On Tue, Nov 06, 2007 at 02:33:53AM -0800, akpm@linux-foundation.org wrote:

[mmotm.git] / kernel / 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, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) IBM Corporation, 2005, 2006
 *
 * Authors: Paul E. McKenney <paulmck@us.ibm.com>
 *        Josh Triplett <josh@freedesktop.org>
 *
 * See also:  Documentation/RCU/torture.txt
 */
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kthread.h>
#include <linux/err.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/rcupdate.h>
#include <linux/interrupt.h>
#include <linux/sched.h>
#include <asm/atomic.h>
#include <linux/bitops.h>
#include <linux/completion.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/notifier.h>
#include <linux/reboot.h>
#include <linux/freezer.h>
#include <linux/cpu.h>
#include <linux/delay.h>
#include <linux/stat.h>
#include <linux/srcu.h>
#include <linux/slab.h>
#include <asm/byteorder.h>

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

static int nreaders = -1;       /* # reader threads, defaults to 2*ncpus */
static int nfakewriters = 4;    /* # fake writer threads */
static int stat_interval;       /* Interval between stats, in seconds. */
                                /*  Defaults to "only at end of test". */
static int verbose;             /* Print more debug info. */
static int test_no_idle_hz;     /* Test RCU's support for tickless idle CPUs. */
static int shuffle_interval = 3; /* Interval between shuffles (in sec)*/
static int stutter = 5;         /* Start/stop testing interval (in sec) */
static int irqreader = 1;       /* RCU readers from irq (timers). */
static char *torture_type = "rcu"; /* What RCU implementation to torture. */

module_param(nreaders, int, 0444);
MODULE_PARM_DESC(nreaders, "Number of RCU reader threads");
module_param(nfakewriters, int, 0444);
MODULE_PARM_DESC(nfakewriters, "Number of RCU fake writer threads");
module_param(stat_interval, int, 0444);
MODULE_PARM_DESC(stat_interval, "Number of seconds between stats printk()s");
module_param(verbose, bool, 0444);
MODULE_PARM_DESC(verbose, "Enable verbose debugging printk()s");
module_param(test_no_idle_hz, bool, 0444);
MODULE_PARM_DESC(test_no_idle_hz, "Test support for tickless idle CPUs");
module_param(shuffle_interval, int, 0444);
MODULE_PARM_DESC(shuffle_interval, "Number of seconds between shuffles");
module_param(stutter, int, 0444);
MODULE_PARM_DESC(stutter, "Number of seconds to run/halt test");
module_param(irqreader, int, 0444);
MODULE_PARM_DESC(irqreader, "Allow RCU readers from irq handlers");
module_param(torture_type, charp, 0444);
MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, rcu_bh, srcu)");

#define TORTURE_FLAG "-torture:"
#define PRINTK_STRING(s) \
        do { printk(KERN_ALERT "%s" TORTURE_FLAG s "\n", torture_type); } while (0)
#define VERBOSE_PRINTK_STRING(s) \
        do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG s "\n", torture_type); } while (0)
#define VERBOSE_PRINTK_ERRSTRING(s) \
        do { if (verbose) printk(KERN_ALERT "%s" TORTURE_FLAG "!!! " s "\n", torture_type); } while (0)

static char printk_buf[4096];

static int nrealreaders;
static struct task_struct *writer_task;
static struct task_struct **fakewriter_tasks;
static struct task_struct **reader_tasks;
static struct task_struct *stats_task;
static struct task_struct *shuffler_task;
static struct task_struct *stutter_task;

#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_torture_current;
static 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_timers;
static struct list_head rcu_torture_removed;
static cpumask_var_t shuffle_tmp_mask;

static int stutter_pause_test;

