diff options
| -rw-r--r-- | ipc/sem.c | 18 |
1 files changed, 14 insertions, 4 deletions
diff --git a/ipc/sem.c b/ipc/sem.c index 178f303deea5..b471e5a3863d 100644 --- a/ipc/sem.c +++ b/ipc/sem.c @@ -253,6 +253,16 @@ static void sem_rcu_free(struct rcu_head *head) } /* + * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they + * are only control barriers. + * The code must pair with spin_unlock(&sem->lock) or + * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient. + * + * smp_rmb() is sufficient, as writes cannot pass the control barrier. + */ +#define ipc_smp_acquire__after_spin_is_unlocked() smp_rmb() + +/* * Wait until all currently ongoing simple ops have completed. * Caller must own sem_perm.lock. * New simple ops cannot start, because simple ops first check @@ -275,6 +285,7 @@ static void sem_wait_array(struct sem_array *sma) sem = sma->sem_base + i; spin_unlock_wait(&sem->lock); } + ipc_smp_acquire__after_spin_is_unlocked(); } /* @@ -327,13 +338,12 @@ static inline int sem_lock(struct sem_array *sma, struct sembuf *sops, /* Then check that the global lock is free */ if (!spin_is_locked(&sma->sem_perm.lock)) { /* - * The ipc object lock check must be visible on all - * cores before rechecking the complex count. Otherwise - * we can race with another thread that does: + * We need a memory barrier with acquire semantics, + * otherwise we can race with another thread that does: * complex_count++; * spin_unlock(sem_perm.lock); */ - smp_rmb(); + ipc_smp_acquire__after_spin_is_unlocked(); /* * Now repeat the test of complex_count: |