From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: linux-next: PowerPC WARN_ON_ONCE() after merge of the final
 tree (tip related)
Date: Fri, 16 Apr 2010 12:38:43 +0200
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To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, Stephen Rothwell <sfr@canb.auug.org.au>, Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>, linux-next@vger.kernel.org, linux-kernel@vger.kernel.org, ppc-dev <linuxppc-dev@lists.ozlabs.org>

On Thu, 2010-04-15 at 19:15 +0200, Frederic Weisbecker wrote:
> > 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.


How so, its a pure per-cpu variable right? so either the increment
happens before the interrupts hits, or after, in either case there
should not be a race with interrupts.