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TOMOYO Linux Cross Reference
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 <uapi/linux/sched/types.h>
  9 #include <linux/sched.h>
 10 #include <linux/sched/task.h>
 11 #include <linux/kthread.h>
 12 #include <linux/completion.h>
 13 #include <linux/err.h>
 14 #include <linux/cpuset.h>
 15 #include <linux/unistd.h>
 16 #include <linux/file.h>
 17 #include <linux/export.h>
 18 #include <linux/mutex.h>
 19 #include <linux/slab.h>
 20 #include <linux/freezer.h>
 21 #include <linux/ptrace.h>
 22 #include <linux/uaccess.h>
 23 #include <trace/events/sched.h>
 24 
 25 static DEFINE_SPINLOCK(kthread_create_lock);
 26 static LIST_HEAD(kthread_create_list);
 27 struct task_struct *kthreadd_task;
 28 
 29 struct kthread_create_info
 30 {
 31         /* Information passed to kthread() from kthreadd. */
 32         int (*threadfn)(void *data);
 33         void *data;
 34         int node;
 35 
 36         /* Result passed back to kthread_create() from kthreadd. */
 37         struct task_struct *result;
 38         struct completion *done;
 39 
 40         struct list_head list;
 41 };
 42 
 43 struct kthread {
 44         unsigned long flags;
 45         unsigned int cpu;
 46         void *data;
 47         struct completion parked;
 48         struct completion exited;
 49 #ifdef CONFIG_BLK_CGROUP
 50         struct cgroup_subsys_state *blkcg_css;
 51 #endif
 52 };
 53 
 54 enum KTHREAD_BITS {
 55         KTHREAD_IS_PER_CPU = 0,
 56         KTHREAD_SHOULD_STOP,
 57         KTHREAD_SHOULD_PARK,
 58 };
 59 
 60 static inline void set_kthread_struct(void *kthread)
 61 {
 62         /*
 63          * We abuse ->set_child_tid to avoid the new member and because it
 64          * can't be wrongly copied by copy_process(). We also rely on fact
 65          * that the caller can't exec, so PF_KTHREAD can't be cleared.
 66          */
 67         current->set_child_tid = (__force void __user *)kthread;
 68 }
 69 
 70 static inline struct kthread *to_kthread(struct task_struct *k)
 71 {
 72         WARN_ON(!(k->flags & PF_KTHREAD));
 73         return (__force void *)k->set_child_tid;
 74 }
 75 
 76 void free_kthread_struct(struct task_struct *k)
 77 {
 78         struct kthread *kthread;
 79 
 80         /*
 81          * Can be NULL if this kthread was created by kernel_thread()
 82          * or if kmalloc() in kthread() failed.
 83          */
 84         kthread = to_kthread(k);
 85 #ifdef CONFIG_BLK_CGROUP
 86         WARN_ON_ONCE(kthread && kthread->blkcg_css);
 87 #endif
 88         kfree(kthread);
 89 }
 90 
 91 /**
 92  * kthread_should_stop - should this kthread return now?
 93  *
 94  * When someone calls kthread_stop() on your kthread, it will be woken
 95  * and this will return true.  You should then return, and your return
 96  * value will be passed through to kthread_stop().
 97  */
 98 bool kthread_should_stop(void)
 99 {
100         return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
101 }
102 EXPORT_SYMBOL(kthread_should_stop);
103 
104 /**
105  * kthread_should_park - should this kthread park now?
106  *
107  * When someone calls kthread_park() on your kthread, it will be woken
108  * and this will return true.  You should then do the necessary
109  * cleanup and call kthread_parkme()
110  *
111  * Similar to kthread_should_stop(), but this keeps the thread alive
112  * and in a park position. kthread_unpark() "restarts" the thread and
113  * calls the thread function again.
114  */
115 bool kthread_should_park(void)
116 {
117         return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
118 }
119 EXPORT_SYMBOL_GPL(kthread_should_park);
120 
121 /**
122  * kthread_freezable_should_stop - should this freezable kthread return now?
123  * @was_frozen: optional out parameter, indicates whether %current was frozen
124  *
125  * kthread_should_stop() for freezable kthreads, which will enter
126  * refrigerator if necessary.  This function is safe from kthread_stop() /
127  * freezer deadlock and freezable kthreads should use this function instead
128  * of calling try_to_freeze() directly.
129  */
130 bool kthread_freezable_should_stop(bool *was_frozen)
131 {
132         bool frozen = false;
133 
134         might_sleep();
135 
136         if (unlikely(freezing(current)))
137                 frozen = __refrigerator(true);
138 
139         if (was_frozen)
140                 *was_frozen = frozen;
141 
142         return kthread_should_stop();
143 }
144 EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);
145 
146 /**
147  * kthread_data - return data value specified on kthread creation
148  * @task: kthread task in question
149  *
150  * Return the data value specified when kthread @task was created.
151  * The caller is responsible for ensuring the validity of @task when
152  * calling this function.
