// SPDX-License-Identifier: GPL-2.0+
/*
 * Read-Copy Update module-based torture test facility
 *
 * Copyright (C) IBM Corporation, 2005, 2006
 *
 * Authors: Paul E. McKenney <paulmck@linux.ibm.com>
 *        Josh Triplett <josh@joshtriplett.org>
 *
 * See also:  Documentation/RCU/torture.txt
 */

#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/signal.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 <linux/trace_clock.h>
#include <asm/byteorder.h>
#include <linux/torture.h>
#include <linux/vmalloc.h>
#include <linux/sched/debug.h>
#include <linux/sched/sysctl.h>
#include <linux/oom.h>

#include "rcu.h"

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


/* Bits for ->extendables field, extendables param, and related definitions. */
#define RCUTORTURE_RDR_SHIFT     8      /* Put SRCU index in upper bits. */
#define RCUTORTURE_RDR_MASK      ((1 << RCUTORTURE_RDR_SHIFT) - 1)
#define RCUTORTURE_RDR_BH        0x01   /* Extend readers by disabling bh. */
#define RCUTORTURE_RDR_IRQ       0x02   /*  ... disabling interrupts. */
#define RCUTORTURE_RDR_PREEMPT   0x04   /*  ... disabling preemption. */
#define RCUTORTURE_RDR_RBH       0x08   /*  ... rcu_read_lock_bh(). */
#define RCUTORTURE_RDR_SCHED     0x10   /*  ... rcu_read_lock_sched(). */
#define RCUTORTURE_RDR_RCU       0x20   /*  ... entering another RCU reader. */
#define RCUTORTURE_RDR_NBITS     6      /* Number of bits defined above. */
#define RCUTORTURE_MAX_EXTEND    \
        (RCUTORTURE_RDR_BH | RCUTORTURE_RDR_IRQ | RCUTORTURE_RDR_PREEMPT | \
         RCUTORTURE_RDR_RBH | RCUTORTURE_RDR_SCHED)
#define RCUTORTURE_RDR_MAX_LOOPS 0x7    /* Maximum reader extensions. */
                                        /* Must be power of two minus one. */
#define RCUTORTURE_RDR_MAX_SEGS (RCUTORTURE_RDR_MAX_LOOPS + 3)

torture_param(int, extendables, RCUTORTURE_MAX_EXTEND,
              "Extend readers by disabling bh (1), irqs (2), or preempt (4)");
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, fwd_progress, 1, "Test grace-period forward progress");
torture_param(int, fwd_progress_div, 4, "Fraction of CPU stall to wait");
torture_param(int, fwd_progress_holdoff, 60,
              "Time between forward-progress tests (s)");
torture_param(bool, fwd_progress_need_resched, 1,
              "Hide cond_resched() behind need_resched()");
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 (jiffies), 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, stall_cpu_irqsoff, 0, "Disable interrupts while stalling.");
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(int, verbose, 1,
             "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, srcu, ...)");

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 *fqs_task;
static struct task_struct *boost_tasks[NR_CPUS];
static struct task_struct *stall_task;
static struct task_struct *fwd_prog_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);
static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_batch);
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 atomic_long_t n_rcu_torture_timers;
static long n_barrier_attempts;
static long n_barrier_successes; /* did rcu_barrier test succeed? */
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
static const char * const rcu_torture_writer_state_names[] = {
        "RTWS_FIXED_DELAY",
        "RTWS_DELAY",
        "RTWS_REPLACE",
        "RTWS_DEF_FREE",
        "RTWS_EXP_SYNC",
        "RTWS_COND_GET",
        "RTWS_COND_SYNC",
        "RTWS_SYNC",
        "RTWS_STUTTER",
        "RTWS_STOPPING",
};

/* Record reader segment types and duration for first failing read. */
struct rt_read_seg {
        int rt_readstate;
        unsigned long rt_delay_jiffies;
        unsigned long rt_delay_ms;
        unsigned long rt_delay_us;
        bool rt_preempted;
};
static int err_segs_recorded;
static struct rt_read_seg err_segs[RCUTORTURE_RDR_MAX_SEGS];
static int rt_read_nsegs;

static const char *rcu_torture_writer_state_getname(void)
{
        unsigned int i = READ_ONCE(rcu_torture_writer_state);

        if (i >= ARRAY_SIZE(rcu_torture_writer_state_names))
                return "???";
        return rcu_torture_writer_state_names[i];
}

#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();

        (void)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);

static bool rcu_fwd_cb_nodelay;         /* Short rcu_torture_delay() delays. */

/*
 * 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);
        void (*cleanup)(void);
        int (*readlock)(void);
        void (*read_delay)(struct torture_random_state *rrsp,
                           struct rt_read_seg *rtrsp);
        void (*readunlock)(int idx);
        unsigned long (*get_gp_seq)(void);
        unsigned long (*gp_diff)(unsigned long new, unsigned long old);
        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);
        call_rcu_func_t call;
        void (*cb_barrier)(void);
        void (*fqs)(void);
        void (*stats)(void);
        int (*stall_dur)(void);
        int irq_capable;
        int can_boost;
        int extendables;
        int slow_gps;
        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, struct rt_read_seg *rtrsp)
{
        unsigned long started;
        unsigned long completed;
        const unsigned long shortdelay_us = 200;
        unsigned long longdelay_ms = 300;
        unsigned long long ts;

        /* 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_fwd_cb_nodelay &&
            !(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {
                started = cur_ops->get_gp_seq();
                ts = rcu_trace_clock_local();
                if (preempt_count() & (SOFTIRQ_MASK | HARDIRQ_MASK))
                        longdelay_ms = 5; /* Avoid triggering BH limits. */
                mdelay(longdelay_ms);
                rtrsp->rt_delay_ms = longdelay_ms;
                completed = cur_ops->get_gp_seq();
                do_trace_rcu_torture_read(cur_ops->name, NULL, ts,
                                          started, completed);
        }
        if (!(torture_random(rrsp) % (nrealreaders * 2 * shortdelay_us))) {
                udelay(shortdelay_us);
                rtrsp->rt_delay_us = shortdelay_us;
        }
        if (!preempt_count() &&
            !(torture_random(rrsp) % (nrealreaders * 500))) {
                torture_preempt_schedule();  /* QS only if preemptible. */
                rtrsp->rt_preempted = true;
        }
}

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,
        .get_gp_seq     = rcu_get_gp_seq,
        .gp_diff        = rcu_seq_diff,
        .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,
        .stall_dur      = rcu_jiffies_till_stall_check,
        .irq_capable    = 1,
        .can_boost      = rcu_can_boost(),
        .extendables    = RCUTORTURE_MAX_EXTEND,
        .name           = "rcu"
};

