We will no longer hold RTNL for ipmr_mfc_add() and ipmr_mfc_delete().

MFC entry can be loosely connected with VIF by its index for
mrt->vif_table[] (stored in mfc_parent), but the two tables are
not synchronised.  i.e. Even if VIF 1 is removed, MFC for VIF 1
is not automatically removed.

The only field that the MFC/VIF interfaces share is
net->ipv[46].ipmr_seq, which is protected by RTNL.

Adding a new mutex for both just to protect a single field is overkill.

Let's convert the field to atomic_t.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/linux/mroute_base.h | 8 ++++----
 include/net/netns/ipv4.h    | 2 +-
 include/net/netns/ipv6.h    | 2 +-
 net/ipv4/ipmr.c             | 4 ++--
 net/ipv6/ip6mr.c            | 4 ++--
 5 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/linux/mroute_base.h b/include/linux/mroute_base.h
index 0075f6e5c3da..0baa6f994da9 100644
--- a/include/linux/mroute_base.h
+++ b/include/linux/mroute_base.h
@@ -76,7 +76,7 @@ static inline int mr_call_vif_notifiers(struct net *net,
 					struct vif_device *vif,
 					struct net_device *vif_dev,
 					unsigned short vif_index, u32 tb_id,
-					unsigned int *ipmr_seq)
+					atomic_t *ipmr_seq)
 {
 	struct vif_entry_notifier_info info = {
 		.info = {
@@ -89,7 +89,7 @@ static inline int mr_call_vif_notifiers(struct net *net,
 	};
 
 	ASSERT_RTNL();
-	(*ipmr_seq)++;
+	atomic_inc(ipmr_seq);
 	return call_fib_notifiers(net, event_type, &info.info);
 }
 
@@ -198,7 +198,7 @@ static inline int mr_call_mfc_notifiers(struct net *net,
 					unsigned short family,
 					enum fib_event_type event_type,
 					struct mr_mfc *mfc, u32 tb_id,
-					unsigned int *ipmr_seq)
+					atomic_t *ipmr_seq)
 {
 	struct mfc_entry_notifier_info info = {
 		.info = {
@@ -209,7 +209,7 @@ static inline int mr_call_mfc_notifiers(struct net *net,
 	};
 
 	ASSERT_RTNL();
-	(*ipmr_seq)++;
+	atomic_inc(ipmr_seq);
 	return call_fib_notifiers(net, event_type, &info.info);
 }
 
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 380ff34c0233..94dca64fec41 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -280,7 +280,7 @@ struct netns_ipv4 {
 	struct fib_rules_ops	*mr_rules_ops;
 #endif
 	struct fib_notifier_ops	*ipmr_notifier_ops;
-	unsigned int		ipmr_seq;	/* protected by rtnl_mutex */
+	atomic_t		ipmr_seq;
 #endif
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 	struct sysctl_fib_multipath_hash_seed sysctl_fib_multipath_hash_seed;
diff --git a/include/net/netns/ipv6.h b/include/net/netns/ipv6.h
index 34bdb1308e8f..499e4288170f 100644
--- a/include/net/netns/ipv6.h
+++ b/include/net/netns/ipv6.h
@@ -118,7 +118,7 @@ struct netns_ipv6 {
 	struct seg6_pernet_data *seg6_data;
 	struct fib_notifier_ops	*notifier_ops;
 	struct fib_notifier_ops	*ip6mr_notifier_ops;
-	unsigned int ipmr_seq; /* protected by rtnl_mutex */
+	atomic_t		ipmr_seq;
 	struct {
 		struct hlist_head head;
 		spinlock_t	lock;
diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 77ae0fd9ec31..77684acc8ad4 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -3226,7 +3226,7 @@ static const struct net_protocol pim_protocol = {
 
 static unsigned int ipmr_seq_read(const struct net *net)
 {
-	return READ_ONCE(net->ipv4.ipmr_seq) + ipmr_rules_seq_read(net);
+	return atomic_read(&net->ipv4.ipmr_seq) + ipmr_rules_seq_read(net);
 }
 
 static int ipmr_dump(struct net *net, struct notifier_block *nb,
@@ -3247,7 +3247,7 @@ static int __net_init ipmr_notifier_init(struct net *net)
 {
 	struct fib_notifier_ops *ops;
 
-	net->ipv4.ipmr_seq = 0;
+	atomic_set(&net->ipv4.ipmr_seq, 0);
 
 	ops = fib_notifier_ops_register(&ipmr_notifier_ops_template, net);
 	if (IS_ERR(ops))
diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index e047a4680ab0..85010ff21c98 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1280,7 +1280,7 @@ static int ip6mr_device_event(struct notifier_block *this,
 
 static unsigned int ip6mr_seq_read(const struct net *net)
 {
-	return READ_ONCE(net->ipv6.ipmr_seq) + ip6mr_rules_seq_read(net);
+	return atomic_read(&net->ipv6.ipmr_seq) + ip6mr_rules_seq_read(net);
 }
 
 static int ip6mr_dump(struct net *net, struct notifier_block *nb,
@@ -1305,7 +1305,7 @@ static int __net_init ip6mr_notifier_init(struct net *net)
 {
 	struct fib_notifier_ops *ops;
 
-	net->ipv6.ipmr_seq = 0;
+	atomic_set(&net->ipv6.ipmr_seq, 0);
 
 	ops = fib_notifier_ops_register(&ip6mr_notifier_ops_template, net);
 	if (IS_ERR(ops))
-- 
2.53.0.473.g4a7958ca14-goog