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

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

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

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

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

/*
 * Allocate an element from the rcu_tortures pool.
 */
static struct rcu_torture *
rcu_torture_alloc(void)
{
        struct list_head *p;

        spin_lock_bh(&rcu_torture_lock);
        if (list_empty(&rcu_torture_freelist)) {
                atomic_inc(&n_rcu_torture_alloc_fail);
                spin_unlock_bh(&rcu_torture_lock);
                return NULL;
        }
        atomic_inc(&n_rcu_torture_alloc);
        p = rcu_torture_freelist.next;
        list_del_init(p);
        spin_unlock_bh(&rcu_torture_lock);
        return container_of(p, struct rcu_torture, rtort_free);
}

/*
 * Free an element to the rcu_tortures pool.
 */
static void
rcu_torture_free(struct rcu_torture *p)
{
        atomic_inc(&n_rcu_torture_free);
        spin_lock_bh(&rcu_torture_lock);
        list_add_tail(&p->rtort_free, &rcu_torture_freelist);
        spin_unlock_bh(&rcu_torture_lock);
}

struct rcu_random_state {
        unsigned long rrs_state;
        long rrs_count;
};

#define RCU_RANDOM_MULT 39916801  /* prime */
#define RCU_RANDOM_ADD  479001701 /* prime */
#define RCU_RANDOM_REFRESH 10000

#define DEFINE_RCU_RANDOM(name) struct rcu_random_state name = { 0, 0 }

/*
 * Crude but fast random-number generator.  Uses a linear congruential
 * generator, with occasional help from cpu_clock().
 */
static unsigned long
rcu_random(struct rcu_random_state *rrsp)
{
        if (--rrsp->rrs_count < 0) {
                rrsp->rrs_state +=
                        (unsigned long)cpu_clock(raw_smp_processor_id());
                rrsp->rrs_count = RCU_RANDOM_REFRESH;
        }
        rrsp->rrs_state = rrsp->rrs_state * RCU_RANDOM_MULT + RCU_RANDOM_ADD;
        return swahw32(rrsp->rrs_state);
}

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

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

struct rcu_torture_ops {
        void (*init)(void);
        void (*cleanup)(void);
        int (*readlock)(void);
        void (*read_delay)(struct rcu_random_state *rrsp);
        void (*readunlock)(int idx);
        int (*completed)(void);
        void (*deferred_free)(struct rcu_torture *p);
        void (*sync)(void);
        void (*cb_barrier)(void);
        int (*stats)(char *page);
        int irq_capable;
        char *name;
};

static struct rcu_torture_ops *cur_ops;

/*
 * Definitions for rcu torture testing.
 */

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

static void rcu_read_delay(struct rcu_random_state *rrsp)
{
        const unsigned long shortdelay_us = 200;
        const unsigned long longdelay_ms = 50;

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

        if (!(rcu_random(rrsp) % (nrealreaders * 2000 * longdelay_ms)))
                mdelay(longdelay_ms);
        if (!(rcu_random(rrsp) % (nrealreaders * 2 * shortdelay_us)))
                udelay(shortdelay_us);
}

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

static int rcu_torture_completed(void)
{
        return rcu_batches_completed();
}

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

        if (fullstop != FULLSTOP_DONTSTOP) {
                /* Test is ending, just drop callbacks on the floor. */
                /* The next initialization will pick up the pieces. */
                return;
        }
        i = rp->rtort_pipe_count;
        if (i > RCU_TORTURE_PIPE_LEN)
                i = RCU_TORTURE_PIPE_LEN;
        atomic_inc(&rcu_torture_wcount[i]);
        if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
                rp->rtort_mbtest = 0;
                rcu_torture_free(rp);
        } else
                cur_ops->deferred_free(rp);
}

