// 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_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
  ", 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 */