rtnetlink: Add assertion helpers for per-netns RTNL.

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

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

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

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: q2ven

include/linux/rtnetlink.h

@@ -51,6 +51,10 @@ extern atomic_t dev_unreg_count;
 extern struct rw_semaphore pernet_ops_rwsem;
 extern struct rw_semaphore net_rwsem;
 
+#define ASSERT_RTNL() \
+	WARN_ONCE(!rtnl_is_locked(), \
+		  "RTNL: assertion failed at %s (%d)\n", __FILE__,  __LINE__)
+
 #ifdef CONFIG_PROVE_LOCKING
 extern bool lockdep_rtnl_is_held(void);
 #else
@@ -98,6 +102,22 @@ 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
 static inline void __rtnl_net_lock(struct net *net) {}
 static inline void __rtnl_net_unlock(struct net *net) {}
@@ -111,6 +131,27 @@ static inline void rtnl_net_unlock(struct net *net)
 {
 	rtnl_unlock();
 }
+
+static inline void ASSERT_RTNL_NET(struct net *net)
+{
+	ASSERT_RTNL();
+}
+
+static inline void *rcu_dereference_rtnl_net(struct net *net, void *p)
+{
+	return rcu_dereference_rtnl(p);
+}
+
+static inline void *rtnl_net_dereference(struct net *net, void *p)
+{
+	return rtnl_dereference(p);
+}
+
+static inline void *rcu_replace_pointer_rtnl_net(struct net *net,
+						 void *rp, void *p)
+{
+	return rcu_replace_pointer_rtnl(rp, p);
+}
 #endif
 
 static inline struct netdev_queue *dev_ingress_queue(struct net_device *dev)
@@ -140,10 +181,6 @@ void rtnetlink_init(void);
 void __rtnl_unlock(void);
 void rtnl_kfree_skbs(struct sk_buff *head, struct sk_buff *tail);
 
-#define ASSERT_RTNL() \
-	WARN_ONCE(!rtnl_is_locked(), \
-		  "RTNL: assertion failed at %s (%d)\n", __FILE__,  __LINE__)
-
 extern int ndo_dflt_fdb_dump(struct sk_buff *skb,
 			     struct netlink_callback *cb,
 			     struct net_device *dev,

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];