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[cbs-scheduler.git] / kernel / smp.c

/*
 * 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/module.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <linux/cpu.h>

static DEFINE_PER_CPU(struct call_single_queue, call_single_queue);

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;
        raw_spinlock_t          lock;
        unsigned int            refs;
        cpumask_var_t           cpumask;
};

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

static DEFINE_PER_CPU(struct call_function_data, cfd_data) = {
        .lock                   = RAW_SPIN_LOCK_UNLOCKED(cfd_data.lock),
};

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 (!alloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
                                cpu_to_node(cpu)))
                        return NOTIFY_BAD;
                break;

#ifdef CONFIG_CPU_HOTPLUG
        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,
};

static int __cpuinit init_call_single_data(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);

                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);

        return 0;
}
early_initcall(init_call_single_data);

/*
 * 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;

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

                spin_lock(&data->lock);
                if (!cpumask_test_cpu(cpu, data->cpumask)) {
                        spin_unlock(&data->lock);
                        continue;
                }
                cpumask_clear_cpu(cpu, data->cpumask);
                spin_unlock(&data->lock);

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

                spin_lock(&data->lock);
                WARN_ON(data->refs == 0);
                refs = --data->refs;
                if (!refs) {
                        spin_lock(&call_function.lock);
                        list_del_rcu(&data->csd.list);
                        spin_unlock(&call_function.lock);
                }
                spin_unlock(&data->lock);

                if (refs)
                        continue;

                csd_unlock(&data->csd);
        }

        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);
        unsigned int data_flags;
        LIST_HEAD(list);

        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);

                /*
                 * Unlocked CSDs are valid through generic_exec_single():
                 */
                if (data_flags & CSD_FLAG_LOCK)
                        csd_unlock(data);
        }
}

static DEFINE_PER_CPU(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. 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 = {
                .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 */
        WARN_ON_ONCE(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_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,
                                int wait)
{
        csd_lock(data);

        /* Can deadlock when called with interrupts disabled */
        WARN_ON_ONCE(wait && irqs_disabled() && !oops_in_progress);

        generic_exec_single(cpu, data, wait);
}

/* Deprecated: shim for archs using old arch_send_call_function_ipi API. */

#ifndef arch_send_call_function_ipi_mask
# define arch_send_call_function_ipi_mask(maskp) \
         arch_send_call_function_ipi(*(maskp))
#endif

/**
 * 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. 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.
 */
void smp_call_function_many(const struct cpumask *mask,
                            void (*func)(void *), void *info, bool wait)
{
        struct call_function_data *data;
        unsigned long flags;
        int cpu, next_cpu, this_cpu = smp_processor_id();

        /* Can deadlock when called with interrupts disabled */
        WARN_ON_ONCE(irqs_disabled() && !oops_in_progress);

        /* 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);

        spin_lock_irqsave(&data->lock, flags);
        data->csd.func = func;
        data->csd.info = info;
        cpumask_and(data->cpumask, mask, cpu_online_mask);
        cpumask_clear_cpu(this_cpu, data->cpumask);
        data->refs = cpumask_weight(data->cpumask);

        spin_lock(&call_function.lock);
        /*
         * 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);
        spin_unlock(&call_function.lock);

        spin_unlock_irqrestore(&data->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. 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)
{
        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)
{
        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);
}