linux-kernel - Re: [PATCH bpf-next 2/2] selftests/bpf: add test for legacy/perf kprobe/uprobe attach mode

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Date:   Thu, 9 Feb 2023 22:08:16 +0800
From:   Menglong Dong <menglong8.dong@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alan Maguire <alan.maguire@...cle.com>, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
        song@...nel.org, yhs@...com, john.fastabend@...il.com,
        kpsingh@...nel.org, sdf@...gle.com, haoluo@...gle.com,
        jolsa@...nel.org, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, Menglong Dong <imagedong@...cent.com>
Subject: Re: [PATCH bpf-next 2/2] selftests/bpf: add test for legacy/perf
 kprobe/uprobe attach mode

On Thu, Feb 9, 2023 at 7:31 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Wed, Feb 8, 2023 at 3:49 AM Alan Maguire <alan.maguire@...cle.com> wrote:
> >
> > On 07/02/2023 22:50, Andrii Nakryiko wrote:
> > > On Mon, Feb 6, 2023 at 6:39 PM Menglong Dong <menglong8.dong@...il.com> wrote:
> > >>
> > >> On Tue, Feb 7, 2023 at 4:05 AM Andrii Nakryiko
> > >> <andrii.nakryiko@...il.com> wrote:
> > >>>
> > >>> On Thu, Feb 2, 2023 at 7:18 PM <menglong8.dong@...il.com> wrote:
> > >>>>
> > >>>> From: Menglong Dong <imagedong@...cent.com>
> > >>>>
> > >>>> Add the testing for kprobe/uprobe attaching in legacy and perf mode.
> > >>>> And the testing passed:
> > >>>>
> > >>>> ./test_progs -t attach_probe
> > >>>> $5       attach_probe:OK
> > >>>> Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
> > >>>>
> > >>>> Signed-off-by: Menglong Dong <imagedong@...cent.com>
> > >>>> ---
> > >>>
> > >>> Do you mind refactoring attach_probe test into multiple subtests,
> > >>> where each subtest will only test one of the attach mode and type. The
> > >>> reason is that libbpf CI runs tests with latest selftests and libbpf
> > >>> against old kernels (4.9 and 5.5, currently). Due to attach_probe
> > >>> testing all these uprobe/kprobe attach modes with extra features (like
> > >>> cookie, ref count, etc), we had to disable attach_probe test in libbpf
> > >>> CI on old kernels.
> > >>>
> > >>> If we can split each individual uprobe/kprobe mode, that will give us
> > >>> flexibility to selectively allowlist those tests that don't force
> > >>> libbpf to use newer features (like cookies, LINK or PERF mode, etc).
> > >>>
> > >>> It would be a great improvement and highly appreciated! If you don't
> > >>> mind doing this, let's do the split of existing use cases into subtest
> > >>> in a separate patch, and then add PERF/LEGACY/LINK mode tests on top
> > >>> of that patch.
> > >>>
> > >>
> > >> Of course, with pleasure. For the existing use cases, we split it into
> > >> subtests, such as:
> > >>
> > >>   kprobe/kretprobe auto attach
> > >>   kprobe/kretprobe manual attach
> > >>   uprobe/uretprobe ref_ctr test
> > >>   uprobe/uretprobe auto attach
> > >>   sleepable kprobe/uprobe
> > >>   ......
> > >>
> > >> Am I right?
> > >
> > > I haven't analysed all the different cases, but roughly it makes
> > > sense. With more granular subtests we can also drop `legacy` flag and
> > > rely on subtest allowlisting in CI.
> > >
> >
> > I'm probably rusty on the details, but when you talk about subtest
> > splitting for the [uk]probe manual attach, are we talking about running
> > the same manual attach test for the different modes, with each as a
> > separate subtest, such that each registers as a distinct pass/fail (and
> > can thus be allowlisted as appropriate)? So in other words
> >
> > test__start_subtest("manual_attach_kprobe_link");
> > attach_kprobe_manual(link_options);
> > test__start_subtest("manual_attach_kprobe_legacy");
> > attach_kprobe_manual(legay_options);
> > test__start_subtest("manual_attach_kprobe_perf");
> > attach_kprobe_manual(perf_options);
> >
> > ?
>
> Yep. One of the reasons is that on 4.9 kernel there won't be link or
> perf method available, so it is expected for such modes to fail. I
> want to be able to still test the legacy code path on 4.9, though.
> Similarly tests that are using ref_ctr_offset or bpf_cookie won't work
> on older kernels as well. Right now because of all of them being in a
> single test, I have to block entire test, losing coverage on older
> kernels.
>

I think I am beginning to understand it now. So we need 2 patches
for the selftests part. In the 1th patch, we split the existing testings
into multi subtests, such as:

test__start_subtest("manual_attach_probe") // test kprobe/uprobe manual attach
test__start_subtest("auto_attach_probe") // test kprobe/uprobe auto attach
test__start_subtest("bpf_cookie") // test bpf_cookie
test__start_subtest("ref_ctr_offset") test ref_ctr_offset
test__start_subtest("sleepable_probe") // test sleepable
uprobe/uretprobe, and sleepable kprobe
......

And in the 2th patch, we change the subtest "manual_attach_probe" into
the following tests:

test__start_subtest("manual_attach_kprobe_link");
test__start_subtest("manual_attach_kprobe_legacy");
test__start_subtest("manual_attach_kprobe_perf");

Therefore, every feature can be tested in a subtest alone.

Am I right?

Thanks!
Menglong Dong
> >
> > >>
> > >> Thanks!
> > >> Dongmeng Long
> > >>
> > >>>
> > >>>>  .../selftests/bpf/prog_tests/attach_probe.c   | 61 ++++++++++++++++++-
> > >>>>  .../selftests/bpf/progs/test_attach_probe.c   | 32 ++++++++++
> > >>>>  2 files changed, 92 insertions(+), 1 deletion(-)
> > >>>>
> > >>>
> > >>> [...]