[RESEND x5][PATCH 0/3] test-ww_mutex improvements

[RESEND x5][PATCH 0/3] test-ww_mutex improvements

[John Stultz]

Hey all,
  Felt like yelling into the void again to resend my improvements
to the test-ww_mutex test driver. These changes have been
particularly helpful for tripping issues in the proxy-exec series.

Despite sending these a few times, I've not gotten any response.
I get its sort of a minor test driver, and isn't super urgent,
but it would be nice to move these forward upstream instead of
having them carried in one of my branches and having to remember
to pull them in when I test with vanilla upstream trees.

As always feedback would be appreciated. Do let me know if I 
hould be cc'ing someone I'm missing to get these reviewed and
eventually pulled in.

thanks
-john

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: kernel-team@android.com

John Stultz (3):
  test-ww_mutex: Extend ww_mutex tests to test both classes of
    ww_mutexes
  test-ww_mutex: Move work to its own UNBOUND workqueue
  test-ww_mutex: Allow test to be run (and re-run) from userland

 kernel/locking/test-ww_mutex.c | 165 ++++++++++++++++++++++++---------
 1 file changed, 122 insertions(+), 43 deletions(-)

-- 
2.52.0.223.gf5cc29aaa4-goog

[RESEND x5][PATCH 1/3] test-ww_mutex: Extend ww_mutex tests to test both classes of ww_mutexes

[John Stultz]

Currently the test-ww_mutex tool only utilizes the wait-die
class of ww_mutexes, and thus isn't very helpful in exercising
the wait-wound class of ww_mutexes.

So extend the test to exercise both classes of ww_mutexes for
all of the subtests.

Signed-off-by: John Stultz <jstultz@google.com>
---
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: kernel-team@android.com
---
 kernel/locking/test-ww_mutex.c | 114 +++++++++++++++++++++------------
 1 file changed, 73 insertions(+), 41 deletions(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index bcb1b9fea5880..d27aaaa860a36 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -13,7 +13,8 @@
 #include <linux/slab.h>
 #include <linux/ww_mutex.h>
 
-static DEFINE_WD_CLASS(ww_class);
+static DEFINE_WD_CLASS(wd_class);
+static DEFINE_WW_CLASS(ww_class);
 struct workqueue_struct *wq;
 
 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
@@ -54,16 +55,16 @@ static void test_mutex_work(struct work_struct *work)
 	ww_mutex_unlock(&mtx->mutex);
 }
 
-static int __test_mutex(unsigned int flags)
+static int __test_mutex(struct ww_class *class, unsigned int flags)
 {
 #define TIMEOUT (HZ / 16)
 	struct test_mutex mtx;
 	struct ww_acquire_ctx ctx;
 	int ret;
 
-	ww_mutex_init(&mtx.mutex, &ww_class);
+	ww_mutex_init(&mtx.mutex, class);
 	if (flags & TEST_MTX_CTX)
-		ww_acquire_init(&ctx, &ww_class);
+		ww_acquire_init(&ctx, class);
 
 	INIT_WORK_ONSTACK(&mtx.work, test_mutex_work);
 	init_completion(&mtx.ready);
@@ -106,13 +107,13 @@ static int __test_mutex(unsigned int flags)
 #undef TIMEOUT
 }
 
-static int test_mutex(void)
+static int test_mutex(struct ww_class *class)
 {
 	int ret;
 	int i;
 
 	for (i = 0; i < __TEST_MTX_LAST; i++) {
-		ret = __test_mutex(i);
+		ret = __test_mutex(class, i);
 		if (ret)
 			return ret;
 	}
@@ -120,15 +121,15 @@ static int test_mutex(void)
 	return 0;
 }
 
-static int test_aa(bool trylock)
+static int test_aa(struct ww_class *class, bool trylock)
 {
 	struct ww_mutex mutex;
 	struct ww_acquire_ctx ctx;
 	int ret;
 	const char *from = trylock ? "trylock" : "lock";
 
