linux-kernel - Re: [PATCH 1/5] Add a global synchronization point for pvclock

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Date:	Mon, 19 Apr 2010 12:39:05 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Glauber Costa <glommer@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, avi@...hat.com,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

On Fri, 2010-04-16 at 13:36 -0700, Jeremy Fitzhardinge wrote:
> > +     do {
> > +             last = last_value;
> >   
> Does this need a barrier() to prevent the compiler from re-reading
> last_value for the subsequent lines?  Otherwise "(ret < last)" and
> "return last" could execute with different values for "last".
> 
ACCESS_ONCE() is your friend.

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