[linux-2.6-block.git] / kernel / smpboot.c

/*
 * Common SMP CPU bringup/teardown functions
 */
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/smp.h>
#include <linux/delay.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/kthread.h>
#include <linux/smpboot.h>

#include "smpboot.h"

#ifdef CONFIG_SMP

#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
/*
 * For the hotplug case we keep the task structs around and reuse
 * them.
 */
static DEFINE_PER_CPU(struct task_struct *, idle_threads);

struct task_struct *idle_thread_get(unsigned int cpu)
{
	struct task_struct *tsk = per_cpu(idle_threads, cpu);

	if (!tsk)
		return ERR_PTR(-ENOMEM);
	init_idle(tsk, cpu);
	return tsk;
}

void __init idle_thread_set_boot_cpu(void)
{
	per_cpu(idle_threads, smp_processor_id()) = current;
}

/**
 * idle_init - Initialize the idle thread for a cpu
 * @cpu:	The cpu for which the idle thread should be initialized
 *
 * Creates the thread if it does not exist.
 */
static inline void idle_init(unsigned int cpu)
{
	struct task_struct *tsk = per_cpu(idle_threads, cpu);

	if (!tsk) {
		tsk = fork_idle(cpu);
		if (IS_ERR(tsk))
			pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
		else
			per_cpu(idle_threads, cpu) = tsk;
	}
}

/**
 * idle_threads_init - Initialize idle threads for all cpus
 */
void __init idle_threads_init(void)
{
	unsigned int cpu, boot_cpu;

	boot_cpu = smp_processor_id();

	for_each_possible_cpu(cpu) {
		if (cpu != boot_cpu)
			idle_init(cpu);
	}
}
#endif

#endif /* #ifdef CONFIG_SMP */

static LIST_HEAD(hotplug_threads);
static DEFINE_MUTEX(smpboot_threads_lock);

struct smpboot_thread_data {
	unsigned int			cpu;
	unsigned int			status;
	struct smp_hotplug_thread	*ht;
};

enum {
	HP_THREAD_NONE = 0,
	HP_THREAD_ACTIVE,
	HP_THREAD_PARKED,
};

/**
 * smpboot_thread_fn - percpu hotplug thread loop function
 * @data:	thread data pointer
 *
 * Checks for thread stop and park conditions. Calls the necessary
 * setup, cleanup, park and unpark functions for the registered
 * thread.
 *
 * Returns 1 when the thread should exit, 0 otherwise.
 */
static int smpboot_thread_fn(void *data)
{
	struct smpboot_thread_data *td = data;
	struct smp_hotplug_thread *ht = td->ht;

	while (1) {
		set_current_state(TASK_INTERRUPTIBLE);
		preempt_disable();
		if (kthread_should_stop()) {
			__set_current_state(TASK_RUNNING);
			preempt_enable();
			/* cleanup must mirror setup */
			if (ht->cleanup && td->status != HP_THREAD_NONE)
				ht->cleanup(td->cpu, cpu_online(td->cpu));
			kfree(td);
			return 0;
		}

		if (kthread_should_park()) {
			__set_current_state(TASK_RUNNING);
			preempt_enable();
			if (ht->park && td->status == HP_THREAD_ACTIVE) {
				BUG_ON(td->cpu != smp_processor_id());
				ht->park(td->cpu);
				td->status = HP_THREAD_PARKED;
			}
			kthread_parkme();
			/* We might have been woken for stop */
			continue;
		}

		BUG_ON(td->cpu != smp_processor_id());

