net-sysfs: move the rtnl unlock up in the xps show helpers

Now that nr_ids and num_tc are stored in the xps dev_maps, which are RCU
protected, we do not have the need to protect the maps in the rtnl lock.
Move the rtnl unlock up so we reduce the rtnl locking section.

We also increase the reference count on the subordinate device if any,
as we don't want this device to be freed while we use it (now that the
rtnl lock isn't protecting it in the whole function).
Signed-off-by: NAntoine Tenart <atenart@kernel.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/core/net-sysfs.c

@@ -1383,10 +1383,14 @@ static ssize_t xps_cpus_show(struct netdev_queue *queue,
 
 	tc = netdev_txq_to_tc(dev, index);
 	if (tc < 0) {
-		ret = -EINVAL;
-		goto err_rtnl_unlock;
+		rtnl_unlock();
+		return -EINVAL;
 	}
 
+	/* Make sure the subordinate device can't be freed */
+	get_device(&dev->dev);
+	rtnl_unlock();
+
 	rcu_read_lock();
 	dev_maps = rcu_dereference(dev->xps_maps[XPS_CPUS]);
 	nr_ids = dev_maps ? dev_maps->nr_ids : nr_cpu_ids;
@@ -1417,8 +1421,7 @@ static ssize_t xps_cpus_show(struct netdev_queue *queue,
 	}
 out_no_maps:
 	rcu_read_unlock();
-
-	rtnl_unlock();
+	put_device(&dev->dev);
 
 	len = bitmap_print_to_pagebuf(false, buf, mask, nr_ids);
 	bitmap_free(mask);
@@ -1426,8 +1429,7 @@ static ssize_t xps_cpus_show(struct netdev_queue *queue,
 
 err_rcu_unlock:
 	rcu_read_unlock();
-err_rtnl_unlock:
-	rtnl_unlock();
+	put_device(&dev->dev);
 	return ret;
 }
 
@@ -1486,10 +1488,9 @@ static ssize_t xps_rxqs_show(struct netdev_queue *queue, char *buf)
 		return restart_syscall();
 
 	tc = netdev_txq_to_tc(dev, index);
-	if (tc < 0) {
-		ret = -EINVAL;
-		goto err_rtnl_unlock;
-	}
+	rtnl_unlock();
+	if (tc < 0)
+		return -EINVAL;
 
 	rcu_read_lock();
 	dev_maps = rcu_dereference(dev->xps_maps[XPS_RXQS]);
@@ -1522,8 +1523,6 @@ static ssize_t xps_rxqs_show(struct netdev_queue *queue, char *buf)
 out_no_maps:
 	rcu_read_unlock();
 
-	rtnl_unlock();
-
 	len = bitmap_print_to_pagebuf(false, buf, mask, nr_ids);
 	bitmap_free(mask);
 
@@ -1531,8 +1530,6 @@ static ssize_t xps_rxqs_show(struct netdev_queue *queue, char *buf)
 
 err_rcu_unlock:
 	rcu_read_unlock();
-err_rtnl_unlock:
-	rtnl_unlock();
 	return ret;
 }