diff mbox series

[v2,2/2] nptl: Move cancel type out of cancelhandling

Message ID 20200520174819.1138124-2-adhemerval.zanella@linaro.org
State New
Headers show
Series [v2,1/2] nptl: Move cancel state out of cancelhandling | expand

Commit Message

Adhemerval Zanella May 20, 2020, 5:48 p.m. UTC
Changes from previous version:

  - Extended some comments.

---

The thread cancellation type is not accessed concurrently internally
neither its pthread interface allows changing the state of a different
thread than its own.

By removing the cancel state out of the internal thread cancel handling
state there is no need to check if cancelled bit was set in CAS
operation.

It allows simplifing the cancellation wrappers and the
CANCEL_CANCELED_AND_ASYNCHRONOUS is removed.

Checked on x86_64-linux-gnu.
---
 nptl/allocatestack.c         |  1 +
 nptl/cancellation.c          | 60 ++++++++++--------------------------
 nptl/cleanup_defer.c         | 46 +++------------------------
 nptl/cleanup_defer_compat.c  | 46 +++------------------------
 nptl/descr.h                 | 14 +++------
 nptl/nptl-init.c             |  2 +-
 nptl/pthread_cancel.c        |  5 ++-
 nptl/pthread_setcanceltype.c | 42 +++----------------------
 nptl/pthread_testcancel.c    |  2 +-
 9 files changed, 43 insertions(+), 175 deletions(-)
diff mbox series

Patch

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index d9174274c2..481487bbb4 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -233,6 +233,7 @@  get_cached_stack (size_t *sizep, void **memp)
   /* Cancellation handling is back to the default.  */
   result->cancelhandling = 0;
   result->cancelstate = PTHREAD_CANCEL_ENABLE;
+  result->canceltype = PTHREAD_CANCEL_DEFERRED;
   result->cleanup = NULL;
 
   /* No pending event.  */
diff --git a/nptl/cancellation.c b/nptl/cancellation.c
index 7e8cbe9fe1..90974c0b18 100644
--- a/nptl/cancellation.c
+++ b/nptl/cancellation.c
@@ -32,31 +32,19 @@  attribute_hidden
 __pthread_enable_asynccancel (void)
 {
   struct pthread *self = THREAD_SELF;
-  int oldval = THREAD_GETMEM (self, cancelhandling);
 
-  while (1)
-    {
-      int newval = oldval | CANCELTYPE_BITMASK;
-
-      if (newval == oldval)
-	break;
-
-      int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
-					      oldval);
-      if (__glibc_likely (curval == oldval))
-	{
-	  if (self->cancelstate == PTHREAD_CANCEL_ENABLE
-	      && CANCEL_CANCELED_AND_ASYNCHRONOUS (newval))
-	    {
-	      THREAD_SETMEM (self, result, PTHREAD_CANCELED);
-	      __do_cancel ();
-	    }
+  int oldval = THREAD_GETMEM (self, canceltype);
+  THREAD_SETMEM (self, canceltype, PTHREAD_CANCEL_ASYNCHRONOUS);
 
-	  break;
-	}
+  int ch = THREAD_GETMEM (self, cancelhandling);
 
-      /* Prepare the next round.  */
-      oldval = curval;
+  if (self->cancelstate == PTHREAD_CANCEL_ENABLE
+      && (ch & CANCELED_BITMASK)
+      && !(ch & EXITING_BITMASK)
+      && !(ch & TERMINATED_BITMASK))
+    {
+      THREAD_SETMEM (self, result, PTHREAD_CANCELED);
+      __do_cancel ();
     }
 
   return oldval;
@@ -70,36 +58,22 @@  __pthread_disable_asynccancel (int oldtype)
 {
   /* If asynchronous cancellation was enabled before we do not have
      anything to do.  */
-  if (oldtype & CANCELTYPE_BITMASK)
+  if (oldtype == PTHREAD_CANCEL_ASYNCHRONOUS)
     return;
 
   struct pthread *self = THREAD_SELF;
-  int newval;
-
-  int oldval = THREAD_GETMEM (self, cancelhandling);
-
-  while (1)
-    {
-      newval = oldval & ~CANCELTYPE_BITMASK;
-
-      int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
-					      oldval);
-      if (__glibc_likely (curval == oldval))
-	break;
-
-      /* Prepare the next round.  */
-      oldval = curval;
-    }
+  THREAD_SETMEM (self, canceltype, PTHREAD_CANCEL_DEFERRED);
 
