diff --git a/tools/testing/selftests/damon/sysfs.py b/tools/testing/selftests/damon/sysfs.py
index cd4d82c85211..aa03a1187489 100755
--- a/tools/testing/selftests/damon/sysfs.py
+++ b/tools/testing/selftests/damon/sysfs.py
@@ -24,9 +24,12 @@ def dump_damon_status_dict(pid):
     except Exception as e:
         return None, 'json.load fail (%s)' % e
 
+kdamonds = None
 def fail(expectation, status):
     print('unexpected %s' % expectation)
     print(json.dumps(status, indent=4))
+    if kdamonds is not None:
+        kdamonds.stop()
     exit(1)
 
 def assert_true(condition, expectation, status):
@@ -248,6 +251,7 @@ def assert_ctxs_committed(kdamonds):
                 ctx.pause = False
 
 def main():
+    global kdamonds
     kdamonds = _damon_sysfs.Kdamonds(
             [_damon_sysfs.Kdamond(
                 contexts=[_damon_sysfs.DamonCtx(