gre: Simplify gre protocol registration locking.

Use cmpxchg() for atomic protocol registration which saves
code and data space.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 27 deletions

diff --git a/net/ipv4/gre.c b/net/ipv4/gre.c
index b2e805af9b87..1e294d510ac3 100644
--- a/net/ipv4/gre.c
+++ b/net/ipv4/gre.c
@@ -26,46 +26,32 @@
 
 
 static const struct gre_protocol __rcu *gre_proto[GREPROTO_MAX] __read_mostly;
-static DEFINE_SPINLOCK(gre_proto_lock);
 
 int gre_add_protocol(const struct gre_protocol *proto, u8 version)
 {
         if (version >= GREPROTO_MAX)
-                goto err_out;
-
-        spin_lock(&gre_proto_lock);
-        if (gre_proto[version])
-                goto err_out_unlock;
-
-        RCU_INIT_POINTER(gre_proto[version], proto);
-        spin_unlock(&gre_proto_lock);
-        return 0;
+                return -EINVAL;
 
-err_out_unlock:
-        spin_unlock(&gre_proto_lock);
-err_out:
-        return -1;
+        return (cmpxchg((const struct gre_protocol **)&gre_proto[version], NULL, proto) == NULL) ?
+                0 : -EBUSY;
 }
 EXPORT_SYMBOL_GPL(gre_add_protocol);
 
 int gre_del_protocol(const struct gre_protocol *proto, u8 version)
 {
+        int ret;
+
         if (version >= GREPROTO_MAX)
-                goto err_out;
-
-        spin_lock(&gre_proto_lock);
-        if (rcu_dereference_protected(gre_proto[version],
-                        lockdep_is_held(&gre_proto_lock)) != proto)
-                goto err_out_unlock;
-        RCU_INIT_POINTER(gre_proto[version], NULL);
-        spin_unlock(&gre_proto_lock);
+                return -EINVAL;
+
+        ret = (cmpxchg((const struct gre_protocol **)&gre_proto[version], proto, NULL) == proto) ?
+                0 : -EBUSY;
+
+        if (ret)
+                return ret;
+
         synchronize_rcu();
         return 0;
-
-err_out_unlock:
-        spin_unlock(&gre_proto_lock);
-err_out:
-        return -1;
 }
 EXPORT_SYMBOL_GPL(gre_del_protocol);