net: add dev->dev_registered_tracker

Convert one dev_hold()/dev_put() pair in register_netdevice()
and unregister_netdevice_many() to dev_hold_track()
and dev_put_track().

This would allow to detect a rogue dev_put() a bit earlier.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/20220207184107.1401096-1-eric.dumazet@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/netdevice.h

@@ -1948,6 +1948,8 @@ enum netdev_ml_priv_type {
  *	@dev_addr_shadow:	Copy of @dev_addr to catch direct writes.
  *	@linkwatch_dev_tracker:	refcount tracker used by linkwatch.
  *	@watchdog_dev_tracker:	refcount tracker used by watchdog.
+ *	@dev_registered_tracker:	tracker for reference held while
+ *					registered
  *
  *	FIXME: cleanup struct net_device such that network protocol info
  *	moves out.
@@ -2282,6 +2284,7 @@ struct net_device {
 	u8 dev_addr_shadow[MAX_ADDR_LEN];
 	netdevice_tracker	linkwatch_dev_tracker;
 	netdevice_tracker	watchdog_dev_tracker;
+	netdevice_tracker	dev_registered_tracker;
 };
 #define to_net_dev(d) container_of(d, struct net_device, dev)
 

net/core/dev.c

@@ -9683,8 +9683,10 @@ int register_netdevice(struct net_device *dev)
 	linkwatch_init_dev(dev);
 
 	dev_init_scheduler(dev);
-	dev_hold(dev);
+
+	dev_hold_track(dev, &dev->dev_registered_tracker, GFP_KERNEL);
 	list_netdevice(dev);
+
 	add_device_randomness(dev->dev_addr, dev->addr_len);
 
 	/* If the device has permanent device address, driver should
@@ -10449,7 +10451,7 @@ void unregister_netdevice_many(struct list_head *head)
 	synchronize_net();
 
 	list_for_each_entry(dev, head, unreg_list) {
-		dev_put(dev);
+		dev_put_track(dev, &dev->dev_registered_tracker);
 		net_set_todo(dev);
 	}