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Sender: Tejun Heo <htejun@gmail.com>
Date:   Tue, 12 Jul 2022 17:00:52 -1000
From:   Tejun Heo <tj@kernel.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Qais Yousef <qais.yousef@arm.com>,
        Xuewen Yan <xuewen.yan@unisoc.com>, rafael@kernel.org,
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Subject: Re: [PATCH] sched/schedutil: Fix deadlock between cpuset and cpu
 hotplug when using schedutil
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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