linux/kernel/kthread.c
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   1/* Kernel thread helper functions.
   2 *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
   3 *
   4 * Creation is done via kthreadd, so that we get a clean environment
   5 * even if we're invoked from userspace (think modprobe, hotplug cpu,
   6 * etc.).
   7 */
   8#include <linux/sched.h>
   9#include <linux/kthread.h>
  10#include <linux/completion.h>
  11#include <linux/err.h>
  12#include <linux/cpuset.h>
  13#include <linux/unistd.h>
  14#include <linux/file.h>
  15#include <linux/export.h>
  16#include <linux/mutex.h>
  17#include <linux/slab.h>
  18#include <linux/freezer.h>
  19#include <linux/ptrace.h>
  20#include <linux/uaccess.h>
  21#include <trace/events/sched.h>
  22
  23static DEFINE_SPINLOCK(kthread_create_lock);
  24static LIST_HEAD(kthread_create_list);
  25struct task_struct *kthreadd_task;
  26
  27struct kthread_create_info
  28{
  29        /* Information passed to kthread() from kthreadd. */
  30        int (*threadfn)(void *data);
  31        void *data;
  32        int node;
  33
  34        /* Result passed back to kthread_create() from kthreadd. */
  35        struct task_struct *result;
  36        struct completion *done;
  37
  38        struct list_head list;
  39};
  40
  41struct kthread {
  42        unsigned long flags;
  43        unsigned int cpu;
  44        void *data;
  45        struct completion parked;
  46        struct completion exited;
  47};
  48
  49enum KTHREAD_BITS {
  50        KTHREAD_IS_PER_CPU = 0,
  51        KTHREAD_SHOULD_STOP,
  52        KTHREAD_SHOULD_PARK,
  53        KTHREAD_IS_PARKED,
  54};
  55
  56#define __to_kthread(vfork)     \
  57        container_of(vfork, struct kthread, exited)
  58
  59static inline struct kthread *to_kthread(struct task_struct *k)
  60{
  61        return __to_kthread(k->vfork_done);
  62}
  63
  64static struct kthread *to_live_kthread(struct task_struct *k)
  65{
  66        struct completion *vfork = ACCESS_ONCE(k->vfork_done);
  67        if (likely(vfork))
  68                return __to_kthread(vfork);
  69        return NULL;
  70}
  71
  72/**
  73 * kthread_should_stop - should this kthread return now?
  74 *
  75 * When someone calls kthread_stop() on your kthread, it will be woken
  76 * and this will return true.  You should then return, and your return
  77 * value will be passed through to kthread_stop().
  78 */
  79bool kthread_should_stop(void)
  80{
  81        return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
  82}
  83EXPORT_SYMBOL(kthread_should_stop);
  84
  85/**
  86 * kthread_should_park - should this kthread park now?
  87 *
  88 * When someone calls kthread_park() on your kthread, it will be woken
  89 * and this will return true.  You should then do the necessary
  90 * cleanup and call kthread_parkme()
  91 *
  92 * Similar to kthread_should_stop(), but this keeps the thread alive
  93 * and in a park position. kthread_unpark() "restarts" the thread and
  94 * calls the thread function again.
  95 */
  96bool kthread_should_park(void)
  97{
  98        return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
  99}
 100
 101/**
 102 * kthread_freezable_should_stop - should this freezable kthread return now?
 103 * @was_frozen: optional out parameter, indicates whether %current was frozen
 104 *
 105 * kthread_should_stop() for freezable kthreads, which will enter
 106 * refrigerator if necessary.  This function is safe from kthread_stop() /
 107 * freezer deadlock and freezable kthreads should use this function instead
 108 * of calling try_to_freeze() directly.
 109 */
 110bool kthread_freezable_should_stop(bool *was_frozen)
 111{
 112        bool frozen = false;
 113
 114        might_sleep();
 115
 116        if (unlikely(freezing(current)))
 117                frozen = __refrigerator(true);
 118
 119        if (was_frozen)
 120                *was_frozen = frozen;
 121
 122        return kthread_should_stop();
 123}
 124EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
 125
 126/**
 127 * kthread_data - return data value specified on kthread creation
 128 * @task: kthread task in question
 129 *
 130 * Return the data value specified when kthread @task was created.
 131 * The caller is responsible for ensuring the validity of @task when
 132 * calling this function.
 133 */
 134void *kthread_data(struct task_struct *task)
 135{
 136        return to_kthread(task)->data;
 137}
 138
 139/**
 140 * probe_kthread_data - speculative version of kthread_data()
 141 * @task: possible kthread task in question
 142 *
 143 * @task could be a kthread task.  Return the data value specified when it
 144 * was created if accessible.  If @task isn't a kthread task or its data is
 145 * inaccessible for any reason, %NULL is returned.  This function requires
 146 * that @task itself is safe to dereference.
