linux-kernel - [PATCH] x86 : spinlock use LOCK

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Date:	Fri, 15 Aug 2008 12:56:59 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Jeremy Fitzhardinge <jeremy@...p.org>,
	Harvey Harrison <harvey.harrison@...il.com>,
	Andi Kleen <andi@...stfloor.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Steven Rostedt <srostedt@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Roland McGrath <roland@...hat.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Luis Claudio R. Goncalves" <lclaudio@...g.org>,
	Clark Williams <williams@...hat.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86 : spinlock use LOCK_PREFIX


x86 : spinlock use LOCK_PREFIX

* Linus Torvalds (torvalds@...ux-foundation.org) wrote:
> 
> 
> On Thu, 14 Aug 2008, Mathieu Desnoyers wrote:
> >
> > Changing the 0x90 (single-byte nop) currently used into a 0x3E DS segment
> > override prefix should fix this issue. Since the default of the atomic
> > instructions is to use the DS segment anyway, it should not affect the
> > behavior.
> 
> Ok, so I think this is an _excellent_ patch, but I'd like to also then use 
> LOCK_PREFIX in include/asm-x86/futex.h.
> 
> See commit 9d55b9923a1b7ea8193b8875c57ec940dc2ff027.
> 
>     Linus

Unless there a rationale for this, I think these be changed to LOCK_PREFIX
too.

grep "lock ;" include/asm-x86/spinlock.h
         "lock ; cmpxchgw %w1,%2\n\t"
  asm volatile("lock ; xaddl %0, %1\n"
         "lock ; cmpxchgl %1,%2\n\t"

Applies to 2.6.27-rc2.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
CC: Linus Torvalds <torvalds@...ux-foundation.org>
CC: H. Peter Anvin <hpa@...or.com>
CC: Jeremy Fitzhardinge <jeremy@...p.org>
CC: Roland McGrath <roland@...hat.com>
CC: Ingo Molnar <mingo@...e.hu>
Cc: Steven Rostedt <rostedt@...dmis.org>
CC: Steven Rostedt <srostedt@...hat.com>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: Peter Zijlstra <peterz@...radead.org>
CC: Andrew Morton <akpm@...ux-foundation.org>
CC: David Miller <davem@...emloft.net>
CC: Ulrich Drepper <drepper@...hat.com>
CC: Rusty Russell <rusty@...tcorp.com.au>
CC: Gregory Haskins <ghaskins@...ell.com>
CC: Arnaldo Carvalho de Melo <acme@...hat.com>
CC: "Luis Claudio R. Goncalves" <lclaudio@...g.org>
CC: Clark Williams <williams@...hat.com>
CC: Christoph Lameter <cl@...ux-foundation.org>
CC: Andi Kleen <andi@...stfloor.org>
CC: Harvey Harrison <harvey.harrison@...il.com>

---
 include/asm-x86/spinlock.h |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-2.6-lttng/include/asm-x86/spinlock.h
===================================================================
--- linux-2.6-lttng.orig/include/asm-x86/spinlock.h	2008-08-15 12:51:59.000000000 -0400
+++ linux-2.6-lttng/include/asm-x86/spinlock.h	2008-08-15 12:52:10.000000000 -0400
@@ -97,7 +97,7 @@ static __always_inline int __ticket_spin
 		     "jne 1f\n\t"
 		     "movw %w0,%w1\n\t"
 		     "incb %h1\n\t"
-		     "lock ; cmpxchgw %w1,%2\n\t"
+		     LOCK_PREFIX "cmpxchgw %w1,%2\n\t"
 		     "1:"
 		     "sete %b1\n\t"
 		     "movzbl %b1,%0\n\t"
@@ -135,7 +135,7 @@ static __always_inline void __ticket_spi
 	int inc = 0x00010000;
 	int tmp;
 
-	asm volatile("lock ; xaddl %0, %1\n"
+	asm volatile(LOCK_PREFIX "xaddl %0, %1\n"
 		     "movzwl %w0, %2\n\t"
 		     "shrl $16, %0\n\t"
 		     "1:\t"
@@ -162,7 +162,7 @@ static __always_inline int __ticket_spin
 		     "cmpl %0,%1\n\t"
 		     "jne 1f\n\t"
 		     "addl $0x00010000, %1\n\t"
-		     "lock ; cmpxchgl %1,%2\n\t"
+		     LOCK_PREFIX "cmpxchgl %1,%2\n\t"
 		     "1:"
 		     "sete %b1\n\t"
 		     "movzbl %b1,%0\n\t"
-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
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