From bafe4dbbd54cf167809c8c4a3c98f7592fa7a7a7 Mon Sep 17 00:00:00 2001
From: Sailesh Nandanavanam <saileshnandanavanam@gmail.com>
Date: Mon, 29 Jun 2026 07:55:36 -0700
Subject: [PATCH] mm/damon/tests/core-kunit: add KUnit test for
 walk_control_obsolete behavior

Add a KUnit test to verify that damos_walk() rejects new requests when
walk_control_obsolete is set.

Commit 33c3f6c2b48c ("mm/damon/core: fix damos_walk() vs kdamond_fn() exit
race") introduced walk_control_obsolete to prevent a race condition where
new requests could be registered during kdamond shutdown and never
handled.

This test simulates the shutdown condition by setting
walk_control_obsolete and verifies that damos_walk() returns -ECANCELED
immediately.

This validates the invariant introduced by the fix and helps prevent
regressions.

Link: https://patch.msgid.link/20260612062337.2459-1-saileshnandanavanam@gmail.com
Link: https://lore.kernel.org/20260629145538.134832-6-sj@kernel.org
Suggested-by: SJ Park <sj@kernel.org>
Signed-off-by: Sailesh Nandanavanam <saileshnandanavanam@gmail.com>
Signed-off-by: SJ Park <sj@kernel.org>
Reviewed-by: SJ Park <sj@kernel.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Asier Gutierrez <gutierrez.asier@huawei-partners.com>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Doehyun Baek <doehyunbaek@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: "Liam R. Howlett" <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Philippe Laferriere <plafer@proton.me>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 mm/damon/tests/core-kunit.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/mm/damon/tests/core-kunit.h b/mm/damon/tests/core-kunit.h
index fcf7c7fadb5f..c5f5124c3d1f 100644
--- a/mm/damon/tests/core-kunit.h
+++ b/mm/damon/tests/core-kunit.h
@@ -1456,6 +1456,33 @@ static void damon_test_is_last_region(struct kunit *test)
 	damon_free_target(t);
 }
 
+/*
+ * Verify that damos_walk() rejects new requests when
+ * walk_control_obsolete is set.
+ *
+ * This tests the invariant introduced by:
+ * commit 33c3f6c2b48c ("mm/damon/core: fix damos_walk() vs kdamond_fn() exit race")
+ */
+static void damon_test_walk_control_obsolete(struct kunit *test)
+{
+	struct damon_ctx *ctx;
+	struct damos_walk_control control = {};
+	int ret;
+
+	ctx = damon_new_ctx();
+	if (!ctx)
+		kunit_skip(test, "ctx alloc fail");
+
+	/* Simulate shutdown phase */
+	ctx->walk_control_obsolete = true;
+
+	ret = damos_walk(ctx, &control);
+
+	KUNIT_EXPECT_EQ(test, ret, -ECANCELED);
+
+	damon_destroy_ctx(ctx);
+}
+
 static struct kunit_case damon_test_cases[] = {
 	KUNIT_CASE(damon_test_target),
 	KUNIT_CASE(damon_test_regions),
@@ -1485,6 +1512,7 @@ static struct kunit_case damon_test_cases[] = {
 	KUNIT_CASE(damon_test_set_filters_default_reject),
 	KUNIT_CASE(damon_test_apply_min_nr_regions),
 	KUNIT_CASE(damon_test_is_last_region),
+	KUNIT_CASE(damon_test_walk_control_obsolete),
 	{},
 };