/*
   * kernel/stop_machine.c
   *
   * Copyright (C) 2008, 2005	IBM Corporation.
   * Copyright (C) 2008, 2005	Rusty Russell rusty@rustcorp.com.au
   * Copyright (C) 2010		SUSE Linux Products GmbH
   * Copyright (C) 2010		Tejun Heo <tj@kernel.org>
   *
   * This file is released under the GPLv2 and any later version.

   */

  #include <linux/completion.h>

  #include <linux/cpu.h>

  #include <linux/init.h>

  #include <linux/kthread.h>

  #include <linux/export.h>

  #include <linux/percpu.h>

  #include <linux/sched.h>
  #include <linux/stop_machine.h>

  #include <linux/interrupt.h>

  #include <linux/kallsyms.h>

  #include <linux/smpboot.h>

  #include <linux/atomic.h>

  #include <linux/nmi.h>

  #include <linux/sched/wake_q.h>

  
  /*
   * Structure to determine completion condition and record errors.  May
   * be shared by works on different cpus.
   */
  struct cpu_stop_done {
  	atomic_t		nr_todo;	/* nr left to execute */

  	int			ret;		/* collected return value */
  	struct completion	completion;	/* fired if nr_todo reaches 0 */
  };
  
  /* the actual stopper, one per every possible cpu, enabled on online cpus */
  struct cpu_stopper {

  	struct task_struct	*thread;

  	raw_spinlock_t		lock;

  	bool			enabled;	/* is this stopper enabled? */

  	struct list_head	works;		/* list of pending works */

  
  	struct cpu_stop_work	stop_work;	/* for stop_cpus */

  };
  
  static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);

  static bool stop_machine_initialized = false;

  /* static data for stop_cpus */
  static DEFINE_MUTEX(stop_cpus_mutex);
  static bool stop_cpus_in_progress;

  static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
  {
  	memset(done, 0, sizeof(*done));
  	atomic_set(&done->nr_todo, nr_todo);
  	init_completion(&done->completion);
  }
  
  /* signal completion unless @done is NULL */

  static void cpu_stop_signal_done(struct cpu_stop_done *done)

  {

  	if (atomic_dec_and_test(&done->nr_todo))
  		complete(&done->completion);

  }

  static void __cpu_stop_queue_work(struct cpu_stopper *stopper,

  					struct cpu_stop_work *work,
  					struct wake_q_head *wakeq)

  {
  	list_add_tail(&work->list, &stopper->works);

  	wake_q_add(wakeq, stopper->thread);

  }

  /* queue @work to @stopper.  if offline, @work is completed immediately */

  static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)

  {

  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

  	DEFINE_WAKE_Q(wakeq);

  	unsigned long flags;

  	bool enabled;

  	preempt_disable();

  	raw_spin_lock_irqsave(&stopper->lock, flags);

  	enabled = stopper->enabled;
  	if (enabled)

  		__cpu_stop_queue_work(stopper, work, &wakeq);

  	else if (work->done)

  		cpu_stop_signal_done(work->done);

  	raw_spin_unlock_irqrestore(&stopper->lock, flags);

  	wake_up_q(&wakeq);

  	preempt_enable();

  	return enabled;

  }
  
  /**
   * stop_one_cpu - stop a cpu
   * @cpu: cpu to stop
   * @fn: function to execute
   * @arg: argument to @fn
   *
   * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
   * the highest priority preempting any task on the cpu and
   * monopolizing it.  This function returns after the execution is
   * complete.
   *
   * This function doesn't guarantee @cpu stays online till @fn
   * completes.  If @cpu goes down in the middle, execution may happen
   * partially or fully on different cpus.  @fn should either be ready
   * for that or the caller should ensure that @cpu stays online until
   * this function completes.
   *
   * CONTEXT:
   * Might sleep.
   *
   * RETURNS:
   * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
   * otherwise, the return value of @fn.
   */
  int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
  {
  	struct cpu_stop_done done;
  	struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
  
  	cpu_stop_init_done(&done, 1);

  	if (!cpu_stop_queue_work(cpu, &work))
  		return -ENOENT;

  	/*
  	 * In case @cpu == smp_proccessor_id() we can avoid a sleep+wakeup
  	 * cycle by doing a preemption:
  	 */
  	cond_resched();

  	wait_for_completion(&done.completion);

  	return done.ret;

