summaryrefslogtreecommitdiffstats
path: root/kernel/kthread.c
blob: be2cc1f9dd571b8407044de18710c8695e8af220 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
/* Kernel thread helper functions.
 *   Copyright (C) 2004 IBM Corporation, Rusty Russell.
 *
 * Creation is done via kthreadd, so that we get a clean environment
 * even if we're invoked from userspace (think modprobe, hotplug cpu,
 * etc.).
 */
#include <linux/sched.h>
#include <linux/kthread.h>
#include <linux/completion.h>
#include <linux/err.h>
#include <linux/cpuset.h>
#include <linux/unistd.h>
#include <linux/file.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/freezer.h>
#include <linux/ptrace.h>
#include <linux/uaccess.h>
#include <trace/events/sched.h>

static DEFINE_SPINLOCK(kthread_create_lock);
static LIST_HEAD(kthread_create_list);
struct task_struct *kthreadd_task;

struct kthread_create_info
{
	/* Information passed to kthread() from kthreadd. */
	int (*threadfn)(void *data);
	void *data;
	int node;

	/* Result passed back to kthread_create() from kthreadd. */
	struct task_struct *result;
	struct completion *done;

	struct list_head list;
};

struct kthread {
	unsigned long flags;
	unsigned int cpu;
	void *data;
	struct completion parked;
	struct completion exited;
};

enum KTHREAD_BITS {
	KTHREAD_IS_PER_CPU = 0,
	KTHREAD_SHOULD_STOP,
	KTHREAD_SHOULD_PARK,
	KTHREAD_IS_PARKED,
};

#define __to_kthread(vfork)	\
	container_of(vfork, struct kthread, exited)

static inline struct kthread *to_kthread(struct task_struct *k)
{
	return __to_kthread(k->vfork_done);
}

static struct kthread *to_live_kthread(struct task_struct *k)
{
	struct completion *vfork = ACCESS_ONCE(k->vfork_done);
	if (likely(vfork) && try_get_task_stack(k))
		return __to_kthread(vfork);
	return NULL;
}

/**
 * kthread_should_stop - should this kthread return now?
 *
 * When someone calls kthread_stop() on your kthread, it will be woken
 * and this will return true.  You should then return, and your return
 * value will be passed through to kthread_stop().
 */
bool kthread_should_stop(void)
{
	return test_bit(KTHREAD_SHOULD_STOP, &to_kthread(current)->flags);
}
EXPORT_SYMBOL(kthread_should_stop);

/**
 * kthread_should_park - should this kthread park now?
 *
 * When someone calls kthread_park() on your kthread, it will be woken
 * and this will return true.  You should then do the necessary
 * cleanup and call kthread_parkme()
 *
 * Similar to kthread_should_stop(), but this keeps the thread alive
 * and in a park position. kthread_unpark() "restarts" the thread and
 * calls the thread function again.
 */
bool kthread_should_park(void)
{
	return test_bit(KTHREAD_SHOULD_PARK, &to_kthread(current)->flags);
}
EXPORT_SYMBOL_GPL(kthread_should_park);

/**
 * kthread_freezable_should_stop - should this freezable kthread return now?
 * @was_frozen: optional out parameter, indicates whether %current was frozen
 *
 * kthread_should_stop() for freezable kthreads, which will enter
 * refrigerator if necessary.  This function is safe from kthread_stop() /
 * freezer deadlock and freezable kthreads should use this function instead
 * of calling try_to_freeze() directly.
 */
bool kthread_freezable_should_stop(bool *was_frozen)
{
	bool frozen = false;

	might_sleep();

	if (unlikely(freezing(current)))
		frozen = __refrigerator(true);

	if (was_frozen)
		*was_frozen = frozen;

	return kthread_should_stop();
}
EXPORT_SYMBOL_GPL(kthread_freezable_should_stop);

/**
 * kthread_data - return data value specified on kthread creation
 * @task: kthread task in question
 *
 * Return the data value specified when kthread @task was created.
 * The caller is responsible for ensuring the validity of @task when
 * calling this function.
 */
void *kthread_data(struct task_struct *task)
{
	return to_kthread(task)->data;
}

