2.6.15-mm4 failure on power5

[Ingo Molnar]

* Andrew Morton <akpm at osdl.org> wrote:

> > If I revert just that patch, mm4 boots fine.  Its really not obvious to
> > me at all why that patch is breaking things though...
> 
> Yes, that is strange.  I do recall that if something accidentally 
> enables interrupts too early in boot, ppc64 machines tend to go 
> comatose.  But if we'd been running that code under 
> local_irq_disable(), down() would have spat a warning.

perhaps it was just luck it worked so far, and the bug could have had 
worse incarnations that the current clear hang if a certain generic 
codepath is touched in a perfectly valid way. Does CONFIG_DEBUG_MUTEXES 
(or any of the other debugging options) make any noise?

	Ingo