Re: [PATCH bpf-next v1 2/5] cgroup: bpf: add cgroup_rstat_updated() and cgroup_rstat_flush() kfuncs

[Yosry Ahmed]

On Fri, May 20, 2022 at 12:24 AM Tejun Heo <tj@xxxxxxxxxx> wrote:
>
> On Fri, May 20, 2022 at 01:21:30AM +0000, Yosry Ahmed wrote:
> > Add cgroup_rstat_updated() and cgroup_rstat_flush() kfuncs to bpf
> > tracing programs. bpf programs that make use of rstat can use these
> > functions to inform rstat when they update stats for a cgroup, and when
> > they need to flush the stats.
> >
> > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx>
>
> Do patch 1 and 2 need to be separate? Also, can you explain and comment why
> it's __weak?

I will squash them in the next version.

As for the declaration, I took the __weak annotation from Alexei's
reply to the previous version. I thought it had something to do with
how fentry progs attach to functions with BTF and all.
When I try the same code with a static noinline declaration instead,
fentry attachment fails to find the BTF type ID of bpf_rstat_flush.
When I try it with just noinline (without __weak), the fentry program
attaches, but is never invoked. I tried looking at the attach code but
I couldn't figure out why this happens.

In retrospect, I should have given this more thought. It would be
great if Alexei could shed some light on this.

>
> Thanks.


>
> --
> tejun