/**
 * kthread_probe_data - speculative version of kthread_data()
 * @task: possible kthread task in question
 *
 * @task could be a kthread task.  Return the data value specified when it
 * was created if accessible.  If @task isn't a kthread task or its data is
 * inaccessible for any reason, %NULL is returned.  This function requires
 * that @task itself is safe to dereference.
 */
void *kthread_probe_data(struct task_struct *task)
{
	struct kthread *kthread = to_kthread(task);
	void *data = NULL;

	probe_kernel_read(&data, &kthread->data, sizeof(data));
	return data;
}

static void __kthread_parkme(struct kthread *self)
{
	__set_current_state(TASK_PARKED);
	while (test_bit(KTHREAD_SHOULD_PARK, &self->flags)) {
		if (!test_and_set_bit(KTHREAD_IS_PARKED, &self->flags))
			complete(&self->parked);
		schedule();
		__set_current_state(TASK_PARKED);
	}
	clear_bit(KTHREAD_IS_PARKED, &self->flags);
	__set_current_state(TASK_RUNNING);
}

void kthread_parkme(void)
{
	__kthread_parkme(to_kthread(current));
}
EXPORT_SYMBOL_GPL(kthread_parkme);

static int kthread(void *_create)
{
	/* Copy data: it's on kthread's stack */
	struct kthread_create_info *create = _create;
	int (*threadfn)(void *data) = create->threadfn;
	void *data = create->data;
	struct completion *done;
	struct kthread self;
	int ret;

	self.flags = 0;
	self.data = data;
	init_completion(&self.exited);
	init_completion(&self.parked);
	current->vfork_done = &self.exited;

	/* If user was SIGKILLed, I release the structure. */
	done = xchg(&create->done, NULL);
	if (!done) {
		kfree(create);
		do_exit(-EINTR);
	}
	/* OK, tell user we're spawned, wait for stop or wakeup */
	__set_current_state(TASK_UNINTERRUPTIBLE);
	create->result = current;
	complete(done);
	schedule();

	ret = -EINTR;

	if (!test_bit(KTHREAD_SHOULD_STOP, &self.flags)) {
		__kthread_parkme(&self);
		ret = threadfn(data);
	}
	/* we can't just return, we must preserve "self" on stack */
	do_exit(ret);
}

/* called from do_fork() to get node information for about to be created task */
int tsk_fork_get_node(struct task_struct *tsk)
{
#ifdef CONFIG_NUMA
	if (tsk == kthreadd_task)
		return tsk->pref_node_fork;
#endif
	return NUMA_NO_NODE;
}

static void create_kthread(struct kthread_create_info *create)
{
	int pid;

#ifdef CONFIG_NUMA
	current->pref_node_fork = create->node;
#endif
	/* We want our own signal handler (we take no signals by default). */
	pid = kernel_thread(kthread, create, CLONE_FS | CLONE_FILES | SIGCHLD);
	if (pid < 0) {
		/* If user was SIGKILLed, I release the structure. */
		struct completion *done = xchg(&create->done, NULL);

		if (!done) {
			kfree(create);
			return;
		}
		create->result = ERR_PTR(pid);
		complete(done);
	}
}

static struct task_struct *__kthread_create_on_node(int (*threadfn)(void *data),
						    void *data, int node,
						    const char namefmt[],
						    va_list args)
{
	DECLARE_COMPLETION_ONSTACK(done);
	struct task_struct *task;
	struct kthread_create_info *create = kmalloc(sizeof(*create),
						     GFP_KERNEL);

	if (!create)
		return ERR_PTR(-ENOMEM);
	create->threadfn = threadfn;
	create->data = data;
	create->node = node;
	create->done = &done;

	spin_lock(&kthread_create_lock);
	list_add_tail(&create->list, &kthread_create_list);
	spin_unlock(&kthread_create_lock);

	wake_up_process(kthreadd_task);
	/*
	 * Wait for completion in killable state, for I might be chosen by
	 * the OOM killer while kthreadd is trying to allocate memory for
	 * new kernel thread.
	 */
	if (unlikely(wait_for_completion_killable(&done))) {
		/*
		 * If I was SIGKILLed before kthreadd (or new kernel thread)
		 * calls complete(), leave the cleanup of this structure to
		 * that thread.
		 */
		if (xchg(&create->done, NULL))
			return ERR_PTR(-EINTR);
		/*
		 * kthreadd (or new kernel thread) will call complete()
		 * shortly.
		 */
		wait_for_completion(&done);
	}
	task = create->result;
	if (!IS_ERR(task)) {
		static const struct sched_param param = { .sched_priority = 0 };

		vsnprintf(task->comm, sizeof(task->comm), namefmt, args);
		/*
		 * root may have changed our (kthreadd's) priority or CPU mask.
		 * The kernel thread should not inherit these properties.
		 */
		sched_setscheduler_nocheck(task, SCHED_NORMAL, &param);
		set_cpus_allowed_ptr(task, cpu_all_mask);
	}
	kfree(create);
	return task;
}

