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

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Jussi Maki <joamaki@gmail.com>, Hangbin Liu <haliu@redhat.com>,
	Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
	Martin KaFai Lau <kafai@fb.com>, Song Liu <songliubraving@fb.com>,
	Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@chromium.org>
Subject: Re: [PATCH] bpf/selftests: Fix namespace mount setup in tc_redirect
Date: Wed, 5 Jan 2022 12:40:34 -0800	[thread overview]
Message-ID: <CAEf4BzZK1=zdy1_ZdwWXK7Ryk+uWQeSApcpxFT9yMp4bRNanDQ@mail.gmail.com> (raw)
In-Reply-To: <20220104121030.138216-1-jolsa@kernel.org>

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.

>
> 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
>