netdev - [PATCH net-next] mlx4: do not use priv->stats_lock in mlx4_en_auto

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Date:   Wed, 23 Nov 2016 09:46:52 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>, Tariq Toukan <tariqt@...lanox.com>
Subject: [PATCH net-next] mlx4: do not use priv->stats_lock in
 mlx4_en_auto_moderation()

From: Eric Dumazet <edumazet@...gle.com>

Per RX ring packets/bytes counters are not protected by global
priv->stats_lock.

Better not confuse the reader, and use READ_ONCE() to show we read
these counters without surrounding synchronization.

Interrupt moderation is best effort, and we do not really care of
ultra precise counters.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 drivers/net/ethernet/mellanox/mlx4/en_netdev.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
index 9a807e93c9fdd81e61e561208aa1480a244d0bdb..b964bdcd4ae509a7e693215e8b32f040218e252c 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
@@ -1391,10 +1391,8 @@ static void mlx4_en_auto_moderation(struct mlx4_en_priv *priv)
 		return;
 
 	for (ring = 0; ring < priv->rx_ring_num; ring++) {
-		spin_lock_bh(&priv->stats_lock);
-		rx_packets = priv->rx_ring[ring]->packets;
-		rx_bytes = priv->rx_ring[ring]->bytes;
-		spin_unlock_bh(&priv->stats_lock);
+		rx_packets = READ_ONCE(priv->rx_ring[ring]->packets);
+		rx_bytes = READ_ONCE(priv->rx_ring[ring]->bytes);
 
 		rx_pkt_diff = ((unsigned long) (rx_packets -
 				priv->last_moder_packets[ring]));