jbd: Check return value of __getblk()

Fail journal creation if __getblk() returns NULL.  unlikely() is
added because it is called in a loop and we've been OK without
the check until now.
Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/jbd/journal.c

@@ -952,6 +952,8 @@ int journal_create(journal_t *journal)
 		if (err)
 			return err;
 		bh = __getblk(journal->j_dev, blocknr, journal->j_blocksize);
+		if (unlikely(!bh))
+			return -ENOMEM;
 		lock_buffer(bh);
 		memset (bh->b_data, 0, journal->j_blocksize);
 		BUFFER_TRACE(bh, "marking dirty");