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
  18#ifdef CONFIG_SMP
  19/* Serializes the updates to cpu_online_mask, cpu_present_mask */
  20static DEFINE_MUTEX(cpu_add_remove_lock);
  21
  22static __cpuinitdata RAW_NOTIFIER_HEAD(cpu_chain);
  23
  24/* If set, cpu_up and cpu_down will return -EBUSY and do nothing.
  25 * Should always be manipulated under cpu_add_remove_lock
  26 */
  27static int cpu_hotplug_disabled;
  28
  29static struct {
  30        struct task_struct *active_writer;
  31        struct mutex lock; /* Synchronizes accesses to refcount, */
  32        /*
  33         * Also blocks the new readers during
  34         * an ongoing cpu hotplug operation.
  35         */
  36        int refcount;
  37} cpu_hotplug;
  38
  39void __init cpu_hotplug_init(void)
  40{
  41        cpu_hotplug.active_writer = NULL;
  42        mutex_init(&cpu_hotplug.lock);
  43        cpu_hotplug.refcount = 0;
  44}
  45
  46#ifdef CONFIG_HOTPLUG_CPU
  47
  48void get_online_cpus(void)
  49{
  50        might_sleep();
  51        if (cpu_hotplug.active_writer == current)
  52                return;
  53        mutex_lock(&cpu_hotplug.lock);
  54        cpu_hotplug.refcount++;
  55        mutex_unlock(&cpu_hotplug.lock);
  56
  57}
  58EXPORT_SYMBOL_GPL(get_online_cpus);
  59
  60void put_online_cpus(void)
  61{
  62        if (cpu_hotplug.active_writer == current)
  63                return;
  64        mutex_lock(&cpu_hotplug.lock);
  65        if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer))
  66                wake_up_process(cpu_hotplug.active_writer);
  67        mutex_unlock(&cpu_hotplug.lock);
  68
  69}
  70EXPORT_SYMBOL_GPL(put_online_cpus);
  71
  72#endif  /* CONFIG_HOTPLUG_CPU */
  73
  74/*
  75 * The following two API's must be used when attempting
  76 * to serialize the updates to cpu_online_mask, cpu_present_mask.
  77 */
  78void cpu_maps_update_begin(void)
  79{
  80        mutex_lock(&cpu_add_remove_lock);
  81}
  82
  83void cpu_maps_update_done(void)
  84{
  85        mutex_unlock(&cpu_add_remove_lock);
  86}
  87
  88/*
  89 * This ensures that the hotplug operation can begin only when the
  90 * refcount goes to zero.
  91 *
  92 * Note that during a cpu-hotplug operation, the new readers, if any,
  93 * will be blocked by the cpu_hotplug.lock
  94 *
  95 * Since cpu_hotplug_begin() is always called after invoking
  96 * cpu_maps_update_begin(), we can be sure that only one writer is active.
  97 *
  98 * Note that theoretically, there is a possibility of a livelock:
  99 * - Refcount goes to zero, last reader wakes up the sleeping
 100 *   writer.
 101 * - Last reader unlocks the cpu_hotplug.lock.
 102 * - A new reader arrives at this moment, bumps up the refcount.
 103 * - The writer acquires the cpu_hotplug.lock finds the refcount
 104 *   non zero and goes to sleep again.
 105 *
 106 * However, this is very difficult to achieve in practice since
 107 * get_online_cpus() not an api which is called all that often.
