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>

4 files changed, 20 insertions, 25 deletions

diff --git a/drivers/net/dummy.c b/drivers/net/dummy.c
index e9c5e1e11fa0..72618b6af44e 100644
--- a/drivers/net/dummy.c
+++ b/drivers/net/dummy.c
@@ -166,6 +166,7 @@ err:
 
 static int __init dummy_init_module(void)
 {
+	bool need_unregister = false;
 	int i, err = 0;
 
 	down_write(&pernet_ops_rwsem);
@@ -179,12 +180,15 @@ static int __init dummy_init_module(void)
 		cond_resched();
 	}
 	if (err < 0)
-		__rtnl_link_unregister(&dummy_link_ops);
+		need_unregister = true;
 
 out:
 	rtnl_unlock();
 	up_write(&pernet_ops_rwsem);
 
+	if (need_unregister)
+		rtnl_link_unregister(&dummy_link_ops);
+
 	return err;
 }
 
diff --git a/drivers/net/ifb.c b/drivers/net/ifb.c
index 2c1b5def4a0b..a4b9ec4e8f30 100644
--- a/drivers/net/ifb.c
+++ b/drivers/net/ifb.c
@@ -424,6 +424,7 @@ err:
 
 static int __init ifb_init_module(void)
 {
+	bool need_unregister = false;
 	int i, err;
 
 	down_write(&pernet_ops_rwsem);
@@ -437,12 +438,15 @@ static int __init ifb_init_module(void)
 		cond_resched();
 	}
 	if (err)
-		__rtnl_link_unregister(&ifb_link_ops);
+		need_unregister = true;
 
 out:
 	rtnl_unlock();
 	up_write(&pernet_ops_rwsem);
 
+	if (need_unregister)
+		rtnl_link_unregister(&ifb_link_ops);
+
 	return err;
 }
 
diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index b260c0cc9671..3ebfcc6e56fd 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -165,7 +165,6 @@ struct rtnl_link_ops {
 };
 
 int __rtnl_link_register(struct rtnl_link_ops *ops);
-void __rtnl_link_unregister(struct rtnl_link_ops *ops);
 
 int rtnl_link_register(struct rtnl_link_ops *ops);
 void rtnl_link_unregister(struct rtnl_link_ops *ops);
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);
 }