linux-kernel - Re: [PATCH cgroup/for-4.13-fixes] cgroup: create dfl

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Message-ID: <d44b7b53-0be6-7019-169a-aa45b4d02598@redhat.com>
Date:   Tue, 18 Jul 2017 18:09:16 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH cgroup/for-4.13-fixes] cgroup: create dfl_root files on
 subsys registration

On 07/18/2017 05:57 PM, Tejun Heo wrote:
> On subsystem registration, css_populate_dir() is not called on the new
> root css, so the interface files for the subsystem on cgrp_dfl_root
> aren't created on registration.  This is a residue from the days when
> cgrp_dfl_root was used only as the parking spot for unused subsystems,
> which no longer is true as it's used as the root for cgroup2.
>
> This is often fine as later operations tend to create them as a part
> of mount (cgroup1) or subtree_control operations (cgroup2); however,
> it's not difficult to mount cgroup2 with the controller interface
> files missing as Waiman found out.
>
> Fix it by invoking css_populate_dir() on the root css on subsys
> registration.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Waiman Long <longman@...hat.com>
> Cc: stable@...r.kernel.org # v4.5+
> ---
> Hello, Waiman.
>
> Can you please verify that this fixes the bug?
>

Yes, this patch fix the problem.

Tested-by:  Waiman Long <longman@...hat.com>