rcutorture.c

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/*
 * 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 <[email protected]>
 *    Josh Triplett <[email protected]>
 *
 * 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 <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/srcu.h>
#include <linux/slab.h>
#include <asm/byteorder.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Paul E. McKenney <[email protected]> and Josh Triplett <[email protected]>");

static int nreaders = -1;   /* # reader threads, defaults to 2*ncpus */
static int nfakewriters = 4;    /* # fake writer threads */
static int stat_interval = 60;  /* Interval between stats, in seconds. */
                /*  Zero means "only at end of test". */
static bool verbose;        /* Print more debug info. */
static bool test_no_idle_hz = true;
                /* Test RCU 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 int fqs_duration;    /* Duration of bursts (us), 0 to disable. */
static int fqs_holdoff;     /* Hold time within burst (us). */
static int fqs_stutter = 3; /* Wait time between bursts (s). */
static int n_barrier_cbs;   /* Number of callbacks to test RCU barriers. */
static int onoff_interval;  /* Wait time between CPU hotplugs, 0=disable. */
static int onoff_holdoff;   /* Seconds after boot before CPU hotplugs. */
static int shutdown_secs;   /* Shutdown time (s).  <=0 for no shutdown. */
static int stall_cpu;       /* CPU-stall duration (s).  0 for no stall. */
static int stall_cpu_holdoff = 10; /* Time to wait until stall (s).  */
static int test_boost = 1;  /* Test RCU prio boost: 0=no, 1=maybe, 2=yes. */
static int test_boost_interval = 7; /* Interval between boost tests, seconds. */
static int test_boost_duration = 4; /* Duration of each boost test, seconds. */
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, 0644);
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(fqs_duration, int, 0444);
MODULE_PARM_DESC(fqs_duration, "Duration of fqs bursts (us)");
module_param(fqs_holdoff, int, 0444);
MODULE_PARM_DESC(fqs_holdoff, "Holdoff time within fqs bursts (us)");
module_param(fqs_stutter, int, 0444);
MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
module_param(n_barrier_cbs, int, 0444);
MODULE_PARM_DESC(n_barrier_cbs, "# of callbacks/kthreads for barrier testing");
module_param(onoff_interval, int, 0444);
MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable");
module_param(onoff_holdoff, int, 0444);
MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)");
module_param(shutdown_secs, int, 0444);
MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), zero to disable.");
module_param(stall_cpu, int, 0444);
MODULE_PARM_DESC(stall_cpu, "Stall duration (s), zero to disable.");
module_param(stall_cpu_holdoff, int, 0444);
MODULE_PARM_DESC(stall_cpu_holdoff, "Time to wait before starting stall (s).");
module_param(test_boost, int, 0444);
MODULE_PARM_DESC(test_boost, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
module_param(test_boost_interval, int, 0444);
MODULE_PARM_DESC(test_boost_interval, "Interval between boost tests, seconds.");
module_param(test_boost_duration, int, 0444);
MODULE_PARM_DESC(test_boost_duration, "Duration of each boost test, seconds.");
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 { pr_alert("%s" TORTURE_FLAG s "\n", torture_type); } while (0)
#define VERBOSE_PRINTK_STRING(s) \
    do { if (verbose) pr_alert("%s" TORTURE_FLAG s "\n", torture_type); } while (0)
#define VERBOSE_PRINTK_ERRSTRING(s) \
    do { if (verbose) pr_alert("%s" TORTURE_FLAG "!!! " s "\n", 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;
static struct task_struct *fqs_task;
static struct task_struct *boost_tasks[NR_CPUS];
static struct task_struct *shutdown_task;
#ifdef CONFIG_HOTPLUG_CPU
static struct task_struct *onoff_task;
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
static struct task_struct *stall_task;
static struct task_struct **barrier_cbs_tasks;
static struct task_struct *barrier_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 LIST_HEAD(rcu_torture_freelist);
static struct rcu_torture __rcu *rcu_torture_current;
static unsigned long rcu_torture_current_version;
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_barrier_error;
static long n_rcu_torture_boost_ktrerror;
static long n_rcu_torture_boost_rterror;
static long n_rcu_torture_boost_failure;
static long n_rcu_torture_boosts;
static long n_rcu_torture_timers;
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;
static long n_barrier_attempts;
static long n_barrier_successes;
static struct list_head rcu_torture_removed;
static cpumask_var_t shuffle_tmp_mask;

static int stutter_pause_test;

#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;
module_param(rcutorture_runnable, int, 0444);
MODULE_PARM_DESC(rcutorture_runnable, "Start rcutorture at boot");

#if defined(CONFIG_RCU_BOOST) && !defined(CONFIG_HOTPLUG_CPU)
#define rcu_can_boost() 1
#else /* #if defined(CONFIG_RCU_BOOST) && !defined(CONFIG_HOTPLUG_CPU) */
#define rcu_can_boost() 0
#endif /* #else #if defined(CONFIG_RCU_BOOST) && !defined(CONFIG_HOTPLUG_CPU) */

static unsigned long shutdown_time; /* jiffies to system shutdown. */
static unsigned long boost_starttime;   /* jiffies of next boost test start. */
DEFINE_MUTEX(boost_mutex);      /* protect setting boost_starttime */
                    /*  and boost task create/destroy. */
static atomic_t barrier_cbs_count;  /* Barrier callbacks registered. */
static bool barrier_phase;      /* Test phase. */
static atomic_t barrier_cbs_invoked;    /* Barrier callbacks invoked. */
static wait_queue_head_t *barrier_cbs_wq; /* Coordinate barrier testing. */
static DECLARE_WAIT_QUEUE_HEAD(barrier_wq);

/* Mediate rmmod and system shutdown.  Concurrent rmmod & shutdown illegal! */

#define FULLSTOP_DONTSTOP 0 /* Normal operation. */
#define FULLSTOP_SHUTDOWN 1 /* System shutdown with rcutorture running. */
#define FULLSTOP_RMMOD    2 /* Normal rmmod of rcutorture. */
static int fullstop = FULLSTOP_RMMOD;
/*
 * Protect fullstop transitions and spawning of kthreads.
 */
static DEFINE_MUTEX(fullstop_mutex);

