From patchwork Wed Feb 10 21:48:30 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Florian Weimer X-Patchwork-Id: 10812 Received: (qmail 8461 invoked by alias); 10 Feb 2016 21:48:36 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 8438 invoked by uid 89); 10 Feb 2016 21:48:35 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-2.1 required=5.0 tests=BAYES_00, RP_MATCHES_RCVD, SPF_HELO_PASS autolearn=ham version=3.3.2 spammy=1986, 10748, 1074, 8, suspend X-HELO: mx1.redhat.com To: GNU C Library Cc: Torvald Riegel From: Florian Weimer Subject: [PATCH] malloc: Remove malloc hooks from fork handler Message-ID: <56BBB02E.5020906@redhat.com> Date: Wed, 10 Feb 2016 22:48:30 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 The fork handler now runs so late that there is no risk anymore that other fork handlers in the same thread use malloc, so it is no longer necessary to install malloc hooks which made a subset of malloc functionality available to the thread that called fork. Florian 2016-02-10 Florian Weimer Remove malloc hooks from fork handler. They are no longer needed because malloc runs right before fork, and no malloc calls from other fork handlers are possible anymore. * malloc/malloc.c (malloc_atfork, free_atfork): Remove declarations. * malloc/arena.c (save_malloc_hook, save_free_hook, save_arena) (ATFORK_ARENA_PTR, malloc_atfork, free_atfork) (atfork_recursive_cntr): Remove. (__malloc_fork_lock_parent): Do not override malloc hooks and thread_arena. (__malloc_fork_unlock_parent): Do not restore malloc hooks and thread_arena. (__malloc_fork_unlock_child): Do not restore malloc hooks. Use thread_arena instead of save_arena. diff --git a/malloc/arena.c b/malloc/arena.c index 8c3c3a5..c6ac0bd 100644 --- a/malloc/arena.c +++ b/malloc/arena.c @@ -129,75 +129,6 @@ int __malloc_initialized = -1; /* atfork support. */ -static void *(*save_malloc_hook)(size_t __size, const void *); -static void (*save_free_hook) (void *__ptr, const void *); -static void *save_arena; - -/* Magic value for the thread-specific arena pointer when - malloc_atfork() is in use. */ - -# define ATFORK_ARENA_PTR ((void *) -1) - -/* The following hooks are used while the `atfork' handling mechanism - is active. */ - -static void * -malloc_atfork (size_t sz, const void *caller) -{ - void *victim; - - if (thread_arena == ATFORK_ARENA_PTR) - { - /* We are the only thread that may allocate at all. */ - if (save_malloc_hook != malloc_check) - { - return _int_malloc (&main_arena, sz); - } - else - { - if (top_check () < 0) - return 0; - - victim = _int_malloc (&main_arena, sz + 1); - return mem2mem_check (victim, sz); - } - } - else - { - /* Suspend the thread until the `atfork' handlers have completed. - By that time, the hooks will have been reset as well, so that - mALLOc() can be used again. */ - (void) mutex_lock (&list_lock); - (void) mutex_unlock (&list_lock); - return __libc_malloc (sz); - } -} - -static void -free_atfork (void *mem, const void *caller) -{ - mstate ar_ptr; - mchunkptr p; /* chunk corresponding to mem */ - - if (mem == 0) /* free(0) has no effect */ - return; - - p = mem2chunk (mem); /* do not bother to replicate free_check here */ - - if (chunk_is_mmapped (p)) /* release mmapped memory. */ - { - munmap_chunk (p); - return; - } - - ar_ptr = arena_for_chunk (p); - _int_free (ar_ptr, p, thread_arena == ATFORK_ARENA_PTR); -} - - -/* Counter for number of times the list is locked by the same thread. */ -static unsigned int atfork_recursive_cntr; - /* The following three functions are called around fork from a multi-threaded process. We do not use the general fork handler mechanism to make sure that our handlers are the last ones being @@ -206,63 +137,30 @@ static unsigned int atfork_recursive_cntr; void __malloc_fork_lock_parent (void) { - mstate ar_ptr; - if (__malloc_initialized < 1) return; /* We do not acquire free_list_lock here because we completely reconstruct free_list in __malloc_fork_unlock_child. */ - if (mutex_trylock (&list_lock)) - { - if (thread_arena == ATFORK_ARENA_PTR) - /* This is the same thread which already locks the global list. - Just bump the counter. */ - goto out; + (void) mutex_lock (&list_lock); - /* This thread has to wait its turn. */ - (void) mutex_lock (&list_lock); - } - for (ar_ptr = &main_arena;; ) + for (mstate ar_ptr = &main_arena;; ) { (void) mutex_lock (&ar_ptr->mutex); ar_ptr = ar_ptr->next; if (ar_ptr == &main_arena) break; } - save_malloc_hook = __malloc_hook; - save_free_hook = __free_hook; - __malloc_hook = malloc_atfork; - __free_hook = free_atfork; - /* Only the current thread may perform malloc/free calls now. - save_arena will be reattached to the current thread, in - __malloc_fork_lock_parent, so save_arena->attached_threads is not - updated. */ - save_arena = thread_arena; - thread_arena = ATFORK_ARENA_PTR; -out: - ++atfork_recursive_cntr; } void __malloc_fork_unlock_parent (void) { - mstate ar_ptr; - if (__malloc_initialized < 1) return; - if (--atfork_recursive_cntr != 0) - return; - - /* Replace ATFORK_ARENA_PTR with save_arena. - save_arena->attached_threads was not changed in - __malloc_fork_lock_parent and is still correct. */ - thread_arena = save_arena; - __malloc_hook = save_malloc_hook; - __free_hook = save_free_hook; - for (ar_ptr = &main_arena;; ) + for (mstate ar_ptr = &main_arena;; ) { (void) mutex_unlock (&ar_ptr->mutex); ar_ptr = ar_ptr->next; @@ -275,25 +173,19 @@ __malloc_fork_unlock_parent (void) void __malloc_fork_unlock_child (void) { - mstate ar_ptr; - if (__malloc_initialized < 1) return; - thread_arena = save_arena; - __malloc_hook = save_malloc_hook; - __free_hook = save_free_hook; - - /* Push all arenas to the free list, except save_arena, which is + /* Push all arenas to the free list, except thread_arena, which is attached to the current thread. */ mutex_init (&free_list_lock); - if (save_arena != NULL) - ((mstate) save_arena)->attached_threads = 1; + if (thread_arena != NULL) + thread_arena->attached_threads = 1; free_list = NULL; - for (ar_ptr = &main_arena;; ) + for (mstate ar_ptr = &main_arena;; ) { mutex_init (&ar_ptr->mutex); - if (ar_ptr != save_arena) + if (ar_ptr != thread_arena) { /* This arena is no longer attached to any thread. */ ar_ptr->attached_threads = 0; @@ -306,7 +198,6 @@ __malloc_fork_unlock_child (void) } mutex_init (&list_lock); - atfork_recursive_cntr = 0; } /* Initialization routine. */ diff --git a/malloc/malloc.c b/malloc/malloc.c index 527332f..809512c 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -1074,8 +1074,6 @@ static void* realloc_check(void* oldmem, size_t bytes, const void *caller); static void* memalign_check(size_t alignment, size_t bytes, const void *caller); -static void* malloc_atfork(size_t sz, const void *caller); -static void free_atfork(void* mem, const void *caller); /* ------------------ MMAP support ------------------ */