ext4: annotate data race in jbd2_journal_dirty_metadata()

Assertion checks in jbd2_journal_dirty_metadata() are known to be racy
but we don't want to be grabbing locks just for them.  We thus recheck
them under b_state_lock only if it looks like they would fail. Annotate
the checks with data_race().

Cc: stable@kernel.org
Reported-by: Hao Sun <sunhao.th@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20210406161804.20150-2-jack@suse.czSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/jbd2/transaction.c

@@ -1479,8 +1479,8 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 	 * crucial to catch bugs so let's do a reliable check until the
 	 * lockless handling is fully proven.
 	 */
-	if (jh->b_transaction != transaction &&
-	    jh->b_next_transaction != transaction) {
+	if (data_race(jh->b_transaction != transaction &&
+	    jh->b_next_transaction != transaction)) {
 		spin_lock(&jh->b_state_lock);
 		J_ASSERT_JH(jh, jh->b_transaction == transaction ||
 				jh->b_next_transaction == transaction);
@@ -1488,8 +1488,8 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
 	}
 	if (jh->b_modified == 1) {
 		/* If it's in our transaction it must be in BJ_Metadata list. */
-		if (jh->b_transaction == transaction &&
-		    jh->b_jlist != BJ_Metadata) {
+		if (data_race(jh->b_transaction == transaction &&
+		    jh->b_jlist != BJ_Metadata)) {
 			spin_lock(&jh->b_state_lock);
 			if (jh->b_transaction == transaction &&
 			    jh->b_jlist != BJ_Metadata)