		/* Check for state change setup */
		switch (td->status) {
		case HP_THREAD_NONE:
			__set_current_state(TASK_RUNNING);
			preempt_enable();
			if (ht->setup)
				ht->setup(td->cpu);
			td->status = HP_THREAD_ACTIVE;
			continue;

		case HP_THREAD_PARKED:
			__set_current_state(TASK_RUNNING);
			preempt_enable();
			if (ht->unpark)
				ht->unpark(td->cpu);
			td->status = HP_THREAD_ACTIVE;
			continue;
		}

		if (!ht->thread_should_run(td->cpu)) {
			preempt_enable_no_resched();
			schedule();
		} else {
			__set_current_state(TASK_RUNNING);
			preempt_enable();
			ht->thread_fn(td->cpu);
		}
	}
}

static int
__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
{
	struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);
	struct smpboot_thread_data *td;

	if (tsk)
		return 0;

	td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
	if (!td)
		return -ENOMEM;
	td->cpu = cpu;
	td->ht = ht;

	tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
				    ht->thread_comm);
	if (IS_ERR(tsk)) {
		kfree(td);
		return PTR_ERR(tsk);
	}
	/*
	 * Park the thread so that it could start right on the CPU
	 * when it is available.
	 */
	kthread_park(tsk);
	get_task_struct(tsk);
	*per_cpu_ptr(ht->store, cpu) = tsk;
	if (ht->create) {
		/*
		 * Make sure that the task has actually scheduled out
		 * into park position, before calling the create
		 * callback. At least the migration thread callback
		 * requires that the task is off the runqueue.
		 */
		if (!wait_task_inactive(tsk, TASK_PARKED))
			WARN_ON(1);
		else
			ht->create(cpu);
	}
	return 0;
}

int smpboot_create_threads(unsigned int cpu)
{
	struct smp_hotplug_thread *cur;
	int ret = 0;

	mutex_lock(&smpboot_threads_lock);
	list_for_each_entry(cur, &hotplug_threads, list) {
		ret = __smpboot_create_thread(cur, cpu);
		if (ret)
			break;
	}
	mutex_unlock(&smpboot_threads_lock);
	return ret;
}

static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
{
	struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);

	if (!ht->selfparking)
		kthread_unpark(tsk);
}

int smpboot_unpark_threads(unsigned int cpu)
{
	struct smp_hotplug_thread *cur;

	mutex_lock(&smpboot_threads_lock);
	list_for_each_entry(cur, &hotplug_threads, list)
		smpboot_unpark_thread(cur, cpu);
	mutex_unlock(&smpboot_threads_lock);
	return 0;
}

static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
{
	struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);

	if (tsk && !ht->selfparking)
		kthread_park(tsk);
}

int smpboot_park_threads(unsigned int cpu)
{
	struct smp_hotplug_thread *cur;

	mutex_lock(&smpboot_threads_lock);
	list_for_each_entry_reverse(cur, &hotplug_threads, list)
		smpboot_park_thread(cur, cpu);
	mutex_unlock(&smpboot_threads_lock);
	return 0;
}

static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
{
	unsigned int cpu;

	/* We need to destroy also the parked threads of offline cpus */
	for_each_possible_cpu(cpu) {
		struct task_struct *tsk = *per_cpu_ptr(ht->store, cpu);

		if (tsk) {
			kthread_stop(tsk);
			put_task_struct(tsk);
			*per_cpu_ptr(ht->store, cpu) = NULL;
		}
	}
}

/**
 * smpboot_register_percpu_thread - Register a per_cpu thread related
 * 					    to hotplug
 * @plug_thread:	Hotplug thread descriptor
 *
 * Creates and starts the threads on all online cpus.
 */
int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
{
	unsigned int cpu;
	int ret = 0;

	get_online_cpus();
	mutex_lock(&smpboot_threads_lock);
	for_each_online_cpu(cpu) {
		ret = __smpboot_create_thread(plug_thread, cpu);
		if (ret) {
			smpboot_destroy_threads(plug_thread);
			goto out;
		}
		smpboot_unpark_thread(plug_thread, cpu);
	}
	list_add(&plug_thread->list, &hotplug_threads);
out:
	mutex_unlock(&smpboot_threads_lock);
	put_online_cpus();
	return ret;
}
EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);

