xref: /openbmc/linux/kernel/kthread.c (revision b34e08d5)
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 <linux/uaccess.h>
21 #include <trace/events/sched.h>
22 
23 static DEFINE_SPINLOCK(kthread_create_lock);
24 static LIST_HEAD(kthread_create_list);
25 struct task_struct *kthreadd_task;
26 
27 struct kthread_create_info
28 {
29 	/* Information passed to kthread() from kthreadd. */
30 	int (*threadfn)(void *data);
31 	void *data;
32 	int node;
33 
34 	/* Result passed back to kthread_create() from kthreadd. */
35 	struct task_struct *result;
36 	struct completion *done;
37 
38 	struct list_head list;
39 };
40 
41 struct kthread {
42 	unsigned long flags;
43 	unsigned int cpu;
44 	void *data;
45 	struct completion parked;
46 	struct completion exited;
47 };
48 
49 enum KTHREAD_BITS {
50 	KTHREAD_IS_PER_CPU = 0,
51 	KTHREAD_SHOULD_STOP,
52 	KTHREAD_SHOULD_PARK,
53 	KTHREAD_IS_PARKED,
54 };
55 
56 #define __to_kthread(vfork)	\
57 	container_of(vfork, struct kthread, exited)
58 
59 static inline struct kthread *to_kthread(struct task_struct *k)
60 {
61 	return __to_kthread(k->vfork_done);
62 }
63 
64 static struct kthread *to_live_kthread(struct task_struct *k)
65 {
66 	struct completion *vfork = ACCESS_ONCE(k->vfork_done);
67 	if (likely(vfork))
68 		return __to_kthread(vfork);
69 	return NULL;
70 }
71 
72 /**
73  * kthread_should_stop - should this kthread return now?
74  *
75  * When someone calls kthread_stop() on your kthread, it will be woken
76  * and this will return true.  You should then return, and your return
77  * value will be passed through to kthread_stop().
78  */
79 bool kthread_should_stop(void)
80 {
81 	return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
82 }
83 EXPORT_SYMBOL(kthread_should_stop);
84 
85 /**
86  * kthread_should_park - should this kthread park now?
87  *
88  * When someone calls kthread_park() on your kthread, it will be woken
89  * and this will return true.  You should then do the necessary
90  * cleanup and call kthread_parkme()
91  *
92  * Similar to kthread_should_stop(), but this keeps the thread alive
93  * and in a park position. kthread_unpark() "restarts" the thread and
94  * calls the thread function again.
95  */
96 bool kthread_should_park(void)
97 {
98 	return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
99 }
100 
101 /**
102  * kthread_freezable_should_stop - should this freezable kthread return now?
103  * @was_frozen: optional out parameter, indicates whether %current was frozen
104  *
105  * kthread_should_stop() for freezable kthreads, which will enter
106  * refrigerator if necessary.  This function is safe from kthread_stop() /
107  * freezer deadlock and freezable kthreads should use this function instead
108  * of calling try_to_freeze() directly.
109  */
110 bool kthread_freezable_should_stop(bool *was_frozen)
111 {
112 	bool frozen = false;
113 
114 	might_sleep();
115 
116 	if (unlikely(freezing(current)))
117 		frozen = __refrigerator(true);
118 
119 	if (was_frozen)
120 		*was_frozen = frozen;
121 
122 	return kthread_should_stop();
123 }
124 EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
125 
126 /**
127  * kthread_data - return data value specified on kthread creation
128  * @task: kthread task in question
129  *
130  * Return the data value specified when kthread @task was created.
131  * The caller is responsible for ensuring the validity of @task when
132  * calling this function.
133  */
134 void *kthread_data(struct task_struct *task)
135 {
136 	return to_kthread(task)->data;
137 }
138 
139 /**
140  * probe_kthread_data - speculative version of kthread_data()
141  * @task: possible kthread task in question
142  *
143  * @task could be a kthread task.  Return the data value specified when it
144  * was created if accessible.  If @task isn't a kthread task or its data is
145  * inaccessible for any reason, %NULL is returned.  This function requires
146  * that @task itself is safe to dereference.
