From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id AA6046B0047 for ; Fri, 1 May 2009 09:55:06 -0400 (EDT) Date: Fri, 1 May 2009 14:55:51 +0100 (BST) From: Hugh Dickins Subject: Re: [PATCH mmotm] memcg: fix mem_cgroup_update_mapped_file_stat oops In-Reply-To: <20090430090646.a1443096.kamezawa.hiroyu@jp.fujitsu.com> Message-ID: References: <20090430090646.a1443096.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org To: KAMEZAWA Hiroyuki Cc: Andrew Morton , Balbir Singh , KOSAKI Motohiro , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: 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. Alternatively, could the SPARSEMEM case have been corrupting or otherwise misbehaving in a hidden way until now? Seems unlikely. Hugh -- 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