Re: [PATCH] bpf/selftests: Fix namespace mount setup in tc_redirect

[Jiri Olsa <jolsa@redhat.com>]

On Wed, Jan 05, 2022 at 12:40:34PM -0800, Andrii Nakryiko wrote:
> On Tue, Jan 4, 2022 at 4:10 AM Jiri Olsa <jolsa@redhat.com> wrote:
> >
> > The tc_redirect umounts /sys in the new namespace, which can be
> > mounted as shared and cause global umount. The lazy umount also
> > takes down mounted trees under /sys like debugfs, which won't be
> > available after sysfs mounts again and could cause fails in other
> > tests.
> >
> >   # cat /proc/self/mountinfo | grep debugfs
> >   34 23 0:7 / /sys/kernel/debug rw,nosuid,nodev,noexec,relatime shared:14 - debugfs debugfs rw
> >   # cat /proc/self/mountinfo | grep sysfs
> >   23 86 0:22 / /sys rw,nosuid,nodev,noexec,relatime shared:2 - sysfs sysfs rw
> >   # mount | grep debugfs
> >   debugfs on /sys/kernel/debug type debugfs (rw,nosuid,nodev,noexec,relatime)
> >
> >   # ./test_progs -t tc_redirect
> >   #164 tc_redirect:OK
> >   Summary: 1/4 PASSED, 0 SKIPPED, 0 FAILED
> >
> >   # mount | grep debugfs
> >   # cat /proc/self/mountinfo | grep debugfs
> >   # cat /proc/self/mountinfo | grep sysfs
> >   25 86 0:22 / /sys rw,relatime shared:2 - sysfs sysfs rw
> >
> > Making the sysfs private under the new namespace so the umount won't
> > trigger the global sysfs umount.
> 
> Hey Jiri,
> 
> Thanks for the fix. Did you try making tc_redirect non-serial again
> (s/serial_test_tc_redirect/test_tc_redirect/) and doing parallelized
> test_progs run (./test_progs -j) in a tight loop for a while? I
> suspect this might have been an issue forcing us to make this test
> serial in the first place, so now that it's fixed, we can make
> parallel test_progs a bit faster.

hi,
right, will try

jirka

> 
> >
> > Cc: Jussi Maki <joamaki@gmail.com>
> > Reported-by: Hangbin Liu <haliu@redhat.com>
> > Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> > ---
> >  tools/testing/selftests/bpf/prog_tests/tc_redirect.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/tc_redirect.c b/tools/testing/selftests/bpf/prog_tests/tc_redirect.c
> > index 4b18b73df10b..c2426df58e17 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/tc_redirect.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/tc_redirect.c
> > @@ -105,6 +105,13 @@ static int setns_by_fd(int nsfd)
> >         if (!ASSERT_OK(err, "unshare"))
> >                 return err;
> >
> > +       /* Make our /sys mount private, so the following umount won't
> > +        * trigger the global umount in case it's shared.
> > +        */
> > +       err = mount("none", "/sys", NULL, MS_PRIVATE, NULL);
> > +       if (!ASSERT_OK(err, "remount private /sys"))
> > +               return err;
> > +
> >         err = umount2("/sys", MNT_DETACH);
> >         if (!ASSERT_OK(err, "umount2 /sys"))
> >                 return err;
> > --
> > 2.33.1
> >
>