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

/*
 * Detect and respond to a system shutdown.
 */
static int
rcutorture_shutdown_notify(struct notifier_block *unused1,
               unsigned long unused2, void *unused3)
{
    mutex_lock(&fullstop_mutex);
    if (fullstop == FULLSTOP_DONTSTOP)
        fullstop = FULLSTOP_SHUTDOWN;
    else
        pr_warn(/* but going down anyway, so... */
               "Concurrent 'rmmod rcutorture' and shutdown illegal!\n");
    mutex_unlock(&fullstop_mutex);
    return NOTIFY_DONE;
}

/*
 * Absorb kthreads into a kernel function that won't return, so that
 * they won't ever access module text or data again.
 */
static void rcutorture_shutdown_absorb(char *title)
{
    if (ACCESS_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {
        pr_notice(
               "rcutorture thread %s parking due to system shutdown\n",
               title);
        schedule_timeout_uninterruptible(MAX_SCHEDULE_TIMEOUT);
    }
}

/*
 * 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)local_clock();
        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(char *title)
{
    while (stutter_pause_test || !rcutorture_runnable) {
        if (rcutorture_runnable)
            schedule_timeout_interruptible(1);
        else
            schedule_timeout_interruptible(round_jiffies_relative(HZ));
        rcutorture_shutdown_absorb(title);
    }
}

/*
 * Operations vector for selecting different types of tests.
 */

struct rcu_torture_ops {
    void (*init)(void);
    void (*cleanup)(void);
    int (*readlock)(void);
    void (*read_delay)(struct rcu_random_state *rrsp);
    void (*readunlock)(int idx);
    int (*completed)(void);
    void (*deferred_free)(struct rcu_torture *p);
    void (*sync)(void);
    void (*call)(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
    void (*cb_barrier)(void);
    void (*fqs)(void);
    int (*stats)(char *page);
    int irq_capable;
    int can_boost;
    char *name;
};

static struct rcu_torture_ops *cur_ops;

/*
 * 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)
{
    const unsigned long shortdelay_us = 200;
    const unsigned long longdelay_ms = 50;

    /* We want a short delay sometimes to make a reader delay the grace
     * period, and we want a long delay occasionally to trigger
     * force_quiescent_state. */

    if (!(rcu_random(rrsp) % (nrealreaders * 2000 * longdelay_ms)))
        mdelay(longdelay_ms);
    if (!(rcu_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
        udelay(shortdelay_us);
#ifdef CONFIG_PREEMPT
    if (!preempt_count() && !(rcu_random(rrsp) % (nrealreaders * 20000)))
        preempt_schedule();  /* No QS if preempt_disable() in effect */
#endif
}

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 != FULLSTOP_DONTSTOP) {
        /* 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->deferred_free(rp);
    }
}

static int rcu_no_completed(void)
{
    return 0;
}

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,
    .read_delay = rcu_read_delay,
    .readunlock = rcu_torture_read_unlock,
    .completed  = rcu_torture_completed,
    .deferred_free  = rcu_torture_deferred_free,
    .sync       = synchronize_rcu,
    .call       = call_rcu,
    .cb_barrier = rcu_barrier,
    .fqs        = rcu_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 1,
    .can_boost  = rcu_can_boost(),
    .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,
    .read_delay = rcu_read_delay,
    .readunlock = rcu_torture_read_unlock,
    .completed  = rcu_torture_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = synchronize_rcu,
    .call       = NULL,
    .cb_barrier = NULL,
    .fqs        = rcu_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 1,
    .can_boost  = rcu_can_boost(),
    .name       = "rcu_sync"
};

static struct rcu_torture_ops rcu_expedited_ops = {
    .init       = rcu_sync_torture_init,
    .cleanup    = NULL,
    .readlock   = rcu_torture_read_lock,
    .read_delay = rcu_read_delay,  /* just reuse rcu's version. */
    .readunlock = rcu_torture_read_unlock,
    .completed  = rcu_no_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = synchronize_rcu_expedited,
    .call       = NULL,
    .cb_barrier = NULL,
    .fqs        = rcu_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 1,
    .can_boost  = rcu_can_boost(),
    .name       = "rcu_expedited"
};

/*
 * 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);
}

static struct rcu_torture_ops rcu_bh_ops = {
    .init       = NULL,
    .cleanup    = NULL,
    .readlock   = rcu_bh_torture_read_lock,
    .read_delay = rcu_read_delay,  /* just reuse rcu's version. */
    .readunlock = rcu_bh_torture_read_unlock,
    .completed  = rcu_bh_torture_completed,
    .deferred_free  = rcu_bh_torture_deferred_free,
    .sync       = synchronize_rcu_bh,
    .call       = call_rcu_bh,
    .cb_barrier = rcu_barrier_bh,
    .fqs        = rcu_bh_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 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,
    .read_delay = rcu_read_delay,  /* just reuse rcu's version. */
    .readunlock = rcu_bh_torture_read_unlock,
    .completed  = rcu_bh_torture_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = synchronize_rcu_bh,
    .call       = NULL,
    .cb_barrier = NULL,
    .fqs        = rcu_bh_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 1,
    .name       = "rcu_bh_sync"
};

static struct rcu_torture_ops rcu_bh_expedited_ops = {
    .init       = rcu_sync_torture_init,
    .cleanup    = NULL,
    .readlock   = rcu_bh_torture_read_lock,
    .read_delay = rcu_read_delay,  /* just reuse rcu's version. */
    .readunlock = rcu_bh_torture_read_unlock,
    .completed  = rcu_bh_torture_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = synchronize_rcu_bh_expedited,
    .call       = NULL,
    .cb_barrier = NULL,
    .fqs        = rcu_bh_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 1,
    .name       = "rcu_bh_expedited"
};

/*
 * 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);
    else
        rcu_read_delay(rrsp);
}

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_deferred_free(struct rcu_torture *rp)
{
    call_srcu(&srcu_ctl, &rp->rtort_rcu, rcu_torture_cb);
}

