kernel/stop_machine.c

   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/export.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  */
  28 struct 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 */
  36 struct cpu_stopper {
  37         spinlock_t              lock;
  38         bool                    enabled;        /* is this stopper enabled? */
  39         struct list_head        works;          /* list of pending works */
  40 };
  41
  42 static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
  43 static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task);
  44 static bool stop_machine_initialized = false;
  45
  46 static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
  47 {
  48         memset(done, 0, sizeof(*done));
  49         atomic_set(&done->nr_todo, nr_todo);
  50         init_completion(&done->completion);
  51 }
  52
  53 /* signal completion unless @done is NULL */
  54 static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
  55 {
  56         if (done) {
  57                 if (executed)
  58                         done->executed = true;
  59                 if (atomic_dec_and_test(&done->nr_todo))
  60                         complete(&done->completion);
  61         }
  62 }
  63
  64 /* queue @work to @stopper.  if offline, @work is completed immediately */
  65 static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
  66 {
  67         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
  68         struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
  69
  70         unsigned long flags;
  71
  72         spin_lock_irqsave(&stopper->lock, flags);
  73
  74         if (stopper->enabled) {
  75                 list_add_tail(&work->list, &stopper->works);
  76                 wake_up_process(p);
  77         } else
  78                 cpu_stop_signal_done(work->done, false);
  79
  80         spin_unlock_irqrestore(&stopper->lock, flags);
  81 }
  82
  83 /**
  84  * stop_one_cpu - stop a cpu
  85  * @cpu: cpu to stop
  86  * @fn: function to execute
  87  * @arg: argument to @fn
  88  *
  89  * Execute @fn(@arg) on @cpu.  @fn is run in a process context with
  90  * the highest priority preempting any task on the cpu and
  91  * monopolizing it.  This function returns after the execution is
  92  * complete.
  93  *
  94  * This function doesn't guarantee @cpu stays online till @fn
  95  * completes.  If @cpu goes down in the middle, execution may happen
  96  * partially or fully on different cpus.  @fn should either be ready
  97  * for that or the caller should ensure that @cpu stays online until
  98  * this function completes.
  99  *
 100  * CONTEXT:
 101  * Might sleep.
 102  *
 103  * RETURNS:
 104  * -ENOENT if @fn(@arg) was not executed because @cpu was offline;
 105  * otherwise, the return value of @fn.
 106  */
 107 int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
 108 {
 109         struct cpu_stop_done done;
 110         struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
 111
 112         cpu_stop_init_done(&done, 1);
 113         cpu_stop_queue_work(cpu, &work);
 114         wait_for_completion(&done.completion);
 115         return done.executed ? done.ret : -ENOENT;
 116 }
 117
 118 /**
 119  * stop_one_cpu_nowait - stop a cpu but don't wait for completion
 120  * @cpu: cpu to stop
 121  * @fn: function to execute
 122  * @arg: argument to @fn
 123  *
 124  * Similar to stop_one_cpu() but doesn't wait for completion.  The
 125  * caller is responsible for ensuring @work_buf is currently unused
 126  * and will remain untouched until stopper starts executing @fn.
 127  *
 128  * CONTEXT:
 129  * Don't care.
 130  */
 131 void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
 132                         struct cpu_stop_work *work_buf)
 133 {
 134         *work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
 135         cpu_stop_queue_work(cpu, work_buf);
 136 }
 137
 138 /* static data for stop_cpus */
 139 static DEFINE_MUTEX(stop_cpus_mutex);
 140 static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
 141
 142 static void queue_stop_cpus_work(const struct cpumask *cpumask,
 143                                  cpu_stop_fn_t fn, void *arg,
 144                                  struct cpu_stop_done *done)
 145 {
 146         struct cpu_stop_work *work;
 147         unsigned int cpu;
 148
 149         /* initialize works and done */
 150         for_each_cpu(cpu, cpumask) {
 151                 work = &per_cpu(stop_cpus_work, cpu);
 152                 work->fn = fn;
 153                 work->arg = arg;
 154                 work->done = done;
 155         }
 156
 157         /*
 158          * Disable preemption while queueing to avoid getting
 159          * preempted by a stopper which might wait for other stoppers
 160          * to enter @fn which can lead to deadlock.
