From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754334AbaGHVFF (ORCPT ); Tue, 8 Jul 2014 17:05:05 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36383 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753137AbaGHVFD (ORCPT ); Tue, 8 Jul 2014 17:05:03 -0400 Date: Tue, 8 Jul 2014 14:05:01 -0700 From: Andrew Morton To: Cyrill Gorcunov Cc: LKML , Linux MM , Pavel Emelyanov Subject: Re: [PATCH] mm: Don't forget to set softdirty on file mapped fault Message-Id: <20140708140501.6c293226bfd87e4dff7ef7fb@linux-foundation.org> In-Reply-To: <20140708205448.GH17860@moon.sw.swsoft.com> References: <20140708192151.GD17860@moon.sw.swsoft.com> <20140708131920.2a857d573e8cc89780c9fa1c@linux-foundation.org> <20140708204017.GG17860@moon.sw.swsoft.com> <20140708134511.4a32b7400a952541a31e9078@linux-foundation.org> <20140708205448.GH17860@moon.sw.swsoft.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 9 Jul 2014 00:54:48 +0400 Cyrill Gorcunov wrote: > On Tue, Jul 08, 2014 at 01:45:11PM -0700, Andrew Morton wrote: > > > > The user doesn't know or care about pte bits. > > > > What actually *happens*? Does criu migration hang? Does it lose data? > > Does it take longer? > > Ah, I see. Yes, the softdirty bit might be lost that usespace program > won't see that a page was modified. So data lose is possible. > > > IOW, what would an end-user's bug report look like? > > > > It's important to think this way because a year from now some person > > we've never heard of may be looking at a user's bug report and > > wondering whether backporting this patch will fix it. Amongst other > > reasons. > > Here is updated changelog, sounds better? > --- > > In case if page fault happend on dirty filemapping the newly created pte > may loose softdirty bit thus if a userspace program is tracking memory > changes with help of a memory tracker (CONFIG_MEM_SOFT_DIRTY) it might > miss modification of a memory page (which in worts case may lead to > data inconsistency). Much better, thanks. It's a rather gross-looking bug and data inconsistency sounds serious. Do you think a -stable backport is needed?