summaryrefslogtreecommitdiff
path: root/kernel/smp.c
blob: 6a1f1daa3dc44f3cf57e412e564e0b5d60d7da4e (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
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Generic helpers for smp ipi calls
 *
 * (C) Jens Axboe <jens.axboe@oracle.com> 2008
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

#include <linux/irq_work.h>
#include <linux/rcupdate.h>
#include <linux/rculist.h>
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/percpu.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/gfp.h>
#include <linux/smp.h>
#include <linux/cpu.h>
#include <linux/sched.h>
#include <linux/sched/idle.h>
#include <linux/hypervisor.h>
#include <linux/sched/clock.h>
#include <linux/nmi.h>
#include <linux/sched/debug.h>
#include <linux/jump_label.h>

#include "smpboot.h"
#include "sched/smp.h"

#define CSD_TYPE(_csd)	((_csd)->node.u_flags & CSD_FLAG_TYPE_MASK)

#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
union cfd_seq_cnt {
	u64		val;
	struct {
		u64	src:16;
		u64	dst:16;
#define CFD_SEQ_NOCPU	0xffff
		u64	type:4;
#define CFD_SEQ_QUEUE	0
#define CFD_SEQ_IPI	1
#define CFD_SEQ_NOIPI	2
#define CFD_SEQ_PING	3
#define CFD_SEQ_PINGED	4
#define CFD_SEQ_HANDLE	5
#define CFD_SEQ_DEQUEUE	6
#define CFD_SEQ_IDLE	7
#define CFD_SEQ_GOTIPI	8
#define CFD_SEQ_HDLEND	9
		u64	cnt:28;
	}		u;
};

static char *seq_type[] = {
	[CFD_SEQ_QUEUE]		= "queue",
	[CFD_SEQ_IPI]		= "ipi",
	[CFD_SEQ_NOIPI]		= "noipi",
	[CFD_SEQ_PING]		= "ping",
	[CFD_SEQ_PINGED]	= "pinged",
	[CFD_SEQ_HANDLE]	= "handle",
	[CFD_SEQ_DEQUEUE]	= "dequeue (src CPU 0 == empty)",
	[CFD_SEQ_IDLE]		= "idle",
	[CFD_SEQ_GOTIPI]	= "gotipi",
	[CFD_SEQ_HDLEND]	= "hdlend (src CPU 0 == early)",
};

struct cfd_seq_local {
	u64	ping;
	u64	pinged;
	u64	handle;
	u64	dequeue;
	u64	idle;
	u64	gotipi;
	u64	hdlend;
};
#endif

struct cfd_percpu {
	call_single_data_t	csd;
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
	u64	seq_queue;
	u64	seq_ipi;
	u64	seq_noipi;
#endif
};

struct call_function_data {
	struct cfd_percpu	__percpu *pcpu;
	cpumask_var_t		cpumask;
	cpumask_var_t		cpumask_ipi;
};

static DEFINE_PER_CPU_ALIGNED(struct call_function_data, cfd_data);

static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue);

static void flush_smp_call_function_queue(bool warn_cpu_offline);

int smpcfd_prepare_cpu(unsigned int cpu)
{
	struct call_function_data *cfd = &per_cpu(cfd_data, cpu);

	if (!zalloc_cpumask_var_node(&cfd->cpumask, GFP_KERNEL,
				     cpu_to_node(cpu)))
		return -ENOMEM;
	if (!zalloc_cpumask_var_node(&cfd->cpumask_ipi, GFP_KERNEL,
				     cpu_to_node(cpu))) {
		free_cpumask_var(cfd->cpumask);
		return -ENOMEM;
	}
	cfd->pcpu = alloc_percpu(struct cfd_percpu);
	if (!cfd->pcpu) {
		free_cpumask_var(cfd->cpumask);
		free_cpumask_var(cfd->cpumask_ipi);
		return -ENOMEM;
	}

	return 0;
}

int smpcfd_dead_cpu(unsigned int cpu)
{
	struct call_function_data *cfd = &per_cpu(cfd_data, cpu);

	free_cpumask_var(cfd->cpumask);
	free_cpumask_var(cfd->cpumask_ipi);
	free_percpu(cfd->pcpu);
	return 0;
}

int smpcfd_dying_cpu(unsigned int cpu)
{
	/*
	 * The IPIs for the smp-call-function callbacks queued by other
	 * CPUs might arrive late, either due to hardware latencies or
	 * because this CPU disabled interrupts (inside stop-machine)
	 * before the IPIs were sent. So flush out any pending callbacks
	 * explicitly (without waiting for the IPIs to arrive), to
	 * ensure that the outgoing CPU doesn't go offline with work
	 * still pending.
	 */
	flush_smp_call_function_queue(false);
	irq_work_run();
	return 0;
}

void __init call_function_init(void)
{
	int i;

	for_each_possible_cpu(i)
		init_llist_head(&per_cpu(call_single_queue, i));

	smpcfd_prepare_cpu(smp_processor_id());
}

#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG

static DEFINE_STATIC_KEY_FALSE(csdlock_debug_enabled);
static DEFINE_STATIC_KEY_FALSE(csdlock_debug_extended);

static int __init csdlock_debug(char *str)
{
	unsigned int val = 0;

