[IPV4] fib_trie: fix warning from rcu_assign_poinger

This gets rid of a warning caused by the test in rcu_assign_pointer.
I tried to fix rcu_assign_pointer, but that devolved into a long set
of discussions about doing it right that came to no real solution.
Since the test in rcu_assign_pointer for constant NULL would never
succeed in fib_trie, just open code instead.
Signed-off-by: NStephen Hemminger <shemminger@vyatta.com>
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -177,10 +177,13 @@ static inline struct tnode *node_parent_rcu(struct node *node)
 	return rcu_dereference(ret);
 }
 
+/* Same as rcu_assign_pointer
+ * but that macro() assumes that value is a pointer.
+ */
 static inline void node_set_parent(struct node *node, struct tnode *ptr)
 {
-	rcu_assign_pointer(node->parent,
-			   (unsigned long)ptr | NODE_TYPE(node));
+	smp_wmb();
+	node->parent = (unsigned long)ptr | NODE_TYPE(node);
 }
 
 static inline struct node *tnode_get_child(struct tnode *tn, unsigned int i)