PLEASE TEST: IPI deadlock avoidance patch

[Craig Boston]

On Sun, Aug 22, 2004 at 12:05:39PM -0700, Doug White wrote:
> 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:

Just a follow-up to my off-list message and another data point, with
this patch I no longer get deadlocks, however I now get random data
corruption.

The first time, it managed to complete the installworld and I didn't
notice anything until trying to portupgrade Xorg failed.  It turns out
that the installed ranlib coredumped when run, but the one in /usr/obj
worked fine.

After that I was not able to successfully buildworld again.  Every time
one of the source files would inevitably end up corrupted with blocks of
garbage, even after removing /usr/src entirely and re-cvsupping.

Disabling the second processor or falling back to an older kernel (one
from before the IPI hangs started) both fix the problem.

Craig