Commit e797203f authored by Dmitry Vyukov's avatar Dmitry Vyukov Committed by Thomas Gleixner
Browse files

selftests/timers/posix_timers: Test delivery of signals across threads 



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: default avatarDmitry Vyukov <dvyukov@google.com>
Signed-off-by: default avatarMarco Elver <elver@google.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20230316123028.2890338-2-elver@google.com
parent bcb7ee79

tools/testing/selftests/timers/posix_timers.c

+77 −0
Original line number Diff line number Diff line
@@ -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... ");

	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");

		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");

	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();

}