linux-kernel - Re: [PATCH] selftests/timers/posix_timers: reimplement check_timer

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Message-ID: <CACT4Y+Ych4+pdpcTk=yWYUOJcceL5RYoE_B9djX_pwrgOcGmFA@mail.gmail.com>
Date: Mon, 8 Apr 2024 10:30:32 +0200
From: Dmitry Vyukov <dvyukov@...gle.com>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, John Stultz <jstultz@...gle.com>, 
	Marco Elver <elver@...gle.com>, Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, 
	"Eric W. Biederman" <ebiederm@...ssion.com>, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, kasan-dev@...glegroups.com, 
	Edward Liaw <edliaw@...gle.com>, Carlos Llamas <cmllamas@...gle.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] selftests/timers/posix_timers: reimplement check_timer_distribution()

On Sat, 6 Apr 2024 at 17:12, Oleg Nesterov <oleg@...hat.com> wrote:
>
> Dmitry, Thomas,
>
> To simplify the review I've attached the code with this patch applied below.
>
> Yes, this changes the "semantics" of check_timer_distribution(), perhaps it
> should be renamed.
>
> But I do not see a better approach, and in fact I think that
>
>         Test that all running threads _eventually_ receive CLOCK_PROCESS_CPUTIME_ID
>
> is the wrong goal.
>
> Do you agree?
>
> Oleg.
> -------------------------------------------------------------------------------
>
> static pthread_t ctd_thread;
> static volatile int ctd_count, ctd_failed;
>
> static void ctd_sighandler(int sig)
> {
>         if (pthread_self() != ctd_thread)
>                 ctd_failed = 1;
>         ctd_count--;
> }
>
> static void *ctd_thread_func(void *arg)
> {
>         struct itimerspec val = {
>                 .it_value.tv_sec = 0,
>                 .it_value.tv_nsec = 1000 * 1000,
>                 .it_interval.tv_sec = 0,
>                 .it_interval.tv_nsec = 1000 * 1000,
>         };
>         timer_t id;
>
>         /* 1/10 seconds to ensure the leader sleeps */
>         usleep(10000);
>
>         ctd_count = 100;
>         if (timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id))
>                 return "Can't create timer";
>         if (timer_settime(id, 0, &val, NULL))
>                 return "Can't set timer";
>
>         while (ctd_count > 0 && !ctd_failed)
>                 ;
>
>         if (timer_delete(id))
>                 return "Can't delete timer";
>
>         return NULL;
> }
>
> /*
>  * Test that only the running thread receives the timer signal.
>  */
> static int check_timer_distribution(void)
> {
>         const char *errmsg;
>
>         signal(SIGALRM, ctd_sighandler);
>
>         errmsg = "Can't create thread";
>         if (pthread_create(&ctd_thread, NULL, ctd_thread_func, NULL))
>                 goto err;
>
>         errmsg = "Can't join thread";
>         if (pthread_join(ctd_thread, (void **)&errmsg) || errmsg)
>                 goto err;
>
>         if (ctd_failed)
>                 ksft_test_result_skip("No signal distribution. Assuming old kernel\n");

Shouldn't the test fail here? The goal of a test is to fail when
things don't work.
I don't see any other ksft_test_result_fail() calls, and it does not
look that the test will hang on incorrect distribution.


>         else
>                 ksft_test_result_pass("check signal distribution\n");
>
>         return 0;
> err:
>         ksft_print_msg(errmsg);
>         return -1;
> }
>