To the OP's point about infotainment being okay, I wonder if the core functional components of space flight (RCS, etc), are controlled through linux. It would surprise me if it wasn't used for high level things (displays), but not the "keep the rocket flying on course" stuff. I can't really find anything about what's controlled by that Linux box in the Falcon 9.
Yes they are. iirc, they run a modified kernel that is closer to realtime, and everything is a single thread for determinism. Code runs on a dual core processor, with one copy on each core, to detect bitflips. Three such modules are connected together in most places.
I believe this is the setup they use for the main stabilization computer on each stage, as well as the engine controllers for each engine.
