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, 5 insertions, 1 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;
 }