linux/kernel/smp.c
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   1/*
   2 * Generic helpers for smp ipi calls
   3 *
   4 * (C) Jens Axboe <jens.axboe@oracle.com> 2008
   5 */
   6#include <linux/rcupdate.h>
   7#include <linux/rculist.h>
   8#include <linux/kernel.h>
   9#include <linux/export.h>
  10#include <linux/percpu.h>
  11#include <linux/init.h>
  12#include <linux/gfp.h>
  13#include <linux/smp.h>
  14#include <linux/cpu.h>
  15
  16#include "smpboot.h"
  17
  18#ifdef CONFIG_USE_GENERIC_SMP_HELPERS
  19enum {
  20        CSD_FLAG_LOCK           = 0x01,
  21};
  22
  23struct call_function_data {
  24        struct call_single_data __percpu *csd;
  25        cpumask_var_t           cpumask;
  26        cpumask_var_t           cpumask_ipi;
  27};
  28
  29static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
  30
  31struct call_single_queue {
  32        struct list_head        list;
  33        raw_spinlock_t          lock;
  34};
  35
  36static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue);
  37
  38static int
  39hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
  40{
  41        long cpu = (long)hcpu;
  42        struct call_function_data *cfd = &per_cpu(cfd_data, cpu);
  43
  44        switch (action) {
  45        case CPU_UP_PREPARE:
  46        case CPU_UP_PREPARE_FROZEN:
  47                if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
  48                                cpu_to_node(cpu)))
  49                        return notifier_from_errno(-ENOMEM);
  50                if (!zalloc_cpumask_var_node(&cfd->cpumask_ipi, GFP_KERNEL,
  51                                cpu_to_node(cpu)))
  52                        return notifier_from_errno(-ENOMEM);
  53                cfd->csd = alloc_percpu(struct call_single_data);
  54                if (!cfd->csd) {
  55                        free_cpumask_var(cfd->cpumask);
  56                        return notifier_from_errno(-ENOMEM);
  57                }
  58                break;
  59
  60#ifdef CONFIG_HOTPLUG_CPU
  61        case CPU_UP_CANCELED:
  62        case CPU_UP_CANCELED_FROZEN:
  63
  64        case CPU_DEAD:
  65        case CPU_DEAD_FROZEN:
  66                free_cpumask_var(cfd->cpumask);
  67                free_cpumask_var(cfd->cpumask_ipi);
  68                free_percpu(cfd->csd);
  69                break;
  70#endif
  71        };
  72
  73        return NOTIFY_OK;
  74}
  75
  76static struct notifier_block __cpuinitdata hotplug_cfd_notifier = {
  77        .notifier_call          = hotplug_cfd,
  78};
  79
  80void __init call_function_init(void)
  81{
  82        void *cpu = (void *)(long)smp_processor_id();
  83        int i;
  84
  85        for_each_possible_cpu(i) {
  86                struct call_single_queue *q = &per_cpu(call_single_queue, i);
  87
  88                raw_spin_lock_init(&q->lock);
  89                INIT_LIST_HEAD(&q->list);
  90        }
  91
  92        hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
  93        register_cpu_notifier(&hotplug_cfd_notifier);
  94}
  95
  96/*
  97 * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
  98 *
  99 * For non-synchronous ipi calls the csd can still be in use by the
 100 * previous function call. For multi-cpu calls its even more interesting
 101 * as we'll have to ensure no other cpu is observing our csd.
 102 */
 103static void csd_lock_wait(struct call_single_data *csd)
 104{
 105        while (csd->flags & CSD_FLAG_LOCK)
 106                cpu_relax();
 107}
 108
 109static void csd_lock(struct call_single_data *csd)
 110{
 111        csd_lock_wait(csd);
 112        csd->flags |= CSD_FLAG_LOCK;
 113
 114        /*
 115         * prevent CPU from reordering the above assignment
 116         * to ->flags with any subsequent assignments to other
 117         * fields of the specified call_single_data structure:
 118         */
 119        smp_mb();
 120}
 121
 122static void csd_unlock(struct call_single_data *csd)
 123{
 124        WARN_ON(!(csd->flags & CSD_FLAG_LOCK));
 125
 126        /*
 127         * ensure we're all done before releasing data:
 128         */
 129        smp_mb();
 130
 131        csd->flags &= ~CSD_FLAG_LOCK;
 132}
 133
 134/*
 135 * Insert a previously allocated call_single_data element
 136 * for execution on the given CPU. data must already have
 137 * ->func, ->info, and ->flags set.
