linux-kernel - Re: [PATCH] cgroup: remove unnecessary empty check when enabling threaded mode

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Message-ID: <20170725171607.GC3216015@devbig577.frc2.facebook.com>
Date:   Tue, 25 Jul 2017 13:16:08 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...com, pjt@...gle.com,
        luto@...capital.net, efault@....de, torvalds@...ux-foundation.org,
        guro@...com
Subject: Re: [PATCH] cgroup: remove unnecessary empty check when enabling
 threaded mode

On Sun, Jul 23, 2017 at 08:18:26AM -0400, Tejun Heo wrote:
> cgroup_enable_threaded() checks that the cgroup doesn't have any tasks
> or children and fails the operation if so.  This test is unnecessary
> because the first part is already checked by
> cgroup_can_be_thread_root() and the latter is unnecessary.  The latter
> actually cause a behavioral oddity.  Please consider the following
> hierarchy.  All cgroups are domains.
> 
>     A
>    / \
>   B   C
>        \
>         D
> 
> If B is made threaded, C and D becomes invalid domains.  Due to the no
> children restriction, threaded mode can't be enabled on C.  For C and
> D, the only thing the user can do is removal.
> 
> There is no reason for this restriction.  Remove it.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Waiman Long <longman@...hat.com>

Applied to cgroup/for-4.14 with Waiman's ack.

Thanks.

-- 
tejun