xen-netback: reintroduce guest Rx stall detection

If a frontend not receiving packets it is useful to detect this and
turn off the carrier so packets are dropped early instead of being
queued and drained when they expire.

A to-guest queue is stalled if it doesn't have enough free slots for a
an extended period of time (default 60 s).

If at least one queue is stalled, the carrier is turned off (in the
expectation that the other queues will soon stall as well).  The
carrier is only turned on once all queues are ready.

When the frontend connects, all the queues start in the stalled state
and only become ready once the frontend queues enough Rx requests.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/net/xen-netback/interface.c b/drivers/net/xen-netback/interface.c
index a134d52f55b4..895fe84011e7 100644
--- a/drivers/net/xen-netback/interface.c
+++ b/drivers/net/xen-netback/interface.c
@@ -419,6 +419,8 @@ struct xenvif *xenvif_alloc(struct device *parent, domid_t domid,
         vif->queues = NULL;
         vif->num_queues = 0;
 
+        spin_lock_init(&vif->lock);
+
         dev->netdev_ops = &xenvif_netdev_ops;
         dev->hw_features = NETIF_F_SG |
                 NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |
@@ -505,7 +507,6 @@ void xenvif_carrier_on(struct xenvif *vif)
                 dev_set_mtu(vif->dev, ETH_DATA_LEN);
         netdev_update_features(vif->dev);
         set_bit(VIF_STATUS_CONNECTED, &vif->status);
-        netif_carrier_on(vif->dev);
         if (netif_running(vif->dev))
                 xenvif_up(vif);
         rtnl_unlock();
@@ -565,6 +566,8 @@ int xenvif_connect(struct xenvif_queue *queue, unsigned long tx_ring_ref,
                 disable_irq(queue->rx_irq);
         }
 
+        queue->stalled = true;
+
         task = kthread_create(xenvif_kthread_guest_rx,
                               (void *)queue, "%s-guest-rx", queue->name);
         if (IS_ERR(task)) {