tests: kernel: mutex: test for lock timeout race

/*

 * Copyright (c) 2022 SeediqQ from Issue 48056

 *

 * SPDX-License-Identifier: Apache-2.0

 */

#include <zephyr/ztest.h>

#define TIMEOUT_MS 100

#define STACKSZ	   8192

static struct k_mutex mutex;

static struct k_thread thread;

K_THREAD_STACK_DEFINE(stack, STACKSZ);

static void test_thread(void *p1, void *p2, void *p3)

{

	ARG_UNUSED(p1);

	ARG_UNUSED(p2);

	ARG_UNUSED(p3);

	zassert_equal(-EAGAIN, k_mutex_lock(&mutex, K_MSEC(TIMEOUT_MS)));

}

/**

 * @brief Test fix for subtle race during priority inversion

 *

 * - A low priority thread (Tlow) locks mutex A.

 * - A high priority thread (Thigh) blocks on mutex A, boosting the priority

 *   of Tlow.

 * - Thigh times out waiting for mutex A.

 * - Before Thigh has a chance to execute, Tlow unlocks mutex A (which now

 *   has no owner) and drops its own priority.

 * - Thigh now gets a chance to execute and finds that it timed out, and

 *   then enters the block of code to lower the priority of the thread that

 *   owns mutex A (now nobody).

 * - Thigh tries to the dereference the owner of mutex A (which is nobody,

 *   and thus it is NULL). This leads to an exception.

 *

 * @ingroup kernel_mutex_tests

 *

 * @see k_mutex_lock()

 */

ZTEST(mutex_timeout_race_during_priority_inversion, test_mutex_timeout_error)

{

	k_mutex_init(&mutex);

	/* align to tick boundary */

	k_sleep(K_TICKS(1));

	k_thread_create(&thread, stack, K_THREAD_STACK_SIZEOF(stack), test_thread, NULL, NULL, NULL,

			8, 0, K_NO_WAIT);

	k_mutex_lock(&mutex, K_FOREVER);

	k_sleep(K_MSEC(TIMEOUT_MS));

	k_mutex_unlock(&mutex);

}

ZTEST_SUITE(mutex_timeout_race_during_priority_inversion, NULL, NULL, NULL, NULL, NULL);