diff options
Diffstat (limited to 'nptl')
| -rw-r--r-- | nptl/pthread_mutex_unlock.c | 34 |
1 files changed, 22 insertions, 12 deletions
diff --git a/nptl/pthread_mutex_unlock.c b/nptl/pthread_mutex_unlock.c index 334ce38342..82aaa95d7b 100644 --- a/nptl/pthread_mutex_unlock.c +++ b/nptl/pthread_mutex_unlock.c @@ -237,15 +237,24 @@ __pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr) int private = (robust ? PTHREAD_ROBUST_MUTEX_PSHARED (mutex) : PTHREAD_MUTEX_PSHARED (mutex)); - if ((mutex->__data.__lock & FUTEX_WAITERS) != 0 - || atomic_compare_and_exchange_bool_rel (&mutex->__data.__lock, 0, - THREAD_GETMEM (THREAD_SELF, - tid))) + /* Unlock the mutex using a CAS unless there are futex waiters or our + TID is not the value of __lock anymore, in which case we let the + kernel take care of the situation. Use release MO in the CAS to + synchronize with acquire MO in lock acquisitions. */ + int l = atomic_load_relaxed (&mutex->__data.__lock); + do { - INTERNAL_SYSCALL_DECL (__err); - INTERNAL_SYSCALL (futex, __err, 2, &mutex->__data.__lock, - __lll_private_flag (FUTEX_UNLOCK_PI, private)); + if (((l & FUTEX_WAITERS) != 0) + || (l != THREAD_GETMEM (THREAD_SELF, tid))) + { + INTERNAL_SYSCALL_DECL (__err); + INTERNAL_SYSCALL (futex, __err, 2, &mutex->__data.__lock, + __lll_private_flag (FUTEX_UNLOCK_PI, private)); + break; + } } + while (!atomic_compare_exchange_weak_release (&mutex->__data.__lock, + &l, 0)); THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL); break; @@ -278,15 +287,16 @@ __pthread_mutex_unlock_full (pthread_mutex_t *mutex, int decr) /* One less user. */ --mutex->__data.__nusers; - /* Unlock. */ - int newval, oldval; + /* Unlock. Use release MO in the CAS to synchronize with acquire MO in + lock acquisitions. */ + int newval; + int oldval = atomic_load_relaxed (&mutex->__data.__lock); do { - oldval = mutex->__data.__lock; newval = oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK; } - while (atomic_compare_and_exchange_bool_rel (&mutex->__data.__lock, - newval, oldval)); + while (!atomic_compare_exchange_weak_release (&mutex->__data.__lock, + &oldval, newval)); if ((oldval & ~PTHREAD_MUTEX_PRIO_CEILING_MASK) > 1) lll_futex_wake (&mutex->__data.__lock, 1, |