selftests/damon: test no-op commit broke DAMON status

Add test to verify that DAMON status is not changed after a no-op commit.

[ekffu200098@gmail.com: change wrong json.dump usage to json.dumps]
  Link: https://lkml.kernel.org/r/20250816014033.190451-1-ekffu200098@gmail.com
Link: https://lkml.kernel.org/r/20250810124354.16456-1-ekffu200098@gmail.com
Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Reviewed-by: SeongJae Park <sj@kernel.org>
Cc: Honggyu Kim <honggyu.kim@sk.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

tools/testing/selftests/damon/Makefile

@@ -18,6 +18,7 @@ TEST_PROGS += reclaim.sh lru_sort.sh
 TEST_PROGS += sysfs_update_removed_scheme_dir.sh
 TEST_PROGS += sysfs_update_schemes_tried_regions_hang.py
 TEST_PROGS += sysfs_memcg_path_leak.sh
+TEST_PROGS += sysfs_no_op_commit_break.py
 
 EXTRA_CLEAN = __pycache__
 

tools/testing/selftests/damon/sysfs_no_op_commit_break.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: GPL-2.0
+
+import json
+import os
+import subprocess
+import sys
+
+import _damon_sysfs
+
+def dump_damon_status_dict(pid):
+    try:
+        subprocess.check_output(['which', 'drgn'], stderr=subprocess.DEVNULL)
+    except:
+        return None, 'drgn not found'
+    file_dir = os.path.dirname(os.path.abspath(__file__))
+    dump_script = os.path.join(file_dir, 'drgn_dump_damon_status.py')
+    rc = subprocess.call(['drgn', dump_script, pid, 'damon_dump_output'],
+        stderr=subprocess.DEVNULL)
+
+    if rc != 0:
+        return None, f'drgn fail: return code({rc})'
+    try:
+        with open('damon_dump_output', 'r') as f:
+            return json.load(f), None
+    except Exception as e:
+        return None, 'json.load fail (%s)' % e
+
+def main():
+    kdamonds = _damon_sysfs.Kdamonds(
+        [_damon_sysfs.Kdamond(
+            contexts=[_damon_sysfs.DamonCtx(
+                schemes=[_damon_sysfs.Damos(
+                    ops_filters=[
+                        _damon_sysfs.DamosFilter(
+                            type_='anon',
+                            matching=True,
+                            allow=True,
+                        )
+                    ]
+                )],
+            )])]
+    )
+
+    err = kdamonds.start()
+    if err is not None:
+        print('kdamond start failed: %s' % err)
+        exit(1)
+
+    before_commit_status, err = \
+        dump_damon_status_dict(kdamonds.kdamonds[0].pid)
+    if err is not None:
+        print('before-commit status dump failed: %s' % err)
+        exit(1)
+
+    kdamonds.kdamonds[0].commit()
+
+    after_commit_status, err = \
+        dump_damon_status_dict(kdamonds.kdamonds[0].pid)
+    if err is not None:
+        print('after-commit status dump failed: %s' % err)
+        exit(1)
+
+    if before_commit_status != after_commit_status:
+        print(f'before: {json.dumps(before_commit_status, indent=2)}')
+        print(f'after: {json.dumps(after_commit_status, indent=2)}')
+        exit(1)
+
+    kdamonds.stop()
+
+if __name__ == '__main__':
+    main()