sysctl -a hangs system after r240281

I'm running 10-CURRENT amd64 on a Dell M6500:

FreeBSD m6500.local 10.0-CURRENT FreeBSD 10.0-CURRENT #22 r240281M:
Fri Sep 14 21:18:50 CDT 2012
root_at_m6500.local:/usr/obj/usr/src/sys/DELL_M6500  amd64

I ran into a strange issue when running `sysctl -a` in which my system
would "freeze" -- the only interaction with the system which was
registered was a press of the power button (which wouldn't actually
initialize a shutdown). This is a big problem when
/etc/rc.d/initrandom calls `sysctl -a` during system startup...

I traced this behavior back to commit r240281 which added support for
USB Dual Mode Drivers:

http://svnweb.freebsd.org/base/head/sys/dev/usb/controller/usb_controller.c?r1=240281&r2=240280&pathrev=240281

At r240280, my system boots fine and I can run `sysctl -a` at will
with no bad behavior.

I haven't dug deeply into this issue, so this e-mail is more of a
heads-up report in case anyone else runs into this issue. I'll add
more debugging in my kernel config and capture the information from
dmesg and others before and after the r240281 commit.

Of course, any hints are appreciated as I delve into this.