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

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Message-ID: <87y0ouuc8c.fsf@linux.dev>
Date: Tue, 28 Oct 2025 11:12:35 -0700
From: Roman Gushchin <roman.gushchin@...ux.dev>
To: Tejun Heo <tj@...nel.org>
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

Tejun Heo <tj@...nel.org> writes:

> 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()?

Good call, will update in the next version.

Thank you!