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

static void srcu_torture_call(struct rcu_head *head,
                  void (*func)(struct rcu_head *head))
{
    call_srcu(&srcu_ctl, head, func);
}

static void srcu_torture_barrier(void)
{
    srcu_barrier(&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(%lu,%lu)", 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], "\n");
    return cnt;
}

static struct rcu_torture_ops srcu_ops = {
    .init       = srcu_torture_init,
    .cleanup    = srcu_torture_cleanup,
    .readlock   = srcu_torture_read_lock,
    .read_delay = srcu_read_delay,
    .readunlock = srcu_torture_read_unlock,
    .completed  = srcu_torture_completed,
    .deferred_free  = srcu_torture_deferred_free,
    .sync       = srcu_torture_synchronize,
    .call       = srcu_torture_call,
    .cb_barrier = srcu_torture_barrier,
    .stats      = srcu_torture_stats,
    .name       = "srcu"
};

static struct rcu_torture_ops srcu_sync_ops = {
    .init       = srcu_torture_init,
    .cleanup    = srcu_torture_cleanup,
    .readlock   = srcu_torture_read_lock,
    .read_delay = srcu_read_delay,
    .readunlock = srcu_torture_read_unlock,
    .completed  = srcu_torture_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = srcu_torture_synchronize,
    .call       = NULL,
    .cb_barrier = NULL,
    .stats      = srcu_torture_stats,
    .name       = "srcu_sync"
};

static int srcu_torture_read_lock_raw(void) __acquires(&srcu_ctl)
{
    return srcu_read_lock_raw(&srcu_ctl);
}

static void srcu_torture_read_unlock_raw(int idx) __releases(&srcu_ctl)
{
    srcu_read_unlock_raw(&srcu_ctl, idx);
}

static struct rcu_torture_ops srcu_raw_ops = {
    .init       = srcu_torture_init,
    .cleanup    = srcu_torture_cleanup,
    .readlock   = srcu_torture_read_lock_raw,
    .read_delay = srcu_read_delay,
    .readunlock = srcu_torture_read_unlock_raw,
    .completed  = srcu_torture_completed,
    .deferred_free  = srcu_torture_deferred_free,
    .sync       = srcu_torture_synchronize,
    .call       = NULL,
    .cb_barrier = NULL,
    .stats      = srcu_torture_stats,
    .name       = "srcu_raw"
};

static struct rcu_torture_ops srcu_raw_sync_ops = {
    .init       = srcu_torture_init,
    .cleanup    = srcu_torture_cleanup,
    .readlock   = srcu_torture_read_lock_raw,
    .read_delay = srcu_read_delay,
    .readunlock = srcu_torture_read_unlock_raw,
    .completed  = srcu_torture_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = srcu_torture_synchronize,
    .call       = NULL,
    .cb_barrier = NULL,
    .stats      = srcu_torture_stats,
    .name       = "srcu_raw_sync"
};

static void srcu_torture_synchronize_expedited(void)
{
    synchronize_srcu_expedited(&srcu_ctl);
}

static struct rcu_torture_ops srcu_expedited_ops = {
    .init       = srcu_torture_init,
    .cleanup    = srcu_torture_cleanup,
    .readlock   = srcu_torture_read_lock,
    .read_delay = srcu_read_delay,
    .readunlock = srcu_torture_read_unlock,
    .completed  = srcu_torture_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = srcu_torture_synchronize_expedited,
    .call       = NULL,
    .cb_barrier = NULL,
    .stats      = srcu_torture_stats,
    .name       = "srcu_expedited"
};

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

static struct rcu_torture_ops sched_ops = {
    .init       = rcu_sync_torture_init,
    .cleanup    = NULL,
    .readlock   = sched_torture_read_lock,
    .read_delay = rcu_read_delay,  /* just reuse rcu's version. */
    .readunlock = sched_torture_read_unlock,
    .completed  = rcu_no_completed,
    .deferred_free  = rcu_sched_torture_deferred_free,
    .sync       = synchronize_sched,
    .cb_barrier = rcu_barrier_sched,
    .fqs        = rcu_sched_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 1,
    .name       = "sched"
};

static struct rcu_torture_ops sched_sync_ops = {
    .init       = rcu_sync_torture_init,
    .cleanup    = NULL,
    .readlock   = sched_torture_read_lock,
    .read_delay = rcu_read_delay,  /* just reuse rcu's version. */
    .readunlock = sched_torture_read_unlock,
    .completed  = rcu_no_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = synchronize_sched,
    .cb_barrier = NULL,
    .fqs        = rcu_sched_force_quiescent_state,
    .stats      = NULL,
    .name       = "sched_sync"
};

static struct rcu_torture_ops sched_expedited_ops = {
    .init       = rcu_sync_torture_init,
    .cleanup    = NULL,
    .readlock   = sched_torture_read_lock,
    .read_delay = rcu_read_delay,  /* just reuse rcu's version. */
    .readunlock = sched_torture_read_unlock,
    .completed  = rcu_no_completed,
    .deferred_free  = rcu_sync_torture_deferred_free,
    .sync       = synchronize_sched_expedited,
    .cb_barrier = NULL,
    .fqs        = rcu_sched_force_quiescent_state,
    .stats      = NULL,
    .irq_capable    = 1,
    .name       = "sched_expedited"
};

/*
 * RCU torture priority-boost testing.  Runs one real-time thread per
 * CPU for moderate bursts, repeatedly registering RCU callbacks and
 * spinning waiting for them to be invoked.  If a given callback takes
 * too long to be invoked, we assume that priority inversion has occurred.
 */

struct rcu_boost_inflight {
    struct rcu_head rcu;
    int inflight;
};

static void rcu_torture_boost_cb(struct rcu_head *head)
{
    struct rcu_boost_inflight *rbip =
        container_of(head, struct rcu_boost_inflight, rcu);

    smp_mb(); /* Ensure RCU-core accesses precede clearing ->inflight */
    rbip->inflight = 0;
}

static int rcu_torture_boost(void *arg)
{
    unsigned long call_rcu_time;
    unsigned long endtime;
    unsigned long oldstarttime;
    struct rcu_boost_inflight rbi = { .inflight = 0 };
    struct sched_param sp;

    VERBOSE_PRINTK_STRING("rcu_torture_boost started");

    /* Set real-time priority. */
    sp.sched_priority = 1;
    if (sched_setscheduler(current, SCHED_FIFO, &sp) < 0) {
        VERBOSE_PRINTK_STRING("rcu_torture_boost RT prio failed!");
        n_rcu_torture_boost_rterror++;
    }

    init_rcu_head_on_stack(&rbi.rcu);
    /* Each pass through the following loop does one boost-test cycle. */
    do {
        /* Wait for the next test interval. */
        oldstarttime = boost_starttime;
        while (ULONG_CMP_LT(jiffies, oldstarttime)) {
            schedule_timeout_uninterruptible(1);
            rcu_stutter_wait("rcu_torture_boost");
            if (kthread_should_stop() ||
                fullstop != FULLSTOP_DONTSTOP)
                goto checkwait;
        }

