[PATCH v2 1/3] selftests/damon: prevent cross-context state pollution in DamonCtx

[Kunwu Chan <kunwu.chan@linux.dev>]

From: Kunwu Chan <chentao@kylinos.cn>

DamonCtx.__init__() uses mutable default values for
monitoring_attrs, targets, and schemes.  In Python these are
evaluated once at function definition time, so multiple
DamonCtx instances can unintentionally share the same lists
and DamonAttrs instance.

Replace the mutable defaults with None sentinels and
initialize the objects when needed.

Co-developed-by: Wang Lian <lianux.mm@gmail.com>
Signed-off-by: Wang Lian <lianux.mm@gmail.com>
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Reviewed-by: SeongJae Park <sj@kernel.org>
---
 tools/testing/selftests/damon/_damon_sysfs.py | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/damon/_damon_sysfs.py b/tools/testing/selftests/damon/_damon_sysfs.py
index 8b12cc048440..2f6f2699db25 100644
--- a/tools/testing/selftests/damon/_damon_sysfs.py
+++ b/tools/testing/selftests/damon/_damon_sysfs.py
@@ -624,17 +624,23 @@ class DamonCtx:
     pause = None
     idx = None
 
-    def __init__(self, ops='paddr', monitoring_attrs=DamonAttrs(), targets=[],
-            schemes=[], pause=False):
+    def __init__(self, ops='paddr', monitoring_attrs=None, targets=None,
+            schemes=None, pause=False):
         self.ops = ops
+        if monitoring_attrs is None:
+            monitoring_attrs = DamonAttrs()
         self.monitoring_attrs = monitoring_attrs
         self.monitoring_attrs.context = self
 
+        if targets is None:
+            targets = []
         self.targets = targets
         for idx, target in enumerate(self.targets):
             target.idx = idx
             target.context = self
 
+        if schemes is None:
+            schemes = []
         self.schemes = schemes
         for idx, scheme in enumerate(self.schemes):
             scheme.idx = idx
-- 
2.43.0