/*
 * 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 <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 <linux/trace_clock.h>
#include <asm/byteorder.h>

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

static int fqs_duration;
module_param(fqs_duration, int, 0444);
MODULE_PARM_DESC(fqs_duration, "Duration of fqs bursts (us), 0 to disable");
static int fqs_holdoff;
module_param(fqs_holdoff, int, 0444);
MODULE_PARM_DESC(fqs_holdoff, "Holdoff time within fqs bursts (us)");
static int fqs_stutter = 3;
module_param(fqs_stutter, int, 0444);
MODULE_PARM_DESC(fqs_stutter, "Wait time between fqs bursts (s)");
static bool gp_exp;
module_param(gp_exp, bool, 0444);
MODULE_PARM_DESC(gp_exp, "Use expedited GP wait primitives");
static bool gp_normal;
module_param(gp_normal, bool, 0444);
MODULE_PARM_DESC(gp_normal, "Use normal (non-expedited) GP wait primitives");
static int irqreader = 1;
module_param(irqreader, int, 0444);
MODULE_PARM_DESC(irqreader, "Allow RCU readers from irq handlers");
static int n_barrier_cbs;
module_param(n_barrier_cbs, int, 0444);
MODULE_PARM_DESC(n_barrier_cbs, "# of callbacks/kthreads for barrier testing");
static int nfakewriters = 4;
module_param(nfakewriters, int, 0444);
MODULE_PARM_DESC(nfakewriters, "Number of RCU fake writer threads");
static int nreaders = -1;
module_param(nreaders, int, 0444);
MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");
static int object_debug;
module_param(object_debug, int, 0444);
MODULE_PARM_DESC(object_debug, "Enable debug-object double call_rcu() testing");
static int onoff_holdoff;
module_param(onoff_holdoff, int, 0444);
MODULE_PARM_DESC(onoff_holdoff, "Time after boot before CPU hotplugs (s)");
static int onoff_interval;
module_param(onoff_interval, int, 0444);
MODULE_PARM_DESC(onoff_interval, "Time between CPU hotplugs (s), 0=disable");
static int shuffle_interval = 3;
module_param(shuffle_interval, int, 0444);
MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");
static int shutdown_secs;
module_param(shutdown_secs, int, 0444);
MODULE_PARM_DESC(shutdown_secs, "Shutdown time (s), <= zero to disable.");
static int stall_cpu;
module_param(stall_cpu, int, 0444);
MODULE_PARM_DESC(stall_cpu, "Stall duration (s), zero to disable.");
static int stall_cpu_holdoff = 10;
module_param(stall_cpu_holdoff, int, 0444);
MODULE_PARM_DESC(stall_cpu_holdoff, "Time to wait before starting stall (s).");
static int stat_interval = 60;
module_param(stat_interval, int, 0644);
MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");
static int stutter = 5;
module_param(stutter, int, 0444);
MODULE_PARM_DESC(stutter, "Number of seconds to run/halt test");
static int test_boost = 1;
module_param(test_boost, int, 0444);
MODULE_PARM_DESC(test_boost, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
static int test_boost_duration = 4;
module_param(test_boost_duration, int, 0444);
MODULE_PARM_DESC(test_boost_duration, "Duration of each boost test, seconds.");
static int test_boost_interval = 7;
module_param(test_boost_interval, int, 0444);
MODULE_PARM_DESC(test_boost_interval, "Interval between boost tests, seconds.");
static bool test_no_idle_hz = true;
module_param(test_no_idle_hz, bool, 0444);
MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");
static char *torture_type = "rcu";
module_param(torture_type, charp, 0444);
MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, ...)");
static bool verbose;
module_param(verbose, bool, 0444);
MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");

#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) */

#ifdef CONFIG_RCU_TRACE
static u64 notrace rcu_trace_clock_local(void)
{
        u64 ts = trace_clock_local();
        unsigned long __maybe_unused ts_rem = do_div(ts, NSEC_PER_USEC);
        return ts;
}
#else /* #ifdef CONFIG_RCU_TRACE */
static u64 notrace rcu_trace_clock_local(void)
{
        return 0ULL;
}
#endif /* #else #ifdef CONFIG_RCU_TRACE */

