jbd: don't write superblock when unmounting an ro filesystem
This sequence:
results in an IO error when unmounting the RO filesystem. The bug was
introduced by:
commit 9754e39c7bc51328f145e933bfb0df47cd67b6e9
Author: Jan Kara <jack@suse.cz>
Date: Sat Apr 7 12:33:03 2012 +0200
jbd: Split updating of journal superblock and marking journal empty
which lost some of the magic in journal_update_superblock() which
used to test for a journal with no outstanding transactions.
This is a port of a jbd2 fix by Eric Sandeen.
CC: <stable@vger.kernel.org> # 3.4.x
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index 0935750..a286233 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -1113,6 +1113,11 @@
BUG_ON(!mutex_is_locked(&journal->j_checkpoint_mutex));
spin_lock(&journal->j_state_lock);
+ /* Is it already empty? */
+ if (sb->s_start == 0) {
+ spin_unlock(&journal->j_state_lock);
+ return;
+ }
jbd_debug(1, "JBD: Marking journal as empty (seq %d)\n",
journal->j_tail_sequence);