A safe SCHED_IDLE implementation

A safe SCHED_IDLE implementation

As discussed, surely it is still possible for a priority inversion to occur if a SCHED_BATCH process holds a shared resource in userspace?

Priority inversion can be simulated by merely taking a resource and never releasing it. So if you can't trust your users not to DOS you with a priority inversion, you shouldn't give them permission to lock those shared resources in the first place.

As for unintentional priority inversion - yes, it's a userspace problem. (: