linux/kernel/cpu.c
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   1/* CPU control.
   2 * (C) 2001, 2002, 2003, 2004 Rusty Russell
   3 *
   4 * This code is licenced under the GPL.
   5 */
   6#include <linux/proc_fs.h>
   7#include <linux/smp.h>
   8#include <linux/init.h>
   9#include <linux/notifier.h>
  10#include <linux/sched.h>
  11#include <linux/unistd.h>
  12#include <linux/cpu.h>
  13#include <linux/module.h>
  14#include <linux/kthread.h>
  15#include <linux/stop_machine.h>
  16#include <linux/mutex.h>
  17#include <linux/gfp.h>
  18
  19#ifdef CONFIG_SMP
  20/* Serializes the updates to cpu_online_mask, cpu_present_mask */
  21static DEFINE_MUTEX(cpu_add_remove_lock);
  22
  23/*
  24 * The following two API's must be used when attempting
  25 * to serialize the updates to cpu_online_mask, cpu_present_mask.
  26 */
  27void cpu_maps_update_begin(void)
  28{
  29        mutex_lock(&cpu_add_remove_lock);
  30}
  31
  32void cpu_maps_update_done(void)
  33{
  34        mutex_unlock(&cpu_add_remove_lock);
  35}
  36
  37static RAW_NOTIFIER_HEAD(cpu_chain);
  38
  39/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  40 * Should always be manipulated under cpu_add_remove_lock
  41 */
  42static int cpu_hotplug_disabled;
  43
  44#ifdef CONFIG_HOTPLUG_CPU
  45
  46static struct {
  47        struct task_struct *active_writer;
  48        struct mutex lock; /* Synchronizes accesses to refcount, */
  49        /*
  50         * Also blocks the new readers during
  51         * an ongoing cpu hotplug operation.
  52         */
  53        int refcount;
  54} cpu_hotplug = {
  55        .active_writer = NULL,
  56        .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
  57        .refcount = 0,
  58};
  59
  60void get_online_cpus(void)
  61{
  62        might_sleep();
  63        if (cpu_hotplug.active_writer == current)
  64                return;
  65        mutex_lock(&cpu_hotplug.lock);
  66        cpu_hotplug.refcount++;
  67        mutex_unlock(&cpu_hotplug.lock);
  68
  69}
  70EXPORT_SYMBOL_GPL(get_online_cpus);
  71
  72void put_online_cpus(void)
  73{
  74        if (cpu_hotplug.active_writer == current)
  75                return;
  76        mutex_lock(&cpu_hotplug.lock);
  77        if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
  78                wake_up_process(cpu_hotplug.active_writer);
  79        mutex_unlock(&cpu_hotplug.lock);
  80
  81}
  82EXPORT_SYMBOL_GPL(put_online_cpus);
  83
  84/*
  85 * This ensures that the hotplug operation can begin only when the
  86 * refcount goes to zero.
  87 *
  88 * Note that during a cpu-hotplug operation, the new readers, if any,
  89 * will be blocked by the cpu_hotplug.lock
  90 *
  91 * Since cpu_hotplug_begin() is always called after invoking
  92 * cpu_maps_update_begin(), we can be sure that only one writer is active.
  93 *
  94 * Note that theoretically, there is a possibility of a livelock:
  95 * - Refcount goes to zero, last reader wakes up the sleeping
  96 *   writer.
  97 * - Last reader unlocks the cpu_hotplug.lock.
  98 * - A new reader arrives at this moment, bumps up the refcount.
  99 * - The writer acquires the cpu_hotplug.lock finds the refcount
 100 *   non zero and goes to sleep again.
 101 *
 102 * However, this is very difficult to achieve in practice since
 103 * get_online_cpus() not an api which is called all that often.
