Revert "dm raid: remove unnecessary discard limits for raid10"

This reverts commit f0e90b6c663a7e3b4736cb318c6c7c589f152c28.

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]>
Cc: Mike Snitzer <[e-mail]>
Acked-by: Mike Snitzer <[e-mail]>
Signed-off-by: Song Liu <[e-mail]>

drivers/md/dm-raid.c

···
 
 	blk_limits_io_min(limits, chunk_size_bytes);
 	blk_limits_io_opt(limits, chunk_size_bytes * mddev_data_stripes(rs));
+
+	/*
+	 * RAID10 personality requires bio splitting,
+	 * RAID0/1/4/5/6 don't and process large discard bios properly.
+	 */
+	if (rs_is_raid10(rs)) {
+		limits->discard_granularity = max(chunk_size_bytes,
+						  limits->discard_granularity);
+		limits->max_discard_sectors = min_not_zero(rs->md.chunk_sectors,
+							   limits->max_discard_sectors);
+	}
 }
 
 static void raid_postsuspend(struct dm_target *ti)