smp.c

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/*
 * Generic helpers for smp ipi calls
 *
 * (C) Jens Axboe <[email protected]> 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;
};

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\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);

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();
}

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);

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);

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)
{
}

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);