Date: Tue, 4 Jan 2011 00:16:38 +0000 (UTC) From: Colin Percival <cperciva@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r216944 - head/sys/i386/xen Message-ID: <201101040016.p040GcNf010998@svn.freebsd.org>
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Author: cperciva Date: Tue Jan 4 00:16:38 2011 New Revision: 216944 URL: http://svn.freebsd.org/changeset/base/216944 Log: Adjust the critical section protecting _xen_flush_queue to cover the entire range where the page mapping request queue needs to be atomically examined and modified. Oddly, while this doesn't seem to affect the overall rate of panics (running 'make index' on EC2 t1.micro instances, there are 0.6 +/- 0.1 panics per hour, both before and after this change), it eliminates vm_fault from panic backtraces, leaving only backtraces going through vmspace_fork. Modified: head/sys/i386/xen/xen_machdep.c Modified: head/sys/i386/xen/xen_machdep.c ============================================================================== --- head/sys/i386/xen/xen_machdep.c Tue Jan 4 00:11:09 2011 (r216943) +++ head/sys/i386/xen/xen_machdep.c Tue Jan 4 00:16:38 2011 (r216944) @@ -42,6 +42,7 @@ __FBSDID("$FreeBSD$"); #include <sys/malloc.h> #include <sys/mutex.h> #include <sys/kernel.h> +#include <sys/proc.h> #include <sys/reboot.h> #include <sys/sysproto.h> @@ -249,10 +250,13 @@ _xen_flush_queue(void) SET_VCPU(); int _xpq_idx = XPQ_IDX; int error, i; - /* window of vulnerability here? */ +#ifdef INVARIANTS if (__predict_true(gdtset)) - critical_enter(); + KASSERT(curthread->td_critnest > 0, + ("xen queue flush should be in a critical section")); +#endif + XPQ_IDX = 0; /* Make sure index is cleared first to avoid double updates. */ error = HYPERVISOR_mmu_update((mmu_update_t *)&XPQ_QUEUE, @@ -286,8 +290,6 @@ _xen_flush_queue(void) } } #endif - if (__predict_true(gdtset)) - critical_exit(); if (__predict_false(error < 0)) { for (i = 0; i < _xpq_idx; i++) printf("val: %llx ptr: %llx\n", @@ -301,7 +303,12 @@ void xen_flush_queue(void) { SET_VCPU(); + + if (__predict_true(gdtset)) + critical_enter(); if (XPQ_IDX != 0) _xen_flush_queue(); + if (__predict_true(gdtset)) + critical_exit(); } static __inline void
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