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

static struct rcu_torture_ops rcu_ops = {
        .init           = NULL,
        .cleanup        = NULL,
        .readlock       = rcu_torture_read_lock,
        .read_delay     = rcu_read_delay,
        .readunlock     = rcu_torture_read_unlock,
        .completed      = rcu_torture_completed,
        .deferred_free  = rcu_torture_deferred_free,
        .sync           = synchronize_rcu,
        .cb_barrier     = rcu_barrier,
        .stats          = NULL,
        .irq_capable    = 1,
        .name           = "rcu"
};

static void rcu_sync_torture_deferred_free(struct rcu_torture *p)
{
        int i;
        struct rcu_torture *rp;
        struct rcu_torture *rp1;

        cur_ops->sync();
        list_add(&p->rtort_free, &rcu_torture_removed);
        list_for_each_entry_safe(rp, rp1, &rcu_torture_removed, rtort_free) {
                i = rp->rtort_pipe_count;
                if (i > RCU_TORTURE_PIPE_LEN)
                        i = RCU_TORTURE_PIPE_LEN;
                atomic_inc(&rcu_torture_wcount[i]);
                if (++rp->rtort_pipe_count >= RCU_TORTURE_PIPE_LEN) {
                        rp->rtort_mbtest = 0;
                        list_del(&rp->rtort_free);
                        rcu_torture_free(rp);
                }
        }
}

static void rcu_sync_torture_init(void)
{
        INIT_LIST_HEAD(&rcu_torture_removed);
}

static struct rcu_torture_ops rcu_sync_ops = {
        .init           = rcu_sync_torture_init,
        .cleanup        = NULL,
        .readlock       = rcu_torture_read_lock,
        .read_delay     = rcu_read_delay,
        .readunlock     = rcu_torture_read_unlock,
        .completed      = rcu_torture_completed,
        .deferred_free  = rcu_sync_torture_deferred_free,
        .sync           = synchronize_rcu,
        .cb_barrier     = NULL,
        .stats          = NULL,
        .irq_capable    = 1,
        .name           = "rcu_sync"
};

/*
 * Definitions for rcu_bh torture testing.
 */

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

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

static int rcu_bh_torture_completed(void)
{
        return rcu_batches_completed_bh();
}

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

struct rcu_bh_torture_synchronize {
        struct rcu_head head;
        struct completion completion;
};

static void rcu_bh_torture_wakeme_after_cb(struct rcu_head *head)
{
        struct rcu_bh_torture_synchronize *rcu;

        rcu = container_of(head, struct rcu_bh_torture_synchronize, head);
        complete(&rcu->completion);
}

static void rcu_bh_torture_synchronize(void)
{
        struct rcu_bh_torture_synchronize rcu;

        init_completion(&rcu.completion);
        call_rcu_bh(&rcu.head, rcu_bh_torture_wakeme_after_cb);
        wait_for_completion(&rcu.completion);
}

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

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

/*
 * Definitions for srcu torture testing.
 */

static struct srcu_struct srcu_ctl;

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

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

static int srcu_torture_read_lock(void) __acquires(&srcu_ctl)
{
        return srcu_read_lock(&srcu_ctl);
}

static void srcu_read_delay(struct rcu_random_state *rrsp)
{
        long delay;
        const long uspertick = 1000000 / HZ;
        const long longdelay = 10;

        /* We want there to be long-running readers, but not all the time. */

        delay = rcu_random(rrsp) % (nrealreaders * 2 * longdelay * uspertick);
        if (!delay)
                schedule_timeout_interruptible(longdelay);
}

static void srcu_torture_read_unlock(int idx) __releases(&srcu_ctl)
{
        srcu_read_unlock(&srcu_ctl, idx);
}

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

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

static int srcu_torture_stats(char *page)
{
        int cnt = 0;
        int cpu;
        int idx = srcu_ctl.completed & 0x1;

        cnt += sprintf(&page[cnt], "%s%s per-CPU(idx=%d):",
                       torture_type, TORTURE_FLAG, idx);
        for_each_possible_cpu(cpu) {
                cnt += sprintf(&page[cnt], " %d(%d,%d)", cpu,
                               per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[!idx],
                               per_cpu_ptr(srcu_ctl.per_cpu_ref, cpu)->c[idx]);
        }
        cnt += sprintf(&page[cnt], "\n");
        return cnt;
}

