Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754041AbaGHUpO (ORCPT ); Tue, 8 Jul 2014 16:45:14 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36196 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753137AbaGHUpN (ORCPT ); Tue, 8 Jul 2014 16:45:13 -0400 Date: Tue, 8 Jul 2014 13:45:11 -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: <20140708134511.4a32b7400a952541a31e9078@linux-foundation.org> In-Reply-To: <20140708204017.GG17860@moon.sw.swsoft.com> References: <20140708192151.GD17860@moon.sw.swsoft.com> <20140708131920.2a857d573e8cc89780c9fa1c@linux-foundation.org> <20140708204017.GG17860@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 00:40:17 +0400 Cyrill Gorcunov wrote: > On Tue, Jul 08, 2014 at 01:19:20PM -0700, Andrew Morton wrote: > > On Tue, 8 Jul 2014 23:21:51 +0400 Cyrill Gorcunov wrote: > > > > > Otherwise we may not notice that pte was softdirty because pte_mksoft_dirty > > > helper _returns_ new pte but not modifies argument. > > > > When fixing a bug, please describe the end-user visible effects of that > > bug. > > > > [for the 12,000th time :(] > > "we may not notice that pte was softdirty" I thought it's enough, because > that's the effect user sees -- pte is not dirtified where it should. > > Really sorry Andrew if I were not clear enough. What about: In case if page > fault happend on dirty filemapping the newly created pte may not > notice if old one were already softdirtified because pte_mksoft_dirty > doesn't modify its argument but rather returns new pte value. 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? 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/