From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751801Ab3LKLVp (ORCPT ); Wed, 11 Dec 2013 06:21:45 -0500 Received: from cantor2.suse.de ([195.135.220.15]:44572 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751051Ab3LKLVo (ORCPT ); Wed, 11 Dec 2013 06:21:44 -0500 Date: Wed, 11 Dec 2013 11:21:37 +0000 From: Mel Gorman To: "Paul E. McKenney" Cc: Rik van Riel , Andrew Morton , Alex Thorlton , Linux-MM , LKML , Peter Zijlstra Subject: Re: [PATCH 11/18] mm: fix TLB flush race between migration, and change_protection_range Message-ID: <20131211112137.GZ11295@suse.de> References: <1386572952-1191-1-git-send-email-mgorman@suse.de> <1386572952-1191-12-git-send-email-mgorman@suse.de> <52A72463.9080108@redhat.com> <20131210171936.GM11295@suse.de> <20131210180208.GY4208@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <20131210180208.GY4208@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 10, 2013 at 10:02:08AM -0800, Paul E. McKenney wrote: > > > Should this be smp_mb__after_unlock_lock(); ? > > > > I think this is still ok. Minimally, it's missing the unlock/lock pair that > > would cause smp_mb__after_unlock_lock() to be treated as a full barrier > > on architectures that care. The CPU executing this code as already seen > > the pmd_numa update if it's in the fault handler so it just needs to be > > sure to not reorder the check with respect to the page copy. > > You really do need a lock operation somewhere shortly before the > smp_mb__after_unlock_lock(). > My badly phrased point was that there was no unlock/lock operation nearby that needs to be ordered with respect to the tlb_flush_pending check. I do not see a need for smp_mb__after_unlock_lock() here and just this hunk is required. > > index c122bb1..33e5519 100644 > > --- a/include/linux/mm_types.h > > +++ b/include/linux/mm_types.h > > @@ -482,7 +482,12 @@ static inline bool tlb_flush_pending(struct mm_struct *mm) > > static inline void set_tlb_flush_pending(struct mm_struct *mm) > > { > > mm->tlb_flush_pending = true; > > - barrier(); > > + > > + /* > > + * Guarantee that the tlb_flush_pending store does not leak into the > > + * critical section updating the page tables > > + */ > > + smp_mb_before_spinlock(); > > } > > /* Clearing is done after a TLB flush, which also provides a barrier. */ > > static inline void clear_tlb_flush_pending(struct mm_struct *mm) > > A double check would be nice please. -- Mel Gorman SUSE Labs