Subject: [PATCH v1 net-next 2/3] rtnetlink: Add assertion helpers for per-net RTNL.

From: Kuniyuki Iwashima <[email-masked]>
Date: Mon, 30 Sep 2024 23:25:25 +0300

Once an RTNL scope is converted with rtnl_net_lock(), we will replace RTNL
helper functions inside the scope with the following per-net alternatives:

  ASSERT_RTNL()           -> ASSERT_RTNL_NET(net)
  rcu_dereference_rtnl(p) -> rcu_dereference_rtnl_net(net, p)

Note that the per-net helpers are equivalent to the conventional helpers
unless CONFIG_DEBUG_NET_SMALL_RTNL is enabled.

Signed-off-by: Kuniyuki Iwashima <[email-masked]>
---
 include/linux/rtnetlink.h | 25 +++++++++++++++++++++++++
 net/core/rtnetlink.c      | 12 ++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index c4afe6c49651..458d2320e6d3 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -55,11 +55,36 @@ void __rtnl_net_unlock(struct net *net);
 void rtnl_net_lock(struct net *net);
 void rtnl_net_unlock(struct net *net);
 int rtnl_net_lock_cmp_fn(const struct lockdep_map *a, const struct lockdep_map *b);
+
+bool rtnl_net_is_locked(struct net *net);
+
+#define ASSERT_RTNL_NET(net)						\
+	WARN_ONCE(!rtnl_net_is_locked(net),				\
+		  "RTNL_NET: assertion failed at %s (%d)\n",		\
+		  __FILE__,  __LINE__)
+
+bool lockdep_rtnl_net_is_held(struct net *net);
+
+#define rcu_dereference_rtnl_net(net, p)				\
+	rcu_dereference_check(p, lockdep_rtnl_net_is_held(net))
+#define rtnl_net_dereference(net, p)					\
+	rcu_dereference_protected(p, lockdep_rtnl_net_is_held(net))
+#define rcu_replace_pointer_rtnl_net(net, rp, p)			\
+	rcu_replace_pointer(rp, p, lockdep_rtnl_net_is_held(net))
 #else
 #define __rtnl_net_lock(net)
 #define __rtnl_net_unlock(net)
 #define rtnl_net_lock(net) rtnl_lock()
 #define rtnl_net_unlock(net) rtnl_unlock()
+
+#define ASSERT_RTNL_NET(net)	ASSERT_RTNL()
+
+#define rcu_dereference_rtnl_net(net, p)		\
+	rcu_dereference_rtnl(p)
+#define rtnl_net_dereference(net, p)			\
+	rtnl_dereference(p)
+#define rcu_replace_pointer_rtnl_net(net, rp, p)	\
+	rcu_replace_pointer_rtnl(rp, p)
 #endif
 
 extern wait_queue_head_t netdev_unregistering_wq;
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index edf530441b65..2b44ec690780 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -235,6 +235,18 @@ int rtnl_net_lock_cmp_fn(const struct lockdep_map *a, const struct lockdep_map *
 
 	return rtnl_net_cmp_locks(net_a, net_b);
 }
+
+bool rtnl_net_is_locked(struct net *net)
+{
+	return rtnl_is_locked() && mutex_is_locked(&net->rtnl_mutex);
+}
+EXPORT_SYMBOL(rtnl_net_is_locked);
+
+bool lockdep_rtnl_net_is_held(struct net *net)
+{
+	return lockdep_rtnl_is_held() && lockdep_is_held(&net->rtnl_mutex);
+}
+EXPORT_SYMBOL(lockdep_rtnl_net_is_held);
 #endif
 
 static struct rtnl_link __rcu *__rcu *rtnl_msg_handlers[RTNL_FAMILY_MAX + 1];
-- 
2.30.2