[PATCH v2] kasan: test: prevent cache merging in kmem_cache_double_destroy

[andrey.konovalov@linux.dev]

From: Andrey Konovalov <andreyknvl@google.com>

With HW_TAGS KASAN and kasan.stacktrace=off, the cache created in the
kmem_cache_double_destroy() test might get merged with an existing one.
Thus, the first kmem_cache_destroy() call won't actually destroy it
but will only decrease the refcount. This causes the test to fail.

Provide an empty constructor for the created cache to prevent the cache
from getting merged.

Fixes: f98f966cd750 ("kasan: test: add test case for double-kmem_cache_destroy()")
Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/test_kasan.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/test_kasan.c b/lib/test_kasan.c
index 26a5c9007653..3b413f8c8a71 100644
--- a/lib/test_kasan.c
+++ b/lib/test_kasan.c
@@ -869,11 +869,14 @@ static void kmem_cache_invalid_free(struct kunit *test)
 	kmem_cache_destroy(cache);
 }
 
+static void empty_cache_ctor(void *object) { }
+
 static void kmem_cache_double_destroy(struct kunit *test)
 {
 	struct kmem_cache *cache;
 
-	cache = kmem_cache_create("test_cache", 200, 0, 0, NULL);
+	/* Provide a constructor to prevent cache merging. */
+	cache = kmem_cache_create("test_cache", 200, 0, 0, empty_cache_ctor);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, cache);
 	kmem_cache_destroy(cache);
 	KUNIT_EXPECT_KASAN_FAIL(test, kmem_cache_destroy(cache));
-- 
2.25.1