147  */
148 void *probe_kthread_data(struct task_struct *task)
149 {
150 	struct kthread *kthread = to_kthread(task);
151 	void *data = NULL;
152 
153 	probe_kernel_read(&data, &kthread->data, sizeof(data));
154 	return data;
155 }
156 
157 static void __kthread_parkme(struct kthread *self)
158 {
159 	__set_current_state(TASK_PARKED);
160 	while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
161 		if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
162 			complete(&self->parked);
163 		schedule();
164 		__set_current_state(TASK_PARKED);
165 	}
166 	clear_bit(KTHREAD_IS_PARKED, &self->flags);
167 	__set_current_state(TASK_RUNNING);
168 }
169 
170 void kthread_parkme(void)
171 {
172 	__kthread_parkme(to_kthread(current));
173 }
174 
175 static int kthread(void *_create)
176 {
177 	/* Copy data: it's on kthread's stack */
178 	struct kthread_create_info *create = _create;
179 	int (*threadfn)(void *data) = create->threadfn;
180 	void *data = create->data;
181 	struct completion *done;
182 	struct kthread self;
183 	int ret;
184 
185 	self.flags = 0;
186 	self.data = data;
187 	init_completion(&self.exited);
188 	init_completion(&self.parked);
189 	current->vfork_done = &self.exited;
190 
191 	/* If user was SIGKILLed, I release the structure. */
192 	done = xchg(&create->done, NULL);
193 	if (!done) {
194 		kfree(create);
195 		do_exit(-EINTR);
196 	}
197 	/* OK, tell user we're spawned, wait for stop or wakeup */
198 	__set_current_state(TASK_UNINTERRUPTIBLE);
199 	create->result = current;
200 	complete(done);
201 	schedule();
202 
203 	ret = -EINTR;
204 
205 	if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
206 		__kthread_parkme(&self);
207 		ret = threadfn(data);
208 	}
209 	/* we can't just return, we must preserve "self" on stack */
210 	do_exit(ret);
211 }
212 
213 /* called from do_fork() to get node information for about to be created task */
214 int tsk_fork_get_node(struct task_struct *tsk)
215 {
216 #ifdef CONFIG_NUMA
217 	if (tsk == kthreadd_task)
218 		return tsk->pref_node_fork;
219 #endif
220 	return NUMA_NO_NODE;
221 }
222 
223 static void create_kthread(struct kthread_create_info *create)
224 {
225 	int pid;
226 
227 #ifdef CONFIG_NUMA
228 	current->pref_node_fork = create->node;
229 #endif
230 	/* We want our own signal handler (we take no signals by default). */
231 	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
232 	if (pid < 0) {
233 		/* If user was SIGKILLed, I release the structure. */
234 		struct completion *done = xchg(&create->done, NULL);
235 
236 		if (!done) {
237 			kfree(create);
238 			return;
239 		}
240 		create->result = ERR_PTR(pid);
241 		complete(done);
242 	}
243 }
244 
245 /**
246  * kthread_create_on_node - create a kthread.
247  * @threadfn: the function to run until signal_pending(current).
248  * @data: data ptr for @threadfn.
249  * @node: memory node number.
250  * @namefmt: printf-style name for the thread.
251  *
252  * Description: This helper function creates and names a kernel
253  * thread.  The thread will be stopped: use wake_up_process() to start
254  * it.  See also kthread_run().
255  *
256  * If thread is going to be bound on a particular cpu, give its node
257  * in @node, to get NUMA affinity for kthread stack, or else give -1.
258  * When woken, the thread will run @threadfn() with @data as its
259  * argument. @threadfn() can either call do_exit() directly if it is a
260  * standalone thread for which no one will call kthread_stop(), or
261  * return when 'kthread_should_stop()' is true (which means
262  * kthread_stop() has been called).  The return value should be zero
263  * or a negative error number; it will be passed to kthread_stop().
264  *
265  * Returns a task_struct or ERR_PTR(-ENOMEM).
266  */
267 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
268 					   void *data, int node,
269 					   const char namefmt[],
270 					   ...)
271 {
272 	DECLARE_COMPLETION_ONSTACK(done);
273 	struct task_struct *task;
274 	struct kthread_create_info *create = kmalloc(sizeof(*create),
275 						     GFP_KERNEL);
276 
277 	if (!create)
278 		return ERR_PTR(-ENOMEM);
279 	create->threadfn = threadfn;
280 	create->data = data;
281 	create->node = node;
282 	create->done = &done;
283 
284 	spin_lock(&kthread_create_lock);
285 	list_add_tail(&create->list, &kthread_create_list);
286 	spin_unlock(&kthread_create_lock);
287 
288 	wake_up_process(kthreadd_task);
289 	/*
290 	 * Wait for completion in killable state, for I might be chosen by
291 	 * the OOM killer while kthreadd is trying to allocate memory for
292 	 * new kernel thread.
