net: rtnl: introduce rcu_replace_pointer_rtnl

Introduce the rcu_replace_pointer_rtnl helper to lockdep check rtnl lock
rcu replacements, alongside the already existing helpers.

This is a quality of life helper so instead of using:
   rcu_replace_pointer(rp, p, lockdep_rtnl_is_held())
   .. or the open coded..
   rtnl_dereference() / rcu_assign_pointer()
   .. or the lazy check version ..
   rcu_replace_pointer(rp, p, 1)
Use:
   rcu_replace_pointer_rtnl(rp, p)
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Victor Nogueira <victor@mojatatu.com>
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/rtnetlink.h

@@ -79,6 +79,18 @@ static inline bool lockdep_rtnl_is_held(void)
 #define rtnl_dereference(p)					\
 	rcu_dereference_protected(p, lockdep_rtnl_is_held())
 
+/**
+ * rcu_replace_pointer_rtnl - replace an RCU pointer under rtnl_lock, returning
+ * its old value
+ * @rp: RCU pointer, whose value is returned
+ * @p: regular pointer
+ *
+ * Perform a replacement under rtnl_lock, where @rp is an RCU-annotated
+ * pointer. The old value of @rp is returned, and @rp is set to @p
+ */
+#define rcu_replace_pointer_rtnl(rp, p)			\
+	rcu_replace_pointer(rp, p, lockdep_rtnl_is_held())
+
 static inline struct netdev_queue *dev_ingress_queue(struct net_device *dev)
 {
 	return rtnl_dereference(dev->ingress_queue);