/*
   * Common functions for in-kernel torture tests.
   *
   * 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/types.h>
  #include <linux/kernel.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/kthread.h>
  #include <linux/err.h>
  #include <linux/spinlock.h>
  #include <linux/smp.h>
  #include <linux/interrupt.h>
  #include <linux/sched.h>
  #include <linux/atomic.h>
  #include <linux/bitops.h>
  #include <linux/completion.h>
  #include <linux/moduleparam.h>
  #include <linux/percpu.h>
  #include <linux/notifier.h>
  #include <linux/reboot.h>
  #include <linux/freezer.h>
  #include <linux/cpu.h>
  #include <linux/delay.h>
  #include <linux/stat.h>
  #include <linux/slab.h>
  #include <linux/trace_clock.h>
  #include <asm/byteorder.h>
  #include <linux/torture.h>
  
  MODULE_LICENSE("GPL");
  MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com>");

  static char *torture_type;
  static bool verbose;

  /* Mediate rmmod and system shutdown.  Concurrent rmmod & shutdown illegal! */
  #define FULLSTOP_DONTSTOP 0	/* Normal operation. */
  #define FULLSTOP_SHUTDOWN 1	/* System shutdown with torture running. */
  #define FULLSTOP_RMMOD    2	/* Normal rmmod of torture. */
  static int fullstop = FULLSTOP_RMMOD;

  static DEFINE_MUTEX(fullstop_mutex);

  static int *torture_runnable;

  #ifdef CONFIG_HOTPLUG_CPU
  
  /*
   * Variables for online-offline handling.  Only present if CPU hotplug
   * is enabled, otherwise does nothing.
   */
  
  static struct task_struct *onoff_task;
  static long onoff_holdoff;
  static long onoff_interval;
  static long n_offline_attempts;
  static long n_offline_successes;
  static unsigned long sum_offline;
  static int min_offline = -1;
  static int max_offline;
  static long n_online_attempts;
  static long n_online_successes;
  static unsigned long sum_online;
  static int min_online = -1;
  static int max_online;
  
  /*
   * Execute random CPU-hotplug operations at the interval specified
   * by the onoff_interval.
   */
  static int
  torture_onoff(void *arg)
  {
  	int cpu;
  	unsigned long delta;
  	int maxcpu = -1;
  	DEFINE_TORTURE_RANDOM(rand);
  	int ret;
  	unsigned long starttime;
  
  	VERBOSE_TOROUT_STRING("torture_onoff task started");
  	for_each_online_cpu(cpu)
  		maxcpu = cpu;
  	WARN_ON(maxcpu < 0);
  	if (onoff_holdoff > 0) {
  		VERBOSE_TOROUT_STRING("torture_onoff begin holdoff");
  		schedule_timeout_interruptible(onoff_holdoff);
  		VERBOSE_TOROUT_STRING("torture_onoff end holdoff");
  	}
  	while (!torture_must_stop()) {
  		cpu = (torture_random(&rand) >> 4) % (maxcpu + 1);
  		if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) {
  			if (verbose)
  				pr_alert("%s" TORTURE_FLAG
  					 "torture_onoff task: offlining %d
  ",
  					 torture_type, cpu);
  			starttime = jiffies;
  			n_offline_attempts++;
  			ret = cpu_down(cpu);
  			if (ret) {
  				if (verbose)
  					pr_alert("%s" TORTURE_FLAG
  						 "torture_onoff task: offline %d failed: errno %d
  ",
  						 torture_type, cpu, ret);
  			} else {
  				if (verbose)
  					pr_alert("%s" TORTURE_FLAG
  						 "torture_onoff task: offlined %d
  ",
  						 torture_type, cpu);
  				n_offline_successes++;
  				delta = jiffies - starttime;
  				sum_offline += delta;
  				if (min_offline < 0) {
  					min_offline = delta;
  					max_offline = delta;
  				}
  				if (min_offline > delta)
  					min_offline = delta;
  				if (max_offline < delta)
  					max_offline = delta;
  			}
  		} else if (cpu_is_hotpluggable(cpu)) {
  			if (verbose)
  				pr_alert("%s" TORTURE_FLAG
  					 "torture_onoff task: onlining %d
  ",
  					 torture_type, cpu);
  			starttime = jiffies;
  			n_online_attempts++;
  			ret = cpu_up(cpu);
  			if (ret) {
  				if (verbose)
  					pr_alert("%s" TORTURE_FLAG
  						 "torture_onoff task: online %d failed: errno %d
  ",
  						 torture_type, cpu, ret);
  			} else {
  				if (verbose)
  					pr_alert("%s" TORTURE_FLAG
  						 "torture_onoff task: onlined %d
  ",
  						 torture_type, cpu);
  				n_online_successes++;
  				delta = jiffies - starttime;
  				sum_online += delta;
  				if (min_online < 0) {
  					min_online = delta;
  					max_online = delta;
  				}
  				if (min_online > delta)
  					min_online = delta;
  				if (max_online < delta)
  					max_online = delta;
  			}
  		}
  		schedule_timeout_interruptible(onoff_interval);
  	}

