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

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Message-ID: <CAB8ipk_Y5vaUMnRQVJsbHUue_J00qqy0E1ifu3W_hFSspL1r1w@mail.gmail.com>
Date:   Mon, 11 Jul 2022 15:43:17 +0800
From:   Xuewen Yan <xuewen.yan94@...il.com>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     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 Mon, Jul 11, 2022 at 3:32 PM Lukasz Luba <lukasz.luba@....com> wrote:
>
> Hi Xuewen,
>
> On 7/11/22 08:21, Xuewen Yan wrote:
> > Hi all
> >
> > This deadlock is inevitable, any comment?
>
> Could you tell me how to reproduce this?
> Is there a need of special cgroup setup?

This deadlock occurs when we run the monkey test on an Android phone,
at the same time, randomly put online or offline a cpu core.
Indeed the thread-A which get the cgroup_threadgroup_rwsem and waiting
for the cpu_hotplug_lock is the thread whose name is "OomAdjuster" in
android.

And I see the cpu_hotplug_lock is added by the patch:
https://lore.kernel.org/all/20220121101210.84926-1-zhangqiao22@huawei.com/

Thanks!

>
> Regards,
> Lukasz