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
31    /* Result passed back to kthread_create() from kthreadd. */
32    struct task_struct *result;
33    struct completion done;
34
35    struct list_head list;
36};
37
38struct kthread {
39    int should_stop;
40    void *data;
41    struct completion exited;
42};
43
44#define to_kthread(tsk) \
45    container_of((tsk)->vfork_done, struct kthread, exited)
46
47/**
48 * kthread_should_stop - should this kthread return now?
49 *
50 * When someone calls kthread_stop() on your kthread, it will be woken
51 * and this will return true. You should then return, and your return
52 * value will be passed through to kthread_stop().
53 */
54int kthread_should_stop(void)
55{
56    return to_kthread(current)->should_stop;
57}
58EXPORT_SYMBOL(kthread_should_stop);
59
60/**
61 * kthread_data - return data value specified on kthread creation
62 * @task: kthread task in question
63 *
64 * Return the data value specified when kthread @task was created.
65 * The caller is responsible for ensuring the validity of @task when
66 * calling this function.
67 */
68void *kthread_data(struct task_struct *task)
69{
70    return to_kthread(task)->data;
71}
72
73static int kthread(void *_create)
74{
75    /* Copy data: it's on kthread's stack */
76    struct kthread_create_info *create = _create;
77    int (*threadfn)(void *data) = create->threadfn;
78    void *data = create->data;
79    struct kthread self;
80    int ret;
81
82    self.should_stop = 0;
83    self.data = data;
84    init_completion(&self.exited);
85    current->vfork_done = &self.exited;
86
87    /* OK, tell user we're spawned, wait for stop or wakeup */
88    __set_current_state(TASK_UNINTERRUPTIBLE);
89    create->result = current;
90    complete(&create->done);
91    schedule();
92
93    ret = -EINTR;
94    if (!self.should_stop)
95        ret = threadfn(data);
96
97    /* we can't just return, we must preserve "self" on stack */
98    do_exit(ret);
99}
100
101static void create_kthread(struct kthread_create_info *create)
102{
103    int pid;
104
105    /* We want our own signal handler (we take no signals by default). */
106    pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
107    if (pid < 0) {
108        create->result = ERR_PTR(pid);
109        complete(&create->done);
110    }
111}
112
113/**
114 * kthread_create - create a kthread.
115 * @threadfn: the function to run until signal_pending(current).
116 * @data: data ptr for @threadfn.
117 * @namefmt: printf-style name for the thread.
118 *
119 * Description: This helper function creates and names a kernel
120 * thread. The thread will be stopped: use wake_up_process() to start
121 * it. See also kthread_run().
122 *
123 * When woken, the thread will run @threadfn() with @data as its
124 * argument. @threadfn() can either call do_exit() directly if it is a
125 * standalone thread for which noone will call kthread_stop(), or
126 * return when 'kthread_should_stop()' is true (which means
127 * kthread_stop() has been called). The return value should be zero
128 * or a negative error number; it will be passed to kthread_stop().
129 *
130 * Returns a task_struct or ERR_PTR(-ENOMEM).
131 */
132struct task_struct *kthread_create(int (*threadfn)(void *data),
133                   void *data,
134                   const char namefmt[],
135                   ...)
136{
137    struct kthread_create_info create;
138
139    create.threadfn = threadfn;
140    create.data = data;
141    init_completion(&create.done);
142
143    spin_lock(&kthread_create_lock);
144    list_add_tail(&create.list, &kthread_create_list);
145    spin_unlock(&kthread_create_lock);
146
147    wake_up_process(kthreadd_task);
148    wait_for_completion(&create.done);
149
150    if (!IS_ERR(create.result)) {
151        struct sched_param param = { .sched_priority = 0 };
152        va_list args;
153
154        va_start(args, namefmt);
155        vsnprintf(create.result->comm, sizeof(create.result->comm),
156              namefmt, args);
157        va_end(args);
158        /*
159         * root may have changed our (kthreadd's) priority or CPU mask.
160         * The kernel thread should not inherit these properties.
