Date: Tue, 4 Jan 2011 08:00:44 -0500 From: John Baldwin <jhb@freebsd.org> To: Colin Percival <cperciva@freebsd.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r216944 - head/sys/i386/xen Message-ID: <201101040800.45155.jhb@freebsd.org> In-Reply-To: <201101040016.p040GcNf010998@svn.freebsd.org> References: <201101040016.p040GcNf010998@svn.freebsd.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Monday, January 03, 2011 7:16:38 pm Colin Percival wrote: > 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 > + You can use CRITICAL_ASSERT(curthread) instead perhaps. > 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 > -- John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201101040800.45155.jhb>