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/module.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_data - return data value specified on kthread creation
  63 * @task: kthread task in question
  64 *
  65 * Return the data value specified when kthread @task was created.
  66 * The caller is responsible for ensuring the validity of @task when
  67 * calling this function.
  68 */
  69void *kthread_data(struct task_struct *task)
  70{
  71        return to_kthread(task)->data;
  72}
  73
  74static int kthread(void *_create)
  75{
  76        /* Copy data: it's on kthread's stack */
  77        struct kthread_create_info *create = _create;
  78        int (*threadfn)(void *data) = create->threadfn;
  79        void *data = create->data;
  80        struct kthread self;
  81        int ret;
  82
  83        self.should_stop = 0;
  84        self.data = data;
  85        init_completion(&self.exited);
  86        current->vfork_done = &self.exited;
  87
  88        /* OK, tell user we're spawned, wait for stop or wakeup */
  89        __set_current_state(TASK_UNINTERRUPTIBLE);
  90        create->result = current;
  91        complete(&create->done);
  92        schedule();
  93
  94        ret = -EINTR;
  95        if (!self.should_stop)
  96                ret = threadfn(data);
  97
  98        /* we can't just return, we must preserve "self" on stack */
  99        do_exit(ret);
 100}
 101
 102/* called from do_fork() to get node information for about to be created task */
 103int tsk_fork_get_node(struct task_struct *tsk)
 104{
 105#ifdef CONFIG_NUMA
 106        if (tsk == kthreadd_task)
 107                return tsk->pref_node_fork;
 108#endif
 109        return numa_node_id();
 110}
 111
 112static void create_kthread(struct kthread_create_info *create)
 113{
 114        int pid;
 115
 116#ifdef CONFIG_NUMA
 117        current->pref_node_fork = create->node;
 118#endif
 119        /* We want our own signal handler (we take no signals by default). */
 120        pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
 121        if (pid < 0) {
 122                create->result = ERR_PTR(pid);
 123                complete(&create->done);
 124        }
 125}
 126
 127/**
 128 * kthread_create_on_node - create a kthread.
 129 * @threadfn: the function to run until signal_pending(current).
 130 * @data: data ptr for @threadfn.
 131 * @node: memory node number.
 132 * @namefmt: printf-style name for the thread.
 133 *
 134 * Description: This helper function creates and names a kernel
 135 * thread.  The thread will be stopped: use wake_up_process() to start
 136 * it.  See also kthread_run().
 137 *
 138 * If thread is going to be bound on a particular cpu, give its node
 139 * in @node, to get NUMA affinity for kthread stack, or else give -1.
 140 * When woken, the thread will run @threadfn() with @data as its
 141 * argument. @threadfn() can either call do_exit() directly if it is a
 142 * standalone thread for which no one will call kthread_stop(), or
 143 * return when 'kthread_should_stop()' is true (which means
 144 * kthread_stop() has been called).  The return value should be zero
 145 * or a negative error number; it will be passed to kthread_stop().
 146 *
 147 * Returns a task_struct or ERR_PTR(-ENOMEM).
 148 */
 149struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
 150                                           void *data,
 151                                           int node,
 152                                           const char namefmt[],
 153                                           ...)
 154{
 155        struct kthread_create_info create;
 156
 157        create.threadfn = threadfn;
 158        create.data = data;
 159        create.node = node;
 160        init_completion(&create.done);
 161
 162        spin_lock(&kthread_create_lock);
 163        list_add_tail(&create.list, &kthread_create_list);
 164        spin_unlock(&kthread_create_lock);
 165
 166        wake_up_process(kthreadd_task);
 167        wait_for_completion(&create.done);
 168
 169        if (!IS_ERR(create.result)) {
 170                static const struct sched_param param = { .sched_priority = 0 };
 171                va_list args;
 172
 173                va_start(args, namefmt);
 174                vsnprintf(create.result->comm, sizeof(create.result->comm),
 175                          namefmt, args);
 176                va_end(args);
 177                /*
 178                 * root may have changed our (kthreadd's) priority or CPU mask.
 179                 * The kernel thread should not inherit these properties.
 180                 */
 181                sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
 182                set_cpus_allowed_ptr(create.result, cpu_all_mask);
 183        }
 184        return create.result;
 185}
 186EXPORT_SYMBOL(kthread_create_on_node);
 187
 188/**
 189 * kthread_bind - bind a just-created kthread to a cpu.
