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

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Date: Sat, 6 Apr 2024 17:10:58 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: 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,
	Dmitry Vyukov <dvyukov@...gle.com>, 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()

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");
	else
		ksft_test_result_pass("check signal distribution\n");

	return 0;
err:
	ksft_print_msg(errmsg);
	return -1;
}