netdev - Re: [PATCH bpf-next 07/10] bpf: selftests: Restore netns after each test

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Message-ID: <20200627002302.3tqklvjxxuetjoxr@kafai-mbp.dhcp.thefacebook.com>
Date:   Fri, 26 Jun 2020 17:23:02 -0700
From:   Martin KaFai Lau <kafai@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Kernel Team <kernel-team@...com>,
        Lawrence Brakmo <brakmo@...com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Networking <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH bpf-next 07/10] bpf: selftests: Restore netns after each
 test

On Fri, Jun 26, 2020 at 03:45:04PM -0700, Andrii Nakryiko wrote:
> On Fri, Jun 26, 2020 at 10:56 AM Martin KaFai Lau <kafai@...com> wrote:
> >
> > It is common for networking tests creating its netns and making its own
> > setting under this new netns (e.g. changing tcp sysctl).  If the test
> > forgot to restore to the original netns, it would affect the
> > result of other tests.
> >
> > This patch saves the original netns at the beginning and then restores it
> > after every test.  Since the restore "setns()" is not expensive, it does it
> > on all tests without tracking if a test has created a new netns or not.
> >
> > Signed-off-by: Martin KaFai Lau <kafai@...com>
> > ---
> >  tools/testing/selftests/bpf/test_progs.c | 21 +++++++++++++++++++++
> >  tools/testing/selftests/bpf/test_progs.h |  2 ++
> >  2 files changed, 23 insertions(+)
> >
> > diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> > index 54fa5fa688ce..b521ce366381 100644
> > --- a/tools/testing/selftests/bpf/test_progs.c
> > +++ b/tools/testing/selftests/bpf/test_progs.c
> > @@ -121,6 +121,24 @@ static void reset_affinity() {
> >         }
> >  }
> >
> > +static void save_netns(void)
> > +{
> > +       env.saved_netns_fd = open("/proc/self/ns/net", O_RDONLY);
> > +       if (env.saved_netns_fd == -1) {
> > +               perror("open(/proc/self/ns/net)");
> > +               exit(-1);
> > +       }
> > +}
> > +
> > +static void restore_netns(void)
> > +{
> > +       if (setns(env.saved_netns_fd, CLONE_NEWNET) == -1) {
> > +               stdio_restore();
> > +               perror("setns(CLONE_NEWNS)");
> > +               exit(-1);
> > +       }
> > +}
> > +
> >  void test__end_subtest()
> >  {
> >         struct prog_test_def *test = env.test;
> > @@ -643,6 +661,7 @@ int main(int argc, char **argv)
> >                 return -1;
> >         }
> >
> > +       save_netns();
> 
> you should probably do this also after each sub-test in test__end_subtest()?
You mean restore_netns()?

It is a tough call.
Some tests may only want to create a netns at the beginning for all the subtests
to use (e.g. sk_assign.c).  restore_netns() after each subtest may catch
tester in surprise that the netns is not in its full control while its
own test is running.

I think an individual test should have managed the netns properly within its
subtests already if it wants a correct test result.  It can unshare at the
beginning of each subtest to get a clean state (e.g. in patch 8).
test_progs.c only ensures a config made by an earlier test does
not affect the following tests.