/*
 * Read-Copy Update module-based performance-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, 2015
 *
 * Authors: Paul E. McKenney <paulmck@us.ibm.com>
 */

#define pr_fmt(fmt) fmt

#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 <uapi/linux/sched/types.h>
#include <linux/atomic.h>
#include <linux/bitops.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/reboot.h>
#include <linux/freezer.h>
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/stat.h>
#include <linux/srcu.h>
#include <linux/slab.h>
#include <asm/byteorder.h>
#include <linux/torture.h>
#include <linux/vmalloc.h>

#include "rcu.h"

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.vnet.ibm.com>");

#define PERF_FLAG "-perf:"
#define PERFOUT_STRING(s) \
        pr_alert("%s" PERF_FLAG " %s\n", perf_type, s)
#define VERBOSE_PERFOUT_STRING(s) \
        do { if (verbose) pr_alert("%s" PERF_FLAG " %s\n", perf_type, s); } while (0)
#define VERBOSE_PERFOUT_ERRSTRING(s) \
        do { if (verbose) pr_alert("%s" PERF_FLAG "!!! %s\n", perf_type, s); } while (0)

/*
 * The intended use cases for the nreaders and nwriters module parameters
 * are as follows:
 *
 * 1.   Specify only the nr_cpus kernel boot parameter.  This will
 *      set both nreaders and nwriters to the value specified by
 *      nr_cpus for a mixed reader/writer test.
 *
 * 2.   Specify the nr_cpus kernel boot parameter, but set
 *      rcuperf.nreaders to zero.  This will set nwriters to the
 *      value specified by nr_cpus for an update-only test.
 *
 * 3.   Specify the nr_cpus kernel boot parameter, but set
 *      rcuperf.nwriters to zero.  This will set nreaders to the
 *      value specified by nr_cpus for a read-only test.
 *
 * Various other use cases may of course be specified.
 */

torture_param(bool, gp_async, false, "Use asynchronous GP wait primitives");
torture_param(int, gp_async_max, 1000, "Max # outstanding waits per reader");
torture_param(bool, gp_exp, false, "Use expedited GP wait primitives");
torture_param(int, holdoff, 10, "Holdoff time before test start (s)");
torture_param(int, nreaders, -1, "Number of RCU reader threads");
torture_param(int, nwriters, -1, "Number of RCU updater threads");
torture_param(bool, shutdown, !IS_ENABLED(MODULE),
              "Shutdown at end of performance tests.");
torture_param(int, verbose, 1, "Enable verbose debugging printk()s");
torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable");

static char *perf_type = "rcu";
module_param(perf_type, charp, 0444);
MODULE_PARM_DESC(perf_type, "Type of RCU to performance-test (rcu, rcu_bh, ...)");

static int nrealreaders;
static int nrealwriters;
static struct task_struct **writer_tasks;
static struct task_struct **reader_tasks;
static struct task_struct *shutdown_task;

static u64 **writer_durations;
static int *writer_n_durations;
static atomic_t n_rcu_perf_reader_started;
static atomic_t n_rcu_perf_writer_started;
static atomic_t n_rcu_perf_writer_finished;
static wait_queue_head_t shutdown_wq;
static u64 t_rcu_perf_writer_started;
static u64 t_rcu_perf_writer_finished;
static unsigned long b_rcu_perf_writer_started;
static unsigned long b_rcu_perf_writer_finished;
static DEFINE_PER_CPU(atomic_t, n_async_inflight);

static int rcu_perf_writer_state;
#define RTWS_INIT               0
#define RTWS_ASYNC              1
#define RTWS_BARRIER            2
#define RTWS_EXP_SYNC           3
#define RTWS_SYNC               4
#define RTWS_IDLE               5
#define RTWS_STOPPING           6

