kernel/torture.c - kernel/common - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Common functions for in-kernel torture tests.
  *
  * Copyright (C) IBM Corporation, 2014
  *
  * Author: Paul E. McKenney <paulmck@linux.ibm.com>
  *	Based on kernel/rcu/torture.c.
  */

 #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/interrupt.h>
 #include <linux/sched.h>
 #include <linux/sched/clock.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/slab.h>
 #include <linux/trace_clock.h>
 #include <linux/ktime.h>
 #include <asm/byteorder.h>
 #include <linux/torture.h>
 #include "rcu/rcu.h"

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

 static bool disable_onoff_at_boot;
 module_param(disable_onoff_at_boot, bool, 0444);

 static bool ftrace_dump_at_shutdown;
 module_param(ftrace_dump_at_shutdown, bool, 0444);

 static int verbose_sleep_frequency;
 module_param(verbose_sleep_frequency, int, 0444);

 static int verbose_sleep_duration = 1;
 module_param(verbose_sleep_duration, int, 0444);

 static char *torture_type;
 static int verbose;

 /* Mediate rmmod and system shutdown.  Concurrent rmmod & shutdown illegal! */
 #define FULLSTOP_DONTSTOP 0	/* Normal operation. */
 #define FULLSTOP_SHUTDOWN 1	/* System shutdown with torture running. */
 #define FULLSTOP_RMMOD    2	/* Normal rmmod of torture. */
 static int fullstop = FULLSTOP_RMMOD;
 static DEFINE_MUTEX(fullstop_mutex);

 static atomic_t verbose_sleep_counter;

 /*
  * Sleep if needed from VERBOSE_TOROUT*().
  */
 void verbose_torout_sleep(void)
 {
 	if (verbose_sleep_frequency > 0 &&
 	    verbose_sleep_duration > 0 &&
 	    !(atomic_inc_return(&verbose_sleep_counter) % verbose_sleep_frequency))
 		schedule_timeout_uninterruptible(verbose_sleep_duration);
 }
 EXPORT_SYMBOL_GPL(verbose_torout_sleep);

 /*
  * Schedule a high-resolution-timer sleep in nanoseconds, with a 32-bit
  * nanosecond random fuzz.  This function and its friends desynchronize
  * testing from the timer wheel.
  */
 int torture_hrtimeout_ns(ktime_t baset_ns, u32 fuzzt_ns, struct torture_random_state *trsp)
 {
 	ktime_t hto = baset_ns;

 	if (trsp)
 		hto += (torture_random(trsp) >> 3) % fuzzt_ns;
 	set_current_state(TASK_UNINTERRUPTIBLE);
 	return schedule_hrtimeout(&hto, HRTIMER_MODE_REL);
 }
 EXPORT_SYMBOL_GPL(torture_hrtimeout_ns);

 /*
  * Schedule a high-resolution-timer sleep in microseconds, with a 32-bit
  * nanosecond (not microsecond!) random fuzz.
  */
 int torture_hrtimeout_us(u32 baset_us, u32 fuzzt_ns, struct torture_random_state *trsp)
 {
 	ktime_t baset_ns = baset_us * NSEC_PER_USEC;

 	return torture_hrtimeout_ns(baset_ns, fuzzt_ns, trsp);
 }
 EXPORT_SYMBOL_GPL(torture_hrtimeout_us);

 /*
  * Schedule a high-resolution-timer sleep in milliseconds, with a 32-bit
  * microsecond (not millisecond!) random fuzz.
  */
 int torture_hrtimeout_ms(u32 baset_ms, u32 fuzzt_us, struct torture_random_state *trsp)
 {
 	ktime_t baset_ns = baset_ms * NSEC_PER_MSEC;
 	u32 fuzzt_ns;

 	if ((u32)~0U / NSEC_PER_USEC < fuzzt_us)
 		fuzzt_ns = (u32)~0U;
 	else
 		fuzzt_ns = fuzzt_us * NSEC_PER_USEC;
 	return torture_hrtimeout_ns(baset_ns, fuzzt_ns, trsp);
 }
 EXPORT_SYMBOL_GPL(torture_hrtimeout_ms);