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

/*
 * Definitions for sched torture testing.
 */

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

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

static int sched_torture_completed(void)
{
        return 0;
}

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

static void sched_torture_synchronize(void)
{
        synchronize_sched();
}

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

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

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

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

        VERBOSE_PRINTK_STRING("rcu_torture_writer task started");
        set_user_nice(current, 19);

        do {
                schedule_timeout_uninterruptible(1);
                rp = rcu_torture_alloc();
                if (rp == NULL)
                        continue;
                rp->rtort_pipe_count = 0;
                udelay(rcu_random(&rand) & 0x3ff);
                old_rp = rcu_torture_current;
                rp->rtort_mbtest = 1;
                rcu_assign_pointer(rcu_torture_current, rp);
                smp_wmb(); /* Mods to old_rp must follow rcu_assign_pointer() */
                if (old_rp) {
                        i = old_rp->rtort_pipe_count;
                        if (i > RCU_TORTURE_PIPE_LEN)
                                i = RCU_TORTURE_PIPE_LEN;
                        atomic_inc(&rcu_torture_wcount[i]);
                        old_rp->rtort_pipe_count++;
                        cur_ops->deferred_free(old_rp);
                }
                rcu_torture_current_version++;
                oldbatch = cur_ops->completed();
                rcu_stutter_wait("rcu_torture_writer");
        } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
        VERBOSE_PRINTK_STRING("rcu_torture_writer task stopping");
        rcutorture_shutdown_absorb("rcu_torture_writer");
        while (!kthread_should_stop())
                schedule_timeout_uninterruptible(1);
        return 0;
}

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

        VERBOSE_PRINTK_STRING("rcu_torture_fakewriter task started");
        set_user_nice(current, 19);

        do {
                schedule_timeout_uninterruptible(1 + rcu_random(&rand)%10);
                udelay(rcu_random(&rand) & 0x3ff);
                cur_ops->sync();
                rcu_stutter_wait("rcu_torture_fakewriter");
        } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);

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

/*
 * RCU torture reader from timer handler.  Dereferences rcu_torture_current,
 * incrementing the corresponding element of the pipeline array.  The
 * counter in the element should never be greater than 1, otherwise, the
 * RCU implementation is broken.
 */
static void rcu_torture_timer(unsigned long unused)
{
        int idx;
        int completed;
        static DEFINE_RCU_RANDOM(rand);
        static DEFINE_SPINLOCK(rand_lock);
        struct rcu_torture *p;
        int pipe_count;

        idx = cur_ops->readlock();
        completed = cur_ops->completed();
        p = rcu_dereference(rcu_torture_current);
        if (p == NULL) {
                /* Leave because rcu_torture_writer is not yet underway */
                cur_ops->readunlock(idx);
                return;
        }
        if (p->rtort_mbtest == 0)
                atomic_inc(&n_rcu_torture_mberror);
        spin_lock(&rand_lock);
        cur_ops->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;
        }
        __this_cpu_inc(per_cpu_var(rcu_torture_count)[pipe_count]);
        completed = cur_ops->completed() - completed;
        if (completed > RCU_TORTURE_PIPE_LEN) {
                /* Should not happen, but... */
                completed = RCU_TORTURE_PIPE_LEN;
        }
        __this_cpu_inc(per_cpu_var(rcu_torture_batch)[completed]);
        preempt_enable();
        cur_ops->readunlock(idx);
}

