Does this work for multiprocessors?

void blocking_lock(mutex_t *mut) {
  spin_lock(mut->spinlock);
  if (mut->holder != 0)
    enqueue(mut->wait_queue,
       CurrentThread);
    spin_unlock(mut->spinlock);
    thread_switch();
  } else {
    mut->holder = CurrentThread;
    spin_unlock(mut->spinlock);
  }
}
void blocking_unlock(mutex_t *mut) {
  spin_lock(mut->spinlock);
  if (queue_empty(
     mut->wait_queue)) {
    mut->holder = 0;
  else {
    mut->holder =
     dequeue(mut->wait_queue);
    enqueue(RunQueue,
     mut->holder);
  }
  spin_unlock(mut->spinlock);
}
   

Suppose

• Mutex locked, but its wait queue is empty
• Holder is unlocking it
• Another thread is trying to lock it.