linux-kernel - Re: [PATCH] cgroup: Show control files in cgroup2 root after mount

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Message-ID: <20170718201229.GD3365493@devbig577.frc2.facebook.com>
Date:   Tue, 18 Jul 2017 16:12:29 -0400
From:   Tejun Heo <tj@...nel.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup: Show control files in cgroup2 root after mount

Hello,

On Tue, Jul 18, 2017 at 04:00:45PM -0400, Waiman Long wrote:
> From my own debugging, the controller files (e.g. the debug controller)
> were indirectly populated by the rebind_subsystems() call.
> 
> [    1.628103] css_populate_dir: init subsystem debug
...
> [    1.654975]  cgroup_apply_control_enable+0x103/0x340
> [    1.657719]  cgroup_apply_control+0x1a/0x30
> [    1.658521]  rebind_subsystems+0x18a/0x3b0
...

But there's kernfs_activate() call at the end of rebind_subsystems(),
so if the files were being added there, it should have been activated
there and I can confirm that the files are correctly added / removed
from the cgroup2 root directory when controllers are attached to /
detached from it.

> For the default cgroup2 root, kernfs_activate() was only called at the
> beginning in cgroup_init() with only the base cgroup files added. No
> more call after that until I touched the cgroup.subtree_control file.

Hmm... we're activating at the end of

* cgroup_setup_root()
* rebind_subsystems()
* cgroup_subtree_control_write()
* cgroup_apply_cftypes() after successful addition
* cgroup_mkdir()

I *think* this should cover everything.  Just in case, are you looking
at the mainline kernel?  Can you share how you can reproduce the
issue?

Thanks.

-- 
tejun