From: Jan Kara Subject: Re: [PATCH] jbd2: don't write superblock when unmounting an ro filesystem Date: Wed, 15 Aug 2012 14:14:03 +0200 Message-ID: <20120815121403.GA29223@quack.suse.cz> References: <500F1C28.8010800@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: ext4 development , Jan Kara To: Eric Sandeen Return-path: Received: from cantor2.suse.de ([195.135.220.15]:44306 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750781Ab2HOMOF (ORCPT ); Wed, 15 Aug 2012 08:14:05 -0400 Content-Disposition: inline In-Reply-To: <500F1C28.8010800@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue 24-07-12 17:05:28, 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. Ted, did this patch fall through cracks? I've ported the fix to JBD and added it to my tree. I plan to send it to Linus in a few days. Also I've CC'd stable since this is a bit annoying regression. Honza > 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! > > diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c > index e9a3c4c..987ec76 100644 > --- a/fs/jbd2/journal.c > +++ b/fs/jbd2/journal.c > @@ -1354,6 +1354,11 @@ static void jbd2_mark_journal_empty(journal_t *journal) > > BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex)); > read_lock(&journal->j_state_lock); > + /* Is it already empty? */ > + if (sb->s_start == 0) { > + read_unlock(&journal->j_state_lock); > + return; > + } > jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n", > journal->j_tail_sequence); > > -- Jan Kara SUSE Labs, CR