C++ clear_tsk_need_resched函数代码示例

static struct task_struct *dup_task_struct(struct task_struct *orig)
{
	struct task_struct *tsk;
	struct thread_info *ti;
	int node = tsk_fork_get_node(orig);
	int err;

	tsk = alloc_task_struct_node(node);
	if (!tsk)
		return NULL;

	ti = alloc_thread_info_node(tsk, node);
	if (!ti)
		goto free_tsk;

	err = arch_dup_task_struct(tsk, orig);
	if (err)
		goto free_ti;

	tsk->stack = ti;
#ifdef CONFIG_SECCOMP
	/*
	 * We must handle setting up seccomp filters once we're under
	 * the sighand lock in case orig has changed between now and
	 * then. Until then, filter must be NULL to avoid messing up
	 * the usage counts on the error path calling free_task.
	 */
	tsk->seccomp.filter = NULL;
#endif

	setup_thread_stack(tsk, orig);
	clear_user_return_notifier(tsk);
	clear_tsk_need_resched(tsk);
	set_task_stack_end_magic(tsk);

#ifdef CONFIG_CC_STACKPROTECTOR
	tsk->stack_canary = get_random_int();
#endif

	/*
	 * One for us, one for whoever does the "release_task()" (usually
	 * parent)
	 */
	atomic_set(&tsk->usage, 2);
#ifdef CONFIG_BLK_DEV_IO_TRACE
	tsk->btrace_seq = 0;
#endif
	tsk->splice_pipe = NULL;
	tsk->task_frag.page = NULL;

	account_kernel_stack(ti, 1);

	return tsk;

free_ti:
	free_thread_info(ti);
free_tsk:
	free_task_struct(tsk);
	return NULL;
}

static struct task_struct *dup_task_struct(struct task_struct *orig)
{
	struct task_struct *tsk;
	struct thread_info *ti;
	unsigned long *stackend;
	int node = tsk_fork_get_node(orig);
	int err;

	prepare_to_copy(orig);

	tsk = alloc_task_struct_node(node);
	if (!tsk)
		return NULL;

	ti = alloc_thread_info_node(tsk, node);
	if (!ti) {
		free_task_struct(tsk);
		return NULL;
	}

	err = arch_dup_task_struct(tsk, orig);
	if (err)
		goto out;

	tsk->stack = ti;

	err = prop_local_init_single(&tsk->dirties);
	if (err)
		goto out;

	setup_thread_stack(tsk, orig);
	clear_user_return_notifier(tsk);
	clear_tsk_need_resched(tsk);
	stackend = end_of_stack(tsk);
	*stackend = STACK_END_MAGIC;	/* for overflow detection */

#ifdef CONFIG_CC_STACKPROTECTOR
	tsk->stack_canary = get_random_int();
#endif

	/*
	 * One for us, one for whoever does the "release_task()" (usually
	 * parent)
	 */
	atomic_set(&tsk->usage, 2);
#ifdef CONFIG_BLK_DEV_IO_TRACE
	tsk->btrace_seq = 0;
#endif
	tsk->splice_pipe = NULL;

	account_kernel_stack(ti, 1);

	return tsk;

out:
	free_thread_info(ti);
	free_task_struct(tsk);
	return NULL;
}

int schedule(void)
{
	struct task_struct *next = pick_next_task();
	struct task_struct *prev = current;

	clear_tsk_need_resched(prev);
	switch_to(prev, next, prev);
	if (unlikely(prev->state == TASK_DEAD))
		put_task_struct(prev);

	return 0;
}

/*
 * schedule() is the main scheduler function.
 */
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_sched_qs(cpu);
        prev = rq->curr;
        switch_count = &prev->nivcsw;

        release_kernel_lock(prev);
need_resched_nonpreemptible:

        schedule_debug(prev);

        if (sched_feat(HRTICK))
                hrtick_clear(rq);

        raw_spin_lock_irq(&rq->lock);
        update_rq_clock(rq);
        clear_tsk_need_resched(prev);

	        if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
                if (unlikely(signal_pending_state(prev->state, prev)))
                        prev->state = TASK_RUNNING;
                else
                        deactivate_task(rq, prev, 1);
                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);

