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 kthread self;
 182        int ret;
 183
 184        self.flags = 0;
 185        self.data = data;
 186        init_completion(&self.exited);
 187        init_completion(&self.parked);
 188        current->vfork_done = &self.exited;
 189
 190        /* OK, tell user we're spawned, wait for stop or wakeup */
 191        __set_current_state(TASK_UNINTERRUPTIBLE);
 192        create->result = current;
 193        complete(&create->done);
 194        schedule();
 195
 196        ret = -EINTR;
 197
 198        if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
 199                __kthread_parkme(&self);
 200                ret = threadfn(data);
 201        }
 202        /* we can't just return, we must preserve "self" on stack */
 203        do_exit(ret);
 204}
 205
 206/* called from do_fork() to get node information for about to be created task */
 207int tsk_fork_get_node(struct task_struct *tsk)
 208{
 209#ifdef CONFIG_NUMA
 210        if (tsk == kthreadd_task)
 211                return tsk->pref_node_fork;
 212#endif
 213        return numa_node_id();
 214}
 215
 216static void create_kthread(struct kthread_create_info *create)
 217{
 218        int pid;
 219
 220#ifdef CONFIG_NUMA
 221        current->pref_node_fork = create->node;
 222#endif
 223        /* We want our own signal handler (we take no signals by default). */
 224        pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 225        if (pid < 0) {
 226                create->result = ERR_PTR(pid);
 227                complete(&create->done);
 228        }
 229}
 230
 231/**
 232 * kthread_create_on_node - create a kthread.
 233 * @threadfn: the function to run until signal_pending(current).
 234 * @data: data ptr for @threadfn.
 235 * @node: memory node number.
 236 * @namefmt: printf-style name for the thread.
 237 *
 238 * Description: This helper function creates and names a kernel
 239 * thread.  The thread will be stopped: use wake_up_process() to start
 240 * it.  See also kthread_run().
 241 *
 242 * If thread is going to be bound on a particular cpu, give its node
 243 * in @node, to get NUMA affinity for kthread stack, or else give -1.
 244 * When woken, the thread will run @threadfn() with @data as its
 245 * argument. @threadfn() can either call do_exit() directly if it is a
 246 * standalone thread for which no one will call kthread_stop(), or
 247 * return when 'kthread_should_stop()' is true (which means
 248 * kthread_stop() has been called).  The return value should be zero
 249 * or a negative error number; it will be passed to kthread_stop().
 250 *
 251 * Returns a task_struct or ERR_PTR(-ENOMEM).
 252 */
 253struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 254                                           void *data, int node,
 255                                           const char namefmt[],
 256                                           ...)
 257{
 258        struct kthread_create_info create;
 259
 260        create.threadfn = threadfn;
 261        create.data = data;
 262        create.node = node;
 263        init_completion(&create.done);
 264
 265        spin_lock(&kthread_create_lock);
 266        list_add_tail(&create.list, &kthread_create_list);
 267        spin_unlock(&kthread_create_lock);
 268
 269        wake_up_process(kthreadd_task);
 270        wait_for_completion(&create.done);
 271
 272        if (!IS_ERR(create.result)) {
 273                static const struct sched_param param = { .sched_priority = 0 };
 274                va_list args;
 275
 276                va_start(args, namefmt);
 277                vsnprintf(create.result->comm, sizeof(create.result->comm),
 278                          namefmt, args);
 279                va_end(args);
 280                /*
 281                 * root may have changed our (kthreadd's) priority or CPU mask.
 282                 * The kernel thread should not inherit these properties.
 283                 */
 284                sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 285                set_cpus_allowed_ptr(create.result, cpu_all_mask);
 286        }
 287        return create.result;
 288}
 289EXPORT_SYMBOL(kthread_create_on_node);
 290
 291static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
 292{
 293        /* Must have done schedule() in kthread() before we set_task_cpu */
 294        if (!wait_task_inactive(p, state)) {
 295                WARN_ON(1);
 296                return;
 297        }
 298        /* It's safe because the task is inactive. */
 299        do_set_cpus_allowed(p, cpumask_of(cpu));
 300        p->flags |= PF_NO_SETAFFINITY;
 301}
 302
 303/**
 304 * kthread_bind - bind a just-created kthread to a cpu.
