Re: [PATCH] selftests/seccomp: Actually sleep for 1/10th second

[Guenter Roeck]

On 1/27/19 11:36 AM, Nick Desaulniers wrote:
> On Sun, Jan 27, 2019 at 11:13 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > On Sun, Jan 27, 2019 at 11:25 PM Nick Desaulniers
> > <ndesaulniers@xxxxxxxxxx> wrote:
> > > On Sun, Jan 27, 2019 at 1:44 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> > > > Clang noticed that some none-zero sleep()s were actually using zero
> > > > anyway. This switches to nanosleep() to gain sub-second granularity.
> > > >
> > > > seccomp_bpf.c:2625:9: warning: implicit conversion from 'double' to
> > > >        'unsigned int' changes value from 0.1 to 0 [-Wliteral-conversion]
> > > >                  sleep(0.1);
> > > >                  ~~~~~ ^~~
> > > >
> > > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > > > ---
> > > >   tools/testing/selftests/seccomp/seccomp_bpf.c | 5 +++--
> > > >   1 file changed, 3 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> > > > index 067cb4607d6c..a9f278c13f13 100644
> > > > --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> > > > +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> > > > @@ -2569,6 +2569,7 @@ TEST_F(TSYNC, two_siblings_not_under_filter)
> > > >   {
> > > >          long ret, sib;
> > > >          void *status;
> > > > +       struct timespec delay = { .tv_nsec = 100000000 };
> > >
> > > "Omitted fields are implicitly initialized the same as for objects
> > > that have static storage duration."
> > > https://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
> > > https://godbolt.org/z/cuGqxM
> > > (So this wont sleep an arbitrary amount of seconds, phew)
> >
> > Yup. :) Even an empty initializer works ... = { };
> > (Except that padding bytes aren't always included in the zeroing...)
> >
> > > >          ASSERT_EQ(0, prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
> > > >                  TH_LOG("Kernel does not support PR_SET_NO_NEW_PRIVS!");
> > > > @@ -2622,7 +2623,7 @@ TEST_F(TSYNC, two_siblings_not_under_filter)
> > > >          EXPECT_EQ(SIBLING_EXIT_UNKILLED, (long)status);
> > > >          /* Poll for actual task death. pthread_join doesn't guarantee it. */
> > > >          while (!kill(self->sibling[sib].system_tid, 0))
> > > > -               sleep(0.1);
> > > > +               nanosleep(&delay, NULL);
> > > >          /* Switch to the remaining sibling */
> > > >          sib = !sib;
> > > >
> > > > @@ -2647,7 +2648,7 @@ TEST_F(TSYNC, two_siblings_not_under_filter)
> > > >          EXPECT_EQ(0, (long)status);
> > > >          /* Poll for actual task death. pthread_join doesn't guarantee it. */
> > > >          while (!kill(self->sibling[sib].system_tid, 0))
> > > > -               sleep(0.1);
> > > > +               nanosleep(&delay, NULL);
> > >
> > > Interesting bug.  If the sleeps weren't doing anything, are they even
> > > needed? Does adding the tests cause them to continue to pass, or start
> > > to fail?  If they weren't doing anything, and the tests were passing,
> > > maybe it's just better to remove them?
> >
> > It was just spinning.
>
> So this test has been broken? If so, do you know for how long? Or
> who's monitoring them?  Either way, thanks for noticing and fixing.
>
> +Guenter; did you notice if this test was failing? Are your boot tests
> running kselftests?

No, I don't run kselftests at this time.

Guenter

> > This restores the intention of not being so
> > aggressive in the wait loop. While the sleep could be removed, that
> > wasn't the intention.
>
> Oh, yeah I guess the comment above it about pthread_join is relevant.
> I just get highly highly suspicious whenever I see sleeps added to any
> code.
> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>