	if (str && !strcmp(str, "ext")) {
		val = 1;
		static_branch_enable(&csdlock_debug_extended);
	} else
		get_option(&str, &val);

	if (val)
		static_branch_enable(&csdlock_debug_enabled);

	return 0;
}
early_param("csdlock_debug", csdlock_debug);

static DEFINE_PER_CPU(call_single_data_t *, cur_csd);
static DEFINE_PER_CPU(smp_call_func_t, cur_csd_func);
static DEFINE_PER_CPU(void *, cur_csd_info);
static DEFINE_PER_CPU(struct cfd_seq_local, cfd_seq_local);

static ulong csd_lock_timeout = 5000;  /* CSD lock timeout in milliseconds. */
module_param(csd_lock_timeout, ulong, 0444);

static atomic_t csd_bug_count = ATOMIC_INIT(0);
static u64 cfd_seq;

#define CFD_SEQ(s, d, t, c)	\
	(union cfd_seq_cnt){ .u.src = s, .u.dst = d, .u.type = t, .u.cnt = c }

static u64 cfd_seq_inc(unsigned int src, unsigned int dst, unsigned int type)
{
	union cfd_seq_cnt new, old;

	new = CFD_SEQ(src, dst, type, 0);

	do {
		old.val = READ_ONCE(cfd_seq);
		new.u.cnt = old.u.cnt + 1;
	} while (cmpxchg(&cfd_seq, old.val, new.val) != old.val);

	return old.val;
}

#define cfd_seq_store(var, src, dst, type)				\
	do {								\
		if (static_branch_unlikely(&csdlock_debug_extended))	\
			var = cfd_seq_inc(src, dst, type);		\
	} while (0)

/* Record current CSD work for current CPU, NULL to erase. */
static void __csd_lock_record(struct __call_single_data *csd)
{
	if (!csd) {
		smp_mb(); /* NULL cur_csd after unlock. */
		__this_cpu_write(cur_csd, NULL);
		return;
	}
	__this_cpu_write(cur_csd_func, csd->func);
	__this_cpu_write(cur_csd_info, csd->info);
	smp_wmb(); /* func and info before csd. */
	__this_cpu_write(cur_csd, csd);
	smp_mb(); /* Update cur_csd before function call. */
		  /* Or before unlock, as the case may be. */
}

static __always_inline void csd_lock_record(struct __call_single_data *csd)
{
	if (static_branch_unlikely(&csdlock_debug_enabled))
		__csd_lock_record(csd);
}

static int csd_lock_wait_getcpu(struct __call_single_data *csd)
{
	unsigned int csd_type;

	csd_type = CSD_TYPE(csd);
	if (csd_type == CSD_TYPE_ASYNC || csd_type == CSD_TYPE_SYNC)
		return csd->node.dst; /* Other CSD_TYPE_ values might not have ->dst. */
	return -1;
}

static void cfd_seq_data_add(u64 val, unsigned int src, unsigned int dst,
			     unsigned int type, union cfd_seq_cnt *data,
			     unsigned int *n_data, unsigned int now)
{
	union cfd_seq_cnt new[2];
	unsigned int i, j, k;

	new[0].val = val;
	new[1] = CFD_SEQ(src, dst, type, new[0].u.cnt + 1);

	for (i = 0; i < 2; i++) {
		if (new[i].u.cnt <= now)
			new[i].u.cnt |= 0x80000000U;
		for (j = 0; j < *n_data; j++) {
			if (new[i].u.cnt == data[j].u.cnt) {
				/* Direct read value trumps generated one. */
				if (i == 0)
					data[j].val = new[i].val;
				break;
			}
			if (new[i].u.cnt < data[j].u.cnt) {
				for (k = *n_data; k > j; k--)
					data[k].val = data[k - 1].val;
				data[j].val = new[i].val;
				(*n_data)++;
				break;
			}
		}
		if (j == *n_data) {
			data[j].val = new[i].val;
			(*n_data)++;
		}
	}
}

static const char *csd_lock_get_type(unsigned int type)
{
	return (type >= ARRAY_SIZE(seq_type)) ? "?" : seq_type[type];
}

static void csd_lock_print_extended(struct __call_single_data *csd, int cpu)
{
	struct cfd_seq_local *seq = &per_cpu(cfd_seq_local, cpu);
	unsigned int srccpu = csd->node.src;
	struct call_function_data *cfd = per_cpu_ptr(&cfd_data, srccpu);
	struct cfd_percpu *pcpu = per_cpu_ptr(cfd->pcpu, cpu);
	unsigned int now;
	union cfd_seq_cnt data[2 * ARRAY_SIZE(seq_type)];
	unsigned int n_data = 0, i;

	data[0].val = READ_ONCE(cfd_seq);
	now = data[0].u.cnt;

	cfd_seq_data_add(pcpu->seq_queue,			srccpu, cpu,	       CFD_SEQ_QUEUE,  data, &n_data, now);
	cfd_seq_data_add(pcpu->seq_ipi,				srccpu, cpu,	       CFD_SEQ_IPI,    data, &n_data, now);
	cfd_seq_data_add(pcpu->seq_noipi,			srccpu, cpu,	       CFD_SEQ_NOIPI,  data, &n_data, now);