/**
 * smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
 * @plug_thread:	Hotplug thread descriptor
 *
 * Stops all threads on all possible cpus.
 */
void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
{
	get_online_cpus();
	mutex_lock(&smpboot_threads_lock);
	list_del(&plug_thread->list);
	smpboot_destroy_threads(plug_thread);
	mutex_unlock(&smpboot_threads_lock);
	put_online_cpus();
}
EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);

static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);

/*
 * Called to poll specified CPU's state, for example, when waiting for
 * a CPU to come online.
 */
int cpu_report_state(int cpu)
{
	return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
}

/*
 * If CPU has died properly, set its state to CPU_UP_PREPARE and
 * return success.  Otherwise, return -EBUSY if the CPU died after
 * cpu_wait_death() timed out.  And yet otherwise again, return -EAGAIN
 * if cpu_wait_death() timed out and the CPU still hasn't gotten around
 * to dying.  In the latter two cases, the CPU might not be set up
 * properly, but it is up to the arch-specific code to decide.
 * Finally, -EIO indicates an unanticipated problem.
 *
 * Note that it is permissible to omit this call entirely, as is
 * done in architectures that do no CPU-hotplug error checking.
 */
int cpu_check_up_prepare(int cpu)
{
	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
		atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
		return 0;
	}

	switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {

	case CPU_POST_DEAD:

		/* The CPU died properly, so just start it up again. */
		atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
		return 0;

	case CPU_DEAD_FROZEN:

		/*
		 * Timeout during CPU death, so let caller know.
		 * The outgoing CPU completed its processing, but after
		 * cpu_wait_death() timed out and reported the error. The
		 * caller is free to proceed, in which case the state
		 * will be reset properly by cpu_set_state_online().
		 * Proceeding despite this -EBUSY return makes sense
		 * for systems where the outgoing CPUs take themselves
		 * offline, with no post-death manipulation required from
		 * a surviving CPU.
		 */
		return -EBUSY;

	case CPU_BROKEN:

		/*
		 * The most likely reason we got here is that there was
		 * a timeout during CPU death, and the outgoing CPU never
		 * did complete its processing.  This could happen on
		 * a virtualized system if the outgoing VCPU gets preempted
		 * for more than five seconds, and the user attempts to
		 * immediately online that same CPU.  Trying again later
		 * might return -EBUSY above, hence -EAGAIN.
		 */
		return -EAGAIN;

	default:

		/* Should not happen.  Famous last words. */
		return -EIO;
	}
}

/*
 * Mark the specified CPU online.
 *
 * Note that it is permissible to omit this call entirely, as is
 * done in architectures that do no CPU-hotplug error checking.
 */
void cpu_set_state_online(int cpu)
{
	(void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
}

#ifdef CONFIG_HOTPLUG_CPU

/*
 * Wait for the specified CPU to exit the idle loop and die.
 */
bool cpu_wait_death(unsigned int cpu, int seconds)
{
	int jf_left = seconds * HZ;
	int oldstate;
	bool ret = true;
	int sleep_jf = 1;

	might_sleep();

	/* The outgoing CPU will normally get done quite quickly. */
	if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
		goto update_state;
	udelay(5);

	/* But if the outgoing CPU dawdles, wait increasingly long times. */
	while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
		schedule_timeout_uninterruptible(sleep_jf);
		jf_left -= sleep_jf;
		if (jf_left <= 0)
			break;
		sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
	}
update_state:
	oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
	if (oldstate == CPU_DEAD) {
		/* Outgoing CPU died normally, update state. */
		smp_mb(); /* atomic_read() before update. */
		atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
	} else {
		/* Outgoing CPU still hasn't died, set state accordingly. */
		if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
				   oldstate, CPU_BROKEN) != oldstate)
			goto update_state;
		ret = false;
	}
	return ret;
}

