTEX_WAIT_REQUEUE_PI:
-	case FUTEX_CMP_REQUEUE_PI:
-		if (!futex_cmpxchg_enabled)
-			return -ENOSYS;
-	}
-
-	switch (cmd) {
-	case FUTEX_WAIT:
-		val3 = FUTEX_BITSET_MATCH_ANY;
-		fallthrough;
-	case FUTEX_WAIT_BITSET:
-		return futex_wait(uaddr, flags, val, timeout, val3);
-	case FUTEX_WAKE:
-		val3 = FUTEX_BITSET_MATCH_ANY;
-		fallthrough;
-	case FUTEX_WAKE_BITSET:
-		return futex_wake(uaddr, flags, val, val3);
-	case FUTEX_REQUEUE:
-		return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
-	case FUTEX_CMP_REQUEUE:
-		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
-	case FUTEX_WAKE_OP:
-		return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
-	case FUTEX_LOCK_PI:
-		flags |= FLAGS_CLOCKRT;
-		fallthrough;
-	case FUTEX_LOCK_PI2:
-		return futex_lock_pi(uaddr, flags, timeout, 0);
-	case FUTEX_UNLOCK_PI:
-		return futex_unlock_pi(uaddr, flags);
-	case FUTEX_TRYLOCK_PI:
-		return futex_lock_pi(uaddr, flags, NULL, 1);
-	case FUTEX_WAIT_REQUEUE_PI:
-		val3 = FUTEX_BITSET_MATCH_ANY;
-		return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
-					     uaddr2);
-	case FUTEX_CMP_REQUEUE_PI:
-		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
-	}
-	return -ENOSYS;
-}
-
-static __always_inline bool futex_cmd_has_timeout(u32 cmd)
-{
-	switch (cmd) {
-	case FUTEX_WAIT:
-	case FUTEX_LOCK_PI:
-	case FUTEX_LOCK_PI2:
-	case FUTEX_WAIT_BITSET:
-	case FUTEX_WAIT_REQUEUE_PI:
-		return true;
-	}
-	return false;
-}
-
-static __always_inline int
-futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
-{
-	if (!timespec64_valid(ts))
-		return -EINVAL;
-
-	*t = timespec64_to_ktime(*ts);
-	if (cmd == FUTEX_WAIT)
-		*t = ktime_add_safe(ktime_get(), *t);
-	else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
-		*t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
-	return 0;
-}
-
-SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
-		const struct __kernel_timespec __user *, utime,
-		u32 __user *, uaddr2, u32, val3)
-{
-	int ret, cmd = op & FUTEX_CMD_MASK;
-	ktime_t t, *tp = NULL;
-	struct timespec64 ts;
-
-	if (utime && futex_cmd_has_timeout(cmd)) {
-		if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
-			return -EFAULT;
-		if (get_timespec64(&ts, utime))
-			return -EFAULT;
-		ret = futex_init_timeout(cmd, op, &ts, &t);
-		if (ret)
-			return ret;
-		tp = &t;
-	}
-
-	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
-}
-
-#ifdef CONFIG_COMPAT
-/*
- * Fetch a robust-list pointer. Bit 0 signals PI futexes:
- */
-static inline int
-compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
-		   compat_uptr_t __user *head, unsigned int *pi)
-{
-	if (get_user(*uentry, head))
-		return -EFAULT;
-
-	*entry = compat_ptr((*uentry) & ~1);
-	*pi = (unsigned int)(*uentry) & 1;
-
-	return 0;
-}
-
-static void __user *futex_uaddr(struct robust_list __user *entry,
-				compat_long_t futex_offset)
-{
-	compat_uptr_t base = ptr_to_compat(entry);
-	void __user *uaddr = compat_ptr(base + futex_offset);
-
-	return uaddr;
-}
-
-/*
- * Walk curr->robust_list (very carefully, it's a userspace list!)
- * and mark any locks found there dead, and notify any waiters.
- *
- * We silently return on any sign of list-walking problem.
- */
-static void compat_exit_robust_list(struct task_struct *curr)
-{
-	struct compat_robust_list_head __user *head = curr->compat_robust_list;
-	struct robust_list __user *entry, *next_entry, *pending;
-	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
-	unsigned int next_pi;
-	compat_uptr_t uentry, next_uentry, upending;
-	compat_long_t futex_offset;
-	int rc;
-
-	if (!futex_cmpxchg_enabled)
-		return;
-
-	/*
-	 * Fetch the list head (which was registered earlier, via
-	 * sys_set_robust_list()):
-	 */
-	if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
-		return;
-	/*
-	 * Fetch the relative futex offset:
-	 */
-	if (get_user(futex_offset, &head->futex_offset))
-		return;
-	/*
-	 * Fetch any possibly pending lock-add first, and handle it
-	 * if it exists:
-	 */
-	if (compat_fetch_robust_entry(&upending, &pending,
-			       &head->list_op_pending, &pip))
-		return;
-
-	next_entry = NULL;	/* avoid warning with gcc */
-	while (entry != (struct robust_list __user *) &head->list) {
-		/*
-		 * Fetch the next entry in the list before calling
-		 * handle_futex_death:
-		 */
-		rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
-			(compat_uptr_t __user *)&entry->next, &next_pi);
-		/*
-		 * A pending lock might already be on the list, so
-		 * dont process it twice:
-		 */
-		if (entry != pending) {
-			void __user *uaddr = futex_uaddr(entry, futex_offset);
-
-			if (handle_futex_death(uaddr, curr, pi,
-					       HANDLE_DEATH_LIST))
-				return;
-		}
-		if (rc)
-			return;
-		uentry = next_uentry;
-		entry = next_entry;
-		pi = next_pi;
-		/*
-		 * Avoid excessively long or circular lists:
-		 */
-		if (!--limit)
-			break;
-
-		cond_resched();
-	}
-	if (pending) {
-		void __user *uaddr = futex_uaddr(pending, futex_offset);
-
-		handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
-	}
-}
-
-COMPAT_SYSCALL_DEFINE2(set_robust_list,
-		struct compat_robust_list_head __user *, head,
-		compat_size_t, len)
-{
-	if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
-
-	if (unlikely(len != sizeof(*head)))
-		return -EINVAL;
-
-	current->compat_robust_list = head;
-
-	return 0;
-}
-
-COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
-			compat_uptr_t __user *, head_ptr,
-			compat_size_t __user *, len_ptr)
-{
-	struct compat_robust_list_head __user *head;
-	unsigned long ret;
-	struct task_struct *p;
-
-	if (!futex_cmpxchg_enabled)
-		return -ENOSYS;
-
-	rcu_read_lock();
-
-	ret = -ESRCH;
-	if (!pid)
-		p = current;
-	else {
-		p = find_task_by_vpid(pid);
-		if (!p)
-			goto err_unlock;
-	}
-
-	ret = -EPERM;
-	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
-		goto err_unlock;
-
-	head = p->compat_robust_list;
-	rcu_read_unlock();
-
-	if (put_user(sizeof(*head), len_ptr))
-		return -EFAULT;
-	return put_user(ptr_to_compat(head), head_ptr);
-
-err_unlock:
-	rcu_read_unlock();
-
-	return ret;
-}
-#endif /* CONFIG_COMPAT */
-
-#ifdef CONFIG_COMPAT_32BIT_TIME
-SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
-		const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
-		u32, val3)
-{
-	int ret, cmd = op & FUTEX_CMD_MASK;
-	ktime_t t, *tp = NULL;
-	struct timespec64 ts;
-
-	if (utime && futex_cmd_has_timeout(cmd)) {
-		if (get_old_timespec32(&ts, utime))
-			return -EFAULT;
-		ret = futex_init_timeout(cmd, op, &ts, &t);
-		if (ret)
-			return ret;
-		tp = &t;
-	}
-
-	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
-}
-#endif /* CONFIG_COMPAT_32BIT_TIME */
-
-static void __init futex_detect_cmpxchg(void)
-{
-#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
-	u32 curval;
-
-	/*
-	 * This will fail and we want it. Some arch implementations do
-	 * runtime detection of the futex_atomic_cmpxchg_inatomic()
-	 * functionality. We want to know that before we call in any
-	 * of the complex code paths. Also we want to prevent
-	 * registration of robust lists in that case. NULL is
-	 * guaranteed to fault and we get -EFAULT on functional
-	 * implementation, the non-functional ones will return
-	 * -ENOSYS.
-	 */
-	if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
-		futex_cmpxchg_enabled = 1;
-#endif
-}
-
-static int __init futex_init(void)
-{
-	unsigned int futex_shift;
-	unsigned long i;
-
-#if CONFIG_BASE_SMALL
-	futex_hashsize = 16;
-#else
-	futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
-#endif
-
-	futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
-					       futex_hashsize, 0,
-					       futex_hashsize < 256 ? HASH_SMALL : 0,
-					       &futex_shift, NULL,
-					       futex_hashsize, futex_hashsize);
-	futex_hashsize = 1UL << futex_shift;
-
-	futex_detect_cmpxchg();
-
-	for (i = 0; i < futex_hashsize; i++) {
-		atomic_set(&futex_queues[i].waiters, 0);
-		plist_head_init(&futex_queues[i].chain);
-		spin_lock_init(&futex_queues[i].lock);
-	}
-
-	return 0;
-}
-core_initcall(futex_init);
--- /dev/null
+++ b/kernel/futex/Makefile
@@ -0,0 +1,3 @@ 
+# SPDX-License-Identifier: GPL-2.0
+
+obj-y += core.o
--- /dev/null
+++ b/kernel/futex/core.c
@@ -0,0 +1,4272 @@ 
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Fast Userspace Mutexes (which I call "Futexes!").
+ *  (C) Rusty Russell, IBM 2002
+ *
+ *  Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
+ *  (C) Copyright 2003 Red Hat Inc, All Rights Reserved
+ *
+ *  Removed page pinning, fix privately mapped COW pages and other cleanups
+ *  (C) Copyright 2003, 2004 Jamie Lokier
+ *
+ *  Robust futex support started by Ingo Molnar
+ *  (C) Copyright 2006 Red Hat Inc, All Rights Reserved
+ *  Thanks to Thomas Gleixner for suggestions, analysis and fixes.
+ *
+ *  PI-futex support started by Ingo Molnar and Thomas Gleixner
+ *  Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ *  Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
+ *
+ *  PRIVATE futexes by Eric Dumazet
+ *  Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
+ *
+ *  Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
+ *  Copyright (C) IBM Corporation, 2009
+ *  Thanks to Thomas Gleixner for conceptual design and careful reviews.
+ *
+ *  Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
+ *  enough at me, Linus for the original (flawed) idea, Matthew
+ *  Kirkwood for proof-of-concept implementation.
+ *
+ *  "The futexes are also cursed."
+ *  "But they come in a choice of three flavours!"
+ */
+#include <linux/compat.h>
+#include <linux/jhash.h>
+#include <linux/pagemap.h>
+#include <linux/syscalls.h>
+#include <linux/freezer.h>
+#include <linux/memblock.h>
+#include <linux/fault-inject.h>
+#include <linux/time_namespace.h>
+
+#include <asm/futex.h>
+
+#include "../locking/rtmutex_common.h"
+
+/*
+ * READ this before attempting to hack on futexes!
+ *
+ * Basic futex operation and ordering guarantees
+ * =============================================
+ *
+ * The waiter reads the futex value in user space and calls
+ * futex_wait(). This function computes the hash bucket and acquires
+ * the hash bucket lock. After that it reads the futex user space value
+ * again and verifies that the data has not changed. If it has not changed
+ * it enqueues itself into the hash bucket, releases the hash bucket lock
+ * and schedules.
+ *
+ * The waker side modifies the user space value of the futex and calls
+ * futex_wake(). This function computes the hash bucket and acquires the
+ * hash bucket lock. Then it looks for waiters on that futex in the hash
+ * bucket and wakes them.
+ *
+ * In futex wake up scenarios where no tasks are blocked on a futex, taking
+ * the hb spinlock can be avoided and simply return. In order for this
+ * optimization to work, ordering guarantees must exist so that the waiter
+ * being added to the list is acknowledged when the list is concurrently being
+ * checked by the waker, avoiding scenarios like the following:
+ *
+ * CPU 0                               CPU 1
+ * val = *futex;
+ * sys_futex(WAIT, futex, val);
+ *   futex_wait(futex, val);
+ *   uval = *futex;
+ *                                     *futex = newval;
+ *                                     sys_futex(WAKE, futex);
+ *                                       futex_wake(futex);
+ *                                       if (queue_empty())
+ *                                         return;
+ *   if (uval == val)
+ *      lock(hash_bucket(futex));
+ *      queue();
+ *     unlock(hash_bucket(futex));
+ *     schedule();
+ *
+ * This would cause the waiter on CPU 0 to wait forever because it
+ * missed the transition of the user space value from val to newval
+ * and the waker did not find the waiter in the hash bucket queue.
+ *
+ * The correct serialization ensures that a waiter either observes
+ * the changed user space value before blocking or is woken by a
+ * concurrent waker:
+ *
+ * CPU 0                                 CPU 1
+ * val = *futex;
+ * sys_futex(WAIT, futex, val);
+ *   futex_wait(futex, val);
+ *
+ *   waiters++; (a)
+ *   smp_mb(); (A) <-- paired with -.
+ *                                  |
+ *   lock(hash_bucket(futex));      |
+ *                                  |
+ *   uval = *futex;                 |
+ *                                  |        *futex = newval;
+ *                                  |        sys_futex(WAKE, futex);
+ *                                  |          futex_wake(futex);
+ *                                  |
+ *                                  `--------> smp_mb(); (B)
+ *   if (uval == val)
+ *     queue();
+ *     unlock(hash_bucket(futex));
+ *     schedule();                         if (waiters)
+ *                                           lock(hash_bucket(futex));
+ *   else                                    wake_waiters(futex);
+ *     waiters--; (b)                        unlock(hash_bucket(futex));
+ *
+ * Where (A) orders the waiters increment and the futex value read through
+ * atomic operations (see hb_waiters_inc) and where (B) orders the write
+ * to futex and the waiters read (see hb_waiters_pending()).
+ *
+ * This yields the following case (where X:=waiters, Y:=futex):
+ *
+ *	X = Y = 0
+ *
+ *	w[X]=1		w[Y]=1
+ *	MB		MB
+ *	r[Y]=y		r[X]=x
+ *
+ * Which guarantees that x==0 && y==0 is impossible; which translates back into
+ * the guarantee that we cannot both miss the futex variable change and the
+ * enqueue.
+ *
+ * Note that a new waiter is accounted for in (a) even when it is possible that
+ * the wait call can return error, in which case we backtrack from it in (b).
+ * Refer to the comment in queue_lock().
+ *
+ * Similarly, in order to account for waiters being requeued on another
+ * address we always increment the waiters for the destination bucket before
+ * acquiring the lock. It then decrements them again  after releasing it -
+ * the code that actually moves the futex(es) between hash buckets (requeue_futex)
+ * will do the additional required waiter count housekeeping. This is done for
+ * double_lock_hb() and double_unlock_hb(), respectively.
+ */
+
+#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
+#define futex_cmpxchg_enabled 1
+#else
+static int  __read_mostly futex_cmpxchg_enabled;
+#endif
+
+/*
+ * Futex flags used to encode options to functions and preserve them across
+ * restarts.
+ */
+#ifdef CONFIG_MMU
+# define FLAGS_SHARED		0x01
+#else
+/*
+ * NOMMU does not have per process address space. Let the compiler optimize
+ * code away.
+ */
+# define FLAGS_SHARED		0x00
+#endif
+#define FLAGS_CLOCKRT		0x02
+#define FLAGS_HAS_TIMEOUT	0x04
+
+/*
+ * Priority Inheritance state:
+ */
+struct futex_pi_state {
+	/*
+	 * list of 'owned' pi_state instances - these have to be
+	 * cleaned up in do_exit() if the task exits prematurely:
+	 */
+	struct list_head list;
+
+	/*
+	 * The PI object:
+	 */
+	struct rt_mutex_base pi_mutex;
+
+	struct task_struct *owner;
+	refcount_t refcount;
+
+	union futex_key key;
+} __randomize_layout;
+
+/**
+ * struct futex_q - The hashed futex queue entry, one per waiting task
+ * @list:		priority-sorted list of tasks waiting on this futex
+ * @task:		the task waiting on the futex
+ * @lock_ptr:		the hash bucket lock
+ * @key:		the key the futex is hashed on
+ * @pi_state:		optional priority inheritance state
+ * @rt_waiter:		rt_waiter storage for use with requeue_pi
+ * @requeue_pi_key:	the requeue_pi target futex key
+ * @bitset:		bitset for the optional bitmasked wakeup
+ * @requeue_state:	State field for futex_requeue_pi()
+ * @requeue_wait:	RCU wait for futex_requeue_pi() (RT only)
+ *
+ * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
+ * we can wake only the relevant ones (hashed queues may be shared).
+ *
+ * A futex_q has a woken state, just like tasks have TASK_RUNNING.
+ * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
+ * The order of wakeup is always to make the first condition true, then
+ * the second.
+ *
+ * PI futexes are typically woken before they are removed from the hash list via
+ * the rt_mutex code. See unqueue_me_pi().
+ */
+struct futex_q {
+	struct plist_node list;
+
+	struct task_struct *task;
+	spinlock_t *lock_ptr;
+	union futex_key key;
+	struct futex_pi_state *pi_state;
+	struct rt_mutex_waiter *rt_waiter;
+	union futex_key *requeue_pi_key;
+	u32 bitset;
+	atomic_t requeue_state;
+#ifdef CONFIG_PREEMPT_RT
+	struct rcuwait requeue_wait;
+#endif
+} __randomize_layout;
+
+/*
+ * On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
+ * underlying rtmutex. The task which is about to be requeued could have
+ * just woken up (timeout, signal). After the wake up the task has to
+ * acquire hash bucket lock, which is held by the requeue code.  As a task
+ * can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking
+ * and the hash bucket lock blocking would collide and corrupt state.
