kthread_stop — 
     stop a thread created by kthread_create.
 
| int kthread_stop ( | struct task_struct * k ); | 
   Sets kthread_should_stop for k to return true, wakes it, and
   waits for it to exit. This can also be called after kthread_create
   instead of calling wake_up_process: the thread will exit without
   calling threadfn.
   
   If threadfn may call do_exit itself, the caller must ensure
   task_struct can't go away.
   
   Returns the result of threadfn, or -EINTR if wake_up_process
   was never called.