drm/vc4: Release fence after signalling

We were never releasing the initial fence reference that is obtained
through dma_fence_init.

Link: https://github.com/anholt/linux/issues/122
Fixes: cdec4d36 ("drm/vc4: Expose dma-buf fences for V3D rendering.")
Signed-off-by: Stefan Schake <stschake@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/1512236444-301-1-git-send-email-stschake@gmail.com

drivers/gpu/drm/vc4/vc4_gem.c

@@ -888,8 +888,10 @@ vc4_complete_exec(struct drm_device *dev, struct vc4_exec_info *exec)
 	/* If we got force-completed because of GPU reset rather than
 	 * through our IRQ handler, signal the fence now.
 	 */
-	if (exec->fence)
+	if (exec->fence) {
 		dma_fence_signal(exec->fence);
+		dma_fence_put(exec->fence);
+	}
 
 	if (exec->bo) {
 		for (i = 0; i < exec->bo_count; i++) {

drivers/gpu/drm/vc4/vc4_irq.c

@@ -139,6 +139,7 @@ vc4_irq_finish_render_job(struct drm_device *dev)
 	list_move_tail(&exec->head, &vc4->job_done_list);
 	if (exec->fence) {
 		dma_fence_signal_locked(exec->fence);
+		dma_fence_put(exec->fence);
 		exec->fence = NULL;
 	}
 	vc4_submit_next_render_job(dev);