struct rcu_head {
	struct rcu_head *next;
	void (*func)(struct rcu_head *head);
};

struct rcu_synchronize {
	struct rcu_head head;
	struct completion completion;
};

struct completion {
	unsigned int done;
	wait_queue_head_t wait;
};

struct __wait_queue_head {
	spinlock_t lock;
	struct list_head task_list;
};
typedef struct __wait_queue_head wait_queue_head_t;

static inline void rcu_read_lock(void) {
    // 禁止抢占
//	__rcu_read_lock();
    preempt_disable();
    
//	__acquire(RCU);
//	rcu_read_acquire();
}

static inline void rcu_read_unlock(void) {
//	rcu_read_release();
//	__release(RCU);
//	__rcu_read_unlock();
    // 开启抢占
    preempt_enable();
}

static inline void synchronize_rcu(void) {
//	synchronize_sched();
    struct rcu_synchronize rcu;

//	if (rcu_blocking_is_gp())
//	if (num_online_cpus() == 1)
    if (cpumask_weight(cpu_online_mask) == 1)
		return;

	init_rcu_head_on_stack(&rcu.head);
	init_completion(&rcu.completion);
	/* Will wake me after RCU finished. */
	call_rcu_sched(&rcu.head, wakeme_after_rcu);
	/* Wait for it. */
	wait_for_completion(&rcu.completion);
	destroy_rcu_head_on_stack(&rcu.head);
}