summaryrefslogtreecommitdiff
path: root/include/linux/seqlock.h
blob: e92f9d5577bac46c34896ca2565063019cd3b036 (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
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_SEQLOCK_H
#define __LINUX_SEQLOCK_H

/*
 * seqcount_t / seqlock_t - a reader-writer consistency mechanism with
 * lockless readers (read-only retry loops), and no writer starvation.
 *
 * See Documentation/locking/seqlock.rst
 *
 * Copyrights:
 * - Based on x86_64 vsyscall gettimeofday: Keith Owens, Andrea Arcangeli
 * - Sequence counters with associated locks, (C) 2020 Linutronix GmbH
 */

#include <linux/compiler.h>
#include <linux/kcsan-checks.h>
#include <linux/lockdep.h>
#include <linux/mutex.h>
#include <linux/preempt.h>
#include <linux/spinlock.h>

#include <asm/processor.h>

/*
 * The seqlock seqcount_t interface does not prescribe a precise sequence of
 * read begin/retry/end. For readers, typically there is a call to
 * read_seqcount_begin() and read_seqcount_retry(), however, there are more
 * esoteric cases which do not follow this pattern.
 *
 * As a consequence, we take the following best-effort approach for raw usage
 * via seqcount_t under KCSAN: upon beginning a seq-reader critical section,
 * pessimistically mark the next KCSAN_SEQLOCK_REGION_MAX memory accesses as
 * atomics; if there is a matching read_seqcount_retry() call, no following
 * memory operations are considered atomic. Usage of the seqlock_t interface
 * is not affected.
 */
#define KCSAN_SEQLOCK_REGION_MAX 1000

/*
 * Sequence counters (seqcount_t)
 *
 * This is the raw counting mechanism, without any writer protection.
 *
 * Write side critical sections must be serialized and non-preemptible.
 *
 * If readers can be invoked from hardirq or softirq contexts,
 * interrupts or bottom halves must also be respectively disabled before
 * entering the write section.
 *
 * This mechanism can't be used if the protected data contains pointers,
 * as the writer can invalidate a pointer that a reader is following.
 *
 * If the write serialization mechanism is one of the common kernel
 * locking primitives, use a sequence counter with associated lock
 * (seqcount_LOCKNAME_t) instead.
 *
 * If it's desired to automatically handle the sequence counter writer
 * serialization and non-preemptibility requirements, use a sequential
 * lock (seqlock_t) instead.
 *
 * See Documentation/locking/seqlock.rst
 */
typedef struct seqcount {
	unsigned sequence;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map dep_map;
#endif
} seqcount_t;

static inline void __seqcount_init(seqcount_t *s, const char *name,
					  struct lock_class_key *key)
{
	/*
	 * Make sure we are not reinitializing a held lock:
	 */
	lockdep_init_map(&s->dep_map, name, key, 0);
	s->sequence = 0;
}

#ifdef CONFIG_DEBUG_LOCK_ALLOC

# define SEQCOUNT_DEP_MAP_INIT(lockname)				\
		.dep_map = { .name = #lockname }

/**
 * seqcount_init() - runtime initializer for seqcount_t
 * @s: Pointer to the seqcount_t instance
 */
# define seqcount_init(s)						\
	do {								\
		static struct lock_class_key __key;			\
		__seqcount_init((s), #s, &__key);			\
	} while (0)

static inline void seqcount_lockdep_reader_access(const seqcount_t *s)
{
	seqcount_t *l = (seqcount_t *)s;
	unsigned long flags;

	local_irq_save(flags);
	seqcount_acquire_read(&l->dep_map, 0, 0, _RET_IP_);
	seqcount_release(&l->dep_map, _RET_IP_);
	local_irq_restore(flags);
}

#else
# define SEQCOUNT_DEP_MAP_INIT(lockname)
# define seqcount_init(s) __seqcount_init(s, NULL, NULL)
# define seqcount_lockdep_reader_access(x)
#endif

/**
 * SEQCNT_ZERO() - static initializer for seqcount_t
 * @name: Name of the seqcount_t instance
 */
#define SEQCNT_ZERO(name) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(name) }

/*
 * Sequence counters with associated locks (seqcount_LOCKNAME_t)
 *
 * A sequence counter which associates the lock used for writer
 * serialization at initialization time. This enables lockdep to validate
 * that the write side critical section is properly serialized.
 *
 * For associated locks which do not implicitly disable preemption,
 * preemption protection is enforced in the write side function.
 *
 * Lockdep is never used in any for the raw write variants.
 *
 * See Documentation/locking/seqlock.rst
 */

/*
 * For PREEMPT_RT, seqcount_LOCKNAME_t write side critical sections cannot
 * disable preemption. It can lead to higher latencies, and the write side
 * sections will not be able to acquire locks which become sleeping locks
 * (e.g. spinlock_t).
 *
 * To remain preemptible while avoiding a possible livelock caused by the
 * reader preempting the writer, use a different technique: let the reader
 * detect if a seqcount_LOCKNAME_t writer is in progress. If that is the
 * case, acquire then release the associated LOCKNAME writer serialization
 * lock. This will allow any possibly-preempted writer to make progress
 * until the end of its writer serialization lock critical section.
 *
 * This lock-unlock technique must be implemented for all of PREEMPT_RT
 * sleeping locks.  See Documentation/locking/locktypes.rst
 */
#if defined(CONFIG_LOCKDEP) || defined(CONFIG_PREEMPT_RT)
#define __SEQ_LOCK(expr)	expr
#else
#define __SEQ_LOCK(expr)
#endif