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(const 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(const 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);
        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 (*exp_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;
        const 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 void rcu_sync_torture_init(void)
{
        INIT_LIST_HEAD(&rcu_torture_removed);
}

static struct rcu_torture_ops rcu_ops = {
        .init           = rcu_sync_torture_init,
        .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,
        .exp_sync       = synchronize_rcu_expedited,
        .call           = call_rcu,
        .cb_barrier     = rcu_barrier,
        .fqs            = rcu_force_quiescent_state,
        .stats          = NULL,
        .irq_capable    = 1,
        .can_boost      = rcu_can_boost(),
        .name           = "rcu"
};

/*
 * 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           = rcu_sync_torture_init,
        .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,
        .exp_sync       = synchronize_rcu_bh_expedited,
        .call           = call_rcu_bh,
        .cb_barrier     = rcu_barrier_bh,
        .fqs            = rcu_bh_force_quiescent_state,
        .stats          = NULL,
        .irq_capable    = 1,
        .name           = "rcu_bh"
};

/*
 * Definitions for srcu torture testing.
 */

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

static struct rcu_torture_ops srcu_ops = {
        .init           = rcu_sync_torture_init,
        .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,
        .exp_sync       = srcu_torture_synchronize_expedited,
        .call           = srcu_torture_call,
        .cb_barrier     = srcu_torture_barrier,
        .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 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,
        .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,
        .exp_sync       = synchronize_sched_expedited,
        .call           = call_rcu_sched,
        .cb_barrier     = rcu_barrier_sched,
        .fqs            = rcu_sched_force_quiescent_state,
        .stats          = NULL,
        .irq_capable    = 1,
        .name           = "sched"
};

/*
 * 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_interruptible(oldstarttime - jiffies);
                        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)
{
        bool exp;
        int i;
        struct rcu_torture *rp;
        struct rcu_torture *rp1;
        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++;
                        if (gp_normal == gp_exp)
                                exp = !!(rcu_random(&rand) & 0x80);
                        else
                                exp = gp_exp;
                        if (!exp) {
                                cur_ops->deferred_free(old_rp);
                        } else {
                                cur_ops->exp_sync();
                                list_add(&old_rp->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);
                                        }
                                 }
                        }
                }
                rcutorture_record_progress(++rcu_torture_current_version);
                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 if (gp_normal == gp_exp) {
                        if (rcu_random(&rand) & 0x80)
                                cur_ops->sync();
                        else
                                cur_ops->exp_sync();
                } else if (gp_normal) {
                        cur_ops->sync();
                } else {
                        cur_ops->exp_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;
        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;
        int completed_end;
        static DEFINE_RCU_RANDOM(rand);
        static DEFINE_SPINLOCK(rand_lock);
        struct rcu_torture *p;
        int pipe_count;
        unsigned long long ts;

        idx = cur_ops->readlock();
        completed = cur_ops->completed();
        ts = rcu_trace_clock_local();
        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;
        }
        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;
        }
        completed_end = cur_ops->completed();
        if (pipe_count > 1) {
                do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu, ts,
                                          completed, completed_end);
                rcutorture_trace_dump();
        }
        __this_cpu_inc(rcu_torture_count[pipe_count]);
        completed = completed_end - 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 completed_end;
        int idx;
        DEFINE_RCU_RANDOM(rand);
        struct rcu_torture *p;
        int pipe_count;
        struct timer_list t;
        unsigned long long ts;

