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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef __LINUX_SEQLOCK_H
3#define __LINUX_SEQLOCK_H
4
5/*
6 * seqcount_t / seqlock_t - a reader-writer consistency mechanism with
7 * lockless readers (read-only retry loops), and no writer starvation.
8 *
9 * See Documentation/locking/seqlock.rst
10 *
11 * Copyrights:
12 * - Based on x86_64 vsyscall gettimeofday: Keith Owens, Andrea Arcangeli
13 * - Sequence counters with associated locks, (C) 2020 Linutronix GmbH
14 */
15
16#include <linux/compiler.h>
17#include <linux/cleanup.h>
18#include <linux/kcsan-checks.h>
19#include <linux/lockdep.h>
20#include <linux/mutex.h>
21#include <linux/preempt.h>
22#include <linux/seqlock_types.h>
23#include <linux/spinlock.h>
24
25#include <asm/processor.h>
26
27/*
28 * The seqlock seqcount_t interface does not prescribe a precise sequence of
29 * read begin/retry/end. For readers, typically there is a call to
30 * read_seqcount_begin() and read_seqcount_retry(), however, there are more
31 * esoteric cases which do not follow this pattern.
32 *
33 * As a consequence, we take the following best-effort approach for raw usage
34 * via seqcount_t under KCSAN: upon beginning a seq-reader critical section,
35 * pessimistically mark the next KCSAN_SEQLOCK_REGION_MAX memory accesses as
36 * atomics; if there is a matching read_seqcount_retry() call, no following
37 * memory operations are considered atomic. Usage of the seqlock_t interface
38 * is not affected.
39 */
40#define KCSAN_SEQLOCK_REGION_MAX 1000
41
42static inline void __seqcount_init(seqcount_t *s, const char *name,
43 struct lock_class_key *key)
44{
45 /*
46 * Make sure we are not reinitializing a held lock:
47 */
48 lockdep_init_map(&s->dep_map, name, key, 0);
49 s->sequence = 0;
50}
51
52#ifdef CONFIG_DEBUG_LOCK_ALLOC
53
54# define SEQCOUNT_DEP_MAP_INIT(lockname) \
55 .dep_map = { .name = #lockname }
56
57/**
58 * seqcount_init() - runtime initializer for seqcount_t
59 * @s: Pointer to the seqcount_t instance
60 */
61# define seqcount_init(s) \
62 do { \
63 static struct lock_class_key __key; \
64 __seqcount_init((s), #s, &__key); \
65 } while (0)
66
67static inline void seqcount_lockdep_reader_access(const seqcount_t *s)
68{
69 seqcount_t *l = (seqcount_t *)s;
70 unsigned long flags;
71
72 local_irq_save(flags);
73 seqcount_acquire_read(&l->dep_map, 0, 0, _RET_IP_);
74 seqcount_release(&l->dep_map, _RET_IP_);
75 local_irq_restore(flags);
76}
77
78#else
79# define SEQCOUNT_DEP_MAP_INIT(lockname)
80# define seqcount_init(s) __seqcount_init(s, NULL, NULL)
81# define seqcount_lockdep_reader_access(x)
82#endif
83
84/**
85 * SEQCNT_ZERO() - static initializer for seqcount_t
86 * @name: Name of the seqcount_t instance
87 */
88#define SEQCNT_ZERO(name) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(name) }
89
90/*
91 * Sequence counters with associated locks (seqcount_LOCKNAME_t)
92 *
93 * A sequence counter which associates the lock used for writer
94 * serialization at initialization time. This enables lockdep to validate
95 * that the write side critical section is properly serialized.
96 *
97 * For associated locks which do not implicitly disable preemption,
98 * preemption protection is enforced in the write side function.
99 *
100 * Lockdep is never used in any for the raw write variants.
101 *
102 * See Documentation/locking/seqlock.rst
103 */
104
105/*
106 * typedef seqcount_LOCKNAME_t - sequence counter with LOCKNAME associated
107 * @seqcount: The real sequence counter
108 * @lock: Pointer to the associated lock
109 *
110 * A plain sequence counter with external writer synchronization by
111 * LOCKNAME @lock. The lock is associated to the sequence counter in the
112 * static initializer or init function. This enables lockdep to validate
113 * that the write side critical section is properly serialized.
