/*
   * 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/atomic.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 */
  	bool			executed;	/* actually executed? */
  	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 {
  	spinlock_t		lock;

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

  	struct list_head	works;		/* list of pending works */
  	struct task_struct	*thread;	/* stopper thread */

  };
  
  static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);

  static bool stop_machine_initialized = false;

  
  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, bool executed)
  {
  	if (done) {
  		if (executed)
  			done->executed = true;
  		if (atomic_dec_and_test(&done->nr_todo))
  			complete(&done->completion);
  	}
  }
  
  /* queue @work to @stopper.  if offline, @work is completed immediately */
  static void cpu_stop_queue_work(struct cpu_stopper *stopper,
  				struct cpu_stop_work *work)
  {
  	unsigned long flags;
  
  	spin_lock_irqsave(&stopper->lock, flags);
  
  	if (stopper->enabled) {
  		list_add_tail(&work->list, &stopper->works);
  		wake_up_process(stopper->thread);
  	} else
  		cpu_stop_signal_done(work->done, false);
  
  	spin_unlock_irqrestore(&stopper->lock, flags);
  }
  
  /**
   * 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);
  	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
  	wait_for_completion(&done.completion);
  	return done.executed ? done.ret : -ENOENT;
  }
  
  /**
   * 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
   *
   * 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.
   */
  void 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, };
  	cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
  }
  
  /* static data for stop_cpus */

  static DEFINE_MUTEX(stop_cpus_mutex);

  static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);

  static void 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;
  
  	/* initialize works and done */
  	for_each_cpu(cpu, cpumask) {
  		work = &per_cpu(stop_cpus_work, cpu);
  		work->fn = fn;
  		work->arg = arg;

  		work->done = done;

  	}

  
  	/*
  	 * 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();
  	for_each_cpu(cpu, cpumask)
  		cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
  				    &per_cpu(stop_cpus_work, cpu));
  	preempt_enable();

  }

  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));
  	queue_stop_cpus_work(cpumask, fn, arg, &done);

  	wait_for_completion(&done.completion);
  	return done.executed ? done.ret : -ENOENT;
  }
  
  /**
   * 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_stopper_thread(void *data)
  {
  	struct cpu_stopper *stopper = data;
  	struct cpu_stop_work *work;
  	int ret;
  
  repeat:
  	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
  
  	if (kthread_should_stop()) {
  		__set_current_state(TASK_RUNNING);
  		return 0;
  	}
  
  	work = NULL;
  	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);
  	}
  	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;

  		char ksym_buf[KSYM_NAME_LEN] __maybe_unused;

  
  		__set_current_state(TASK_RUNNING);
  
  		/* cpu stop callbacks are not allowed to sleep */
  		preempt_disable();
  
  		ret = fn(arg);
  		if (ret)
  			done->ret = ret;
  
  		/* restore preemption and check it's still balanced */
  		preempt_enable();
  		WARN_ONCE(preempt_count(),
  			  "cpu_stop: %s(%p) leaked preempt count
  ",
  			  kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
  					  ksym_buf), arg);
  
  		cpu_stop_signal_done(done, true);
  	} else
  		schedule();
  
  	goto repeat;
  }

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

  /* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
  static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
  					   unsigned long action, void *hcpu)
  {

  	unsigned int cpu = (unsigned long)hcpu;
  	struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);

  	struct task_struct *p;
  
  	switch (action & ~CPU_TASKS_FROZEN) {
  	case CPU_UP_PREPARE:
  		BUG_ON(stopper->thread || stopper->enabled ||
  		       !list_empty(&stopper->works));

  		p = kthread_create_on_node(cpu_stopper_thread,
  					   stopper,
  					   cpu_to_node(cpu),
  					   "migration/%d", cpu);

  		if (IS_ERR(p))

  			return notifier_from_errno(PTR_ERR(p));

  		get_task_struct(p);

  		kthread_bind(p, cpu);
  		sched_set_stop_task(cpu, p);

  		stopper->thread = p;
  		break;
  
  	case CPU_ONLINE:

  		/* strictly unnecessary, as first user will wake it */
  		wake_up_process(stopper->thread);
  		/* mark enabled */
  		spin_lock_irq(&stopper->lock);
  		stopper->enabled = true;
  		spin_unlock_irq(&stopper->lock);
  		break;
  
  #ifdef CONFIG_HOTPLUG_CPU
  	case CPU_UP_CANCELED:

  	case CPU_POST_DEAD:

  	{
  		struct cpu_stop_work *work;

  		sched_set_stop_task(cpu, NULL);