 104 *
 105 */
 106static void cpu_hotplug_begin(void)
 107{
 108        cpu_hotplug.active_writer = current;
 109
 110        for (;;) {
 111                mutex_lock(&cpu_hotplug.lock);
 112                if (likely(!cpu_hotplug.refcount))
 113                        break;
 114                __set_current_state(TASK_UNINTERRUPTIBLE);
 115                mutex_unlock(&cpu_hotplug.lock);
 116                schedule();
 117        }
 118}
 119
 120static void cpu_hotplug_done(void)
 121{
 122        cpu_hotplug.active_writer = NULL;
 123        mutex_unlock(&cpu_hotplug.lock);
 124}
 125
 126#else /* #if CONFIG_HOTPLUG_CPU */
 127static void cpu_hotplug_begin(void) {}
 128static void cpu_hotplug_done(void) {}
 129#endif  /* #else #if CONFIG_HOTPLUG_CPU */
 130
 131/* Need to know about CPUs going up/down? */
 132int __ref register_cpu_notifier(struct notifier_block *nb)
 133{
 134        int ret;
 135        cpu_maps_update_begin();
 136        ret = raw_notifier_chain_register(&cpu_chain, nb);
 137        cpu_maps_update_done();
 138        return ret;
 139}
 140
 141static int __cpu_notify(unsigned long val, void *v, int nr_to_call,
 142                        int *nr_calls)
 143{
 144        int ret;
 145
 146        ret = __raw_notifier_call_chain(&cpu_chain, val, v, nr_to_call,
 147                                        nr_calls);
 148
 149        return notifier_to_errno(ret);
 150}
 151
 152static int cpu_notify(unsigned long val, void *v)
 153{
 154        return __cpu_notify(val, v, -1, NULL);
 155}
 156
 157#ifdef CONFIG_HOTPLUG_CPU
 158
 159static void cpu_notify_nofail(unsigned long val, void *v)
 160{
 161        BUG_ON(cpu_notify(val, v));
 162}
 163EXPORT_SYMBOL(register_cpu_notifier);
 164
 165void __ref unregister_cpu_notifier(struct notifier_block *nb)
 166{
 167        cpu_maps_update_begin();
 168        raw_notifier_chain_unregister(&cpu_chain, nb);
 169        cpu_maps_update_done();
 170}
 171EXPORT_SYMBOL(unregister_cpu_notifier);
 172
 173static inline void check_for_tasks(int cpu)
 174{
 175        struct task_struct *p;
 176
 177        write_lock_irq(&tasklist_lock);
 178        for_each_process(p) {
 179                if (task_cpu(p) == cpu && p->state == TASK_RUNNING &&
 180                    (!cputime_eq(p->utime, cputime_zero) ||
 181                     !cputime_eq(p->stime, cputime_zero)))
 182                        printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d "
 183                                "(state = %ld, flags = %x)\n",
 184                                p->comm, task_pid_nr(p), cpu,
 185                                p->state, p->flags);
 186        }
 187        write_unlock_irq(&tasklist_lock);
 188}
 189
 190struct take_cpu_down_param {
 191        unsigned long mod;
 192        void *hcpu;
 193};
 194
 195/* Take this CPU down. */
 196static int __ref take_cpu_down(void *_param)
 197{
 198        struct take_cpu_down_param *param = _param;
 199        int err;
 200
 201        /* Ensure this CPU doesn't handle any more interrupts. */
 202        err = __cpu_disable();
 203        if (err < 0)
 204                return err;
 205
 206        cpu_notify(CPU_DYING | param->mod, param->hcpu);
 207        return 0;
 208}
 209
 210/* Requires cpu_add_remove_lock to be held */
 211static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 212{
 213        int err, nr_calls = 0;
 214        void *hcpu = (void *)(long)cpu;
 215        unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 216        struct take_cpu_down_param tcd_param = {
 217                .mod = mod,
 218                .hcpu = hcpu,
 219        };
 220
 221        if (num_online_cpus() == 1)
 222                return -EBUSY;
 223
 224        if (!cpu_online(cpu))
 225                return -EINVAL;
 226
 227        cpu_hotplug_begin();
 228
 229        err = __cpu_notify(CPU_DOWN_PREPARE | mod, hcpu, -1, &nr_calls);
 230        if (err) {
 231                nr_calls--;
 232                __cpu_notify(CPU_DOWN_FAILED | mod, hcpu, nr_calls, NULL);
 233                printk("%s: attempt to take down CPU %u failed\n",
 234                                __func__, cpu);
 235                goto out_release;
 236        }
 237
 238        err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
 239        if (err) {
 240                /* CPU didn't die: tell everyone.  Can't complain. */
 241                cpu_notify_nofail(CPU_DOWN_FAILED | mod, hcpu);
 242
 243                goto out_release;
 244        }
 245        BUG_ON(cpu_online(cpu));
 246
 247        /*
 248         * The migration_call() CPU_DYING callback will have removed all
 249         * runnable tasks from the cpu, there's only the idle task left now
 250         * that the migration thread is done doing the stop_machine thing.
 251         *
 252         * Wait for the stop thread to go away.
