/*

   * Read-Copy Update module-based torture test facility

   *
   * 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, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   *

   * Copyright (C) IBM Corporation, 2005, 2006

   *
   * Authors: Paul E. McKenney <paulmck@us.ibm.com>

   *          Josh Triplett <josh@freedesktop.org>

   *
   * See also:  Documentation/RCU/torture.txt
   */
  #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/rcupdate.h>
  #include <linux/interrupt.h>
  #include <linux/sched.h>
  #include <asm/atomic.h>
  #include <linux/bitops.h>

  #include <linux/completion.h>
  #include <linux/moduleparam.h>
  #include <linux/percpu.h>
  #include <linux/notifier.h>

  #include <linux/freezer.h>

  #include <linux/cpu.h>

  #include <linux/delay.h>
  #include <linux/byteorder/swabb.h>
  #include <linux/stat.h>

  #include <linux/srcu.h>

  #include <linux/slab.h>

  
  MODULE_LICENSE("GPL");

  MODULE_AUTHOR("Paul E. McKenney <paulmck@us.ibm.com> and "
                "Josh Triplett <josh@freedesktop.org>");

  static int nreaders = -1;	/* # reader threads, defaults to 2*ncpus */

  static int nfakewriters = 4;	/* # fake writer threads */

  static int stat_interval;	/* Interval between stats, in seconds. */

  				/*  Defaults to "only at end of test". */

  static int verbose;		/* Print more debug info. */
  static int test_no_idle_hz;	/* Test RCU's support for tickless idle CPUs. */

  static int shuffle_interval = 3; /* Interval between shuffles (in sec)*/
  static int stutter = 5;		/* Start/stop testing interval (in sec) */

  static int irqreader = 1;	/* RCU readers from irq (timers). */

  static char *torture_type = "rcu"; /* What RCU implementation to torture. */

  module_param(nreaders, int, 0444);

  MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");

  module_param(nfakewriters, int, 0444);

  MODULE_PARM_DESC(nfakewriters, "Number of RCU fake writer threads");

  module_param(stat_interval, int, 0444);

  MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");

  module_param(verbose, bool, 0444);

  MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");

  module_param(test_no_idle_hz, bool, 0444);

  MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");

  module_param(shuffle_interval, int, 0444);

  MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");

  module_param(stutter, int, 0444);
  MODULE_PARM_DESC(stutter, "Number of seconds to run/halt test");

  module_param(irqreader, int, 0444);
  MODULE_PARM_DESC(irqreader, "Allow RCU readers from irq handlers");

  module_param(torture_type, charp, 0444);

  MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, srcu)");

  
  #define TORTURE_FLAG "-torture:"

  #define PRINTK_STRING(s) \

  	do { printk(KERN_ALERT "%s" TORTURE_FLAG s "
  ", torture_type); } while (0)

  #define VERBOSE_PRINTK_STRING(s) \

  	do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG s "
  ", torture_type); } while (0)

  #define VERBOSE_PRINTK_ERRSTRING(s) \

  	do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG "!!! " s "
  ", torture_type); } while (0)

  
  static char printk_buf[4096];
  
  static int nrealreaders;
  static struct task_struct *writer_task;

  static struct task_struct **fakewriter_tasks;

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

  static struct task_struct *shuffler_task;

  static struct task_struct *stutter_task;

  
  #define RCU_TORTURE_PIPE_LEN 10
  
  struct rcu_torture {
  	struct rcu_head rtort_rcu;
  	int rtort_pipe_count;
  	struct list_head rtort_free;

  	int rtort_mbtest;

  };
  
  static int fullstop = 0;	/* stop generating callbacks at test end. */
  static LIST_HEAD(rcu_torture_freelist);
  static struct rcu_torture *rcu_torture_current = NULL;
  static long rcu_torture_current_version = 0;
  static struct rcu_torture rcu_tortures[10 * RCU_TORTURE_PIPE_LEN];
  static DEFINE_SPINLOCK(rcu_torture_lock);
  static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_count) =
  	{ 0 };
  static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_batch) =
  	{ 0 };
  static atomic_t rcu_torture_wcount[RCU_TORTURE_PIPE_LEN + 1];

  static atomic_t n_rcu_torture_alloc;
  static atomic_t n_rcu_torture_alloc_fail;
  static atomic_t n_rcu_torture_free;
  static atomic_t n_rcu_torture_mberror;
  static atomic_t n_rcu_torture_error;

  static long n_rcu_torture_timers = 0;

  static struct list_head rcu_torture_removed;

  static int stutter_pause_test = 0;

  #if defined(MODULE) || defined(CONFIG_RCU_TORTURE_TEST_RUNNABLE)
  #define RCUTORTURE_RUNNABLE_INIT 1
  #else
  #define RCUTORTURE_RUNNABLE_INIT 0
  #endif
  int rcutorture_runnable = RCUTORTURE_RUNNABLE_INIT;