/**
 * kthread_create_on_node - create a kthread.
 * @threadfn: the function to run until signal_pending(current).
 * @data: data ptr for @threadfn.
 * @node: task and thread structures for the thread are allocated on this node
 * @namefmt: printf-style name for the thread.
 *
 * Description: This helper function creates and names a kernel
 * thread.  The thread will be stopped: use wake_up_process() to start
 * it.  See also kthread_run().  The new thread has SCHED_NORMAL policy and
 * is affine to all CPUs.
 *
 * If thread is going to be bound on a particular cpu, give its node
 * in @node, to get NUMA affinity for kthread stack, or else give NUMA_NO_NODE.
 * When woken, the thread will run @threadfn() with @data as its
 * argument. @threadfn() can either call do_exit() directly if it is a
 * standalone thread for which no one will call kthread_stop(), or
 * return when 'kthread_should_stop()' is true (which means
 * kthread_stop() has been called).  The return value should be zero
 * or a negative error number; it will be passed to kthread_stop().
 *
 * Returns a task_struct or ERR_PTR(-ENOMEM) or ERR_PTR(-EINTR).
 */
struct task_struct *kthread_create_on_node(int (*threadfn)(void *data),
					   void *data, int node,
					   const char namefmt[],
					   ...)
{
	struct task_struct *task;
	va_list args;

	va_start(args, namefmt);
	task = __kthread_create_on_node(threadfn, data, node, namefmt, args);
	va_end(args);

	return task;
}
EXPORT_SYMBOL(kthread_create_on_node);

static void __kthread_bind_mask(struct task_struct *p, const struct cpumask *mask, long state)
{
	unsigned long flags;

	if (!wait_task_inactive(p, state)) {
		WARN_ON(1);
		return;
	}

	/* It's safe because the task is inactive. */
	raw_spin_lock_irqsave(&p->pi_lock, flags);
	do_set_cpus_allowed(p, mask);
	p->flags |= PF_NO_SETAFFINITY;
	raw_spin_unlock_irqrestore(&p->pi_lock, flags);
}

static void __kthread_bind(struct task_struct *p, unsigned int cpu, long state)
{
	__kthread_bind_mask(p, cpumask_of(cpu), state);
}

void kthread_bind_mask(struct task_struct *p, const struct cpumask *mask)
{
	__kthread_bind_mask(p, mask, TASK_UNINTERRUPTIBLE);
}

/**
 * kthread_bind - bind a just-created kthread to a cpu.
 * @p: thread created by kthread_create().
 * @cpu: cpu (might not be online, must be possible) for @k to run on.
 *
 * Description: This function is equivalent to set_cpus_allowed(),
 * except that @cpu doesn't need to be online, and the thread must be
 * stopped (i.e., just returned from kthread_create()).
 */
void kthread_bind(struct task_struct *p, unsigned int cpu)
{
	__kthread_bind(p, cpu, TASK_UNINTERRUPTIBLE);
}
EXPORT_SYMBOL(kthread_bind);

/**
 * kthread_create_on_cpu - Create a cpu bound kthread
 * @threadfn: the function to run until signal_pending(current).
 * @data: data ptr for @threadfn.
 * @cpu: The cpu on which the thread should be bound,
 * @namefmt: printf-style name for the thread. Format is restricted
 *	     to "name.*%u". Code fills in cpu number.
 *
 * Description: This helper function creates and names a kernel thread
 * The thread will be woken and put into park mode.
 */
struct task_struct *kthread_create_on_cpu(int (*threadfn)(void *data),
					  void *data, unsigned int cpu,
					  const char *namefmt)
{
	struct task_struct *p;

	p = kthread_create_on_node(threadfn, data, cpu_to_node(cpu), namefmt,
				   cpu);
	if (IS_ERR(p))
		return p;
	kthread_bind(p, cpu);
	/* CPU hotplug need to bind once again when unparking the thread. */
	set_bit(KTHREAD_IS_PER_CPU, &to_kthread(p)->flags);
	to_kthread(p)->cpu = cpu;
	return p;
}

static void __kthread_unpark(struct task_struct *k, struct kthread *kthread)
{
	clear_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
	/*
	 * We clear the IS_PARKED bit here as we don't wait
	 * until the task has left the park code. So if we'd
	 * park before that happens we'd see the IS_PARKED bit
	 * which might be about to be cleared.
	 */
	if (test_and_clear_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
		/*
		 * Newly created kthread was parked when the CPU was offline.
		 * The binding was lost and we need to set it again.
		 */
		if (test_bit(KTHREAD_IS_PER_CPU, &kthread->flags))
			__kthread_bind(k, kthread->cpu, TASK_PARKED);
		wake_up_state(k, TASK_PARKED);
	}
}