 253         */
 254        while (!idle_cpu(cpu))
 255                cpu_relax();
 256
 257        /* This actually kills the CPU. */
 258        __cpu_die(cpu);
 259
 260        /* CPU is completely dead: tell everyone.  Too late to complain. */
 261        cpu_notify_nofail(CPU_DEAD | mod, hcpu);
 262
 263        check_for_tasks(cpu);
 264
 265out_release:
 266        cpu_hotplug_done();
 267        if (!err)
 268                cpu_notify_nofail(CPU_POST_DEAD | mod, hcpu);
 269        return err;
 270}
 271
 272int __ref cpu_down(unsigned int cpu)
 273{
 274        int err;
 275
 276        cpu_maps_update_begin();
 277
 278        if (cpu_hotplug_disabled) {
 279                err = -EBUSY;
 280                goto out;
 281        }
 282
 283        err = _cpu_down(cpu, 0);
 284
 285out:
 286        cpu_maps_update_done();
 287        return err;
 288}
 289EXPORT_SYMBOL(cpu_down);
 290#endif /*CONFIG_HOTPLUG_CPU*/
 291
 292/* Requires cpu_add_remove_lock to be held */
 293static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 294{
 295        int ret, nr_calls = 0;
 296        void *hcpu = (void *)(long)cpu;
 297        unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 298
 299        if (cpu_online(cpu) || !cpu_present(cpu))
 300                return -EINVAL;
 301
 302        cpu_hotplug_begin();
 303        ret = __cpu_notify(CPU_UP_PREPARE | mod, hcpu, -1, &nr_calls);
 304        if (ret) {
 305                nr_calls--;
 306                printk(KERN_WARNING "%s: attempt to bring up CPU %u failed\n",
 307                                __func__, cpu);
 308                goto out_notify;
 309        }
 310
 311        /* Arch-specific enabling code. */
 312        ret = __cpu_up(cpu);
 313        if (ret != 0)
 314                goto out_notify;
 315        BUG_ON(!cpu_online(cpu));
 316
 317        /* Now call notifier in preparation. */
 318        cpu_notify(CPU_ONLINE | mod, hcpu);
 319
 320out_notify:
 321        if (ret != 0)
 322                __cpu_notify(CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 323        cpu_hotplug_done();
 324
 325        return ret;
 326}
 327
 328int __cpuinit cpu_up(unsigned int cpu)
 329{
 330        int err = 0;
 331
 332#ifdef  CONFIG_MEMORY_HOTPLUG
 333        int nid;
 334        pg_data_t       *pgdat;
 335#endif
 336
 337        if (!cpu_possible(cpu)) {
 338                printk(KERN_ERR "can't online cpu %d because it is not "
 339                        "configured as may-hotadd at boot time\n", cpu);
 340#if defined(CONFIG_IA64)
 341                printk(KERN_ERR "please check additional_cpus= boot "
 342                                "parameter\n");
 343#endif
 344                return -EINVAL;
 345        }
 346
 347#ifdef  CONFIG_MEMORY_HOTPLUG
 348        nid = cpu_to_node(cpu);
 349        if (!node_online(nid)) {
 350                err = mem_online_node(nid);
 351                if (err)
 352                        return err;
 353        }
 354
 355        pgdat = NODE_DATA(nid);
 356        if (!pgdat) {
 357                printk(KERN_ERR
 358                        "Can't online cpu %d due to NULL pgdat\n", cpu);
 359                return -ENOMEM;
 360        }
 361
 362        if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
 363                mutex_lock(&zonelists_mutex);
 364                build_all_zonelists(NULL);
 365                mutex_unlock(&zonelists_mutex);
 366        }
 367#endif
 368
 369        cpu_maps_update_begin();
 370
 371        if (cpu_hotplug_disabled) {
 372                err = -EBUSY;
 373                goto out;
 374        }
 375
 376        err = _cpu_up(cpu, 0);
 377
 378out:
 379        cpu_maps_update_done();
 380        return err;
 381}
 382
 383#ifdef CONFIG_PM_SLEEP_SMP
 384static cpumask_var_t frozen_cpus;
 385
 386void __weak arch_disable_nonboot_cpus_begin(void)
 387{
 388}
 389
 390void __weak arch_disable_nonboot_cpus_end(void)
 391{
 392}
 393
 394int disable_nonboot_cpus(void)
 395{
 396        int cpu, first_cpu, error = 0;
 397
 398        cpu_maps_update_begin();
 399        first_cpu = cpumask_first(cpu_online_mask);
 400        /*
 401         * We take down all of the non-boot CPUs in one shot to avoid races
 402         * with the userspace trying to use the CPU hotplug at the same time
 403         */
 404        cpumask_clear(frozen_cpus);
 405        arch_disable_nonboot_cpus_begin();
 406
 407        printk("Disabling non-boot CPUs ...\n");
 408        for_each_online_cpu(cpu) {
 409                if (cpu == first_cpu)
 410                        continue;
 411                error = _cpu_down(cpu, 1);
 412                if (!error)
 413                        cpumask_set_cpu(cpu, frozen_cpus);
 414                else {
 415                        printk(KERN_ERR "Error taking CPU%d down: %d\n",
 416                                cpu, error);
 417                        break;
 418                }
 419        }
 420
 421        arch_disable_nonboot_cpus_end();
 422
 423        if (!error) {
 424                BUG_ON(num_online_cpus() > 1);
 425                /* Make sure the CPUs won't be enabled by someone else */
 426                cpu_hotplug_disabled = 1;
 427        } else {
 428                printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 429        }
 430        cpu_maps_update_done();
 431        return error;
 432}
 433
 434void __weak arch_enable_nonboot_cpus_begin(void)
