xref: /openbmc/linux/kernel/kthread.c (revision 4800cd83)
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 
21 static DEFINE_SPINLOCK(kthread_create_lock);
22 static LIST_HEAD(kthread_create_list);
23 struct task_struct *kthreadd_task;
24 
25 struct 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 
38 struct 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  */
54 int kthread_should_stop(void)
55 {
56 	return to_kthread(current)->should_stop;
57 }
58 EXPORT_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  */
68 void *kthread_data(struct task_struct *task)
69 {
70 	return to_kthread(task)->data;
71 }
72 
73 static 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 
101 static 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  */
132 struct 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 		static const 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 }
167 EXPORT_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  */
178 void 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 }
190 EXPORT_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  */
207 int 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 }
229 EXPORT_SYMBOL(kthread_stop);
230 
231 int 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 void __init_kthread_worker(struct kthread_worker *worker,
269 				const char *name,
270 				struct lock_class_key *key)
271 {
272 	spin_lock_init(&worker->lock);
273 	lockdep_set_class_and_name(&worker->lock, key, name);
274 	INIT_LIST_HEAD(&worker->work_list);
275 	worker->task = NULL;
276 }
277 EXPORT_SYMBOL_GPL(__init_kthread_worker);
278 
279 /**
280  * kthread_worker_fn - kthread function to process kthread_worker
281  * @worker_ptr: pointer to initialized kthread_worker
282  *
283  * This function can be used as @threadfn to kthread_create() or
284  * kthread_run() with @worker_ptr argument pointing to an initialized
285  * kthread_worker.  The started kthread will process work_list until
286  * the it is stopped with kthread_stop().  A kthread can also call
287  * this function directly after extra initialization.
288  *
289  * Different kthreads can be used for the same kthread_worker as long
290  * as there's only one kthread attached to it at any given time.  A
291  * kthread_worker without an attached kthread simply collects queued
292  * kthread_works.
293  */
294 int kthread_worker_fn(void *worker_ptr)
295 {
296 	struct kthread_worker *worker = worker_ptr;
297 	struct kthread_work *work;
298 
299 	WARN_ON(worker->task);
300 	worker->task = current;
301 repeat:
302 	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */
303 
304 	if (kthread_should_stop()) {
305 		__set_current_state(TASK_RUNNING);
306 		spin_lock_irq(&worker->lock);
307 		worker->task = NULL;
308 		spin_unlock_irq(&worker->lock);
309 		return 0;
310 	}
311 
312 	work = NULL;
313 	spin_lock_irq(&worker->lock);
314 	if (!list_empty(&worker->work_list)) {
315 		work = list_first_entry(&worker->work_list,
316 					struct kthread_work, node);
317 		list_del_init(&work->node);
318 	}
319 	spin_unlock_irq(&worker->lock);
320 
321 	if (work) {
322 		__set_current_state(TASK_RUNNING);
323 		work->func(work);
324 		smp_wmb();	/* wmb worker-b0 paired with flush-b1 */
325 		work->done_seq = work->queue_seq;
326 		smp_mb();	/* mb worker-b1 paired with flush-b0 */
327 		if (atomic_read(&work->flushing))
328 			wake_up_all(&work->done);
329 	} else if (!freezing(current))
330 		schedule();
331 
332 	try_to_freeze();
333 	goto repeat;
334 }
335 EXPORT_SYMBOL_GPL(kthread_worker_fn);
336 
337 /**
338  * queue_kthread_work - queue a kthread_work
339  * @worker: target kthread_worker
340  * @work: kthread_work to queue
341  *
342  * Queue @work to work processor @task for async execution.  @task
343  * must have been created with kthread_worker_create().  Returns %true
344  * if @work was successfully queued, %false if it was already pending.
345  */
346 bool queue_kthread_work(struct kthread_worker *worker,
347 			struct kthread_work *work)
348 {
349 	bool ret = false;
350 	unsigned long flags;
351 
352 	spin_lock_irqsave(&worker->lock, flags);
353 	if (list_empty(&work->node)) {
354 		list_add_tail(&work->node, &worker->work_list);
355 		work->queue_seq++;
356 		if (likely(worker->task))
357 			wake_up_process(worker->task);
358 		ret = true;
359 	}
360 	spin_unlock_irqrestore(&worker->lock, flags);
361 	return ret;
362 }
363 EXPORT_SYMBOL_GPL(queue_kthread_work);
364 
365 /**
366  * flush_kthread_work - flush a kthread_work
367  * @work: work to flush
368  *
369  * If @work is queued or executing, wait for it to finish execution.
370  */
371 void flush_kthread_work(struct kthread_work *work)
372 {
373 	int seq = work->queue_seq;
374 
375 	atomic_inc(&work->flushing);
376 
377 	/*
378 	 * mb flush-b0 paired with worker-b1, to make sure either
379 	 * worker sees the above increment or we see done_seq update.
380 	 */
381 	smp_mb__after_atomic_inc();
382 
383 	/* A - B <= 0 tests whether B is in front of A regardless of overflow */
384 	wait_event(work->done, seq - work->done_seq <= 0);
385 	atomic_dec(&work->flushing);
386 
387 	/*
388 	 * rmb flush-b1 paired with worker-b0, to make sure our caller
389 	 * sees every change made by work->func().
390 	 */
391 	smp_mb__after_atomic_dec();
392 }
393 EXPORT_SYMBOL_GPL(flush_kthread_work);
394 
395 struct kthread_flush_work {
396 	struct kthread_work	work;
397 	struct completion	done;
398 };
399 
400 static void kthread_flush_work_fn(struct kthread_work *work)
401 {
402 	struct kthread_flush_work *fwork =
403 		container_of(work, struct kthread_flush_work, work);
404 	complete(&fwork->done);
405 }
406 
407 /**
408  * flush_kthread_worker - flush all current works on a kthread_worker
409  * @worker: worker to flush
410  *
411  * Wait until all currently executing or pending works on @worker are
412  * finished.
413  */
414 void flush_kthread_worker(struct kthread_worker *worker)
415 {
416 	struct kthread_flush_work fwork = {
417 		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
418 		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
419 	};
420 
421 	queue_kthread_work(worker, &fwork.work);
422 	wait_for_completion(&fwork.done);
423 }
424 EXPORT_SYMBOL_GPL(flush_kthread_worker);
425