ipv6: use READ_ONCE()/WRITE_ONCE() on fib6_table->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 fib6_tables_seq_read() and
fib6_rules_seq_read().

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20241009184405.3752829-4-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 12 insertions, 12 deletions

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 6cb867ce4878..7c87873ae211 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -394,7 +394,7 @@ struct fib6_table {
 	struct fib6_node	tb6_root;
 	struct inet_peer_base	tb6_peers;
 	unsigned int		flags;
-	unsigned int		fib_seq;
+	unsigned int		fib_seq; /* writes protected by rtnl_mutex */
 	struct hlist_head       tb6_gc_hlist;	/* GC candidates */
 #define RT6_TABLE_HAS_DFLT_ROUTER	BIT(0)
 };
@@ -563,7 +563,7 @@ int call_fib6_notifiers(struct net *net, enum fib_event_type event_type,
 int __net_init fib6_notifier_init(struct net *net);
 void __net_exit fib6_notifier_exit(struct net *net);
 
-unsigned int fib6_tables_seq_read(struct net *net);
+unsigned int fib6_tables_seq_read(const struct net *net);
 int fib6_tables_dump(struct net *net, struct notifier_block *nb,
 		     struct netlink_ext_ack *extack);
 
@@ -632,7 +632,7 @@ void fib6_rules_cleanup(void);
 bool fib6_rule_default(const struct fib_rule *rule);
 int fib6_rules_dump(struct net *net, struct notifier_block *nb,
 		    struct netlink_ext_ack *extack);
-unsigned int fib6_rules_seq_read(struct net *net);
+unsigned int fib6_rules_seq_read(const struct net *net);
 
 static inline bool fib6_rules_early_flow_dissect(struct net *net,
 						 struct sk_buff *skb,
@@ -676,7 +676,7 @@ static inline int fib6_rules_dump(struct net *net, struct notifier_block *nb,
 {
 	return 0;
 }
-static inline unsigned int fib6_rules_seq_read(struct net *net)
+static inline unsigned int fib6_rules_seq_read(const struct net *net)
 {
 	return 0;
 }
diff --git a/net/ipv6/fib6_rules.c b/net/ipv6/fib6_rules.c
index 04a9ed5e8310..c85c1627cb16 100644
--- a/net/ipv6/fib6_rules.c
+++ b/net/ipv6/fib6_rules.c
@@ -56,7 +56,7 @@ int fib6_rules_dump(struct net *net, struct notifier_block *nb,
 	return fib_rules_dump(net, nb, AF_INET6, extack);
 }
 
-unsigned int fib6_rules_seq_read(struct net *net)
+unsigned int fib6_rules_seq_read(const struct net *net)
 {
 	return fib_rules_seq_read(net, AF_INET6);
 }
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index eb111d20615c..cea160b249d2 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -345,17 +345,17 @@ static void __net_init fib6_tables_init(struct net *net)
 
 #endif
 
-unsigned int fib6_tables_seq_read(struct net *net)
+unsigned int fib6_tables_seq_read(const struct net *net)
 {
 	unsigned int h, fib_seq = 0;
 
 	rcu_read_lock();
 	for (h = 0; h < FIB6_TABLE_HASHSZ; h++) {
-		struct hlist_head *head = &net->ipv6.fib_table_hash[h];
-		struct fib6_table *tb;
+		const struct hlist_head *head = &net->ipv6.fib_table_hash[h];
+		const struct fib6_table *tb;
 
 		hlist_for_each_entry_rcu(tb, head, tb6_hlist)
-			fib_seq += tb->fib_seq;
+			fib_seq += READ_ONCE(tb->fib_seq);
 	}
 	rcu_read_unlock();
 
@@ -400,7 +400,7 @@ int call_fib6_entry_notifiers(struct net *net,
 		.rt = rt,
 	};
 
-	rt->fib6_table->fib_seq++;
+	WRITE_ONCE(rt->fib6_table->fib_seq, rt->fib6_table->fib_seq + 1);
 	return call_fib6_notifiers(net, event_type, &info.info);
 }
 
@@ -416,7 +416,7 @@ int call_fib6_multipath_entry_notifiers(struct net *net,
 		.nsiblings = nsiblings,
 	};
 
-	rt->fib6_table->fib_seq++;
+	WRITE_ONCE(rt->fib6_table->fib_seq, rt->fib6_table->fib_seq + 1);
 	return call_fib6_notifiers(net, event_type, &info.info);
 }
 
@@ -427,7 +427,7 @@ int call_fib6_entry_notifiers_replace(struct net *net, struct fib6_info *rt)
 		.nsiblings = rt->fib6_nsiblings,
 	};
 
-	rt->fib6_table->fib_seq++;
+	WRITE_ONCE(rt->fib6_table->fib_seq, rt->fib6_table->fib_seq + 1);
 	return call_fib6_notifiers(net, FIB_EVENT_ENTRY_REPLACE, &info.info);
 }