Re: [PATCH] dm: pass origin bio's bdev to bio_alloc_clone

[Zhihao Cheng]

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@xxxxxxxxxx>

> 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@xxxxxxxxxx>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> ---
>   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.