 161          */
 162         preempt_disable();
 163         for_each_cpu(cpu, cpumask)
 164                 cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
 165         preempt_enable();
 166 }
 167
 168 static int __stop_cpus(const struct cpumask *cpumask,
 169                        cpu_stop_fn_t fn, void *arg)
 170 {
 171         struct cpu_stop_done done;
 172
 173         cpu_stop_init_done(&done, cpumask_weight(cpumask));
 174         queue_stop_cpus_work(cpumask, fn, arg, &done);
 175         wait_for_completion(&done.completion);
 176         return done.executed ? done.ret : -ENOENT;
 177 }
 178
 179 /**
 180  * stop_cpus - stop multiple cpus
 181  * @cpumask: cpus to stop
 182  * @fn: function to execute
 183  * @arg: argument to @fn
 184  *
 185  * Execute @fn(@arg) on online cpus in @cpumask.  On each target cpu,
 186  * @fn is run in a process context with the highest priority
 187  * preempting any task on the cpu and monopolizing it.  This function
 188  * returns after all executions are complete.
 189  *
 190  * This function doesn't guarantee the cpus in @cpumask stay online
 191  * till @fn completes.  If some cpus go down in the middle, execution
 192  * on the cpu may happen partially or fully on different cpus.  @fn
 193  * should either be ready for that or the caller should ensure that
 194  * the cpus stay online until this function completes.
 195  *
 196  * All stop_cpus() calls are serialized making it safe for @fn to wait
 197  * for all cpus to start executing it.
 198  *
 199  * CONTEXT:
 200  * Might sleep.
 201  *
 202  * RETURNS:
 203  * -ENOENT if @fn(@arg) was not executed at all because all cpus in
 204  * @cpumask were offline; otherwise, 0 if all executions of @fn
 205  * returned 0, any non zero return value if any returned non zero.
 206  */
 207 int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 208 {
 209         int ret;
 210
 211         /* static works are used, process one request at a time */
 212         mutex_lock(&stop_cpus_mutex);
 213         ret = __stop_cpus(cpumask, fn, arg);
 214         mutex_unlock(&stop_cpus_mutex);
 215         return ret;
 216 }
 217
 218 /**
 219  * try_stop_cpus - try to stop multiple cpus
 220  * @cpumask: cpus to stop
 221  * @fn: function to execute
 222  * @arg: argument to @fn
 223  *
 224  * Identical to stop_cpus() except that it fails with -EAGAIN if
 225  * someone else is already using the facility.
 226  *
 227  * CONTEXT:
 228  * Might sleep.
 229  *
 230  * RETURNS:
 231  * -EAGAIN if someone else is already stopping cpus, -ENOENT if
 232  * @fn(@arg) was not executed at all because all cpus in @cpumask were
 233  * offline; otherwise, 0 if all executions of @fn returned 0, any non
 234  * zero return value if any returned non zero.
 235  */
 236 int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
 237 {
 238         int ret;
 239
 240         /* static works are used, process one request at a time */
 241         if (!mutex_trylock(&stop_cpus_mutex))
 242                 return -EAGAIN;
 243         ret = __stop_cpus(cpumask, fn, arg);
 244         mutex_unlock(&stop_cpus_mutex);
 245         return ret;
 246 }
 247
 248 static int cpu_stopper_thread(void *data)
 249 {
 250         struct cpu_stopper *stopper = data;
 251         struct cpu_stop_work *work;
 252         int ret;
 253
 254 repeat:
 255         set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 256
 257         if (kthread_should_stop()) {
 258                 __set_current_state(TASK_RUNNING);
 259                 return 0;
 260         }
 261
 262         work = NULL;
 263         spin_lock_irq(&stopper->lock);
 264         if (!list_empty(&stopper->works)) {
 265                 work = list_first_entry(&stopper->works,
 266                                         struct cpu_stop_work, list);
 267                 list_del_init(&work->list);
 268         }
 269         spin_unlock_irq(&stopper->lock);
 270
 271         if (work) {
 272                 cpu_stop_fn_t fn = work->fn;
 273                 void *arg = work->arg;
 274                 struct cpu_stop_done *done = work->done;
 275                 char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
 276
 277                 __set_current_state(TASK_RUNNING);
 278
 279                 /* cpu stop callbacks are not allowed to sleep */
 280                 preempt_disable();
 281
 282                 ret = fn(arg);
 283                 if (ret)
 284                         done->ret = ret;
 285
 286                 /* restore preemption and check it's still balanced */
 287                 preempt_enable();
 288                 WARN_ONCE(preempt_count(),
 289                           "cpu_stop: %s(%p) leaked preempt count\n",
 290                           kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
 291                                           ksym_buf), arg);
 292
 293                 cpu_stop_signal_done(done, true);
 294         } else
 295                 schedule();
 296
 297         goto repeat;
 298 }
 299
 300 extern void sched_set_stop_task(int cpu, struct task_struct *stop);
 301
 302 /* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
 303 static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
 304                                            unsigned long action, void *hcpu)
 305 {
 306         unsigned int cpu = (unsigned long)hcpu;