  /*
   * Allocate an element from the rcu_tortures pool.
   */

  static struct rcu_torture *

  rcu_torture_alloc(void)
  {
  	struct list_head *p;

  	spin_lock_bh(&rcu_torture_lock);

  	if (list_empty(&rcu_torture_freelist)) {
  		atomic_inc(&n_rcu_torture_alloc_fail);

  		spin_unlock_bh(&rcu_torture_lock);

  		return NULL;
  	}
  	atomic_inc(&n_rcu_torture_alloc);
  	p = rcu_torture_freelist.next;
  	list_del_init(p);

  	spin_unlock_bh(&rcu_torture_lock);

  	return container_of(p, struct rcu_torture, rtort_free);
  }
  
  /*
   * Free an element to the rcu_tortures pool.
   */
  static void
  rcu_torture_free(struct rcu_torture *p)
  {
  	atomic_inc(&n_rcu_torture_free);

  	spin_lock_bh(&rcu_torture_lock);

  	list_add_tail(&p->rtort_free, &rcu_torture_freelist);

  	spin_unlock_bh(&rcu_torture_lock);

  }

  struct rcu_random_state {
  	unsigned long rrs_state;

  	long rrs_count;

  };
  
  #define RCU_RANDOM_MULT 39916801  /* prime */
  #define RCU_RANDOM_ADD	479001701 /* prime */
  #define RCU_RANDOM_REFRESH 10000
  
  #define DEFINE_RCU_RANDOM(name) struct rcu_random_state name = { 0, 0 }
  
  /*
   * Crude but fast random-number generator.  Uses a linear congruential

   * generator, with occasional help from cpu_clock().

   */

  static unsigned long

  rcu_random(struct rcu_random_state *rrsp)
  {

  	if (--rrsp->rrs_count < 0) {

  		rrsp->rrs_state +=
  			(unsigned long)cpu_clock(raw_smp_processor_id());

  		rrsp->rrs_count = RCU_RANDOM_REFRESH;
  	}
  	rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;
  	return swahw32(rrsp->rrs_state);
  }

  static void
  rcu_stutter_wait(void)
  {

  	while (stutter_pause_test || !rcutorture_runnable)

  		if (rcutorture_runnable)
  			schedule_timeout_interruptible(1);
  		else

  			schedule_timeout_interruptible(round_jiffies_relative(HZ));

  }

  /*

   * Operations vector for selecting different types of tests.
   */
  
  struct rcu_torture_ops {
  	void (*init)(void);
  	void (*cleanup)(void);
  	int (*readlock)(void);

  	void (*readdelay)(struct rcu_random_state *rrsp);

  	void (*readunlock)(int idx);
  	int (*completed)(void);
  	void (*deferredfree)(struct rcu_torture *p);

  	void (*sync)(void);

  	void (*cb_barrier)(void);

  	int (*stats)(char *page);

  	int irqcapable;

  	char *name;
  };
  static struct rcu_torture_ops *cur_ops = NULL;
  
  /*
   * Definitions for rcu torture testing.
   */

  static int rcu_torture_read_lock(void) __acquires(RCU)

  {
  	rcu_read_lock();
  	return 0;
  }

  static void rcu_read_delay(struct rcu_random_state *rrsp)
  {
  	long delay;
  	const long longdelay = 200;
  
  	/* We want there to be long-running readers, but not all the time. */
  
  	delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay);
  	if (!delay)
  		udelay(longdelay);
  }

  static void rcu_torture_read_unlock(int idx) __releases(RCU)

  {
  	rcu_read_unlock();
  }
  
  static int rcu_torture_completed(void)
  {
  	return rcu_batches_completed();
  }
  
  static void
  rcu_torture_cb(struct rcu_head *p)
  {
  	int i;
  	struct rcu_torture *rp = container_of(p, struct rcu_torture, rtort_rcu);
  
  	if (fullstop) {
  		/* Test is ending, just drop callbacks on the floor. */
  		/* The next initialization will pick up the pieces. */
  		return;
  	}
  	i = rp->rtort_pipe_count;
  	if (i > RCU_TORTURE_PIPE_LEN)
  		i = RCU_TORTURE_PIPE_LEN;
  	atomic_inc(&rcu_torture_wcount[i]);
  	if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
  		rp->rtort_mbtest = 0;
  		rcu_torture_free(rp);
  	} else
  		cur_ops->deferredfree(rp);
  }
  
  static void rcu_torture_deferred_free(struct rcu_torture *p)
  {
  	call_rcu(&p->rtort_rcu, rcu_torture_cb);
  }
  
  static struct rcu_torture_ops rcu_ops = {
  	.init = NULL,
  	.cleanup = NULL,
  	.readlock = rcu_torture_read_lock,

  	.readdelay = rcu_read_delay,

  	.readunlock = rcu_torture_read_unlock,
  	.completed = rcu_torture_completed,
  	.deferredfree = rcu_torture_deferred_free,