	cfd_seq_data_add(per_cpu(cfd_seq_local.ping, srccpu),	srccpu, CFD_SEQ_NOCPU, CFD_SEQ_PING,   data, &n_data, now);
	cfd_seq_data_add(per_cpu(cfd_seq_local.pinged, srccpu), srccpu, CFD_SEQ_NOCPU, CFD_SEQ_PINGED, data, &n_data, now);

	cfd_seq_data_add(seq->idle,    CFD_SEQ_NOCPU, cpu, CFD_SEQ_IDLE,    data, &n_data, now);
	cfd_seq_data_add(seq->gotipi,  CFD_SEQ_NOCPU, cpu, CFD_SEQ_GOTIPI,  data, &n_data, now);
	cfd_seq_data_add(seq->handle,  CFD_SEQ_NOCPU, cpu, CFD_SEQ_HANDLE,  data, &n_data, now);
	cfd_seq_data_add(seq->dequeue, CFD_SEQ_NOCPU, cpu, CFD_SEQ_DEQUEUE, data, &n_data, now);
	cfd_seq_data_add(seq->hdlend,  CFD_SEQ_NOCPU, cpu, CFD_SEQ_HDLEND,  data, &n_data, now);

	for (i = 0; i < n_data; i++) {
		pr_alert("\tcsd: cnt(%07x): %04x->%04x %s\n",
			 data[i].u.cnt & ~0x80000000U, data[i].u.src,
			 data[i].u.dst, csd_lock_get_type(data[i].u.type));
	}
	pr_alert("\tcsd: cnt now: %07x\n", now);
}

/*
 * Complain if too much time spent waiting.  Note that only
 * the CSD_TYPE_SYNC/ASYNC types provide the destination CPU,
 * so waiting on other types gets much less information.
 */
static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *ts1, int *bug_id)
{
	int cpu = -1;
	int cpux;
	bool firsttime;
	u64 ts2, ts_delta;
	call_single_data_t *cpu_cur_csd;
	unsigned int flags = READ_ONCE(csd->node.u_flags);
	unsigned long long csd_lock_timeout_ns = csd_lock_timeout * NSEC_PER_MSEC;

	if (!(flags & CSD_FLAG_LOCK)) {
		if (!unlikely(*bug_id))
			return true;
		cpu = csd_lock_wait_getcpu(csd);
		pr_alert("csd: CSD lock (#%d) got unstuck on CPU#%02d, CPU#%02d released the lock.\n",
			 *bug_id, raw_smp_processor_id(), cpu);
		return true;
	}

	ts2 = sched_clock();
	ts_delta = ts2 - *ts1;
	if (likely(ts_delta <= csd_lock_timeout_ns || csd_lock_timeout_ns == 0))
		return false;

	firsttime = !*bug_id;
	if (firsttime)
		*bug_id = atomic_inc_return(&csd_bug_count);
	cpu = csd_lock_wait_getcpu(csd);
	if (WARN_ONCE(cpu < 0 || cpu >= nr_cpu_ids, "%s: cpu = %d\n", __func__, cpu))
		cpux = 0;
	else
		cpux = cpu;
	cpu_cur_csd = smp_load_acquire(&per_cpu(cur_csd, cpux)); /* Before func and info. */
	pr_alert("csd: %s non-responsive CSD lock (#%d) on CPU#%d, waiting %llu ns for CPU#%02d %pS(%ps).\n",
		 firsttime ? "Detected" : "Continued", *bug_id, raw_smp_processor_id(), ts2 - ts0,
		 cpu, csd->func, csd->info);
	if (cpu_cur_csd && csd != cpu_cur_csd) {
		pr_alert("\tcsd: CSD lock (#%d) handling prior %pS(%ps) request.\n",
			 *bug_id, READ_ONCE(per_cpu(cur_csd_func, cpux)),
			 READ_ONCE(per_cpu(cur_csd_info, cpux)));
	} else {
		pr_alert("\tcsd: CSD lock (#%d) %s.\n",
			 *bug_id, !cpu_cur_csd ? "unresponsive" : "handling this request");
	}
	if (cpu >= 0) {
		if (static_branch_unlikely(&csdlock_debug_extended))
			csd_lock_print_extended(csd, cpu);
		if (!trigger_single_cpu_backtrace(cpu))
			dump_cpu_task(cpu);
		if (!cpu_cur_csd) {
			pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\n", *bug_id, raw_smp_processor_id(), cpu);
			arch_send_call_function_single_ipi(cpu);
		}
	}
	dump_stack();
	*ts1 = ts2;

	return false;
}

/*
 * csd_lock/csd_unlock used to serialize access to per-cpu csd resources
 *
 * For non-synchronous ipi calls the csd can still be in use by the
 * previous function call. For multi-cpu calls its even more interesting
 * as we'll have to ensure no other cpu is observing our csd.
 */
static void __csd_lock_wait(struct __call_single_data *csd)
{
	int bug_id = 0;
	u64 ts0, ts1;

	ts1 = ts0 = sched_clock();
	for (;;) {
		if (csd_lock_wait_toolong(csd, ts0, &ts1, &bug_id))
			break;
		cpu_relax();
	}
	smp_acquire__after_ctrl_dep();
}

static __always_inline void csd_lock_wait(struct __call_single_data *csd)
{
	if (static_branch_unlikely(&csdlock_debug_enabled)) {
		__csd_lock_wait(csd);
		return;
	}

	smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
}

static void __smp_call_single_queue_debug(int cpu, struct llist_node *node)
{
	unsigned int this_cpu = smp_processor_id();
	struct cfd_seq_local *seq = this_cpu_ptr(&cfd_seq_local);
	struct call_function_data *cfd = this_cpu_ptr(&cfd_data);
	struct cfd_percpu *pcpu = per_cpu_ptr(cfd->pcpu, cpu);

	cfd_seq_store(pcpu->seq_queue, this_cpu, cpu, CFD_SEQ_QUEUE);
	if (llist_add(node, &per_cpu(call_single_queue, cpu))) {
		cfd_seq_store(pcpu->seq_ipi, this_cpu, cpu, CFD_SEQ_IPI);
		cfd_seq_store(seq->ping, this_cpu, cpu, CFD_SEQ_PING);
		send_call_function_single_ipi(cpu);
		cfd_seq_store(seq->pinged, this_cpu, cpu, CFD_SEQ_PINGED);
	} else {
		cfd_seq_store(pcpu->seq_noipi, this_cpu, cpu, CFD_SEQ_NOIPI);
	}
}
#else
#define cfd_seq_store(var, src, dst, type)

static void csd_lock_record(struct __call_single_data *csd)
{
}

static __always_inline void csd_lock_wait(struct __call_single_data *csd)
{
	smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
}
#endif

static __always_inline void csd_lock(struct __call_single_data *csd)
{
	csd_lock_wait(csd);
	csd->node.u_flags |= CSD_FLAG_LOCK;

	/*
	 * prevent CPU from reordering the above assignment
	 * to ->flags with any subsequent assignments to other
	 * fields of the specified call_single_data_t structure:
	 */
	smp_wmb();
}

static __always_inline void csd_unlock(struct __call_single_data *csd)
{
	WARN_ON(!(csd->node.u_flags & CSD_FLAG_LOCK));

	/*
	 * ensure we're all done before releasing data:
	 */
	smp_store_release(&csd->node.u_flags, 0);
}

static DEFINE_PER_CPU_SHARED_ALIGNED(call_single_data_t, csd_data);

void __smp_call_single_queue(int cpu, struct llist_node *node)
{
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
	if (static_branch_unlikely(&csdlock_debug_extended)) {
		unsigned int type;

		type = CSD_TYPE(container_of(node, call_single_data_t,
					     node.llist));
		if (type == CSD_TYPE_SYNC || type == CSD_TYPE_ASYNC) {
			__smp_call_single_queue_debug(cpu, node);
			return;
		}
	}
#endif

	/*
	 * The list addition should be visible before sending the IPI
	 * handler locks the list to pull the entry off it because of
	 * normal cache coherency rules implied by spinlocks.
	 *
	 * If IPIs can go out of order to the cache coherency protocol
	 * in an architecture, sufficient synchronisation should be added
	 * to arch code to make it appear to obey cache coherency WRT
	 * locking and barrier primitives. Generic code isn't really
	 * equipped to do the right thing...
	 */
	if (llist_add(node, &per_cpu(call_single_queue, cpu)))
		send_call_function_single_ipi(cpu);
}

/*
 * Insert a previously allocated call_single_data_t element
 * for execution on the given CPU. data must already have
 * ->func, ->info, and ->flags set.
 */
static int generic_exec_single(int cpu, struct __call_single_data *csd)
{
	if (cpu == smp_processor_id()) {
		smp_call_func_t func = csd->func;
		void *info = csd->info;
		unsigned long flags;

		/*
		 * We can unlock early even for the synchronous on-stack case,
		 * since we're doing this from the same CPU..
		 */
		csd_lock_record(csd);
		csd_unlock(csd);
		local_irq_save(flags);
		func(info);
		csd_lock_record(NULL);
		local_irq_restore(flags);
		return 0;
	}

	if ((unsigned)cpu >= nr_cpu_ids || !cpu_online(cpu)) {
		csd_unlock(csd);
		return -ENXIO;
	}

	__smp_call_single_queue(cpu, &csd->node.llist);

	return 0;
}

/**
 * generic_smp_call_function_single_interrupt - Execute SMP IPI callbacks
 *
 * Invoked by arch to handle an IPI for call function single.
 * Must be called with interrupts disabled.
 */
void generic_smp_call_function_single_interrupt(void)
{
	cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->gotipi, CFD_SEQ_NOCPU,
		      smp_processor_id(), CFD_SEQ_GOTIPI);
	flush_smp_call_function_queue(true);
}

/**
 * flush_smp_call_function_queue - Flush pending smp-call-function callbacks
 *
 * @warn_cpu_offline: If set to 'true', warn if callbacks were queued on an
 *		      offline CPU. Skip this check if set to 'false'.
 *
 * Flush any pending smp-call-function callbacks queued on this CPU. This is
 * invoked by the generic IPI handler, as well as by a CPU about to go offline,
 * to ensure that all pending IPI callbacks are run before it goes completely
 * offline.
 *
 * Loop through the call_single_queue and run all the queued callbacks.
 * Must be called with interrupts disabled.
 */
static void flush_smp_call_function_queue(bool warn_cpu_offline)
{
	call_single_data_t *csd, *csd_next;
	struct llist_node *entry, *prev;
	struct llist_head *head;
	static bool warned;

	lockdep_assert_irqs_disabled();

	head = this_cpu_ptr(&call_single_queue);
	cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->handle, CFD_SEQ_NOCPU,
		      smp_processor_id(), CFD_SEQ_HANDLE);
	entry = llist_del_all(head);
	cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->dequeue,
		      /* Special meaning of source cpu: 0 == queue empty */
		      entry ? CFD_SEQ_NOCPU : 0,
		      smp_processor_id(), CFD_SEQ_DEQUEUE);
	entry = llist_reverse_order(entry);