/*
 * 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, rcu_callback_t func)
{
        /* 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,
        .get_gp_seq     = 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           = "busted"
};

/*
 * Definitions for srcu torture testing.
 */

DEFINE_STATIC_SRCU(srcu_ctl);
static struct srcu_struct srcu_ctld;
static struct srcu_struct *srcu_ctlp = &srcu_ctl;

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

static void
srcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
{
        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 && in_task()) {
                schedule_timeout_interruptible(longdelay);
                rtrsp->rt_delay_jiffies = longdelay;
        } else {
                rcu_read_delay(rrsp, rtrsp);
        }
}

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

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

static void srcu_torture_deferred_free(struct rcu_torture *rp)
{
        call_srcu(srcu_ctlp, &rp->rtort_rcu, rcu_torture_cb);
}

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

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

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

static void srcu_torture_stats(void)
{
        srcu_torture_stats_print(srcu_ctlp, torture_type, TORTURE_FLAG);
}

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

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,
        .get_gp_seq     = 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,
        .irq_capable    = 1,
        .name           = "srcu"
};

static void srcu_torture_init(void)
{
        rcu_sync_torture_init();
        WARN_ON(init_srcu_struct(&srcu_ctld));
        srcu_ctlp = &srcu_ctld;
}

static void srcu_torture_cleanup(void)
{
        cleanup_srcu_struct(&srcu_ctld);
        srcu_ctlp = &srcu_ctl; /* In case of a later rcutorture run. */
}

/* As above, but dynamically allocated. */
static struct rcu_torture_ops srcud_ops = {
        .ttype          = SRCU_FLAVOR,
        .init           = srcu_torture_init,
        .cleanup        = srcu_torture_cleanup,
        .readlock       = srcu_torture_read_lock,
        .read_delay     = srcu_read_delay,
        .readunlock     = srcu_torture_read_unlock,
        .get_gp_seq     = 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,
        .irq_capable    = 1,
        .name           = "srcud"
};

/* As above, but broken due to inappropriate reader extension. */
static struct rcu_torture_ops busted_srcud_ops = {
        .ttype          = SRCU_FLAVOR,
        .init           = srcu_torture_init,
        .cleanup        = srcu_torture_cleanup,
        .readlock       = srcu_torture_read_lock,
        .read_delay     = rcu_read_delay,
        .readunlock     = srcu_torture_read_unlock,
        .get_gp_seq     = 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,
        .irq_capable    = 1,
        .extendables    = RCUTORTURE_MAX_EXTEND,
        .name           = "busted_srcud"
};

/*
 * 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,
        .get_gp_seq     = 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,
        .slow_gps       = 1,
        .name           = "tasks"
};

/*
 * Definitions for trivial CONFIG_PREEMPT=n-only torture testing.
 * This implementation does not necessarily work well with CPU hotplug.
 */

static void synchronize_rcu_trivial(void)
{
        int cpu;

        for_each_online_cpu(cpu) {
                rcutorture_sched_setaffinity(current->pid, cpumask_of(cpu));
                WARN_ON_ONCE(raw_smp_processor_id() != cpu);
        }
}

static int rcu_torture_read_lock_trivial(void) __acquires(RCU)
{
        preempt_disable();
        return 0;
}

static void rcu_torture_read_unlock_trivial(int idx) __releases(RCU)
{
        preempt_enable();
}

static struct rcu_torture_ops trivial_ops = {
        .ttype          = RCU_TRIVIAL_FLAVOR,
        .init           = rcu_sync_torture_init,
        .readlock       = rcu_torture_read_lock_trivial,
        .read_delay     = rcu_read_delay,  /* just reuse rcu's version. */
        .readunlock     = rcu_torture_read_unlock_trivial,
        .get_gp_seq     = rcu_no_completed,
        .sync           = synchronize_rcu_trivial,
        .exp_sync       = synchronize_rcu_trivial,
        .fqs            = NULL,
        .stats          = NULL,
        .irq_capable    = 1,
        .name           = "trivial"
};

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

static bool __maybe_unused torturing_tasks(void)
{
        return cur_ops == &tasks_ops;
}

/*
 * 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);

        /* Ensure RCU-core accesses precede clearing ->inflight */
        smp_store_release(&rbip->inflight, 0);
}

static int old_rt_runtime = -1;

static void rcu_torture_disable_rt_throttle(void)
{
        /*
         * Disable RT throttling so that rcutorture's boost threads don't get
         * throttled. Only possible if rcutorture is built-in otherwise the
         * user should manually do this by setting the sched_rt_period_us and
         * sched_rt_runtime sysctls.
         */
        if (!IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) || old_rt_runtime != -1)
                return;

        old_rt_runtime = sysctl_sched_rt_runtime;
        sysctl_sched_rt_runtime = -1;
}

static void rcu_torture_enable_rt_throttle(void)
{
        if (!IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) || old_rt_runtime == -1)
                return;

        sysctl_sched_rt_runtime = old_rt_runtime;
        old_rt_runtime = -1;
}

static bool rcu_torture_boost_failed(unsigned long start, unsigned long end)
{
        if (end - start > test_boost_duration * HZ - HZ / 2) {
                VERBOSE_TOROUT_STRING("rcu_torture_boost boosting failed");
                n_rcu_torture_boost_failure++;

                return true; /* failed */
        }

        return false; /* passed */
}

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 {
                /* Track if the test failed already in this test interval? */
                bool failed = false;

                /* Increment n_rcu_torture_boosts once per boost-test */
                while (!kthread_should_stop()) {
                        if (mutex_trylock(&boost_mutex)) {
                                n_rcu_torture_boosts++;
                                mutex_unlock(&boost_mutex);
                                break;
                        }
                        schedule_timeout_uninterruptible(1);
                }
                if (kthread_should_stop())
                        goto checkwait;

                /* 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 (!smp_load_acquire(&rbi.inflight)) {
                                /* RCU core before ->inflight = 1. */
                                smp_store_release(&rbi.inflight, 1);
                                call_rcu(&rbi.rcu, rcu_torture_boost_cb);
                                /* Check if the boost test failed */
                                failed = failed ||
                                         rcu_torture_boost_failed(call_rcu_time,
                                                                 jiffies);
                                call_rcu_time = jiffies;
                        }
                        stutter_wait("rcu_torture_boost");
                        if (torture_must_stop())
                                goto checkwait;
                }