293 	 */
294 	if (unlikely(wait_for_completion_killable(&done))) {
295 		/*
296 		 * If I was SIGKILLed before kthreadd (or new kernel thread)
297 		 * calls complete(), leave the cleanup of this structure to
298 		 * that thread.
299 		 */
300 		if (xchg(&create->done, NULL))
301 			return ERR_PTR(-ENOMEM);
302 		/*
303 		 * kthreadd (or new kernel thread) will call complete()
304 		 * shortly.
305 		 */
306 		wait_for_completion(&done);
307 	}
308 	task = create->result;
309 	if (!IS_ERR(task)) {
310 		static const struct sched_param param = { .sched_priority = 0 };
311 		va_list args;
312 
313 		va_start(args, namefmt);
314 		vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
315 		va_end(args);
316 		/*
317 		 * root may have changed our (kthreadd's) priority or CPU mask.
318 		 * The kernel thread should not inherit these properties.
319 		 */
320 		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
321 		set_cpus_allowed_ptr(task, cpu_all_mask);
322 	}
323 	kfree(create);
324 	return task;
325 }
326 EXPORT_SYMBOL(kthread_create_on_node);
327 
328 static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
329 {
330 	/* Must have done schedule() in kthread() before we set_task_cpu */
331 	if (!wait_task_inactive(p, state)) {
332 		WARN_ON(1);
333 		return;
334 	}
335 	/* It's safe because the task is inactive. */
336 	do_set_cpus_allowed(p, cpumask_of(cpu));
337 	p->flags |= PF_NO_SETAFFINITY;
338 }
339 
340 /**
341  * kthread_bind - bind a just-created kthread to a cpu.
342  * @p: thread created by kthread_create().
343  * @cpu: cpu (might not be online, must be possible) for @k to run on.
344  *
345  * Description: This function is equivalent to set_cpus_allowed(),
346  * except that @cpu doesn't need to be online, and the thread must be
347  * stopped (i.e., just returned from kthread_create()).
348  */
349 void kthread_bind(struct task_struct *p, unsigned int cpu)
350 {
351 	__kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
352 }
353 EXPORT_SYMBOL(kthread_bind);
354 
355 /**
356  * kthread_create_on_cpu - Create a cpu bound kthread
357  * @threadfn: the function to run until signal_pending(current).
358  * @data: data ptr for @threadfn.
359  * @cpu: The cpu on which the thread should be bound,
360  * @namefmt: printf-style name for the thread. Format is restricted
361  *	     to "name.*%u". Code fills in cpu number.
362  *
363  * Description: This helper function creates and names a kernel thread
364  * The thread will be woken and put into park mode.
365  */
366 struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
367 					  void *data, unsigned int cpu,
368 					  const char *namefmt)
369 {
370 	struct task_struct *p;
371 
372 	p = kthread_create_on_node(threadfn, data, cpu_to_mem(cpu), namefmt,
373 				   cpu);
374 	if (IS_ERR(p))
375 		return p;
376 	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
377 	to_kthread(p)->cpu = cpu;
378 	/* Park the thread to get it out of TASK_UNINTERRUPTIBLE state */
379 	kthread_park(p);
380 	return p;
381 }
382 
383 static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
384 {
385 	clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
386 	/*
387 	 * We clear the IS_PARKED bit here as we don't wait
388 	 * until the task has left the park code. So if we'd
389 	 * park before that happens we'd see the IS_PARKED bit
390 	 * which might be about to be cleared.
391 	 */
392 	if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
393 		if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
394 			__kthread_bind(k, kthread->cpu, TASK_PARKED);
395 		wake_up_state(k, TASK_PARKED);
396 	}
397 }
398 
399 /**
400  * kthread_unpark - unpark a thread created by kthread_create().
401  * @k:		thread created by kthread_create().
402  *
403  * Sets kthread_should_park() for @k to return false, wakes it, and
404  * waits for it to return. If the thread is marked percpu then its
405  * bound to the cpu again.
406  */
407 void kthread_unpark(struct task_struct *k)
408 {
409 	struct kthread *kthread = to_live_kthread(k);
410 
411 	if (kthread)
412 		__kthread_unpark(k, kthread);
413 }
414 
415 /**
416  * kthread_park - park a thread created by kthread_create().
417  * @k: thread created by kthread_create().
