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

[Christoph Hellwig]

So I actually noticed this during code inspection a while ago, but I
think we need to use the actual underlying device instead of NULL here
to keep our block layer gurantees.  See the patch in my queue below.

---
>From 1e330b8e57fc0d6c6fb07c0ec2915dca5d7a585a Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch at lst.de>
Date: Thu, 13 Jan 2022 10:53:59 +0100
Subject: block: assign bi_bdev for cloned bios in blk_rq_prep_clone

The cloned bios for the cloned request in blk_rq_prep_clone currently
still point to the original bi_bdev.  This is harmless because dm-mpath
doesn't look at bi_bdev but violates the invariants of always having
the correct bi_bdev.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/blk-mq.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index a6d4780580fcd..b5e35e63adad4 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2976,6 +2976,7 @@ int blk_rq_prep_clone(struct request *rq, struct request *rq_src,
 		bio = bio_clone_fast(bio_src, gfp_mask, bs);
 		if (!bio)
 			goto free_and_out;
+		bio->bi_bdev = rq->q->disk->part0;
 
 		if (bio_ctr && bio_ctr(bio, bio_src, data))
 			goto free_and_out;
-- 
2.30.2