linux-kernel - Re: [PATCH 01/10] blk-cgroup: use cgroup lock and rcu to protect iterating blkcg blkgs

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Message-ID: <01e7eccd-3529-4d12-8ad2-fd9e034a026d@yukuai.org.cn>
Date: Fri, 26 Sep 2025 01:07:39 +0800
From: Yu Kuai <hailan@...uai.org.cn>
To: Bart Van Assche <bvanassche@....org>, Yu Kuai <yukuai1@...weicloud.com>,
 tj@...nel.org, ming.lei@...hat.com, nilay@...ux.ibm.com, hch@....de,
 josef@...icpanda.com, axboe@...nel.dk, akpm@...ux-foundation.org,
 vgoyal@...hat.com
Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, yukuai3@...wei.com,
 yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH 01/10] blk-cgroup: use cgroup lock and rcu to protect
 iterating blkcg blkgs

Hi,

在 2025/9/25 23:57, Bart Van Assche 写道:
> On 9/25/25 1:15 AM, Yu Kuai wrote:
>> It's safe to iterate blkgs with cgroup lock or rcu lock held, prevent
>> nested queue_lock under rcu lock, and prepare to convert protecting
>> blkcg with blkcg_mutex instead of queuelock.
>
> Iterating blkgs without holding q->queue_lock is safe but accessing the
> blkg members without holding that lock is not safe since q->queue_lock
> is acquired by all code that modifies blkg members. Should perhaps a new
> spinlock be introduced to serialize blkg modifications?
>
No need for a new lock, I think blkcg->lock can do that.

Thanks,
Kuai

> Thanks,
>
> Bart.
>