Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1423097AbWJYIKO (ORCPT ); Wed, 25 Oct 2006 04:10:14 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1423102AbWJYIKO (ORCPT ); Wed, 25 Oct 2006 04:10:14 -0400 Received: from gprs189-60.eurotel.cz ([160.218.189.60]:13710 "EHLO amd.ucw.cz") by vger.kernel.org with ESMTP id S1423097AbWJYIKN (ORCPT ); Wed, 25 Oct 2006 04:10:13 -0400 Date: Wed, 25 Oct 2006 10:10:01 +0200 From: Pavel Machek To: David Chinner Cc: "Rafael J. Wysocki" , Nigel Cunningham , Andrew Morton , LKML , xfs@oss.sgi.com Subject: Re: [PATCH] Freeze bdevs when freezing processes. Message-ID: <20061025081001.GL5851@elf.ucw.cz> References: <1161576735.3466.7.camel@nigel.suspend2.net> <200610231236.54317.rjw@sisk.pl> <20061024144446.GD11034@melbourne.sgi.com> <200610241730.00488.rjw@sisk.pl> <20061024163345.GG11034@melbourne.sgi.com> <20061024213737.GD5662@elf.ucw.cz> <20061025001331.GP8394166@melbourne.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20061025001331.GP8394166@melbourne.sgi.com> X-Warning: Reading this can be dangerous to your mental health. User-Agent: Mutt/1.5.11+cvs20060126 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2427 Lines: 54 Hi! > > > > Do you mean calling sys_sync() after the userspace has been frozen > > > > may not be sufficient? > > > > > > In most cases it probably is, but sys_sync() doesn't provide any > > > guarantees that the filesystem is not being used or written to after > > > it completes. Given that every so often I hear about an XFS filesystem > > > that was corrupted by suspend, I don't think this is sufficient... > > > > Userspace is frozen. There's noone that can write to the XFS > > filesystem. > > Sure, no new userspace processes can write data, but what about the > internal state of the filesystem? > > All a sync guarantees is that the filesystem is consistent when the > sync returns and XFS provides this guarantee by writing all data and > ensuring all metadata changes are logged so if a crash occurs it can > be recovered (which provides the sync guarantee). hence after a > sys_sync(), XFS will still have lots of dirty metadata that needs to > be written to disk at some time in the future so the transactions > can be removed from the log. > > This dirty metadata can be flushed at any time, and the dirty state > is kept in XFS structures and not always in page structures (think > multipage metadata buffers). Hence I cannot see how suspend can > guarantee that it has saved all the dirty data in XFS, nor > restore it correctly on resume. Once you toss dirty metadata that > is currently in the log, further operations will result in that log > transaction being overwritten without it ever being written to disk. > That then means any subsequent operations after resume will corrupt > the filesystem.... > > Hence the only way to correctly rebuild the XFS state on resume is > to quiesce the filesystem on suspend and thaw it on resume so as to > trigger log recovery. No, during suspend/resume, memory image is saved, and no state is lost. We would not even have to do sys_sync(), and suspend/resume would still work properly. sys_sync() is there only to limit damage in case of suspend/resume failure. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html - 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/