unkillable qemu: sleeping in devdrn state

With  a fairly recent -current kernel qemu sleeps in "devdrn"
state and is unkillable.  /proc doesn't have qemu's pid entry
but it does show up in a ps listing!  This bug is not 100%
repeatable but close enough.  AFAIK this problem appears only
when kqemu is used with qemu.

This refcounting related problem has been reported for a
number of other devices.  In one such thread (on cvs-all,
Subject: Re: cvs commit: src/sys/kern kern_conf.c) Tai-hwa
Liang has analyzed the problem and suggested a workaround for
a couple of devices.  Rather than mucking with all the device
drivers, I hope a global fix is possible.  Perhaps the
original fix by Tor Egge is not the only way to fix the bug?
I haven't analyzed the problem so likely I am talking through
my hat.

"You are in a maze of twisty little passages, all alike"