I believe this is meant to handle the case where a process exits without having called wait() on its children. Imagine two processes, A and B, where A is B's parent and A's parent is some process other than init. B calls exit(), becomes a zombie, and awakens A. Some time later, A calls exit() without ever having called wait(). This will cause B to become a child of init, and as B is a zombie, init should awaken so that B can die. However, A might have any number of zombie children, and it would be redundant to call wakeup(&proc[1]) for each one. Therefore, the wakeup call to init is done up front, whether it is needed or not. This does result in some unnecessary wakeup calls but on the whole it seems a good tradeoff for code simplicity.