/*
   * Generic helpers for smp ipi calls
   *
   * (C) Jens Axboe <jens.axboe@oracle.com> 2008

   */

  #include <linux/rcupdate.h>

  #include <linux/rculist.h>

  #include <linux/kernel.h>

  #include <linux/export.h>

  #include <linux/percpu.h>
  #include <linux/init.h>

  #include <linux/gfp.h>

  #include <linux/smp.h>

  #include <linux/cpu.h>

  #ifdef CONFIG_USE_GENERIC_SMP_HELPERS

  static struct {
  	struct list_head	queue;

  	raw_spinlock_t		lock;

  } call_function __cacheline_aligned_in_smp =
  	{
  		.queue		= LIST_HEAD_INIT(call_function.queue),

  		.lock		= __RAW_SPIN_LOCK_UNLOCKED(call_function.lock),

  	};

  
  enum {

  	CSD_FLAG_LOCK		= 0x01,

  };
  
  struct call_function_data {

  	struct call_single_data	csd;

  	atomic_t		refs;

  	cpumask_var_t		cpumask;

  };

  static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);

  struct call_single_queue {

  	struct list_head	list;

  	raw_spinlock_t		lock;

  };

  static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue);

  
  static int
  hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
  {
  	long cpu = (long)hcpu;
  	struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
  
  	switch (action) {
  	case CPU_UP_PREPARE:
  	case CPU_UP_PREPARE_FROZEN:

  		if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,

  				cpu_to_node(cpu)))

  			return notifier_from_errno(-ENOMEM);

  		break;

  #ifdef CONFIG_HOTPLUG_CPU

  	case CPU_UP_CANCELED:
  	case CPU_UP_CANCELED_FROZEN:
  
  	case CPU_DEAD:
  	case CPU_DEAD_FROZEN:
  		free_cpumask_var(cfd->cpumask);
  		break;
  #endif
  	};
  
  	return NOTIFY_OK;
  }
  
  static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {

  	.notifier_call		= hotplug_cfd,

  };

  void __init call_function_init(void)

  {

  	void *cpu = (void *)(long)smp_processor_id();

  	int i;
  
  	for_each_possible_cpu(i) {
  		struct call_single_queue *q = &per_cpu(call_single_queue, i);

  		raw_spin_lock_init(&q->lock);

  		INIT_LIST_HEAD(&q->list);
  	}

  
  	hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
  	register_cpu_notifier(&hotplug_cfd_notifier);

  }

  /*

   * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
   *

   * For non-synchronous ipi calls the csd can still be in use by the
   * previous function call. For multi-cpu calls its even more interesting
   * as we'll have to ensure no other cpu is observing our csd.

   */

  static void csd_lock_wait(struct call_single_data *data)

  {
  	while (data->flags & CSD_FLAG_LOCK)
  		cpu_relax();

  }
  
  static void csd_lock(struct call_single_data *data)
  {
  	csd_lock_wait(data);

  	data->flags = CSD_FLAG_LOCK;
  
  	/*

  	 * prevent CPU from reordering the above assignment
  	 * to ->flags with any subsequent assignments to other
  	 * fields of the specified call_single_data structure:

  	 */

  	smp_mb();
  }
  
  static void csd_unlock(struct call_single_data *data)
  {
  	WARN_ON(!(data->flags & CSD_FLAG_LOCK));

  	/*

  	 * ensure we're all done before releasing data:

  	 */
  	smp_mb();

  	data->flags &= ~CSD_FLAG_LOCK;

  }
  
  /*

   * Insert a previously allocated call_single_data element
   * for execution on the given CPU. data must already have
   * ->func, ->info, and ->flags set.

   */

  static
  void generic_exec_single(int cpu, struct call_single_data *data, int wait)

  {
  	struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);

  	unsigned long flags;

  	int ipi;

  	raw_spin_lock_irqsave(&dst->lock, flags);

  	ipi = list_empty(&dst->list);
  	list_add_tail(&data->list, &dst->list);

  	raw_spin_unlock_irqrestore(&dst->lock, flags);

  	/*

  	 * The list addition should be visible before sending the IPI
  	 * handler locks the list to pull the entry off it because of
  	 * normal cache coherency rules implied by spinlocks.
  	 *
  	 * If IPIs can go out of order to the cache coherency protocol
  	 * in an architecture, sufficient synchronisation should be added
  	 * to arch code to make it appear to obey cache coherency WRT

  	 * locking and barrier primitives. Generic code isn't really
  	 * equipped to do the right thing...

