[PATCH 3.8-rc] net: mvneta: fix driver operation in SMP context

[Thomas Petazzoni]

From: Dmitri Epshtein <dima at marvell.com>

In order for the driver to behave properly in a SMP context, the same
transmit queue should be used by the kernel in dev_queue_xmit() and in
the driver's mvneta_tx() function. To achieve that, the driver now
implements the ->ndo_select_txq() operation.

For now, it always returns the same transmit queue, txq_def, until the
driver is expanded to properly take advantage of the multiqueue
capabilities of the hardware.

Without this patch, the network driver crashes the kernel almost
immediately on Armada XP platforms, if the network load is at least a
little bit parallel (i.e several threads).

[Thomas Petazzoni: reword commit message]
Signed-off-by: Dmitri Epshtein <dima at marvell.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
---
This is 3.8-rc material.
---
 drivers/net/ethernet/marvell/mvneta.c |   17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
index b6025c3..af2c421 100644
--- a/drivers/net/ethernet/marvell/mvneta.c
+++ b/drivers/net/ethernet/marvell/mvneta.c
@@ -1310,6 +1310,17 @@ static u32 mvneta_skb_tx_csum(struct mvneta_port *pp, struct sk_buff *skb)
 	return MVNETA_TX_L4_CSUM_NOT;
 }
 
+static u16 mvneta_tx_policy(struct mvneta_port *pp, struct sk_buff *skb)
+{
+	return (u16)txq_def;
+}
+
+static u16 mvneta_select_txq(struct net_device *dev, struct sk_buff *skb)
+{
+	struct mvneta_port *pp = netdev_priv(dev);
+	return mvneta_tx_policy(pp, skb);
+}
+
 /* Returns rx queue pointer (find last set bit) according to causeRxTx
  * value
  */
@@ -1476,7 +1487,8 @@ error:
 static int mvneta_tx(struct sk_buff *skb, struct net_device *dev)
 {
 	struct mvneta_port *pp = netdev_priv(dev);
-	struct mvneta_tx_queue *txq = &pp->txqs[txq_def];
+	u16 txq_id = mvneta_tx_policy(pp, skb);
+	struct mvneta_tx_queue *txq = &pp->txqs[txq_id];
 	struct mvneta_tx_desc *tx_desc;
 	struct netdev_queue *nq;
 	int frags = 0;
@@ -1486,7 +1498,7 @@ static int mvneta_tx(struct sk_buff *skb, struct net_device *dev)
 		goto out;
 
 	frags = skb_shinfo(skb)->nr_frags + 1;
-	nq    = netdev_get_tx_queue(dev, txq_def);
+	nq    = netdev_get_tx_queue(dev, txq_id);
 
 	/* Get a descriptor for the first part of the packet */
 	tx_desc = mvneta_txq_next_desc_get(txq);
@@ -2550,6 +2562,7 @@ static const struct net_device_ops mvneta_netdev_ops = {
 	.ndo_change_mtu      = mvneta_change_mtu,
 	.ndo_tx_timeout      = mvneta_tx_timeout,
 	.ndo_get_stats64     = mvneta_get_stats64,
+	.ndo_select_queue    = mvneta_select_txq,
 };
 
 const struct ethtool_ops mvneta_eth_tool_ops = {
-- 
1.7.9.5