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Date:   Tue, 4 Apr 2023 10:12:48 -0400
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Subject: Re: [PATCH 3/3] cgroup/cpuset: Allow only one active attach operation
 per cpuset
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To:     =?UTF-8?Q?Michal_Koutn=c3=bd?= <mkoutny@suse.com>
Cc:     Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Christian Brauner <brauner@kernel.org>,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org,
        Juri Lelli <juri.lelli@redhat.com>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        gscrivan@redhat.com
References: <20230331145045.2251683-1-longman@redhat.com>
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 <24b67530-62ce-4f9c-7b74-d41d2ccc710e@redhat.com>
 <20230404090737.3g3uxga52bojgdu5@blackpad>
From:   Waiman Long <longman@redhat.com>
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On 4/4/23 05:07, Michal Koutný wrote:
> Hi.
>
> On Mon, Apr 03, 2023 at 01:41:33PM -0400, Waiman Long <longman@redhat.com> wrote:
>> This patch is actually not related to the CLONE_INTO_GROUP problem in patch
>> 1. It is a generic problem when multiple users are moving threads into
>> cgroup.threads of the same or different cpusets simultaneously.
> I meant this:
> 	__cgroup_procs_write
> 	  cgroup_kn_lock_live
> 	    mutex_lock(&cgroup_mutex)
>
> and (more succintly)
> 	cgroup_update_dfl_csses
> 	  lockdep_assert_held(&cgroup_mutex)
>
> Even the threaded migrations should be synchronized here.
> Can you please explain in more detail what's the problematic case?

You are right. I missed the cgroup_mutex synchronization here. So this 
patch isn't needed. I will drop it in the next version.

Cheers,
Longman