  	 */

  	if (ipi)
  		arch_send_call_function_single_ipi(cpu);
  
  	if (wait)

  		csd_lock_wait(data);

  }
  
  /*
   * Invoked by arch to handle an IPI for call function. Must be called with
   * interrupts disabled.
   */
  void generic_smp_call_function_interrupt(void)
  {
  	struct call_function_data *data;

  	int cpu = smp_processor_id();

  
  	/*

  	 * Shouldn't receive this interrupt on a cpu that is not yet online.
  	 */
  	WARN_ON_ONCE(!cpu_online(cpu));
  
  	/*

  	 * Ensure entry is visible on call_function_queue after we have
  	 * entered the IPI. See comment in smp_call_function_many.
  	 * If we don't have this, then we may miss an entry on the list
  	 * and never get another IPI to process it.
  	 */
  	smp_mb();
  
  	/*

  	 * It's ok to use list_for_each_rcu() here even though we may
  	 * delete 'pos', since list_del_rcu() doesn't clear ->next

  	 */

  	list_for_each_entry_rcu(data, &call_function.queue, csd.list) {

  		int refs;

  		smp_call_func_t func;

  		/*
  		 * Since we walk the list without any locks, we might
  		 * see an entry that was completed, removed from the
  		 * list and is in the process of being reused.
  		 *
  		 * We must check that the cpu is in the cpumask before
  		 * checking the refs, and both must be set before
  		 * executing the callback on this cpu.
  		 */
  
  		if (!cpumask_test_cpu(cpu, data->cpumask))
  			continue;
  
  		smp_rmb();
  
  		if (atomic_read(&data->refs) == 0)
  			continue;

  		func = data->csd.func;		/* save for later warn */
  		func(data->csd.info);

  		/*

  		 * If the cpu mask is not still set then func enabled
  		 * interrupts (BUG), and this cpu took another smp call
  		 * function interrupt and executed func(info) twice
  		 * on this cpu.  That nested execution decremented refs.

  		 */
  		if (!cpumask_test_and_clear_cpu(cpu, data->cpumask)) {

  			WARN(1, "%pf enabled interrupts and double executed
  ", func);

  			continue;
  		}

  		refs = atomic_dec_return(&data->refs);
  		WARN_ON(refs < 0);

  
  		if (refs)
  			continue;

  		WARN_ON(!cpumask_empty(data->cpumask));
  
  		raw_spin_lock(&call_function.lock);
  		list_del_rcu(&data->csd.list);
  		raw_spin_unlock(&call_function.lock);

  		csd_unlock(&data->csd);

  	}

  }
  
  /*

   * Invoked by arch to handle an IPI for call function single. Must be
   * called from the arch with interrupts disabled.

   */
  void generic_smp_call_function_single_interrupt(void)
  {
  	struct call_single_queue *q = &__get_cpu_var(call_single_queue);

  	unsigned int data_flags;

  	LIST_HEAD(list);

  	/*
  	 * Shouldn't receive this interrupt on a cpu that is not yet online.
  	 */
  	WARN_ON_ONCE(!cpu_online(smp_processor_id()));

  	raw_spin_lock(&q->lock);

  	list_replace_init(&q->list, &list);

  	raw_spin_unlock(&q->lock);

  	while (!list_empty(&list)) {
  		struct call_single_data *data;

  		data = list_entry(list.next, struct call_single_data, list);

  		list_del(&data->list);

  		/*

  		 * 'data' can be invalid after this call if flags == 0
  		 * (when called through generic_exec_single()),
  		 * so save them away before making the call:

  		 */

  		data_flags = data->flags;
  
  		data->func(data->info);

  		/*

  		 * Unlocked CSDs are valid through generic_exec_single():

  		 */
  		if (data_flags & CSD_FLAG_LOCK)
  			csd_unlock(data);

  	}
  }

  static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);

  /*
   * smp_call_function_single - Run a function on a specific CPU
   * @func: The function to run. This must be fast and non-blocking.
   * @info: An arbitrary pointer to pass to the function.

   * @wait: If true, wait until function has completed on other CPUs.
   *

   * Returns 0 on success, else a negative status code.

