linux-kernel - [RFC][PATCH] test-ww_mutex: Allow test to be run (and re-run) from userland

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Message-ID: <20241115235919.1029490-1-jstultz@google.com>
Date: Fri, 15 Nov 2024 15:59:10 -0800
From: John Stultz <jstultz@...gle.com>
To: LKML <linux-kernel@...r.kernel.org>
Cc: John Stultz <jstultz@...gle.com>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>, 
	Boqun Feng <boqun.feng@...il.com>, "Paul E . McKenney" <paulmck@...nel.org>, 
	Joel Fernandes <joelaf@...gle.com>, Dietmar Eggemann <dietmar.eggemann@....com>, kernel-team@...roid.com
Subject: [RFC][PATCH] test-ww_mutex: Allow test to be run (and re-run) from userland

In cases where the ww_mutex test was occasionally tripping on
hard to find issues, leaving qemu in a reboot loop was my best
way to reproduce problems. These reboots however wasted time
when I just wanted to run the test-ww_mutex logic.

So tweak the test-ww_mutex test so that it can be re-triggered
via a sysfs file, so the test can be run repeatedly without
doing module loads or restarting.

To use, run as root:
  echo 1 > /sys/kernel/test_ww_mutex/run_tests

Thoughts or feedback would be appreciated!

Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Will Deacon <will@...nel.org>
Cc: Waiman Long <longman@...hat.com>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: "Paul E . McKenney" <paulmck@...nel.org>
Cc: Joel Fernandes <joelaf@...gle.com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: kernel-team@...roid.com
Signed-off-by: John Stultz <jstultz@...gle.com>
---
 kernel/locking/test-ww_mutex.c | 70 ++++++++++++++++++++++++++++++----
 1 file changed, 63 insertions(+), 7 deletions(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 10a5736a21c2..cc0d2e59049a 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -636,19 +636,15 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
 	return 0;
 }
 
-static int __init test_ww_mutex_init(void)
+static DEFINE_MUTEX(run_lock);
+
+static int run_tests(void)
 {
 	int ncpus = num_online_cpus();
 	int ret, i;
 
 	printk(KERN_INFO "Beginning ww mutex selftests\n");
 
-	prandom_seed_state(&rng, get_random_u64());
-
-	wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0);
-	if (!wq)
-		return -ENOMEM;
-
 	ret = test_mutex();
 	if (ret)
 		return ret;
@@ -687,8 +683,68 @@ static int __init test_ww_mutex_init(void)
 	return 0;
 }
 
+static ssize_t run_tests_store(struct kobject *kobj, struct kobj_attribute *attr,
+			       const char *buf, size_t count)
+{
+	if (!mutex_trylock(&run_lock)) {
+		pr_err("Test already running\n");
+		return count;
+	}
+
+	run_tests();
+	mutex_unlock(&run_lock);
+
+	return count;
+}
+
+static struct kobj_attribute run_tests_attribute =
+	__ATTR(run_tests, 0664, NULL, run_tests_store);
+
+static struct attribute *attrs[] = {
+	&run_tests_attribute.attr,
+	NULL,   /* need to NULL terminate the list of attributes */
+};
+
+static struct attribute_group attr_group = {
+	.attrs = attrs,
+};
+
+static struct kobject *test_ww_mutex_kobj;
+
+static int __init test_ww_mutex_init(void)
+{
+	int ret;
+
+	prandom_seed_state(&rng, get_random_u64());
+
+	wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0);
+	if (!wq)
+		return -ENOMEM;
+
+	test_ww_mutex_kobj = kobject_create_and_add("test_ww_mutex", kernel_kobj);
+	if (!test_ww_mutex_kobj) {
+		destroy_workqueue(wq);
+		return -ENOMEM;
+	}
+
+	/* Create the files associated with this kobject */
+	ret = sysfs_create_group(test_ww_mutex_kobj, &attr_group);
+	if (ret) {
+		kobject_put(test_ww_mutex_kobj);
+		destroy_workqueue(wq);
+		return ret;
+	}
+
+	mutex_lock(&run_lock);
+	ret = run_tests();
+	mutex_unlock(&run_lock);
+
+	return ret;
+}
+
 static void __exit test_ww_mutex_exit(void)
 {
+	kobject_put(test_ww_mutex_kobj);
 	destroy_workqueue(wq);
 }
 
-- 
2.47.0.338.g60cca15819-goog