These scenarios are all pretty complex and will be difficult to understand for the user of these APIs. I think the easiest solution (and most comprehensible) is for the user space process that does per cpu operations to get some sort of signal. If its not able to handle that then terminate it. The code makes a basic assumption after all that the process is running on a specific cpu. If this is no longer the case then its better to abort if the process cannot handle moving to a different processor.