/*
 * typedef seqcount_LOCKNAME_t - sequence counter with LOCKNAME associated
 * @seqcount:	The real sequence counter
 * @lock:	Pointer to the associated lock
 *
 * A plain sequence counter with external writer synchronization by
 * LOCKNAME @lock. The lock is associated to the sequence counter in the
 * static initializer or init function. This enables lockdep to validate
 * that the write side critical section is properly serialized.
 *
 * LOCKNAME:	raw_spinlock, spinlock, rwlock or mutex
 */

/*
 * seqcount_LOCKNAME_init() - runtime initializer for seqcount_LOCKNAME_t
 * @s:		Pointer to the seqcount_LOCKNAME_t instance
 * @lock:	Pointer to the associated lock
 */

#define seqcount_LOCKNAME_init(s, _lock, lockname)			\
	do {								\
		seqcount_##lockname##_t *____s = (s);			\
		seqcount_init(&____s->seqcount);			\
		__SEQ_LOCK(____s->lock = (_lock));			\
	} while (0)

#define seqcount_raw_spinlock_init(s, lock)	seqcount_LOCKNAME_init(s, lock, raw_spinlock)
#define seqcount_spinlock_init(s, lock)		seqcount_LOCKNAME_init(s, lock, spinlock)
#define seqcount_rwlock_init(s, lock)		seqcount_LOCKNAME_init(s, lock, rwlock)
#define seqcount_mutex_init(s, lock)		seqcount_LOCKNAME_init(s, lock, mutex)

/*
 * SEQCOUNT_LOCKNAME()	- Instantiate seqcount_LOCKNAME_t and helpers
 * seqprop_LOCKNAME_*()	- Property accessors for seqcount_LOCKNAME_t
 *
 * @lockname:		"LOCKNAME" part of seqcount_LOCKNAME_t
 * @locktype:		LOCKNAME canonical C data type
 * @preemptible:	preemptibility of above locktype
 * @lockbase:		prefix for associated lock/unlock
 */
#define SEQCOUNT_LOCKNAME(lockname, locktype, preemptible, lockbase)	\
typedef struct seqcount_##lockname {					\
	seqcount_t		seqcount;				\
	__SEQ_LOCK(locktype	*lock);					\
} seqcount_##lockname##_t;						\
									\
static __always_inline seqcount_t *					\
__seqprop_##lockname##_ptr(seqcount_##lockname##_t *s)			\
{									\
	return &s->seqcount;						\
}									\
									\
static __always_inline const seqcount_t *				\
__seqprop_##lockname##_const_ptr(const seqcount_##lockname##_t *s)	\
{									\
	return &s->seqcount;						\
}									\
									\
static __always_inline unsigned						\
__seqprop_##lockname##_sequence(const seqcount_##lockname##_t *s)	\
{									\
	unsigned seq = READ_ONCE(s->seqcount.sequence);			\
									\
	if (!IS_ENABLED(CONFIG_PREEMPT_RT))				\
		return seq;						\
									\
	if (preemptible && unlikely(seq & 1)) {				\
		__SEQ_LOCK(lockbase##_lock(s->lock));			\
		__SEQ_LOCK(lockbase##_unlock(s->lock));			\
									\
		/*							\
		 * Re-read the sequence counter since the (possibly	\
		 * preempted) writer made progress.			\
		 */							\
		seq = READ_ONCE(s->seqcount.sequence);			\
	}								\
									\
	return seq;							\
}									\
									\
static __always_inline bool						\
__seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s)	\
{									\
	if (!IS_ENABLED(CONFIG_PREEMPT_RT))				\
		return preemptible;					\
									\
	/* PREEMPT_RT relies on the above LOCK+UNLOCK */		\
	return false;							\
}									\
									\
static __always_inline void						\
__seqprop_##lockname##_assert(const seqcount_##lockname##_t *s)		\
{									\
	__SEQ_LOCK(lockdep_assert_held(s->lock));			\
}

/*
 * __seqprop() for seqcount_t
 */

static inline seqcount_t *__seqprop_ptr(seqcount_t *s)
{
	return s;
}

static inline const seqcount_t *__seqprop_const_ptr(const seqcount_t *s)
{
	return s;
}

static inline unsigned __seqprop_sequence(const seqcount_t *s)
{
	return READ_ONCE(s->sequence);
}

static inline bool __seqprop_preemptible(const seqcount_t *s)
{
	return false;
}

static inline void __seqprop_assert(const seqcount_t *s)
{
	lockdep_assert_preemption_disabled();
}

#define __SEQ_RT	IS_ENABLED(CONFIG_PREEMPT_RT)

SEQCOUNT_LOCKNAME(raw_spinlock, raw_spinlock_t,  false,    raw_spin)
SEQCOUNT_LOCKNAME(spinlock,     spinlock_t,      __SEQ_RT, spin)
SEQCOUNT_LOCKNAME(rwlock,       rwlock_t,        __SEQ_RT, read)
SEQCOUNT_LOCKNAME(mutex,        struct mutex,    true,     mutex)

