netdev - [PATCH net-next 2/5] ipv4: use READ_ONCE()/WRITE_ONCE() on net->ipv4.fib

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Message-ID: <20241009184405.3752829-3-edumazet@google.com>
Date: Wed,  9 Oct 2024 18:44:02 +0000
From: Eric Dumazet <edumazet@...gle.com>
To: "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>
Cc: David Ahern <dsahern@...nel.org>, Kuniyuki Iwashima <kuniyu@...zon.com>, Jiri Pirko <jiri@...nulli.us>, 
	netdev@...r.kernel.org, eric.dumazet@...il.com, 
	Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 2/5] ipv4: use READ_ONCE()/WRITE_ONCE() on net->ipv4.fib_seq

Using RTNL to protect ops->fib_rules_seq reads seems a big hammer.

Writes are protected by RTNL.
We can use READ_ONCE() when reading it.

Constify 'struct net' argument of fib4_rules_seq_read()

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/ip_fib.h     | 4 ++--
 include/net/netns/ipv4.h | 2 +-
 net/ipv4/fib_notifier.c  | 8 ++++----
 net/ipv4/fib_rules.c     | 2 +-
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 967e4dc555face31a736f6108cea6b929478beba..4c2e2d1481ebff5292b9e433f56fa7289ba8e139 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -347,7 +347,7 @@ static inline int fib4_rules_dump(struct net *net, struct notifier_block *nb,
 	return 0;
 }
 
-static inline unsigned int fib4_rules_seq_read(struct net *net)
+static inline unsigned int fib4_rules_seq_read(const struct net *net)
 {
 	return 0;
 }
@@ -411,7 +411,7 @@ static inline bool fib4_has_custom_rules(const struct net *net)
 bool fib4_rule_default(const struct fib_rule *rule);
 int fib4_rules_dump(struct net *net, struct notifier_block *nb,
 		    struct netlink_ext_ack *extack);
-unsigned int fib4_rules_seq_read(struct net *net);
+unsigned int fib4_rules_seq_read(const struct net *net);
 
 static inline bool fib4_rules_early_flow_dissect(struct net *net,
 						 struct sk_buff *skb,
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 276f622f3516871c438be27bafe61c039445b335..10c0a8dc37a23e793007ee47706b402fffbd08da 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -263,7 +263,7 @@ struct netns_ipv4 {
 #endif
 
 	struct fib_notifier_ops	*notifier_ops;
-	unsigned int	fib_seq;	/* protected by rtnl_mutex */
+	unsigned int	fib_seq;	/* writes protected by rtnl_mutex */
 
 	struct fib_notifier_ops	*ipmr_notifier_ops;
 	unsigned int	ipmr_seq;	/* protected by rtnl_mutex */
diff --git a/net/ipv4/fib_notifier.c b/net/ipv4/fib_notifier.c
index 0e23ade74493ce10a3f2572c39e091f132684884..21c85c80de641112d66a28645b1fb17c7071863f 100644
--- a/net/ipv4/fib_notifier.c
+++ b/net/ipv4/fib_notifier.c
@@ -22,15 +22,15 @@ int call_fib4_notifiers(struct net *net, enum fib_event_type event_type,
 	ASSERT_RTNL();
 
 	info->family = AF_INET;
-	net->ipv4.fib_seq++;
+	/* Paired with READ_ONCE() in fib4_seq_read() */
+	WRITE_ONCE(net->ipv4.fib_seq, net->ipv4.fib_seq + 1);
 	return call_fib_notifiers(net, event_type, info);
 }
 
 static unsigned int fib4_seq_read(struct net *net)
 {
-	ASSERT_RTNL();
-
-	return net->ipv4.fib_seq + fib4_rules_seq_read(net);
+	/* Paired with WRITE_ONCE() in call_fib4_notifiers() */
+	return READ_ONCE(net->ipv4.fib_seq) + fib4_rules_seq_read(net);
 }
 
 static int fib4_dump(struct net *net, struct notifier_block *nb,
diff --git a/net/ipv4/fib_rules.c b/net/ipv4/fib_rules.c
index b07292d50ee76603f983c81a55d45abca89266e1..8325224ef07232d05b59c58011625daae847af30 100644
--- a/net/ipv4/fib_rules.c
+++ b/net/ipv4/fib_rules.c
@@ -74,7 +74,7 @@ int fib4_rules_dump(struct net *net, struct notifier_block *nb,
 	return fib_rules_dump(net, nb, AF_INET, extack);
 }
 
-unsigned int fib4_rules_seq_read(struct net *net)
+unsigned int fib4_rules_seq_read(const struct net *net)
 {
 	return fib_rules_seq_read(net, AF_INET);
 }
-- 
2.47.0.rc0.187.ge670bccf7e-goog