Hm, like MRI machines? Air traffic control systems? Airplane flight navigation? Coal fired power generators? Windmill controls? Yacht stabilizers? Spacecraft control systems? Laser welding robots? High-speed milling machines?
I could go on and on. Linux is used for lots of things like this, and has been for years (something like over 85% of the US power production is controlled directly by Linux machines). A lot of these systems use the real-time patches, and others don't, but to think that Linux isn't being used in these type of situations is wrong.