[RESEND x4][PATCH 3/3] test-ww_mutex: Allow test to be run (and re-run) from userland

[John Stultz <jstultz@google.com>]

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.rc1.455.g30608eb744-goog