114 *
115 * LOCKNAME: raw_spinlock, spinlock, rwlock or mutex
116 */
117
118/*
119 * seqcount_LOCKNAME_init() - runtime initializer for seqcount_LOCKNAME_t
120 * @s: Pointer to the seqcount_LOCKNAME_t instance
121 * @lock: Pointer to the associated lock
122 */
123
124#define seqcount_LOCKNAME_init(s, _lock, lockname) \
125 do { \
126 seqcount_##lockname##_t *____s = (s); \
127 seqcount_init(&____s->seqcount); \
128 __SEQ_LOCK(____s->lock = (_lock)); \
129 } while (0)
130
131#define seqcount_raw_spinlock_init(s, lock) seqcount_LOCKNAME_init(s, lock, raw_spinlock)
132#define seqcount_spinlock_init(s, lock) seqcount_LOCKNAME_init(s, lock, spinlock)
133#define seqcount_rwlock_init(s, lock) seqcount_LOCKNAME_init(s, lock, rwlock)
134#define seqcount_mutex_init(s, lock) seqcount_LOCKNAME_init(s, lock, mutex)
135
136/*
137 * SEQCOUNT_LOCKNAME() - Instantiate seqcount_LOCKNAME_t and helpers
138 * seqprop_LOCKNAME_*() - Property accessors for seqcount_LOCKNAME_t
139 *
140 * @lockname: "LOCKNAME" part of seqcount_LOCKNAME_t
141 * @locktype: LOCKNAME canonical C data type
142 * @preemptible: preemptibility of above locktype
143 * @lockbase: prefix for associated lock/unlock
144 */
145#define SEQCOUNT_LOCKNAME(lockname, locktype, preemptible, lockbase) \
146static __always_inline seqcount_t * \
147__seqprop_##lockname##_ptr(seqcount_##lockname##_t *s) \
148{ \
149 return &s->seqcount; \
150} \
151 \
152static __always_inline const seqcount_t * \
153__seqprop_##lockname##_const_ptr(const seqcount_##lockname##_t *s) \
154{ \
155 return &s->seqcount; \
156} \
157 \
158static __always_inline unsigned \
159__seqprop_##lockname##_sequence(const seqcount_##lockname##_t *s) \
160{ \
161 unsigned seq = smp_load_acquire(&s->seqcount.sequence); \
162 \
163 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
164 return seq; \
165 \
166 if (preemptible && unlikely(seq & 1)) { \
167 __SEQ_LOCK(lockbase##_lock(s->lock)); \
168 __SEQ_LOCK(lockbase##_unlock(s->lock)); \
169 \
170 /* \
171 * Re-read the sequence counter since the (possibly \
172 * preempted) writer made progress. \
173 */ \
174 seq = smp_load_acquire(&s->seqcount.sequence); \
175 } \
176 \
177 return seq; \
178} \
179 \
180static __always_inline bool \
181__seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s) \
182{ \
183 if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
184 return preemptible; \
185 \
186 /* PREEMPT_RT relies on the above LOCK+UNLOCK */ \
187 return false; \
188} \
189 \
190static __always_inline void \
191__seqprop_##lockname##_assert(const seqcount_##lockname##_t *s) \
192{ \
193 __SEQ_LOCK(lockdep_assert_held(s->lock)); \
194}
195
196/*
197 * __seqprop() for seqcount_t
198 */
199
200static inline seqcount_t *__seqprop_ptr(seqcount_t *s)
201{
202 return s;
203}
204
205static inline const seqcount_t *__seqprop_const_ptr(const seqcount_t *s)
206{
207 return s;
208}
209
210static inline unsigned __seqprop_sequence(const seqcount_t *s)
211{
212 return smp_load_acquire(&s->sequence);
213}
214
215static inline bool __seqprop_preemptible(const seqcount_t *s)
216{
217 return false;
218}
219
220static inline void __seqprop_assert(const seqcount_t *s)
221{
222 lockdep_assert_preemption_disabled();
223}
224
225#define __SEQ_RT IS_ENABLED(CONFIG_PREEMPT_RT)
226
227SEQCOUNT_LOCKNAME(raw_spinlock, raw_spinlock_t, false, raw_spin)
228SEQCOUNT_LOCKNAME(spinlock, spinlock_t, __SEQ_RT, spin)
229SEQCOUNT_LOCKNAME(rwlock, rwlock_t, __SEQ_RT, read)
230SEQCOUNT_LOCKNAME(mutex, struct mutex, true, mutex)
231#undef SEQCOUNT_LOCKNAME
232
233/*
234 * SEQCNT_LOCKNAME_ZERO - static initializer for seqcount_LOCKNAME_t
235 * @name: Name of the seqcount_LOCKNAME_t instance
236 * @lock: Pointer to the associated LOCKNAME
237 */
238
239#define SEQCOUNT_LOCKNAME_ZERO(seq_name, assoc_lock) { \
240 .seqcount = SEQCNT_ZERO(seq_name.seqcount), \
241 __SEQ_LOCK(.lock = (assoc_lock)) \
242}
243
244#define SEQCNT_RAW_SPINLOCK_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
245#define SEQCNT_SPINLOCK_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
246#define SEQCNT_RWLOCK_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
