From mboxrd@z Thu Jan  1 00:00:00 1970
From: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 3/3] cgroup/cpuset: Allow only one active attach operation
 per cpuset
Date: Tue, 4 Apr 2023 10:12:48 -0400
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Cc: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Christian Brauner <brauner-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Juri Lelli <juri.lelli-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Dietmar Eggemann <dietmar.eggemann-5wv7dgnIgG8@public.gmane.org>, gscrivan-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org


On 4/4/23 05:07, Michal Koutn=C3=BD wrote:
> Hi.
>
> On Mon, Apr 03, 2023 at 01:41:33PM -0400, Waiman Long <longman-H+wXaHxf7a=
LQT0dZR+AlfA@public.gmane.org> wrote:
>> This patch is actually not related to the CLONE_INTO_GROUP problem in pa=
tch
>> 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=20
patch isn't needed. I will drop it in the next version.

Cheers,
Longman