Why use SIGKILL? The idea here is that there's a race between us getting a parent death signal and setting it, this just checks is parent died in the mean time and makes sure it's delivered. It's a stretch, but what if parent death signal was something completely benign, like SIGUSR1, and wasn't even meant to kill current process, just notify it about the death of a parent? It should just be `return syscall.Kill(syscall.Getpid(), syscall.Signal(old))` in my opinion.