/*
 * Called by the outgoing CPU to report its successful death.  Return
 * false if this report follows the surviving CPU's timing out.
 *
 * A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
 * timed out.  This approach allows architectures to omit calls to
 * cpu_check_up_prepare() and cpu_set_state_online() without defeating
 * the next cpu_wait_death()'s polling loop.
 */
bool cpu_report_death(void)
{
	int oldstate;
	int newstate;
	int cpu = smp_processor_id();

	do {
		oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
		if (oldstate != CPU_BROKEN)
			newstate = CPU_DEAD;
		else
			newstate = CPU_DEAD_FROZEN;
	} while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
				oldstate, newstate) != oldstate);
	return newstate == CPU_DEAD;
}

#endif /* #ifdef CONFIG_HOTPLUG_CPU */
Commit	Line	Data
38498a67 TG	1	/*
	2	* Common SMP CPU bringup/teardown functions
	3	*/
f97f8f06	4	#include <linux/cpu.h>
29d5e047 TG	5	#include <linux/err.h>
29d5e047 TG	6	#include <linux/smp.h>
8038dad7	7	#include <linux/delay.h>
38498a67	8	#include <linux/init.h>
f97f8f06 TG	9	#include <linux/list.h>
f97f8f06 TG	10	#include <linux/slab.h>
29d5e047	11	#include <linux/sched.h>
29930025	12	#include <linux/sched/task.h>
f97f8f06	13	#include <linux/export.h>
29d5e047	14	#include <linux/percpu.h>
f97f8f06 TG	15	#include <linux/kthread.h>
f97f8f06 TG	16	#include <linux/smpboot.h>
38498a67 TG	17
	18	#include "smpboot.h"
	19
3180d89b PM	20	#ifdef CONFIG_SMP
3180d89b PM	21
29d5e047	22	#ifdef CONFIG_GENERIC_SMP_IDLE_THREAD
29d5e047 TG	23	/*
	24	* For the hotplug case we keep the task structs around and reuse
	25	* them.
	26	*/
	27	static DEFINE_PER_CPU(struct task_struct *, idle_threads);
	28
0db0628d	29	struct task_struct *idle_thread_get(unsigned int cpu)
29d5e047 TG	30	{
	31	struct task_struct *tsk = per_cpu(idle_threads, cpu);
	32
	33	if (!tsk)
3bb5d2ee	34	return ERR_PTR(-ENOMEM);
29d5e047 TG	35	init_idle(tsk, cpu);
	36	return tsk;
	37	}
	38
3bb5d2ee	39	void __init idle_thread_set_boot_cpu(void)
29d5e047	40	{
3bb5d2ee	41	per_cpu(idle_threads, smp_processor_id()) = current;
29d5e047 TG	42	}
29d5e047 TG	43
4a70d2d9 SB	44	/**
	45	* idle_init - Initialize the idle thread for a cpu
	46	* @cpu: The cpu for which the idle thread should be initialized
	47	*
	48	* Creates the thread if it does not exist.
	49	*/
3bb5d2ee	50	static inline void idle_init(unsigned int cpu)
29d5e047	51	{
3bb5d2ee SS	52	struct task_struct *tsk = per_cpu(idle_threads, cpu);
	53
	54	if (!tsk) {
	55	tsk = fork_idle(cpu);
	56	if (IS_ERR(tsk))
	57	pr_err("SMP: fork_idle() failed for CPU %u\n", cpu);
	58	else
	59	per_cpu(idle_threads, cpu) = tsk;
	60	}
29d5e047 TG	61	}
	62
	63	/**
4a70d2d9	64	* idle_threads_init - Initialize idle threads for all cpus
29d5e047	65	*/
3bb5d2ee	66	void __init idle_threads_init(void)
29d5e047	67	{
ee74d132 SB	68	unsigned int cpu, boot_cpu;
	69
	70	boot_cpu = smp_processor_id();
29d5e047	71
3bb5d2ee	72	for_each_possible_cpu(cpu) {
ee74d132	73	if (cpu != boot_cpu)
3bb5d2ee	74	idle_init(cpu);
29d5e047	75	}
29d5e047	76	}
29d5e047	77	#endif
f97f8f06	78