247#define SEQCNT_MUTEX_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
248#define SEQCNT_WW_MUTEX_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
249
250#define __seqprop_case(s, lockname, prop) \
251 seqcount_##lockname##_t: __seqprop_##lockname##_##prop
252
253#define __seqprop(s, prop) _Generic(*(s), \
254 seqcount_t: __seqprop_##prop, \
255 __seqprop_case((s), raw_spinlock, prop), \
256 __seqprop_case((s), spinlock, prop), \
257 __seqprop_case((s), rwlock, prop), \
258 __seqprop_case((s), mutex, prop))
259
260#define seqprop_ptr(s) __seqprop(s, ptr)(s)
261#define seqprop_const_ptr(s) __seqprop(s, const_ptr)(s)
262#define seqprop_sequence(s) __seqprop(s, sequence)(s)
263#define seqprop_preemptible(s) __seqprop(s, preemptible)(s)
264#define seqprop_assert(s) __seqprop(s, assert)(s)
265
266/**
267 * __read_seqcount_begin() - begin a seqcount_t read section
268 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
269 *
270 * Return: count to be passed to read_seqcount_retry()
271 */
272#define __read_seqcount_begin(s) \
273({ \
274 unsigned __seq; \
275 \
276 while (unlikely((__seq = seqprop_sequence(s)) & 1)) \
277 cpu_relax(); \
278 \
279 kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
280 __seq; \
281})
282
283/**
284 * raw_read_seqcount_begin() - begin a seqcount_t read section w/o lockdep
285 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
286 *
287 * Return: count to be passed to read_seqcount_retry()
288 */
289#define raw_read_seqcount_begin(s) __read_seqcount_begin(s)
290
291/**
292 * read_seqcount_begin() - begin a seqcount_t read critical section
293 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
294 *
295 * Return: count to be passed to read_seqcount_retry()
296 */
297#define read_seqcount_begin(s) \
298({ \
299 seqcount_lockdep_reader_access(seqprop_const_ptr(s)); \
300 raw_read_seqcount_begin(s); \
301})
302
303/**
304 * raw_read_seqcount() - read the raw seqcount_t counter value
305 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
306 *
307 * raw_read_seqcount opens a read critical section of the given
308 * seqcount_t, without any lockdep checking, and without checking or
309 * masking the sequence counter LSB. Calling code is responsible for
310 * handling that.
311 *
312 * Return: count to be passed to read_seqcount_retry()
313 */
314#define raw_read_seqcount(s) \
315({ \
316 unsigned __seq = seqprop_sequence(s); \
317 \
318 kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
319 __seq; \
320})
321
322/**
323 * raw_seqcount_try_begin() - begin a seqcount_t read critical section
324 * w/o lockdep and w/o counter stabilization
325 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
326 * @start: count to be passed to read_seqcount_retry()
327 *
328 * Similar to raw_seqcount_begin(), except it enables eliding the critical
329 * section entirely if odd, instead of doing the speculation knowing it will
330 * fail.
331 *
332 * Useful when counter stabilization is more or less equivalent to taking
333 * the lock and there is a slowpath that does that.
334 *
335 * If true, start will be set to the (even) sequence count read.
336 *
337 * Return: true when a read critical section is started.
338 */
339#define raw_seqcount_try_begin(s, start) \
340({ \
341 start = raw_read_seqcount(s); \
342 !(start & 1); \
343})
344
345/**
346 * raw_seqcount_begin() - begin a seqcount_t read critical section w/o
347 * lockdep and w/o counter stabilization
348 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
349 *
350 * raw_seqcount_begin opens a read critical section of the given
351 * seqcount_t. Unlike read_seqcount_begin(), this function will not wait
352 * for the count to stabilize. If a writer is active when it begins, it
353 * will fail the read_seqcount_retry() at the end of the read critical
354 * section instead of stabilizing at the beginning of it.
355 *
356 * Use this only in special kernel hot paths where the read section is
357 * small and has a high probability of success through other external
358 * means. It will save a single branching instruction.
