xen-netback: Turn off the carrier if the guest is not able to receive

Currently when the guest is not able to receive more packets, qdisc layer starts
a timer, and when it goes off, qdisc is started again to deliver a packet again.
This is a very slow way to drain the queues, consumes unnecessary resources and
slows down other guests shutdown.
This patch change the behaviour by turning the carrier off when that timer
fires, so all the packets are freed up which were stucked waiting for that vif.
Instead of the rx_queue_purge bool it uses the VIF_STATUS_RX_PURGE_EVENT bit to
signal the thread that either the timeout happened or an RX interrupt arrived,
so the thread can check what it should do. It also disables NAPI, so the guest
can't transmit, but leaves the interrupts on, so it can resurrect.
Only the queues which brought down the interface can enable it again, the bit
QUEUE_STATUS_RX_STALLED makes sure of that.

Signed-off-by: Zoltan Kiss <zoltan.kiss@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Cc: netdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: xen-devel@lists.xenproject.org
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 83 insertions, 14 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index 6c4cc0f..aa20933 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1869,8 +1869,7 @@ void xenvif_idx_unmap(struct xenvif_queue *queue, u16 pending_idx)
 static inline int rx_work_todo(struct xenvif_queue *queue)
 {
 	return (!skb_queue_empty(&queue->rx_queue) &&
-	       xenvif_rx_ring_slots_available(queue, queue->rx_last_skb_slots)) ||
-	       queue->rx_queue_purge;
+	       xenvif_rx_ring_slots_available(queue, queue->rx_last_skb_slots));
 }
 
 static inline int tx_work_todo(struct xenvif_queue *queue)
@@ -1935,6 +1934,75 @@ static void xenvif_start_queue(struct xenvif_queue *queue)
 		xenvif_wake_queue(queue);
 }
 
+/* Only called from the queue's thread, it handles the situation when the guest
+ * doesn't post enough requests on the receiving ring.
+ * First xenvif_start_xmit disables QDisc and start a timer, and then either the
+ * timer fires, or the guest send an interrupt after posting new request. If it
+ * is the timer, the carrier is turned off here.
+ * */
+static void xenvif_rx_purge_event(struct xenvif_queue *queue)
+{
+	/* Either the last unsuccesful skb or at least 1 slot should fit */
+	int needed = queue->rx_last_skb_slots ?
+		     queue->rx_last_skb_slots : 1;
+
+	/* It is assumed that if the guest post new slots after this, the RX
+	 * interrupt will set the QUEUE_STATUS_RX_PURGE_EVENT bit and wake up
+	 * the thread again
+	 */
+	set_bit(QUEUE_STATUS_RX_STALLED, &queue->status);
+	if (!xenvif_rx_ring_slots_available(queue, needed)) {
+		rtnl_lock();
+		if (netif_carrier_ok(queue->vif->dev)) {
+			/* Timer fired and there are still no slots. Turn off
+			 * everything except the interrupts
+			 */
+			netif_carrier_off(queue->vif->dev);
+			skb_queue_purge(&queue->rx_queue);
+			queue->rx_last_skb_slots = 0;
+			if (net_ratelimit())
+				netdev_err(queue->vif->dev, "Carrier off due to lack of guest response on queue %d\n", queue->id);
+		} else {
+			/* Probably an another queue already turned the carrier
+			 * off, make sure nothing is stucked in the internal
+			 * queue of this queue
+			 */
+			skb_queue_purge(&queue->rx_queue);
+			queue->rx_last_skb_slots = 0;
+		}
+		rtnl_unlock();
+	} else if (!netif_carrier_ok(queue->vif->dev)) {
+		unsigned int num_queues = queue->vif->num_queues;
+		unsigned int i;
+		/* The carrier was down, but an interrupt kicked
+		 * the thread again after new requests were
+		 * posted
+		 */
+		clear_bit(QUEUE_STATUS_RX_STALLED,
+			  &queue->status);
+		rtnl_lock();
+		netif_carrier_on(queue->vif->dev);
+		netif_tx_wake_all_queues(queue->vif->dev);
+		rtnl_unlock();
+
+		for (i = 0; i < num_queues; i++) {
+			struct xenvif_queue *temp = &queue->vif->queues[i];
+
+			xenvif_napi_schedule_or_enable_events(temp);
+		}
+		if (net_ratelimit())
+			netdev_err(queue->vif->dev, "Carrier on again\n");
+	} else {
+		/* Queuing were stopped, but the guest posted
+		 * new requests and sent an interrupt
+		 */
+		clear_bit(QUEUE_STATUS_RX_STALLED,
+			  &queue->status);
+		del_timer_sync(&queue->rx_stalled);
+		xenvif_start_queue(queue);
+	}
+}
+
 int xenvif_kthread_guest_rx(void *data)
 {
 	struct xenvif_queue *queue = data;
@@ -1944,8 +2012,12 @@ int xenvif_kthread_guest_rx(void *data)
 		wait_event_interruptible(queue->wq,
 					 rx_work_todo(queue) ||
 					 queue->vif->disabled ||
+					 test_bit(QUEUE_STATUS_RX_PURGE_EVENT, &queue->status) ||
 					 kthread_should_stop());
 
+		if (kthread_should_stop())
+			break;
+
 		/* This frontend is found to be rogue, disable it in
 		 * kthread context. Currently this is only set when
 		 * netback finds out frontend sends malformed packet,
@@ -1955,24 +2027,21 @@ int xenvif_kthread_guest_rx(void *data)
 		 */
 		if (unlikely(queue->vif->disabled && queue->id == 0))
 			xenvif_carrier_off(queue->vif);
-
-		if (kthread_should_stop())
-			break;
-
-		if (queue->rx_queue_purge) {
+		else if (unlikely(test_and_clear_bit(QUEUE_STATUS_RX_PURGE_EVENT,
+						     &queue->status))) {
+			xenvif_rx_purge_event(queue);
+		} else if (!netif_carrier_ok(queue->vif->dev)) {
+			/* Another queue stalled and turned the carrier off, so
+			 * purge the internal queue of queues which were not
+			 * blocked
+			 */
 			skb_queue_purge(&queue->rx_queue);
-			queue->rx_queue_purge = false;
+			queue->rx_last_skb_slots = 0;
 		}
 
 		if (!skb_queue_empty(&queue->rx_queue))
 			xenvif_rx_action(queue);
 
-		if (skb_queue_empty(&queue->rx_queue) &&
-		    xenvif_queue_stopped(queue)) {
-			del_timer_sync(&queue->wake_queue);
-			xenvif_start_queue(queue);
-		}
-
 		cond_resched();
 	}