153  */
154 void *kthread_data(struct task_struct *task)
155 {
156         return to_kthread(task)->data;
157 }
158 
159 /**
160  * kthread_probe_data - speculative version of kthread_data()
161  * @task: possible kthread task in question
162  *
163  * @task could be a kthread task.  Return the data value specified when it
164  * was created if accessible.  If @task isn't a kthread task or its data is
165  * inaccessible for any reason, %NULL is returned.  This function requires
166  * that @task itself is safe to dereference.
167  */
168 void *kthread_probe_data(struct task_struct *task)
169 {
170         struct kthread *kthread = to_kthread(task);
171         void *data = NULL;
172 
173         probe_kernel_read(&data, &kthread->data, sizeof(data));
174         return data;
175 }
176 
177 static void __kthread_parkme(struct kthread *self)
178 {
179         for (;;) {
180                 set_current_state(TASK_PARKED);
181                 if (!test_bit(KTHREAD_SHOULD_PARK, &self->flags))
182                         break;
183                 schedule();
184         }
185         __set_current_state(TASK_RUNNING);
186 }
187 
188 void kthread_parkme(void)
189 {
190         __kthread_parkme(to_kthread(current));
191 }
192 EXPORT_SYMBOL_GPL(kthread_parkme);
193 
194 void kthread_park_complete(struct task_struct *k)
195 {
196         complete_all(&to_kthread(k)->parked);
197 }
198 
199 static int kthread(void *_create)
200 {
201         /* Copy data: it's on kthread's stack */
202         struct kthread_create_info *create = _create;
203         int (*threadfn)(void *data) = create->threadfn;
204         void *data = create->data;
205         struct completion *done;
206         struct kthread *self;
207         int ret;
208 
209         self = kzalloc(sizeof(*self), GFP_KERNEL);
210         set_kthread_struct(self);
211 
212         /* If user was SIGKILLed, I release the structure. */
213         done = xchg(&create->done, NULL);
214         if (!done) {
215                 kfree(create);
216                 do_exit(-EINTR);
217         }
218 
219         if (!self) {
220                 create->result = ERR_PTR(-ENOMEM);
221                 complete(done);
222                 do_exit(-ENOMEM);
223         }
224 
225         self->data = data;
226         init_completion(&self->exited);
227         init_completion(&self->parked);
228         current->vfork_done = &self->exited;
229 
230         /* OK, tell user we're spawned, wait for stop or wakeup */
231         __set_current_state(TASK_UNINTERRUPTIBLE);
232         create->result = current;
233         complete(done);
234         schedule();
235 
236         ret = -EINTR;
237         if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
238                 cgroup_kthread_ready();
239                 __kthread_parkme(self);
240                 ret = threadfn(data);
241         }
242         do_exit(ret);
243 }
244 
245 /* called from do_fork() to get node information for about to be created task */
246 int tsk_fork_get_node(struct task_struct *tsk)
247 {
248 #ifdef CONFIG_NUMA
249         if (tsk == kthreadd_task)
250                 return tsk->pref_node_fork;
251 #endif
252         return NUMA_NO_NODE;
253 }
254 
255 static void create_kthread(struct kthread_create_info *create)
256 {
257         int pid;
258 
259 #ifdef CONFIG_NUMA
260         current->pref_node_fork = create->node;
261 #endif
262         /* We want our own signal handler (we take no signals by default). */
263         pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
264         if (pid < 0) {
265                 /* If user was SIGKILLed, I release the structure. */
266                 struct completion *done = xchg(&create->done, NULL);
267 
268                 if (!done) {
269                         kfree(create);
270                         return;
271                 }
272                 create->result = ERR_PTR(pid);
273                 complete(done);
274         }
275 }
276 
277 static __printf(4, 0)
278 struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
279                                                     void *data, int node,
280                                                     const char namefmt[],
281                                                     va_list args)
282 {
283         DECLARE_COMPLETION_ONSTACK(done);
284         struct task_struct *task;
285         struct kthread_create_info *create = kmalloc(sizeof(*create),
286                                                      GFP_KERNEL);
287 
288         if (!create)
289                 return ERR_PTR(-ENOMEM);
290         create->threadfn = threadfn;
291         create->data = data;
292         create->node = node;
293         create->done = &done;
294 
295         spin_lock(&kthread_create_lock);
296         list_add_tail(&create->list, &kthread_create_list);
297         spin_unlock(&kthread_create_lock);
298 
299         wake_up_process(kthreadd_task);
300         /*
301          * Wait for completion in killable state, for I might be chosen by
302          * the OOM killer while kthreadd is trying to allocate memory for
303          * new kernel thread.
304          */
305         if (unlikely(wait_for_completion_killable(&done))) {
306                 /*
307                  * If I was SIGKILLed before kthreadd (or new kernel thread)
308                  * calls complete(), leave the cleanup of this structure to
309                  * that thread.
310                  */
311                 if (xchg(&create->done, NULL))
312                         return ERR_PTR(-EINTR);
313                 /*
314                  * kthreadd (or new kernel thread) will call complete()
315                  * shortly.
