Date: Mon, 22 Nov 2010 02:42:02 +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: r215652 - head/sys/kern Message-ID: <201011220242.oAM2g2mE075523@svn.freebsd.org>
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Author: davidxu Date: Mon Nov 22 02:42:02 2010 New Revision: 215652 URL: http://svn.freebsd.org/changeset/base/215652 Log: Use atomic instruction to set _has_writer, otherwise there is a race causes userland to not wake up a thread sleeping in kernel. MFC after: 3 days Modified: head/sys/kern/kern_umtx.c Modified: head/sys/kern/kern_umtx.c ============================================================================== --- head/sys/kern/kern_umtx.c Mon Nov 22 01:28:29 2010 (r215651) +++ head/sys/kern/kern_umtx.c Mon Nov 22 02:42:02 2010 (r215652) @@ -2839,7 +2839,8 @@ do_sem_wait(struct thread *td, struct _u umtxq_insert(uq); umtxq_unlock(&uq->uq_key); - suword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 1); + if (fuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters)) == 0) + casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1); count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count)); if (count != 0) {
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