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

        VERBOSE_PRINTK_STRING("rcu_torture_reader task started");
        set_user_nice(current, 19);
        if (irqreader && cur_ops->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, 1);
                }
                idx = cur_ops->readlock();
                completed = cur_ops->completed();
                p = rcu_dereference(rcu_torture_current);
                if (p == NULL) {
                        /* Wait for rcu_torture_writer to get underway */
                        cur_ops->readunlock(idx);
                        schedule_timeout_interruptible(HZ);
                        continue;
                }
                if (p->rtort_mbtest == 0)
                        atomic_inc(&n_rcu_torture_mberror);
                cur_ops->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;
                }
                __this_cpu_inc(per_cpu_var(rcu_torture_count)[pipe_count]);
                completed = cur_ops->completed() - completed;
                if (completed > RCU_TORTURE_PIPE_LEN) {
                        /* Should not happen, but... */
                        completed = RCU_TORTURE_PIPE_LEN;
                }
                __this_cpu_inc(per_cpu_var(rcu_torture_batch)[completed]);
                preempt_enable();
                cur_ops->readunlock(idx);
                schedule();
                rcu_stutter_wait("rcu_torture_reader");
        } while (!kthread_should_stop() && fullstop == FULLSTOP_DONTSTOP);
        VERBOSE_PRINTK_STRING("rcu_torture_reader task stopping");
        rcutorture_shutdown_absorb("rcu_torture_reader");
        if (irqreader && cur_ops->irq_capable)
                del_timer_sync(&t);
        while (!kthread_should_stop())
                schedule_timeout_uninterruptible(1);
        return 0;
}

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

        for_each_possible_cpu(cpu) {
                for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
                        pipesummary[i] += per_cpu(rcu_torture_count, cpu)[i];
                        batchsummary[i] += per_cpu(rcu_torture_batch, cpu)[i];
                }
        }
        for (i = RCU_TORTURE_PIPE_LEN - 1; i >= 0; i--) {
                if (pipesummary[i] != 0)
                        break;
        }
        cnt += sprintf(&page[cnt], "%s%s ", torture_type, TORTURE_FLAG);
        cnt += sprintf(&page[cnt],
                       "rtc: %p ver: %ld tfle: %d rta: %d rtaf: %d rtf: %d "
                       "rtmbe: %d nt: %ld",
                       rcu_torture_current,
                       rcu_torture_current_version,
                       list_empty(&rcu_torture_freelist),
                       atomic_read(&n_rcu_torture_alloc),
                       atomic_read(&n_rcu_torture_alloc_fail),
                       atomic_read(&n_rcu_torture_free),
                       atomic_read(&n_rcu_torture_mberror),
                       n_rcu_torture_timers);
        if (atomic_read(&n_rcu_torture_mberror) != 0)
                cnt += sprintf(&page[cnt], " !!!");
        cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
        if (i > 1) {
                cnt += sprintf(&page[cnt], "!!! ");
                atomic_inc(&n_rcu_torture_error);
                WARN_ON_ONCE(1);
        }
        cnt += sprintf(&page[cnt], "Reader Pipe: ");
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
                cnt += sprintf(&page[cnt], " %ld", pipesummary[i]);
        cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
        cnt += sprintf(&page[cnt], "Reader Batch: ");
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
                cnt += sprintf(&page[cnt], " %ld", batchsummary[i]);
        cnt += sprintf(&page[cnt], "\n%s%s ", torture_type, TORTURE_FLAG);
        cnt += sprintf(&page[cnt], "Free-Block Circulation: ");
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
                cnt += sprintf(&page[cnt], " %d",
                               atomic_read(&rcu_torture_wcount[i]));
        }
        cnt += sprintf(&page[cnt], "\n");
        if (cur_ops->stats)
                cnt += cur_ops->stats(&page[cnt]);
        return cnt;
}

/*
 * Print torture statistics.  Caller must ensure that there is only
 * one call to this function at a given time!!!  This is normally
 * accomplished by relying on the module system to only have one copy
 * of the module loaded, and then by giving the rcu_torture_stats
 * kthread full control (or the init/cleanup functions when rcu_torture_stats
 * thread is not running).
 */
static void
rcu_torture_stats_print(void)
{
        int cnt;

        cnt = rcu_torture_printk(printk_buf);
        printk(KERN_ALERT "%s", printk_buf);
}

