md/raid10: add a new r10bio flag R10BIO_Returned

The new helper bio_submit_split_bioset() can failed the orginal bio on
split errors, prepare to handle this case in raid_end_bio_io().

The flag name is refer to the r1bio flag name.

Signed-off-by: Yu Kuai <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/md/raid10.c

···
 	struct bio *bio = r10_bio->master_bio;
 	struct r10conf *conf = r10_bio->mddev->private;
 
-	if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
-		bio->bi_status = BLK_STS_IOERR;
+	if (!test_and_set_bit(R10BIO_Returned, &r10_bio->state)) {
+		if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
+			bio->bi_status = BLK_STS_IOERR;
+		bio_endio(bio);
+	}
 
-	bio_endio(bio);
 	/*
 	 * Wake up any possible resync thread that waits for the device
 	 * to go idle.

drivers/md/raid10.h

···
  * so that raid10d knows what to do with them.
  */
 	R10BIO_ReadError,
+/* For bio_split errors, record that bi_end_io was called. */
+	R10BIO_Returned,
 /* If a write for this request means we can clear some
  * known-bad-block records, we set this flag.
  */