/*
 * SEQCNT_LOCKNAME_ZERO - static initializer for seqcount_LOCKNAME_t
 * @name:	Name of the seqcount_LOCKNAME_t instance
 * @lock:	Pointer to the associated LOCKNAME
 */

#define SEQCOUNT_LOCKNAME_ZERO(seq_name, assoc_lock) {			\
	.seqcount		= SEQCNT_ZERO(seq_name.seqcount),	\
	__SEQ_LOCK(.lock	= (assoc_lock))				\
}

#define SEQCNT_RAW_SPINLOCK_ZERO(name, lock)	SEQCOUNT_LOCKNAME_ZERO(name, lock)
#define SEQCNT_SPINLOCK_ZERO(name, lock)	SEQCOUNT_LOCKNAME_ZERO(name, lock)
#define SEQCNT_RWLOCK_ZERO(name, lock)		SEQCOUNT_LOCKNAME_ZERO(name, lock)
#define SEQCNT_MUTEX_ZERO(name, lock)		SEQCOUNT_LOCKNAME_ZERO(name, lock)
#define SEQCNT_WW_MUTEX_ZERO(name, lock) 	SEQCOUNT_LOCKNAME_ZERO(name, lock)

#define __seqprop_case(s, lockname, prop)				\
	seqcount_##lockname##_t: __seqprop_##lockname##_##prop

#define __seqprop(s, prop) _Generic(*(s),				\
	seqcount_t:		__seqprop_##prop,			\
	__seqprop_case((s),	raw_spinlock,	prop),			\
	__seqprop_case((s),	spinlock,	prop),			\
	__seqprop_case((s),	rwlock,		prop),			\
	__seqprop_case((s),	mutex,		prop))

#define seqprop_ptr(s)			__seqprop(s, ptr)(s)
#define seqprop_const_ptr(s)		__seqprop(s, const_ptr)(s)
#define seqprop_sequence(s)		__seqprop(s, sequence)(s)
#define seqprop_preemptible(s)		__seqprop(s, preemptible)(s)
#define seqprop_assert(s)		__seqprop(s, assert)(s)

/**
 * __read_seqcount_begin() - begin a seqcount_t read section w/o barrier
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * __read_seqcount_begin is like read_seqcount_begin, but has no smp_rmb()
 * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
 * provided before actually loading any of the variables that are to be
 * protected in this critical section.
 *
 * Use carefully, only in critical code, and comment how the barrier is
 * provided.
 *
 * Return: count to be passed to read_seqcount_retry()
 */
#define __read_seqcount_begin(s)					\
({									\
	unsigned __seq;							\
									\
	while ((__seq = seqprop_sequence(s)) & 1)			\
		cpu_relax();						\
									\
	kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);			\
	__seq;								\
})

/**
 * raw_read_seqcount_begin() - begin a seqcount_t read section w/o lockdep
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * Return: count to be passed to read_seqcount_retry()
 */
#define raw_read_seqcount_begin(s)					\
({									\
	unsigned _seq = __read_seqcount_begin(s);			\
									\
	smp_rmb();							\
	_seq;								\
})

/**
 * read_seqcount_begin() - begin a seqcount_t read critical section
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * Return: count to be passed to read_seqcount_retry()
 */
#define read_seqcount_begin(s)						\
({									\
	seqcount_lockdep_reader_access(seqprop_const_ptr(s));		\
	raw_read_seqcount_begin(s);					\
})

/**
 * raw_read_seqcount() - read the raw seqcount_t counter value
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * raw_read_seqcount opens a read critical section of the given
 * seqcount_t, without any lockdep checking, and without checking or
 * masking the sequence counter LSB. Calling code is responsible for
 * handling that.
 *
 * Return: count to be passed to read_seqcount_retry()
 */
#define raw_read_seqcount(s)						\
({									\
	unsigned __seq = seqprop_sequence(s);				\
									\
	smp_rmb();							\
	kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);			\
	__seq;								\
})

/**
 * raw_seqcount_begin() - begin a seqcount_t read critical section w/o
 *                        lockdep and w/o counter stabilization
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * raw_seqcount_begin opens a read critical section of the given
 * seqcount_t. Unlike read_seqcount_begin(), this function will not wait
 * for the count to stabilize. If a writer is active when it begins, it
 * will fail the read_seqcount_retry() at the end of the read critical
 * section instead of stabilizing at the beginning of it.
 *
 * Use this only in special kernel hot paths where the read section is
 * small and has a high probability of success through other external
 * means. It will save a single branching instruction.
 *
 * Return: count to be passed to read_seqcount_retry()
 */
#define raw_seqcount_begin(s)						\
({									\
	/*								\
	 * If the counter is odd, let read_seqcount_retry() fail	\
	 * by decrementing the counter.					\
	 */								\
	raw_read_seqcount(s) & ~1;					\
})

/**
 * __read_seqcount_retry() - end a seqcount_t read section w/o barrier
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 * @start: count, from read_seqcount_begin()
 *
 * __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb()
 * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
 * provided before actually loading any of the variables that are to be
 * protected in this critical section.
 *
 * Use carefully, only in critical code, and comment how the barrier is
 * provided.
 *
 * Return: true if a read section retry is required, else false
 */
#define __read_seqcount_retry(s, start)					\
	do___read_seqcount_retry(seqprop_const_ptr(s), start)

static inline int do___read_seqcount_retry(const seqcount_t *s, unsigned start)
{
	kcsan_atomic_next(0);
	return unlikely(READ_ONCE(s->sequence) != start);
}