+ *
+ * On !PREEMPT_RT this is not a problem and everything could be serialized
+ * on hash bucket lock, but aside of having the benefit of common code,
+ * this allows to avoid doing the requeue when the task is already on the
+ * way out and taking the hash bucket lock of the original uaddr1 when the
+ * requeue has been completed.
+ *
+ * The following state transitions are valid:
+ *
+ * On the waiter side:
+ *   Q_REQUEUE_PI_NONE		-> Q_REQUEUE_PI_IGNORE
+ *   Q_REQUEUE_PI_IN_PROGRESS	-> Q_REQUEUE_PI_WAIT
+ *
+ * On the requeue side:
+ *   Q_REQUEUE_PI_NONE		-> Q_REQUEUE_PI_INPROGRESS
+ *   Q_REQUEUE_PI_IN_PROGRESS	-> Q_REQUEUE_PI_DONE/LOCKED
+ *   Q_REQUEUE_PI_IN_PROGRESS	-> Q_REQUEUE_PI_NONE (requeue failed)
+ *   Q_REQUEUE_PI_WAIT		-> Q_REQUEUE_PI_DONE/LOCKED
+ *   Q_REQUEUE_PI_WAIT		-> Q_REQUEUE_PI_IGNORE (requeue failed)
+ *
+ * The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this
+ * signals that the waiter is already on the way out. It also means that
+ * the waiter is still on the 'wait' futex, i.e. uaddr1.
+ *
+ * The waiter side signals early wakeup to the requeue side either through
+ * setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending
+ * on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately
+ * proceed to take the hash bucket lock of uaddr1. If it set state to WAIT,
+ * which means the wakeup is interleaving with a requeue in progress it has
+ * to wait for the requeue side to change the state. Either to DONE/LOCKED
+ * or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex
+ * and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by
+ * the requeue side when the requeue attempt failed via deadlock detection
+ * and therefore the waiter q is still on the uaddr1 futex.
+ */
+enum {
+	Q_REQUEUE_PI_NONE		=  0,
+	Q_REQUEUE_PI_IGNORE,
+	Q_REQUEUE_PI_IN_PROGRESS,
+	Q_REQUEUE_PI_WAIT,
+	Q_REQUEUE_PI_DONE,
+	Q_REQUEUE_PI_LOCKED,
+};
+
+static const struct futex_q futex_q_init = {
+	/* list gets initialized in queue_me()*/
+	.key		= FUTEX_KEY_INIT,
+	.bitset		= FUTEX_BITSET_MATCH_ANY,
+	.requeue_state	= ATOMIC_INIT(Q_REQUEUE_PI_NONE),
+};
+
+/*
+ * Hash buckets are shared by all the futex_keys that hash to the same
+ * location.  Each key may have multiple futex_q structures, one for each task
+ * waiting on a futex.
+ */
+struct futex_hash_bucket {
+	atomic_t waiters;
+	spinlock_t lock;
+	struct plist_head chain;
+} ____cacheline_aligned_in_smp;
+
+/*
+ * The base of the bucket array and its size are always used together
+ * (after initialization only in hash_futex()), so ensure that they
+ * reside in the same cacheline.
+ */
+static struct {
+	struct futex_hash_bucket *queues;
+	unsigned long            hashsize;
+} __futex_data __read_mostly __aligned(2*sizeof(long));
+#define futex_queues   (__futex_data.queues)
+#define futex_hashsize (__futex_data.hashsize)
+
+
+/*
+ * Fault injections for futexes.
+ */
+#ifdef CONFIG_FAIL_FUTEX
+
+static struct {
+	struct fault_attr attr;
+
+	bool ignore_private;
+} fail_futex = {
+	.attr = FAULT_ATTR_INITIALIZER,
+	.ignore_private = false,
+};
+
+static int __init setup_fail_futex(char *str)
+{
+	return setup_fault_attr(&fail_futex.attr, str);
+}
+__setup("fail_futex=", setup_fail_futex);
+
+static bool should_fail_futex(bool fshared)
+{
+	if (fail_futex.ignore_private && !fshared)
+		return false;
+
+	return should_fail(&fail_futex.attr, 1);
+}
+
+#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
+
+static int __init fail_futex_debugfs(void)
+{
+	umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
+	struct dentry *dir;
+
+	dir = fault_create_debugfs_attr("fail_futex", NULL,
+					&fail_futex.attr);
+	if (IS_ERR(dir))
+		return PTR_ERR(dir);
+
+	debugfs_create_bool("ignore-private", mode, dir,
+			    &fail_futex.ignore_private);
+	return 0;
+}
+
+late_initcall(fail_futex_debugfs);
+
+#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
+
+#else
+static inline bool should_fail_futex(bool fshared)
+{
+	return false;
+}
+#endif /* CONFIG_FAIL_FUTEX */
+
+#ifdef CONFIG_COMPAT
+static void compat_exit_robust_list(struct task_struct *curr);
+#endif
+
+/*
+ * Reflects a new waiter being added to the waitqueue.
+ */
+static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
+{
+#ifdef CONFIG_SMP
+	atomic_inc(&hb->waiters);
+	/*
+	 * Full barrier (A), see the ordering comment above.
+	 */
+	smp_mb__after_atomic();
+#endif
+}
+
+/*
+ * Reflects a waiter being removed from the waitqueue by wakeup
+ * paths.
+ */
+static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
+{
+#ifdef CONFIG_SMP
+	atomic_dec(&hb->waiters);
+#endif
+}
+
+static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
+{
+#ifdef CONFIG_SMP
+	/*
+	 * Full barrier (B), see the ordering comment above.
+	 */
+	smp_mb();
+	return atomic_read(&hb->waiters);
+#else
+	return 1;
+#endif
+}
+
+/**
+ * hash_futex - Return the hash bucket in the global hash
+ * @key:	Pointer to the futex key for which the hash is calculated
+ *
+ * We hash on the keys returned from get_futex_key (see below) and return the
+ * corresponding hash bucket in the global hash.
+ */
+static struct futex_hash_bucket *hash_futex(union futex_key *key)
+{
+	u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
+			  key->both.offset);
+
+	return &futex_queues[hash & (futex_hashsize - 1)];
+}
+
+
+/**
+ * match_futex - Check whether two futex keys are equal
+ * @key1:	Pointer to key1
+ * @key2:	Pointer to key2
+ *
+ * Return 1 if two futex_keys are equal, 0 otherwise.
+ */
+static inline int match_futex(union futex_key *key1, union futex_key *key2)
+{
+	return (key1 && key2
+		&& key1->both.word == key2->both.word
+		&& key1->both.ptr == key2->both.ptr
+		&& key1->both.offset == key2->both.offset);
+}
+
+enum futex_access {
+	FUTEX_READ,
+	FUTEX_WRITE
+};
+
+/**
+ * futex_setup_timer - set up the sleeping hrtimer.
+ * @time:	ptr to the given timeout value
+ * @timeout:	the hrtimer_sleeper structure to be set up
+ * @flags:	futex flags
+ * @range_ns:	optional range in ns
+ *
+ * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
+ *	   value given
+ */
+static inline struct hrtimer_sleeper *
+futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
+		  int flags, u64 range_ns)
+{
+	if (!time)
+		return NULL;
+
+	hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
+				      CLOCK_REALTIME : CLOCK_MONOTONIC,
+				      HRTIMER_MODE_ABS);
+	/*
+	 * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
+	 * effectively the same as calling hrtimer_set_expires().
+	 */
+	hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
+
+	return timeout;
+}
+
+/*
+ * Generate a machine wide unique identifier for this inode.
+ *
+ * This relies on u64 not wrapping in the life-time of the machine; which with
+ * 1ns resolution means almost 585 years.
+ *
+ * This further relies on the fact that a well formed program will not unmap
+ * the file while it has a (shared) futex waiting on it. This mapping will have
+ * a file reference which pins the mount and inode.
+ *
+ * If for some reason an inode gets evicted and read back in again, it will get
+ * a new sequence number and will _NOT_ match, even though it is the exact same
+ * file.
+ *
+ * It is important that match_futex() will never have a false-positive, esp.
+ * for PI futexes that can mess up the state. The above argues that false-negatives
+ * are only possible for malformed programs.
+ */
+static u64 get_inode_sequence_number(struct inode *inode)
+{
+	static atomic64_t i_seq;
+	u64 old;
+
+	/* Does the inode already have a sequence number? */
+	old = atomic64_read(&inode->i_sequence);
+	if (likely(old))
+		return old;
+
+	for (;;) {
+		u64 new = atomic64_add_return(1, &i_seq);
+		if (WARN_ON_ONCE(!new))
+			continue;
+
+		old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
+		if (old)
+			return old;
+		return new;
+	}
+}
+
+/**
+ * get_futex_key() - Get parameters which are the keys for a futex
+ * @uaddr:	virtual address of the futex
+ * @fshared:	false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
+ * @key:	address where result is stored.
+ * @rw:		mapping needs to be read/write (values: FUTEX_READ,
+ *              FUTEX_WRITE)
+ *
+ * Return: a negative error code or 0
+ *
+ * The key words are stored in @key on success.
+ *
+ * For shared mappings (when @fshared), the key is:
+ *
+ *   ( inode->i_sequence, page->index, offset_within_page )
+ *
+ * [ also see get_inode_sequence_number() ]
+ *
+ * For private mappings (or when !@fshared), the key is:
+ *
+ *   ( current->mm, address, 0 )
+ *
+ * This allows (cross process, where applicable) identification of the futex
+ * without keeping the page pinned for the duration of the FUTEX_WAIT.
+ *
+ * lock_page() might sleep, the caller should not hold a spinlock.
+ */
+static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
+			 enum futex_access rw)
+{
+	unsigned long address = (unsigned long)uaddr;
+	struct mm_struct *mm = current->mm;
+	struct page *page, *tail;
+	struct address_space *mapping;
+	int err, ro = 0;
+
+	/*
+	 * The futex address must be "naturally" aligned.
+	 */
+	key->both.offset = address % PAGE_SIZE;
+	if (unlikely((address % sizeof(u32)) != 0))
+		return -EINVAL;
+	address -= key->both.offset;
+
+	if (unlikely(!access_ok(uaddr, sizeof(u32))))
+		return -EFAULT;
+
+	if (unlikely(should_fail_futex(fshared)))
+		return -EFAULT;
+
+	/*
+	 * PROCESS_PRIVATE futexes are fast.
+	 * As the mm cannot disappear under us and the 'key' only needs
+	 * virtual address, we dont even have to find the underlying vma.
+	 * Note : We do have to check 'uaddr' is a valid user address,
+	 *        but access_ok() should be faster than find_vma()
+	 */
+	if (!fshared) {
+		key->private.mm = mm;
+		key->private.address = address;
+		return 0;
+	}
+
+again:
+	/* Ignore any VERIFY_READ mapping (futex common case) */
+	if (unlikely(should_fail_futex(true)))
+		return -EFAULT;
+
+	err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
+	/*
+	 * If write access is not required (eg. FUTEX_WAIT), try
+	 * and get read-only access.
+	 */
+	if (err == -EFAULT && rw == FUTEX_READ) {
+		err = get_user_pages_fast(address, 1, 0, &page);
+		ro = 1;
+	}
+	if (err < 0)
+		return err;
+	else
+		err = 0;
+
+	/*
+	 * The treatment of mapping from this point on is critical. The page
+	 * lock protects many things but in this context the page lock
+	 * stabilizes mapping, prevents inode freeing in the shared
+	 * file-backed region case and guards against movement to swap cache.
+	 *
+	 * Strictly speaking the page lock is not needed in all cases being
+	 * considered here and page lock forces unnecessarily serialization
+	 * From this point on, mapping will be re-verified if necessary and
+	 * page lock will be acquired only if it is unavoidable
+	 *
+	 * Mapping checks require the head page for any compound page so the
+	 * head page and mapping is looked up now. For anonymous pages, it
+	 * does not matter if the page splits in the future as the key is
+	 * based on the address. For filesystem-backed pages, the tail is
+	 * required as the index of the page determines the key. For
+	 * base pages, there is no tail page and tail == page.
+	 */
+	tail = page;
+	page = compound_head(page);
+	mapping = READ_ONCE(page->mapping);
+
+	/*
+	 * If page->mapping is NULL, then it cannot be a PageAnon
+	 * page; but it might be the ZERO_PAGE or in the gate area or
+	 * in a special mapping (all cases which we are happy to fail);
+	 * or it may have been a good file page when get_user_pages_fast
+	 * found it, but truncated or holepunched or subjected to
+	 * invalidate_complete_page2 before we got the page lock (also
+	 * cases which we are happy to fail).  And we hold a reference,
+	 * so refcount care in invalidate_complete_page's remove_mapping
+	 * prevents drop_caches from setting mapping to NULL beneath us.
+	 *
+	 * The case we do have to guard against is when memory pressure made
+	 * shmem_writepage move it from filecache to swapcache beneath us:
+	 * an unlikely race, but we do need to retry for page->mapping.
+	 */
+	if (unlikely(!mapping)) {
+		int shmem_swizzled;
+
+		/*
+		 * Page lock is required to identify which special case above
+		 * applies. If this is really a shmem page then the page lock
+		 * will prevent unexpected transitions.
+		 */
+		lock_page(page);
+		shmem_swizzled = PageSwapCache(page) || page->mapping;
+		unlock_page(page);
+		put_page(page);
+
+		if (shmem_swizzled)
+			goto again;
+
+		return -EFAULT;
+	}
+
+	/*
+	 * Private mappings are handled in a simple way.
+	 *
+	 * If the futex key is stored on an anonymous page, then the associated
+	 * object is the mm which is implicitly pinned by the calling process.
+	 *
+	 * NOTE: When userspace waits on a MAP_SHARED mapping, even if
+	 * it's a read-only handle, it's expected that futexes attach to
+	 * the object not the particular process.
+	 */
+	if (PageAnon(page)) {
+		/*
+		 * A RO anonymous page will never change and thus doesn't make
+		 * sense for futex operations.
+		 */
+		if (unlikely(should_fail_futex(true)) || ro) {
+			err = -EFAULT;
+			goto out;
+		}
+
+		key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
+		key->private.mm = mm;
+		key->private.address = address;
+
+	} else {
+		struct inode *inode;
+
+		/*
+		 * The associated futex object in this case is the inode and
+		 * the page->mapping must be traversed. Ordinarily this should
+		 * be stabilised under page lock but it's not strictly
+		 * necessary in this case as we just want to pin the inode, not
+		 * update the radix tree or anything like that.
+		 *
+		 * The RCU read lock is taken as the inode is finally freed
+		 * under RCU. If the mapping still matches expectations then the
+		 * mapping->host can be safely accessed as being a valid inode.
+		 */
+		rcu_read_lock();
+
+		if (READ_ONCE(page->mapping) != mapping) {
+			rcu_read_unlock();
+			put_page(page);
+
+			goto again;
+		}
+
+		inode = READ_ONCE(mapping->host);
+		if (!inode) {
+			rcu_read_unlock();
+			put_page(page);
+
+			goto again;
+		}
+
+		key->both.offset |= FUT_OFF_INODE; /* inode-based key */
+		key->shared.i_seq = get_inode_sequence_number(inode);
+		key->shared.pgoff = page_to_pgoff(tail);
+		rcu_read_unlock();
+	}
+
+out:
+	put_page(page);
+	return err;
+}
+
+/**
+ * fault_in_user_writeable() - Fault in user address and verify RW access
+ * @uaddr:	pointer to faulting user space address
+ *
+ * Slow path to fixup the fault we just took in the atomic write
+ * access to @uaddr.
+ *
+ * We have no generic implementation of a non-destructive write to the
+ * user address. We know that we faulted in the atomic pagefault
+ * disabled section so we can as well avoid the #PF overhead by
+ * calling get_user_pages() right away.
+ */
+static int fault_in_user_writeable(u32 __user *uaddr)
+{
+	struct mm_struct *mm = current->mm;
+	int ret;
+
+	mmap_read_lock(mm);
+	ret = fixup_user_fault(mm, (unsigned long)uaddr,
+			       FAULT_FLAG_WRITE, NULL);
+	mmap_read_unlock(mm);
+
+	return ret < 0 ? ret : 0;
+}
+
+/**
+ * futex_top_waiter() - Return the highest priority waiter on a futex
+ * @hb:		the hash bucket the futex_q's reside in
+ * @key:	the futex key (to distinguish it from other futex futex_q's)
+ *
+ * Must be called with the hb lock held.
