linux/kernel/stop_machine.c
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   1/*
   2 * kernel/stop_machine.c
   3 *
   4 * Copyright (C) 2008, 2005     IBM Corporation.
   5 * Copyright (C) 2008, 2005     Rusty Russell rusty@rustcorp.com.au
   6 * Copyright (C) 2010           SUSE Linux Products GmbH
   7 * Copyright (C) 2010           Tejun Heo <tj@kernel.org>
   8 *
   9 * This file is released under the GPLv2 and any later version.
  10 */
  11#include <linux/completion.h>
  12#include <linux/cpu.h>
  13#include <linux/init.h>
  14#include <linux/kthread.h>
  15#include <linux/module.h>
  16#include <linux/percpu.h>
  17#include <linux/sched.h>
  18#include <linux/stop_machine.h>
  19#include <linux/interrupt.h>
  20#include <linux/kallsyms.h>
  21
  22#include <linux/atomic.h>
  23
  24/*
  25 * Structure to determine completion condition and record errors.  May
  26 * be shared by works on different cpus.
  27 */
  28struct cpu_stop_done {
  29        atomic_t                nr_todo;        /* nr left to execute */
  30        bool                    executed;       /* actually executed? */
  31        int                     ret;            /* collected return value */
  32        struct completion       completion;     /* fired if nr_todo reaches 0 */
  33};
  34
  35/* the actual stopper, one per every possible cpu, enabled on online cpus */
  36struct cpu_stopper {
  37        spinlock_t              lock;
  38        bool                    enabled;        /* is this stopper enabled? */
  39        struct list_head        works;          /* list of pending works */
  40        struct task_struct      *thread;        /* stopper thread */
  41};
  42
  43static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
  44
  45static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
  46{
  47        memset(done, 0, sizeof(*done));
  48        atomic_set(&done->nr_todo, nr_todo);
  49        init_completion(&done->completion);
  50}
  51
  52/* signal completion unless @done is NULL */
  53static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
  54{
  55        if (done) {
  56                if (executed)
  57                        done->executed = true;
  58                if (atomic_dec_and_test(&done->nr_todo))
  59                        complete(&done->completion);
  60        }
  61}
  62
  63/* queue @work to @stopper.  if offline, @work is completed immediately */
  64static void cpu_stop_queue_work(struct cpu_stopper *stopper,
  65                                struct cpu_stop_work *work)
  66{
  67        unsigned long flags;
  68
  69        spin_lock_irqsave(&stopper->lock, flags);
  70
  71        if (stopper->enabled) {
  72                list_add_tail(&work->list, &stopper->works);
  73                wake_up_process(stopper->thread);
  74        } else
  75                cpu_stop_signal_done(work->done, false);
  76
  77        spin_unlock_irqrestore(&stopper->lock, flags);
  78}
  79
  80/**
  81 * stop_one_cpu - stop a cpu
  82 * @cpu: cpu to stop
  83 * @fn: function to execute
  84 * @arg: argument to @fn
  85 *
  86 * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
  87 * the highest priority preempting any task on the cpu and
  88 * monopolizing it.  This function returns after the execution is
  89 * complete.
  90 *
  91 * This function doesn't guarantee @cpu stays online till @fn
  92 * completes.  If @cpu goes down in the middle, execution may happen
  93 * partially or fully on different cpus.  @fn should either be ready
  94 * for that or the caller should ensure that @cpu stays online until
  95 * this function completes.
  96 *
  97 * CONTEXT:
  98 * Might sleep.
  99 *
 100 * RETURNS:
 101 * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
 102 * otherwise, the return value of @fn.
 103 */
 104int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
 105{
 106        struct cpu_stop_done done;
 107        struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
 108
 109        cpu_stop_init_done(&done, 1);
 110        cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), &work);
 111        wait_for_completion(&done.completion);
 112        return done.executed ? done.ret : -ENOENT;
 113}
 114
 115/**
 116 * stop_one_cpu_nowait - stop a cpu but don't wait for completion
 117 * @cpu: cpu to stop
 118 * @fn: function to execute
 119 * @arg: argument to @fn
 120 *
 121 * Similar to stop_one_cpu() but doesn't wait for completion.  The
 122 * caller is responsible for ensuring @work_buf is currently unused
 123 * and will remain untouched until stopper starts executing @fn.
 124 *
 125 * CONTEXT:
 126 * Don't care.
