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 <trace/events/sched.h>
  20
  21static DEFINE_SPINLOCK(kthread_create_lock);
  22static LIST_HEAD(kthread_create_list);
  23struct task_struct *kthreadd_task;
  24
  25struct kthread_create_info
  26{
  27        /* Information passed to kthread() from kthreadd. */
  28        int (*threadfn)(void *data);
  29        void *data;
  30        int node;
  31
  32        /* Result passed back to kthread_create() from kthreadd. */
  33        struct task_struct *result;
  34        struct completion done;
  35
  36        struct list_head list;
  37};
  38
  39struct kthread {
  40        int should_stop;
  41        void *data;
  42        struct completion exited;
  43};
  44
  45#define to_kthread(tsk) \
  46        container_of((tsk)->vfork_done, struct kthread, exited)
  47
  48/**
  49 * kthread_should_stop - should this kthread return now?
  50 *
  51 * When someone calls kthread_stop() on your kthread, it will be woken
  52 * and this will return true.  You should then return, and your return
  53 * value will be passed through to kthread_stop().
  54 */
  55int kthread_should_stop(void)
  56{
  57        return to_kthread(current)->should_stop;
  58}
  59EXPORT_SYMBOL(kthread_should_stop);
  60
  61/**
  62 * kthread_freezable_should_stop - should this freezable kthread return now?
  63 * @was_frozen: optional out parameter, indicates whether %current was frozen
  64 *
  65 * kthread_should_stop() for freezable kthreads, which will enter
  66 * refrigerator if necessary.  This function is safe from kthread_stop() /
  67 * freezer deadlock and freezable kthreads should use this function instead
  68 * of calling try_to_freeze() directly.
  69 */
  70bool kthread_freezable_should_stop(bool *was_frozen)
  71{
  72        bool frozen = false;
  73
  74        might_sleep();
  75
  76        if (unlikely(freezing(current)))
  77                frozen = __refrigerator(true);
  78
  79        if (was_frozen)
  80                *was_frozen = frozen;
  81
  82        return kthread_should_stop();
  83}
  84EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
  85
  86/**
  87 * kthread_data - return data value specified on kthread creation
  88 * @task: kthread task in question
  89 *
  90 * Return the data value specified when kthread @task was created.
  91 * The caller is responsible for ensuring the validity of @task when
  92 * calling this function.
  93 */
  94void *kthread_data(struct task_struct *task)
  95{
  96        return to_kthread(task)->data;
  97}
  98
  99static int kthread(void *_create)
 100{
 101        /* Copy data: it's on kthread's stack */
 102        struct kthread_create_info *create = _create;
 103        int (*threadfn)(void *data) = create->threadfn;
 104        void *data = create->data;
 105        struct kthread self;
 106        int ret;
 107
 108        self.should_stop = 0;
 109        self.data = data;
 110        init_completion(&self.exited);
 111        current->vfork_done = &self.exited;
 112
 113        /* OK, tell user we're spawned, wait for stop or wakeup */
 114        __set_current_state(TASK_UNINTERRUPTIBLE);
 115        create->result = current;
 116        complete(&create->done);
 117        schedule();
 118
 119        ret = -EINTR;
 120        if (!self.should_stop)
 121                ret = threadfn(data);
 122
 123        /* we can't just return, we must preserve "self" on stack */
 124        do_exit(ret);
 125}
 126
 127/* called from do_fork() to get node information for about to be created task */
 128int tsk_fork_get_node(struct task_struct *tsk)
 129{
 130#ifdef CONFIG_NUMA
 131        if (tsk == kthreadd_task)
 132                return tsk->pref_node_fork;
 133#endif
 134        return numa_node_id();
 135}
 136
 137static void create_kthread(struct kthread_create_info *create)
 138{
 139        int pid;
 140
 141#ifdef CONFIG_NUMA
 142        current->pref_node_fork = create->node;
 143#endif
 144        /* We want our own signal handler (we take no signals by default). */
 145        pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 146        if (pid < 0) {
 147                create->result = ERR_PTR(pid);
 148                complete(&create->done);
 149        }
 150}
 151
 152/**
 153 * kthread_create_on_node - create a kthread.
