From: Eric Sandeen Subject: Re: [PATCH] jbd2: don't write superblock when unmounting an ro filesystem Date: Mon, 30 Jul 2012 10:49:39 -0500 Message-ID: <5016AD13.2030804@redhat.com> References: <500F1C28.8010800@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: ext4 development , Jan Kara To: =?UTF-8?B?THVrw6HFoSBDemVybmVy?= Return-path: Received: from mx1.redhat.com ([209.132.183.28]:55586 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752887Ab2G3Ptn (ORCPT ); Mon, 30 Jul 2012 11:49:43 -0400 In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-ID: On 7/26/12 4:24 AM, Luk=C3=A1=C5=A1 Czerner wrote: > On Tue, 24 Jul 2012, Eric Sandeen wrote: >=20 >> Date: Tue, 24 Jul 2012 17:05:28 -0500 >> From: Eric Sandeen >> To: ext4 development >> Cc: Jan Kara >> Subject: [PATCH] jbd2: don't write superblock when unmounting an ro = filesystem >> >> This sequence: >> >> # truncate --size=3D65536 fsfile >> # losetup --offset 65536 /dev/loop0 fsfile=20 >> # mkfs.ext4 /dev/loop0=20 >> # losetup -d /dev/loop0 >> # mount -o loop,ro,offset=3D65536 fsfile mnt/ >> # umount mnt >> # dmesg | tail >=20 > Hi Eric, >=20 > I am having hard time understanding what the sequence should be > doing. I actually can not reproduce it, because I can not create the > file system on such loop device because it seems like the size of > /dev/loop0 is zero, which makes sense considering that you set > offset to 65536 in the 65536 sized file. sorry, that must have been a cut & paste error. :( The offset was leftover from trying to match the original reporter's ca= se. This simpler test shows the same problem: 1014 truncate --size=3D2g fsfile 1015 mkfs.ext4 fsfile 1016 mount -o loop,ro fsfile mnt 1017 umount mnt 1018 dmesg | tail [ 417.631105] EXT4-fs (loop0): mounted filesystem with ordered data mo= de. Opts: (null) [ 417.639183] SELinux: initialized (dev loop0, type ext4), uses xattr [ 420.903970] Buffer I/O error on device loop0, logical block 262144 [ 420.910448] lost page write due to I/O error on loop0 [ 420.915662] JBD2: Error -5 detected when updating journal superblock= for loop0-8. > Also, is the use of lo device really needed ? We can create the file > system on the file itself right ? Moreover, when I do that I can see > that the journal is not created because the device (file) is too > small, maybe it have something to do with the problem ? >=20 > Anyway, maybe I am missing something, but I do not understand what > kind of problem are you reproducing there. >=20 > -Lukas >=20 >> >> results in an IO error when unmounting the RO filesystem: >> >> [ 312.386074] SELinux: initialized (dev loop1, type ext4), uses xat= tr >> [ 318.020828] Buffer I/O error on device loop1, logical block 19660= 8 >> [ 318.027024] lost page write due to I/O error on loop1 >> [ 318.032088] JBD2: Error -5 detected when updating journal superbl= ock 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 e= mpty >> >> which lost some of the magic in jbd2_journal_update_superblock() whi= ch >> used to test for a journal with no outstanding transactions. >> >> I'm not sure if the following is quite the right approach, but it fi= xes >> it for me. >> >> Signed-off-by: Eric Sandeen >> --- >> >> p.s. no idea why this only happens if I use a loop device with an of= fset! >> >> 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) >> =20 >> BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex)); >> read_lock(&journal->j_state_lock); >> + /* Is it already empty? */ >> + if (sb->s_start =3D=3D 0) { >> + read_unlock(&journal->j_state_lock); >> + return; >> + } >> jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n", >> journal->j_tail_sequence); >> =20 >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-ext4= " in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html