 /*
  * Schedule a high-resolution-timer sleep in jiffies, with an
  * implied one-jiffy random fuzz.  This is intended to replace calls to
  * schedule_timeout_interruptible() and friends.
  */
 int torture_hrtimeout_jiffies(u32 baset_j, struct torture_random_state *trsp)
 {
 	ktime_t baset_ns = jiffies_to_nsecs(baset_j);

 	return torture_hrtimeout_ns(baset_ns, jiffies_to_nsecs(1), trsp);
 }
 EXPORT_SYMBOL_GPL(torture_hrtimeout_jiffies);

 /*
  * Schedule a high-resolution-timer sleep in milliseconds, with a 32-bit
  * millisecond (not second!) random fuzz.
  */
 int torture_hrtimeout_s(u32 baset_s, u32 fuzzt_ms, struct torture_random_state *trsp)
 {
 	ktime_t baset_ns = baset_s * NSEC_PER_SEC;
 	u32 fuzzt_ns;

 	if ((u32)~0U / NSEC_PER_MSEC < fuzzt_ms)
 		fuzzt_ns = (u32)~0U;
 	else
 		fuzzt_ns = fuzzt_ms * NSEC_PER_MSEC;
 	return torture_hrtimeout_ns(baset_ns, fuzzt_ns, trsp);
 }
 EXPORT_SYMBOL_GPL(torture_hrtimeout_s);

 #ifdef CONFIG_HOTPLUG_CPU

 /*
  * Variables for online-offline handling.  Only present if CPU hotplug
  * is enabled, otherwise does nothing.
  */

 static struct task_struct *onoff_task;
 static long onoff_holdoff;
 static long onoff_interval;
 static torture_ofl_func *onoff_f;
 static long n_offline_attempts;
 static long n_offline_successes;
 static unsigned long sum_offline;
 static int min_offline = -1;
 static int max_offline;
 static long n_online_attempts;
 static long n_online_successes;
 static unsigned long sum_online;
 static int min_online = -1;
 static int max_online;

 static int torture_online_cpus = NR_CPUS;

 /*
  * Some torture testing leverages confusion as to the number of online
  * CPUs.  This function returns the torture-testing view of this number,
  * which allows torture tests to load-balance appropriately.
  */
 int torture_num_online_cpus(void)
 {
 	return READ_ONCE(torture_online_cpus);
 }
 EXPORT_SYMBOL_GPL(torture_num_online_cpus);

 /*
  * Attempt to take a CPU offline.  Return false if the CPU is already
  * offline or if it is not subject to CPU-hotplug operations.  The
  * caller can detect other failures by looking at the statistics.
  */
 bool torture_offline(int cpu, long *n_offl_attempts, long *n_offl_successes,
 		     unsigned long *sum_offl, int *min_offl, int *max_offl)
 {
 	unsigned long delta;
 	int ret;
 	char *s;
 	unsigned long starttime;

 	if (!cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
 		return false;
 	if (num_online_cpus() <= 1)
 		return false;  /* Can't offline the last CPU. */

 	if (verbose > 1)
 		pr_alert("%s" TORTURE_FLAG
 			 "torture_onoff task: offlining %d\n",
 			 torture_type, cpu);
 	starttime = jiffies;
 	(*n_offl_attempts)++;
 	ret = remove_cpu(cpu);
 	if (ret) {
 		s = "";
 		if (!rcu_inkernel_boot_has_ended() && ret == -EBUSY) {
 			// PCI probe frequently disables hotplug during boot.
 			(*n_offl_attempts)--;
 			s = " (-EBUSY forgiven during boot)";
 		}
 		if (verbose)
 			pr_alert("%s" TORTURE_FLAG
 				 "torture_onoff task: offline %d failed%s: errno %d\n",
 				 torture_type, cpu, s, ret);
 	} else {
 		if (verbose > 1)
 			pr_alert("%s" TORTURE_FLAG
 				 "torture_onoff task: offlined %d\n",
 				 torture_type, cpu);
 		if (onoff_f)
 			onoff_f();
 		(*n_offl_successes)++;
 		delta = jiffies - starttime;
 		*sum_offl += delta;
 		if (*min_offl < 0) {
 			*min_offl = delta;
 			*max_offl = delta;
 		}
 		if (*min_offl > delta)
 			*min_offl = delta;
 		if (*max_offl < delta)
 			*max_offl = delta;
 		WRITE_ONCE(torture_online_cpus, torture_online_cpus - 1);
 		WARN_ON_ONCE(torture_online_cpus <= 0);
 	}

 	return true;
 }
 EXPORT_SYMBOL_GPL(torture_offline);

