[arch-general] Keyboard and mouse not working in X

[pants]

Last night, I updated my system with everything from the past week or
so.  Everything went smoothly.  Today, however, I discovered that upon
launching X, using, for instance,
> xinit /usr/bin/xterm
my computer stops responding to my USB keyboard and mouse.  I can't even
switch back to the console using CTRL-ALT-FN.  If I SIGTERM the process
from ssh, X closes normally and my keyboard resumes function in the
console.  I've checked, and none of the files in /etc/X11 were modified
anytime recently.

Any advice?

pants.