From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934789Ab0COA2P (ORCPT ); Sun, 14 Mar 2010 20:28:15 -0400 Received: from mail-pw0-f46.google.com ([209.85.160.46]:61080 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751284Ab0COA2J convert rfc822-to-8bit (ORCPT ); Sun, 14 Mar 2010 20:28:09 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=GBXxhZGdDGD0x5A0Lo+l175IBlN8y0JZWHaKBGFhNOT9IYpHgyY82afaquqjFS6u1z 1+XPBM/0xCpDwI+k/G2Ti353VRFNXCWZAelQEaeeDXoiNOCc6roowiB3WzGqYyxDwgUa CKESJog2unxviowYtnCZuCrpmLijmu4tOfTy0= MIME-Version: 1.0 In-Reply-To: <1268412087-13536-3-git-send-email-mel@csn.ul.ie> References: <1268412087-13536-1-git-send-email-mel@csn.ul.ie> <1268412087-13536-3-git-send-email-mel@csn.ul.ie> Date: Mon, 15 Mar 2010 09:28:08 +0900 Message-ID: <28c262361003141728g4aa40901hb040144c5a4aeeed@mail.gmail.com> Subject: Re: [PATCH 02/11] mm,migration: Do not try to migrate unmapped anonymous pages From: Minchan Kim To: Mel Gorman Cc: Andrew Morton , Andrea Arcangeli , Christoph Lameter , Adam Litke , Avi Kivity , David Rientjes , KOSAKI Motohiro , Rik van Riel , linux-kernel@vger.kernel.org, linux-mm@kvack.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Mel. On Sat, Mar 13, 2010 at 1:41 AM, Mel Gorman wrote: > rmap_walk_anon() was triggering errors in memory compaction that looks like > use-after-free errors in anon_vma. The problem appears to be that between > the page being isolated from the LRU and rcu_read_lock() being taken, the > mapcount of the page dropped to 0 and the anon_vma was freed. This patch > skips the migration of anon pages that are not mapped by anyone. > > Signed-off-by: Mel Gorman > Acked-by: Rik van Riel > --- >  mm/migrate.c |   10 ++++++++++ >  1 files changed, 10 insertions(+), 0 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 98eaaf2..3c491e3 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -602,6 +602,16 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private, >         * just care Anon page here. >         */ >        if (PageAnon(page)) { > +               /* > +                * If the page has no mappings any more, just bail. An > +                * unmapped anon page is likely to be freed soon but worse, > +                * it's possible its anon_vma disappeared between when > +                * the page was isolated and when we reached here while > +                * the RCU lock was not held > +                */ > +               if (!page_mapcount(page)) As looking code about mapcount of page, I got confused. I think mapcount of page is protected by pte lock. But I can't find pte lock in unmap_and_move. If I am right, what protects race between this condition check and rcu_read_lock? This patch makes race window very small but It can't remove race totally. I think I am missing something. Pz, point me out. :) > +                       goto uncharge; > + >                rcu_read_lock(); >                rcu_locked = 1; >                anon_vma = page_anon_vma(page); > -- > 1.6.5 > -- Kind regards, Minchan Kim