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

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Message-ID: <4BCC69D5.3050209@redhat.com>
Date:	Mon, 19 Apr 2010 17:33:57 +0300
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock

On 04/19/2010 05:21 PM, Glauber Costa wrote:
>
>> Oh yes, just trying to avoid a patch with both atomic64_read() and
>> ACCESS_ONCE().
>>      
> you're mixing the private version of the patch you saw with this one.
> there isn't any atomic reads in here. I'll use a barrier then
>    

This patch writes last_value atomically, but reads it non-atomically.  A 
barrier is insufficient.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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