ext4: Fix buffer head reference leak in no-journal mode

We found a problem with buffer head reference leaks when using an ext4
partition without a journal. In particular, calls to ext4_forget() would
not to a brelse() on the input buffer head, which will cause pages they
belong to to not be reclaimable.

Further investigation showed that all places where ext4_journal_forget() and
ext4_journal_revoke() are called are subject to the same problem. The patch
below changes __ext4_journal_forget/__ext4_journal_revoke to do an explicit
release of the buffer head when the journal handle isn't valid.

Signed-off-by: Curt Wohlgemuth <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

fs/ext4/ext4_jbd2.c

···
 			ext4_journal_abort_handle(where, __func__, bh,
 						  handle, err);
 	}
+	else
+		brelse(bh);
 	return err;
 }
 
···
 			ext4_journal_abort_handle(where, __func__, bh,
 						  handle, err);
 	}
+	else
+		brelse(bh);
 	return err;
 }
 

fs/ext4/ext4_jbd2.h

···
 int __ext4_journal_get_write_access(const char *where, handle_t *handle,
 				struct buffer_head *bh);
 
+/* When called with an invalid handle, this will still do a put on the BH */
 int __ext4_journal_forget(const char *where, handle_t *handle,
 				struct buffer_head *bh);
 
+/* When called with an invalid handle, this will still do a put on the BH */
 int __ext4_journal_revoke(const char *where, handle_t *handle,
 				ext4_fsblk_t blocknr, struct buffer_head *bh);
 

fs/ext4/inode.c

···
  * but there may still be a record of it in the journal, and that record
  * still needs to be revoked.
  *
- * If the handle isn't valid we're not journaling so there's nothing to do.
+ * If the handle isn't valid we're not journaling, but we still need to
+ * call into ext4_journal_revoke() to put the buffer head.
  */
 int ext4_forget(handle_t *handle, int is_metadata, struct inode *inode,
 		struct buffer_head *bh, ext4_fsblk_t blocknr)
 {
 	int err;
-
-	if (!ext4_handle_valid(handle))
-		return 0;
 
 	might_sleep();