xen-netback: bookkeep number of active queues in our own module

The original code uses netdev->real_num_tx_queues to bookkeep number of
queues and invokes netif_set_real_num_tx_queues to set the number of
queues. However, netif_set_real_num_tx_queues doesn't allow
real_num_tx_queues to be smaller than 1, which means setting the number
to 0 will not work and real_num_tx_queues is untouched.

This is bogus when xenvif_free is invoked before any number of queues is
allocated. That function needs to iterate through all queues to free
resources. Using the wrong number of queues results in NULL pointer
dereference.

So we bookkeep the number of queues in xen-netback to solve this
problem. This fixes a regression introduced by multiqueue patchset in
3.16-rc1.

There's another bug in original code that the real number of RX queues
is never set. In current Xen multiqueue design, the number of TX queues
and RX queues are in fact the same. We need to set the numbers of TX and
RX queues to the same value.

Also remove xenvif_select_queue and leave queue selection to core
driver, as suggested by David Miller.

Reported-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
CC: Ian Campbell <ian.campbell@citrix.com>
CC: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 14 insertions, 14 deletions

diff --git a/drivers/net/xen-netback/xenbus.c b/drivers/net/xen-netback/xenbus.c
index 96c63dc2509e..3d85acd84bad 100644
--- a/drivers/net/xen-netback/xenbus.c
+++ b/drivers/net/xen-netback/xenbus.c
@@ -527,9 +527,7 @@ static void connect(struct backend_info *be)
 	/* Use the number of queues requested by the frontend */
 	be->vif->queues = vzalloc(requested_num_queues *
 				  sizeof(struct xenvif_queue));
-	rtnl_lock();
-	netif_set_real_num_tx_queues(be->vif->dev, requested_num_queues);
-	rtnl_unlock();
+	be->vif->num_queues = requested_num_queues;
 
 	for (queue_index = 0; queue_index < requested_num_queues; ++queue_index) {
 		queue = &be->vif->queues[queue_index];
@@ -546,9 +544,7 @@ static void connect(struct backend_info *be)
 			 * earlier queues can be destroyed using the regular
 			 * disconnect logic.
 			 */
-			rtnl_lock();
-			netif_set_real_num_tx_queues(be->vif->dev, queue_index);
-			rtnl_unlock();
+			be->vif->num_queues = queue_index;
 			goto err;
 		}
 
@@ -561,13 +557,19 @@ static void connect(struct backend_info *be)
 			 * and also clean up any previously initialised queues.
 			 */
 			xenvif_deinit_queue(queue);
-			rtnl_lock();
-			netif_set_real_num_tx_queues(be->vif->dev, queue_index);
-			rtnl_unlock();
+			be->vif->num_queues = queue_index;
 			goto err;
 		}
 	}
 
+	/* Initialisation completed, tell core driver the number of
+	 * active queues.
+	 */
+	rtnl_lock();
+	netif_set_real_num_tx_queues(be->vif->dev, requested_num_queues);
+	netif_set_real_num_rx_queues(be->vif->dev, requested_num_queues);
+	rtnl_unlock();
+
 	xenvif_carrier_on(be->vif);
 
 	unregister_hotplug_status_watch(be);
@@ -582,13 +584,11 @@ static void connect(struct backend_info *be)
 	return;
 
 err:
-	if (be->vif->dev->real_num_tx_queues > 0)
+	if (be->vif->num_queues > 0)
 		xenvif_disconnect(be->vif); /* Clean up existing queues */
 	vfree(be->vif->queues);
 	be->vif->queues = NULL;
-	rtnl_lock();
-	netif_set_real_num_tx_queues(be->vif->dev, 0);
-	rtnl_unlock();
+	be->vif->num_queues = 0;
 	return;
 }
 
@@ -596,7 +596,7 @@ err:
 static int connect_rings(struct backend_info *be, struct xenvif_queue *queue)
 {
 	struct xenbus_device *dev = be->dev;
-	unsigned int num_queues = queue->vif->dev->real_num_tx_queues;
+	unsigned int num_queues = queue->vif->num_queues;
 	unsigned long tx_ring_ref, rx_ring_ref;
 	unsigned int tx_evtchn, rx_evtchn;
 	int err;