-	ww_mutex_init(&mutex, &ww_class);
-	ww_acquire_init(&ctx, &ww_class);
+	ww_mutex_init(&mutex, class);
+	ww_acquire_init(&ctx, class);
 
 	if (!trylock) {
 		ret = ww_mutex_lock(&mutex, &ctx);
@@ -177,6 +178,7 @@ static int test_aa(bool trylock)
 
 struct test_abba {
 	struct work_struct work;
+	struct ww_class *class;
 	struct ww_mutex a_mutex;
 	struct ww_mutex b_mutex;
 	struct completion a_ready;
@@ -191,7 +193,7 @@ static void test_abba_work(struct work_struct *work)
 	struct ww_acquire_ctx ctx;
 	int err;
 
-	ww_acquire_init_noinject(&ctx, &ww_class);
+	ww_acquire_init_noinject(&ctx, abba->class);
 	if (!abba->trylock)
 		ww_mutex_lock(&abba->b_mutex, &ctx);
 	else
@@ -217,23 +219,24 @@ static void test_abba_work(struct work_struct *work)
 	abba->result = err;
 }
 
-static int test_abba(bool trylock, bool resolve)
+static int test_abba(struct ww_class *class, bool trylock, bool resolve)
 {
 	struct test_abba abba;
 	struct ww_acquire_ctx ctx;
 	int err, ret;
 
-	ww_mutex_init(&abba.a_mutex, &ww_class);
-	ww_mutex_init(&abba.b_mutex, &ww_class);
+	ww_mutex_init(&abba.a_mutex, class);
+	ww_mutex_init(&abba.b_mutex, class);
 	INIT_WORK_ONSTACK(&abba.work, test_abba_work);
 	init_completion(&abba.a_ready);
 	init_completion(&abba.b_ready);
+	abba.class = class;
 	abba.trylock = trylock;
 	abba.resolve = resolve;
 
 	schedule_work(&abba.work);
 
-	ww_acquire_init_noinject(&ctx, &ww_class);
+	ww_acquire_init_noinject(&ctx, class);
 	if (!trylock)
 		ww_mutex_lock(&abba.a_mutex, &ctx);
 	else
@@ -278,6 +281,7 @@ static int test_abba(bool trylock, bool resolve)
 
 struct test_cycle {
 	struct work_struct work;
+	struct ww_class *class;
 	struct ww_mutex a_mutex;
 	struct ww_mutex *b_mutex;
 	struct completion *a_signal;
@@ -291,7 +295,7 @@ static void test_cycle_work(struct work_struct *work)
 	struct ww_acquire_ctx ctx;
 	int err, erra = 0;
 
-	ww_acquire_init_noinject(&ctx, &ww_class);
+	ww_acquire_init_noinject(&ctx, cycle->class);
 	ww_mutex_lock(&cycle->a_mutex, &ctx);
 
 	complete(cycle->a_signal);
@@ -314,7 +318,7 @@ static void test_cycle_work(struct work_struct *work)
 	cycle->result = err ?: erra;
 }
 
-static int __test_cycle(unsigned int nthreads)
+static int __test_cycle(struct ww_class *class, unsigned int nthreads)
 {
 	struct test_cycle *cycles;
 	unsigned int n, last = nthreads - 1;
@@ -327,7 +331,8 @@ static int __test_cycle(unsigned int nthreads)
 	for (n = 0; n < nthreads; n++) {
 		struct test_cycle *cycle = &cycles[n];
 
-		ww_mutex_init(&cycle->a_mutex, &ww_class);
+		cycle->class = class;
+		ww_mutex_init(&cycle->a_mutex, class);
 		if (n == last)
 			cycle->b_mutex = &cycles[0].a_mutex;
 		else
@@ -367,13 +372,13 @@ static int __test_cycle(unsigned int nthreads)
 	return ret;
 }
 
