Man page 9 : __wake_up

__wake_up - wake up threads blocked on a waitqueue.

void __wake_up(wait_queue_head_t *  q , unsigned int  mode , int  nr_exclusive , void *  key );

q
    the waitqueue

mode
    which threads

nr_exclusive
    how many wake-one or wake-many threads to wake up

key
    is directly passed to the wakeup function

It may be assumed that this function implies a write memory barrier before changing the task state if and only if any tasks are woken up.