From 4a6dae6d382e9edf3ff440b819e554ed706359bc Mon Sep 17 00:00:00 2001
From: Nick Piggin <nickpiggin@yahoo.com.au>
Date: Sun, 13 Nov 2005 16:07:24 -0800
Subject: [PATCH] atomic: cmpxchg

Introduce an atomic_cmpxchg operation.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
---
 arch/sparc/lib/atomic32.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

(limited to 'arch/sparc')

diff --git a/arch/sparc/lib/atomic32.c b/arch/sparc/lib/atomic32.c
index 2e64e8c3e8e5..be46f6545184 100644
--- a/arch/sparc/lib/atomic32.c
+++ b/arch/sparc/lib/atomic32.c
@@ -37,17 +37,28 @@ int __atomic_add_return(int i, atomic_t *v)
 	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);
 	return ret;
 }
+EXPORT_SYMBOL(__atomic_add_return);
 
-void atomic_set(atomic_t *v, int i)
+int atomic_cmpxchg(atomic_t *v, int old, int new)
 {
+	int ret;
 	unsigned long flags;
-	spin_lock_irqsave(ATOMIC_HASH(v), flags);
 
-	v->counter = i;
+	spin_lock_irqsave(ATOMIC_HASH(v), flags);
+	ret = v->counter;
+	if (likely(ret == old))
+		v->counter = new;
 
 	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);
+	return ret;
 }
 
-EXPORT_SYMBOL(__atomic_add_return);
-EXPORT_SYMBOL(atomic_set);
+void atomic_set(atomic_t *v, int i)
+{
+	unsigned long flags;
 
+	spin_lock_irqsave(ATOMIC_HASH(v), flags);
+	v->counter = i;
+	spin_unlock_irqrestore(ATOMIC_HASH(v), flags);
+}
+EXPORT_SYMBOL(atomic_set);
-- 
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