  	.sync = synchronize_rcu,

  	.cb_barrier = rcu_barrier,

  	.stats = NULL,

  	.irqcapable = 1,

  	.name = "rcu"
  };

  static void rcu_sync_torture_deferred_free(struct rcu_torture *p)
  {
  	int i;
  	struct rcu_torture *rp;
  	struct rcu_torture *rp1;
  
  	cur_ops->sync();
  	list_add(&p->rtort_free, &rcu_torture_removed);
  	list_for_each_entry_safe(rp, rp1, &rcu_torture_removed, rtort_free) {
  		i = rp->rtort_pipe_count;
  		if (i > RCU_TORTURE_PIPE_LEN)
  			i = RCU_TORTURE_PIPE_LEN;
  		atomic_inc(&rcu_torture_wcount[i]);
  		if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
  			rp->rtort_mbtest = 0;
  			list_del(&rp->rtort_free);
  			rcu_torture_free(rp);
  		}
  	}
  }
  
  static void rcu_sync_torture_init(void)
  {
  	INIT_LIST_HEAD(&rcu_torture_removed);
  }

  static struct rcu_torture_ops rcu_sync_ops = {
  	.init = rcu_sync_torture_init,
  	.cleanup = NULL,
  	.readlock = rcu_torture_read_lock,
  	.readdelay = rcu_read_delay,
  	.readunlock = rcu_torture_read_unlock,
  	.completed = rcu_torture_completed,
  	.deferredfree = rcu_sync_torture_deferred_free,
  	.sync = synchronize_rcu,

  	.cb_barrier = NULL,

  	.stats = NULL,

  	.irqcapable = 1,

  	.name = "rcu_sync"
  };

  /*
   * Definitions for rcu_bh torture testing.
   */

  static int rcu_bh_torture_read_lock(void) __acquires(RCU_BH)

  {
  	rcu_read_lock_bh();
  	return 0;
  }

  static void rcu_bh_torture_read_unlock(int idx) __releases(RCU_BH)

  {
  	rcu_read_unlock_bh();
  }
  
  static int rcu_bh_torture_completed(void)
  {
  	return rcu_batches_completed_bh();
  }
  
  static void rcu_bh_torture_deferred_free(struct rcu_torture *p)
  {
  	call_rcu_bh(&p->rtort_rcu, rcu_torture_cb);
  }

  struct rcu_bh_torture_synchronize {
  	struct rcu_head head;
  	struct completion completion;
  };
  
  static void rcu_bh_torture_wakeme_after_cb(struct rcu_head *head)
  {
  	struct rcu_bh_torture_synchronize *rcu;
  
  	rcu = container_of(head, struct rcu_bh_torture_synchronize, head);
  	complete(&rcu->completion);
  }
  
  static void rcu_bh_torture_synchronize(void)
  {
  	struct rcu_bh_torture_synchronize rcu;
  
  	init_completion(&rcu.completion);
  	call_rcu_bh(&rcu.head, rcu_bh_torture_wakeme_after_cb);
  	wait_for_completion(&rcu.completion);
  }

  static struct rcu_torture_ops rcu_bh_ops = {
  	.init = NULL,
  	.cleanup = NULL,
  	.readlock = rcu_bh_torture_read_lock,

  	.readdelay = rcu_read_delay,  /* just reuse rcu's version. */

  	.readunlock = rcu_bh_torture_read_unlock,
  	.completed = rcu_bh_torture_completed,
  	.deferredfree = rcu_bh_torture_deferred_free,

  	.sync = rcu_bh_torture_synchronize,

  	.cb_barrier = rcu_barrier_bh,

  	.stats = NULL,

  	.irqcapable = 1,

  	.name = "rcu_bh"
  };

  static struct rcu_torture_ops rcu_bh_sync_ops = {
  	.init = rcu_sync_torture_init,
  	.cleanup = NULL,
  	.readlock = rcu_bh_torture_read_lock,
  	.readdelay = rcu_read_delay,  /* just reuse rcu's version. */
  	.readunlock = rcu_bh_torture_read_unlock,
  	.completed = rcu_bh_torture_completed,
  	.deferredfree = rcu_sync_torture_deferred_free,
  	.sync = rcu_bh_torture_synchronize,

  	.cb_barrier = NULL,

  	.stats = NULL,

  	.irqcapable = 1,

  	.name = "rcu_bh_sync"
  };

  /*
   * Definitions for srcu torture testing.
   */
  
  static struct srcu_struct srcu_ctl;

  
  static void srcu_torture_init(void)
  {
  	init_srcu_struct(&srcu_ctl);

  	rcu_sync_torture_init();

  }
  
  static void srcu_torture_cleanup(void)
  {
  	synchronize_srcu(&srcu_ctl);
  	cleanup_srcu_struct(&srcu_ctl);
  }

  static int srcu_torture_read_lock(void) __acquires(&srcu_ctl)

  {
  	return srcu_read_lock(&srcu_ctl);
  }
  
  static void srcu_read_delay(struct rcu_random_state *rrsp)
  {
  	long delay;
  	const long uspertick = 1000000 / HZ;
  	const long longdelay = 10;
  