 /*
  * Attempt to bring a CPU online.  Return false if the CPU is already
  * online or if it is not subject to CPU-hotplug operations.  The
  * caller can detect other failures by looking at the statistics.
  */
 bool torture_online(int cpu, long *n_onl_attempts, long *n_onl_successes,
 		    unsigned long *sum_onl, int *min_onl, int *max_onl)
 {
 	unsigned long delta;
 	int ret;
 	char *s;
 	unsigned long starttime;

 	if (cpu_online(cpu) || !cpu_is_hotpluggable(cpu))
 		return false;

 	if (verbose > 1)
 		pr_alert("%s" TORTURE_FLAG
 			 "torture_onoff task: onlining %d\n",
 			 torture_type, cpu);
 	starttime = jiffies;
 	(*n_onl_attempts)++;
 	ret = add_cpu(cpu);
 	if (ret) {
 		s = "";
 		if (!rcu_inkernel_boot_has_ended() && ret == -EBUSY) {
 			// PCI probe frequently disables hotplug during boot.
 			(*n_onl_attempts)--;
 			s = " (-EBUSY forgiven during boot)";
 		}
 		if (verbose)
 			pr_alert("%s" TORTURE_FLAG
 				 "torture_onoff task: online %d failed%s: errno %d\n",
 				 torture_type, cpu, s, ret);
 	} else {
 		if (verbose > 1)
 			pr_alert("%s" TORTURE_FLAG
 				 "torture_onoff task: onlined %d\n",
 				 torture_type, cpu);
 		(*n_onl_successes)++;
 		delta = jiffies - starttime;
 		*sum_onl += delta;
 		if (*min_onl < 0) {
 			*min_onl = delta;
 			*max_onl = delta;
 		}
 		if (*min_onl > delta)
 			*min_onl = delta;
 		if (*max_onl < delta)
 			*max_onl = delta;
 		WRITE_ONCE(torture_online_cpus, torture_online_cpus + 1);
 	}

 	return true;
 }
 EXPORT_SYMBOL_GPL(torture_online);

 /*
  * Get everything online at the beginning and ends of tests.
  */
 static void torture_online_all(char *phase)
 {
 	int cpu;
 	int ret;

 	for_each_possible_cpu(cpu) {
 		if (cpu_online(cpu))
 			continue;
 		ret = add_cpu(cpu);
 		if (ret && verbose) {
 			pr_alert("%s" TORTURE_FLAG
 				 "%s: %s online %d: errno %d\n",
 				 __func__, phase, torture_type, cpu, ret);
 		}
 	}
 }

 /*
  * Execute random CPU-hotplug operations at the interval specified
  * by the onoff_interval.
  */
 static int
 torture_onoff(void *arg)
 {
 	int cpu;
 	int maxcpu = -1;
 	DEFINE_TORTURE_RANDOM(rand);

 	VERBOSE_TOROUT_STRING("torture_onoff task started");
 	for_each_online_cpu(cpu)
 		maxcpu = cpu;
 	WARN_ON(maxcpu < 0);
 	torture_online_all("Initial");
 	if (maxcpu == 0) {
 		VERBOSE_TOROUT_STRING("Only one CPU, so CPU-hotplug testing is disabled");
 		goto stop;
 	}

