uapi: Remove kernel internal declaration

[deliverable/linux.git] / kernel / rcu / rcutorture.c

/*
 * 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, you can access it online at
 * http://www.gnu.org/licenses/gpl-2.0.html.
 *
 * Copyright (C) IBM Corporation, 2005, 2006
 *
 * Authors: Paul E. McKenney <paulmck@us.ibm.com>
 *        Josh Triplett <josh@joshtriplett.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>
#include <linux/torture.h>
#include <linux/vmalloc.h>

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


torture_param(int, cbflood_inter_holdoff, HZ,
              "Holdoff between floods (jiffies)");
torture_param(int, cbflood_intra_holdoff, 1,
              "Holdoff between bursts (jiffies)");
torture_param(int, cbflood_n_burst, 3, "# bursts in flood, zero to disable");
torture_param(int, cbflood_n_per_burst, 20000,
              "# callbacks per burst in flood");
torture_param(int, fqs_duration, 0,
              "Duration of fqs bursts (us), 0 to disable");
torture_param(int, fqs_holdoff, 0, "Holdoff time within fqs bursts (us)");
torture_param(int, fqs_stutter, 3, "Wait time between fqs bursts (s)");
torture_param(bool, gp_cond, false, "Use conditional/async GP wait primitives");
torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
torture_param(bool, gp_normal, false,
             "Use normal (non-expedited) GP wait primitives");
torture_param(bool, gp_sync, false, "Use synchronous GP wait primitives");
torture_param(int, irqreader, 1, "Allow RCU readers from irq handlers");
torture_param(int, n_barrier_cbs, 0,
             "# of callbacks/kthreads for barrier testing");
torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads");
torture_param(int, nreaders, -1, "Number of RCU reader threads");
torture_param(int, object_debug, 0,
             "Enable debug-object double call_rcu() testing");
torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)");
torture_param(int, onoff_interval, 0,
             "Time between CPU hotplugs (s), 0=disable");
torture_param(int, shuffle_interval, 3, "Number of seconds between shuffles");
torture_param(int, shutdown_secs, 0, "Shutdown time (s), <= zero to disable.");
torture_param(int, stall_cpu, 0, "Stall duration (s), zero to disable.");
torture_param(int, stall_cpu_holdoff, 10,
             "Time to wait before starting stall (s).");
torture_param(int, stat_interval, 60,
             "Number of seconds between stats printk()s");
torture_param(int, stutter, 5, "Number of seconds to run/halt test");
torture_param(int, test_boost, 1, "Test RCU prio boost: 0=no, 1=maybe, 2=yes.");
torture_param(int, test_boost_duration, 4,
             "Duration of each boost test, seconds.");
torture_param(int, test_boost_interval, 7,
             "Interval between boost tests, seconds.");
torture_param(bool, test_no_idle_hz, true,
             "Test support for tickless idle CPUs");
torture_param(bool, verbose, true,
             "Enable verbose debugging printk()s");

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 int nrealreaders;
static int ncbflooders;
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 **cbflood_task;
static struct task_struct *fqs_task;
static struct task_struct *boost_tasks[NR_CPUS];
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_barrier_attempts;
static long n_barrier_successes;
static atomic_long_t n_cbfloods;
static struct list_head rcu_torture_removed;

static int rcu_torture_writer_state;
#define RTWS_FIXED_DELAY        0
#define RTWS_DELAY              1
#define RTWS_REPLACE            2
#define RTWS_DEF_FREE           3
#define RTWS_EXP_SYNC           4
#define RTWS_COND_GET           5
#define RTWS_COND_SYNC          6
#define RTWS_SYNC               7
#define RTWS_STUTTER            8
#define RTWS_STOPPING           9

#if defined(MODULE) || defined(CONFIG_RCU_TORTURE_TEST_RUNNABLE)
#define RCUTORTURE_RUNNABLE_INIT 1
#else
#define RCUTORTURE_RUNNABLE_INIT 0
#endif
static int torture_runnable = RCUTORTURE_RUNNABLE_INIT;
module_param(torture_runnable, int, 0444);
MODULE_PARM_DESC(torture_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 boost_starttime;   /* jiffies of next boost test start. */
static 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);