/*
 * Periodically prints torture statistics, if periodic statistics printing
 * was specified via the stat_interval module parameter.
 *
 * No need to worry about fullstop here, since this one doesn't reference
 * volatile state or register callbacks.
 */
static int
rcu_torture_stats(void *arg)
{
        VERBOSE_PRINTK_STRING("rcu_torture_stats task started");
        do {
                schedule_timeout_interruptible(stat_interval * HZ);
                rcu_torture_stats_print();
                rcutorture_shutdown_absorb("rcu_torture_stats");
        } while (!kthread_should_stop());
        VERBOSE_PRINTK_STRING("rcu_torture_stats task stopping");
        return 0;
}

static int rcu_idle_cpu;        /* Force all torture tasks off this CPU */

/* Shuffle tasks such that we allow @rcu_idle_cpu to become idle. A special case
 * is when @rcu_idle_cpu = -1, when we allow the tasks to run on all CPUs.
 */
static void rcu_torture_shuffle_tasks(void)
{
        int i;

        cpumask_setall(shuffle_tmp_mask);
        get_online_cpus();

        /* No point in shuffling if there is only one online CPU (ex: UP) */
        if (num_online_cpus() == 1) {
                put_online_cpus();
                return;
        }

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

        set_cpus_allowed_ptr(current, shuffle_tmp_mask);

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

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

        if (writer_task)
                set_cpus_allowed_ptr(writer_task, shuffle_tmp_mask);

        if (stats_task)
                set_cpus_allowed_ptr(stats_task, shuffle_tmp_mask);

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

        put_online_cpus();
}

/* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
 * system to become idle at a time and cut off its timer ticks. This is meant
 * to test the support for such tickless idle CPU in RCU.
 */
static int
rcu_torture_shuffle(void *arg)
{
        VERBOSE_PRINTK_STRING("rcu_torture_shuffle task started");
        do {
                schedule_timeout_interruptible(shuffle_interval * HZ);
                rcu_torture_shuffle_tasks();
                rcutorture_shutdown_absorb("rcu_torture_shuffle");
        } while (!kthread_should_stop());
        VERBOSE_PRINTK_STRING("rcu_torture_shuffle task stopping");
        return 0;
}

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

static inline void
rcu_torture_print_module_parms(char *tag)
{
        printk(KERN_ALERT "%s" TORTURE_FLAG
                "--- %s: nreaders=%d nfakewriters=%d "
                "stat_interval=%d verbose=%d test_no_idle_hz=%d "
                "shuffle_interval=%d stutter=%d irqreader=%d\n",
                torture_type, tag, nrealreaders, nfakewriters,
                stat_interval, verbose, test_no_idle_hz, shuffle_interval,
                stutter, irqreader);
}

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

static void
rcu_torture_cleanup(void)
{
        int i;

        mutex_lock(&fullstop_mutex);
        if (fullstop == FULLSTOP_SHUTDOWN) {
                printk(KERN_WARNING /* but going down anyway, so... */
                       "Concurrent 'rmmod rcutorture' and shutdown illegal!\n");
                mutex_unlock(&fullstop_mutex);
                schedule_timeout_uninterruptible(10);
                if (cur_ops->cb_barrier != NULL)
                        cur_ops->cb_barrier();
                return;
        }
        fullstop = FULLSTOP_RMMOD;
        mutex_unlock(&fullstop_mutex);
        unregister_reboot_notifier(&rcutorture_nb);
        if (stutter_task) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_stutter task");
                kthread_stop(stutter_task);
        }
        stutter_task = NULL;
        if (shuffler_task) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_shuffle task");
                kthread_stop(shuffler_task);
                free_cpumask_var(shuffle_tmp_mask);
        }
        shuffler_task = NULL;