 138 */
 139static
 140void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
 141{
 142        struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
 143        unsigned long flags;
 144        int ipi;
 145
 146        raw_spin_lock_irqsave(&dst->lock, flags);
 147        ipi = list_empty(&dst->list);
 148        list_add_tail(&csd->list, &dst->list);
 149        raw_spin_unlock_irqrestore(&dst->lock, flags);
 150
 151        /*
 152         * The list addition should be visible before sending the IPI
 153         * handler locks the list to pull the entry off it because of
 154         * normal cache coherency rules implied by spinlocks.
 155         *
 156         * If IPIs can go out of order to the cache coherency protocol
 157         * in an architecture, sufficient synchronisation should be added
 158         * to arch code to make it appear to obey cache coherency WRT
 159         * locking and barrier primitives. Generic code isn't really
 160         * equipped to do the right thing...
 161         */
 162        if (ipi)
 163                arch_send_call_function_single_ipi(cpu);
 164
 165        if (wait)
 166                csd_lock_wait(csd);
 167}
 168
 169/*
 170 * Invoked by arch to handle an IPI for call function single. Must be
 171 * called from the arch with interrupts disabled.
 172 */
 173void generic_smp_call_function_single_interrupt(void)
 174{
 175        struct call_single_queue *q = &__get_cpu_var(call_single_queue);
 176        LIST_HEAD(list);
 177
 178        /*
 179         * Shouldn't receive this interrupt on a cpu that is not yet online.
 180         */
 181        WARN_ON_ONCE(!cpu_online(smp_processor_id()));
 182
 183        raw_spin_lock(&q->lock);
 184        list_replace_init(&q->list, &list);
 185        raw_spin_unlock(&q->lock);
 186
 187        while (!list_empty(&list)) {
 188                struct call_single_data *csd;
 189                unsigned int csd_flags;
 190
 191                csd = list_entry(list.next, struct call_single_data, list);
 192                list_del(&csd->list);
 193
 194                /*
 195                 * 'csd' can be invalid after this call if flags == 0
 196                 * (when called through generic_exec_single()),
 197                 * so save them away before making the call:
 198                 */
 199                csd_flags = csd->flags;
 200
 201                csd->func(csd->info);
 202
 203                /*
 204                 * Unlocked CSDs are valid through generic_exec_single():
 205                 */
 206                if (csd_flags & CSD_FLAG_LOCK)
 207                        csd_unlock(csd);
 208        }
 209}
 210
 211static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_data, csd_data);
 212
 213/*
 214 * smp_call_function_single - Run a function on a specific CPU
 215 * @func: The function to run. This must be fast and non-blocking.
 216 * @info: An arbitrary pointer to pass to the function.
 217 * @wait: If true, wait until function has completed on other CPUs.
 218 *
 219 * Returns 0 on success, else a negative status code.
 220 */
 221int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
 222                             int wait)
 223{
 224        struct call_single_data d = {
 225                .flags = 0,
 226        };
 227        unsigned long flags;
 228        int this_cpu;
 229        int err = 0;
 230
 231        /*
 232         * prevent preemption and reschedule on another processor,
 233         * as well as CPU removal
 234         */
 235        this_cpu = get_cpu();
 236
 237        /*
 238         * Can deadlock when called with interrupts disabled.
 239         * We allow cpu's that are not yet online though, as no one else can
 240         * send smp call function interrupt to this cpu and as such deadlocks
 241         * can't happen.
