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>

diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 8b119e16aa36d9970c881a5c41b0f98ff06962fa..ebc667bc54a8e1ac3c28e8ab6a40ce83f5274ad9 100644 (file)
--- 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);