  	torture_kthread_stopping("torture_onoff");

  	return 0;
  }
  
  #endif /* #ifdef CONFIG_HOTPLUG_CPU */
  
  /*
   * Initiate online-offline handling.
   */
  int torture_onoff_init(long ooholdoff, long oointerval)
  {

  	int ret = 0;

  #ifdef CONFIG_HOTPLUG_CPU

  	onoff_holdoff = ooholdoff;
  	onoff_interval = oointerval;
  	if (onoff_interval <= 0)
  		return 0;

  	ret = torture_create_kthread(torture_onoff, NULL, onoff_task);

  #endif /* #ifdef CONFIG_HOTPLUG_CPU */

  	return ret;

  }
  EXPORT_SYMBOL_GPL(torture_onoff_init);
  
  /*
   * Clean up after online/offline testing.
   */

  static void torture_onoff_cleanup(void)

  {
  #ifdef CONFIG_HOTPLUG_CPU
  	if (onoff_task == NULL)
  		return;
  	VERBOSE_TOROUT_STRING("Stopping torture_onoff task");
  	kthread_stop(onoff_task);
  	onoff_task = NULL;
  #endif /* #ifdef CONFIG_HOTPLUG_CPU */
  }
  EXPORT_SYMBOL_GPL(torture_onoff_cleanup);
  
  /*
   * Print online/offline testing statistics.
   */

  void torture_onoff_stats(void)

  {
  #ifdef CONFIG_HOTPLUG_CPU

  	pr_cont("onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
  		n_online_successes, n_online_attempts,
  		n_offline_successes, n_offline_attempts,
  		min_online, max_online,
  		min_offline, max_offline,
  		sum_online, sum_offline, HZ);

  #endif /* #ifdef CONFIG_HOTPLUG_CPU */

  }
  EXPORT_SYMBOL_GPL(torture_onoff_stats);
  
  /*
   * Were all the online/offline operations successful?
   */
  bool torture_onoff_failures(void)
  {
  #ifdef CONFIG_HOTPLUG_CPU
  	return n_online_successes != n_online_attempts ||
  	       n_offline_successes != n_offline_attempts;
  #else /* #ifdef CONFIG_HOTPLUG_CPU */
  	return false;
  #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
  }
  EXPORT_SYMBOL_GPL(torture_onoff_failures);

  #define TORTURE_RANDOM_MULT	39916801  /* prime */
  #define TORTURE_RANDOM_ADD	479001701 /* prime */
  #define TORTURE_RANDOM_REFRESH	10000
  
  /*
   * Crude but fast random-number generator.  Uses a linear congruential
   * generator, with occasional help from cpu_clock().
   */
  unsigned long
  torture_random(struct torture_random_state *trsp)
  {
  	if (--trsp->trs_count < 0) {
  		trsp->trs_state += (unsigned long)local_clock();
  		trsp->trs_count = TORTURE_RANDOM_REFRESH;
  	}
  	trsp->trs_state = trsp->trs_state * TORTURE_RANDOM_MULT +
  		TORTURE_RANDOM_ADD;
  	return swahw32(trsp->trs_state);
  }
  EXPORT_SYMBOL_GPL(torture_random);