359 *
360 * Return: count to be passed to read_seqcount_retry()
361 */
362#define raw_seqcount_begin(s) \
363({ \
364 /* \
365 * If the counter is odd, let read_seqcount_retry() fail \
366 * by decrementing the counter. \
367 */ \
368 raw_read_seqcount(s) & ~1; \
369})
370
371/**
372 * __read_seqcount_retry() - end a seqcount_t read section w/o barrier
373 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
374 * @start: count, from read_seqcount_begin()
375 *
376 * __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb()
377 * barrier. Callers should ensure that smp_rmb() or equivalent ordering is
378 * provided before actually loading any of the variables that are to be
379 * protected in this critical section.
380 *
381 * Use carefully, only in critical code, and comment how the barrier is
382 * provided.
383 *
384 * Return: true if a read section retry is required, else false
385 */
386#define __read_seqcount_retry(s, start) \
387 do___read_seqcount_retry(seqprop_const_ptr(s), start)
388
389static inline int do___read_seqcount_retry(const seqcount_t *s, unsigned start)
390{
391 kcsan_atomic_next(0);
392 return unlikely(READ_ONCE(s->sequence) != start);
393}
394
395/**
396 * read_seqcount_retry() - end a seqcount_t read critical section
397 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
398 * @start: count, from read_seqcount_begin()
399 *
400 * read_seqcount_retry closes the read critical section of given
401 * seqcount_t. If the critical section was invalid, it must be ignored
402 * (and typically retried).
403 *
404 * Return: true if a read section retry is required, else false
405 */
406#define read_seqcount_retry(s, start) \
407 do_read_seqcount_retry(seqprop_const_ptr(s), start)
408
409static inline int do_read_seqcount_retry(const seqcount_t *s, unsigned start)
410{
411 smp_rmb();
412 return do___read_seqcount_retry(s, start);
413}
414
415/**
416 * raw_write_seqcount_begin() - start a seqcount_t write section w/o lockdep
417 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
418 *
419 * Context: check write_seqcount_begin()
420 */
421#define raw_write_seqcount_begin(s) \
422do { \
423 if (seqprop_preemptible(s)) \
424 preempt_disable(); \
425 \
426 do_raw_write_seqcount_begin(seqprop_ptr(s)); \
427} while (0)
428
429static inline void do_raw_write_seqcount_begin(seqcount_t *s)
430{
431 kcsan_nestable_atomic_begin();
432 s->sequence++;
433 smp_wmb();
434}
435
436/**
437 * raw_write_seqcount_end() - end a seqcount_t write section w/o lockdep
438 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
439 *
440 * Context: check write_seqcount_end()
441 */
442#define raw_write_seqcount_end(s) \
443do { \
444 do_raw_write_seqcount_end(seqprop_ptr(s)); \
445 \
446 if (seqprop_preemptible(s)) \
447 preempt_enable(); \
448} while (0)
449
450static inline void do_raw_write_seqcount_end(seqcount_t *s)
451{
452 smp_wmb();
453 s->sequence++;
454 kcsan_nestable_atomic_end();
455}
456
457/**
458 * write_seqcount_begin_nested() - start a seqcount_t write section with
459 * custom lockdep nesting level
460 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
461 * @subclass: lockdep nesting level
462 *
463 * See Documentation/locking/lockdep-design.rst
464 * Context: check write_seqcount_begin()
465 */
466#define write_seqcount_begin_nested(s, subclass) \
467do { \
468 seqprop_assert(s); \
469 \
470 if (seqprop_preemptible(s)) \
471 preempt_disable(); \
472 \
473 do_write_seqcount_begin_nested(seqprop_ptr(s), subclass); \
474} while (0)
475
476static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass)
477{
478 seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_);
479 do_raw_write_seqcount_begin(s);
480}
481
482/**
483 * write_seqcount_begin() - start a seqcount_t write side critical section
484 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
485 *
486 * Context: sequence counter write side sections must be serialized and
487 * non-preemptible. Preemption will be automatically disabled if and
488 * only if the seqcount write serialization lock is associated, and
489 * preemptible. If readers can be invoked from hardirq or softirq
490 * context, interrupts or bottom halves must be respectively disabled.
491 */
492#define write_seqcount_begin(s) \
493do { \
494 seqprop_assert(s); \
495 \
496 if (seqprop_preemptible(s)) \
497 preempt_disable(); \
498 \
499 do_write_seqcount_begin(seqprop_ptr(s)); \
500} while (0)
501
502static inline void do_write_seqcount_begin(seqcount_t *s)
503{
504 do_write_seqcount_begin_nested(s, 0);
505}
506
507/**
508 * write_seqcount_end() - end a seqcount_t write side critical section
509 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
510 *
511 * Context: Preemption will be automatically re-enabled if and only if
512 * the seqcount write serialization lock is associated, and preemptible.
