[PATCH 2/4] revocable: Add KUnit test for provider lifetime races

Tzung-Bi Shih
2026-01-29T14:38:06Z

Add a test to verify that revocable_alloc() correctly handles race
conditions where the provider is being released.

The test covers three scenarios:
1. Allocating from a NULL provider.
2. Allocating from a provider that has been detached (pointer is NULL).
3. Allocating from a provider that is in the process of destruction
(refcount is 0), simulating a race between revocable_alloc() and
revocable_provider_release().

A way to run the test:
$ ./tools/testing/kunit/kunit.py run \
--kconfig_add CONFIG_REVOCABLE_KUNIT_TEST=y \
--kconfig_add CONFIG_PROVE_LOCKING=y \
--kconfig_add CONFIG_DEBUG_KERNEL=y \
--kconfig_add CONFIG_DEBUG_INFO=y \
--kconfig_add CONFIG_DEBUG_INFO_DWARF5=y \
--kconfig_add CONFIG_KASAN=y \
--kconfig_add CONFIG_DETECT_HUNG_TASK=y \
--kconfig_add CONFIG_DEFAULT_HUNG_TASK_TIMEOUT="10" \
--arch=x86_64 --raw_output=all \
revocable_test

Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
drivers/base/revocable_test.c | 41 +++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)

diff --git a/drivers/base/revocable_test.c b/drivers/base/revocable_test.c
index 1622aae92fd3..7fc4d6a3dff6 100644
--- a/drivers/base/revocable_test.c
+++ b/drivers/base/revocable_test.c
@@ -14,9 +14,13 @@
*
* - Try Access Macro: Same as "Revocation" but uses the
* REVOCABLE_TRY_ACCESS_WITH() and REVOCABLE_TRY_ACCESS_SCOPED().
+ *
+ * - Provider Use-after-free: Verifies revocable_alloc() correctly handles
+ * race conditions where the provider is being released.
*/

#include <kunit/test.h>
+#include <linux/refcount.h>
#include <linux/revocable.h>

static void revocable_test_basic(struct kunit *test)
@@ -127,11 +131,48 @@ static void revocable_test_try_access_macro2(struct kunit *test)
revocable_free(rev);
}

+static void revocable_test_provider_use_after_free(struct kunit *test)
+{
+ struct revocable_provider __rcu *rp;
+ struct revocable_provider *old_rp;
+ void *real_res = (void *)0x12345678;
+ struct revocable *rev;
+
+ rp = revocable_provider_alloc(real_res);
+ KUNIT_ASSERT_NOT_ERR_OR_NULL(test, rp);
+
+ rev = revocable_alloc(NULL);
+ KUNIT_EXPECT_PTR_EQ(test, rev, NULL);
+
+ /* Simulate the provider has been freed. */
+ old_rp = rcu_replace_pointer(rp, NULL, 1);
+ rev = revocable_alloc(rp);
+ KUNIT_EXPECT_PTR_EQ(test, rev, NULL);
+ rcu_replace_pointer(rp, old_rp, 1);
+
+ struct {
+ struct srcu_struct srcu;
+ void __rcu *res;
+ struct kref kref;
+ struct rcu_head rcu;
+ } *rp_internal = (void *)rp;
+
+ /* Simulate the provider is releasing. */
+ refcount_set(&rp_internal->kref.refcount, 0);
+ rev = revocable_alloc(rp);
+ KUNIT_EXPECT_PTR_EQ(test, rev, NULL);
+ refcount_set(&rp_internal->kref.refcount, 1);
+
+ revocable_provider_revoke(&rp);
+ KUNIT_EXPECT_PTR_EQ(test, unrcu_pointer(rp), NULL);
+}
+
static struct kunit_case revocable_test_cases[] = {
KUNIT_CASE(revocable_test_basic),
KUNIT_CASE(revocable_test_revocation),
KUNIT_CASE(revocable_test_try_access_macro),
KUNIT_CASE(revocable_test_try_access_macro2),
+ KUNIT_CASE(revocable_test_provider_use_after_free),
{}