net/mlx4_en: get rid of ret_stats

mlx4 uses a private struct net_device_stats in a vain attempt
to avoid races.

This is buggy because multiple cpus could call mlx4_en_get_stats()
at the same time, so ret_stats can not guarantee stable results.

To fix this, we need to switch to ndo_get_stats64() as this
method provides per-thread storage.

This allows to reduce mlx4_en_priv bloat.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Eugenia Emantayev <eugenia@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx4/en_netdev.c

@@ -1296,15 +1296,16 @@ static void mlx4_en_tx_timeout(struct net_device *dev)
 }
 
 
-static struct net_device_stats *mlx4_en_get_stats(struct net_device *dev)
+static struct rtnl_link_stats64 *
+mlx4_en_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
 {
 	struct mlx4_en_priv *priv = netdev_priv(dev);
 
 	spin_lock_bh(&priv->stats_lock);
-	memcpy(&priv->ret_stats, &priv->stats, sizeof(priv->stats));
+	netdev_stats_to_stats64(stats, &priv->stats);
 	spin_unlock_bh(&priv->stats_lock);
 
-	return &priv->ret_stats;
+	return stats;
 }
 
 static void mlx4_en_set_default_moderation(struct mlx4_en_priv *priv)
@@ -2487,7 +2488,7 @@ static const struct net_device_ops mlx4_netdev_ops = {
 	.ndo_stop		= mlx4_en_close,
 	.ndo_start_xmit		= mlx4_en_xmit,
 	.ndo_select_queue	= mlx4_en_select_queue,
-	.ndo_get_stats		= mlx4_en_get_stats,
+	.ndo_get_stats64	= mlx4_en_get_stats64,
 	.ndo_set_rx_mode	= mlx4_en_set_rx_mode,
 	.ndo_set_mac_address	= mlx4_en_set_mac,
 	.ndo_validate_addr	= eth_validate_addr,
@@ -2519,7 +2520,7 @@ static const struct net_device_ops mlx4_netdev_ops_master = {
 	.ndo_stop		= mlx4_en_close,
 	.ndo_start_xmit		= mlx4_en_xmit,
 	.ndo_select_queue	= mlx4_en_select_queue,
-	.ndo_get_stats		= mlx4_en_get_stats,
+	.ndo_get_stats64	= mlx4_en_get_stats64,
 	.ndo_set_rx_mode	= mlx4_en_set_rx_mode,
 	.ndo_set_mac_address	= mlx4_en_set_mac,
 	.ndo_validate_addr	= eth_validate_addr,

drivers/net/ethernet/mellanox/mlx4/mlx4_en.h

@@ -484,7 +484,6 @@ struct mlx4_en_priv {
 	struct net_device *dev;
 	unsigned long active_vlans[BITS_TO_LONGS(VLAN_N_VID)];
 	struct net_device_stats stats;
-	struct net_device_stats ret_stats;
 	struct mlx4_en_port_state port_state;
 	spinlock_t stats_lock;
 	struct ethtool_flow_id ethtool_rules[MAX_NUM_OF_FS_RULES];