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

Yafang Shao
2025-10-30T06:34:06Z

On Thu, Oct 30, 2025 at 8:16 AM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Oct 29, 2025 at 5:03 PM Tejun Heo <tj@kernel.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".
>

I also share the concern that supporting the attachment of a single
struct-ops to multiple cgroups appears over-engineered for the current
needs. Given that we do not anticipate a large number of cgroup
attachments in real-world use, implementing such a generalized
mechanism now seems premature. We can always introduce this
functionality later in a backward-compatible manner if concrete use
cases emerge.

That said, if we still decide to move forward with this approach, I
would suggest merging this patch as a standalone change. Doing so
would allow my BPF-THP series to build upon the same mechanism.

--
Regards
Yafang