-static int test_cycle(unsigned int ncpus)
+static int test_cycle(struct ww_class *class, unsigned int ncpus)
 {
 	unsigned int n;
 	int ret;
 
 	for (n = 2; n <= ncpus + 1; n++) {
-		ret = __test_cycle(n);
+		ret = __test_cycle(class, n);
 		if (ret)
 			return ret;
 	}
@@ -384,6 +389,7 @@ static int test_cycle(unsigned int ncpus)
 struct stress {
 	struct work_struct work;
 	struct ww_mutex *locks;
+	struct ww_class *class;
 	unsigned long timeout;
 	int nlocks;
 };
@@ -443,7 +449,7 @@ static void stress_inorder_work(struct work_struct *work)
 		int contended = -1;
 		int n, err;
 
-		ww_acquire_init(&ctx, &ww_class);
+		ww_acquire_init(&ctx, stress->class);
 retry:
 		err = 0;
 		for (n = 0; n < nlocks; n++) {
@@ -511,7 +517,7 @@ static void stress_reorder_work(struct work_struct *work)
 	order = NULL;
 
 	do {
-		ww_acquire_init(&ctx, &ww_class);
+		ww_acquire_init(&ctx, stress->class);
 
 		list_for_each_entry(ll, &locks, link) {
 			err = ww_mutex_lock(ll->lock, &ctx);
@@ -570,7 +576,7 @@ static void stress_one_work(struct work_struct *work)
 #define STRESS_ONE BIT(2)
 #define STRESS_ALL (STRESS_INORDER | STRESS_REORDER | STRESS_ONE)
 
-static int stress(int nlocks, int nthreads, unsigned int flags)
+static int stress(struct ww_class *class, int nlocks, int nthreads, unsigned int flags)
 {
 	struct ww_mutex *locks;
 	struct stress *stress_array;
@@ -588,7 +594,7 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
 	}
 
 	for (n = 0; n < nlocks; n++)
-		ww_mutex_init(&locks[n], &ww_class);
+		ww_mutex_init(&locks[n], class);
 
 	count = 0;
 	for (n = 0; nthreads; n++) {
@@ -617,6 +623,7 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
 		stress = &stress_array[count++];
 
 		INIT_WORK(&stress->work, fn);
+		stress->class = class;
 		stress->locks = locks;
 		stress->nlocks = nlocks;
 		stress->timeout = jiffies + 2*HZ;
@@ -635,57 +642,82 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
 	return 0;
 }
 
-static int __init test_ww_mutex_init(void)
+static int __init run_tests(struct ww_class *class)
 {
 	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();
+	ret = test_mutex(class);
 	if (ret)
 		return ret;
 
-	ret = test_aa(false);
+	ret = test_aa(class, false);
 	if (ret)
 		return ret;
 
-	ret = test_aa(true);
+	ret = test_aa(class, true);
 	if (ret)
 		return ret;
 
 	for (i = 0; i < 4; i++) {
-		ret = test_abba(i & 1, i & 2);
+		ret = test_abba(class, i & 1, i & 2);
 		if (ret)
 			return ret;
 	}
 
-	ret = test_cycle(ncpus);
+	ret = test_cycle(class, ncpus);
 	if (ret)
 		return ret;
 
-	ret = stress(16, 2*ncpus, STRESS_INORDER);
+	ret = stress(class, 16, 2 * ncpus, STRESS_INORDER);
 	if (ret)
 		return ret;
 
-	ret = stress(16, 2*ncpus, STRESS_REORDER);
+	ret = stress(class, 16, 2 * ncpus, STRESS_REORDER);
 	if (ret)
 		return ret;
 
-	ret = stress(2046, hweight32(STRESS_ALL)*ncpus, STRESS_ALL);
+	ret = stress(class, 2046, hweight32(STRESS_ALL) * ncpus, STRESS_ALL);
 	if (ret)
 		return ret;
 
