Strange lockup on MP macppcs

Hey folks,

I see some strange regular lockups on MP macppc under load, one way to 
trigger it (not reliably, but often) is to run the rum threxec test,
like:

	cd /usr/tests/lib/librumpclient
	atf-run t_exec | atf-report

Often the test succeeds, but sometimes it hangs and gets the kernel
into a state where apparently no new commands [or only very few before
it totally locks up] can be executed (though the execargs pool is not
exhausted). Next that springs to mind are uarea and uareasys, but both
have no hard limit. Maybe they need growing and trigger a pagedaemon
issue?

Since I can't run a full grown DIAGNOSTIC/DEBUG/LOCKDEBUG kernel I have
a hard time figuring out exact details - anyone happen to have a good
idea?

Martin