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 <asm/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
 139int __stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 140{
 141        struct cpu_stop_work *work;
 142        struct cpu_stop_done done;
 143        unsigned int cpu;
 144
 145        /* initialize works and done */
 146        for_each_cpu(cpu, cpumask) {
 147                work = &per_cpu(stop_cpus_work, cpu);
 148                work->fn = fn;
 149                work->arg = arg;
 150                work->done = &done;
 151        }
 152        cpu_stop_init_done(&done, cpumask_weight(cpumask));
 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        wait_for_completion(&done.completion);
 166        return done.executed ? done.ret : -ENOENT;
 167}
 168
 169/**
 170 * stop_cpus - stop multiple cpus
 171 * @cpumask: cpus to stop
 172 * @fn: function to execute
 173 * @arg: argument to @fn
 174 *
 175 * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
 176 * @fn is run in a process context with the highest priority
 177 * preempting any task on the cpu and monopolizing it.  This function
 178 * returns after all executions are complete.
 179 *
 180 * This function doesn't guarantee the cpus in @cpumask stay online
 181 * till @fn completes.  If some cpus go down in the middle, execution
 182 * on the cpu may happen partially or fully on different cpus.  @fn
 183 * should either be ready for that or the caller should ensure that
 184 * the cpus stay online until this function completes.
 185 *
 186 * All stop_cpus() calls are serialized making it safe for @fn to wait
 187 * for all cpus to start executing it.
 188 *
 189 * CONTEXT:
 190 * Might sleep.
 191 *
 192 * RETURNS:
 193 * -ENOENT if @fn(@arg) was not executed at all because all cpus in
 194 * @cpumask were offline; otherwise, 0 if all executions of @fn
 195 * returned 0, any non zero return value if any returned non zero.
 196 */
 197int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 198{
 199        int ret;
 200
 201        /* static works are used, process one request at a time */
 202        mutex_lock(&stop_cpus_mutex);
 203        ret = __stop_cpus(cpumask, fn, arg);
 204        mutex_unlock(&stop_cpus_mutex);
 205        return ret;
 206}
 207
 208/**
 209 * try_stop_cpus - try to stop multiple cpus
 210 * @cpumask: cpus to stop
 211 * @fn: function to execute
 212 * @arg: argument to @fn
 213 *
 214 * Identical to stop_cpus() except that it fails with -EAGAIN if
 215 * someone else is already using the facility.
 216 *
 217 * CONTEXT:
 218 * Might sleep.
 219 *
 220 * RETURNS:
 221 * -EAGAIN if someone else is already stopping cpus, -ENOENT if
 222 * @fn(@arg) was not executed at all because all cpus in @cpumask were
 223 * offline; otherwise, 0 if all executions of @fn returned 0, any non
 224 * zero return value if any returned non zero.
 225 */
 226int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 227{
 228        int ret;
 229
 230        /* static works are used, process one request at a time */
 231        if (!mutex_trylock(&stop_cpus_mutex))
 232                return -EAGAIN;
 233        ret = __stop_cpus(cpumask, fn, arg);
 234        mutex_unlock(&stop_cpus_mutex);
 235        return ret;
 236}
 237
 238static int cpu_stopper_thread(void *data)
 239{
 240        struct cpu_stopper *stopper = data;
 241        struct cpu_stop_work *work;
 242        int ret;
 243
 244repeat:
 245        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 246
 247        if (kthread_should_stop()) {
 248                __set_current_state(TASK_RUNNING);
 249                return 0;
 250        }
 251
 252        work = NULL;
 253        spin_lock_irq(&stopper->lock);
 254        if (!list_empty(&stopper->works)) {
 255                work = list_first_entry(&stopper->works,
 256                                        struct cpu_stop_work, list);
 257                list_del_init(&work->list);
 258        }
 259        spin_unlock_irq(&stopper->lock);
 260
 261        if (work) {
 262                cpu_stop_fn_t fn = work->fn;
 263                void *arg = work->arg;
 264                struct cpu_stop_done *done = work->done;
 265                char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
 266
 267                __set_current_state(TASK_RUNNING);
 268
 269                /* cpu stop callbacks are not allowed to sleep */
 270                preempt_disable();
 271
 272                ret = fn(arg);
 273                if (ret)
 274                        done->ret = ret;
 275
 276                /* restore preemption and check it's still balanced */
 277                preempt_enable();
 278                WARN_ONCE(preempt_count(),
 279                          "cpu_stop: %s(%p) leaked preempt count\n",
 280                          kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
 281                                          ksym_buf), arg);
 282
 283                cpu_stop_signal_done(done, true);
 284        } else
 285                schedule();
 286
 287        goto repeat;
 288}
 289
 290extern void sched_set_stop_task(int cpu, struct task_struct *stop);
 291
 292/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
 293static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
 294                                           unsigned long action, void *hcpu)
 295{
 296        unsigned int cpu = (unsigned long)hcpu;
 297        struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 298        struct task_struct *p;
 299
 300        switch (action & ~CPU_TASKS_FROZEN) {
 301        case CPU_UP_PREPARE:
 302                BUG_ON(stopper->thread || stopper->enabled ||
 303                       !list_empty(&stopper->works));
 304                p = kthread_create(cpu_stopper_thread, stopper, "migration/%d",
 305                                   cpu);
 306                if (IS_ERR(p))
 307                        return notifier_from_errno(PTR_ERR(p));
 308                get_task_struct(p);
 309                kthread_bind(p, cpu);
 310                sched_set_stop_task(cpu, p);
 311                stopper->thread = p;
 312                break;
 313
 314        case CPU_ONLINE:
 315                /* strictly unnecessary, as first user will wake it */
 316                wake_up_process(stopper->thread);
 317                /* mark enabled */
 318                spin_lock_irq(&stopper->lock);
 319                stopper->enabled = true;
 320                spin_unlock_irq(&stopper->lock);
 321                break;
 322
 323#ifdef CONFIG_HOTPLUG_CPU
 324        case CPU_UP_CANCELED:
 325        case CPU_POST_DEAD:
 326        {
 327                struct cpu_stop_work *work;
 328
 329                sched_set_stop_task(cpu, NULL);
 330                /* kill the stopper */
 331                kthread_stop(stopper->thread);
 332                /* drain remaining works */
 333                spin_lock_irq(&stopper->lock);
 334                list_for_each_entry(work, &stopper->works, list)
 335                        cpu_stop_signal_done(work->done, false);
 336                stopper->enabled = false;
 337                spin_unlock_irq(&stopper->lock);
 338                /* release the stopper */
 339                put_task_struct(stopper->thread);
 340                stopper->thread = NULL;
 341                break;
 342        }
 343#endif
 344        }
 345
 346        return NOTIFY_OK;
 347}
 348
 349/*
 350 * Give it a higher priority so that cpu stopper is available to other
 351 * cpu notifiers.  It currently shares the same priority as sched
 352 * migration_notifier.