418  *
419  * Sets kthread_should_park() for @k to return true, wakes it, and
420  * waits for it to return. This can also be called after kthread_create()
421  * instead of calling wake_up_process(): the thread will park without
422  * calling threadfn().
423  *
424  * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
425  * If called by the kthread itself just the park bit is set.
426  */
427 int kthread_park(struct task_struct *k)
428 {
429 	struct kthread *kthread = to_live_kthread(k);
430 	int ret = -ENOSYS;
431 
432 	if (kthread) {
433 		if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
434 			set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
435 			if (k != current) {
436 				wake_up_process(k);
437 				wait_for_completion(&kthread->parked);
438 			}
439 		}
440 		ret = 0;
441 	}
442 	return ret;
443 }
444 
445 /**
446  * kthread_stop - stop a thread created by kthread_create().
447  * @k: thread created by kthread_create().
448  *
449  * Sets kthread_should_stop() for @k to return true, wakes it, and
450  * waits for it to exit. This can also be called after kthread_create()
451  * instead of calling wake_up_process(): the thread will exit without
452  * calling threadfn().
453  *
454  * If threadfn() may call do_exit() itself, the caller must ensure
455  * task_struct can't go away.
456  *
457  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
458  * was never called.
459  */
460 int kthread_stop(struct task_struct *k)
461 {
462 	struct kthread *kthread;
463 	int ret;
464 
465 	trace_sched_kthread_stop(k);
466 
467 	get_task_struct(k);
468 	kthread = to_live_kthread(k);
469 	if (kthread) {
470 		set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
471 		__kthread_unpark(k, kthread);
472 		wake_up_process(k);
473 		wait_for_completion(&kthread->exited);
474 	}
475 	ret = k->exit_code;
476 	put_task_struct(k);
477 
478 	trace_sched_kthread_stop_ret(ret);
479 	return ret;
480 }
481 EXPORT_SYMBOL(kthread_stop);
482 
483 int kthreadd(void *unused)
484 {
485 	struct task_struct *tsk = current;
486 
487 	/* Setup a clean context for our children to inherit. */
488 	set_task_comm(tsk, "kthreadd");
489 	ignore_signals(tsk);
490 	set_cpus_allowed_ptr(tsk, cpu_all_mask);
491 	set_mems_allowed(node_states[N_MEMORY]);
492 
493 	current->flags |= PF_NOFREEZE;
494 
495 	for (;;) {
496 		set_current_state(TASK_INTERRUPTIBLE);
497 		if (list_empty(&kthread_create_list))
498 			schedule();
499 		__set_current_state(TASK_RUNNING);
500 
501 		spin_lock(&kthread_create_lock);
502 		while (!list_empty(&kthread_create_list)) {
503 			struct kthread_create_info *create;
504 
505 			create = list_entry(kthread_create_list.next,
506 					    struct kthread_create_info, list);
507 			list_del_init(&create->list);
508 			spin_unlock(&kthread_create_lock);
509 
510 			create_kthread(create);
511 
512 			spin_lock(&kthread_create_lock);
513 		}
514 		spin_unlock(&kthread_create_lock);
515 	}
516 
517 	return 0;
518 }
519 
520 void __init_kthread_worker(struct kthread_worker *worker,
521 				const char *name,
522 				struct lock_class_key *key)
523 {
524 	spin_lock_init(&worker->lock);
525 	lockdep_set_class_and_name(&worker->lock, key, name);
526 	INIT_LIST_HEAD(&worker->work_list);
527 	worker->task = NULL;
528 }
529 EXPORT_SYMBOL_GPL(__init_kthread_worker);
530 
531 /**
532  * kthread_worker_fn - kthread function to process kthread_worker
533  * @worker_ptr: pointer to initialized kthread_worker
534  *
535  * This function can be used as @threadfn to kthread_create() or
536  * kthread_run() with @worker_ptr argument pointing to an initialized
537  * kthread_worker.  The started kthread will process work_list until
538  * the it is stopped with kthread_stop().  A kthread can also call
539  * this function directly after extra initialization.
540  *
541  * Different kthreads can be used for the same kthread_worker as long
542  * as there's only one kthread attached to it at any given time.  A
543  * kthread_worker without an attached kthread simply collects queued
544  * kthread_works.
