xen-netback: protect resource cleaning on XenBus disconnect

vif->lock is used to protect statistics gathering agents from using the
queue structure during cleaning.

Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/xen-netback/interface.c

@@ -221,18 +221,18 @@ static struct net_device_stats *xenvif_get_stats(struct net_device *dev)
 {
 	struct xenvif *vif = netdev_priv(dev);
 	struct xenvif_queue *queue = NULL;
-	unsigned int num_queues = vif->num_queues;
 	unsigned long rx_bytes = 0;
 	unsigned long rx_packets = 0;
 	unsigned long tx_bytes = 0;
 	unsigned long tx_packets = 0;
 	unsigned int index;
 
+	spin_lock(&vif->lock);
 	if (vif->queues == NULL)
 		goto out;
 
 	/* Aggregate tx and rx stats from each queue */
-	for (index = 0; index < num_queues; ++index) {
+	for (index = 0; index < vif->num_queues; ++index) {
 		queue = &vif->queues[index];
 		rx_bytes += queue->stats.rx_bytes;
 		rx_packets += queue->stats.rx_packets;
@@ -241,6 +241,8 @@ static struct net_device_stats *xenvif_get_stats(struct net_device *dev)
 	}
 
 out:
+	spin_unlock(&vif->lock);
+
 	vif->dev->stats.rx_bytes = rx_bytes;
 	vif->dev->stats.rx_packets = rx_packets;
 	vif->dev->stats.tx_bytes = tx_bytes;

drivers/net/xen-netback/xenbus.c

@@ -503,9 +503,11 @@ static void backend_disconnect(struct backend_info *be)
 		for (queue_index = 0; queue_index < be->vif->num_queues; ++queue_index)
 			xenvif_deinit_queue(&be->vif->queues[queue_index]);
 
+		spin_lock(&be->vif->lock);
 		vfree(be->vif->queues);
 		be->vif->num_queues = 0;
 		be->vif->queues = NULL;
+		spin_unlock(&be->vif->lock);
 
 		xenvif_disconnect_ctrl(be->vif);
 	}