[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>

1 files changed, 16 insertions, 5 deletions

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);