        /* Do one boost-test interval. */
        endtime = oldstarttime + test_boost_duration * HZ;
        call_rcu_time = jiffies;
        while (ULONG_CMP_LT(jiffies, endtime)) {
            /* If we don't have a callback in flight, post one. */
            if (!rbi.inflight) {
                smp_mb(); /* RCU core before ->inflight = 1. */
                rbi.inflight = 1;
                call_rcu(&rbi.rcu, rcu_torture_boost_cb);
                if (jiffies - call_rcu_time >
                     test_boost_duration * HZ - HZ / 2) {
                    VERBOSE_PRINTK_STRING("rcu_torture_boost boosting failed");
                    n_rcu_torture_boost_failure++;
                }
                call_rcu_time = jiffies;
            }
            cond_resched();
            rcu_stutter_wait("rcu_torture_boost");
            if (kthread_should_stop() ||
                fullstop != FULLSTOP_DONTSTOP)
                goto checkwait;
        }

        /*
         * Set the start time of the next test interval.
         * Yes, this is vulnerable to long delays, but such
         * delays simply cause a false negative for the next
         * interval.  Besides, we are running at RT priority,
         * so delays should be relatively rare.
         */
        while (oldstarttime == boost_starttime &&
               !kthread_should_stop()) {
            if (mutex_trylock(&boost_mutex)) {
                boost_starttime = jiffies +
                          test_boost_interval * HZ;
                n_rcu_torture_boosts++;
                mutex_unlock(&boost_mutex);
                break;
            }
            schedule_timeout_uninterruptible(1);
        }

        /* Go do the stutter. */
checkwait:  rcu_stutter_wait("rcu_torture_boost");
    } while (!kthread_should_stop() && fullstop  == FULLSTOP_DONTSTOP);

    /* Clean up and exit. */
    VERBOSE_PRINTK_STRING("rcu_torture_boost task stopping");
    rcutorture_shutdown_absorb("rcu_torture_boost");
    while (!kthread_should_stop() || rbi.inflight)
        schedule_timeout_uninterruptible(1);
    smp_mb(); /* order accesses to ->inflight before stack-frame death. */
    destroy_rcu_head_on_stack(&rbi.rcu);
    return 0;
}

/*
 * RCU torture force-quiescent-state kthread.  Repeatedly induces
 * bursts of calls to force_quiescent_state(), increasing the probability
 * of occurrence of some important types of race conditions.
 */
static int
rcu_torture_fqs(void *arg)
{
    unsigned long fqs_resume_time;
    int fqs_burst_remaining;

    VERBOSE_PRINTK_STRING("rcu_torture_fqs task started");
    do {
        fqs_resume_time = jiffies + fqs_stutter * HZ;
        while (ULONG_CMP_LT(jiffies, fqs_resume_time) &&
               !kthread_should_stop()) {
            schedule_timeout_interruptible(1);
        }
        fqs_burst_remaining = fqs_duration;
        while (fqs_burst_remaining > 0 &&
               !kthread_should_stop()) {
            cur_ops->fqs();
            udelay(fqs_holdoff);
            fqs_burst_remaining -= fqs_holdoff;
        }
        rcu_stutter_wait("rcu_torture_fqs");
    } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
    VERBOSE_PRINTK_STRING("rcu_torture_fqs task stopping");
    rcutorture_shutdown_absorb("rcu_torture_fqs");
    while (!kthread_should_stop())
        schedule_timeout_uninterruptible(1);
    return 0;
}

/*
 * 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);
        rp = rcu_torture_alloc();
        if (rp == NULL)
            continue;
        rp->rtort_pipe_count = 0;
        udelay(rcu_random(&rand) & 0x3ff);
        old_rp = rcu_dereference_check(rcu_torture_current,
                           current == writer_task);
        rp->rtort_mbtest = 1;
        rcu_assign_pointer(rcu_torture_current, rp);
        smp_wmb(); /* Mods to old_rp must follow rcu_assign_pointer() */
        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->deferred_free(old_rp);
        }
        rcutorture_record_progress(++rcu_torture_current_version);
        oldbatch = cur_ops->completed();
        rcu_stutter_wait("rcu_torture_writer");
    } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
    VERBOSE_PRINTK_STRING("rcu_torture_writer task stopping");
    rcutorture_shutdown_absorb("rcu_torture_writer");
    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);
        if (cur_ops->cb_barrier != NULL &&
            rcu_random(&rand) % (nfakewriters * 8) == 0)
            cur_ops->cb_barrier();
        else
            cur_ops->sync();
        rcu_stutter_wait("rcu_torture_fakewriter");
    } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);

    VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task stopping");
    rcutorture_shutdown_absorb("rcu_torture_fakewriter");
    while (!kthread_should_stop())
        schedule_timeout_uninterruptible(1);
    return 0;
}

void rcutorture_trace_dump(void)
{
    static atomic_t beenhere = ATOMIC_INIT(0);

    if (atomic_read(&beenhere))
        return;
    if (atomic_xchg(&beenhere, 1) != 0)
        return;
    do_trace_rcu_torture_read(cur_ops->name, (struct rcu_head *)~0UL);
    ftrace_dump(DUMP_ALL);
}

