rtnetlink: Add per-netns RTNL.

The goal is to break RTNL down into per-netns mutex.

This patch adds per-netns mutex and its helper functions, rtnl_net_lock()
and rtnl_net_unlock().

rtnl_net_lock() acquires the global RTNL and per-netns RTNL mutex, and
rtnl_net_unlock() releases them.

We will replace 800+ rtnl_lock() with rtnl_net_lock() and finally removes
rtnl_lock() in rtnl_net_lock().

When we need to nest per-netns RTNL mutex, we will use __rtnl_net_lock(),
and its locking order is defined by rtnl_net_lock_cmp_fn() as follows:

  1. init_net is first
  2. netns address ascending order

Note that the conversion will be done under CONFIG_DEBUG_NET_SMALL_RTNL
with LOCKDEP so that we can carefully add the extra mutex without slowing
down RTNL operations during conversion.

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

1 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/rtnetlink.h b/include/linux/rtnetlink.h
index cdfc897f1e3c..edd840a49989 100644
--- a/include/linux/rtnetlink.h
+++ b/include/linux/rtnetlink.h
@@ -92,6 +92,27 @@ static inline bool lockdep_rtnl_is_held(void)
 #define rcu_replace_pointer_rtnl(rp, p)			\
 	rcu_replace_pointer(rp, p, lockdep_rtnl_is_held())
 
+#ifdef CONFIG_DEBUG_NET_SMALL_RTNL
+void __rtnl_net_lock(struct net *net);
+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);
+#else
+static inline void __rtnl_net_lock(struct net *net) {}
+static inline void __rtnl_net_unlock(struct net *net) {}
+
+static inline void rtnl_net_lock(struct net *net)
+{
+	rtnl_lock();
+}
+
+static inline void rtnl_net_unlock(struct net *net)
+{
+	rtnl_unlock();
+}
+#endif
+
 static inline struct netdev_queue *dev_ingress_queue(struct net_device *dev)
 {
 	return rtnl_dereference(dev->ingress_queue);