vlan: rcu annotations

(struct net_device)->vlgrp is rcu protected :

add __rcu annotation and proper rcu primitives.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 05b867e..52077ca 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -112,7 +112,7 @@
 
 	ASSERT_RTNL();
 
-	grp = real_dev->vlgrp;
+	grp = rtnl_dereference(real_dev->vlgrp);
 	BUG_ON(!grp);
 
 	/* Take it out of our own structures, but be sure to interlock with
@@ -177,7 +177,7 @@
 	struct vlan_group *grp, *ngrp = NULL;
 	int err;
 
-	grp = real_dev->vlgrp;
+	grp = rtnl_dereference(real_dev->vlgrp);
 	if (!grp) {
 		ngrp = grp = vlan_group_alloc(real_dev);
 		if (!grp)
@@ -385,7 +385,7 @@
 		dev->netdev_ops->ndo_vlan_rx_add_vid(dev, 0);
 	}
 
-	grp = dev->vlgrp;
+	grp = rtnl_dereference(dev->vlgrp);
 	if (!grp)
 		goto out;