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

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Date:	Wed, 14 Jul 2010 00:53:46 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Peter Palfrader <peter@...frader.org>
Cc:	Avi Kivity <avi@...hat.com>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Zachary Amsden <zamsden@...hat.com>, akpm@...ux-foundation.org,
	Glauber Costa <glommer@...hat.com>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, stable-review@...nel.org,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...nel.org, alan@...rguk.ukuu.org.uk,
	H Peter Anvin <hpa@...or.com>
Subject: Re: [Stable-review] [patch 134/149] x86, paravirt: Add a global
 synchronization	point for pvclock

On Tue, 2010-07-13 at 20:25 +0200, Peter Palfrader wrote:
> On Tue, 13 Jul 2010, Avi Kivity wrote:
> 
> > Well, current upstream uses "m":
> >
> >>         case 8:                                                         \
> >>                 asm volatile(lock "cmpxchgq %1,%2"                      \
> >>                              : "=a"(__ret)                              \
> >>                              : "r"(__new), "m"(*__xg(ptr)), "0"(__old)  \
> >>                              : "memory");                               \
> >>                 break;                                                  \
> >
> > and works; I also failed to reproduce with 2.6.32.16.  So I expect some  
> > toolchain involvement.
> >
> > Peter, what gcc are you using?
> 
> gcc (Debian 4.3.2-1.1) 4.3.2

The experimental Debian packages of 2.6.35-rc5 are built with gcc 4.4
and they don't have this bug - last_value is marked as 'b' in
System.map, which I assume means BSS.  So this may be specific to gcc
4.3.

Ben.

-- 
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.





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