  }

  /* This controls the threads on each CPU. */
  enum multi_stop_state {
  	/* Dummy starting state for thread. */
  	MULTI_STOP_NONE,
  	/* Awaiting everyone to be scheduled. */
  	MULTI_STOP_PREPARE,
  	/* Disable interrupts. */
  	MULTI_STOP_DISABLE_IRQ,
  	/* Run the function */
  	MULTI_STOP_RUN,
  	/* Exit */
  	MULTI_STOP_EXIT,
  };
  
  struct multi_stop_data {

  	cpu_stop_fn_t		fn;

  	void			*data;
  	/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
  	unsigned int		num_threads;
  	const struct cpumask	*active_cpus;
  
  	enum multi_stop_state	state;
  	atomic_t		thread_ack;
  };
  
  static void set_state(struct multi_stop_data *msdata,
  		      enum multi_stop_state newstate)
  {
  	/* Reset ack counter. */
  	atomic_set(&msdata->thread_ack, msdata->num_threads);
  	smp_wmb();
  	msdata->state = newstate;
  }
  
  /* Last one to ack a state moves to the next state. */
  static void ack_state(struct multi_stop_data *msdata)
  {
  	if (atomic_dec_and_test(&msdata->thread_ack))
  		set_state(msdata, msdata->state + 1);
  }
  
  /* This is the cpu_stop function which stops the CPU. */
  static int multi_cpu_stop(void *data)
  {
  	struct multi_stop_data *msdata = data;
  	enum multi_stop_state curstate = MULTI_STOP_NONE;
  	int cpu = smp_processor_id(), err = 0;
  	unsigned long flags;
  	bool is_active;
  
  	/*
  	 * When called from stop_machine_from_inactive_cpu(), irq might
  	 * already be disabled.  Save the state and restore it on exit.
  	 */
  	local_save_flags(flags);
  
  	if (!msdata->active_cpus)
  		is_active = cpu == cpumask_first(cpu_online_mask);
  	else
  		is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
  
  	/* Simple state machine */
  	do {
  		/* Chill out and ensure we re-read multi_stop_state. */

  		cpu_relax_yield();

  		if (msdata->state != curstate) {
  			curstate = msdata->state;
  			switch (curstate) {
  			case MULTI_STOP_DISABLE_IRQ:
  				local_irq_disable();
  				hard_irq_disable();
  				break;
  			case MULTI_STOP_RUN:
  				if (is_active)
  					err = msdata->fn(msdata->data);
  				break;
  			default:
  				break;
  			}
  			ack_state(msdata);

  		} else if (curstate > MULTI_STOP_PREPARE) {
  			/*
  			 * At this stage all other CPUs we depend on must spin
  			 * in the same loop. Any reason for hard-lockup should
  			 * be detected and reported on their side.
  			 */
  			touch_nmi_watchdog();

  		}
  	} while (curstate != MULTI_STOP_EXIT);
  
  	local_irq_restore(flags);
  	return err;
  }

  static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1,
  				    int cpu2, struct cpu_stop_work *work2)
  {

  	struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1);
  	struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2);

  	DEFINE_WAKE_Q(wakeq);

  	int err;

  retry:

  	/*
  	 * The waking up of stopper threads has to happen in the same
  	 * scheduling context as the queueing.  Otherwise, there is a
  	 * possibility of one of the above stoppers being woken up by another
  	 * CPU, and preempting us. This will cause us to not wake up the other
  	 * stopper forever.
  	 */
  	preempt_disable();

  	raw_spin_lock_irq(&stopper1->lock);
  	raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING);

  	if (!stopper1->enabled || !stopper2->enabled) {
  		err = -ENOENT;

  		goto unlock;

  	}

  	/*
  	 * Ensure that if we race with __stop_cpus() the stoppers won't get
  	 * queued up in reverse order leading to system deadlock.
  	 *
  	 * We can't miss stop_cpus_in_progress if queue_stop_cpus_work() has
  	 * queued a work on cpu1 but not on cpu2, we hold both locks.
  	 *
  	 * It can be falsely true but it is safe to spin until it is cleared,
  	 * queue_stop_cpus_work() does everything under preempt_disable().
  	 */

  	if (unlikely(stop_cpus_in_progress)) {
  		err = -EDEADLK;
  		goto unlock;
  	}

  
  	err = 0;

