selftests: ntsync: Add a stress test for contended waits.

Test a more realistic usage pattern, and one with heavy contention, in order to
actually exercise ntsync's internal synchronization.

This test has several threads in a tight loop acquiring a mutex, modifying some
shared data, and then releasing the mutex. At the end we check if the data is
consistent.

Signed-off-by: Elizabeth Figura <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

tools/testing/selftests/drivers/ntsync/ntsync.c

···
 	close(fd);
 }
 
+#define STRESS_LOOPS 10000
+#define STRESS_THREADS 4
+
+static unsigned int stress_counter;
+static int stress_device, stress_start_event, stress_mutex;
+
+static void *stress_thread(void *arg)
+{
+	struct ntsync_wait_args wait_args = {0};
+	__u32 index, count, i;
+	int ret;
+
+	wait_args.timeout = UINT64_MAX;
+	wait_args.count = 1;
+	wait_args.objs = (uintptr_t)&stress_start_event;
+	wait_args.owner = gettid();
+	wait_args.index = 0xdeadbeef;
+
+	ioctl(stress_device, NTSYNC_IOC_WAIT_ANY, &wait_args);
+
+	wait_args.objs = (uintptr_t)&stress_mutex;
+
+	for (i = 0; i < STRESS_LOOPS; ++i) {
+		ioctl(stress_device, NTSYNC_IOC_WAIT_ANY, &wait_args);
+
+		++stress_counter;
+
+		unlock_mutex(stress_mutex, wait_args.owner, &count);
+	}
+
+	return NULL;
+}
+
+TEST(stress_wait)
+{
+	struct ntsync_event_args event_args;
+	struct ntsync_mutex_args mutex_args;
+	pthread_t threads[STRESS_THREADS];
+	__u32 signaled, i;
+	int ret;
+
+	stress_device = open("/dev/ntsync", O_CLOEXEC | O_RDONLY);
+	ASSERT_LE(0, stress_device);
+
+	mutex_args.owner = 0;
+	mutex_args.count = 0;
+	stress_mutex = ioctl(stress_device, NTSYNC_IOC_CREATE_MUTEX, &mutex_args);
+	EXPECT_LE(0, stress_mutex);
+
+	event_args.manual = 1;
+	event_args.signaled = 0;
+	stress_start_event = ioctl(stress_device, NTSYNC_IOC_CREATE_EVENT, &event_args);
+	EXPECT_LE(0, stress_start_event);
+
+	for (i = 0; i < STRESS_THREADS; ++i)
+		pthread_create(&threads[i], NULL, stress_thread, NULL);
+
+	ret = ioctl(stress_start_event, NTSYNC_IOC_EVENT_SET, &signaled);
+	EXPECT_EQ(0, ret);
+
+	for (i = 0; i < STRESS_THREADS; ++i) {
+		ret = pthread_join(threads[i], NULL);
+		EXPECT_EQ(0, ret);
+	}
+
+	EXPECT_EQ(STRESS_LOOPS * STRESS_THREADS, stress_counter);
+
+	close(stress_start_event);
+	close(stress_mutex);
+	close(stress_device);
+}
+
 TEST_HARNESS_MAIN