[PATCH v2 0/2] kunit: add optional assertions to catch taint and lockdep warnings

[PATCH v2 0/2] kunit: add optional assertions to catch taint and lockdep warnings

[Malte Wechter]

this patch tries to expand KUnit by using existing kernel diagnostics to
catch certain locking related bugs. Specifically this adds assertions for
`debug_locks` from `lockdep` and the `TAINT_WARN` flag from `panic`.
This tries to prevent bugs as: circular locking dependency and sleeping
function called from invalid context. 

Add config CONFIG_KUNIT_EXTRA_ASSERTS that enables extra assertions
to be emitted: First, before _any_ KUnit test suite is ran, this is to ensure
that the extra assertions are triggered by a KUnit test and not prior.
Secondly, assertions a made for each test case, failing them if the
assertions fail, even if the KUnit test is marked as passed.

Signed-off-by: Malte Wechter <maltewechter@gmail.com>
---
Changes in v2:
- Implement changes directly in C KUnit instead of Rust KUnit wrapper
- Remove rust specific configs and add general CONFIG_KUNIT_EXTRA_ASSERTS config
- Link to v1: https://patch.msgid.link/20260818-lockdep-kunit-v1-0-66ceb1a272e3@gmail.com

To: Brendan Higgins <brendan.higgins@linux.dev>
To: David Gow <david@davidgow.net>
To: Rae Moar <raemoar63@gmail.com>
To: Miguel Ojeda <ojeda@kernel.org>
To: Boqun Feng <boqun@kernel.org>
To: Gary Guo <gary@garyguo.net>
To: Björn Roy Baron <bjorn3_gh@protonmail.com>
To: Benno Lossin <lossin@kernel.org>
To: Andreas Hindborg <a.hindborg@kernel.org>
To: Alice Ryhl <aliceryhl@google.com>
To: Trevor Gross <tmgross@umich.edu>
To: Danilo Krummrich <dakr@kernel.org>
To: Daniel Almeida <daniel.almeida@collabora.com>
To: Tamir Duberstein <tamird@kernel.org>
To: Alexandre Courbot <acourbot@nvidia.com>
To: Onur Özkan <work@onurozkan.dev>
Cc: linux-kselftest@vger.kernel.org
Cc: kunit-dev@googlegroups.com
Cc: linux-kernel@vger.kernel.org
Cc: rust-for-linux@vger.kernel.org

---
Malte Wechter (2):
      kunit: add extra assertions to KUnit test cases
      kunit: add KUnit test to assert kernel state before KUnit suites are run

 lib/kunit/Kconfig     | 12 ++++++++++++
 lib/kunit/executor.c  |  8 +++++++-
 lib/kunit/test.c      | 30 ++++++++++++++++++++++++++++++
 lib/kunit/try-catch.c | 23 ++++++++++++++++++++++-
 4 files changed, 71 insertions(+), 2 deletions(-)
---
base-commit: 8cdeaa50eae8dad34885515f62559ee83e7e8dda
change-id: 20260812-lockdep-kunit-9628f4bcad90

Best regards,
--  
Malte Wechter <maltewechter@gmail.com>

[PATCH v2 1/2] kunit: add extra assertions to KUnit test cases

[Malte Wechter]

add extra assertions for each individual test case, that checks that
both `debug_locks` and `TAINT_WARN` are intact after the test is run.
The assertions are optional behind CONFIG_KUNIT_EXTRA_ASSERTS.

Signed-off-by: Malte Wechter <maltewechter@gmail.com>
---
 lib/kunit/Kconfig     | 12 ++++++++++++
 lib/kunit/try-catch.c | 23 ++++++++++++++++++++++-
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/lib/kunit/Kconfig b/lib/kunit/Kconfig
index 94ff8e4089bfb..38801f7493669 100644
--- a/lib/kunit/Kconfig
+++ b/lib/kunit/Kconfig
@@ -142,4 +142,16 @@ config KUNIT_UML_PCI
 
 	  If unsure, say N.
 
+config KUNIT_EXTRA_ASSERTS
+	bool "Enable extra assertions in KUnit tests"
+	depends on LOCKDEP
+	default n
+	help
+		Enables all extra assertions for KUnit which includes asserting `TAINT_WARN` and
+		`debug_locks` from lockdep. A KUnit test suite (and test case) is inserted
+		at the start of all KUnit test suites. This makes assertions prior to running any
+		tests, as a pre-test integrity check. Assertions are made after each test case which
+		asserts that each test case did not trigger either `TAINT_WARN` or `debug_locks`.
+
+		If unsure, say N.
 endif # KUNIT
diff --git a/lib/kunit/try-catch.c b/lib/kunit/try-catch.c
index d84a879f0a789..7eea3af4c9671 100644
--- a/lib/kunit/try-catch.c
+++ b/lib/kunit/try-catch.c
@@ -41,6 +41,11 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
 	struct completion *task_done;
 	int exit_code, time_remaining;
 