  	__cpu_stop_queue_work(stopper1, work1, &wakeq);
  	__cpu_stop_queue_work(stopper2, work2, &wakeq);

  unlock:

  	raw_spin_unlock(&stopper2->lock);
  	raw_spin_unlock_irq(&stopper1->lock);

  	if (unlikely(err == -EDEADLK)) {

  		preempt_enable();

  		while (stop_cpus_in_progress)
  			cpu_relax();

  		goto retry;
  	}

  	wake_up_q(&wakeq);
  	preempt_enable();

  	return err;

  }

  /**
   * stop_two_cpus - stops two cpus
   * @cpu1: the cpu to stop
   * @cpu2: the other cpu to stop
   * @fn: function to execute
   * @arg: argument to @fn
   *
   * Stops both the current and specified CPU and runs @fn on one of them.
   *
   * returns when both are completed.
   */
  int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
  {

  	struct cpu_stop_done done;
  	struct cpu_stop_work work1, work2;

  	struct multi_stop_data msdata;

  	msdata = (struct multi_stop_data){

  		.fn = fn,
  		.data = arg,
  		.num_threads = 2,
  		.active_cpus = cpumask_of(cpu1),
  	};
  
  	work1 = work2 = (struct cpu_stop_work){
  		.fn = multi_cpu_stop,
  		.arg = &msdata,
  		.done = &done
  	};

  	cpu_stop_init_done(&done, 2);
  	set_state(&msdata, MULTI_STOP_PREPARE);

  	if (cpu1 > cpu2)
  		swap(cpu1, cpu2);

  	if (cpu_stop_queue_two_works(cpu1, &work1, cpu2, &work2))

  		return -ENOENT;

  
  	wait_for_completion(&done.completion);

  	return done.ret;

  }

  /**
   * stop_one_cpu_nowait - stop a cpu but don't wait for completion
   * @cpu: cpu to stop
   * @fn: function to execute
   * @arg: argument to @fn

   * @work_buf: pointer to cpu_stop_work structure

   *
   * Similar to stop_one_cpu() but doesn't wait for completion.  The
   * caller is responsible for ensuring @work_buf is currently unused
   * and will remain untouched until stopper starts executing @fn.
   *
   * CONTEXT:
   * Don't care.

   *
   * RETURNS:
   * true if cpu_stop_work was queued successfully and @fn will be called,
   * false otherwise.

   */

  bool stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,

  			struct cpu_stop_work *work_buf)
  {
  	*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };

  	return cpu_stop_queue_work(cpu, work_buf);

  }

  static bool queue_stop_cpus_work(const struct cpumask *cpumask,

  				 cpu_stop_fn_t fn, void *arg,
  				 struct cpu_stop_done *done)

  {
  	struct cpu_stop_work *work;

  	unsigned int cpu;

  	bool queued = false;

  	/*
  	 * Disable preemption while queueing to avoid getting
  	 * preempted by a stopper which might wait for other stoppers
  	 * to enter @fn which can lead to deadlock.
  	 */

  	preempt_disable();
  	stop_cpus_in_progress = true;

  	for_each_cpu(cpu, cpumask) {
  		work = &per_cpu(cpu_stopper.stop_work, cpu);
  		work->fn = fn;
  		work->arg = arg;
  		work->done = done;

  		if (cpu_stop_queue_work(cpu, work))
  			queued = true;

  	}

  	stop_cpus_in_progress = false;
  	preempt_enable();

  
  	return queued;

  }

  static int __stop_cpus(const struct cpumask *cpumask,
  		       cpu_stop_fn_t fn, void *arg)
  {
  	struct cpu_stop_done done;
  
  	cpu_stop_init_done(&done, cpumask_weight(cpumask));

  	if (!queue_stop_cpus_work(cpumask, fn, arg, &done))
  		return -ENOENT;

  	wait_for_completion(&done.completion);

  	return done.ret;

