SMP deadlock during multi-user mode transition after r204866

My build machine (dmesg attached) is a dual CPU, single-core box; my
laptop is a single CPU, single-core box.  I track head on each daily;
while the build machine has been locking up during the transition to
multi-user mode since Tuesday (when I had built CURRENT at r204909;
previous was r204866, on Monday) -- and it boots to single-user mode OK
-- the laptop has not exhibited the problem.

This build machine was deployed fairly recently, and since a GENERIC
kernel had been working OK, I had left it that way (so that's the kernel
config).  I have a more customized config I had used on its predecessor;
I'm pretty sure I had that set up with DDB & assorted other "goodies" to
try to get something useful out of a misbehaviing system, and am willing
to set that up (but probably won't have time for several hours, at
least, as I need to give a presentation at a work meeting).

One of the more peculiar symptoms is that after such a lock-up, I
power-cycle the machine, then boot to single-user mode, at which point I
typically start with 

	fsck -p

However, since Tuesday, that attempt yields:

Enter full pathname of shell or RETURN for /bin/sh: 
# fsck -p
/dev/aacd0s4a: LINK COUNT DIR I=2  OWNER=root MODE=40755
/dev/aacd0s4a: SIZE=1024 MTIME=Mar 11 08:30 2010  COUNT 26 SHOULD BE 27
/dev/aacd0s4a: LINK COUNT INCREASING
/dev/aacd0s4a: UNEXPECTED SOFT UPDATE INCONSISTENCY; RUN fsck MANUALLY.
# 

My circumvention of choice at the moment is:

# fsck -y / && fsck -p

as it appears that the root file system is the only one thus affected.

Is this sufficently well understood already that I should stop
disturbing folks who are trying to fix it?  Would it be usful for me to
configure a kernel that supports DDB & provide a backtrace (and maybe
additional stuff)?

To clarify, it appears that something after r204866 but no later than
r204909 has caused the observed problem.

Thanks.

Peace,
david
-- 
David H. Wolfskill				david_at_catwhisker.org
Depriving a girl or boy of an opportunity for education is evil.

See http://www.catwhisker.org/~david/publickey.gpg for my public key.