+ */
+static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
+					union futex_key *key)
+{
+	struct futex_q *this;
+
+	plist_for_each_entry(this, &hb->chain, list) {
+		if (match_futex(&this->key, key))
+			return this;
+	}
+	return NULL;
+}
+
+static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
+				      u32 uval, u32 newval)
+{
+	int ret;
+
+	pagefault_disable();
+	ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
+	pagefault_enable();
+
+	return ret;
+}
+
+static int get_futex_value_locked(u32 *dest, u32 __user *from)
+{
+	int ret;
+
+	pagefault_disable();
+	ret = __get_user(*dest, from);
+	pagefault_enable();
+
+	return ret ? -EFAULT : 0;
+}
+
+
+/*
+ * PI code:
+ */
+static int refill_pi_state_cache(void)
+{
+	struct futex_pi_state *pi_state;
+
+	if (likely(current->pi_state_cache))
+		return 0;
+
+	pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
+
+	if (!pi_state)
+		return -ENOMEM;
+
+	INIT_LIST_HEAD(&pi_state->list);
+	/* pi_mutex gets initialized later */
+	pi_state->owner = NULL;
+	refcount_set(&pi_state->refcount, 1);
+	pi_state->key = FUTEX_KEY_INIT;
+
+	current->pi_state_cache = pi_state;
+
+	return 0;
+}
+
+static struct futex_pi_state *alloc_pi_state(void)
+{
+	struct futex_pi_state *pi_state = current->pi_state_cache;
+
+	WARN_ON(!pi_state);
+	current->pi_state_cache = NULL;
+
+	return pi_state;
+}
+
+static void pi_state_update_owner(struct futex_pi_state *pi_state,
+				  struct task_struct *new_owner)
+{
+	struct task_struct *old_owner = pi_state->owner;
+
+	lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
+
+	if (old_owner) {
+		raw_spin_lock(&old_owner->pi_lock);
+		WARN_ON(list_empty(&pi_state->list));
+		list_del_init(&pi_state->list);
+		raw_spin_unlock(&old_owner->pi_lock);
+	}
+
+	if (new_owner) {
+		raw_spin_lock(&new_owner->pi_lock);
+		WARN_ON(!list_empty(&pi_state->list));
+		list_add(&pi_state->list, &new_owner->pi_state_list);
+		pi_state->owner = new_owner;
+		raw_spin_unlock(&new_owner->pi_lock);
+	}
+}
+
+static void get_pi_state(struct futex_pi_state *pi_state)
+{
+	WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
+}
+
+/*
+ * Drops a reference to the pi_state object and frees or caches it
+ * when the last reference is gone.
+ */
+static void put_pi_state(struct futex_pi_state *pi_state)
+{
+	if (!pi_state)
+		return;
+
+	if (!refcount_dec_and_test(&pi_state->refcount))
+		return;
+
+	/*
+	 * If pi_state->owner is NULL, the owner is most probably dying
+	 * and has cleaned up the pi_state already
+	 */
+	if (pi_state->owner) {
+		unsigned long flags;
+
+		raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
+		pi_state_update_owner(pi_state, NULL);
+		rt_mutex_proxy_unlock(&pi_state->pi_mutex);
+		raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
+	}
+
+	if (current->pi_state_cache) {
+		kfree(pi_state);
+	} else {
+		/*
+		 * pi_state->list is already empty.
+		 * clear pi_state->owner.
+		 * refcount is at 0 - put it back to 1.
+		 */
+		pi_state->owner = NULL;
+		refcount_set(&pi_state->refcount, 1);
+		current->pi_state_cache = pi_state;
+	}
+}
+
+#ifdef CONFIG_FUTEX_PI
+
+/*
+ * This task is holding PI mutexes at exit time => bad.
+ * Kernel cleans up PI-state, but userspace is likely hosed.
+ * (Robust-futex cleanup is separate and might save the day for userspace.)
+ */
+static void exit_pi_state_list(struct task_struct *curr)
+{
+	struct list_head *next, *head = &curr->pi_state_list;
+	struct futex_pi_state *pi_state;
+	struct futex_hash_bucket *hb;
+	union futex_key key = FUTEX_KEY_INIT;
+
+	if (!futex_cmpxchg_enabled)
+		return;
+	/*
+	 * We are a ZOMBIE and nobody can enqueue itself on
+	 * pi_state_list anymore, but we have to be careful
+	 * versus waiters unqueueing themselves:
+	 */
+	raw_spin_lock_irq(&curr->pi_lock);
+	while (!list_empty(head)) {
+		next = head->next;
+		pi_state = list_entry(next, struct futex_pi_state, list);
+		key = pi_state->key;
+		hb = hash_futex(&key);
+
+		/*
+		 * We can race against put_pi_state() removing itself from the
+		 * list (a waiter going away). put_pi_state() will first
+		 * decrement the reference count and then modify the list, so
+		 * its possible to see the list entry but fail this reference
+		 * acquire.
+		 *
+		 * In that case; drop the locks to let put_pi_state() make
+		 * progress and retry the loop.
+		 */
+		if (!refcount_inc_not_zero(&pi_state->refcount)) {
+			raw_spin_unlock_irq(&curr->pi_lock);
+			cpu_relax();
+			raw_spin_lock_irq(&curr->pi_lock);
+			continue;
+		}
+		raw_spin_unlock_irq(&curr->pi_lock);
+
+		spin_lock(&hb->lock);
+		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+		raw_spin_lock(&curr->pi_lock);
+		/*
+		 * We dropped the pi-lock, so re-check whether this
+		 * task still owns the PI-state:
+		 */
+		if (head->next != next) {
+			/* retain curr->pi_lock for the loop invariant */
+			raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
+			spin_unlock(&hb->lock);
+			put_pi_state(pi_state);
+			continue;
+		}
+
+		WARN_ON(pi_state->owner != curr);
+		WARN_ON(list_empty(&pi_state->list));
+		list_del_init(&pi_state->list);
+		pi_state->owner = NULL;
+
+		raw_spin_unlock(&curr->pi_lock);
+		raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+		spin_unlock(&hb->lock);
+
+		rt_mutex_futex_unlock(&pi_state->pi_mutex);
+		put_pi_state(pi_state);
+
+		raw_spin_lock_irq(&curr->pi_lock);
+	}
+	raw_spin_unlock_irq(&curr->pi_lock);
+}
+#else
+static inline void exit_pi_state_list(struct task_struct *curr) { }
+#endif
+
+/*
+ * We need to check the following states:
+ *
+ *      Waiter | pi_state | pi->owner | uTID      | uODIED | ?
+ *
+ * [1]  NULL   | ---      | ---       | 0         | 0/1    | Valid
+ * [2]  NULL   | ---      | ---       | >0        | 0/1    | Valid
+ *
+ * [3]  Found  | NULL     | --        | Any       | 0/1    | Invalid
+ *
+ * [4]  Found  | Found    | NULL      | 0         | 1      | Valid
+ * [5]  Found  | Found    | NULL      | >0        | 1      | Invalid
+ *
+ * [6]  Found  | Found    | task      | 0         | 1      | Valid
+ *
+ * [7]  Found  | Found    | NULL      | Any       | 0      | Invalid
+ *
+ * [8]  Found  | Found    | task      | ==taskTID | 0/1    | Valid
+ * [9]  Found  | Found    | task      | 0         | 0      | Invalid
+ * [10] Found  | Found    | task      | !=taskTID | 0/1    | Invalid
+ *
+ * [1]	Indicates that the kernel can acquire the futex atomically. We
+ *	came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
+ *
+ * [2]	Valid, if TID does not belong to a kernel thread. If no matching
+ *      thread is found then it indicates that the owner TID has died.
+ *
+ * [3]	Invalid. The waiter is queued on a non PI futex
+ *
+ * [4]	Valid state after exit_robust_list(), which sets the user space
+ *	value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
+ *
+ * [5]	The user space value got manipulated between exit_robust_list()
+ *	and exit_pi_state_list()
+ *
+ * [6]	Valid state after exit_pi_state_list() which sets the new owner in
+ *	the pi_state but cannot access the user space value.
+ *
+ * [7]	pi_state->owner can only be NULL when the OWNER_DIED bit is set.
+ *
+ * [8]	Owner and user space value match
+ *
+ * [9]	There is no transient state which sets the user space TID to 0
+ *	except exit_robust_list(), but this is indicated by the
+ *	FUTEX_OWNER_DIED bit. See [4]
+ *
+ * [10] There is no transient state which leaves owner and user space
+ *	TID out of sync. Except one error case where the kernel is denied
+ *	write access to the user address, see fixup_pi_state_owner().
+ *
+ *
+ * Serialization and lifetime rules:
+ *
+ * hb->lock:
+ *
+ *	hb -> futex_q, relation
+ *	futex_q -> pi_state, relation
+ *
+ *	(cannot be raw because hb can contain arbitrary amount
+ *	 of futex_q's)
+ *
+ * pi_mutex->wait_lock:
+ *
+ *	{uval, pi_state}
+ *
+ *	(and pi_mutex 'obviously')
+ *
+ * p->pi_lock:
+ *
+ *	p->pi_state_list -> pi_state->list, relation
+ *	pi_mutex->owner -> pi_state->owner, relation
+ *
+ * pi_state->refcount:
+ *
+ *	pi_state lifetime
+ *
+ *
+ * Lock order:
+ *
+ *   hb->lock
+ *     pi_mutex->wait_lock
+ *       p->pi_lock
+ *
+ */
+
+/*
+ * Validate that the existing waiter has a pi_state and sanity check
+ * the pi_state against the user space value. If correct, attach to
+ * it.
+ */
+static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
+			      struct futex_pi_state *pi_state,
+			      struct futex_pi_state **ps)
+{
+	pid_t pid = uval & FUTEX_TID_MASK;
+	u32 uval2;
+	int ret;
+
+	/*
+	 * Userspace might have messed up non-PI and PI futexes [3]
+	 */
+	if (unlikely(!pi_state))
+		return -EINVAL;
+
+	/*
+	 * We get here with hb->lock held, and having found a
+	 * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
+	 * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
+	 * which in turn means that futex_lock_pi() still has a reference on
+	 * our pi_state.
+	 *
+	 * The waiter holding a reference on @pi_state also protects against
+	 * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
+	 * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
+	 * free pi_state before we can take a reference ourselves.
+	 */
+	WARN_ON(!refcount_read(&pi_state->refcount));
+
+	/*
+	 * Now that we have a pi_state, we can acquire wait_lock
+	 * and do the state validation.
+	 */
+	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+	/*
+	 * Since {uval, pi_state} is serialized by wait_lock, and our current
+	 * uval was read without holding it, it can have changed. Verify it
+	 * still is what we expect it to be, otherwise retry the entire
+	 * operation.
+	 */
+	if (get_futex_value_locked(&uval2, uaddr))
+		goto out_efault;
+
+	if (uval != uval2)
+		goto out_eagain;
+
+	/*
+	 * Handle the owner died case:
+	 */
+	if (uval & FUTEX_OWNER_DIED) {
+		/*
+		 * exit_pi_state_list sets owner to NULL and wakes the
+		 * topmost waiter. The task which acquires the
+		 * pi_state->rt_mutex will fixup owner.
+		 */
+		if (!pi_state->owner) {
+			/*
+			 * No pi state owner, but the user space TID
+			 * is not 0. Inconsistent state. [5]
+			 */
+			if (pid)
+				goto out_einval;
+			/*
+			 * Take a ref on the state and return success. [4]
+			 */
+			goto out_attach;
+		}
+
+		/*
+		 * If TID is 0, then either the dying owner has not
+		 * yet executed exit_pi_state_list() or some waiter
+		 * acquired the rtmutex in the pi state, but did not
+		 * yet fixup the TID in user space.
+		 *
+		 * Take a ref on the state and return success. [6]
+		 */
+		if (!pid)
+			goto out_attach;
+	} else {
+		/*
+		 * If the owner died bit is not set, then the pi_state
+		 * must have an owner. [7]
+		 */
+		if (!pi_state->owner)
+			goto out_einval;
+	}
+
+	/*
+	 * Bail out if user space manipulated the futex value. If pi
+	 * state exists then the owner TID must be the same as the
+	 * user space TID. [9/10]
+	 */
+	if (pid != task_pid_vnr(pi_state->owner))
+		goto out_einval;
+
+out_attach:
+	get_pi_state(pi_state);
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	*ps = pi_state;
+	return 0;
+
+out_einval:
+	ret = -EINVAL;
+	goto out_error;
+
+out_eagain:
+	ret = -EAGAIN;
+	goto out_error;
+
+out_efault:
+	ret = -EFAULT;
+	goto out_error;
+
+out_error:
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	return ret;
+}
+
+/**
+ * wait_for_owner_exiting - Block until the owner has exited
+ * @ret: owner's current futex lock status
+ * @exiting:	Pointer to the exiting task
+ *
+ * Caller must hold a refcount on @exiting.
+ */
+static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
+{
+	if (ret != -EBUSY) {
+		WARN_ON_ONCE(exiting);
+		return;
+	}
+
+	if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
+		return;
+
+	mutex_lock(&exiting->futex_exit_mutex);
+	/*
+	 * No point in doing state checking here. If the waiter got here
+	 * while the task was in exec()->exec_futex_release() then it can
+	 * have any FUTEX_STATE_* value when the waiter has acquired the
+	 * mutex. OK, if running, EXITING or DEAD if it reached exit()
+	 * already. Highly unlikely and not a problem. Just one more round
+	 * through the futex maze.
+	 */
+	mutex_unlock(&exiting->futex_exit_mutex);
+
+	put_task_struct(exiting);
+}
+
+static int handle_exit_race(u32 __user *uaddr, u32 uval,
+			    struct task_struct *tsk)
+{
+	u32 uval2;
+
+	/*
+	 * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
+	 * caller that the alleged owner is busy.
+	 */
+	if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
+		return -EBUSY;
+
+	/*
+	 * Reread the user space value to handle the following situation:
+	 *
+	 * CPU0				CPU1
+	 *
+	 * sys_exit()			sys_futex()
+	 *  do_exit()			 futex_lock_pi()
+	 *                                futex_lock_pi_atomic()
+	 *   exit_signals(tsk)		    No waiters:
+	 *    tsk->flags |= PF_EXITING;	    *uaddr == 0x00000PID
+	 *  mm_release(tsk)		    Set waiter bit
+	 *   exit_robust_list(tsk) {	    *uaddr = 0x80000PID;
+	 *      Set owner died		    attach_to_pi_owner() {
+	 *    *uaddr = 0xC0000000;	     tsk = get_task(PID);
+	 *   }				     if (!tsk->flags & PF_EXITING) {
+	 *  ...				       attach();
+	 *  tsk->futex_state =               } else {
+	 *	FUTEX_STATE_DEAD;              if (tsk->futex_state !=
+	 *					  FUTEX_STATE_DEAD)
+	 *				         return -EAGAIN;
+	 *				       return -ESRCH; <--- FAIL
+	 *				     }
+	 *
+	 * Returning ESRCH unconditionally is wrong here because the
+	 * user space value has been changed by the exiting task.
+	 *
+	 * The same logic applies to the case where the exiting task is
+	 * already gone.
+	 */
+	if (get_futex_value_locked(&uval2, uaddr))
+		return -EFAULT;
+
+	/* If the user space value has changed, try again. */
+	if (uval2 != uval)
+		return -EAGAIN;
+
+	/*
+	 * The exiting task did not have a robust list, the robust list was
+	 * corrupted or the user space value in *uaddr is simply bogus.
+	 * Give up and tell user space.
+	 */
+	return -ESRCH;
+}
+
+static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
+				 struct futex_pi_state **ps)
+{
+	/*
+	 * No existing pi state. First waiter. [2]
+	 *
+	 * This creates pi_state, we have hb->lock held, this means nothing can
+	 * observe this state, wait_lock is irrelevant.
+	 */
+	struct futex_pi_state *pi_state = alloc_pi_state();
+
+	/*
+	 * Initialize the pi_mutex in locked state and make @p
+	 * the owner of it:
+	 */
+	rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
+
+	/* Store the key for possible exit cleanups: */
+	pi_state->key = *key;
+
+	WARN_ON(!list_empty(&pi_state->list));
+	list_add(&pi_state->list, &p->pi_state_list);
+	/*
+	 * Assignment without holding pi_state->pi_mutex.wait_lock is safe
+	 * because there is no concurrency as the object is not published yet.
+	 */
+	pi_state->owner = p;
+
+	*ps = pi_state;
+}
+/*
+ * Lookup the task for the TID provided from user space and attach to
+ * it after doing proper sanity checks.
+ */
+static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
+			      struct futex_pi_state **ps,
+			      struct task_struct **exiting)
+{
+	pid_t pid = uval & FUTEX_TID_MASK;
+	struct task_struct *p;
+
+	/*
+	 * We are the first waiter - try to look up the real owner and attach
+	 * the new pi_state to it, but bail out when TID = 0 [1]
+	 *
+	 * The !pid check is paranoid. None of the call sites should end up
+	 * with pid == 0, but better safe than sorry. Let the caller retry
+	 */
+	if (!pid)
+		return -EAGAIN;
+	p = find_get_task_by_vpid(pid);
+	if (!p)
+		return handle_exit_race(uaddr, uval, NULL);
+
+	if (unlikely(p->flags & PF_KTHREAD)) {
+		put_task_struct(p);
+		return -EPERM;
+	}
+
+	/*
+	 * We need to look at the task state to figure out, whether the
+	 * task is exiting. To protect against the change of the task state
+	 * in futex_exit_release(), we do this protected by p->pi_lock:
+	 */
+	raw_spin_lock_irq(&p->pi_lock);
+	if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
+		/*
+		 * The task is on the way out. When the futex state is
+		 * FUTEX_STATE_DEAD, we know that the task has finished
+		 * the cleanup:
+		 */
+		int ret = handle_exit_race(uaddr, uval, p);
+
+		raw_spin_unlock_irq(&p->pi_lock);
+		/*
+		 * If the owner task is between FUTEX_STATE_EXITING and
+		 * FUTEX_STATE_DEAD then store the task pointer and keep
+		 * the reference on the task struct. The calling code will
+		 * drop all locks, wait for the task to reach
+		 * FUTEX_STATE_DEAD and then drop the refcount. This is
+		 * required to prevent a live lock when the current task
+		 * preempted the exiting task between the two states.