  
  /*

   * Variables for shuffling.  The idea is to ensure that each CPU stays
   * idle for an extended period to test interactions with dyntick idle,
   * as well as interactions with any per-CPU varibles.
   */
  struct shuffle_task {
  	struct list_head st_l;
  	struct task_struct *st_t;
  };
  
  static long shuffle_interval;	/* In jiffies. */
  static struct task_struct *shuffler_task;
  static cpumask_var_t shuffle_tmp_mask;
  static int shuffle_idle_cpu;	/* Force all torture tasks off this CPU */
  static struct list_head shuffle_task_list = LIST_HEAD_INIT(shuffle_task_list);
  static DEFINE_MUTEX(shuffle_task_mutex);
  
  /*
   * Register a task to be shuffled.  If there is no memory, just splat
   * and don't bother registering.
   */
  void torture_shuffle_task_register(struct task_struct *tp)
  {
  	struct shuffle_task *stp;
  
  	if (WARN_ON_ONCE(tp == NULL))
  		return;
  	stp = kmalloc(sizeof(*stp), GFP_KERNEL);
  	if (WARN_ON_ONCE(stp == NULL))
  		return;
  	stp->st_t = tp;
  	mutex_lock(&shuffle_task_mutex);
  	list_add(&stp->st_l, &shuffle_task_list);
  	mutex_unlock(&shuffle_task_mutex);
  }
  EXPORT_SYMBOL_GPL(torture_shuffle_task_register);
  
  /*
   * Unregister all tasks, for example, at the end of the torture run.
   */
  static void torture_shuffle_task_unregister_all(void)
  {
  	struct shuffle_task *stp;
  	struct shuffle_task *p;
  
  	mutex_lock(&shuffle_task_mutex);
  	list_for_each_entry_safe(stp, p, &shuffle_task_list, st_l) {
  		list_del(&stp->st_l);
  		kfree(stp);
  	}
  	mutex_unlock(&shuffle_task_mutex);
  }
  
  /* Shuffle tasks such that we allow shuffle_idle_cpu to become idle.
   * A special case is when shuffle_idle_cpu = -1, in which case we allow
   * the tasks to run on all CPUs.
   */
  static void torture_shuffle_tasks(void)
  {
  	struct shuffle_task *stp;
  
  	cpumask_setall(shuffle_tmp_mask);
  	get_online_cpus();
  
  	/* No point in shuffling if there is only one online CPU (ex: UP) */
  	if (num_online_cpus() == 1) {
  		put_online_cpus();
  		return;
  	}
  
  	/* Advance to the next CPU.  Upon overflow, don't idle any CPUs. */
  	shuffle_idle_cpu = cpumask_next(shuffle_idle_cpu, shuffle_tmp_mask);
  	if (shuffle_idle_cpu >= nr_cpu_ids)
  		shuffle_idle_cpu = -1;

  	else

  		cpumask_clear_cpu(shuffle_idle_cpu, shuffle_tmp_mask);

  
  	mutex_lock(&shuffle_task_mutex);
  	list_for_each_entry(stp, &shuffle_task_list, st_l)
  		set_cpus_allowed_ptr(stp->st_t, shuffle_tmp_mask);
  	mutex_unlock(&shuffle_task_mutex);
  
  	put_online_cpus();
  }
  
  /* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
   * system to become idle at a time and cut off its timer ticks. This is meant
   * to test the support for such tickless idle CPU in RCU.
   */
  static int torture_shuffle(void *arg)
  {
  	VERBOSE_TOROUT_STRING("torture_shuffle task started");
  	do {
  		schedule_timeout_interruptible(shuffle_interval);
  		torture_shuffle_tasks();
  		torture_shutdown_absorb("torture_shuffle");
  	} while (!torture_must_stop());

  	torture_kthread_stopping("torture_shuffle");

  	return 0;
  }
  
  /*
   * Start the shuffler, with shuffint in jiffies.
   */
  int torture_shuffle_init(long shuffint)
  {

  	shuffle_interval = shuffint;
  
  	shuffle_idle_cpu = -1;
  
  	if (!alloc_cpumask_var(&shuffle_tmp_mask, GFP_KERNEL)) {
  		VERBOSE_TOROUT_ERRSTRING("Failed to alloc mask");
  		return -ENOMEM;
  	}
  
  	/* Create the shuffler thread */

  	return torture_create_kthread(torture_shuffle, NULL, shuffler_task);