        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 */

static struct task_struct *dup_task_struct(struct task_struct *orig)
{
	struct task_struct *tsk;
	struct thread_info *ti;
	unsigned long *stackend;
	int node = tsk_fork_get_node(orig);
	int err;

	prepare_to_copy(orig);

	tsk = alloc_task_struct_node(node);
	if (!tsk)
		return NULL;

	ti = alloc_thread_info_node(tsk, node);
	if (!ti) {
		free_task_struct(tsk);
		return NULL;
	}

	err = arch_dup_task_struct(tsk, orig);
	if (err)
		goto out;

	tsk->stack = ti;

	setup_thread_stack(tsk, orig);
	clear_user_return_notifier(tsk);
	clear_tsk_need_resched(tsk);
	stackend = end_of_stack(tsk);
	*stackend = STACK_END_MAGIC;	

#ifdef CONFIG_CC_STACKPROTECTOR
	tsk->stack_canary = get_random_int();
#endif

	atomic_set(&tsk->usage, 2);
#ifdef CONFIG_BLK_DEV_IO_TRACE
	tsk->btrace_seq = 0;
#endif
	tsk->splice_pipe = NULL;

	account_kernel_stack(ti, 1);

	return tsk;

out:
	free_thread_info(ti);
	free_task_struct(tsk);
	return NULL;
}

static struct task_struct *dup_task_struct(struct task_struct *orig)
{
	struct task_struct *tsk;
	struct thread_info *ti;
	unsigned long *stackend;
	int node = tsk_fork_get_node(orig);
	int err;

	prepare_to_copy(orig);

	tsk = alloc_task_struct_node(node);
	if (!tsk)
		return NULL;

	ti = alloc_thread_info_node(tsk, node);
	if (!ti) {
		free_task_struct(tsk);
		return NULL;
	}

	err = arch_dup_task_struct(tsk, orig);
	if (err)
		goto out;

	tsk->stack = ti;
#ifdef CONFIG_SECCOMP
	/*
	 * We must handle setting up seccomp filters once we're under
	 * the sighand lock in case orig has changed between now and
	 * then. Until then, filter must be NULL to avoid messing up
	 * the usage counts on the error path calling free_task.
	 */
	tsk->seccomp.filter = NULL;
#endif

	setup_thread_stack(tsk, orig);
	clear_user_return_notifier(tsk);
	clear_tsk_need_resched(tsk);
	stackend = end_of_stack(tsk);
	*stackend = STACK_END_MAGIC;	/* for overflow detection */

#ifdef CONFIG_CC_STACKPROTECTOR
	tsk->stack_canary = get_random_int();
#endif

	/*
	 * One for us, one for whoever does the "release_task()" (usually
	 * parent)
	 */
	atomic_set(&tsk->usage, 2);
#ifdef CONFIG_BLK_DEV_IO_TRACE
	tsk->btrace_seq = 0;
#endif
	tsk->splice_pipe = NULL;

	account_kernel_stack(ti, 1);

#ifdef CONFIG_ANDROID_LMK_ADJ_RBTREE
	RB_CLEAR_NODE(&tsk->adj_node);
#endif
	return tsk;

out:
	free_thread_info(ti);
	free_task_struct(tsk);
	return NULL;
}

//.........这里部分代码省略.........
    smp_mb__before_spinlock();
    /*  锁住该队列  */
    raw_spin_lock(&rq->lock);
    lockdep_pin_lock(&rq->lock);

    rq->clock_skip_update <<= 1; /* promote REQ to ACT */

    /*  切换次数记录, 默认认为非主动调度计数(抢占)  */
    switch_count = &prev->nivcsw;
    
