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

From: Jiri Olsa <[email-masked]>
Date: Mon, 17 Jan 2022 20:25:37 +0100

On Thu, Jan 06, 2022 at 08:35:18AM +0100, Jiri Olsa wrote:
> On Wed, Jan 05, 2022 at 12:40:34PM -0800, Andrii Nakryiko wrote:
> > On Tue, Jan 4, 2022 at 4:10 AM Jiri Olsa <[email-masked]> 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

so I can't reproduce the issue in the first place - that means without my
fix and with reverted serial_test_tc_redirect change - by running parallelized
test_progs, could you guys try it?

jirka