  	/* We want there to be long-running readers, but not all the time. */
  
  	delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay * uspertick);
  	if (!delay)
  		schedule_timeout_interruptible(longdelay);
  }

  static void srcu_torture_read_unlock(int idx) __releases(&srcu_ctl)

  {
  	srcu_read_unlock(&srcu_ctl, idx);
  }
  
  static int srcu_torture_completed(void)
  {
  	return srcu_batches_completed(&srcu_ctl);
  }

  static void srcu_torture_synchronize(void)
  {
  	synchronize_srcu(&srcu_ctl);
  }

  static int srcu_torture_stats(char *page)
  {
  	int cnt = 0;
  	int cpu;
  	int idx = srcu_ctl.completed & 0x1;
  
  	cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
  		       torture_type, TORTURE_FLAG, idx);
  	for_each_possible_cpu(cpu) {
  		cnt += sprintf(&page[cnt], " %d(%d,%d)", cpu,
  			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
  			       per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
  	}
  	cnt += sprintf(&page[cnt], "
  ");
  	return cnt;
  }
  
  static struct rcu_torture_ops srcu_ops = {
  	.init = srcu_torture_init,
  	.cleanup = srcu_torture_cleanup,
  	.readlock = srcu_torture_read_lock,
  	.readdelay = srcu_read_delay,
  	.readunlock = srcu_torture_read_unlock,
  	.completed = srcu_torture_completed,

  	.deferredfree = rcu_sync_torture_deferred_free,

  	.sync = srcu_torture_synchronize,

  	.cb_barrier = NULL,

  	.stats = srcu_torture_stats,
  	.name = "srcu"
  };

  /*
   * Definitions for sched torture testing.
   */
  
  static int sched_torture_read_lock(void)
  {
  	preempt_disable();
  	return 0;
  }
  
  static void sched_torture_read_unlock(int idx)
  {
  	preempt_enable();
  }
  
  static int sched_torture_completed(void)
  {
  	return 0;
  }

  static void rcu_sched_torture_deferred_free(struct rcu_torture *p)
  {
  	call_rcu_sched(&p->rtort_rcu, rcu_torture_cb);
  }

  static void sched_torture_synchronize(void)
  {
  	synchronize_sched();
  }
  
  static struct rcu_torture_ops sched_ops = {
  	.init = rcu_sync_torture_init,
  	.cleanup = NULL,
  	.readlock = sched_torture_read_lock,
  	.readdelay = rcu_read_delay,  /* just reuse rcu's version. */
  	.readunlock = sched_torture_read_unlock,
  	.completed = sched_torture_completed,

  	.deferredfree = rcu_sched_torture_deferred_free,

  	.sync = sched_torture_synchronize,

  	.cb_barrier = rcu_barrier_sched,

  	.stats = NULL,

  	.irqcapable = 1,

  	.name = "sched"
  };

  static struct rcu_torture_ops sched_ops_sync = {
  	.init = rcu_sync_torture_init,
  	.cleanup = NULL,
  	.readlock = sched_torture_read_lock,
  	.readdelay = rcu_read_delay,  /* just reuse rcu's version. */
  	.readunlock = sched_torture_read_unlock,
  	.completed = sched_torture_completed,
  	.deferredfree = rcu_sync_torture_deferred_free,
  	.sync = sched_torture_synchronize,
  	.cb_barrier = NULL,
  	.stats = NULL,
  	.name = "sched_sync"
  };

  /*

   * RCU torture writer kthread.  Repeatedly substitutes a new structure
   * for that pointed to by rcu_torture_current, freeing the old structure
   * after a series of grace periods (the "pipeline").
   */
  static int
  rcu_torture_writer(void *arg)
  {
  	int i;
  	long oldbatch = rcu_batches_completed();
  	struct rcu_torture *rp;
  	struct rcu_torture *old_rp;
  	static DEFINE_RCU_RANDOM(rand);
  
  	VERBOSE_PRINTK_STRING("rcu_torture_writer task started");

  	set_user_nice(current, 19);

  	do {
  		schedule_timeout_uninterruptible(1);

  		if ((rp = rcu_torture_alloc()) == NULL)
  			continue;
  		rp->rtort_pipe_count = 0;
  		udelay(rcu_random(&rand) & 0x3ff);
  		old_rp = rcu_torture_current;

  		rp->rtort_mbtest = 1;

  		rcu_assign_pointer(rcu_torture_current, rp);
  		smp_wmb();

  		if (old_rp) {

  			i = old_rp->rtort_pipe_count;
  			if (i > RCU_TORTURE_PIPE_LEN)
  				i = RCU_TORTURE_PIPE_LEN;
  			atomic_inc(&rcu_torture_wcount[i]);
  			old_rp->rtort_pipe_count++;

  			cur_ops->deferredfree(old_rp);

  		}
  		rcu_torture_current_version++;

  		oldbatch = cur_ops->completed();

  		rcu_stutter_wait();