3180d89b PM	79	#endif /* #ifdef CONFIG_SMP */
3180d89b PM	80
f97f8f06 TG	81	static LIST_HEAD(hotplug_threads);
	82	static DEFINE_MUTEX(smpboot_threads_lock);
	83
	84	struct smpboot_thread_data {
	85	unsigned int cpu;
	86	unsigned int status;
	87	struct smp_hotplug_thread *ht;
	88	};
	89
	90	enum {
	91	HP_THREAD_NONE = 0,
	92	HP_THREAD_ACTIVE,
	93	HP_THREAD_PARKED,
	94	};
	95
	96	/**
	97	* smpboot_thread_fn - percpu hotplug thread loop function
	98	* @data: thread data pointer
	99	*
	100	* Checks for thread stop and park conditions. Calls the necessary
	101	* setup, cleanup, park and unpark functions for the registered
	102	* thread.
	103	*
	104	* Returns 1 when the thread should exit, 0 otherwise.
	105	*/
	106	static int smpboot_thread_fn(void *data)
	107	{
	108	struct smpboot_thread_data *td = data;
	109	struct smp_hotplug_thread *ht = td->ht;
	110
	111	while (1) {
	112	set_current_state(TASK_INTERRUPTIBLE);
	113	preempt_disable();
	114	if (kthread_should_stop()) {
7d4d2696	115	__set_current_state(TASK_RUNNING);
f97f8f06	116	preempt_enable();
3dd08c0c FW	117	/* cleanup must mirror setup */
3dd08c0c FW	118	if (ht->cleanup && td->status != HP_THREAD_NONE)
f97f8f06 TG	119	ht->cleanup(td->cpu, cpu_online(td->cpu));
	120	kfree(td);
	121	return 0;
	122	}
	123
	124	if (kthread_should_park()) {
	125	__set_current_state(TASK_RUNNING);
be6a2e4c	126	preempt_enable();
f97f8f06 TG	127	if (ht->park && td->status == HP_THREAD_ACTIVE) {
	128	BUG_ON(td->cpu != smp_processor_id());
	129	ht->park(td->cpu);
	130	td->status = HP_THREAD_PARKED;
	131	}
	132	kthread_parkme();
	133	/* We might have been woken for stop */
	134	continue;
	135	}
	136
dc893e19	137	BUG_ON(td->cpu != smp_processor_id());
f97f8f06 TG	138
	139	/* Check for state change setup */
	140	switch (td->status) {
	141	case HP_THREAD_NONE:
7d4d2696	142	__set_current_state(TASK_RUNNING);
f97f8f06 TG	143	preempt_enable();
	144	if (ht->setup)
	145	ht->setup(td->cpu);
	146	td->status = HP_THREAD_ACTIVE;
7d4d2696 PZ	147	continue;
7d4d2696 PZ	148
f97f8f06	149	case HP_THREAD_PARKED:
7d4d2696	150	__set_current_state(TASK_RUNNING);
f97f8f06 TG	151	preempt_enable();
	152	if (ht->unpark)
	153	ht->unpark(td->cpu);
	154	td->status = HP_THREAD_ACTIVE;
7d4d2696	155	continue;
f97f8f06 TG	156	}
	157
	158	if (!ht->thread_should_run(td->cpu)) {
7d4d2696	159	preempt_enable_no_resched();
f97f8f06 TG	160	schedule();
f97f8f06 TG	161	} else {
7d4d2696	162	__set_current_state(TASK_RUNNING);
f97f8f06 TG	163	preempt_enable();
	164	ht->thread_fn(td->cpu);
	165	}
	166	}
	167	}
	168
	169	static int
	170	__smpboot_create_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
	171	{
	172	struct task_struct tsk = per_cpu_ptr(ht->store, cpu);
	173	struct smpboot_thread_data *td;
	174
	175	if (tsk)
	176	return 0;
	177
	178	td = kzalloc_node(sizeof(*td), GFP_KERNEL, cpu_to_node(cpu));
	179	if (!td)
	180	return -ENOMEM;
	181	td->cpu = cpu;
	182	td->ht = ht;
	183
	184	tsk = kthread_create_on_cpu(smpboot_thread_fn, td, cpu,
	185	ht->thread_comm);
	186	if (IS_ERR(tsk)) {
	187	kfree(td);
	188	return PTR_ERR(tsk);
	189	}
