md/raid0: attach correct cgroup info in bio

The discard bio doesn't attach the original bio cgroup info. Normal bio
is cloned, so is fine.
Signed-off-by: Shaohua Li <shli@fb.com>

block/bio.c

@@ -2085,7 +2085,7 @@ void bio_clone_blkcg_association(struct bio *dst, struct bio *src)
 	if (src->bi_css)
 		WARN_ON(bio_associate_blkcg(dst, src->bi_css));
 }
-
+EXPORT_SYMBOL_GPL(bio_clone_blkcg_association);
 #endif /* CONFIG_BLK_CGROUP */
 
 static void __init biovec_init_slabs(void)

drivers/md/raid0.c

@@ -539,6 +539,7 @@ static void raid0_handle_discard(struct mddev *mddev, struct bio *bio)
 		    !discard_bio)
 			continue;
 		bio_chain(discard_bio, bio);
+		bio_clone_blkcg_association(discard_bio, bio);
 		if (mddev->gendisk)
 			trace_block_bio_remap(bdev_get_queue(rdev->bdev),
 				discard_bio, disk_devt(mddev->gendisk),