net: netpoll: extract core of netpoll_cleanup

Extract the core part of netpoll_cleanup(), so, it could be called from
a caller that has the rtnl lock already.

Netconsole uses this in a weird way right now:

	__netpoll_cleanup(&nt->np);
	spin_lock_irqsave(&target_list_lock, flags);
	netdev_put(nt->np.dev, &nt->np.dev_tracker);
	nt->np.dev = NULL;
	nt->enabled = false;

This will be replaced by do_netpoll_cleanup() as the locking situation
is overhauled.
Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

include/linux/netpoll.h

@@ -64,6 +64,7 @@ int netpoll_setup(struct netpoll *np);
 void __netpoll_cleanup(struct netpoll *np);
 void __netpoll_free(struct netpoll *np);
 void netpoll_cleanup(struct netpoll *np);
+void do_netpoll_cleanup(struct netpoll *np);
 netdev_tx_t netpoll_send_skb(struct netpoll *np, struct sk_buff *skb);
 
 #ifdef CONFIG_NETPOLL

net/core/netpoll.c

@@ -853,14 +853,20 @@ void __netpoll_free(struct netpoll *np)
 }
 EXPORT_SYMBOL_GPL(__netpoll_free);
 
+void do_netpoll_cleanup(struct netpoll *np)
+{
+	__netpoll_cleanup(np);
+	netdev_put(np->dev, &np->dev_tracker);
+	np->dev = NULL;
+}
+EXPORT_SYMBOL(do_netpoll_cleanup);
+
 void netpoll_cleanup(struct netpoll *np)
 {
 	rtnl_lock();
 	if (!np->dev)
 		goto out;
-	__netpoll_cleanup(np);
-	netdev_put(np->dev, &np->dev_tracker);
-	np->dev = NULL;
+	do_netpoll_cleanup(np);
 out:
 	rtnl_unlock();
 }