                /*
                 * If boost never happened, then inflight will always be 1, in
                 * this case the boost check would never happen in the above
                 * loop so do another one here.
                 */
                if (!failed && smp_load_acquire(&rbi.inflight))
                        rcu_torture_boost_failed(call_rcu_time, jiffies);

                /*
                 * 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;
                                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() || smp_load_acquire(&rbi.inflight)) {
                torture_shutdown_absorb("rcu_torture_boost");
                schedule_timeout_uninterruptible(1);
        }
        destroy_rcu_head_on_stack(&rbi.rcu);
        torture_kthread_stopping("rcu_torture_boost");
        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)
{
        bool can_expedite = !rcu_gp_is_expedited() && !rcu_gp_is_normal();
        int expediting = 0;
        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");
        if (!can_expedite)
                pr_alert("%s" TORTURE_FLAG
                         " GP expediting controlled from boot/sysfs for %s.\n",
                         torture_type, cur_ops->name);

        /* Initialize synctype[] array.  If none set, take default. */
        if (!gp_cond1 && !gp_exp1 && !gp_normal1 && !gp_sync1)
                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;
                pr_info("%s: Testing conditional GPs.\n", __func__);
        } else if (gp_cond && (!cur_ops->get_state || !cur_ops->cond_sync)) {
                pr_alert("%s: gp_cond without primitives.\n", __func__);
        }
        if (gp_exp1 && cur_ops->exp_sync) {
                synctype[nsynctypes++] = RTWS_EXP_SYNC;
                pr_info("%s: Testing expedited GPs.\n", __func__);
        } else if (gp_exp && !cur_ops->exp_sync) {
                pr_alert("%s: gp_exp without primitives.\n", __func__);
        }
        if (gp_normal1 && cur_ops->deferred_free) {
                synctype[nsynctypes++] = RTWS_DEF_FREE;
                pr_info("%s: Testing asynchronous GPs.\n", __func__);
        } else if (gp_normal && !cur_ops->deferred_free) {
                pr_alert("%s: gp_normal without primitives.\n", __func__);
        }
        if (gp_sync1 && cur_ops->sync) {
                synctype[nsynctypes++] = RTWS_SYNC;
                pr_info("%s: Testing normal GPs.\n", __func__);
        } else if (gp_sync && !cur_ops->sync) {
                pr_alert("%s: gp_sync without primitives.\n", __func__);
        }
        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;
                        }
                }
                WRITE_ONCE(rcu_torture_current_version,
                           rcu_torture_current_version + 1);
                /* Cycle through nesting levels of rcu_expedite_gp() calls. */
                if (can_expedite &&
                    !(torture_random(&rand) & 0xff & (!!expediting - 1))) {
                        WARN_ON_ONCE(expediting == 0 && rcu_gp_is_expedited());
                        if (expediting >= 0)
                                rcu_expedite_gp();
                        else
                                rcu_unexpedite_gp();
                        if (++expediting > 3)
                                expediting = -expediting;
                } else if (!can_expedite) { /* Disabled during boot, recheck. */
                        can_expedite = !rcu_gp_is_expedited() &&
                                       !rcu_gp_is_normal();
                }
                rcu_torture_writer_state = RTWS_STUTTER;
                if (stutter_wait("rcu_torture_writer") &&
                    !READ_ONCE(rcu_fwd_cb_nodelay) &&
                    !cur_ops->slow_gps &&
                    !torture_must_stop())
                        for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++)
                                if (list_empty(&rcu_tortures[i].rtort_free) &&
                                    rcu_access_pointer(rcu_torture_current) !=
                                    &rcu_tortures[i]) {
                                        rcu_ftrace_dump(DUMP_ALL);
                                        WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count);
                                }
        } while (!torture_must_stop());
        /* Reset expediting back to unexpedited. */
        if (expediting > 0)
                expediting = -expediting;
        while (can_expedite && expediting++ < 0)
                rcu_unexpedite_gp();
        WARN_ON_ONCE(can_expedite && rcu_gp_is_expedited());
        if (!can_expedite)
                pr_alert("%s" TORTURE_FLAG
                         " Dynamic grace-period expediting was disabled.\n",
                         torture_type);
        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 (cur_ops->sync && torture_random(&rand) & 0x80)
                                cur_ops->sync();
                        else if (cur_ops->exp_sync)
                                cur_ops->exp_sync();
                } else if (gp_normal && cur_ops->sync) {
                        cur_ops->sync();
                } else if (cur_ops->exp_sync) {
                        cur_ops->exp_sync();
                }
                stutter_wait("rcu_torture_fakewriter");
        } while (!torture_must_stop());

        torture_kthread_stopping("rcu_torture_fakewriter");
        return 0;
}

static void rcu_torture_timer_cb(struct rcu_head *rhp)
{
        kfree(rhp);
}

/*
 * Do one extension of an RCU read-side critical section using the
 * current reader state in readstate (set to zero for initial entry
 * to extended critical section), set the new state as specified by
 * newstate (set to zero for final exit from extended critical section),
 * and random-number-generator state in trsp.  If this is neither the
 * beginning or end of the critical section and if there was actually a
 * change, do a ->read_delay().
 */
static void rcutorture_one_extend(int *readstate, int newstate,
                                  struct torture_random_state *trsp,
                                  struct rt_read_seg *rtrsp)
{
        int idxnew = -1;
        int idxold = *readstate;
        int statesnew = ~*readstate & newstate;
        int statesold = *readstate & ~newstate;

        WARN_ON_ONCE(idxold < 0);
        WARN_ON_ONCE((idxold >> RCUTORTURE_RDR_SHIFT) > 1);
        rtrsp->rt_readstate = newstate;

        /* First, put new protection in place to avoid critical-section gap. */
        if (statesnew & RCUTORTURE_RDR_BH)
                local_bh_disable();
        if (statesnew & RCUTORTURE_RDR_IRQ)
                local_irq_disable();
        if (statesnew & RCUTORTURE_RDR_PREEMPT)
                preempt_disable();
        if (statesnew & RCUTORTURE_RDR_RBH)
                rcu_read_lock_bh();
        if (statesnew & RCUTORTURE_RDR_SCHED)
                rcu_read_lock_sched();
        if (statesnew & RCUTORTURE_RDR_RCU)
                idxnew = cur_ops->readlock() << RCUTORTURE_RDR_SHIFT;

        /* Next, remove old protection, irq first due to bh conflict. */
        if (statesold & RCUTORTURE_RDR_IRQ)
                local_irq_enable();
        if (statesold & RCUTORTURE_RDR_BH)
                local_bh_enable();
        if (statesold & RCUTORTURE_RDR_PREEMPT)
                preempt_enable();
        if (statesold & RCUTORTURE_RDR_RBH)
                rcu_read_unlock_bh();
        if (statesold & RCUTORTURE_RDR_SCHED)
                rcu_read_unlock_sched();
        if (statesold & RCUTORTURE_RDR_RCU)
                cur_ops->readunlock(idxold >> RCUTORTURE_RDR_SHIFT);

