netdev - Re: [PATCH] x86: fix and improve cmpxchg_double{,

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Date:	Tue, 03 Jan 2012 16:41:30 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jan Beulich <JBeulich@...e.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, hpa@...or.com,
	Christoph Lameter <cl@...ux.com>, linux-kernel@...r.kernel.org,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] x86: fix and improve cmpxchg_double{,_local}()

Le mardi 03 janvier 2012 à 16:15 +0100, Eric Dumazet a écrit :

> Very old it seems...
> 
> arch/x86/lib/atomic64_cx8_32.S
> 
> all "jxx 1b" are wrong if a LOCK_PREFIX is included after the 1: label
> 
> 1:
> 	inst1
> 	LOCK_PREFIX
> 	cmpxchg8b (%ebp)
> 	jne 1b  / jumps to beginning of LOCK_PREFIX, inst1 is not replayed
> 
> 
> 
> 

A possible fix would be to not use "1" label in LOCK_PREFIX macro,
but 672 magic value.

Not sure if we can use a local label in a macro ?

 arch/x86/include/asm/alternative-asm.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/alternative-asm.h b/arch/x86/include/asm/alternative-asm.h
index 091508b..952bd01 100644
--- a/arch/x86/include/asm/alternative-asm.h
+++ b/arch/x86/include/asm/alternative-asm.h
@@ -4,10 +4,10 @@
 
 #ifdef CONFIG_SMP
 	.macro LOCK_PREFIX
-1:	lock
+672:	lock
 	.section .smp_locks,"a"
 	.balign 4
-	.long 1b - .
+	.long 672b - .
 	.previous
 	.endm
 #else


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