list: add kunit test for private list primitives

Add a KUnit test suite for the new private list primitives.

The test defines a struct with a __private list_head and exercises every
macro defined in <linux/list_private.h>.

This ensures that the macros correctly handle the ACCESS_PRIVATE()
abstraction and compile without warnings when acting on private members,
verifying that qualifiers are stripped and offsets are calculated
correctly.

Link: https://lkml.kernel.org/r/20251218155752.3045808-3-pasha.tatashin@soleen.com
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Reviewed-by: David Gow <davidgow@google.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: David Matlack <dmatlack@google.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kees Cook <kees@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Pratyush Yadav <pratyush@kernel.org>
Cc: Samiullah Khawaja <skhawaja@google.com>
Cc: Tamir Duberstein <tamird@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/Kconfig.debug

@@ -2786,6 +2786,20 @@ config LIST_KUNIT_TEST
 
 	  If unsure, say N.
 
+config LIST_PRIVATE_KUNIT_TEST
+	tristate "KUnit Test for Kernel Private Linked-list structures" if !KUNIT_ALL_TESTS
+	depends on KUNIT
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the KUnit test for the private linked-list primitives
+	  defined in include/linux/list_private.h.
+
+	  These primitives allow manipulation of list_head members that are
+	  marked as private and require special accessors (ACCESS_PRIVATE)
+	  to strip qualifiers or handle encapsulation.
+
+	  If unsure, say N.
+
 config HASHTABLE_KUNIT_TEST
 	tristate "KUnit Test for Kernel Hashtable structures" if !KUNIT_ALL_TESTS
 	depends on KUNIT

lib/tests/Makefile

@@ -26,6 +26,7 @@ obj-$(CONFIG_TEST_IOV_ITER) += kunit_iov_iter.o
 obj-$(CONFIG_IS_SIGNED_TYPE_KUNIT_TEST) += is_signed_type_kunit.o
 obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
 obj-$(CONFIG_LIST_KUNIT_TEST) += list-test.o
+obj-$(CONFIG_LIST_PRIVATE_KUNIT_TEST) += list-private-test.o
 obj-$(CONFIG_KFIFO_KUNIT_TEST) += kfifo_kunit.o
 obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
 obj-$(CONFIG_LINEAR_RANGES_TEST) += test_linear_ranges.o

lib/tests/list-private-test.c

@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit compilation/smoke test for Private list primitives.
+ *
+ * Copyright (c) 2025, Google LLC.
+ * Pasha Tatashin <pasha.tatashin@soleen.com>
+ */
+#include <linux/list_private.h>
+#include <kunit/test.h>
+
+/*
+ * This forces compiler to warn if you access it directly, because list
+ * primitives expect (struct list_head *), not (volatile struct list_head *).
+ */
+#undef __private
+#define __private volatile
+
+/* Redefine ACCESS_PRIVATE for this test. */
+#undef ACCESS_PRIVATE
+#define ACCESS_PRIVATE(p, member) \
+	(*((struct list_head *)((unsigned long)&((p)->member))))
+
+struct list_test_struct {
+	int data;
+	struct list_head __private list;
+};
+
+static void list_private_compile_test(struct kunit *test)
+{
+	struct list_test_struct entry;
+	struct list_test_struct *pos, *n;
+	LIST_HEAD(head);
+
+	INIT_LIST_HEAD(&ACCESS_PRIVATE(&entry, list));
+	list_add(&ACCESS_PRIVATE(&entry, list), &head);
+	pos = &entry;
+
+	pos = list_private_entry(&ACCESS_PRIVATE(&entry, list), struct list_test_struct, list);
+	pos = list_private_first_entry(&head, struct list_test_struct, list);
+	pos = list_private_last_entry(&head, struct list_test_struct, list);
+	pos = list_private_next_entry(pos, list);
+	pos = list_private_prev_entry(pos, list);
+	pos = list_private_next_entry_circular(pos, &head, list);
+	pos = list_private_prev_entry_circular(pos, &head, list);
+
+	if (list_private_entry_is_head(pos, &head, list))
+		return;
+
+	list_private_for_each_entry(pos, &head, list) { }
+	list_private_for_each_entry_reverse(pos, &head, list) { }
+	list_private_for_each_entry_continue(pos, &head, list) { }
+	list_private_for_each_entry_continue_reverse(pos, &head, list) { }
+	list_private_for_each_entry_from(pos, &head, list) { }
+	list_private_for_each_entry_from_reverse(pos, &head, list) { }
+
+	list_private_for_each_entry_safe(pos, n, &head, list)
+		list_private_safe_reset_next(pos, n, list);
+	list_private_for_each_entry_safe_continue(pos, n, &head, list) { }
+	list_private_for_each_entry_safe_from(pos, n, &head, list) { }
+	list_private_for_each_entry_safe_reverse(pos, n, &head, list) { }
+}
+
+static struct kunit_case list_private_test_cases[] = {
+	KUNIT_CASE(list_private_compile_test),
+	{},
+};
+
+static struct kunit_suite list_private_test_module = {
+	.name = "list-private-kunit-test",
+	.test_cases = list_private_test_cases,
+};
+
+kunit_test_suite(list_private_test_module);
+
+MODULE_DESCRIPTION("KUnit compilation test for private list primitives");
+MODULE_LICENSE("GPL");