Date: Mon, 8 Feb 2010 07:31:05 +0000 (UTC) From: David Xu <davidxu@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r203657 - head/sys/kern Message-ID: <201002080731.o187V5Pk072517@svn.freebsd.org>
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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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