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

        if (reader_tasks) {
                for (i = 0; i < nrealreaders; i++) {
                        if (reader_tasks[i]) {
                                VERBOSE_PRINTK_STRING(
                                        "Stopping rcu_torture_reader task");
                                kthread_stop(reader_tasks[i]);
                        }
                        reader_tasks[i] = NULL;
                }
                kfree(reader_tasks);
                reader_tasks = NULL;
        }
        rcu_torture_current = NULL;

        if (fakewriter_tasks) {
                for (i = 0; i < nfakewriters; i++) {
                        if (fakewriter_tasks[i]) {
                                VERBOSE_PRINTK_STRING(
                                        "Stopping rcu_torture_fakewriter task");
                                kthread_stop(fakewriter_tasks[i]);
                        }
                        fakewriter_tasks[i] = NULL;
                }
                kfree(fakewriter_tasks);
                fakewriter_tasks = NULL;
        }

        if (stats_task) {
                VERBOSE_PRINTK_STRING("Stopping rcu_torture_stats task");
                kthread_stop(stats_task);
        }
        stats_task = NULL;

        /* Wait for all RCU callbacks to fire.  */

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

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

        if (cur_ops->cleanup)
                cur_ops->cleanup();
        if (atomic_read(&n_rcu_torture_error))
                rcu_torture_print_module_parms("End of test: FAILURE");
        else
                rcu_torture_print_module_parms("End of test: SUCCESS");
}

static int __init
rcu_torture_init(void)
{
        int i;
        int cpu;
        int firsterr = 0;
        static struct rcu_torture_ops *torture_ops[] =
                { &rcu_ops, &rcu_sync_ops, &rcu_bh_ops, &rcu_bh_sync_ops,
                  &sched_expedited_ops,
                  &srcu_ops, &sched_ops, &sched_ops_sync, };

        mutex_lock(&fullstop_mutex);

        /* Process args and tell the world that the torturer is on the job. */
        for (i = 0; i < ARRAY_SIZE(torture_ops); i++) {
                cur_ops = torture_ops[i];
                if (strcmp(torture_type, cur_ops->name) == 0)
                        break;
        }
        if (i == ARRAY_SIZE(torture_ops)) {
                printk(KERN_ALERT "rcutorture: invalid torture type: \"%s\"\n",
                       torture_type);
                mutex_unlock(&fullstop_mutex);
                return -EINVAL;
        }
        if (cur_ops->init)
                cur_ops->init(); /* no "goto unwind" prior to this point!!! */

        if (nreaders >= 0)
                nrealreaders = nreaders;
        else
                nrealreaders = 2 * num_online_cpus();
        rcu_torture_print_module_parms("Start of test");
        fullstop = FULLSTOP_DONTSTOP;

        /* Set up the freelist. */

        INIT_LIST_HEAD(&rcu_torture_freelist);
        for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++) {
                rcu_tortures[i].rtort_mbtest = 0;
                list_add_tail(&rcu_tortures[i].rtort_free,
                              &rcu_torture_freelist);
        }

        /* Initialize the statistics so that each run gets its own numbers. */

        rcu_torture_current = NULL;
        rcu_torture_current_version = 0;
        atomic_set(&n_rcu_torture_alloc, 0);
        atomic_set(&n_rcu_torture_alloc_fail, 0);
        atomic_set(&n_rcu_torture_free, 0);
        atomic_set(&n_rcu_torture_mberror, 0);
        atomic_set(&n_rcu_torture_error, 0);
        for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++)
                atomic_set(&rcu_torture_wcount[i], 0);
        for_each_possible_cpu(cpu) {
                for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) {
                        per_cpu(rcu_torture_count, cpu)[i] = 0;
                        per_cpu(rcu_torture_batch, cpu)[i] = 0;
                }
        }

