drm/virtio: fix virtio_gpu_execbuffer_ioctl locking

Lockdep says we can't call vmemdup() while having objects reserved
because it needs the mmap semaphore.  So reorder the calls reserve
the objects later.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20200211135047.22261-2-kraxel@redhat.com

drivers/gpu/drm/virtio/virtgpu_ioctl.c

@@ -126,22 +126,22 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 		bo_handles = NULL;
 	}
 
-	if (buflist) {
-		ret = virtio_gpu_array_lock_resv(buflist);
-		if (ret)
-			goto out_unused_fd;
-	}
-
 	buf = vmemdup_user(u64_to_user_ptr(exbuf->command), exbuf->size);
 	if (IS_ERR(buf)) {
 		ret = PTR_ERR(buf);
-		goto out_unresv;
+		goto out_unused_fd;
+	}
+
+	if (buflist) {
+		ret = virtio_gpu_array_lock_resv(buflist);
+		if (ret)
+			goto out_memdup;
 	}
 
 	out_fence = virtio_gpu_fence_alloc(vgdev);
 	if(!out_fence) {
 		ret = -ENOMEM;
-		goto out_memdup;
+		goto out_unresv;
 	}
 
 	if (out_fence_fd >= 0) {
@@ -160,11 +160,11 @@ static int virtio_gpu_execbuffer_ioctl(struct drm_device *dev, void *data,
 			      vfpriv->ctx_id, buflist, out_fence);
 	return 0;
 
-out_memdup:
-	kvfree(buf);
 out_unresv:
 	if (buflist)
 		virtio_gpu_array_unlock_resv(buflist);
+out_memdup:
+	kvfree(buf);
 out_unused_fd:
 	kvfree(bo_handles);
 	if (buflist)