virtio-net: refill only when device is up during setting queues

We used to schedule the refill work unconditionally after changing the
number of queues. This may lead an issue if the device is not
up. Since we only try to cancel the work in ndo_stop(), this may cause
the refill work still work after removing the device. Fix this by only
schedule the work when device is up.

The bug were introduce by commit 9b9cd8024a2882e896c65222aa421d461354e3f2.
(virtio-net: fix the race between channels setting and refill)

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

drivers/net/virtio_net.c

@@ -938,7 +938,9 @@ static int virtnet_set_queues(struct virtnet_info *vi, u16 queue_pairs)
 		return -EINVAL;
 	} else {
 		vi->curr_queue_pairs = queue_pairs;
-		schedule_delayed_work(&vi->refill, 0);
+		/* virtnet_open() will refill when device is going to up. */
+		if (dev->flags & IFF_UP)
+			schedule_delayed_work(&vi->refill, 0);
 	}
 
 	return 0;
@@ -1741,7 +1743,9 @@ static int virtnet_restore(struct virtio_device *vdev)
 	vi->config_enable = true;
 	mutex_unlock(&vi->config_lock);
 
+	rtnl_lock();
 	virtnet_set_queues(vi, vi->curr_queue_pairs);
+	rtnl_unlock();
 
 	return 0;
 }