Date: Wed, 31 Aug 2011 09:14:56 +0000 (UTC) From: Attilio Rao <attilio@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-8@freebsd.org Subject: svn commit: r225288 - stable/8/sys/kern Message-ID: <201108310914.p7V9Eulo091537@svn.freebsd.org>
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Author: attilio Date: Wed Aug 31 09:14:56 2011 New Revision: 225288 URL: http://svn.freebsd.org/changeset/base/225288 Log: MFC r225057: Fix a race that can happen when switching spinlocks in callout_cpu_switch() and curthread is preempted. Modified: stable/8/sys/kern/kern_timeout.c Directory Properties: stable/8/sys/ (props changed) stable/8/sys/amd64/include/xen/ (props changed) stable/8/sys/cddl/contrib/opensolaris/ (props changed) stable/8/sys/contrib/dev/acpica/ (props changed) stable/8/sys/contrib/pf/ (props changed) Modified: stable/8/sys/kern/kern_timeout.c ============================================================================== --- stable/8/sys/kern/kern_timeout.c Wed Aug 31 08:44:45 2011 (r225287) +++ stable/8/sys/kern/kern_timeout.c Wed Aug 31 09:14:56 2011 (r225288) @@ -267,10 +267,17 @@ callout_cpu_switch(struct callout *c, st MPASS(c != NULL && cc != NULL); CC_LOCK_ASSERT(cc); + /* + * Avoid interrupts and preemption firing after the callout cpu + * is blocked in order to avoid deadlocks as the new thread + * may be willing to acquire the callout cpu lock. + */ c->c_cpu = CPUBLOCK; + spinlock_enter(); CC_UNLOCK(cc); new_cc = CC_CPU(new_cpu); CC_LOCK(new_cc); + spinlock_exit(); c->c_cpu = new_cpu; return (new_cc); }
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