/**
 * kthread_unpark - unpark a thread created by kthread_create().
 * @k:		thread created by kthread_create().
 *
 * Sets kthread_should_park() for @k to return false, wakes it, and
 * waits for it to return. If the thread is marked percpu then its
 * bound to the cpu again.
 */
void kthread_unpark(struct task_struct *k)
{
	struct kthread *kthread = to_live_kthread(k);

	if (kthread) {
		__kthread_unpark(k, kthread);
		put_task_stack(k);
	}
}
EXPORT_SYMBOL_GPL(kthread_unpark);

/**
 * kthread_park - park a thread created by kthread_create().
 * @k: thread created by kthread_create().
 *
 * Sets kthread_should_park() for @k to return true, wakes it, and
 * waits for it to return. This can also be called after kthread_create()
 * instead of calling wake_up_process(): the thread will park without
 * calling threadfn().
 *
 * Returns 0 if the thread is parked, -ENOSYS if the thread exited.
 * If called by the kthread itself just the park bit is set.
 */
int kthread_park(struct task_struct *k)
{
	struct kthread *kthread = to_live_kthread(k);
	int ret = -ENOSYS;

	if (kthread) {
		if (!test_bit(KTHREAD_IS_PARKED, &kthread->flags)) {
			set_bit(KTHREAD_SHOULD_PARK, &kthread->flags);
			if (k != current) {
				wake_up_process(k);
				wait_for_completion(&kthread->parked);
			}
		}
		put_task_stack(k);
		ret = 0;
	}
	return ret;
}
EXPORT_SYMBOL_GPL(kthread_park);

/**
 * kthread_stop - stop a thread created by kthread_create().
 * @k: thread created by kthread_create().
 *
 * Sets kthread_should_stop() for @k to return true, wakes it, and
 * waits for it to exit. This can also be called after kthread_create()
 * instead of calling wake_up_process(): the thread will exit without
 * calling threadfn().
 *
 * If threadfn() may call do_exit() itself, the caller must ensure
 * task_struct can't go away.
 *
 * Returns the result of threadfn(), or %-EINTR if wake_up_process()
 * was never called.
 */
int kthread_stop(struct task_struct *k)
{
	struct kthread *kthread;
	int ret;

	trace_sched_kthread_stop(k);

	get_task_struct(k);
	kthread = to_live_kthread(k);
	if (kthread) {
		set_bit(KTHREAD_SHOULD_STOP, &kthread->flags);
		__kthread_unpark(k, kthread);
		wake_up_process(k);
		wait_for_completion(&kthread->exited);
		put_task_stack(k);
	}
	ret = k->exit_code;
	put_task_struct(k);

	trace_sched_kthread_stop_ret(ret);
	return ret;
}
EXPORT_SYMBOL(kthread_stop);

int kthreadd(void *unused)
{
	struct task_struct *tsk = current;

	/* Setup a clean context for our children to inherit. */
	set_task_comm(tsk, "kthreadd");
	ignore_signals(tsk);
	set_cpus_allowed_ptr(tsk, cpu_all_mask);
	set_mems_allowed(node_states[N_MEMORY]);

	current->flags |= PF_NOFREEZE;

	for (;;) {
		set_current_state(TASK_INTERRUPTIBLE);
		if (list_empty(&kthread_create_list))
			schedule();
		__set_current_state(TASK_RUNNING);

		spin_lock(&kthread_create_lock);
		while (!list_empty(&kthread_create_list)) {
			struct kthread_create_info *create;

			create = list_entry(kthread_create_list.next,
					    struct kthread_create_info, list);
			list_del_init(&create->list);
			spin_unlock(&kthread_create_lock);

			create_kthread(create);

			spin_lock(&kthread_create_lock);
		}
		spin_unlock(&kthread_create_lock);
	}

	return 0;
}

void __kthread_init_worker(struct kthread_worker *worker,
				const char *name,
				struct lock_class_key *key)
{
	memset(worker, 0, sizeof(struct kthread_worker));
	spin_lock_init(&worker->lock);
	lockdep_set_class_and_name(&worker->lock, key, name);
	INIT_LIST_HEAD(&worker->work_list);
	INIT_LIST_HEAD(&worker->delayed_work_list);
}
EXPORT_SYMBOL_GPL(__kthread_init_worker);

