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tag: v3.8-rc4
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/*
* Common SMP CPU bringup/teardown functions
*/
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/slab.h>
#include <linux/sched.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 * __cpuinit 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();
if (ht->cleanup)
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:
preempt_enable();
if (ht->setup)
ht->setup(td->cpu);
td->status = HP_THREAD_ACTIVE;
preempt_disable();
break;
case HP_THREAD_PARKED:
preempt_enable();
if (ht->unpark)
ht->unpark(td->cpu);
td->status = HP_THREAD_ACTIVE;
preempt_disable();
break;
}

if (!ht->thread_should_run(td->cpu)) {
preempt_enable();
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);
}

get_task_struct(tsk);
*per_cpu_ptr(ht->store, cpu) = tsk;
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);

kthread_unpark(tsk);
}

void 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);
}

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)
kthread_park(tsk);
}

void 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);
}

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;

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);
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);
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