Question

(short answer question)

How does an OS regain control if a process enters an infinite loop?

Answer 1

There are many ideas to regain control if a process enters an infinite loop for different OS. But, as you didn't mention, I will mention about the most common and oldest techniquie used for regaining control from an infinite loop :-

1) Interrupt Mode (Normal Case) :- It is normal case when OS is in infinite loop and if we kept OS in interrupt mode then whenever an interrupt is occurred or any event is occured then interrupt is raised. And, the control will go to interrupt handler and we can control through there.

2) WatchDog Timer (Fault protection case ) :- To prevent fault case and minimize the damange; this method is used. Normally, watchdog timer is started and periodically the timer is reset to starting value of the timer so that it won't get expired. So, when a OS process enters infinite loop ; the watchdog timer won't be able to reset and it will expire. On expiring; watchdog timer will reset the OS and control is regained again.