   */

  int smp_call_function_single(int cpu, smp_call_func_t func, void *info,

  			     int wait)

  {

  	struct call_single_data d = {
  		.flags = 0,
  	};

  	unsigned long flags;

  	int this_cpu;

  	int err = 0;

  	/*
  	 * prevent preemption and reschedule on another processor,
  	 * as well as CPU removal
  	 */
  	this_cpu = get_cpu();

  	/*
  	 * Can deadlock when called with interrupts disabled.
  	 * We allow cpu's that are not yet online though, as no one else can
  	 * send smp call function interrupt to this cpu and as such deadlocks
  	 * can't happen.
  	 */
  	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
  		     && !oops_in_progress);

  	if (cpu == this_cpu) {

  		local_irq_save(flags);
  		func(info);
  		local_irq_restore(flags);

  	} else {
  		if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
  			struct call_single_data *data = &d;

  			if (!wait)
  				data = &__get_cpu_var(csd_data);

  			csd_lock(data);

  			data->func = func;
  			data->info = info;
  			generic_exec_single(cpu, data, wait);
  		} else {
  			err = -ENXIO;	/* CPU not online */
  		}

  	}
  
  	put_cpu();

  	return err;

  }
  EXPORT_SYMBOL(smp_call_function_single);

  /*
   * smp_call_function_any - Run a function on any of the given cpus
   * @mask: The mask of cpus it can run on.
   * @func: The function to run. This must be fast and non-blocking.
   * @info: An arbitrary pointer to pass to the function.
   * @wait: If true, wait until function has completed.
   *
   * Returns 0 on success, else a negative status code (if no cpus were online).
   * Note that @wait will be implicitly turned on in case of allocation failures,
   * since we fall back to on-stack allocation.
   *
   * Selection preference:
   *	1) current cpu if in @mask
   *	2) any cpu of current node if in @mask
   *	3) any other online cpu in @mask
   */
  int smp_call_function_any(const struct cpumask *mask,

  			  smp_call_func_t func, void *info, int wait)

  {
  	unsigned int cpu;
  	const struct cpumask *nodemask;
  	int ret;
  
  	/* Try for same CPU (cheapest) */
  	cpu = get_cpu();
  	if (cpumask_test_cpu(cpu, mask))
  		goto call;
  
  	/* Try for same node. */

  	nodemask = cpumask_of_node(cpu_to_node(cpu));

  	for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
  	     cpu = cpumask_next_and(cpu, nodemask, mask)) {
  		if (cpu_online(cpu))
  			goto call;
  	}
  
  	/* Any online will do: smp_call_function_single handles nr_cpu_ids. */
  	cpu = cpumask_any_and(mask, cpu_online_mask);
  call:
  	ret = smp_call_function_single(cpu, func, info, wait);
  	put_cpu();
  	return ret;
  }
  EXPORT_SYMBOL_GPL(smp_call_function_any);

  /**

   * __smp_call_function_single(): Run a function on a specific CPU

   * @cpu: The CPU to run on.
   * @data: Pre-allocated and setup data structure

   * @wait: If true, wait until function has completed on specified CPU.

   *

   * Like smp_call_function_single(), but allow caller to pass in a
   * pre-allocated data structure. Useful for embedding @data inside
   * other structures, for instance.

   */

  void __smp_call_function_single(int cpu, struct call_single_data *data,
  				int wait)

  {

  	unsigned int this_cpu;
  	unsigned long flags;

  	this_cpu = get_cpu();

  	/*
  	 * Can deadlock when called with interrupts disabled.
  	 * We allow cpu's that are not yet online though, as no one else can
  	 * send smp call function interrupt to this cpu and as such deadlocks
  	 * can't happen.
  	 */
  	WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
  		     && !oops_in_progress);

  	if (cpu == this_cpu) {
  		local_irq_save(flags);
  		data->func(data->info);
  		local_irq_restore(flags);
  	} else {
  		csd_lock(data);
  		generic_exec_single(cpu, data, wait);
  	}
  	put_cpu();

  }
  
  /**

   * smp_call_function_many(): Run a function on a set of other CPUs.
   * @mask: The set of cpus to run on (only runs on online subset).

   * @func: The function to run. This must be fast and non-blocking.
   * @info: An arbitrary pointer to pass to the function.

   * @wait: If true, wait (atomically) until function has completed
   *        on other CPUs.