  }
  EXPORT_SYMBOL_GPL(torture_shuffle_init);
  
  /*
   * Stop the shuffling.
   */

  static void torture_shuffle_cleanup(void)

  {
  	torture_shuffle_task_unregister_all();
  	if (shuffler_task) {
  		VERBOSE_TOROUT_STRING("Stopping torture_shuffle task");
  		kthread_stop(shuffler_task);
  		free_cpumask_var(shuffle_tmp_mask);
  	}
  	shuffler_task = NULL;
  }
  EXPORT_SYMBOL_GPL(torture_shuffle_cleanup);
  
  /*

   * Variables for auto-shutdown.  This allows "lights out" torture runs
   * to be fully scripted.
   */
  static int shutdown_secs;		/* desired test duration in seconds. */
  static struct task_struct *shutdown_task;
  static unsigned long shutdown_time;	/* jiffies to system shutdown. */
  static void (*torture_shutdown_hook)(void);
  
  /*

   * Absorb kthreads into a kernel function that won't return, so that
   * they won't ever access module text or data again.
   */
  void torture_shutdown_absorb(const char *title)
  {
  	while (ACCESS_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {

  		pr_notice("torture thread %s parking due to system shutdown
  ",
  			  title);

  		schedule_timeout_uninterruptible(MAX_SCHEDULE_TIMEOUT);
  	}
  }
  EXPORT_SYMBOL_GPL(torture_shutdown_absorb);

  
  /*

   * Cause the torture test to shutdown the system after the test has
   * run for the time specified by the shutdown_secs parameter.
   */
  static int torture_shutdown(void *arg)
  {
  	long delta;
  	unsigned long jiffies_snap;
  
  	VERBOSE_TOROUT_STRING("torture_shutdown task started");
  	jiffies_snap = jiffies;
  	while (ULONG_CMP_LT(jiffies_snap, shutdown_time) &&
  	       !torture_must_stop()) {
  		delta = shutdown_time - jiffies_snap;
  		if (verbose)
  			pr_alert("%s" TORTURE_FLAG
  				 "torture_shutdown task: %lu jiffies remaining
  ",
  				 torture_type, delta);
  		schedule_timeout_interruptible(delta);
  		jiffies_snap = jiffies;
  	}
  	if (torture_must_stop()) {

  		torture_kthread_stopping("torture_shutdown");

  		return 0;
  	}
  
  	/* OK, shut down the system. */
  
  	VERBOSE_TOROUT_STRING("torture_shutdown task shutting down system");
  	shutdown_task = NULL;	/* Avoid self-kill deadlock. */

  	if (torture_shutdown_hook)
  		torture_shutdown_hook();
  	else
  		VERBOSE_TOROUT_STRING("No torture_shutdown_hook(), skipping.");

  	kernel_power_off();	/* Shut down the system. */
  	return 0;
  }
  
  /*
   * Start up the shutdown task.
   */
  int torture_shutdown_init(int ssecs, void (*cleanup)(void))
  {

  	int ret = 0;

  
  	shutdown_secs = ssecs;
  	torture_shutdown_hook = cleanup;
  	if (shutdown_secs > 0) {
  		shutdown_time = jiffies + shutdown_secs * HZ;

  		ret = torture_create_kthread(torture_shutdown, NULL,
  					     shutdown_task);

  	}

  	return ret;

  }
  EXPORT_SYMBOL_GPL(torture_shutdown_init);
  
  /*

   * Detect and respond to a system shutdown.
   */
  static int torture_shutdown_notify(struct notifier_block *unused1,
  				   unsigned long unused2, void *unused3)
  {
  	mutex_lock(&fullstop_mutex);

  	if (ACCESS_ONCE(fullstop) == FULLSTOP_DONTSTOP) {

  		VERBOSE_TOROUT_STRING("Unscheduled system shutdown detected");

  		ACCESS_ONCE(fullstop) = FULLSTOP_SHUTDOWN;

  	} else {

  		pr_warn("Concurrent rmmod and shutdown illegal!
  ");

  	}

  	mutex_unlock(&fullstop_mutex);
  	return NOTIFY_DONE;
  }
  
  static struct notifier_block torture_shutdown_nb = {
  	.notifier_call = torture_shutdown_notify,
  };
  
