stmmac: protect tx process with lock (V4)

This patch fixes a problem raised on Orly ARM SMP platform
where, in case of fragmented frames, the descriptors
in the TX ring resulted broken. This was due to a missing lock
protection in the tx process.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Tested-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/stmmac.h

@@ -70,6 +70,7 @@ struct stmmac_priv {
 
 	u32 msg_enable;
 	spinlock_t lock;
+	spinlock_t tx_lock;
 	int wolopts;
 	int wolenabled;
 	int wol_irq;

drivers/net/ethernet/stmicro/stmmac/stmmac_main.c

@@ -588,6 +588,8 @@ static void stmmac_tx(struct stmmac_priv *priv)
 {
 	unsigned int txsize = priv->dma_tx_size;
 
+	spin_lock(&priv->tx_lock);
+
 	while (priv->dirty_tx != priv->cur_tx) {
 		int last;
 		unsigned int entry = priv->dirty_tx % txsize;
@@ -651,6 +653,7 @@ static void stmmac_tx(struct stmmac_priv *priv)
 		}
 		netif_tx_unlock(priv->dev);
 	}
+	spin_unlock(&priv->tx_lock);
 }
 
 static inline void stmmac_enable_irq(struct stmmac_priv *priv)
@@ -1078,6 +1081,8 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 		return NETDEV_TX_BUSY;
 	}
 
+	spin_lock(&priv->tx_lock);
+
 	entry = priv->cur_tx % txsize;
 
 #ifdef STMMAC_XMIT_DEBUG
@@ -1166,6 +1171,8 @@ static netdev_tx_t stmmac_xmit(struct sk_buff *skb, struct net_device *dev)
 
 	priv->hw->dma->enable_dma_transmission(priv->ioaddr);
 
+	spin_unlock(&priv->tx_lock);
+
 	return NETDEV_TX_OK;
 }
 
@@ -1731,6 +1738,7 @@ static int stmmac_probe(struct net_device *dev)
 			"please, use ifconfig or nwhwconfig!\n");
 
 	spin_lock_init(&priv->lock);
+	spin_lock_init(&priv->tx_lock);
 
 	ret = register_netdev(dev);
 	if (ret) {