  	} while (!kthread_should_stop() && !fullstop);
  	VERBOSE_PRINTK_STRING("rcu_torture_writer task stopping");
  	while (!kthread_should_stop())
  		schedule_timeout_uninterruptible(1);
  	return 0;
  }
  
  /*

   * RCU torture fake writer kthread.  Repeatedly calls sync, with a random
   * delay between calls.
   */
  static int
  rcu_torture_fakewriter(void *arg)
  {
  	DEFINE_RCU_RANDOM(rand);
  
  	VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task started");
  	set_user_nice(current, 19);
  
  	do {
  		schedule_timeout_uninterruptible(1 + rcu_random(&rand)%10);
  		udelay(rcu_random(&rand) & 0x3ff);
  		cur_ops->sync();

  		rcu_stutter_wait();

  	} while (!kthread_should_stop() && !fullstop);
  
  	VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task stopping");
  	while (!kthread_should_stop())
  		schedule_timeout_uninterruptible(1);
  	return 0;
  }
  
  /*

   * RCU torture reader from timer handler.  Dereferences rcu_torture_current,
   * incrementing the corresponding element of the pipeline array.  The
   * counter in the element should never be greater than 1, otherwise, the
   * RCU implementation is broken.
   */
  static void rcu_torture_timer(unsigned long unused)
  {
  	int idx;
  	int completed;
  	static DEFINE_RCU_RANDOM(rand);
  	static DEFINE_SPINLOCK(rand_lock);
  	struct rcu_torture *p;
  	int pipe_count;
  
  	idx = cur_ops->readlock();
  	completed = cur_ops->completed();
  	p = rcu_dereference(rcu_torture_current);
  	if (p == NULL) {
  		/* Leave because rcu_torture_writer is not yet underway */
  		cur_ops->readunlock(idx);
  		return;
  	}
  	if (p->rtort_mbtest == 0)
  		atomic_inc(&n_rcu_torture_mberror);
  	spin_lock(&rand_lock);
  	cur_ops->readdelay(&rand);
  	n_rcu_torture_timers++;
  	spin_unlock(&rand_lock);
  	preempt_disable();
  	pipe_count = p->rtort_pipe_count;
  	if (pipe_count > RCU_TORTURE_PIPE_LEN) {
  		/* Should not happen, but... */
  		pipe_count = RCU_TORTURE_PIPE_LEN;
  	}
  	++__get_cpu_var(rcu_torture_count)[pipe_count];
  	completed = cur_ops->completed() - completed;
  	if (completed > RCU_TORTURE_PIPE_LEN) {
  		/* Should not happen, but... */
  		completed = RCU_TORTURE_PIPE_LEN;
  	}
  	++__get_cpu_var(rcu_torture_batch)[completed];
  	preempt_enable();
  	cur_ops->readunlock(idx);
  }
  
  /*

   * RCU torture reader kthread.  Repeatedly dereferences rcu_torture_current,
   * incrementing the corresponding element of the pipeline array.  The
   * counter in the element should never be greater than 1, otherwise, the
   * RCU implementation is broken.
   */
  static int
  rcu_torture_reader(void *arg)
  {
  	int completed;

  	int idx;

  	DEFINE_RCU_RANDOM(rand);
  	struct rcu_torture *p;
  	int pipe_count;

  	struct timer_list t;

  
  	VERBOSE_PRINTK_STRING("rcu_torture_reader task started");

  	set_user_nice(current, 19);

  	if (irqreader && cur_ops->irqcapable)
  		setup_timer_on_stack(&t, rcu_torture_timer, 0);

  	do {

  		if (irqreader && cur_ops->irqcapable) {
  			if (!timer_pending(&t))
  				mod_timer(&t, 1);
  		}

  		idx = cur_ops->readlock();
  		completed = cur_ops->completed();

  		p = rcu_dereference(rcu_torture_current);
  		if (p == NULL) {
  			/* Wait for rcu_torture_writer to get underway */

  			cur_ops->readunlock(idx);

  			schedule_timeout_interruptible(HZ);
  			continue;
  		}

  		if (p->rtort_mbtest == 0)
  			atomic_inc(&n_rcu_torture_mberror);

  		cur_ops->readdelay(&rand);

  		preempt_disable();
  		pipe_count = p->rtort_pipe_count;
  		if (pipe_count > RCU_TORTURE_PIPE_LEN) {
  			/* Should not happen, but... */
  			pipe_count = RCU_TORTURE_PIPE_LEN;
  		}
  		++__get_cpu_var(rcu_torture_count)[pipe_count];

  		completed = cur_ops->completed() - completed;

  		if (completed > RCU_TORTURE_PIPE_LEN) {
  			/* Should not happen, but... */
  			completed = RCU_TORTURE_PIPE_LEN;
  		}
  		++__get_cpu_var(rcu_torture_batch)[completed];
  		preempt_enable();

  		cur_ops->readunlock(idx);

  		schedule();

  		rcu_stutter_wait();