  /*

   * Shut down the shutdown task.  Say what???  Heh!  This can happen if
   * the torture module gets an rmmod before the shutdown time arrives.  ;-)
   */
  static void torture_shutdown_cleanup(void)
  {
  	unregister_reboot_notifier(&torture_shutdown_nb);
  	if (shutdown_task != NULL) {
  		VERBOSE_TOROUT_STRING("Stopping torture_shutdown task");
  		kthread_stop(shutdown_task);
  	}
  	shutdown_task = NULL;
  }
  
  /*

   * Variables for stuttering, which means to periodically pause and
   * restart testing in order to catch bugs that appear when load is
   * suddenly applied to or removed from the system.
   */
  static struct task_struct *stutter_task;
  static int stutter_pause_test;
  static int stutter;
  
  /*
   * Block until the stutter interval ends.  This must be called periodically
   * by all running kthreads that need to be subject to stuttering.
   */
  void stutter_wait(const char *title)
  {
  	while (ACCESS_ONCE(stutter_pause_test) ||
  	       (torture_runnable && !ACCESS_ONCE(*torture_runnable))) {
  		if (stutter_pause_test)

  			if (ACCESS_ONCE(stutter_pause_test) == 1)
  				schedule_timeout_interruptible(1);
  			else
  				while (ACCESS_ONCE(stutter_pause_test))
  					cond_resched();

  		else
  			schedule_timeout_interruptible(round_jiffies_relative(HZ));
  		torture_shutdown_absorb(title);
  	}
  }
  EXPORT_SYMBOL_GPL(stutter_wait);
  
  /*
   * Cause the torture test to "stutter", starting and stopping all
   * threads periodically.
   */
  static int torture_stutter(void *arg)
  {
  	VERBOSE_TOROUT_STRING("torture_stutter task started");
  	do {
  		if (!torture_must_stop()) {

  			if (stutter > 1) {
  				schedule_timeout_interruptible(stutter - 1);
  				ACCESS_ONCE(stutter_pause_test) = 2;
  			}
  			schedule_timeout_interruptible(1);

  			ACCESS_ONCE(stutter_pause_test) = 1;
  		}
  		if (!torture_must_stop())
  			schedule_timeout_interruptible(stutter);
  		ACCESS_ONCE(stutter_pause_test) = 0;
  		torture_shutdown_absorb("torture_stutter");
  	} while (!torture_must_stop());

  	torture_kthread_stopping("torture_stutter");

  	return 0;
  }
  
  /*
   * Initialize and kick off the torture_stutter kthread.
   */
  int torture_stutter_init(int s)
  {
  	int ret;
  
  	stutter = s;

  	ret = torture_create_kthread(torture_stutter, NULL, stutter_task);
  	return ret;

  }
  EXPORT_SYMBOL_GPL(torture_stutter_init);
  
  /*
   * Cleanup after the torture_stutter kthread.
   */

  static void torture_stutter_cleanup(void)

  {
  	if (!stutter_task)
  		return;
  	VERBOSE_TOROUT_STRING("Stopping torture_stutter task");
  	kthread_stop(stutter_task);
  	stutter_task = NULL;
  }

  
  /*

   * Initialize torture module.  Please note that this is -not- invoked via
   * the usual module_init() mechanism, but rather by an explicit call from
   * the client torture module.  This call must be paired with a later
   * torture_init_end().

   *
   * The runnable parameter points to a flag that controls whether or not
   * the test is currently runnable.  If there is no such flag, pass in NULL.

   */

  bool torture_init_begin(char *ttype, bool v, int *runnable)

  {
  	mutex_lock(&fullstop_mutex);

  	if (torture_type != NULL) {
  		pr_alert("torture_init_begin: refusing %s init: %s running",
  			 ttype, torture_type);
  		mutex_unlock(&fullstop_mutex);
  		return false;
  	}

  	torture_type = ttype;
  	verbose = v;

  	torture_runnable = runnable;

  	fullstop = FULLSTOP_DONTSTOP;

  	return true;

  }
  EXPORT_SYMBOL_GPL(torture_init_begin);
  
  /*
   * Tell the torture module that initialization is complete.
   */

  void torture_init_end(void)

  {
  	mutex_unlock(&fullstop_mutex);

  	register_reboot_notifier(&torture_shutdown_nb);

  }
  EXPORT_SYMBOL_GPL(torture_init_end);

  
  /*
   * Clean up torture module.  Please note that this is -not- invoked via
   * the usual module_exit() mechanism, but rather by an explicit call from
   * the client torture module.  Returns true if a race with system shutdown

   * is detected, otherwise, all kthreads started by functions in this file
   * will be shut down.

