Merge branch 'rtnl-rcu'

Pedro Tammela says:

====================
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.

Patch 2 uses the new helper in the rtnl_unregister_* functions.

Originally this change was part of the P4TC series, as it's a recurrent
pattern there, but since it has a use case in mainline we are pushing it
separately.
====================

Signed-off-by: David S. Miller <[email protected]>

Author: davem330

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);

net/core/rtnetlink.c

@@ -342,8 +342,7 @@ int rtnl_unregister(int protocol, int msgtype)
 		return -ENOENT;
 	}
 
-	link = rtnl_dereference(tab[msgindex]);
-	RCU_INIT_POINTER(tab[msgindex], NULL);
+	link = rcu_replace_pointer_rtnl(tab[msgindex], NULL);
 	rtnl_unlock();
 
 	kfree_rcu(link, rcu);
@@ -368,18 +367,13 @@ void rtnl_unregister_all(int protocol)
 	BUG_ON(protocol < 0 || protocol > RTNL_FAMILY_MAX);
 
 	rtnl_lock();
-	tab = rtnl_dereference(rtnl_msg_handlers[protocol]);
+	tab = rcu_replace_pointer_rtnl(rtnl_msg_handlers[protocol], NULL);
 	if (!tab) {
 		rtnl_unlock();
 		return;
 	}
-	RCU_INIT_POINTER(rtnl_msg_handlers[protocol], NULL);
 	for (msgindex = 0; msgindex < RTM_NR_MSGTYPES; msgindex++) {
-		link = rtnl_dereference(tab[msgindex]);
-		if (!link)
-			continue;
-
-		RCU_INIT_POINTER(tab[msgindex], NULL);
+		link = rcu_replace_pointer_rtnl(tab[msgindex], NULL);
 		kfree_rcu(link, rcu);
 	}
 	rtnl_unlock();