From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752085AbdARJbg (ORCPT ); Wed, 18 Jan 2017 04:31:36 -0500 Received: from mx2.suse.de ([195.135.220.15]:34223 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751157AbdARJbe (ORCPT ); Wed, 18 Jan 2017 04:31:34 -0500 Date: Wed, 18 Jan 2017 10:31:31 +0100 From: Michal Hocko To: Vlastimil Babka Cc: Mel Gorman , Ganapatrao Kulkarni , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone Message-ID: <20170118093131.GH7015@dhcp22.suse.cz> References: <20170117221610.22505-1-vbabka@suse.cz> <20170117221610.22505-2-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170117221610.22505-2-vbabka@suse.cz> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 17-01-17 23:16:07, Vlastimil Babka wrote: > Since commit c33d6c06f60f ("mm, page_alloc: avoid looking up the first zone in > a zonelist twice") we have a wrong check for NULL preferred_zone, which can > theoretically happen due to concurrent cpuset modification. We check the > zoneref pointer which is never NULL and we should check the zone pointer. > > Fixes: c33d6c06f60f ("mm, page_alloc: avoid looking up the first zone in a zonelist twice") > Signed-off-by: Vlastimil Babka > --- > mm/page_alloc.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 34ada718ef47..593a11d8bc6b 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3763,7 +3763,7 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order, > */ > ac.preferred_zoneref = first_zones_zonelist(ac.zonelist, > ac.high_zoneidx, ac.nodemask); > - if (!ac.preferred_zoneref) { > + if (!ac.preferred_zoneref->zone) { When can the ->zone be NULL? > page = NULL; > goto no_zone; > } > -- > 2.11.0 -- Michal Hocko SUSE Labs