316                  */
317                 wait_for_completion(&done);
318         }
319         task = create->result;
320         if (!IS_ERR(task)) {
321                 static const struct sched_param param = { .sched_priority = 0 };
322 
323                 vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
324                 /*
325                  * root may have changed our (kthreadd's) priority or CPU mask.
326                  * The kernel thread should not inherit these properties.
327                  */
328                 sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
329                 set_cpus_allowed_ptr(task, cpu_all_mask);
330         }
331         kfree(create);
332         return task;
333 }
334 
335 /**
336  * kthread_create_on_node - create a kthread.
337  * @threadfn: the function to run until signal_pending(current).
338  * @data: data ptr for @threadfn.
339  * @node: task and thread structures for the thread are allocated on this node
340  * @namefmt: printf-style name for the thread.
341  *
342  * Description: This helper function creates and names a kernel
343  * thread.  The thread will be stopped: use wake_up_process() to start
344  * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
345  * is affine to all CPUs.
346  *
347  * If thread is going to be bound on a particular cpu, give its node
348  * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
349  * When woken, the thread will run @threadfn() with @data as its
350  * argument. @threadfn() can either call do_exit() directly if it is a
351  * standalone thread for which no one will call kthread_stop(), or
352  * return when 'kthread_should_stop()' is true (which means
353  * kthread_stop() has been called).  The return value should be zero
354  * or a negative error number; it will be passed to kthread_stop().
355  *
356  * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
357  */
358 struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
359                                            void *data, int node,
360                                            const char namefmt[],
361                                            ...)
362 {
363         struct task_struct *task;
364         va_list args;
365 
366         va_start(args, namefmt);
367         task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
368         va_end(args);
369 
370         return task;
371 }
372 EXPORT_SYMBOL(kthread_create_on_node);
373 
374 static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, long state)
375 {
376         unsigned long flags;
377 
378         if (!wait_task_inactive(p, state)) {
379                 WARN_ON(1);
380                 return;
381         }
382 
383         /* It's safe because the task is inactive. */
384         raw_spin_lock_irqsave(&p->pi_lock, flags);
385         do_set_cpus_allowed(p, mask);
386         p->flags |= PF_NO_SETAFFINITY;
387         raw_spin_unlock_irqrestore(&p->pi_lock, flags);
388 }
389 
390 static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
391 {
392         __kthread_bind_mask(p, cpumask_of(cpu), state);
393 }
394 
395 void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
396 {
397         __kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
398 }
399 
400 /**
401  * kthread_bind - bind a just-created kthread to a cpu.
402  * @p: thread created by kthread_create().
403  * @cpu: cpu (might not be online, must be possible) for @k to run on.
404  *
405  * Description: This function is equivalent to set_cpus_allowed(),
406  * except that @cpu doesn't need to be online, and the thread must be
407  * stopped (i.e., just returned from kthread_create()).
408  */
409 void kthread_bind(struct task_struct *p, unsigned int cpu)
410 {
411         __kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
412 }
413 EXPORT_SYMBOL(kthread_bind);
414 
415 /**
416  * kthread_create_on_cpu - Create a cpu bound kthread
417  * @threadfn: the function to run until signal_pending(current).
418  * @data: data ptr for @threadfn.
419  * @cpu: The cpu on which the thread should be bound,
420  * @namefmt: printf-style name for the thread. Format is restricted
421  *           to "name.*%u". Code fills in cpu number.
422  *
423  * Description: This helper function creates and names a kernel thread
424  * The thread will be woken and put into park mode.
425  */
426 struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
427                                           void *data, unsigned int cpu,
428                                           const char *namefmt)
429 {
430         struct task_struct *p;
431 
432         p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
433                                    cpu);
434         if (IS_ERR(p))
435                 return p;
436         kthread_bind(p, cpu);
437         /* CPU hotplug need to bind once again when unparking the thread. */
438         set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
439         to_kthread(p)->cpu = cpu;
440         return p;
441 }
442 
443 /**
444  * kthread_unpark - unpark a thread created by kthread_create().
445  * @k:          thread created by kthread_create().
446  *
447  * Sets kthread_should_park() for @k to return false, wakes it, and
448  * waits for it to return. If the thread is marked percpu then its
449  * bound to the cpu again.
450  */
451 void kthread_unpark(struct task_struct *k)
452 {
453         struct kthread *kthread = to_kthread(k);
454 
455         /*
456          * Newly created kthread was parked when the CPU was offline.
457          * The binding was lost and we need to set it again.
458          */
459         if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
460                 __kthread_bind(k, kthread->cpu, TASK_PARKED);
461 
462         reinit_completion(&kthread->parked);
463         clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
464         wake_up_state(k, TASK_PARKED);
465 }
466 EXPORT_SYMBOL_GPL(kthread_unpark);
467 
468 /**
469  * kthread_park - park a thread created by kthread_create().
470  * @k: thread created by kthread_create().
