rtnetlink: Remove __rtnl_link_unregister().

rtnl_link_unregister() holds RTNL and calls __rtnl_link_unregister(),
where we call synchronize_srcu() to wait inflight RTM_NEWLINK requests
for per-netns RTNL.

We put synchronize_srcu() in __rtnl_link_unregister() due to ifb.ko
and dummy.ko.

However, rtnl_newlink() will acquire SRCU before RTNL later in this
series.  Then, lockdep will detect the deadlock:

   rtnl_link_unregister()       rtnl_newlink()
   ----                         ----
   lock(rtnl_mutex);
                                lock(&ops->srcu);
                                lock(rtnl_mutex);
   sync(&ops->srcu);

To avoid the problem, we must call synchronize_srcu() before RTNL in
rtnl_link_unregister().

As a preparation, let's remove __rtnl_link_unregister().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20241108004823.29419-2-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 10 insertions, 22 deletions

diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index a5c386a45501..f0246ecec7fa 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -568,27 +568,6 @@ static void __rtnl_kill_links(struct net *net, struct rtnl_link_ops *ops)
 	unregister_netdevice_many(&list_kill);
 }
 
-/**
- * __rtnl_link_unregister - Unregister rtnl_link_ops from rtnetlink.
- * @ops: struct rtnl_link_ops * to unregister
- *
- * The caller must hold the rtnl_mutex and guarantee net_namespace_list
- * integrity (hold pernet_ops_rwsem for writing to close the race
- * with setup_net() and cleanup_net()).
- */
-void __rtnl_link_unregister(struct rtnl_link_ops *ops)
-{
-	struct net *net;
-
-	list_del_rcu(&ops->list);
-	synchronize_srcu(&ops->srcu);
-	cleanup_srcu_struct(&ops->srcu);
-
-	for_each_net(net)
-		__rtnl_kill_links(net, ops);
-}
-EXPORT_SYMBOL_GPL(__rtnl_link_unregister);
-
 /* Return with the rtnl_lock held when there are no network
  * devices unregistering in any network namespace.
  */
@@ -617,10 +596,19 @@ static void rtnl_lock_unregistering_all(void)
  */
 void rtnl_link_unregister(struct rtnl_link_ops *ops)
 {
+	struct net *net;
+
 	/* Close the race with setup_net() and cleanup_net() */
 	down_write(&pernet_ops_rwsem);
 	rtnl_lock_unregistering_all();
-	__rtnl_link_unregister(ops);
+
+	list_del_rcu(&ops->list);
+	synchronize_srcu(&ops->srcu);
+	cleanup_srcu_struct(&ops->srcu);
+
+	for_each_net(net)
+		__rtnl_kill_links(net, ops);
+
 	rtnl_unlock();
 	up_write(&pernet_ops_rwsem);
 }