 305 * @p: thread created by kthread_create().
 306 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 307 *
 308 * Description: This function is equivalent to set_cpus_allowed(),
 309 * except that @cpu doesn't need to be online, and the thread must be
 310 * stopped (i.e., just returned from kthread_create()).
 311 */
 312void kthread_bind(struct task_struct *p, unsigned int cpu)
 313{
 314        __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
 315}
 316EXPORT_SYMBOL(kthread_bind);
 317
 318/**
 319 * kthread_create_on_cpu - Create a cpu bound kthread
 320 * @threadfn: the function to run until signal_pending(current).
 321 * @data: data ptr for @threadfn.
 322 * @cpu: The cpu on which the thread should be bound,
 323 * @namefmt: printf-style name for the thread. Format is restricted
 324 *           to "name.*%u". Code fills in cpu number.
 325 *
 326 * Description: This helper function creates and names a kernel thread
 327 * The thread will be woken and put into park mode.
 328 */
 329struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
 330                                          void *data, unsigned int cpu,
 331                                          const char *namefmt)
 332{
 333        struct task_struct *p;
 334
 335        p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
 336                                   cpu);
 337        if (IS_ERR(p))
 338                return p;
 339        set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
 340        to_kthread(p)->cpu = cpu;
 341        /* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
 342        kthread_park(p);
 343        return p;
 344}
 345
 346static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
 347{
 348        clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
 349        /*
 350         * We clear the IS_PARKED bit here as we don't wait
 351         * until the task has left the park code. So if we'd
 352         * park before that happens we'd see the IS_PARKED bit
 353         * which might be about to be cleared.
 354         */
 355        if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
 356                if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
 357                        __kthread_bind(k, kthread->cpu, TASK_PARKED);
 358                wake_up_state(k, TASK_PARKED);
 359        }
 360}
 361
 362/**
 363 * kthread_unpark - unpark a thread created by kthread_create().
 364 * @k:          thread created by kthread_create().
 365 *
 366 * Sets kthread_should_park() for @k to return false, wakes it, and
 367 * waits for it to return. If the thread is marked percpu then its
 368 * bound to the cpu again.
 369 */
 370void kthread_unpark(struct task_struct *k)
 371{
 372        struct kthread *kthread = to_live_kthread(k);
 373
 374        if (kthread)
 375                __kthread_unpark(k, kthread);
 376}
 377
 378/**
 379 * kthread_park - park a thread created by kthread_create().
 380 * @k: thread created by kthread_create().
 381 *
 382 * Sets kthread_should_park() for @k to return true, wakes it, and
 383 * waits for it to return. This can also be called after kthread_create()
 384 * instead of calling wake_up_process(): the thread will park without
 385 * calling threadfn().
 386 *
 387 * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
 388 * If called by the kthread itself just the park bit is set.
 389 */
 390int kthread_park(struct task_struct *k)
 391{
 392        struct kthread *kthread = to_live_kthread(k);
 393        int ret = -ENOSYS;
 394
 395        if (kthread) {
 396                if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
 397                        set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
 398                        if (k != current) {
 399                                wake_up_process(k);
 400                                wait_for_completion(&kthread->parked);
 401                        }
 402                }
 403                ret = 0;
 404        }
 405        return ret;
 406}
 407
 408/**
 409 * kthread_stop - stop a thread created by kthread_create().
 410 * @k: thread created by kthread_create().
 411 *
 412 * Sets kthread_should_stop() for @k to return true, wakes it, and
 413 * waits for it to exit. This can also be called after kthread_create()
 414 * instead of calling wake_up_process(): the thread will exit without
 415 * calling threadfn().
