linux-kernel - Re: [RFC][PATCH 4/5] printk: Have wake_up_klogd() use __this_cpu

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Date:	Tue, 20 Sep 2011 16:55:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Christoph Lameter <cl@...two.org>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC][PATCH 4/5] printk: Have wake_up_klogd() use
 __this_cpu_write()

On Tue, 2011-09-20 at 09:54 -0500, Christoph Lameter wrote:
> On Mon, 19 Sep 2011, Steven Rostedt wrote:
> 
> > Note, just because something is always in a location that preemption is
> > disabled, does not mean it should use the __this_cpu*() variants.
> 
> Why not? If preemption is disabled then the process cannot be migrated to
> another processor. And thus doing the address calculations and operations
> on variables step by step is okay.
> 
> > Because if things change, it may become a problem later on.
> 
> What things may change? Someone calls the function with preemption
> enabled? 

Yes, also, for !x86 you get a redundant preempt_disable/enable pair.


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