    /*
     *  scheduler检查prev的状态state和内核抢占表示
     *  如果prev是不可运行的, 并且在内核态没有被抢占
     *  
     *  此时当前进程不是处于运行态, 并且不是被抢占
     *  此时不能只检查抢占计数
     *  因为可能某个进程(如网卡轮询)直接调用了schedule
     *  如果不判断prev->stat就可能误认为task进程为RUNNING状态
     *  到达这里，有两种可能，一种是主动schedule, 另外一种是被抢占
     *  被抢占有两种情况, 一种是时间片到点, 一种是时间片没到点
     *  时间片到点后, 主要是置当前进程的need_resched标志
     *  接下来在时钟中断结束后, 会preempt_schedule_irq抢占调度
     *  
     *  那么我们正常应该做的是应该将进程prev从就绪队列rq中删除, 
     *  但是如果当前进程prev有非阻塞等待信号, 
     *  并且它的状态是TASK_INTERRUPTIBLE
     *  我们就不应该从就绪队列总删除它 
     *  而是配置其状态为TASK_RUNNING, 并且把他留在rq中

    /*  如果内核态没有被抢占, 并且内核抢占有效
        即是否同时满足以下条件：
        1  该进程处于停止状态
        2  该进程没有在内核态被抢占 */
    if (!preempt && prev->state)
    {

        /*  如果当前进程有非阻塞等待信号，并且它的状态是TASK_INTERRUPTIBLE  */
        if (unlikely(signal_pending_state(prev->state, prev)))
        {
            /*  将当前进程的状态设为：TASK_RUNNING  */
            prev->state = TASK_RUNNING;
        }
        else   /*  否则需要将prev进程从就绪队列中删除*/
        {
            /*  将当前进程从runqueue(运行队列)中删除  */
            deactivate_task(rq, prev, DEQUEUE_SLEEP);

            /*  标识当前进程不在runqueue中  */
            prev->on_rq = 0;

            /*
             * If a worker went to sleep, notify and ask workqueue
             * whether it wants to wake up a task to maintain
             * concurrency.
             */
            if (prev->flags & PF_WQ_WORKER) {
                struct task_struct *to_wakeup;

                to_wakeup = wq_worker_sleeping(prev);
                if (to_wakeup)
                    try_to_wake_up_local(to_wakeup);
            }
        }
        /*  如果不是被抢占的，就累加主动切换次数  */
        switch_count = &prev->nvcsw;
    }

    /*  如果prev进程仍然在就绪队列上没有被删除  */
    if (task_on_rq_queued(prev))
        update_rq_clock(rq);  /*  跟新就绪队列的时钟  */

    /*  挑选一个优先级最高的任务将其排进队列  */
    next = pick_next_task(rq, prev);
    /*  清除pre的TIF_NEED_RESCHED标志  */
    clear_tsk_need_resched(prev);
    /*  清楚内核抢占标识  */
    clear_preempt_need_resched();

    rq->clock_skip_update = 0;

    /*  如果prev和next非同一个进程  */
    if (likely(prev != next))
    {
        rq->nr_switches++;  /*  队列切换次数更新  */
        rq->curr = next;    /*  将next标记为队列的curr进程  */
        ++*switch_count;    /* 进程切换次数更新  */

        trace_sched_switch(preempt, prev, next);

        /*  进程之间上下文切换    */
        rq = context_switch(rq, prev, next); /* unlocks the rq */
    }
    else    /*  如果prev和next为同一进程，则不进行进程切换  */
    {
        lockdep_unpin_lock(&rq->lock);
        raw_spin_unlock_irq(&rq->lock);
    }

    balance_callback(rq);
}

/*
 * schedule() is the main scheduler function.
 */
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;

    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);

            /*
             * If we are going to sleep and we have plugged IO queued, make
             * sure to submit it to avoid deadlocks.
             */
            if (blk_needs_flush_plug(prev)) {
                raw_spin_unlock(&rq->lock);
                blk_schedule_flush_plug(prev);
                raw_spin_lock(&rq->lock);
            }
        }
        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)) {
        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);

    preempt_enable_no_resched();
    if (need_resched())
        goto need_resched;
}