Re: [RESEND PATCH bpf-next v6 8/8] selftests/bpf: Add tests for open-coded task and css iter

[Chuyi Zhou]

Hello,

在 2023/10/20 08:03, Alexei Starovoitov 写道:
> On Tue, Oct 17, 2023 at 11:18 PM Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx> wrote:
> > +
> > +SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
> > +__failure __msg("css_task_iter is only allowed in bpf_lsm and bpf iter-s")
> > +int BPF_PROG(iter_css_task_for_each)
> > +{
> > +       u64 cg_id = bpf_get_current_cgroup_id();
> > +       struct cgroup *cgrp = bpf_cgroup_from_id(cg_id);
> > +       struct cgroup_subsys_state *css;
> > +       struct task_struct *task;
> > +
> > +       if (cgrp == NULL)
> > +               return 0;
> > +       css = &cgrp->self;
> > +
> > +       bpf_for_each(css_task, task, css, CSS_TASK_ITER_PROCS) {
> > +
> > +       }
> > +       bpf_cgroup_release(cgrp);
> > +       return 0;
> > +}
>
> I think we should relax allowlist in patch 2 further.
> Any sleepable is safe.
> Allowlist is needed to avoid dead locking on css_set_lock.
> Any lsm and any iter (even non-sleepable) and any sleepable
> seems to be safe.
>
> Then the above test would need s/fentry.s/fentry/ to stay relevant.
>
> I would also add:
>
> SEC("iter/cgroup")
> int cgroup_id_printer(struct bpf_iter__cgroup *ctx)
> {
>          struct seq_file *seq = ctx->meta->seq;
>          struct cgroup *cgrp = ctx->cgroup;
>
>          /* epilogue */
>          if (cgrp == NULL) ..
>
>          bpf_for_each(css_task, task, css, CSS_TASK_ITER_PROCS) {
>             BPF_SEQ_PRINTF(); // something about task
>          }
>
> To demonstrate how new kfunc iter can be combined with cgroup iter and
> it won't deadlock, though cgroup iter is not sleepable.

OK.

> I've applied the current set. Pls send a follow up. Thanks


I would try to send a follow up patch next week.

Thank.