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SubjectRe: linux-next: PowerPC WARN_ON_ONCE() after merge of the final tree (tip related)
On Thu, Apr 15, 2010 at 04:03:58PM +0200, Ingo Molnar wrote:
> > In this case, I guess the following fix should be sufficient?
> > I'm going to test it and provide a sane changelog.
> >
> >
> > diff --git a/kernel/lockdep.c b/kernel/lockdep.c
> > index 78325f8..65d4336 100644
> > --- a/kernel/lockdep.c
> > +++ b/kernel/lockdep.c
> > @@ -2298,7 +2298,11 @@ void trace_hardirqs_on_caller(unsigned long ip)
> > return;
> >
> > if (unlikely(curr->hardirqs_enabled)) {
> > + unsigned long flags;
> > +
> > + raw_local_irq_save(flags);
> > debug_atomic_inc(redundant_hardirqs_on);
> > + raw_local_irq_restore(flags);
> > return;
> > }
> > /* we'll do an OFF -> ON transition: */
>
> that looks rather ugly. Why not do a raw:
>
> this_cpu_inc(lockdep_stats.redundant_hardirqs_on);
>
> which basically open-codes debug_atomic_inc(), but without the warning?


Because that would open a race against interrupts that might
touch lockdep_stats.redundant_hardirqs_on too.

If you think it's not very important (this race must be pretty rare I guess),
I can use your solution.



>
> Btw., using the this_cpu() methods might result in faster code for all the
> debug_atomic_inc() macros as well?


Indeed, will change that too.

Thanks.



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