+		 */
+		if (ret == -EBUSY)
+			*exiting = p;
+		else
+			put_task_struct(p);
+		return ret;
+	}
+
+	__attach_to_pi_owner(p, key, ps);
+	raw_spin_unlock_irq(&p->pi_lock);
+
+	put_task_struct(p);
+
+	return 0;
+}
+
+static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
+{
+	int err;
+	u32 curval;
+
+	if (unlikely(should_fail_futex(true)))
+		return -EFAULT;
+
+	err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
+	if (unlikely(err))
+		return err;
+
+	/* If user space value changed, let the caller retry */
+	return curval != uval ? -EAGAIN : 0;
+}
+
+/**
+ * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
+ * @uaddr:		the pi futex user address
+ * @hb:			the pi futex hash bucket
+ * @key:		the futex key associated with uaddr and hb
+ * @ps:			the pi_state pointer where we store the result of the
+ *			lookup
+ * @task:		the task to perform the atomic lock work for.  This will
+ *			be "current" except in the case of requeue pi.
+ * @exiting:		Pointer to store the task pointer of the owner task
+ *			which is in the middle of exiting
+ * @set_waiters:	force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Return:
+ *  -  0 - ready to wait;
+ *  -  1 - acquired the lock;
+ *  - <0 - error
+ *
+ * The hb->lock must be held by the caller.
+ *
+ * @exiting is only set when the return value is -EBUSY. If so, this holds
+ * a refcount on the exiting task on return and the caller needs to drop it
+ * after waiting for the exit to complete.
+ */
+static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
+				union futex_key *key,
+				struct futex_pi_state **ps,
+				struct task_struct *task,
+				struct task_struct **exiting,
+				int set_waiters)
+{
+	u32 uval, newval, vpid = task_pid_vnr(task);
+	struct futex_q *top_waiter;
+	int ret;
+
+	/*
+	 * Read the user space value first so we can validate a few
+	 * things before proceeding further.
+	 */
+	if (get_futex_value_locked(&uval, uaddr))
+		return -EFAULT;
+
+	if (unlikely(should_fail_futex(true)))
+		return -EFAULT;
+
+	/*
+	 * Detect deadlocks.
+	 */
+	if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
+		return -EDEADLK;
+
+	if ((unlikely(should_fail_futex(true))))
+		return -EDEADLK;
+
+	/*
+	 * Lookup existing state first. If it exists, try to attach to
+	 * its pi_state.
+	 */
+	top_waiter = futex_top_waiter(hb, key);
+	if (top_waiter)
+		return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
+
+	/*
+	 * No waiter and user TID is 0. We are here because the
+	 * waiters or the owner died bit is set or called from
+	 * requeue_cmp_pi or for whatever reason something took the
+	 * syscall.
+	 */
+	if (!(uval & FUTEX_TID_MASK)) {
+		/*
+		 * We take over the futex. No other waiters and the user space
+		 * TID is 0. We preserve the owner died bit.
+		 */
+		newval = uval & FUTEX_OWNER_DIED;
+		newval |= vpid;
+
+		/* The futex requeue_pi code can enforce the waiters bit */
+		if (set_waiters)
+			newval |= FUTEX_WAITERS;
+
+		ret = lock_pi_update_atomic(uaddr, uval, newval);
+		if (ret)
+			return ret;
+
+		/*
+		 * If the waiter bit was requested the caller also needs PI
+		 * state attached to the new owner of the user space futex.
+		 *
+		 * @task is guaranteed to be alive and it cannot be exiting
+		 * because it is either sleeping or waiting in
+		 * futex_requeue_pi_wakeup_sync().
+		 *
+		 * No need to do the full attach_to_pi_owner() exercise
+		 * because @task is known and valid.
+		 */
+		if (set_waiters) {
+			raw_spin_lock_irq(&task->pi_lock);
+			__attach_to_pi_owner(task, key, ps);
+			raw_spin_unlock_irq(&task->pi_lock);
+		}
+		return 1;
+	}
+
+	/*
+	 * First waiter. Set the waiters bit before attaching ourself to
+	 * the owner. If owner tries to unlock, it will be forced into
+	 * the kernel and blocked on hb->lock.
+	 */
+	newval = uval | FUTEX_WAITERS;
+	ret = lock_pi_update_atomic(uaddr, uval, newval);
+	if (ret)
+		return ret;
+	/*
+	 * If the update of the user space value succeeded, we try to
+	 * attach to the owner. If that fails, no harm done, we only
+	 * set the FUTEX_WAITERS bit in the user space variable.
+	 */
+	return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
+}
+
+/**
+ * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
+ * @q:	The futex_q to unqueue
+ *
+ * The q->lock_ptr must not be NULL and must be held by the caller.
+ */
+static void __unqueue_futex(struct futex_q *q)
+{
+	struct futex_hash_bucket *hb;
+
+	if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
+		return;
+	lockdep_assert_held(q->lock_ptr);
+
+	hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
+	plist_del(&q->list, &hb->chain);
+	hb_waiters_dec(hb);
+}
+
+/*
+ * The hash bucket lock must be held when this is called.
+ * Afterwards, the futex_q must not be accessed. Callers
+ * must ensure to later call wake_up_q() for the actual
+ * wakeups to occur.
+ */
+static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
+{
+	struct task_struct *p = q->task;
+
+	if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
+		return;
+
+	get_task_struct(p);
+	__unqueue_futex(q);
+	/*
+	 * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
+	 * is written, without taking any locks. This is possible in the event
+	 * of a spurious wakeup, for example. A memory barrier is required here
+	 * to prevent the following store to lock_ptr from getting ahead of the
+	 * plist_del in __unqueue_futex().
+	 */
+	smp_store_release(&q->lock_ptr, NULL);
+
+	/*
+	 * Queue the task for later wakeup for after we've released
+	 * the hb->lock.
+	 */
+	wake_q_add_safe(wake_q, p);
+}
+
+/*
+ * Caller must hold a reference on @pi_state.
+ */
+static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
+{
+	struct rt_mutex_waiter *top_waiter;
+	struct task_struct *new_owner;
+	bool postunlock = false;
+	DEFINE_RT_WAKE_Q(wqh);
+	u32 curval, newval;
+	int ret = 0;
+
+	top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
+	if (WARN_ON_ONCE(!top_waiter)) {
+		/*
+		 * As per the comment in futex_unlock_pi() this should not happen.
+		 *
+		 * When this happens, give up our locks and try again, giving
+		 * the futex_lock_pi() instance time to complete, either by
+		 * waiting on the rtmutex or removing itself from the futex
+		 * queue.
+		 */
+		ret = -EAGAIN;
+		goto out_unlock;
+	}
+
+	new_owner = top_waiter->task;
+
+	/*
+	 * We pass it to the next owner. The WAITERS bit is always kept
+	 * enabled while there is PI state around. We cleanup the owner
+	 * died bit, because we are the owner.
+	 */
+	newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
+
+	if (unlikely(should_fail_futex(true))) {
+		ret = -EFAULT;
+		goto out_unlock;
+	}
+
+	ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
+	if (!ret && (curval != uval)) {
+		/*
+		 * If a unconditional UNLOCK_PI operation (user space did not
+		 * try the TID->0 transition) raced with a waiter setting the
+		 * FUTEX_WAITERS flag between get_user() and locking the hash
+		 * bucket lock, retry the operation.
+		 */
+		if ((FUTEX_TID_MASK & curval) == uval)
+			ret = -EAGAIN;
+		else
+			ret = -EINVAL;
+	}
+
+	if (!ret) {
+		/*
+		 * This is a point of no return; once we modified the uval
+		 * there is no going back and subsequent operations must
+		 * not fail.
+		 */
+		pi_state_update_owner(pi_state, new_owner);
+		postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
+	}
+
+out_unlock:
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+
+	if (postunlock)
+		rt_mutex_postunlock(&wqh);
+
+	return ret;
+}
+
+/*
+ * Express the locking dependencies for lockdep:
+ */
+static inline void
+double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
+{
+	if (hb1 <= hb2) {
+		spin_lock(&hb1->lock);
+		if (hb1 < hb2)
+			spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
+	} else { /* hb1 > hb2 */
+		spin_lock(&hb2->lock);
+		spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
+	}
+}
+
+static inline void
+double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
+{
+	spin_unlock(&hb1->lock);
+	if (hb1 != hb2)
+		spin_unlock(&hb2->lock);
+}
+
+/*
+ * Wake up waiters matching bitset queued on this futex (uaddr).
+ */
+static int
+futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
+{
+	struct futex_hash_bucket *hb;
+	struct futex_q *this, *next;
+	union futex_key key = FUTEX_KEY_INIT;
+	int ret;
+	DEFINE_WAKE_Q(wake_q);
+
+	if (!bitset)
+		return -EINVAL;
+
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
+	if (unlikely(ret != 0))
+		return ret;
+
+	hb = hash_futex(&key);
+
+	/* Make sure we really have tasks to wakeup */
+	if (!hb_waiters_pending(hb))
+		return ret;
+
+	spin_lock(&hb->lock);
+
+	plist_for_each_entry_safe(this, next, &hb->chain, list) {
+		if (match_futex (&this->key, &key)) {
+			if (this->pi_state || this->rt_waiter) {
+				ret = -EINVAL;
+				break;
+			}
+
+			/* Check if one of the bits is set in both bitsets */
+			if (!(this->bitset & bitset))
+				continue;
+
+			mark_wake_futex(&wake_q, this);
+			if (++ret >= nr_wake)
+				break;
+		}
+	}
+
+	spin_unlock(&hb->lock);
+	wake_up_q(&wake_q);
+	return ret;
+}
+
+static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
+{
+	unsigned int op =	  (encoded_op & 0x70000000) >> 28;
+	unsigned int cmp =	  (encoded_op & 0x0f000000) >> 24;
+	int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
+	int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
+	int oldval, ret;
+
+	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
+		if (oparg < 0 || oparg > 31) {
+			char comm[sizeof(current->comm)];
+			/*
+			 * kill this print and return -EINVAL when userspace
+			 * is sane again
+			 */
+			pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
+					get_task_comm(comm, current), oparg);
+			oparg &= 31;
+		}
+		oparg = 1 << oparg;
+	}
+
+	pagefault_disable();
+	ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
+	pagefault_enable();
+	if (ret)
+		return ret;
+
+	switch (cmp) {
+	case FUTEX_OP_CMP_EQ:
+		return oldval == cmparg;
+	case FUTEX_OP_CMP_NE:
+		return oldval != cmparg;
+	case FUTEX_OP_CMP_LT:
+		return oldval < cmparg;
+	case FUTEX_OP_CMP_GE:
+		return oldval >= cmparg;
+	case FUTEX_OP_CMP_LE:
+		return oldval <= cmparg;
+	case FUTEX_OP_CMP_GT:
+		return oldval > cmparg;
+	default:
+		return -ENOSYS;
+	}
+}
+
+/*
+ * Wake up all waiters hashed on the physical page that is mapped
+ * to this virtual address:
+ */
+static int
+futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
+	      int nr_wake, int nr_wake2, int op)
+{
+	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
+	struct futex_hash_bucket *hb1, *hb2;
+	struct futex_q *this, *next;
+	int ret, op_ret;
+	DEFINE_WAKE_Q(wake_q);
+
+retry:
+	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
+	if (unlikely(ret != 0))
+		return ret;
+	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
+	if (unlikely(ret != 0))
+		return ret;
+
+	hb1 = hash_futex(&key1);
+	hb2 = hash_futex(&key2);
+
+retry_private:
+	double_lock_hb(hb1, hb2);
+	op_ret = futex_atomic_op_inuser(op, uaddr2);
+	if (unlikely(op_ret < 0)) {
+		double_unlock_hb(hb1, hb2);
+
+		if (!IS_ENABLED(CONFIG_MMU) ||
+		    unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
+			/*
+			 * we don't get EFAULT from MMU faults if we don't have
+			 * an MMU, but we might get them from range checking
+			 */
+			ret = op_ret;
+			return ret;
+		}
+
+		if (op_ret == -EFAULT) {
+			ret = fault_in_user_writeable(uaddr2);
+			if (ret)
+				return ret;
+		}
+
+		cond_resched();
+		if (!(flags & FLAGS_SHARED))
+			goto retry_private;
+		goto retry;
+	}
+
+	plist_for_each_entry_safe(this, next, &hb1->chain, list) {
+		if (match_futex (&this->key, &key1)) {
+			if (this->pi_state || this->rt_waiter) {
+				ret = -EINVAL;
+				goto out_unlock;
+			}
+			mark_wake_futex(&wake_q, this);
+			if (++ret >= nr_wake)
+				break;
+		}
+	}
+
+	if (op_ret > 0) {
+		op_ret = 0;
+		plist_for_each_entry_safe(this, next, &hb2->chain, list) {
+			if (match_futex (&this->key, &key2)) {
+				if (this->pi_state || this->rt_waiter) {
+					ret = -EINVAL;
+					goto out_unlock;
+				}
+				mark_wake_futex(&wake_q, this);
+				if (++op_ret >= nr_wake2)
+					break;
+			}
+		}
+		ret += op_ret;
+	}
+
+out_unlock:
+	double_unlock_hb(hb1, hb2);
+	wake_up_q(&wake_q);
+	return ret;
+}
+
+/**
+ * requeue_futex() - Requeue a futex_q from one hb to another
+ * @q:		the futex_q to requeue
+ * @hb1:	the source hash_bucket
+ * @hb2:	the target hash_bucket
+ * @key2:	the new key for the requeued futex_q
+ */
+static inline
+void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
+		   struct futex_hash_bucket *hb2, union futex_key *key2)
+{
+
+	/*
+	 * If key1 and key2 hash to the same bucket, no need to
+	 * requeue.
+	 */
+	if (likely(&hb1->chain != &hb2->chain)) {
+		plist_del(&q->list, &hb1->chain);
+		hb_waiters_dec(hb1);
+		hb_waiters_inc(hb2);
+		plist_add(&q->list, &hb2->chain);
+		q->lock_ptr = &hb2->lock;
+	}
+	q->key = *key2;
+}
+
+static inline bool futex_requeue_pi_prepare(struct futex_q *q,
+					    struct futex_pi_state *pi_state)
+{
+	int old, new;
+
+	/*
+	 * Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has
+	 * already set Q_REQUEUE_PI_IGNORE to signal that requeue should
+	 * ignore the waiter.
+	 */
+	old = atomic_read_acquire(&q->requeue_state);
+	do {
+		if (old == Q_REQUEUE_PI_IGNORE)
+			return false;
+
+		/*
+		 * futex_proxy_trylock_atomic() might have set it to
+		 * IN_PROGRESS and a interleaved early wake to WAIT.
+		 *
+		 * It was considered to have an extra state for that
+		 * trylock, but that would just add more conditionals
+		 * all over the place for a dubious value.
+		 */
+		if (old != Q_REQUEUE_PI_NONE)
+			break;
+
+		new = Q_REQUEUE_PI_IN_PROGRESS;
+	} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
+
+	q->pi_state = pi_state;
+	return true;
+}
+
+static inline void futex_requeue_pi_complete(struct futex_q *q, int locked)
+{
+	int old, new;
+
+	old = atomic_read_acquire(&q->requeue_state);
+	do {
+		if (old == Q_REQUEUE_PI_IGNORE)
+			return;
+
+		if (locked >= 0) {
+			/* Requeue succeeded. Set DONE or LOCKED */
+			WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS &&
+				     old != Q_REQUEUE_PI_WAIT);
+			new = Q_REQUEUE_PI_DONE + locked;
+		} else if (old == Q_REQUEUE_PI_IN_PROGRESS) {
+			/* Deadlock, no early wakeup interleave */
+			new = Q_REQUEUE_PI_NONE;
+		} else {
+			/* Deadlock, early wakeup interleave. */
+			WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT);
+			new = Q_REQUEUE_PI_IGNORE;
+		}
+	} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
+
+#ifdef CONFIG_PREEMPT_RT
+	/* If the waiter interleaved with the requeue let it know */
+	if (unlikely(old == Q_REQUEUE_PI_WAIT))
+		rcuwait_wake_up(&q->requeue_wait);
+#endif
+}
+
+static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
+{
+	int old, new;
+
+	old = atomic_read_acquire(&q->requeue_state);
+	do {
+		/* Is requeue done already? */
+		if (old >= Q_REQUEUE_PI_DONE)
+			return old;
+
+		/*
+		 * If not done, then tell the requeue code to either ignore
+		 * the waiter or to wake it up once the requeue is done.
+		 */
+		new = Q_REQUEUE_PI_WAIT;
+		if (old == Q_REQUEUE_PI_NONE)
+			new = Q_REQUEUE_PI_IGNORE;
+	} while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
+
+	/* If the requeue was in progress, wait for it to complete */
+	if (old == Q_REQUEUE_PI_IN_PROGRESS) {
+#ifdef CONFIG_PREEMPT_RT
+		rcuwait_wait_event(&q->requeue_wait,
+				   atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT,
+				   TASK_UNINTERRUPTIBLE);
+#else
+		(void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT);
+#endif
+	}
+
+	/*
+	 * Requeue is now either prohibited or complete. Reread state
+	 * because during the wait above it might have changed. Nothing
+	 * will modify q->requeue_state after this point.
+	 */
+	return atomic_read(&q->requeue_state);
+}
+
+/**
+ * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
+ * @q:		the futex_q
+ * @key:	the key of the requeue target futex
+ * @hb:		the hash_bucket of the requeue target futex
+ *
+ * During futex_requeue, with requeue_pi=1, it is possible to acquire the
+ * target futex if it is uncontended or via a lock steal.
+ *
+ * 1) Set @q::key to the requeue target futex key so the waiter can detect
+ *    the wakeup on the right futex.
+ *
+ * 2) Dequeue @q from the hash bucket.
+ *
+ * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock
+ *    acquisition.
+ *
+ * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that
+ *    the waiter has to fixup the pi state.
