2.6.15-mm4 failure on power5

[Andrew Morton]

Ingo Molnar <mingo at elte.hu> wrote:
>
> 
> * 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?
> 

The bug happens on the G5 too.  There's nothing useful on the screen,
nothing on netconsole.  Could the people whose machines have a fscking
serial port please try CONFIG_DEBUG_MUTEXES?