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

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Message-ID: <CAADnVQJPcqq+w0qDjMV+fx-gYfp6kjuc7m8VD-7saCZ7-bvaBw@mail.gmail.com>
Date: Wed, 29 Oct 2025 17:16:09 -0700
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Tejun Heo <tj@...nel.org>
Cc: Roman Gushchin <roman.gushchin@...ux.dev>, Song Liu <song@...nel.org>, 
	Andrew Morton <akpm@...ux-foundation.org>, LKML <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 <linux-mm@...ck.org>, 
	"open list:CONTROL GROUP (CGROUP)" <cgroups@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	Martin KaFai Lau <martin.lau@...nel.org>, Kumar Kartikeya Dwivedi <memxor@...il.com>
Subject: Re: [PATCH v2 02/23] bpf: initial support for attaching struct ops to cgroups

On Wed, Oct 29, 2025 at 5:03 PM Tejun Heo <tj@...nel.org> wrote:
>
> Oh, if there are other mechanisms to enforce boundaries, it's not a problem,
> but I can almost guarantee as the framework grows, there will be needs for
> kfuncs to identify and verify the callers and handlers communicating with
> each other along the hierarchy requiring recursive calls.

tbh I think it's a combination of sched_ext_ops and bpf infra problem.
All of the scx ops are missing "this" pointer which would have
been there if it was a C++ class.
And "this" should be pointing to an instance of class.
If sched-ext progs are attached to different cgroups, then
every attachment would have been a different instance and
different "this".
Then all kfuncs would effectively be declared as helper
methods within a class. In this case within "struct sched_ext_ops"
as functions that ops callback can call but they will
also have implicit "this" that points back to a particular instance.

Special aux__prog and prog_assoc are not exactly pretty
workarounds for lack of "this".