        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();
                ts = rcu_trace_clock_local();
                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;
                }
                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;
                }
                completed_end = cur_ops->completed();
                if (pipe_count > 1) {
                        do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu,
                                                  ts, completed, completed_end);
                        rcutorture_trace_dump();
                }
                __this_cpu_inc(rcu_torture_count[pipe_count]);
                completed = completed_end - 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 (stutter_task)
                set_cpus_allowed_ptr(stutter_task, shuffle_tmp_mask);
        if (fqs_task)
                set_cpus_allowed_ptr(fqs_task, shuffle_tmp_mask);
        if (shutdown_task)
                set_cpus_allowed_ptr(shutdown_task, shuffle_tmp_mask);
#ifdef CONFIG_HOTPLUG_CPU
        if (onoff_task)
                set_cpus_allowed_ptr(onoff_task, shuffle_tmp_mask);
#endif /* #ifdef CONFIG_HOTPLUG_CPU */
        if (stall_task)
                set_cpus_allowed_ptr(stall_task, shuffle_tmp_mask);
        if (barrier_cbs_tasks)
                for (i = 0; i < n_barrier_cbs; i++)
                        if (barrier_cbs_tasks[i])
                                set_cpus_allowed_ptr(barrier_cbs_tasks[i],
                                                     shuffle_tmp_mask);
        if (barrier_task)
                set_cpus_allowed_ptr(barrier_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, const 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 "
                 "stall_cpu=%d stall_cpu_holdoff=%d "
                 "n_barrier_cbs=%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,
                 stall_cpu, stall_cpu_holdoff,
                 n_barrier_cbs,
                 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
rcu_torture_onoff(void *arg)
{
        int cpu;
        unsigned long delta;
        int maxcpu = -1;
        DEFINE_RCU_RANDOM(rand);
        int ret;
        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++;
                        ret = cpu_down(cpu);
                        if (ret) {
                                if (verbose)
                                        pr_alert("%s" TORTURE_FLAG
                                                 "rcu_torture_onoff task: offline %d failed: errno %d\n",
                                                 torture_type, cpu, ret);
                        } else {
                                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++;
                        ret = cpu_up(cpu);
                        if (ret) {
                                if (verbose)
                                        pr_alert("%s" TORTURE_FLAG
                                                 "rcu_torture_onoff task: online %d failed: errno %d\n",
                                                 torture_type, cpu, ret);
                        } else {
                                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
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 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)
                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 (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");
}

#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
static void rcu_torture_leak_cb(struct rcu_head *rhp)
{
}

static void rcu_torture_err_cb(struct rcu_head *rhp)
{
        /*
         * This -might- happen due to race conditions, but is unlikely.
         * The scenario that leads to this happening is that the
         * first of the pair of duplicate callbacks is queued,
         * someone else starts a grace period that includes that
         * callback, then the second of the pair must wait for the
         * next grace period.  Unlikely, but can happen.  If it
         * does happen, the debug-objects subsystem won't have splatted.
         */
        pr_alert("rcutorture: duplicated callback was invoked.\n");
}
#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */

/*
 * Verify that double-free causes debug-objects to complain, but only
 * if CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.  Otherwise, say that the test
 * cannot be carried out.
 */
static void rcu_test_debug_objects(void)
{
#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
        struct rcu_head rh1;
        struct rcu_head rh2;

        init_rcu_head_on_stack(&rh1);
        init_rcu_head_on_stack(&rh2);
        pr_alert("rcutorture: WARN: Duplicate call_rcu() test starting.\n");

        /* Try to queue the rh2 pair of callbacks for the same grace period. */
        preempt_disable(); /* Prevent preemption from interrupting test. */
        rcu_read_lock(); /* Make it impossible to finish a grace period. */
        call_rcu(&rh1, rcu_torture_leak_cb); /* Start grace period. */
        local_irq_disable(); /* Make it harder to start a new grace period. */
        call_rcu(&rh2, rcu_torture_leak_cb);
        call_rcu(&rh2, rcu_torture_err_cb); /* Duplicate callback. */
        local_irq_enable();
        rcu_read_unlock();
        preempt_enable();

        /* Wait for them all to get done so we can safely return. */
        rcu_barrier();
        pr_alert("rcutorture: WARN: Duplicate call_rcu() test complete.\n");
        destroy_rcu_head_on_stack(&rh1);
        destroy_rcu_head_on_stack(&rh2);
#else /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
        pr_alert("rcutorture: !CONFIG_DEBUG_OBJECTS_RCU_HEAD, not testing duplicate call_rcu()\n");
#endif /* #else #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
}

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_bh_ops, &srcu_ops, &sched_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;
        }
        if (object_debug)
                rcu_test_debug_objects();
        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);