#define __wait_event(wq, condition) \
do { \
/*定义新的等待队列节点*/
DEFINE_WAIT(__wait); \
\
for (;;) {/*一个循环的过程，可能导致堵塞*/
/*将添加的节点添加到队列中，并改变进程的运行状态*/ \
prepare_to_wait(&wq, &__wait, TASK_UNINTERRUPTIBLE); \
if (condition)/*如果条件合适了，就跳出当前的循环，也就是等待条件获得*/ \
break; \
/*当前进程放弃CPU，进行调度其他的进程，这时的进程进入睡眠状态
也就是说在schedule中函数就不在继续执行，只有调用wake_up函数唤
醒当前的进程，才会退出schedule函数，然后继续执行下面的函数，也就是继续循环
真正的退出循环，只有当条件满足时，如果条件不满足，调用wake_up函数
仍然不会满足条件，只会再次调度，再次失去CPU，
根据上面的分析可知，只有上面的条件满足了，并调用
wake_up函数才能跳出当前的for循环。
*/
schedule(); \
}
/*完成等待*/ \
finish_wait(&wq, &__wait); \
} while (0)
#define DEFINE_WAIT(name) DEFINE_WAIT_FUNC(name, autoremove_wake_function)
#define DEFINE_WAIT_FUNC(name, function) \
wait_queue_t name = { \
.private = current, \
.func = function, \
.task_list = LIST_HEAD_INIT((name).task_list), \
}
void prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
{
unsigned long flags;
/*改变状态*/
wait->flags &= ~WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&q->lock, flags);
/*如果链表是空，则将当前的这个节点添加进来，这样能避免wait被反复的添加，造成大量的浪费*/
if (list_empty(&wait->task_list))
__add_wait_queue(q, wait);
/*修改当前进程的状态*/
set_current_state(state);
spin_unlock_irqrestore(&q->lock, flags);
}
#define set_current_state(state_value) \
set_mb(current->state, (state_value))
static inline void __add_wait_queue(wait_queue_head_t *head, wait_queue_t *new)
{
/*就是将链表添加进来而已*/
list_add(&new->task_list, &head->task_list);
}
void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
{
unsigned long flags;
wait->flags &= ~WQ_FLAG_EXCLUSIVE;
spin_lock_irqsave(&q->lock, flags);
__add_wait_queue(q, wait);
spin_unlock_irqrestore(&q->lock, flags);
}
void finish_wait(wait_queue_head_t *q, wait_queue_t *wait)
{
unsigned long flags;
/*修改当前进程的状态为TASK_RUNNING,因此可以被执行*/
__set_current_state(TASK_RUNNING);
/*
* We can check for list emptiness outside the lock
* IFF:
* - we use the "careful" check that verifies both
* the next and prev pointers, so that there cannot
* be any half-pending updates in progress on other
* CPU's that we haven't seen yet (and that might
* still change the stack area.
* and
* - all other users take the lock (ie we can only
* have _one_ other CPU that looks at or modifies
* the list).
*/
/*删除链表，实质上就是释放*/
if (!list_empty_careful(&wait->task_list)) {
spin_lock_irqsave(&q->lock, flags);
list_del_init(&wait->task_list);
spin_unlock_irqrestore(&q->lock, flags);
}
}
asmlinkage void __sched schedule(void)
{
struct task_struct *prev, *next;
unsigned long *switch_count;
struct rq *rq;
int cpu;
need_resched:
preempt_disable();
cpu = smp_processor_id();
rq = cpu_rq(cpu);
rcu_note_context_switch(cpu);
prev = rq->curr;
release_kernel_lock(prev);
need_resched_nonpreemptible:
schedule_debug(prev);
if (sched_feat(HRTICK))
hrtick_clear(rq);
raw_spin_lock_irq(&rq->lock);
switch_count = &prev->nivcsw;
if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
if (unlikely(signal_pending_state(prev->state, prev))) {
prev->state = TASK_RUNNING;
} else {
/*
* If a worker is going to sleep, notify and
* ask workqueue whether it wants to wake up a
* task to maintain concurrency. If so, wake
* up the task.
*/
if (prev->flags & PF_WQ_WORKER) {
struct task_struct *to_wakeup;
to_wakeup = wq_worker_sleeping(prev, cpu);
if (to_wakeup)
try_to_wake_up_local(to_wakeup);
}
deactivate_task(rq, prev, DEQUEUE_SLEEP);
}
switch_count = &prev->nvcsw;
}
pre_schedule(rq, prev);
if (unlikely(!rq->nr_running))
idle_balance(cpu, rq);
put_prev_task(rq, prev);
next = pick_next_task(rq);
clear_tsk_need_resched(prev);
rq->skip_clock_update = 0;
if (likely(prev != next)) {
sched_info_switch(prev, next);
perf_event_task_sched_out(prev, next);
rq->nr_switches++;
rq->curr = next;
++*switch_count;
context_switch(rq, prev, next); /* unlocks the rq */
/*
* The context switch have flipped the stack from under us
* and restored the local variables which were saved when
* this task called schedule() in the past. prev == current
* is still correct, but it can be moved to another cpu/rq.
*/
cpu = smp_processor_id();
rq = cpu_rq(cpu);
} else
raw_spin_unlock_irq(&rq->lock);
post_schedule(rq);
if (unlikely(reacquire_kernel_lock(prev)))
goto need_resched_nonpreemptible;
preempt_enable_no_resched();
if (need_resched())
goto need_resched;
}
