bonding: use exit_batch_rtnl() method

exit_batch_rtnl() is called while RTNL is held,
and devices to be unregistered can be queued in the dev_kill_list.

This saves one rtnl_lock()/rtnl_unlock() pair,
and one unregister_netdevice_many() call.

v2: Added bond_net_pre_exit() method to make sure bond_destroy_sysfs()
    is called before we unregister the devices in bond_net_exit_batch_rtnl
 (Antoine Tenart : https://lore.kernel.org/netdev/170688415193.5216.10499830272732622816@kwain/)

Signed-off-by: Eric Dumazet <[email protected]>
Acked-by: Jay Vosburgh <[email protected]>
Cc: Andy Gospodarek <[email protected]>
Reviewed-by: Antoine Tenart <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: Eric Dumazet

drivers/net/bonding/bond_main.c

@@ -6416,28 +6416,41 @@ static int __net_init bond_net_init(struct net *net)
 	return 0;
 }
 
-static void __net_exit bond_net_exit_batch(struct list_head *net_list)
+/* According to commit 69b0216ac255 ("bonding: fix bonding_masters
+ * race condition in bond unloading") we need to remove sysfs files
+ * before we remove our devices (done later in bond_net_exit_batch_rtnl())
+ */
+static void __net_exit bond_net_pre_exit(struct net *net)
+{
+	struct bond_net *bn = net_generic(net, bond_net_id);
+
+	bond_destroy_sysfs(bn);
+}
+
+static void __net_exit bond_net_exit_batch_rtnl(struct list_head *net_list,
+						struct list_head *dev_kill_list)
 {
 	struct bond_net *bn;
 	struct net *net;
-	LIST_HEAD(list);
-
-	list_for_each_entry(net, net_list, exit_list) {
-		bn = net_generic(net, bond_net_id);
-		bond_destroy_sysfs(bn);
-	}
 
 	/* Kill off any bonds created after unregistering bond rtnl ops */
-	rtnl_lock();
 	list_for_each_entry(net, net_list, exit_list) {
 		struct bonding *bond, *tmp_bond;
 
 		bn = net_generic(net, bond_net_id);
 		list_for_each_entry_safe(bond, tmp_bond, &bn->dev_list, bond_list)
-			unregister_netdevice_queue(bond->dev, &list);
+			unregister_netdevice_queue(bond->dev, dev_kill_list);
 	}
-	unregister_netdevice_many(&list);
-	rtnl_unlock();
+}
+
+/* According to commit 23fa5c2caae0 ("bonding: destroy proc directory
+ * only after all bonds are gone") bond_destroy_proc_dir() is called
+ * after bond_net_exit_batch_rtnl() has completed.
+ */
+static void __net_exit bond_net_exit_batch(struct list_head *net_list)
+{
+	struct bond_net *bn;
+	struct net *net;
 
 	list_for_each_entry(net, net_list, exit_list) {
 		bn = net_generic(net, bond_net_id);
@@ -6447,6 +6460,8 @@ static void __net_exit bond_net_exit_batch(struct list_head *net_list)
 
 static struct pernet_operations bond_net_ops = {
 	.init = bond_net_init,
+	.pre_exit = bond_net_pre_exit,
+	.exit_batch_rtnl = bond_net_exit_batch_rtnl,
 	.exit_batch = bond_net_exit_batch,
 	.id   = &bond_net_id,
 	.size = sizeof(struct bond_net),