513 */
514#define write_seqcount_end(s) \
515do { \
516 do_write_seqcount_end(seqprop_ptr(s)); \
517 \
518 if (seqprop_preemptible(s)) \
519 preempt_enable(); \
520} while (0)
521
522static inline void do_write_seqcount_end(seqcount_t *s)
523{
524 seqcount_release(&s->dep_map, _RET_IP_);
525 do_raw_write_seqcount_end(s);
526}
527
528/**
529 * raw_write_seqcount_barrier() - do a seqcount_t write barrier
530 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
531 *
532 * This can be used to provide an ordering guarantee instead of the usual
533 * consistency guarantee. It is one wmb cheaper, because it can collapse
534 * the two back-to-back wmb()s.
535 *
536 * Note that writes surrounding the barrier should be declared atomic (e.g.
537 * via WRITE_ONCE): a) to ensure the writes become visible to other threads
538 * atomically, avoiding compiler optimizations; b) to document which writes are
539 * meant to propagate to the reader critical section. This is necessary because
540 * neither writes before nor after the barrier are enclosed in a seq-writer
541 * critical section that would ensure readers are aware of ongoing writes::
542 *
543 * seqcount_t seq;
544 * bool X = true, Y = false;
545 *
546 * void read(void)
547 * {
548 * bool x, y;
549 *
550 * do {
551 * int s = read_seqcount_begin(&seq);
552 *
553 * x = X; y = Y;
554 *
555 * } while (read_seqcount_retry(&seq, s));
556 *
557 * BUG_ON(!x && !y);
558 * }
559 *
560 * void write(void)
561 * {
562 * WRITE_ONCE(Y, true);
563 *
564 * raw_write_seqcount_barrier(seq);
565 *
566 * WRITE_ONCE(X, false);
567 * }
568 */
569#define raw_write_seqcount_barrier(s) \
570 do_raw_write_seqcount_barrier(seqprop_ptr(s))
571
572static inline void do_raw_write_seqcount_barrier(seqcount_t *s)
573{
574 kcsan_nestable_atomic_begin();
575 s->sequence++;
576 smp_wmb();
577 s->sequence++;
578 kcsan_nestable_atomic_end();
579}
580
581/**
582 * write_seqcount_invalidate() - invalidate in-progress seqcount_t read
583 * side operations
584 * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
585 *
586 * After write_seqcount_invalidate, no seqcount_t read side operations
587 * will complete successfully and see data older than this.
588 */
589#define write_seqcount_invalidate(s) \
590 do_write_seqcount_invalidate(seqprop_ptr(s))
591
592static inline void do_write_seqcount_invalidate(seqcount_t *s)
593{
594 smp_wmb();
595 kcsan_nestable_atomic_begin();
596 s->sequence+=2;
597 kcsan_nestable_atomic_end();
598}
599
600/*
601 * Latch sequence counters (seqcount_latch_t)
602 *
603 * A sequence counter variant where the counter even/odd value is used to
604 * switch between two copies of protected data. This allows the read path,
605 * typically NMIs, to safely interrupt the write side critical section.
606 *
607 * As the write sections are fully preemptible, no special handling for
608 * PREEMPT_RT is needed.
609 */
610typedef struct {
611 seqcount_t seqcount;
612} seqcount_latch_t;
613
614/**
615 * SEQCNT_LATCH_ZERO() - static initializer for seqcount_latch_t
616 * @seq_name: Name of the seqcount_latch_t instance
617 */
618#define SEQCNT_LATCH_ZERO(seq_name) { \
619 .seqcount = SEQCNT_ZERO(seq_name.seqcount), \
620}
621
622/**
623 * seqcount_latch_init() - runtime initializer for seqcount_latch_t
624 * @s: Pointer to the seqcount_latch_t instance
625 */
626#define seqcount_latch_init(s) seqcount_init(&(s)->seqcount)
627
628/**
629 * raw_read_seqcount_latch() - pick even/odd latch data copy
630 * @s: Pointer to seqcount_latch_t
631 *
632 * See raw_write_seqcount_latch() for details and a full reader/writer
633 * usage example.
634 *
635 * Return: sequence counter raw value. Use the lowest bit as an index for
636 * picking which data copy to read. The full counter must then be checked
637 * with raw_read_seqcount_latch_retry().
638 */
639static __always_inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s)
640{
641 /*
642 * Pairs with the first smp_wmb() in raw_write_seqcount_latch().