 190 * @p: thread created by kthread_create().
 191 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 192 *
 193 * Description: This function is equivalent to set_cpus_allowed(),
 194 * except that @cpu doesn't need to be online, and the thread must be
 195 * stopped (i.e., just returned from kthread_create()).
 196 */
 197void kthread_bind(struct task_struct *p, unsigned int cpu)
 198{
 199        /* Must have done schedule() in kthread() before we set_task_cpu */
 200        if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
 201                WARN_ON(1);
 202                return;
 203        }
 204
 205        /* It's safe because the task is inactive. */
 206        do_set_cpus_allowed(p, cpumask_of(cpu));
 207        p->flags |= PF_THREAD_BOUND;
 208}
 209EXPORT_SYMBOL(kthread_bind);
 210
 211/**
 212 * kthread_stop - stop a thread created by kthread_create().
 213 * @k: thread created by kthread_create().
 214 *
 215 * Sets kthread_should_stop() for @k to return true, wakes it, and
 216 * waits for it to exit. This can also be called after kthread_create()
 217 * instead of calling wake_up_process(): the thread will exit without
 218 * calling threadfn().
 219 *
 220 * If threadfn() may call do_exit() itself, the caller must ensure
 221 * task_struct can't go away.
 222 *
 223 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 224 * was never called.
 225 */
 226int kthread_stop(struct task_struct *k)
 227{
 228        struct kthread *kthread;
 229        int ret;
 230
 231        trace_sched_kthread_stop(k);
 232        get_task_struct(k);
 233
 234        kthread = to_kthread(k);
 235        barrier(); /* it might have exited */
 236        if (k->vfork_done != NULL) {
 237                kthread->should_stop = 1;
 238                wake_up_process(k);
 239                wait_for_completion(&kthread->exited);
 240        }
 241        ret = k->exit_code;
 242
 243        put_task_struct(k);
 244        trace_sched_kthread_stop_ret(ret);
 245
 246        return ret;
 247}
 248EXPORT_SYMBOL(kthread_stop);
 249
 250int kthreadd(void *unused)
 251{
 252        struct task_struct *tsk = current;
 253
 254        /* Setup a clean context for our children to inherit. */
 255        set_task_comm(tsk, "kthreadd");
 256        ignore_signals(tsk);
 257        set_cpus_allowed_ptr(tsk, cpu_all_mask);
 258        set_mems_allowed(node_states[N_HIGH_MEMORY]);
 259
 260        current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
 261
 262        for (;;) {
 263                set_current_state(TASK_INTERRUPTIBLE);
 264                if (list_empty(&kthread_create_list))
 265                        schedule();
 266                __set_current_state(TASK_RUNNING);
 267
 268                spin_lock(&kthread_create_lock);
 269                while (!list_empty(&kthread_create_list)) {
 270                        struct kthread_create_info *create;
 271
 272                        create = list_entry(kthread_create_list.next,
 273                                            struct kthread_create_info, list);
 274                        list_del_init(&create->list);
 275                        spin_unlock(&kthread_create_lock);
 276
 277                        create_kthread(create);
 278
 279                        spin_lock(&kthread_create_lock);
 280                }
 281                spin_unlock(&kthread_create_lock);
 282        }
 283
 284        return 0;
 285}
 286
 287void __init_kthread_worker(struct kthread_worker *worker,
 288                                const char *name,
 289                                struct lock_class_key *key)
 290{
 291        spin_lock_init(&worker->lock);
 292        lockdep_set_class_and_name(&worker->lock, key, name);
 293        INIT_LIST_HEAD(&worker->work_list);
 294        worker->task = NULL;
 295}
 296EXPORT_SYMBOL_GPL(__init_kthread_worker);
 297
 298/**
 299 * kthread_worker_fn - kthread function to process kthread_worker
 300 * @worker_ptr: pointer to initialized kthread_worker
 301 *
 302 * This function can be used as @threadfn to kthread_create() or
 303 * kthread_run() with @worker_ptr argument pointing to an initialized
 304 * kthread_worker.  The started kthread will process work_list until
 305 * the it is stopped with kthread_stop().  A kthread can also call
 306 * this function directly after extra initialization.
 307 *
 308 * Different kthreads can be used for the same kthread_worker as long
 309 * as there's only one kthread attached to it at any given time.  A
 310 * kthread_worker without an attached kthread simply collects queued
 311 * kthread_works.
