hard lockup, RELENG_5 from tueday 14.9 on true SMP box

Hi,
yesterday I updated to a recent RELENG_5, build a GENERIC with ALTQ 
options and ALTQ_NOPPC.
the system panics several times a day or even worst several times an hour.
As this is a semi-productive system i had to switch the kernel back to 
CURRENT from late in july.
I never saw a message like kernel panic nor did the system automatically 
reboot. It just hung, and nothing happens.
I hope Julians recent threadfix will avoid this problem, when is MFC 
date? tomorrow?

by the way i have no problems with beta4 on singleprocessor boxes.

regards,
-Dennis