/**
 * read_seqcount_retry() - end a seqcount_t read critical section
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 * @start: count, from read_seqcount_begin()
 *
 * read_seqcount_retry closes the read critical section of given
 * seqcount_t.  If the critical section was invalid, it must be ignored
 * (and typically retried).
 *
 * Return: true if a read section retry is required, else false
 */
#define read_seqcount_retry(s, start)					\
	do_read_seqcount_retry(seqprop_const_ptr(s), start)

static inline int do_read_seqcount_retry(const seqcount_t *s, unsigned start)
{
	smp_rmb();
	return do___read_seqcount_retry(s, start);
}

/**
 * raw_write_seqcount_begin() - start a seqcount_t write section w/o lockdep
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * Context: check write_seqcount_begin()
 */
#define raw_write_seqcount_begin(s)					\
do {									\
	if (seqprop_preemptible(s))					\
		preempt_disable();					\
									\
	do_raw_write_seqcount_begin(seqprop_ptr(s));			\
} while (0)

static inline void do_raw_write_seqcount_begin(seqcount_t *s)
{
	kcsan_nestable_atomic_begin();
	s->sequence++;
	smp_wmb();
}

/**
 * raw_write_seqcount_end() - end a seqcount_t write section w/o lockdep
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * Context: check write_seqcount_end()
 */
#define raw_write_seqcount_end(s)					\
do {									\
	do_raw_write_seqcount_end(seqprop_ptr(s));			\
									\
	if (seqprop_preemptible(s))					\
		preempt_enable();					\
} while (0)

static inline void do_raw_write_seqcount_end(seqcount_t *s)
{
	smp_wmb();
	s->sequence++;
	kcsan_nestable_atomic_end();
}

/**
 * write_seqcount_begin_nested() - start a seqcount_t write section with
 *                                 custom lockdep nesting level
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 * @subclass: lockdep nesting level
 *
 * See Documentation/locking/lockdep-design.rst
 * Context: check write_seqcount_begin()
 */
#define write_seqcount_begin_nested(s, subclass)			\
do {									\
	seqprop_assert(s);						\
									\
	if (seqprop_preemptible(s))					\
		preempt_disable();					\
									\
	do_write_seqcount_begin_nested(seqprop_ptr(s), subclass);	\
} while (0)

static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass)
{
	seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
	do_raw_write_seqcount_begin(s);
}

/**
 * write_seqcount_begin() - start a seqcount_t write side critical section
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * Context: sequence counter write side sections must be serialized and
 * non-preemptible. Preemption will be automatically disabled if and
 * only if the seqcount write serialization lock is associated, and
 * preemptible.  If readers can be invoked from hardirq or softirq
 * context, interrupts or bottom halves must be respectively disabled.
 */
#define write_seqcount_begin(s)						\
do {									\
	seqprop_assert(s);						\
									\
	if (seqprop_preemptible(s))					\
		preempt_disable();					\
									\
	do_write_seqcount_begin(seqprop_ptr(s));			\
} while (0)

static inline void do_write_seqcount_begin(seqcount_t *s)
{
	do_write_seqcount_begin_nested(s, 0);
}

/**
 * write_seqcount_end() - end a seqcount_t write side critical section
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * Context: Preemption will be automatically re-enabled if and only if
 * the seqcount write serialization lock is associated, and preemptible.
 */
#define write_seqcount_end(s)						\
do {									\
	do_write_seqcount_end(seqprop_ptr(s));				\
									\
	if (seqprop_preemptible(s))					\
		preempt_enable();					\
} while (0)

static inline void do_write_seqcount_end(seqcount_t *s)
{
	seqcount_release(&s->dep_map, _RET_IP_);
	do_raw_write_seqcount_end(s);
}

/**
 * raw_write_seqcount_barrier() - do a seqcount_t write barrier
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * This can be used to provide an ordering guarantee instead of the usual
 * consistency guarantee. It is one wmb cheaper, because it can collapse
 * the two back-to-back wmb()s.
 *
 * Note that writes surrounding the barrier should be declared atomic (e.g.
 * via WRITE_ONCE): a) to ensure the writes become visible to other threads
 * atomically, avoiding compiler optimizations; b) to document which writes are
 * meant to propagate to the reader critical section. This is necessary because
 * neither writes before nor after the barrier are enclosed in a seq-writer
 * critical section that would ensure readers are aware of ongoing writes::
 *
 *	seqcount_t seq;
 *	bool X = true, Y = false;
 *
 *	void read(void)
 *	{
 *		bool x, y;
 *
 *		do {
 *			int s = read_seqcount_begin(&seq);
 *
 *			x = X; y = Y;
 *
 *		} while (read_seqcount_retry(&seq, s));
 *
 *		BUG_ON(!x && !y);
 *      }
 *
 *      void write(void)
 *      {
 *		WRITE_ONCE(Y, true);
 *
 *		raw_write_seqcount_barrier(seq);
 *
 *		WRITE_ONCE(X, false);
 *      }
 */
#define raw_write_seqcount_barrier(s)					\
	do_raw_write_seqcount_barrier(seqprop_ptr(s))

static inline void do_raw_write_seqcount_barrier(seqcount_t *s)
{
	kcsan_nestable_atomic_begin();
	s->sequence++;
	smp_wmb();
	s->sequence++;
	kcsan_nestable_atomic_end();
}

