Reservations for must-succeed memory allocations

Uninterruptible sleeping, and sleeping with sigkill blocked. Doing either one in a syscall means the process won't act on sigkill until it is woken up. I believe when sleeping uninterruptibly, sigkill is ignored. (I'm pretty sure.)

One particularly fun thing in multi-threaded systems I've actually seen: The intended waker is killed and the sleeper is now unwakeable and unkillable.