Linux in mixed-criticality systems

The SCHED_DEADLINE developers have been pushing forward on a set of WIP patches from Peter Zijlstra to revamp PI to use a bandwidth-server-based approach to PI: https://www.spinics.net/lists/linux-rt-users/msg19573.html

This is good for mixed-criticality systems, because it helps isolates potential side-effects of PI to the threads that share resources. Independent threads are generally isolated from the effects of bandwidth-server-based PI employed by other threads (this is not the case with simple PI). This helps realize the "freedom from interference" requirement of some safety standards (e.g., the automotive ISO-26262 standard).

Folks have used real-time Linux in mission-critical applications. SpaceX has been open about their heavy use of Linux on their rockets: https://lwn.net/Articles/540368/