linux/kernel/locking/locktorture.c

/*
 * Module-based torture test facility for locking
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
 *
 * Copyright (C) IBM Corporation, 2014
 *
 * Author: Paul E. McKenney <paulmck@us.ibm.com>
 *	Based on kernel/rcu/torture.c.
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/spinlock.h>
#include <linux/rwlock.h>
#include <linux/mutex.h>
#include <linux/rwsem.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <linux/atomic.h>
#include <linux/moduleparam.h>
#include <linux/delay.h>
#include <linux/slab.h>
#include <linux/torture.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com>");

torture_param(int, nwriters_stress, -1,
	     "Number of write-locking stress-test threads");
torture_param(int, nreaders_stress, -1,
	     "Number of read-locking stress-test threads");
torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
torture_param(int, onoff_interval, 0,
	     "Time between CPU hotplugs (s), 0=disable");
torture_param(int, shuffle_interval, 3,
	     "Number of jiffies between shuffles, 0=disable");
torture_param(int, shutdown_secs, 0, "Shutdown time (j), <= zero to disable.");
torture_param(int, stat_interval, 60,
	     "Number of seconds between stats printk()s");
torture_param(int, stutter, 5, "Number of jiffies to run/halt test, 0=disable");
torture_param(bool, verbose, true,
	     "Enable verbose debugging printk()s");

static char *torture_type = "spin_lock";
module_param(torture_type, charp, 0444);
MODULE_PARM_DESC(torture_type,
		 "Type of lock to torture (spin_lock, spin_lock_irq, mutex_lock, ...)");

static struct task_struct *stats_task;
static struct task_struct **writer_tasks;
static struct task_struct **reader_tasks;

static bool lock_is_write_held;
static bool lock_is_read_held;

struct lock_stress_stats {
	long n_lock_fail;
	long n_lock_acquired;
};

#if defined(MODULE)
#define LOCKTORTURE_RUNNABLE_INIT 1
#else
#define LOCKTORTURE_RUNNABLE_INIT 0
#endif
int torture_runnable = LOCKTORTURE_RUNNABLE_INIT;
module_param(torture_runnable, int, 0444);
MODULE_PARM_DESC(torture_runnable, "Start locktorture at module init");

/* Forward reference. */
static void lock_torture_cleanup(void);

/*
 * Operations vector for selecting different types of tests.
 */
struct lock_torture_ops {
	void (*init)(void);
	int (*writelock)(void);
	void (*write_delay)(struct torture_random_state *trsp);
	void (*writeunlock)(void);
	int (*readlock)(void);
	void (*read_delay)(struct torture_random_state *trsp);
	void (*readunlock)(void);
	unsigned long flags;
	const char *name;
};

struct lock_torture_cxt {
	int nrealwriters_stress;
	int nrealreaders_stress;
	bool debug_lock;
	atomic_t n_lock_torture_errors;
	struct lock_torture_ops *cur_ops;
	struct lock_stress_stats *lwsa; /* writer statistics */
	struct lock_stress_stats *lrsa; /* reader statistics */
};
static struct lock_torture_cxt cxt = { 0, 0, false,
				       ATOMIC_INIT(0),
				       NULL, NULL};
/*
 * Definitions for lock torture testing.
 */

static int torture_lock_busted_write_lock(void)
{
	return 0;  /* BUGGY, do not use in real life!!! */
}

static void torture_lock_busted_write_delay(struct torture_random_state *trsp)
{
	const unsigned long longdelay_ms = 100;

	/* We want a long delay occasionally to force massive contention.  */
	if (!(torture_random(trsp) %
	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
		mdelay(longdelay_ms);
#ifdef CONFIG_PREEMPT
	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
		preempt_schedule();  /* Allow test to be preempted. */
#endif
}

static void torture_lock_busted_write_unlock(void)
{
	  /* BUGGY, do not use in real life!!! */
}

static struct lock_torture_ops lock_busted_ops = {
	.writelock	= torture_lock_busted_write_lock,
	.write_delay	= torture_lock_busted_write_delay,
	.writeunlock	= torture_lock_busted_write_unlock,
	.readlock       = NULL,
	.read_delay     = NULL,
	.readunlock     = NULL,
	.name		= "lock_busted"
};

static DEFINE_SPINLOCK(torture_spinlock);

static int torture_spin_lock_write_lock(void) __acquires(torture_spinlock)
{
	spin_lock(&torture_spinlock);
	return 0;
}

static void torture_spin_lock_write_delay(struct torture_random_state *trsp)
{
	const unsigned long shortdelay_us = 2;
	const unsigned long longdelay_ms = 100;

