Interrupt storm
The state in which a source interrupts the processor so often that servicing interrupts is all it ever gets done.
In firmware the usual cause is mundane: a level-triggered interrupt whose flag never gets cleared. The service routine returns, the hardware sees the line still asserted, and jumps straight back in. A floating input without a pull-up achieves the same by picking up noise. The main loop freezes, and with luck it's the watchdog that eventually resets the chip.
On bigger systems it may be a network card drowning in packets — receive livelock, where all the time goes into accepting work that never gets processed. Linux answers with NAPI and IRQ coalescing, and for sources nobody claims, the message "irq N: nobody cared", after which the kernel disables the line. Unusually clear, as kernel error messages go.