 242         */
 243        WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 244                     && !oops_in_progress);
 245
 246        if (cpu == this_cpu) {
 247                local_irq_save(flags);
 248                func(info);
 249                local_irq_restore(flags);
 250        } else {
 251                if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
 252                        struct call_single_data *csd = &d;
 253
 254                        if (!wait)
 255                                csd = &__get_cpu_var(csd_data);
 256
 257                        csd_lock(csd);
 258
 259                        csd->func = func;
 260                        csd->info = info;
 261                        generic_exec_single(cpu, csd, wait);
 262                } else {
 263                        err = -ENXIO;   /* CPU not online */
 264                }
 265        }
 266
 267        put_cpu();
 268
 269        return err;
 270}
 271EXPORT_SYMBOL(smp_call_function_single);
 272
 273/*
 274 * smp_call_function_any - Run a function on any of the given cpus
 275 * @mask: The mask of cpus it can run on.
 276 * @func: The function to run. This must be fast and non-blocking.
 277 * @info: An arbitrary pointer to pass to the function.
 278 * @wait: If true, wait until function has completed.
 279 *
 280 * Returns 0 on success, else a negative status code (if no cpus were online).
 281 * Note that @wait will be implicitly turned on in case of allocation failures,
 282 * since we fall back to on-stack allocation.
 283 *
 284 * Selection preference:
 285 *      1) current cpu if in @mask
 286 *      2) any cpu of current node if in @mask
 287 *      3) any other online cpu in @mask
 288 */
 289int smp_call_function_any(const struct cpumask *mask,
 290                          smp_call_func_t func, void *info, int wait)
 291{
 292        unsigned int cpu;
 293        const struct cpumask *nodemask;
 294        int ret;
 295
 296        /* Try for same CPU (cheapest) */
 297        cpu = get_cpu();
 298        if (cpumask_test_cpu(cpu, mask))
 299                goto call;
 300
 301        /* Try for same node. */
 302        nodemask = cpumask_of_node(cpu_to_node(cpu));
 303        for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
 304             cpu = cpumask_next_and(cpu, nodemask, mask)) {
 305                if (cpu_online(cpu))
 306                        goto call;
 307        }
 308
 309        /* Any online will do: smp_call_function_single handles nr_cpu_ids. */
 310        cpu = cpumask_any_and(mask, cpu_online_mask);
 311call:
 312        ret = smp_call_function_single(cpu, func, info, wait);
 313        put_cpu();
 314        return ret;
 315}
 316EXPORT_SYMBOL_GPL(smp_call_function_any);
 317
 318/**
 319 * __smp_call_function_single(): Run a function on a specific CPU
 320 * @cpu: The CPU to run on.
 321 * @data: Pre-allocated and setup data structure
 322 * @wait: If true, wait until function has completed on specified CPU.
 323 *
 324 * Like smp_call_function_single(), but allow caller to pass in a
 325 * pre-allocated data structure. Useful for embedding @data inside
 326 * other structures, for instance.
 327 */
 328void __smp_call_function_single(int cpu, struct call_single_data *csd,
 329                                int wait)
 330{
 331        unsigned int this_cpu;
 332        unsigned long flags;
 333
 334        this_cpu = get_cpu();
 335        /*
 336         * Can deadlock when called with interrupts disabled.
 337         * We allow cpu's that are not yet online though, as no one else can
 338         * send smp call function interrupt to this cpu and as such deadlocks
 339         * can't happen.
 340         */
 341        WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
 342                     && !oops_in_progress);
 343
 344        if (cpu == this_cpu) {
 345                local_irq_save(flags);
 346                csd->func(csd->info);
 347                local_irq_restore(flags);
 348        } else {
 349                csd_lock(csd);
 350                generic_exec_single(cpu, csd, wait);
 351        }
 352        put_cpu();
 353}
 354
 355/**
 356 * smp_call_function_many(): Run a function on a set of other CPUs.
 357 * @mask: The set of cpus to run on (only runs on online subset).
 358 * @func: The function to run. This must be fast and non-blocking.
