void __lockfunc _raw_spin_lock_nest_lock(raw_spinlock_t *lock,
				     struct lockdep_map *nest_lock)
{
	preempt_disable();
	spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_);
	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
}

void down_read_nested(struct rw_semaphore *sem, int subclass)
{
	might_sleep();
	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);

	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
	rwsem_set_reader_owned(sem);
}

unsigned long __lockfunc _write_lock_irqsave(rwlock_t *lock)
{
	unsigned long flags;

	local_irq_save(flags);
	preempt_disable();
	rwlock_acquire(&lock->dep_map, 0, 0, _RET_IP_);
	LOCK_CONTENDED(lock, _raw_write_trylock, _raw_write_lock);
	return flags;
}

//在单CPU的系统中，进入临界区代码只需要关闭中断就可以了，
//而多CPU的系统中，还需要测试自旋锁的状态
void __lockfunc _spin_lock_irq(spinlock_t *lock)
{
	local_irq_disable();//关闭中断
	//关闭进程抢占，由于中观或系统调用之后，可能会调度其他进程运行
	//(例如当前进程时间片用完，或者有一个拥有更高优先级的进程已经进入了就绪状态)，
	//preempt_disable()关闭调度器的这个功能，从而保证当前进程在执行临界区代码的过程中不会被其他进程干扰
	preempt_disable();
	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
	//其实就是调用_raw_spin_lock()函数。#define LOCK_CONTENDED(_lock, try, lock) lock(_lock)
	LOCK_CONTENDED(lock, _raw_spin_trylock, _raw_spin_lock);
}

void __lockfunc _raw_spin_lock_nested(raw_spinlock_t *lock, int subclass)
{
	preempt_disable();
	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
	LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
}