        /* Start up the kthreads. */

        VERBOSE_PRINTK_STRING("Creating rcu_torture_writer task");
        writer_task = kthread_run(rcu_torture_writer, NULL,
                                  "rcu_torture_writer");
        if (IS_ERR(writer_task)) {
                firsterr = PTR_ERR(writer_task);
                VERBOSE_PRINTK_ERRSTRING("Failed to create writer");
                writer_task = NULL;
                goto unwind;
        }
        fakewriter_tasks = kzalloc(nfakewriters * sizeof(fakewriter_tasks[0]),
                                   GFP_KERNEL);
        if (fakewriter_tasks == NULL) {
                VERBOSE_PRINTK_ERRSTRING("out of memory");
                firsterr = -ENOMEM;
                goto unwind;
        }
        for (i = 0; i < nfakewriters; i++) {
                VERBOSE_PRINTK_STRING("Creating rcu_torture_fakewriter task");
                fakewriter_tasks[i] = kthread_run(rcu_torture_fakewriter, NULL,
                                                  "rcu_torture_fakewriter");
                if (IS_ERR(fakewriter_tasks[i])) {
                        firsterr = PTR_ERR(fakewriter_tasks[i]);
                        VERBOSE_PRINTK_ERRSTRING("Failed to create fakewriter");
                        fakewriter_tasks[i] = NULL;
                        goto unwind;
                }
        }
        reader_tasks = kzalloc(nrealreaders * sizeof(reader_tasks[0]),
                               GFP_KERNEL);
        if (reader_tasks == NULL) {
                VERBOSE_PRINTK_ERRSTRING("out of memory");
                firsterr = -ENOMEM;
                goto unwind;
        }
        for (i = 0; i < nrealreaders; i++) {
                VERBOSE_PRINTK_STRING("Creating rcu_torture_reader task");
                reader_tasks[i] = kthread_run(rcu_torture_reader, NULL,
                                              "rcu_torture_reader");
                if (IS_ERR(reader_tasks[i])) {
                        firsterr = PTR_ERR(reader_tasks[i]);
                        VERBOSE_PRINTK_ERRSTRING("Failed to create reader");
                        reader_tasks[i] = NULL;
                        goto unwind;
                }
        }
        if (stat_interval > 0) {
                VERBOSE_PRINTK_STRING("Creating rcu_torture_stats task");
                stats_task = kthread_run(rcu_torture_stats, NULL,
                                        "rcu_torture_stats");
                if (IS_ERR(stats_task)) {
                        firsterr = PTR_ERR(stats_task);
                        VERBOSE_PRINTK_ERRSTRING("Failed to create stats");
                        stats_task = NULL;
                        goto unwind;
                }
        }
        if (test_no_idle_hz) {
                rcu_idle_cpu = num_online_cpus() - 1;

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

                /* Create the shuffler thread */
                shuffler_task = kthread_run(rcu_torture_shuffle, NULL,
                                          "rcu_torture_shuffle");
                if (IS_ERR(shuffler_task)) {
                        free_cpumask_var(shuffle_tmp_mask);
                        firsterr = PTR_ERR(shuffler_task);
                        VERBOSE_PRINTK_ERRSTRING("Failed to create shuffler");
                        shuffler_task = NULL;
                        goto unwind;
                }
        }
        if (stutter < 0)
                stutter = 0;
        if (stutter) {
                /* Create the stutter thread */
                stutter_task = kthread_run(rcu_torture_stutter, NULL,
                                          "rcu_torture_stutter");
                if (IS_ERR(stutter_task)) {
                        firsterr = PTR_ERR(stutter_task);
                        VERBOSE_PRINTK_ERRSTRING("Failed to create stutter");
                        stutter_task = NULL;
                        goto unwind;
                }
        }
        register_reboot_notifier(&rcutorture_nb);
        mutex_unlock(&fullstop_mutex);
        return 0;

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

module_init(rcu_torture_init);
module_exit(rcu_torture_cleanup);