Author: davidxu
Date: Mon Feb 8 07:31:05 2010
New Revision: 203657
URL: http://svn.freebsd.org/changeset/base/203657
Log:
Set waiters flag before checking semaphore's counter,
otherwise we might lose a wakeup. Tested on postgresql database server.
Modified:
head/sys/kern/kern_umtx.c
Modified: head/sys/kern/kern_umtx.c
==============================================================================
--- head/sys/kern/kern_umtx.c Mon Feb 8 06:28:33 2010 (r203656)
+++ head/sys/kern/kern_umtx.c Mon Feb 8 07:31:05 2010 (r203657)
@@ -2853,6 +2853,8 @@ do_sem_wait(struct thread *td, struct _u
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 _u
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);
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