From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756761AbXGHNsg (ORCPT ); Sun, 8 Jul 2007 09:48:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753246AbXGHNs3 (ORCPT ); Sun, 8 Jul 2007 09:48:29 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:36095 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752624AbXGHNs2 convert rfc822-to-8bit (ORCPT ); Sun, 8 Jul 2007 09:48:28 -0400 From: "Rafael J. Wysocki" To: Pavel Machek Subject: Re: [RFC][PATCH -mm] Freezer: Handle uninterruptible tasks Date: Sun, 8 Jul 2007 15:55:51 +0200 User-Agent: KMail/1.9.5 Cc: Alan Stern , pm list , LKML , Nigel Cunningham , Oliver Neukum , Miklos Szeredi , Benjamin Herrenschmidt , Matthew Garrett , Ingo Molnar References: <200707080108.17371.rjw@sisk.pl> <20070708120933.GA3866@ucw.cz> In-Reply-To: <20070708120933.GA3866@ucw.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Content-Disposition: inline Message-Id: <200707081555.53094.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sunday, 8 July 2007 14:09, Pavel Machek wrote: > Hi! > > > > And then you will face the problem of a user task doing I/O during > > > hibernate after the atomic snapshot has been made. > > > > I don't think that this is possible in normal conditions. It would be possible > > if, for example, the task were waiting for an unavailable resource and that > > resource became available after the hibernation image had been created. > > In that case, however, to do any damage, the task would have to cause some > > filesystem-related data to be flushed in the same syscall (ie. before returning > > to user space). > > I agree that it is relatively unlikely to trigger (if you avoid > freezing the tasks that were uninterruptible for long), but it will > trigger in error cases etc. Yes, it will. > > Such situations may be prevented by a mechanizm detecting if any uniterruptible > > and freezing task has been woken up after creating the image and aborting the > > hibernation in that cases. For this purpose, we only need to add an > > appropriate condition to try_to_wake_up() and make it start to trigger after, > > for example, enabling the nonboot CPUs. > > I don't know how to do that mechanism... but if we knew where to trap > filesystem writes, we could simply freeze at that point, and at that > point only, no? >>From the image/filesystems integrity standpoint, yes, that should be sufficient. Greetings, Rafael -- "Premature optimization is the root of all evil." - Donald Knuth