 127 */
 128void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
 129                        struct cpu_stop_work *work_buf)
 130{
 131        *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
 132        cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu), work_buf);
 133}
 134
 135/* static data for stop_cpus */
 136static DEFINE_MUTEX(stop_cpus_mutex);
 137static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
 138
 139static void queue_stop_cpus_work(const struct cpumask *cpumask,
 140                                 cpu_stop_fn_t fn, void *arg,
 141                                 struct cpu_stop_done *done)
 142{
 143        struct cpu_stop_work *work;
 144        unsigned int cpu;
 145
 146        /* initialize works and done */
 147        for_each_cpu(cpu, cpumask) {
 148                work = &per_cpu(stop_cpus_work, cpu);
 149                work->fn = fn;
 150                work->arg = arg;
 151                work->done = done;
 152        }
 153
 154        /*
 155         * Disable preemption while queueing to avoid getting
 156         * preempted by a stopper which might wait for other stoppers
 157         * to enter @fn which can lead to deadlock.
 158         */
 159        preempt_disable();
 160        for_each_cpu(cpu, cpumask)
 161                cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
 162                                    &per_cpu(stop_cpus_work, cpu));
 163        preempt_enable();
 164}
 165
 166static int __stop_cpus(const struct cpumask *cpumask,
 167                       cpu_stop_fn_t fn, void *arg)
 168{
 169        struct cpu_stop_done done;
 170
 171        cpu_stop_init_done(&done, cpumask_weight(cpumask));
 172        queue_stop_cpus_work(cpumask, fn, arg, &done);
 173        wait_for_completion(&done.completion);
 174        return done.executed ? done.ret : -ENOENT;
 175}
 176
 177/**
 178 * stop_cpus - stop multiple cpus
 179 * @cpumask: cpus to stop
 180 * @fn: function to execute
 181 * @arg: argument to @fn
 182 *
 183 * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
 184 * @fn is run in a process context with the highest priority
 185 * preempting any task on the cpu and monopolizing it.  This function
 186 * returns after all executions are complete.
 187 *
 188 * This function doesn't guarantee the cpus in @cpumask stay online
 189 * till @fn completes.  If some cpus go down in the middle, execution
 190 * on the cpu may happen partially or fully on different cpus.  @fn
 191 * should either be ready for that or the caller should ensure that
 192 * the cpus stay online until this function completes.
 193 *
 194 * All stop_cpus() calls are serialized making it safe for @fn to wait
 195 * for all cpus to start executing it.
 196 *
 197 * CONTEXT:
 198 * Might sleep.
 199 *
 200 * RETURNS:
 201 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
 202 * @cpumask were offline; otherwise, 0 if all executions of @fn
 203 * returned 0, any non zero return value if any returned non zero.
 204 */
 205int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 206{
 207        int ret;
 208
 209        /* static works are used, process one request at a time */
 210        mutex_lock(&stop_cpus_mutex);
 211        ret = __stop_cpus(cpumask, fn, arg);
 212        mutex_unlock(&stop_cpus_mutex);
 213        return ret;
 214}
 215
 216/**
 217 * try_stop_cpus - try to stop multiple cpus
 218 * @cpumask: cpus to stop
 219 * @fn: function to execute
 220 * @arg: argument to @fn
 221 *
 222 * Identical to stop_cpus() except that it fails with -EAGAIN if
 223 * someone else is already using the facility.
 224 *
 225 * CONTEXT:
 226 * Might sleep.
 227 *
 228 * RETURNS:
 229 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
 230 * @fn(@arg) was not executed at all because all cpus in @cpumask were
 231 * offline; otherwise, 0 if all executions of @fn returned 0, any non
 232 * zero return value if any returned non zero.