/**
 * kthread_worker_fn - kthread function to process kthread_worker
 * @worker_ptr: pointer to initialized kthread_worker
 *
 * This function implements the main cycle of kthread worker. It processes
 * work_list until it is stopped with kthread_stop(). It sleeps when the queue
 * is empty.
 *
 * The works are not allowed to keep any locks, disable preemption or interrupts
 * when they finish. There is defined a safe point for freezing when one work
 * finishes and before a new one is started.
 *
 * Also the works must not be handled by more than one worker at the same time,
 * see also kthread_queue_work().
 */
int kthread_worker_fn(void *worker_ptr)
{
	struct kthread_worker *worker = worker_ptr;
	struct kthread_work *work;

	/*
	 * FIXME: Update the check and remove the assignment when all kthread
	 * worker users are created using kthread_create_worker*() functions.
	 */
	WARN_ON(worker->task && worker->task != current);
	worker->task = current;

	if (worker->flags & KTW_FREEZABLE)
		set_freezable();

repeat:
	set_current_state(TASK_INTERRUPTIBLE);	/* mb paired w/ kthread_stop */

	if (kthread_should_stop()) {
		__set_current_state(TASK_RUNNING);
		spin_lock_irq(&worker->lock);
		worker->task = NULL;
		spin_unlock_irq(&worker->lock);
		return 0;
	}

	work = NULL;
	spin_lock_irq(&worker->lock);
	if (!list_empty(&worker->work_list)) {
		work = list_first_entry(&worker->work_list,
					struct kthread_work, node);
		list_del_init(&work->node);
	}
	worker->current_work = work;
	spin_unlock_irq(&worker->lock);

	if (work) {
		__set_current_state(TASK_RUNNING);
		work->func(work);
	} else if (!freezing(current))
		schedule();

	try_to_freeze();
	goto repeat;
}
EXPORT_SYMBOL_GPL(kthread_worker_fn);

static struct kthread_worker *
__kthread_create_worker(int cpu, unsigned int flags,
			const char namefmt[], va_list args)
{
	struct kthread_worker *worker;
	struct task_struct *task;

	worker = kzalloc(sizeof(*worker), GFP_KERNEL);
	if (!worker)
		return ERR_PTR(-ENOMEM);

	kthread_init_worker(worker);

	if (cpu >= 0) {
		char name[TASK_COMM_LEN];

		/*
		 * kthread_create_worker_on_cpu() allows to pass a generic
		 * namefmt in compare with kthread_create_on_cpu. We need
		 * to format it here.
		 */
		vsnprintf(name, sizeof(name), namefmt, args);
		task = kthread_create_on_cpu(kthread_worker_fn, worker,
					     cpu, name);
	} else {
		task = __kthread_create_on_node(kthread_worker_fn, worker,
						-1, namefmt, args);
	}

	if (IS_ERR(task))
		goto fail_task;

	worker->flags = flags;
	worker->task = task;
	wake_up_process(task);
	return worker;

fail_task:
	kfree(worker);
	return ERR_CAST(task);
}

/**
 * kthread_create_worker - create a kthread worker
 * @flags: flags modifying the default behavior of the worker
 * @namefmt: printf-style name for the kthread worker (task).
 *
 * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
 * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
 * when the worker was SIGKILLed.
 */
struct kthread_worker *
kthread_create_worker(unsigned int flags, const char namefmt[], ...)
{
	struct kthread_worker *worker;
	va_list args;

	va_start(args, namefmt);
	worker = __kthread_create_worker(-1, flags, namefmt, args);
	va_end(args);

	return worker;
}
EXPORT_SYMBOL(kthread_create_worker);

/**
 * kthread_create_worker_on_cpu - create a kthread worker and bind it
 *	it to a given CPU and the associated NUMA node.
 * @cpu: CPU number
 * @flags: flags modifying the default behavior of the worker
 * @namefmt: printf-style name for the kthread worker (task).
 *
 * Use a valid CPU number if you want to bind the kthread worker
 * to the given CPU and the associated NUMA node.
 *
 * A good practice is to add the cpu number also into the worker name.
 * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu).
 *
 * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM)
 * when the needed structures could not get allocated, and ERR_PTR(-EINTR)
 * when the worker was SIGKILLed.
 */
struct kthread_worker *
kthread_create_worker_on_cpu(int cpu, unsigned int flags,
			     const char namefmt[], ...)
{
	struct kthread_worker *worker;
	va_list args;

	va_start(args, namefmt);
	worker = __kthread_create_worker(cpu, flags, namefmt, args);
	va_end(args);

	return worker;
}
EXPORT_SYMBOL(kthread_create_worker_on_cpu);

