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

Tejun Heo
2017-07-18T19:51:48Z

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-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
> 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