-current lockup (how to diagnose?)

I got lockups in recent -current box.  This box is my main workstation
and usually be up to date kernel.

In recent days, I usually locked up.  This is not a panic, only locks
up.  My situation is:

o KDE's clock is working.
o KDE's virtual screen switching is working.
o Apache does not reply on 80/tcp from remote.
o ssh from this box is still working.
o zsh on this box does not go next prompt when I press enter key at
  promprt.

It looks kernel is working, but fork/exec is not working when I enter
to this situation.

So, what can I diagnose with this situation?  Of course this box has
serial console.


-- 
Jun Kuriyama <kuriyama_at_imgsrc.co.jp> // IMG SRC, Inc.
             <kuriyama_at_FreeBSD.org> // FreeBSD Project