ipmr_net_ops uses ->exit_batch() to acquire RTNL only once
for dying network namespaces.

ipmr does not depend on the ordering of ->exit_rtnl() and
->exit_batch() of other pernet_operations (unlike fib_net_ops).

Once ipmr_free_table() is called and all devices are
queued for destruction in ->exit_rtnl(), later during
NETDEV_UNREGISTER, ipmr_device_event() will not see anything
in vif table and just do nothing.

Let's convert ipmr_net_exit_batch() to ->exit_rtnl().

Note that fib_rules_unregister() does not need RTNL and
we will remove RTNL and unregister_netdevice_many() in
ipmr_net_init().

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/ipv4/ipmr.c | 31 +++++++++++++------------------
 1 file changed, 13 insertions(+), 18 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 3fb50307fc2f..3526c9afcb03 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -285,18 +285,17 @@ static int __net_init ipmr_rules_init(struct net *net)
 	return err;
 }
 
-static void __net_exit ipmr_rules_exit(struct net *net)
+static void __net_exit ipmr_rules_exit_rtnl(struct net *net,
+					    struct list_head *dev_kill_list)
 {
 	struct mr_table *mrt, *next;
-	LIST_HEAD(dev_kill_list);
 
 	ASSERT_RTNL();
 	list_for_each_entry_safe(mrt, next, &net->ipv4.mr_tables, list) {
 		list_del(&mrt->list);
-		ipmr_free_table(mrt, &dev_kill_list);
+		ipmr_free_table(mrt, dev_kill_list);
 	}
 
-	unregister_netdevice_many(&dev_kill_list);
 	fib_rules_unregister(net->ipv4.mr_rules_ops);
 }
 
@@ -353,14 +352,12 @@ static int __net_init ipmr_rules_init(struct net *net)
 	return 0;
 }
 
-static void __net_exit ipmr_rules_exit(struct net *net)
+static void __net_exit ipmr_rules_exit_rtnl(struct net *net,
+					    struct list_head *dev_kill_list)
 {
-	LIST_HEAD(dev_kill_list);
-
 	ASSERT_RTNL();
 
-	ipmr_free_table(net->ipv4.mrt, &dev_kill_list);
-	unregister_netdevice_many(&dev_kill_list);
+	ipmr_free_table(net->ipv4.mrt, dev_kill_list);
 
 	net->ipv4.mrt = NULL;
 }
@@ -3264,6 +3261,7 @@ static void __net_exit ipmr_notifier_exit(struct net *net)
 /* Setup for IP multicast routing */
 static int __net_init ipmr_net_init(struct net *net)
 {
+	LIST_HEAD(dev_kill_list);
 	int err;
 
 	err = ipmr_notifier_init(net);
@@ -3290,7 +3288,8 @@ static int __net_init ipmr_net_init(struct net *net)
 	remove_proc_entry("ip_mr_vif", net->proc_net);
 proc_vif_fail:
 	rtnl_lock();
-	ipmr_rules_exit(net);
+	ipmr_rules_exit_rtnl(net, &dev_kill_list);
+	unregister_netdevice_many(&dev_kill_list);
 	rtnl_unlock();
 #endif
 ipmr_rules_fail:
@@ -3308,20 +3307,16 @@ static void __net_exit ipmr_net_exit(struct net *net)
 	ipmr_notifier_exit(net);
 }
 
-static void __net_exit ipmr_net_exit_batch(struct list_head *net_list)
+static void __net_exit ipmr_net_exit_rtnl(struct net *net,
+					  struct list_head *dev_kill_list)
 {
-	struct net *net;
-
-	rtnl_lock();
-	list_for_each_entry(net, net_list, exit_list)
-		ipmr_rules_exit(net);
-	rtnl_unlock();
+	ipmr_rules_exit_rtnl(net, dev_kill_list);
 }
 
 static struct pernet_operations ipmr_net_ops = {
 	.init = ipmr_net_init,
 	.exit = ipmr_net_exit,
-	.exit_batch = ipmr_net_exit_batch,
+	.exit_rtnl = ipmr_net_exit_rtnl,
 };
 
 static const struct rtnl_msg_handler ipmr_rtnl_msg_handlers[] __initconst = {
-- 
2.53.0.414.gf7e9f6c205-goog