Re: [PATCHv2 bpf-next 7/9] selftests/bpf: Add test for missed counts of perf event link kprobe

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Sep 08, 2023 at 04:25:30PM -0700, Andrii Nakryiko wrote:

SNIP

> > +/*
> > + * Putting kprobe on bpf_fentry_test1 that calls bpf_kfunc_common_test
> > + * kfunc, which has also kprobe on. The latter won't get triggered due
> > + * to kprobe recursion check and kprobe missed counter is incremented.
> > + */
> > +static void test_missed_perf_kprobe(void)
> > +{
> > +       LIBBPF_OPTS(bpf_test_run_opts, topts);
> > +       struct bpf_link_info info = {};
> > +       struct missed_kprobe *skel;
> > +       __u32 len = sizeof(info);
> > +       int err, prog_fd;
> > +
> > +       skel = missed_kprobe__open_and_load();
> > +       if (!ASSERT_OK_PTR(skel, "missed_kprobe__open_and_load"))
> > +               goto cleanup;
> > +
> > +       err = missed_kprobe__attach(skel);
> > +       if (!ASSERT_OK(err, "missed_kprobe__attach"))
> > +               goto cleanup;
> > +
> > +       prog_fd = bpf_program__fd(skel->progs.trigger);
> > +       err = bpf_prog_test_run_opts(prog_fd, &topts);
> > +       ASSERT_OK(err, "test_run");
> > +       ASSERT_EQ(topts.retval, 0, "test_run");
> > +
> > +       err = bpf_link_get_info_by_fd(bpf_link__fd(skel->links.test2), &info, &len);
> > +       if (!ASSERT_OK(err, "bpf_link_get_info_by_fd"))
> > +               goto cleanup;
> > +
> > +       ASSERT_EQ(info.type, BPF_LINK_TYPE_PERF_EVENT, "info.type");
> > +       ASSERT_EQ(info.perf_event.type, BPF_PERF_EVENT_KPROBE, "info.perf_event.type");
> > +       ASSERT_EQ(info.perf_event.kprobe.missed, 1, "info.perf_event.kprobe.missed");
> > +
> > +cleanup:
> > +       missed_kprobe__destroy(skel);
> > +}
> > +
> > +void serial_test_missed(void)
> 
> why serial? if you check for kprobe.missed >= 1, it should be fine
> even if some other test calls this testmod kfunc, right?

hm, I think the reason for me was the testmod getting unloaded
in serial_test_bpf_mod_race test.. but it's serial, so I guess
we should be fine

thanks,
jirka