linux-kernel - Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic

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Message-Id: <200905221453.41895.lkml@morethan.org>
Date:	Fri, 22 May 2009 14:53:39 -0500
From:	"Michael S. Zick" <lkml@...ethan.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic

On Fri May 22 2009, Andi Kleen wrote:
> On Fri, May 22, 2009 at 01:43:27PM -0500, Michael S. Zick wrote:
> > On Fri May 22 2009, you wrote:
> > > "Michael S. Zick" <lkml@...ethan.org> writes:
> > > 
> > > > Found in the bit-rot for 32-bit, x86, Uni-processor builds:
> > > 
> > > Actually uni processor should not use the lock prefix 
> > > because it doesn't need it; the only exception are some special
> > > ops used in para-virtualization which are special cased.
> > > 
> > 
> > Unless you have interrupts enabled, then you have two contexts.
> 
> Interrupts on the local CPU don't interrupt instructions, only
> inbetween.
>

Ref: http://developer.intel.com/Assets/PDF/manual/253666.pdf
Manual page: 3-590  PDF page: 638
Summary: Processors prior to P-4 can take an interrupt between
the read cycle and the write cycle. Which is why opcode 0xF0 exists.

Mike

> -Andi

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