We just got one of these on the pkgsrc bulk-build machine, which is a
4-core (2 x dual-core Opteron) amd64 machine.  Unfortunately, as one
can see from the traceback below, well, it's a bit hard to get a
traceback.

The kernel is -current as of today, cross-compiled on macppc for various
obscure reasons.  Any ideas what causes this?  I am a bit curious about
Opteron erratum 106: 

http://lists.freebsd.org/pipermail/freebsd-amd64/2005-May/004693.html

WARNING: SPL NOT LOWERED ON SYSCALL 0 0 EXIT 536e08 d 
^MStopped in pid 21631.1 (cat) at netbsd:Xsyscall+0x1dd:  movl
$0,%gs:0x28c(%
ri
^Mp)
^Mdb{1}> trace   ^H ^H^H ^H^H ^H
^MXsyscall() at netbsd:Xsyscall+0x1dd
^Mcpu1: spinout while in debugger

--and it then hangs so hard I can't drop back to DDB.  Next time I will
try to get a core, without the traceback, but I'm not optimistic.

-- 
  Thor Lancelot Simon	                                     tls@rek.tjls.com

  "The inconsistency is startling, though admittedly, if consistency is to
   be abandoned or transcended, there is no problem."	      - Noam Chomsky