virtio-gpu: add & use virtio_gpu_queue_fenced_ctrl_buffer

Add helper function to handle the submission of fenced control requests.
Make sure we initialize the fence while holding the virtqueue lock, so
requests can't be reordered.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/drivers/gpu/drm/virtio/virtgpu_fence.c b/drivers/gpu/drm/virtio/virtgpu_fence.c
index 1da6326..793ad9f 100644
--- a/drivers/gpu/drm/virtio/virtgpu_fence.c
+++ b/drivers/gpu/drm/virtio/virtgpu_fence.c
@@ -81,7 +81,7 @@
 	struct virtio_gpu_fence_driver *drv = &vgdev->fence_drv;
 	unsigned long irq_flags;
 
-	*fence = kmalloc(sizeof(struct virtio_gpu_fence), GFP_KERNEL);
+	*fence = kmalloc(sizeof(struct virtio_gpu_fence), GFP_ATOMIC);
 	if ((*fence) == NULL)
 		return -ENOMEM;