+ *
+ * 5) Complete the requeue state so the waiter can make progress. After
+ *    this point the waiter task can return from the syscall immediately in
+ *    case that the pi state does not have to be fixed up.
+ *
+ * 6) Wake the waiter task.
+ *
+ * Must be called with both q->lock_ptr and hb->lock held.
+ */
+static inline
+void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
+			   struct futex_hash_bucket *hb)
+{
+	q->key = *key;
+
+	__unqueue_futex(q);
+
+	WARN_ON(!q->rt_waiter);
+	q->rt_waiter = NULL;
+
+	q->lock_ptr = &hb->lock;
+
+	/* Signal locked state to the waiter */
+	futex_requeue_pi_complete(q, 1);
+	wake_up_state(q->task, TASK_NORMAL);
+}
+
+/**
+ * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
+ * @pifutex:		the user address of the to futex
+ * @hb1:		the from futex hash bucket, must be locked by the caller
+ * @hb2:		the to futex hash bucket, must be locked by the caller
+ * @key1:		the from futex key
+ * @key2:		the to futex key
+ * @ps:			address to store the pi_state pointer
+ * @exiting:		Pointer to store the task pointer of the owner task
+ *			which is in the middle of exiting
+ * @set_waiters:	force setting the FUTEX_WAITERS bit (1) or not (0)
+ *
+ * Try and get the lock on behalf of the top waiter if we can do it atomically.
+ * Wake the top waiter if we succeed.  If the caller specified set_waiters,
+ * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
+ * hb1 and hb2 must be held by the caller.
+ *
+ * @exiting is only set when the return value is -EBUSY. If so, this holds
+ * a refcount on the exiting task on return and the caller needs to drop it
+ * after waiting for the exit to complete.
+ *
+ * Return:
+ *  -  0 - failed to acquire the lock atomically;
+ *  - >0 - acquired the lock, return value is vpid of the top_waiter
+ *  - <0 - error
+ */
+static int
+futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
+			   struct futex_hash_bucket *hb2, union futex_key *key1,
+			   union futex_key *key2, struct futex_pi_state **ps,
+			   struct task_struct **exiting, int set_waiters)
+{
+	struct futex_q *top_waiter = NULL;
+	u32 curval;
+	int ret;
+
+	if (get_futex_value_locked(&curval, pifutex))
+		return -EFAULT;
+
+	if (unlikely(should_fail_futex(true)))
+		return -EFAULT;
+
+	/*
+	 * Find the top_waiter and determine if there are additional waiters.
+	 * If the caller intends to requeue more than 1 waiter to pifutex,
+	 * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
+	 * as we have means to handle the possible fault.  If not, don't set
+	 * the bit unnecessarily as it will force the subsequent unlock to enter
+	 * the kernel.
+	 */
+	top_waiter = futex_top_waiter(hb1, key1);
+
+	/* There are no waiters, nothing for us to do. */
+	if (!top_waiter)
+		return 0;
+
+	/*
+	 * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
+	 * and waiting on the 'waitqueue' futex which is always !PI.
+	 */
+	if (!top_waiter->rt_waiter || top_waiter->pi_state)
+		return -EINVAL;
+
+	/* Ensure we requeue to the expected futex. */
+	if (!match_futex(top_waiter->requeue_pi_key, key2))
+		return -EINVAL;
+
+	/* Ensure that this does not race against an early wakeup */
+	if (!futex_requeue_pi_prepare(top_waiter, NULL))
+		return -EAGAIN;
+
+	/*
+	 * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
+	 * in the contended case or if @set_waiters is true.
+	 *
+	 * In the contended case PI state is attached to the lock owner. If
+	 * the user space lock can be acquired then PI state is attached to
+	 * the new owner (@top_waiter->task) when @set_waiters is true.
+	 */
+	ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
+				   exiting, set_waiters);
+	if (ret == 1) {
+		/*
+		 * Lock was acquired in user space and PI state was
+		 * attached to @top_waiter->task. That means state is fully
+		 * consistent and the waiter can return to user space
+		 * immediately after the wakeup.
+		 */
+		requeue_pi_wake_futex(top_waiter, key2, hb2);
+	} else if (ret < 0) {
+		/* Rewind top_waiter::requeue_state */
+		futex_requeue_pi_complete(top_waiter, ret);
+	} else {
+		/*
+		 * futex_lock_pi_atomic() did not acquire the user space
+		 * futex, but managed to establish the proxy lock and pi
+		 * state. top_waiter::requeue_state cannot be fixed up here
+		 * because the waiter is not enqueued on the rtmutex
+		 * yet. This is handled at the callsite depending on the
+		 * result of rt_mutex_start_proxy_lock() which is
+		 * guaranteed to be reached with this function returning 0.
+		 */
+	}
+	return ret;
+}
+
+/**
+ * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
+ * @uaddr1:	source futex user address
+ * @flags:	futex flags (FLAGS_SHARED, etc.)
+ * @uaddr2:	target futex user address
+ * @nr_wake:	number of waiters to wake (must be 1 for requeue_pi)
+ * @nr_requeue:	number of waiters to requeue (0-INT_MAX)
+ * @cmpval:	@uaddr1 expected value (or %NULL)
+ * @requeue_pi:	if we are attempting to requeue from a non-pi futex to a
+ *		pi futex (pi to pi requeue is not supported)
+ *
+ * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
+ * uaddr2 atomically on behalf of the top waiter.
+ *
+ * Return:
+ *  - >=0 - on success, the number of tasks requeued or woken;
+ *  -  <0 - on error
+ */
+static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
+			 u32 __user *uaddr2, int nr_wake, int nr_requeue,
+			 u32 *cmpval, int requeue_pi)
+{
+	union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
+	int task_count = 0, ret;
+	struct futex_pi_state *pi_state = NULL;
+	struct futex_hash_bucket *hb1, *hb2;
+	struct futex_q *this, *next;
+	DEFINE_WAKE_Q(wake_q);
+
+	if (nr_wake < 0 || nr_requeue < 0)
+		return -EINVAL;
+
+	/*
+	 * When PI not supported: return -ENOSYS if requeue_pi is true,
+	 * consequently the compiler knows requeue_pi is always false past
+	 * this point which will optimize away all the conditional code
+	 * further down.
+	 */
+	if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
+		return -ENOSYS;
+
+	if (requeue_pi) {
+		/*
+		 * Requeue PI only works on two distinct uaddrs. This
+		 * check is only valid for private futexes. See below.
+		 */
+		if (uaddr1 == uaddr2)
+			return -EINVAL;
+
+		/*
+		 * futex_requeue() allows the caller to define the number
+		 * of waiters to wake up via the @nr_wake argument. With
+		 * REQUEUE_PI, waking up more than one waiter is creating
+		 * more problems than it solves. Waking up a waiter makes
+		 * only sense if the PI futex @uaddr2 is uncontended as
+		 * this allows the requeue code to acquire the futex
+		 * @uaddr2 before waking the waiter. The waiter can then
+		 * return to user space without further action. A secondary
+		 * wakeup would just make the futex_wait_requeue_pi()
+		 * handling more complex, because that code would have to
+		 * look up pi_state and do more or less all the handling
+		 * which the requeue code has to do for the to be requeued
+		 * waiters. So restrict the number of waiters to wake to
+		 * one, and only wake it up when the PI futex is
+		 * uncontended. Otherwise requeue it and let the unlock of
+		 * the PI futex handle the wakeup.
+		 *
+		 * All REQUEUE_PI users, e.g. pthread_cond_signal() and
+		 * pthread_cond_broadcast() must use nr_wake=1.
+		 */
+		if (nr_wake != 1)
+			return -EINVAL;
+
+		/*
+		 * requeue_pi requires a pi_state, try to allocate it now
+		 * without any locks in case it fails.
+		 */
+		if (refill_pi_state_cache())
+			return -ENOMEM;
+	}
+
+retry:
+	ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
+	if (unlikely(ret != 0))
+		return ret;
+	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
+			    requeue_pi ? FUTEX_WRITE : FUTEX_READ);
+	if (unlikely(ret != 0))
+		return ret;
+
+	/*
+	 * The check above which compares uaddrs is not sufficient for
+	 * shared futexes. We need to compare the keys:
+	 */
+	if (requeue_pi && match_futex(&key1, &key2))
+		return -EINVAL;
+
+	hb1 = hash_futex(&key1);
+	hb2 = hash_futex(&key2);
+
+retry_private:
+	hb_waiters_inc(hb2);
+	double_lock_hb(hb1, hb2);
+
+	if (likely(cmpval != NULL)) {
+		u32 curval;
+
+		ret = get_futex_value_locked(&curval, uaddr1);
+
+		if (unlikely(ret)) {
+			double_unlock_hb(hb1, hb2);
+			hb_waiters_dec(hb2);
+
+			ret = get_user(curval, uaddr1);
+			if (ret)
+				return ret;
+
+			if (!(flags & FLAGS_SHARED))
+				goto retry_private;
+
+			goto retry;
+		}
+		if (curval != *cmpval) {
+			ret = -EAGAIN;
+			goto out_unlock;
+		}
+	}
+
+	if (requeue_pi) {
+		struct task_struct *exiting = NULL;
+
+		/*
+		 * Attempt to acquire uaddr2 and wake the top waiter. If we
+		 * intend to requeue waiters, force setting the FUTEX_WAITERS
+		 * bit.  We force this here where we are able to easily handle
+		 * faults rather in the requeue loop below.
+		 *
+		 * Updates topwaiter::requeue_state if a top waiter exists.
+		 */
+		ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
+						 &key2, &pi_state,
+						 &exiting, nr_requeue);
+
+		/*
+		 * At this point the top_waiter has either taken uaddr2 or
+		 * is waiting on it. In both cases pi_state has been
+		 * established and an initial refcount on it. In case of an
+		 * error there's nothing.
+		 *
+		 * The top waiter's requeue_state is up to date:
+		 *
+		 *  - If the lock was acquired atomically (ret == 1), then
+		 *    the state is Q_REQUEUE_PI_LOCKED.
+		 *
+		 *    The top waiter has been dequeued and woken up and can
+		 *    return to user space immediately. The kernel/user
+		 *    space state is consistent. In case that there must be
+		 *    more waiters requeued the WAITERS bit in the user
+		 *    space futex is set so the top waiter task has to go
+		 *    into the syscall slowpath to unlock the futex. This
+		 *    will block until this requeue operation has been
+		 *    completed and the hash bucket locks have been
+		 *    dropped.
+		 *
+		 *  - If the trylock failed with an error (ret < 0) then
+		 *    the state is either Q_REQUEUE_PI_NONE, i.e. "nothing
+		 *    happened", or Q_REQUEUE_PI_IGNORE when there was an
+		 *    interleaved early wakeup.
+		 *
+		 *  - If the trylock did not succeed (ret == 0) then the
+		 *    state is either Q_REQUEUE_PI_IN_PROGRESS or
+		 *    Q_REQUEUE_PI_WAIT if an early wakeup interleaved.
+		 *    This will be cleaned up in the loop below, which
+		 *    cannot fail because futex_proxy_trylock_atomic() did
+		 *    the same sanity checks for requeue_pi as the loop
+		 *    below does.
+		 */
+		switch (ret) {
+		case 0:
+			/* We hold a reference on the pi state. */
+			break;
+
+		case 1:
+			/*
+			 * futex_proxy_trylock_atomic() acquired the user space
+			 * futex. Adjust task_count.
+			 */
+			task_count++;
+			ret = 0;
+			break;
+
+		/*
+		 * If the above failed, then pi_state is NULL and
+		 * waiter::requeue_state is correct.
+		 */
+		case -EFAULT:
+			double_unlock_hb(hb1, hb2);
+			hb_waiters_dec(hb2);
+			ret = fault_in_user_writeable(uaddr2);
+			if (!ret)
+				goto retry;
+			return ret;
+		case -EBUSY:
+		case -EAGAIN:
+			/*
+			 * Two reasons for this:
+			 * - EBUSY: Owner is exiting and we just wait for the
+			 *   exit to complete.
+			 * - EAGAIN: The user space value changed.
+			 */
+			double_unlock_hb(hb1, hb2);
+			hb_waiters_dec(hb2);
+			/*
+			 * Handle the case where the owner is in the middle of
+			 * exiting. Wait for the exit to complete otherwise
+			 * this task might loop forever, aka. live lock.
+			 */
+			wait_for_owner_exiting(ret, exiting);
+			cond_resched();
+			goto retry;
+		default:
+			goto out_unlock;
+		}
+	}
+
+	plist_for_each_entry_safe(this, next, &hb1->chain, list) {
+		if (task_count - nr_wake >= nr_requeue)
+			break;
+
+		if (!match_futex(&this->key, &key1))
+			continue;
+
+		/*
+		 * FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always
+		 * be paired with each other and no other futex ops.
+		 *
+		 * We should never be requeueing a futex_q with a pi_state,
+		 * which is awaiting a futex_unlock_pi().
+		 */
+		if ((requeue_pi && !this->rt_waiter) ||
+		    (!requeue_pi && this->rt_waiter) ||
+		    this->pi_state) {
+			ret = -EINVAL;
+			break;
+		}
+
+		/* Plain futexes just wake or requeue and are done */
+		if (!requeue_pi) {
+			if (++task_count <= nr_wake)
+				mark_wake_futex(&wake_q, this);
+			else
+				requeue_futex(this, hb1, hb2, &key2);
+			continue;
+		}
+
+		/* Ensure we requeue to the expected futex for requeue_pi. */
+		if (!match_futex(this->requeue_pi_key, &key2)) {
+			ret = -EINVAL;
+			break;
+		}
+
+		/*
+		 * Requeue nr_requeue waiters and possibly one more in the case
+		 * of requeue_pi if we couldn't acquire the lock atomically.
+		 *
+		 * Prepare the waiter to take the rt_mutex. Take a refcount
+		 * on the pi_state and store the pointer in the futex_q
+		 * object of the waiter.
+		 */
+		get_pi_state(pi_state);
+
+		/* Don't requeue when the waiter is already on the way out. */
+		if (!futex_requeue_pi_prepare(this, pi_state)) {
+			/*
+			 * Early woken waiter signaled that it is on the
+			 * way out. Drop the pi_state reference and try the
+			 * next waiter. @this->pi_state is still NULL.
+			 */
+			put_pi_state(pi_state);
+			continue;
+		}
+
+		ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
+						this->rt_waiter,
+						this->task);
+
+		if (ret == 1) {
+			/*
+			 * We got the lock. We do neither drop the refcount
+			 * on pi_state nor clear this->pi_state because the
+			 * waiter needs the pi_state for cleaning up the
+			 * user space value. It will drop the refcount
+			 * after doing so. this::requeue_state is updated
+			 * in the wakeup as well.
+			 */
+			requeue_pi_wake_futex(this, &key2, hb2);
+			task_count++;
+		} else if (!ret) {
+			/* Waiter is queued, move it to hb2 */
+			requeue_futex(this, hb1, hb2, &key2);
+			futex_requeue_pi_complete(this, 0);
+			task_count++;
+		} else {
+			/*
+			 * rt_mutex_start_proxy_lock() detected a potential
+			 * deadlock when we tried to queue that waiter.
+			 * Drop the pi_state reference which we took above
+			 * and remove the pointer to the state from the
+			 * waiters futex_q object.
+			 */
+			this->pi_state = NULL;
+			put_pi_state(pi_state);
+			futex_requeue_pi_complete(this, ret);
+			/*
+			 * We stop queueing more waiters and let user space
+			 * deal with the mess.
+			 */
+			break;
+		}
+	}
+
+	/*
+	 * We took an extra initial reference to the pi_state in
+	 * futex_proxy_trylock_atomic(). We need to drop it here again.
+	 */
+	put_pi_state(pi_state);
+
+out_unlock:
+	double_unlock_hb(hb1, hb2);
+	wake_up_q(&wake_q);
+	hb_waiters_dec(hb2);
+	return ret ? ret : task_count;
+}
+
+/* The key must be already stored in q->key. */
+static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
+	__acquires(&hb->lock)
+{
+	struct futex_hash_bucket *hb;
+
+	hb = hash_futex(&q->key);
+
+	/*
+	 * Increment the counter before taking the lock so that
+	 * a potential waker won't miss a to-be-slept task that is
+	 * waiting for the spinlock. This is safe as all queue_lock()
+	 * users end up calling queue_me(). Similarly, for housekeeping,
+	 * decrement the counter at queue_unlock() when some error has
+	 * occurred and we don't end up adding the task to the list.
+	 */
+	hb_waiters_inc(hb); /* implies smp_mb(); (A) */
+
+	q->lock_ptr = &hb->lock;
+
+	spin_lock(&hb->lock);
+	return hb;
+}
+
+static inline void
+queue_unlock(struct futex_hash_bucket *hb)
+	__releases(&hb->lock)
+{
+	spin_unlock(&hb->lock);
+	hb_waiters_dec(hb);
+}
+
+static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+{
+	int prio;
+
+	/*
+	 * The priority used to register this element is
+	 * - either the real thread-priority for the real-time threads
+	 * (i.e. threads with a priority lower than MAX_RT_PRIO)
+	 * - or MAX_RT_PRIO for non-RT threads.
+	 * Thus, all RT-threads are woken first in priority order, and
+	 * the others are woken last, in FIFO order.
+	 */
+	prio = min(current->normal_prio, MAX_RT_PRIO);
+
+	plist_node_init(&q->list, prio);
+	plist_add(&q->list, &hb->chain);
+	q->task = current;
+}
+
+/**
+ * queue_me() - Enqueue the futex_q on the futex_hash_bucket
+ * @q:	The futex_q to enqueue
+ * @hb:	The destination hash bucket
+ *
+ * The hb->lock must be held by the caller, and is released here. A call to
+ * queue_me() is typically paired with exactly one call to unqueue_me().  The
+ * exceptions involve the PI related operations, which may use unqueue_me_pi()
+ * or nothing if the unqueue is done as part of the wake process and the unqueue
+ * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
+ * an example).