  	} while (!kthread_should_stop() && !fullstop);
  	VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");

  	if (irqreader && cur_ops->irqcapable)
  		del_timer_sync(&t);

  	while (!kthread_should_stop())
  		schedule_timeout_uninterruptible(1);
  	return 0;
  }
  
  /*
   * Create an RCU-torture statistics message in the specified buffer.
   */
  static int
  rcu_torture_printk(char *page)
  {
  	int cnt = 0;
  	int cpu;
  	int i;
  	long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
  	long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };

  	for_each_possible_cpu(cpu) {

  		for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
  			pipesummary[i] += per_cpu(rcu_torture_count, cpu)[i];
  			batchsummary[i] += per_cpu(rcu_torture_batch, cpu)[i];
  		}
  	}
  	for (i = RCU_TORTURE_PIPE_LEN - 1; i >= 0; i--) {
  		if (pipesummary[i] != 0)
  			break;
  	}

  	cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG);

  	cnt += sprintf(&page[cnt],

  		       "rtc: %p ver: %ld tfle: %d rta: %d rtaf: %d rtf: %d "

  		       "rtmbe: %d nt: %ld",

  		       rcu_torture_current,
  		       rcu_torture_current_version,
  		       list_empty(&rcu_torture_freelist),
  		       atomic_read(&n_rcu_torture_alloc),
  		       atomic_read(&n_rcu_torture_alloc_fail),

  		       atomic_read(&n_rcu_torture_free),

  		       atomic_read(&n_rcu_torture_mberror),
  		       n_rcu_torture_timers);

  	if (atomic_read(&n_rcu_torture_mberror) != 0)
  		cnt += sprintf(&page[cnt], " !!!");

  	cnt += sprintf(&page[cnt], "
  %s%s ", torture_type, TORTURE_FLAG);

  	if (i > 1) {

  		cnt += sprintf(&page[cnt], "!!! ");

  		atomic_inc(&n_rcu_torture_error);

  		WARN_ON_ONCE(1);

  	}

  	cnt += sprintf(&page[cnt], "Reader Pipe: ");
  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
  		cnt += sprintf(&page[cnt], " %ld", pipesummary[i]);

  	cnt += sprintf(&page[cnt], "
  %s%s ", torture_type, TORTURE_FLAG);

  	cnt += sprintf(&page[cnt], "Reader Batch: ");

  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)

  		cnt += sprintf(&page[cnt], " %ld", batchsummary[i]);

  	cnt += sprintf(&page[cnt], "
  %s%s ", torture_type, TORTURE_FLAG);

  	cnt += sprintf(&page[cnt], "Free-Block Circulation: ");
  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
  		cnt += sprintf(&page[cnt], " %d",
  			       atomic_read(&rcu_torture_wcount[i]));
  	}
  	cnt += sprintf(&page[cnt], "
  ");

  	if (cur_ops->stats)

  		cnt += cur_ops->stats(&page[cnt]);

  	return cnt;
  }
  
  /*
   * 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 rcu_torture_stats
   * kthread full control (or the init/cleanup functions when rcu_torture_stats
   * thread is not running).
   */
  static void
  rcu_torture_stats_print(void)
  {
  	int cnt;
  
  	cnt = rcu_torture_printk(printk_buf);
  	printk(KERN_ALERT "%s", printk_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
  rcu_torture_stats(void *arg)
  {
  	VERBOSE_PRINTK_STRING("rcu_torture_stats task started");
  	do {
  		schedule_timeout_interruptible(stat_interval * HZ);
  		rcu_torture_stats_print();
  	} while (!kthread_should_stop());
  	VERBOSE_PRINTK_STRING("rcu_torture_stats task stopping");
  	return 0;
  }

  static int rcu_idle_cpu;	/* Force all torture tasks off this CPU */
  
  /* Shuffle tasks such that we allow @rcu_idle_cpu to become idle. A special case
   * is when @rcu_idle_cpu = -1, when we allow the tasks to run on all CPUs.
   */

  static void rcu_torture_shuffle_tasks(void)

  {

  	cpumask_t tmp_mask;

  	int i;

  	cpus_setall(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;
  	}
  
  	if (rcu_idle_cpu != -1)
  		cpu_clear(rcu_idle_cpu, tmp_mask);

  	set_cpus_allowed_ptr(current, &tmp_mask);

  	if (reader_tasks) {

  		for (i = 0; i < nrealreaders; i++)
  			if (reader_tasks[i])

  				set_cpus_allowed_ptr(reader_tasks[i],
  						     &tmp_mask);

  	}

  	if (fakewriter_tasks) {

  		for (i = 0; i < nfakewriters; i++)
  			if (fakewriter_tasks[i])

  				set_cpus_allowed_ptr(fakewriter_tasks[i],
  						     &tmp_mask);

  	}

  	if (writer_task)

  		set_cpus_allowed_ptr(writer_task, &tmp_mask);

  
  	if (stats_task)

  		set_cpus_allowed_ptr(stats_task, &tmp_mask);

  
  	if (rcu_idle_cpu == -1)
  		rcu_idle_cpu = num_online_cpus() - 1;
  	else
  		rcu_idle_cpu--;