/**
 * write_seqcount_invalidate() - invalidate in-progress seqcount_t read
 *                               side operations
 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
 *
 * After write_seqcount_invalidate, no seqcount_t read side operations
 * will complete successfully and see data older than this.
 */
#define write_seqcount_invalidate(s)					\
	do_write_seqcount_invalidate(seqprop_ptr(s))

static inline void do_write_seqcount_invalidate(seqcount_t *s)
{
	smp_wmb();
	kcsan_nestable_atomic_begin();
	s->sequence+=2;
	kcsan_nestable_atomic_end();
}

/*
 * Latch sequence counters (seqcount_latch_t)
 *
 * A sequence counter variant where the counter even/odd value is used to
 * switch between two copies of protected data. This allows the read path,
 * typically NMIs, to safely interrupt the write side critical section.
 *
 * As the write sections are fully preemptible, no special handling for
 * PREEMPT_RT is needed.
 */
typedef struct {
	seqcount_t seqcount;
} seqcount_latch_t;

/**
 * SEQCNT_LATCH_ZERO() - static initializer for seqcount_latch_t
 * @seq_name: Name of the seqcount_latch_t instance
 */
#define SEQCNT_LATCH_ZERO(seq_name) {					\
	.seqcount		= SEQCNT_ZERO(seq_name.seqcount),	\
}

/**
 * seqcount_latch_init() - runtime initializer for seqcount_latch_t
 * @s: Pointer to the seqcount_latch_t instance
 */
#define seqcount_latch_init(s) seqcount_init(&(s)->seqcount)

/**
 * raw_read_seqcount_latch() - pick even/odd latch data copy
 * @s: Pointer to seqcount_latch_t
 *
 * See raw_write_seqcount_latch() for details and a full reader/writer
 * usage example.
 *
 * Return: sequence counter raw value. Use the lowest bit as an index for
 * picking which data copy to read. The full counter must then be checked
 * with raw_read_seqcount_latch_retry().
 */
static __always_inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s)
{
	/*
	 * Pairs with the first smp_wmb() in raw_write_seqcount_latch().
	 * Due to the dependent load, a full smp_rmb() is not needed.
	 */
	return READ_ONCE(s->seqcount.sequence);
}

/**
 * raw_read_seqcount_latch_retry() - end a seqcount_latch_t read section
 * @s:		Pointer to seqcount_latch_t
 * @start:	count, from raw_read_seqcount_latch()
 *
 * Return: true if a read section retry is required, else false
 */
static __always_inline int
raw_read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start)
{
	smp_rmb();
	return unlikely(READ_ONCE(s->seqcount.sequence) != start);
}

/**
 * raw_write_seqcount_latch() - redirect latch readers to even/odd copy
 * @s: Pointer to seqcount_latch_t
 *
 * The latch technique is a multiversion concurrency control method that allows
 * queries during non-atomic modifications. If you can guarantee queries never
 * interrupt the modification -- e.g. the concurrency is strictly between CPUs
 * -- you most likely do not need this.
 *
 * Where the traditional RCU/lockless data structures rely on atomic
 * modifications to ensure queries observe either the old or the new state the
 * latch allows the same for non-atomic updates. The trade-off is doubling the
 * cost of storage; we have to maintain two copies of the entire data
 * structure.
 *
 * Very simply put: we first modify one copy and then the other. This ensures
 * there is always one copy in a stable state, ready to give us an answer.
 *
 * The basic form is a data structure like::
 *
 *	struct latch_struct {
 *		seqcount_latch_t	seq;
 *		struct data_struct	data[2];
 *	};
 *
 * Where a modification, which is assumed to be externally serialized, does the
 * following::
 *
 *	void latch_modify(struct latch_struct *latch, ...)
 *	{
 *		smp_wmb();	// Ensure that the last data[1] update is visible
 *		latch->seq.sequence++;
 *		smp_wmb();	// Ensure that the seqcount update is visible
 *
 *		modify(latch->data[0], ...);
 *
 *		smp_wmb();	// Ensure that the data[0] update is visible
 *		latch->seq.sequence++;
 *		smp_wmb();	// Ensure that the seqcount update is visible
 *
 *		modify(latch->data[1], ...);
 *	}
 *
 * The query will have a form like::
 *
 *	struct entry *latch_query(struct latch_struct *latch, ...)
 *	{
 *		struct entry *entry;
 *		unsigned seq, idx;
 *
 *		do {
 *			seq = raw_read_seqcount_latch(&latch->seq);
 *
 *			idx = seq & 0x01;
 *			entry = data_query(latch->data[idx], ...);
 *
 *		// This includes needed smp_rmb()
 *		} while (raw_read_seqcount_latch_retry(&latch->seq, seq));
 *
 *		return entry;
 *	}
 *
 * So during the modification, queries are first redirected to data[1]. Then we
 * modify data[0]. When that is complete, we redirect queries back to data[0]
 * and we can modify data[1].
 *
 * NOTE:
 *
 *	The non-requirement for atomic modifications does _NOT_ include
 *	the publishing of new entries in the case where data is a dynamic
 *	data structure.
 *
 *	An iteration might start in data[0] and get suspended long enough
 *	to miss an entire modification sequence, once it resumes it might
 *	observe the new entry.
 *
 * NOTE2:
 *
 *	When data is a dynamic data structure; one should use regular RCU
 *	patterns to manage the lifetimes of the objects within.
 */
static inline void raw_write_seqcount_latch(seqcount_latch_t *s)
{
	smp_wmb();	/* prior stores before incrementing "sequence" */
	s->seqcount.sequence++;
	smp_wmb();      /* increment "sequence" before following stores */
}

