diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/locking/rwsem-xadd.c | 25 |
1 files changed, 18 insertions, 7 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index fcbf75ac3dcb..b957da7fcb19 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -261,17 +261,28 @@ struct rw_semaphore __sched *rwsem_down_read_failed(struct rw_semaphore *sem) } EXPORT_SYMBOL(rwsem_down_read_failed); +/* + * This function must be called with the sem->wait_lock held to prevent + * race conditions between checking the rwsem wait list and setting the + * sem->count accordingly. + */ static inline bool rwsem_try_write_lock(long count, struct rw_semaphore *sem) { /* - * Try acquiring the write lock. Check count first in order - * to reduce unnecessary expensive cmpxchg() operations. + * Avoid trying to acquire write lock if count isn't RWSEM_WAITING_BIAS. */ - if (count == RWSEM_WAITING_BIAS && - cmpxchg_acquire(&sem->count, RWSEM_WAITING_BIAS, - RWSEM_ACTIVE_WRITE_BIAS) == RWSEM_WAITING_BIAS) { - if (!list_is_singular(&sem->wait_list)) - rwsem_atomic_update(RWSEM_WAITING_BIAS, sem); + if (count != RWSEM_WAITING_BIAS) + return false; + + /* + * Acquire the lock by trying to set it to ACTIVE_WRITE_BIAS. If there + * are other tasks on the wait list, we need to add on WAITING_BIAS. + */ + count = list_is_singular(&sem->wait_list) ? + RWSEM_ACTIVE_WRITE_BIAS : + RWSEM_ACTIVE_WRITE_BIAS + RWSEM_WAITING_BIAS; + + if (cmpxchg_acquire(&sem->count, RWSEM_WAITING_BIAS, count) == RWSEM_WAITING_BIAS) { rwsem_set_owner(sem); return true; } |