	/* We want a short delay mostly to emulate likely code, and
	 * we want a long delay occasionally to force massive contention.
	 */
	if (!(torture_random(trsp) %
	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
		mdelay(longdelay_ms);
	if (!(torture_random(trsp) %
	      (cxt.nrealwriters_stress * 2 * shortdelay_us)))
		udelay(shortdelay_us);
#ifdef CONFIG_PREEMPT
	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
		preempt_schedule();  /* Allow test to be preempted. */
#endif
}

static void torture_spin_lock_write_unlock(void) __releases(torture_spinlock)
{
	spin_unlock(&torture_spinlock);
}

static struct lock_torture_ops spin_lock_ops = {
	.writelock	= torture_spin_lock_write_lock,
	.write_delay	= torture_spin_lock_write_delay,
	.writeunlock	= torture_spin_lock_write_unlock,
	.readlock       = NULL,
	.read_delay     = NULL,
	.readunlock     = NULL,
	.name		= "spin_lock"
};

static int torture_spin_lock_write_lock_irq(void)
__acquires(torture_spinlock)
{
	unsigned long flags;

	spin_lock_irqsave(&torture_spinlock, flags);
	cxt.cur_ops->flags = flags;
	return 0;
}

static void torture_lock_spin_write_unlock_irq(void)
__releases(torture_spinlock)
{
	spin_unlock_irqrestore(&torture_spinlock, cxt.cur_ops->flags);
}

static struct lock_torture_ops spin_lock_irq_ops = {
	.writelock	= torture_spin_lock_write_lock_irq,
	.write_delay	= torture_spin_lock_write_delay,
	.writeunlock	= torture_lock_spin_write_unlock_irq,
	.readlock       = NULL,
	.read_delay     = NULL,
	.readunlock     = NULL,
	.name		= "spin_lock_irq"
};

static DEFINE_RWLOCK(torture_rwlock);

static int torture_rwlock_write_lock(void) __acquires(torture_rwlock)
{
	write_lock(&torture_rwlock);
	return 0;
}

static void torture_rwlock_write_delay(struct torture_random_state *trsp)
{
	const unsigned long shortdelay_us = 2;
	const unsigned long longdelay_ms = 100;

	/* We want a short delay mostly to emulate likely code, and
	 * we want a long delay occasionally to force massive contention.
	 */
	if (!(torture_random(trsp) %
	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
		mdelay(longdelay_ms);
	else
		udelay(shortdelay_us);
}

static void torture_rwlock_write_unlock(void) __releases(torture_rwlock)
{
	write_unlock(&torture_rwlock);
}

static int torture_rwlock_read_lock(void) __acquires(torture_rwlock)
{
	read_lock(&torture_rwlock);
	return 0;
}

static void torture_rwlock_read_delay(struct torture_random_state *trsp)
{
	const unsigned long shortdelay_us = 10;
	const unsigned long longdelay_ms = 100;

	/* We want a short delay mostly to emulate likely code, and
	 * we want a long delay occasionally to force massive contention.
	 */
	if (!(torture_random(trsp) %
	      (cxt.nrealreaders_stress * 2000 * longdelay_ms)))
		mdelay(longdelay_ms);
	else
		udelay(shortdelay_us);
}

static void torture_rwlock_read_unlock(void) __releases(torture_rwlock)
{
	read_unlock(&torture_rwlock);
}

static struct lock_torture_ops rw_lock_ops = {
	.writelock	= torture_rwlock_write_lock,
	.write_delay	= torture_rwlock_write_delay,
	.writeunlock	= torture_rwlock_write_unlock,
	.readlock       = torture_rwlock_read_lock,
	.read_delay     = torture_rwlock_read_delay,
	.readunlock     = torture_rwlock_read_unlock,
	.name		= "rw_lock"
};

static int torture_rwlock_write_lock_irq(void) __acquires(torture_rwlock)
{
	unsigned long flags;

	write_lock_irqsave(&torture_rwlock, flags);
	cxt.cur_ops->flags = flags;
	return 0;
}

static void torture_rwlock_write_unlock_irq(void)
__releases(torture_rwlock)
{
	write_unlock_irqrestore(&torture_rwlock, cxt.cur_ops->flags);
}

