virtio_net: return NETDEV_TX_BUSY instead of queueing an extra skb.

This effectively reverts 99ffc696d10b28580fe93441d627cf290ac4484c
"virtio: wean net driver off NETDEV_TX_BUSY".

The complexity of queuing an skb (setting a tasklet to re-xmit) is
questionable, especially once we get rid of the other reason for the
tasklet in the next patch.

If the skb won't fit in the tx queue, just return NETDEV_TX_BUSY.
This is frowned upon, so a followup patch uses a more complex solution.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 10 insertions, 36 deletions

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index dc4c68718976..222f3d098ae4 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -48,9 +48,6 @@ struct virtnet_info
         struct napi_struct napi;
         unsigned int status;
 
-        /* The skb we couldn't send because buffers were full. */
-        struct sk_buff *last_xmit_skb;
-
         /* If we need to free in a timer, this is it. */
         struct timer_list xmit_free_timer;
 
@@ -120,9 +117,8 @@ static void skb_xmit_done(struct virtqueue *svq)
         /* We were probably 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);
+        if (vi->free_in_tasklet)
+                tasklet_schedule(&vi->tasklet);
 }
 
 static void receive_skb(struct net_device *dev, struct sk_buff *skb,
@@ -543,12 +539,7 @@ 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;
-        }
-        if (vi->free_in_tasklet)
-                free_old_xmit_skbs(vi);
+        free_old_xmit_skbs(vi);
         netif_tx_unlock_bh(vi->dev);
 }
 
@@ -560,28 +551,16 @@ again:
         /* Free up any pending old buffers before queueing new ones. */
         free_old_xmit_skbs(vi);
 
-        /* If we has a buffer left over from last time, send it now. */
-        if (unlikely(vi->last_xmit_skb) &&
-            xmit_skb(vi, vi->last_xmit_skb) < 0)
-                goto stop_queue;
-
-        vi->last_xmit_skb = NULL;
-
         /* Put new one in send queue and do transmit */
-        if (likely(skb)) {
-                __skb_queue_head(&vi->send, skb);
-                if (xmit_skb(vi, skb) < 0) {
-                        vi->last_xmit_skb = skb;
-                        skb = NULL;
-                        goto stop_queue;
-                }
+        __skb_queue_head(&vi->send, skb);
+        if (likely(xmit_skb(vi, skb) >= 0)) {
+                vi->svq->vq_ops->kick(vi->svq);
+                return NETDEV_TX_OK;
         }
-done:
-        vi->svq->vq_ops->kick(vi->svq);
-        return NETDEV_TX_OK;
 
-stop_queue:
+        /* Ring too full for this packet, remove it from queue again. */
         pr_debug("%s: virtio not prepared to send\n", dev->name);
+        __skb_unlink(skb, &vi->send);
         netif_stop_queue(dev);
 
         /* Activate callback for using skbs: if this returns false it
@@ -591,12 +570,7 @@ stop_queue:
                 netif_start_queue(dev);
                 goto again;
         }
-        if (skb) {
-                /* Drop this skb: we only queue one. */
-                vi->dev->stats.tx_dropped++;
-                kfree_skb(skb);
-        }
-        goto done;
+        return NETDEV_TX_BUSY;
 }
 
 static int virtnet_set_mac_address(struct net_device *dev, void *p)