linux-kernel - [PATCH] x86: fix spin_is

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Message-Id: <4897228E.76E4.0078.0@novell.com>
Date:	Mon, 04 Aug 2008 14:38:54 +0100
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	<mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com>
Cc:	"Nick Piggin" <npiggin@...e.de>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86: fix spin_is_contended()

The masked difference is what needs to be compared against 1, rather
than the difference of masked values (which can be negative).

Signed-off-by: Jan Beulich <jbeulich@...ell.com>
Cc: Nick Piggin <npiggin@...e.de>

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

--- linux-2.6.27-rc1/include/asm-x86/spinlock.h	2008-07-31 17:08:34.000000000 +0200
+++ 2.6.27-rc1-x86-spin-is-contended/include/asm-x86/spinlock.h	2008-08-04 11:09:33.000000000 +0200
@@ -65,7 +65,7 @@ static inline int __ticket_spin_is_conte
 {
 	int tmp = ACCESS_ONCE(lock->slock);
 
-	return (((tmp >> 8) & 0xff) - (tmp & 0xff)) > 1;
+	return (((tmp >> 8) - tmp) & 0xff) > 1;
 }
 
 static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
@@ -127,7 +127,7 @@ static inline int __ticket_spin_is_conte
 {
 	int tmp = ACCESS_ONCE(lock->slock);
 
-	return (((tmp >> 16) & 0xffff) - (tmp & 0xffff)) > 1;
+	return (((tmp >> 16) - tmp) & 0xffff) > 1;
 }
 
 static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)



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