From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH] cgroup: remove unnecessary empty check when enabling
 threaded mode
Date: Tue, 25 Jul 2017 13:16:08 -0400
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To: Waiman Long <longman@redhat.com>
Cc: Li Zefan <lizefan@huawei.com>, Johannes Weiner <hannes@cmpxchg.org>, Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, pjt@google.com, luto@amacapital.net, efault@gmx.de, torvalds@linux-foundation.org, guro@fb.com

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@kernel.org>
> Cc: Waiman Long <longman@redhat.com>

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

Thanks.

-- 
tejun