Re: [PATCH v2] selftests/timers/posix_timers: reimplement check_timer_distribution()

[John Stultz]

On Tue, Apr 9, 2024 at 6:39 AM Oleg Nesterov <oleg@xxxxxxxxxx> wrote:
>
> Thomas says:
>
>         The signal distribution test has a tendency to hang for a long
>         time as the signal delivery is not really evenly distributed. In
>         fact it might never be distributed across all threads ever in
>         the way it is written.
>
> To me even the
>
>         This primarily tests that the kernel does not favour any one.
>
> comment doesn't look right. The kernel does favour a thread which hits
> the timer interrupt when CLOCK_PROCESS_CPUTIME_ID expires.
>
> The new version simply checks that the group leader sleeping in join()
> never receives SIGALRM, cpu_timer_fire() should always send the signal
> to the thread which burns cpu.
>
> Without the commit bcb7ee79029d ("posix-timers: Prefer delivery of signals
> to the current thread") the test-case fails immediately, the very 1st tick
> wakes the leader up. Otherwise it quickly succeeds after 100 ticks.
>
> As Thomas suggested, the new version doesn't report the failure on the
> pre v6.3 kernels that do not have the commit bcb7ee79029d; this is a
> feature that obviously fails on the older kernels. So the patch adds the
> new simple ksft_ck_kernel_version() helper and uses ksft_test_result_skip()
> if check_timer_distribution() fails on the older kernel.
>
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>

This is working great here (on both 6.6 and the older 6.1)! Thanks so
much for fixing this!
One nit below, but otherwise:
  Tested-by: John Stultz <jstultz@xxxxxxxxxx>

> +err:
> +       ksft_print_msg(errmsg);

This bit is causing the following warning:
posix_timers.c:250:2: warning: format not a string literal and no
format arguments [-Wformat-security]
  250 |  ksft_print_msg(errmsg);
      |  ^~~~~~~~~~~~~~

A simple fix is just to switch it to:
  ksft_print_msg("%s", errmsg);

thanks
-john