        /* Delay if neither beginning nor end and there was a change. */
        if ((statesnew || statesold) && *readstate && newstate)
                cur_ops->read_delay(trsp, rtrsp);

        /* Update the reader state. */
        if (idxnew == -1)
                idxnew = idxold & ~RCUTORTURE_RDR_MASK;
        WARN_ON_ONCE(idxnew < 0);
        WARN_ON_ONCE((idxnew >> RCUTORTURE_RDR_SHIFT) > 1);
        *readstate = idxnew | newstate;
        WARN_ON_ONCE((*readstate >> RCUTORTURE_RDR_SHIFT) < 0);
        WARN_ON_ONCE((*readstate >> RCUTORTURE_RDR_SHIFT) > 1);
}

/* Return the biggest extendables mask given current RCU and boot parameters. */
static int rcutorture_extend_mask_max(void)
{
        int mask;

        WARN_ON_ONCE(extendables & ~RCUTORTURE_MAX_EXTEND);
        mask = extendables & RCUTORTURE_MAX_EXTEND & cur_ops->extendables;
        mask = mask | RCUTORTURE_RDR_RCU;
        return mask;
}

/* Return a random protection state mask, but with at least one bit set. */
static int
rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp)
{
        int mask = rcutorture_extend_mask_max();
        unsigned long randmask1 = torture_random(trsp) >> 8;
        unsigned long randmask2 = randmask1 >> 3;

        WARN_ON_ONCE(mask >> RCUTORTURE_RDR_SHIFT);
        /* Mostly only one bit (need preemption!), sometimes lots of bits. */
        if (!(randmask1 & 0x7))
                mask = mask & randmask2;
        else
                mask = mask & (1 << (randmask2 % RCUTORTURE_RDR_NBITS));
        /* Can't enable bh w/irq disabled. */
        if ((mask & RCUTORTURE_RDR_IRQ) &&
            ((!(mask & RCUTORTURE_RDR_BH) && (oldmask & RCUTORTURE_RDR_BH)) ||
             (!(mask & RCUTORTURE_RDR_RBH) && (oldmask & RCUTORTURE_RDR_RBH))))
                mask |= RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH;
        return mask ?: RCUTORTURE_RDR_RCU;
}

/*
 * Do a randomly selected number of extensions of an existing RCU read-side
 * critical section.
 */
static struct rt_read_seg *
rcutorture_loop_extend(int *readstate, struct torture_random_state *trsp,
                       struct rt_read_seg *rtrsp)
{
        int i;
        int j;
        int mask = rcutorture_extend_mask_max();

        WARN_ON_ONCE(!*readstate); /* -Existing- RCU read-side critsect! */
        if (!((mask - 1) & mask))
                return rtrsp;  /* Current RCU reader not extendable. */
        /* Bias towards larger numbers of loops. */
        i = (torture_random(trsp) >> 3);
        i = ((i | (i >> 3)) & RCUTORTURE_RDR_MAX_LOOPS) + 1;
        for (j = 0; j < i; j++) {
                mask = rcutorture_extend_mask(*readstate, trsp);
                rcutorture_one_extend(readstate, mask, trsp, &rtrsp[j]);
        }
        return &rtrsp[j];
}

/*
 * Do one read-side critical section, returning false if there was
 * no data to read.  Can be invoked both from process context and
 * from a timer handler.
 */
static bool rcu_torture_one_read(struct torture_random_state *trsp)
{
        int i;
        unsigned long started;
        unsigned long completed;
        int newstate;
        struct rcu_torture *p;
        int pipe_count;
        int readstate = 0;
        struct rt_read_seg rtseg[RCUTORTURE_RDR_MAX_SEGS] = { { 0 } };
        struct rt_read_seg *rtrsp = &rtseg[0];
        struct rt_read_seg *rtrsp1;
        unsigned long long ts;

        newstate = rcutorture_extend_mask(readstate, trsp);
        rcutorture_one_extend(&readstate, newstate, trsp, rtrsp++);
        started = cur_ops->get_gp_seq();
        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_ctlp) ||
                                  torturing_tasks());
        if (p == NULL) {
                /* Wait for rcu_torture_writer to get underway */
                rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
                return false;
        }
        if (p->rtort_mbtest == 0)
                atomic_inc(&n_rcu_torture_mberror);
        rtrsp = rcutorture_loop_extend(&readstate, trsp, rtrsp);
        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->get_gp_seq();
        if (pipe_count > 1) {
                do_trace_rcu_torture_read(cur_ops->name, &p->rtort_rcu,
                                          ts, started, completed);
                rcu_ftrace_dump(DUMP_ALL);
        }
        __this_cpu_inc(rcu_torture_count[pipe_count]);
        completed = rcutorture_seq_diff(completed, started);
        if (completed > RCU_TORTURE_PIPE_LEN) {
                /* Should not happen, but... */
                completed = RCU_TORTURE_PIPE_LEN;
        }
        __this_cpu_inc(rcu_torture_batch[completed]);
        preempt_enable();
        rcutorture_one_extend(&readstate, 0, trsp, rtrsp);
        WARN_ON_ONCE(readstate & RCUTORTURE_RDR_MASK);

        /* If error or close call, record the sequence of reader protections. */
        if ((pipe_count > 1 || completed > 1) && !xchg(&err_segs_recorded, 1)) {
                i = 0;
                for (rtrsp1 = &rtseg[0]; rtrsp1 < rtrsp; rtrsp1++)
                        err_segs[i++] = *rtrsp1;
                rt_read_nsegs = i;
        }

        return true;
}

static DEFINE_TORTURE_RANDOM_PERCPU(rcu_torture_timer_rand);

/*
 * 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(struct timer_list *unused)
{
        atomic_long_inc(&n_rcu_torture_timers);
        (void)rcu_torture_one_read(this_cpu_ptr(&rcu_torture_timer_rand));

        /* Test call_rcu() invocation from interrupt handler. */
        if (cur_ops->call) {
                struct rcu_head *rhp = kmalloc(sizeof(*rhp), GFP_NOWAIT);

                if (rhp)
                        cur_ops->call(rhp, rcu_torture_timer_cb);
        }
}

/*
 * 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 lastsleep = jiffies;
        long myid = (long)arg;
        int mynumonline = myid;
        DEFINE_TORTURE_RANDOM(rand);
        struct timer_list t;

