Date: Mon, 22 Nov 2010 08:19:19 +0000 (UTC) From: David Xu <davidxu@FreeBSD.org> To: src-committers@freebsd.org, svn-src-user@freebsd.org Subject: svn commit: r215660 - user/davidxu/libthr/sys/kern Message-ID: <201011220819.oAM8JJFA083047@svn.freebsd.org>
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Author: davidxu Date: Mon Nov 22 08:19:18 2010 New Revision: 215660 URL: http://svn.freebsd.org/changeset/base/215660 Log: Merge from r215652: Use atomic instruction to set _has_writer, otherwise there is a race causes userland to not wake up a thread sleeping in kernel. Modified: user/davidxu/libthr/sys/kern/kern_umtx.c Modified: user/davidxu/libthr/sys/kern/kern_umtx.c ============================================================================== --- user/davidxu/libthr/sys/kern/kern_umtx.c Mon Nov 22 07:17:27 2010 (r215659) +++ user/davidxu/libthr/sys/kern/kern_umtx.c Mon Nov 22 08:19:18 2010 (r215660) @@ -3565,9 +3565,8 @@ do_sem_wait(struct thread *td, struct _u umtxq_insert(uq); umtxq_unlock(&uq->uq_key); - /* Don't modify cacheline when unnecessary. */ if (fuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters)) == 0) - suword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 1); + casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1); count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count)); if (count != 0) {
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