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Set waiters flag before checking semaphore's counter,

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otherwise we might lose a wakeup. Tested on postgresql database server.
This commit is contained in:
David Xu 2010-02-08 07:31:05 +00:00
parent 530a5fb294
commit 93f0162799
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=203657
1 changed files with 2 additions and 5 deletions
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7
sys/kern/kern_umtx.c
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@ -2853,6 +2853,8 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct timespec *timeout)
umtxq_insert(uq);
umtxq_unlock(&uq->uq_key);
suword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 1);
count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
if (count != 0) {
umtxq_lock(&uq->uq_key);
@ -2863,11 +2865,6 @@ do_sem_wait(struct thread *td, struct _usem *sem, struct timespec *timeout)
return (0);
}
/*
* set waiters byte and sleep.
*/
suword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 1);
umtxq_lock(&uq->uq_key);
umtxq_unbusy(&uq->uq_key);
umtxq_unlock(&uq->uq_key);