#define MAX_MEAS 10000
#define MIN_MEAS 100

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

struct rcu_perf_ops {
        int ptype;
        void (*init)(void);
        void (*cleanup)(void);
        int (*readlock)(void);
        void (*readunlock)(int idx);
        unsigned long (*get_gp_seq)(void);
        unsigned long (*gp_diff)(unsigned long new, unsigned long old);
        unsigned long (*exp_completed)(void);
        void (*async)(struct rcu_head *head, rcu_callback_t func);
        void (*gp_barrier)(void);
        void (*sync)(void);
        void (*exp_sync)(void);
        const char *name;
};

static struct rcu_perf_ops *cur_ops;

/*
 * Definitions for rcu perf testing.
 */

static int rcu_perf_read_lock(void) __acquires(RCU)
{
        rcu_read_lock();
        return 0;
}

static void rcu_perf_read_unlock(int idx) __releases(RCU)
{
        rcu_read_unlock();
}

static unsigned long __maybe_unused rcu_no_completed(void)
{
        return 0;
}

static void rcu_sync_perf_init(void)
{
}

static struct rcu_perf_ops rcu_ops = {
        .ptype          = RCU_FLAVOR,
        .init           = rcu_sync_perf_init,
        .readlock       = rcu_perf_read_lock,
        .readunlock     = rcu_perf_read_unlock,
        .get_gp_seq     = rcu_get_gp_seq,
        .gp_diff        = rcu_seq_diff,
        .exp_completed  = rcu_exp_batches_completed,
        .async          = call_rcu,
        .gp_barrier     = rcu_barrier,
        .sync           = synchronize_rcu,
        .exp_sync       = synchronize_rcu_expedited,
        .name           = "rcu"
};

/*
 * Definitions for rcu_bh perf testing.
 */

static int rcu_bh_perf_read_lock(void) __acquires(RCU_BH)
{
        rcu_read_lock_bh();
        return 0;
}

static void rcu_bh_perf_read_unlock(int idx) __releases(RCU_BH)
{
        rcu_read_unlock_bh();
}

static struct rcu_perf_ops rcu_bh_ops = {
        .ptype          = RCU_BH_FLAVOR,
        .init           = rcu_sync_perf_init,
        .readlock       = rcu_bh_perf_read_lock,
        .readunlock     = rcu_bh_perf_read_unlock,
        .get_gp_seq     = rcu_bh_get_gp_seq,
        .gp_diff        = rcu_seq_diff,
        .exp_completed  = rcu_exp_batches_completed_sched,
        .async          = call_rcu_bh,
        .gp_barrier     = rcu_barrier_bh,
        .sync           = synchronize_rcu_bh,
        .exp_sync       = synchronize_rcu_bh_expedited,
        .name           = "rcu_bh"
};

/*
 * Definitions for srcu perf testing.
 */

DEFINE_STATIC_SRCU(srcu_ctl_perf);
static struct srcu_struct *srcu_ctlp = &srcu_ctl_perf;

static int srcu_perf_read_lock(void) __acquires(srcu_ctlp)
{
        return srcu_read_lock(srcu_ctlp);
}

static void srcu_perf_read_unlock(int idx) __releases(srcu_ctlp)
{
        srcu_read_unlock(srcu_ctlp, idx);
}

static unsigned long srcu_perf_completed(void)
{
        return srcu_batches_completed(srcu_ctlp);
}

static void srcu_call_rcu(struct rcu_head *head, rcu_callback_t func)
{
        call_srcu(srcu_ctlp, head, func);
}

static void srcu_rcu_barrier(void)
{
        srcu_barrier(srcu_ctlp);
}

static void srcu_perf_synchronize(void)
{
        synchronize_srcu(srcu_ctlp);
}

static void srcu_perf_synchronize_expedited(void)
{
        synchronize_srcu_expedited(srcu_ctlp);
}

static struct rcu_perf_ops srcu_ops = {
        .ptype          = SRCU_FLAVOR,
        .init           = rcu_sync_perf_init,
        .readlock       = srcu_perf_read_lock,
        .readunlock     = srcu_perf_read_unlock,
        .get_gp_seq     = srcu_perf_completed,
        .gp_diff        = rcu_seq_diff,
        .exp_completed  = srcu_perf_completed,
        .async          = srcu_call_rcu,
        .gp_barrier     = srcu_rcu_barrier,
        .sync           = srcu_perf_synchronize,
        .exp_sync       = srcu_perf_synchronize_expedited,
        .name           = "srcu"
};

