/*
 * 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>

#include "smpboot.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;
        cpumask_var_t           cpumask_ipi;
};

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);
                if (!zalloc_cpumask_var_node(&cfd->cpumask_ipi, 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);
                free_cpumask_var(cfd->cpumask_ipi);
                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\n", 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;
        }

        /*
         * After we put an entry into the list, data->cpumask
         * may be cleared again when another CPU sends another IPI for
         * a SMP function call, so data->cpumask will be zero.
         */
        cpumask_copy(data->cpumask_ipi, data->cpumask);
        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_ipi);

        /* 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);
#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;

        idle_threads_init();

        /* 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\n", (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);

/**
 * on_each_cpu_mask(): Run a function on processors specified by
 * cpumask, which may include the local processor.
 * @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.
 */
void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
                        void *info, bool wait)
{
        int cpu = get_cpu();

        smp_call_function_many(mask, func, info, wait);
        if (cpumask_test_cpu(cpu, mask)) {
                local_irq_disable();
                func(info);
                local_irq_enable();
        }
        put_cpu();
}
EXPORT_SYMBOL(on_each_cpu_mask);

/*
 * on_each_cpu_cond(): Call a function on each processor for which
 * the supplied function cond_func returns true, optionally waiting
 * for all the required CPUs to finish. This may include the local
 * processor.
 * @cond_func:  A callback function that is passed a cpu id and
 *              the the info parameter. The function is called
 *              with preemption disabled. The function should
 *              return a blooean value indicating whether to IPI
 *              the specified CPU.
 * @func:       The function to run on all applicable CPUs.
 *              This must be fast and non-blocking.
 * @info:       An arbitrary pointer to pass to both functions.
 * @wait:       If true, wait (atomically) until function has
 *              completed on other CPUs.
 * @gfp_flags:  GFP flags to use when allocating the cpumask
 *              used internally by the function.
 *
 * The function might sleep if the GFP flags indicates a non
 * atomic allocation is allowed.
 *
 * Preemption is disabled to protect against CPUs going offline but not online.
 * CPUs going online during the call will not be seen or sent an IPI.
 *
 * You must not call this function with disabled interrupts or
 * from a hardware interrupt handler or from a bottom half handler.
 */
void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
                        smp_call_func_t func, void *info, bool wait,
                        gfp_t gfp_flags)
{
        cpumask_var_t cpus;
        int cpu, ret;

        might_sleep_if(gfp_flags & __GFP_WAIT);

        if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
                preempt_disable();
                for_each_online_cpu(cpu)
                        if (cond_func(cpu, info))
                                cpumask_set_cpu(cpu, cpus);
                on_each_cpu_mask(cpus, func, info, wait);
                preempt_enable();
                free_cpumask_var(cpus);
        } else {
                /*
                 * No free cpumask, bother. No matter, we'll
                 * just have to IPI them one by one.
                 */
                preempt_disable();
                for_each_online_cpu(cpu)
                        if (cond_func(cpu, info)) {
                                ret = smp_call_function_single(cpu, func,
                                                                info, wait);
                                WARN_ON_ONCE(!ret);
                        }
                preempt_enable();
        }
}
EXPORT_SYMBOL(on_each_cpu_cond);

static void do_nothing(void *unused)
{
}

/**
 * kick_all_cpus_sync - Force all cpus out of idle
 *
 * Used to synchronize the update of pm_idle function pointer. It's
 * called after the pointer is updated and returns after the dummy
 * callback function has been executed on all cpus. The execution of
 * the function can only happen on the remote cpus after they have
 * left the idle function which had been called via pm_idle function
 * pointer. So it's guaranteed that nothing uses the previous pointer
 * anymore.
 */
void kick_all_cpus_sync(void)
{
        /* Make sure the change is visible before we kick the cpus */
        smp_mb();
        smp_call_function(do_nothing, NULL, 1);
}
EXPORT_SYMBOL_GPL(kick_all_cpus_sync);