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malloc: Remove malloc hooks from fork handler

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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.
This commit is contained in:
Florian Weimer 2016-04-14 09:18:30 +02:00
parent ae9e94e744
commit 8a727af925
3 changed files with 25 additions and 119 deletions
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17
ChangeLog
View file

@ -1,3 +1,20 @@
2016-04-14 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 not 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.
2016-04-14 Florian Weimer <fweimer@redhat.com>
* sysdeps/nptl/malloc-machine.h (ATFORK_MEM, __dso_handle)

125
malloc/arena.c
View file

@ -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
@ -207,63 +138,30 @@ 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;
@ -276,25 +174,19 @@ __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;
@ -307,7 +199,6 @@ __malloc_fork_unlock_child (void)
}
mutex_init (&list_lock);
atfork_recursive_cntr = 0;
}
/* Initialization routine. */

2
malloc/malloc.c
View file

@ -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 ------------------ */