	/* There shouldn't be any pending callbacks on an offline CPU. */
	if (unlikely(warn_cpu_offline && !cpu_online(smp_processor_id()) &&
		     !warned && !llist_empty(head))) {
		warned = true;
		WARN(1, "IPI on offline CPU %d\n", smp_processor_id());

		/*
		 * We don't have to use the _safe() variant here
		 * because we are not invoking the IPI handlers yet.
		 */
		llist_for_each_entry(csd, entry, node.llist) {
			switch (CSD_TYPE(csd)) {
			case CSD_TYPE_ASYNC:
			case CSD_TYPE_SYNC:
			case CSD_TYPE_IRQ_WORK:
				pr_warn("IPI callback %pS sent to offline CPU\n",
					csd->func);
				break;

			case CSD_TYPE_TTWU:
				pr_warn("IPI task-wakeup sent to offline CPU\n");
				break;

			default:
				pr_warn("IPI callback, unknown type %d, sent to offline CPU\n",
					CSD_TYPE(csd));
				break;
			}
		}
	}

	/*
	 * First; run all SYNC callbacks, people are waiting for us.
	 */
	prev = NULL;
	llist_for_each_entry_safe(csd, csd_next, entry, node.llist) {
		/* Do we wait until *after* callback? */
		if (CSD_TYPE(csd) == CSD_TYPE_SYNC) {
			smp_call_func_t func = csd->func;
			void *info = csd->info;

			if (prev) {
				prev->next = &csd_next->node.llist;
			} else {
				entry = &csd_next->node.llist;
			}

			csd_lock_record(csd);
			func(info);
			csd_unlock(csd);
			csd_lock_record(NULL);
		} else {
			prev = &csd->node.llist;
		}
	}

	if (!entry) {
		cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->hdlend,
			      0, smp_processor_id(),
			      CFD_SEQ_HDLEND);
		return;
	}

	/*
	 * Second; run all !SYNC callbacks.
	 */
	prev = NULL;
	llist_for_each_entry_safe(csd, csd_next, entry, node.llist) {
		int type = CSD_TYPE(csd);

		if (type != CSD_TYPE_TTWU) {
			if (prev) {
				prev->next = &csd_next->node.llist;
			} else {
				entry = &csd_next->node.llist;
			}

			if (type == CSD_TYPE_ASYNC) {
				smp_call_func_t func = csd->func;
				void *info = csd->info;

				csd_lock_record(csd);
				csd_unlock(csd);
				func(info);
				csd_lock_record(NULL);
			} else if (type == CSD_TYPE_IRQ_WORK) {
				irq_work_single(csd);
			}

		} else {
			prev = &csd->node.llist;
		}
	}

	/*
	 * Third; only CSD_TYPE_TTWU is left, issue those.
	 */
	if (entry)
		sched_ttwu_pending(entry);

	cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->hdlend, CFD_SEQ_NOCPU,
		      smp_processor_id(), CFD_SEQ_HDLEND);
}

void flush_smp_call_function_from_idle(void)
{
	unsigned long flags;

	if (llist_empty(this_cpu_ptr(&call_single_queue)))
		return;

	cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->idle, CFD_SEQ_NOCPU,
		      smp_processor_id(), CFD_SEQ_IDLE);
	local_irq_save(flags);
	flush_smp_call_function_queue(true);
	if (local_softirq_pending())
		do_softirq();

	local_irq_restore(flags);
}

/*
 * smp_call_function_single - Run a function on a specific CPU
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait until function has completed on other CPUs.
 *
 * Returns 0 on success, else a negative status code.
 */
int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
			     int wait)
{
	call_single_data_t *csd;
	call_single_data_t csd_stack = {
		.node = { .u_flags = CSD_FLAG_LOCK | CSD_TYPE_SYNC, },
	};
	int this_cpu;
	int err;

	/*
	 * prevent preemption and reschedule on another processor,
	 * as well as CPU removal
	 */
	this_cpu = get_cpu();

	/*
	 * Can deadlock when called with interrupts disabled.
	 * We allow cpu's that are not yet online though, as no one else can
	 * send smp call function interrupt to this cpu and as such deadlocks
	 * can't happen.
	 */
	WARN_ON_ONCE(cpu_online(this_cpu) && irqs_disabled()
		     && !oops_in_progress);

	/*
	 * When @wait we can deadlock when we interrupt between llist_add() and
	 * arch_send_call_function_ipi*(); when !@wait we can deadlock due to
	 * csd_lock() on because the interrupt context uses the same csd
	 * storage.
	 */
	WARN_ON_ONCE(!in_task());

	csd = &csd_stack;
	if (!wait) {
		csd = this_cpu_ptr(&csd_data);
		csd_lock(csd);
	}

	csd->func = func;
	csd->info = info;
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
	csd->node.src = smp_processor_id();
	csd->node.dst = cpu;
#endif

	err = generic_exec_single(cpu, csd);

	if (wait)
		csd_lock_wait(csd);

	put_cpu();

	return err;
}
EXPORT_SYMBOL(smp_call_function_single);