static int torture_rwlock_read_lock_irq(void) __acquires(torture_rwlock)
{
	unsigned long flags;

	read_lock_irqsave(&torture_rwlock, flags);
	cxt.cur_ops->flags = flags;
	return 0;
}

static void torture_rwlock_read_unlock_irq(void)
__releases(torture_rwlock)
{
	read_unlock_irqrestore(&torture_rwlock, cxt.cur_ops->flags);
}

static struct lock_torture_ops rw_lock_irq_ops = {
	.writelock	= torture_rwlock_write_lock_irq,
	.write_delay	= torture_rwlock_write_delay,
	.writeunlock	= torture_rwlock_write_unlock_irq,
	.readlock       = torture_rwlock_read_lock_irq,
	.read_delay     = torture_rwlock_read_delay,
	.readunlock     = torture_rwlock_read_unlock_irq,
	.name		= "rw_lock_irq"
};

static DEFINE_MUTEX(torture_mutex);

static int torture_mutex_lock(void) __acquires(torture_mutex)
{
	mutex_lock(&torture_mutex);
	return 0;
}

static void torture_mutex_delay(struct torture_random_state *trsp)
{
	const unsigned long longdelay_ms = 100;

	/* We want a long delay occasionally to force massive contention.  */
	if (!(torture_random(trsp) %
	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
		mdelay(longdelay_ms * 5);
	else
		mdelay(longdelay_ms / 5);
#ifdef CONFIG_PREEMPT
	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
		preempt_schedule();  /* Allow test to be preempted. */
#endif
}

static void torture_mutex_unlock(void) __releases(torture_mutex)
{
	mutex_unlock(&torture_mutex);
}

static struct lock_torture_ops mutex_lock_ops = {
	.writelock	= torture_mutex_lock,
	.write_delay	= torture_mutex_delay,
	.writeunlock	= torture_mutex_unlock,
	.readlock       = NULL,
	.read_delay     = NULL,
	.readunlock     = NULL,
	.name		= "mutex_lock"
};

static DECLARE_RWSEM(torture_rwsem);
static int torture_rwsem_down_write(void) __acquires(torture_rwsem)
{
	down_write(&torture_rwsem);
	return 0;
}

static void torture_rwsem_write_delay(struct torture_random_state *trsp)
{
	const unsigned long longdelay_ms = 100;

	/* We want a long delay occasionally to force massive contention.  */
	if (!(torture_random(trsp) %
	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
		mdelay(longdelay_ms * 10);
	else
		mdelay(longdelay_ms / 10);
#ifdef CONFIG_PREEMPT
	if (!(torture_random(trsp) % (cxt.nrealwriters_stress * 20000)))
		preempt_schedule();  /* Allow test to be preempted. */
#endif
}

static void torture_rwsem_up_write(void) __releases(torture_rwsem)
{
	up_write(&torture_rwsem);
}

static int torture_rwsem_down_read(void) __acquires(torture_rwsem)
{
	down_read(&torture_rwsem);
	return 0;
}

static void torture_rwsem_read_delay(struct torture_random_state *trsp)
{
	const unsigned long longdelay_ms = 100;

	/* We want a long delay occasionally to force massive contention.  */
	if (!(torture_random(trsp) %
	      (cxt.nrealwriters_stress * 2000 * longdelay_ms)))
		mdelay(longdelay_ms * 2);
	else
		mdelay(longdelay_ms / 2);
#ifdef CONFIG_PREEMPT
	if (!(torture_random(trsp) % (cxt.nrealreaders_stress * 20000)))
		preempt_schedule();  /* Allow test to be preempted. */
#endif
}

static void torture_rwsem_up_read(void) __releases(torture_rwsem)
{
	up_read(&torture_rwsem);
}

static struct lock_torture_ops rwsem_lock_ops = {
	.writelock	= torture_rwsem_down_write,
	.write_delay	= torture_rwsem_write_delay,
	.writeunlock	= torture_rwsem_up_write,
	.readlock       = torture_rwsem_down_read,
	.read_delay     = torture_rwsem_read_delay,
	.readunlock     = torture_rwsem_up_read,
	.name		= "rwsem_lock"
};

/*
 * Lock torture writer kthread.  Repeatedly acquires and releases
 * the lock, checking for duplicate acquisitions.
 */
static int lock_torture_writer(void *arg)
{
	struct lock_stress_stats *lwsp = arg;
	static DEFINE_TORTURE_RANDOM(rand);

