jbd2: Call the commit callback before the transaction could get dropped

The transaction can potentially get dropped if there are no buffers
that need to be written.  Make sure we call the commit callback before
potentially deciding to drop the transaction.  Also avoid
dereferencing the commit_transaction pointer in the marker for the
same reason.

This patch fixes the bug reported by Eric Paris at:
http://bugzilla.kernel.org/show_bug.cgi?id=11838

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Acked-by: Eric Sandeen <sandeen@redhat.com>
Tested-by: Eric Paris <eparis@redhat.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 8b119e16aa36..ebc667bc54a8 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -974,6 +974,9 @@ restart_loop:
         journal->j_committing_transaction = NULL;
         spin_unlock(&journal->j_state_lock);
 
+        if (journal->j_commit_callback)
+                journal->j_commit_callback(journal, commit_transaction);
+
         if (commit_transaction->t_checkpoint_list == NULL &&
             commit_transaction->t_checkpoint_io_list == NULL) {
                 __jbd2_journal_drop_transaction(journal, commit_transaction);
@@ -995,11 +998,8 @@ restart_loop:
         }
         spin_unlock(&journal->j_list_lock);
 
-        if (journal->j_commit_callback)
-                journal->j_commit_callback(journal, commit_transaction);
-
         trace_mark(jbd2_end_commit, "dev %s transaction %d head %d",
-                   journal->j_devname, commit_transaction->t_tid,
+                   journal->j_devname, journal->j_commit_sequence,
                    journal->j_tail_sequence);
         jbd_debug(1, "JBD: commit %d complete, head %d\n",
                   journal->j_commit_sequence, journal->j_tail_sequence);