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From:   Xuewen Yan <xuewen.yan94@gmail.com>
Date:   Mon, 15 Aug 2022 17:25:52 +0800
Message-ID: <CAB8ipk90LxNNbq5OKamd-ArkqhEZjxS1fFZJXtnbQwGzyyJ3wQ@mail.gmail.com>
Subject: Re: Query regarding deadlock involving cgroup_threadgroup_rwsem and cpu_hotplug_lock
To:     =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Cc:     Mukesh Ojha <quic_mojha@quicinc.com>, Tejun Heo <tj@kernel.org>,
        Imran Khan <imran.f.khan@oracle.com>, lizefan.x@bytedance.com,
        hannes@cmpxchg.org, tglx@linutronix.de, steven.price@arm.com,
        peterz@infradead.org, cgroups@vger.kernel.org,
        linux-kernel@vger.kernel.org, Zhao Gongyi <zhaogongyi@huawei.com>,
        Zhang Qiao <zhangqiao22@huawei.com>
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Hi Michal

On Mon, Aug 15, 2022 at 5:06 PM Michal Koutn=C3=BD <mkoutny@suse.com> wrote=
:
>
> +Cc: Zhao Gongyi <zhaogongyi@huawei.com>, Zhang Qiao <zhangqiao22@huawei.=
com>
>
> On Fri, Aug 12, 2022 at 03:57:00PM +0530, Mukesh Ojha <quic_mojha@quicinc=
.com> wrote:
> > The original patch of yours [1]  and the revert of [2] is fixing the is=
sue
> > and it is also confirmed here [3].
> > Can we get proper fix merge on your tree?
> >
> > [1] https://lore.kernel.org/lkml/YuGbYCfAG81mZBnN@slm.duckdns.org/
> >
> > [2]
> > https://lore.kernel.org/all/20220121101210.84926-1-zhangqiao22@huawei.c=
om/
>
> The revert + Tejun's patch looks fine wrt the problem of the reverted
> patch (just moves cpus_read_lock to upper callers).

Your means is that the problem should be fixed by [1]+[2]'s revert ?
I just tested the case which reverted the [2]. Need I test with [1] and [2]=
?

Thanks!

>
> I'd just suggest a comment that'd explicitly document also the lock
> order that we stick to, IIUC, it should be:
>
>         cpu_hotplug_lock // cpus_read_lock
>         cgroup_threadgroup_rwsem
>         cpuset_rwsem
>
> Michal
>
> >
> > [3] https://lore.kernel.org/lkml/CAB8ipk-72V-bYRfL-VcSRSyXTeQqkBVj+1d5M=
HSVV5CTar9a0Q@mail.gmail.com/
> >
> > -Mukesh