Interesting concept: Ksplice: Rebootless Linux kernel security updates. As long a patch doesn´t change data structures in the kernel, ksplice can update a running kernel.

Ksplice allows system administrators to apply security patches to the Linux kernel without having to reboot. Ksplice takes as input a source code change in unified diff format and the kernel source code to be patched, and it applies the patch to the corresponding running kernel. The running kernel does not need to have been prepared in advance in any way.