virtio-net: don't respond to cpu hotplug notifier if we're not ready

We're trying to re-configure the affinity unconditionally in cpu hotplug
callback. This may lead the issue during resuming from s3/s4 since

- virt queues haven't been allocated at that time.
- it's unnecessary since thaw method will re-configure the affinity.

Fix this issue by checking the config_enable and do nothing is we're not ready.

The bug were introduced by commit 8de4b2f
(virtio-net: reset virtqueue affinity when doing cpu hotplug).

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -1116,6 +1116,11 @@ static int virtnet_cpu_callback(struct notifier_block *nfb,
 {
  struct virtnet_info *vi = container_of(nfb, struct virtnet_info, nb);
 
+ mutex_lock(&vi->config_lock);
+
+ if (!vi->config_enable)
+ goto done;
+
  switch(action & ~CPU_TASKS_FROZEN) {
  case CPU_ONLINE:
  case CPU_DOWN_FAILED:
@@ -1128,6 +1133,9 @@ static int virtnet_cpu_callback(struct notifier_block *nfb,
  default:
  break;
  }
+
+done:
+ mutex_unlock(&vi->config_lock);
  return NOTIFY_OK;
 }