   *

   * If @wait is true, then returns once @func has returned.

   *
   * You must not call this function with disabled interrupts or from a
   * hardware interrupt handler or from a bottom half handler. Preemption
   * must be disabled when calling this function.
   */

  void smp_call_function_many(const struct cpumask *mask,

  			    smp_call_func_t func, void *info, bool wait)

  {

  	struct call_function_data *data;

  	unsigned long flags;

  	int refs, cpu, next_cpu, this_cpu = smp_processor_id();

  	/*
  	 * Can deadlock when called with interrupts disabled.
  	 * We allow cpu's that are not yet online though, as no one else can
  	 * send smp call function interrupt to this cpu and as such deadlocks
  	 * can't happen.
  	 */
  	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()

  		     && !oops_in_progress && !early_boot_irqs_disabled);

  	/* Try to fastpath.  So, what's a CPU they want? Ignoring this one. */

  	cpu = cpumask_first_and(mask, cpu_online_mask);

  	if (cpu == this_cpu)

  		cpu = cpumask_next_and(cpu, mask, cpu_online_mask);

  	/* No online cpus?  We're done. */
  	if (cpu >= nr_cpu_ids)
  		return;
  
  	/* Do we have another CPU which isn't us? */
  	next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);

  	if (next_cpu == this_cpu)

  		next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
  
  	/* Fastpath: do that cpu by itself. */
  	if (next_cpu >= nr_cpu_ids) {
  		smp_call_function_single(cpu, func, info, wait);
  		return;

  	}

  	data = &__get_cpu_var(cfd_data);
  	csd_lock(&data->csd);

  	/* This BUG_ON verifies our reuse assertions and can be removed */
  	BUG_ON(atomic_read(&data->refs) || !cpumask_empty(data->cpumask));

  
  	/*

  	 * The global call function queue list add and delete are protected
  	 * by a lock, but the list is traversed without any lock, relying
  	 * on the rcu list add and delete to allow safe concurrent traversal.

  	 * We reuse the call function data without waiting for any grace
  	 * period after some other cpu removes it from the global queue.

  	 * This means a cpu might find our data block as it is being
  	 * filled out.
  	 *
  	 * We hold off the interrupt handler on the other cpu by
  	 * ordering our writes to the cpu mask vs our setting of the
  	 * refs counter.  We assert only the cpu owning the data block
  	 * will set a bit in cpumask, and each bit will only be cleared
  	 * by the subject cpu.  Each cpu must first find its bit is
  	 * set and then check that refs is set indicating the element is
  	 * ready to be processed, otherwise it must skip the entry.
  	 *
  	 * On the previous iteration refs was set to 0 by another cpu.
  	 * To avoid the use of transitivity, set the counter to 0 here
  	 * so the wmb will pair with the rmb in the interrupt handler.

  	 */

  	atomic_set(&data->refs, 0);	/* convert 3rd to 1st party write */
  
  	data->csd.func = func;
  	data->csd.info = info;
  
  	/* Ensure 0 refs is visible before mask.  Also orders func and info */
  	smp_wmb();
  
  	/* We rely on the "and" being processed before the store */
  	cpumask_and(data->cpumask, mask, cpu_online_mask);
  	cpumask_clear_cpu(this_cpu, data->cpumask);

  	refs = cpumask_weight(data->cpumask);
  
  	/* Some callers race with other cpus changing the passed mask */
  	if (unlikely(!refs)) {
  		csd_unlock(&data->csd);
  		return;
  	}

  	raw_spin_lock_irqsave(&call_function.lock, flags);

  	/*
  	 * Place entry at the _HEAD_ of the list, so that any cpu still

  	 * observing the entry in generic_smp_call_function_interrupt()
  	 * will not miss any other list entries:

  	 */
  	list_add_rcu(&data->csd.list, &call_function.queue);

  	/*

  	 * We rely on the wmb() in list_add_rcu to complete our writes
  	 * to the cpumask before this write to refs, which indicates
  	 * data is on the list and is ready to be processed.

  	 */

  	atomic_set(&data->refs, refs);

  	raw_spin_unlock_irqrestore(&call_function.lock, flags);

  	/*
  	 * Make the list addition visible before sending the ipi.

  	 * (IPIs must obey or appear to obey normal Linux cache
  	 * coherency rules -- see comment in generic_exec_single).