 416 *
 417 * If threadfn() may call do_exit() itself, the caller must ensure
 418 * task_struct can't go away.
 419 *
 420 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 421 * was never called.
 422 */
 423int kthread_stop(struct task_struct *k)
 424{
 425        struct kthread *kthread;
 426        int ret;
 427
 428        trace_sched_kthread_stop(k);
 429
 430        get_task_struct(k);
 431        kthread = to_live_kthread(k);
 432        if (kthread) {
 433                set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
 434                __kthread_unpark(k, kthread);
 435                wake_up_process(k);
 436                wait_for_completion(&kthread->exited);
 437        }
 438        ret = k->exit_code;
 439        put_task_struct(k);
 440
 441        trace_sched_kthread_stop_ret(ret);
 442        return ret;
 443}
 444EXPORT_SYMBOL(kthread_stop);
 445
 446int kthreadd(void *unused)
 447{
 448        struct task_struct *tsk = current;
 449
 450        /* Setup a clean context for our children to inherit. */
 451        set_task_comm(tsk, "kthreadd");
 452        ignore_signals(tsk);
 453        set_cpus_allowed_ptr(tsk, cpu_all_mask);
 454        set_mems_allowed(node_states[N_MEMORY]);
 455
 456        current->flags |= PF_NOFREEZE;
 457
 458        for (;;) {
 459                set_current_state(TASK_INTERRUPTIBLE);
 460                if (list_empty(&kthread_create_list))
 461                        schedule();
 462                __set_current_state(TASK_RUNNING);
 463
 464                spin_lock(&kthread_create_lock);
 465                while (!list_empty(&kthread_create_list)) {
 466                        struct kthread_create_info *create;
 467
 468                        create = list_entry(kthread_create_list.next,
 469                                            struct kthread_create_info, list);
 470                        list_del_init(&create->list);
 471                        spin_unlock(&kthread_create_lock);
 472
 473                        create_kthread(create);
 474
 475                        spin_lock(&kthread_create_lock);
 476                }
 477                spin_unlock(&kthread_create_lock);
 478        }
 479
 480        return 0;
 481}
 482
 483void __init_kthread_worker(struct kthread_worker *worker,
 484                                const char *name,
 485                                struct lock_class_key *key)
 486{
 487        spin_lock_init(&worker->lock);
 488        lockdep_set_class_and_name(&worker->lock, key, name);
 489        INIT_LIST_HEAD(&worker->work_list);
 490        worker->task = NULL;
 491}
 492EXPORT_SYMBOL_GPL(__init_kthread_worker);
 493
 494/**
 495 * kthread_worker_fn - kthread function to process kthread_worker
 496 * @worker_ptr: pointer to initialized kthread_worker
 497 *
 498 * This function can be used as @threadfn to kthread_create() or
 499 * kthread_run() with @worker_ptr argument pointing to an initialized
 500 * kthread_worker.  The started kthread will process work_list until
 501 * the it is stopped with kthread_stop().  A kthread can also call
 502 * this function directly after extra initialization.
 503 *
 504 * Different kthreads can be used for the same kthread_worker as long
 505 * as there's only one kthread attached to it at any given time.  A
 506 * kthread_worker without an attached kthread simply collects queued
 507 * kthread_works.
