net: mvneta: fix improper tx queue usage in mvneta_tx()

mvneta_tx() was using a static tx queue number causing crashes as
soon as a little bit of traffic was sent via the interface, because
it is normally expected that the same queue should be used as in
dev_queue_xmit().

As suggested by Ben Hutchings, let's use skb_get_queue_mapping() to
get the proper Tx queue number, and use alloc_etherdev_mqs() instead
of alloc_etherdev_mq() to create the queues.

Both my Mirabox and my OpenBlocks AX3 used to crash without this patch
and don't anymore with it. The issue appeared in 3.8 but became more
visible after the fix allowing GSO to be enabled.

Original work was done by Dmitri Epshtein and Thomas Petazzoni. I
just adapted it to take care of Ben's comments.
Signed-off-by: Willy Tarreau <w@1wt.eu>
Cc: Dmitri Epshtein <dima@marvell.com>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Tested-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/marvell/mvneta.c

@@ -374,7 +374,6 @@ static int rxq_number = 8;
 static int txq_number = 8;
 
 static int rxq_def;
-static int txq_def;
 
 #define MVNETA_DRIVER_NAME "mvneta"
 #define MVNETA_DRIVER_VERSION "1.0"
@@ -1475,7 +1474,8 @@ static int mvneta_tx_frag_process(struct mvneta_port *pp, struct sk_buff *skb,
 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 = skb_get_queue_mapping(skb);
+	struct mvneta_tx_queue *txq = &pp->txqs[txq_id];
 	struct mvneta_tx_desc *tx_desc;
 	struct netdev_queue *nq;
 	int frags = 0;
@@ -1485,7 +1485,7 @@ 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);
@@ -2689,7 +2689,7 @@ static int mvneta_probe(struct platform_device *pdev)
 		return -EINVAL;
 	}
 
-	dev = alloc_etherdev_mq(sizeof(struct mvneta_port), 8);
+	dev = alloc_etherdev_mqs(sizeof(struct mvneta_port), txq_number, rxq_number);
 	if (!dev)
 		return -ENOMEM;
 
@@ -2844,4 +2844,3 @@ module_param(rxq_number, int, S_IRUGO);
 module_param(txq_number, int, S_IRUGO);
 
 module_param(rxq_def, int, S_IRUGO);
-module_param(txq_def, int, S_IRUGO);