 	if (onoff_holdoff > 0) {
 		VERBOSE_TOROUT_STRING("torture_onoff begin holdoff");
 		schedule_timeout_interruptible(onoff_holdoff);
 		VERBOSE_TOROUT_STRING("torture_onoff end holdoff");
 	}
 	while (!torture_must_stop()) {
 		if (disable_onoff_at_boot && !rcu_inkernel_boot_has_ended()) {
 			schedule_timeout_interruptible(HZ / 10);
 			continue;
 		}
 		cpu = (torture_random(&rand) >> 4) % (maxcpu + 1);
 		if (!torture_offline(cpu,
 				     &n_offline_attempts, &n_offline_successes,
 				     &sum_offline, &min_offline, &max_offline))
 			torture_online(cpu,
 				       &n_online_attempts, &n_online_successes,
 				       &sum_online, &min_online, &max_online);
 		schedule_timeout_interruptible(onoff_interval);
 	}

 stop:
 	torture_kthread_stopping("torture_onoff");
 	torture_online_all("Final");
 	return 0;
 }

 #endif /* #ifdef CONFIG_HOTPLUG_CPU */

 /*
  * Initiate online-offline handling.
  */
 int torture_onoff_init(long ooholdoff, long oointerval, torture_ofl_func *f)
 {
 #ifdef CONFIG_HOTPLUG_CPU
 	onoff_holdoff = ooholdoff;
 	onoff_interval = oointerval;
 	onoff_f = f;
 	if (onoff_interval <= 0)
 		return 0;
 	return torture_create_kthread(torture_onoff, NULL, onoff_task);
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
 	return 0;
 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
 }
 EXPORT_SYMBOL_GPL(torture_onoff_init);

 /*
  * Clean up after online/offline testing.
  */
 static void torture_onoff_cleanup(void)
 {
 #ifdef CONFIG_HOTPLUG_CPU
 	if (onoff_task == NULL)
 		return;
 	VERBOSE_TOROUT_STRING("Stopping torture_onoff task");
 	kthread_stop(onoff_task);
 	onoff_task = NULL;
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 }

 /*
  * Print online/offline testing statistics.
  */
 void torture_onoff_stats(void)
 {
 #ifdef CONFIG_HOTPLUG_CPU
 	pr_cont("onoff: %ld/%ld:%ld/%ld %d,%d:%d,%d %lu:%lu (HZ=%d) ",
 		n_online_successes, n_online_attempts,
 		n_offline_successes, n_offline_attempts,
 		min_online, max_online,
 		min_offline, max_offline,
 		sum_online, sum_offline, HZ);
 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
 }
 EXPORT_SYMBOL_GPL(torture_onoff_stats);

 /*
  * Were all the online/offline operations successful?
  */
 bool torture_onoff_failures(void)
 {
 #ifdef CONFIG_HOTPLUG_CPU
 	return n_online_successes != n_online_attempts ||
 	       n_offline_successes != n_offline_attempts;
 #else /* #ifdef CONFIG_HOTPLUG_CPU */
 	return false;
 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
 }
 EXPORT_SYMBOL_GPL(torture_onoff_failures);

 #define TORTURE_RANDOM_MULT	39916801  /* prime */
 #define TORTURE_RANDOM_ADD	479001701 /* prime */
 #define TORTURE_RANDOM_REFRESH	10000

 /*
  * Crude but fast random-number generator.  Uses a linear congruential
  * generator, with occasional help from cpu_clock().
  */
 unsigned long
 torture_random(struct torture_random_state *trsp)
 {
 	if (--trsp->trs_count < 0) {
 		trsp->trs_state += (unsigned long)local_clock();
 		trsp->trs_count = TORTURE_RANDOM_REFRESH;
 	}
 	trsp->trs_state = trsp->trs_state * TORTURE_RANDOM_MULT +
 		TORTURE_RANDOM_ADD;
 	return swahw32(trsp->trs_state);
 }
 EXPORT_SYMBOL_GPL(torture_random);

 /*
  * Variables for shuffling.  The idea is to ensure that each CPU stays
  * idle for an extended period to test interactions with dyntick idle,
  * as well as interactions with any per-CPU variables.
  */
 struct shuffle_task {
 	struct list_head st_l;
 	struct task_struct *st_t;
 };

 static long shuffle_interval;	/* In jiffies. */
 static struct task_struct *shuffler_task;
 static cpumask_var_t shuffle_tmp_mask;
 static int shuffle_idle_cpu;	/* Force all torture tasks off this CPU */
 static struct list_head shuffle_task_list = LIST_HEAD_INIT(shuffle_task_list);
 static DEFINE_MUTEX(shuffle_task_mutex);

