(5.4) System hangs during shutdown

[Adam Jensen]

I've been using a KVM switch (USB keyboard and mouse) on a couple of 
machines recently and I noticed that when the Keyboard, Video, and Mouse 
connections are switched away from the OpenBSD machine, a USB disconnect 
is reported (as expected). When switched back, the keyboard and mouse 
are not reconnected (video is displayed, of course). Once the machine is 
in this state, I can continue to work with it through ssh but if the 
machine is "shutdown -hp" or "halt -p" it hangs during the "Syncing 
disks..." stage and stays there indefinitely (or until the power cable 
is pulled). The file-systems are not cleanly unmounted. This behavior 
occurs with an i386 machine and with an amd64 machine.

It seems like it might be a serious issue if the USB software stack is 
preventing a disk sync.