 359 * @info: An arbitrary pointer to pass to the function.
 360 * @wait: If true, wait (atomically) until function has completed
 361 *        on other CPUs.
 362 *
 363 * If @wait is true, then returns once @func has returned.
 364 *
 365 * You must not call this function with disabled interrupts or from a
 366 * hardware interrupt handler or from a bottom half handler. Preemption
 367 * must be disabled when calling this function.
 368 */
 369void smp_call_function_many(const struct cpumask *mask,
 370                            smp_call_func_t func, void *info, bool wait)
 371{
 372        struct call_function_data *cfd;
 373        int cpu, next_cpu, this_cpu = smp_processor_id();
 374
 375        /*
 376         * Can deadlock when called with interrupts disabled.
 377         * We allow cpu's that are not yet online though, as no one else can
 378         * send smp call function interrupt to this cpu and as such deadlocks
 379         * can't happen.
 380         */
 381        WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
 382                     && !oops_in_progress && !early_boot_irqs_disabled);
 383
 384        /* Try to fastpath.  So, what's a CPU they want? Ignoring this one. */
 385        cpu = cpumask_first_and(mask, cpu_online_mask);
 386        if (cpu == this_cpu)
 387                cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 388
 389        /* No online cpus?  We're done. */
 390        if (cpu >= nr_cpu_ids)
 391                return;
 392
 393        /* Do we have another CPU which isn't us? */
 394        next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
 395        if (next_cpu == this_cpu)
 396                next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);
 397
 398        /* Fastpath: do that cpu by itself. */
 399        if (next_cpu >= nr_cpu_ids) {
 400                smp_call_function_single(cpu, func, info, wait);
 401                return;
 402        }
 403
 404        cfd = &__get_cpu_var(cfd_data);
 405
 406        cpumask_and(cfd->cpumask, mask, cpu_online_mask);
 407        cpumask_clear_cpu(this_cpu, cfd->cpumask);
 408
 409        /* Some callers race with other cpus changing the passed mask */
 410        if (unlikely(!cpumask_weight(cfd->cpumask)))
 411                return;
 412
 413        /*
 414         * After we put an entry into the list, cfd->cpumask may be cleared
 415         * again when another CPU sends another IPI for a SMP function call, so
 416         * cfd->cpumask will be zero.
 417         */
 418        cpumask_copy(cfd->cpumask_ipi, cfd->cpumask);
 419
 420        for_each_cpu(cpu, cfd->cpumask) {
 421                struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
 422                struct call_single_queue *dst =
 423                                        &per_cpu(call_single_queue, cpu);
 424                unsigned long flags;
 425
 426                csd_lock(csd);
 427                csd->func = func;
 428                csd->info = info;
 429
 430                raw_spin_lock_irqsave(&dst->lock, flags);
 431                list_add_tail(&csd->list, &dst->list);
 432                raw_spin_unlock_irqrestore(&dst->lock, flags);
 433        }
 434
 435        /* Send a message to all CPUs in the map */
 436        arch_send_call_function_ipi_mask(cfd->cpumask_ipi);
 437
 438        if (wait) {
 439                for_each_cpu(cpu, cfd->cpumask) {
 440                        struct call_single_data *csd;
 441
 442                        csd = per_cpu_ptr(cfd->csd, cpu);
 443                        csd_lock_wait(csd);
 444                }
 445        }
 446}
 447EXPORT_SYMBOL(smp_call_function_many);
 448
 449/**
 450 * smp_call_function(): Run a function on all other CPUs.
 451 * @func: The function to run. This must be fast and non-blocking.
 452 * @info: An arbitrary pointer to pass to the function.
 453 * @wait: If true, wait (atomically) until function has completed
 454 *        on other CPUs.
 455 *
 456 * Returns 0.
 457 *
 458 * If @wait is true, then returns once @func has returned; otherwise
 459 * it returns just before the target cpu calls @func.
 460 *
 461 * You must not call this function with disabled interrupts or from a
 462 * hardware interrupt handler or from a bottom half handler.
