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

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Message-ID: <2ae755f4-43ea-1e8d-48f8-dffb38ee9773@huawei.com>
Date: Sat, 24 Jan 2026 15:23:28 +0800
From: Zhihao Cheng <chengzhihao1@...wei.com>
To: Mikulas Patocka <mpatocka@...hat.com>
CC: <agk@...hat.com>, <snitzer@...nel.org>, <bmarzins@...hat.com>,
	<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 2026/1/24 0:16, Mikulas Patocka 写道:
> 
> 
> On Fri, 23 Jan 2026, Zhihao Cheng wrote:
> 
>> 在 2026/1/16 20:07, Zhihao Cheng 写道:
>>
>> friendly ping
> 
> Hi
> 
> I find it quite hacky to set bi_bdev and overwrite it later. I came up
> with this patch that clones the control group association explictely, it
> fixes your testcase. Please test it and report if it works for you.
> 
> Mikulas
> 

Thanks for the patch, it works.

Tested-by: Zhihao Cheng <chengzhihao1@...wei.com>

> 
> dm: use bio_clone_blkg_association
> 
> 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 using bio_clone_blkg_association when submitting a cloned bio.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=220985
> Fixes: ca522482e3eaf ("dm: pass NULL bdev to bio_alloc_clone")
> Reported-by: Zhihao Cheng <chengzhihao1@...wei.com>
> Signed-off-by: Mikulas Patocka <mpatocka@...hat.com>
> 
> ---
>   drivers/md/dm.c |    2 ++
>   1 file changed, 2 insertions(+)
> 
> Index: linux-2.6/drivers/md/dm.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm.c	2026-01-06 15:55:41.000000000 +0100
> +++ linux-2.6/drivers/md/dm.c	2026-01-23 17:07:50.000000000 +0100
> @@ -1364,6 +1364,8 @@ void dm_submit_bio_remap(struct bio *clo
>   	if (!tgt_clone)
>   		tgt_clone = clone;
>   
> +	bio_clone_blkg_association(tgt_clone, io->orig_bio);
> +
>   	/*
>   	 * Account io->origin_bio to DM dev on behalf of target
>   	 * that took ownership of IO with DM_MAPIO_SUBMITTED.
>