	VERBOSE_TOROUT_STRING("lock_torture_writer task started");
	set_user_nice(current, MAX_NICE);

	do {
		if ((torture_random(&rand) & 0xfffff) == 0)
			schedule_timeout_uninterruptible(1);

		cxt.cur_ops->writelock();
		if (WARN_ON_ONCE(lock_is_write_held))
			lwsp->n_lock_fail++;
		lock_is_write_held = 1;
		if (WARN_ON_ONCE(lock_is_read_held))
			lwsp->n_lock_fail++; /* rare, but... */

		lwsp->n_lock_acquired++;
		cxt.cur_ops->write_delay(&rand);
		lock_is_write_held = 0;
		cxt.cur_ops->writeunlock();

		stutter_wait("lock_torture_writer");
	} while (!torture_must_stop());
	torture_kthread_stopping("lock_torture_writer");
	return 0;
}

/*
 * Lock torture reader kthread.  Repeatedly acquires and releases
 * the reader lock.
 */
static int lock_torture_reader(void *arg)
{
	struct lock_stress_stats *lrsp = arg;
	static DEFINE_TORTURE_RANDOM(rand);

	VERBOSE_TOROUT_STRING("lock_torture_reader task started");
	set_user_nice(current, MAX_NICE);

	do {
		if ((torture_random(&rand) & 0xfffff) == 0)
			schedule_timeout_uninterruptible(1);

		cxt.cur_ops->readlock();
		lock_is_read_held = 1;
		if (WARN_ON_ONCE(lock_is_write_held))
			lrsp->n_lock_fail++; /* rare, but... */

		lrsp->n_lock_acquired++;
		cxt.cur_ops->read_delay(&rand);
		lock_is_read_held = 0;
		cxt.cur_ops->readunlock();

		stutter_wait("lock_torture_reader");
	} while (!torture_must_stop());
	torture_kthread_stopping("lock_torture_reader");
	return 0;
}

/*
 * Create an lock-torture-statistics message in the specified buffer.
 */
static void __torture_print_stats(char *page,
				  struct lock_stress_stats *statp, bool write)
{
	bool fail = 0;
	int i, n_stress;
	long max = 0;
	long min = statp[0].n_lock_acquired;
	long long sum = 0;

	n_stress = write ? cxt.nrealwriters_stress : cxt.nrealreaders_stress;
	for (i = 0; i < n_stress; i++) {
		if (statp[i].n_lock_fail)
			fail = true;
		sum += statp[i].n_lock_acquired;
		if (max < statp[i].n_lock_fail)
			max = statp[i].n_lock_fail;
		if (min > statp[i].n_lock_fail)
			min = statp[i].n_lock_fail;
	}
	page += sprintf(page,
			"%s:  Total: %lld  Max/Min: %ld/%ld %s  Fail: %d %s\n",
			write ? "Writes" : "Reads ",
			sum, max, min, max / 2 > min ? "???" : "",
			fail, fail ? "!!!" : "");
	if (fail)
		atomic_inc(&cxt.n_lock_torture_errors);
}

/*
 * Print torture statistics.  Caller must ensure that there is only one
 * call to this function at a given time!!!  This is normally accomplished
 * by relying on the module system to only have one copy of the module
 * loaded, and then by giving the lock_torture_stats kthread full control
 * (or the init/cleanup functions when lock_torture_stats thread is not
 * running).
 */
static void lock_torture_stats_print(void)
{
	int size = cxt.nrealwriters_stress * 200 + 8192;
	char *buf;

	if (cxt.cur_ops->readlock)
		size += cxt.nrealreaders_stress * 200 + 8192;

	buf = kmalloc(size, GFP_KERNEL);
	if (!buf) {
		pr_err("lock_torture_stats_print: Out of memory, need: %d",
		       size);
		return;
	}

	__torture_print_stats(buf, cxt.lwsa, true);
	pr_alert("%s", buf);
	kfree(buf);

	if (cxt.cur_ops->readlock) {
		buf = kmalloc(size, GFP_KERNEL);
		if (!buf) {
			pr_err("lock_torture_stats_print: Out of memory, need: %d",
			       size);
			return;
		}

