can: c_can: Provide protection in the xmit path

The network core does not serialize the access to the hardware. The
xmit related code lets the following happen:

CPU0 	     	       CPU1
interrupt()
 do_poll()
   c_can_do_tx()
    Fiddle with HW and	xmit()
    internal data	  Fiddle with HW and
    	     		  internal data

due the complete lack of serialization.

Add proper locking.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/c_can/c_can.c

@@ -549,6 +549,7 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
 	if (can_dropped_invalid_skb(dev, skb))
 		return NETDEV_TX_OK;
 
+	spin_lock_bh(&priv->xmit_lock);
 	msg_obj_no = get_tx_next_msg_obj(priv);
 
 	/* prepare message object for transmission */
@@ -563,6 +564,7 @@ static netdev_tx_t c_can_start_xmit(struct sk_buff *skb,
 	if (c_can_is_next_tx_obj_busy(priv, get_tx_next_msg_obj(priv)) ||
 			(priv->tx_next & C_CAN_NEXT_MSG_OBJ_MASK) == 0)
 		netif_stop_queue(dev);
+	spin_unlock_bh(&priv->xmit_lock);
 
 	return NETDEV_TX_OK;
 }
@@ -787,7 +789,9 @@ static void c_can_do_tx(struct net_device *dev)
 	struct c_can_priv *priv = netdev_priv(dev);
 	struct net_device_stats *stats = &dev->stats;
 
-	for (/* nix */; (priv->tx_next - priv->tx_echo) > 0; priv->tx_echo++) {
+	spin_lock_bh(&priv->xmit_lock);
+
+	for (; (priv->tx_next - priv->tx_echo) > 0; priv->tx_echo++) {
 		msg_obj_no = get_tx_echo_msg_obj(priv);
 		val = c_can_read_reg32(priv, C_CAN_TXRQST1_REG);
 		if (!(val & (1 << (msg_obj_no - 1)))) {
@@ -809,6 +813,8 @@ static void c_can_do_tx(struct net_device *dev)
 	if (((priv->tx_next & C_CAN_NEXT_MSG_OBJ_MASK) != 0) ||
 			((priv->tx_echo & C_CAN_NEXT_MSG_OBJ_MASK) == 0))
 		netif_wake_queue(dev);
+
+	spin_unlock_bh(&priv->xmit_lock);
 }
 
 /*
@@ -1262,6 +1268,7 @@ struct net_device *alloc_c_can_dev(void)
 		return NULL;
 
 	priv = netdev_priv(dev);
+	spin_lock_init(&priv->xmit_lock);
 	netif_napi_add(dev, &priv->napi, c_can_poll, C_CAN_NAPI_WEIGHT);
 
 	priv->dev = dev;

drivers/net/can/c_can/c_can.h

@@ -156,6 +156,7 @@ struct c_can_priv {
 	struct napi_struct napi;
 	struct net_device *dev;
 	struct device *device;
+	spinlock_t xmit_lock;
 	int tx_object;
 	int current_status;
 	int last_status;