  		/* kill the stopper */
  		kthread_stop(stopper->thread);
  		/* drain remaining works */
  		spin_lock_irq(&stopper->lock);
  		list_for_each_entry(work, &stopper->works, list)
  			cpu_stop_signal_done(work->done, false);
  		stopper->enabled = false;
  		spin_unlock_irq(&stopper->lock);
  		/* release the stopper */
  		put_task_struct(stopper->thread);
  		stopper->thread = NULL;
  		break;

  	}

  #endif
  	}
  
  	return NOTIFY_OK;
  }
  
  /*
   * Give it a higher priority so that cpu stopper is available to other
   * cpu notifiers.  It currently shares the same priority as sched
   * migration_notifier.
   */
  static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
  	.notifier_call	= cpu_stop_cpu_callback,
  	.priority	= 10,
  };
  
  static int __init cpu_stop_init(void)
  {
  	void *bcpu = (void *)(long)smp_processor_id();
  	unsigned int cpu;
  	int err;
  
  	for_each_possible_cpu(cpu) {
  		struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
  
  		spin_lock_init(&stopper->lock);
  		INIT_LIST_HEAD(&stopper->works);
  	}
  
  	/* start one for the boot cpu */
  	err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
  				    bcpu);

  	BUG_ON(err != NOTIFY_OK);

  	cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
  	register_cpu_notifier(&cpu_stop_cpu_notifier);

  	stop_machine_initialized = true;

  	return 0;
  }
  early_initcall(cpu_stop_init);

  #ifdef CONFIG_STOP_MACHINE

  /* This controls the threads on each CPU. */

  enum stopmachine_state {

  	/* Dummy starting state for thread. */
  	STOPMACHINE_NONE,
  	/* Awaiting everyone to be scheduled. */

  	STOPMACHINE_PREPARE,

  	/* Disable interrupts. */

  	STOPMACHINE_DISABLE_IRQ,

  	/* Run the function */

  	STOPMACHINE_RUN,

  	/* Exit */

  	STOPMACHINE_EXIT,
  };

  struct stop_machine_data {

  	int			(*fn)(void *);
  	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 stopmachine_state	state;
  	atomic_t		thread_ack;

  };

  static void set_state(struct stop_machine_data *smdata,
  		      enum stopmachine_state newstate)

  {

  	/* Reset ack counter. */

  	atomic_set(&smdata->thread_ack, smdata->num_threads);

  	smp_wmb();

  	smdata->state = newstate;

  }

  /* Last one to ack a state moves to the next state. */

  static void ack_state(struct stop_machine_data *smdata)

  {

  	if (atomic_dec_and_test(&smdata->thread_ack))
  		set_state(smdata, smdata->state + 1);

  }

  /* This is the cpu_stop function which stops the CPU. */
  static int stop_machine_cpu_stop(void *data)

  {

  	struct stop_machine_data *smdata = data;

  	enum stopmachine_state curstate = STOPMACHINE_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 (!smdata->active_cpus)
  		is_active = cpu == cpumask_first(cpu_online_mask);
  	else
  		is_active = cpumask_test_cpu(cpu, smdata->active_cpus);

  	/* Simple state machine */
  	do {
  		/* Chill out and ensure we re-read stopmachine_state. */

  		cpu_relax();

  		if (smdata->state != curstate) {
  			curstate = smdata->state;

  			switch (curstate) {
  			case STOPMACHINE_DISABLE_IRQ:
  				local_irq_disable();
  				hard_irq_disable();
  				break;
  			case STOPMACHINE_RUN:

  				if (is_active)
  					err = smdata->fn(smdata->data);

  				break;
  			default:
  				break;
  			}

  			ack_state(smdata);

  		}
  	} while (curstate != STOPMACHINE_EXIT);

  	local_irq_restore(flags);

  	return err;

  }

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

  {

  	struct stop_machine_data smdata = { .fn = fn, .data = data,
  					    .num_threads = num_online_cpus(),
  					    .active_cpus = cpus };

  	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(smdata.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(&smdata, STOPMACHINE_PREPARE);
  	return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);

  }

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

  {

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

  	get_online_cpus();

  	ret = __stop_machine(fn, data, cpus);

  	put_online_cpus();

  	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(int (*fn)(void *), void *data,
  				  const struct cpumask *cpus)
  {
  	struct stop_machine_data smdata = { .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()));
  	smdata.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(&smdata, STOPMACHINE_PREPARE);
  	cpu_stop_init_done(&done, num_active_cpus());
  	queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
  			     &done);
  	ret = stop_machine_cpu_stop(&smdata);
  
  	/* Busy wait for completion. */
  	while (!completion_done(&done.completion))
  		cpu_relax();
  
  	mutex_unlock(&stop_cpus_mutex);
  	return ret ?: done.ret;
  }

  #endif	/* CONFIG_STOP_MACHINE */