I don’t think I get this. How can a supervisor guard against the Linux side locking up? What does it do if it notices a problem, and how can whatever it does no

I don’t think I get this. How can a supervisor guard against the Linux side locking up? What does it do if it notices a problem, and how can whatever it does not affect the behavior of the system for periods of time that are noticeable or dangerous while traveling at high speed?