/*
 * 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);
}

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

struct rcu_torture_ops {
        int ttype;
        void (*init)(void);
        int (*readlock)(void);
        void (*read_delay)(struct torture_random_state *rrsp);
        void (*readunlock)(int idx);
        unsigned long (*started)(void);
        unsigned long (*completed)(void);
        void (*deferred_free)(struct rcu_torture *p);
        void (*sync)(void);
        void (*exp_sync)(void);
        unsigned long (*get_state)(void);
        void (*cond_sync)(unsigned long oldstate);
        void (*call)(struct rcu_head *head, void (*func)(struct rcu_head *rcu));
        void (*cb_barrier)(void);
        void (*fqs)(void);
        void (*stats)(void);
        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 torture_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 (!(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms)))
                mdelay(longdelay_ms);
        if (!(torture_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
                udelay(shortdelay_us);
#ifdef CONFIG_PREEMPT
        if (!preempt_count() &&
            !(torture_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();
}

/*
 * Update callback in the pipe.  This should be invoked after a grace period.
 */
static bool
rcu_torture_pipe_update_one(struct rcu_torture *rp)
{
        int i;

        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;
                return true;
        }
        return false;
}

/*
 * Update all callbacks in the pipe.  Suitable for synchronous grace-period
 * primitives.
 */
static void
rcu_torture_pipe_update(struct rcu_torture *old_rp)
{
        struct rcu_torture *rp;
        struct rcu_torture *rp1;

        if (old_rp)
                list_add(&old_rp->rtort_free, &rcu_torture_removed);
        list_for_each_entry_safe(rp, rp1, &rcu_torture_removed, rtort_free) {
                if (rcu_torture_pipe_update_one(rp)) {
                        list_del(&rp->rtort_free);
                        rcu_torture_free(rp);
                }
        }
}

static void
rcu_torture_cb(struct rcu_head *p)
{
        struct rcu_torture *rp = container_of(p, struct rcu_torture, rtort_rcu);

        if (torture_must_stop_irq()) {
                /* Test is ending, just drop callbacks on the floor. */
                /* The next initialization will pick up the pieces. */
                return;
        }
        if (rcu_torture_pipe_update_one(rp))
                rcu_torture_free(rp);
        else
                cur_ops->deferred_free(rp);
}

static unsigned long 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 = {
        .ttype          = RCU_FLAVOR,
        .init           = rcu_sync_torture_init,
        .readlock       = rcu_torture_read_lock,
        .read_delay     = rcu_read_delay,
        .readunlock     = rcu_torture_read_unlock,
        .started        = rcu_batches_started,
        .completed      = rcu_batches_completed,
        .deferred_free  = rcu_torture_deferred_free,
        .sync           = synchronize_rcu,
        .exp_sync       = synchronize_rcu_expedited,
        .get_state      = get_state_synchronize_rcu,
        .cond_sync      = cond_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"
};

/*
 * 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 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 = {
        .ttype          = RCU_BH_FLAVOR,
        .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,
        .started        = rcu_batches_started_bh,
        .completed      = rcu_batches_completed_bh,
        .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"
};

/*
 * Don't even think about trying any of these in real life!!!
 * The names includes "busted", and they really means it!
 * The only purpose of these functions is to provide a buggy RCU
 * implementation to make sure that rcutorture correctly emits
 * buggy-RCU error messages.
 */
static void rcu_busted_torture_deferred_free(struct rcu_torture *p)
{
        /* This is a deliberate bug for testing purposes only! */
        rcu_torture_cb(&p->rtort_rcu);
}

static void synchronize_rcu_busted(void)
{
        /* This is a deliberate bug for testing purposes only! */
}

static void
call_rcu_busted(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
{
        /* This is a deliberate bug for testing purposes only! */
        func(head);
}

