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d360fa845f
glibc/glibc-rh1276112.patch
Florian Weimer d360fa845f Resolves: #1276112 
Prevent malloc arena free list from becoming cyclic.
2015-10-30 13:05:21 +01:00

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commit 85ee11e317058d44d5c6c29bb4c53acc6c0e22c9
Author: Florian Weimer <fweimer@redhat.com>
Date: Wed Oct 28 19:32:46 2015 +0100
malloc: Prevent arena free_list from turning cyclic [BZ #19048]
[BZ# 19048]
* malloc/malloc.c (struct malloc_state): Update comment. Add
attached_threads member.
(main_arena): Initialize attached_threads.
* malloc/arena.c (list_lock): Update comment.
(ptmalloc_lock_all, ptmalloc_unlock_all): Likewise.
(ptmalloc_unlock_all2): Reinitialize arena reference counts.
(deattach_arena): New function.
(_int_new_arena): Initialize arena reference count and deattach
replaced arena.
(get_free_list, reused_arena): Update reference count and deattach
replaced arena.
(arena_thread_freeres): Update arena reference count and only put
unreferenced arenas on the free list.
(Backport reintroduces tsd_getspecific, tsd_setspecific.)
diff -up glibc-2.21/malloc/arena.c.bz1276112 glibc-2.21/malloc/arena.c
--- glibc-2.21/malloc/arena.c.bz1276112 2015-10-28 20:04:37.043402183 +0100
+++ glibc-2.21/malloc/arena.c 2015-10-28 20:19:32.570584876 +0100
@@ -67,6 +67,12 @@ extern int sanity_check_heap_info_alignm
/* Thread specific data */
static tsd_key_t arena_key;
+
+/* Arena free list. list_lock protects the free_list variable below,
+ and the next_free and attached_threads members of the mstate
+ objects. No other (malloc) locks must be taken while list_lock is
+ active, otherwise deadlocks may occur. */
+
static mutex_t list_lock = MUTEX_INITIALIZER;
static size_t narenas = 1;
static mstate free_list;
@@ -233,7 +239,10 @@ ptmalloc_lock_all (void)
save_free_hook = __free_hook;
__malloc_hook = malloc_atfork;
__free_hook = free_atfork;
- /* Only the current thread may perform malloc/free calls now. */
+ /* Only the current thread may perform malloc/free calls now.
+ save_arena will be reattached to the current thread, in
+ ptmalloc_lock_all, so save_arena->attached_threads is not
+ updated. */
tsd_getspecific (arena_key, save_arena);
tsd_setspecific (arena_key, ATFORK_ARENA_PTR);
out:
@@ -251,6 +260,9 @@ ptmalloc_unlock_all (void)
if (--atfork_recursive_cntr != 0)
return;
+ /* Replace ATFORK_ARENA_PTR with save_arena.
+ save_arena->attached_threads was not changed in ptmalloc_lock_all
+ and is still correct. */
tsd_setspecific (arena_key, save_arena);
__malloc_hook = save_malloc_hook;
__free_hook = save_free_hook;
@@ -282,12 +294,19 @@ ptmalloc_unlock_all2 (void)
tsd_setspecific (arena_key, save_arena);
__malloc_hook = save_malloc_hook;
__free_hook = save_free_hook;
+
+ /* Push all arenas to the free list, except save_arena, which is
+ attached to the current thread. */
+ if (save_arena != NULL)
+ ((mstate) save_arena)->attached_threads = 1;
free_list = NULL;
for (ar_ptr = &main_arena;; )
{
mutex_init (&ar_ptr->mutex);
if (ar_ptr != save_arena)
{
+ /* This arena is no longer attached to any thread. */
+ ar_ptr->attached_threads = 0;
ar_ptr->next_free = free_list;
free_list = ar_ptr;
}
@@ -714,6 +733,22 @@ heap_trim (heap_info *heap, size_t pad)
/* Create a new arena with initial size "size". */
+/* If REPLACED_ARENA is not NULL, detach it from this thread. Must be
+ called while list_lock is held. */
+static void
+detach_arena (mstate replaced_arena)
+{
+ if (replaced_arena != NULL)
+ {
+ assert (replaced_arena->attached_threads > 0);
+ /* The current implementation only detaches from main_arena in