/**
 * smp_call_function_single_async() - Run an asynchronous function on a
 * 			         specific CPU.
 * @cpu: The CPU to run on.
 * @csd: Pre-allocated and setup data structure
 *
 * Like smp_call_function_single(), but the call is asynchonous and
 * can thus be done from contexts with disabled interrupts.
 *
 * The caller passes his own pre-allocated data structure
 * (ie: embedded in an object) and is responsible for synchronizing it
 * such that the IPIs performed on the @csd are strictly serialized.
 *
 * If the function is called with one csd which has not yet been
 * processed by previous call to smp_call_function_single_async(), the
 * function will return immediately with -EBUSY showing that the csd
 * object is still in progress.
 *
 * NOTE: Be careful, there is unfortunately no current debugging facility to
 * validate the correctness of this serialization.
 *
 * Return: %0 on success or negative errno value on error
 */
int smp_call_function_single_async(int cpu, struct __call_single_data *csd)
{
	int err = 0;

	preempt_disable();

	if (csd->node.u_flags & CSD_FLAG_LOCK) {
		err = -EBUSY;
		goto out;
	}

	csd->node.u_flags = CSD_FLAG_LOCK;
	smp_wmb();

	err = generic_exec_single(cpu, csd);

out:
	preempt_enable();

	return err;
}
EXPORT_SYMBOL_GPL(smp_call_function_single_async);

/*
 * smp_call_function_any - Run a function on any of the given cpus
 * @mask: The mask of cpus it can run on.
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait until function has completed.
 *
 * Returns 0 on success, else a negative status code (if no cpus were online).
 *
 * Selection preference:
 *	1) current cpu if in @mask
 *	2) any cpu of current node if in @mask
 *	3) any other online cpu in @mask
 */
int smp_call_function_any(const struct cpumask *mask,
			  smp_call_func_t func, void *info, int wait)
{
	unsigned int cpu;
	const struct cpumask *nodemask;
	int ret;

	/* Try for same CPU (cheapest) */
	cpu = get_cpu();
	if (cpumask_test_cpu(cpu, mask))
		goto call;

	/* Try for same node. */
	nodemask = cpumask_of_node(cpu_to_node(cpu));
	for (cpu = cpumask_first_and(nodemask, mask); cpu < nr_cpu_ids;
	     cpu = cpumask_next_and(cpu, nodemask, mask)) {
		if (cpu_online(cpu))
			goto call;
	}

	/* Any online will do: smp_call_function_single handles nr_cpu_ids. */
	cpu = cpumask_any_and(mask, cpu_online_mask);
call:
	ret = smp_call_function_single(cpu, func, info, wait);
	put_cpu();
	return ret;
}
EXPORT_SYMBOL_GPL(smp_call_function_any);

/*
 * Flags to be used as scf_flags argument of smp_call_function_many_cond().
 *
 * %SCF_WAIT:		Wait until function execution is completed
 * %SCF_RUN_LOCAL:	Run also locally if local cpu is set in cpumask
 */
#define SCF_WAIT	(1U << 0)
#define SCF_RUN_LOCAL	(1U << 1)

static void smp_call_function_many_cond(const struct cpumask *mask,
					smp_call_func_t func, void *info,
					unsigned int scf_flags,
					smp_cond_func_t cond_func)
{
	int cpu, last_cpu, this_cpu = smp_processor_id();
	struct call_function_data *cfd;
	bool wait = scf_flags & SCF_WAIT;
	bool run_remote = false;
	bool run_local = false;
	int nr_cpus = 0;

	lockdep_assert_preemption_disabled();

	/*
	 * Can deadlock when called with interrupts disabled.
	 * We allow cpu's that are not yet online though, as no one else can
	 * send smp call function interrupt to this cpu and as such deadlocks
	 * can't happen.
	 */
	if (cpu_online(this_cpu) && !oops_in_progress &&
	    !early_boot_irqs_disabled)
		lockdep_assert_irqs_enabled();

	/*
	 * When @wait we can deadlock when we interrupt between llist_add() and
	 * arch_send_call_function_ipi*(); when !@wait we can deadlock due to
	 * csd_lock() on because the interrupt context uses the same csd
	 * storage.
	 */
	WARN_ON_ONCE(!in_task());

	/* Check if we need local execution. */
	if ((scf_flags & SCF_RUN_LOCAL) && cpumask_test_cpu(this_cpu, mask))
		run_local = true;

