worst-case I will reboot the server with a known-good xen kernel. (I was using 3.4.2-rc; I will downgrade to 3.4.1.)
One way or another, the problem will be solved tonight.
Users who have not shut down are thusfar unaffected. I will try to reboot without interfering much with their operation.
I should have reported this the other night
Update: rebooting branch (2:56 PST on Oct 19th. )
update: branch is up and everything is confirmed good (4:08 PSD on Oct 19th)