[ 058/108] jbd: dont write superblock when unmounting an ro filesystem

[Greg Kroah-Hartman]

From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>

3.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Kara <jack@xxxxxxx>

commit 2e84f2641ea91a730642ead558a4ee3bd52310c9 upstream.

This sequence:

results in an IO error when unmounting the RO filesystem. The bug was
introduced by:

commit 9754e39c7bc51328f145e933bfb0df47cd67b6e9
Author: Jan Kara <jack@xxxxxxx>
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.

Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/jbd/journal.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -1113,6 +1113,11 @@ static void mark_journal_empty(journal_t
 
 	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);
 


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