   /* We cannot return when we are being canceled.  Upon return the
      thread might be things which would have to be undone.  The
      following loop should loop until the cancellation signal is
      delivered.  */
-  while (__builtin_expect ((newval & (CANCELING_BITMASK | CANCELED_BITMASK))
-			   == CANCELING_BITMASK, 0))
+  int ch = THREAD_GETMEM (self, cancelhandling);
+  while (__glibc_unlikely ((ch & CANCELING_BITMASK)
+			    && !(ch & CANCELED_BITMASK)))
     {
-      futex_wait_simple ((unsigned int *) &self->cancelhandling, newval,
+      futex_wait_simple ((unsigned int *) &self->cancelhandling, ch,
 			 FUTEX_PRIVATE);
-      newval = THREAD_GETMEM (self, cancelhandling);
+      ch = THREAD_GETMEM (self, cancelhandling);
     }
 }
diff --git a/nptl/cleanup_defer.c b/nptl/cleanup_defer.c
index 33d4ea6eef..3300b4df46 100644
--- a/nptl/cleanup_defer.c
+++ b/nptl/cleanup_defer.c
@@ -31,27 +31,9 @@  __pthread_register_cancel_defer (__pthread_unwind_buf_t *buf)
   ibuf->priv.data.prev = THREAD_GETMEM (self, cleanup_jmp_buf);
   ibuf->priv.data.cleanup = THREAD_GETMEM (self, cleanup);
 
-  int cancelhandling = THREAD_GETMEM (self, cancelhandling);
-
   /* Disable asynchronous cancellation for now.  */
-  if (__glibc_unlikely (cancelhandling & CANCELTYPE_BITMASK))
-    while (1)
-      {
-	int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						cancelhandling
-						& ~CANCELTYPE_BITMASK,
-						cancelhandling);
-	if (__glibc_likely (curval == cancelhandling))
-	  /* Successfully replaced the value.  */
-	  break;
-
-	/* Prepare for the next round.  */
-	cancelhandling = curval;
-      }
-
-  ibuf->priv.data.canceltype = (cancelhandling & CANCELTYPE_BITMASK
-				? PTHREAD_CANCEL_ASYNCHRONOUS
-				: PTHREAD_CANCEL_DEFERRED);
+  ibuf->priv.data.canceltype = THREAD_GETMEM (self, canceltype);
+  THREAD_SETMEM (self, canceltype, PTHREAD_CANCEL_DEFERRED);
 
   /* Store the new cleanup handler info.  */
   THREAD_SETMEM (self, cleanup_jmp_buf, (struct pthread_unwind_buf *) buf);
@@ -67,25 +49,7 @@  __pthread_unregister_cancel_restore (__pthread_unwind_buf_t *buf)
 
   THREAD_SETMEM (self, cleanup_jmp_buf, ibuf->priv.data.prev);
 
-  int cancelhandling;
-  if (ibuf->priv.data.canceltype != PTHREAD_CANCEL_DEFERRED
-      && ((cancelhandling = THREAD_GETMEM (self, cancelhandling))
-	  & CANCELTYPE_BITMASK) == 0)
-    {
-      while (1)
-	{
-	  int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						  cancelhandling
-						  | CANCELTYPE_BITMASK,
-						  cancelhandling);
-	  if (__glibc_likely (curval == cancelhandling))
-	    /* Successfully replaced the value.  */
-	    break;
-
-	  /* Prepare for the next round.  */
-	  cancelhandling = curval;
-	}
-
-      __pthread_testcancel ();
-    }
+  THREAD_SETMEM (self, canceltype, ibuf->priv.data.canceltype);
+  if (ibuf->priv.data.canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
+    __pthread_testcancel ();
 }
diff --git a/nptl/cleanup_defer_compat.c b/nptl/cleanup_defer_compat.c
index a1ad291fcc..77655c1b0a 100644
--- a/nptl/cleanup_defer_compat.c
+++ b/nptl/cleanup_defer_compat.c
@@ -29,27 +29,9 @@  _pthread_cleanup_push_defer (struct _pthread_cleanup_buffer *buffer,
   buffer->__arg = arg;
   buffer->__prev = THREAD_GETMEM (self, cleanup);
 