 233 */
 234int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 235{
 236        int ret;
 237
 238        /* static works are used, process one request at a time */
 239        if (!mutex_trylock(&stop_cpus_mutex))
 240                return -EAGAIN;
 241        ret = __stop_cpus(cpumask, fn, arg);
 242        mutex_unlock(&stop_cpus_mutex);
 243        return ret;
 244}
 245
 246static int cpu_stopper_thread(void *data)
 247{
 248        struct cpu_stopper *stopper = data;
 249        struct cpu_stop_work *work;
 250        int ret;
 251
 252repeat:
 253        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 254
 255        if (kthread_should_stop()) {
 256                __set_current_state(TASK_RUNNING);
 257                return 0;
 258        }
 259
 260        work = NULL;
 261        spin_lock_irq(&stopper->lock);
 262        if (!list_empty(&stopper->works)) {
 263                work = list_first_entry(&stopper->works,
 264                                        struct cpu_stop_work, list);
 265                list_del_init(&work->list);
 266        }
 267        spin_unlock_irq(&stopper->lock);
 268
 269        if (work) {
 270                cpu_stop_fn_t fn = work->fn;
 271                void *arg = work->arg;
 272                struct cpu_stop_done *done = work->done;
 273                char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
 274
 275                __set_current_state(TASK_RUNNING);
 276
 277                /* cpu stop callbacks are not allowed to sleep */
 278                preempt_disable();
 279
 280                ret = fn(arg);
 281                if (ret)
 282                        done->ret = ret;
 283
 284                /* restore preemption and check it's still balanced */
 285                preempt_enable();
 286                WARN_ONCE(preempt_count(),
 287                          "cpu_stop: %s(%p) leaked preempt count\n",
 288                          kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
 289                                          ksym_buf), arg);
 290
 291                cpu_stop_signal_done(done, true);
 292        } else
 293                schedule();
 294
 295        goto repeat;
 296}
 297
 298extern void sched_set_stop_task(int cpu, struct task_struct *stop);
 299
 300/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
 301static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
 302                                           unsigned long action, void *hcpu)
 303{
 304        unsigned int cpu = (unsigned long)hcpu;
 305        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 306        struct task_struct *p;
 307
 308        switch (action & ~CPU_TASKS_FROZEN) {
 309        case CPU_UP_PREPARE:
 310                BUG_ON(stopper->thread || stopper->enabled ||
 311                       !list_empty(&stopper->works));
 312                p = kthread_create_on_node(cpu_stopper_thread,
 313                                           stopper,
 314                                           cpu_to_node(cpu),
 315                                           "migration/%d", cpu);
 316                if (IS_ERR(p))
 317                        return notifier_from_errno(PTR_ERR(p));
 318                get_task_struct(p);
 319                kthread_bind(p, cpu);
 320                sched_set_stop_task(cpu, p);
 321                stopper->thread = p;
 322                break;
 323
 324        case CPU_ONLINE:
 325                /* strictly unnecessary, as first user will wake it */
 326                wake_up_process(stopper->thread);
 327                /* mark enabled */
 328                spin_lock_irq(&stopper->lock);
 329                stopper->enabled = true;
 330                spin_unlock_irq(&stopper->lock);
 331                break;
 332
 333#ifdef CONFIG_HOTPLUG_CPU
 334        case CPU_UP_CANCELED:
 335        case CPU_POST_DEAD:
 336        {
 337                struct cpu_stop_work *work;
 338
 339                sched_set_stop_task(cpu, NULL);
 340                /* kill the stopper */
 341                kthread_stop(stopper->thread);
 342                /* drain remaining works */
 343                spin_lock_irq(&stopper->lock);
 344                list_for_each_entry(work, &stopper->works, list)
 345                        cpu_stop_signal_done(work->done, false);
 346                stopper->enabled = false;
 347                spin_unlock_irq(&stopper->lock);
 348                /* release the stopper */
 349                put_task_struct(stopper->thread);
 350                stopper->thread = NULL;
 351                break;
 352        }
 353#endif
 354        }
 355
 356        return NOTIFY_OK;
 357}
 358
 359/*
 360 * Give it a higher priority so that cpu stopper is available to other
 361 * cpu notifiers.  It currently shares the same priority as sched
 362 * migration_notifier.
 363 */
 364static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
 365        .notifier_call  = cpu_stop_cpu_callback,
 366        .priority       = 10,
 367};
 368
 369static int __init cpu_stop_init(void)
 370{
 371        void *bcpu = (void *)(long)smp_processor_id();
 372        unsigned int cpu;
 373        int err;
 374
 375        for_each_possible_cpu(cpu) {
 376                struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 377
 378                spin_lock_init(&stopper->lock);
 379                INIT_LIST_HEAD(&stopper->works);
 380        }
 381
 382        /* start one for the boot cpu */
 383        err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
 384                                    bcpu);
 385        BUG_ON(err != NOTIFY_OK);
 386        cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
 387        register_cpu_notifier(&cpu_stop_cpu_notifier);
 388
 389        return 0;
 390}
 391early_initcall(cpu_stop_init);
 392
 393#ifdef CONFIG_STOP_MACHINE
 394
 395/* This controls the threads on each CPU. */
 396enum stopmachine_state {
 397        /* Dummy starting state for thread. */
 398        STOPMACHINE_NONE,
 399        /* Awaiting everyone to be scheduled. */
 400        STOPMACHINE_PREPARE,
 401        /* Disable interrupts. */
 402        STOPMACHINE_DISABLE_IRQ,
 403        /* Run the function */
 404        STOPMACHINE_RUN,
 405        /* Exit */
 406        STOPMACHINE_EXIT,
 407};
 408
 409struct stop_machine_data {
 410        int                     (*fn)(void *);
 411        void                    *data;
 412        /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
 413        unsigned int            num_threads;
 414        const struct cpumask    *active_cpus;
 415
 416        enum stopmachine_state  state;
 417        atomic_t                thread_ack;
 418};
 419
 420static void set_state(struct stop_machine_data *smdata,
 421                      enum stopmachine_state newstate)
 422{
 423        /* Reset ack counter. */
 424        atomic_set(&smdata->thread_ack, smdata->num_threads);
 425        smp_wmb();
 426        smdata->state = newstate;
 427}
 428
 429/* Last one to ack a state moves to the next state. */
 430static void ack_state(struct stop_machine_data *smdata)
 431{
 432        if (atomic_dec_and_test(&smdata->thread_ack))
 433                set_state(smdata, smdata->state + 1);
 434}
 435
 436/* This is the cpu_stop function which stops the CPU. */
 437static int stop_machine_cpu_stop(void *data)
 438{
 439        struct stop_machine_data *smdata = data;
 440        enum stopmachine_state curstate = STOPMACHINE_NONE;
 441        int cpu = smp_processor_id(), err = 0;
 442        unsigned long flags;
 443        bool is_active;
 444
 445        /*
 446         * When called from stop_machine_from_inactive_cpu(), irq might
 447         * already be disabled.  Save the state and restore it on exit.