   *
   * This must be called before the caller starts shutting down its own
   * kthreads.

   *
   * Both torture_cleanup_begin() and torture_cleanup_end() must be paired,
   * in order to correctly perform the cleanup. They are separated because
   * threads can still need to reference the torture_type type, thus nullify
   * only after completing all other relevant calls.

   */

  bool torture_cleanup_begin(void)

  {
  	mutex_lock(&fullstop_mutex);

  	if (ACCESS_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {

  		pr_warn("Concurrent rmmod and shutdown illegal!
  ");
  		mutex_unlock(&fullstop_mutex);
  		schedule_timeout_uninterruptible(10);
  		return true;
  	}

  	ACCESS_ONCE(fullstop) = FULLSTOP_RMMOD;

  	mutex_unlock(&fullstop_mutex);

  	torture_shutdown_cleanup();

  	torture_shuffle_cleanup();

  	torture_stutter_cleanup();

  	torture_onoff_cleanup();

  	return false;
  }
  EXPORT_SYMBOL_GPL(torture_cleanup_begin);
  
  void torture_cleanup_end(void)
  {

  	mutex_lock(&fullstop_mutex);
  	torture_type = NULL;
  	mutex_unlock(&fullstop_mutex);

  }

  EXPORT_SYMBOL_GPL(torture_cleanup_end);

  
  /*
   * Is it time for the current torture test to stop?
   */
  bool torture_must_stop(void)
  {
  	return torture_must_stop_irq() || kthread_should_stop();
  }
  EXPORT_SYMBOL_GPL(torture_must_stop);
  
  /*
   * Is it time for the current torture test to stop?  This is the irq-safe
   * version, hence no check for kthread_should_stop().
   */
  bool torture_must_stop_irq(void)
  {

  	return ACCESS_ONCE(fullstop) != FULLSTOP_DONTSTOP;

  }
  EXPORT_SYMBOL_GPL(torture_must_stop_irq);

  
  /*
   * Each kthread must wait for kthread_should_stop() before returning from
   * its top-level function, otherwise segfaults ensue.  This function
   * prints a "stopping" message and waits for kthread_should_stop(), and
   * should be called from all torture kthreads immediately prior to
   * returning.
   */
  void torture_kthread_stopping(char *title)
  {

  	char buf[128];
  
  	snprintf(buf, sizeof(buf), "Stopping %s", title);
  	VERBOSE_TOROUT_STRING(buf);

  	while (!kthread_should_stop()) {
  		torture_shutdown_absorb(title);
  		schedule_timeout_uninterruptible(1);
  	}
  }
  EXPORT_SYMBOL_GPL(torture_kthread_stopping);

  
  /*
   * Create a generic torture kthread that is immediately runnable.  If you
   * need the kthread to be stopped so that you can do something to it before
   * it starts, you will need to open-code your own.
   */
  int _torture_create_kthread(int (*fn)(void *arg), void *arg, char *s, char *m,
  			    char *f, struct task_struct **tp)
  {
  	int ret = 0;
  
  	VERBOSE_TOROUT_STRING(m);

  	*tp = kthread_run(fn, arg, "%s", s);

  	if (IS_ERR(*tp)) {
  		ret = PTR_ERR(*tp);
  		VERBOSE_TOROUT_ERRSTRING(f);
  		*tp = NULL;
  	}
  	torture_shuffle_task_register(*tp);
  	return ret;
  }
  EXPORT_SYMBOL_GPL(_torture_create_kthread);

  
  /*
   * Stop a generic kthread, emitting a message.
   */
  void _torture_stop_kthread(char *m, struct task_struct **tp)
  {
  	if (*tp == NULL)
  		return;
  	VERBOSE_TOROUT_STRING(m);
  	kthread_stop(*tp);
  	*tp = NULL;
  }
  EXPORT_SYMBOL_GPL(_torture_stop_kthread);