        VERBOSE_TOROUT_STRING("rcu_torture_reader task started");
        set_user_nice(current, MAX_NICE);
        if (irqreader && cur_ops->irq_capable)
                timer_setup_on_stack(&t, rcu_torture_timer, 0);

        do {
                if (irqreader && cur_ops->irq_capable) {
                        if (!timer_pending(&t))
                                mod_timer(&t, jiffies + 1);
                }
                if (!rcu_torture_one_read(&rand))
                        schedule_timeout_interruptible(HZ);
                if (time_after(jiffies, lastsleep)) {
                        schedule_timeout_interruptible(1);
                        lastsleep = jiffies + 10;
                }
                while (num_online_cpus() < mynumonline && !torture_must_stop())
                        schedule_timeout_interruptible(HZ / 5);
                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;
        static bool splatted;
        struct task_struct *wtp;

        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 %s: %lu tfle: %d rta: %d rtaf: %d rtf: %d ",
                rcu_torture_current,
                rcu_torture_current ? "ver" : "VER",
                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 rtbe: %ld rtbke: %ld rtbre: %ld ",
                atomic_read(&n_rcu_torture_mberror),
                n_rcu_torture_barrier_error,
                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,
                atomic_long_read(&n_rcu_torture_timers));
        torture_onoff_stats();
        pr_cont("barrier: %ld/%ld:%ld\n",
                n_barrier_successes,
                n_barrier_attempts,
                n_rcu_torture_barrier_error);

        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 = 0;
                unsigned long __maybe_unused gp_seq = 0;

                rcutorture_get_gp_data(cur_ops->ttype,
                                       &flags, &gp_seq);
                srcutorture_get_gp_data(cur_ops->ttype, srcu_ctlp,
                                        &flags, &gp_seq);
                wtp = READ_ONCE(writer_task);
                pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %#lx cpu %d\n",
                         rcu_torture_writer_state_getname(),
                         rcu_torture_writer_state, gp_seq, flags,
                         wtp == NULL ? ~0UL : wtp->state,
                         wtp == NULL ? -1 : (int)task_cpu(wtp));
                if (!splatted && wtp) {
                        sched_show_task(wtp);
                        splatted = true;
                }
                show_rcu_gp_kthreads();
                rcu_ftrace_dump(DUMP_ALL);
        }
        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 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 stall_cpu_irqsoff=%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, stall_cpu_irqsoff,
                 n_barrier_cbs,
                 onoff_interval, onoff_holdoff);
}

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

        if (boost_tasks[cpu] == NULL)
                return 0;
        mutex_lock(&boost_mutex);
        t = boost_tasks[cpu];
        boost_tasks[cpu] = NULL;
        rcu_torture_enable_rt_throttle();
        mutex_unlock(&boost_mutex);

        /* This must be outside of the mutex, otherwise deadlock! */
        torture_stop_kthread(rcu_torture_boost, t);
        return 0;
}

static int rcutorture_booster_init(unsigned 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);
        rcu_torture_disable_rt_throttle();
        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 = ktime_get_seconds() + stall_cpu;
                /* RCU CPU stall is expected behavior in following code. */
                rcu_read_lock();
                if (stall_cpu_irqsoff)
                        local_irq_disable();
                else
                        preempt_disable();
                pr_alert("rcu_torture_stall start on CPU %d.\n",
                         smp_processor_id());
                while (ULONG_CMP_LT((unsigned long)ktime_get_seconds(),
                                    stop_at))
                        continue;  /* Induce RCU CPU stall warning. */
                if (stall_cpu_irqsoff)
                        local_irq_enable();
                else
                        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);
}

/* State structure for forward-progress self-propagating RCU callback. */
struct fwd_cb_state {
        struct rcu_head rh;
        int stop;
};

/*
 * Forward-progress self-propagating RCU callback function.  Because
 * callbacks run from softirq, this function is an implicit RCU read-side
 * critical section.
 */
static void rcu_torture_fwd_prog_cb(struct rcu_head *rhp)
{
        struct fwd_cb_state *fcsp = container_of(rhp, struct fwd_cb_state, rh);

        if (READ_ONCE(fcsp->stop)) {
                WRITE_ONCE(fcsp->stop, 2);
                return;
        }
        cur_ops->call(&fcsp->rh, rcu_torture_fwd_prog_cb);
}

/* State for continuous-flood RCU callbacks. */
struct rcu_fwd_cb {
        struct rcu_head rh;
        struct rcu_fwd_cb *rfc_next;
        int rfc_gps;
};
static DEFINE_SPINLOCK(rcu_fwd_lock);
static struct rcu_fwd_cb *rcu_fwd_cb_head;
static struct rcu_fwd_cb **rcu_fwd_cb_tail = &rcu_fwd_cb_head;
static long n_launders_cb;
static unsigned long rcu_fwd_startat;
static bool rcu_fwd_emergency_stop;
#define MAX_FWD_CB_JIFFIES      (8 * HZ) /* Maximum CB test duration. */
#define MIN_FWD_CB_LAUNDERS     3       /* This many CB invocations to count. */
#define MIN_FWD_CBS_LAUNDERED   100     /* Number of counted CBs. */
#define FWD_CBS_HIST_DIV        10      /* Histogram buckets/second. */
struct rcu_launder_hist {
        long n_launders;
        unsigned long launder_gp_seq;
};
#define N_LAUNDERS_HIST (2 * MAX_FWD_CB_JIFFIES / (HZ / FWD_CBS_HIST_DIV))
static struct rcu_launder_hist n_launders_hist[N_LAUNDERS_HIST];
static unsigned long rcu_launder_gp_seq_start;

static void rcu_torture_fwd_cb_hist(void)
{
        unsigned long gps;
        unsigned long gps_old;
        int i;
        int j;

        for (i = ARRAY_SIZE(n_launders_hist) - 1; i > 0; i--)
                if (n_launders_hist[i].n_launders > 0)
                        break;
        pr_alert("%s: Callback-invocation histogram (duration %lu jiffies):",
                 __func__, jiffies - rcu_fwd_startat);
        gps_old = rcu_launder_gp_seq_start;
        for (j = 0; j <= i; j++) {
                gps = n_launders_hist[j].launder_gp_seq;
                pr_cont(" %ds/%d: %ld:%ld",
                        j + 1, FWD_CBS_HIST_DIV, n_launders_hist[j].n_launders,
                        rcutorture_seq_diff(gps, gps_old));
                gps_old = gps;
        }
        pr_cont("\n");
}

