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Date:	Wed, 2 Jul 2008 10:59:56 +0100
From:	Thiemo Seufer <ths@networkno.de>
To:	Morten Larsen <mlarsen@broadcom.com>
Cc:	linux-mips@linux-mips.org
Subject: Re: Bug in atomic_sub_if_positive
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Morten Larsen wrote:
> 
> > As far as I can tell the branch optimization fixes in 2.6.21 introduced
> > a bug in atomic_sub_if_positive that causes it to return even when the
> > sc instruction fails. The result is that e.g. down_trylock becomes
> > unreliable as the semaphore counter is not always decremented.
> 
> Previous patch was garbled by Outlook - this one should be clean:
> 
> --- a/include/asm-mips/atomic.h	2008-06-25 22:38:43.159739000 -0700
> +++ b/include/asm-mips/atomic.h	2008-06-25 22:39:07.552065000 -0700
> @@ -292,10 +292,10 @@ static __inline__ int atomic_sub_if_posi
>  		"	beqz	%0, 2f					\n"
>  		"	 subu	%0, %1, %3				\n"
>  		"	.set	reorder					\n"
> -		"1:							\n"
>  		"	.subsection 2					\n"
>  		"2:	b	1b					\n"
>  		"	.previous					\n"
> +		"1:							\n"

AFAICS this change should make no difference to the generated code. I
suspect you assembler handles .subsection incorrectly. Can you provide
a disassembled exapmle which gets altered by this patch? Also, please
tell us the exact version of the assembler you use.


Thiemo