lib/posix/mutex.c

/*
 * Copyright (c) 2017 Intel Corporation
 * Copyright (c) 2023 Meta
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include "posix_internal.h"

#include <zephyr/init.h>
#include <zephyr/kernel.h>
#include <zephyr/logging/log.h>
#include <zephyr/posix/pthread.h>
#include <zephyr/sys/bitarray.h>

LOG_MODULE_REGISTER(pthread_mutex, CONFIG_PTHREAD_MUTEX_LOG_LEVEL);

static struct k_spinlock pthread_mutex_spinlock;

int64_t timespec_to_timeoutms(const struct timespec *abstime);

#define MUTEX_MAX_REC_LOCK 32767

/*
 *  Default mutex attrs.
 */
static const struct pthread_mutexattr def_attr = {
	.type = PTHREAD_MUTEX_DEFAULT,
};

static struct k_mutex posix_mutex_pool[CONFIG_MAX_PTHREAD_MUTEX_COUNT];
static uint8_t posix_mutex_type[CONFIG_MAX_PTHREAD_MUTEX_COUNT];
SYS_BITARRAY_DEFINE_STATIC(posix_mutex_bitarray, CONFIG_MAX_PTHREAD_MUTEX_COUNT);

/*
 * We reserve the MSB to mark a pthread_mutex_t as initialized (from the
 * perspective of the application). With a linear space, this means that
 * the theoretical pthread_mutex_t range is [0,2147483647].
 */
BUILD_ASSERT(CONFIG_MAX_PTHREAD_MUTEX_COUNT < PTHREAD_OBJ_MASK_INIT,
	"CONFIG_MAX_PTHREAD_MUTEX_COUNT is too high");

static inline size_t posix_mutex_to_offset(struct k_mutex *m)
{
	return m - posix_mutex_pool;
}

static inline size_t to_posix_mutex_idx(pthread_mutex_t mut)
{
	return mark_pthread_obj_uninitialized(mut);
}

static struct k_mutex *get_posix_mutex(pthread_mutex_t mu)
{
	int actually_initialized;
	size_t bit = to_posix_mutex_idx(mu);

	/* if the provided mutex does not claim to be initialized, its invalid */
	if (!is_pthread_obj_initialized(mu)) {
		LOG_ERR("Mutex is uninitialized (%x)", mu);
		return NULL;
	}

	/* Mask off the MSB to get the actual bit index */
	if (sys_bitarray_test_bit(&posix_mutex_bitarray, bit, &actually_initialized) < 0) {
		LOG_ERR("Mutex is invalid (%x)", mu);
		return NULL;
	}

	if (actually_initialized == 0) {
		/* The mutex claims to be initialized but is actually not */
		LOG_ERR("Mutex claims to be initialized (%x)", mu);
		return NULL;
	}

	return &posix_mutex_pool[bit];
}

struct k_mutex *to_posix_mutex(pthread_mutex_t *mu)
{
	int err;
	size_t bit;
	struct k_mutex *m;

	if (*mu != PTHREAD_MUTEX_INITIALIZER) {
		return get_posix_mutex(*mu);
	}

	/* Try and automatically associate a posix_mutex */
	if (sys_bitarray_alloc(&posix_mutex_bitarray, 1, &bit) < 0) {
		LOG_ERR("Unable to allocate pthread_mutex_t");
		return NULL;
	}

	/* Record the associated posix_mutex in mu and mark as initialized */
	*mu = mark_pthread_obj_initialized(bit);

	/* Initialize the posix_mutex */
	m = &posix_mutex_pool[bit];

	err = k_mutex_init(m);
	__ASSERT_NO_MSG(err == 0);

	return m;
}

static int acquire_mutex(pthread_mutex_t *mu, k_timeout_t timeout)
{
	int type;
	size_t bit;
	int ret = 0;
	struct k_mutex *m;
	k_spinlock_key_t key;

	key = k_spin_lock(&pthread_mutex_spinlock);

	m = to_posix_mutex(mu);
	if (m == NULL) {
		k_spin_unlock(&pthread_mutex_spinlock, key);
		return EINVAL;
	}

	LOG_DBG("Locking mutex %p with timeout %llx", m, timeout.ticks);

	bit = posix_mutex_to_offset(m);
	type = posix_mutex_type[bit];

	if (m->owner == k_current_get()) {
		switch (type) {
		case PTHREAD_MUTEX_NORMAL:
			if (K_TIMEOUT_EQ(timeout, K_NO_WAIT)) {
				k_spin_unlock(&pthread_mutex_spinlock, key);
				LOG_ERR("Timeout locking mutex %p", m);
				return EBUSY;
			}
			/* On most POSIX systems, this usually results in an infinite loop */
			k_spin_unlock(&pthread_mutex_spinlock, key);
			LOG_ERR("Attempt to relock non-recursive mutex %p", m);
			do {
				(void)k_sleep(K_FOREVER);
			} while (true);
			CODE_UNREACHABLE;
			break;
		case PTHREAD_MUTEX_RECURSIVE:
			if (m->lock_count >= MUTEX_MAX_REC_LOCK) {
				LOG_ERR("Mutex %p locked recursively too many times", m);
				ret = EAGAIN;
			}
			break;
		case PTHREAD_MUTEX_ERRORCHECK:
			LOG_ERR("Attempt to recursively lock non-recursive mutex %p", m);
			ret = EDEADLK;
			break;
		default:
			__ASSERT(false, "invalid pthread type %d", type);
			ret = EINVAL;
			break;
		}
	}
	k_spin_unlock(&pthread_mutex_spinlock, key);

