[PATCH 4/4] revocable: Add KUnit test for concurrent access

Tzung-Bi Shih
2026-01-29T14:38:10Z

Add a test case to verify correct synchronization between concurrent
readers and a revocation.

The test setup involves:
1. Consumer 1 enters the critical section (SRCU read lock) and verifies
access to the resource.
2. Provider attempts to revoke the resource. This should block until
Consumer 1 releases the lock.
3. Consumer 2 attempts to enter the critical section while revocation
is pending. It should see the resource as revoked (NULL).
4. Consumer 1 exits, allowing the revocation to complete.

This ensures that the SRCU mechanism correctly enforces grace periods
and that new readers are properly prevented from accessing the resource
once revocation has begun.

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 | 104 ++++++++++++++++++++++++++++++++++
1 file changed, 104 insertions(+)

diff --git a/drivers/base/revocable_test.c b/drivers/base/revocable_test.c
index a2818ec01298..27f5d7d96f4b 100644
--- a/drivers/base/revocable_test.c
+++ b/drivers/base/revocable_test.c
@@ -17,9 +17,14 @@
*
* - Provider Use-after-free: Verifies revocable_init() correctly handles
* race conditions where the provider is being released.
+ *
+ * - Concurrent Access: Verifies multiple threads can access the resource.
*/

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

@@ -160,12 +165,111 @@ static void revocable_test_provider_use_after_free(struct kunit *test)
KUNIT_EXPECT_NE(test, ret, 0);
}

+struct test_concurrent_access_context {
+ struct kunit *test;
+ struct revocable_provider __rcu *rp;
+ struct revocable rev;
+ struct completion started, enter, exit;
+ struct task_struct *thread;
+ void *expected_res;
+};
+
+static int test_concurrent_access_provider(void *data)
+{
+ struct test_concurrent_access_context *ctx = data;
+
+ complete(&ctx->started);
+
+ wait_for_completion(&ctx->enter);
+ revocable_provider_revoke(&ctx->rp);
+ KUNIT_EXPECT_PTR_EQ(ctx->test, unrcu_pointer(ctx->rp), NULL);
+
+ return 0;
+}
+
+static int test_concurrent_access_consumer(void *data)
+{
+ struct test_concurrent_access_context *ctx = data;
+ void *res;
+
+ complete(&ctx->started);
+
+ wait_for_completion(&ctx->enter);
+ res = revocable_try_access(&ctx->rev);
+ KUNIT_EXPECT_PTR_EQ(ctx->test, res, ctx->expected_res);
+
+ wait_for_completion(&ctx->exit);
+ revocable_withdraw_access(&ctx->rev);
+
+ return 0;
+}
+
+static void revocable_test_concurrent_access(struct kunit *test)
+{
+ struct revocable_provider __rcu *rp;
+ void *real_res = (void *)0x12345678;
+ struct test_concurrent_access_context *ctx;
+ int ret, i;
+
+ rp = revocable_provider_alloc(real_res);
+ KUNIT_ASSERT_NOT_ERR_OR_NULL(test, rp);
+
+ ctx = kunit_kmalloc_array(test, 3, sizeof(*ctx), GFP_KERNEL);
+ KUNIT_ASSERT_NOT_NULL(test, ctx);
+
+ for (i = 0; i < 3; ++i) {
+ ctx[i].test = test;
+ init_completion(&ctx[i].started);
+ init_completion(&ctx[i].enter);
+ init_completion(&ctx[i].exit);
+
+ if (i == 0) {
+ ctx[i].rp = rp;
+ ctx[i].thread = kthread_run(
+ test_concurrent_access_provider, ctx + i,
+ "revocable_provider_%d", i);
+ } else {
+ ret = revocable_init(rp, &ctx[i].rev);
+ KUNIT_ASSERT_EQ(test, ret, 0);
+
+ ctx[i].thread = kthread_run(
+ test_concurrent_access_consumer, ctx + i,
+ "revocable_consumer_%d", i);
+ }
+ KUNIT_ASSERT_FALSE(test, IS_ERR(ctx[i].thread));
+
+ wait_for_completion(&ctx[i].started);
+ }
+ ctx[1].expected_res = real_res;
+ ctx[2].expected_res = NULL;
+
+ /* consumer1 enters read-side critical section */
+ complete(&ctx[1].enter);
+ msleep(100);
+ /* provider0 revokes the resource */
+ complete(&ctx[0].enter);
+ msleep(100);
+ /* consumer2 enters read-side critical section */
+ complete(&ctx[2].enter);
+ msleep(100);
+
+ /* consumer{1,2} exit read-side critical section */
+ complete(&ctx[1].exit);
+ complete(&ctx[2].exit);
+
+ for (i = 0; i < 3; ++i)
+ kthread_stop(ctx[i].thread);
+ for (i = 1; i < 3; ++i)
+ revocable_deinit(&ctx[i].rev);
+}
+
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),
+ KUNIT_CASE(revocable_test_concurrent_access),
{}