471  *
472  * Sets kthread_should_park() for @k to return true, wakes it, and
473  * waits for it to return. This can also be called after kthread_create()
474  * instead of calling wake_up_process(): the thread will park without
475  * calling threadfn().
476  *
477  * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
478  * If called by the kthread itself just the park bit is set.
479  */
480 int kthread_park(struct task_struct *k)
481 {
482         struct kthread *kthread = to_kthread(k);
483 
484         if (WARN_ON(k->flags & PF_EXITING))
485                 return -ENOSYS;
486 
487         set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
488         if (k != current) {
489                 wake_up_process(k);
490                 wait_for_completion(&kthread->parked);
491         }
492 
493         return 0;
494 }
495 EXPORT_SYMBOL_GPL(kthread_park);
496 
497 /**
498  * kthread_stop - stop a thread created by kthread_create().
499  * @k: thread created by kthread_create().
500  *
501  * Sets kthread_should_stop() for @k to return true, wakes it, and
502  * waits for it to exit. This can also be called after kthread_create()
503  * instead of calling wake_up_process(): the thread will exit without
504  * calling threadfn().
505  *
506  * If threadfn() may call do_exit() itself, the caller must ensure
507  * task_struct can't go away.
508  *
509  * Returns the result of threadfn(), or %-EINTR if wake_up_process()
510  * was never called.
511  */
512 int kthread_stop(struct task_struct *k)
513 {
514         struct kthread *kthread;
515         int ret;
516 
517         trace_sched_kthread_stop(k);
518 
519         get_task_struct(k);
520         kthread = to_kthread(k);
521         set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
522         kthread_unpark(k);
523         wake_up_process(k);
524         wait_for_completion(&kthread->exited);
525         ret = k->exit_code;
526         put_task_struct(k);
527 
528         trace_sched_kthread_stop_ret(ret);
529         return ret;
530 }
531 EXPORT_SYMBOL(kthread_stop);
532 
533 int kthreadd(void *unused)
534 {
535         struct task_struct *tsk = current;
536 
537         /* Setup a clean context for our children to inherit. */
538         set_task_comm(tsk, "kthreadd");
539         ignore_signals(tsk);
540         set_cpus_allowed_ptr(tsk, cpu_all_mask);
541         set_mems_allowed(node_states[N_MEMORY]);
542 
543         current->flags |= PF_NOFREEZE;
544         cgroup_init_kthreadd();
545 
546         for (;;) {
547                 set_current_state(TASK_INTERRUPTIBLE);
548                 if (list_empty(&kthread_create_list))
549                         schedule();
550                 __set_current_state(TASK_RUNNING);
551 
552                 spin_lock(&kthread_create_lock);
553                 while (!list_empty(&kthread_create_list)) {
554                         struct kthread_create_info *create;
555 
556                         create = list_entry(kthread_create_list.next,
557                                             struct kthread_create_info, list);
558                         list_del_init(&create->list);
559                         spin_unlock(&kthread_create_lock);
560 
561                         create_kthread(create);
562 
563                         spin_lock(&kthread_create_lock);
564                 }
565                 spin_unlock(&kthread_create_lock);
566         }
567 
568         return 0;
569 }
570 
571 void __kthread_init_worker(struct kthread_worker *worker,
572                                 const char *name,
573                                 struct lock_class_key *key)
574 {
575         memset(worker, 0, sizeof(struct kthread_worker));
576         spin_lock_init(&worker->lock);
577         lockdep_set_class_and_name(&worker->lock, key, name);
578         INIT_LIST_HEAD(&worker->work_list);
579         INIT_LIST_HEAD(&worker->delayed_work_list);
580 }
581 EXPORT_SYMBOL_GPL(__kthread_init_worker);
582 
583 /**
584  * kthread_worker_fn - kthread function to process kthread_worker
585  * @worker_ptr: pointer to initialized kthread_worker
586  *
587  * This function implements the main cycle of kthread worker. It processes
588  * work_list until it is stopped with kthread_stop(). It sleeps when the queue
589  * is empty.
590  *
591  * The works are not allowed to keep any locks, disable preemption or interrupts
592  * when they finish. There is defined a safe point for freezing when one work
593  * finishes and before a new one is started.
594  *
595  * Also the works must not be handled by more than one worker at the same time,
596  * see also kthread_queue_work().
597  */
598 int kthread_worker_fn(void *worker_ptr)
599 {
600         struct kthread_worker *worker = worker_ptr;
601         struct kthread_work *work;
602 
603         /*
604          * FIXME: Update the check and remove the assignment when all kthread
605          * worker users are created using kthread_create_worker*() functions.
