sched

Task state and queues

• from run queues to wait queues(two ways):

0. create wait_queue_t with DECLARE_WAITQUEUE().
1. call add_wait_queue()/__add_wait_queue() to add the task to a wait queue
2. set the state of task to TASK_INTERRUPTIBLE
3. call schedule() to switch contexts and schedule() will call deactivate_task() to remove the task from a run queue

• from wait queues to run queues:

1. call try_to_wake_up()