 463 */
 464int smp_call_function(smp_call_func_t func, void *info, int wait)
 465{
 466        preempt_disable();
 467        smp_call_function_many(cpu_online_mask, func, info, wait);
 468        preempt_enable();
 469
 470        return 0;
 471}
 472EXPORT_SYMBOL(smp_call_function);
 473#endif /* USE_GENERIC_SMP_HELPERS */
 474
 475/* Setup configured maximum number of CPUs to activate */
 476unsigned int setup_max_cpus = NR_CPUS;
 477EXPORT_SYMBOL(setup_max_cpus);
 478
 479
 480/*
 481 * Setup routine for controlling SMP activation
 482 *
 483 * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
 484 * activation entirely (the MPS table probe still happens, though).
 485 *
 486 * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
 487 * greater than 0, limits the maximum number of CPUs activated in
 488 * SMP mode to <NUM>.
 489 */
 490
 491void __weak arch_disable_smp_support(void) { }
 492
 493static int __init nosmp(char *str)
 494{
 495        setup_max_cpus = 0;
 496        arch_disable_smp_support();
 497
 498        return 0;
 499}
 500
 501early_param("nosmp", nosmp);
 502
 503/* this is hard limit */
 504static int __init nrcpus(char *str)
 505{
 506        int nr_cpus;
 507
 508        get_option(&str, &nr_cpus);
 509        if (nr_cpus > 0 && nr_cpus < nr_cpu_ids)
 510                nr_cpu_ids = nr_cpus;
 511
 512        return 0;
 513}
 514
 515early_param("nr_cpus", nrcpus);
 516
 517static int __init maxcpus(char *str)
 518{
 519        get_option(&str, &setup_max_cpus);
 520        if (setup_max_cpus == 0)
 521                arch_disable_smp_support();
 522
 523        return 0;
 524}
 525
 526early_param("maxcpus", maxcpus);
 527
 528/* Setup number of possible processor ids */
 529int nr_cpu_ids __read_mostly = NR_CPUS;
 530EXPORT_SYMBOL(nr_cpu_ids);
 531
 532/* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
 533void __init setup_nr_cpu_ids(void)
 534{
 535        nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
 536}
 537
 538/* Called by boot processor to activate the rest. */
 539void __init smp_init(void)
 540{
 541        unsigned int cpu;
 542
 543        idle_threads_init();
 544
 545        /* FIXME: This should be done in userspace --RR */
 546        for_each_present_cpu(cpu) {
 547                if (num_online_cpus() >= setup_max_cpus)
 548                        break;
 549                if (!cpu_online(cpu))
 550                        cpu_up(cpu);
 551        }
 552
 553        /* Any cleanup work */
 554        printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
 555        smp_cpus_done(setup_max_cpus);
 556}
 557
 558/*
 559 * Call a function on all processors.  May be used during early boot while
 560 * early_boot_irqs_disabled is set.  Use local_irq_save/restore() instead
 561 * of local_irq_disable/enable().
 562 */
 563int on_each_cpu(void (*func) (void *info), void *info, int wait)
 564{
 565        unsigned long flags;
 566        int ret = 0;
 567
 568        preempt_disable();
 569        ret = smp_call_function(func, info, wait);
 570        local_irq_save(flags);
 571        func(info);
 572        local_irq_restore(flags);
 573        preempt_enable();
 574        return ret;
 575}
 576EXPORT_SYMBOL(on_each_cpu);
 577
 578/**
 579 * on_each_cpu_mask(): Run a function on processors specified by
 580 * cpumask, which may include the local processor.
 581 * @mask: The set of cpus to run on (only runs on online subset).
 582 * @func: The function to run. This must be fast and non-blocking.
 583 * @info: An arbitrary pointer to pass to the function.
 584 * @wait: If true, wait (atomically) until function has completed
 585 *        on other CPUs.
 586 *
 587 * If @wait is true, then returns once @func has returned.
 588 *
 589 * You must not call this function with disabled interrupts or
 590 * from a hardware interrupt handler or from a bottom half handler.
