Re: [PATCH bpf-next] selftests/bpf: Mount debugfs in setns_by_fd

[Alexei Starovoitov <alexei.starovoitov@gmail.com>]

On Wed, Nov 23, 2022 at 2:39 PM Stanislav Fomichev <sdf@google.com> wrote:
>
> On Wed, Nov 23, 2022 at 12:39 PM Alexei Starovoitov
> <alexei.starovoitov@gmail.com> wrote:
> >
> > On Wed, Nov 23, 2022 at 12:08 PM Stanislav Fomichev <sdf@google.com> wrote:
> > >
> > > Jiri reports broken test_progs after recent commit 68f8e3d4b916
> > > ("selftests/bpf: Make sure zero-len skbs aren't redirectable").
> > > Apparently we don't remount debugfs when we switch back networking namespace.
> > > Let's explicitly mount /sys/kernel/debug.
> > >
> > > 0: https://lore.kernel.org/bpf/63b85917-a2ea-8e35-620c-808560910819@meta.com/T/#ma66ca9c92e99eee0a25e40f422489b26ee0171c1
> > >
> > > Fixes: a30338840fa5 ("selftests/bpf: Move open_netns() and close_netns() into network_helpers.c")
> > > Reported-by: Jiri Olsa <olsajiri@gmail.com>
> > > Signed-off-by: Stanislav Fomichev <sdf@google.com>
> > > ---
> > >  tools/testing/selftests/bpf/network_helpers.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/tools/testing/selftests/bpf/network_helpers.c b/tools/testing/selftests/bpf/network_helpers.c
> > > index bec15558fd93..1f37adff7632 100644
> > > --- a/tools/testing/selftests/bpf/network_helpers.c
> > > +++ b/tools/testing/selftests/bpf/network_helpers.c
> > > @@ -426,6 +426,10 @@ static int setns_by_fd(int nsfd)
> > >         if (!ASSERT_OK(err, "mount /sys/fs/bpf"))
> > >                 return err;
> > >
> > > +       err = mount("debugfs", "/sys/kernel/debug", "debugfs", 0, NULL);
> > > +       if (!ASSERT_OK(err, "mount /sys/kernel/debug"))
> > > +               return err;
> > > +
> > >         return 0;
> > >  }
> >
> > Thanks.
> > It fixes part of it but it's still racy.
> > I see:
> > do_read:FAIL:open open /sys/fs/bpf/bpf_iter_test1 failed: No such file
> > or directory
> >
> > I suspect it happens when iter tests are running while test_empty_skb
> > is cleaning the netns.
> >
> > So I've added:
> > -void test_empty_skb(void)
> > +void serial_test_empty_skb(void)
> > -void test_xdp_do_redirect(void)
> > +void serial_test_xdp_do_redirect(void)
> > -void test_xdp_synproxy(void)
> > +void serial_test_xdp_synproxy(void)
> >
> > to stop the bleeding and applied.
>
> Not sure I understand where the race is coming from and no luck
> reproducing locally :-(
> Looks like we run the tests in the forked workers, so that
> unshare(mountns) shouldn't theoretically affect the rest, but
> obviously I'm missing something..

I'm equally confused.
If what you're describing was the case than the bug of
not mounting debugfs wouldn't have caused issues in parallel run.
That close_netns is somehow messing with other forked processes.