Subject: Re: [PATCH 4/4] locking: Add kselftests for ww_mutex stress
To: Chris Wilson <chris@chris-wilson.co.uk>, linux-kernel@vger.kernel.org
References: <1480335612-12069-1-git-send-email-nhaehnle@gmail.com>
 <20161130003548.22266-1-chris@chris-wilson.co.uk>
 <20161130003548.22266-4-chris@chris-wilson.co.uk>
Cc: Peter Zijlstra <peterz@infradead.org>,
        =?UTF-8?Q?Nicolai_H=c3=a4hnle?= <nhaehnle@gmail.com>
From: Maarten Lankhorst <dev@mblankhorst.nl>
Message-ID: <67628c55-e8a1-cc33-f99a-ec458c83657c@mblankhorst.nl>
Date: Wed, 30 Nov 2016 13:29:39 +0100
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Op 30-11-16 om 01:35 schreef Chris Wilson:
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Maarten Lankhorst <dev@mblankhorst.nl>
> Cc: Nicolai Hähnle <nhaehnle@gmail.com>
> ---
>  kernel/locking/test-ww_mutex.c | 134 +++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 134 insertions(+)
>
> diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
> index 63a5031de138..c367014f62dc 100644
> --- a/kernel/locking/test-ww_mutex.c
> +++ b/kernel/locking/test-ww_mutex.c
> @@ -21,6 +21,9 @@
>  #include <linux/kthread.h>
>  #include <linux/ww_mutex.h>
>  #include <linux/completion.h>
> +#include <linux/random.h>
> +#include <linux/slab.h>
> +#include <linux/delay.h>
>  
>  MODULE_LICENSE("GPL");
>  MODULE_AUTHOR("Intel Corporation");
> @@ -224,6 +227,129 @@ static int test_abba(void)
>  	return ret;
>  }
>  
> +struct stress {
> +	struct work_struct work;
> +	struct ww_mutex *locks;
> +	int nlocks;
> +};
> +
> +static int *get_random_order(int count)
> +{
> +	int *order;
> +	int n, r, tmp;
> +
> +	order = kmalloc_array(count, sizeof(*order), GFP_TEMPORARY);
> +	if (!order)
> +		return order;
> +
> +	for (n = 0; n < count; n++)
> +		order[n] = n;
> +
> +	for (n = count - 1; n > 1; n--) {
> +		r = get_random_int() % (n + 1);
> +		if (r != n) {
> +			tmp = order[n];
> +			order[n] = order[r];
> +			order[r] = tmp;
> +		}
> +	}
> +
> +	return order;
> +}
> +
> +static void stress_work(struct work_struct *work)
> +{
> +	struct stress *stress = container_of(work, typeof(*stress), work);
> +	const int nlocks = stress->nlocks;
> +	struct ww_mutex *locks = stress->locks;
> +	struct ww_acquire_ctx ctx;
> +	int contended = -1;
> +	int *order;
> +	int n, ret;
> +
> +	order = get_random_order(nlocks);
> +	if (!order)
> +		return;
> +
> +	ww_acquire_init(&ctx, &ww_class);
> +
> +retry:
> +	ret = 0;
> +	for (n = 0; n < nlocks; n++) {
> +		if (n == contended)
> +			continue;
> +
> +		ret = ww_mutex_lock(&locks[order[n]], &ctx);
> +		if (ret < 0)
> +			break;
> +	}
What's wrong with attempting to lock the contended lock here?
Who knows, this might find some more bugs than the functional tests already do.
> +	if (!ret)
> +		usleep_range(1000, 2000); /* dummy load */
> +
> +	if (contended > n)
> +		ww_mutex_unlock(&locks[order[contended]]);
> +	contended = n;
> +	while (n--)
> +		ww_mutex_unlock(&locks[order[n]]);
> +
> +	if (ret == -EDEADLK) {
> +		ww_mutex_lock_slow(&locks[order[contended]], &ctx);
> +		goto retry;
> +	}
> +
> +	if (ret)
> +		pr_err_once("ww_mutex stress test failed with %d\n", ret);
> +
> +	ww_acquire_fini(&ctx);
> +
> +	kfree(order);
> +	kfree(stress);
> +}
> +
> +static int stress(int nlocks, int count)
> +{
> +	struct ww_mutex *locks;
> +	struct workqueue_struct *wq;
> +	int ret = -ENOMEM;
> +	int n;
> +
> +	wq = alloc_workqueue("test-ww_mutex", WQ_UNBOUND, 0);
> +	if (!wq)
> +		return -ENOMEM;
> +
> +	locks = kmalloc_array(nlocks, sizeof(*locks), GFP_KERNEL);
> +	if (!locks)
> +		goto err;
> +
> +	for (n = 0; n < nlocks; n++)
> +		ww_mutex_init(&locks[n], &ww_class);
> +
> +	for (n = 0; n < count; n++) {
> +		struct stress *stress;
> +
> +		stress = kmalloc(sizeof(*stress), GFP_KERNEL);
> +		if (!stress)
> +			break;
> +
> +		INIT_WORK(&stress->work, stress_work);
> +		stress->locks = locks;
> +		stress->nlocks = nlocks;
> +
> +		queue_work(wq, &stress->work);
> +	}
> +
> +	flush_workqueue(wq);
> +
> +	for (n = 0; n < nlocks; n++)
> +		ww_mutex_destroy(&locks[n]);
> +	kfree(locks);
> +
> +	ret = 0;
> +err:
> +	destroy_workqueue(wq);
> +	return ret;
> +}
> +
>  static int __init test_ww_mutex_init(void)
>  {
>  	int ret;
> @@ -240,6 +366,14 @@ static int __init test_ww_mutex_init(void)
>  	if (ret)
>  		return ret;
>  
> +	ret = stress(16, 1024);
> +	if (ret)
> +		return ret;
> +
> +	ret = stress(4096, 1024);
> +	if (ret)
> +		return ret;
> +
>  	return 0;
>  }
>