jbd2: don't write superblock when if its empty
This sequence:
# truncate --size=1g fsfile
# mkfs.ext4 -F fsfile
# mount -o loop,ro fsfile /mnt
# umount /mnt
# dmesg | tail
results in an IO error when unmounting the RO filesystem:
[ 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 was a regression introduced by commit 24bcc89c7e7c: "jbd2: split
updating of journal superblock and marking journal empty".
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index bd23f2e..0f16edd 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1354,6 +1354,11 @@
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);