Re: [PATCH 3/20] powerpc/mm: Add HW threads support to no_hash TLB management

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2009-07-30 at 22:35 -0500, Kumar Gala wrote:
> >               /* XXX This clear should ultimately be part of
> local_flush_tlb_mm */
> > -             __clear_bit(id, stale_map[cpu]);
> > +             for (cpu = cpu_first_thread_in_core(cpu);
> > +                  cpu <= cpu_last_thread_in_core(cpu); cpu++)
> > +                     __clear_bit(id, stale_map[cpu]);
> >       }
> 
> This looks a bit dodgy.  using 'cpu' as both the loop variable and  
> what you are computing to determine loop start/end..
> 
Hrm... I would have thought that it was still correct... do you see any
reason why the above code is wrong ? because if not we may be hitting a
gcc issue...

IE. At loop init, cpu gets clamped down to the first thread in the core,
which should be fine. Then, we compare CPU to the last thread in core
for the current CPU which should always return the same value.

So I'm very interested to know what is actually wrong, ie, either I'm
just missing something obvious, or you are just pushing a bug under the
carpet which could come back and bit us later :-)

Cheers,
Ben.