	/* Check if we need remote execution, i.e., any CPU excluding this one. */
	cpu = cpumask_first_and(mask, cpu_online_mask);
	if (cpu == this_cpu)
		cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
	if (cpu < nr_cpu_ids)
		run_remote = true;

	if (run_remote) {
		cfd = this_cpu_ptr(&cfd_data);
		cpumask_and(cfd->cpumask, mask, cpu_online_mask);
		__cpumask_clear_cpu(this_cpu, cfd->cpumask);

		cpumask_clear(cfd->cpumask_ipi);
		for_each_cpu(cpu, cfd->cpumask) {
			struct cfd_percpu *pcpu = per_cpu_ptr(cfd->pcpu, cpu);
			call_single_data_t *csd = &pcpu->csd;

			if (cond_func && !cond_func(cpu, info))
				continue;

			csd_lock(csd);
			if (wait)
				csd->node.u_flags |= CSD_TYPE_SYNC;
			csd->func = func;
			csd->info = info;
#ifdef CONFIG_CSD_LOCK_WAIT_DEBUG
			csd->node.src = smp_processor_id();
			csd->node.dst = cpu;
#endif
			cfd_seq_store(pcpu->seq_queue, this_cpu, cpu, CFD_SEQ_QUEUE);
			if (llist_add(&csd->node.llist, &per_cpu(call_single_queue, cpu))) {
				__cpumask_set_cpu(cpu, cfd->cpumask_ipi);
				nr_cpus++;
				last_cpu = cpu;

				cfd_seq_store(pcpu->seq_ipi, this_cpu, cpu, CFD_SEQ_IPI);
			} else {
				cfd_seq_store(pcpu->seq_noipi, this_cpu, cpu, CFD_SEQ_NOIPI);
			}
		}

		cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->ping, this_cpu, CFD_SEQ_NOCPU, CFD_SEQ_PING);

		/*
		 * Choose the most efficient way to send an IPI. Note that the
		 * number of CPUs might be zero due to concurrent changes to the
		 * provided mask.
		 */
		if (nr_cpus == 1)
			send_call_function_single_ipi(last_cpu);
		else if (likely(nr_cpus > 1))
			arch_send_call_function_ipi_mask(cfd->cpumask_ipi);

		cfd_seq_store(this_cpu_ptr(&cfd_seq_local)->pinged, this_cpu, CFD_SEQ_NOCPU, CFD_SEQ_PINGED);
	}

	if (run_local && (!cond_func || cond_func(this_cpu, info))) {
		unsigned long flags;

		local_irq_save(flags);
		func(info);
		local_irq_restore(flags);
	}

	if (run_remote && wait) {
		for_each_cpu(cpu, cfd->cpumask) {
			call_single_data_t *csd;

			csd = &per_cpu_ptr(cfd->pcpu, cpu)->csd;
			csd_lock_wait(csd);
		}
	}
}

/**
 * smp_call_function_many(): Run a function on a set of CPUs.
 * @mask: The set of cpus to run on (only runs on online subset).
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: Bitmask that controls the operation. If %SCF_WAIT is set, wait
 *        (atomically) until function has completed on other CPUs. If
 *        %SCF_RUN_LOCAL is set, the function will also be run locally
 *        if the local CPU is set in the @cpumask.
 *
 * If @wait is true, then returns once @func has returned.
 *
 * You must not call this function with disabled interrupts or from a
 * hardware interrupt handler or from a bottom half handler. Preemption
 * must be disabled when calling this function.
 */
void smp_call_function_many(const struct cpumask *mask,
			    smp_call_func_t func, void *info, bool wait)
{
	smp_call_function_many_cond(mask, func, info, wait * SCF_WAIT, NULL);
}
EXPORT_SYMBOL(smp_call_function_many);

/**
 * smp_call_function(): Run a function on all other CPUs.
 * @func: The function to run. This must be fast and non-blocking.
 * @info: An arbitrary pointer to pass to the function.
 * @wait: If true, wait (atomically) until function has completed
 *        on other CPUs.
 *
 * Returns 0.
 *
 * If @wait is true, then returns once @func has returned; otherwise
 * it returns just before the target cpu calls @func.
 *
 * You must not call this function with disabled interrupts or from a
 * hardware interrupt handler or from a bottom half handler.
 */
void smp_call_function(smp_call_func_t func, void *info, int wait)
{
	preempt_disable();
	smp_call_function_many(cpu_online_mask, func, info, wait);
	preempt_enable();
}
EXPORT_SYMBOL(smp_call_function);

/* Setup configured maximum number of CPUs to activate */
unsigned int setup_max_cpus = NR_CPUS;
EXPORT_SYMBOL(setup_max_cpus);


/*
 * Setup routine for controlling SMP activation
 *
 * Command-line option of "nosmp" or "maxcpus=0" will disable SMP
 * activation entirely (the MPS table probe still happens, though).
 *
 * Command-line option of "maxcpus=<NUM>", where <NUM> is an integer
 * greater than 0, limits the maximum number of CPUs activated in
 * SMP mode to <NUM>.
 */

void __weak arch_disable_smp_support(void) { }

static int __init nosmp(char *str)
{
	setup_max_cpus = 0;
	arch_disable_smp_support();

	return 0;
}

early_param("nosmp", nosmp);

/* this is hard limit */
static int __init nrcpus(char *str)
{
	int nr_cpus;

	if (get_option(&str, &nr_cpus) && nr_cpus > 0 && nr_cpus < nr_cpu_ids)
		nr_cpu_ids = nr_cpus;

	return 0;
}

early_param("nr_cpus", nrcpus);

static int __init maxcpus(char *str)
{
	get_option(&str, &setup_max_cpus);
	if (setup_max_cpus == 0)
		arch_disable_smp_support();

	return 0;
}

early_param("maxcpus", maxcpus);

/* Setup number of possible processor ids */
unsigned int nr_cpu_ids __read_mostly = NR_CPUS;
EXPORT_SYMBOL(nr_cpu_ids);

