linux-kernel - Re: [PATCH bpf-next v2 4/8] bpf: Introduce cgroup iter

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Date:   Thu, 7 Jul 2022 16:36:23 -0700
From:   Hao Luo <haoluo@...gle.com>
To:     Yonghong Song <yhs@...com>
Cc:     Yosry Ahmed <yosryahmed@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shuah Khan <shuah@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        David Rientjes <rientjes@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 4/8] bpf: Introduce cgroup iter

On Mon, Jun 27, 2022 at 9:14 PM Yonghong Song <yhs@...com> wrote:
>
> > +static int __cgroup_iter_seq_show(struct seq_file *seq,
> > +                               struct cgroup_subsys_state *css, int in_stop)
> > +{
> > +     struct cgroup_iter_priv *p = seq->private;
> > +     struct bpf_iter__cgroup ctx;
> > +     struct bpf_iter_meta meta;
> > +     struct bpf_prog *prog;
> > +     int ret = 0;
> > +
> > +     /* cgroup is dead, skip this element */
> > +     if (css && cgroup_is_dead(css->cgroup))
> > +             return 0;
> > +
> > +     ctx.meta = &meta;
> > +     ctx.cgroup = css ? css->cgroup : NULL;
> > +     meta.seq = seq;
> > +     prog = bpf_iter_get_info(&meta, in_stop);
> > +     if (prog)
> > +             ret = bpf_iter_run_prog(prog, &ctx);
>
> Do we need to do anything special to ensure bpf program gets
> up-to-date stat from ctx.cgroup?
>

Let's leave that to be handled by bpf programs. The kfunc rstat_flush
can be called to sync stats, if using rstat.

> > +
> > +     /* if prog returns > 0, terminate after this element. */
> > +     if (ret != 0)
> > +             p->terminate = true;
> > +
> > +     return 0;
> > +}
> > +
> [...]