linux-kernel - Re: [PATCH 6/6] percpu: Add preemption checks to __this

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Message-ID: <20131017211317.GZ10651@twins.programming.kicks-ass.net>
Date:	Thu, 17 Oct 2013 23:13:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Tejun Heo <tj@...nel.org>, akpm@...uxfoundation.org,
	rostedt@...dmis.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 6/6] percpu: Add preemption checks to __this_cpu ops

On Thu, Oct 17, 2013 at 07:22:12PM +0000, Christoph Lameter wrote:
> On Wed, 16 Oct 2013, Peter Zijlstra wrote:
> > diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
> > index 8729723..95e3532 100644
> > --- a/arch/x86/include/asm/preempt.h
> > +++ b/arch/x86/include/asm/preempt.h
> > @@ -13,12 +13,12 @@ DECLARE_PER_CPU(int, __preempt_count);
> >   */
> >  static __always_inline int preempt_count(void)
> >  {
> > -	return __this_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
> > +	return raw_cpu_read_4(__preempt_count) & ~PREEMPT_NEED_RESCHED;
> >  }
> >
> >  static __always_inline void preempt_count_set(int pc)
> >  {
> > -	__this_cpu_write_4(__preempt_count, pc);
> > +	raw_cpu_write_4(__preempt_count, pc);
> >  }
> 
> Huh? What happened here? Why do we use the __this_cpu_read_4 here?
> This should be just raw_cpu_write()

Header inclusion hell; I could only easily get away with including
asm/percpu.h, so I had to use the _4 stuff.
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