RAID1: ignore discard error

If a write error occurs, raid1 will try to rewrite the bio in small
chunk size. If the rewrite fails, raid1 will record the error in bad
block. narrow_write_error will always use WRITE for the bio, but
actually it could be a discard. Since discard bio hasn't payload, write
the bio will cause different issues. But discard error isn't fatal, we
can safely ignore it. This is what this patch does.

This issue should exist since discard is added, but only exposed with
recent arbitrary bio size feature.
Reported-and-tested-by: Sitsofe Wheeler <sitsofe@gmail.com>
Cc: stable@vger.kernel.org (v3.6)
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid1.c

@@ -403,11 +403,14 @@ static void raid1_end_write_request(struct bio *bio)
 	struct bio *to_put = NULL;
 	int mirror = find_bio_disk(r1_bio, bio);
 	struct md_rdev *rdev = conf->mirrors[mirror].rdev;
+	bool discard_error;
+
+	discard_error = bio->bi_error && bio_op(bio) == REQ_OP_DISCARD;
 
 	/*
 	 * 'one mirror IO has finished' event handler:
 	 */
-	if (bio->bi_error) {
+	if (bio->bi_error && !discard_error) {
 		set_bit(WriteErrorSeen,	&rdev->flags);
 		if (!test_and_set_bit(WantReplacement, &rdev->flags))
 			set_bit(MD_RECOVERY_NEEDED, &
@@ -444,7 +447,7 @@ static void raid1_end_write_request(struct bio *bio)
 
 		/* Maybe we can clear some bad blocks. */
 		if (is_badblock(rdev, r1_bio->sector, r1_bio->sectors,
-				&first_bad, &bad_sectors)) {
+				&first_bad, &bad_sectors) && !discard_error) {
 			r1_bio->bios[mirror] = IO_MADE_GOOD;
 			set_bit(R1BIO_MadeGood, &r1_bio->state);
 		}