net: convert dev->reg_state to u8

Prepares things so that dev->reg_state reads can be lockless,
by adding WRITE_ONCE() on write side.

READ_ONCE()/WRITE_ONCE() do not support bitfields.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -1815,6 +1815,15 @@ enum netdev_stat_type {
 	NETDEV_PCPU_STAT_DSTATS, /* struct pcpu_dstats */
 };
 
+enum netdev_reg_state {
+	NETREG_UNINITIALIZED = 0,
+	NETREG_REGISTERED,	/* completed register_netdevice */
+	NETREG_UNREGISTERING,	/* called unregister_netdevice */
+	NETREG_UNREGISTERED,	/* completed unregister todo */
+	NETREG_RELEASED,	/* called free_netdev */
+	NETREG_DUMMY,		/* dummy device for NAPI poll */
+};
+
 /**
  *	struct net_device - The DEVICE structure.
  *
@@ -2372,13 +2381,7 @@ struct net_device {
 
 	struct list_head	link_watch_list;
 
-	enum { NETREG_UNINITIALIZED=0,
-	       NETREG_REGISTERED,	/* completed register_netdevice */
-	       NETREG_UNREGISTERING,	/* called unregister_netdevice */
-	       NETREG_UNREGISTERED,	/* completed unregister todo */
-	       NETREG_RELEASED,		/* called free_netdev */
-	       NETREG_DUMMY,		/* dummy device for NAPI poll */
-	} reg_state:8;
+	u8 reg_state;
 
 	bool dismantle;
 
@@ -5254,7 +5257,9 @@ static inline const char *netdev_name(const struct net_device *dev)
 
 static inline const char *netdev_reg_state(const struct net_device *dev)
 {
-	switch (dev->reg_state) {
+	u8 reg_state = READ_ONCE(dev->reg_state);
+
+	switch (reg_state) {
 	case NETREG_UNINITIALIZED: return " (uninitialized)";
 	case NETREG_REGISTERED: return "";
 	case NETREG_UNREGISTERING: return " (unregistering)";
@@ -5263,7 +5268,7 @@ static inline const char *netdev_reg_state(const struct net_device *dev)
 	case NETREG_DUMMY: return " (dummy)";
 	}
 
-	WARN_ONCE(1, "%s: unknown reg_state %d\n", dev->name, dev->reg_state);
+	WARN_ONCE(1, "%s: unknown reg_state %d\n", dev->name, reg_state);
 	return " (unknown)";
 }
 

net/core/dev.c

@@ -10339,7 +10339,7 @@ int register_netdevice(struct net_device *dev)
 
 	ret = netdev_register_kobject(dev);
 	write_lock(&dev_base_lock);
-	dev->reg_state = ret ? NETREG_UNREGISTERED : NETREG_REGISTERED;
+	WRITE_ONCE(dev->reg_state, ret ? NETREG_UNREGISTERED : NETREG_REGISTERED);
 	write_unlock(&dev_base_lock);
 	if (ret)
 		goto err_uninit_notify;
@@ -10630,7 +10630,7 @@ void netdev_run_todo(void)
 		}
 
 		write_lock(&dev_base_lock);
-		dev->reg_state = NETREG_UNREGISTERED;
+		WRITE_ONCE(dev->reg_state, NETREG_UNREGISTERED);
 		write_unlock(&dev_base_lock);
 		linkwatch_sync_dev(dev);
 	}
@@ -11050,7 +11050,7 @@ void free_netdev(struct net_device *dev)
 	}
 
 	BUG_ON(dev->reg_state != NETREG_UNREGISTERED);
-	dev->reg_state = NETREG_RELEASED;
+	WRITE_ONCE(dev->reg_state, NETREG_RELEASED);
 
 	/* will free via device release */
 	put_device(&dev->dev);
@@ -11140,7 +11140,7 @@ void unregister_netdevice_many_notify(struct list_head *head,
 		/* And unlink it from device chain. */
 		write_lock(&dev_base_lock);
 		unlist_netdevice(dev, false);
-		dev->reg_state = NETREG_UNREGISTERING;
+		WRITE_ONCE(dev->reg_state, NETREG_UNREGISTERING);
 		write_unlock(&dev_base_lock);
 	}
 	flush_all_backlogs();