Merge branch 'net-avoid-slow-rcu'

Eric Dumazet says:

====================
net: avoid slow rcu synchronizations in cleanup_net()

RTNL is a contended mutex, we prefer to expedite rcu synchronizations
in contexts we hold RTNL.

Similarly, cleanup_net() is a single threaded critical component and
should also use synchronize_rcu_expedited() even when not holding RTNL.

First patch removes a barrier with no clear purpose in ipv6_mc_down()
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_vlan.c

@@ -841,7 +841,7 @@ void br_vlan_flush(struct net_bridge *br)
 	vg = br_vlan_group(br);
 	__vlan_flush(br, NULL, vg);
 	RCU_INIT_POINTER(br->vlgrp, NULL);
-	synchronize_rcu();
+	synchronize_net();
 	__vlan_group_free(vg);
 }
 
@@ -1372,7 +1372,7 @@ void nbp_vlan_flush(struct net_bridge_port *port)
 	vg = nbp_vlan_group(port);
 	__vlan_flush(port->br, port, vg);
 	RCU_INIT_POINTER(port->vlgrp, NULL);
-	synchronize_rcu();
+	synchronize_net();
 	__vlan_group_free(vg);
 }
 

net/core/dev.c

@@ -1239,7 +1239,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
 	netdev_name_node_del(dev->name_node);
 	write_unlock(&dev_base_lock);
 
-	synchronize_rcu();
+	synchronize_net();
 
 	write_lock(&dev_base_lock);
 	netdev_name_node_add(net, dev->name_node);

net/core/net_namespace.c

@@ -622,7 +622,7 @@ static void cleanup_net(struct work_struct *work)
 	 * the rcu_barrier() below isn't sufficient alone.
 	 * Also the pre_exit() and exit() methods need this barrier.
 	 */
-	synchronize_rcu();
+	synchronize_rcu_expedited();
 
 	rtnl_lock();
 	list_for_each_entry_reverse(ops, &pernet_list, list) {

net/ipv4/fib_trie.c

@@ -501,7 +501,7 @@ static void tnode_free(struct key_vector *tn)
 
 	if (tnode_free_size >= READ_ONCE(sysctl_fib_sync_mem)) {
 		tnode_free_size = 0;
-		synchronize_rcu();
+		synchronize_net();
 	}
 }
 

net/ipv6/mcast.c

@@ -2719,7 +2719,6 @@ void ipv6_mc_down(struct inet6_dev *idev)
 	/* Should stop work after group drop. or we will
 	 * start work again in mld_ifc_event()
 	 */
-	synchronize_net();
 	mld_query_stop_work(idev);
 	mld_report_stop_work(idev);
 

net/netfilter/nf_conntrack_core.c

@@ -2530,7 +2530,7 @@ void nf_conntrack_cleanup_net_list(struct list_head *net_exit_list)
 	 *  netfilter framework.  Roll on, two-stage module
 	 *  delete...
 	 */
-	synchronize_net();
+	synchronize_rcu_expedited();
 i_see_dead_people:
 	busy = 0;
 	list_for_each_entry(net, net_exit_list, exit_list) {