xen-netback: support frontends without feature-rx-notify again

Commit bc96f648df1bbc2729abbb84513cf4f64273a1f1 (xen-netback: make
feature-rx-notify mandatory) incorrectly assumed that there were no
frontends in use that did not support this feature.  But the frontend
driver in MiniOS does not and since this is used by (qemu) stubdoms,
these stopped working.

Netback sort of works as-is in this mode except:

- If there are no Rx requests and the internal Rx queue fills, only
  the drain timeout will wake the thread.  The default drain timeout
  of 10 s would give unacceptable pauses.

- If an Rx stall was detected and the internal Rx queue is drained,
  then the Rx thread would never wake.

Handle these two cases (when feature-rx-notify is disabled) by:

- Reducing the drain timeout to 30 ms.

- Disabling Rx stall detection.

Reported-by: John <jw@nuclearfallout.net>
Tested-by: John <jw@nuclearfallout.net>
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, 14 insertions, 13 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 4a509f715fe8..908e65e9b821 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -60,14 +60,12 @@ module_param(separate_tx_rx_irq, bool, 0644);
  */
 unsigned int rx_drain_timeout_msecs = 10000;
 module_param(rx_drain_timeout_msecs, uint, 0444);
-unsigned int rx_drain_timeout_jiffies;
 
 /* The length of time before the frontend is considered unresponsive
  * because it isn't providing Rx slots.
  */
-static unsigned int rx_stall_timeout_msecs = 60000;
+unsigned int rx_stall_timeout_msecs = 60000;
 module_param(rx_stall_timeout_msecs, uint, 0444);
-static unsigned int rx_stall_timeout_jiffies;
 
 unsigned int xenvif_max_queues;
 module_param_named(max_queues, xenvif_max_queues, uint, 0644);
@@ -2020,7 +2018,7 @@ static bool xenvif_rx_queue_stalled(struct xenvif_queue *queue)
 	return !queue->stalled
 		&& prod - cons < XEN_NETBK_RX_SLOTS_MAX
 		&& time_after(jiffies,
-			      queue->last_rx_time + rx_stall_timeout_jiffies);
+			      queue->last_rx_time + queue->vif->stall_timeout);
 }
 
 static bool xenvif_rx_queue_ready(struct xenvif_queue *queue)
@@ -2038,8 +2036,9 @@ static bool xenvif_have_rx_work(struct xenvif_queue *queue)
 {
 	return (!skb_queue_empty(&queue->rx_queue)
 		&& xenvif_rx_ring_slots_available(queue, XEN_NETBK_RX_SLOTS_MAX))
-		|| xenvif_rx_queue_stalled(queue)
-		|| xenvif_rx_queue_ready(queue)
+		|| (queue->vif->stall_timeout &&
+		    (xenvif_rx_queue_stalled(queue)
+		     || xenvif_rx_queue_ready(queue)))
 		|| kthread_should_stop()
 		|| queue->vif->disabled;
 }
@@ -2092,6 +2091,9 @@ int xenvif_kthread_guest_rx(void *data)
 	struct xenvif_queue *queue = data;
 	struct xenvif *vif = queue->vif;
 
+	if (!vif->stall_timeout)
+		xenvif_queue_carrier_on(queue);
+
 	for (;;) {
 		xenvif_wait_for_rx_work(queue);
 
@@ -2118,10 +2120,12 @@ int xenvif_kthread_guest_rx(void *data)
 		 * while it's probably not responsive, drop the
 		 * carrier so packets are dropped earlier.
 		 */
-		if (xenvif_rx_queue_stalled(queue))
-			xenvif_queue_carrier_off(queue);
-		else if (xenvif_rx_queue_ready(queue))
-			xenvif_queue_carrier_on(queue);
+		if (vif->stall_timeout) {
+			if (xenvif_rx_queue_stalled(queue))
+				xenvif_queue_carrier_off(queue);
+			else if (xenvif_rx_queue_ready(queue))
+				xenvif_queue_carrier_on(queue);
+		}
 
 		/* Queued packets may have foreign pages from other
 		 * domains.  These cannot be queued indefinitely as
@@ -2192,9 +2196,6 @@ static int __init netback_init(void)
 	if (rc)
 		goto failed_init;
 
-	rx_drain_timeout_jiffies = msecs_to_jiffies(rx_drain_timeout_msecs);
-	rx_stall_timeout_jiffies = msecs_to_jiffies(rx_stall_timeout_msecs);
-
 #ifdef CONFIG_DEBUG_FS
 	xen_netback_dbg_root = debugfs_create_dir("xen-netback", NULL);
 	if (IS_ERR_OR_NULL(xen_netback_dbg_root))