Runaway real-time processes can cause the system to halt. Such runaway processes can also slow the system response so much that the system appears to halt.
If you have a runaway process on a SPARC system, press Stop-A. You might have to do press Stop-A more than one time. If pressing Stop-A does not work, turn the power off, wait a moment, then turn the power back on. If you have a runaway process on a non-SPARC system, turn the power off, wait a moment, then turn the power back on.
When a high priority real-time process does not relinquish control of the CPU, you must break the infinite loop in order to regain control of the system. Such a runaway process does not respond to Control-C. Attempts to use a shell set at a higher priority than the priority of the runaway process do not work.