161         */
162        sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
163        set_cpus_allowed_ptr(create.result, cpu_all_mask);
164    }
165    return create.result;
166}
167EXPORT_SYMBOL(kthread_create);
168
169/**
170 * kthread_bind - bind a just-created kthread to a cpu.
171 * @p: thread created by kthread_create().
172 * @cpu: cpu (might not be online, must be possible) for @k to run on.
173 *
174 * Description: This function is equivalent to set_cpus_allowed(),
175 * except that @cpu doesn't need to be online, and the thread must be
176 * stopped (i.e., just returned from kthread_create()).
177 */
178void kthread_bind(struct task_struct *p, unsigned int cpu)
179{
180    /* Must have done schedule() in kthread() before we set_task_cpu */
181    if (!wait_task_inactive(p, TASK_UNINTERRUPTIBLE)) {
182        WARN_ON(1);
183        return;
184    }
185
186    p->cpus_allowed = cpumask_of_cpu(cpu);
187    p->rt.nr_cpus_allowed = 1;
188    p->flags |= PF_THREAD_BOUND;
189}
190EXPORT_SYMBOL(kthread_bind);
191
192/**
193 * kthread_stop - stop a thread created by kthread_create().
194 * @k: thread created by kthread_create().
195 *
196 * Sets kthread_should_stop() for @k to return true, wakes it, and
197 * waits for it to exit. This can also be called after kthread_create()
198 * instead of calling wake_up_process(): the thread will exit without
199 * calling threadfn().
200 *
201 * If threadfn() may call do_exit() itself, the caller must ensure
202 * task_struct can't go away.
203 *
204 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
205 * was never called.
206 */
207int kthread_stop(struct task_struct *k)
208{
209    struct kthread *kthread;
210    int ret;
211
212    trace_sched_kthread_stop(k);
213    get_task_struct(k);
214
215    kthread = to_kthread(k);
216    barrier(); /* it might have exited */
217    if (k->vfork_done != NULL) {
218        kthread->should_stop = 1;
219        wake_up_process(k);
220        wait_for_completion(&kthread->exited);
221    }
222    ret = k->exit_code;
223
224    put_task_struct(k);
225    trace_sched_kthread_stop_ret(ret);
226
227    return ret;
228}
229EXPORT_SYMBOL(kthread_stop);
230
231int kthreadd(void *unused)
232{
233    struct task_struct *tsk = current;
234
235    /* Setup a clean context for our children to inherit. */
236    set_task_comm(tsk, "kthreadd");
237    ignore_signals(tsk);
238    set_cpus_allowed_ptr(tsk, cpu_all_mask);
239    set_mems_allowed(node_states[N_HIGH_MEMORY]);
240
241    current->flags |= PF_NOFREEZE | PF_FREEZER_NOSIG;
242
243    for (;;) {
244        set_current_state(TASK_INTERRUPTIBLE);
245        if (list_empty(&kthread_create_list))
246            schedule();
247        __set_current_state(TASK_RUNNING);
248
249        spin_lock(&kthread_create_lock);
250        while (!list_empty(&kthread_create_list)) {
251            struct kthread_create_info *create;
252
253            create = list_entry(kthread_create_list.next,
254                        struct kthread_create_info, list);
255            list_del_init(&create->list);
256            spin_unlock(&kthread_create_lock);
257
258            create_kthread(create);
259
260            spin_lock(&kthread_create_lock);
261        }
262        spin_unlock(&kthread_create_lock);
263    }
264
265    return 0;
266}
267
268/**
269 * kthread_worker_fn - kthread function to process kthread_worker
270 * @worker_ptr: pointer to initialized kthread_worker
271 *
272 * This function can be used as @threadfn to kthread_create() or
273 * kthread_run() with @worker_ptr argument pointing to an initialized
274 * kthread_worker. The started kthread will process work_list until
275 * the it is stopped with kthread_stop(). A kthread can also call
276 * this function directly after extra initialization.
277 *
278 * Different kthreads can be used for the same kthread_worker as long
279 * as there's only one kthread attached to it at any given time. A
280 * kthread_worker without an attached kthread simply collects queued
281 * kthread_works.
