Quelle smpboot.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
* 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_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);
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 __always_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

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);
}
kthread_set_per_cpu(tsk, cpu);
/*
* 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_put(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;

cpus_read_lock();
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);
cpus_read_unlock();
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)
{
cpus_read_lock();
mutex_lock(&smpboot_threads_lock);
list_del(&plug_thread->list);
smpboot_destroy_threads(plug_thread);
mutex_unlock(&smpboot_threads_lock);
cpus_read_unlock();
}
EXPORT_SYMBOL_GPL(smpboot_unregister_percpu_thread);

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