jbd2: check jh->b_transaction without taking j_list_lock

jh->b_transaction is adequately protected for reading by the
jbd_lock_bh_state(bh), so we don't need to take j_list_lock in
__journal_try_to_free_buffer().
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/jbd2/transaction.c

@@ -1821,11 +1821,11 @@ __journal_try_to_free_buffer(journal_t *journal, struct buffer_head *bh)
 	if (buffer_locked(bh) || buffer_dirty(bh))
 		goto out;
 
-	if (jh->b_next_transaction != NULL)
+	if (jh->b_next_transaction != NULL || jh->b_transaction != NULL)
 		goto out;
 
 	spin_lock(&journal->j_list_lock);
-	if (jh->b_cp_transaction != NULL && jh->b_transaction == NULL) {
+	if (jh->b_cp_transaction != NULL) {
 		/* written-back checkpointed metadata buffer */
 		JBUFFER_TRACE(jh, "remove from checkpoint list");
 		__jbd2_journal_remove_checkpoint(jh);