netdev - Re: [RFC PATCH bpf-next v6 12/12] samples/bpf: Add memcg priority control example

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <a1f4a2908ada3a81838bdddc64907529c53a5be29de83c928a70f2b3736783da@mail.kernel.org>
Date: Wed,  4 Feb 2026 09:28:36 +0000 (UTC)
From: bot+bpf-ci@...nel.org
To: hui.zhu@...ux.dev,akpm@...ux-foundation.org,hannes@...xchg.org,mhocko@...nel.org,roman.gushchin@...ux.dev,shakeel.butt@...ux.dev,muchun.song@...ux.dev,ast@...nel.org,daniel@...earbox.net,andrii@...nel.org,martin.lau@...ux.dev,eddyz87@...il.com,song@...nel.org,yonghong.song@...ux.dev,john.fastabend@...il.com,kpsingh@...nel.org,sdf@...ichev.me,haoluo@...gle.com,jolsa@...nel.org,shuah@...nel.org,peterz@...radead.org,ojeda@...nel.org,nathan@...nel.org,kees@...nel.org,tj@...nel.org,jeffxu@...omium.org,mkoutny@...e.com,kernel@...rr.cc,brauner@...nel.org,rdunlap@...radead.org,brgerst@...il.com,masahiroy@...nel.org,davem@...emloft.net,kuba@...nel.org,hawk@...nel.org,inwardvessel@...il.com,willemb@...gle.com,kerneljasonxing@...il.com,paul.chaignon@...il.com,a.s.protopopov@...il.com,ameryhung@...il.com,chenridong@...weicloud.com,lance.yang@...ux.dev,jiayuan.chen@...ux.dev,linux-kernel@...r.kernel.org,linux-mm@...ck.org,cgroups@...r.kernel.org,bpf@...r.kernel.org,netdev@...r.kernel.org,linu
 x-kselftest@...r.kernel.org
Cc: zhuhui@...inos.cn,geliang@...nel.org,ast@...nel.org,andrii@...nel.org,daniel@...earbox.net,martin.lau@...nel.org,eddyz87@...il.com,yonghong.song@...ux.dev,clm@...a.com,ihor.solodrai@...ux.dev
Subject: Re: [RFC PATCH bpf-next v6 12/12] samples/bpf: Add memcg priority control example

> 1. memcg.bpf.c: A BPF program that monitors PGFAULT events on a
>    high-priority cgroup. When activity exceeds a threshold, it uses
>    the `get_high_delay_ms`, `below_low`, or `below_min` hooks to
>    apply pressure on a low-priority cgroup.

Is this description accurate? Looking at the code, below_low and
below_min are implemented in high_mcg_ops which is attached to the
high-priority cgroup:

    high_mcg_ops = {
        .below_low = (void *)below_low_impl,
        .below_min = (void *)below_min_impl,
    };

And in memcg.c, high_mcg_ops is attached via:

    .relative_fd = high_cgroup_fd,

According to the memcg_bpf_ops documentation, below_low and below_min
provide protection for a cgroup (returning true means the cgroup is
protected from reclaim), rather than applying pressure. Only
get_high_delay_ms (attached to the low-priority cgroup via low_mcg_ops)
actually throttles/applies pressure.

Could the commit message clarify that below_low/below_min protect the
high-priority cgroup, while get_high_delay_ms throttles the low-priority
one?

> diff --git a/samples/bpf/memcg.c b/samples/bpf/memcg.c
> new file mode 100644
> index 000000000..0ed174608
> --- /dev/null
> +++ b/samples/bpf/memcg.c

[ ... ]

> +	prog = bpf_object__find_program_by_name(obj,
> +						"handle_count_memcg_events");
> +	if (!prog) {
> +		fprintf(stderr,
> +			"ERROR: finding a prog in BPF object file failed\n");
> +		goto out;
> +	}

If bpf_object__find_program_by_name() fails here, should the err variable
be set to an error code before the goto? As written, err could be 0 (from
the previous successful bpf_map_update_elem() call), causing main() to
return 0 (success) even though the program failed.

---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/21665371660

AI-authorship-score: low
AI-authorship-explanation: The technical misunderstanding about hook purposes and dual authorship suggest human collaboration rather than AI generation.
issues-found: 2
issue-severity-score: low
issue-severity-explanation: The issues found are a misleading commit message description and a missing error code assignment in sample code, neither of which causes system instability.