 154 * @threadfn: the function to run until signal_pending(current).
 155 * @data: data ptr for @threadfn.
 156 * @node: memory node number.
 157 * @namefmt: printf-style name for the thread.
 158 *
 159 * Description: This helper function creates and names a kernel
 160 * thread.  The thread will be stopped: use wake_up_process() to start
 161 * it.  See also kthread_run().
 162 *
 163 * If thread is going to be bound on a particular cpu, give its node
 164 * in @node, to get NUMA affinity for kthread stack, or else give -1.
 165 * When woken, the thread will run @threadfn() with @data as its
 166 * argument. @threadfn() can either call do_exit() directly if it is a
 167 * standalone thread for which no one will call kthread_stop(), or
 168 * return when 'kthread_should_stop()' is true (which means
 169 * kthread_stop() has been called).  The return value should be zero
 170 * or a negative error number; it will be passed to kthread_stop().
 171 *
 172 * Returns a task_struct or ERR_PTR(-ENOMEM).
 173 */
 174struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 175                                           void *data,
 176                                           int node,
 177                                           const char namefmt[],
 178                                           ...)
 179{
 180        struct kthread_create_info create;
 181
 182        create.threadfn = threadfn;
 183        create.data = data;
 184        create.node = node;
 185        init_completion(&create.done);
 186
 187        spin_lock(&kthread_create_lock);
 188        list_add_tail(&create.list, &kthread_create_list);
 189        spin_unlock(&kthread_create_lock);
 190
 191        wake_up_process(kthreadd_task);
 192        wait_for_completion(&create.done);
 193
 194        if (!IS_ERR(create.result)) {
 195                static const struct sched_param param = { .sched_priority = 0 };
 196                va_list args;
 197
 198                va_start(args, namefmt);
 199                vsnprintf(create.result->comm, sizeof(create.result->comm),
 200                          namefmt, args);
 201                va_end(args);
 202                /*
 203                 * root may have changed our (kthreadd's) priority or CPU mask.
 204                 * The kernel thread should not inherit these properties.
 205                 */
 206                sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 207                set_cpus_allowed_ptr(create.result, cpu_all_mask);
 208        }
 209        return create.result;
 210}
 211EXPORT_SYMBOL(kthread_create_on_node);
 212
 213/**
 214 * kthread_bind - bind a just-created kthread to a cpu.
 215 * @p: thread created by kthread_create().
 216 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 217 *
 218 * Description: This function is equivalent to set_cpus_allowed(),
 219 * except that @cpu doesn't need to be online, and the thread must be
 220 * stopped (i.e., just returned from kthread_create()).
 221 */
 222void kthread_bind(struct task_struct *p, unsigned int cpu)
 223{
 224        /* Must have done schedule() in kthread() before we set_task_cpu */
 225        if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
 226                WARN_ON(1);
 227                return;
 228        }
 229
 230        /* It's safe because the task is inactive. */
 231        do_set_cpus_allowed(p, cpumask_of(cpu));
 232        p->flags |= PF_THREAD_BOUND;
 233}
 234EXPORT_SYMBOL(kthread_bind);
 235
 236/**
 237 * kthread_stop - stop a thread created by kthread_create().
 238 * @k: thread created by kthread_create().
 239 *
 240 * Sets kthread_should_stop() for @k to return true, wakes it, and
 241 * waits for it to exit. This can also be called after kthread_create()
 242 * instead of calling wake_up_process(): the thread will exit without
 243 * calling threadfn().
 244 *
 245 * If threadfn() may call do_exit() itself, the caller must ensure
 246 * task_struct can't go away.
 247 *
 248 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 249 * was never called.