 /*
  * Register a task to be shuffled.  If there is no memory, just splat
  * and don't bother registering.
  */
 void torture_shuffle_task_register(struct task_struct *tp)
 {
 	struct shuffle_task *stp;

 	if (WARN_ON_ONCE(tp == NULL))
 		return;
 	stp = kmalloc(sizeof(*stp), GFP_KERNEL);
 	if (WARN_ON_ONCE(stp == NULL))
 		return;
 	stp->st_t = tp;
 	mutex_lock(&shuffle_task_mutex);
 	list_add(&stp->st_l, &shuffle_task_list);
 	mutex_unlock(&shuffle_task_mutex);
 }
 EXPORT_SYMBOL_GPL(torture_shuffle_task_register);

 /*
  * Unregister all tasks, for example, at the end of the torture run.
  */
 static void torture_shuffle_task_unregister_all(void)
 {
 	struct shuffle_task *stp;
 	struct shuffle_task *p;

 	mutex_lock(&shuffle_task_mutex);
 	list_for_each_entry_safe(stp, p, &shuffle_task_list, st_l) {
 		list_del(&stp->st_l);
 		kfree(stp);
 	}
 	mutex_unlock(&shuffle_task_mutex);
 }

 /* Shuffle tasks such that we allow shuffle_idle_cpu to become idle.
  * A special case is when shuffle_idle_cpu = -1, in which case we allow
  * the tasks to run on all CPUs.
  */
 static void torture_shuffle_tasks(void)
 {
 	struct shuffle_task *stp;

 	cpumask_setall(shuffle_tmp_mask);
 	get_online_cpus();

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

 	/* Advance to the next CPU.  Upon overflow, don't idle any CPUs. */
 	shuffle_idle_cpu = cpumask_next(shuffle_idle_cpu, shuffle_tmp_mask);
 	if (shuffle_idle_cpu >= nr_cpu_ids)
 		shuffle_idle_cpu = -1;
 	else
 		cpumask_clear_cpu(shuffle_idle_cpu, shuffle_tmp_mask);

 	mutex_lock(&shuffle_task_mutex);
 	list_for_each_entry(stp, &shuffle_task_list, st_l)
 		set_cpus_allowed_ptr(stp->st_t, shuffle_tmp_mask);
 	mutex_unlock(&shuffle_task_mutex);

 	put_online_cpus();
 }

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

 /*
  * Start the shuffler, with shuffint in jiffies.
  */
 int torture_shuffle_init(long shuffint)
 {
 	shuffle_interval = shuffint;

 	shuffle_idle_cpu = -1;

 	if (!alloc_cpumask_var(&shuffle_tmp_mask, GFP_KERNEL)) {
 		VERBOSE_TOROUT_ERRSTRING("Failed to alloc mask");
 		return -ENOMEM;
 	}

 	/* Create the shuffler thread */
 	return torture_create_kthread(torture_shuffle, NULL, shuffler_task);
 }
 EXPORT_SYMBOL_GPL(torture_shuffle_init);

 /*
  * Stop the shuffling.
  */
 static void torture_shuffle_cleanup(void)
 {
 	torture_shuffle_task_unregister_all();
 	if (shuffler_task) {
 		VERBOSE_TOROUT_STRING("Stopping torture_shuffle task");
 		kthread_stop(shuffler_task);
 		free_cpumask_var(shuffle_tmp_mask);
 	}
 	shuffler_task = NULL;
 }

 /*
  * Variables for auto-shutdown.  This allows "lights out" torture runs
  * to be fully scripted.
  */
 static struct task_struct *shutdown_task;
 static ktime_t shutdown_time;		/* time to system shutdown. */
 static void (*torture_shutdown_hook)(void);

