From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754750Ab3KGV6d (ORCPT ); Thu, 7 Nov 2013 16:58:33 -0500 Received: from e35.co.us.ibm.com ([32.97.110.153]:59650 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753303Ab3KGV6Y (ORCPT ); Thu, 7 Nov 2013 16:58:24 -0500 Message-ID: <527C0CF7.705@linux.vnet.ibm.com> Date: Thu, 07 Nov 2013 13:58:15 -0800 From: Cody P Schafer User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.0 MIME-Version: 1.0 To: Andrew Morton CC: EXT4 , Jan Kara , rostedt@goodmis.org, Seth Jennings , LKML Subject: Re: [PATCH v2 01/11] rbtree: Fix rbtree_postorder_for_each_entry_safe() iterator References: <1383788572-25938-1-git-send-email-cody@linux.vnet.ibm.com> <1383788572-25938-2-git-send-email-cody@linux.vnet.ibm.com> <20131107133800.c779b2f2b2ec73c91cd25f47@linux-foundation.org> In-Reply-To: <20131107133800.c779b2f2b2ec73c91cd25f47@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13110721-6688-0000-0000-000003473B25 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/07/2013 01:38 PM, Andrew Morton wrote: > On Wed, 6 Nov 2013 17:42:30 -0800 Cody P Schafer wrote: > >> The iterator rbtree_postorder_for_each_entry_safe() relies on pointer >> underflow behavior when testing for loop termination. In particular >> it expects that >> &rb_entry(NULL, type, field)->field >> is NULL. But the result of this expression is not defined by a C standard >> and some gcc versions (e.g. 4.3.4) assume the above expression can never >> be equal to NULL. The net result is an oops because the iteration is not >> properly terminated. >> >> Fix the problem by modifying the iterator to avoid pointer underflows. > > So the sole caller is in zswap.c. Is that code actually generating oopses? I can't reproduce the oopses (at all) with my build/gcc version, but Jan has reported seeing them (not in zswap, however). > > IOW, is there any need to fix this in 3.12 or earlier? > The zswap usage change showed up in 3.12. In my opinion, it is probably a good idea to apply the fix to 3.12.