Pkg xen devel - Jul 2012 - Bug#630984: shutdown hangs with xenwatch and reboot being blocked

This is actually a kernel bug not a Xen one but I don't know which
kernel you were running so I won't reassign yet.

In any case please can you make sure you are running the latest kernel.
Also if you can try the Wheezy kernel that would be very useful. I know
that upstream have fixed some deadlocks in the xenbus kernel driver
since Squeeze, there's probably a good chance that this is now fixed.

Ian.