/* Callback function for continuous-flood RCU callbacks. */
static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)
{
        unsigned long flags;
        int i;
        struct rcu_fwd_cb *rfcp = container_of(rhp, struct rcu_fwd_cb, rh);
        struct rcu_fwd_cb **rfcpp;

        rfcp->rfc_next = NULL;
        rfcp->rfc_gps++;
        spin_lock_irqsave(&rcu_fwd_lock, flags);
        rfcpp = rcu_fwd_cb_tail;
        rcu_fwd_cb_tail = &rfcp->rfc_next;
        WRITE_ONCE(*rfcpp, rfcp);
        WRITE_ONCE(n_launders_cb, n_launders_cb + 1);
        i = ((jiffies - rcu_fwd_startat) / (HZ / FWD_CBS_HIST_DIV));
        if (i >= ARRAY_SIZE(n_launders_hist))
                i = ARRAY_SIZE(n_launders_hist) - 1;
        n_launders_hist[i].n_launders++;
        n_launders_hist[i].launder_gp_seq = cur_ops->get_gp_seq();
        spin_unlock_irqrestore(&rcu_fwd_lock, flags);
}

// Give the scheduler a chance, even on nohz_full CPUs.
static void rcu_torture_fwd_prog_cond_resched(void)
{
        if (IS_ENABLED(CONFIG_PREEMPT) && IS_ENABLED(CONFIG_NO_HZ_FULL)) {
                if (need_resched())
                        schedule();
        } else {
                cond_resched();
        }
}

/*
 * Free all callbacks on the rcu_fwd_cb_head list, either because the
 * test is over or because we hit an OOM event.
 */
static unsigned long rcu_torture_fwd_prog_cbfree(void)
{
        unsigned long flags;
        unsigned long freed = 0;
        struct rcu_fwd_cb *rfcp;

        for (;;) {
                spin_lock_irqsave(&rcu_fwd_lock, flags);
                rfcp = rcu_fwd_cb_head;
                if (!rfcp) {
                        spin_unlock_irqrestore(&rcu_fwd_lock, flags);
                        break;
                }
                rcu_fwd_cb_head = rfcp->rfc_next;
                if (!rcu_fwd_cb_head)
                        rcu_fwd_cb_tail = &rcu_fwd_cb_head;
                spin_unlock_irqrestore(&rcu_fwd_lock, flags);
                kfree(rfcp);
                freed++;
                rcu_torture_fwd_prog_cond_resched();
        }
        return freed;
}

/* Carry out need_resched()/cond_resched() forward-progress testing. */
static void rcu_torture_fwd_prog_nr(int *tested, int *tested_tries)
{
        unsigned long cver;
        unsigned long dur;
        struct fwd_cb_state fcs;
        unsigned long gps;
        int idx;
        int sd;
        int sd4;
        bool selfpropcb = false;
        unsigned long stopat;
        static DEFINE_TORTURE_RANDOM(trs);

        if  (cur_ops->call && cur_ops->sync && cur_ops->cb_barrier) {
                init_rcu_head_on_stack(&fcs.rh);
                selfpropcb = true;
        }

        /* Tight loop containing cond_resched(). */
        WRITE_ONCE(rcu_fwd_cb_nodelay, true);
        cur_ops->sync(); /* Later readers see above write. */
        if  (selfpropcb) {
                WRITE_ONCE(fcs.stop, 0);
                cur_ops->call(&fcs.rh, rcu_torture_fwd_prog_cb);
        }
        cver = READ_ONCE(rcu_torture_current_version);
        gps = cur_ops->get_gp_seq();
        sd = cur_ops->stall_dur() + 1;
        sd4 = (sd + fwd_progress_div - 1) / fwd_progress_div;
        dur = sd4 + torture_random(&trs) % (sd - sd4);
        WRITE_ONCE(rcu_fwd_startat, jiffies);
        stopat = rcu_fwd_startat + dur;
        while (time_before(jiffies, stopat) &&
               !READ_ONCE(rcu_fwd_emergency_stop) && !torture_must_stop()) {
                idx = cur_ops->readlock();
                udelay(10);
                cur_ops->readunlock(idx);
                if (!fwd_progress_need_resched || need_resched())
                        rcu_torture_fwd_prog_cond_resched();
        }
        (*tested_tries)++;
        if (!time_before(jiffies, stopat) &&
            !READ_ONCE(rcu_fwd_emergency_stop) && !torture_must_stop()) {
                (*tested)++;
                cver = READ_ONCE(rcu_torture_current_version) - cver;
                gps = rcutorture_seq_diff(cur_ops->get_gp_seq(), gps);
                WARN_ON(!cver && gps < 2);
                pr_alert("%s: Duration %ld cver %ld gps %ld\n", __func__, dur, cver, gps);
        }
        if (selfpropcb) {
                WRITE_ONCE(fcs.stop, 1);
                cur_ops->sync(); /* Wait for running CB to complete. */
                cur_ops->cb_barrier(); /* Wait for queued callbacks. */
        }

        if (selfpropcb) {
                WARN_ON(READ_ONCE(fcs.stop) != 2);
                destroy_rcu_head_on_stack(&fcs.rh);
        }
        schedule_timeout_uninterruptible(HZ / 10); /* Let kthreads recover. */
        WRITE_ONCE(rcu_fwd_cb_nodelay, false);
}

/* Carry out call_rcu() forward-progress testing. */
static void rcu_torture_fwd_prog_cr(void)
{
        unsigned long cver;
        unsigned long gps;
        int i;
        long n_launders;
        long n_launders_cb_snap;
        long n_launders_sa;
        long n_max_cbs;
        long n_max_gps;
        struct rcu_fwd_cb *rfcp;
        struct rcu_fwd_cb *rfcpn;
        unsigned long stopat;
        unsigned long stoppedat;

        if (READ_ONCE(rcu_fwd_emergency_stop))
                return; /* Get out of the way quickly, no GP wait! */
        if (!cur_ops->call)
                return; /* Can't do call_rcu() fwd prog without ->call. */