606          */
607         WARN_ON(worker->task && worker->task != current);
608         worker->task = current;
609 
610         if (worker->flags & KTW_FREEZABLE)
611                 set_freezable();
612 
613 repeat:
614         set_current_state(TASK_INTERRUPTIBLE);  /* mb paired w/ kthread_stop */
615 
616         if (kthread_should_stop()) {
617                 __set_current_state(TASK_RUNNING);
618                 spin_lock_irq(&worker->lock);
619                 worker->task = NULL;
620                 spin_unlock_irq(&worker->lock);
621                 return 0;
622         }
623 
624         work = NULL;
625         spin_lock_irq(&worker->lock);
626         if (!list_empty(&worker->work_list)) {
627                 work = list_first_entry(&worker->work_list,
628                                         struct kthread_work, node);
629                 list_del_init(&work->node);
630         }
631         worker->current_work = work;
632         spin_unlock_irq(&worker->lock);
633 
634         if (work) {
635                 __set_current_state(TASK_RUNNING);
636                 work->func(work);
637         } else if (!freezing(current))
638                 schedule();
639 
640         try_to_freeze();
641         cond_resched();
642         goto repeat;
643 }
644 EXPORT_SYMBOL_GPL(kthread_worker_fn);
645 
646 static __printf(3, 0) struct kthread_worker *
647 __kthread_create_worker(int cpu, unsigned int flags,
648                         const char namefmt[], va_list args)
649 {
650         struct kthread_worker *worker;
651         struct task_struct *task;
652         int node = -1;
653 
654         worker = kzalloc(sizeof(*worker), GFP_KERNEL);
655         if (!worker)
656                 return ERR_PTR(-ENOMEM);
657 
658         kthread_init_worker(worker);
659 
660         if (cpu >= 0)
661                 node = cpu_to_node(cpu);
662 
663         task = __kthread_create_on_node(kthread_worker_fn, worker,
664                                                 node, namefmt, args);
665         if (IS_ERR(task))
666                 goto fail_task;
667 
668         if (cpu >= 0)
669                 kthread_bind(task, cpu);
670 
671         worker->flags = flags;
672         worker->task = task;
673         wake_up_process(task);
674         return worker;
675 
676 fail_task:
677         kfree(worker);
678         return ERR_CAST(task);
679 }
680 
681 /**
682  * kthread_create_worker - create a kthread worker
683  * @flags: flags modifying the default behavior of the worker
684  * @namefmt: printf-style name for the kthread worker (task).
685  *
686  * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
687  * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
688  * when the worker was SIGKILLed.
689  */
690 struct kthread_worker *
691 kthread_create_worker(unsigned int flags, const char namefmt[], ...)
692 {
693         struct kthread_worker *worker;
694         va_list args;
695 
696         va_start(args, namefmt);
697         worker = __kthread_create_worker(-1, flags, namefmt, args);
698         va_end(args);
699 
700         return worker;
701 }
702 EXPORT_SYMBOL(kthread_create_worker);
703 
704 /**
705  * kthread_create_worker_on_cpu - create a kthread worker and bind it
706  *      it to a given CPU and the associated NUMA node.
707  * @cpu: CPU number
708  * @flags: flags modifying the default behavior of the worker
709  * @namefmt: printf-style name for the kthread worker (task).
710  *
711  * Use a valid CPU number if you want to bind the kthread worker
712  * to the given CPU and the associated NUMA node.
713  *
714  * A good practice is to add the cpu number also into the worker name.
715  * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
716  *
717  * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
718  * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
719  * when the worker was SIGKILLed.
720  */
721 struct kthread_worker *
722 kthread_create_worker_on_cpu(int cpu, unsigned int flags,
723                              const char namefmt[], ...)
724 {
725         struct kthread_worker *worker;
726         va_list args;
727 
728         va_start(args, namefmt);
729         worker = __kthread_create_worker(cpu, flags, namefmt, args);
730         va_end(args);
731 
732         return worker;
733 }
734 EXPORT_SYMBOL(kthread_create_worker_on_cpu);
735 
736 /*
737  * Returns true when the work could not be queued at the moment.
738  * It happens when it is already pending in a worker list
739  * or when it is being cancelled.
740  */
741 static inline bool queuing_blocked(struct kthread_worker *worker,
742                                    struct kthread_work *work)
743 {
744         lockdep_assert_held(&worker->lock);
745 
746         return !list_empty(&work->node) || work->canceling;
747 }
748 
749 static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
750                                              struct kthread_work *work)
751 {
752         lockdep_assert_held(&worker->lock);
753         WARN_ON_ONCE(!list_empty(&work->node));
754         /* Do not use a work with >1 worker, see kthread_queue_work() */
755         WARN_ON_ONCE(work->worker && work->worker != worker);
756 }
757 
758 /* insert @work before @pos in @worker */
759 static void kthread_insert_work(struct kthread_worker *worker,
760                                 struct kthread_work *work,
761                                 struct list_head *pos)
762 {
763         kthread_insert_work_sanity_check(worker, work);
764 
765         list_add_tail(&work->node, pos);
766         work->worker = worker;
767         if (!worker->current_work && likely(worker->task))
768                 wake_up_process(worker->task);
769 }
770 
771 /**
772  * kthread_queue_work - queue a kthread_work
773  * @worker: target kthread_worker
774  * @work: kthread_work to queue
775  *
776  * Queue @work to work processor @task for async execution.  @task
777  * must have been created with kthread_worker_create().  Returns %true
778  * if @work was successfully queued, %false if it was already pending.