+ */
+static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
+	__releases(&hb->lock)
+{
+	__queue_me(q, hb);
+	spin_unlock(&hb->lock);
+}
+
+/**
+ * unqueue_me() - Remove the futex_q from its futex_hash_bucket
+ * @q:	The futex_q to unqueue
+ *
+ * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
+ * be paired with exactly one earlier call to queue_me().
+ *
+ * Return:
+ *  - 1 - if the futex_q was still queued (and we removed unqueued it);
+ *  - 0 - if the futex_q was already removed by the waking thread
+ */
+static int unqueue_me(struct futex_q *q)
+{
+	spinlock_t *lock_ptr;
+	int ret = 0;
+
+	/* In the common case we don't take the spinlock, which is nice. */
+retry:
+	/*
+	 * q->lock_ptr can change between this read and the following spin_lock.
+	 * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
+	 * optimizing lock_ptr out of the logic below.
+	 */
+	lock_ptr = READ_ONCE(q->lock_ptr);
+	if (lock_ptr != NULL) {
+		spin_lock(lock_ptr);
+		/*
+		 * q->lock_ptr can change between reading it and
+		 * spin_lock(), causing us to take the wrong lock.  This
+		 * corrects the race condition.
+		 *
+		 * Reasoning goes like this: if we have the wrong lock,
+		 * q->lock_ptr must have changed (maybe several times)
+		 * between reading it and the spin_lock().  It can
+		 * change again after the spin_lock() but only if it was
+		 * already changed before the spin_lock().  It cannot,
+		 * however, change back to the original value.  Therefore
+		 * we can detect whether we acquired the correct lock.
+		 */
+		if (unlikely(lock_ptr != q->lock_ptr)) {
+			spin_unlock(lock_ptr);
+			goto retry;
+		}
+		__unqueue_futex(q);
+
+		BUG_ON(q->pi_state);
+
+		spin_unlock(lock_ptr);
+		ret = 1;
+	}
+
+	return ret;
+}
+
+/*
+ * PI futexes can not be requeued and must remove themselves from the
+ * hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
+ */
+static void unqueue_me_pi(struct futex_q *q)
+{
+	__unqueue_futex(q);
+
+	BUG_ON(!q->pi_state);
+	put_pi_state(q->pi_state);
+	q->pi_state = NULL;
+}
+
+static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+				  struct task_struct *argowner)
+{
+	struct futex_pi_state *pi_state = q->pi_state;
+	struct task_struct *oldowner, *newowner;
+	u32 uval, curval, newval, newtid;
+	int err = 0;
+
+	oldowner = pi_state->owner;
+
+	/*
+	 * We are here because either:
+	 *
+	 *  - we stole the lock and pi_state->owner needs updating to reflect
+	 *    that (@argowner == current),
+	 *
+	 * or:
+	 *
+	 *  - someone stole our lock and we need to fix things to point to the
+	 *    new owner (@argowner == NULL).
+	 *
+	 * Either way, we have to replace the TID in the user space variable.
+	 * This must be atomic as we have to preserve the owner died bit here.
+	 *
+	 * Note: We write the user space value _before_ changing the pi_state
+	 * because we can fault here. Imagine swapped out pages or a fork
+	 * that marked all the anonymous memory readonly for cow.
+	 *
+	 * Modifying pi_state _before_ the user space value would leave the
+	 * pi_state in an inconsistent state when we fault here, because we
+	 * need to drop the locks to handle the fault. This might be observed
+	 * in the PID checks when attaching to PI state .
+	 */
+retry:
+	if (!argowner) {
+		if (oldowner != current) {
+			/*
+			 * We raced against a concurrent self; things are
+			 * already fixed up. Nothing to do.
+			 */
+			return 0;
+		}
+
+		if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
+			/* We got the lock. pi_state is correct. Tell caller. */
+			return 1;
+		}
+
+		/*
+		 * The trylock just failed, so either there is an owner or
+		 * there is a higher priority waiter than this one.
+		 */
+		newowner = rt_mutex_owner(&pi_state->pi_mutex);
+		/*
+		 * If the higher priority waiter has not yet taken over the
+		 * rtmutex then newowner is NULL. We can't return here with
+		 * that state because it's inconsistent vs. the user space
+		 * state. So drop the locks and try again. It's a valid
+		 * situation and not any different from the other retry
+		 * conditions.
+		 */
+		if (unlikely(!newowner)) {
+			err = -EAGAIN;
+			goto handle_err;
+		}
+	} else {
+		WARN_ON_ONCE(argowner != current);
+		if (oldowner == current) {
+			/*
+			 * We raced against a concurrent self; things are
+			 * already fixed up. Nothing to do.
+			 */
+			return 1;
+		}
+		newowner = argowner;
+	}
+
+	newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
+	/* Owner died? */
+	if (!pi_state->owner)
+		newtid |= FUTEX_OWNER_DIED;
+
+	err = get_futex_value_locked(&uval, uaddr);
+	if (err)
+		goto handle_err;
+
+	for (;;) {
+		newval = (uval & FUTEX_OWNER_DIED) | newtid;
+
+		err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
+		if (err)
+			goto handle_err;
+
+		if (curval == uval)
+			break;
+		uval = curval;
+	}
+
+	/*
+	 * We fixed up user space. Now we need to fix the pi_state
+	 * itself.
+	 */
+	pi_state_update_owner(pi_state, newowner);
+
+	return argowner == current;
+
+	/*
+	 * In order to reschedule or handle a page fault, we need to drop the
+	 * locks here. In the case of a fault, this gives the other task
+	 * (either the highest priority waiter itself or the task which stole
+	 * the rtmutex) the chance to try the fixup of the pi_state. So once we
+	 * are back from handling the fault we need to check the pi_state after
+	 * reacquiring the locks and before trying to do another fixup. When
+	 * the fixup has been done already we simply return.
+	 *
+	 * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
+	 * drop hb->lock since the caller owns the hb -> futex_q relation.
+	 * Dropping the pi_mutex->wait_lock requires the state revalidate.
+	 */
+handle_err:
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	spin_unlock(q->lock_ptr);
+
+	switch (err) {
+	case -EFAULT:
+		err = fault_in_user_writeable(uaddr);
+		break;
+
+	case -EAGAIN:
+		cond_resched();
+		err = 0;
+		break;
+
+	default:
+		WARN_ON_ONCE(1);
+		break;
+	}
+
+	spin_lock(q->lock_ptr);
+	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+
+	/*
+	 * Check if someone else fixed it for us:
+	 */
+	if (pi_state->owner != oldowner)
+		return argowner == current;
+
+	/* Retry if err was -EAGAIN or the fault in succeeded */
+	if (!err)
+		goto retry;
+
+	/*
+	 * fault_in_user_writeable() failed so user state is immutable. At
+	 * best we can make the kernel state consistent but user state will
+	 * be most likely hosed and any subsequent unlock operation will be
+	 * rejected due to PI futex rule [10].
+	 *
+	 * Ensure that the rtmutex owner is also the pi_state owner despite
+	 * the user space value claiming something different. There is no
+	 * point in unlocking the rtmutex if current is the owner as it
+	 * would need to wait until the next waiter has taken the rtmutex
+	 * to guarantee consistent state. Keep it simple. Userspace asked
+	 * for this wreckaged state.
+	 *
+	 * The rtmutex has an owner - either current or some other
+	 * task. See the EAGAIN loop above.
+	 */
+	pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
+
+	return err;
+}
+
+static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
+				struct task_struct *argowner)
+{
+	struct futex_pi_state *pi_state = q->pi_state;
+	int ret;
+
+	lockdep_assert_held(q->lock_ptr);
+
+	raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+	ret = __fixup_pi_state_owner(uaddr, q, argowner);
+	raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
+	return ret;
+}
+
+static long futex_wait_restart(struct restart_block *restart);
+
+/**
+ * fixup_owner() - Post lock pi_state and corner case management
+ * @uaddr:	user address of the futex
+ * @q:		futex_q (contains pi_state and access to the rt_mutex)
+ * @locked:	if the attempt to take the rt_mutex succeeded (1) or not (0)
+ *
+ * After attempting to lock an rt_mutex, this function is called to cleanup
+ * the pi_state owner as well as handle race conditions that may allow us to
+ * acquire the lock. Must be called with the hb lock held.
+ *
+ * Return:
+ *  -  1 - success, lock taken;
+ *  -  0 - success, lock not taken;
+ *  - <0 - on error (-EFAULT)
+ */
+static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
+{
+	if (locked) {
+		/*
+		 * Got the lock. We might not be the anticipated owner if we
+		 * did a lock-steal - fix up the PI-state in that case:
+		 *
+		 * Speculative pi_state->owner read (we don't hold wait_lock);
+		 * since we own the lock pi_state->owner == current is the
+		 * stable state, anything else needs more attention.
+		 */
+		if (q->pi_state->owner != current)
+			return fixup_pi_state_owner(uaddr, q, current);
+		return 1;
+	}
+
+	/*
+	 * If we didn't get the lock; check if anybody stole it from us. In
+	 * that case, we need to fix up the uval to point to them instead of
+	 * us, otherwise bad things happen. [10]
+	 *
+	 * Another speculative read; pi_state->owner == current is unstable
+	 * but needs our attention.
+	 */
+	if (q->pi_state->owner == current)
+		return fixup_pi_state_owner(uaddr, q, NULL);
+
+	/*
+	 * Paranoia check. If we did not take the lock, then we should not be
+	 * the owner of the rt_mutex. Warn and establish consistent state.
+	 */
+	if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
+		return fixup_pi_state_owner(uaddr, q, current);
+
+	return 0;
+}
+
+/**
+ * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
+ * @hb:		the futex hash bucket, must be locked by the caller
+ * @q:		the futex_q to queue up on
+ * @timeout:	the prepared hrtimer_sleeper, or null for no timeout
+ */
+static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
+				struct hrtimer_sleeper *timeout)
+{
+	/*
+	 * The task state is guaranteed to be set before another task can
+	 * wake it. set_current_state() is implemented using smp_store_mb() and
+	 * queue_me() calls spin_unlock() upon completion, both serializing
+	 * access to the hash list and forcing another memory barrier.
+	 */
+	set_current_state(TASK_INTERRUPTIBLE);
+	queue_me(q, hb);
+
+	/* Arm the timer */
+	if (timeout)
+		hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
+
+	/*
+	 * If we have been removed from the hash list, then another task
+	 * has tried to wake us, and we can skip the call to schedule().
+	 */
+	if (likely(!plist_node_empty(&q->list))) {
+		/*
+		 * If the timer has already expired, current will already be
+		 * flagged for rescheduling. Only call schedule if there
+		 * is no timeout, or if it has yet to expire.
+		 */
+		if (!timeout || timeout->task)
+			freezable_schedule();
+	}
+	__set_current_state(TASK_RUNNING);
+}
+
+/**
+ * futex_wait_setup() - Prepare to wait on a futex
+ * @uaddr:	the futex userspace address
+ * @val:	the expected value
+ * @flags:	futex flags (FLAGS_SHARED, etc.)
+ * @q:		the associated futex_q
+ * @hb:		storage for hash_bucket pointer to be returned to caller
+ *
+ * Setup the futex_q and locate the hash_bucket.  Get the futex value and
+ * compare it with the expected value.  Handle atomic faults internally.
+ * Return with the hb lock held on success, and unlocked on failure.
+ *
+ * Return:
+ *  -  0 - uaddr contains val and hb has been locked;
+ *  - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
+ */
+static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
+			   struct futex_q *q, struct futex_hash_bucket **hb)
+{
+	u32 uval;
+	int ret;
+
+	/*
+	 * Access the page AFTER the hash-bucket is locked.
+	 * Order is important:
+	 *
+	 *   Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
+	 *   Userspace waker:  if (cond(var)) { var = new; futex_wake(&var); }
+	 *
+	 * The basic logical guarantee of a futex is that it blocks ONLY
+	 * if cond(var) is known to be true at the time of blocking, for
+	 * any cond.  If we locked the hash-bucket after testing *uaddr, that
+	 * would open a race condition where we could block indefinitely with
+	 * cond(var) false, which would violate the guarantee.
+	 *
+	 * On the other hand, we insert q and release the hash-bucket only
+	 * after testing *uaddr.  This guarantees that futex_wait() will NOT
+	 * absorb a wakeup if *uaddr does not match the desired values
+	 * while the syscall executes.
+	 */
+retry:
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
+	if (unlikely(ret != 0))
+		return ret;
+
+retry_private:
+	*hb = queue_lock(q);
+
+	ret = get_futex_value_locked(&uval, uaddr);
+
+	if (ret) {
+		queue_unlock(*hb);
+
+		ret = get_user(uval, uaddr);
+		if (ret)
+			return ret;
+
+		if (!(flags & FLAGS_SHARED))
+			goto retry_private;
+
+		goto retry;
+	}
+
+	if (uval != val) {
+		queue_unlock(*hb);
+		ret = -EWOULDBLOCK;
+	}
+
+	return ret;
+}
+
+static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
+		      ktime_t *abs_time, u32 bitset)
+{
+	struct hrtimer_sleeper timeout, *to;
+	struct restart_block *restart;
+	struct futex_hash_bucket *hb;
+	struct futex_q q = futex_q_init;
+	int ret;
+
+	if (!bitset)
+		return -EINVAL;
+	q.bitset = bitset;
+
+	to = futex_setup_timer(abs_time, &timeout, flags,
+			       current->timer_slack_ns);
+retry:
+	/*
+	 * Prepare to wait on uaddr. On success, it holds hb->lock and q
+	 * is initialized.
+	 */
+	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
+	if (ret)
+		goto out;
+
+	/* queue_me and wait for wakeup, timeout, or a signal. */
+	futex_wait_queue_me(hb, &q, to);
+
+	/* If we were woken (and unqueued), we succeeded, whatever. */
+	ret = 0;
+	if (!unqueue_me(&q))
+		goto out;
+	ret = -ETIMEDOUT;
+	if (to && !to->task)
+		goto out;
+
+	/*
+	 * We expect signal_pending(current), but we might be the
+	 * victim of a spurious wakeup as well.
+	 */
+	if (!signal_pending(current))
+		goto retry;
+
+	ret = -ERESTARTSYS;
+	if (!abs_time)
+		goto out;
+
+	restart = &current->restart_block;
+	restart->futex.uaddr = uaddr;
+	restart->futex.val = val;
+	restart->futex.time = *abs_time;
+	restart->futex.bitset = bitset;
+	restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
+
+	ret = set_restart_fn(restart, futex_wait_restart);
+
+out:
+	if (to) {
+		hrtimer_cancel(&to->timer);
+		destroy_hrtimer_on_stack(&to->timer);
+	}
+	return ret;
+}
+
+
+static long futex_wait_restart(struct restart_block *restart)
+{
+	u32 __user *uaddr = restart->futex.uaddr;
+	ktime_t t, *tp = NULL;
+
+	if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
+		t = restart->futex.time;
+		tp = &t;
+	}
+	restart->fn = do_no_restart_syscall;
+
+	return (long)futex_wait(uaddr, restart->futex.flags,
+				restart->futex.val, tp, restart->futex.bitset);
+}
+
+
+/*
+ * Userspace tried a 0 -> TID atomic transition of the futex value
+ * and failed. The kernel side here does the whole locking operation:
+ * if there are waiters then it will block as a consequence of relying
+ * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
+ * a 0 value of the futex too.).
+ *
+ * Also serves as futex trylock_pi()'ing, and due semantics.
+ */
+static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
+			 ktime_t *time, int trylock)
+{
+	struct hrtimer_sleeper timeout, *to;
+	struct task_struct *exiting = NULL;
+	struct rt_mutex_waiter rt_waiter;
+	struct futex_hash_bucket *hb;
+	struct futex_q q = futex_q_init;
+	int res, ret;
+
+	if (!IS_ENABLED(CONFIG_FUTEX_PI))
+		return -ENOSYS;
+
+	if (refill_pi_state_cache())
+		return -ENOMEM;
+
+	to = futex_setup_timer(time, &timeout, flags, 0);
+
+retry:
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
+	if (unlikely(ret != 0))
+		goto out;
+
+retry_private:
+	hb = queue_lock(&q);
+
+	ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
+				   &exiting, 0);
+	if (unlikely(ret)) {
+		/*
+		 * Atomic work succeeded and we got the lock,
+		 * or failed. Either way, we do _not_ block.
+		 */
+		switch (ret) {
+		case 1:
+			/* We got the lock. */
+			ret = 0;
+			goto out_unlock_put_key;
+		case -EFAULT:
+			goto uaddr_faulted;
+		case -EBUSY:
+		case -EAGAIN:
+			/*
+			 * Two reasons for this:
+			 * - EBUSY: Task is exiting and we just wait for the
+			 *   exit to complete.
+			 * - EAGAIN: The user space value changed.
+			 */
+			queue_unlock(hb);
+			/*
+			 * Handle the case where the owner is in the middle of
+			 * exiting. Wait for the exit to complete otherwise
+			 * this task might loop forever, aka. live lock.
+			 */
+			wait_for_owner_exiting(ret, exiting);
+			cond_resched();
+			goto retry;
+		default:
+			goto out_unlock_put_key;
+		}
+	}
+
+	WARN_ON(!q.pi_state);
+
+	/*
+	 * Only actually queue now that the atomic ops are done:
+	 */
+	__queue_me(&q, hb);
+
+	if (trylock) {
+		ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
+		/* Fixup the trylock return value: */
+		ret = ret ? 0 : -EWOULDBLOCK;
+		goto no_block;
+	}
+
+	rt_mutex_init_waiter(&rt_waiter);
+
+	/*
+	 * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
+	 * hold it while doing rt_mutex_start_proxy(), because then it will
+	 * include hb->lock in the blocking chain, even through we'll not in
+	 * fact hold it while blocking. This will lead it to report -EDEADLK
+	 * and BUG when futex_unlock_pi() interleaves with this.