643 * Due to the dependent load, a full smp_rmb() is not needed.
644 */
645 return READ_ONCE(s->seqcount.sequence);
646}
647
648/**
649 * read_seqcount_latch() - pick even/odd latch data copy
650 * @s: Pointer to seqcount_latch_t
651 *
652 * See write_seqcount_latch() for details and a full reader/writer usage
653 * example.
654 *
655 * Return: sequence counter raw value. Use the lowest bit as an index for
656 * picking which data copy to read. The full counter must then be checked
657 * with read_seqcount_latch_retry().
658 */
659static __always_inline unsigned read_seqcount_latch(const seqcount_latch_t *s)
660{
661 kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX);
662 return raw_read_seqcount_latch(s);
663}
664
665/**
666 * raw_read_seqcount_latch_retry() - end a seqcount_latch_t read section
667 * @s: Pointer to seqcount_latch_t
668 * @start: count, from raw_read_seqcount_latch()
669 *
670 * Return: true if a read section retry is required, else false
671 */
672static __always_inline int
673raw_read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start)
674{
675 smp_rmb();
676 return unlikely(READ_ONCE(s->seqcount.sequence) != start);
677}
678
679/**
680 * read_seqcount_latch_retry() - end a seqcount_latch_t read section
681 * @s: Pointer to seqcount_latch_t
682 * @start: count, from read_seqcount_latch()
683 *
684 * Return: true if a read section retry is required, else false
685 */
686static __always_inline int
687read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start)
688{
689 kcsan_atomic_next(0);
690 return raw_read_seqcount_latch_retry(s, start);
691}
692
693/**
694 * raw_write_seqcount_latch() - redirect latch readers to even/odd copy
695 * @s: Pointer to seqcount_latch_t
696 */
697static __always_inline void raw_write_seqcount_latch(seqcount_latch_t *s)
698{
699 smp_wmb(); /* prior stores before incrementing "sequence" */
700 s->seqcount.sequence++;
701 smp_wmb(); /* increment "sequence" before following stores */
702}
703
704/**
705 * write_seqcount_latch_begin() - redirect latch readers to odd copy
706 * @s: Pointer to seqcount_latch_t
707 *
708 * The latch technique is a multiversion concurrency control method that allows
709 * queries during non-atomic modifications. If you can guarantee queries never
710 * interrupt the modification -- e.g. the concurrency is strictly between CPUs
711 * -- you most likely do not need this.
712 *
713 * Where the traditional RCU/lockless data structures rely on atomic
714 * modifications to ensure queries observe either the old or the new state the
715 * latch allows the same for non-atomic updates. The trade-off is doubling the
716 * cost of storage; we have to maintain two copies of the entire data
717 * structure.
718 *
719 * Very simply put: we first modify one copy and then the other. This ensures
720 * there is always one copy in a stable state, ready to give us an answer.
721 *
722 * The basic form is a data structure like::
723 *
724 * struct latch_struct {
725 * seqcount_latch_t seq;
726 * struct data_struct data[2];
727 * };
728 *
729 * Where a modification, which is assumed to be externally serialized, does the
730 * following::
731 *
732 * void latch_modify(struct latch_struct *latch, ...)
733 * {
734 * write_seqcount_latch_begin(&latch->seq);
735 * modify(latch->data[0], ...);
736 * write_seqcount_latch(&latch->seq);
737 * modify(latch->data[1], ...);
738 * write_seqcount_latch_end(&latch->seq);
739 * }
740 *
741 * The query will have a form like::
742 *
743 * struct entry *latch_query(struct latch_struct *latch, ...)
744 * {
745 * struct entry *entry;
746 * unsigned seq, idx;
747 *
748 * do {
749 * seq = read_seqcount_latch(&latch->seq);
750 *
751 * idx = seq & 0x01;
752 * entry = data_query(latch->data[idx], ...);
753 *
754 * // This includes needed smp_rmb()
755 * } while (read_seqcount_latch_retry(&latch->seq, seq));
756 *
757 * return entry;
758 * }
759 *
760 * So during the modification, queries are first redirected to data[1]. Then we
761 * modify data[0]. When that is complete, we redirect queries back to data[0]
762 * and we can modify data[1].
763 *
764 * NOTE:
765 *
766 * The non-requirement for atomic modifications does _NOT_ include
767 * the publishing of new entries in the case where data is a dynamic
768 * data structure.
769 *
770 * An iteration might start in data[0] and get suspended long enough
771 * to miss an entire modification sequence, once it resumes it might
772 * observe the new entry.
