xen-netback: Timeout packets in RX path

A malicious or buggy guest can leave its queue filled indefinitely, in which
case qdisc start to queue packets for that VIF. If those packets came from an
another guest, it can block its slots and prevent shutdown. To avoid that, we
make sure the queue is drained in every 10 seconds.
The QDisc queue in worst case takes 3 round to flush usually.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 35 insertions, 2 deletions

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index b646039e539b..9cc9f638f442 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -115,6 +115,18 @@ static irqreturn_t xenvif_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static void xenvif_wake_queue(unsigned long data)
+{
+	struct xenvif *vif = (struct xenvif *)data;
+
+	if (netif_queue_stopped(vif->dev)) {
+		netdev_err(vif->dev, "draining TX queue\n");
+		vif->rx_queue_purge = true;
+		xenvif_kick_thread(vif);
+		netif_wake_queue(vif->dev);
+	}
+}
+
 static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct xenvif *vif = netdev_priv(dev);
@@ -144,8 +156,13 @@ static int xenvif_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	 * then turn off the queue to give the ring a chance to
 	 * drain.
 	 */
-	if (!xenvif_rx_ring_slots_available(vif, min_slots_needed))
+	if (!xenvif_rx_ring_slots_available(vif, min_slots_needed)) {
+		vif->wake_queue.function = xenvif_wake_queue;
+		vif->wake_queue.data = (unsigned long)vif;
 		xenvif_stop_queue(vif);
+		mod_timer(&vif->wake_queue,
+			jiffies + rx_drain_timeout_jiffies);
+	}
 
 	skb_queue_tail(&vif->rx_queue, skb);
 	xenvif_kick_thread(vif);
@@ -353,6 +370,8 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
 	init_timer(&vif->credit_timeout);
 	vif->credit_window_start = get_jiffies_64();
 
+	init_timer(&vif->wake_queue);
+
 	dev->netdev_ops	= &xenvif_netdev_ops;
 	dev->hw_features = NETIF_F_SG |
 		NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |
@@ -531,6 +550,7 @@ void xenvif_disconnect(struct xenvif *vif)
 		xenvif_carrier_off(vif);
 
 	if (vif->task) {
+		del_timer_sync(&vif->wake_queue);
 		kthread_stop(vif->task);
 		vif->task = NULL;
 	}
@@ -556,12 +576,25 @@ void xenvif_disconnect(struct xenvif *vif)
 void xenvif_free(struct xenvif *vif)
 {
 	int i, unmap_timeout = 0;
+	/* Here we want to avoid timeout messages if an skb can be legitimatly
+	 * stucked somewhere else. Realisticly this could be an another vif's
+	 * internal or QDisc queue. That another vif also has this
+	 * rx_drain_timeout_msecs timeout, but the timer only ditches the
+	 * internal queue. After that, the QDisc queue can put in worst case
+	 * XEN_NETIF_RX_RING_SIZE / MAX_SKB_FRAGS skbs into that another vif's
+	 * internal queue, so we need several rounds of such timeouts until we
+	 * can be sure that no another vif should have skb's from us. We are
+	 * not sending more skb's, so newly stucked packets are not interesting
+	 * for us here.
+	 */
+	unsigned int worst_case_skb_lifetime = (rx_drain_timeout_msecs/1000) *
+		DIV_ROUND_UP(XENVIF_QUEUE_LENGTH, (XEN_NETIF_RX_RING_SIZE / MAX_SKB_FRAGS));
 
 	for (i = 0; i < MAX_PENDING_REQS; ++i) {
 		if (vif->grant_tx_handle[i] != NETBACK_INVALID_HANDLE) {
 			unmap_timeout++;
 			schedule_timeout(msecs_to_jiffies(1000));
-			if (unmap_timeout > 9 &&
+			if (unmap_timeout > worst_case_skb_lifetime &&
 			    net_ratelimit())
 				netdev_err(vif->dev,
 					   "Page still granted! Index: %x\n",