 312 */
 313int kthread_worker_fn(void *worker_ptr)
 314{
 315        struct kthread_worker *worker = worker_ptr;
 316        struct kthread_work *work;
 317
 318        WARN_ON(worker->task);
 319        worker->task = current;
 320repeat:
 321        set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
 322
 323        if (kthread_should_stop()) {
 324                __set_current_state(TASK_RUNNING);
 325                spin_lock_irq(&worker->lock);
 326                worker->task = NULL;
 327                spin_unlock_irq(&worker->lock);
 328                return 0;
 329        }
 330
 331        work = NULL;
 332        spin_lock_irq(&worker->lock);
 333        if (!list_empty(&worker->work_list)) {
 334                work = list_first_entry(&worker->work_list,
 335                                        struct kthread_work, node);
 336                list_del_init(&work->node);
 337        }
 338        spin_unlock_irq(&worker->lock);
 339
 340        if (work) {
 341                __set_current_state(TASK_RUNNING);
 342                work->func(work);
 343                smp_wmb();      /* wmb worker-b0 paired with flush-b1 */
 344                work->done_seq = work->queue_seq;
 345                smp_mb();       /* mb worker-b1 paired with flush-b0 */
 346                if (atomic_read(&work->flushing))
 347                        wake_up_all(&work->done);
 348        } else if (!freezing(current))
 349                schedule();
 350
 351        try_to_freeze();
 352        goto repeat;
 353}
 354EXPORT_SYMBOL_GPL(kthread_worker_fn);
 355
 356/**
 357 * queue_kthread_work - queue a kthread_work
 358 * @worker: target kthread_worker
 359 * @work: kthread_work to queue
 360 *
 361 * Queue @work to work processor @task for async execution.  @task
 362 * must have been created with kthread_worker_create().  Returns %true
 363 * if @work was successfully queued, %false if it was already pending.
 364 */
 365bool queue_kthread_work(struct kthread_worker *worker,
 366                        struct kthread_work *work)
 367{
 368        bool ret = false;
 369        unsigned long flags;
 370
 371        spin_lock_irqsave(&worker->lock, flags);
 372        if (list_empty(&work->node)) {
 373                list_add_tail(&work->node, &worker->work_list);
 374                work->queue_seq++;
 375                if (likely(worker->task))
 376                        wake_up_process(worker->task);
 377                ret = true;
 378        }
 379        spin_unlock_irqrestore(&worker->lock, flags);
 380        return ret;
 381}
 382EXPORT_SYMBOL_GPL(queue_kthread_work);
 383
 384/**
 385 * flush_kthread_work - flush a kthread_work
 386 * @work: work to flush
 387 *
 388 * If @work is queued or executing, wait for it to finish execution.
 389 */
 390void flush_kthread_work(struct kthread_work *work)
 391{
 392        int seq = work->queue_seq;
 393
 394        atomic_inc(&work->flushing);
 395
 396        /*
 397         * mb flush-b0 paired with worker-b1, to make sure either
 398         * worker sees the above increment or we see done_seq update.
 399         */
 400        smp_mb__after_atomic_inc();
 401
 402        /* A - B <= 0 tests whether B is in front of A regardless of overflow */
 403        wait_event(work->done, seq - work->done_seq <= 0);
 404        atomic_dec(&work->flushing);
 405
 406        /*
 407         * rmb flush-b1 paired with worker-b0, to make sure our caller
 408         * sees every change made by work->func().
 409         */
 410        smp_mb__after_atomic_dec();
 411}
 412EXPORT_SYMBOL_GPL(flush_kthread_work);
 413
 414struct kthread_flush_work {
 415        struct kthread_work     work;
 416        struct completion       done;
 417};
 418
 419static void kthread_flush_work_fn(struct kthread_work *work)
 420{
 421        struct kthread_flush_work *fwork =
 422                container_of(work, struct kthread_flush_work, work);
 423        complete(&fwork->done);
 424}
 425
 426/**
 427 * flush_kthread_worker - flush all current works on a kthread_worker
 428 * @worker: worker to flush
 429 *
 430 * Wait until all currently executing or pending works on @worker are
 431 * finished.
 432 */
 433void flush_kthread_worker(struct kthread_worker *worker)
 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
 440        queue_kthread_work(worker, &fwork.work);
 441        wait_for_completion(&fwork.done);
 442}
 443EXPORT_SYMBOL_GPL(flush_kthread_worker);
 444
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