virtio: fix delayed xmit of packet and freeing of old packets.

Because we cache the last failed-to-xmit packet, if there are no
packets queued behind that one we may never send it (reproduced here
as TCP stalls, "cured" by an outgoing ping).

Cc: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index d50f4fe352b3..5450eac9e263 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -47,6 +47,9 @@ struct virtnet_info
         /* Number of input buffers, and max we've ever had. */
         unsigned int num, max;
 
+        /* For cleaning up after transmission. */
+        struct tasklet_struct tasklet;
+
         /* Receive & send queues. */
         struct sk_buff_head recv;
         struct sk_buff_head send;
@@ -68,8 +71,13 @@ static void skb_xmit_done(struct virtqueue *svq)
 
         /* Suppress further interrupts. */
         svq->vq_ops->disable_cb(svq);
+
         /* We were waiting for more output buffers. */
         netif_wake_queue(vi->dev);
+
+        /* Make sure we re-xmit last_xmit_skb: if there are no more packets
+         * queued, start_xmit won't be called. */
+        tasklet_schedule(&vi->tasklet);
 }
 
 static void receive_skb(struct net_device *dev, struct sk_buff *skb,
@@ -278,6 +286,18 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
         return vi->svq->vq_ops->add_buf(vi->svq, sg, num, 0, skb);
 }
 
+static void xmit_tasklet(unsigned long data)
+{
+        struct virtnet_info *vi = (void *)data;
+
+        netif_tx_lock_bh(vi->dev);
+        if (vi->last_xmit_skb && xmit_skb(vi, vi->last_xmit_skb) == 0) {
+                vi->svq->vq_ops->kick(vi->svq);
+                vi->last_xmit_skb = NULL;
+        }
+        netif_tx_unlock_bh(vi->dev);
+}
+
 static int start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
         struct virtnet_info *vi = netdev_priv(dev);
@@ -432,6 +452,8 @@ static int virtnet_probe(struct virtio_device *vdev)
         skb_queue_head_init(&vi->recv);
         skb_queue_head_init(&vi->send);
 
+        tasklet_init(&vi->tasklet, xmit_tasklet, (unsigned long)vi);
+
         err = register_netdev(dev);
         if (err) {
                 pr_debug("virtio_net: registering device failed\n");