static struct srcu_struct srcud;

static void srcu_sync_perf_init(void)
{
        srcu_ctlp = &srcud;
        init_srcu_struct(srcu_ctlp);
}

static void srcu_sync_perf_cleanup(void)
{
        cleanup_srcu_struct(srcu_ctlp);
}

static struct rcu_perf_ops srcud_ops = {
        .ptype          = SRCU_FLAVOR,
        .init           = srcu_sync_perf_init,
        .cleanup        = srcu_sync_perf_cleanup,
        .readlock       = srcu_perf_read_lock,
        .readunlock     = srcu_perf_read_unlock,
        .get_gp_seq     = srcu_perf_completed,
        .gp_diff        = rcu_seq_diff,
        .exp_completed  = srcu_perf_completed,
        .async          = srcu_call_rcu,
        .gp_barrier     = srcu_rcu_barrier,
        .sync           = srcu_perf_synchronize,
        .exp_sync       = srcu_perf_synchronize_expedited,
        .name           = "srcud"
};

/*
 * Definitions for sched perf testing.
 */

static int sched_perf_read_lock(void)
{
        preempt_disable();
        return 0;
}

static void sched_perf_read_unlock(int idx)
{
        preempt_enable();
}

static struct rcu_perf_ops sched_ops = {
        .ptype          = RCU_SCHED_FLAVOR,
        .init           = rcu_sync_perf_init,
        .readlock       = sched_perf_read_lock,
        .readunlock     = sched_perf_read_unlock,
        .get_gp_seq     = rcu_sched_get_gp_seq,
        .gp_diff        = rcu_seq_diff,
        .exp_completed  = rcu_exp_batches_completed_sched,
        .async          = call_rcu_sched,
        .gp_barrier     = rcu_barrier_sched,
        .sync           = synchronize_sched,
        .exp_sync       = synchronize_sched_expedited,
        .name           = "sched"
};

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

static int tasks_perf_read_lock(void)
{
        return 0;
}

static void tasks_perf_read_unlock(int idx)
{
}

static struct rcu_perf_ops tasks_ops = {
        .ptype          = RCU_TASKS_FLAVOR,
        .init           = rcu_sync_perf_init,
        .readlock       = tasks_perf_read_lock,
        .readunlock     = tasks_perf_read_unlock,
        .get_gp_seq     = rcu_no_completed,
        .gp_diff        = rcu_seq_diff,
        .async          = call_rcu_tasks,
        .gp_barrier     = rcu_barrier_tasks,
        .sync           = synchronize_rcu_tasks,
        .exp_sync       = synchronize_rcu_tasks,
        .name           = "tasks"
};

static unsigned long rcuperf_seq_diff(unsigned long new, unsigned long old)
{
        if (!cur_ops->gp_diff)
                return new - old;
        return cur_ops->gp_diff(new, old);
}

/*
 * If performance tests complete, wait for shutdown to commence.
 */
static void rcu_perf_wait_shutdown(void)
{
        cond_resched_tasks_rcu_qs();
        if (atomic_read(&n_rcu_perf_writer_finished) < nrealwriters)
                return;
        while (!torture_must_stop())
                schedule_timeout_uninterruptible(1);
}

/*
 * RCU perf reader kthread.  Repeatedly does empty RCU read-side
 * critical section, minimizing update-side interference.
 */
static int
rcu_perf_reader(void *arg)
{
        unsigned long flags;
        int idx;
        long me = (long)arg;

        VERBOSE_PERFOUT_STRING("rcu_perf_reader task started");
        set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
        set_user_nice(current, MAX_NICE);
        atomic_inc(&n_rcu_perf_reader_started);

        do {
                local_irq_save(flags);
                idx = cur_ops->readlock();
                cur_ops->readunlock(idx);
                local_irq_restore(flags);
                rcu_perf_wait_shutdown();
        } while (!torture_must_stop());
        torture_kthread_stopping("rcu_perf_reader");
        return 0;
}