+	 *
+	 * Therefore acquire wait_lock while holding hb->lock, but drop the
+	 * latter before calling __rt_mutex_start_proxy_lock(). This
+	 * interleaves with futex_unlock_pi() -- which does a similar lock
+	 * handoff -- such that the latter can observe the futex_q::pi_state
+	 * before __rt_mutex_start_proxy_lock() is done.
+	 */
+	raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
+	spin_unlock(q.lock_ptr);
+	/*
+	 * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
+	 * such that futex_unlock_pi() is guaranteed to observe the waiter when
+	 * it sees the futex_q::pi_state.
+	 */
+	ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
+	raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
+
+	if (ret) {
+		if (ret == 1)
+			ret = 0;
+		goto cleanup;
+	}
+
+	if (unlikely(to))
+		hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
+
+	ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
+
+cleanup:
+	spin_lock(q.lock_ptr);
+	/*
+	 * If we failed to acquire the lock (deadlock/signal/timeout), we must
+	 * first acquire the hb->lock before removing the lock from the
+	 * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
+	 * lists consistent.
+	 *
+	 * In particular; it is important that futex_unlock_pi() can not
+	 * observe this inconsistency.
+	 */
+	if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
+		ret = 0;
+
+no_block:
+	/*
+	 * Fixup the pi_state owner and possibly acquire the lock if we
+	 * haven't already.
+	 */
+	res = fixup_owner(uaddr, &q, !ret);
+	/*
+	 * If fixup_owner() returned an error, propagate that.  If it acquired
+	 * the lock, clear our -ETIMEDOUT or -EINTR.
+	 */
+	if (res)
+		ret = (res < 0) ? res : 0;
+
+	unqueue_me_pi(&q);
+	spin_unlock(q.lock_ptr);
+	goto out;
+
+out_unlock_put_key:
+	queue_unlock(hb);
+
+out:
+	if (to) {
+		hrtimer_cancel(&to->timer);
+		destroy_hrtimer_on_stack(&to->timer);
+	}
+	return ret != -EINTR ? ret : -ERESTARTNOINTR;
+
+uaddr_faulted:
+	queue_unlock(hb);
+
+	ret = fault_in_user_writeable(uaddr);
+	if (ret)
+		goto out;
+
+	if (!(flags & FLAGS_SHARED))
+		goto retry_private;
+
+	goto retry;
+}
+
+/*
+ * Userspace attempted a TID -> 0 atomic transition, and failed.
+ * This is the in-kernel slowpath: we look up the PI state (if any),
+ * and do the rt-mutex unlock.
+ */
+static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
+{
+	u32 curval, uval, vpid = task_pid_vnr(current);
+	union futex_key key = FUTEX_KEY_INIT;
+	struct futex_hash_bucket *hb;
+	struct futex_q *top_waiter;
+	int ret;
+
+	if (!IS_ENABLED(CONFIG_FUTEX_PI))
+		return -ENOSYS;
+
+retry:
+	if (get_user(uval, uaddr))
+		return -EFAULT;
+	/*
+	 * We release only a lock we actually own:
+	 */
+	if ((uval & FUTEX_TID_MASK) != vpid)
+		return -EPERM;
+
+	ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
+	if (ret)
+		return ret;
+
+	hb = hash_futex(&key);
+	spin_lock(&hb->lock);
+
+	/*
+	 * Check waiters first. We do not trust user space values at
+	 * all and we at least want to know if user space fiddled
+	 * with the futex value instead of blindly unlocking.
+	 */
+	top_waiter = futex_top_waiter(hb, &key);
+	if (top_waiter) {
+		struct futex_pi_state *pi_state = top_waiter->pi_state;
+
+		ret = -EINVAL;
+		if (!pi_state)
+			goto out_unlock;
+
+		/*
+		 * If current does not own the pi_state then the futex is
+		 * inconsistent and user space fiddled with the futex value.
+		 */
+		if (pi_state->owner != current)
+			goto out_unlock;
+
+		get_pi_state(pi_state);
+		/*
+		 * By taking wait_lock while still holding hb->lock, we ensure
+		 * there is no point where we hold neither; and therefore
+		 * wake_futex_pi() must observe a state consistent with what we
+		 * observed.
+		 *
+		 * In particular; this forces __rt_mutex_start_proxy() to
+		 * complete such that we're guaranteed to observe the
+		 * rt_waiter. Also see the WARN in wake_futex_pi().
+		 */
+		raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
+		spin_unlock(&hb->lock);
+
+		/* drops pi_state->pi_mutex.wait_lock */
+		ret = wake_futex_pi(uaddr, uval, pi_state);
+
+		put_pi_state(pi_state);
+
+		/*
+		 * Success, we're done! No tricky corner cases.
+		 */
+		if (!ret)
+			return ret;
+		/*
+		 * The atomic access to the futex value generated a
+		 * pagefault, so retry the user-access and the wakeup:
+		 */
+		if (ret == -EFAULT)
+			goto pi_faulted;
+		/*
+		 * A unconditional UNLOCK_PI op raced against a waiter
+		 * setting the FUTEX_WAITERS bit. Try again.
+		 */
+		if (ret == -EAGAIN)
+			goto pi_retry;
+		/*
+		 * wake_futex_pi has detected invalid state. Tell user
+		 * space.
+		 */
+		return ret;
+	}
+
+	/*
+	 * We have no kernel internal state, i.e. no waiters in the
+	 * kernel. Waiters which are about to queue themselves are stuck
+	 * on hb->lock. So we can safely ignore them. We do neither
+	 * preserve the WAITERS bit not the OWNER_DIED one. We are the
+	 * owner.
+	 */
+	if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
+		spin_unlock(&hb->lock);
+		switch (ret) {
+		case -EFAULT:
+			goto pi_faulted;
+
+		case -EAGAIN:
+			goto pi_retry;
+
+		default:
+			WARN_ON_ONCE(1);
+			return ret;
+		}
+	}
+
+	/*
+	 * If uval has changed, let user space handle it.
+	 */
+	ret = (curval == uval) ? 0 : -EAGAIN;
+
+out_unlock:
+	spin_unlock(&hb->lock);
+	return ret;
+
+pi_retry:
+	cond_resched();
+	goto retry;
+
+pi_faulted:
+
+	ret = fault_in_user_writeable(uaddr);
+	if (!ret)
+		goto retry;
+
+	return ret;
+}
+
+/**
+ * handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
+ * @hb:		the hash_bucket futex_q was original enqueued on
+ * @q:		the futex_q woken while waiting to be requeued
+ * @timeout:	the timeout associated with the wait (NULL if none)
+ *
+ * Determine the cause for the early wakeup.
+ *
+ * Return:
+ *  -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR
+ */
+static inline
+int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
+				   struct futex_q *q,
+				   struct hrtimer_sleeper *timeout)
+{
+	int ret;
+
+	/*
+	 * With the hb lock held, we avoid races while we process the wakeup.
+	 * We only need to hold hb (and not hb2) to ensure atomicity as the
+	 * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
+	 * It can't be requeued from uaddr2 to something else since we don't
+	 * support a PI aware source futex for requeue.
+	 */
+	WARN_ON_ONCE(&hb->lock != q->lock_ptr);
+
+	/*
+	 * We were woken prior to requeue by a timeout or a signal.
+	 * Unqueue the futex_q and determine which it was.
+	 */
+	plist_del(&q->list, &hb->chain);
+	hb_waiters_dec(hb);
+
+	/* Handle spurious wakeups gracefully */
+	ret = -EWOULDBLOCK;
+	if (timeout && !timeout->task)
+		ret = -ETIMEDOUT;
+	else if (signal_pending(current))
+		ret = -ERESTARTNOINTR;
+	return ret;
+}
+
+/**
+ * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
+ * @uaddr:	the futex we initially wait on (non-pi)
+ * @flags:	futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
+ *		the same type, no requeueing from private to shared, etc.
+ * @val:	the expected value of uaddr
+ * @abs_time:	absolute timeout
+ * @bitset:	32 bit wakeup bitset set by userspace, defaults to all
+ * @uaddr2:	the pi futex we will take prior to returning to user-space
+ *
+ * The caller will wait on uaddr and will be requeued by futex_requeue() to
+ * uaddr2 which must be PI aware and unique from uaddr.  Normal wakeup will wake
+ * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
+ * userspace.  This ensures the rt_mutex maintains an owner when it has waiters;
+ * without one, the pi logic would not know which task to boost/deboost, if
+ * there was a need to.
+ *
+ * We call schedule in futex_wait_queue_me() when we enqueue and return there
+ * via the following--
+ * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
+ * 2) wakeup on uaddr2 after a requeue
+ * 3) signal
+ * 4) timeout
+ *
+ * If 3, cleanup and return -ERESTARTNOINTR.
+ *
+ * If 2, we may then block on trying to take the rt_mutex and return via:
+ * 5) successful lock
+ * 6) signal
+ * 7) timeout
+ * 8) other lock acquisition failure
+ *
+ * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
+ *
+ * If 4 or 7, we cleanup and return with -ETIMEDOUT.
+ *
+ * Return:
+ *  -  0 - On success;
+ *  - <0 - On error
+ */
+static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
+				 u32 val, ktime_t *abs_time, u32 bitset,
+				 u32 __user *uaddr2)
+{
+	struct hrtimer_sleeper timeout, *to;
+	struct rt_mutex_waiter rt_waiter;
+	struct futex_hash_bucket *hb;
+	union futex_key key2 = FUTEX_KEY_INIT;
+	struct futex_q q = futex_q_init;
+	struct rt_mutex_base *pi_mutex;
+	int res, ret;
+
+	if (!IS_ENABLED(CONFIG_FUTEX_PI))
+		return -ENOSYS;
+
+	if (uaddr == uaddr2)
+		return -EINVAL;
+
+	if (!bitset)
+		return -EINVAL;
+
+	to = futex_setup_timer(abs_time, &timeout, flags,
+			       current->timer_slack_ns);
+
+	/*
+	 * The waiter is allocated on our stack, manipulated by the requeue
+	 * code while we sleep on uaddr.
+	 */
+	rt_mutex_init_waiter(&rt_waiter);
+
+	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
+	if (unlikely(ret != 0))
+		goto out;
+
+	q.bitset = bitset;
+	q.rt_waiter = &rt_waiter;
+	q.requeue_pi_key = &key2;
+
+	/*
+	 * Prepare to wait on uaddr. On success, it holds hb->lock and q
+	 * is initialized.
+	 */
+	ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
+	if (ret)
+		goto out;
+
+	/*
+	 * The check above which compares uaddrs is not sufficient for
+	 * shared futexes. We need to compare the keys:
+	 */
+	if (match_futex(&q.key, &key2)) {
+		queue_unlock(hb);
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* Queue the futex_q, drop the hb lock, wait for wakeup. */
+	futex_wait_queue_me(hb, &q, to);
+
+	switch (futex_requeue_pi_wakeup_sync(&q)) {
+	case Q_REQUEUE_PI_IGNORE:
+		/* The waiter is still on uaddr1 */
+		spin_lock(&hb->lock);
+		ret = handle_early_requeue_pi_wakeup(hb, &q, to);
+		spin_unlock(&hb->lock);
+		break;
+
+	case Q_REQUEUE_PI_LOCKED:
+		/* The requeue acquired the lock */
+		if (q.pi_state && (q.pi_state->owner != current)) {
+			spin_lock(q.lock_ptr);
+			ret = fixup_owner(uaddr2, &q, true);
+			/*
+			 * Drop the reference to the pi state which the
+			 * requeue_pi() code acquired for us.
+			 */
+			put_pi_state(q.pi_state);
+			spin_unlock(q.lock_ptr);
+			/*
+			 * Adjust the return value. It's either -EFAULT or
+			 * success (1) but the caller expects 0 for success.
+			 */
+			ret = ret < 0 ? ret : 0;
+		}
+		break;
+
+	case Q_REQUEUE_PI_DONE:
+		/* Requeue completed. Current is 'pi_blocked_on' the rtmutex */
+		pi_mutex = &q.pi_state->pi_mutex;
+		ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
+
+		/* Current is not longer pi_blocked_on */
+		spin_lock(q.lock_ptr);
+		if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
+			ret = 0;
+
+		debug_rt_mutex_free_waiter(&rt_waiter);
+		/*
+		 * Fixup the pi_state owner and possibly acquire the lock if we
+		 * haven't already.
+		 */
+		res = fixup_owner(uaddr2, &q, !ret);
+		/*
+		 * If fixup_owner() returned an error, propagate that.  If it
+		 * acquired the lock, clear -ETIMEDOUT or -EINTR.
+		 */
+		if (res)
+			ret = (res < 0) ? res : 0;
+
+		unqueue_me_pi(&q);
+		spin_unlock(q.lock_ptr);
+
+		if (ret == -EINTR) {
+			/*
+			 * We've already been requeued, but cannot restart
+			 * by calling futex_lock_pi() directly. We could
+			 * restart this syscall, but it would detect that
+			 * the user space "val" changed and return
+			 * -EWOULDBLOCK.  Save the overhead of the restart
+			 * and return -EWOULDBLOCK directly.
+			 */
+			ret = -EWOULDBLOCK;
+		}
+		break;
+	default:
+		BUG();
+	}
+
+out:
+	if (to) {
+		hrtimer_cancel(&to->timer);
+		destroy_hrtimer_on_stack(&to->timer);
+	}
+	return ret;
+}
+
+/*
+ * Support for robust futexes: the kernel cleans up held futexes at
+ * thread exit time.
+ *
+ * Implementation: user-space maintains a per-thread list of locks it
+ * is holding. Upon do_exit(), the kernel carefully walks this list,
+ * and marks all locks that are owned by this thread with the
+ * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
+ * always manipulated with the lock held, so the list is private and
+ * per-thread. Userspace also maintains a per-thread 'list_op_pending'
+ * field, to allow the kernel to clean up if the thread dies after
+ * acquiring the lock, but just before it could have added itself to
+ * the list. There can only be one such pending lock.
+ */
+
+/**
+ * sys_set_robust_list() - Set the robust-futex list head of a task
+ * @head:	pointer to the list-head
+ * @len:	length of the list-head, as userspace expects
+ */
+SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
+		size_t, len)
+{
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+	/*
+	 * The kernel knows only one size for now:
+	 */
+	if (unlikely(len != sizeof(*head)))
+		return -EINVAL;
+
+	current->robust_list = head;
+
+	return 0;
+}
+
+/**
+ * sys_get_robust_list() - Get the robust-futex list head of a task
+ * @pid:	pid of the process [zero for current task]
+ * @head_ptr:	pointer to a list-head pointer, the kernel fills it in
+ * @len_ptr:	pointer to a length field, the kernel fills in the header size
+ */
+SYSCALL_DEFINE3(get_robust_list, int, pid,
+		struct robust_list_head __user * __user *, head_ptr,
+		size_t __user *, len_ptr)
+{
+	struct robust_list_head __user *head;
+	unsigned long ret;
+	struct task_struct *p;
+
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+
+	rcu_read_lock();
+
+	ret = -ESRCH;
+	if (!pid)
+		p = current;
+	else {
+		p = find_task_by_vpid(pid);
+		if (!p)
+			goto err_unlock;
+	}
+
+	ret = -EPERM;
+	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
+		goto err_unlock;
+
+	head = p->robust_list;
+	rcu_read_unlock();
+
+	if (put_user(sizeof(*head), len_ptr))
+		return -EFAULT;
+	return put_user(head, head_ptr);
+
+err_unlock:
+	rcu_read_unlock();
+
+	return ret;
+}
+
+/* Constants for the pending_op argument of handle_futex_death */
+#define HANDLE_DEATH_PENDING	true
+#define HANDLE_DEATH_LIST	false
+
+/*
+ * Process a futex-list entry, check whether it's owned by the
+ * dying task, and do notification if so:
+ */
+static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
+			      bool pi, bool pending_op)
+{
+	u32 uval, nval, mval;
+	int err;
+
+	/* Futex address must be 32bit aligned */
+	if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
+		return -1;
+
+retry:
+	if (get_user(uval, uaddr))
+		return -1;
+
+	/*
+	 * Special case for regular (non PI) futexes. The unlock path in
+	 * user space has two race scenarios:
+	 *
+	 * 1. The unlock path releases the user space futex value and
+	 *    before it can execute the futex() syscall to wake up
+	 *    waiters it is killed.
+	 *
+	 * 2. A woken up waiter is killed before it can acquire the
+	 *    futex in user space.
+	 *
+	 * In both cases the TID validation below prevents a wakeup of
+	 * potential waiters which can cause these waiters to block
+	 * forever.
+	 *
+	 * In both cases the following conditions are met:
+	 *
+	 *	1) task->robust_list->list_op_pending != NULL
+	 *	   @pending_op == true
+	 *	2) User space futex value == 0
+	 *	3) Regular futex: @pi == false
+	 *
+	 * If these conditions are met, it is safe to attempt waking up a
+	 * potential waiter without touching the user space futex value and
+	 * trying to set the OWNER_DIED bit. The user space futex value is
+	 * uncontended and the rest of the user space mutex state is
+	 * consistent, so a woken waiter will just take over the
+	 * uncontended futex. Setting the OWNER_DIED bit would create
+	 * inconsistent state and malfunction of the user space owner died
+	 * handling.
