linux-kernel - Re: [PATCH] sched/schedutil: Fix deadlock between cpuset and cpu hotplug when using schedutil

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Message-ID: <Ys41ZF5TmSnLLNRB@slm.duckdns.org>
Date:   Tue, 12 Jul 2022 17:00:52 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Qais Yousef <qais.yousef@....com>,
        Xuewen Yan <xuewen.yan@...soc.com>, rafael@...nel.org,
        viresh.kumar@...aro.org, mingo@...hat.com, peterz@...radead.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        mgorman@...e.de, bristot@...hat.com, linux-kernel@...r.kernel.org,
        ke.wang@...soc.com, xuewyan@...mail.com, linux-pm@...r.kernel.org
Subject: Re: [PATCH] sched/schedutil: Fix deadlock between cpuset and cpu
 hotplug when using schedutil

On Tue, Jul 12, 2022 at 10:49:57PM -0400, Waiman Long wrote:
> > Well, the only thing I can think of is always grabbing cpus_read_lock()
> > before grabbing threadgroup_rwsem. Waiman, what do you think?
> 
> That is a possible solution as cpus_read_lock() is rather lightweight. It is
> a good practice to acquire it first.

On a similar note, I think we probably should re-enable percpu operations on
threadgroup_rwsem too by default and allow users who are affected by slower
write path operations to opt-in. After the new CLONE_INTO_CGROUP which
doesn't need the rwsem, we have far fewer write lockers after all.

Thanks.

-- 
tejun