netdev - [PATCH net-next 1/5] fib: rules: use READ_ONCE()/WRITE_ONCE() on ops->fib_rules

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Message-ID: <20241009184405.3752829-2-edumazet@google.com>
Date: Wed,  9 Oct 2024 18:44:01 +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 1/5] fib: rules: use READ_ONCE()/WRITE_ONCE() on ops->fib_rules_seq

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

Writes are protected by RTNL.
We can use READ_ONCE() on readers.

Constify 'struct net' argument of fib_rules_seq_read()
and lookup_rules_ops().

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/fib_rules.h |  2 +-
 net/core/fib_rules.c    | 14 ++++++++------
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/include/net/fib_rules.h b/include/net/fib_rules.h
index d17855c52ef926383f2585a6f31094899f1e7908..04383d90a1e38847d9d10f8fd0c4bf2ef67af713 100644
--- a/include/net/fib_rules.h
+++ b/include/net/fib_rules.h
@@ -176,7 +176,7 @@ int fib_default_rule_add(struct fib_rules_ops *, u32 pref, u32 table);
 bool fib_rule_matchall(const struct fib_rule *rule);
 int fib_rules_dump(struct net *net, struct notifier_block *nb, int family,
 		   struct netlink_ext_ack *extack);
-unsigned int fib_rules_seq_read(struct net *net, int family);
+unsigned int fib_rules_seq_read(const struct net *net, int family);
 
 int fib_nl_newrule(struct sk_buff *skb, struct nlmsghdr *nlh,
 		   struct netlink_ext_ack *extack);
diff --git a/net/core/fib_rules.c b/net/core/fib_rules.c
index 154a2681f55cc6861d418927c396bec5d840578c..82ef090c0037817f15902d8784467f21419b5af7 100644
--- a/net/core/fib_rules.c
+++ b/net/core/fib_rules.c
@@ -101,7 +101,8 @@ static void notify_rule_change(int event, struct fib_rule *rule,
 			       struct fib_rules_ops *ops, struct nlmsghdr *nlh,
 			       u32 pid);
 
-static struct fib_rules_ops *lookup_rules_ops(struct net *net, int family)
+static struct fib_rules_ops *lookup_rules_ops(const struct net *net,
+					      int family)
 {
 	struct fib_rules_ops *ops;
 
@@ -370,7 +371,9 @@ static int call_fib_rule_notifiers(struct net *net,
 		.rule = rule,
 	};
 
-	ops->fib_rules_seq++;
+	ASSERT_RTNL();
+	/* Paired with READ_ONCE() in fib_rules_seq() */
+	WRITE_ONCE(ops->fib_rules_seq, ops->fib_rules_seq + 1);
 	return call_fib_notifiers(net, event_type, &info.info);
 }
 
@@ -397,17 +400,16 @@ int fib_rules_dump(struct net *net, struct notifier_block *nb, int family,
 }
 EXPORT_SYMBOL_GPL(fib_rules_dump);
 
-unsigned int fib_rules_seq_read(struct net *net, int family)
+unsigned int fib_rules_seq_read(const struct net *net, int family)
 {
 	unsigned int fib_rules_seq;
 	struct fib_rules_ops *ops;
 
-	ASSERT_RTNL();
-
 	ops = lookup_rules_ops(net, family);
 	if (!ops)
 		return 0;
-	fib_rules_seq = ops->fib_rules_seq;
+	/* Paired with WRITE_ONCE() in call_fib_rule_notifiers() */
+	fib_rules_seq = READ_ONCE(ops->fib_rules_seq);
 	rules_ops_put(ops);
 
 	return fib_rules_seq;
-- 
2.47.0.rc0.187.ge670bccf7e-goog