 108 *
 109 */
 110static void cpu_hotplug_begin(void)
 111{
 112        cpu_hotplug.active_writer = current;
 113
 114        for (;;) {
 115                mutex_lock(&cpu_hotplug.lock);
 116                if (likely(!cpu_hotplug.refcount))
 117                        break;
 118                __set_current_state(TASK_UNINTERRUPTIBLE);
 119                mutex_unlock(&cpu_hotplug.lock);
 120                schedule();
 121        }
 122}
 123
 124static void cpu_hotplug_done(void)
 125{
 126        cpu_hotplug.active_writer = NULL;
 127        mutex_unlock(&cpu_hotplug.lock);
 128}
 129/* Need to know about CPUs going up/down? */
 130int __ref register_cpu_notifier(struct notifier_block *nb)
 131{
 132        int ret;
 133        cpu_maps_update_begin();
 134        ret = raw_notifier_chain_register(&cpu_chain, nb);
 135        cpu_maps_update_done();
 136        return ret;
 137}
 138
 139#ifdef CONFIG_HOTPLUG_CPU
 140
 141EXPORT_SYMBOL(register_cpu_notifier);
 142
 143void __ref unregister_cpu_notifier(struct notifier_block *nb)
 144{
 145        cpu_maps_update_begin();
 146        raw_notifier_chain_unregister(&cpu_chain, nb);
 147        cpu_maps_update_done();
 148}
 149EXPORT_SYMBOL(unregister_cpu_notifier);
 150
 151static inline void check_for_tasks(int cpu)
 152{
 153        struct task_struct *p;
 154
 155        write_lock_irq(&tasklist_lock);
 156        for_each_process(p) {
 157                if (task_cpu(p) == cpu &&
 158                    (!cputime_eq(p->utime, cputime_zero) ||
 159                     !cputime_eq(p->stime, cputime_zero)))
 160                        printk(KERN_WARNING "Task %s (pid = %d) is on cpu %d\
 161                                (state = %ld, flags = %x) \n",
 162                                 p->comm, task_pid_nr(p), cpu,
 163                                 p->state, p->flags);
 164        }
 165        write_unlock_irq(&tasklist_lock);
 166}
 167
 168struct take_cpu_down_param {
 169        unsigned long mod;
 170        void *hcpu;
 171};
 172
 173/* Take this CPU down. */
 174static int __ref take_cpu_down(void *_param)
 175{
 176        struct take_cpu_down_param *param = _param;
 177        int err;
 178
 179        /* Ensure this CPU doesn't handle any more interrupts. */
 180        err = __cpu_disable();
 181        if (err < 0)
 182                return err;
 183
 184        raw_notifier_call_chain(&cpu_chain, CPU_DYING | param->mod,
 185                                param->hcpu);
 186
 187        /* Force idle task to run as soon as we yield: it should
 188           immediately notice cpu is offline and die quickly. */
 189        sched_idle_next();
 190        return 0;
 191}
 192
 193/* Requires cpu_add_remove_lock to be held */
 194static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
 195{
 196        int err, nr_calls = 0;
 197        cpumask_var_t old_allowed;
 198        void *hcpu = (void *)(long)cpu;
 199        unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 200        struct take_cpu_down_param tcd_param = {
 201                .mod = mod,
 202                .hcpu = hcpu,
 203        };
 204
 205        if (num_online_cpus() == 1)
 206                return -EBUSY;
 207
 208        if (!cpu_online(cpu))
 209                return -EINVAL;
 210
 211        if (!alloc_cpumask_var(&old_allowed, GFP_KERNEL))
 212                return -ENOMEM;
 213
 214        cpu_hotplug_begin();
 215        err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
 216                                        hcpu, -1, &nr_calls);
 217        if (err == NOTIFY_BAD) {
 218                nr_calls--;
 219                __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 220                                          hcpu, nr_calls, NULL);
 221                printk("%s: attempt to take down CPU %u failed\n",
 222                                __func__, cpu);
 223                err = -EINVAL;
 224                goto out_release;
 225        }
 226
 227        /* Ensure that we are not runnable on dying cpu */
 228        cpumask_copy(old_allowed, &current->cpus_allowed);
 229        set_cpus_allowed_ptr(current,
 230                             cpumask_of(cpumask_any_but(cpu_online_mask, cpu)));
 231
 232        err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
 233        if (err) {
 234                /* CPU didn't die: tell everyone.  Can't complain. */
 235                if (raw_notifier_call_chain(&cpu_chain, CPU_DOWN_FAILED | mod,
 236                                            hcpu) == NOTIFY_BAD)
 237                        BUG();
 238
 239                goto out_allowed;
 240        }
 241        BUG_ON(cpu_online(cpu));
 242
 243        /* Wait for it to sleep (leaving idle task). */
 244        while (!idle_cpu(cpu))
 245                yield();
 246
 247        /* This actually kills the CPU. */
 248        __cpu_die(cpu);
 249
 250        /* CPU is completely dead: tell everyone.  Too late to complain. */
 251        if (raw_notifier_call_chain(&cpu_chain, CPU_DEAD | mod,
 252                                    hcpu) == NOTIFY_BAD)
 253                BUG();
 254
 255        check_for_tasks(cpu);
 256
 257out_allowed:
 258        set_cpus_allowed_ptr(current, old_allowed);
 259out_release:
 260        cpu_hotplug_done();
 261        if (!err) {
 262                if (raw_notifier_call_chain(&cpu_chain, CPU_POST_DEAD | mod,
 263                                            hcpu) == NOTIFY_BAD)
 264                        BUG();
 265        }
 266        free_cpumask_var(old_allowed);
 267        return err;
 268}
 269
 270int __ref cpu_down(unsigned int cpu)
 271{
 272        int err;
 273
 274        err = stop_machine_create();
 275        if (err)
 276                return err;
 277        cpu_maps_update_begin();
 278
 279        if (cpu_hotplug_disabled) {
 280                err = -EBUSY;
 281                goto out;
 282        }
 283
 284        set_cpu_active(cpu, false);
 285
 286        /*
 287         * Make sure the all cpus did the reschedule and are not
 288         * using stale version of the cpu_active_mask.
