【内核调度】【休眠进程的唤醒】【wake_up_process】

wake_up_process

一般当队列里面为空的时候，核心调度器（是否是核心调度器还需要后续去confirm）会在已经睡眠的task中通过调用wake_up_process函数将其唤醒，然后选择合适的cpu来运行

/**
 * wake_up_process - Wake up a specific process
 * @p: The process to be woken up.
 *
 * Attempt to wake up the nominated process and move it to the set of runnable
 * processes.
 *
 * Return: 1 if the process was woken up, 0 if it was already running.
 *
 * It may be assumed that this function implies a write memory barrier before
 * changing the task state if and only if any tasks are woken up.
 */
int wake_up_process(struct task_struct *p)
{
    /*wake_up_process直接调用try_to_wake_up函数,并添加三个限定参数*/
	return try_to_wake_up(p, TASK_NORMAL, 0, 1);
}
EXPORT_SYMBOL(wake_up_process);

/* Convenience macros for the sake of wake_up */  
#define TASK_NORMAL     (TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE)  

/**
 * try_to_wake_up - wake up a thread
 * @p: the thread to be awakened
 * @state: the mask of task states that can be woken
 * @wake_flags: wake modifier flags (WF_*)
 * @sibling_count_hint: A hint at the number of threads that are being woken up
 *                      in this event.
 *
 * If (@state & @p->state) @p->state = TASK_RUNNING.
 *
 * If the task was not queued/runnable, also place it back on a runqueue.
 *
 * Atomic against schedule() which would dequeue a task, also see
 * set_current_state().
 *
 * Return: %true if @p->state changes (an actual wakeup was done),
 *	   %false otherwise.
 */
static int
try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags,
	       int sibling_count_hint)
{
	unsigned long flags;
	int cpu, success = 0;

	/*
	 * If we are going to wake up a thread waiting for CONDITION we
	 * need to ensure that CONDITION=1 done by the caller can not be
	 * reordered with p->state check below. This pairs with mb() in
	 * set_curr