 /*
  * Absorb kthreads into a kernel function that won't return, so that
  * they won't ever access module text or data again.
  */
 void torture_shutdown_absorb(const char *title)
 {
 	while (READ_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {
 		pr_notice("torture thread %s parking due to system shutdown\n",
 			  title);
 		schedule_timeout_uninterruptible(MAX_SCHEDULE_TIMEOUT);
 	}
 }
 EXPORT_SYMBOL_GPL(torture_shutdown_absorb);

 /*
  * Cause the torture test to shutdown the system after the test has
  * run for the time specified by the shutdown_secs parameter.
  */
 static int torture_shutdown(void *arg)
 {
 	ktime_t ktime_snap;

 	VERBOSE_TOROUT_STRING("torture_shutdown task started");
 	ktime_snap = ktime_get();
 	while (ktime_before(ktime_snap, shutdown_time) &&
 	       !torture_must_stop()) {
 		if (verbose)
 			pr_alert("%s" TORTURE_FLAG
 				 "torture_shutdown task: %llu ms remaining\n",
 				 torture_type,
 				 ktime_ms_delta(shutdown_time, ktime_snap));
 		set_current_state(TASK_INTERRUPTIBLE);
 		schedule_hrtimeout(&shutdown_time, HRTIMER_MODE_ABS);
 		ktime_snap = ktime_get();
 	}
 	if (torture_must_stop()) {
 		torture_kthread_stopping("torture_shutdown");
 		return 0;
 	}

 	/* OK, shut down the system. */

 	VERBOSE_TOROUT_STRING("torture_shutdown task shutting down system");
 	shutdown_task = NULL;	/* Avoid self-kill deadlock. */
 	if (torture_shutdown_hook)
 		torture_shutdown_hook();
 	else
 		VERBOSE_TOROUT_STRING("No torture_shutdown_hook(), skipping.");
 	if (ftrace_dump_at_shutdown)
 		rcu_ftrace_dump(DUMP_ALL);
 	kernel_power_off();	/* Shut down the system. */
 	return 0;
 }

 /*
  * Start up the shutdown task.
  */
 int torture_shutdown_init(int ssecs, void (*cleanup)(void))
 {
 	torture_shutdown_hook = cleanup;
 	if (ssecs > 0) {
 		shutdown_time = ktime_add(ktime_get(), ktime_set(ssecs, 0));
 		return torture_create_kthread(torture_shutdown, NULL,
 					     shutdown_task);
 	}
 	return 0;
 }
 EXPORT_SYMBOL_GPL(torture_shutdown_init);

 /*
  * Detect and respond to a system shutdown.
  */
 static int torture_shutdown_notify(struct notifier_block *unused1,
 				   unsigned long unused2, void *unused3)
 {
 	mutex_lock(&fullstop_mutex);
 	if (READ_ONCE(fullstop) == FULLSTOP_DONTSTOP) {
 		VERBOSE_TOROUT_STRING("Unscheduled system shutdown detected");
 		WRITE_ONCE(fullstop, FULLSTOP_SHUTDOWN);
 	} else {
 		pr_warn("Concurrent rmmod and shutdown illegal!\n");
 	}
 	mutex_unlock(&fullstop_mutex);
 	return NOTIFY_DONE;
 }

 static struct notifier_block torture_shutdown_nb = {
 	.notifier_call = torture_shutdown_notify,
 };

 /*
  * Shut down the shutdown task.  Say what???  Heh!  This can happen if
  * the torture module gets an rmmod before the shutdown time arrives.  ;-)
  */
 static void torture_shutdown_cleanup(void)
 {
 	unregister_reboot_notifier(&torture_shutdown_nb);
 	if (shutdown_task != NULL) {
 		VERBOSE_TOROUT_STRING("Stopping torture_shutdown task");
 		kthread_stop(shutdown_task);
 	}
 	shutdown_task = NULL;
 }

 /*
  * Variables for stuttering, which means to periodically pause and
  * restart testing in order to catch bugs that appear when load is
  * suddenly applied to or removed from the system.
  */
 static struct task_struct *stutter_task;
 static int stutter_pause_test;
 static int stutter;
 static int stutter_gap;