static struct rcu_torture_ops rcu_busted_ops = {
        .ttype          = INVALID_RCU_FLAVOR,
        .init           = rcu_sync_torture_init,
        .readlock       = rcu_torture_read_lock,
        .read_delay     = rcu_read_delay,  /* just reuse rcu's version. */
        .readunlock     = rcu_torture_read_unlock,
        .started        = rcu_no_completed,
        .completed      = rcu_no_completed,
        .deferred_free  = rcu_busted_torture_deferred_free,
        .sync           = synchronize_rcu_busted,
        .exp_sync       = synchronize_rcu_busted,
        .call           = call_rcu_busted,
        .cb_barrier     = NULL,
        .fqs            = NULL,
        .stats          = NULL,
        .irq_capable    = 1,
        .name           = "rcu_busted"
};

/*
 * 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 torture_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 = torture_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 unsigned long 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 void srcu_torture_stats(void)
{
        int cpu;
        int idx = srcu_ctl.completed & 0x1;

        pr_alert("%s%s per-CPU(idx=%d):",
                 torture_type, TORTURE_FLAG, idx);
        for_each_possible_cpu(cpu) {
                long c0, c1;

                c0 = (long)per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx];
                c1 = (long)per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx];
                pr_cont(" %d(%ld,%ld)", cpu, c0, c1);
        }
        pr_cont("\n");
}

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

static struct rcu_torture_ops srcu_ops = {
        .ttype          = SRCU_FLAVOR,
        .init           = rcu_sync_torture_init,
        .readlock       = srcu_torture_read_lock,
        .read_delay     = srcu_read_delay,
        .readunlock     = srcu_torture_read_unlock,
        .started        = NULL,
        .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 = {
        .ttype          = RCU_SCHED_FLAVOR,
        .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,
        .started        = rcu_batches_started_sched,
        .completed      = rcu_batches_completed_sched,
        .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"
};

#ifdef CONFIG_TASKS_RCU

/*
 * Definitions for RCU-tasks torture testing.
 */

static int tasks_torture_read_lock(void)
{
        return 0;
}

static void tasks_torture_read_unlock(int idx)
{
}

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

static struct rcu_torture_ops tasks_ops = {
        .ttype          = RCU_TASKS_FLAVOR,
        .init           = rcu_sync_torture_init,
        .readlock       = tasks_torture_read_lock,
        .read_delay     = rcu_read_delay,  /* just reuse rcu's version. */
        .readunlock     = tasks_torture_read_unlock,
        .started        = rcu_no_completed,
        .completed      = rcu_no_completed,
        .deferred_free  = rcu_tasks_torture_deferred_free,
        .sync           = synchronize_rcu_tasks,
        .exp_sync       = synchronize_rcu_tasks,
        .call           = call_rcu_tasks,
        .cb_barrier     = rcu_barrier_tasks,
        .fqs            = NULL,
        .stats          = NULL,
        .irq_capable    = 1,
        .name           = "tasks"
};

#define RCUTORTURE_TASKS_OPS &tasks_ops,

#else /* #ifdef CONFIG_TASKS_RCU */

#define RCUTORTURE_TASKS_OPS

#endif /* #else #ifdef CONFIG_TASKS_RCU */

/*
 * 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_TOROUT_STRING("rcu_torture_boost started");

        /* Set real-time priority. */
        sp.sched_priority = 1;
        if (sched_setscheduler(current, SCHED_FIFO, &sp) < 0) {
                VERBOSE_TOROUT_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);
                        stutter_wait("rcu_torture_boost");
                        if (torture_must_stop())
                                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_TOROUT_STRING("rcu_torture_boost boosting failed");
                                        n_rcu_torture_boost_failure++;
                                }
                                call_rcu_time = jiffies;
                        }
                        cond_resched_rcu_qs();
                        stutter_wait("rcu_torture_boost");
                        if (torture_must_stop())
                                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:      stutter_wait("rcu_torture_boost");
        } while (!torture_must_stop());