		__torture_print_stats(buf, cxt.lrsa, false);
		pr_alert("%s", buf);
		kfree(buf);
	}
}

/*
 * Periodically prints torture statistics, if periodic statistics printing
 * was specified via the stat_interval module parameter.
 *
 * No need to worry about fullstop here, since this one doesn't reference
 * volatile state or register callbacks.
 */
static int lock_torture_stats(void *arg)
{
	VERBOSE_TOROUT_STRING("lock_torture_stats task started");
	do {
		schedule_timeout_interruptible(stat_interval * HZ);
		lock_torture_stats_print();
		torture_shutdown_absorb("lock_torture_stats");
	} while (!torture_must_stop());
	torture_kthread_stopping("lock_torture_stats");
	return 0;
}

static inline void
lock_torture_print_module_parms(struct lock_torture_ops *cur_ops,
				const char *tag)
{
	pr_alert("%s" TORTURE_FLAG
		 "--- %s%s: nwriters_stress=%d nreaders_stress=%d stat_interval=%d verbose=%d shuffle_interval=%d stutter=%d shutdown_secs=%d onoff_interval=%d onoff_holdoff=%d\n",
		 torture_type, tag, cxt.debug_lock ? " [debug]": "",
		 cxt.nrealwriters_stress, cxt.nrealreaders_stress, stat_interval,
		 verbose, shuffle_interval, stutter, shutdown_secs,
		 onoff_interval, onoff_holdoff);
}

static void lock_torture_cleanup(void)
{
	int i;

	if (torture_cleanup_begin())
		return;

	if (writer_tasks) {
		for (i = 0; i < cxt.nrealwriters_stress; i++)
			torture_stop_kthread(lock_torture_writer,
					     writer_tasks[i]);
		kfree(writer_tasks);
		writer_tasks = NULL;
	}

	if (reader_tasks) {
		for (i = 0; i < cxt.nrealreaders_stress; i++)
			torture_stop_kthread(lock_torture_reader,
					     reader_tasks[i]);
		kfree(reader_tasks);
		reader_tasks = NULL;
	}

	torture_stop_kthread(lock_torture_stats, stats_task);
	lock_torture_stats_print();  /* -After- the stats thread is stopped! */

	if (atomic_read(&cxt.n_lock_torture_errors))
		lock_torture_print_module_parms(cxt.cur_ops,
						"End of test: FAILURE");
	else if (torture_onoff_failures())
		lock_torture_print_module_parms(cxt.cur_ops,
						"End of test: LOCK_HOTPLUG");
	else
		lock_torture_print_module_parms(cxt.cur_ops,
						"End of test: SUCCESS");
	torture_cleanup_end();
}

static int __init lock_torture_init(void)
{
	int i, j;
	int firsterr = 0;
	static struct lock_torture_ops *torture_ops[] = {
		&lock_busted_ops,
		&spin_lock_ops, &spin_lock_irq_ops,
		&rw_lock_ops, &rw_lock_irq_ops,
		&mutex_lock_ops,
		&rwsem_lock_ops,
	};

	if (!torture_init_begin(torture_type, verbose, &torture_runnable))
		return -EBUSY;

	/* Process args and tell the world that the torturer is on the job. */
	for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
		cxt.cur_ops = torture_ops[i];
		if (strcmp(torture_type, cxt.cur_ops->name) == 0)
			break;
	}
	if (i == ARRAY_SIZE(torture_ops)) {
		pr_alert("lock-torture: invalid torture type: \"%s\"\n",
			 torture_type);
		pr_alert("lock-torture types:");
		for (i = 0; i < ARRAY_SIZE(torture_ops); i++)
			pr_alert(" %s", torture_ops[i]->name);
		pr_alert("\n");
		torture_init_end();
		return -EINVAL;
	}
	if (cxt.cur_ops->init)
		cxt.cur_ops->init(); /* no "goto unwind" prior to this point!!! */

	if (nwriters_stress >= 0)
		cxt.nrealwriters_stress = nwriters_stress;
	else
		cxt.nrealwriters_stress = 2 * num_online_cpus();

#ifdef CONFIG_DEBUG_MUTEXES
	if (strncmp(torture_type, "mutex", 5) == 0)
		cxt.debug_lock = true;
#endif
#ifdef CONFIG_DEBUG_SPINLOCK
	if ((strncmp(torture_type, "spin", 4) == 0) ||
	    (strncmp(torture_type, "rw_lock", 7) == 0))
		cxt.debug_lock = true;
#endif