/*
 * 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_check(rcu_torture_current,
                  rcu_read_lock_bh_held() ||
                  rcu_read_lock_sched_held() ||
                  srcu_read_lock_held(&srcu_ctl));
    if (p == NULL) {
        /* Leave because rcu_torture_writer is not yet underway */
        cur_ops->readunlock(idx);
        return;
    }
    do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
    if (p->rtort_mbtest == 0)
        atomic_inc(&n_rcu_torture_mberror);
    spin_lock(&rand_lock);
    cur_ops->read_delay(&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;
    }
    if (pipe_count > 1)
        rcutorture_trace_dump();
    __this_cpu_inc(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;
    }
    __this_cpu_inc(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->irq_capable)
        setup_timer_on_stack(&t, rcu_torture_timer, 0);

    do {
        if (irqreader && cur_ops->irq_capable) {
            if (!timer_pending(&t))
                mod_timer(&t, jiffies + 1);
        }
        idx = cur_ops->readlock();
        completed = cur_ops->completed();
        p = rcu_dereference_check(rcu_torture_current,
                      rcu_read_lock_bh_held() ||
                      rcu_read_lock_sched_held() ||
                      srcu_read_lock_held(&srcu_ctl));
        if (p == NULL) {
            /* Wait for rcu_torture_writer to get underway */
            cur_ops->readunlock(idx);
            schedule_timeout_interruptible(HZ);
            continue;
        }
        do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu);
        if (p->rtort_mbtest == 0)
            atomic_inc(&n_rcu_torture_mberror);
        cur_ops->read_delay(&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;
        }
        if (pipe_count > 1)
            rcutorture_trace_dump();
        __this_cpu_inc(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;
        }
        __this_cpu_inc(rcu_torture_batch[completed]);
        preempt_enable();
        cur_ops->readunlock(idx);
        schedule();
        rcu_stutter_wait("rcu_torture_reader");
    } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
    VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");
    rcutorture_shutdown_absorb("rcu_torture_reader");
    if (irqreader && cur_ops->irq_capable)
        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: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
               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));
    cnt += sprintf(&page[cnt], "rtmbe: %d rtbke: %ld rtbre: %ld ",
               atomic_read(&n_rcu_torture_mberror),
               n_rcu_torture_boost_ktrerror,
               n_rcu_torture_boost_rterror);
    cnt += sprintf(&page[cnt], "rtbf: %ld rtb: %ld nt: %ld ",
               n_rcu_torture_boost_failure,
               n_rcu_torture_boosts,
               n_rcu_torture_timers);
    cnt += sprintf(&page[cnt],
               "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);
    cnt += sprintf(&page[cnt], "barrier: %ld/%ld:%ld",
               n_barrier_successes,
               n_barrier_attempts,
               n_rcu_torture_barrier_error);
    cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
    if (atomic_read(&n_rcu_torture_mberror) != 0 ||
        n_rcu_torture_barrier_error != 0 ||
        n_rcu_torture_boost_ktrerror != 0 ||
        n_rcu_torture_boost_rterror != 0 ||
        n_rcu_torture_boost_failure != 0 ||
        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], "\n%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], "\n%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], "\n");
    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);
    pr_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();
        rcutorture_shutdown_absorb("rcu_torture_stats");
    } 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)
{
    int i;

    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;
    }

    if (rcu_idle_cpu != -1)
        cpumask_clear_cpu(rcu_idle_cpu, shuffle_tmp_mask);

    set_cpus_allowed_ptr(current, shuffle_tmp_mask);

    if (reader_tasks) {
        for (i = 0; i < nrealreaders; i++)
            if (reader_tasks[i])
                set_cpus_allowed_ptr(reader_tasks[i],
                             shuffle_tmp_mask);
    }

    if (fakewriter_tasks) {
        for (i = 0; i < nfakewriters; i++)
            if (fakewriter_tasks[i])
                set_cpus_allowed_ptr(fakewriter_tasks[i],
                             shuffle_tmp_mask);
    }

    if (writer_task)
        set_cpus_allowed_ptr(writer_task, shuffle_tmp_mask);

    if (stats_task)
        set_cpus_allowed_ptr(stats_task, shuffle_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();
        rcutorture_shutdown_absorb("rcu_torture_shuffle");
    } 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;
        rcutorture_shutdown_absorb("rcu_torture_stutter");
    } while (!kthread_should_stop());
    VERBOSE_PRINTK_STRING("rcu_torture_stutter task stopping");
    return 0;
}

static inline void
rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, char *tag)
{
    pr_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 "
         "fqs_duration=%d fqs_holdoff=%d fqs_stutter=%d "
         "test_boost=%d/%d test_boost_interval=%d "
         "test_boost_duration=%d shutdown_secs=%d "
         "onoff_interval=%d onoff_holdoff=%d\n",
         torture_type, tag, nrealreaders, nfakewriters,
         stat_interval, verbose, test_no_idle_hz, shuffle_interval,
         stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter,
         test_boost, cur_ops->can_boost,
         test_boost_interval, test_boost_duration, shutdown_secs,
         onoff_interval, onoff_holdoff);
}

static struct notifier_block rcutorture_shutdown_nb = {
    .notifier_call = rcutorture_shutdown_notify,
};

static void rcutorture_booster_cleanup(int cpu)
{
    struct task_struct *t;

    if (boost_tasks[cpu] == NULL)
        return;
    mutex_lock(&boost_mutex);
    VERBOSE_PRINTK_STRING("Stopping rcu_torture_boost task");
    t = boost_tasks[cpu];
    boost_tasks[cpu] = NULL;
    mutex_unlock(&boost_mutex);

    /* This must be outside of the mutex, otherwise deadlock! */
    kthread_stop(t);
    boost_tasks[cpu] = NULL;
}

static int rcutorture_booster_init(int cpu)
{
    int retval;

    if (boost_tasks[cpu] != NULL)
        return 0;  /* Already created, nothing more to do. */

    /* Don't allow time recalculation while creating a new task. */
    mutex_lock(&boost_mutex);
    VERBOSE_PRINTK_STRING("Creating rcu_torture_boost task");
    boost_tasks[cpu] = kthread_create_on_node(rcu_torture_boost, NULL,
                          cpu_to_node(cpu),
                          "rcu_torture_boost");
    if (IS_ERR(boost_tasks[cpu])) {
        retval = PTR_ERR(boost_tasks[cpu]);
        VERBOSE_PRINTK_STRING("rcu_torture_boost task create failed");
        n_rcu_torture_boost_ktrerror++;
        boost_tasks[cpu] = NULL;
        mutex_unlock(&boost_mutex);
        return retval;
    }
    kthread_bind(boost_tasks[cpu], cpu);
    wake_up_process(boost_tasks[cpu]);
    mutex_unlock(&boost_mutex);
    return 0;
}

/*
 * Cause the rcutorture test to shutdown the system after the test has
 * run for the time specified by the shutdown_secs module parameter.
 */
static int
rcu_torture_shutdown(void *arg)
{
    long delta;
    unsigned long jiffies_snap;

