linux-kernel - [PATCH v1 1/3] selftests/timers/posix_timers: Make signal distribution test less fragile

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Date: Mon,  4 Mar 2024 18:11:32 +0000
From: Edward Liaw <edliaw@...gle.com>
To: linux-kernel@...r.kernel.org, John Stultz <jstultz@...gle.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Stephen Boyd <sboyd@...nel.org>, Shuah Khan <shuah@...nel.org>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: linux-kselftest@...r.kernel.org, kernel-team@...roid.com, 
	Edward Liaw <edliaw@...gle.com>, llvm@...ts.linux.dev
Subject: [PATCH v1 1/3] selftests/timers/posix_timers: Make signal
 distribution test less fragile

The signal distribution test has a tendency to hang for a long time as the
signal delivery is not really evenly distributed.

Increasing the timer interval to 10ms makes this less likely. Add a timeout
to catch the case where it hangs and terminate the test gracefully.

While at it get rid of the pointless atomic operation on a the thread local
variable in the signal handler.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
[edliaw: Rebase and fix checkpatch recommendations]
Signed-off-by: Edward Liaw <edliaw@...gle.com>
---
 tools/testing/selftests/timers/posix_timers.c | 43 ++++++++++++-------
 1 file changed, 27 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/timers/posix_timers.c b/tools/testing/selftests/timers/posix_timers.c
index d49dd3ffd0d9..03779b6b3c20 100644
--- a/tools/testing/selftests/timers/posix_timers.c
+++ b/tools/testing/selftests/timers/posix_timers.c
@@ -24,7 +24,8 @@ static volatile int done;
 /* Busy loop in userspace to elapse ITIMER_VIRTUAL */
 static void user_loop(void)
 {
-	while (!done);
+	while (!done)
+		continue;
 }
 
 /*
@@ -184,18 +185,19 @@ static int check_timer_create(int which)
 	return 0;
 }
 
-int remain;
-__thread int got_signal;
+static int remain;
+static __thread int got_signal;
 
 static void *distribution_thread(void *arg)
 {
-	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
+	while (__atomic_load_n(&remain, __ATOMIC_RELAXED) && !done)
+		continue;
 	return NULL;
 }
 
 static void distribution_handler(int nr)
 {
-	if (!__atomic_exchange_n(&got_signal, 1, __ATOMIC_RELAXED))
+	if (++got_signal == 1)
 		__atomic_fetch_sub(&remain, 1, __ATOMIC_RELAXED);
 }
 
@@ -205,17 +207,19 @@ static void distribution_handler(int nr)
  */
 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_value.tv_nsec = 20 * 1000 * 1000,
 		.it_interval.tv_sec = 0,
-		.it_interval.tv_nsec = 1000 * 1000,
+		.it_interval.tv_nsec = 20 * 1000 * 1000,
 	};
+	time_t start, now;
+	int err, i;
+	timer_t id;
 
+	done = 0;
 	remain = nthreads + 1;  /* worker threads + this thread */
 	signal(SIGALRM, distribution_handler);
 	err = timer_create(CLOCK_PROCESS_CPUTIME_ID, NULL, &id);
@@ -240,7 +244,18 @@ static int check_timer_distribution(void)
 	}
 
 	/* Wait for all threads to receive the signal. */
-	while (__atomic_load_n(&remain, __ATOMIC_RELAXED));
+	now = start = time(NULL);
+	while (__atomic_load_n(&remain, __ATOMIC_RELAXED)) {
+		now = time(NULL);
+		if (now - start > 5)
+			break;
+	}
+	done = 1;
+
+	if (timer_delete(id)) {
+		ksft_perror("Can't delete timer\n");
+		return -1;
+	}
 
 	for (i = 0; i < nthreads; i++) {
 		err = pthread_join(threads[i], NULL);
@@ -251,12 +266,8 @@ static int check_timer_distribution(void)
 		}
 	}
 
-	if (timer_delete(id)) {
-		ksft_perror("Can't delete timer");
-		return -1;
-	}
+	ksft_test_result((now - start <= 5), "%s\n", __func__);
 
-	ksft_test_result_pass("check_timer_distribution\n");
 	return 0;
 }
 
@@ -265,7 +276,7 @@ int main(int argc, char **argv)
 	ksft_print_header();
 	ksft_set_plan(6);
 
-	ksft_print_msg("Testing posix timers. False negative may happen on CPU execution \n");
+	ksft_print_msg("Testing posix timers. False negative may happen on CPU execution\n");
 	ksft_print_msg("based timers if other threads run on the CPU...\n");
 
 	if (check_itimer(ITIMER_VIRTUAL) < 0)
-- 
2.44.0.rc1.240.g4c46232300-goog