779  *
780  * Reinitialize the work if it needs to be used by another worker.
781  * For example, when the worker was stopped and started again.
782  */
783 bool kthread_queue_work(struct kthread_worker *worker,
784                         struct kthread_work *work)
785 {
786         bool ret = false;
787         unsigned long flags;
788 
789         spin_lock_irqsave(&worker->lock, flags);
790         if (!queuing_blocked(worker, work)) {
791                 kthread_insert_work(worker, work, &worker->work_list);
792                 ret = true;
793         }
794         spin_unlock_irqrestore(&worker->lock, flags);
795         return ret;
796 }
797 EXPORT_SYMBOL_GPL(kthread_queue_work);
798 
799 /**
800  * kthread_delayed_work_timer_fn - callback that queues the associated kthread
801  *      delayed work when the timer expires.
802  * @t: pointer to the expired timer
803  *
804  * The format of the function is defined by struct timer_list.
805  * It should have been called from irqsafe timer with irq already off.
806  */
807 void kthread_delayed_work_timer_fn(struct timer_list *t)
808 {
809         struct kthread_delayed_work *dwork = from_timer(dwork, t, timer);
810         struct kthread_work *work = &dwork->work;
811         struct kthread_worker *worker = work->worker;
812 
813         /*
814          * This might happen when a pending work is reinitialized.
815          * It means that it is used a wrong way.
816          */
817         if (WARN_ON_ONCE(!worker))
818                 return;
819 
820         spin_lock(&worker->lock);
821         /* Work must not be used with >1 worker, see kthread_queue_work(). */
822         WARN_ON_ONCE(work->worker != worker);
823 
824         /* Move the work from worker->delayed_work_list. */
825         WARN_ON_ONCE(list_empty(&work->node));
826         list_del_init(&work->node);
827         kthread_insert_work(worker, work, &worker->work_list);
828 
829         spin_unlock(&worker->lock);
830 }
831 EXPORT_SYMBOL(kthread_delayed_work_timer_fn);
832 
833 void __kthread_queue_delayed_work(struct kthread_worker *worker,
834                                   struct kthread_delayed_work *dwork,
835                                   unsigned long delay)
836 {
837         struct timer_list *timer = &dwork->timer;
838         struct kthread_work *work = &dwork->work;
839 
840         WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn);
841 
842         /*
843          * If @delay is 0, queue @dwork->work immediately.  This is for
844          * both optimization and correctness.  The earliest @timer can
845          * expire is on the closest next tick and delayed_work users depend
846          * on that there's no such delay when @delay is 0.
847          */
848         if (!delay) {
849                 kthread_insert_work(worker, work, &worker->work_list);
850                 return;
851         }
852 
853         /* Be paranoid and try to detect possible races already now. */
854         kthread_insert_work_sanity_check(worker, work);
855 
856         list_add(&work->node, &worker->delayed_work_list);
857         work->worker = worker;
858         timer->expires = jiffies + delay;
859         add_timer(timer);
860 }
861 
862 /**
863  * kthread_queue_delayed_work - queue the associated kthread work
864  *      after a delay.
865  * @worker: target kthread_worker
866  * @dwork: kthread_delayed_work to queue
867  * @delay: number of jiffies to wait before queuing
868  *
869  * If the work has not been pending it starts a timer that will queue
870  * the work after the given @delay. If @delay is zero, it queues the
871  * work immediately.
872  *
873  * Return: %false if the @work has already been pending. It means that
874  * either the timer was running or the work was queued. It returns %true
875  * otherwise.
876  */
877 bool kthread_queue_delayed_work(struct kthread_worker *worker,
878                                 struct kthread_delayed_work *dwork,
879                                 unsigned long delay)
880 {
881         struct kthread_work *work = &dwork->work;
882         unsigned long flags;
883         bool ret = false;
884 
885         spin_lock_irqsave(&worker->lock, flags);
886 
887         if (!queuing_blocked(worker, work)) {
888                 __kthread_queue_delayed_work(worker, dwork, delay);
889                 ret = true;
890         }
891 
892         spin_unlock_irqrestore(&worker->lock, flags);
893         return ret;
894 }
895 EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);
896 
897 struct kthread_flush_work {
898         struct kthread_work     work;
899         struct completion       done;
900 };
901 
902 static void kthread_flush_work_fn(struct kthread_work *work)
903 {
904         struct kthread_flush_work *fwork =
905                 container_of(work, struct kthread_flush_work, work);
906         complete(&fwork->done);
907 }
908 
909 /**
910  * kthread_flush_work - flush a kthread_work
911  * @work: work to flush
912  *
913  * If @work is queued or executing, wait for it to finish execution.
