From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757532AbZDWLKx (ORCPT ); Thu, 23 Apr 2009 07:10:53 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755526AbZDWLKm (ORCPT ); Thu, 23 Apr 2009 07:10:42 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:58523 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753759AbZDWLKl (ORCPT ); Thu, 23 Apr 2009 07:10:41 -0400 Date: Thu, 23 Apr 2009 07:10:40 -0400 From: Christoph Hellwig To: Jan Kara Cc: LKML , linux-fsdevel@vger.kernel.org, Andrew Morton , Jens Axboe Subject: Re: [PATCH] vfs: Fix sys_sync() and fsync_super() reliability Message-ID: <20090423111040.GB4833@infradead.org> References: <1240415781-17834-1-git-send-email-jack@suse.cz> <1240415781-17834-2-git-send-email-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1240415781-17834-2-git-send-email-jack@suse.cz> User-Agent: Mutt/1.5.18 (2008-05-17) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 22, 2009 at 05:56:20PM +0200, Jan Kara wrote: > So far, do_sync() called: > sync_inodes(0); > sync_supers(); > sync_filesystems(0); > sync_filesystems(1); > sync_inodes(1); > > This ordering makes it kind of hard for filesystems as sync_inodes(0) need not > submit all the IO (for example it skips inodes with I_SYNC set) so e.g. forcing > transaction to disk in ->sync_fs() is not really enough. Therefore sys_sync has > not been completely reliable on some filesystems (ext3, ext4, reiserfs, ocfs2 > and others are hit by this) when racing e.g. with background writeback. A > similar problem hits also other filesystems (e.g. ext2) because of > write_supers() being called before the sync_inodes(1). > > Change the ordering of calls in do_sync() - this requires a new function > sync_blkdevs() to preserve the property that block devices are always synced > after write_super() / sync_fs() call. > > The same issue is fixed in __fsync_super() function used on umount / > remount read-only. This looks reasonable, but I always fear we break something when touching this path. It would be really nice if we could rewrite do_sync to sit ontop of __fsync_super. E.g. do a for_each_sb() __fsync_super(sb, ASYNC); for_each_sb() __fsync_super(sb, SYNC); so that we have one central place that makes sure a filesystem is properly synced. Another thing I want to do in this area is sort out the meaning of write_super. I'd really prefer to have every filesystem implement ->sync_fs for actual data-integerity syncs, and only leave ->write_super for the periodic writeouts, as the current implementation is extrenly confusing and causes a lot of trouble for filesystems doing their own periodic sb writeback.