 307         struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 308         struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
 309
 310         switch (action & ~CPU_TASKS_FROZEN) {
 311         case CPU_UP_PREPARE:
 312                 BUG_ON(p || stopper->enabled || !list_empty(&stopper->works));
 313                 p = kthread_create_on_node(cpu_stopper_thread,
 314                                            stopper,
 315                                            cpu_to_node(cpu),
 316                                            "migration/%d", cpu);
 317                 if (IS_ERR(p))
 318                         return notifier_from_errno(PTR_ERR(p));
 319                 get_task_struct(p);
 320                 kthread_bind(p, cpu);
 321                 sched_set_stop_task(cpu, p);
 322                 per_cpu(cpu_stopper_task, cpu) = p;
 323                 break;
 324
 325         case CPU_ONLINE:
 326                 /* strictly unnecessary, as first user will wake it */
 327                 wake_up_process(p);
 328                 /* mark enabled */
 329                 spin_lock_irq(&stopper->lock);
 330                 stopper->enabled = true;
 331                 spin_unlock_irq(&stopper->lock);
 332                 break;
 333
 334 #ifdef CONFIG_HOTPLUG_CPU
 335         case CPU_UP_CANCELED:
 336         case CPU_POST_DEAD:
 337         {
 338                 struct cpu_stop_work *work;
 339
 340                 sched_set_stop_task(cpu, NULL);
 341                 /* kill the stopper */
 342                 kthread_stop(p);
 343                 /* drain remaining works */
 344                 spin_lock_irq(&stopper->lock);
 345                 list_for_each_entry(work, &stopper->works, list)
 346                         cpu_stop_signal_done(work->done, false);
 347                 stopper->enabled = false;
 348                 spin_unlock_irq(&stopper->lock);
 349                 /* release the stopper */
 350                 put_task_struct(p);
 351                 per_cpu(cpu_stopper_task, cpu) = NULL;
 352                 break;
 353         }
 354 #endif
 355         }
 356
 357         return NOTIFY_OK;
 358 }
 359
 360 /*
 361  * Give it a higher priority so that cpu stopper is available to other
 362  * cpu notifiers.  It currently shares the same priority as sched
 363  * migration_notifier.
 364  */
 365 static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
 366         .notifier_call  = cpu_stop_cpu_callback,
 367         .priority       = 10,
 368 };
 369
 370 static int __init cpu_stop_init(void)
 371 {
 372         void *bcpu = (void *)(long)smp_processor_id();
 373         unsigned int cpu;
 374         int err;
 375
 376         for_each_possible_cpu(cpu) {
 377                 struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
 378
 379                 spin_lock_init(&stopper->lock);
 380                 INIT_LIST_HEAD(&stopper->works);
 381         }
 382
 383         /* start one for the boot cpu */
 384         err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
 385                                     bcpu);
 386         BUG_ON(err != NOTIFY_OK);
 387         cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
 388         register_cpu_notifier(&cpu_stop_cpu_notifier);
 389
 390         stop_machine_initialized = true;
 391
 392         return 0;
 393 }
 394 early_initcall(cpu_stop_init);
 395
 396 #ifdef CONFIG_STOP_MACHINE
 397
 398 /* This controls the threads on each CPU. */
 399 enum stopmachine_state {
 400         /* Dummy starting state for thread. */
 401         STOPMACHINE_NONE,
 402         /* Awaiting everyone to be scheduled. */
 403         STOPMACHINE_PREPARE,
 404         /* Disable interrupts. */
 405         STOPMACHINE_DISABLE_IRQ,
 406         /* Run the function */
 407         STOPMACHINE_RUN,
 408         /* Exit */
 409         STOPMACHINE_EXIT,
 410 };
 411
 412 struct stop_machine_data {
 413         int                     (*fn)(void *);
 414         void                    *data;
 415         /* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
 416         unsigned int            num_threads;
 417         const struct cpumask    *active_cpus;
 418
 419         enum stopmachine_state  state;
 420         atomic_t                thread_ack;
 421 };
 422
 423 static void set_state(struct stop_machine_data *smdata,
 424                       enum stopmachine_state newstate)
 425 {
 426         /* Reset ack counter. */
 427         atomic_set(&smdata->thread_ack, smdata->num_threads);
 428         smp_wmb();
 429         smdata->state = newstate;
 430 }
 431
 432 /* Last one to ack a state moves to the next state. */
 433 static void ack_state(struct stop_machine_data *smdata)
 434 {
 435         if (atomic_dec_and_test(&smdata->thread_ack))
 436                 set_state(smdata, smdata->state + 1);
 437 }
 438
 439 /* This is the cpu_stop function which stops the CPU. */
 440 static int stop_machine_cpu_stop(void *data)
 441 {
 442         struct stop_machine_data *smdata = data;
 443         enum stopmachine_state curstate = STOPMACHINE_NONE;
 444         int cpu = smp_processor_id(), err = 0;
 445         unsigned long flags;
 446         bool is_active;
 447
 448         /*
 449          * When called from stop_machine_from_inactive_cpu(), irq might
 450          * already be disabled.  Save the state and restore it on exit.
