linux-kernel - Re: [PATCH] dm: pass origin bio's bdev to bio_alloc

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Message-ID: <bb49f820-473a-a951-60b0-32dcd8fb0110@huawei.com>
Date: Fri, 23 Jan 2026 09:12:53 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: <agk@...hat.com>, <snitzer@...nel.org>, <mpatocka@...hat.com>,
	<bmarzins@...hat.com>
CC: <dm-devel@...ts.linux.dev>, <linux-kernel@...r.kernel.org>,
	<yangerkun@...wei.com>, <lilingfeng3@...wei.com>
Subject: Re: [PATCH] dm: pass origin bio's bdev to bio_alloc_clone

在 2026/1/16 20:07, Zhihao Cheng 写道:

friendly ping

> The origin bio carries blk-cgroup information which could be set from
> foreground(task_css(css) - wbc->wb->blkcg_css), so the blkcg won't
> control buffer io since commit ca522482e3eaf ("dm: pass NULL bdev to
> bio_alloc_clone"). The synchronous io is still under control by blkcg,
> because 'bio->bi_blkg' is set by io submitting task which has been
> added into 'cgroup.procs'.
> 
> Fix it by passing origin bio's bdev to bio_alloc_clone.
> 
> Fetch a reproducer in [Link].
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=220985
> Fixes: ca522482e3eaf ("dm: pass NULL bdev to bio_alloc_clone")
> Signed-off-by: Zhihao Cheng <chengzhihao1@...wei.com>
> ---
>   drivers/md/dm.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index b63279202260..e763e3b02a9f 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -574,7 +574,8 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio, gfp_t g
>   	struct dm_target_io *tio;
>   	struct bio *clone;
>   
> -	clone = bio_alloc_clone(NULL, bio, gfp_mask, &md->mempools->io_bs);
> +	clone = bio_alloc_clone(bio->bi_bdev, bio,
> +				gfp_mask, &md->mempools->io_bs);
>   	if (unlikely(!clone))
>   		return NULL;
>   	tio = clone_to_tio(clone);
> @@ -623,7 +624,7 @@ static struct bio *alloc_tio(struct clone_info *ci, struct dm_target *ti,
>   		/* alloc_io() already initialized embedded clone */
>   		clone = &tio->clone;
>   	} else {
> -		clone = bio_alloc_clone(NULL, ci->bio, gfp_mask,
> +		clone = bio_alloc_clone(ci->bio->bi_bdev, ci->bio, gfp_mask,
>   					&md->mempools->bs);
>   		if (!clone)
>   			return NULL;
>