        /* Loop continuously posting RCU callbacks. */
        WRITE_ONCE(rcu_fwd_cb_nodelay, true);
        cur_ops->sync(); /* Later readers see above write. */
        WRITE_ONCE(rcu_fwd_startat, jiffies);
        stopat = rcu_fwd_startat + MAX_FWD_CB_JIFFIES;
        n_launders = 0;
        n_launders_cb = 0;
        n_launders_sa = 0;
        n_max_cbs = 0;
        n_max_gps = 0;
        for (i = 0; i < ARRAY_SIZE(n_launders_hist); i++)
                n_launders_hist[i].n_launders = 0;
        cver = READ_ONCE(rcu_torture_current_version);
        gps = cur_ops->get_gp_seq();
        rcu_launder_gp_seq_start = gps;
        while (time_before(jiffies, stopat) &&
               !READ_ONCE(rcu_fwd_emergency_stop) && !torture_must_stop()) {
                rfcp = READ_ONCE(rcu_fwd_cb_head);
                rfcpn = NULL;
                if (rfcp)
                        rfcpn = READ_ONCE(rfcp->rfc_next);
                if (rfcpn) {
                        if (rfcp->rfc_gps >= MIN_FWD_CB_LAUNDERS &&
                            ++n_max_gps >= MIN_FWD_CBS_LAUNDERED)
                                break;
                        rcu_fwd_cb_head = rfcpn;
                        n_launders++;
                        n_launders_sa++;
                } else {
                        rfcp = kmalloc(sizeof(*rfcp), GFP_KERNEL);
                        if (WARN_ON_ONCE(!rfcp)) {
                                schedule_timeout_interruptible(1);
                                continue;
                        }
                        n_max_cbs++;
                        n_launders_sa = 0;
                        rfcp->rfc_gps = 0;
                }
                cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr);
                rcu_torture_fwd_prog_cond_resched();
        }
        stoppedat = jiffies;
        n_launders_cb_snap = READ_ONCE(n_launders_cb);
        cver = READ_ONCE(rcu_torture_current_version) - cver;
        gps = rcutorture_seq_diff(cur_ops->get_gp_seq(), gps);
        cur_ops->cb_barrier(); /* Wait for callbacks to be invoked. */
        (void)rcu_torture_fwd_prog_cbfree();

        if (!torture_must_stop() && !READ_ONCE(rcu_fwd_emergency_stop)) {
                WARN_ON(n_max_gps < MIN_FWD_CBS_LAUNDERED);
                pr_alert("%s Duration %lu barrier: %lu pending %ld n_launders: %ld n_launders_sa: %ld n_max_gps: %ld n_max_cbs: %ld cver %ld gps %ld\n",
                         __func__,
                         stoppedat - rcu_fwd_startat, jiffies - stoppedat,
                         n_launders + n_max_cbs - n_launders_cb_snap,
                         n_launders, n_launders_sa,
                         n_max_gps, n_max_cbs, cver, gps);
                rcu_torture_fwd_cb_hist();
        }
        schedule_timeout_uninterruptible(HZ); /* Let CBs drain. */
        WRITE_ONCE(rcu_fwd_cb_nodelay, false);
}


/*
 * OOM notifier, but this only prints diagnostic information for the
 * current forward-progress test.
 */
static int rcutorture_oom_notify(struct notifier_block *self,
                                 unsigned long notused, void *nfreed)
{
        WARN(1, "%s invoked upon OOM during forward-progress testing.\n",
             __func__);
        rcu_torture_fwd_cb_hist();
        rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rcu_fwd_startat)) / 2);
        WRITE_ONCE(rcu_fwd_emergency_stop, true);
        smp_mb(); /* Emergency stop before free and wait to avoid hangs. */
        pr_info("%s: Freed %lu RCU callbacks.\n",
                __func__, rcu_torture_fwd_prog_cbfree());
        rcu_barrier();
        pr_info("%s: Freed %lu RCU callbacks.\n",
                __func__, rcu_torture_fwd_prog_cbfree());
        rcu_barrier();
        pr_info("%s: Freed %lu RCU callbacks.\n",
                __func__, rcu_torture_fwd_prog_cbfree());
        smp_mb(); /* Frees before return to avoid redoing OOM. */
        (*(unsigned long *)nfreed)++; /* Forward progress CBs freed! */
        pr_info("%s returning after OOM processing.\n", __func__);
        return NOTIFY_OK;
}

static struct notifier_block rcutorture_oom_nb = {
        .notifier_call = rcutorture_oom_notify
};

/* Carry out grace-period forward-progress testing. */
static int rcu_torture_fwd_prog(void *args)
{
        int tested = 0;
        int tested_tries = 0;

        VERBOSE_TOROUT_STRING("rcu_torture_fwd_progress task started");
        rcu_bind_current_to_nocb();
        if (!IS_ENABLED(CONFIG_SMP) || !IS_ENABLED(CONFIG_RCU_BOOST))
                set_user_nice(current, MAX_NICE);
        do {
                schedule_timeout_interruptible(fwd_progress_holdoff * HZ);
                WRITE_ONCE(rcu_fwd_emergency_stop, false);
                register_oom_notifier(&rcutorture_oom_nb);
                rcu_torture_fwd_prog_nr(&tested, &tested_tries);
                rcu_torture_fwd_prog_cr();
                unregister_oom_notifier(&rcutorture_oom_nb);

                /* Avoid slow periods, better to test when busy. */
                stutter_wait("rcu_torture_fwd_prog");
        } while (!torture_must_stop());
        /* Short runs might not contain a valid forward-progress attempt. */
        WARN_ON(!tested && tested_tries >= 5);
        pr_alert("%s: tested %d tested_tries %d\n", __func__, tested, tested_tries);
        torture_kthread_stopping("rcu_torture_fwd_prog");
        return 0;
}

/* If forward-progress checking is requested and feasible, spawn the thread. */
static int __init rcu_torture_fwd_prog_init(void)
{
        if (!fwd_progress)
                return 0; /* Not requested, so don't do it. */
        if (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0 ||
            cur_ops == &rcu_busted_ops) {
                VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test");
                return 0;
        }
        if (stall_cpu > 0) {
                VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, conflicts with CPU-stall testing");
                if (IS_MODULE(CONFIG_RCU_TORTURE_TESTS))
                        return -EINVAL; /* In module, can fail back to user. */
                WARN_ON(1); /* Make sure rcutorture notices conflict. */
                return 0;
        }
        if (fwd_progress_holdoff <= 0)
                fwd_progress_holdoff = 1;
        if (fwd_progress_div <= 0)
                fwd_progress_div = 4;
        return torture_create_kthread(rcu_torture_fwd_prog,
                                      NULL, fwd_prog_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 =
                            smp_load_acquire(&barrier_phase)) != lastphase ||
                           torture_must_stop());
                lastphase = newphase;
                if (torture_must_stop())
                        break;
                /*
                 * The above smp_load_acquire() ensures barrier_phase load
                 * is ordered before the following ->call().
                 */
                local_irq_disable(); /* Just to test no-irq call_rcu(). */
                cur_ops->call(&rcu, rcu_torture_barrier_cbf);
                local_irq_enable();
                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);
                /* Ensure barrier_phase ordered after prior assignments. */
                smp_store_release(&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);
                } else {
                        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 =
                kcalloc(n_barrier_cbs, sizeof(barrier_cbs_tasks[0]),
                        GFP_KERNEL);
        barrier_cbs_wq =
                kcalloc(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 bool rcu_torture_can_boost(void)
{
        static int boost_warn_once;
        int prio;

