From: Tao Cui <cui.tao@linux.dev>
To: Guopeng Zhang <guopeng.zhang@linux.dev>,
Tejun Heo <tj@kernel.org>, Josef Bacik <josef@toxicpanda.com>,
Jens Axboe <axboe@kernel.dk>
Cc: cui.tao@linux.dev, Yu Kuai <yukuai@fygo.io>,
cgroups@vger.kernel.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org,
Guopeng Zhang <zhangguopeng@kylinos.cn>
Subject: Re: [PATCH] blk-cgroup: clear blkg->pd[] with WRITE_ONCE() in blkcg_deactivate_policy()
Date: Wed, 8 Jul 2026 13:29:13 +0800 [thread overview]
Message-ID: <f2f3f741-3420-4dbb-92e1-1598370922d8@linux.dev> (raw)
In-Reply-To: <841e91db-a51e-4df5-8cfc-e3762a2fecf1@linux.dev>
FYI, this WRITE_ONCE() change is also in Yu Kuai's in-flight series that
factors the pd teardown loop into a helper:
https://lore.kernel.org/all/20260625025739.2459651-5-yukuai@kernel.org/
That series isn't merged yet (v3, 2026-06-25), so this minimal Fixes
patch is still useful in the meantime -- just flagging the overlap.
在 2026/7/8 13:10, Tao Cui 写道:
>
>
> 在 2026/7/7 20:58, Guopeng Zhang 写道:
>> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>>
>> blkcg_activate_policy() installs blkg->pd[] entries with WRITE_ONCE()
>> and also uses WRITE_ONCE() when clearing them on its error path.
>> blkg_to_pd() is used by RCU readers and reads the same array with
>> READ_ONCE().
>>
>> blkcg_deactivate_policy() clears the entry with a plain store. Use
>> WRITE_ONCE() there as well.
>>
>> Fixes: 56cc24f59c14 ("blk-cgroup: don't nest queue_lock under rcu in blkcg_print_blkgs()")
>> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
>> ---
>> block/blk-cgroup.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
>> index d2a1f5903f24..a1dd69f99f5c 100644
>> --- a/block/blk-cgroup.c
>> +++ b/block/blk-cgroup.c
>> @@ -1691,7 +1691,7 @@ void blkcg_deactivate_policy(struct gendisk *disk,
>> if (blkg->pd[pol->plid]->online && pol->pd_offline_fn)
>> pol->pd_offline_fn(blkg->pd[pol->plid]);
>> pol->pd_free_fn(blkg->pd[pol->plid]);
>> - blkg->pd[pol->plid] = NULL;
>> + WRITE_ONCE(blkg->pd[pol->plid], NULL);
>> }
>> spin_unlock(&blkcg->lock);
>> }
>
> Reviewed-by: Tao Cui <cuitao@kylinos.cn>
>
next prev parent reply other threads:[~2026-07-08 5:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-07 12:58 [PATCH] blk-cgroup: clear blkg->pd[] with WRITE_ONCE() in blkcg_deactivate_policy() Guopeng Zhang
2026-07-08 5:10 ` Tao Cui
2026-07-08 5:29 ` Tao Cui [this message]
2026-07-08 5:59 ` Guopeng Zhang
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