-  int cancelhandling = THREAD_GETMEM (self, cancelhandling);
-
   /* Disable asynchronous cancellation for now.  */
-  if (__glibc_unlikely (cancelhandling & CANCELTYPE_BITMASK))
-    while (1)
-      {
-	int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						cancelhandling
-						& ~CANCELTYPE_BITMASK,
-						cancelhandling);
-	if (__glibc_likely (curval == cancelhandling))
-	  /* Successfully replaced the value.  */
-	  break;
-
-	/* Prepare for the next round.  */
-	cancelhandling = curval;
-      }
-
-  buffer->__canceltype = (cancelhandling & CANCELTYPE_BITMASK
-			  ? PTHREAD_CANCEL_ASYNCHRONOUS
-			  : PTHREAD_CANCEL_DEFERRED);
+  buffer->__canceltype = THREAD_GETMEM (self, canceltype);
+  THREAD_SETMEM (self, canceltype, PTHREAD_CANCEL_DEFERRED);
 
   THREAD_SETMEM (self, cleanup, buffer);
 }
@@ -64,27 +46,9 @@  _pthread_cleanup_pop_restore (struct _pthread_cleanup_buffer *buffer,
 
   THREAD_SETMEM (self, cleanup, buffer->__prev);
 
-  int cancelhandling;
-  if (__builtin_expect (buffer->__canceltype != PTHREAD_CANCEL_DEFERRED, 0)
-      && ((cancelhandling = THREAD_GETMEM (self, cancelhandling))
-	  & CANCELTYPE_BITMASK) == 0)
-    {
-      while (1)
-	{
-	  int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling,
-						  cancelhandling
-						  | CANCELTYPE_BITMASK,
-						  cancelhandling);
-	  if (__glibc_likely (curval == cancelhandling))
-	    /* Successfully replaced the value.  */
-	    break;
-
-	  /* Prepare for the next round.  */
-	  cancelhandling = curval;
-	}
-
-      __pthread_testcancel ();
-    }
+  THREAD_SETMEM (self, canceltype, buffer->__canceltype);
+  if (buffer->__canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
+    __pthread_testcancel ();
 
   /* If necessary call the cleanup routine after we removed the
      current cleanup block from the list.  */
diff --git a/nptl/descr.h b/nptl/descr.h
index 279df680d6..e7dc865c91 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -269,9 +269,6 @@  struct pthread
 
   /* Flags determining processing of cancellation.  */
   int cancelhandling;
-  /* Bit set if asynchronous cancellation mode is selected.  */
-#define CANCELTYPE_BIT		1
-#define CANCELTYPE_BITMASK	(0x01 << CANCELTYPE_BIT)
   /* Bit set if canceling has been initiated.  */
 #define CANCELING_BIT		2
 #define CANCELING_BITMASK	(0x01 << CANCELING_BIT)
@@ -287,13 +284,6 @@  struct pthread
   /* Bit set if thread is supposed to change XID.  */
 #define SETXID_BIT		6
 #define SETXID_BITMASK		(0x01 << SETXID_BIT)
-  /* Mask for the rest.  Helps the compiler to optimize.  */
-#define CANCEL_RESTMASK		0xffffff80
-
-#define CANCEL_CANCELED_AND_ASYNCHRONOUS(value) \
-  (((value) & (CANCELTYPE_BITMASK | CANCELED_BITMASK    \
-	       | EXITING_BITMASK | CANCEL_RESTMASK | TERMINATED_BITMASK))     \
-   == (CANCELTYPE_BITMASK | CANCELED_BITMASK))
 
   /* Flags.  Including those copied from the thread attribute.  */
   int flags;
@@ -396,6 +386,10 @@  struct pthread
      PTHREAD_CANCEL_DISABLE).  */
   unsigned char cancelstate;
 