 /*
  * Block until the stutter interval ends.  This must be called periodically
  * by all running kthreads that need to be subject to stuttering.
  */
 bool stutter_wait(const char *title)
 {
 	unsigned int i = 0;
 	bool ret = false;
 	int spt;

 	cond_resched_tasks_rcu_qs();
 	spt = READ_ONCE(stutter_pause_test);
 	for (; spt; spt = READ_ONCE(stutter_pause_test)) {
 		if (!ret) {
 			sched_set_normal(current, MAX_NICE);
 			ret = true;
 		}
 		if (spt == 1) {
 			schedule_timeout_interruptible(1);
 		} else if (spt == 2) {
 			while (READ_ONCE(stutter_pause_test)) {
 				if (!(i++ & 0xffff))
 					torture_hrtimeout_us(10, 0, NULL);
 				cond_resched();
 			}
 		} else {
 			schedule_timeout_interruptible(round_jiffies_relative(HZ));
 		}
 		torture_shutdown_absorb(title);
 	}
 	return ret;
 }
 EXPORT_SYMBOL_GPL(stutter_wait);

 /*
  * Cause the torture test to "stutter", starting and stopping all
  * threads periodically.
  */
 static int torture_stutter(void *arg)
 {
 	DEFINE_TORTURE_RANDOM(rand);
 	int wtime;

 	VERBOSE_TOROUT_STRING("torture_stutter task started");
 	do {
 		if (!torture_must_stop() && stutter > 1) {
 			wtime = stutter;
 			if (stutter > 2) {
 				WRITE_ONCE(stutter_pause_test, 1);
 				wtime = stutter - 3;
 				torture_hrtimeout_jiffies(wtime, &rand);
 				wtime = 2;
 			}
 			WRITE_ONCE(stutter_pause_test, 2);
 			torture_hrtimeout_jiffies(wtime, NULL);
 		}
 		WRITE_ONCE(stutter_pause_test, 0);
 		if (!torture_must_stop())
 			torture_hrtimeout_jiffies(stutter_gap, NULL);
 		torture_shutdown_absorb("torture_stutter");
 	} while (!torture_must_stop());
 	torture_kthread_stopping("torture_stutter");
 	return 0;
 }

 /*
  * Initialize and kick off the torture_stutter kthread.
  */
 int torture_stutter_init(const int s, const int sgap)
 {
 	stutter = s;
 	stutter_gap = sgap;
 	return torture_create_kthread(torture_stutter, NULL, stutter_task);
 }
 EXPORT_SYMBOL_GPL(torture_stutter_init);

 /*
  * Cleanup after the torture_stutter kthread.
  */
 static void torture_stutter_cleanup(void)
 {
 	if (!stutter_task)
 		return;
 	VERBOSE_TOROUT_STRING("Stopping torture_stutter task");
 	kthread_stop(stutter_task);
 	stutter_task = NULL;
 }

 /*
  * Initialize torture module.  Please note that this is -not- invoked via
  * the usual module_init() mechanism, but rather by an explicit call from
  * the client torture module.  This call must be paired with a later
  * torture_init_end().
  *
  * The runnable parameter points to a flag that controls whether or not
  * the test is currently runnable.  If there is no such flag, pass in NULL.
  */
 bool torture_init_begin(char *ttype, int v)
 {
 	mutex_lock(&fullstop_mutex);
 	if (torture_type != NULL) {
 		pr_alert("%s: Refusing %s init: %s running.\n",
 			  __func__, ttype, torture_type);
 		pr_alert("%s: One torture test at a time!\n", __func__);
 		mutex_unlock(&fullstop_mutex);
 		return false;
 	}
 	torture_type = ttype;
 	verbose = v;
 	fullstop = FULLSTOP_DONTSTOP;
 	return true;
 }
 EXPORT_SYMBOL_GPL(torture_init_begin);

 /*
  * Tell the torture module that initialization is complete.
  */
 void torture_init_end(void)
 {
 	mutex_unlock(&fullstop_mutex);
 	register_reboot_notifier(&torture_shutdown_nb);
 }
 EXPORT_SYMBOL_GPL(torture_init_end);

