struct softirq_action
{
	void	(*action)(struct softirq_action *);
};

static struct softirq_action softirq_vec[NR_SOFTIRQS] __cacheline_aligned_in_smp;

asmlinkage void __do_softirq(void)
{
	struct softirq_action *h;
	__u32 pending;
	int max_restart = MAX_SOFTIRQ_RESTART;
	int cpu;

	pending = local_softirq_pending();
	account_system_vtime(current);

	__local_bh_disable((unsigned long)__builtin_return_address(0),
				SOFTIRQ_OFFSET);
	lockdep_softirq_enter();

	cpu = smp_processor_id();
restart:
	/* Reset the pending bitmask before enabling irqs */
	set_softirq_pending(0);

	local_irq_enable();

	h = softirq_vec;

	do {
		if (pending & 1) {
			unsigned int vec_nr = h - softirq_vec;
			int prev_count = preempt_count();

			kstat_incr_softirqs_this_cpu(vec_nr);

			trace_softirq_entry(vec_nr);
			h->action(h);
			trace_softirq_exit(vec_nr);
			if (unlikely(prev_count != preempt_count())) {
				printk(KERN_ERR "huh, entered softirq %u %s %p"
				       "with preempt_count %08x,"
				       " exited with %08x?\n", vec_nr,
				       softirq_to_name[vec_nr], h->action,
				       prev_count, preempt_count());
				preempt_count() = prev_count;
			}

			rcu_bh_qs(cpu);
		}
		h++;
		pending >>= 1;
	} while (pending);

	local_irq_disable();

	pending = local_softirq_pending();
	if (pending && --max_restart)
		goto restart;

	if (pending)
		wakeup_softirqd();

	lockdep_softirq_exit();

	account_system_vtime(current);
	__local_bh_enable(SOFTIRQ_OFFSET);
}

struct tasklet_struct
{
	struct tasklet_struct *next;
	unsigned long state;
	atomic_t count;             /* 引用计数 */
	void (*func)(unsigned long);
	unsigned long data;         /* 参数 */
};

// tasklet_schedule
static inline void tasklet_schedule(struct tasklet_struct *t)
{
	if (!test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
		__tasklet_schedule(t);
}

...

void __tasklet_schedule(struct tasklet_struct *t)
{
	unsigned long flags;

	local_irq_save(flags); // 保存中断状态
	t->next = NULL;
	*__this_cpu_read(tasklet_vec.tail) = t;
	__this_cpu_write(tasklet_vec.tail, &(t->next)); // 添加到每一个处理器中 tasklet_vec 中
	raise_softirq_irqoff(TASKLET_SOFTIRQ);          // 唤起 TASKLET_SOFTIRQ, 下次调用 do_softirq 时会执行该 tasklet
	local_irq_restore(flags); // 恢复中断状态
}

// tasklet_hi_schedule
static inline void tasklet_hi_schedule(struct tasklet_struct *t)
{
	if (!test_and_set_bit(TASKLET_STATE_SCHED, &t->state))
		__tasklet_hi_schedule(t);
}

...

void __tasklet_hi_schedule(struct tasklet_struct *t)
{
	unsigned long flags;

	local_irq_save(flags);
	t->next = NULL;
	*__this_cpu_read(tasklet_hi_vec.tail) = t;
	__this_cpu_write(tasklet_hi_vec.tail,  &(t->next));
	raise_softirq_irqoff(HI_SOFTIRQ);
	local_irq_restore(flags);
}

static void tasklet_action(struct softirq_action *a)
{
	struct tasklet_struct *list;

	local_irq_disable(); // 禁止中断
	list = __this_cpu_read(tasklet_vec.head); // 检索当前 cpu 的 tasklet_vec
	__this_cpu_write(tasklet_vec.head, NULL); // 检索保存后将 tasklet_vec 置 NULL
	__this_cpu_write(tasklet_vec.tail, &__get_cpu_var(tasklet_vec).head);
	local_irq_enable(); // 允许中断响应

	while (list) {
		struct tasklet_struct *t = list;

		list = list->next;

		if (tasklet_trylock(t)) {
			if (!atomic_read(&t->count)) { // 检查 count 是否为 0,确保没有被禁止。如果是多处理器，在这之前还需检查 TASKLET_STATE_RUN
				if (!test_and_clear_bit(TASKLET_STATE_SCHED, &t->state))
					BUG();
				t->func(t->data);
				tasklet_unlock(t);
				continue;
			}
			tasklet_unlock(t);
		}

		local_irq_disable();
		t->next = NULL;
		*__this_cpu_read(tasklet_vec.tail) = t;
		__this_cpu_write(tasklet_vec.tail, &(t->next));
		__raise_softirq_irqoff(TASKLET_SOFTIRQ);
		local_irq_enable();
	}
}

// tasklet_hi_action 类似， 不再重复

/*
 * 外部可见的工作队列抽象是由每个工作队列组成的数组
 */
struct workqueue_struct {
	unsigned int		flags;		/* I: WQ_* flags */
	union {
		struct cpu_workqueue_struct __percpu	*pcpu;
		struct cpu_workqueue_struct		*single;
		unsigned long				v;
	} cpu_wq;				/* I: cwq's */
	struct list_head	list;		/* W: list of all workqueues */

	struct mutex		flush_mutex;	/* protects wq flushing */
	int			work_color;	/* F: current work color */
	int			flush_color;	/* F: current flush color */
	atomic_t		nr_cwqs_to_flush; /* flush in progress */
	struct wq_flusher	*first_flusher;	/* F: first flusher */
	struct list_head	flusher_queue;	/* F: flush waiters */
	struct list_head	flusher_overflow; /* F: flush overflow list */

	mayday_mask_t		mayday_mask;	/* cpus requesting rescue */
	struct worker		*rescuer;	/* I: rescue worker */

	int			saved_max_active; /* W: saved cwq max_active */
	const char		*name;		/* I: workqueue name */
#ifdef CONFIG_LOCKDEP
	struct lockdep_map	lockdep_map;
#endif
};

struct cpu_workqueue_struct {
	struct global_cwq	*gcwq;		/* I: the associated gcwq */
	struct workqueue_struct *wq;		/* I: the owning workqueue */
	int			work_color;	/* L: current color */
	int			flush_color;	/* L: flushing color */
	int			nr_in_flight[WORK_NR_COLORS];
						/* L: nr of in_flight works */
	int			nr_active;	/* L: nr of active works */
	int			max_active;	/* L: max active works */
	struct list_head	delayed_works;	/* L: delayed works */
};

struct work_struct {
	atomic_long_t data;
	struct list_head entry;
	work_func_t func;
#ifdef CONFIG_LOCKDEP
	struct lockdep_map lockdep_map;
#endif
};