/*
 * Returns true when the work could not be queued at the moment.
 * It happens when it is already pending in a worker list
 * or when it is being cancelled.
 */
static inline bool queuing_blocked(struct kthread_worker *worker,
				   struct kthread_work *work)
{
	lockdep_assert_held(&worker->lock);

	return !list_empty(&work->node) || work->canceling;
}

static void kthread_insert_work_sanity_check(struct kthread_worker *worker,
					     struct kthread_work *work)
{
	lockdep_assert_held(&worker->lock);
	WARN_ON_ONCE(!list_empty(&work->node));
	/* Do not use a work with >1 worker, see kthread_queue_work() */
	WARN_ON_ONCE(work->worker && work->worker != worker);
}

/* insert @work before @pos in @worker */
static void kthread_insert_work(struct kthread_worker *worker,
				struct kthread_work *work,
				struct list_head *pos)
{
	kthread_insert_work_sanity_check(worker, work);

	list_add_tail(&work->node, pos);
	work->worker = worker;
	if (!worker->current_work && likely(worker->task))
		wake_up_process(worker->task);
}

/**
 * kthread_queue_work - queue a kthread_work
 * @worker: target kthread_worker
 * @work: kthread_work to queue
 *
 * Queue @work to work processor @task for async execution.  @task
 * must have been created with kthread_worker_create().  Returns %true
 * if @work was successfully queued, %false if it was already pending.
 *
 * Reinitialize the work if it needs to be used by another worker.
 * For example, when the worker was stopped and started again.
 */
bool kthread_queue_work(struct kthread_worker *worker,
			struct kthread_work *work)
{
	bool ret = false;
	unsigned long flags;

	spin_lock_irqsave(&worker->lock, flags);
	if (!queuing_blocked(worker, work)) {
		kthread_insert_work(worker, work, &worker->work_list);
		ret = true;
	}
	spin_unlock_irqrestore(&worker->lock, flags);
	return ret;
}
EXPORT_SYMBOL_GPL(kthread_queue_work);

/**
 * kthread_delayed_work_timer_fn - callback that queues the associated kthread
 *	delayed work when the timer expires.
 * @__data: pointer to the data associated with the timer
 *
 * The format of the function is defined by struct timer_list.
 * It should have been called from irqsafe timer with irq already off.
 */
void kthread_delayed_work_timer_fn(unsigned long __data)
{
	struct kthread_delayed_work *dwork =
		(struct kthread_delayed_work *)__data;
	struct kthread_work *work = &dwork->work;
	struct kthread_worker *worker = work->worker;

	/*
	 * This might happen when a pending work is reinitialized.
	 * It means that it is used a wrong way.
	 */
	if (WARN_ON_ONCE(!worker))
		return;

	spin_lock(&worker->lock);
	/* Work must not be used with >1 worker, see kthread_queue_work(). */
	WARN_ON_ONCE(work->worker != worker);

	/* Move the work from worker->delayed_work_list. */
	WARN_ON_ONCE(list_empty(&work->node));
	list_del_init(&work->node);
	kthread_insert_work(worker, work, &worker->work_list);

	spin_unlock(&worker->lock);
}
EXPORT_SYMBOL(kthread_delayed_work_timer_fn);

void __kthread_queue_delayed_work(struct kthread_worker *worker,
				  struct kthread_delayed_work *dwork,
				  unsigned long delay)
{
	struct timer_list *timer = &dwork->timer;
	struct kthread_work *work = &dwork->work;

	WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn ||
		     timer->data != (unsigned long)dwork);

	/*
	 * If @delay is 0, queue @dwork->work immediately.  This is for
	 * both optimization and correctness.  The earliest @timer can
	 * expire is on the closest next tick and delayed_work users depend
	 * on that there's no such delay when @delay is 0.
	 */
	if (!delay) {
		kthread_insert_work(worker, work, &worker->work_list);
		return;
	}

	/* Be paranoid and try to detect possible races already now. */
	kthread_insert_work_sanity_check(worker, work);

	list_add(&work->node, &worker->delayed_work_list);
	work->worker = worker;
	timer_stats_timer_set_start_info(&dwork->timer);
	timer->expires = jiffies + delay;
	add_timer(timer);
}