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

static void rcu_torture_cbflood_cb(struct rcu_head *rhp)
{
}

/*
 * RCU torture callback-flood kthread.  Repeatedly induces bursts of calls
 * to call_rcu() or analogous, increasing the probability of occurrence
 * of callback-overflow corner cases.
 */
static int
rcu_torture_cbflood(void *arg)
{
        int err = 1;
        int i;
        int j;
        struct rcu_head *rhp;

        if (cbflood_n_per_burst > 0 &&
            cbflood_inter_holdoff > 0 &&
            cbflood_intra_holdoff > 0 &&
            cur_ops->call &&
            cur_ops->cb_barrier) {
                rhp = vmalloc(sizeof(*rhp) *
                              cbflood_n_burst * cbflood_n_per_burst);
                err = !rhp;
        }
        if (err) {
                VERBOSE_TOROUT_STRING("rcu_torture_cbflood disabled: Bad args or OOM");
                while (!torture_must_stop())
                        schedule_timeout_interruptible(HZ);
                return 0;
        }
        VERBOSE_TOROUT_STRING("rcu_torture_cbflood task started");
        do {
                schedule_timeout_interruptible(cbflood_inter_holdoff);
                atomic_long_inc(&n_cbfloods);
                WARN_ON(signal_pending(current));
                for (i = 0; i < cbflood_n_burst; i++) {
                        for (j = 0; j < cbflood_n_per_burst; j++) {
                                cur_ops->call(&rhp[i * cbflood_n_per_burst + j],
                                              rcu_torture_cbflood_cb);
                        }
                        schedule_timeout_interruptible(cbflood_intra_holdoff);
                        WARN_ON(signal_pending(current));
                }
                cur_ops->cb_barrier();
                stutter_wait("rcu_torture_cbflood");
        } while (!torture_must_stop());
        vfree(rhp);
        torture_kthread_stopping("rcu_torture_cbflood");
        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_TOROUT_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;
                }
                stutter_wait("rcu_torture_fqs");
        } while (!torture_must_stop());
        torture_kthread_stopping("rcu_torture_fqs");
        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)
{
        unsigned long gp_snap;
        bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal;
        bool gp_sync1 = gp_sync;
        int i;
        struct rcu_torture *rp;
        struct rcu_torture *old_rp;
        static DEFINE_TORTURE_RANDOM(rand);
        int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC,
                           RTWS_COND_GET, RTWS_SYNC };
        int nsynctypes = 0;

        VERBOSE_TOROUT_STRING("rcu_torture_writer task started");

        /* Initialize synctype[] array.  If none set, take default. */
        if (!gp_cond1 && !gp_exp1 && !gp_normal1 && !gp_sync)
                gp_cond1 = gp_exp1 = gp_normal1 = gp_sync1 = true;
        if (gp_cond1 && cur_ops->get_state && cur_ops->cond_sync)
                synctype[nsynctypes++] = RTWS_COND_GET;
        else if (gp_cond && (!cur_ops->get_state || !cur_ops->cond_sync))
                pr_alert("rcu_torture_writer: gp_cond without primitives.\n");
        if (gp_exp1 && cur_ops->exp_sync)
                synctype[nsynctypes++] = RTWS_EXP_SYNC;
        else if (gp_exp && !cur_ops->exp_sync)
                pr_alert("rcu_torture_writer: gp_exp without primitives.\n");
        if (gp_normal1 && cur_ops->deferred_free)
                synctype[nsynctypes++] = RTWS_DEF_FREE;
        else if (gp_normal && !cur_ops->deferred_free)
                pr_alert("rcu_torture_writer: gp_normal without primitives.\n");
        if (gp_sync1 && cur_ops->sync)
                synctype[nsynctypes++] = RTWS_SYNC;
        else if (gp_sync && !cur_ops->sync)
                pr_alert("rcu_torture_writer: gp_sync without primitives.\n");
        if (WARN_ONCE(nsynctypes == 0,
                      "rcu_torture_writer: No update-side primitives.\n")) {
                /*
                 * No updates primitives, so don't try updating.
                 * The resulting test won't be testing much, hence the
                 * above WARN_ONCE().
                 */
                rcu_torture_writer_state = RTWS_STOPPING;
                torture_kthread_stopping("rcu_torture_writer");
        }

