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/*
* Copyright (c) 2016 Wind River Systems, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* @file @brief mutex kernel services
*
* This module contains routines for handling mutex locking and unlocking.
*
* Mutexes implement a priority inheritance algorithm that boosts the priority
* level of the owning thread to match the priority level of the highest
* priority thread waiting on the mutex.
*
* Each mutex that contributes to priority inheritance must be released in the
* reverse order in which is was acquired. Furthermore each subsequent mutex
* that contributes to raising the owning thread's priority level must be
* acquired at a point after the most recent "bumping" of the priority level.
*
* For example, if thread A has two mutexes contributing to the raising of its
* priority level, the second mutex M2 must be acquired by thread A after
* thread A's priority level was bumped due to owning the first mutex M1.
* When releasing the mutex, thread A must release M2 before it releases M1.
* Failure to follow this nested model may result in threads running at
* unexpected priority levels (too high, or too low).
*/
#include <kernel.h>
#include <kernel_structs.h>
#include <toolchain.h>
#include <sections.h>
#include <wait_q.h>
#include <misc/dlist.h>
#include <debug/object_tracing_common.h>
#include <errno.h>
#include <init.h>
#ifdef CONFIG_OBJECT_MONITOR
#define RECORD_STATE_CHANGE(mutex) \
do { (mutex)->num_lock_state_changes++; } while ((0))
#define RECORD_CONFLICT(mutex) \
do { (mutex)->num_conflicts++; } while ((0))
#else
#define RECORD_STATE_CHANGE(mutex) do { } while ((0))
#define RECORD_CONFLICT(mutex) do { } while ((0))
#endif
#ifdef CONFIG_OBJECT_MONITOR
#define INIT_OBJECT_MONITOR(mutex) do { \
mutex->num_lock_state_changes = 0; \
mutex->num_conflicts = 0; \
} while ((0))
#else
#define INIT_OBJECT_MONITOR(mutex) do { } while ((0))
#endif
extern struct k_mutex _k_mutex_list_start[];
extern struct k_mutex _k_mutex_list_end[];
struct k_mutex *_trace_list_k_mutex;
#ifdef CONFIG_OBJECT_TRACING
/*
* Complete initialization of statically defined mutexes.
*/
static int init_mutex_module(struct device *dev)
{
ARG_UNUSED(dev);
struct k_mutex *mutex;
for (mutex = _k_mutex_list_start; mutex < _k_mutex_list_end; mutex++) {
SYS_TRACING_OBJ_INIT(k_mutex, mutex);
}
return 0;
}
SYS_INIT(init_mutex_module, PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_OBJECTS);
#endif /* CONFIG_OBJECT_TRACING */
void k_mutex_init(struct k_mutex *mutex)
{
mutex->owner = NULL;
mutex->lock_count = 0;
/* initialized upon first use */
/* mutex->owner_orig_prio = 0; */
sys_dlist_init(&mutex->wait_q);
SYS_TRACING_OBJ_INIT(k_mutex, mutex);
INIT_OBJECT_MONITOR(mutex);
}
static int new_prio_for_inheritance(int target, int limit)
{
int new_prio = _is_prio_higher(target, limit) ? target : limit;
new_prio = _get_new_prio_with_ceiling(new_prio);
return new_prio;
}
static void adjust_owner_prio(struct k_mutex *mutex, int new_prio)
{
if (mutex->owner->base.prio != new_prio) {
K_DEBUG("%p (ready (y/n): %c) prio changed to %d (was %d)\n",
mutex->owner, _is_thread_ready(mutex->owner) ?
'y' : 'n',
new_prio, mutex->owner->base.prio);
_thread_priority_set(mutex->owner, new_prio);
}
}
int k_mutex_lock(struct k_mutex *mutex, int32_t timeout)
{
int new_prio, key;
_sched_lock();
if (likely(mutex->lock_count == 0 || mutex->owner == _current)) {
RECORD_STATE_CHANGE();
mutex->owner_orig_prio = mutex->lock_count == 0 ?
_current->base.prio :
mutex->owner_orig_prio;
mutex->lock_count++;
mutex->owner = _current;
K_DEBUG("%p took mutex %p, count: %d, orig prio: %d\n",
_current, mutex, mutex->lock_count,
mutex->owner_orig_prio);
k_sched_unlock();
return 0;
}
RECORD_CONFLICT();
if (unlikely(timeout == K_NO_WAIT)) {
k_sched_unlock();
return -EBUSY;
}
#if 0
if (_is_prio_higher(_current->prio, mutex->owner->prio)) {
new_prio = _current->prio;
}
new_prio = _get_new_prio_with_ceiling(new_prio);
#endif
new_prio = new_prio_for_inheritance(_current->base.prio,
mutex->owner->base.prio);
key = irq_lock();
K_DEBUG("adjusting prio up on mutex %p\n", mutex);
adjust_owner_prio(mutex, new_prio);
_pend_current_thread(&mutex->wait_q, timeout);
int got_mutex = _Swap(key);
K_DEBUG("on mutex %p got_mutex value: %d\n", mutex, got_mutex);
K_DEBUG("%p got mutex %p (y/n): %c\n", _current, mutex,
got_mutex ? 'y' : 'n');
if (got_mutex == 0) {
k_sched_unlock();
return 0;
}
/* timed out */
K_DEBUG("%p timeout on mutex %p\n", _current, mutex);
struct k_thread *waiter =
(struct k_thread *)sys_dlist_peek_head(&mutex->wait_q);
new_prio = mutex->owner_orig_prio;
new_prio = waiter ? new_prio_for_inheritance(waiter->base.prio,
new_prio) : new_prio;
K_DEBUG("adjusting prio down on mutex %p\n", mutex);
key = irq_lock();
adjust_owner_prio(mutex, new_prio);
irq_unlock(key);
k_sched_unlock();
return -EAGAIN;
}
void k_mutex_unlock(struct k_mutex *mutex)
{
int key;
__ASSERT(mutex->lock_count > 0, "");
__ASSERT(mutex->owner == _current, "");
_sched_lock();
RECORD_STATE_CHANGE();
mutex->lock_count--;
K_DEBUG("mutex %p lock_count: %d\n", mutex, mutex->lock_count);
if (mutex->lock_count != 0) {
k_sched_unlock();
return;
}
key = irq_lock();
adjust_owner_prio(mutex, mutex->owner_orig_prio);
struct k_thread *new_owner = _unpend_first_thread(&mutex->wait_q);
K_DEBUG("new owner of mutex %p: %p (prio: %d)\n",
mutex, new_owner, new_owner ? new_owner->base.prio : -1000);
if (new_owner) {
_abort_thread_timeout(new_owner);
_ready_thread(new_owner);
irq_unlock(key);
_set_thread_return_value(new_owner, 0);
/*
* new owner is already of higher or equal prio than first
* waiter since the wait queue is priority-based: no need to
* ajust its priority
*/
mutex->owner = new_owner;
mutex->lock_count++;
mutex->owner_orig_prio = new_owner->base.prio;
} else {
irq_unlock(key);
mutex->owner = NULL;
}
k_sched_unlock();
}