linux-kernel - Re: [patch 134/149] x86, paravirt: Add a global synchronization point for pvclock

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Date:	Tue, 13 Jul 2010 19:25:26 +0200
From:	Peter Palfrader <peter@...frader.org>
To:	Avi Kivity <avi@...hat.com>
Cc:	Greg KH <gregkh@...e.de>, linux-kernel@...r.kernel.org,
	stable@...nel.org, stable-review@...nel.org,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Glauber Costa <glommer@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: Re: [patch 134/149] x86, paravirt: Add a global synchronization
	point for pvclock

On Tue, 13 Jul 2010, Avi Kivity wrote:

> On 07/13/2010 07:40 PM, Avi Kivity wrote:
>> On 07/13/2010 07:34 PM, Avi Kivity wrote:
>>>
>>> My bet is that dropping 'static' will fix it.  We may have the wrong  
>>> constraints on atomic64_cmpxchg64(), so the compiler thinks we never  
>>> change last_value.
>>>
>>
>> The constraints are there, but maybe the toolchain is confused.
>>
>
> No they aren't, as Linus just pointed out.  His patch should fix the  
> problem.

Linus's patch touches __xchg() whereas we're using __cmpxchg() in this
particular case I think.

At least, applying it to my 2.6.32.16 tree didn't help, last_value was
still read-only.  Or I backported it wrong.
-- 
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