xpt related hang on sparc64

Greetings.

I updated my dual-processor V240 the other day:

FreeBSD 12.0-CURRENT #26 r311929: Wed Jan 11 18:52:46 EST 2017
     lidl_at_spork.pix.net:/usr/obj/usr/src/sys/GENERIC sparc64

It works fine.

I update a uniprocessor V120 today, to a slightly newer tree,
and it hangs when attempting to boot the new kernel:

FreeBSD 12.0-CURRENT #27 f72e57262fe(master): Fri Jan 13 17:25:40 EST 2017
     lidl_at_ton.pix.net:/usr/obj/usr/src/sys/V120 sparc64
uhub0: 4 ports with 4 removable, self powered
uhub1: 4 ports with 4 removable, self powered
run_interrupt_driven_hooks: still waiting after 60 seconds for xpt_config
run_interrupt_driven_hooks: still waiting after 120 seconds for xpt_config
run_interrupt_driven_hooks: still waiting after 180 seconds for xpt_config
run_interrupt_driven_hooks: still waiting after 240 seconds for xpt_config
run_interrupt_driven_hooks: still waiting after 300 seconds for xpt_config

GIT hash f72e57262fe == svn r312003

I haven't had a chance to look into this any more deeply...

-Kurt