xen-netfront: recreate queues correctly when reconnecting

When reconnecting to the backend (after a resume/migration, for example),
a different number of queues may be required (since the guest may have
moved to a different host with different capabilities).  During the
reconnection the old queues are torn down and new ones created.

Introduce xennet_create_queues() and xennet_destroy_queues() that fixes
three bugs during the reconnection.

- The old info->queues was leaked.
- The old queue's napi instances were not deleted.
- The new queue's napi instances were left disabled (which meant no
  packets could be received).

The xennet_destroy_queues() calls is deferred until the reconnection
instead of the disconnection (in xennet_disconnect_backend()) because
napi_disable() might sleep.

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, 72 insertions, 32 deletions

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index daaf1e56e41e..2ccb4a02368b 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -1699,8 +1699,6 @@ static int xennet_init_queue(struct netfront_queue *queue)
                 goto exit_free_tx;
         }
 
-        netif_napi_add(queue->info->netdev, &queue->napi, xennet_poll, 64);
-
         return 0;
 
  exit_free_tx:
@@ -1791,6 +1789,70 @@ error:
         return err;
 }
 
+static void xennet_destroy_queues(struct netfront_info *info)
+{
+        unsigned int i;
+
+        rtnl_lock();
+
+        for (i = 0; i < info->netdev->real_num_tx_queues; i++) {
+                struct netfront_queue *queue = &info->queues[i];
+
+                if (netif_running(info->netdev))
+                        napi_disable(&queue->napi);
+                netif_napi_del(&queue->napi);
+        }
+
+        rtnl_unlock();
+
+        kfree(info->queues);
+        info->queues = NULL;
+}
+
+static int xennet_create_queues(struct netfront_info *info,
+                                unsigned int num_queues)
+{
+        unsigned int i;
+        int ret;
+
+        info->queues = kcalloc(num_queues, sizeof(struct netfront_queue),
+                               GFP_KERNEL);
+        if (!info->queues)
+                return -ENOMEM;
+
+        rtnl_lock();
+
+        for (i = 0; i < num_queues; i++) {
+                struct netfront_queue *queue = &info->queues[i];
+
+                queue->id = i;
+                queue->info = info;
+
+                ret = xennet_init_queue(queue);
+                if (ret < 0) {
+                        dev_warn(&info->netdev->dev, "only created %d queues\n",
+                                 num_queues);
+                        num_queues = i;
+                        break;
+                }
+
+                netif_napi_add(queue->info->netdev, &queue->napi,
+                               xennet_poll, 64);
+                if (netif_running(info->netdev))
+                        napi_enable(&queue->napi);
+        }
+
+        netif_set_real_num_tx_queues(info->netdev, num_queues);
+
+        rtnl_unlock();
+
+        if (num_queues == 0) {
+                dev_err(&info->netdev->dev, "no queues\n");
+                return -EINVAL;
+        }
+        return 0;
+}
+
 /* Common code used when first setting up, and when resuming. */
 static int talk_to_netback(struct xenbus_device *dev,
                            struct netfront_info *info)
@@ -1827,42 +1889,20 @@ static int talk_to_netback(struct xenbus_device *dev,
                 goto out;
         }
 
-        /* Allocate array of queues */
-        info->queues = kcalloc(num_queues, sizeof(struct netfront_queue), GFP_KERNEL);
-        if (!info->queues) {
-                err = -ENOMEM;
-                goto out;
-        }
-        rtnl_lock();
-        netif_set_real_num_tx_queues(info->netdev, num_queues);
-        rtnl_unlock();
+        if (info->queues)
+                xennet_destroy_queues(info);
+
+        err = xennet_create_queues(info, num_queues);
+        if (err < 0)
+                goto destroy_ring;
 
         /* Create shared ring, alloc event channel -- for each queue */
         for (i = 0; i < num_queues; ++i) {
                 queue = &info->queues[i];
-                queue->id = i;
-                queue->info = info;
-                err = xennet_init_queue(queue);
-                if (err) {
-                        /* xennet_init_queue() cleans up after itself on failure,
-                         * but we still have to clean up any previously initialised
-                         * queues. If i > 0, set num_queues to i, then goto
-                         * destroy_ring, which calls xennet_disconnect_backend()
-                         * to tidy up.
-                         */
-                        if (i > 0) {
-                                rtnl_lock();
-                                netif_set_real_num_tx_queues(info->netdev, i);
-                                rtnl_unlock();
-                                goto destroy_ring;
-                        } else {
-                                goto out;
-                        }
-                }
                 err = setup_netfront(dev, queue, feature_split_evtchn);
                 if (err) {
-                        /* As for xennet_init_queue(), setup_netfront() will tidy
-                         * up the current queue on error, but we need to clean up
+                        /* setup_netfront() will tidy up the current
+                         * queue on error, but we need to clean up
                          * those already allocated.
                          */
                         if (i > 0) {