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

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Date:	Fri, 22 May 2009 11:59:55 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	"Michael S. Zick" <lkml@...ethan.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [BUG FIX] Make x86_32 uni-processor Atomic ops, Atomic

Ingo Molnar wrote:
> * Michael S. Zick <lkml@...ethan.org> wrote:
> 
>> Found in the bit-rot for 32-bit, x86, Uni-processor builds:
>>
>> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
>> index f6aa18e..3c790ef 100644
>> --- a/arch/x86/include/asm/alternative.h
>> +++ b/arch/x86/include/asm/alternative.h
>> @@ -35,7 +35,7 @@
>>                 "661:\n\tlock; "
>>
>>  #else /* ! CONFIG_SMP */
>> -#define LOCK_PREFIX ""
>> +#define LOCK_PREFIX "\n\tlock; "
>>  #endif
> 
> What is your motivation for this change? At first sight this makes 
> the UP kernel a bit larger and a bit smaller. Are you fixing some 
> real regression/bug here?
> 

That looks very odd indeed.  The whole point of the LOCK_PREFIX macro is
to squelch it on UP (locks that should not be squelched on UP should not
be annotated LOCK_PREFIX.)

	-hpa

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