From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 87A0D6B0038 for ; Wed, 18 Jan 2017 04:45:37 -0500 (EST) Received: by mail-wm0-f72.google.com with SMTP id r144so1984564wme.0 for ; Wed, 18 Jan 2017 01:45:37 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id o15si28487531wrb.191.2017.01.18.01.45.36 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 18 Jan 2017 01:45:36 -0800 (PST) Subject: Re: [RFC 1/4] mm, page_alloc: fix check for NULL preferred_zone References: <20170117221610.22505-1-vbabka@suse.cz> <20170117221610.22505-2-vbabka@suse.cz> <20170118093131.GH7015@dhcp22.suse.cz> From: Vlastimil Babka Message-ID: Date: Wed, 18 Jan 2017 10:45:33 +0100 MIME-Version: 1.0 In-Reply-To: <20170118093131.GH7015@dhcp22.suse.cz> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Mel Gorman , Ganapatrao Kulkarni , linux-kernel@vger.kernel.org, linux-mm@kvack.org On 01/18/2017 10:31 AM, Michal Hocko wrote: > 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? Either we get a genuinely screwed nodemask, or there's a concurrent cpuset update and nodes in zonelist are ordered in such a way that we see all of them as not being available to us in the nodemask/current->mems_alowed, when we iterate the zonelist, so we reach the end of zonelist. The zonelists are terminated with a zoneref with NULL zone pointer. > >> page = NULL; >> goto no_zone; >> } >> -- >> 2.11.0 > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org