linux-kernel - Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups

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Message-ID: <CAHzjS_uagf3G4hAcJK0QWao88a4sRzXjdkQGgRMH8RZYd_C4Cw@mail.gmail.com>
Date: Wed, 29 Oct 2025 14:04:24 -0700
From: Song Liu <song@...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>, Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups

On Mon, Oct 27, 2025 at 4:17 PM Roman Gushchin <roman.gushchin@...ux.dev> wrote:
>
> When a struct ops is being attached and a bpf link is created,
> allow to pass a cgroup fd using bpf attr, so that struct ops
> can be attached to a cgroup instead of globally.
>
> Attached struct ops doesn't hold a reference to the cgroup,
> only preserves cgroup id.

With the current model, when a cgroup is freed, the bpf link still
holds a reference to the struct_ops. Can we make the cgroup to hold
a reference to the struct_ops, so that the struct_ops is freed
automatically when the cgroup is freed?

I think the downside is that we will need an API to remove/change
per cgroup OOM handler.

Thanks,
Song