malloc: Remove malloc hooks from fork handler

2016-02-10  Florian Weimer  <fweimer@redhat.com>

	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 ------------------  */