282 */
283int kthread_worker_fn(void *worker_ptr)
284{
285    struct kthread_worker *worker = worker_ptr;
286    struct kthread_work *work;
287
288    WARN_ON(worker->task);
289    worker->task = current;
290repeat:
291    set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
292
293    if (kthread_should_stop()) {
294        __set_current_state(TASK_RUNNING);
295        spin_lock_irq(&worker->lock);
296        worker->task = NULL;
297        spin_unlock_irq(&worker->lock);
298        return 0;
299    }
300
301    work = NULL;
302    spin_lock_irq(&worker->lock);
303    if (!list_empty(&worker->work_list)) {
304        work = list_first_entry(&worker->work_list,
305                    struct kthread_work, node);
306        list_del_init(&work->node);
307    }
308    spin_unlock_irq(&worker->lock);
309
310    if (work) {
311        __set_current_state(TASK_RUNNING);
312        work->func(work);
313        smp_wmb(); /* wmb worker-b0 paired with flush-b1 */
314        work->done_seq = work->queue_seq;
315        smp_mb(); /* mb worker-b1 paired with flush-b0 */
316        if (atomic_read(&work->flushing))
317            wake_up_all(&work->done);
318    } else if (!freezing(current))
319        schedule();
320
321    try_to_freeze();
322    goto repeat;
323}
324EXPORT_SYMBOL_GPL(kthread_worker_fn);
325
326/**
327 * queue_kthread_work - queue a kthread_work
328 * @worker: target kthread_worker
329 * @work: kthread_work to queue
330 *
331 * Queue @work to work processor @task for async execution. @task
332 * must have been created with kthread_worker_create(). Returns %true
333 * if @work was successfully queued, %false if it was already pending.
334 */
335bool queue_kthread_work(struct kthread_worker *worker,
336            struct kthread_work *work)
337{
338    bool ret = false;
339    unsigned long flags;
340
341    spin_lock_irqsave(&worker->lock, flags);
342    if (list_empty(&work->node)) {
343        list_add_tail(&work->node, &worker->work_list);
344        work->queue_seq++;
345        if (likely(worker->task))
346            wake_up_process(worker->task);
347        ret = true;
348    }
349    spin_unlock_irqrestore(&worker->lock, flags);
350    return ret;
351}
352EXPORT_SYMBOL_GPL(queue_kthread_work);
353
354/**
355 * flush_kthread_work - flush a kthread_work
356 * @work: work to flush
357 *
358 * If @work is queued or executing, wait for it to finish execution.
359 */
360void flush_kthread_work(struct kthread_work *work)
361{
362    int seq = work->queue_seq;
363
364    atomic_inc(&work->flushing);
365
366    /*
367     * mb flush-b0 paired with worker-b1, to make sure either
368     * worker sees the above increment or we see done_seq update.
369     */
370    smp_mb__after_atomic_inc();
371
372    /* A - B <= 0 tests whether B is in front of A regardless of overflow */
373    wait_event(work->done, seq - work->done_seq <= 0);
374    atomic_dec(&work->flushing);
375
376    /*
377     * rmb flush-b1 paired with worker-b0, to make sure our caller
378     * sees every change made by work->func().
379     */
380    smp_mb__after_atomic_dec();
381}
382EXPORT_SYMBOL_GPL(flush_kthread_work);
383
384struct kthread_flush_work {
385    struct kthread_work work;
386    struct completion done;
387};
388
389static void kthread_flush_work_fn(struct kthread_work *work)
390{
391    struct kthread_flush_work *fwork =
392        container_of(work, struct kthread_flush_work, work);
393    complete(&fwork->done);
394}
395
396/**
397 * flush_kthread_worker - flush all current works on a kthread_worker
398 * @worker: worker to flush
399 *
400 * Wait until all currently executing or pending works on @worker are
401 * finished.
402 */
403void flush_kthread_worker(struct kthread_worker *worker)
404{
405    struct kthread_flush_work fwork = {
406        KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
407        COMPLETION_INITIALIZER_ONSTACK(fwork.done),
408    };
409
410    queue_kthread_work(worker, &fwork.work);
411    wait_for_completion(&fwork.done);
412}
413EXPORT_SYMBOL_GPL(flush_kthread_worker);
414

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