 147 */
 148void *probe_kthread_data(struct task_struct *task)
 149{
 150        struct kthread *kthread = to_kthread(task);
 151        void *data = NULL;
 152
 153        probe_kernel_read(&data, &kthread->data, sizeof(data));
 154        return data;
 155}
 156
 157static void __kthread_parkme(struct kthread *self)
 158{
 159        __set_current_state(TASK_PARKED);
 160        while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
 161                if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
 162                        complete(&self->parked);
 163                schedule();
 164                __set_current_state(TASK_PARKED);
 165        }
 166        clear_bit(KTHREAD_IS_PARKED, &self->flags);
 167        __set_current_state(TASK_RUNNING);
 168}
 169
 170void kthread_parkme(void)
 171{
 172        __kthread_parkme(to_kthread(current));
 173}
 174
 175static int kthread(void *_create)
 176{
 177        /* Copy data: it's on kthread's stack */
 178        struct kthread_create_info *create = _create;
 179        int (*threadfn)(void *data) = create->threadfn;
 180        void *data = create->data;
 181        struct completion *done;
 182        struct kthread self;
 183        int ret;
 184
 185        self.flags = 0;
 186        self.data = data;
 187        init_completion(&self.exited);
 188        init_completion(&self.parked);
 189        current->vfork_done = &self.exited;
 190
 191        /* If user was SIGKILLed, I release the structure. */
 192        done = xchg(&create->done, NULL);
 193        if (!done) {
 194                kfree(create);
 195                do_exit(-EINTR);
 196        }
 197        /* OK, tell user we're spawned, wait for stop or wakeup */
 198        __set_current_state(TASK_UNINTERRUPTIBLE);
 199        create->result = current;
 200        complete(done);
 201        schedule();
 202
 203        ret = -EINTR;
 204
 205        if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
 206                __kthread_parkme(&self);
 207                ret = threadfn(data);
 208        }
 209        /* we can't just return, we must preserve "self" on stack */
 210        do_exit(ret);
 211}
 212
 213/* called from do_fork() to get node information for about to be created task */
 214int tsk_fork_get_node(struct task_struct *tsk)
 215{
 216#ifdef CONFIG_NUMA
 217        if (tsk == kthreadd_task)
 218                return tsk->pref_node_fork;
 219#endif
 220        return numa_node_id();
 221}
 222
 223static void create_kthread(struct kthread_create_info *create)
 224{
 225        int pid;
 226
 227#ifdef CONFIG_NUMA
 228        current->pref_node_fork = create->node;
 229#endif
 230        /* We want our own signal handler (we take no signals by default). */
 231        pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 232        if (pid < 0) {
 233                /* If user was SIGKILLed, I release the structure. */
 234                struct completion *done = xchg(&create->done, NULL);
 235
 236                if (!done) {
 237                        kfree(create);
 238                        return;
 239                }
 240                create->result = ERR_PTR(pid);
 241                complete(done);
 242        }
 243}
 244
 245/**
 246 * kthread_create_on_node - create a kthread.
 247 * @threadfn: the function to run until signal_pending(current).
 248 * @data: data ptr for @threadfn.
 249 * @node: memory node number.
 250 * @namefmt: printf-style name for the thread.
 251 *
 252 * Description: This helper function creates and names a kernel
 253 * thread.  The thread will be stopped: use wake_up_process() to start
 254 * it.  See also kthread_run().
 255 *
 256 * If thread is going to be bound on a particular cpu, give its node
 257 * in @node, to get NUMA affinity for kthread stack, or else give -1.
 258 * When woken, the thread will run @threadfn() with @data as its
 259 * argument. @threadfn() can either call do_exit() directly if it is a
 260 * standalone thread for which no one will call kthread_stop(), or
 261 * return when 'kthread_should_stop()' is true (which means
 262 * kthread_stop() has been called).  The return value should be zero
 263 * or a negative error number; it will be passed to kthread_stop().
 264 *
 265 * Returns a task_struct or ERR_PTR(-ENOMEM).
 266 */
 267struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 268                                           void *data, int node,
 269                                           const char namefmt[],
 270                                           ...)
