wait_event_interruptible_locked的使用方法

wait_event_interruptible_locked() interface

New wait_event_interruptible{,_exclusive}_locked{,_irq} macros added.
They work just like versions without _locked* suffix but require the
wait queue's lock to be held.  Also __wake_up_locked() is now exported
as to pair it with the above macros.

The use case of this new facility is when one uses wait queue's lock
to  protect a data structure.  This may be advantageous if the
structure needs to be protected by a spinlock anyway.  In particular,
with additional spinlock the following code has to be used to wait
for a condition:

spin_lock(&data.lock);
...
for (ret = 0; !ret && !(condition); ) {
	spin_unlock(&data.lock);
	ret = wait_event_interruptible(data.wqh, (condition));
	spin_lock(&data.lock);
}
...
spin_unlock(&data.lock);

This looks bizarre plus wait_event_interruptible() locks the wait
queue's lock anyway so there is a unlock+lock sequence where it could
be avoided.

To avoid those problems and benefit from wait queue's lock, a code
similar to the following should be used:

/* Waiting */
spin_lock(&data.wqh.lock);
...
ret = wait_event_interruptible_locked(data.wqh, (condition));
...
spin_unlock(&data.wqh.lock);

/* Waiting exclusively */
spin_lock(&data.whq.lock);
...
ret = wait_event_interruptible_exclusive_locked(data.whq, (condition));
...
spin_unlock(&data.whq.lock);

/* Waking up */
spin_lock(&data.wqh.lock);
...
wake_up_locked(&data.wqh);
...
spin_unlock(&data.wqh.lock);

When spin_lock_irq() is used matching versions of macros need to be
used (*_locked_irq()).  

 看到wait_event_interruptible_locked这个api我内心是迷茫的，不知道这个玩意儿怎么用，搜了下看到了别人的解释如上。

翻译下：

因为自旋锁锁定期间不能进入睡眠，那么进入睡眠前就应该释放自旋锁，如果手动操作会比较繁琐，这个接口就是为了统一一下操作，他操作的时候 wait_queue_head_t自带的自旋锁lock，在进入休眠前释放这个锁，然后睡眠，醒了以后再获取到这个锁，这样就是在睡眠过程中自旋锁是释放的状态。

注意，使用这个函数之前，这个自带的自旋锁应该是先获取到的。