 353 */
 354static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
 355        .notifier_call  = cpu_stop_cpu_callback,
 356        .priority       = 10,
 357};
 358
 359static int __init cpu_stop_init(void)
 360{
 361        void *bcpu = (void *)(long)smp_processor_id();
 362        unsigned int cpu;
 363        int err;
 364
 365        for_each_possible_cpu(cpu) {
 366                struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 367
 368                spin_lock_init(&stopper->lock);
 369                INIT_LIST_HEAD(&stopper->works);
 370        }
 371
 372        /* start one for the boot cpu */
 373        err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
 374                                    bcpu);
 375        BUG_ON(err != NOTIFY_OK);
 376        cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
 377        register_cpu_notifier(&cpu_stop_cpu_notifier);
 378
 379        return 0;
 380}
 381early_initcall(cpu_stop_init);
 382
 383#ifdef CONFIG_STOP_MACHINE
 384
 385/* This controls the threads on each CPU. */
 386enum stopmachine_state {
 387        /* Dummy starting state for thread. */
 388        STOPMACHINE_NONE,
 389        /* Awaiting everyone to be scheduled. */
 390        STOPMACHINE_PREPARE,
 391        /* Disable interrupts. */
 392        STOPMACHINE_DISABLE_IRQ,
 393        /* Run the function */
 394        STOPMACHINE_RUN,
 395        /* Exit */
 396        STOPMACHINE_EXIT,
 397};
 398
 399struct stop_machine_data {
 400        int                     (*fn)(void *);
 401        void                    *data;
 402        /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
 403        unsigned int            num_threads;
 404        const struct cpumask    *active_cpus;
 405
 406        enum stopmachine_state  state;
 407        atomic_t                thread_ack;
 408};
 409
 410static void set_state(struct stop_machine_data *smdata,
 411                      enum stopmachine_state newstate)
 412{
 413        /* Reset ack counter. */
 414        atomic_set(&smdata->thread_ack, smdata->num_threads);
 415        smp_wmb();
 416        smdata->state = newstate;
 417}
 418
 419/* Last one to ack a state moves to the next state. */
 420static void ack_state(struct stop_machine_data *smdata)
 421{
 422        if (atomic_dec_and_test(&smdata->thread_ack))
 423                set_state(smdata, smdata->state + 1);
 424}
 425
 426/* This is the cpu_stop function which stops the CPU. */
 427static int stop_machine_cpu_stop(void *data)
 428{
 429        struct stop_machine_data *smdata = data;
 430        enum stopmachine_state curstate = STOPMACHINE_NONE;
 431        int cpu = smp_processor_id(), err = 0;
 432        bool is_active;
 433
 434        if (!smdata->active_cpus)
 435                is_active = cpu == cpumask_first(cpu_online_mask);
 436        else
 437                is_active = cpumask_test_cpu(cpu, smdata->active_cpus);
 438
 439        /* Simple state machine */
 440        do {
 441                /* Chill out and ensure we re-read stopmachine_state. */
 442                cpu_relax();
 443                if (smdata->state != curstate) {
 444                        curstate = smdata->state;
 445                        switch (curstate) {
 446                        case STOPMACHINE_DISABLE_IRQ:
 447                                local_irq_disable();
 448                                hard_irq_disable();
 449                                break;
 450                        case STOPMACHINE_RUN:
 451                                if (is_active)
 452                                        err = smdata->fn(smdata->data);
 453                                break;
 454                        default:
 455                                break;
 456                        }
 457                        ack_state(smdata);
 458                }
 459        } while (curstate != STOPMACHINE_EXIT);
 460
 461        local_irq_enable();
 462        return err;
 463}
 464
 465int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 466{
 467        struct stop_machine_data smdata = { .fn = fn, .data = data,
 468                                            .num_threads = num_online_cpus(),
 469                                            .active_cpus = cpus };
 470
 471        /* Set the initial state and stop all online cpus. */
 472        set_state(&smdata, STOPMACHINE_PREPARE);
 473        return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
 474}
 475
 476int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 477{
 478        int ret;
 479
 480        /* No CPUs can come up or down during this. */
 481        get_online_cpus();
 482        ret = __stop_machine(fn, data, cpus);
 483        put_online_cpus();
 484        return ret;
 485}
 486EXPORT_SYMBOL_GPL(stop_machine);
 487
 488#endif  /* CONFIG_STOP_MACHINE */
 489