l2tp: avoid to use synchronize_rcu in tunnel free function

Avoid to use synchronize_rcu in l2tp_tunnel_free because context may be
atomic.
Signed-off-by: Dmitry Kozlov <xeb@mail.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_core.c

@@ -1347,11 +1347,10 @@ static void l2tp_tunnel_free(struct l2tp_tunnel *tunnel)
 	/* Remove from tunnel list */
 	spin_lock_bh(&pn->l2tp_tunnel_list_lock);
 	list_del_rcu(&tunnel->list);
+	kfree_rcu(tunnel, rcu);
 	spin_unlock_bh(&pn->l2tp_tunnel_list_lock);
-	synchronize_rcu();
 
 	atomic_dec(&l2tp_tunnel_count);
-	kfree(tunnel);
 }
 
 /* Create a socket for the tunnel, if one isn't set up by

net/l2tp/l2tp_core.h

@@ -163,6 +163,7 @@ struct l2tp_tunnel_cfg {
 
 struct l2tp_tunnel {
 	int			magic;		/* Should be L2TP_TUNNEL_MAGIC */
+	struct rcu_head rcu;
 	rwlock_t		hlist_lock;	/* protect session_hlist */
 	struct hlist_head	session_hlist[L2TP_HASH_SIZE];
 						/* hashed list of sessions,