drm/i915/selftests: Take an explicit ref for rq->batch

Since we are peeking into the batch object of the request, it is
beholden on us to hold a reference to it.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1634Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200408091723.28937-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/selftest_lrc.c

@@ -2655,7 +2655,7 @@ static int create_gang(struct intel_engine_cs *engine,
 	if (IS_ERR(rq))
 		goto err_obj;
 
-	rq->batch = vma;
+	rq->batch = i915_vma_get(vma);
 	i915_request_get(rq);
 
 	i915_vma_lock(vma);
@@ -2679,6 +2679,7 @@ static int create_gang(struct intel_engine_cs *engine,
 	return 0;
 
 err_rq:
+	i915_vma_put(rq->batch);
 	i915_request_put(rq);
 err_obj:
 	i915_gem_object_put(obj);
@@ -2775,6 +2776,7 @@ static int live_preempt_gang(void *arg)
 				err = -ETIME;
 			}
 
+			i915_vma_put(rq->batch);
 			i915_request_put(rq);
 			rq = n;
 		}