linux-kernel - Re: [PATCH] percpu: use raw_local_irq_* in _this

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Date:	Tue, 14 Feb 2012 08:19:01 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org, yong.zhang0@...il.com
Subject: Re: [PATCH] percpu: use raw_local_irq_* in _this_cpu op

On Tue, Feb 14, 2012 at 11:30:06AM +0800, Ming Lei wrote:
> On Tue, Feb 14, 2012 at 1:23 AM, Tejun Heo <tj@...nel.org> wrote:
> > On Mon, Feb 13, 2012 at 07:03:38PM +0800, Ming Lei wrote:
> >> It doesn't make sense to trace irq off or do irq flags
> >> lock proving inside 'this_cpu' operations, so replace local_irq_*
> >> with raw_local_irq_* in 'this_cpu' op.
> >>
> >> Also the patch fixes one lockdep warning[1], which is caused
> >> by the added local_irq_save/restore(flags) in this_cpu_inc
> >> called by __debug_atomic_inc: kernel/lockdep.c
> >
> > I think this isn't gonna hurt anything but I don't understand why the
> > lockdep warning is triggering when using traced version.  Can you
> > please explain that in a bit more detail in the patch description?
> 
> In trace_hardirqs_on_caller:kernel/lockdep.c, __debug_atomic_inc
> will be called to add on 'this_cpu' variable, so may introduce recursive
> trace_hardirqs_on|off_caller called.

Ah, okay, so lockdep itself is using this_cpu ops.  Can you please
repost the patch with the above info in the description?

Thank you.

-- 
tejun
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