 271{
 272        DECLARE_COMPLETION_ONSTACK(done);
 273        struct task_struct *task;
 274        struct kthread_create_info *create = kmalloc(sizeof(*create),
 275                                                     GFP_KERNEL);
 276
 277        if (!create)
 278                return ERR_PTR(-ENOMEM);
 279        create->threadfn = threadfn;
 280        create->data = data;
 281        create->node = node;
 282        create->done = &done;
 283
 284        spin_lock(&kthread_create_lock);
 285        list_add_tail(&create->list, &kthread_create_list);
 286        spin_unlock(&kthread_create_lock);
 287
 288        wake_up_process(kthreadd_task);
 289        /*
 290         * Wait for completion in killable state, for I might be chosen by
 291         * the OOM killer while kthreadd is trying to allocate memory for
 292         * new kernel thread.
 293         */
 294        if (unlikely(wait_for_completion_killable(&done))) {
 295                /*
 296                 * If I was SIGKILLed before kthreadd (or new kernel thread)
 297                 * calls complete(), leave the cleanup of this structure to
 298                 * that thread.
 299                 */
 300                if (xchg(&create->done, NULL))
 301                        return ERR_PTR(-ENOMEM);
 302                /*
 303                 * kthreadd (or new kernel thread) will call complete()
 304                 * shortly.
 305                 */
 306                wait_for_completion(&done);
 307        }
 308        task = create->result;
 309        if (!IS_ERR(task)) {
 310                static const struct sched_param param = { .sched_priority = 0 };
 311                va_list args;
 312
 313                va_start(args, namefmt);
 314                vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
 315                va_end(args);
 316                /*
 317                 * root may have changed our (kthreadd's) priority or CPU mask.
 318                 * The kernel thread should not inherit these properties.
 319                 */
 320                sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
 321                set_cpus_allowed_ptr(task, cpu_all_mask);
 322        }
 323        kfree(create);
 324        return task;
 325}
 326EXPORT_SYMBOL(kthread_create_on_node);
 327
 328static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
 329{
 330        /* Must have done schedule() in kthread() before we set_task_cpu */
 331        if (!wait_task_inactive(p, state)) {
 332                WARN_ON(1);
 333                return;
 334        }
 335        /* It's safe because the task is inactive. */
 336        do_set_cpus_allowed(p, cpumask_of(cpu));
 337        p->flags |= PF_NO_SETAFFINITY;
 338}
 339
 340/**
 341 * kthread_bind - bind a just-created kthread to a cpu.
 342 * @p: thread created by kthread_create().
 343 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 344 *
 345 * Description: This function is equivalent to set_cpus_allowed(),
 346 * except that @cpu doesn't need to be online, and the thread must be
 347 * stopped (i.e., just returned from kthread_create()).
 348 */
 349void kthread_bind(struct task_struct *p, unsigned int cpu)
 350{
 351        __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
 352}
 353EXPORT_SYMBOL(kthread_bind);
 354
 355/**
 356 * kthread_create_on_cpu - Create a cpu bound kthread
 357 * @threadfn: the function to run until signal_pending(current).
 358 * @data: data ptr for @threadfn.
 359 * @cpu: The cpu on which the thread should be bound,
 360 * @namefmt: printf-style name for the thread. Format is restricted
 361 *           to "name.*%u". Code fills in cpu number.
 362 *
 363 * Description: This helper function creates and names a kernel thread
 364 * The thread will be woken and put into park mode.
 365 */
 366struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
 367                                          void *data, unsigned int cpu,
 368                                          const char *namefmt)
 369{
 370        struct task_struct *p;
 371
 372        p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
 373                                   cpu);
 374        if (IS_ERR(p))
 375                return p;
 376        set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
 377        to_kthread(p)->cpu = cpu;
 378        /* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
 379        kthread_park(p);
 380        return p;
 381}
 382
 383static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
 384{
 385        clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
 386        /*
 387         * We clear the IS_PARKED bit here as we don't wait
 388         * until the task has left the park code. So if we'd
 389         * park before that happens we'd see the IS_PARKED bit
 390         * which might be about to be cleared.
 391         */
 392        if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
 393                if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
 394                        __kthread_bind(k, kthread->cpu, TASK_PARKED);
 395                wake_up_state(k, TASK_PARKED);
 396        }
 397}
 398
 399/**
 400 * kthread_unpark - unpark a thread created by kthread_create().
 401 * @k:          thread created by kthread_create().
 402 *
 403 * Sets kthread_should_park() for @k to return false, wakes it, and
 404 * waits for it to return. If the thread is marked percpu then its
 405 * bound to the cpu again.
 406 */
 407void kthread_unpark(struct task_struct *k)
 408{
 409        struct kthread *kthread = to_live_kthread(k);
 410
 411        if (kthread)
 412                __kthread_unpark(k, kthread);
 413}
 414
 415/**
 416 * kthread_park - park a thread created by kthread_create().