 591 */
 592void on_each_cpu_mask(const struct cpumask *mask, smp_call_func_t func,
 593                        void *info, bool wait)
 594{
 595        int cpu = get_cpu();
 596
 597        smp_call_function_many(mask, func, info, wait);
 598        if (cpumask_test_cpu(cpu, mask)) {
 599                local_irq_disable();
 600                func(info);
 601                local_irq_enable();
 602        }
 603        put_cpu();
 604}
 605EXPORT_SYMBOL(on_each_cpu_mask);
 606
 607/*
 608 * on_each_cpu_cond(): Call a function on each processor for which
 609 * the supplied function cond_func returns true, optionally waiting
 610 * for all the required CPUs to finish. This may include the local
 611 * processor.
 612 * @cond_func:  A callback function that is passed a cpu id and
 613 *              the the info parameter. The function is called
 614 *              with preemption disabled. The function should
 615 *              return a blooean value indicating whether to IPI
 616 *              the specified CPU.
 617 * @func:       The function to run on all applicable CPUs.
 618 *              This must be fast and non-blocking.
 619 * @info:       An arbitrary pointer to pass to both functions.
 620 * @wait:       If true, wait (atomically) until function has
 621 *              completed on other CPUs.
 622 * @gfp_flags:  GFP flags to use when allocating the cpumask
 623 *              used internally by the function.
 624 *
 625 * The function might sleep if the GFP flags indicates a non
 626 * atomic allocation is allowed.
 627 *
 628 * Preemption is disabled to protect against CPUs going offline but not online.
 629 * CPUs going online during the call will not be seen or sent an IPI.
 630 *
 631 * You must not call this function with disabled interrupts or
 632 * from a hardware interrupt handler or from a bottom half handler.
 633 */
 634void on_each_cpu_cond(bool (*cond_func)(int cpu, void *info),
 635                        smp_call_func_t func, void *info, bool wait,
 636                        gfp_t gfp_flags)
 637{
 638        cpumask_var_t cpus;
 639        int cpu, ret;
 640
 641        might_sleep_if(gfp_flags & __GFP_WAIT);
 642
 643        if (likely(zalloc_cpumask_var(&cpus, (gfp_flags|__GFP_NOWARN)))) {
 644                preempt_disable();
 645                for_each_online_cpu(cpu)
 646                        if (cond_func(cpu, info))
 647                                cpumask_set_cpu(cpu, cpus);
 648                on_each_cpu_mask(cpus, func, info, wait);
 649                preempt_enable();
 650                free_cpumask_var(cpus);
 651        } else {
 652                /*
 653                 * No free cpumask, bother. No matter, we'll
 654                 * just have to IPI them one by one.
 655                 */
 656                preempt_disable();
 657                for_each_online_cpu(cpu)
 658                        if (cond_func(cpu, info)) {
 659                                ret = smp_call_function_single(cpu, func,
 660                                                                info, wait);
 661                                WARN_ON_ONCE(!ret);
 662                        }
 663                preempt_enable();
 664        }
 665}
 666EXPORT_SYMBOL(on_each_cpu_cond);
 667
 668static void do_nothing(void *unused)
 669{
 670}
 671
 672/**
 673 * kick_all_cpus_sync - Force all cpus out of idle
 674 *
 675 * Used to synchronize the update of pm_idle function pointer. It's
 676 * called after the pointer is updated and returns after the dummy
 677 * callback function has been executed on all cpus. The execution of
 678 * the function can only happen on the remote cpus after they have
 679 * left the idle function which had been called via pm_idle function
 680 * pointer. So it's guaranteed that nothing uses the previous pointer
 681 * anymore.
 682 */
 683void kick_all_cpus_sync(void)
 684{
 685        /* Make sure the change is visible before we kick the cpus */
 686        smp_mb();
 687        smp_call_function(do_nothing, NULL, 1);
 688}
 689EXPORT_SYMBOL_GPL(kick_all_cpus_sync);
 690
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