-	printk(KERN_INFO "All ww mutex selftests passed\n");
 	return 0;
 }
 
+static int __init run_test_classes(void)
+{
+	int ret;
+
+	pr_info("Beginning ww (wound) mutex selftests\n");
+
+	ret = run_tests(&ww_class);
+	if (ret)
+		return ret;
+
+	pr_info("Beginning ww (die) mutex selftests\n");
+	ret = run_tests(&wd_class);
+	if (ret)
+		return ret;
+
+	pr_info("All ww mutex selftests passed\n");
+	return 0;
+}
+
+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;
+
+	ret = run_test_classes();
+
+	return ret;
+}
+
 static void __exit test_ww_mutex_exit(void)
 {
 	destroy_workqueue(wq);
-- 
2.52.0.223.gf5cc29aaa4-goog

[RESEND x5][PATCH 2/3] test-ww_mutex: Move work to its own UNBOUND workqueue

[John Stultz]

The test-ww_mutex test already allocates its own workqueue
so be sure to use it for the mtx.work and abba.work rather
then the default system workqueue.

This resolves numerous messages of the sort:
"workqueue: test_abba_work hogged CPU... consider switching to WQ_UNBOUND"
"workqueue: test_mutex_work hogged CPU... consider switching to WQ_UNBOUND"

Signed-off-by: John Stultz <jstultz@google.com>
---
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: kernel-team@android.com
---
 kernel/locking/test-ww_mutex.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index d27aaaa860a36..30512b3e95c99 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -72,7 +72,7 @@ static int __test_mutex(struct ww_class *class, unsigned int flags)
 	init_completion(&mtx.done);
 	mtx.flags = flags;
 
-	schedule_work(&mtx.work);
+	queue_work(wq, &mtx.work);
 
 	wait_for_completion(&mtx.ready);
 	ww_mutex_lock(&mtx.mutex, (flags & TEST_MTX_CTX) ? &ctx : NULL);
@@ -234,7 +234,7 @@ static int test_abba(struct ww_class *class, bool trylock, bool resolve)
 	abba.trylock = trylock;
 	abba.resolve = resolve;
 
-	schedule_work(&abba.work);
+	queue_work(wq, &abba.work);
 
 	ww_acquire_init_noinject(&ctx, class);
 	if (!trylock)
-- 
2.52.0.223.gf5cc29aaa4-goog

[RESEND x5][PATCH 3/3] test-ww_mutex: Allow test to be run (and re-run) from userland

[John Stultz]

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.

This has been particularly valuable to stressing and finding
issues with the proxy-exec series.

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

Signed-off-by: John Stultz <jstultz@google.com>
---
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Joel Fernandes <joelagnelf@nvidia.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Suleiman Souhlal <suleiman@google.com>
Cc: kernel-team@android.com
---
 kernel/locking/test-ww_mutex.c | 51 ++++++++++++++++++++++++++++++++--
 1 file changed, 49 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 30512b3e95c99..79b5e45f8d4c2 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -642,7 +642,7 @@ static int stress(struct ww_class *class, int nlocks, int nthreads, unsigned int
 	return 0;
 }
 
-static int __init run_tests(struct ww_class *class)
+static int run_tests(struct ww_class *class)
 {
 	int ncpus = num_online_cpus();
 	int ret, i;
@@ -684,7 +684,7 @@ static int __init run_tests(struct ww_class *class)
 	return 0;
 }
 
-static int __init run_test_classes(void)
+static int run_test_classes(void)
 {
 	int ret;
 
@@ -703,6 +703,36 @@ static int __init run_test_classes(void)
 	return 0;
 }
 
+static DEFINE_MUTEX(run_lock);
+
+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_test_classes();
+	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;
@@ -713,13 +743,30 @@ static int __init test_ww_mutex_init(void)
 	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_test_classes();
+	mutex_unlock(&run_lock);
 
 	return ret;
 }
 
 static void __exit test_ww_mutex_exit(void)
 {
+	kobject_put(test_ww_mutex_kobj);
 	destroy_workqueue(wq);
 }
 
-- 
2.52.0.223.gf5cc29aaa4-goog

Re: [RESEND x5][PATCH 0/3] test-ww_mutex improvements

[Peter Zijlstra]

On Fri, Dec 05, 2025 at 01:35:08AM +0000, John Stultz wrote:
> Hey all,
>   Felt like yelling into the void again to resend my improvements
> to the test-ww_mutex test driver. These changes have been
> particularly helpful for tripping issues in the proxy-exec series.