a65d4096 PM	190	/*
	191	* Park the thread so that it could start right on the CPU
	192	* when it is available.
	193	*/
	194	kthread_park(tsk);
f97f8f06 TG	195	get_task_struct(tsk);
f97f8f06 TG	196	*per_cpu_ptr(ht->store, cpu) = tsk;
f2530dc7 TG	197	if (ht->create) {
	198	/*
	199	* Make sure that the task has actually scheduled out
	200	* into park position, before calling the create
	201	* callback. At least the migration thread callback
	202	* requires that the task is off the runqueue.
	203	*/
	204	if (!wait_task_inactive(tsk, TASK_PARKED))
	205	WARN_ON(1);
	206	else
	207	ht->create(cpu);
	208	}
f97f8f06 TG	209	return 0;
	210	}
	211
	212	int smpboot_create_threads(unsigned int cpu)
	213	{
	214	struct smp_hotplug_thread *cur;
	215	int ret = 0;
	216
	217	mutex_lock(&smpboot_threads_lock);
	218	list_for_each_entry(cur, &hotplug_threads, list) {
	219	ret = __smpboot_create_thread(cur, cpu);
	220	if (ret)
	221	break;
	222	}
	223	mutex_unlock(&smpboot_threads_lock);
	224	return ret;
	225	}
	226
	227	static void smpboot_unpark_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
	228	{
	229	struct task_struct tsk = per_cpu_ptr(ht->store, cpu);
	230
c00166d8 ON	231	if (!ht->selfparking)
c00166d8 ON	232	kthread_unpark(tsk);
f97f8f06 TG	233	}
f97f8f06 TG	234
931ef163	235	int smpboot_unpark_threads(unsigned int cpu)
f97f8f06 TG	236	{
	237	struct smp_hotplug_thread *cur;
	238
	239	mutex_lock(&smpboot_threads_lock);
	240	list_for_each_entry(cur, &hotplug_threads, list)
167a8867	241	smpboot_unpark_thread(cur, cpu);
f97f8f06	242	mutex_unlock(&smpboot_threads_lock);
931ef163	243	return 0;
f97f8f06 TG	244	}
	245
	246	static void smpboot_park_thread(struct smp_hotplug_thread *ht, unsigned int cpu)
	247	{
	248	struct task_struct tsk = per_cpu_ptr(ht->store, cpu);
	249
7d7e499f	250	if (tsk && !ht->selfparking)
f97f8f06 TG	251	kthread_park(tsk);
	252	}
	253
931ef163	254	int smpboot_park_threads(unsigned int cpu)
f97f8f06 TG	255	{
	256	struct smp_hotplug_thread *cur;
	257
	258	mutex_lock(&smpboot_threads_lock);
	259	list_for_each_entry_reverse(cur, &hotplug_threads, list)
	260	smpboot_park_thread(cur, cpu);
	261	mutex_unlock(&smpboot_threads_lock);
931ef163	262	return 0;
f97f8f06 TG	263	}
	264
	265	static void smpboot_destroy_threads(struct smp_hotplug_thread *ht)
	266	{
	267	unsigned int cpu;
	268
	269	/* We need to destroy also the parked threads of offline cpus */
	270	for_each_possible_cpu(cpu) {
	271	struct task_struct tsk = per_cpu_ptr(ht->store, cpu);
	272
	273	if (tsk) {
	274	kthread_stop(tsk);
	275	put_task_struct(tsk);
	276	*per_cpu_ptr(ht->store, cpu) = NULL;
	277	}
	278	}
	279	}
	280
	281	/**
167a8867	282	* smpboot_register_percpu_thread - Register a per_cpu thread related
230ec939	283	* to hotplug
f97f8f06 TG	284	* @plug_thread: Hotplug thread descriptor
	285	*
	286	* Creates and starts the threads on all online cpus.
	287	*/
167a8867	288	int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread)
f97f8f06 TG	289	{
	290	unsigned int cpu;
	291	int ret = 0;
	292
4bee9686	293	get_online_cpus();
f97f8f06 TG	294	mutex_lock(&smpboot_threads_lock);
