linux-kernel - Re: [PATCH v2 08/23] mm: introduce BPF kfuncs to deal with memcg pointers

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Message-ID: <aQEAnB7Gjs4vew8x@slm.duckdns.org>
Date: Tue, 28 Oct 2025 07:42:52 -1000
From: Tejun Heo <tj@...nel.org>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	Alexei Starovoitov <ast@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...nel.org>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Johannes Weiner <hannes@...xchg.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	JP Kobryn <inwardvessel@...il.com>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, bpf@...r.kernel.org,
	Martin KaFai Lau <martin.lau@...nel.org>,
	Song Liu <song@...nel.org>,
	Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH v2 08/23] mm: introduce BPF kfuncs to deal with memcg
 pointers

On Mon, Oct 27, 2025 at 04:17:11PM -0700, Roman Gushchin wrote:
> +__bpf_kfunc struct mem_cgroup *
> +bpf_get_mem_cgroup(struct cgroup_subsys_state *css)
> +{
> +	struct mem_cgroup *memcg = NULL;
> +	bool rcu_unlock = false;
> +
> +	if (!root_mem_cgroup)
> +		return NULL;
> +
> +	if (root_mem_cgroup->css.ss != css->ss) {
> +		struct cgroup *cgroup = css->cgroup;
> +		int ssid = root_mem_cgroup->css.ss->id;
> +
> +		rcu_read_lock();
> +		rcu_unlock = true;
> +		css = rcu_dereference_raw(cgroup->subsys[ssid]);

Would it make more sense to use cgroup_e_css()?

Thanks.

-- 
tejun