Right you are. I've thrown these on the pile to sort out post rc1.

[tip: locking/core] test-ww_mutex: Allow test to be run (and re-run) from userland

[tip-bot2 for John Stultz]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     de2c5a1523fde38411b6259064258a0c0a3c896a
Gitweb:        https://git.kernel.org/tip/de2c5a1523fde38411b6259064258a0c0a3c896a
Author:        John Stultz <jstultz@google.com>
AuthorDate:    Fri, 05 Dec 2025 01:35:11 
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 18 Dec 2025 10:45:23 +01:00

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.

This has been particularly valuable to stressing and finding
issues with the proxy-exec series.

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

Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251205013515.759030-4-jstultz@google.com
---
 kernel/locking/test-ww_mutex.c | 51 +++++++++++++++++++++++++++++++--
 1 file changed, 49 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 30512b3..79b5e45 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -642,7 +642,7 @@ static int stress(struct ww_class *class, int nlocks, int nthreads, unsigned int
 	return 0;
 }
 
-static int __init run_tests(struct ww_class *class)
+static int run_tests(struct ww_class *class)
 {
 	int ncpus = num_online_cpus();
 	int ret, i;
@@ -684,7 +684,7 @@ static int __init run_tests(struct ww_class *class)
 	return 0;
 }
 
-static int __init run_test_classes(void)
+static int run_test_classes(void)
 {
 	int ret;
 
@@ -703,6 +703,36 @@ static int __init run_test_classes(void)
 	return 0;
 }
 
+static DEFINE_MUTEX(run_lock);
+
+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_test_classes();
+	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;
@@ -713,13 +743,30 @@ static int __init test_ww_mutex_init(void)
 	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_test_classes();
+	mutex_unlock(&run_lock);
 
 	return ret;
 }
 
 static void __exit test_ww_mutex_exit(void)
 {
+	kobject_put(test_ww_mutex_kobj);
 	destroy_workqueue(wq);
 }
 

[tip: locking/core] test-ww_mutex: Move work to its own UNBOUND workqueue

[tip-bot2 for John Stultz]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     d327e7166efa24c69719890ea332b55a9dea21a7
Gitweb:        https://git.kernel.org/tip/d327e7166efa24c69719890ea332b55a9dea21a7
Author:        John Stultz <jstultz@google.com>
AuthorDate:    Fri, 05 Dec 2025 01:35:10 
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 18 Dec 2025 10:45:23 +01:00

test-ww_mutex: Move work to its own UNBOUND workqueue

The test-ww_mutex test already allocates its own workqueue
so be sure to use it for the mtx.work and abba.work rather
then the default system workqueue.

This resolves numerous messages of the sort:
"workqueue: test_abba_work hogged CPU... consider switching to WQ_UNBOUND"
"workqueue: test_mutex_work hogged CPU... consider switching to WQ_UNBOUND"

Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251205013515.759030-3-jstultz@google.com
---
 kernel/locking/test-ww_mutex.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index d27aaaa..30512b3 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -72,7 +72,7 @@ static int __test_mutex(struct ww_class *class, unsigned int flags)
 	init_completion(&mtx.done);
 	mtx.flags = flags;
 
-	schedule_work(&mtx.work);
+	queue_work(wq, &mtx.work);
 
 	wait_for_completion(&mtx.ready);
 	ww_mutex_lock(&mtx.mutex, (flags & TEST_MTX_CTX) ? &ctx : NULL);
@@ -234,7 +234,7 @@ static int test_abba(struct ww_class *class, bool trylock, bool resolve)
 	abba.trylock = trylock;
 	abba.resolve = resolve;
 