 250 */
 251int kthread_stop(struct task_struct *k)
 252{
 253        struct kthread *kthread;
 254        int ret;
 255
 256        trace_sched_kthread_stop(k);
 257        get_task_struct(k);
 258
 259        kthread = to_kthread(k);
 260        barrier(); /* it might have exited */
 261        if (k->vfork_done != NULL) {
 262                kthread->should_stop = 1;
 263                wake_up_process(k);
 264                wait_for_completion(&kthread->exited);
 265        }
 266        ret = k->exit_code;
 267
 268        put_task_struct(k);
 269        trace_sched_kthread_stop_ret(ret);
 270
 271        return ret;
 272}
 273EXPORT_SYMBOL(kthread_stop);
 274
 275int kthreadd(void *unused)
 276{
 277        struct task_struct *tsk = current;
 278
 279        /* Setup a clean context for our children to inherit. */
 280        set_task_comm(tsk, "kthreadd");
 281        ignore_signals(tsk);
 282        set_cpus_allowed_ptr(tsk, cpu_all_mask);
 283        set_mems_allowed(node_states[N_HIGH_MEMORY]);
 284
 285        current->flags |= PF_NOFREEZE;
 286
 287        for (;;) {
 288                set_current_state(TASK_INTERRUPTIBLE);
 289                if (list_empty(&kthread_create_list))
 290                        schedule();
 291                __set_current_state(TASK_RUNNING);
 292
 293                spin_lock(&kthread_create_lock);
 294                while (!list_empty(&kthread_create_list)) {
 295                        struct kthread_create_info *create;
 296
 297                        create = list_entry(kthread_create_list.next,
 298                                            struct kthread_create_info, list);
 299                        list_del_init(&create->list);
 300                        spin_unlock(&kthread_create_lock);
 301
 302                        create_kthread(create);
 303
 304                        spin_lock(&kthread_create_lock);
 305                }
 306                spin_unlock(&kthread_create_lock);
 307        }
 308
 309        return 0;
 310}
 311
 312void __init_kthread_worker(struct kthread_worker *worker,
 313                                const char *name,
 314                                struct lock_class_key *key)
 315{
 316        spin_lock_init(&worker->lock);
 317        lockdep_set_class_and_name(&worker->lock, key, name);
 318        INIT_LIST_HEAD(&worker->work_list);
 319        worker->task = NULL;
 320}
 321EXPORT_SYMBOL_GPL(__init_kthread_worker);
 322
 323/**
 324 * kthread_worker_fn - kthread function to process kthread_worker
 325 * @worker_ptr: pointer to initialized kthread_worker
 326 *
 327 * This function can be used as @threadfn to kthread_create() or
 328 * kthread_run() with @worker_ptr argument pointing to an initialized
 329 * kthread_worker.  The started kthread will process work_list until
 330 * the it is stopped with kthread_stop().  A kthread can also call
 331 * this function directly after extra initialization.
 332 *
 333 * Different kthreads can be used for the same kthread_worker as long
 334 * as there's only one kthread attached to it at any given time.  A
 335 * kthread_worker without an attached kthread simply collects queued
 336 * kthread_works.
