/*
 * Generic helpers for smp ipi calls
 *
 * (C) Jens Axboe <jens.axboe@oracle.com> 2008
 *
 */
#include <linux/init.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/smp.h>

static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);
static LIST_HEAD(call_function_queue);
__cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);

enum {
        CSD_FLAG_WAIT           = 0x01,
        CSD_FLAG_ALLOC          = 0x02,
};

struct call_function_data {
        struct call_single_data csd;
        spinlock_t lock;
        unsigned int refs;
        cpumask_t cpumask;
        struct rcu_head rcu_head;
};

struct call_single_queue {
        struct list_head list;
        spinlock_t lock;
};

static int __cpuinit init_call_single_data(void)
{
        int i;

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

                spin_lock_init(&q->lock);
                INIT_LIST_HEAD(&q->list);
        }
        return 0;
}
early_initcall(init_call_single_data);

static void csd_flag_wait(struct call_single_data *data)
{
        /* Wait for response */
        do {
                /*
                 * We need to see the flags store in the IPI handler
                 */
                smp_mb();
                if (!(data->flags & CSD_FLAG_WAIT))
                        break;
                cpu_relax();
        } while (1);
}

/*
 * 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)
{
        struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
        int wait = data->flags & CSD_FLAG_WAIT, ipi;
        unsigned long flags;

        spin_lock_irqsave(&dst->lock, flags);
        ipi = list_empty(&dst->list);
        list_add_tail(&data->list, &dst->list);
        spin_unlock_irqrestore(&dst->lock, flags);

        if (ipi)
                arch_send_call_function_single_ipi(cpu);

        if (wait)
                csd_flag_wait(data);
}

static void rcu_free_call_data(struct rcu_head *head)
{
        struct call_function_data *data;

        data = container_of(head, struct call_function_data, rcu_head);

        kfree(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 = get_cpu();

        /*
         * It's ok to use list_for_each_rcu() here even though we may delete
         * 'pos', since list_del_rcu() doesn't clear ->next
         */
        rcu_read_lock();
        list_for_each_entry_rcu(data, &call_function_queue, csd.list) {
                int refs;

                if (!cpu_isset(cpu, data->cpumask))
                        continue;

                data->csd.func(data->csd.info);

                spin_lock(&data->lock);
                cpu_clear(cpu, data->cpumask);
                WARN_ON(data->refs == 0);
                data->refs--;
                refs = data->refs;
                spin_unlock(&data->lock);

                if (refs)
                        continue;

                spin_lock(&call_function_lock);
                list_del_rcu(&data->csd.list);
                spin_unlock(&call_function_lock);

                if (data->csd.flags & CSD_FLAG_WAIT) {
                        /*
                         * serialize stores to data with the flag clear
                         * and wakeup
                         */
                        smp_wmb();
                        data->csd.flags &= ~CSD_FLAG_WAIT;
                }
                if (data->csd.flags & CSD_FLAG_ALLOC)
                        call_rcu(&data->rcu_head, rcu_free_call_data);
        }
        rcu_read_unlock();

        put_cpu();
}

/*
 * 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);
        LIST_HEAD(list);

        /*
         * Need to see other stores to list head for checking whether
         * list is empty without holding q->lock
         */
        smp_mb();
        while (!list_empty(&q->list)) {
                unsigned int data_flags;

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

                        if (data_flags & CSD_FLAG_WAIT) {
                                smp_wmb();
                                data->flags &= ~CSD_FLAG_WAIT;
                        } else if (data_flags & CSD_FLAG_ALLOC)
                                kfree(data);
                }
                /*
                 * See comment on outer loop
                 */
                smp_mb();
        }
}

/*
 * 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. Note that @wait
 * will be implicitly turned on in case of allocation failures, since
 * we fall back to on-stack allocation.
 */
int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
                             int wait)
{
        struct call_single_data d;
        unsigned long flags;
        /* prevent preemption and reschedule on another processor,
           as well as CPU removal */
        int me = get_cpu();
        int err = 0;

        /* Can deadlock when called with interrupts disabled */
        WARN_ON(irqs_disabled());

        if (cpu == me) {
                local_irq_save(flags);
                func(info);
                local_irq_restore(flags);
        } else if ((unsigned)cpu < NR_CPUS && cpu_online(cpu)) {
                struct call_single_data *data = NULL;

                if (!wait) {
                        data = kmalloc(sizeof(*data), GFP_ATOMIC);
                        if (data)
                                data->flags = CSD_FLAG_ALLOC;
                }
                if (!data) {
                        data = &d;
                        data->flags = CSD_FLAG_WAIT;
                }

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

        put_cpu();
        return err;
}
EXPORT_SYMBOL(smp_call_function_single);