        do {
                rcu_torture_writer_state = RTWS_FIXED_DELAY;
                schedule_timeout_uninterruptible(1);
                rp = rcu_torture_alloc();
                if (rp == NULL)
                        continue;
                rp->rtort_pipe_count = 0;
                rcu_torture_writer_state = RTWS_DELAY;
                udelay(torture_random(&rand) & 0x3ff);
                rcu_torture_writer_state = RTWS_REPLACE;
                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++;
                        switch (synctype[torture_random(&rand) % nsynctypes]) {
                        case RTWS_DEF_FREE:
                                rcu_torture_writer_state = RTWS_DEF_FREE;
                                cur_ops->deferred_free(old_rp);
                                break;
                        case RTWS_EXP_SYNC:
                                rcu_torture_writer_state = RTWS_EXP_SYNC;
                                cur_ops->exp_sync();
                                rcu_torture_pipe_update(old_rp);
                                break;
                        case RTWS_COND_GET:
                                rcu_torture_writer_state = RTWS_COND_GET;
                                gp_snap = cur_ops->get_state();
                                i = torture_random(&rand) % 16;
                                if (i != 0)
                                        schedule_timeout_interruptible(i);
                                udelay(torture_random(&rand) % 1000);
                                rcu_torture_writer_state = RTWS_COND_SYNC;
                                cur_ops->cond_sync(gp_snap);
                                rcu_torture_pipe_update(old_rp);
                                break;
                        case RTWS_SYNC:
                                rcu_torture_writer_state = RTWS_SYNC;
                                cur_ops->sync();
                                rcu_torture_pipe_update(old_rp);
                                break;
                        default:
                                WARN_ON_ONCE(1);
                                break;
                        }
                }
                rcutorture_record_progress(++rcu_torture_current_version);
                rcu_torture_writer_state = RTWS_STUTTER;
                stutter_wait("rcu_torture_writer");
        } while (!torture_must_stop());
        rcu_torture_writer_state = RTWS_STOPPING;
        torture_kthread_stopping("rcu_torture_writer");
        return 0;
}

/*
 * RCU torture fake writer kthread.  Repeatedly calls sync, with a random
 * delay between calls.
 */
static int
rcu_torture_fakewriter(void *arg)
{
        DEFINE_TORTURE_RANDOM(rand);

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

        do {
                schedule_timeout_uninterruptible(1 + torture_random(&rand)%10);
                udelay(torture_random(&rand) & 0x3ff);
                if (cur_ops->cb_barrier != NULL &&
                    torture_random(&rand) % (nfakewriters * 8) == 0) {
                        cur_ops->cb_barrier();
                } else if (gp_normal == gp_exp) {
                        if (torture_random(&rand) & 0x80)
                                cur_ops->sync();
                        else
                                cur_ops->exp_sync();
                } else if (gp_normal) {
                        cur_ops->sync();
                } else {
                        cur_ops->exp_sync();
                }
                stutter_wait("rcu_torture_fakewriter");
        } while (!torture_must_stop());

        torture_kthread_stopping("rcu_torture_fakewriter");
        return 0;
}

static 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;
        unsigned long started;
        unsigned long completed;
        static DEFINE_TORTURE_RANDOM(rand);
        static DEFINE_SPINLOCK(rand_lock);
        struct rcu_torture *p;
        int pipe_count;
        unsigned long long ts;

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

        VERBOSE_TOROUT_STRING("rcu_torture_reader task started");
        set_user_nice(current, MAX_NICE);
        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();
                if (cur_ops->started)
                        started = cur_ops->started();
                else
                        started = 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 = cur_ops->completed();
                if (pipe_count > 1) {
                        do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu,
                                                  ts, started, completed);
                        rcutorture_trace_dump();
                }
                __this_cpu_inc(rcu_torture_count[pipe_count]);
                completed = completed - started;
                if (cur_ops->started)
                        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);
                cond_resched_rcu_qs();
                stutter_wait("rcu_torture_reader");
        } while (!torture_must_stop());
        if (irqreader && cur_ops->irq_capable) {
                del_timer_sync(&t);
                destroy_timer_on_stack(&t);
        }
        torture_kthread_stopping("rcu_torture_reader");
        return 0;
}