/**
 * kthread_queue_delayed_work - queue the associated kthread work
 *	after a delay.
 * @worker: target kthread_worker
 * @dwork: kthread_delayed_work to queue
 * @delay: number of jiffies to wait before queuing
 *
 * If the work has not been pending it starts a timer that will queue
 * the work after the given @delay. If @delay is zero, it queues the
 * work immediately.
 *
 * Return: %false if the @work has already been pending. It means that
 * either the timer was running or the work was queued. It returns %true
 * otherwise.
 */
bool kthread_queue_delayed_work(struct kthread_worker *worker,
				struct kthread_delayed_work *dwork,
				unsigned long delay)
{
	struct kthread_work *work = &dwork->work;
	unsigned long flags;
	bool ret = false;

	spin_lock_irqsave(&worker->lock, flags);

	if (!queuing_blocked(worker, work)) {
		__kthread_queue_delayed_work(worker, dwork, delay);
		ret = true;
	}

	spin_unlock_irqrestore(&worker->lock, flags);
	return ret;
}
EXPORT_SYMBOL_GPL(kthread_queue_delayed_work);

struct kthread_flush_work {
	struct kthread_work	work;
	struct completion	done;
};

static void kthread_flush_work_fn(struct kthread_work *work)
{
	struct kthread_flush_work *fwork =
		container_of(work, struct kthread_flush_work, work);
	complete(&fwork->done);
}

/**
 * kthread_flush_work - flush a kthread_work
 * @work: work to flush
 *
 * If @work is queued or executing, wait for it to finish execution.
 */
void kthread_flush_work(struct kthread_work *work)
{
	struct kthread_flush_work fwork = {
		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
	};
	struct kthread_worker *worker;
	bool noop = false;

	worker = work->worker;
	if (!worker)
		return;

	spin_lock_irq(&worker->lock);
	/* Work must not be used with >1 worker, see kthread_queue_work(). */
	WARN_ON_ONCE(work->worker != worker);

	if (!list_empty(&work->node))
		kthread_insert_work(worker, &fwork.work, work->node.next);
	else if (worker->current_work == work)
		kthread_insert_work(worker, &fwork.work,
				    worker->work_list.next);
	else
		noop = true;

	spin_unlock_irq(&worker->lock);

	if (!noop)
		wait_for_completion(&fwork.done);
}
EXPORT_SYMBOL_GPL(kthread_flush_work);

/*
 * This function removes the work from the worker queue. Also it makes sure
 * that it won't get queued later via the delayed work's timer.
 *
 * The work might still be in use when this function finishes. See the
 * current_work proceed by the worker.
 *
 * Return: %true if @work was pending and successfully canceled,
 *	%false if @work was not pending
 */
static bool __kthread_cancel_work(struct kthread_work *work, bool is_dwork,
				  unsigned long *flags)
{
	/* Try to cancel the timer if exists. */
	if (is_dwork) {
		struct kthread_delayed_work *dwork =
			container_of(work, struct kthread_delayed_work, work);
		struct kthread_worker *worker = work->worker;

		/*
		 * del_timer_sync() must be called to make sure that the timer
		 * callback is not running. The lock must be temporary released
		 * to avoid a deadlock with the callback. In the meantime,
		 * any queuing is blocked by setting the canceling counter.
		 */
		work->canceling++;
		spin_unlock_irqrestore(&worker->lock, *flags);
		del_timer_sync(&dwork->timer);
		spin_lock_irqsave(&worker->lock, *flags);
		work->canceling--;
	}

	/*
	 * Try to remove the work from a worker list. It might either
	 * be from worker->work_list or from worker->delayed_work_list.
	 */
	if (!list_empty(&work->node)) {
		list_del_init(&work->node);
		return true;
	}

	return false;
}

/**
 * kthread_mod_delayed_work - modify delay of or queue a kthread delayed work
 * @worker: kthread worker to use
 * @dwork: kthread delayed work to queue
 * @delay: number of jiffies to wait before queuing
 *
 * If @dwork is idle, equivalent to kthread_queue_delayed_work(). Otherwise,
 * modify @dwork's timer so that it expires after @delay. If @delay is zero,
 * @work is guaranteed to be queued immediately.
 *
 * Return: %true if @dwork was pending and its timer was modified,
 * %false otherwise.
 *
 * A special case is when the work is being canceled in parallel.
 * It might be caused either by the real kthread_cancel_delayed_work_sync()
 * or yet another kthread_mod_delayed_work() call. We let the other command
 * win and return %false here. The caller is supposed to synchronize these
 * operations a reasonable way.
 *
 * This function is safe to call from any context including IRQ handler.
 * See __kthread_cancel_work() and kthread_delayed_work_timer_fn()
 * for details.
 */
bool kthread_mod_delayed_work(struct kthread_worker *worker,
			      struct kthread_delayed_work *dwork,
			      unsigned long delay)
{
	struct kthread_work *work = &dwork->work;
	unsigned long flags;
	int ret = false;

	spin_lock_irqsave(&worker->lock, flags);