/**
 * __smp_call_function_single(): Run a function on another CPU
 * @cpu: The CPU to run on.
 * @data: Pre-allocated and setup data structure
 *
 * 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)
{
        /* Can deadlock when called with interrupts disabled */
        WARN_ON((data->flags & CSD_FLAG_WAIT) && irqs_disabled());

        generic_exec_single(cpu, data);
}

/* Dummy function */
static void quiesce_dummy(void *unused)
{
}

/*
 * Ensure stack based data used in call function mask is safe to free.
 *
 * This is needed by smp_call_function_mask when using on-stack data, because
 * a single call function queue is shared by all CPUs, and any CPU may pick up
 * the data item on the queue at any time before it is deleted. So we need to
 * ensure that all CPUs have transitioned through a quiescent state after
 * this call.
 *
 * This is a very slow function, implemented by sending synchronous IPIs to
 * all possible CPUs. For this reason, we have to alloc data rather than use
 * stack based data even in the case of synchronous calls. The stack based
 * data is then just used for deadlock/oom fallback which will be very rare.
 *
 * If a faster scheme can be made, we could go back to preferring stack based
 * data -- the data allocation/free is non-zero cost.
 */
static void smp_call_function_mask_quiesce_stack(cpumask_t mask)
{
        struct call_single_data data;
        int cpu;

        data.func = quiesce_dummy;
        data.info = NULL;

        for_each_cpu_mask(cpu, mask) {
                data.flags = CSD_FLAG_WAIT;
                generic_exec_single(cpu, &data);
        }
}

/**
 * smp_call_function_mask(): Run a function on a set of other CPUs.
 * @mask: The set of cpus to 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 (atomically) until function has completed on other CPUs.
 *
 * Returns 0 on success, else a negative status code.
 *
 * If @wait is true, then returns once @func has returned. Note that @wait
 * will be implicitly turned on in case of allocation failures, since
 * we fall back to on-stack allocation.
 *
 * 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.
 */
int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
                           int wait)
{
        struct call_function_data d;
        struct call_function_data *data = NULL;
        cpumask_t allbutself;
        unsigned long flags;
        int cpu, num_cpus;
        int slowpath = 0;

        /* Can deadlock when called with interrupts disabled */
        WARN_ON(irqs_disabled());

        cpu = smp_processor_id();
        allbutself = cpu_online_map;
        cpu_clear(cpu, allbutself);
        cpus_and(mask, mask, allbutself);
        num_cpus = cpus_weight(mask);

        /*
         * If zero CPUs, return. If just a single CPU, turn this request
         * into a targetted single call instead since it's faster.
         */
        if (!num_cpus)
                return 0;
        else if (num_cpus == 1) {
                cpu = first_cpu(mask);
                return smp_call_function_single(cpu, func, info, wait);
        }

        data = kmalloc(sizeof(*data), GFP_ATOMIC);
        if (data) {
                data->csd.flags = CSD_FLAG_ALLOC;
                if (wait)
                        data->csd.flags |= CSD_FLAG_WAIT;
        } else {
                data = &d;
                data->csd.flags = CSD_FLAG_WAIT;
                wait = 1;
                slowpath = 1;
        }

        spin_lock_init(&data->lock);
        data->csd.func = func;
        data->csd.info = info;
        data->refs = num_cpus;
        data->cpumask = mask;

        spin_lock_irqsave(&call_function_lock, flags);
        list_add_tail_rcu(&data->csd.list, &call_function_queue);
        spin_unlock_irqrestore(&call_function_lock, flags);

        /* Send a message to all CPUs in the map */
        arch_send_call_function_ipi(mask);

        /* optionally wait for the CPUs to complete */
        if (wait) {
                csd_flag_wait(&data->csd);
                if (unlikely(slowpath))
                        smp_call_function_mask_quiesce_stack(mask);
        }

        return 0;
}
EXPORT_SYMBOL(smp_call_function_mask);

/**
 * 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 on success, else a negative status code.
 *
 * If @wait is true, then returns once @func has returned; otherwise
 * it returns just before the target cpu calls @func. In case of allocation
 * failure, @wait will be implicitly turned on.
 *
 * 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(void (*func)(void *), void *info, int wait)
{
        int ret;

        preempt_disable();
        ret = smp_call_function_mask(cpu_online_map, func, info, wait);
        preempt_enable();
        return ret;
}
EXPORT_SYMBOL(smp_call_function);

void ipi_call_lock(void)
{
        spin_lock(&call_function_lock);
}

void ipi_call_unlock(void)
{
        spin_unlock(&call_function_lock);
}

void ipi_call_lock_irq(void)
{
        spin_lock_irq(&call_function_lock);
}

void ipi_call_unlock_irq(void)
{
        spin_unlock_irq(&call_function_lock);
}