/*
 * 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 cpu;
        int i;
        long pipesummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
        long batchsummary[RCU_TORTURE_PIPE_LEN + 1] = { 0 };
        static unsigned long rtcv_snap = ULONG_MAX;

        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;
        }

        pr_alert("%s%s ", torture_type, TORTURE_FLAG);
        pr_cont("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));
        pr_cont("rtmbe: %d rtbke: %ld rtbre: %ld ",
                atomic_read(&n_rcu_torture_mberror),
                n_rcu_torture_boost_ktrerror,
                n_rcu_torture_boost_rterror);
        pr_cont("rtbf: %ld rtb: %ld nt: %ld ",
                n_rcu_torture_boost_failure,
                n_rcu_torture_boosts,
                n_rcu_torture_timers);
        torture_onoff_stats();
        pr_cont("barrier: %ld/%ld:%ld ",
                n_barrier_successes,
                n_barrier_attempts,
                n_rcu_torture_barrier_error);
        pr_cont("cbflood: %ld\n", atomic_long_read(&n_cbfloods));

        pr_alert("%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) {
                pr_cont("%s", "!!! ");
                atomic_inc(&n_rcu_torture_error);
                WARN_ON_ONCE(1);
        }
        pr_cont("Reader Pipe: ");
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
                pr_cont(" %ld", pipesummary[i]);
        pr_cont("\n");

        pr_alert("%s%s ", torture_type, TORTURE_FLAG);
        pr_cont("Reader Batch: ");
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
                pr_cont(" %ld", batchsummary[i]);
        pr_cont("\n");

        pr_alert("%s%s ", torture_type, TORTURE_FLAG);
        pr_cont("Free-Block Circulation: ");
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
                pr_cont(" %d", atomic_read(&rcu_torture_wcount[i]));
        }
        pr_cont("\n");

        if (cur_ops->stats)
                cur_ops->stats();
        if (rtcv_snap == rcu_torture_current_version &&
            rcu_torture_current != NULL) {
                int __maybe_unused flags;
                unsigned long __maybe_unused gpnum;
                unsigned long __maybe_unused completed;

                rcutorture_get_gp_data(cur_ops->ttype,
                                       &flags, &gpnum, &completed);
                pr_alert("??? Writer stall state %d g%lu c%lu f%#x\n",
                         rcu_torture_writer_state,
                         gpnum, completed, flags);
                show_rcu_gp_kthreads();
                rcutorture_trace_dump();
        }
        rtcv_snap = rcu_torture_current_version;
}

/*
 * Periodically prints torture statistics, if periodic statistics printing
 * was specified via the stat_interval module parameter.
 */
static int
rcu_torture_stats(void *arg)
{
        VERBOSE_TOROUT_STRING("rcu_torture_stats task started");
        do {
                schedule_timeout_interruptible(stat_interval * HZ);
                rcu_torture_stats_print();
                torture_shutdown_absorb("rcu_torture_stats");
        } while (!torture_must_stop());
        torture_kthread_stopping("rcu_torture_stats");
        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 void rcutorture_booster_cleanup(int cpu)
{
        struct task_struct *t;

        if (boost_tasks[cpu] == NULL)
                return;
        mutex_lock(&boost_mutex);
        t = boost_tasks[cpu];
        boost_tasks[cpu] = NULL;
        mutex_unlock(&boost_mutex);

        /* This must be outside of the mutex, otherwise deadlock! */
        torture_stop_kthread(rcu_torture_boost, t);
}

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_TOROUT_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_TOROUT_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;
}

/*
 * 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_TOROUT_STRING("rcu_torture_stall task started");
        if (stall_cpu_holdoff > 0) {
                VERBOSE_TOROUT_STRING("rcu_torture_stall begin holdoff");
                schedule_timeout_interruptible(stall_cpu_holdoff * HZ);
                VERBOSE_TOROUT_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");
        }
        torture_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)
{
        if (stall_cpu <= 0)
                return 0;
        return torture_create_kthread(rcu_torture_stall, NULL, stall_task);
}