+ case of allocation failure. This means that it is likely not
+ beneficial to put the arena on free_list even if the
+ reference count reaches zero. */
+ --replaced_arena->attached_threads;
+ }
+}
+
static mstate
_int_new_arena (size_t size)
{
@@ -735,6 +770,7 @@ _int_new_arena (size_t size)
}
a = h->ar_ptr = (mstate) (h + 1);
malloc_init_state (a);
+ a->attached_threads = 1;
/*a->next = NULL;*/
a->system_mem = a->max_system_mem = h->size;
arena_mem += h->size;
@@ -748,12 +784,19 @@ _int_new_arena (size_t size)
set_head (top (a), (((char *) h + h->size) - ptr) | PREV_INUSE);
LIBC_PROBE (memory_arena_new, 2, a, size);
+ mstate replaced_arena;
+ {
+ void *vptr = NULL;
+ replaced_arena = tsd_getspecific (arena_key, vptr);
+ }
tsd_setspecific (arena_key, (void *) a);
mutex_init (&a->mutex);
(void) mutex_lock (&a->mutex);
(void) mutex_lock (&list_lock);
+ detach_arena (replaced_arena);
+
/* Add the new arena to the global list. */
a->next = main_arena.next;
atomic_write_barrier ();
@@ -768,13 +811,24 @@ _int_new_arena (size_t size)
static mstate
get_free_list (void)
{
+ void *vptr = NULL;
+ mstate replaced_arena = tsd_getspecific (arena_key, vptr);
mstate result = free_list;
if (result != NULL)
{
(void) mutex_lock (&list_lock);
result = free_list;
if (result != NULL)
- free_list = result->next_free;
+ {
+ free_list = result->next_free;
+
+ /* Arenas on the free list are not attached to any thread. */
+ assert (result->attached_threads == 0);
+ /* But the arena will now be attached to this thread. */
+ result->attached_threads = 1;
+
+ detach_arena (replaced_arena);
+ }
(void) mutex_unlock (&list_lock);
if (result != NULL)
@@ -819,6 +873,15 @@ reused_arena (mstate avoid_arena)
(void) mutex_lock (&result->mutex);
out:
+ {
+ void *vptr = NULL;
+ mstate replaced_arena = tsd_getspecific (arena_key, vptr);
+ (void) mutex_lock (&list_lock);
+ detach_arena (replaced_arena);
+ ++result->attached_threads;
+ (void) mutex_unlock (&list_lock);
+ }
+
LIBC_PROBE (memory_arena_reuse, 2, result, avoid_arena);
tsd_setspecific (arena_key, (void *) result);
next_to_use = result->next;
@@ -912,8 +975,14 @@ arena_thread_freeres (void)
if (a != NULL)
{
(void) mutex_lock (&list_lock);
- a->next_free = free_list;
- free_list = a;
+ /* If this was the last attached thread for this arena, put the
+ arena on the free list. */
+ assert (a->attached_threads > 0);
+ if (--a->attached_threads == 0)
+ {
+ a->next_free = free_list;
+ free_list = a;
+ }
(void) mutex_unlock (&list_lock);
}
}
diff -up glibc-2.21/malloc/malloc.c.bz1276112 glibc-2.21/malloc/malloc.c
--- glibc-2.21/malloc/malloc.c.bz1276112 2015-10-28 20:04:45.171449221 +0100
+++ glibc-2.21/malloc/malloc.c 2015-10-28 20:05:39.124761465 +0100
@@ -1700,9 +1700,15 @@ struct malloc_state
/* Linked list */
struct malloc_state *next;
- /* Linked list for free arenas. */
+ /* Linked list for free arenas. Access to this field is serialized
+ by list_lock in arena.c. */
struct malloc_state *next_free;
+ /* Number of threads attached to this arena. 0 if the arena is on
+ the free list. Access to this field is serialized by list_lock
+ in arena.c. */
+ INTERNAL_SIZE_T attached_threads;
+
/* Memory allocated from the system in this arena. */
INTERNAL_SIZE_T system_mem;
INTERNAL_SIZE_T max_system_mem;
@@ -1746,7 +1752,8 @@ struct malloc_par
static struct malloc_state main_arena =
{
.mutex = MUTEX_INITIALIZER,
- .next = &main_arena
+ .next = &main_arena,
+ .attached_threads = 1
};
/* There is only one instance of the malloc parameters. */
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