virt_wifi: fix deadlock on RTNL

Fix a regression where everything in virt_wifi would just hang. This
happened due to overlapping changes between commit a05829a
("cfg80211: avoid holding the RTNL when calling the driver") which
had originally needed to change the locking, but then I introduced
commit 2fe8ef1 ("cfg80211: change netdev registration/unregistration
semantics") instead. virt_wifi somehow fell through the cracks when
I undid all the previous locking changes. Fix it now.

Fixes: a05829a ("cfg80211: avoid holding the RTNL when calling the driver")
Reported-by: syzbot+3d2d5e6cc3fb15c6a0fd@syzkaller.appspotmail.com
Link: https://lore.kernel.org/r/20210127215941.2d6a97b09784.I4f1fac32f67045171be50931f44d77e150911bee@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/virt_wifi.c

@@ -537,9 +537,7 @@ static int virt_wifi_newlink(struct net *src_net, struct net_device *dev,
 	dev->ieee80211_ptr->iftype = NL80211_IFTYPE_STATION;
 	dev->ieee80211_ptr->wiphy = common_wiphy;
 
-	wiphy_lock(common_wiphy);
 	err = register_netdevice(dev);
-	wiphy_unlock(common_wiphy);
 	if (err) {
 		dev_err(&priv->lowerdev->dev, "can't register_netdevice: %d\n",
 			err);
@@ -562,9 +560,7 @@ static int virt_wifi_newlink(struct net *src_net, struct net_device *dev,
 
 	return 0;
 unregister_netdev:
-	wiphy_lock(common_wiphy);
 	unregister_netdevice(dev);
-	wiphy_unlock(common_wiphy);
 free_wireless_dev:
 	kfree(dev->ieee80211_ptr);
 	dev->ieee80211_ptr = NULL;
@@ -590,9 +586,7 @@ static void virt_wifi_dellink(struct net_device *dev,
 	netdev_rx_handler_unregister(priv->lowerdev);
 	netdev_upper_dev_unlink(priv->lowerdev, dev);
 
-	wiphy_lock(common_wiphy);
 	unregister_netdevice_queue(dev, head);
-	wiphy_unlock(common_wiphy);
 	module_put(THIS_MODULE);
 
 	/* Deleting the wiphy is handled in the module destructor. */
@@ -631,9 +625,7 @@ static int virt_wifi_event(struct notifier_block *this, unsigned long event,
 		upper_dev = priv->upperdev;
 
 		upper_dev->rtnl_link_ops->dellink(upper_dev, &list_kill);
-		wiphy_lock(common_wiphy);
 		unregister_netdevice_many(&list_kill);
-		wiphy_unlock(common_wiphy);
 		break;
 	}