/* Callback function for RCU barrier testing. */
static 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;
        bool newphase;
        struct rcu_head rcu;

        init_rcu_head_on_stack(&rcu);
        VERBOSE_TOROUT_STRING("rcu_torture_barrier_cbs task started");
        set_user_nice(current, MAX_NICE);
        do {
                wait_event(barrier_cbs_wq[myid],
                           (newphase =
                            ACCESS_ONCE(barrier_phase)) != lastphase ||
                           torture_must_stop());
                lastphase = newphase;
                smp_mb(); /* ensure barrier_phase load before ->call(). */
                if (torture_must_stop())
                        break;
                cur_ops->call(&rcu, rcu_torture_barrier_cbf);
                if (atomic_dec_and_test(&barrier_cbs_count))
                        wake_up(&barrier_wq);
        } while (!torture_must_stop());
        if (cur_ops->cb_barrier != NULL)
                cur_ops->cb_barrier();
        destroy_rcu_head_on_stack(&rcu);
        torture_kthread_stopping("rcu_torture_barrier_cbs");
        return 0;
}

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

        VERBOSE_TOROUT_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 ||
                           torture_must_stop());
                if (torture_must_stop())
                        break;
                n_barrier_attempts++;
                cur_ops->cb_barrier(); /* Implies smp_mb() for wait_event(). */
                if (atomic_read(&barrier_cbs_invoked) != n_barrier_cbs) {
                        n_rcu_torture_barrier_error++;
                        pr_err("barrier_cbs_invoked = %d, n_barrier_cbs = %d\n",
                               atomic_read(&barrier_cbs_invoked),
                               n_barrier_cbs);
                        WARN_ON_ONCE(1);
                }
                n_barrier_successes++;
                schedule_timeout_interruptible(HZ / 10);
        } while (!torture_must_stop());
        torture_kthread_stopping("rcu_torture_barrier");
        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]);
                ret = torture_create_kthread(rcu_torture_barrier_cbs,
                                             (void *)(long)i,
                                             barrier_cbs_tasks[i]);
                if (ret)
                        return ret;
        }
        return torture_create_kthread(rcu_torture_barrier, NULL, barrier_task);
}

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

        torture_stop_kthread(rcu_torture_barrier, barrier_task);
        if (barrier_cbs_tasks != NULL) {
                for (i = 0; i < n_barrier_cbs; i++)
                        torture_stop_kthread(rcu_torture_barrier_cbs,
                                             barrier_cbs_tasks[i]);
                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;

        rcutorture_record_test_transition();
        if (torture_cleanup_begin()) {
                if (cur_ops->cb_barrier != NULL)
                        cur_ops->cb_barrier();
                return;
        }

        rcu_torture_barrier_cleanup();
        torture_stop_kthread(rcu_torture_stall, stall_task);
        torture_stop_kthread(rcu_torture_writer, writer_task);

        if (reader_tasks) {
                for (i = 0; i < nrealreaders; i++)
                        torture_stop_kthread(rcu_torture_reader,
                                             reader_tasks[i]);
                kfree(reader_tasks);
        }
        rcu_torture_current = NULL;

        if (fakewriter_tasks) {
                for (i = 0; i < nfakewriters; i++) {
                        torture_stop_kthread(rcu_torture_fakewriter,
                                             fakewriter_tasks[i]);
                }
                kfree(fakewriter_tasks);
                fakewriter_tasks = NULL;
        }

        torture_stop_kthread(rcu_torture_stats, stats_task);
        torture_stop_kthread(rcu_torture_fqs, fqs_task);
        for (i = 0; i < ncbflooders; i++)
                torture_stop_kthread(rcu_torture_cbflood, cbflood_task[i]);
        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);
        }