/*
 * Callback function for asynchronous grace periods from rcu_perf_writer().
 */
static void rcu_perf_async_cb(struct rcu_head *rhp)
{
        atomic_dec(this_cpu_ptr(&n_async_inflight));
        kfree(rhp);
}

/*
 * RCU perf writer kthread.  Repeatedly does a grace period.
 */
static int
rcu_perf_writer(void *arg)
{
        int i = 0;
        int i_max;
        long me = (long)arg;
        struct rcu_head *rhp = NULL;
        struct sched_param sp;
        bool started = false, done = false, alldone = false;
        u64 t;
        u64 *wdp;
        u64 *wdpp = writer_durations[me];

        VERBOSE_PERFOUT_STRING("rcu_perf_writer task started");
        WARN_ON(!wdpp);
        set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
        sp.sched_priority = 1;
        sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);

        if (holdoff)
                schedule_timeout_uninterruptible(holdoff * HZ);

        t = ktime_get_mono_fast_ns();
        if (atomic_inc_return(&n_rcu_perf_writer_started) >= nrealwriters) {
                t_rcu_perf_writer_started = t;
                if (gp_exp) {
                        b_rcu_perf_writer_started =
                                cur_ops->exp_completed() / 2;
                } else {
                        b_rcu_perf_writer_started = cur_ops->get_gp_seq();
                }
        }

        do {
                if (writer_holdoff)
                        udelay(writer_holdoff);
                wdp = &wdpp[i];
                *wdp = ktime_get_mono_fast_ns();
                if (gp_async) {
retry:
                        if (!rhp)
                                rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
                        if (rhp && atomic_read(this_cpu_ptr(&n_async_inflight)) < gp_async_max) {
                                rcu_perf_writer_state = RTWS_ASYNC;
                                atomic_inc(this_cpu_ptr(&n_async_inflight));
                                cur_ops->async(rhp, rcu_perf_async_cb);
                                rhp = NULL;
                        } else if (!kthread_should_stop()) {
                                rcu_perf_writer_state = RTWS_BARRIER;
                                cur_ops->gp_barrier();
                                goto retry;
                        } else {
                                kfree(rhp); /* Because we are stopping. */
                        }
                } else if (gp_exp) {
                        rcu_perf_writer_state = RTWS_EXP_SYNC;
                        cur_ops->exp_sync();
                } else {
                        rcu_perf_writer_state = RTWS_SYNC;
                        cur_ops->sync();
                }
                rcu_perf_writer_state = RTWS_IDLE;
                t = ktime_get_mono_fast_ns();
                *wdp = t - *wdp;
                i_max = i;
                if (!started &&
                    atomic_read(&n_rcu_perf_writer_started) >= nrealwriters)
                        started = true;
                if (!done && i >= MIN_MEAS) {
                        done = true;
                        sp.sched_priority = 0;
                        sched_setscheduler_nocheck(current,
                                                   SCHED_NORMAL, &sp);
                        pr_alert("%s%s rcu_perf_writer %ld has %d measurements\n",
                                 perf_type, PERF_FLAG, me, MIN_MEAS);
                        if (atomic_inc_return(&n_rcu_perf_writer_finished) >=
                            nrealwriters) {
                                schedule_timeout_interruptible(10);
                                rcu_ftrace_dump(DUMP_ALL);
                                PERFOUT_STRING("Test complete");
                                t_rcu_perf_writer_finished = t;
                                if (gp_exp) {
                                        b_rcu_perf_writer_finished =
                                                cur_ops->exp_completed() / 2;
                                } else {
                                        b_rcu_perf_writer_finished =
                                                cur_ops->get_gp_seq();
                                }
                                if (shutdown) {
                                        smp_mb(); /* Assign before wake. */
                                        wake_up(&shutdown_wq);
                                }
                        }
                }
                if (done && !alldone &&
                    atomic_read(&n_rcu_perf_writer_finished) >= nrealwriters)
                        alldone = true;
                if (started && !alldone && i < MAX_MEAS - 1)
                        i++;
                rcu_perf_wait_shutdown();
        } while (!torture_must_stop());
        if (gp_async) {
                rcu_perf_writer_state = RTWS_BARRIER;
                cur_ops->gp_barrier();
        }
        rcu_perf_writer_state = RTWS_STOPPING;
        writer_n_durations[me] = i_max;
        torture_kthread_stopping("rcu_perf_writer");
        return 0;
}