-	schedule_work(&abba.work);
+	queue_work(wq, &abba.work);
 
 	ww_acquire_init_noinject(&ctx, class);
 	if (!trylock)

[tip: locking/core] test-ww_mutex: Extend ww_mutex tests to test both classes of ww_mutexes

[tip-bot2 for John Stultz]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     34d80c93a5bbf38938e8c215ec6c938807edeaf0
Gitweb:        https://git.kernel.org/tip/34d80c93a5bbf38938e8c215ec6c938807edeaf0
Author:        John Stultz <jstultz@google.com>
AuthorDate:    Fri, 05 Dec 2025 01:35:09 
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 18 Dec 2025 10:45:23 +01:00

test-ww_mutex: Extend ww_mutex tests to test both classes of ww_mutexes

Currently the test-ww_mutex tool only utilizes the wait-die
class of ww_mutexes, and thus isn't very helpful in exercising
the wait-wound class of ww_mutexes.

So extend the test to exercise both classes of ww_mutexes for
all of the subtests.

Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251205013515.759030-2-jstultz@google.com
---
 kernel/locking/test-ww_mutex.c | 114 ++++++++++++++++++++------------
 1 file changed, 73 insertions(+), 41 deletions(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index bcb1b9f..d27aaaa 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -13,7 +13,8 @@
 #include <linux/slab.h>
 #include <linux/ww_mutex.h>
 
-static DEFINE_WD_CLASS(ww_class);
+static DEFINE_WD_CLASS(wd_class);
+static DEFINE_WW_CLASS(ww_class);
 struct workqueue_struct *wq;
 
 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
@@ -54,16 +55,16 @@ static void test_mutex_work(struct work_struct *work)
 	ww_mutex_unlock(&mtx->mutex);
 }
 
-static int __test_mutex(unsigned int flags)
+static int __test_mutex(struct ww_class *class, unsigned int flags)
 {
 #define TIMEOUT (HZ / 16)
 	struct test_mutex mtx;
 	struct ww_acquire_ctx ctx;
 	int ret;
 
-	ww_mutex_init(&mtx.mutex, &ww_class);
+	ww_mutex_init(&mtx.mutex, class);
 	if (flags & TEST_MTX_CTX)
-		ww_acquire_init(&ctx, &ww_class);
+		ww_acquire_init(&ctx, class);
 
 	INIT_WORK_ONSTACK(&mtx.work, test_mutex_work);
 	init_completion(&mtx.ready);
@@ -106,13 +107,13 @@ static int __test_mutex(unsigned int flags)
 #undef TIMEOUT
 }
 
-static int test_mutex(void)
+static int test_mutex(struct ww_class *class)
 {
 	int ret;
 	int i;
 
 	for (i = 0; i < __TEST_MTX_LAST; i++) {
-		ret = __test_mutex(i);
+		ret = __test_mutex(class, i);
 		if (ret)
 			return ret;
 	}
@@ -120,15 +121,15 @@ static int test_mutex(void)
 	return 0;
 }
 
-static int test_aa(bool trylock)
+static int test_aa(struct ww_class *class, bool trylock)
 {
 	struct ww_mutex mutex;
 	struct ww_acquire_ctx ctx;
 	int ret;
 	const char *from = trylock ? "trylock" : "lock";
 
-	ww_mutex_init(&mutex, &ww_class);
-	ww_acquire_init(&ctx, &ww_class);
+	ww_mutex_init(&mutex, class);
+	ww_acquire_init(&ctx, class);
 
 	if (!trylock) {
 		ret = ww_mutex_lock(&mutex, &ctx);
@@ -177,6 +178,7 @@ out:
 
 struct test_abba {
 	struct work_struct work;
+	struct ww_class *class;
 	struct ww_mutex a_mutex;
 	struct ww_mutex b_mutex;
 	struct completion a_ready;
@@ -191,7 +193,7 @@ static void test_abba_work(struct work_struct *work)
 	struct ww_acquire_ctx ctx;
 	int err;
 