+  /* Thread cancel type (PTHREAD_CANCEL_DEFERRED or
+     PTHREAD_CANCEL_ASYNCHRONOUS).  */
+  unsigned char canceltype;
+
   /* This member must be last.  */
   char end_padding[];
 
diff --git a/nptl/nptl-init.c b/nptl/nptl-init.c
index 96b1444a01..89f58d2e5e 100644
--- a/nptl/nptl-init.c
+++ b/nptl/nptl-init.c
@@ -157,7 +157,7 @@  sigcancel_handler (int sig, siginfo_t *si, void *ctx)
 	  THREAD_SETMEM (self, result, PTHREAD_CANCELED);
 
 	  /* Make sure asynchronous cancellation is still enabled.  */
-	  if ((newval & CANCELTYPE_BITMASK) != 0)
+	  if (self->canceltype == PTHREAD_CANCEL_ASYNCHRONOUS)
 	    /* Run the registered destructors and terminate the thread.  */
 	    __do_cancel ();
 
diff --git a/nptl/pthread_cancel.c b/nptl/pthread_cancel.c
index 5b2789d620..266fd77284 100644
--- a/nptl/pthread_cancel.c
+++ b/nptl/pthread_cancel.c
@@ -56,7 +56,10 @@  __pthread_cancel (pthread_t th)
 	 signal.  We avoid this if possible since it's more
 	 expensive.  */
       if (pd->cancelstate == PTHREAD_CANCEL_ENABLE
-	  && CANCEL_CANCELED_AND_ASYNCHRONOUS (newval))
+	  && pd->canceltype == PTHREAD_CANCEL_ASYNCHRONOUS
+	  && (newval & CANCELED_BITMASK)
+	  && !(newval & EXITING_BITMASK)
+	  && !(newval & TERMINATED_BITMASK))
 	{
 	  /* Mark the cancellation as "in progress".  */
 	  if (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling,
diff --git a/nptl/pthread_setcanceltype.c b/nptl/pthread_setcanceltype.c
index cc0507ae04..d8cb54736d 100644
--- a/nptl/pthread_setcanceltype.c
+++ b/nptl/pthread_setcanceltype.c
@@ -29,43 +29,11 @@  __pthread_setcanceltype (int type, int *oldtype)
 
   volatile struct pthread *self = THREAD_SELF;
 
-  int oldval = THREAD_GETMEM (self, cancelhandling);
-  while (1)
-    {
-      int newval = (type == PTHREAD_CANCEL_ASYNCHRONOUS
-		    ? oldval | CANCELTYPE_BITMASK
-		    : oldval & ~CANCELTYPE_BITMASK);
-
-      /* Store the old value.  */
-      if (oldtype != NULL)
-	*oldtype = ((oldval & CANCELTYPE_BITMASK)
-		    ? PTHREAD_CANCEL_ASYNCHRONOUS : PTHREAD_CANCEL_DEFERRED);
-
-      /* Avoid doing unnecessary work.  The atomic operation can
-	 potentially be expensive if the memory has to be locked and
-	 remote cache lines have to be invalidated.  */
-      if (oldval == newval)
-	break;
-
-      /* Update the cancel handling word.  This has to be done
-	 atomically since other bits could be modified as well.  */
-      int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
-					      oldval);
-      if (__glibc_likely (curval == oldval))
-	{
-	  if (self->cancelstate == PTHREAD_CANCEL_ENABLE
-	      && CANCEL_CANCELED_AND_ASYNCHRONOUS (newval))
-	    {
-	      THREAD_SETMEM (self, result, PTHREAD_CANCELED);
-	      __do_cancel ();
-	    }
-
-	  break;
-	}
-
-      /* Prepare for the next round.  */
-      oldval = curval;
-    }
+  if (oldtype != NULL)
+    *oldtype = self->canceltype;
+  self->canceltype = type;
+  if (type == PTHREAD_CANCEL_ASYNCHRONOUS)
+    __pthread_testcancel ();
 
   return 0;
 }
diff --git a/nptl/pthread_testcancel.c b/nptl/pthread_testcancel.c
index cd937bb3a3..cf518bb8a8 100644
--- a/nptl/pthread_testcancel.c
+++ b/nptl/pthread_testcancel.c
@@ -34,5 +34,5 @@  __pthread_testcancel (void)
       __do_cancel ();
     }
 }
-strong_alias (__pthread_testcancel, pthread_testcancel)
+weak_alias (__pthread_testcancel, pthread_testcancel)
 hidden_def (__pthread_testcancel)