linux-kernel - [PATCH 3.16 051/114] net/mlx4_en: fix spurious timestamping callbacks

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Message-ID: <lsq.1465842997.963568950@decadent.org.uk>
Date:	Mon, 13 Jun 2016 19:36:37 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Willem de Bruijn" <willemb@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Eran Ben Elisha" <eranbe@...lanox.com>,
	"Eric Dumazet" <edumazet@...gle.com>
Subject: [PATCH 3.16 051/114] net/mlx4_en: fix spurious timestamping callbacks

3.16.36-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

commit fc96256c906362e845d848d0f6a6354450059e81 upstream.

When multiple skb are TX-completed in a row, we might incorrectly keep
a timestamp of a prior skb and cause extra work.

Fixes: ec693d47010e8 ("net/mlx4_en: Add HW timestamping (TS) support")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Willem de Bruijn <willemb@...gle.com>
Reviewed-by: Eran Ben Elisha <eranbe@...lanox.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/net/ethernet/mellanox/mlx4/en_tx.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -371,7 +371,6 @@ static bool mlx4_en_process_tx_cq(struct
 	u32 packets = 0;
 	u32 bytes = 0;
 	int factor = priv->cqe_factor;
-	u64 timestamp = 0;
 	int done = 0;
 	int budget = priv->tx_work_limit;
 
@@ -405,9 +404,12 @@ static bool mlx4_en_process_tx_cq(struct
 		new_index = be16_to_cpu(cqe->wqe_index) & size_mask;
 
 		do {
+			u64 timestamp = 0;
+
 			txbbs_skipped += ring->last_nr_txbb;
 			ring_index = (ring_index + ring->last_nr_txbb) & size_mask;
-			if (ring->tx_info[ring_index].ts_requested)
+
+			if (unlikely(ring->tx_info[ring_index].ts_requested))
 				timestamp = mlx4_en_get_cqe_ts(cqe);
 
 			/* free next descriptor */