Re: [PATCH v6 2/2] selftests/timers/posix_timers: Test delivery of signals across threads

[Muhammad Usama Anjum <usama.anjum@collabora.com>]

On 3/16/23 5:30 PM, Marco Elver wrote:
> From: Dmitry Vyukov <dvyukov@google.com>
> 
> Test that POSIX timers using CLOCK_PROCESS_CPUTIME_ID eventually deliver
> a signal to all running threads.  This effectively tests that the kernel
> doesn't prefer any one thread (or subset of threads) for signal delivery.
> 
> Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
> Signed-off-by: Marco Elver <elver@google.com>
> ---
> v6:
> - Update wording on what the test aims to test.
> - Fix formatting per checkpatch.pl.
> ---
>  tools/testing/selftests/timers/posix_timers.c | 77 +++++++++++++++++++
>  1 file changed, 77 insertions(+)
> 
> diff --git a/tools/testing/selftests/timers/posix_timers.c b/tools/testing/selftests/timers/posix_timers.c
> index 0ba500056e63..8a17c0e8d82b 100644
> --- a/tools/testing/selftests/timers/posix_timers.c
> +++ b/tools/testing/selftests/timers/posix_timers.c
> @@ -188,6 +188,80 @@ static int check_timer_create(int which)
>  	return 0;
>  }
>  
> +int remain;
> +__thread int got_signal;
> +
> +static void *distribution_thread(void *arg)
> +{
> +	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
> +	return NULL;
> +}
> +
> +static void distribution_handler(int nr)
> +{
> +	if (!__atomic_exchange_n(&got_signal, 1, __ATOMIC_RELAXED))
> +		__atomic_fetch_sub(&remain, 1, __ATOMIC_RELAXED);
> +}
> +
> +/*
> + * Test that all running threads _eventually_ receive CLOCK_PROCESS_CPUTIME_ID
> + * timer signals. This primarily tests that the kernel does not favour any one.
> + */
> +static int check_timer_distribution(void)
> +{
> +	int err, i;
> +	timer_t id;
> +	const int nthreads = 10;
> +	pthread_t threads[nthreads];
> +	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,
> +	};
> +
> +	printf("Check timer_create() per process signal distribution... ");
Use APIs from kselftest.h. Use ksft_print_msg() here.

> +	fflush(stdout);
> +
> +	remain = nthreads + 1;  /* worker threads + this thread */
> +	signal(SIGALRM, distribution_handler);
> +	err = timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id);
> +	if (err < 0) {
> +		perror("Can't create timer\n");
ksft_perror() here

> +		return -1;
> +	}
> +	err = timer_settime(id, 0, &val, NULL);
> +	if (err < 0) {
> +		perror("Can't set timer\n");
> +		return -1;
> +	}
> +
> +	for (i = 0; i < nthreads; i++) {
> +		if (pthread_create(&threads[i], NULL, distribution_thread, NULL)) {
> +			perror("Can't create thread\n");
> +			return -1;
> +		}
> +	}
> +
> +	/* Wait for all threads to receive the signal. */
> +	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
> +
> +	for (i = 0; i < nthreads; i++) {
> +		if (pthread_join(threads[i], NULL)) {
> +			perror("Can't join thread\n");
> +			return -1;
> +		}
> +	}
> +
> +	if (timer_delete(id)) {
> +		perror("Can't delete timer\n");
> +		return -1;
> +	}
> +
> +	printf("[OK]\n");
ksft_test_result or _pass variant as needed?

> +	return 0;
> +}
> +
>  int main(int argc, char **argv)
>  {
>  	printf("Testing posix timers. False negative may happen on CPU execution \n");
> @@ -217,5 +291,8 @@ int main(int argc, char **argv)
>  	if (check_timer_create(CLOCK_PROCESS_CPUTIME_ID) < 0)
>  		return ksft_exit_fail();
>  
> +	if (check_timer_distribution() < 0)
> +		return ksft_exit_fail();
> +
>  	return ksft_exit_pass();
>  }

-- 
BR,
Muhammad Usama Anjum