-	ww_acquire_init_noinject(&ctx, &ww_class);
+	ww_acquire_init_noinject(&ctx, abba->class);
 	if (!abba->trylock)
 		ww_mutex_lock(&abba->b_mutex, &ctx);
 	else
@@ -217,23 +219,24 @@ static void test_abba_work(struct work_struct *work)
 	abba->result = err;
 }
 
-static int test_abba(bool trylock, bool resolve)
+static int test_abba(struct ww_class *class, bool trylock, bool resolve)
 {
 	struct test_abba abba;
 	struct ww_acquire_ctx ctx;
 	int err, ret;
 
-	ww_mutex_init(&abba.a_mutex, &ww_class);
-	ww_mutex_init(&abba.b_mutex, &ww_class);
+	ww_mutex_init(&abba.a_mutex, class);
+	ww_mutex_init(&abba.b_mutex, class);
 	INIT_WORK_ONSTACK(&abba.work, test_abba_work);
 	init_completion(&abba.a_ready);
 	init_completion(&abba.b_ready);
+	abba.class = class;
 	abba.trylock = trylock;
 	abba.resolve = resolve;
 
 	schedule_work(&abba.work);
 
-	ww_acquire_init_noinject(&ctx, &ww_class);
+	ww_acquire_init_noinject(&ctx, class);
 	if (!trylock)
 		ww_mutex_lock(&abba.a_mutex, &ctx);
 	else
@@ -278,6 +281,7 @@ static int test_abba(bool trylock, bool resolve)
 
 struct test_cycle {
 	struct work_struct work;
+	struct ww_class *class;
 	struct ww_mutex a_mutex;
 	struct ww_mutex *b_mutex;
 	struct completion *a_signal;
@@ -291,7 +295,7 @@ static void test_cycle_work(struct work_struct *work)
 	struct ww_acquire_ctx ctx;
 	int err, erra = 0;
 
-	ww_acquire_init_noinject(&ctx, &ww_class);
+	ww_acquire_init_noinject(&ctx, cycle->class);
 	ww_mutex_lock(&cycle->a_mutex, &ctx);
 
 	complete(cycle->a_signal);
@@ -314,7 +318,7 @@ static void test_cycle_work(struct work_struct *work)
 	cycle->result = err ?: erra;
 }
 
-static int __test_cycle(unsigned int nthreads)
+static int __test_cycle(struct ww_class *class, unsigned int nthreads)
 {
 	struct test_cycle *cycles;
 	unsigned int n, last = nthreads - 1;
@@ -327,7 +331,8 @@ static int __test_cycle(unsigned int nthreads)
 	for (n = 0; n < nthreads; n++) {
 		struct test_cycle *cycle = &cycles[n];
 
-		ww_mutex_init(&cycle->a_mutex, &ww_class);
+		cycle->class = class;
+		ww_mutex_init(&cycle->a_mutex, class);
 		if (n == last)
 			cycle->b_mutex = &cycles[0].a_mutex;
 		else
@@ -367,13 +372,13 @@ static int __test_cycle(unsigned int nthreads)
 	return ret;
 }
 
-static int test_cycle(unsigned int ncpus)
+static int test_cycle(struct ww_class *class, unsigned int ncpus)
 {
 	unsigned int n;
 	int ret;
 
 	for (n = 2; n <= ncpus + 1; n++) {
-		ret = __test_cycle(n);
+		ret = __test_cycle(class, n);
 		if (ret)
 			return ret;
 	}
@@ -384,6 +389,7 @@ static int test_cycle(unsigned int ncpus)
 struct stress {
 	struct work_struct work;
 	struct ww_mutex *locks;
+	struct ww_class *class;
 	unsigned long timeout;
 	int nlocks;
 };
@@ -443,7 +449,7 @@ static void stress_inorder_work(struct work_struct *work)
 		int contended = -1;
 		int n, err;
 
