linux-kernel - Re: BUG: HANG_DETECT waiting for migration_cpu

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Message-ID: <YxeR0RoiTdm8sWCJ@slm.duckdns.org>
Date:   Tue, 6 Sep 2022 08:30:41 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Jing-Ting Wu <jing-ting.wu@...iatek.com>
Cc:     Mukesh Ojha <quic_mojha@...cinc.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <vschneid@...hat.com>,
        wsd_upstream@...iatek.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org, Jonathan.JMChen@...iatek.com,
        "chris.redpath@....com" <chris.redpath@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Donnefort <vdonnefort@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Christian Brauner <brauner@...nel.org>,
        cgroups@...r.kernel.org, lixiong.liu@...iatek.com,
        wenju.xu@...iatek.com, Waiman Long <longman@...hat.com>
Subject: Re: BUG: HANG_DETECT waiting for migration_cpu_stop() complete

Hello,

(cc'ing Waiman in case he has a better idea)

On Mon, Sep 05, 2022 at 04:22:29PM +0800, Jing-Ting Wu wrote:
> https://lore.kernel.org/lkml/YvrWaml3F+x9Dk+T@slm.duckdns.org/ is for
> fix cgroup_threadgroup_rwsem <-> cpus_read_lock() deadlock.
> But this issue is cgroup_threadgroup_rwsem <-> cpuset_rwsem deadlock.

If I'm understanding what you're writing correctly, this isn't a deadlock.
The cpuset_hotplug_workfn simply isn't being woken up while holding
cpuset_rwsem and others are just waiting for that lock to be released.

Thanks.

-- 
tejun