net: annotate data-races around dev->name_assign_type

name_assign_type_show() runs locklessly, we should annotate
accesses to dev->name_assign_type.

Alternative would be to grab devnet_rename_sem semaphore
from name_assign_type_show(), but this would not bring
more accuracy.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/dev.c

@@ -1228,13 +1228,13 @@ int dev_change_name(struct net_device *dev, const char *newname)
 			    dev->flags & IFF_UP ? " (while UP)" : "");
 
 	old_assign_type = dev->name_assign_type;
-	dev->name_assign_type = NET_NAME_RENAMED;
+	WRITE_ONCE(dev->name_assign_type, NET_NAME_RENAMED);
 
 rollback:
 	ret = device_rename(&dev->dev, dev->name);
 	if (ret) {
 		memcpy(dev->name, oldname, IFNAMSIZ);
-		dev->name_assign_type = old_assign_type;
+		WRITE_ONCE(dev->name_assign_type, old_assign_type);
 		up_write(&devnet_rename_sem);
 		return ret;
 	}
@@ -1263,7 +1263,7 @@ int dev_change_name(struct net_device *dev, const char *newname)
 			down_write(&devnet_rename_sem);
 			memcpy(dev->name, oldname, IFNAMSIZ);
 			memcpy(oldname, newname, IFNAMSIZ);
-			dev->name_assign_type = old_assign_type;
+			WRITE_ONCE(dev->name_assign_type, old_assign_type);
 			old_assign_type = NET_NAME_RENAMED;
 			goto rollback;
 		} else {

net/core/net-sysfs.c

@@ -125,7 +125,7 @@ static DEVICE_ATTR_RO(iflink);
 
 static ssize_t format_name_assign_type(const struct net_device *dev, char *buf)
 {
-	return sysfs_emit(buf, fmt_dec, dev->name_assign_type);
+	return sysfs_emit(buf, fmt_dec, READ_ONCE(dev->name_assign_type));
 }
 
 static ssize_t name_assign_type_show(struct device *dev,
@@ -135,7 +135,7 @@ static ssize_t name_assign_type_show(struct device *dev,
 	struct net_device *ndev = to_net_dev(dev);
 	ssize_t ret = -EINVAL;
 
-	if (ndev->name_assign_type != NET_NAME_UNKNOWN)
+	if (READ_ONCE(ndev->name_assign_type) != NET_NAME_UNKNOWN)
 		ret = netdev_show(dev, attr, buf, format_name_assign_type);
 
 	return ret;