  	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
  rcu_torture_shuffle(void *arg)
  {
  	VERBOSE_PRINTK_STRING("rcu_torture_shuffle task started");
  	do {
  		schedule_timeout_interruptible(shuffle_interval * HZ);
  		rcu_torture_shuffle_tasks();
  	} while (!kthread_should_stop());
  	VERBOSE_PRINTK_STRING("rcu_torture_shuffle task stopping");
  	return 0;
  }

  /* Cause the rcutorture test to "stutter", starting and stopping all
   * threads periodically.
   */
  static int
  rcu_torture_stutter(void *arg)
  {
  	VERBOSE_PRINTK_STRING("rcu_torture_stutter task started");
  	do {
  		schedule_timeout_interruptible(stutter * HZ);
  		stutter_pause_test = 1;
  		if (!kthread_should_stop())
  			schedule_timeout_interruptible(stutter * HZ);
  		stutter_pause_test = 0;
  	} while (!kthread_should_stop());
  	VERBOSE_PRINTK_STRING("rcu_torture_stutter task stopping");
  	return 0;
  }

  static inline void
  rcu_torture_print_module_parms(char *tag)
  {

  	printk(KERN_ALERT "%s" TORTURE_FLAG
  		"--- %s: nreaders=%d nfakewriters=%d "

  		"stat_interval=%d verbose=%d test_no_idle_hz=%d "

  		"shuffle_interval=%d stutter=%d irqreader=%d
  ",

  		torture_type, tag, nrealreaders, nfakewriters,

  		stat_interval, verbose, test_no_idle_hz, shuffle_interval,

  		stutter, irqreader);

  }

  static void
  rcu_torture_cleanup(void)
  {
  	int i;
  
  	fullstop = 1;

  	if (stutter_task) {
  		VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task");
  		kthread_stop(stutter_task);
  	}
  	stutter_task = NULL;

  	if (shuffler_task) {

  		VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
  		kthread_stop(shuffler_task);
  	}
  	shuffler_task = NULL;

  	if (writer_task) {

  		VERBOSE_PRINTK_STRING("Stopping rcu_torture_writer task");
  		kthread_stop(writer_task);
  	}
  	writer_task = NULL;

  	if (reader_tasks) {

  		for (i = 0; i < nrealreaders; i++) {

  			if (reader_tasks[i]) {

  				VERBOSE_PRINTK_STRING(
  					"Stopping rcu_torture_reader task");
  				kthread_stop(reader_tasks[i]);
  			}
  			reader_tasks[i] = NULL;
  		}
  		kfree(reader_tasks);
  		reader_tasks = NULL;
  	}
  	rcu_torture_current = NULL;

  	if (fakewriter_tasks) {

  		for (i = 0; i < nfakewriters; i++) {

  			if (fakewriter_tasks[i]) {

  				VERBOSE_PRINTK_STRING(
  					"Stopping rcu_torture_fakewriter task");
  				kthread_stop(fakewriter_tasks[i]);
  			}
  			fakewriter_tasks[i] = NULL;
  		}
  		kfree(fakewriter_tasks);
  		fakewriter_tasks = NULL;
  	}

  	if (stats_task) {

  		VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
  		kthread_stop(stats_task);
  	}
  	stats_task = NULL;
  
  	/* Wait for all RCU callbacks to fire.  */

  
  	if (cur_ops->cb_barrier != NULL)
  		cur_ops->cb_barrier();

  	rcu_torture_stats_print();  /* -After- the stats thread is stopped! */

  	if (cur_ops->cleanup)

  		cur_ops->cleanup();

  	if (atomic_read(&n_rcu_torture_error))
  		rcu_torture_print_module_parms("End of test: FAILURE");
  	else
  		rcu_torture_print_module_parms("End of test: SUCCESS");

  }

  static int __init

  rcu_torture_init(void)
  {
  	int i;
  	int cpu;
  	int firsterr = 0;

  	static struct rcu_torture_ops *torture_ops[] =
  		{ &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,

  		  &srcu_ops, &sched_ops, &sched_ops_sync, };

  
  	/* Process args and tell the world that the torturer is on the job. */

  	for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {

  		cur_ops = torture_ops[i];

  		if (strcmp(torture_type, cur_ops->name) == 0)

  			break;

  	}

  	if (i == ARRAY_SIZE(torture_ops)) {

  		printk(KERN_ALERT "rcutorture: invalid torture type: \"%s\"
  ",
  		       torture_type);
  		return (-EINVAL);
  	}

  	if (cur_ops->init)

  		cur_ops->init(); /* no "goto unwind" prior to this point!!! */

  	if (nreaders >= 0)
  		nrealreaders = nreaders;
  	else
  		nrealreaders = 2 * num_online_cpus();

  	rcu_torture_print_module_parms("Start of test");

  	fullstop = 0;
  