 417 * @k: thread created by kthread_create().
 418 *
 419 * Sets kthread_should_park() for @k to return true, wakes it, and
 420 * waits for it to return. This can also be called after kthread_create()
 421 * instead of calling wake_up_process(): the thread will park without
 422 * calling threadfn().
 423 *
 424 * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
 425 * If called by the kthread itself just the park bit is set.
 426 */
 427int kthread_park(struct task_struct *k)
 428{
 429        struct kthread *kthread = to_live_kthread(k);
 430        int ret = -ENOSYS;
 431
 432        if (kthread) {
 433                if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
 434                        set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
 435                        if (k != current) {
 436                                wake_up_process(k);
 437                                wait_for_completion(&kthread->parked);
 438                        }
 439                }
 440                ret = 0;
 441        }
 442        return ret;
 443}
 444
 445/**
 446 * kthread_stop - stop a thread created by kthread_create().
 447 * @k: thread created by kthread_create().
 448 *
 449 * Sets kthread_should_stop() for @k to return true, wakes it, and
 450 * waits for it to exit. This can also be called after kthread_create()
 451 * instead of calling wake_up_process(): the thread will exit without
 452 * calling threadfn().
 453 *
 454 * If threadfn() may call do_exit() itself, the caller must ensure
 455 * task_struct can't go away.
 456 *
 457 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 458 * was never called.
 459 */
 460int kthread_stop(struct task_struct *k)
 461{
 462        struct kthread *kthread;
 463        int ret;
 464
 465        trace_sched_kthread_stop(k);
 466
 467        get_task_struct(k);
 468        kthread = to_live_kthread(k);
 469        if (kthread) {
 470                set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
 471                __kthread_unpark(k, kthread);
 472                wake_up_process(k);
 473                wait_for_completion(&kthread->exited);
 474        }
 475        ret = k->exit_code;
 476        put_task_struct(k);
 477
 478        trace_sched_kthread_stop_ret(ret);
 479        return ret;
 480}
 481EXPORT_SYMBOL(kthread_stop);
 482
 483int kthreadd(void *unused)
 484{
 485        struct task_struct *tsk = current;
 486
 487        /* Setup a clean context for our children to inherit. */
 488        set_task_comm(tsk, "kthreadd");
 489        ignore_signals(tsk);
 490        set_cpus_allowed_ptr(tsk, cpu_all_mask);
 491        set_mems_allowed(node_states[N_MEMORY]);
 492
 493        current->flags |= PF_NOFREEZE;
 494
 495        for (;;) {
 496                set_current_state(TASK_INTERRUPTIBLE);
 497                if (list_empty(&kthread_create_list))
 498                        schedule();
 499                __set_current_state(TASK_RUNNING);
 500
 501                spin_lock(&kthread_create_lock);
 502                while (!list_empty(&kthread_create_list)) {
 503                        struct kthread_create_info *create;
 504
 505                        create = list_entry(kthread_create_list.next,
 506                                            struct kthread_create_info, list);
 507                        list_del_init(&create->list);
 508                        spin_unlock(&kthread_create_lock);
 509
 510                        create_kthread(create);
 511
 512                        spin_lock(&kthread_create_lock);
 513                }
 514                spin_unlock(&kthread_create_lock);
 515        }
 516
 517        return 0;
 518}
 519
 520void __init_kthread_worker(struct kthread_worker *worker,
 521                                const char *name,
 522                                struct lock_class_key *key)
 523{
 524        spin_lock_init(&worker->lock);
 525        lockdep_set_class_and_name(&worker->lock, key, name);
 526        INIT_LIST_HEAD(&worker->work_list);
 527        worker->task = NULL;
 528}
 529EXPORT_SYMBOL_GPL(__init_kthread_worker);
 530
 531/**
 532 * kthread_worker_fn - kthread function to process kthread_worker
 533 * @worker_ptr: pointer to initialized kthread_worker
 534 *
 535 * This function can be used as @threadfn to kthread_create() or
 536 * kthread_run() with @worker_ptr argument pointing to an initialized
 537 * kthread_worker.  The started kthread will process work_list until
 538 * the it is stopped with kthread_stop().  A kthread can also call
 539 * this function directly after extra initialization.
 540 *
 541 * Different kthreads can be used for the same kthread_worker as long
 542 * as there's only one kthread attached to it at any given time.  A
 543 * kthread_worker without an attached kthread simply collects queued
 544 * kthread_works.
