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