net/mlx4_en: Fixing TX queue stop/wake flow

Removing the ring->blocked flag, it is redundant and leads to a race:

We close the TX queue and then set the "blocked" flag.
Between those 2 operations the completion function can check the "blocked"
flag, sees that it is 0, and wouldn't open the TX queue.

Using netif_tx_queue_stopped to check the state of the queue to avoid this race.

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 7 insertions, 11 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index 019d856b133..10bba09c44e 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -164,7 +164,6 @@ int mlx4_en_activate_tx_ring(struct mlx4_en_priv *priv,
         ring->cons = 0xffffffff;
         ring->last_nr_txbb = 1;
         ring->poll_cnt = 0;
-        ring->blocked = 0;
         memset(ring->tx_info, 0, ring->size * sizeof(struct mlx4_en_tx_info));
         memset(ring->buf, 0, ring->buf_size);
 
@@ -365,14 +364,13 @@ static void mlx4_en_process_tx_cq(struct net_device *dev, struct mlx4_en_cq *cq)
         ring->cons += txbbs_skipped;
         netdev_tx_completed_queue(ring->tx_queue, packets, bytes);
 
-        /* Wakeup Tx queue if this ring stopped it */
-        if (unlikely(ring->blocked)) {
-                if ((u32) (ring->prod - ring->cons) <=
-                     ring->size - HEADROOM - MAX_DESC_TXBBS) {
-                        ring->blocked = 0;
-                        netif_tx_wake_queue(ring->tx_queue);
-                        priv->port_stats.wake_queue++;
-                }
+        /*
+         * Wakeup Tx queue if this stopped, and at least 1 packet
+         * was completed
+         */
+        if (netif_tx_queue_stopped(ring->tx_queue) && txbbs_skipped > 0) {
+                netif_tx_wake_queue(ring->tx_queue);
+                priv->port_stats.wake_queue++;
         }
 }
 
@@ -592,7 +590,6 @@ netdev_tx_t mlx4_en_xmit(struct sk_buff *skb, struct net_device *dev)
                      ring->size - HEADROOM - MAX_DESC_TXBBS)) {
                 /* every full Tx ring stops queue */
                 netif_tx_stop_queue(ring->tx_queue);
-                ring->blocked = 1;
                 priv->port_stats.queue_stopped++;
 
                 return NETDEV_TX_BUSY;
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
index 5f1ab105deb..9d27e42264e 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
@@ -248,7 +248,6 @@ struct mlx4_en_tx_ring {
         u32 doorbell_qpn;
         void *buf;
         u16 poll_cnt;
-        int blocked;
         struct mlx4_en_tx_info *tx_info;
         u8 *bounce_buf;
         u32 last_nr_txbb;