/* An arch may set nr_cpu_ids earlier if needed, so this would be redundant */
void __init setup_nr_cpu_ids(void)
{
	nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1;
}

/* Called by boot processor to activate the rest. */
void __init smp_init(void)
{
	int num_nodes, num_cpus;

	idle_threads_init();
	cpuhp_threads_init();

	pr_info("Bringing up secondary CPUs ...\n");

	bringup_nonboot_cpus(setup_max_cpus);

	num_nodes = num_online_nodes();
	num_cpus  = num_online_cpus();
	pr_info("Brought up %d node%s, %d CPU%s\n",
		num_nodes, (num_nodes > 1 ? "s" : ""),
		num_cpus,  (num_cpus  > 1 ? "s" : ""));

	/* Any cleanup work */
	smp_cpus_done(setup_max_cpus);
}

/*
 * on_each_cpu_cond(): Call a function on each processor for which
 * the supplied function cond_func returns true, optionally waiting
 * for all the required CPUs to finish. This may include the local
 * processor.
 * @cond_func:	A callback function that is passed a cpu id and
 *		the info parameter. The function is called
 *		with preemption disabled. The function should
 *		return a blooean value indicating whether to IPI
 *		the specified CPU.
 * @func:	The function to run on all applicable CPUs.
 *		This must be fast and non-blocking.
 * @info:	An arbitrary pointer to pass to both functions.
 * @wait:	If true, wait (atomically) until function has
 *		completed on other CPUs.
 *
 * Preemption is disabled to protect against CPUs going offline but not online.
 * CPUs going online during the call will not be seen or sent an IPI.
 *
 * You must not call this function with disabled interrupts or
 * from a hardware interrupt handler or from a bottom half handler.
 */
void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func,
			   void *info, bool wait, const struct cpumask *mask)
{
	unsigned int scf_flags = SCF_RUN_LOCAL;

	if (wait)
		scf_flags |= SCF_WAIT;

	preempt_disable();
	smp_call_function_many_cond(mask, func, info, scf_flags, cond_func);
	preempt_enable();
}
EXPORT_SYMBOL(on_each_cpu_cond_mask);

static void do_nothing(void *unused)
{
}

/**
 * kick_all_cpus_sync - Force all cpus out of idle
 *
 * Used to synchronize the update of pm_idle function pointer. It's
 * called after the pointer is updated and returns after the dummy
 * callback function has been executed on all cpus. The execution of
 * the function can only happen on the remote cpus after they have
 * left the idle function which had been called via pm_idle function
 * pointer. So it's guaranteed that nothing uses the previous pointer
 * anymore.
 */
void kick_all_cpus_sync(void)
{
	/* Make sure the change is visible before we kick the cpus */
	smp_mb();
	smp_call_function(do_nothing, NULL, 1);
}
EXPORT_SYMBOL_GPL(kick_all_cpus_sync);

/**
 * wake_up_all_idle_cpus - break all cpus out of idle
 * wake_up_all_idle_cpus try to break all cpus which is in idle state even
 * including idle polling cpus, for non-idle cpus, we will do nothing
 * for them.
 */
void wake_up_all_idle_cpus(void)
{
	int cpu;

	for_each_possible_cpu(cpu) {
		preempt_disable();
		if (cpu != smp_processor_id() && cpu_online(cpu))
			wake_up_if_idle(cpu);
		preempt_enable();
	}
}
EXPORT_SYMBOL_GPL(wake_up_all_idle_cpus);

/**
 * struct smp_call_on_cpu_struct - Call a function on a specific CPU
 * @work: &work_struct
 * @done: &completion to signal
 * @func: function to call
 * @data: function's data argument
 * @ret: return value from @func
 * @cpu: target CPU (%-1 for any CPU)
 *
 * Used to call a function on a specific cpu and wait for it to return.
 * Optionally make sure the call is done on a specified physical cpu via vcpu
 * pinning in order to support virtualized environments.
 */
struct smp_call_on_cpu_struct {
	struct work_struct	work;
	struct completion	done;
	int			(*func)(void *);
	void			*data;
	int			ret;
	int			cpu;
};

static void smp_call_on_cpu_callback(struct work_struct *work)
{
	struct smp_call_on_cpu_struct *sscs;

	sscs = container_of(work, struct smp_call_on_cpu_struct, work);
	if (sscs->cpu >= 0)
		hypervisor_pin_vcpu(sscs->cpu);
	sscs->ret = sscs->func(sscs->data);
	if (sscs->cpu >= 0)
		hypervisor_pin_vcpu(-1);

	complete(&sscs->done);
}

int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool phys)
{
	struct smp_call_on_cpu_struct sscs = {
		.done = COMPLETION_INITIALIZER_ONSTACK(sscs.done),
		.func = func,
		.data = par,
		.cpu  = phys ? cpu : -1,
	};

	INIT_WORK_ONSTACK(&sscs.work, smp_call_on_cpu_callback);

	if (cpu >= nr_cpu_ids || !cpu_online(cpu))
		return -ENXIO;

	queue_work_on(cpu, system_wq, &sscs.work);
	wait_for_completion(&sscs.done);

	return sscs.ret;
}
EXPORT_SYMBOL_GPL(smp_call_on_cpu);