jbd2: Fix barrier fallback code to re-lock the buffer head

If the device doesn't support write barriers, the write is retried
without ordered mode.  But the buffer head needs to be re-locked or
submit_bh will fail with on BUG(!buffer_locked(bh)).
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/jbd2/commit.c

@@ -168,6 +168,7 @@ static int journal_submit_commit_record(journal_t *journal,
 		spin_unlock(&journal->j_state_lock);
 
 		/* And try again, without the barrier */
+		lock_buffer(bh);
 		set_buffer_uptodate(bh);
 		set_buffer_dirty(bh);
 		ret = submit_bh(WRITE, bh);