	/* Do not bother with canceling when never queued. */
	if (!work->worker)
		goto fast_queue;

	/* Work must not be used with >1 worker, see kthread_queue_work() */
	WARN_ON_ONCE(work->worker != worker);

	/* Do not fight with another command that is canceling this work. */
	if (work->canceling)
		goto out;

	ret = __kthread_cancel_work(work, true, &flags);
fast_queue:
	__kthread_queue_delayed_work(worker, dwork, delay);
out:
	spin_unlock_irqrestore(&worker->lock, flags);
	return ret;
}
EXPORT_SYMBOL_GPL(kthread_mod_delayed_work);

static bool __kthread_cancel_work_sync(struct kthread_work *work, bool is_dwork)
{
	struct kthread_worker *worker = work->worker;
	unsigned long flags;
	int ret = false;

	if (!worker)
		goto out;

	spin_lock_irqsave(&worker->lock, flags);
	/* Work must not be used with >1 worker, see kthread_queue_work(). */
	WARN_ON_ONCE(work->worker != worker);

	ret = __kthread_cancel_work(work, is_dwork, &flags);

	if (worker->current_work != work)
		goto out_fast;

	/*
	 * The work is in progress and we need to wait with the lock released.
	 * In the meantime, block any queuing by setting the canceling counter.
	 */
	work->canceling++;
	spin_unlock_irqrestore(&worker->lock, flags);
	kthread_flush_work(work);
	spin_lock_irqsave(&worker->lock, flags);
	work->canceling--;

out_fast:
	spin_unlock_irqrestore(&worker->lock, flags);
out:
	return ret;
}

/**
 * kthread_cancel_work_sync - cancel a kthread work and wait for it to finish
 * @work: the kthread work to cancel
 *
 * Cancel @work and wait for its execution to finish.  This function
 * can be used even if the work re-queues itself. On return from this
 * function, @work is guaranteed to be not pending or executing on any CPU.
 *
 * kthread_cancel_work_sync(&delayed_work->work) must not be used for
 * delayed_work's. Use kthread_cancel_delayed_work_sync() instead.
 *
 * The caller must ensure that the worker on which @work was last
 * queued can't be destroyed before this function returns.
 *
 * Return: %true if @work was pending, %false otherwise.
 */
bool kthread_cancel_work_sync(struct kthread_work *work)
{
	return __kthread_cancel_work_sync(work, false);
}
EXPORT_SYMBOL_GPL(kthread_cancel_work_sync);

/**
 * kthread_cancel_delayed_work_sync - cancel a kthread delayed work and
 *	wait for it to finish.
 * @dwork: the kthread delayed work to cancel
 *
 * This is kthread_cancel_work_sync() for delayed works.
 *
 * Return: %true if @dwork was pending, %false otherwise.
 */
bool kthread_cancel_delayed_work_sync(struct kthread_delayed_work *dwork)
{
	return __kthread_cancel_work_sync(&dwork->work, true);
}
EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);

/**
 * kthread_flush_worker - flush all current works on a kthread_worker
 * @worker: worker to flush
 *
 * Wait until all currently executing or pending works on @worker are
 * finished.
 */
void kthread_flush_worker(struct kthread_worker *worker)
{
	struct kthread_flush_work fwork = {
		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
	};

	kthread_queue_work(worker, &fwork.work);
	wait_for_completion(&fwork.done);
}
EXPORT_SYMBOL_GPL(kthread_flush_worker);

/**
 * kthread_destroy_worker - destroy a kthread worker
 * @worker: worker to be destroyed
 *
 * Flush and destroy @worker.  The simple flush is enough because the kthread
 * worker API is used only in trivial scenarios.  There are no multi-step state
 * machines needed.
 */
void kthread_destroy_worker(struct kthread_worker *worker)
{
	struct task_struct *task;

	task = worker->task;
	if (WARN_ON(!task))
		return;

	kthread_flush_worker(worker);
	kthread_stop(task);
	WARN_ON(!list_empty(&worker->work_list));
	kfree(worker);
}
EXPORT_SYMBOL(kthread_destroy_worker);
OpenPOWER on IntegriCloud