 /*
  * Clean up torture module.  Please note that this is -not- invoked via
  * the usual module_exit() mechanism, but rather by an explicit call from
  * the client torture module.  Returns true if a race with system shutdown
  * is detected, otherwise, all kthreads started by functions in this file
  * will be shut down.
  *
  * This must be called before the caller starts shutting down its own
  * kthreads.
  *
  * Both torture_cleanup_begin() and torture_cleanup_end() must be paired,
  * in order to correctly perform the cleanup. They are separated because
  * threads can still need to reference the torture_type type, thus nullify
  * only after completing all other relevant calls.
  */
 bool torture_cleanup_begin(void)
 {
 	mutex_lock(&fullstop_mutex);
 	if (READ_ONCE(fullstop) == FULLSTOP_SHUTDOWN) {
 		pr_warn("Concurrent rmmod and shutdown illegal!\n");
 		mutex_unlock(&fullstop_mutex);
 		schedule_timeout_uninterruptible(10);
 		return true;
 	}
 	WRITE_ONCE(fullstop, FULLSTOP_RMMOD);
 	mutex_unlock(&fullstop_mutex);
 	torture_shutdown_cleanup();
 	torture_shuffle_cleanup();
 	torture_stutter_cleanup();
 	torture_onoff_cleanup();
 	return false;
 }
 EXPORT_SYMBOL_GPL(torture_cleanup_begin);

 void torture_cleanup_end(void)
 {
 	mutex_lock(&fullstop_mutex);
 	torture_type = NULL;
 	mutex_unlock(&fullstop_mutex);
 }
 EXPORT_SYMBOL_GPL(torture_cleanup_end);

 /*
  * Is it time for the current torture test to stop?
  */
 bool torture_must_stop(void)
 {
 	return torture_must_stop_irq() || kthread_should_stop();
 }
 EXPORT_SYMBOL_GPL(torture_must_stop);

 /*
  * Is it time for the current torture test to stop?  This is the irq-safe
  * version, hence no check for kthread_should_stop().
  */
 bool torture_must_stop_irq(void)
 {
 	return READ_ONCE(fullstop) != FULLSTOP_DONTSTOP;
 }
 EXPORT_SYMBOL_GPL(torture_must_stop_irq);

 /*
  * Each kthread must wait for kthread_should_stop() before returning from
  * its top-level function, otherwise segfaults ensue.  This function
  * prints a "stopping" message and waits for kthread_should_stop(), and
  * should be called from all torture kthreads immediately prior to
  * returning.
  */
 void torture_kthread_stopping(char *title)
 {
 	char buf[128];

 	snprintf(buf, sizeof(buf), "Stopping %s", title);
 	VERBOSE_TOROUT_STRING(buf);
 	while (!kthread_should_stop()) {
 		torture_shutdown_absorb(title);
 		schedule_timeout_uninterruptible(1);
 	}
 }
 EXPORT_SYMBOL_GPL(torture_kthread_stopping);

 /*
  * Create a generic torture kthread that is immediately runnable.  If you
  * need the kthread to be stopped so that you can do something to it before
  * it starts, you will need to open-code your own.
  */
 int _torture_create_kthread(int (*fn)(void *arg), void *arg, char *s, char *m,
 			    char *f, struct task_struct **tp)
 {
 	int ret = 0;

 	VERBOSE_TOROUT_STRING(m);
 	*tp = kthread_run(fn, arg, "%s", s);
 	if (IS_ERR(*tp)) {
 		ret = PTR_ERR(*tp);
 		VERBOSE_TOROUT_ERRSTRING(f);
 		*tp = NULL;
 	}
 	torture_shuffle_task_register(*tp);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(_torture_create_kthread);

 /*
  * Stop a generic kthread, emitting a message.
  */
 void _torture_stop_kthread(char *m, struct task_struct **tp)
 {
 	if (*tp == NULL)
 		return;
 	VERBOSE_TOROUT_STRING(m);
 	kthread_stop(*tp);
 	*tp = NULL;
 }
 EXPORT_SYMBOL_GPL(_torture_stop_kthread);