dm: fix request-based dm error reporting

end_clone_bio() is a endio callback for clone bio and should check
and save the clone's bi_error for error reporting.  However,
4246a0b63b ("block: add a bi_error field to struct bio") changed
the function to check the original bio's bi_error, which is 0.

Without this fix, clone's error is ignored and reported to the
original request as success.  Thus data corruption will be observed.

Fixes: 4246a0b63b ("block: add a bi_error field to struct bio")
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

@@ -1001,6 +1001,7 @@ static void end_clone_bio(struct bio *clone)
 	struct dm_rq_target_io *tio = info->tio;
 	struct bio *bio = info->orig;
 	unsigned int nr_bytes = info->orig->bi_iter.bi_size;
+	int error = clone->bi_error;
 
 	bio_put(clone);
 
@@ -1011,13 +1012,13 @@ static void end_clone_bio(struct bio *clone)
 		 * the remainder.
 		 */
 		return;
-	else if (bio->bi_error) {
+	else if (error) {
 		/*
 		 * Don't notice the error to the upper layer yet.
 		 * The error handling decision is made by the target driver,
 		 * when the request is completed.
 		 */
-		tio->error = bio->bi_error;
+		tio->error = error;
 		return;
 	}