 435{
 436}
 437
 438void __weak arch_enable_nonboot_cpus_end(void)
 439{
 440}
 441
 442void __ref enable_nonboot_cpus(void)
 443{
 444        int cpu, error;
 445
 446        /* Allow everyone to use the CPU hotplug again */
 447        cpu_maps_update_begin();
 448        cpu_hotplug_disabled = 0;
 449        if (cpumask_empty(frozen_cpus))
 450                goto out;
 451
 452        printk(KERN_INFO "Enabling non-boot CPUs ...\n");
 453
 454        arch_enable_nonboot_cpus_begin();
 455
 456        for_each_cpu(cpu, frozen_cpus) {
 457                error = _cpu_up(cpu, 1);
 458                if (!error) {
 459                        printk(KERN_INFO "CPU%d is up\n", cpu);
 460                        continue;
 461                }
 462                printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 463        }
 464
 465        arch_enable_nonboot_cpus_end();
 466
 467        cpumask_clear(frozen_cpus);
 468out:
 469        cpu_maps_update_done();
 470}
 471
 472static int alloc_frozen_cpus(void)
 473{
 474        if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
 475                return -ENOMEM;
 476        return 0;
 477}
 478core_initcall(alloc_frozen_cpus);
 479#endif /* CONFIG_PM_SLEEP_SMP */
 480
 481/**
 482 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
 483 * @cpu: cpu that just started
 484 *
 485 * This function calls the cpu_chain notifiers with CPU_STARTING.
 486 * It must be called by the arch code on the new cpu, before the new cpu
 487 * enables interrupts and before the "boot" cpu returns from __cpu_up().
 488 */
 489void __cpuinit notify_cpu_starting(unsigned int cpu)
 490{
 491        unsigned long val = CPU_STARTING;
 492
 493#ifdef CONFIG_PM_SLEEP_SMP
 494        if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
 495                val = CPU_STARTING_FROZEN;
 496#endif /* CONFIG_PM_SLEEP_SMP */
 497        cpu_notify(val, (void *)(long)cpu);
 498}
 499
 500#endif /* CONFIG_SMP */
 501
 502/*
 503 * cpu_bit_bitmap[] is a special, "compressed" data structure that
 504 * represents all NR_CPUS bits binary values of 1<<nr.
 505 *
 506 * It is used by cpumask_of() to get a constant address to a CPU
 507 * mask value that has a single bit set only.
 508 */
 509
 510/* cpu_bit_bitmap[0] is empty - so we can back into it */
 511#define MASK_DECLARE_1(x)       [x+1][0] = (1UL << (x))
 512#define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 513#define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 514#define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
 515
 516const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
 517
 518        MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
 519        MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
 520#if BITS_PER_LONG > 32
 521        MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
 522        MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
 523#endif
 524};
 525EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
 526
 527const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
 528EXPORT_SYMBOL(cpu_all_bits);
 529
 530#ifdef CONFIG_INIT_ALL_POSSIBLE
 531static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
 532        = CPU_BITS_ALL;
 533#else
 534static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
 535#endif
 536const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
 537EXPORT_SYMBOL(cpu_possible_mask);
 538
 539static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
 540const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
 541EXPORT_SYMBOL(cpu_online_mask);
 542
 543static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
 544const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
 545EXPORT_SYMBOL(cpu_present_mask);
 546
 547static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
 548const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
 549EXPORT_SYMBOL(cpu_active_mask);
 550
 551void set_cpu_possible(unsigned int cpu, bool possible)
 552{
 553        if (possible)
 554                cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
 555        else
 556                cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
 557}
 558
 559void set_cpu_present(unsigned int cpu, bool present)
 560{
 561        if (present)
 562                cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
 563        else
 564                cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
 565}
 566
 567void set_cpu_online(unsigned int cpu, bool online)
 568{
 569        if (online)
 570                cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
 571        else
 572                cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
 573}
 574
 575void set_cpu_active(unsigned int cpu, bool active)
 576{
 577        if (active)
 578                cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
 579        else
 580                cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
 581}
 582
 583void init_cpu_present(const struct cpumask *src)
 584{
 585        cpumask_copy(to_cpumask(cpu_present_bits), src);
 586}
 587
 588void init_cpu_possible(const struct cpumask *src)
 589{
 590        cpumask_copy(to_cpumask(cpu_possible_bits), src);
 591}
 592
 593void init_cpu_online(const struct cpumask *src)
 594{
 595        cpumask_copy(to_cpumask(cpu_online_bits), src);
 596}
 597
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