mtree hanging on upgrade from 10.1-STABLE to 10.2-RELEASE

[Chris Nehren]

Trying to upgrade a 10.1-STABLE (kern.osreldate == 1001517) system to
10.2-RELEASE this morning. buildworld + buildkernel finished without any
issue, but now the installworld is stuck on mtree and has been for a few
hours:

--------------------------------------------------------------
>>> Making hierarchy
--------------------------------------------------------------
cd /usr/src; make -f Makefile.inc1  LOCAL_MTREE= hierarchy
cd /usr/src/etc && PATH=/usr/obj/usr/src/tmp/legacy/usr/sbin:/usr/obj/usr/src/tmp/legacy/usr/bin:/usr/obj/usr/src/tmp/legacy/usr/games:/usr/obj/usr/src/tmp/legacy/bin:/usr/obj/usr/src/tmp/usr/sbin:/usr/obj/usr/src/tmp/usr/bin:/usr/obj/usr/src/tmp/usr/games:/usr/obj/usr/src/tmp/legacy/usr/sbin:/usr/obj/usr/src/tmp/legacy/usr/bin:/usr/obj/usr/src/tmp/legacy/usr/games:/usr/obj/usr/src/tmp/legacy/bin:/usr/obj/usr/src/tmp/usr/sbin:/usr/obj/usr/src/tmp/usr/bin:/usr/obj/usr/src/tmp/usr/games:/tmp/install.b1sHRYLs make LOCAL_MTREE= distrib-dirs
mtree -deU -f /usr/src/etc/mtree/BSD.root.dist -p /

I tried trussing the process, but don't see any output. It's not using
excessive CPU; the machine is actually mostly idle right now. I'm not
sure what else I can look at to figure out what it's doing (or more
accurately, not doing, in this case).

-- 
Thanks,
Chris