Root/kernel/kthread.c

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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