PLEASE TEST: IPI deadlock avoidance patch

[Pawel Worach]

Doug White wrote:
> Hey folks,
> 
> If you have a reasonably fast i386 or amd64 multiprocessor and/or
> hyperthreading machine and are experiencing reproducible hangs during -j
> buildwords and other highly parallel operations, please try this patch:
> 
> http://people.freebsd.org/~dwhite/smp_rv_mtx.patch
> 

Worked like a charm, Four way Xeon box with a -j256 buildstone using 
SCHED_ULE. Thanks for tracking this down!

-- 
Pawel