From mboxrd@z Thu Jan 1 00:00:00 1970 From: Konrad Rzeszutek Wilk Subject: Re: [PATCH] xen mmu: fix a race window causing leave_mm BUG() Date: Tue, 10 May 2011 16:27:02 -0400 Message-ID: <20110510202701.GA18283@dumpdata.com> References: <625BA99ED14B2D499DC4E29D8138F1505C843BB4B6@shsmsx502.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <625BA99ED14B2D499DC4E29D8138F1505C843BB4B6@shsmsx502.ccr.corp.intel.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: "Tian, Kevin" Cc: "jeremy@goop.org" , xen devel , MaoXiaoyun List-Id: xen-devel@lists.xenproject.org On Fri, Apr 29, 2011 at 12:10:57PM +0800, Tian, Kevin wrote: > xen mmu: fix a race window causing leave_mm BUG() I've this in mailbox and I am wondering whether this still an issue with the 2.6.39 type kernels? How do you reproduce the failure? When using LVM? > > there's a race window in xen_drop_mm_ref, where remote cpu may exit > dirty bitmap between the check on this cpu and the point where remote > cpu handles drop request. So in drop_other_mm_ref we need check > whether TLB state is still lazy before calling into leave_mm. This > bug is rarely observed in earlier kernel, but exaggerated by the > commit 831d52bc153971b70e64eccfbed2b232394f22f8 which clears bitmap > after changing the TLB state. > > thanks for Maxiaoyun to verify it. > > Signed-off-by: Kevin Tian > > diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c > index 4e5a611..74c6e4a 100644 > --- a/arch/x86/xen/mmu.c > +++ b/arch/x86/xen/mmu.c > @@ -1260,7 +1260,7 @@ static void drop_other_mm_ref(void *info) > > active_mm = percpu_read(cpu_tlbstate.active_mm); > > - if (active_mm == mm) > + if (active_mm == mm && percpu_read(cpu_tlbstate.state) != TLBSTATE_OK) > leave_mm(smp_processor_id()); > > /* If this cpu still has a stale cr3 reference, then make sure > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel