Re: [RFC PATCH bpf-next 1/5] cgroup: Enable task_under_cgroup_hierarchy() on cgroup1

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On Sun, Sep 03, 2023 at 02:27:56PM +0000, Yafang Shao wrote:
> Currently, the function task_under_cgroup_hierarchy() allows us to
> determine if a task resides exclusively within a cgroup2 hierarchy.
> Nevertheless, given the continued prevalence of cgroup1, it's useful that
> we make a minor adjustment to extend its functionality to cgroup1 as well.
> Once this modification is implemented, we will have the ability to
> effortlessly verify a task's cgroup membership within BPF programs. For
> instance, we can easily check if a task belongs to a cgroup1 directory,
> such as /sys/fs/cgroup/cpu,cpuacct/kubepods/burstable/ or
> /sys/fs/cgroup/cpu,cpuacct/kubepods/besteffort/.
> 
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
>  include/linux/cgroup.h | 24 +++++++++++++++++++++---
>  1 file changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index b307013..5414a2c 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -543,15 +543,33 @@ static inline struct cgroup *cgroup_ancestor(struct cgroup *cgrp,
>   * @ancestor: possible ancestor of @task's cgroup
>   *
>   * Tests whether @task's default cgroup hierarchy is a descendant of @ancestor.
> - * It follows all the same rules as cgroup_is_descendant, and only applies
> - * to the default hierarchy.
> + * It follows all the same rules as cgroup_is_descendant.
>   */
>  static inline bool task_under_cgroup_hierarchy(struct task_struct *task,
>  					       struct cgroup *ancestor)
>  {
>  	struct css_set *cset = task_css_set(task);
> +	struct cgroup *cgrp;
> +	bool ret = false;
> +	int ssid;
> +
> +	if (ancestor->root == &cgrp_dfl_root)
> +		return cgroup_is_descendant(cset->dfl_cgrp, ancestor);
> +
> +	for (ssid = 0; ssid < CGROUP_SUBSYS_COUNT; ssid++) {
> +		if (!ancestor->subsys[ssid])
> +			continue;

This looks wrong. I believe cgroup_mutex should be held to iterate.

Tejun ?

>  
> -	return cgroup_is_descendant(cset->dfl_cgrp, ancestor);
> +		cgrp = task_css(task, ssid)->cgroup;
> +		if (!cgrp)
> +			continue;
> +
> +		if (!cgroup_is_descendant(cgrp, ancestor))
> +			return false;
> +		if (!ret)
> +			ret = true;
> +	}
> +	return ret;
>  }
>  
>  /* no synchronization, the result can only be used as a hint */
> -- 
> 1.8.3.1
> 




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