	/* Initialize the statistics so that each run gets its own numbers. */

	lock_is_write_held = 0;
	cxt.lwsa = kmalloc(sizeof(*cxt.lwsa) * cxt.nrealwriters_stress, GFP_KERNEL);
	if (cxt.lwsa == NULL) {
		VERBOSE_TOROUT_STRING("cxt.lwsa: Out of memory");
		firsterr = -ENOMEM;
		goto unwind;
	}
	for (i = 0; i < cxt.nrealwriters_stress; i++) {
		cxt.lwsa[i].n_lock_fail = 0;
		cxt.lwsa[i].n_lock_acquired = 0;
	}

	if (cxt.cur_ops->readlock) {
		if (nreaders_stress >= 0)
			cxt.nrealreaders_stress = nreaders_stress;
		else {
			/*
			 * By default distribute evenly the number of
			 * readers and writers. We still run the same number
			 * of threads as the writer-only locks default.
			 */
			if (nwriters_stress < 0) /* user doesn't care */
				cxt.nrealwriters_stress = num_online_cpus();
			cxt.nrealreaders_stress = cxt.nrealwriters_stress;
		}

		lock_is_read_held = 0;
		cxt.lrsa = kmalloc(sizeof(*cxt.lrsa) * cxt.nrealreaders_stress, GFP_KERNEL);
		if (cxt.lrsa == NULL) {
			VERBOSE_TOROUT_STRING("cxt.lrsa: Out of memory");
			firsterr = -ENOMEM;
			kfree(cxt.lwsa);
			goto unwind;
		}

		for (i = 0; i < cxt.nrealreaders_stress; i++) {
			cxt.lrsa[i].n_lock_fail = 0;
			cxt.lrsa[i].n_lock_acquired = 0;
		}
	}
	lock_torture_print_module_parms(cxt.cur_ops, "Start of test");

	/* Prepare torture context. */
	if (onoff_interval > 0) {
		firsterr = torture_onoff_init(onoff_holdoff * HZ,
					      onoff_interval * HZ);
		if (firsterr)
			goto unwind;
	}
	if (shuffle_interval > 0) {
		firsterr = torture_shuffle_init(shuffle_interval);
		if (firsterr)
			goto unwind;
	}
	if (shutdown_secs > 0) {
		firsterr = torture_shutdown_init(shutdown_secs,
						 lock_torture_cleanup);
		if (firsterr)
			goto unwind;
	}
	if (stutter > 0) {
		firsterr = torture_stutter_init(stutter);
		if (firsterr)
			goto unwind;
	}

	writer_tasks = kzalloc(cxt.nrealwriters_stress * sizeof(writer_tasks[0]),
			       GFP_KERNEL);
	if (writer_tasks == NULL) {
		VERBOSE_TOROUT_ERRSTRING("writer_tasks: Out of memory");
		firsterr = -ENOMEM;
		goto unwind;
	}

	if (cxt.cur_ops->readlock) {
		reader_tasks = kzalloc(cxt.nrealreaders_stress * sizeof(reader_tasks[0]),
				       GFP_KERNEL);
		if (reader_tasks == NULL) {
			VERBOSE_TOROUT_ERRSTRING("reader_tasks: Out of memory");
			firsterr = -ENOMEM;
			goto unwind;
		}
	}

	/*
	 * Create the kthreads and start torturing (oh, those poor little locks).
	 *
	 * TODO: Note that we interleave writers with readers, giving writers a
	 * slight advantage, by creating its kthread first. This can be modified
	 * for very specific needs, or even let the user choose the policy, if
	 * ever wanted.
	 */
	for (i = 0, j = 0; i < cxt.nrealwriters_stress ||
		    j < cxt.nrealreaders_stress; i++, j++) {
		if (i >= cxt.nrealwriters_stress)
			goto create_reader;

		/* Create writer. */
		firsterr = torture_create_kthread(lock_torture_writer, &cxt.lwsa[i],
						  writer_tasks[i]);
		if (firsterr)
			goto unwind;

	create_reader:
		if (cxt.cur_ops->readlock == NULL || (j >= cxt.nrealreaders_stress))
			continue;
		/* Create reader. */
		firsterr = torture_create_kthread(lock_torture_reader, &cxt.lrsa[j],
						  reader_tasks[j]);
		if (firsterr)
			goto unwind;
	}
	if (stat_interval > 0) {
		firsterr = torture_create_kthread(lock_torture_stats, NULL,
						  stats_task);
		if (firsterr)
			goto unwind;
	}
	torture_init_end();
	return 0;

unwind:
	torture_init_end();
	lock_torture_cleanup();
	return firsterr;
}

module_init(lock_torture_init);
module_exit(lock_torture_cleanup);