 337 */
 338int kthread_worker_fn(void *worker_ptr)
 339{
 340        struct kthread_worker *worker = worker_ptr;
 341        struct kthread_work *work;
 342
 343        WARN_ON(worker->task);
 344        worker->task = current;
 345repeat:
 346        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 347
 348        if (kthread_should_stop()) {
 349                __set_current_state(TASK_RUNNING);
 350                spin_lock_irq(&worker->lock);
 351                worker->task = NULL;
 352                spin_unlock_irq(&worker->lock);
 353                return 0;
 354        }
 355
 356        work = NULL;
 357        spin_lock_irq(&worker->lock);
 358        if (!list_empty(&worker->work_list)) {
 359                work = list_first_entry(&worker->work_list,
 360                                        struct kthread_work, node);
 361                list_del_init(&work->node);
 362        }
 363        worker->current_work = work;
 364        spin_unlock_irq(&worker->lock);
 365
 366        if (work) {
 367                __set_current_state(TASK_RUNNING);
 368                work->func(work);
 369        } else if (!freezing(current))
 370                schedule();
 371
 372        try_to_freeze();
 373        goto repeat;
 374}
 375EXPORT_SYMBOL_GPL(kthread_worker_fn);
 376
 377/* insert @work before @pos in @worker */
 378static void insert_kthread_work(struct kthread_worker *worker,
 379                               struct kthread_work *work,
 380                               struct list_head *pos)
 381{
 382        lockdep_assert_held(&worker->lock);
 383
 384        list_add_tail(&work->node, pos);
 385        work->worker = worker;
 386        if (likely(worker->task))
 387                wake_up_process(worker->task);
 388}
 389
 390/**
 391 * queue_kthread_work - queue a kthread_work
 392 * @worker: target kthread_worker
 393 * @work: kthread_work to queue
 394 *
 395 * Queue @work to work processor @task for async execution.  @task
 396 * must have been created with kthread_worker_create().  Returns %true
 397 * if @work was successfully queued, %false if it was already pending.
 398 */
 399bool queue_kthread_work(struct kthread_worker *worker,
 400                        struct kthread_work *work)
 401{
 402        bool ret = false;
 403        unsigned long flags;
 404
 405        spin_lock_irqsave(&worker->lock, flags);
 406        if (list_empty(&work->node)) {
 407                insert_kthread_work(worker, work, &worker->work_list);
 408                ret = true;
 409        }
 410        spin_unlock_irqrestore(&worker->lock, flags);
 411        return ret;
 412}
 413EXPORT_SYMBOL_GPL(queue_kthread_work);
 414
 415struct kthread_flush_work {
 416        struct kthread_work     work;
 417        struct completion       done;
 418};
 419
 420static void kthread_flush_work_fn(struct kthread_work *work)
 421{
 422        struct kthread_flush_work *fwork =
 423                container_of(work, struct kthread_flush_work, work);
 424        complete(&fwork->done);
 425}
 426
 427/**
 428 * flush_kthread_work - flush a kthread_work
 429 * @work: work to flush
 430 *
 431 * If @work is queued or executing, wait for it to finish execution.
 432 */
 433void flush_kthread_work(struct kthread_work *work)
 434{
 435        struct kthread_flush_work fwork = {
 436                KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 437                COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 438        };
 439        struct kthread_worker *worker;
 440        bool noop = false;
 441
 442retry:
 443        worker = work->worker;
 444        if (!worker)
 445                return;
 446
 447        spin_lock_irq(&worker->lock);
 448        if (work->worker != worker) {
 449                spin_unlock_irq(&worker->lock);
 450                goto retry;
 451        }
 452
 453        if (!list_empty(&work->node))
 454                insert_kthread_work(worker, &fwork.work, work->node.next);
 455        else if (worker->current_work == work)
 456                insert_kthread_work(worker, &fwork.work, worker->work_list.next);
 457        else
 458                noop = true;
 459
 460        spin_unlock_irq(&worker->lock);
 461
 462        if (!noop)
 463                wait_for_completion(&fwork.done);
 464}
 465EXPORT_SYMBOL_GPL(flush_kthread_work);
 466
 467/**
 468 * flush_kthread_worker - flush all current works on a kthread_worker
 469 * @worker: worker to flush
 470 *
 471 * Wait until all currently executing or pending works on @worker are
 472 * finished.
 473 */
 474void flush_kthread_worker(struct kthread_worker *worker)
 475{
 476        struct kthread_flush_work fwork = {
 477                KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
 478                COMPLETION_INITIALIZER_ONSTACK(fwork.done),
 479        };
 480
 481        queue_kthread_work(worker, &fwork.work);
 482        wait_for_completion(&fwork.done);
 483}
 484EXPORT_SYMBOL_GPL(flush_kthread_worker);
 485
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