        if (!(test_boost == 1 && cur_ops->can_boost) && test_boost != 2)
                return false;

        prio = rcu_get_gp_kthreads_prio();
        if (!prio)
                return false;

        if (prio < 2) {
                if (boost_warn_once  == 1)
                        return false;

                pr_alert("%s: WARN: RCU kthread priority too low to test boosting.  Skipping RCU boost test. Try passing rcutree.kthread_prio > 1 on the kernel command line.\n", KBUILD_MODNAME);
                boost_warn_once = 1;
                return false;
        }

        return true;
}

static enum cpuhp_state rcutor_hp;

static void
rcu_torture_cleanup(void)
{
        int firsttime;
        int flags = 0;
        unsigned long gp_seq = 0;
        int i;

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

        rcu_torture_barrier_cleanup();
        torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task);
        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;
        }

        rcutorture_get_gp_data(cur_ops->ttype, &flags, &gp_seq);
        srcutorture_get_gp_data(cur_ops->ttype, srcu_ctlp, &flags, &gp_seq);
        pr_alert("%s:  End-test grace-period state: g%lu f%#x\n",
                 cur_ops->name, gp_seq, flags);
        torture_stop_kthread(rcu_torture_stats, stats_task);
        torture_stop_kthread(rcu_torture_fqs, fqs_task);
        if (rcu_torture_can_boost())
                cpuhp_remove_state(rcutor_hp);

        /*
         * Wait for all RCU callbacks to fire, then do torture-type-specific
         * cleanup operations.
         */
        if (cur_ops->cb_barrier != NULL)
                cur_ops->cb_barrier();
        if (cur_ops->cleanup != NULL)
                cur_ops->cleanup();

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

        if (err_segs_recorded) {
                pr_alert("Failure/close-call rcutorture reader segments:\n");
                if (rt_read_nsegs == 0)
                        pr_alert("\t: No segments recorded!!!\n");
                firsttime = 1;
                for (i = 0; i < rt_read_nsegs; i++) {
                        pr_alert("\t%d: %#x ", i, err_segs[i].rt_readstate);
                        if (err_segs[i].rt_delay_jiffies != 0) {
                                pr_cont("%s%ldjiffies", firsttime ? "" : "+",
                                        err_segs[i].rt_delay_jiffies);
                                firsttime = 0;
                        }
                        if (err_segs[i].rt_delay_ms != 0) {
                                pr_cont("%s%ldms", firsttime ? "" : "+",
                                        err_segs[i].rt_delay_ms);
                                firsttime = 0;
                        }
                        if (err_segs[i].rt_delay_us != 0) {
                                pr_cont("%s%ldus", firsttime ? "" : "+",
                                        err_segs[i].rt_delay_us);
                                firsttime = 0;
                        }
                        pr_cont("%s\n",
                                err_segs[i].rt_preempted ? "preempted" : "");

                }
        }
        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("%s: duplicated callback was invoked.\n", KBUILD_MODNAME);
}
#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("%s: WARN: Duplicate call_rcu() test starting.\n", KBUILD_MODNAME);

        /* 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("%s: WARN: Duplicate call_rcu() test complete.\n", KBUILD_MODNAME);
        destroy_rcu_head_on_stack(&rh1);
        destroy_rcu_head_on_stack(&rh2);
#else /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
        pr_alert("%s: !CONFIG_DEBUG_OBJECTS_RCU_HEAD, not testing duplicate call_rcu()\n", KBUILD_MODNAME);
#endif /* #else #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
}

static void rcutorture_sync(void)
{
        static unsigned long n;

        if (cur_ops->sync && !(++n & 0xfff))
                cur_ops->sync();
}

static int __init
rcu_torture_init(void)
{
        long i;
        int cpu;
        int firsterr = 0;
        static struct rcu_torture_ops *torture_ops[] = {
                &rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops,
                &busted_srcud_ops, &tasks_ops, &trivial_ops,
        };

        if (!torture_init_begin(torture_type, verbose))
                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_cont(" %s", torture_ops[i]->name);
                pr_cont("\n");
                WARN_ON(!IS_MODULE(CONFIG_RCU_TORTURE_TEST));
                firsterr = -EINVAL;
                cur_ops = NULL;
                goto unwind;
        }
        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();

        if (nreaders >= 0) {
                nrealreaders = nreaders;
        } else {
                nrealreaders = num_online_cpus() - 2 - nreaders;
                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;
                }
        }
        err_segs_recorded = 0;
        rt_read_nsegs = 0;

        /* Start up the kthreads. */

        firsterr = torture_create_kthread(rcu_torture_writer, NULL,
                                          writer_task);
        if (firsterr)
                goto unwind;
        if (nfakewriters > 0) {
                fakewriter_tasks = kcalloc(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 = kcalloc(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, (void *)i,
                                                  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 && shuffle_interval > 0) {
                firsterr = torture_shuffle_init(shuffle_interval * HZ);
                if (firsterr)
                        goto unwind;
        }
        if (stutter < 0)
                stutter = 0;
        if (stutter) {
                int t;

                t = cur_ops->stall_dur ? cur_ops->stall_dur() : stutter * HZ;
                firsterr = torture_stutter_init(stutter * HZ, t);
                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 (rcu_torture_can_boost()) {

                boost_starttime = jiffies + test_boost_interval * HZ;

                firsterr = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "RCU_TORTURE",
                                             rcutorture_booster_init,
                                             rcutorture_booster_cleanup);
                if (firsterr < 0)
                        goto unwind;
                rcutor_hp = firsterr;
        }
        firsterr = torture_shutdown_init(shutdown_secs, rcu_torture_cleanup);
        if (firsterr)
                goto unwind;
        firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval,
                                      rcutorture_sync);
        if (firsterr)
                goto unwind;
        firsterr = rcu_torture_stall_init();
        if (firsterr)
                goto unwind;
        firsterr = rcu_torture_fwd_prog_init();
        if (firsterr)
                goto unwind;
        firsterr = rcu_torture_barrier_init();
        if (firsterr)
                goto unwind;
        if (object_debug)
                rcu_test_debug_objects();
        torture_init_end();
        return 0;

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

module_init(rcu_torture_init);
module_exit(rcu_torture_cleanup);