+	#ifdef CONFIG_KUNIT_EXTRA_ASSERTS
+	int debug_locks_snapshot = debug_locks;
+	int tainted_warn_snapshot = test_taint(TAINT_WARN);
+	#endif
+
 	try_catch->context = context;
 	try_catch->try_result = 0;
 	task_struct = kthread_create(kunit_generic_run_threadfn_adapter,
@@ -70,7 +75,23 @@ void kunit_try_catch_run(struct kunit_try_catch *try_catch, void *context)
 	put_task_struct(task_struct);
 	exit_code = try_catch->try_result;
 
-	if (!exit_code)
+	#ifdef CONFIG_KUNIT_EXTRA_ASSERTS
+	bool extra_assert = false;
+
+	if (debug_locks_snapshot != debug_locks && !exit_code) {
+		extra_assert = true;
+		try_catch->try_result = -EDEADLK;
+		kunit_err(test, "Test triggered lockdep\n");
+	} else if (tainted_warn_snapshot != test_taint(TAINT_WARN) && !exit_code) {
+		extra_assert = true;
+		try_catch->try_result = -EDEADLK;
+		kunit_err(test, "Test tainted kernel with TAINT_WARN\n");
+	}
+	#else
+	bool extra_assert = false;
+	#endif
+
+	if (!exit_code && !extra_assert)
 		return;
 
 	if (exit_code == -EFAULT)

-- 
2.51.2

[PATCH v2 2/2] kunit: add KUnit test to assert kernel state before KUnit suites are run

[Malte Wechter]

add pre-defined KUnit test suite and test case that asserts both
`debug_locks` and `TAINT_WARN` prior to running any (user) KUnit tests.
This asserts integrity before tests are run.

Signed-off-by: Malte Wechter <maltewechter@gmail.com>
---
 lib/kunit/executor.c |  8 +++++++-
 lib/kunit/test.c     | 30 ++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/lib/kunit/executor.c b/lib/kunit/executor.c
index b0f8a41d61d36..0db67fe7f09f9 100644
--- a/lib/kunit/executor.c
+++ b/lib/kunit/executor.c
@@ -290,9 +290,15 @@ void kunit_exec_run_tests(struct kunit_suite_set *suite_set, bool builtin)
 	size_t num_suites = suite_set->end - suite_set->start;
 	bool autorun = kunit_autorun();
 
+	#ifdef CONFIG_KUNIT_EXTRA_ASSERTS
+	size_t num_suites_plus_extra = num_suites+1;
+	#else
+	size_t num_suites_plus_extra = num_suites;
+	#endif
+
 	if (autorun && (builtin || num_suites)) {
 		pr_info("KTAP version 1\n");
-		pr_info("1..%zu\n", num_suites);
+		pr_info("1..%zu\n", num_suites_plus_extra);
 	}
 
 	__kunit_test_suites_init(suite_set->start, num_suites, autorun);
diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index 99773e000e1b7..e64c6d1575280 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -835,6 +835,30 @@ bool kunit_enabled(void)
 	return enable_param;
 }
 
+#ifdef CONFIG_KUNIT_EXTRA_ASSERTS
+#define DEBUG_LOCKS_OK 1
+#define TAINT_WARN_OK 0
+
+static void pre_kunit_assert(struct kunit *test)
+{
+	KUNIT_EXPECT_EQ_MSG(test, debug_locks, DEBUG_LOCKS_OK,
+		"debug_locks are off before any test ran");
+	KUNIT_EXPECT_EQ_MSG(test, test_taint(TAINT_WARN), TAINT_WARN_OK,
+		"kernel already TAINT_WARN tainted before any test ran");
+}
+
+static struct kunit_case pre_kunit_assert_cases[] = {
+	KUNIT_CASE(pre_kunit_assert),
+	{}
+};
+
+static struct kunit_suite pre_kunit_assert_clean_state_suite = {
+	.name = "pre_kunit_extra_asserts",
+	.test_cases = pre_kunit_assert_cases,
+};
+
+#endif /* CONFIG_RUST_KUNIT_EXTRA_ASSERTS */
+
 int __kunit_test_suites_init(struct kunit_suite * const * const suites, int num_suites,
 			     bool run_tests)
 {
@@ -857,6 +881,12 @@ int __kunit_test_suites_init(struct kunit_suite * const * const suites, int num_
 	}
 	static_branch_inc(&kunit_running);
 
+	#ifdef CONFIG_KUNIT_EXTRA_ASSERTS
+	kunit_init_suite(&pre_kunit_assert_clean_state_suite);
+	if (run_tests)
+		kunit_run_tests(&pre_kunit_assert_clean_state_suite);
+	#endif
+
 	for (i = 0; i < num_suites; i++) {
 		kunit_init_suite(suites[i]);
 		if (run_tests)

-- 
2.51.2