914  */
915 void kthread_flush_work(struct kthread_work *work)
916 {
917         struct kthread_flush_work fwork = {
918                 KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
919                 COMPLETION_INITIALIZER_ONSTACK(fwork.done),
920         };
921         struct kthread_worker *worker;
922         bool noop = false;
923 
924         worker = work->worker;
925         if (!worker)
926                 return;
927 
928         spin_lock_irq(&worker->lock);
929         /* Work must not be used with >1 worker, see kthread_queue_work(). */
930         WARN_ON_ONCE(work->worker != worker);
931 
932         if (!list_empty(&work->node))
933                 kthread_insert_work(worker, &fwork.work, work->node.next);
934         else if (worker->current_work == work)
935                 kthread_insert_work(worker, &fwork.work,
936                                     worker->work_list.next);
937         else
938                 noop = true;
939 
940         spin_unlock_irq(&worker->lock);
941 
942         if (!noop)
943                 wait_for_completion(&fwork.done);
944 }
945 EXPORT_SYMBOL_GPL(kthread_flush_work);
946 
947 /*
948  * This function removes the work from the worker queue. Also it makes sure
949  * that it won't get queued later via the delayed work's timer.
950  *
951  * The work might still be in use when this function finishes. See the
952  * current_work proceed by the worker.
953  *
954  * Return: %true if @work was pending and successfully canceled,
955  *      %false if @work was not pending
956  */
957 static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
958                                   unsigned long *flags)
959 {
960         /* Try to cancel the timer if exists. */
961         if (is_dwork) {
962                 struct kthread_delayed_work *dwork =
963                         container_of(work, struct kthread_delayed_work, work);
964                 struct kthread_worker *worker = work->worker;
965 
966                 /*
967                  * del_timer_sync() must be called to make sure that the timer
968                  * callback is not running. The lock must be temporary released
969                  * to avoid a deadlock with the callback. In the meantime,
970                  * any queuing is blocked by setting the canceling counter.
971                  */
972                 work->canceling++;
973                 spin_unlock_irqrestore(&worker->lock, *flags);
974                 del_timer_sync(&dwork->timer);
975                 spin_lock_irqsave(&worker->lock, *flags);
976                 work->canceling--;
977         }
978 
979         /*
980          * Try to remove the work from a worker list. It might either
981          * be from worker->work_list or from worker->delayed_work_list.
982          */
983         if (!list_empty(&work->node)) {
984                 list_del_init(&work->node);
985                 return true;
986         }
987 
988         return false;
989 }
990 
991 /**
992  * kthread_mod_delayed_work - modify delay of or queue a kthread delayed work
993  * @worker: kthread worker to use
994  * @dwork: kthread delayed work to queue
995  * @delay: number of jiffies to wait before queuing
996  *
997  * If @dwork is idle, equivalent to kthread_queue_delayed_work(). Otherwise,
998  * modify @dwork's timer so that it expires after @delay. If @delay is zero,
999  * @work is guaranteed to be queued immediately.
1000  *
1001  * Return: %true if @dwork was pending and its timer was modified,
1002  * %false otherwise.
1003  *
1004  * A special case is when the work is being canceled in parallel.
1005  * It might be caused either by the real kthread_cancel_delayed_work_sync()
1006  * or yet another kthread_mod_delayed_work() call. We let the other command
1007  * win and return %false here. The caller is supposed to synchronize these
1008  * operations a reasonable way.
1009  *
1010  * This function is safe to call from any context including IRQ handler.
1011  * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
1012  * for details.
1013  */
1014 bool kthread_mod_delayed_work(struct kthread_worker *worker,
1015                               struct kthread_delayed_work *dwork,
1016                               unsigned long delay)
1017 {
1018         struct kthread_work *work = &dwork->work;
1019         unsigned long flags;
1020         int ret = false;
1021 
1022         spin_lock_irqsave(&worker->lock, flags);
1023 
1024         /* Do not bother with canceling when never queued. */
1025         if (!work->worker)
1026                 goto fast_queue;
1027 
1028         /* Work must not be used with >1 worker, see kthread_queue_work() */
1029         WARN_ON_ONCE(work->worker != worker);
1030 
1031         /* Do not fight with another command that is canceling this work. */
1032         if (work->canceling)
1033                 goto out;
1034 
1035         ret = __kthread_cancel_work(work, true, &flags);
1036 fast_queue:
1037         __kthread_queue_delayed_work(worker, dwork, delay);
1038 out:
1039         spin_unlock_irqrestore(&worker->lock, flags);
1040         return ret;
1041 }
1042 EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);
1043 
1044 static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
1045 {
1046         struct kthread_worker *worker = work->worker;
1047         unsigned long flags;
1048         int ret = false;
1049 
1050         if (!worker)
1051                 goto out;
1052 
1053         spin_lock_irqsave(&worker->lock, flags);
1054         /* Work must not be used with >1 worker, see kthread_queue_work(). */
1055         WARN_ON_ONCE(work->worker != worker);
1056 
1057         ret = __kthread_cancel_work(work, is_dwork, &flags);
1058 
1059         if (worker->current_work != work)
1060                 goto out_fast;
1061 
1062         /*
1063          * The work is in progress and we need to wait with the lock released.
