blob: 5590e8f1871f5cd8ea1c110066b10d92d3ad7c76 [file] [log] [blame]
/*
* Copyright (c) 2016 Wind River Systems, Inc.
*
* SPDX-License-Identifier: Apache-2.0
*/
/**
* @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 it 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 <linker/sections.h>
#include <wait_q.h>
#include <sys/dlist.h>
#include <debug/object_tracing_common.h>
#include <errno.h>
#include <init.h>
#include <syscall_handler.h>
#include <debug/tracing.h>
/* We use a global spinlock here because some of the synchronization
* is protecting things like owner thread priorities which aren't
* "part of" a single k_mutex. Should move those bits of the API
* under the scheduler lock so we can break this up.
*/
static struct k_spinlock lock;
#ifdef CONFIG_OBJECT_TRACING
struct k_mutex *_trace_list_k_mutex;
/*
* Complete initialization of statically defined mutexes.
*/
static int init_mutex_module(struct device *dev)
{
ARG_UNUSED(dev);
Z_STRUCT_SECTION_FOREACH(k_mutex, 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 z_impl_k_mutex_init(struct k_mutex *mutex)
{
mutex->owner = NULL;
mutex->lock_count = 0U;
sys_trace_void(SYS_TRACE_ID_MUTEX_INIT);
z_waitq_init(&mutex->wait_q);
SYS_TRACING_OBJ_INIT(k_mutex, mutex);
z_object_init(mutex);
sys_trace_end_call(SYS_TRACE_ID_MUTEX_INIT);
}
#ifdef CONFIG_USERSPACE
Z_SYSCALL_HANDLER(k_mutex_init, mutex)
{
Z_OOPS(Z_SYSCALL_OBJ_INIT(mutex, K_OBJ_MUTEX));
z_impl_k_mutex_init((struct k_mutex *)mutex);
return 0;
}
#endif
static s32_t new_prio_for_inheritance(s32_t target, s32_t limit)
{
int new_prio = z_is_prio_higher(target, limit) ? target : limit;
new_prio = z_get_new_prio_with_ceiling(new_prio);
return new_prio;
}
static bool adjust_owner_prio(struct k_mutex *mutex, s32_t 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, z_is_thread_ready(mutex->owner) ?
'y' : 'n',
new_prio, mutex->owner->base.prio);
return z_set_prio(mutex->owner, new_prio);
}
return false;
}
int z_impl_k_mutex_lock(struct k_mutex *mutex, s32_t timeout)
{
int new_prio;
k_spinlock_key_t key;
bool resched = false;
sys_trace_void(SYS_TRACE_ID_MUTEX_LOCK);
key = k_spin_lock(&lock);
if (likely((mutex->lock_count == 0U) || (mutex->owner == _current))) {
mutex->owner_orig_prio = (mutex->lock_count == 0U) ?
_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_spin_unlock(&lock, key);
sys_trace_end_call(SYS_TRACE_ID_MUTEX_LOCK);
return 0;
}
if (unlikely(timeout == (s32_t)K_NO_WAIT)) {
k_spin_unlock(&lock, key);
sys_trace_end_call(SYS_TRACE_ID_MUTEX_LOCK);
return -EBUSY;
}
new_prio = new_prio_for_inheritance(_current->base.prio,
mutex->owner->base.prio);
K_DEBUG("adjusting prio up on mutex %p\n", mutex);
if (z_is_prio_higher(new_prio, mutex->owner->base.prio)) {
resched = adjust_owner_prio(mutex, new_prio);
}
int got_mutex = z_pend_curr(&lock, key, &mutex->wait_q, timeout);
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) {
sys_trace_end_call(SYS_TRACE_ID_MUTEX_LOCK);
return 0;
}
/* timed out */
K_DEBUG("%p timeout on mutex %p\n", _current, mutex);
key = k_spin_lock(&lock);
struct k_thread *waiter = z_waitq_head(&mutex->wait_q);
new_prio = mutex->owner_orig_prio;
new_prio = (waiter != NULL) ?
new_prio_for_inheritance(waiter->base.prio, new_prio) :
new_prio;
K_DEBUG("adjusting prio down on mutex %p\n", mutex);
resched = adjust_owner_prio(mutex, new_prio) || resched;
if (resched) {
z_reschedule(&lock, key);
} else {
k_spin_unlock(&lock, key);
}
sys_trace_end_call(SYS_TRACE_ID_MUTEX_LOCK);
return -EAGAIN;
}
#ifdef CONFIG_USERSPACE
Z_SYSCALL_HANDLER(k_mutex_lock, mutex, timeout)
{
Z_OOPS(Z_SYSCALL_OBJ(mutex, K_OBJ_MUTEX));
return z_impl_k_mutex_lock((struct k_mutex *)mutex, (s32_t)timeout);
}
#endif
void z_impl_k_mutex_unlock(struct k_mutex *mutex)
{
struct k_thread *new_owner;
__ASSERT(mutex->lock_count > 0U, "");
__ASSERT(mutex->owner == _current, "");
sys_trace_void(SYS_TRACE_ID_MUTEX_UNLOCK);
z_sched_lock();
K_DEBUG("mutex %p lock_count: %d\n", mutex, mutex->lock_count);
if (mutex->lock_count - 1U != 0U) {
mutex->lock_count--;
goto k_mutex_unlock_return;
}
k_spinlock_key_t key = k_spin_lock(&lock);
adjust_owner_prio(mutex, mutex->owner_orig_prio);
new_owner = z_unpend_first_thread(&mutex->wait_q);
mutex->owner = new_owner;
K_DEBUG("new owner of mutex %p: %p (prio: %d)\n",
mutex, new_owner, new_owner ? new_owner->base.prio : -1000);
if (new_owner != NULL) {
z_ready_thread(new_owner);
k_spin_unlock(&lock, key);
z_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_orig_prio = new_owner->base.prio;
} else {
mutex->lock_count = 0U;
k_spin_unlock(&lock, key);
}
k_mutex_unlock_return:
k_sched_unlock();
}
#ifdef CONFIG_USERSPACE
Z_SYSCALL_HANDLER(k_mutex_unlock, mutex)
{
Z_OOPS(Z_SYSCALL_OBJ(mutex, K_OBJ_MUTEX));
Z_OOPS(Z_SYSCALL_VERIFY(((struct k_mutex *)mutex)->lock_count > 0));
Z_OOPS(Z_SYSCALL_VERIFY(((struct k_mutex *)mutex)->owner == _current));
z_impl_k_mutex_unlock((struct k_mutex *)mutex);
return 0;
}
#endif