USB hang setting ttyflags

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

Randomly, my -current/amd64 laptop hangs at "Setting tty flags".
It seems this is because I have (for a long time now)

ttyU0   "/usr/libexec/getty std.9600"   unknown off local
ttyU3   "/usr/libexec/getty std.9600"   unknown off local

in /etc/ttys. They are there on the off-chance that I have a ulpcom
plugged in at boot or thereafter. There is a built-in

umodem0 at uhub3 port 6 configuration 1 interface 1
umodem0: TOSHIBA F5521gw, rev 2.00/0.00, addr 5, iclass 2/2
umodem0: data interface 2, has CM over data, has break
umodem0: status change notification available
ucom0 at umodem0

It seems that ttyflags get stuck in usbxfer. It remains stuck there
after a ctl-c. Thereafter things like dev_mkdb get stuck in tstile.
The only way out seems to be to reboot and roll the dice again.

Thoughts?

Cheers,

Patrick