	if (ret == 0) {
		ret = k_mutex_lock(m, timeout);
		if (ret == -EAGAIN) {
			LOG_ERR("Timeout locking mutex %p", m);
			/*
			 * special quirk - k_mutex_lock() returns EAGAIN if a timeout occurs, but
			 * for pthreads, that means something different
			 */
			ret = ETIMEDOUT;
		}
	}

	if (ret < 0) {
		LOG_ERR("k_mutex_unlock() failed: %d", ret);
		ret = -ret;
	}

	if (ret == 0) {
		LOG_DBG("Locked mutex %p", m);
	}

	return ret;
}

/**
 * @brief Lock POSIX mutex with non-blocking call.
 *
 * See IEEE 1003.1
 */
int pthread_mutex_trylock(pthread_mutex_t *m)
{
	return acquire_mutex(m, K_NO_WAIT);
}

/**
 * @brief Lock POSIX mutex with timeout.
 *
 *
 * See IEEE 1003.1
 */
int pthread_mutex_timedlock(pthread_mutex_t *m,
			    const struct timespec *abstime)
{
	int32_t timeout = (int32_t)timespec_to_timeoutms(abstime);
	return acquire_mutex(m, K_MSEC(timeout));
}

/**
 * @brief Initialize POSIX mutex.
 *
 * See IEEE 1003.1
 */
int pthread_mutex_init(pthread_mutex_t *mu, const pthread_mutexattr_t *_attr)
{
	size_t bit;
	struct k_mutex *m;
	const struct pthread_mutexattr *attr = (const struct pthread_mutexattr *)_attr;

	*mu = PTHREAD_MUTEX_INITIALIZER;

	m = to_posix_mutex(mu);
	if (m == NULL) {
		return ENOMEM;
	}

	bit = posix_mutex_to_offset(m);
	if (attr == NULL) {
		posix_mutex_type[bit] = def_attr.type;
	} else {
		posix_mutex_type[bit] = attr->type;
	}

	LOG_DBG("Initialized mutex %p", m);

	return 0;
}


/**
 * @brief Lock POSIX mutex with blocking call.
 *
 * See IEEE 1003.1
 */
int pthread_mutex_lock(pthread_mutex_t *m)
{
	return acquire_mutex(m, K_FOREVER);
}

/**
 * @brief Unlock POSIX mutex.
 *
 * See IEEE 1003.1
 */
int pthread_mutex_unlock(pthread_mutex_t *mu)
{
	int ret;
	struct k_mutex *m;

	m = get_posix_mutex(*mu);
	if (m == NULL) {
		return EINVAL;
	}

	ret = k_mutex_unlock(m);
	if (ret < 0) {
		LOG_ERR("k_mutex_unlock() failed: %d", ret);
		return -ret;
	}

	__ASSERT_NO_MSG(ret == 0);
	LOG_DBG("Unlocked mutex %p", m);

	return 0;
}

/**
 * @brief Destroy POSIX mutex.
 *
 * See IEEE 1003.1
 */
int pthread_mutex_destroy(pthread_mutex_t *mu)
{
	int err;
	size_t bit;
	struct k_mutex *m;

	m = get_posix_mutex(*mu);
	if (m == NULL) {
		return EINVAL;
	}

	bit = to_posix_mutex_idx(*mu);
	err = sys_bitarray_free(&posix_mutex_bitarray, 1, bit);
	__ASSERT_NO_MSG(err == 0);

	LOG_DBG("Destroyed mutex %p", m);

	return 0;
}

/**
 * @brief Read protocol attribute for mutex.
 *
 * See IEEE 1003.1
 */
int pthread_mutexattr_getprotocol(const pthread_mutexattr_t *attr,
				  int *protocol)
{
	*protocol = PTHREAD_PRIO_NONE;
	return 0;
}

/**
 * @brief Read type attribute for mutex.
 *
 * See IEEE 1003.1
 */
int pthread_mutexattr_gettype(const pthread_mutexattr_t *_attr, int *type)
{
	const struct pthread_mutexattr *attr = (const struct pthread_mutexattr *)_attr;

	*type = attr->type;
	return 0;
}

/**
 * @brief Set type attribute for mutex.
 *
 * See IEEE 1003.1
 */
int pthread_mutexattr_settype(pthread_mutexattr_t *_attr, int type)
{
	struct pthread_mutexattr *attr = (struct pthread_mutexattr *)_attr;
	int retc = EINVAL;

	if ((type == PTHREAD_MUTEX_NORMAL) ||
	    (type == PTHREAD_MUTEX_RECURSIVE) ||
	    (type == PTHREAD_MUTEX_ERRORCHECK)) {
		attr->type = type;
		retc = 0;
	}

	return retc;
}

static int pthread_mutex_pool_init(void)
{
	int err;
	size_t i;

	for (i = 0; i < CONFIG_MAX_PTHREAD_MUTEX_COUNT; ++i) {
		err = k_mutex_init(&posix_mutex_pool[i]);
		__ASSERT_NO_MSG(err == 0);
	}

	return 0;
}
SYS_INIT(pthread_mutex_pool_init, PRE_KERNEL_1, 0);