diff options
Diffstat (limited to 'malloc')
| -rw-r--r-- | malloc/arena.c | 70 | ||||
| -rw-r--r-- | malloc/malloc.c | 11 |
2 files changed, 74 insertions, 7 deletions
diff --git a/malloc/arena.c b/malloc/arena.c index caf718de10..0f00afaf22 100644 --- a/malloc/arena.c +++ b/malloc/arena.c @@ -68,7 +68,10 @@ extern int sanity_check_heap_info_alignment[(sizeof (heap_info) static __thread mstate thread_arena attribute_tls_model_ie; -/* Arena free list. */ +/* 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; @@ -225,7 +228,10 @@ 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. */ save_arena = thread_arena; thread_arena = ATFORK_ARENA_PTR; out: @@ -243,6 +249,9 @@ 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. */ thread_arena = save_arena; __malloc_hook = save_malloc_hook; __free_hook = save_free_hook; @@ -274,12 +283,19 @@ ptmalloc_unlock_all2 (void) 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 + 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; } @@ -718,6 +734,22 @@ 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) { @@ -739,6 +771,7 @@ _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; @@ -752,12 +785,15 @@ _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 = thread_arena; thread_arena = 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 (); @@ -772,13 +808,23 @@ _int_new_arena (size_t size) static mstate get_free_list (void) { + mstate replaced_arena = thread_arena; 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) @@ -837,6 +883,14 @@ reused_arena (mstate avoid_arena) (void) mutex_lock (&result->mutex); out: + { + mstate replaced_arena = thread_arena; + (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); thread_arena = result; next_to_use = result->next; @@ -931,8 +985,14 @@ 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 --git a/malloc/malloc.c b/malloc/malloc.c index 9371b5a224..35c8863a32 100644 --- a/malloc/malloc.c +++ b/malloc/malloc.c @@ -1709,9 +1709,15 @@ 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; @@ -1755,7 +1761,8 @@ 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. */ |