+	 */
+	if (pending_op && !pi && !uval) {
+		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+		return 0;
+	}
+
+	if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
+		return 0;
+
+	/*
+	 * Ok, this dying thread is truly holding a futex
+	 * of interest. Set the OWNER_DIED bit atomically
+	 * via cmpxchg, and if the value had FUTEX_WAITERS
+	 * set, wake up a waiter (if any). (We have to do a
+	 * futex_wake() even if OWNER_DIED is already set -
+	 * to handle the rare but possible case of recursive
+	 * thread-death.) The rest of the cleanup is done in
+	 * userspace.
+	 */
+	mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
+
+	/*
+	 * We are not holding a lock here, but we want to have
+	 * the pagefault_disable/enable() protection because
+	 * we want to handle the fault gracefully. If the
+	 * access fails we try to fault in the futex with R/W
+	 * verification via get_user_pages. get_user() above
+	 * does not guarantee R/W access. If that fails we
+	 * give up and leave the futex locked.
+	 */
+	if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
+		switch (err) {
+		case -EFAULT:
+			if (fault_in_user_writeable(uaddr))
+				return -1;
+			goto retry;
+
+		case -EAGAIN:
+			cond_resched();
+			goto retry;
+
+		default:
+			WARN_ON_ONCE(1);
+			return err;
+		}
+	}
+
+	if (nval != uval)
+		goto retry;
+
+	/*
+	 * Wake robust non-PI futexes here. The wakeup of
+	 * PI futexes happens in exit_pi_state():
+	 */
+	if (!pi && (uval & FUTEX_WAITERS))
+		futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
+
+	return 0;
+}
+
+/*
+ * Fetch a robust-list pointer. Bit 0 signals PI futexes:
+ */
+static inline int fetch_robust_entry(struct robust_list __user **entry,
+				     struct robust_list __user * __user *head,
+				     unsigned int *pi)
+{
+	unsigned long uentry;
+
+	if (get_user(uentry, (unsigned long __user *)head))
+		return -EFAULT;
+
+	*entry = (void __user *)(uentry & ~1UL);
+	*pi = uentry & 1;
+
+	return 0;
+}
+
+/*
+ * Walk curr->robust_list (very carefully, it's a userspace list!)
+ * and mark any locks found there dead, and notify any waiters.
+ *
+ * We silently return on any sign of list-walking problem.
+ */
+static void exit_robust_list(struct task_struct *curr)
+{
+	struct robust_list_head __user *head = curr->robust_list;
+	struct robust_list __user *entry, *next_entry, *pending;
+	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
+	unsigned int next_pi;
+	unsigned long futex_offset;
+	int rc;
+
+	if (!futex_cmpxchg_enabled)
+		return;
+
+	/*
+	 * Fetch the list head (which was registered earlier, via
+	 * sys_set_robust_list()):
+	 */
+	if (fetch_robust_entry(&entry, &head->list.next, &pi))
+		return;
+	/*
+	 * Fetch the relative futex offset:
+	 */
+	if (get_user(futex_offset, &head->futex_offset))
+		return;
+	/*
+	 * Fetch any possibly pending lock-add first, and handle it
+	 * if it exists:
+	 */
+	if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
+		return;
+
+	next_entry = NULL;	/* avoid warning with gcc */
+	while (entry != &head->list) {
+		/*
+		 * Fetch the next entry in the list before calling
+		 * handle_futex_death:
+		 */
+		rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
+		/*
+		 * A pending lock might already be on the list, so
+		 * don't process it twice:
+		 */
+		if (entry != pending) {
+			if (handle_futex_death((void __user *)entry + futex_offset,
+						curr, pi, HANDLE_DEATH_LIST))
+				return;
+		}
+		if (rc)
+			return;
+		entry = next_entry;
+		pi = next_pi;
+		/*
+		 * Avoid excessively long or circular lists:
+		 */
+		if (!--limit)
+			break;
+
+		cond_resched();
+	}
+
+	if (pending) {
+		handle_futex_death((void __user *)pending + futex_offset,
+				   curr, pip, HANDLE_DEATH_PENDING);
+	}
+}
+
+static void futex_cleanup(struct task_struct *tsk)
+{
+	if (unlikely(tsk->robust_list)) {
+		exit_robust_list(tsk);
+		tsk->robust_list = NULL;
+	}
+
+#ifdef CONFIG_COMPAT
+	if (unlikely(tsk->compat_robust_list)) {
+		compat_exit_robust_list(tsk);
+		tsk->compat_robust_list = NULL;
+	}
+#endif
+
+	if (unlikely(!list_empty(&tsk->pi_state_list)))
+		exit_pi_state_list(tsk);
+}
+
+/**
+ * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
+ * @tsk:	task to set the state on
+ *
+ * Set the futex exit state of the task lockless. The futex waiter code
+ * observes that state when a task is exiting and loops until the task has
+ * actually finished the futex cleanup. The worst case for this is that the
+ * waiter runs through the wait loop until the state becomes visible.
+ *
+ * This is called from the recursive fault handling path in do_exit().
+ *
+ * This is best effort. Either the futex exit code has run already or
+ * not. If the OWNER_DIED bit has been set on the futex then the waiter can
+ * take it over. If not, the problem is pushed back to user space. If the
+ * futex exit code did not run yet, then an already queued waiter might
+ * block forever, but there is nothing which can be done about that.
+ */
+void futex_exit_recursive(struct task_struct *tsk)
+{
+	/* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
+	if (tsk->futex_state == FUTEX_STATE_EXITING)
+		mutex_unlock(&tsk->futex_exit_mutex);
+	tsk->futex_state = FUTEX_STATE_DEAD;
+}
+
+static void futex_cleanup_begin(struct task_struct *tsk)
+{
+	/*
+	 * Prevent various race issues against a concurrent incoming waiter
+	 * including live locks by forcing the waiter to block on
+	 * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
+	 * attach_to_pi_owner().
+	 */
+	mutex_lock(&tsk->futex_exit_mutex);
+
+	/*
+	 * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
+	 *
+	 * This ensures that all subsequent checks of tsk->futex_state in
+	 * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
+	 * tsk->pi_lock held.
+	 *
+	 * It guarantees also that a pi_state which was queued right before
+	 * the state change under tsk->pi_lock by a concurrent waiter must
+	 * be observed in exit_pi_state_list().
+	 */
+	raw_spin_lock_irq(&tsk->pi_lock);
+	tsk->futex_state = FUTEX_STATE_EXITING;
+	raw_spin_unlock_irq(&tsk->pi_lock);
+}
+
+static void futex_cleanup_end(struct task_struct *tsk, int state)
+{
+	/*
+	 * Lockless store. The only side effect is that an observer might
+	 * take another loop until it becomes visible.
+	 */
+	tsk->futex_state = state;
+	/*
+	 * Drop the exit protection. This unblocks waiters which observed
+	 * FUTEX_STATE_EXITING to reevaluate the state.
+	 */
+	mutex_unlock(&tsk->futex_exit_mutex);
+}
+
+void futex_exec_release(struct task_struct *tsk)
+{
+	/*
+	 * The state handling is done for consistency, but in the case of
+	 * exec() there is no way to prevent further damage as the PID stays
+	 * the same. But for the unlikely and arguably buggy case that a
+	 * futex is held on exec(), this provides at least as much state
+	 * consistency protection which is possible.
+	 */
+	futex_cleanup_begin(tsk);
+	futex_cleanup(tsk);
+	/*
+	 * Reset the state to FUTEX_STATE_OK. The task is alive and about
+	 * exec a new binary.
+	 */
+	futex_cleanup_end(tsk, FUTEX_STATE_OK);
+}
+
+void futex_exit_release(struct task_struct *tsk)
+{
+	futex_cleanup_begin(tsk);
+	futex_cleanup(tsk);
+	futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
+}
+
+long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
+		u32 __user *uaddr2, u32 val2, u32 val3)
+{
+	int cmd = op & FUTEX_CMD_MASK;
+	unsigned int flags = 0;
+
+	if (!(op & FUTEX_PRIVATE_FLAG))
+		flags |= FLAGS_SHARED;
+
+	if (op & FUTEX_CLOCK_REALTIME) {
+		flags |= FLAGS_CLOCKRT;
+		if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
+		    cmd != FUTEX_LOCK_PI2)
+			return -ENOSYS;
+	}
+
+	switch (cmd) {
+	case FUTEX_LOCK_PI:
+	case FUTEX_LOCK_PI2:
+	case FUTEX_UNLOCK_PI:
+	case FUTEX_TRYLOCK_PI:
+	case FUTEX_WAIT_REQUEUE_PI:
+	case FUTEX_CMP_REQUEUE_PI:
+		if (!futex_cmpxchg_enabled)
+			return -ENOSYS;
+	}
+
+	switch (cmd) {
+	case FUTEX_WAIT:
+		val3 = FUTEX_BITSET_MATCH_ANY;
+		fallthrough;
+	case FUTEX_WAIT_BITSET:
+		return futex_wait(uaddr, flags, val, timeout, val3);
+	case FUTEX_WAKE:
+		val3 = FUTEX_BITSET_MATCH_ANY;
+		fallthrough;
+	case FUTEX_WAKE_BITSET:
+		return futex_wake(uaddr, flags, val, val3);
+	case FUTEX_REQUEUE:
+		return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
+	case FUTEX_CMP_REQUEUE:
+		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
+	case FUTEX_WAKE_OP:
+		return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
+	case FUTEX_LOCK_PI:
+		flags |= FLAGS_CLOCKRT;
+		fallthrough;
+	case FUTEX_LOCK_PI2:
+		return futex_lock_pi(uaddr, flags, timeout, 0);
+	case FUTEX_UNLOCK_PI:
+		return futex_unlock_pi(uaddr, flags);
+	case FUTEX_TRYLOCK_PI:
+		return futex_lock_pi(uaddr, flags, NULL, 1);
+	case FUTEX_WAIT_REQUEUE_PI:
+		val3 = FUTEX_BITSET_MATCH_ANY;
+		return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
+					     uaddr2);
+	case FUTEX_CMP_REQUEUE_PI:
+		return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
+	}
+	return -ENOSYS;
+}
+
+static __always_inline bool futex_cmd_has_timeout(u32 cmd)
+{
+	switch (cmd) {
+	case FUTEX_WAIT:
+	case FUTEX_LOCK_PI:
+	case FUTEX_LOCK_PI2:
+	case FUTEX_WAIT_BITSET:
+	case FUTEX_WAIT_REQUEUE_PI:
+		return true;
+	}
+	return false;
+}
+
+static __always_inline int
+futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
+{
+	if (!timespec64_valid(ts))
+		return -EINVAL;
+
+	*t = timespec64_to_ktime(*ts);
+	if (cmd == FUTEX_WAIT)
+		*t = ktime_add_safe(ktime_get(), *t);
+	else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
+		*t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
+	return 0;
+}
+
+SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
+		const struct __kernel_timespec __user *, utime,
+		u32 __user *, uaddr2, u32, val3)
+{
+	int ret, cmd = op & FUTEX_CMD_MASK;
+	ktime_t t, *tp = NULL;
+	struct timespec64 ts;
+
+	if (utime && futex_cmd_has_timeout(cmd)) {
+		if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
+			return -EFAULT;
+		if (get_timespec64(&ts, utime))
+			return -EFAULT;
+		ret = futex_init_timeout(cmd, op, &ts, &t);
+		if (ret)
+			return ret;
+		tp = &t;
+	}
+
+	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+}
+
+#ifdef CONFIG_COMPAT
+/*
+ * Fetch a robust-list pointer. Bit 0 signals PI futexes:
+ */
+static inline int
+compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
+		   compat_uptr_t __user *head, unsigned int *pi)
+{
+	if (get_user(*uentry, head))
+		return -EFAULT;
+
+	*entry = compat_ptr((*uentry) & ~1);
+	*pi = (unsigned int)(*uentry) & 1;
+
+	return 0;
+}
+
+static void __user *futex_uaddr(struct robust_list __user *entry,
+				compat_long_t futex_offset)
+{
+	compat_uptr_t base = ptr_to_compat(entry);
+	void __user *uaddr = compat_ptr(base + futex_offset);
+
+	return uaddr;
+}
+
+/*
+ * Walk curr->robust_list (very carefully, it's a userspace list!)
+ * and mark any locks found there dead, and notify any waiters.
+ *
+ * We silently return on any sign of list-walking problem.
+ */
+static void compat_exit_robust_list(struct task_struct *curr)
+{
+	struct compat_robust_list_head __user *head = curr->compat_robust_list;
+	struct robust_list __user *entry, *next_entry, *pending;
+	unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
+	unsigned int next_pi;
+	compat_uptr_t uentry, next_uentry, upending;
+	compat_long_t futex_offset;
+	int rc;
+
+	if (!futex_cmpxchg_enabled)
+		return;
+
+	/*
+	 * Fetch the list head (which was registered earlier, via
+	 * sys_set_robust_list()):
+	 */
+	if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
+		return;
+	/*
+	 * Fetch the relative futex offset:
+	 */
+	if (get_user(futex_offset, &head->futex_offset))
+		return;
+	/*
+	 * Fetch any possibly pending lock-add first, and handle it
+	 * if it exists:
+	 */
+	if (compat_fetch_robust_entry(&upending, &pending,
+			       &head->list_op_pending, &pip))
+		return;
+
+	next_entry = NULL;	/* avoid warning with gcc */
+	while (entry != (struct robust_list __user *) &head->list) {
+		/*
+		 * Fetch the next entry in the list before calling
+		 * handle_futex_death:
+		 */
+		rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
+			(compat_uptr_t __user *)&entry->next, &next_pi);
+		/*
+		 * A pending lock might already be on the list, so
+		 * dont process it twice:
+		 */
+		if (entry != pending) {
+			void __user *uaddr = futex_uaddr(entry, futex_offset);
+
+			if (handle_futex_death(uaddr, curr, pi,
+					       HANDLE_DEATH_LIST))
+				return;
+		}
+		if (rc)
+			return;
+		uentry = next_uentry;
+		entry = next_entry;
+		pi = next_pi;
+		/*
+		 * Avoid excessively long or circular lists:
+		 */
+		if (!--limit)
+			break;
+
+		cond_resched();
+	}
+	if (pending) {
+		void __user *uaddr = futex_uaddr(pending, futex_offset);
+
+		handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
+	}
+}
+
+COMPAT_SYSCALL_DEFINE2(set_robust_list,
+		struct compat_robust_list_head __user *, head,
+		compat_size_t, len)
+{
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+
+	if (unlikely(len != sizeof(*head)))
+		return -EINVAL;
+
+	current->compat_robust_list = head;
+
+	return 0;
+}
+
+COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
+			compat_uptr_t __user *, head_ptr,
+			compat_size_t __user *, len_ptr)
+{
+	struct compat_robust_list_head __user *head;
+	unsigned long ret;
+	struct task_struct *p;
+
+	if (!futex_cmpxchg_enabled)
+		return -ENOSYS;
+
+	rcu_read_lock();
+
+	ret = -ESRCH;
+	if (!pid)
+		p = current;
+	else {
+		p = find_task_by_vpid(pid);
+		if (!p)
+			goto err_unlock;
+	}
+
+	ret = -EPERM;
+	if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
+		goto err_unlock;
+
+	head = p->compat_robust_list;
+	rcu_read_unlock();
+
+	if (put_user(sizeof(*head), len_ptr))
+		return -EFAULT;
+	return put_user(ptr_to_compat(head), head_ptr);
+
+err_unlock:
+	rcu_read_unlock();
+
+	return ret;
+}
+#endif /* CONFIG_COMPAT */
+
+#ifdef CONFIG_COMPAT_32BIT_TIME
+SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
+		const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
+		u32, val3)
+{
+	int ret, cmd = op & FUTEX_CMD_MASK;
+	ktime_t t, *tp = NULL;
+	struct timespec64 ts;
+
+	if (utime && futex_cmd_has_timeout(cmd)) {
+		if (get_old_timespec32(&ts, utime))
+			return -EFAULT;
+		ret = futex_init_timeout(cmd, op, &ts, &t);
+		if (ret)
+			return ret;
+		tp = &t;
+	}
+
+	return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
+}
+#endif /* CONFIG_COMPAT_32BIT_TIME */
+
+static void __init futex_detect_cmpxchg(void)
+{
+#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
+	u32 curval;
+
+	/*
+	 * This will fail and we want it. Some arch implementations do
+	 * runtime detection of the futex_atomic_cmpxchg_inatomic()
+	 * functionality. We want to know that before we call in any
+	 * of the complex code paths. Also we want to prevent
+	 * registration of robust lists in that case. NULL is
+	 * guaranteed to fault and we get -EFAULT on functional
+	 * implementation, the non-functional ones will return
+	 * -ENOSYS.
+	 */
+	if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
+		futex_cmpxchg_enabled = 1;
+#endif
+}
+
+static int __init futex_init(void)
+{
+	unsigned int futex_shift;
+	unsigned long i;
+
+#if CONFIG_BASE_SMALL
+	futex_hashsize = 16;
+#else
+	futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
+#endif
+
+	futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
+					       futex_hashsize, 0,
+					       futex_hashsize < 256 ? HASH_SMALL : 0,
+					       &futex_shift, NULL,
+					       futex_hashsize, futex_hashsize);
+	futex_hashsize = 1UL << futex_shift;
+
+	futex_detect_cmpxchg();
+
+	for (i = 0; i < futex_hashsize; i++) {
+		atomic_set(&futex_queues[i].waiters, 0);
+		plist_head_init(&futex_queues[i].chain);
+		spin_lock_init(&futex_queues[i].lock);
+	}
+
+	return 0;
+}
+core_initcall(futex_init);