  	/* Set up the freelist. */
  
  	INIT_LIST_HEAD(&rcu_torture_freelist);

  	for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++) {

  		rcu_tortures[i].rtort_mbtest = 0;

  		list_add_tail(&rcu_tortures[i].rtort_free,
  			      &rcu_torture_freelist);
  	}
  
  	/* Initialize the statistics so that each run gets its own numbers. */
  
  	rcu_torture_current = NULL;
  	rcu_torture_current_version = 0;
  	atomic_set(&n_rcu_torture_alloc, 0);
  	atomic_set(&n_rcu_torture_alloc_fail, 0);
  	atomic_set(&n_rcu_torture_free, 0);

  	atomic_set(&n_rcu_torture_mberror, 0);
  	atomic_set(&n_rcu_torture_error, 0);

  	for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
  		atomic_set(&rcu_torture_wcount[i], 0);

  	for_each_possible_cpu(cpu) {

  		for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
  			per_cpu(rcu_torture_count, cpu)[i] = 0;
  			per_cpu(rcu_torture_batch, cpu)[i] = 0;
  		}
  	}
  
  	/* Start up the kthreads. */
  
  	VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");
  	writer_task = kthread_run(rcu_torture_writer, NULL,
  				  "rcu_torture_writer");
  	if (IS_ERR(writer_task)) {
  		firsterr = PTR_ERR(writer_task);
  		VERBOSE_PRINTK_ERRSTRING("Failed to create writer");
  		writer_task = NULL;
  		goto unwind;
  	}

  	fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),
  	                           GFP_KERNEL);
  	if (fakewriter_tasks == NULL) {
  		VERBOSE_PRINTK_ERRSTRING("out of memory");
  		firsterr = -ENOMEM;
  		goto unwind;
  	}
  	for (i = 0; i < nfakewriters; i++) {
  		VERBOSE_PRINTK_STRING("Creating rcu_torture_fakewriter task");
  		fakewriter_tasks[i] = kthread_run(rcu_torture_fakewriter, NULL,
  		                                  "rcu_torture_fakewriter");
  		if (IS_ERR(fakewriter_tasks[i])) {
  			firsterr = PTR_ERR(fakewriter_tasks[i]);
  			VERBOSE_PRINTK_ERRSTRING("Failed to create fakewriter");
  			fakewriter_tasks[i] = NULL;
  			goto unwind;
  		}
  	}

  	reader_tasks = kzalloc(nrealreaders * sizeof(reader_tasks[0]),

  			       GFP_KERNEL);
  	if (reader_tasks == NULL) {
  		VERBOSE_PRINTK_ERRSTRING("out of memory");
  		firsterr = -ENOMEM;
  		goto unwind;
  	}
  	for (i = 0; i < nrealreaders; i++) {
  		VERBOSE_PRINTK_STRING("Creating rcu_torture_reader task");
  		reader_tasks[i] = kthread_run(rcu_torture_reader, NULL,
  					      "rcu_torture_reader");
  		if (IS_ERR(reader_tasks[i])) {
  			firsterr = PTR_ERR(reader_tasks[i]);
  			VERBOSE_PRINTK_ERRSTRING("Failed to create reader");
  			reader_tasks[i] = NULL;
  			goto unwind;
  		}
  	}
  	if (stat_interval > 0) {
  		VERBOSE_PRINTK_STRING("Creating rcu_torture_stats task");
  		stats_task = kthread_run(rcu_torture_stats, NULL,
  					"rcu_torture_stats");
  		if (IS_ERR(stats_task)) {
  			firsterr = PTR_ERR(stats_task);
  			VERBOSE_PRINTK_ERRSTRING("Failed to create stats");
  			stats_task = NULL;
  			goto unwind;
  		}
  	}

  	if (test_no_idle_hz) {
  		rcu_idle_cpu = num_online_cpus() - 1;
  		/* Create the shuffler thread */
  		shuffler_task = kthread_run(rcu_torture_shuffle, NULL,
  					  "rcu_torture_shuffle");
  		if (IS_ERR(shuffler_task)) {
  			firsterr = PTR_ERR(shuffler_task);
  			VERBOSE_PRINTK_ERRSTRING("Failed to create shuffler");
  			shuffler_task = NULL;
  			goto unwind;
  		}
  	}

  	if (stutter < 0)
  		stutter = 0;
  	if (stutter) {
  		/* Create the stutter thread */
  		stutter_task = kthread_run(rcu_torture_stutter, NULL,
  					  "rcu_torture_stutter");
  		if (IS_ERR(stutter_task)) {
  			firsterr = PTR_ERR(stutter_task);
  			VERBOSE_PRINTK_ERRSTRING("Failed to create stutter");
  			stutter_task = NULL;
  			goto unwind;
  		}
  	}

  	return 0;
  
  unwind:
  	rcu_torture_cleanup();
  	return firsterr;
  }
  
  module_init(rcu_torture_init);
  module_exit(rcu_torture_cleanup);