 289         * This is not strictly necessary becuase stop_machine()
 290         * that we run down the line already provides the required
 291         * synchronization. But it's really a side effect and we do not
 292         * want to depend on the innards of the stop_machine here.
 293         */
 294        synchronize_sched();
 295
 296        err = _cpu_down(cpu, 0);
 297
 298        if (cpu_online(cpu))
 299                set_cpu_active(cpu, true);
 300
 301out:
 302        cpu_maps_update_done();
 303        stop_machine_destroy();
 304        return err;
 305}
 306EXPORT_SYMBOL(cpu_down);
 307#endif /*CONFIG_HOTPLUG_CPU*/
 308
 309/* Requires cpu_add_remove_lock to be held */
 310static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
 311{
 312        int ret, nr_calls = 0;
 313        void *hcpu = (void *)(long)cpu;
 314        unsigned long mod = tasks_frozen ? CPU_TASKS_FROZEN : 0;
 315
 316        if (cpu_online(cpu) || !cpu_present(cpu))
 317                return -EINVAL;
 318
 319        cpu_hotplug_begin();
 320        ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
 321                                                        -1, &nr_calls);
 322        if (ret == NOTIFY_BAD) {
 323                nr_calls--;
 324                printk("%s: attempt to bring up CPU %u failed\n",
 325                                __func__, cpu);
 326                ret = -EINVAL;
 327                goto out_notify;
 328        }
 329
 330        /* Arch-specific enabling code. */
 331        ret = __cpu_up(cpu);
 332        if (ret != 0)
 333                goto out_notify;
 334        BUG_ON(!cpu_online(cpu));
 335
 336        set_cpu_active(cpu, true);
 337
 338        /* Now call notifier in preparation. */
 339        raw_notifier_call_chain(&cpu_chain, CPU_ONLINE | mod, hcpu);
 340
 341out_notify:
 342        if (ret != 0)
 343                __raw_notifier_call_chain(&cpu_chain,
 344                                CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
 345        cpu_hotplug_done();
 346
 347        return ret;
 348}
 349
 350int __cpuinit cpu_up(unsigned int cpu)
 351{
 352        int err = 0;
 353        if (!cpu_possible(cpu)) {
 354                printk(KERN_ERR "can't online cpu %d because it is not "
 355                        "configured as may-hotadd at boot time\n", cpu);
 356#if defined(CONFIG_IA64) || defined(CONFIG_X86_64)
 357                printk(KERN_ERR "please check additional_cpus= boot "
 358                                "parameter\n");
 359#endif
 360                return -EINVAL;
 361        }
 362
 363        cpu_maps_update_begin();
 364
 365        if (cpu_hotplug_disabled) {
 366                err = -EBUSY;
 367                goto out;
 368        }
 369
 370        err = _cpu_up(cpu, 0);
 371
 372out:
 373        cpu_maps_update_done();
 374        return err;
 375}
 376
 377#ifdef CONFIG_PM_SLEEP_SMP
 378static cpumask_var_t frozen_cpus;
 379
 380int disable_nonboot_cpus(void)
 381{
 382        int cpu, first_cpu, error;
 383
 384        error = stop_machine_create();
 385        if (error)
 386                return error;
 387        cpu_maps_update_begin();
 388        first_cpu = cpumask_first(cpu_online_mask);