    VERBOSE_PRINTK_STRING("rcu_torture_shutdown task started");
    jiffies_snap = ACCESS_ONCE(jiffies);
    while (ULONG_CMP_LT(jiffies_snap, shutdown_time) &&
           !kthread_should_stop()) {
        delta = shutdown_time - jiffies_snap;
        if (verbose)
            pr_alert("%s" TORTURE_FLAG
                 "rcu_torture_shutdown task: %lu jiffies remaining\n",
                 torture_type, delta);
        schedule_timeout_interruptible(delta);
        jiffies_snap = ACCESS_ONCE(jiffies);
    }
    if (kthread_should_stop()) {
        VERBOSE_PRINTK_STRING("rcu_torture_shutdown task stopping");
        return 0;
    }

    /* OK, shut down the system. */

    VERBOSE_PRINTK_STRING("rcu_torture_shutdown task shutting down system");
    shutdown_task = NULL;   /* Avoid self-kill deadlock. */
    rcu_torture_cleanup();  /* Get the success/failure message. */
    kernel_power_off(); /* Shut down the system. */
    return 0;
}

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Execute random CPU-hotplug operations at the interval specified
 * by the onoff_interval.
 */
static int __cpuinit
rcu_torture_onoff(void *arg)
{
    int cpu;
    unsigned long delta;
    int maxcpu = -1;
    DEFINE_RCU_RANDOM(rand);
    unsigned long starttime;

    VERBOSE_PRINTK_STRING("rcu_torture_onoff task started");
    for_each_online_cpu(cpu)
        maxcpu = cpu;
    WARN_ON(maxcpu < 0);
    if (onoff_holdoff > 0) {
        VERBOSE_PRINTK_STRING("rcu_torture_onoff begin holdoff");
        schedule_timeout_interruptible(onoff_holdoff * HZ);
        VERBOSE_PRINTK_STRING("rcu_torture_onoff end holdoff");
    }
    while (!kthread_should_stop()) {
        cpu = (rcu_random(&rand) >> 4) % (maxcpu + 1);
        if (cpu_online(cpu) && cpu_is_hotpluggable(cpu)) {
            if (verbose)
                pr_alert("%s" TORTURE_FLAG
                     "rcu_torture_onoff task: offlining %d\n",
                     torture_type, cpu);
            starttime = jiffies;
            n_offline_attempts++;
            if (cpu_down(cpu) == 0) {
                if (verbose)
                    pr_alert("%s" TORTURE_FLAG
                         "rcu_torture_onoff task: offlined %d\n",
                         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
                     "rcu_torture_onoff task: onlining %d\n",
                     torture_type, cpu);
            starttime = jiffies;
            n_online_attempts++;
            if (cpu_up(cpu) == 0) {
                if (verbose)
                    pr_alert("%s" TORTURE_FLAG
                         "rcu_torture_onoff task: onlined %d\n",
                         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 * HZ);
    }
    VERBOSE_PRINTK_STRING("rcu_torture_onoff task stopping");
    return 0;
}

static int __cpuinit
rcu_torture_onoff_init(void)
{
    int ret;

    if (onoff_interval <= 0)
        return 0;
    onoff_task = kthread_run(rcu_torture_onoff, NULL, "rcu_torture_onoff");
    if (IS_ERR(onoff_task)) {
        ret = PTR_ERR(onoff_task);
        onoff_task = NULL;
        return ret;
    }
    return 0;
}

static void rcu_torture_onoff_cleanup(void)
{
    if (onoff_task == NULL)
        return;
    VERBOSE_PRINTK_STRING("Stopping rcu_torture_onoff task");
    kthread_stop(onoff_task);
    onoff_task = NULL;
}

#else /* #ifdef CONFIG_HOTPLUG_CPU */

static int
rcu_torture_onoff_init(void)
{
    return 0;
}

static void rcu_torture_onoff_cleanup(void)
{
}

#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */

/*
 * CPU-stall kthread.  It waits as specified by stall_cpu_holdoff, then
 * induces a CPU stall for the time specified by stall_cpu.
 */
static int __cpuinit rcu_torture_stall(void *args)
{
    unsigned long stop_at;

    VERBOSE_PRINTK_STRING("rcu_torture_stall task started");
    if (stall_cpu_holdoff > 0) {
        VERBOSE_PRINTK_STRING("rcu_torture_stall begin holdoff");
        schedule_timeout_interruptible(stall_cpu_holdoff * HZ);
        VERBOSE_PRINTK_STRING("rcu_torture_stall end holdoff");
    }
    if (!kthread_should_stop()) {
        stop_at = get_seconds() + stall_cpu;
        /* RCU CPU stall is expected behavior in following code. */
        pr_alert("rcu_torture_stall start.\n");
        rcu_read_lock();
        preempt_disable();
        while (ULONG_CMP_LT(get_seconds(), stop_at))
            continue;  /* Induce RCU CPU stall warning. */
        preempt_enable();
        rcu_read_unlock();
        pr_alert("rcu_torture_stall end.\n");
    }
    rcutorture_shutdown_absorb("rcu_torture_stall");
    while (!kthread_should_stop())
        schedule_timeout_interruptible(10 * HZ);
    return 0;
}

/* Spawn CPU-stall kthread, if stall_cpu specified. */
static int __init rcu_torture_stall_init(void)
{
    int ret;

    if (stall_cpu <= 0)
        return 0;
    stall_task = kthread_run(rcu_torture_stall, NULL, "rcu_torture_stall");
    if (IS_ERR(stall_task)) {
        ret = PTR_ERR(stall_task);
        stall_task = NULL;
        return ret;
    }
    return 0;
}

/* Clean up after the CPU-stall kthread, if one was spawned. */
static void rcu_torture_stall_cleanup(void)
{
    if (stall_task == NULL)
        return;
    VERBOSE_PRINTK_STRING("Stopping rcu_torture_stall_task.");
    kthread_stop(stall_task);
    stall_task = NULL;
}

/* Callback function for RCU barrier testing. */
void rcu_torture_barrier_cbf(struct rcu_head *rcu)
{
    atomic_inc(&barrier_cbs_invoked);
}