        /* 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 (torture_onoff_failures())
                rcu_torture_print_module_parms(cur_ops,
                                               "End of test: RCU_HOTPLUG");
        else
                rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS");
        torture_cleanup_end();
}

#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;
        static struct rcu_torture_ops *torture_ops[] = {
                &rcu_ops, &rcu_bh_ops, &rcu_busted_ops, &srcu_ops, &sched_ops,
                RCUTORTURE_TASKS_OPS
        };

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

        /* Process args and tell the world that the torturer is on the job. */
        for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
                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");
                torture_init_end();
                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 = num_online_cpus() - 1;
                if (nrealreaders <= 0)
                        nrealreaders = 1;
        }
        rcu_torture_print_module_parms(cur_ops, "Start of test");

        /* 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. */

        firsterr = torture_create_kthread(rcu_torture_writer, NULL,
                                          writer_task);
        if (firsterr)
                goto unwind;
        fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),
                                   GFP_KERNEL);
        if (fakewriter_tasks == NULL) {
                VERBOSE_TOROUT_ERRSTRING("out of memory");
                firsterr = -ENOMEM;
                goto unwind;
        }
        for (i = 0; i < nfakewriters; i++) {
                firsterr = torture_create_kthread(rcu_torture_fakewriter,
                                                  NULL, fakewriter_tasks[i]);
                if (firsterr)
                        goto unwind;
        }
        reader_tasks = kzalloc(nrealreaders * sizeof(reader_tasks[0]),
                               GFP_KERNEL);
        if (reader_tasks == NULL) {
                VERBOSE_TOROUT_ERRSTRING("out of memory");
                firsterr = -ENOMEM;
                goto unwind;
        }
        for (i = 0; i < nrealreaders; i++) {
                firsterr = torture_create_kthread(rcu_torture_reader, NULL,
                                                  reader_tasks[i]);
                if (firsterr)
                        goto unwind;
        }
        if (stat_interval > 0) {
                firsterr = torture_create_kthread(rcu_torture_stats, NULL,
                                                  stats_task);
                if (firsterr)
                        goto unwind;
        }
        if (test_no_idle_hz) {
                firsterr = torture_shuffle_init(shuffle_interval * HZ);
                if (firsterr)
                        goto unwind;
        }
        if (stutter < 0)
                stutter = 0;
        if (stutter) {
                firsterr = torture_stutter_init(stutter * HZ);
                if (firsterr)
                        goto unwind;
        }
        if (fqs_duration < 0)
                fqs_duration = 0;
        if (fqs_duration) {
                /* Create the fqs thread */
                firsterr = torture_create_kthread(rcu_torture_fqs, NULL,
                                                  fqs_task);
                if (firsterr)
                        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. */
                        firsterr = rcutorture_booster_init(i);
                        if (firsterr)
                                goto unwind;
                }
        }
        firsterr = torture_shutdown_init(shutdown_secs, rcu_torture_cleanup);
        if (firsterr)
                goto unwind;
        firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval * HZ);
        if (firsterr)
                goto unwind;
        firsterr = rcu_torture_stall_init();
        if (firsterr)
                goto unwind;
        firsterr = rcu_torture_barrier_init();
        if (firsterr)
                goto unwind;
        if (object_debug)
                rcu_test_debug_objects();
        if (cbflood_n_burst > 0) {
                /* Create the cbflood threads */
                ncbflooders = (num_online_cpus() + 3) / 4;
                cbflood_task = kcalloc(ncbflooders, sizeof(*cbflood_task),
                                       GFP_KERNEL);
                if (!cbflood_task) {
                        VERBOSE_TOROUT_ERRSTRING("out of memory");
                        firsterr = -ENOMEM;
                        goto unwind;
                }
                for (i = 0; i < ncbflooders; i++) {
                        firsterr = torture_create_kthread(rcu_torture_cbflood,
                                                          NULL,
                                                          cbflood_task[i]);
                        if (firsterr)
                                goto unwind;
                }
        }
        rcutorture_record_test_transition();
        torture_init_end();
        return 0;

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

module_init(rcu_torture_init);
module_exit(rcu_torture_cleanup);