From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 229536B0047 for ; Fri, 1 May 2009 12:41:14 -0400 (EDT) Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by e38.co.us.ibm.com (8.13.1/8.13.1) with ESMTP id n41GdHcR004086 for ; Fri, 1 May 2009 10:39:17 -0600 Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n41GfokR243296 for ; Fri, 1 May 2009 10:41:51 -0600 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n41GfoFp029771 for ; Fri, 1 May 2009 10:41:50 -0600 Date: Fri, 1 May 2009 21:02:06 +0530 From: Balbir Singh Subject: Re: [PATCH mmotm] memcg: fix mem_cgroup_update_mapped_file_stat oops Message-ID: <20090501153206.GA4686@balbir.in.ibm.com> Reply-To: balbir@linux.vnet.ibm.com References: <20090430090646.a1443096.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: KAMEZAWA Hiroyuki , Andrew Morton , KOSAKI Motohiro , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: * Hugh Dickins [2009-05-01 14:55:51]: > On Thu, 30 Apr 2009, KAMEZAWA Hiroyuki wrote: > > On Wed, 29 Apr 2009 22:13:33 +0100 (BST) > > Hugh Dickins wrote: > > > > > CONFIG_SPARSEMEM=y CONFIG_CGROUP_MEM_RES_CTLR=y cgroup_disable=memory > > > bootup is oopsing in mem_cgroup_update_mapped_file_stat(). !SPARSEMEM > > > is fine because its lookup_page_cgroup() contains an explicit check for > > > NULL node_page_cgroup, but the SPARSEMEM version was missing a check for > > > NULL section->page_cgroup. > > > > > Ouch, it's curious this bug alive now.. thank you. > > > > Acked-by: KAMEZAWA Hiroyuki > > > > I think this patch itself is sane but.. Balbir, could you see "caller" ? > > It seems strange. > > I agree with you, it seems strange for it to come alive only now; > but I've not investigated further, may I leave that to you? > > Could it be that all those checks on NULL lookup_page_cgroup() > actually date from before you reworked page cgroup assignment, > and they're now redundant? If so, you'd do better to remove > all the checks, and Balbir put an explicit check in his code. > I agree, it needs investigation. I would propose converting them to a VM_BUG_ON() and then consider removing them, just to catch potential problems, in case we miss anything. > Alternatively, could the SPARSEMEM case have been corrupting or > otherwise misbehaving in a hidden way until now? Seems unlikely. Agreed. -- Balbir -- 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