	295	for_each_online_cpu(cpu) {
	296	ret = __smpboot_create_thread(plug_thread, cpu);
	297	if (ret) {
	298	smpboot_destroy_threads(plug_thread);
	299	goto out;
	300	}
167a8867	301	smpboot_unpark_thread(plug_thread, cpu);
f97f8f06 TG	302	}
	303	list_add(&plug_thread->list, &hotplug_threads);
	304	out:
	305	mutex_unlock(&smpboot_threads_lock);
4bee9686	306	put_online_cpus();
f97f8f06 TG	307	return ret;
f97f8f06 TG	308	}
167a8867	309	EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);
f97f8f06 TG	310
	311	/**
	312	* smpboot_unregister_percpu_thread - Unregister a per_cpu thread related to hotplug
	313	* @plug_thread: Hotplug thread descriptor
	314	*
	315	* Stops all threads on all possible cpus.
	316	*/
	317	void smpboot_unregister_percpu_thread(struct smp_hotplug_thread *plug_thread)
	318	{
	319	get_online_cpus();
	320	mutex_lock(&smpboot_threads_lock);
	321	list_del(&plug_thread->list);
	322	smpboot_destroy_threads(plug_thread);
	323	mutex_unlock(&smpboot_threads_lock);
	324	put_online_cpus();
	325	}
	326	EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);
8038dad7 PM	327
	328	static DEFINE_PER_CPU(atomic_t, cpu_hotplug_state) = ATOMIC_INIT(CPU_POST_DEAD);
	329
	330	/*
	331	* Called to poll specified CPU's state, for example, when waiting for
	332	* a CPU to come online.
	333	*/
	334	int cpu_report_state(int cpu)
	335	{
	336	return atomic_read(&per_cpu(cpu_hotplug_state, cpu));
	337	}
	338
	339	/*
	340	* If CPU has died properly, set its state to CPU_UP_PREPARE and
	341	* return success. Otherwise, return -EBUSY if the CPU died after
	342	* cpu_wait_death() timed out. And yet otherwise again, return -EAGAIN
	343	* if cpu_wait_death() timed out and the CPU still hasn't gotten around
	344	* to dying. In the latter two cases, the CPU might not be set up
	345	* properly, but it is up to the arch-specific code to decide.
	346	* Finally, -EIO indicates an unanticipated problem.
	347	*
	348	* Note that it is permissible to omit this call entirely, as is
	349	* done in architectures that do no CPU-hotplug error checking.
	350	*/
	351	int cpu_check_up_prepare(int cpu)
	352	{
	353	if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
	354	atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
	355	return 0;
	356	}
	357
	358	switch (atomic_read(&per_cpu(cpu_hotplug_state, cpu))) {
	359
	360	case CPU_POST_DEAD:
	361
	362	/* The CPU died properly, so just start it up again. */
	363	atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_UP_PREPARE);
	364	return 0;
	365
	366	case CPU_DEAD_FROZEN:
	367
	368	/*
	369	* Timeout during CPU death, so let caller know.
	370	* The outgoing CPU completed its processing, but after
	371	* cpu_wait_death() timed out and reported the error. The
	372	* caller is free to proceed, in which case the state
	373	* will be reset properly by cpu_set_state_online().
	374	* Proceeding despite this -EBUSY return makes sense
	375	* for systems where the outgoing CPUs take themselves
	376	* offline, with no post-death manipulation required from
	377	* a surviving CPU.
	378	*/
	379	return -EBUSY;
	380