  	 */
  	smp_mb();

  	/* Send a message to all CPUs in the map */

  	arch_send_call_function_ipi_mask(data->cpumask);

  	/* Optionally wait for the CPUs to complete */

  	if (wait)

  		csd_lock_wait(&data->csd);

  }

  EXPORT_SYMBOL(smp_call_function_many);

  
  /**
   * smp_call_function(): Run a function on all other CPUs.
   * @func: The function to run. This must be fast and non-blocking.
   * @info: An arbitrary pointer to pass to the function.

   * @wait: If true, wait (atomically) until function has completed
   *        on other CPUs.

   *

   * Returns 0.

   *
   * If @wait is true, then returns once @func has returned; otherwise

   * it returns just before the target cpu calls @func.

   *
   * You must not call this function with disabled interrupts or from a
   * hardware interrupt handler or from a bottom half handler.
   */

  int smp_call_function(smp_call_func_t func, void *info, int wait)

  {

  	preempt_disable();

  	smp_call_function_many(cpu_online_mask, func, info, wait);

  	preempt_enable();

  	return 0;

  }
  EXPORT_SYMBOL(smp_call_function);
  
  void ipi_call_lock(void)
  {

  	raw_spin_lock(&call_function.lock);

  }
  
  void ipi_call_unlock(void)
  {

  	raw_spin_unlock(&call_function.lock);

  }
  
  void ipi_call_lock_irq(void)
  {

  	raw_spin_lock_irq(&call_function.lock);

  }
  
  void ipi_call_unlock_irq(void)
  {

  	raw_spin_unlock_irq(&call_function.lock);

  }

  #endif /* USE_GENERIC_SMP_HELPERS */

  /* Setup configured maximum number of CPUs to activate */
  unsigned int setup_max_cpus = NR_CPUS;
  EXPORT_SYMBOL(setup_max_cpus);
  
  
  /*
   * Setup routine for controlling SMP activation
   *
   * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
   * activation entirely (the MPS table probe still happens, though).
   *
   * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
   * greater than 0, limits the maximum number of CPUs activated in
   * SMP mode to <NUM>.
   */
  
  void __weak arch_disable_smp_support(void) { }
  
  static int __init nosmp(char *str)
  {
  	setup_max_cpus = 0;
  	arch_disable_smp_support();
  
  	return 0;
  }
  
  early_param("nosmp", nosmp);
  
  /* this is hard limit */
  static int __init nrcpus(char *str)
  {
  	int nr_cpus;
  
  	get_option(&str, &nr_cpus);
  	if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
  		nr_cpu_ids = nr_cpus;
  
  	return 0;
  }
  
  early_param("nr_cpus", nrcpus);
  
  static int __init maxcpus(char *str)
  {
  	get_option(&str, &setup_max_cpus);
  	if (setup_max_cpus == 0)
  		arch_disable_smp_support();
  
  	return 0;
  }
  
  early_param("maxcpus", maxcpus);
  
  /* Setup number of possible processor ids */
  int nr_cpu_ids __read_mostly = NR_CPUS;
  EXPORT_SYMBOL(nr_cpu_ids);
  
  /* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
  void __init setup_nr_cpu_ids(void)
  {
  	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
  }
  
  /* Called by boot processor to activate the rest. */
  void __init smp_init(void)
  {
  	unsigned int cpu;
  
  	/* FIXME: This should be done in userspace --RR */
  	for_each_present_cpu(cpu) {
  		if (num_online_cpus() >= setup_max_cpus)
  			break;
  		if (!cpu_online(cpu))
  			cpu_up(cpu);
  	}
  
  	/* Any cleanup work */
  	printk(KERN_INFO "Brought up %ld CPUs
  ", (long)num_online_cpus());
  	smp_cpus_done(setup_max_cpus);
  }

  /*

   * Call a function on all processors.  May be used during early boot while
   * early_boot_irqs_disabled is set.  Use local_irq_save/restore() instead
   * of local_irq_disable/enable().

   */
  int on_each_cpu(void (*func) (void *info), void *info, int wait)
  {

  	unsigned long flags;

  	int ret = 0;
  
  	preempt_disable();
  	ret = smp_call_function(func, info, wait);

  	local_irq_save(flags);

  	func(info);

  	local_irq_restore(flags);

  	preempt_enable();
  	return ret;
  }
  EXPORT_SYMBOL(on_each_cpu);