 448         */
 449        local_save_flags(flags);
 450
 451        if (!smdata->active_cpus)
 452                is_active = cpu == cpumask_first(cpu_online_mask);
 453        else
 454                is_active = cpumask_test_cpu(cpu, smdata->active_cpus);
 455
 456        /* Simple state machine */
 457        do {
 458                /* Chill out and ensure we re-read stopmachine_state. */
 459                cpu_relax();
 460                if (smdata->state != curstate) {
 461                        curstate = smdata->state;
 462                        switch (curstate) {
 463                        case STOPMACHINE_DISABLE_IRQ:
 464                                local_irq_disable();
 465                                hard_irq_disable();
 466                                break;
 467                        case STOPMACHINE_RUN:
 468                                if (is_active)
 469                                        err = smdata->fn(smdata->data);
 470                                break;
 471                        default:
 472                                break;
 473                        }
 474                        ack_state(smdata);
 475                }
 476        } while (curstate != STOPMACHINE_EXIT);
 477
 478        local_irq_restore(flags);
 479        return err;
 480}
 481
 482int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 483{
 484        struct stop_machine_data smdata = { .fn = fn, .data = data,
 485                                            .num_threads = num_online_cpus(),
 486                                            .active_cpus = cpus };
 487
 488        /* Set the initial state and stop all online cpus. */
 489        set_state(&smdata, STOPMACHINE_PREPARE);
 490        return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
 491}
 492
 493int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 494{
 495        int ret;
 496
 497        /* No CPUs can come up or down during this. */
 498        get_online_cpus();
 499        ret = __stop_machine(fn, data, cpus);
 500        put_online_cpus();
 501        return ret;
 502}
 503EXPORT_SYMBOL_GPL(stop_machine);
 504
 505/**
 506 * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
 507 * @fn: the function to run
 508 * @data: the data ptr for the @fn()
 509 * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
 510 *
 511 * This is identical to stop_machine() but can be called from a CPU which
 512 * is not active.  The local CPU is in the process of hotplug (so no other
 513 * CPU hotplug can start) and not marked active and doesn't have enough
 514 * context to sleep.
 515 *
 516 * This function provides stop_machine() functionality for such state by
 517 * using busy-wait for synchronization and executing @fn directly for local
 518 * CPU.
 519 *
 520 * CONTEXT:
 521 * Local CPU is inactive.  Temporarily stops all active CPUs.
 522 *
 523 * RETURNS:
 524 * 0 if all executions of @fn returned 0, any non zero return value if any
 525 * returned non zero.
 526 */
 527int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
 528                                  const struct cpumask *cpus)
 529{
 530        struct stop_machine_data smdata = { .fn = fn, .data = data,
 531                                            .active_cpus = cpus };
 532        struct cpu_stop_done done;
 533        int ret;
 534
 535        /* Local CPU must be inactive and CPU hotplug in progress. */
 536        BUG_ON(cpu_active(raw_smp_processor_id()));
 537        smdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
 538
 539        /* No proper task established and can't sleep - busy wait for lock. */
 540        while (!mutex_trylock(&stop_cpus_mutex))
 541                cpu_relax();
 542
 543        /* Schedule work on other CPUs and execute directly for local CPU */
 544        set_state(&smdata, STOPMACHINE_PREPARE);
 545        cpu_stop_init_done(&done, num_active_cpus());
 546        queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
 547                             &done);
 548        ret = stop_machine_cpu_stop(&smdata);
 549
 550        /* Busy wait for completion. */
 551        while (!completion_done(&done.completion))
 552                cpu_relax();
 553
 554        mutex_unlock(&stop_cpus_mutex);
 555        return ret ?: done.ret;
 556}
 557
 558#endif  /* CONFIG_STOP_MACHINE */
 559
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