  }
  
  /**
   * stop_cpus - stop multiple cpus
   * @cpumask: cpus to stop
   * @fn: function to execute
   * @arg: argument to @fn
   *
   * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
   * @fn is run in a process context with the highest priority
   * preempting any task on the cpu and monopolizing it.  This function
   * returns after all executions are complete.
   *
   * This function doesn't guarantee the cpus in @cpumask stay online
   * till @fn completes.  If some cpus go down in the middle, execution
   * on the cpu may happen partially or fully on different cpus.  @fn
   * should either be ready for that or the caller should ensure that
   * the cpus stay online until this function completes.
   *
   * All stop_cpus() calls are serialized making it safe for @fn to wait
   * for all cpus to start executing it.
   *
   * CONTEXT:
   * Might sleep.
   *
   * RETURNS:
   * -ENOENT if @fn(@arg) was not executed at all because all cpus in
   * @cpumask were offline; otherwise, 0 if all executions of @fn
   * returned 0, any non zero return value if any returned non zero.
   */
  int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
  {
  	int ret;
  
  	/* static works are used, process one request at a time */
  	mutex_lock(&stop_cpus_mutex);
  	ret = __stop_cpus(cpumask, fn, arg);
  	mutex_unlock(&stop_cpus_mutex);
  	return ret;
  }
  
  /**
   * try_stop_cpus - try to stop multiple cpus
   * @cpumask: cpus to stop
   * @fn: function to execute
   * @arg: argument to @fn
   *
   * Identical to stop_cpus() except that it fails with -EAGAIN if
   * someone else is already using the facility.
   *
   * CONTEXT:
   * Might sleep.
   *
   * RETURNS:
   * -EAGAIN if someone else is already stopping cpus, -ENOENT if
   * @fn(@arg) was not executed at all because all cpus in @cpumask were
   * offline; otherwise, 0 if all executions of @fn returned 0, any non
   * zero return value if any returned non zero.
   */
  int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
  {
  	int ret;
  
  	/* static works are used, process one request at a time */
  	if (!mutex_trylock(&stop_cpus_mutex))
  		return -EAGAIN;
  	ret = __stop_cpus(cpumask, fn, arg);
  	mutex_unlock(&stop_cpus_mutex);
  	return ret;
  }

  static int cpu_stop_should_run(unsigned int cpu)
  {
  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
  	unsigned long flags;
  	int run;

  	raw_spin_lock_irqsave(&stopper->lock, flags);

  	run = !list_empty(&stopper->works);

  	raw_spin_unlock_irqrestore(&stopper->lock, flags);

  	return run;
  }
  
  static void cpu_stopper_thread(unsigned int cpu)

  {

  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

  	struct cpu_stop_work *work;

  
  repeat:

  	work = NULL;

  	raw_spin_lock_irq(&stopper->lock);

  	if (!list_empty(&stopper->works)) {
  		work = list_first_entry(&stopper->works,
  					struct cpu_stop_work, list);
  		list_del_init(&work->list);
  	}

  	raw_spin_unlock_irq(&stopper->lock);

  
  	if (work) {
  		cpu_stop_fn_t fn = work->fn;
  		void *arg = work->arg;
  		struct cpu_stop_done *done = work->done;

  		int ret;

  		/* cpu stop callbacks must not sleep, make in_atomic() == T */
  		preempt_count_inc();

  		ret = fn(arg);

  		if (done) {
  			if (ret)
  				done->ret = ret;
  			cpu_stop_signal_done(done);
  		}

  		preempt_count_dec();

  		WARN_ONCE(preempt_count(),

  			  "cpu_stop: %pf(%p) leaked preempt count
  ", fn, arg);

  		goto repeat;
  	}

  }

  void stop_machine_park(int cpu)
  {
  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
  	/*
  	 * Lockless. cpu_stopper_thread() will take stopper->lock and flush
  	 * the pending works before it parks, until then it is fine to queue
  	 * the new works.
  	 */
  	stopper->enabled = false;
  	kthread_park(stopper->thread);
  }

  extern void sched_set_stop_task(int cpu, struct task_struct *stop);

  static void cpu_stop_create(unsigned int cpu)
  {

  	sched_set_stop_task(cpu, per_cpu(cpu_stopper.thread, cpu));

  }
  
  static void cpu_stop_park(unsigned int cpu)

  {

  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

  	WARN_ON(!list_empty(&stopper->works));