static void
rcu_perf_print_module_parms(struct rcu_perf_ops *cur_ops, const char *tag)
{
        pr_alert("%s" PERF_FLAG
                 "--- %s: nreaders=%d nwriters=%d verbose=%d shutdown=%d\n",
                 perf_type, tag, nrealreaders, nrealwriters, verbose, shutdown);
}

static void
rcu_perf_cleanup(void)
{
        int i;
        int j;
        int ngps = 0;
        u64 *wdp;
        u64 *wdpp;

        /*
         * Would like warning at start, but everything is expedited
         * during the mid-boot phase, so have to wait till the end.
         */
        if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp)
                VERBOSE_PERFOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!");
        if (rcu_gp_is_normal() && gp_exp)
                VERBOSE_PERFOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!");
        if (gp_exp && gp_async)
                VERBOSE_PERFOUT_ERRSTRING("No expedited async GPs, so went with async!");

        if (torture_cleanup_begin())
                return;

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

        if (writer_tasks) {
                for (i = 0; i < nrealwriters; i++) {
                        torture_stop_kthread(rcu_perf_writer,
                                             writer_tasks[i]);
                        if (!writer_n_durations)
                                continue;
                        j = writer_n_durations[i];
                        pr_alert("%s%s writer %d gps: %d\n",
                                 perf_type, PERF_FLAG, i, j);
                        ngps += j;
                }
                pr_alert("%s%s start: %llu end: %llu duration: %llu gps: %d batches: %ld\n",
                         perf_type, PERF_FLAG,
                         t_rcu_perf_writer_started, t_rcu_perf_writer_finished,
                         t_rcu_perf_writer_finished -
                         t_rcu_perf_writer_started,
                         ngps,
                         rcuperf_seq_diff(b_rcu_perf_writer_finished,
                                          b_rcu_perf_writer_started));
                for (i = 0; i < nrealwriters; i++) {
                        if (!writer_durations)
                                break;
                        if (!writer_n_durations)
                                continue;
                        wdpp = writer_durations[i];
                        if (!wdpp)
                                continue;
                        for (j = 0; j <= writer_n_durations[i]; j++) {
                                wdp = &wdpp[j];
                                pr_alert("%s%s %4d writer-duration: %5d %llu\n",
                                        perf_type, PERF_FLAG,
                                        i, j, *wdp);
                                if (j % 100 == 0)
                                        schedule_timeout_uninterruptible(1);
                        }
                        kfree(writer_durations[i]);
                }
                kfree(writer_tasks);
                kfree(writer_durations);
                kfree(writer_n_durations);
        }

        /* Do flavor-specific cleanup operations.  */
        if (cur_ops->cleanup != NULL)
                cur_ops->cleanup();

        torture_cleanup_end();
}

/*
 * Return the number if non-negative.  If -1, the number of CPUs.
 * If less than -1, that much less than the number of CPUs, but
 * at least one.
 */
static int compute_real(int n)
{
        int nr;

        if (n >= 0) {
                nr = n;
        } else {
                nr = num_online_cpus() + 1 + n;
                if (nr <= 0)
                        nr = 1;
        }
        return nr;
}