-		ww_acquire_init(&ctx, &ww_class);
+		ww_acquire_init(&ctx, stress->class);
 retry:
 		err = 0;
 		for (n = 0; n < nlocks; n++) {
@@ -511,7 +517,7 @@ static void stress_reorder_work(struct work_struct *work)
 	order = NULL;
 
 	do {
-		ww_acquire_init(&ctx, &ww_class);
+		ww_acquire_init(&ctx, stress->class);
 
 		list_for_each_entry(ll, &locks, link) {
 			err = ww_mutex_lock(ll->lock, &ctx);
@@ -570,7 +576,7 @@ static void stress_one_work(struct work_struct *work)
 #define STRESS_ONE BIT(2)
 #define STRESS_ALL (STRESS_INORDER | STRESS_REORDER | STRESS_ONE)
 
-static int stress(int nlocks, int nthreads, unsigned int flags)
+static int stress(struct ww_class *class, int nlocks, int nthreads, unsigned int flags)
 {
 	struct ww_mutex *locks;
 	struct stress *stress_array;
@@ -588,7 +594,7 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
 	}
 
 	for (n = 0; n < nlocks; n++)
-		ww_mutex_init(&locks[n], &ww_class);
+		ww_mutex_init(&locks[n], class);
 
 	count = 0;
 	for (n = 0; nthreads; n++) {
@@ -617,6 +623,7 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
 		stress = &stress_array[count++];
 
 		INIT_WORK(&stress->work, fn);
+		stress->class = class;
 		stress->locks = locks;
 		stress->nlocks = nlocks;
 		stress->timeout = jiffies + 2*HZ;
@@ -635,57 +642,82 @@ static int stress(int nlocks, int nthreads, unsigned int flags)
 	return 0;
 }
 
-static int __init test_ww_mutex_init(void)
+static int __init run_tests(struct ww_class *class)
 {
 	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();
+	ret = test_mutex(class);
 	if (ret)
 		return ret;
 
-	ret = test_aa(false);
+	ret = test_aa(class, false);
 	if (ret)
 		return ret;
 
-	ret = test_aa(true);
+	ret = test_aa(class, true);
 	if (ret)
 		return ret;
 
 	for (i = 0; i < 4; i++) {
-		ret = test_abba(i & 1, i & 2);
+		ret = test_abba(class, i & 1, i & 2);
 		if (ret)
 			return ret;
 	}
 
-	ret = test_cycle(ncpus);
+	ret = test_cycle(class, ncpus);
 	if (ret)
 		return ret;
 
-	ret = stress(16, 2*ncpus, STRESS_INORDER);
+	ret = stress(class, 16, 2 * ncpus, STRESS_INORDER);
 	if (ret)
 		return ret;
 
-	ret = stress(16, 2*ncpus, STRESS_REORDER);
+	ret = stress(class, 16, 2 * ncpus, STRESS_REORDER);
 	if (ret)
 		return ret;
 
-	ret = stress(2046, hweight32(STRESS_ALL)*ncpus, STRESS_ALL);
+	ret = stress(class, 2046, hweight32(STRESS_ALL) * ncpus, STRESS_ALL);
 	if (ret)
 		return ret;
 
-	printk(KERN_INFO "All ww mutex selftests passed\n");
 	return 0;
 }
 
+static int __init run_test_classes(void)
+{
+	int ret;
+
+	pr_info("Beginning ww (wound) mutex selftests\n");
+
+	ret = run_tests(&ww_class);
+	if (ret)
+		return ret;
+
+	pr_info("Beginning ww (die) mutex selftests\n");
+	ret = run_tests(&wd_class);
+	if (ret)
+		return ret;
+
+	pr_info("All ww mutex selftests passed\n");
+	return 0;
+}
+
+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;
+
+	ret = run_test_classes();
+
+	return ret;
+}
+
 static void __exit test_ww_mutex_exit(void)
 {
 	destroy_workqueue(wq);