/*
 * Sequential locks (seqlock_t)
 *
 * Sequence counters with an embedded spinlock for writer serialization
 * and non-preemptibility.
 *
 * For more info, see:
 *    - Comments on top of seqcount_t
 *    - Documentation/locking/seqlock.rst
 */
typedef struct {
	/*
	 * Make sure that readers don't starve writers on PREEMPT_RT: use
	 * seqcount_spinlock_t instead of seqcount_t. Check __SEQ_LOCK().
	 */
	seqcount_spinlock_t seqcount;
	spinlock_t lock;
} seqlock_t;

#define __SEQLOCK_UNLOCKED(lockname)					\
	{								\
		.seqcount = SEQCNT_SPINLOCK_ZERO(lockname, &(lockname).lock), \
		.lock =	__SPIN_LOCK_UNLOCKED(lockname)			\
	}

/**
 * seqlock_init() - dynamic initializer for seqlock_t
 * @sl: Pointer to the seqlock_t instance
 */
#define seqlock_init(sl)						\
	do {								\
		spin_lock_init(&(sl)->lock);				\
		seqcount_spinlock_init(&(sl)->seqcount, &(sl)->lock);	\
	} while (0)

/**
 * DEFINE_SEQLOCK(sl) - Define a statically allocated seqlock_t
 * @sl: Name of the seqlock_t instance
 */
#define DEFINE_SEQLOCK(sl) \
		seqlock_t sl = __SEQLOCK_UNLOCKED(sl)

/**
 * read_seqbegin() - start a seqlock_t read side critical section
 * @sl: Pointer to seqlock_t
 *
 * Return: count, to be passed to read_seqretry()
 */
static inline unsigned read_seqbegin(const seqlock_t *sl)
{
	unsigned ret = read_seqcount_begin(&sl->seqcount);

	kcsan_atomic_next(0);  /* non-raw usage, assume closing read_seqretry() */
	kcsan_flat_atomic_begin();
	return ret;
}

/**
 * read_seqretry() - end a seqlock_t read side section
 * @sl: Pointer to seqlock_t
 * @start: count, from read_seqbegin()
 *
 * read_seqretry closes the read side critical section of given seqlock_t.
 * If the critical section was invalid, it must be ignored (and typically
 * retried).
 *
 * Return: true if a read section retry is required, else false
 */
static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
{
	/*
	 * Assume not nested: read_seqretry() may be called multiple times when
	 * completing read critical section.
	 */
	kcsan_flat_atomic_end();

	return read_seqcount_retry(&sl->seqcount, start);
}

/*
 * For all seqlock_t write side functions, use the internal
 * do_write_seqcount_begin() instead of generic write_seqcount_begin().
 * This way, no redundant lockdep_assert_held() checks are added.
 */

/**
 * write_seqlock() - start a seqlock_t write side critical section
 * @sl: Pointer to seqlock_t
 *
 * write_seqlock opens a write side critical section for the given
 * seqlock_t.  It also implicitly acquires the spinlock_t embedded inside
 * that sequential lock. All seqlock_t write side sections are thus
 * automatically serialized and non-preemptible.
 *
 * Context: if the seqlock_t read section, or other write side critical
 * sections, can be invoked from hardirq or softirq contexts, use the
 * _irqsave or _bh variants of this function instead.
 */
static inline void write_seqlock(seqlock_t *sl)
{
	spin_lock(&sl->lock);
	do_write_seqcount_begin(&sl->seqcount.seqcount);
}

/**
 * write_sequnlock() - end a seqlock_t write side critical section
 * @sl: Pointer to seqlock_t
 *
 * write_sequnlock closes the (serialized and non-preemptible) write side
 * critical section of given seqlock_t.
 */
static inline void write_sequnlock(seqlock_t *sl)
{
	do_write_seqcount_end(&sl->seqcount.seqcount);
	spin_unlock(&sl->lock);
}

/**
 * write_seqlock_bh() - start a softirqs-disabled seqlock_t write section
 * @sl: Pointer to seqlock_t
 *
 * _bh variant of write_seqlock(). Use only if the read side section, or
 * other write side sections, can be invoked from softirq contexts.
 */
static inline void write_seqlock_bh(seqlock_t *sl)
{
	spin_lock_bh(&sl->lock);
	do_write_seqcount_begin(&sl->seqcount.seqcount);
}

/**
 * write_sequnlock_bh() - end a softirqs-disabled seqlock_t write section
 * @sl: Pointer to seqlock_t
 *
 * write_sequnlock_bh closes the serialized, non-preemptible, and
 * softirqs-disabled, seqlock_t write side critical section opened with
 * write_seqlock_bh().
 */
static inline void write_sequnlock_bh(seqlock_t *sl)
{
	do_write_seqcount_end(&sl->seqcount.seqcount);
	spin_unlock_bh(&sl->lock);
}