	381	case CPU_BROKEN:
	382
	383	/*
	384	* The most likely reason we got here is that there was
	385	* a timeout during CPU death, and the outgoing CPU never
	386	* did complete its processing. This could happen on
	387	* a virtualized system if the outgoing VCPU gets preempted
	388	* for more than five seconds, and the user attempts to
	389	* immediately online that same CPU. Trying again later
	390	* might return -EBUSY above, hence -EAGAIN.
391	*/
392	return -EAGAIN;
393
394	default:
395
396	/* Should not happen. Famous last words. */
397	return -EIO;
398	}
399	}
400
401	/*
402	* Mark the specified CPU online.
403	*
404	* Note that it is permissible to omit this call entirely, as is
405	* done in architectures that do no CPU-hotplug error checking.
406	*/
407	void cpu_set_state_online(int cpu)
408	{
409	(void)atomic_xchg(&per_cpu(cpu_hotplug_state, cpu), CPU_ONLINE);
410	}
411
412	#ifdef CONFIG_HOTPLUG_CPU
413
414	/*
415	* Wait for the specified CPU to exit the idle loop and die.
416	*/
417	bool cpu_wait_death(unsigned int cpu, int seconds)
418	{
419	int jf_left = seconds * HZ;
420	int oldstate;
421	bool ret = true;
422	int sleep_jf = 1;
423
424	might_sleep();
425
426	/* The outgoing CPU will normally get done quite quickly. */
427	if (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) == CPU_DEAD)
428	goto update_state;
429	udelay(5);
430
431	/* But if the outgoing CPU dawdles, wait increasingly long times. */
432	while (atomic_read(&per_cpu(cpu_hotplug_state, cpu)) != CPU_DEAD) {
433	schedule_timeout_uninterruptible(sleep_jf);
434	jf_left -= sleep_jf;
435	if (jf_left <= 0)
436	break;
437	sleep_jf = DIV_ROUND_UP(sleep_jf * 11, 10);
438	}
439	update_state:
440	oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
441	if (oldstate == CPU_DEAD) {
442	/* Outgoing CPU died normally, update state. */
443	smp_mb(); /* atomic_read() before update. */
444	atomic_set(&per_cpu(cpu_hotplug_state, cpu), CPU_POST_DEAD);
445	} else {
446	/* Outgoing CPU still hasn't died, set state accordingly. */
447	if (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
448	oldstate, CPU_BROKEN) != oldstate)
449	goto update_state;
450	ret = false;
451	}
452	return ret;
453	}
454
455	/*
456	* Called by the outgoing CPU to report its successful death. Return
457	* false if this report follows the surviving CPU's timing out.
458	*
459	* A separate "CPU_DEAD_FROZEN" is used when the surviving CPU
460	* timed out. This approach allows architectures to omit calls to
461	* cpu_check_up_prepare() and cpu_set_state_online() without defeating
462	* the next cpu_wait_death()'s polling loop.
463	*/
464	bool cpu_report_death(void)
465	{
466	int oldstate;
467	int newstate;
468	int cpu = smp_processor_id();
469
470	do {
471	oldstate = atomic_read(&per_cpu(cpu_hotplug_state, cpu));
472	if (oldstate != CPU_BROKEN)
473	newstate = CPU_DEAD;
474	else
475	newstate = CPU_DEAD_FROZEN;
476	} while (atomic_cmpxchg(&per_cpu(cpu_hotplug_state, cpu),
477	oldstate, newstate) != oldstate);
478	return newstate == CPU_DEAD;
479	}
480
481	#endif /* #ifdef CONFIG_HOTPLUG_CPU */