773 *
774 * NOTE2:
775 *
776 * When data is a dynamic data structure; one should use regular RCU
777 * patterns to manage the lifetimes of the objects within.
778 */
779static __always_inline void write_seqcount_latch_begin(seqcount_latch_t *s)
780{
781 kcsan_nestable_atomic_begin();
782 raw_write_seqcount_latch(s);
783}
784
785/**
786 * write_seqcount_latch() - redirect latch readers to even copy
787 * @s: Pointer to seqcount_latch_t
788 */
789static __always_inline void write_seqcount_latch(seqcount_latch_t *s)
790{
791 raw_write_seqcount_latch(s);
792}
793
794/**
795 * write_seqcount_latch_end() - end a seqcount_latch_t write section
796 * @s: Pointer to seqcount_latch_t
797 *
798 * Marks the end of a seqcount_latch_t writer section, after all copies of the
799 * latch-protected data have been updated.
800 */
801static __always_inline void write_seqcount_latch_end(seqcount_latch_t *s)
802{
803 kcsan_nestable_atomic_end();
804}
805
806#define __SEQLOCK_UNLOCKED(lockname) \
807 { \
808 .seqcount = SEQCNT_SPINLOCK_ZERO(lockname, &(lockname).lock), \
809 .lock = __SPIN_LOCK_UNLOCKED(lockname) \
810 }
811
812/**
813 * seqlock_init() - dynamic initializer for seqlock_t
814 * @sl: Pointer to the seqlock_t instance
815 */
816#define seqlock_init(sl) \
817 do { \
818 spin_lock_init(&(sl)->lock); \
819 seqcount_spinlock_init(&(sl)->seqcount, &(sl)->lock); \
820 } while (0)
821
822/**
823 * DEFINE_SEQLOCK(sl) - Define a statically allocated seqlock_t
824 * @sl: Name of the seqlock_t instance
825 */
826#define DEFINE_SEQLOCK(sl) \
827 seqlock_t sl = __SEQLOCK_UNLOCKED(sl)
828
829/**
830 * read_seqbegin() - start a seqlock_t read side critical section
831 * @sl: Pointer to seqlock_t
832 *
833 * Return: count, to be passed to read_seqretry()
834 */
835static inline unsigned read_seqbegin(const seqlock_t *sl)
836 __acquires_shared(sl) __no_context_analysis
837{
838 return read_seqcount_begin(&sl->seqcount);
839}
840
841/**
842 * read_seqretry() - end a seqlock_t read side section
843 * @sl: Pointer to seqlock_t
844 * @start: count, from read_seqbegin()
845 *
846 * read_seqretry closes the read side critical section of given seqlock_t.
847 * If the critical section was invalid, it must be ignored (and typically
848 * retried).
849 *
850 * Return: true if a read section retry is required, else false
851 */
852static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
853 __releases_shared(sl) __no_context_analysis
854{
855 return read_seqcount_retry(&sl->seqcount, start);
856}
857
858/*
859 * For all seqlock_t write side functions, use the internal
860 * do_write_seqcount_begin() instead of generic write_seqcount_begin().
861 * This way, no redundant lockdep_assert_held() checks are added.
862 */
863
864/**
865 * write_seqlock() - start a seqlock_t write side critical section
866 * @sl: Pointer to seqlock_t
867 *
868 * write_seqlock opens a write side critical section for the given
869 * seqlock_t. It also implicitly acquires the spinlock_t embedded inside
870 * that sequential lock. All seqlock_t write side sections are thus
871 * automatically serialized and non-preemptible.
872 *
873 * Context: if the seqlock_t read section, or other write side critical
874 * sections, can be invoked from hardirq or softirq contexts, use the
875 * _irqsave or _bh variants of this function instead.
876 */
877static inline void write_seqlock(seqlock_t *sl)
878 __acquires(sl) __no_context_analysis
879{
880 spin_lock(&sl->lock);
881 do_write_seqcount_begin(&sl->seqcount.seqcount);
882}
883
884/**
885 * write_sequnlock() - end a seqlock_t write side critical section
886 * @sl: Pointer to seqlock_t
887 *
888 * write_sequnlock closes the (serialized and non-preemptible) write side
889 * critical section of given seqlock_t.
890 */
891static inline void write_sequnlock(seqlock_t *sl)
892 __releases(sl) __no_context_analysis
893{
894 do_write_seqcount_end(&sl->seqcount.seqcount);
895 spin_unlock(&sl->lock);
896}
897
898/**
899 * write_seqlock_bh() - start a softirqs-disabled seqlock_t write section
900 * @sl: Pointer to seqlock_t
901 *
902 * _bh variant of write_seqlock(). Use only if the read side section, or
903 * other write side sections, can be invoked from softirq contexts.