 451          */
 452         local_save_flags(flags);
 453
 454         if (!smdata->active_cpus)
 455                 is_active = cpu == cpumask_first(cpu_online_mask);
 456         else
 457                 is_active = cpumask_test_cpu(cpu, smdata->active_cpus);
 458
 459         /* Simple state machine */
 460         do {
 461                 /* Chill out and ensure we re-read stopmachine_state. */
 462                 cpu_relax();
 463                 if (smdata->state != curstate) {
 464                         curstate = smdata->state;
 465                         switch (curstate) {
 466                         case STOPMACHINE_DISABLE_IRQ:
 467                                 local_irq_disable();
 468                                 hard_irq_disable();
 469                                 break;
 470                         case STOPMACHINE_RUN:
 471                                 if (is_active)
 472                                         err = smdata->fn(smdata->data);
 473                                 break;
 474                         default:
 475                                 break;
 476                         }
 477                         ack_state(smdata);
 478                 }
 479         } while (curstate != STOPMACHINE_EXIT);
 480
 481         local_irq_restore(flags);
 482         return err;
 483 }
 484
 485 int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 486 {
 487         struct stop_machine_data smdata = { .fn = fn, .data = data,
 488                                             .num_threads = num_online_cpus(),
 489                                             .active_cpus = cpus };
 490
 491         if (!stop_machine_initialized) {
 492                 /*
 493                  * Handle the case where stop_machine() is called
 494                  * early in boot before stop_machine() has been
 495                  * initialized.
 496                  */
 497                 unsigned long flags;
 498                 int ret;
 499
 500                 WARN_ON_ONCE(smdata.num_threads != 1);
 501
 502                 local_irq_save(flags);
 503                 hard_irq_disable();
 504                 ret = (*fn)(data);
 505                 local_irq_restore(flags);
 506
 507                 return ret;
 508         }
 509
 510         /* Set the initial state and stop all online cpus. */
 511         set_state(&smdata, STOPMACHINE_PREPARE);
 512         return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
 513 }
 514
 515 int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
 516 {
 517         int ret;
 518
 519         /* No CPUs can come up or down during this. */
 520         get_online_cpus();
 521         ret = __stop_machine(fn, data, cpus);
 522         put_online_cpus();
 523         return ret;
 524 }
 525 EXPORT_SYMBOL_GPL(stop_machine);
 526
 527 /**
 528  * stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
 529  * @fn: the function to run
 530  * @data: the data ptr for the @fn()
 531  * @cpus: the cpus to run the @fn() on (NULL = any online cpu)
 532  *
 533  * This is identical to stop_machine() but can be called from a CPU which
 534  * is not active.  The local CPU is in the process of hotplug (so no other
 535  * CPU hotplug can start) and not marked active and doesn't have enough
 536  * context to sleep.
 537  *
 538  * This function provides stop_machine() functionality for such state by
 539  * using busy-wait for synchronization and executing @fn directly for local
 540  * CPU.
 541  *
 542  * CONTEXT:
 543  * Local CPU is inactive.  Temporarily stops all active CPUs.
 544  *
 545  * RETURNS:
 546  * 0 if all executions of @fn returned 0, any non zero return value if any
 547  * returned non zero.
 548  */
 549 int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
 550                                   const struct cpumask *cpus)
 551 {
 552         struct stop_machine_data smdata = { .fn = fn, .data = data,
 553                                             .active_cpus = cpus };
 554         struct cpu_stop_done done;
 555         int ret;
 556
 557         /* Local CPU must be inactive and CPU hotplug in progress. */
 558         BUG_ON(cpu_active(raw_smp_processor_id()));
 559         smdata.num_threads = num_active_cpus() + 1;     /* +1 for local */
 560
 561         /* No proper task established and can't sleep - busy wait for lock. */
 562         while (!mutex_trylock(&stop_cpus_mutex))
 563                 cpu_relax();
 564
 565         /* Schedule work on other CPUs and execute directly for local CPU */
 566         set_state(&smdata, STOPMACHINE_PREPARE);
 567         cpu_stop_init_done(&done, num_active_cpus());
 568         queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
 569                              &done);
 570         ret = stop_machine_cpu_stop(&smdata);
 571
 572         /* Busy wait for completion. */
 573         while (!completion_done(&done.completion))
 574                 cpu_relax();
 575
 576         mutex_unlock(&stop_cpus_mutex);
 577         return ret ?: done.ret;
 578 }
 579
 580 #endif  /* CONFIG_STOP_MACHINE */