@Moon It is a legendary message, I remember how it first appeared. Typically it means that the kernel fails to talk to firmware. Or at least it used to mean that. IIRC it originally was associated with MCEs that Linux didn't know how to handle. It can also be triggered by a failure of communication between SMP CPUs or cores. Although, I didn't see this is in many years. Linux supported MCE and other such stuff for a long time.