drm/i915/selftests: Drain the freedlists between exec passes

During the context execution tests, we issue a lot of work and discard a
lot of objects without releasing the lock and allowing the background
reaper to free those objects. Insert a small break between each pass to
flush the worker.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190704165317.21060-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c

@@ -562,6 +562,8 @@ out_unlock:
 		mock_file_free(i915, file);
 		if (err)
 			return err;
+
+		i915_gem_drain_freed_objects(i915);
 	}
 
 	return 0;
@@ -672,6 +674,10 @@ static int igt_shared_ctx_exec(void *arg)
 
 			dw += rem;
 		}
+
+		mutex_unlock(&i915->drm.struct_mutex);
+		i915_gem_drain_freed_objects(i915);
+		mutex_lock(&i915->drm.struct_mutex);
 	}
 out_test:
 	if (igt_live_test_end(&t))