  }

  void stop_machine_unpark(int cpu)
  {
  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

  	stopper->enabled = true;

  	kthread_unpark(stopper->thread);
  }

  static struct smp_hotplug_thread cpu_stop_threads = {

  	.store			= &cpu_stopper.thread,

  	.thread_should_run	= cpu_stop_should_run,
  	.thread_fn		= cpu_stopper_thread,
  	.thread_comm		= "migration/%u",
  	.create			= cpu_stop_create,

  	.park			= cpu_stop_park,

  	.selfparking		= true,

  };
  
  static int __init cpu_stop_init(void)
  {

  	unsigned int cpu;

  
  	for_each_possible_cpu(cpu) {
  		struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

  		raw_spin_lock_init(&stopper->lock);

  		INIT_LIST_HEAD(&stopper->works);
  	}

  	BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));

  	stop_machine_unpark(raw_smp_processor_id());

  	stop_machine_initialized = true;

  	return 0;
  }
  early_initcall(cpu_stop_init);

  int stop_machine_cpuslocked(cpu_stop_fn_t fn, void *data,
  			    const struct cpumask *cpus)

  {

  	struct multi_stop_data msdata = {
  		.fn = fn,
  		.data = data,
  		.num_threads = num_online_cpus(),
  		.active_cpus = cpus,
  	};

  	lockdep_assert_cpus_held();

  	if (!stop_machine_initialized) {
  		/*
  		 * Handle the case where stop_machine() is called
  		 * early in boot before stop_machine() has been
  		 * initialized.
  		 */
  		unsigned long flags;
  		int ret;

  		WARN_ON_ONCE(msdata.num_threads != 1);

  
  		local_irq_save(flags);
  		hard_irq_disable();
  		ret = (*fn)(data);
  		local_irq_restore(flags);
  
  		return ret;
  	}

  	/* Set the initial state and stop all online cpus. */

  	set_state(&msdata, MULTI_STOP_PREPARE);
  	return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);

  }

  int stop_machine(cpu_stop_fn_t fn, void *data, const struct cpumask *cpus)

  {

  	int ret;
  
  	/* No CPUs can come up or down during this. */

  	cpus_read_lock();
  	ret = stop_machine_cpuslocked(fn, data, cpus);
  	cpus_read_unlock();

  	return ret;
  }

  EXPORT_SYMBOL_GPL(stop_machine);

  /**
   * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
   * @fn: the function to run
   * @data: the data ptr for the @fn()
   * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
   *
   * This is identical to stop_machine() but can be called from a CPU which
   * is not active.  The local CPU is in the process of hotplug (so no other
   * CPU hotplug can start) and not marked active and doesn't have enough
   * context to sleep.
   *
   * This function provides stop_machine() functionality for such state by
   * using busy-wait for synchronization and executing @fn directly for local
   * CPU.
   *
   * CONTEXT:
   * Local CPU is inactive.  Temporarily stops all active CPUs.
   *
   * RETURNS:
   * 0 if all executions of @fn returned 0, any non zero return value if any
   * returned non zero.
   */

  int stop_machine_from_inactive_cpu(cpu_stop_fn_t fn, void *data,

  				  const struct cpumask *cpus)
  {

  	struct multi_stop_data msdata = { .fn = fn, .data = data,

  					    .active_cpus = cpus };
  	struct cpu_stop_done done;
  	int ret;
  
  	/* Local CPU must be inactive and CPU hotplug in progress. */
  	BUG_ON(cpu_active(raw_smp_processor_id()));

  	msdata.num_threads = num_active_cpus() + 1;	/* +1 for local */

  
  	/* No proper task established and can't sleep - busy wait for lock. */
  	while (!mutex_trylock(&stop_cpus_mutex))
  		cpu_relax();
  
  	/* Schedule work on other CPUs and execute directly for local CPU */

  	set_state(&msdata, MULTI_STOP_PREPARE);

  	cpu_stop_init_done(&done, num_active_cpus());

  	queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,

  			     &done);

  	ret = multi_cpu_stop(&msdata);

  
  	/* Busy wait for completion. */
  	while (!completion_done(&done.completion))
  		cpu_relax();
  
  	mutex_unlock(&stop_cpus_mutex);
  	return ret ?: done.ret;
  }