Revert "md/raid10: improve discard request for far layout"

This reverts commit d3ee2d8415a6256c1c41e1be36e80e640c3e6359.

Matthew Ruffell reported data corruption in raid10 due to the changes
in discard handling [1]. Revert these changes before we find a proper fix.

[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1907262/
Cc: Matthew Ruffell <[e-mail]>
Cc: Xiao Ni <[e-mail]>
Signed-off-by: Song Liu <[e-mail]>

drivers/md/raid10.c

···
 	return bio;
 }
 
-static void raid_end_discard_bio(struct r10bio *r10bio)
-{
-	struct r10conf *conf = r10bio->mddev->private;
-	struct r10bio *first_r10bio;
-
-	while (atomic_dec_and_test(&r10bio->remaining)) {
-
-		allow_barrier(conf);
-
-		if (!test_bit(R10BIO_Discard, &r10bio->state)) {
-			first_r10bio = (struct r10bio *)r10bio->master_bio;
-			free_r10bio(r10bio);
-			r10bio = first_r10bio;
-		} else {
-			md_write_end(r10bio->mddev);
-			bio_endio(r10bio->master_bio);
-			free_r10bio(r10bio);
-			break;
-		}
-	}
-}
-
 static void raid10_end_discard_request(struct bio *bio)
 {
 	struct r10bio *r10_bio = bio->bi_private;
···
 		rdev = conf->mirrors[dev].rdev;
 	}
 
-	raid_end_discard_bio(r10_bio);
+	if (atomic_dec_and_test(&r10_bio->remaining)) {
+		md_write_end(r10_bio->mddev);
+		raid_end_bio_io(r10_bio);
+	}
+
 	rdev_dec_pending(rdev, conf->mddev);
 }
 
···
 {
 	struct r10conf *conf = mddev->private;
 	struct geom *geo = &conf->geo;
-	struct r10bio *r10_bio, *first_r10bio;
-	int far_copies = geo->far_copies;
-	bool first_copy = true;
+	struct r10bio *r10_bio;
 
 	int disk;
 	sector_t chunk;
···
 	if (bio_sectors(bio) < stripe_size*2)
 		goto out;
 
-	/* For far and far offset layout, if bio is not aligned with stripe size,
-	 * it splits the part that is not aligned with strip size.
+	/* For far offset layout, if bio is not aligned with stripe size, it splits
+	 * the part that is not aligned with strip size.
 	 */
 	div_u64_rem(bio_start, stripe_size, &remainder);
-	if ((far_copies > 1) && remainder) {
+	if (geo->far_offset && remainder) {
 		split_size = stripe_size - remainder;
 		bio = raid10_split_bio(conf, bio, split_size, false);
 	}
 	div_u64_rem(bio_end, stripe_size, &remainder);
-	if ((far_copies > 1) && remainder) {
+	if (geo->far_offset && remainder) {
 		split_size = bio_sectors(bio) - remainder;
 		bio = raid10_split_bio(conf, bio, split_size, true);
 	}
+
+	r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
+	r10_bio->mddev = mddev;
+	r10_bio->state = 0;
+	r10_bio->sectors = 0;
+	memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * geo->raid_disks);
+
+	wait_blocked_dev(mddev, r10_bio);
+
+	r10_bio->master_bio = bio;
 
 	bio_start = bio->bi_iter.bi_sector;
 	bio_end = bio_end_sector(bio);
···
 		last_stripe_index *= geo->far_copies;
 	end_disk_offset = (bio_end & geo->chunk_mask) +
 				(last_stripe_index << geo->chunk_shift);
-
-retry_discard:
-	r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
-	r10_bio->mddev = mddev;
-	r10_bio->state = 0;
-	r10_bio->sectors = 0;
-	memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * geo->raid_disks);
-	wait_blocked_dev(mddev, r10_bio);
-
-	/* For far layout it needs more than one r10bio to cover all regions.
-	 * Inspired by raid10_sync_request, we can use the first r10bio->master_bio
-	 * to record the discard bio. Other r10bio->master_bio record the first
-	 * r10bio. The first r10bio only release after all other r10bios finish.
-	 * The discard bio returns only first r10bio finishes
-	 */
-	if (first_copy) {
-		r10_bio->master_bio = bio;
-		set_bit(R10BIO_Discard, &r10_bio->state);
-		first_copy = false;
-		first_r10bio = r10_bio;
-	} else
-		r10_bio->master_bio = (struct bio *)first_r10bio;
 
 	rcu_read_lock();
 	for (disk = 0; disk < geo->raid_disks; disk++) {
···
 		}
 	}
 
-	if (!geo->far_offset && --far_copies) {
-		first_stripe_index += geo->stride >> geo->chunk_shift;
-		start_disk_offset += geo->stride;
-		last_stripe_index += geo->stride >> geo->chunk_shift;
-		end_disk_offset += geo->stride;
-		atomic_inc(&first_r10bio->remaining);
-		raid_end_discard_bio(r10_bio);
-		wait_barrier(conf);
-		goto retry_discard;
+	if (atomic_dec_and_test(&r10_bio->remaining)) {
+		md_write_end(r10_bio->mddev);
+		raid_end_bio_io(r10_bio);
 	}
-
-	raid_end_discard_bio(r10_bio);
 
 	return 0;
 out:

drivers/md/raid10.h

···
 	R10BIO_Previous,
 /* failfast devices did receive failfast requests. */
 	R10BIO_FailFast,
-	R10BIO_Discard,
 };
 #endif