545  */
546 int kthread_worker_fn(void *worker_ptr)
547 {
548 	struct kthread_worker *worker = worker_ptr;
549 	struct kthread_work *work;
550 
551 	WARN_ON(worker->task);
552 	worker->task = current;
553 repeat:
554 	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
555 
556 	if (kthread_should_stop()) {
557 		__set_current_state(TASK_RUNNING);
558 		spin_lock_irq(&worker->lock);
559 		worker->task = NULL;
560 		spin_unlock_irq(&worker->lock);
561 		return 0;
562 	}
563 
564 	work = NULL;
565 	spin_lock_irq(&worker->lock);
566 	if (!list_empty(&worker->work_list)) {
567 		work = list_first_entry(&worker->work_list,
568 					struct kthread_work, node);
569 		list_del_init(&work->node);
570 	}
571 	worker->current_work = work;
572 	spin_unlock_irq(&worker->lock);
573 
574 	if (work) {
575 		__set_current_state(TASK_RUNNING);
576 		work->func(work);
577 	} else if (!freezing(current))
578 		schedule();
579 
580 	try_to_freeze();
581 	goto repeat;
582 }
583 EXPORT_SYMBOL_GPL(kthread_worker_fn);
584 
585 /* insert @work before @pos in @worker */
586 static void insert_kthread_work(struct kthread_worker *worker,
587 			       struct kthread_work *work,
588 			       struct list_head *pos)
589 {
590 	lockdep_assert_held(&worker->lock);
591 
592 	list_add_tail(&work->node, pos);
593 	work->worker = worker;
594 	if (likely(worker->task))
595 		wake_up_process(worker->task);
596 }
597 
598 /**
599  * queue_kthread_work - queue a kthread_work
600  * @worker: target kthread_worker
601  * @work: kthread_work to queue
602  *
603  * Queue @work to work processor @task for async execution.  @task
604  * must have been created with kthread_worker_create().  Returns %true
605  * if @work was successfully queued, %false if it was already pending.
606  */
607 bool queue_kthread_work(struct kthread_worker *worker,
608 			struct kthread_work *work)
609 {
610 	bool ret = false;
611 	unsigned long flags;
612 
613 	spin_lock_irqsave(&worker->lock, flags);
614 	if (list_empty(&work->node)) {
615 		insert_kthread_work(worker, work, &worker->work_list);
616 		ret = true;
617 	}
618 	spin_unlock_irqrestore(&worker->lock, flags);
619 	return ret;
620 }
621 EXPORT_SYMBOL_GPL(queue_kthread_work);
622 
623 struct kthread_flush_work {
624 	struct kthread_work	work;
625 	struct completion	done;
626 };
627 
628 static void kthread_flush_work_fn(struct kthread_work *work)
629 {
630 	struct kthread_flush_work *fwork =
631 		container_of(work, struct kthread_flush_work, work);
632 	complete(&fwork->done);
633 }
634 
635 /**
636  * flush_kthread_work - flush a kthread_work
637  * @work: work to flush
638  *
639  * If @work is queued or executing, wait for it to finish execution.
640  */
641 void flush_kthread_work(struct kthread_work *work)
642 {
643 	struct kthread_flush_work fwork = {
644 		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
645 		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
646 	};
647 	struct kthread_worker *worker;
648 	bool noop = false;
649 
650 retry:
651 	worker = work->worker;
652 	if (!worker)
653 		return;
654 
655 	spin_lock_irq(&worker->lock);
656 	if (work->worker != worker) {
657 		spin_unlock_irq(&worker->lock);
658 		goto retry;
659 	}
660 
661 	if (!list_empty(&work->node))
662 		insert_kthread_work(worker, &fwork.work, work->node.next);
663 	else if (worker->current_work == work)
664 		insert_kthread_work(worker, &fwork.work, worker->work_list.next);
665 	else
666 		noop = true;
667 
668 	spin_unlock_irq(&worker->lock);
669 
670 	if (!noop)
671 		wait_for_completion(&fwork.done);
672 }
673 EXPORT_SYMBOL_GPL(flush_kthread_work);
674 
675 /**
676  * flush_kthread_worker - flush all current works on a kthread_worker
677  * @worker: worker to flush
678  *
679  * Wait until all currently executing or pending works on @worker are
680  * finished.
681  */
682 void flush_kthread_worker(struct kthread_worker *worker)
683 {
684 	struct kthread_flush_work fwork = {
685 		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
686 		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
687 	};
688 
689 	queue_kthread_work(worker, &fwork.work);
690 	wait_for_completion(&fwork.done);
691 }
692 EXPORT_SYMBOL_GPL(flush_kthread_worker);
693