 545 */
 546int kthread_worker_fn(void *worker_ptr)
 547{
 548        struct kthread_worker *worker = worker_ptr;
 549        struct kthread_work *work;
 550
 551        WARN_ON(worker->task);
 552        worker->task = current;
 553repeat:
 554        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 555
 556        if (kthread_should_stop()) {
 557                __set_current_state(TASK_RUNNING);
 558                spin_lock_irq(&worker->lock);
 559                worker->task = NULL;
 560                spin_unlock_irq(&worker->lock);
 561                return 0;
 562        }
 563
 564        work = NULL;
 565        spin_lock_irq(&worker->lock);
 566        if (!list_empty(&worker->work_list)) {
 567                work = list_first_entry(&worker->work_list,
 568                                        struct kthread_work, node);
 569                list_del_init(&work->node);
 570        }
 571        worker->current_work = work;
 572        spin_unlock_irq(&worker->lock);
 573
 574        if (work) {
 575                __set_current_state(TASK_RUNNING);
 576                work->func(work);
 577        } else if (!freezing(current))
 578                schedule();
 579
 580        try_to_freeze();
 581        goto repeat;
 582}
 583EXPORT_SYMBOL_GPL(kthread_worker_fn);
 584
 585/* insert @work before @pos in @worker */
 586static void insert_kthread_work(struct kthread_worker *worker,
 587                               struct kthread_work *work,
 588                               struct list_head *pos)
 589{
 590        lockdep_assert_held(&worker->lock);
 591
 592        list_add_tail(&work->node, pos);
 593        work->worker = worker;
 594        if (likely(worker->task))
 595                wake_up_process(worker->task);
 596}
 597
 598/**
 599 * queue_kthread_work - queue a kthread_work
 600 * @worker: target kthread_worker
 601 * @work: kthread_work to queue
 602 *
 603 * Queue @work to work processor @task for async execution.  @task
 604 * must have been created with kthread_worker_create().  Returns %true
 605 * if @work was successfully queued, %false if it was already pending.
 606 */
 607bool queue_kthread_work(struct kthread_worker *worker,
 608                        struct kthread_work *work)
 609{
 610        bool ret = false;
 611        unsigned long flags;
 612
 613        spin_lock_irqsave(&worker->lock, flags);
 614        if (list_empty(&work->node)) {
 615                insert_kthread_work(worker, work, &worker->work_list);
 616                ret = true;
 617        }
 618        spin_unlock_irqrestore(&worker->lock, flags);
 619        return ret;
 620}
 621EXPORT_SYMBOL_GPL(queue_kthread_work);
 622
 623struct kthread_flush_work {
 624        struct kthread_work     work;
 625        struct completion       done;
 626};
 627
 628static void kthread_flush_work_fn(struct kthread_work *work)
 629{
 630        struct kthread_flush_work *fwork =
 631                container_of(work, struct kthread_flush_work, work);
 632        complete(&fwork->done);
 633}
 634
 635/**
 636 * flush_kthread_work - flush a kthread_work
 637 * @work: work to flush
 638 *
 639 * If @work is queued or executing, wait for it to finish execution.
 640 */
 641void flush_kthread_work(struct kthread_work *work)
 642{
 643        struct kthread_flush_work fwork = {
 644                KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 645                COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 646        };
 647        struct kthread_worker *worker;
 648        bool noop = false;
 649
 650retry:
 651        worker = work->worker;
 652        if (!worker)
 653                return;
 654
 655        spin_lock_irq(&worker->lock);
 656        if (work->worker != worker) {
 657                spin_unlock_irq(&worker->lock);
 658                goto retry;
 659        }
 660
 661        if (!list_empty(&work->node))
 662                insert_kthread_work(worker, &fwork.work, work->node.next);
 663        else if (worker->current_work == work)
 664                insert_kthread_work(worker, &fwork.work, worker->work_list.next);
 665        else
 666                noop = true;
 667
 668        spin_unlock_irq(&worker->lock);
 669
 670        if (!noop)
 671                wait_for_completion(&fwork.done);
 672}
 673EXPORT_SYMBOL_GPL(flush_kthread_work);
 674
 675/**
 676 * flush_kthread_worker - flush all current works on a kthread_worker
 677 * @worker: worker to flush
 678 *
 679 * Wait until all currently executing or pending works on @worker are
 680 * finished.
 681 */
 682void flush_kthread_worker(struct kthread_worker *worker)
 683{
 684        struct kthread_flush_work fwork = {
 685                KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 686                COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 687        };
 688
 689        queue_kthread_work(worker, &fwork.work);
 690        wait_for_completion(&fwork.done);
 691}
 692EXPORT_SYMBOL_GPL(flush_kthread_worker);
 693