 508 */
 509int kthread_worker_fn(void *worker_ptr)
 510{
 511        struct kthread_worker *worker = worker_ptr;
 512        struct kthread_work *work;
 513
 514        WARN_ON(worker->task);
 515        worker->task = current;
 516repeat:
 517        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 518
 519        if (kthread_should_stop()) {
 520                __set_current_state(TASK_RUNNING);
 521                spin_lock_irq(&worker->lock);
 522                worker->task = NULL;
 523                spin_unlock_irq(&worker->lock);
 524                return 0;
 525        }
 526
 527        work = NULL;
 528        spin_lock_irq(&worker->lock);
 529        if (!list_empty(&worker->work_list)) {
 530                work = list_first_entry(&worker->work_list,
 531                                        struct kthread_work, node);
 532                list_del_init(&work->node);
 533        }
 534        worker->current_work = work;
 535        spin_unlock_irq(&worker->lock);
 536
 537        if (work) {
 538                __set_current_state(TASK_RUNNING);
 539                work->func(work);
 540        } else if (!freezing(current))
 541                schedule();
 542
 543        try_to_freeze();
 544        goto repeat;
 545}
 546EXPORT_SYMBOL_GPL(kthread_worker_fn);
 547
 548/* insert @work before @pos in @worker */
 549static void insert_kthread_work(struct kthread_worker *worker,
 550                               struct kthread_work *work,
 551                               struct list_head *pos)
 552{
 553        lockdep_assert_held(&worker->lock);
 554
 555        list_add_tail(&work->node, pos);
 556        work->worker = worker;
 557        if (likely(worker->task))
 558                wake_up_process(worker->task);
 559}
 560
 561/**
 562 * queue_kthread_work - queue a kthread_work
 563 * @worker: target kthread_worker
 564 * @work: kthread_work to queue
 565 *
 566 * Queue @work to work processor @task for async execution.  @task
 567 * must have been created with kthread_worker_create().  Returns %true
 568 * if @work was successfully queued, %false if it was already pending.
 569 */
 570bool queue_kthread_work(struct kthread_worker *worker,
 571                        struct kthread_work *work)
 572{
 573        bool ret = false;
 574        unsigned long flags;
 575
 576        spin_lock_irqsave(&worker->lock, flags);
 577        if (list_empty(&work->node)) {
 578                insert_kthread_work(worker, work, &worker->work_list);
 579                ret = true;
 580        }
 581        spin_unlock_irqrestore(&worker->lock, flags);
 582        return ret;
 583}
 584EXPORT_SYMBOL_GPL(queue_kthread_work);
 585
 586struct kthread_flush_work {
 587        struct kthread_work     work;
 588        struct completion       done;
 589};
 590
 591static void kthread_flush_work_fn(struct kthread_work *work)
 592{
 593        struct kthread_flush_work *fwork =
 594                container_of(work, struct kthread_flush_work, work);
 595        complete(&fwork->done);
 596}
 597
 598/**
 599 * flush_kthread_work - flush a kthread_work
 600 * @work: work to flush
 601 *
 602 * If @work is queued or executing, wait for it to finish execution.
 603 */
 604void flush_kthread_work(struct kthread_work *work)
 605{
 606        struct kthread_flush_work fwork = {
 607                KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 608                COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 609        };
 610        struct kthread_worker *worker;
 611        bool noop = false;
 612
 613retry:
 614        worker = work->worker;
 615        if (!worker)
 616                return;
 617
 618        spin_lock_irq(&worker->lock);
 619        if (work->worker != worker) {
 620                spin_unlock_irq(&worker->lock);
 621                goto retry;
 622        }
 623
 624        if (!list_empty(&work->node))
 625                insert_kthread_work(worker, &fwork.work, work->node.next);
 626        else if (worker->current_work == work)
 627                insert_kthread_work(worker, &fwork.work, worker->work_list.next);
 628        else
 629                noop = true;
 630
 631        spin_unlock_irq(&worker->lock);
 632
 633        if (!noop)
 634                wait_for_completion(&fwork.done);
 635}
 636EXPORT_SYMBOL_GPL(flush_kthread_work);
 637
 638/**
 639 * flush_kthread_worker - flush all current works on a kthread_worker
 640 * @worker: worker to flush
 641 *
 642 * Wait until all currently executing or pending works on @worker are
 643 * finished.
 644 */
 645void flush_kthread_worker(struct kthread_worker *worker)
 646{
 647        struct kthread_flush_work fwork = {
 648                KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 649                COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 650        };
 651
 652        queue_kthread_work(worker, &fwork.work);
 653        wait_for_completion(&fwork.done);
 654}
 655EXPORT_SYMBOL_GPL(flush_kthread_worker);
 656
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