On Tue, 24 Jul 2012, Eric Sandeen wrote: > Date: Tue, 24 Jul 2012 17:05:28 -0500 > From: Eric Sandeen <sandeen@xxxxxxxxxx> > To: ext4 development <linux-ext4@xxxxxxxxxxxxxxx> > Cc: Jan Kara <jack@xxxxxxx> > Subject: [PATCH] jbd2: don't write superblock when unmounting an ro filesystem > > 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 Hi Eric, 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. 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 ? Anyway, maybe I am missing something, but I do not understand what kind of problem are you reproducing there. -Lukas > > 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 <jack@xxxxxxx> > 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 <sandeen@xxxxxxxxxx> > --- > > 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); > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html