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Date: Thu, 15 Apr 2010 19:39:55 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>,
       Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
       Peter Zijlstra <peterz@infradead.org>, linux-next@vger.kernel.org,
       linux-kernel@vger.kernel.org, ppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: linux-next: PowerPC WARN_ON_ONCE() after merge of the final tree
 (tip related)
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* Frederic Weisbecker <fweisbec@gmail.com> wrote:

> On Thu, Apr 15, 2010 at 04:03:58PM +0200, Ingo Molnar wrote:
> > > 
> > > 
> > > 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?
> 
> 
> There is also no guarantee we are in a non-preemptable section. We can then
> also race against another cpu.
> 
> I'm not sure what to do.

it's a statistics counter so worst-case we lose a count. It's not a real issue 
- but might be worth adding a comment.

	Ingo