/*
 * RCU perf shutdown kthread.  Just waits to be awakened, then shuts
 * down system.
 */
static int
rcu_perf_shutdown(void *arg)
{
        do {
                wait_event(shutdown_wq,
                           atomic_read(&n_rcu_perf_writer_finished) >=
                           nrealwriters);
        } while (atomic_read(&n_rcu_perf_writer_finished) < nrealwriters);
        smp_mb(); /* Wake before output. */
        rcu_perf_cleanup();
        kernel_power_off();
        return -EINVAL;
}

static int __init
rcu_perf_init(void)
{
        long i;
        int firsterr = 0;
        static struct rcu_perf_ops *perf_ops[] = {
                &rcu_ops, &rcu_bh_ops, &srcu_ops, &srcud_ops, &sched_ops,
                &tasks_ops,
        };

        if (!torture_init_begin(perf_type, verbose))
                return -EBUSY;

        /* Process args and tell the world that the perf'er is on the job. */
        for (i = 0; i < ARRAY_SIZE(perf_ops); i++) {
                cur_ops = perf_ops[i];
                if (strcmp(perf_type, cur_ops->name) == 0)
                        break;
        }
        if (i == ARRAY_SIZE(perf_ops)) {
                pr_alert("rcu-perf: invalid perf type: \"%s\"\n", perf_type);
                pr_alert("rcu-perf types:");
                for (i = 0; i < ARRAY_SIZE(perf_ops); i++)
                        pr_cont(" %s", perf_ops[i]->name);
                pr_cont("\n");
                firsterr = -EINVAL;
                goto unwind;
        }
        if (cur_ops->init)
                cur_ops->init();

        nrealwriters = compute_real(nwriters);
        nrealreaders = compute_real(nreaders);
        atomic_set(&n_rcu_perf_reader_started, 0);
        atomic_set(&n_rcu_perf_writer_started, 0);
        atomic_set(&n_rcu_perf_writer_finished, 0);
        rcu_perf_print_module_parms(cur_ops, "Start of test");

        /* Start up the kthreads. */

        if (shutdown) {
                init_waitqueue_head(&shutdown_wq);
                firsterr = torture_create_kthread(rcu_perf_shutdown, NULL,
                                                  shutdown_task);
                if (firsterr)
                        goto unwind;
                schedule_timeout_uninterruptible(1);
        }
        reader_tasks = kcalloc(nrealreaders, sizeof(reader_tasks[0]),
                               GFP_KERNEL);
        if (reader_tasks == NULL) {
                VERBOSE_PERFOUT_ERRSTRING("out of memory");
                firsterr = -ENOMEM;
                goto unwind;
        }
        for (i = 0; i < nrealreaders; i++) {
                firsterr = torture_create_kthread(rcu_perf_reader, (void *)i,
                                                  reader_tasks[i]);
                if (firsterr)
                        goto unwind;
        }
        while (atomic_read(&n_rcu_perf_reader_started) < nrealreaders)
                schedule_timeout_uninterruptible(1);
        writer_tasks = kcalloc(nrealwriters, sizeof(reader_tasks[0]),
                               GFP_KERNEL);
        writer_durations = kcalloc(nrealwriters, sizeof(*writer_durations),
                                   GFP_KERNEL);
        writer_n_durations =
                kcalloc(nrealwriters, sizeof(*writer_n_durations),
                        GFP_KERNEL);
        if (!writer_tasks || !writer_durations || !writer_n_durations) {
                VERBOSE_PERFOUT_ERRSTRING("out of memory");
                firsterr = -ENOMEM;
                goto unwind;
        }
        for (i = 0; i < nrealwriters; i++) {
                writer_durations[i] =
                        kcalloc(MAX_MEAS, sizeof(*writer_durations[i]),
                                GFP_KERNEL);
                if (!writer_durations[i]) {
                        firsterr = -ENOMEM;
                        goto unwind;
                }
                firsterr = torture_create_kthread(rcu_perf_writer, (void *)i,
                                                  writer_tasks[i]);
                if (firsterr)
                        goto unwind;
        }
        torture_init_end();
        return 0;

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

module_init(rcu_perf_init);
module_exit(rcu_perf_cleanup);