 389        /* We take down all of the non-boot CPUs in one shot to avoid races
 390         * with the userspace trying to use the CPU hotplug at the same time
 391         */
 392        cpumask_clear(frozen_cpus);
 393        printk("Disabling non-boot CPUs ...\n");
 394        for_each_online_cpu(cpu) {
 395                if (cpu == first_cpu)
 396                        continue;
 397                error = _cpu_down(cpu, 1);
 398                if (!error) {
 399                        cpumask_set_cpu(cpu, frozen_cpus);
 400                        printk("CPU%d is down\n", cpu);
 401                } else {
 402                        printk(KERN_ERR "Error taking CPU%d down: %d\n",
 403                                cpu, error);
 404                        break;
 405                }
 406        }
 407        if (!error) {
 408                BUG_ON(num_online_cpus() > 1);
 409                /* Make sure the CPUs won't be enabled by someone else */
 410                cpu_hotplug_disabled = 1;
 411        } else {
 412                printk(KERN_ERR "Non-boot CPUs are not disabled\n");
 413        }
 414        cpu_maps_update_done();
 415        stop_machine_destroy();
 416        return error;
 417}
 418
 419void __ref enable_nonboot_cpus(void)
 420{
 421        int cpu, error;
 422
 423        /* Allow everyone to use the CPU hotplug again */
 424        cpu_maps_update_begin();
 425        cpu_hotplug_disabled = 0;
 426        if (cpumask_empty(frozen_cpus))
 427                goto out;
 428
 429        printk("Enabling non-boot CPUs ...\n");
 430        for_each_cpu(cpu, frozen_cpus) {
 431                error = _cpu_up(cpu, 1);
 432                if (!error) {
 433                        printk("CPU%d is up\n", cpu);
 434                        continue;
 435                }
 436                printk(KERN_WARNING "Error taking CPU%d up: %d\n", cpu, error);
 437        }
 438        cpumask_clear(frozen_cpus);
 439out:
 440        cpu_maps_update_done();
 441}
 442
 443static int alloc_frozen_cpus(void)
 444{
 445        if (!alloc_cpumask_var(&frozen_cpus, GFP_KERNEL|__GFP_ZERO))
 446                return -ENOMEM;
 447        return 0;
 448}
 449core_initcall(alloc_frozen_cpus);
 450#endif /* CONFIG_PM_SLEEP_SMP */
 451
 452/**
 453 * notify_cpu_starting(cpu) - call the CPU_STARTING notifiers
 454 * @cpu: cpu that just started
 455 *
 456 * This function calls the cpu_chain notifiers with CPU_STARTING.
 457 * It must be called by the arch code on the new cpu, before the new cpu
 458 * enables interrupts and before the "boot" cpu returns from __cpu_up().
 459 */
 460void __cpuinit notify_cpu_starting(unsigned int cpu)
 461{
 462        unsigned long val = CPU_STARTING;
 463
 464#ifdef CONFIG_PM_SLEEP_SMP
 465        if (frozen_cpus != NULL && cpumask_test_cpu(cpu, frozen_cpus))
 466                val = CPU_STARTING_FROZEN;
 467#endif /* CONFIG_PM_SLEEP_SMP */
 468        raw_notifier_call_chain(&cpu_chain, val, (void *)(long)cpu);
 469}
 470
 471#endif /* CONFIG_SMP */
 472
 473/*
 474 * cpu_bit_bitmap[] is a special, "compressed" data structure that
 475 * represents all NR_CPUS bits binary values of 1<<nr.
 476 *
 477 * It is used by cpumask_of() to get a constant address to a CPU
 478 * mask value that has a single bit set only.