/**
 * write_seqlock_irq() - start a non-interruptible seqlock_t write section
 * @sl: Pointer to seqlock_t
 *
 * _irq variant of write_seqlock(). Use only if the read side section, or
 * other write sections, can be invoked from hardirq contexts.
 */
static inline void write_seqlock_irq(seqlock_t *sl)
{
	spin_lock_irq(&sl->lock);
	do_write_seqcount_begin(&sl->seqcount.seqcount);
}

/**
 * write_sequnlock_irq() - end a non-interruptible seqlock_t write section
 * @sl: Pointer to seqlock_t
 *
 * write_sequnlock_irq closes the serialized and non-interruptible
 * seqlock_t write side section opened with write_seqlock_irq().
 */
static inline void write_sequnlock_irq(seqlock_t *sl)
{
	do_write_seqcount_end(&sl->seqcount.seqcount);
	spin_unlock_irq(&sl->lock);
}

static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
{
	unsigned long flags;

	spin_lock_irqsave(&sl->lock, flags);
	do_write_seqcount_begin(&sl->seqcount.seqcount);
	return flags;
}

/**
 * write_seqlock_irqsave() - start a non-interruptible seqlock_t write
 *                           section
 * @lock:  Pointer to seqlock_t
 * @flags: Stack-allocated storage for saving caller's local interrupt
 *         state, to be passed to write_sequnlock_irqrestore().
 *
 * _irqsave variant of write_seqlock(). Use it only if the read side
 * section, or other write sections, can be invoked from hardirq context.
 */
#define write_seqlock_irqsave(lock, flags)				\
	do { flags = __write_seqlock_irqsave(lock); } while (0)

/**
 * write_sequnlock_irqrestore() - end non-interruptible seqlock_t write
 *                                section
 * @sl:    Pointer to seqlock_t
 * @flags: Caller's saved interrupt state, from write_seqlock_irqsave()
 *
 * write_sequnlock_irqrestore closes the serialized and non-interruptible
 * seqlock_t write section previously opened with write_seqlock_irqsave().
 */
static inline void
write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
{
	do_write_seqcount_end(&sl->seqcount.seqcount);
	spin_unlock_irqrestore(&sl->lock, flags);
}

/**
 * read_seqlock_excl() - begin a seqlock_t locking reader section
 * @sl:	Pointer to seqlock_t
 *
 * read_seqlock_excl opens a seqlock_t locking reader critical section.  A
 * locking reader exclusively locks out *both* other writers *and* other
 * locking readers, but it does not update the embedded sequence number.
 *
 * Locking readers act like a normal spin_lock()/spin_unlock().
 *
 * Context: if the seqlock_t write section, *or other read sections*, can
 * be invoked from hardirq or softirq contexts, use the _irqsave or _bh
 * variant of this function instead.
 *
 * The opened read section must be closed with read_sequnlock_excl().
 */
static inline void read_seqlock_excl(seqlock_t *sl)
{
	spin_lock(&sl->lock);
}

/**
 * read_sequnlock_excl() - end a seqlock_t locking reader critical section
 * @sl: Pointer to seqlock_t
 */
static inline void read_sequnlock_excl(seqlock_t *sl)
{
	spin_unlock(&sl->lock);
}

/**
 * read_seqlock_excl_bh() - start a seqlock_t locking reader section with
 *			    softirqs disabled
 * @sl: Pointer to seqlock_t
 *
 * _bh variant of read_seqlock_excl(). Use this variant only if the
 * seqlock_t write side section, *or other read sections*, can be invoked
 * from softirq contexts.
 */
static inline void read_seqlock_excl_bh(seqlock_t *sl)
{
	spin_lock_bh(&sl->lock);
}

/**
 * read_sequnlock_excl_bh() - stop a seqlock_t softirq-disabled locking
 *			      reader section
 * @sl: Pointer to seqlock_t
 */
static inline void read_sequnlock_excl_bh(seqlock_t *sl)
{
	spin_unlock_bh(&sl->lock);
}

/**
 * read_seqlock_excl_irq() - start a non-interruptible seqlock_t locking
 *			     reader section
 * @sl: Pointer to seqlock_t
 *
 * _irq variant of read_seqlock_excl(). Use this only if the seqlock_t
 * write side section, *or other read sections*, can be invoked from a
 * hardirq context.
 */
static inline void read_seqlock_excl_irq(seqlock_t *sl)
{
	spin_lock_irq(&sl->lock);
}

/**
 * read_sequnlock_excl_irq() - end an interrupts-disabled seqlock_t
 *                             locking reader section
 * @sl: Pointer to seqlock_t
 */
static inline void read_sequnlock_excl_irq(seqlock_t *sl)
{
	spin_unlock_irq(&sl->lock);
}

static inline unsigned long __read_seqlock_excl_irqsave(seqlock_t *sl)
{
	unsigned long flags;

	spin_lock_irqsave(&sl->lock, flags);
	return flags;
}

/**
 * read_seqlock_excl_irqsave() - start a non-interruptible seqlock_t
 *				 locking reader section
 * @lock:  Pointer to seqlock_t
 * @flags: Stack-allocated storage for saving caller's local interrupt
 *         state, to be passed to read_sequnlock_excl_irqrestore().
 *
 * _irqsave variant of read_seqlock_excl(). Use this only if the seqlock_t
 * write side section, *or other read sections*, can be invoked from a
 * hardirq context.
 */
#define read_seqlock_excl_irqsave(lock, flags)				\
	do { flags = __read_seqlock_excl_irqsave(lock); } while (0)

