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

[Ming Lei]

On Sat, Jan 15, 2022 at 1:59 AM Benjamin Marzinski <bmarzins at redhat.com> wrote:
>
> 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;

Reviewed-by: Ming Lei <ming.lei at redhat.com>