drm/scheduler: fix drm_sched_job_add_implicit_dependencies harder

drm_sched_job_add_dependency() could drop the last ref, so we need to do
the dma_fence_get() first.

Cc: Christian König <christian.koenig@amd.com>
Fixes: 9c2ba26535 ("drm/scheduler: use new iterator in drm_sched_job_add_implicit_dependencies v2")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211116155545.473311-1-robdclark@gmail.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Christian König <christian.koenig@amd.com>
Tested-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/scheduler/sched_main.c

@@ -704,12 +704,13 @@ int drm_sched_job_add_implicit_dependencies(struct drm_sched_job *job,
 	int ret;
 
 	dma_resv_for_each_fence(&cursor, obj->resv, write, fence) {
-		ret = drm_sched_job_add_dependency(job, fence);
-		if (ret)
-			return ret;
-
 		/* Make sure to grab an additional ref on the added fence */
 		dma_fence_get(fence);
+		ret = drm_sched_job_add_dependency(job, fence);
+		if (ret) {
+			dma_fence_put(fence);
+			return ret;
+		}
 	}
 	return 0;
 }