[dm-devel] [PATCH] dm rq: clear cloned bio ->bi_bdev to fix I/O accounting

[Benjamin Marzinski]

bio_clone_fast() sets the cloned bio to have the same ->bi_bdev as the
source bio. This means that when request-based dm called setup_clone(),
the cloned bio had its ->bi_bdev pointing to the dm device. After Commit
0b6e522cdc4a ("blk-mq: use ->bi_bdev for I/O accounting")
__blk_account_io_start() started using the request's ->bio->bi_bdev for
I/O accounting, if it was set. This caused IO going to the underlying
devices to use the dm device for their I/O accounting.

Request-based dm can't be used on top of partitions, so
dm_rq_bio_constructor() can just clear the cloned bio's ->bi_bdev and
have __blk_account_io_start() fall back to using rq->rq_disk->part0 for
the I/O accounting.

Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
---
 drivers/md/dm-rq.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 579ab6183d4d..42099dc76e3c 100644
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -328,6 +328,7 @@ static int dm_rq_bio_constructor(struct bio *bio, struct bio *bio_orig,
 	info->orig = bio_orig;
 	info->tio = tio;
 	bio->bi_end_io = end_clone_bio;
+	bio->bi_bdev = NULL;
 
 	return 0;
 }
-- 
2.30.2