From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f171.google.com (mail-ig0-f171.google.com [209.85.213.171]) by kanga.kvack.org (Postfix) with ESMTP id AC5086B0037 for ; Tue, 8 Jul 2014 17:05:04 -0400 (EDT) Received: by mail-ig0-f171.google.com with SMTP id l13so754579iga.16 for ; Tue, 08 Jul 2014 14:05:04 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id lb5si4762513igb.1.2014.07.08.14.05.03 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 08 Jul 2014 14:05:03 -0700 (PDT) Date: Tue, 8 Jul 2014 14:05:01 -0700 From: Andrew Morton 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> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Cyrill Gorcunov Cc: LKML , Linux MM , Pavel Emelyanov 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? -- 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