From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756192AbZFJDed (ORCPT ); Tue, 9 Jun 2009 23:34:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753823AbZFJDdZ (ORCPT ); Tue, 9 Jun 2009 23:33:25 -0400 Received: from kroah.org ([198.145.64.141]:56594 "EHLO coco.kroah.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754650AbZFJDdY (ORCPT ); Tue, 9 Jun 2009 23:33:24 -0400 X-Mailbox-Line: From greg@blue.kroah.org Tue Jun 9 17:23:41 2009 Message-Id: <20090610002341.027813925@blue.kroah.org> User-Agent: quilt/0.48-1 Date: Tue, 09 Jun 2009 17:13:34 -0700 From: Greg KH To: linux-kernel@vger.kernel.org, stable@kernel.org Cc: Justin Forbes , Zwane Mwaikambo , "Theodore Ts'o" , Randy Dunlap , Dave Jones , Chuck Wolber , Chris Wedgwood , Michael Krufky , Chuck Ebbert , Domenico Andreoli , Willy Tarreau , Rodrigo Rubira Branco , Jake Edge , Eugene Teo , torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, "David S. Miller" , Greg Kroah-Hartman Subject: [patch 06/60] sparc64: Fix MM refcount check in smp_flush_tlb_pending(). References: <20090610001328.251476848@blue.kroah.org> Content-Disposition: inline; filename=sparc64-fix-mm-refcount-check-in-smp_flush_tlb_pending.patch In-Reply-To: <20090610032135.GA19346@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org -stable review patch. If anyone has any objections, please let us know. ------------------ From: David S. Miller [ Upstream commit f9384d41c02408dd404aa64d66d0ef38adcf6479 ] As explained by Benjamin Herrenschmidt: > CPU 0 is running the context, task->mm == task->active_mm == your > context. The CPU is in userspace happily churning things. > > CPU 1 used to run it, not anymore, it's now running fancyfsd which > is a kernel thread, but current->active_mm still points to that > same context. > > Because there's only one "real" user, mm_users is 1 (but mm_count is > elevated, it's just that the presence on CPU 1 as active_mm has no > effect on mm_count(). > > At this point, fancyfsd decides to invalidate a mapping currently mapped > by that context, for example because a networked file has changed > remotely or something like that, using unmap_mapping_ranges(). > > So CPU 1 goes into the zapping code, which eventually ends up calling > flush_tlb_pending(). Your test will succeed, as current->active_mm is > indeed the target mm for the flush, and mm_users is indeed 1. So you > will -not- send an IPI to the other CPU, and CPU 0 will continue happily > accessing the pages that should have been unmapped. To fix this problem, check ->mm instead of ->active_mm, and this means: > So if you test current->mm, you effectively account for mm_users == 1, > so the only way the mm can be active on another processor is as a lazy > mm for a kernel thread. So your test should work properly as long > as you don't have a HW that will do speculative TLB reloads into the > TLB on that other CPU (and even if you do, you flush-on-switch-in should > get rid of any crap here). And therefore we should be OK. Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- arch/sparc64/kernel/smp.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/arch/sparc64/kernel/smp.c +++ b/arch/sparc64/kernel/smp.c @@ -1031,7 +1031,7 @@ void smp_fetch_global_regs(void) * If the address space is non-shared (ie. mm->count == 1) we avoid * cross calls when we want to flush the currently running process's * tlb state. This is done by clearing all cpu bits except the current - * processor's in current->active_mm->cpu_vm_mask and performing the + * processor's in current->mm->cpu_vm_mask and performing the * flush locally only. This will force any subsequent cpus which run * this task to flush the context from the local tlb if the process * migrates to another cpu (again). @@ -1074,7 +1074,7 @@ void smp_flush_tlb_pending(struct mm_str u32 ctx = CTX_HWBITS(mm->context); int cpu = get_cpu(); - if (mm == current->active_mm && atomic_read(&mm->mm_users) == 1) + if (mm == current->mm && atomic_read(&mm->mm_users) == 1) mm->cpu_vm_mask = cpumask_of_cpu(cpu); else smp_cross_call_masked(&xcall_flush_tlb_pending,