revocable: Add KUnit test for concurrent access

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>
Link: https://patch.msgid.link/20260129143733.45618-5-tzungbi@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/base/revocable_test.c b/drivers/base/revocable_test.c
index a2818ec01298899d5ecfe68e5668ad196b0bc7f0..27f5d7d96f4bbf2fecd9de1d29ee8367755bd5bb 100644 (file)
--- 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),
        {}
 };