 479 */
 480
 481/* cpu_bit_bitmap[0] is empty - so we can back into it */
 482#define MASK_DECLARE_1(x)       [x+1][0] = 1UL << (x)
 483#define MASK_DECLARE_2(x)       MASK_DECLARE_1(x), MASK_DECLARE_1(x+1)
 484#define MASK_DECLARE_4(x)       MASK_DECLARE_2(x), MASK_DECLARE_2(x+2)
 485#define MASK_DECLARE_8(x)       MASK_DECLARE_4(x), MASK_DECLARE_4(x+4)
 486
 487const unsigned long cpu_bit_bitmap[BITS_PER_LONG+1][BITS_TO_LONGS(NR_CPUS)] = {
 488
 489        MASK_DECLARE_8(0),      MASK_DECLARE_8(8),
 490        MASK_DECLARE_8(16),     MASK_DECLARE_8(24),
 491#if BITS_PER_LONG > 32
 492        MASK_DECLARE_8(32),     MASK_DECLARE_8(40),
 493        MASK_DECLARE_8(48),     MASK_DECLARE_8(56),
 494#endif
 495};
 496EXPORT_SYMBOL_GPL(cpu_bit_bitmap);
 497
 498const DECLARE_BITMAP(cpu_all_bits, NR_CPUS) = CPU_BITS_ALL;
 499EXPORT_SYMBOL(cpu_all_bits);
 500
 501#ifdef CONFIG_INIT_ALL_POSSIBLE
 502static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly
 503        = CPU_BITS_ALL;
 504#else
 505static DECLARE_BITMAP(cpu_possible_bits, CONFIG_NR_CPUS) __read_mostly;
 506#endif
 507const struct cpumask *const cpu_possible_mask = to_cpumask(cpu_possible_bits);
 508EXPORT_SYMBOL(cpu_possible_mask);
 509
 510static DECLARE_BITMAP(cpu_online_bits, CONFIG_NR_CPUS) __read_mostly;
 511const struct cpumask *const cpu_online_mask = to_cpumask(cpu_online_bits);
 512EXPORT_SYMBOL(cpu_online_mask);
 513
 514static DECLARE_BITMAP(cpu_present_bits, CONFIG_NR_CPUS) __read_mostly;
 515const struct cpumask *const cpu_present_mask = to_cpumask(cpu_present_bits);
 516EXPORT_SYMBOL(cpu_present_mask);
 517
 518static DECLARE_BITMAP(cpu_active_bits, CONFIG_NR_CPUS) __read_mostly;
 519const struct cpumask *const cpu_active_mask = to_cpumask(cpu_active_bits);
 520EXPORT_SYMBOL(cpu_active_mask);
 521
 522void set_cpu_possible(unsigned int cpu, bool possible)
 523{
 524        if (possible)
 525                cpumask_set_cpu(cpu, to_cpumask(cpu_possible_bits));
 526        else
 527                cpumask_clear_cpu(cpu, to_cpumask(cpu_possible_bits));
 528}
 529
 530void set_cpu_present(unsigned int cpu, bool present)
 531{
 532        if (present)
 533                cpumask_set_cpu(cpu, to_cpumask(cpu_present_bits));
 534        else
 535                cpumask_clear_cpu(cpu, to_cpumask(cpu_present_bits));
 536}
 537
 538void set_cpu_online(unsigned int cpu, bool online)
 539{
 540        if (online)
 541                cpumask_set_cpu(cpu, to_cpumask(cpu_online_bits));
 542        else
 543                cpumask_clear_cpu(cpu, to_cpumask(cpu_online_bits));
 544}
 545
 546void set_cpu_active(unsigned int cpu, bool active)
 547{
 548        if (active)
 549                cpumask_set_cpu(cpu, to_cpumask(cpu_active_bits));
 550        else
 551                cpumask_clear_cpu(cpu, to_cpumask(cpu_active_bits));
 552}
 553
 554void init_cpu_present(const struct cpumask *src)
 555{
 556        cpumask_copy(to_cpumask(cpu_present_bits), src);
 557}
 558
 559void init_cpu_possible(const struct cpumask *src)
 560{
 561        cpumask_copy(to_cpumask(cpu_possible_bits), src);
 562}
 563
 564void init_cpu_online(const struct cpumask *src)
 565{
 566        cpumask_copy(to_cpumask(cpu_online_bits), src);
 567}
 568