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

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Message-ID: <20170718195148.GC3365493@devbig577.frc2.facebook.com>
Date:   Tue, 18 Jul 2017 15:51:48 -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, Waiman.

On Tue, Jul 18, 2017 at 03:32:16PM -0400, Waiman Long wrote:
> It was found that when a cgroup2 filesystem was mounted, control
> files other than the base cgroup.* ones were not shown in the root
> directory.  They were shown only after some controllers were activated
> in the root's cgroup.subtree_control file.
> 
> This was caused by a lack of the kernfs_activate() call which was fixed
> by this patch.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  kernel/cgroup/cgroup.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 89a23c6..fb1893b 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -2024,8 +2024,10 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type,
>  
>  		dentry = cgroup_do_mount(&cgroup2_fs_type, flags, &cgrp_dfl_root,
>  					 CGROUP2_SUPER_MAGIC, ns);
> -		if (!IS_ERR(dentry))
> +		if (!IS_ERR(dentry)) {
>  			apply_cgroup_root_flags(root_flags);
> +			kernfs_activate(cgrp_dfl_root.cgrp.kn);
> +		}

Heh, that's tricky.  I'm not quite sure where the unactivated files
are being added tho because that'd be where we should be activating.
I *think* that they are already activated as part of
cgroup_add_cftypes() but I am obviously qmissing something.  I'll try
to repro the issue and find where we're skipping the activation call.

Thanks!

-- 
tejun