From: Eric Sandeen Subject: Re: [PATCH] jbd2: don't write superblock when unmounting an ro filesystem Date: Tue, 24 Jul 2012 17:18:42 -0500 Message-ID: <500F1F42.5010209@redhat.com> References: <500F1C28.8010800@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Jan Kara To: ext4 development Return-path: Received: from mx1.redhat.com ([209.132.183.28]:17147 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754357Ab2GXWSp (ORCPT ); Tue, 24 Jul 2012 18:18:45 -0400 In-Reply-To: <500F1C28.8010800@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 7/24/12 5:05 PM, Eric Sandeen wrote: > This sequence: > > # truncate --size=65536 fsfile > # losetup --offset 65536 /dev/loop0 fsfile > # mkfs.ext4 /dev/loop0 > # losetup -d /dev/loop0 > # mount -o loop,ro,offset=65536 fsfile mnt/ > # umount mnt > # dmesg | tail > > results in an IO error when unmounting the RO filesystem: > > [ 312.386074] SELinux: initialized (dev loop1, type ext4), uses xattr > [ 318.020828] Buffer I/O error on device loop1, logical block 196608 > [ 318.027024] lost page write due to I/O error on loop1 > [ 318.032088] JBD2: Error -5 detected when updating journal superblock for loop1-8. > > This behavior changed with: > > commit 24bcc89c7e7c64982e6192b4952a0a92379fc341 > Author: Jan Kara > Date: Tue Mar 13 15:41:04 2012 -0400 > > jbd2: split updating of journal superblock and marking journal empty > > which lost some of the magic in jbd2_journal_update_superblock() which > used to test for a journal with no outstanding transactions. > > I'm not sure if the following is quite the right approach, but it fixes > it for me. > > Signed-off-by: Eric Sandeen > --- > > p.s. no idea why this only happens if I use a loop device with an offset! PEBKAC. no-offset ro loop mount does the same. -Eric