linux-kernel - Re: [this_cpu_xx V6 3/7] Use this

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Date:	Tue, 13 Oct 2009 10:41:18 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
cc:	linux-kernel@...r.kernel.org,
	Pekka Enberg <penberg@...helsinki.fi>,
	Mel Gorman <mel@....ul.ie>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [this_cpu_xx V6 3/7] Use this_cpu operations in slub

On Tue, 13 Oct 2009, Tejun Heo wrote:

> The only difference between this_cpu_ptr() and __this_cpu_ptr() is the
> usage of my_cpu_offset and __my_cpu_offset which in turn are only
> different in whether they check preemption status to make sure the cpu
> is pinned down when called.

Correct.

> The only places where the underbar prefixed versions should be used
> are places where cpu locality is nice but not critical and preemption
> debug check wouldn't work properly for whatever reason.  The above is
> none of the two and the conversion is buried in a patch which is
> supposed to do something else.  Am I missing something?

I used __this_cpu_* whenever the context is already providing enough
safety that preempt disable or irq disable would not matter. The use of
__this_cpu_ptr was entirely for consistent usage here. this_cpu_ptr would
be safer because it has additional checks that preemption really is
disabled. So if someone gets confused about logic flow later it can be
dtected.
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