/* kthread function to register callbacks used to test RCU barriers. */
static int rcu_torture_barrier_cbs(void *arg)
{
    long myid = (long)arg;
    bool lastphase = 0;
    struct rcu_head rcu;

    init_rcu_head_on_stack(&rcu);
    VERBOSE_PRINTK_STRING("rcu_torture_barrier_cbs task started");
    set_user_nice(current, 19);
    do {
        wait_event(barrier_cbs_wq[myid],
               barrier_phase != lastphase ||
               kthread_should_stop() ||
               fullstop != FULLSTOP_DONTSTOP);
        lastphase = barrier_phase;
        smp_mb(); /* ensure barrier_phase load before ->call(). */
        if (kthread_should_stop() || fullstop != FULLSTOP_DONTSTOP)
            break;
        cur_ops->call(&rcu, rcu_torture_barrier_cbf);
        if (atomic_dec_and_test(&barrier_cbs_count))
            wake_up(&barrier_wq);
    } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
    VERBOSE_PRINTK_STRING("rcu_torture_barrier_cbs task stopping");
    rcutorture_shutdown_absorb("rcu_torture_barrier_cbs");
    while (!kthread_should_stop())
        schedule_timeout_interruptible(1);
    cur_ops->cb_barrier();
    destroy_rcu_head_on_stack(&rcu);
    return 0;
}

/* kthread function to drive and coordinate RCU barrier testing. */
static int rcu_torture_barrier(void *arg)
{
    int i;

    VERBOSE_PRINTK_STRING("rcu_torture_barrier task starting");
    do {
        atomic_set(&barrier_cbs_invoked, 0);
        atomic_set(&barrier_cbs_count, n_barrier_cbs);
        smp_mb(); /* Ensure barrier_phase after prior assignments. */
        barrier_phase = !barrier_phase;
        for (i = 0; i < n_barrier_cbs; i++)
            wake_up(&barrier_cbs_wq[i]);
        wait_event(barrier_wq,
               atomic_read(&barrier_cbs_count) == 0 ||
               kthread_should_stop() ||
               fullstop != FULLSTOP_DONTSTOP);
        if (kthread_should_stop() || fullstop != FULLSTOP_DONTSTOP)
            break;
        n_barrier_attempts++;
        cur_ops->cb_barrier();
        if (atomic_read(&barrier_cbs_invoked) != n_barrier_cbs) {
            n_rcu_torture_barrier_error++;
            WARN_ON_ONCE(1);
        }
        n_barrier_successes++;
        schedule_timeout_interruptible(HZ / 10);
    } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
    VERBOSE_PRINTK_STRING("rcu_torture_barrier task stopping");
    rcutorture_shutdown_absorb("rcu_torture_barrier");
    while (!kthread_should_stop())
        schedule_timeout_interruptible(1);
    return 0;
}

/* Initialize RCU barrier testing. */
static int rcu_torture_barrier_init(void)
{
    int i;
    int ret;

    if (n_barrier_cbs == 0)
        return 0;
    if (cur_ops->call == NULL || cur_ops->cb_barrier == NULL) {
        pr_alert("%s" TORTURE_FLAG
             " Call or barrier ops missing for %s,\n",
             torture_type, cur_ops->name);
        pr_alert("%s" TORTURE_FLAG
             " RCU barrier testing omitted from run.\n",
             torture_type);
        return 0;
    }
    atomic_set(&barrier_cbs_count, 0);
    atomic_set(&barrier_cbs_invoked, 0);
    barrier_cbs_tasks =
        kzalloc(n_barrier_cbs * sizeof(barrier_cbs_tasks[0]),
            GFP_KERNEL);
    barrier_cbs_wq =
        kzalloc(n_barrier_cbs * sizeof(barrier_cbs_wq[0]),
            GFP_KERNEL);
    if (barrier_cbs_tasks == NULL || barrier_cbs_wq == 0)
        return -ENOMEM;
    for (i = 0; i < n_barrier_cbs; i++) {
        init_waitqueue_head(&barrier_cbs_wq[i]);
        barrier_cbs_tasks[i] = kthread_run(rcu_torture_barrier_cbs,
                           (void *)(long)i,
                           "rcu_torture_barrier_cbs");
        if (IS_ERR(barrier_cbs_tasks[i])) {
            ret = PTR_ERR(barrier_cbs_tasks[i]);
            VERBOSE_PRINTK_ERRSTRING("Failed to create rcu_torture_barrier_cbs");
            barrier_cbs_tasks[i] = NULL;
            return ret;
        }
    }
    barrier_task = kthread_run(rcu_torture_barrier, NULL,
                   "rcu_torture_barrier");
    if (IS_ERR(barrier_task)) {
        ret = PTR_ERR(barrier_task);
        VERBOSE_PRINTK_ERRSTRING("Failed to create rcu_torture_barrier");
        barrier_task = NULL;
    }
    return 0;
}

/* Clean up after RCU barrier testing. */
static void rcu_torture_barrier_cleanup(void)
{
    int i;

    if (barrier_task != NULL) {
        VERBOSE_PRINTK_STRING("Stopping rcu_torture_barrier task");
        kthread_stop(barrier_task);
        barrier_task = NULL;
    }
    if (barrier_cbs_tasks != NULL) {
        for (i = 0; i < n_barrier_cbs; i++) {
            if (barrier_cbs_tasks[i] != NULL) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_barrier_cbs task");
                kthread_stop(barrier_cbs_tasks[i]);
                barrier_cbs_tasks[i] = NULL;
            }
        }
        kfree(barrier_cbs_tasks);
        barrier_cbs_tasks = NULL;
    }
    if (barrier_cbs_wq != NULL) {
        kfree(barrier_cbs_wq);
        barrier_cbs_wq = NULL;
    }
}

static int rcutorture_cpu_notify(struct notifier_block *self,
                 unsigned long action, void *hcpu)
{
    long cpu = (long)hcpu;

    switch (action) {
    case CPU_ONLINE:
    case CPU_DOWN_FAILED:
        (void)rcutorture_booster_init(cpu);
        break;
    case CPU_DOWN_PREPARE:
        rcutorture_booster_cleanup(cpu);
        break;
    default:
        break;
    }
    return NOTIFY_OK;
}

static struct notifier_block rcutorture_cpu_nb = {
    .notifier_call = rcutorture_cpu_notify,
};

static void
rcu_torture_cleanup(void)
{
    int i;