/**
 * read_sequnlock_excl_irqrestore() - end non-interruptible seqlock_t
 *				      locking reader section
 * @sl:    Pointer to seqlock_t
 * @flags: Caller saved interrupt state, from read_seqlock_excl_irqsave()
 */
static inline void
read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags)
{
	spin_unlock_irqrestore(&sl->lock, flags);
}

/**
 * read_seqbegin_or_lock() - begin a seqlock_t lockless or locking reader
 * @lock: Pointer to seqlock_t
 * @seq : Marker and return parameter. If the passed value is even, the
 * reader will become a *lockless* seqlock_t reader as in read_seqbegin().
 * If the passed value is odd, the reader will become a *locking* reader
 * as in read_seqlock_excl().  In the first call to this function, the
 * caller *must* initialize and pass an even value to @seq; this way, a
 * lockless read can be optimistically tried first.
 *
 * read_seqbegin_or_lock is an API designed to optimistically try a normal
 * lockless seqlock_t read section first.  If an odd counter is found, the
 * lockless read trial has failed, and the next read iteration transforms
 * itself into a full seqlock_t locking reader.
 *
 * This is typically used to avoid seqlock_t lockless readers starvation
 * (too much retry loops) in the case of a sharp spike in write side
 * activity.
 *
 * Context: if the seqlock_t write section, *or other read sections*, can
 * be invoked from hardirq or softirq contexts, use the _irqsave or _bh
 * variant of this function instead.
 *
 * Check Documentation/locking/seqlock.rst for template example code.
 *
 * Return: the encountered sequence counter value, through the @seq
 * parameter, which is overloaded as a return parameter. This returned
 * value must be checked with need_seqretry(). If the read section need to
 * be retried, this returned value must also be passed as the @seq
 * parameter of the next read_seqbegin_or_lock() iteration.
 */
static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
{
	if (!(*seq & 1))	/* Even */
		*seq = read_seqbegin(lock);
	else			/* Odd */
		read_seqlock_excl(lock);
}

/**
 * need_seqretry() - validate seqlock_t "locking or lockless" read section
 * @lock: Pointer to seqlock_t
 * @seq: sequence count, from read_seqbegin_or_lock()
 *
 * Return: true if a read section retry is required, false otherwise
 */
static inline int need_seqretry(seqlock_t *lock, int seq)
{
	return !(seq & 1) && read_seqretry(lock, seq);
}

/**
 * done_seqretry() - end seqlock_t "locking or lockless" reader section
 * @lock: Pointer to seqlock_t
 * @seq: count, from read_seqbegin_or_lock()
 *
 * done_seqretry finishes the seqlock_t read side critical section started
 * with read_seqbegin_or_lock() and validated by need_seqretry().
 */
static inline void done_seqretry(seqlock_t *lock, int seq)
{
	if (seq & 1)
		read_sequnlock_excl(lock);
}

/**
 * read_seqbegin_or_lock_irqsave() - begin a seqlock_t lockless reader, or
 *                                   a non-interruptible locking reader
 * @lock: Pointer to seqlock_t
 * @seq:  Marker and return parameter. Check read_seqbegin_or_lock().
 *
 * This is the _irqsave variant of read_seqbegin_or_lock(). Use it only if
 * the seqlock_t write section, *or other read sections*, can be invoked
 * from hardirq context.
 *
 * Note: Interrupts will be disabled only for "locking reader" mode.
 *
 * Return:
 *
 *   1. The saved local interrupts state in case of a locking reader, to
 *      be passed to done_seqretry_irqrestore().
 *
 *   2. The encountered sequence counter value, returned through @seq
 *      overloaded as a return parameter. Check read_seqbegin_or_lock().
 */
static inline unsigned long
read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq)
{
	unsigned long flags = 0;

	if (!(*seq & 1))	/* Even */
		*seq = read_seqbegin(lock);
	else			/* Odd */
		read_seqlock_excl_irqsave(lock, flags);

	return flags;
}

/**
 * done_seqretry_irqrestore() - end a seqlock_t lockless reader, or a
 *				non-interruptible locking reader section
 * @lock:  Pointer to seqlock_t
 * @seq:   Count, from read_seqbegin_or_lock_irqsave()
 * @flags: Caller's saved local interrupt state in case of a locking
 *	   reader, also from read_seqbegin_or_lock_irqsave()
 *
 * This is the _irqrestore variant of done_seqretry(). The read section
 * must've been opened with read_seqbegin_or_lock_irqsave(), and validated
 * by need_seqretry().
 */
static inline void
done_seqretry_irqrestore(seqlock_t *lock, int seq, unsigned long flags)
{
	if (seq & 1)
		read_sequnlock_excl_irqrestore(lock, flags);
}
#endif /* __LINUX_SEQLOCK_H */