Spontaneous reboot.

Kernel Extensions in backtrace:
         com.apple.filesystems.hfs.kext(366.70.1)[B0B8A05A-CC75-325C-A3DA-76C4F7B6F21A]@0xffffff7f916ce000->0xffffff7f91736fff
            dependency: com.apple.filesystems.hfs.encodings.kext(1)[057A044B-8E0D-3A57-8861-87193496E893]@0xffffff7f916c7000

Hmmmmm.