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

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Message-ID: <b3731751-c286-f61e-95ab-c59f9aba98d0@redhat.com>
Date: Fri, 23 Jan 2026 17:16:54 +0100 (CET)
From: Mikulas Patocka <mpatocka@...hat.com>
To: Zhihao Cheng <chengzhihao1@...wei.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

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

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.