1064          * In the meantime, block any queuing by setting the canceling counter.
1065          */
1066         work->canceling++;
1067         spin_unlock_irqrestore(&worker->lock, flags);
1068         kthread_flush_work(work);
1069         spin_lock_irqsave(&worker->lock, flags);
1070         work->canceling--;
1071 
1072 out_fast:
1073         spin_unlock_irqrestore(&worker->lock, flags);
1074 out:
1075         return ret;
1076 }
1077 
1078 /**
1079  * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
1080  * @work: the kthread work to cancel
1081  *
1082  * Cancel @work and wait for its execution to finish.  This function
1083  * can be used even if the work re-queues itself. On return from this
1084  * function, @work is guaranteed to be not pending or executing on any CPU.
1085  *
1086  * kthread_cancel_work_sync(&delayed_work->work) must not be used for
1087  * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
1088  *
1089  * The caller must ensure that the worker on which @work was last
1090  * queued can't be destroyed before this function returns.
1091  *
1092  * Return: %true if @work was pending, %false otherwise.
1093  */
1094 bool kthread_cancel_work_sync(struct kthread_work *work)
1095 {
1096         return __kthread_cancel_work_sync(work, false);
1097 }
1098 EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);
1099 
1100 /**
1101  * kthread_cancel_delayed_work_sync - cancel a kthread delayed work and
1102  *      wait for it to finish.
1103  * @dwork: the kthread delayed work to cancel
1104  *
1105  * This is kthread_cancel_work_sync() for delayed works.
1106  *
1107  * Return: %true if @dwork was pending, %false otherwise.
1108  */
1109 bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *dwork)
1110 {
1111         return __kthread_cancel_work_sync(&dwork->work, true);
1112 }
1113 EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);
1114 
1115 /**
1116  * kthread_flush_worker - flush all current works on a kthread_worker
1117  * @worker: worker to flush
1118  *
1119  * Wait until all currently executing or pending works on @worker are
1120  * finished.
1121  */
1122 void kthread_flush_worker(struct kthread_worker *worker)
1123 {
1124         struct kthread_flush_work fwork = {
1125                 KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
1126                 COMPLETION_INITIALIZER_ONSTACK(fwork.done),
1127         };
1128 
1129         kthread_queue_work(worker, &fwork.work);
1130         wait_for_completion(&fwork.done);
1131 }
1132 EXPORT_SYMBOL_GPL(kthread_flush_worker);
1133 
1134 /**
1135  * kthread_destroy_worker - destroy a kthread worker
1136  * @worker: worker to be destroyed
1137  *
1138  * Flush and destroy @worker.  The simple flush is enough because the kthread
1139  * worker API is used only in trivial scenarios.  There are no multi-step state
1140  * machines needed.
1141  */
1142 void kthread_destroy_worker(struct kthread_worker *worker)
1143 {
1144         struct task_struct *task;
1145 
1146         task = worker->task;
1147         if (WARN_ON(!task))
1148                 return;
1149 
1150         kthread_flush_worker(worker);
1151         kthread_stop(task);
1152         WARN_ON(!list_empty(&worker->work_list));
1153         kfree(worker);
1154 }
1155 EXPORT_SYMBOL(kthread_destroy_worker);
1156 
1157 #ifdef CONFIG_BLK_CGROUP
1158 /**
1159  * kthread_associate_blkcg - associate blkcg to current kthread
1160  * @css: the cgroup info
1161  *
1162  * Current thread must be a kthread. The thread is running jobs on behalf of
1163  * other threads. In some cases, we expect the jobs attach cgroup info of
1164  * original threads instead of that of current thread. This function stores
1165  * original thread's cgroup info in current kthread context for later
1166  * retrieval.
1167  */
1168 void kthread_associate_blkcg(struct cgroup_subsys_state *css)
1169 {
1170         struct kthread *kthread;
1171 
1172         if (!(current->flags & PF_KTHREAD))
1173                 return;
1174         kthread = to_kthread(current);
1175         if (!kthread)
1176                 return;
1177 
1178         if (kthread->blkcg_css) {
1179                 css_put(kthread->blkcg_css);
1180                 kthread->blkcg_css = NULL;
1181         }
1182         if (css) {
1183                 css_get(css);
1184                 kthread->blkcg_css = css;
1185         }
1186 }
1187 EXPORT_SYMBOL(kthread_associate_blkcg);
1188 
1189 /**
1190  * kthread_blkcg - get associated blkcg css of current kthread
1191  *
1192  * Current thread must be a kthread.
1193  */
1194 struct cgroup_subsys_state *kthread_blkcg(void)
1195 {
1196         struct kthread *kthread;
1197 
1198         if (current->flags & PF_KTHREAD) {
1199                 kthread = to_kthread(current);
1200                 if (kthread)
1201                         return kthread->blkcg_css;
1202         }
1203         return NULL;
1204 }
1205 EXPORT_SYMBOL(kthread_blkcg);
1206 #endif
1207 

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