    mutex_lock(&fullstop_mutex);
    rcutorture_record_test_transition();
    if (fullstop == FULLSTOP_SHUTDOWN) {
        pr_warn(/* but going down anyway, so... */
               "Concurrent 'rmmod rcutorture' and shutdown illegal!\n");
        mutex_unlock(&fullstop_mutex);
        schedule_timeout_uninterruptible(10);
        if (cur_ops->cb_barrier != NULL)
            cur_ops->cb_barrier();
        return;
    }
    fullstop = FULLSTOP_RMMOD;
    mutex_unlock(&fullstop_mutex);
    unregister_reboot_notifier(&rcutorture_shutdown_nb);
    rcu_torture_barrier_cleanup();
    rcu_torture_stall_cleanup();
    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);
        free_cpumask_var(shuffle_tmp_mask);
    }
    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;

    if (fqs_task) {
        VERBOSE_PRINTK_STRING("Stopping rcu_torture_fqs task");
        kthread_stop(fqs_task);
    }
    fqs_task = NULL;
    if ((test_boost == 1 && cur_ops->can_boost) ||
        test_boost == 2) {
        unregister_cpu_notifier(&rcutorture_cpu_nb);
        for_each_possible_cpu(i)
            rcutorture_booster_cleanup(i);
    }
    if (shutdown_task != NULL) {
        VERBOSE_PRINTK_STRING("Stopping rcu_torture_shutdown task");
        kthread_stop(shutdown_task);
    }
    shutdown_task = NULL;
    rcu_torture_onoff_cleanup();

    /* 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) || n_rcu_torture_barrier_error)
        rcu_torture_print_module_parms(cur_ops, "End of test: FAILURE");
    else if (n_online_successes != n_online_attempts ||
         n_offline_successes != n_offline_attempts)
        rcu_torture_print_module_parms(cur_ops,
                           "End of test: RCU_HOTPLUG");
    else
        rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
}

static int __init
rcu_torture_init(void)
{
    int i;
    int cpu;
    int firsterr = 0;
    int retval;
    static struct rcu_torture_ops *torture_ops[] =
        { &rcu_ops, &rcu_sync_ops, &rcu_expedited_ops,
          &rcu_bh_ops, &rcu_bh_sync_ops, &rcu_bh_expedited_ops,
          &srcu_ops, &srcu_sync_ops, &srcu_expedited_ops,
          &srcu_raw_ops, &srcu_raw_sync_ops,
          &sched_ops, &sched_sync_ops, &sched_expedited_ops, };

    mutex_lock(&fullstop_mutex);

    /* 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)) {
        pr_alert("rcu-torture: invalid torture type: \"%s\"\n",
             torture_type);
        pr_alert("rcu-torture types:");
        for (i = 0; i < ARRAY_SIZE(torture_ops); i++)
            pr_alert(" %s", torture_ops[i]->name);
        pr_alert("\n");
        mutex_unlock(&fullstop_mutex);
        return -EINVAL;
    }
    if (cur_ops->fqs == NULL && fqs_duration != 0) {
        pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n");
        fqs_duration = 0;
    }
    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(cur_ops, "Start of test");
    fullstop = FULLSTOP_DONTSTOP;

    /* 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);
    n_rcu_torture_barrier_error = 0;
    n_rcu_torture_boost_ktrerror = 0;
    n_rcu_torture_boost_rterror = 0;
    n_rcu_torture_boost_failure = 0;
    n_rcu_torture_boosts = 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_create(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;
    }
    wake_up_process(writer_task);
    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;

        if (!alloc_cpumask_var(&shuffle_tmp_mask, GFP_KERNEL)) {
            firsterr = -ENOMEM;
            VERBOSE_PRINTK_ERRSTRING("Failed to alloc mask");
            goto unwind;
        }

        /* Create the shuffler thread */
        shuffler_task = kthread_run(rcu_torture_shuffle, NULL,
                      "rcu_torture_shuffle");
        if (IS_ERR(shuffler_task)) {
            free_cpumask_var(shuffle_tmp_mask);
            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;
        }
    }
    if (fqs_duration < 0)
        fqs_duration = 0;
    if (fqs_duration) {
        /* Create the stutter thread */
        fqs_task = kthread_run(rcu_torture_fqs, NULL,
                       "rcu_torture_fqs");
        if (IS_ERR(fqs_task)) {
            firsterr = PTR_ERR(fqs_task);
            VERBOSE_PRINTK_ERRSTRING("Failed to create fqs");
            fqs_task = NULL;
            goto unwind;
        }
    }
    if (test_boost_interval < 1)
        test_boost_interval = 1;
    if (test_boost_duration < 2)
        test_boost_duration = 2;
    if ((test_boost == 1 && cur_ops->can_boost) ||
        test_boost == 2) {

        boost_starttime = jiffies + test_boost_interval * HZ;
        register_cpu_notifier(&rcutorture_cpu_nb);
        for_each_possible_cpu(i) {
            if (cpu_is_offline(i))
                continue;  /* Heuristic: CPU can go offline. */
            retval = rcutorture_booster_init(i);
            if (retval < 0) {
                firsterr = retval;
                goto unwind;
            }
        }
    }
    if (shutdown_secs > 0) {
        shutdown_time = jiffies + shutdown_secs * HZ;
        shutdown_task = kthread_create(rcu_torture_shutdown, NULL,
                           "rcu_torture_shutdown");
        if (IS_ERR(shutdown_task)) {
            firsterr = PTR_ERR(shutdown_task);
            VERBOSE_PRINTK_ERRSTRING("Failed to create shutdown");
            shutdown_task = NULL;
            goto unwind;
        }
        wake_up_process(shutdown_task);
    }
    i = rcu_torture_onoff_init();
    if (i != 0) {
        firsterr = i;
        goto unwind;
    }
    register_reboot_notifier(&rcutorture_shutdown_nb);
    i = rcu_torture_stall_init();
    if (i != 0) {
        firsterr = i;
        goto unwind;
    }
    retval = rcu_torture_barrier_init();
    if (retval != 0) {
        firsterr = retval;
        goto unwind;
    }
    rcutorture_record_test_transition();
    mutex_unlock(&fullstop_mutex);
    return 0;

unwind:
    mutex_unlock(&fullstop_mutex);
    rcu_torture_cleanup();
    return firsterr;
}

module_init(rcu_torture_init);
module_exit(rcu_torture_cleanup);