904 */
905static inline void write_seqlock_bh(seqlock_t *sl)
906 __acquires(sl) __no_context_analysis
907{
908 spin_lock_bh(&sl->lock);
909 do_write_seqcount_begin(&sl->seqcount.seqcount);
910}
911
912/**
913 * write_sequnlock_bh() - end a softirqs-disabled seqlock_t write section
914 * @sl: Pointer to seqlock_t
915 *
916 * write_sequnlock_bh closes the serialized, non-preemptible, and
917 * softirqs-disabled, seqlock_t write side critical section opened with
918 * write_seqlock_bh().
919 */
920static inline void write_sequnlock_bh(seqlock_t *sl)
921 __releases(sl) __no_context_analysis
922{
923 do_write_seqcount_end(&sl->seqcount.seqcount);
924 spin_unlock_bh(&sl->lock);
925}
926
927/**
928 * write_seqlock_irq() - start a non-interruptible seqlock_t write section
929 * @sl: Pointer to seqlock_t
930 *
931 * _irq variant of write_seqlock(). Use only if the read side section, or
932 * other write sections, can be invoked from hardirq contexts.
933 */
934static inline void write_seqlock_irq(seqlock_t *sl)
935 __acquires(sl) __no_context_analysis
936{
937 spin_lock_irq(&sl->lock);
938 do_write_seqcount_begin(&sl->seqcount.seqcount);
939}
940
941/**
942 * write_sequnlock_irq() - end a non-interruptible seqlock_t write section
943 * @sl: Pointer to seqlock_t
944 *
945 * write_sequnlock_irq closes the serialized and non-interruptible
946 * seqlock_t write side section opened with write_seqlock_irq().
947 */
948static inline void write_sequnlock_irq(seqlock_t *sl)
949 __releases(sl) __no_context_analysis
950{
951 do_write_seqcount_end(&sl->seqcount.seqcount);
952 spin_unlock_irq(&sl->lock);
953}
954
955static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
956 __acquires(sl) __no_context_analysis
957{
958 unsigned long flags;
959
960 spin_lock_irqsave(&sl->lock, flags);
961 do_write_seqcount_begin(&sl->seqcount.seqcount);
962 return flags;
963}
964
965/**
966 * write_seqlock_irqsave() - start a non-interruptible seqlock_t write
967 * section
968 * @lock: Pointer to seqlock_t
969 * @flags: Stack-allocated storage for saving caller's local interrupt
970 * state, to be passed to write_sequnlock_irqrestore().
971 *
972 * _irqsave variant of write_seqlock(). Use it only if the read side
973 * section, or other write sections, can be invoked from hardirq context.
974 */
975#define write_seqlock_irqsave(lock, flags) \
976 do { flags = __write_seqlock_irqsave(lock); } while (0)
977
978/**
979 * write_sequnlock_irqrestore() - end non-interruptible seqlock_t write
980 * section
981 * @sl: Pointer to seqlock_t
982 * @flags: Caller's saved interrupt state, from write_seqlock_irqsave()
983 *
984 * write_sequnlock_irqrestore closes the serialized and non-interruptible
985 * seqlock_t write section previously opened with write_seqlock_irqsave().
986 */
987static inline void
988write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
989 __releases(sl) __no_context_analysis
990{
991 do_write_seqcount_end(&sl->seqcount.seqcount);
992 spin_unlock_irqrestore(&sl->lock, flags);
993}
994
995/**
996 * read_seqlock_excl() - begin a seqlock_t locking reader section
997 * @sl: Pointer to seqlock_t
998 *
999 * read_seqlock_excl opens a seqlock_t locking reader critical section. A
1000 * locking reader exclusively locks out *both* other writers *and* other
1001 * locking readers, but it does not update the embedded sequence number.
1002 *
1003 * Locking readers act like a normal spin_lock()/spin_unlock().
1004 *
1005 * Context: if the seqlock_t write section, *or other read sections*, can
1006 * be invoked from hardirq or softirq contexts, use the _irqsave or _bh
1007 * variant of this function instead.
1008 *
1009 * The opened read section must be closed with read_sequnlock_excl().
1010 */
1011static inline void read_seqlock_excl(seqlock_t *sl)
1012 __acquires_shared(sl) __no_context_analysis
1013{
1014 spin_lock(&sl->lock);
1015}
1016
1017/**
1018 * read_sequnlock_excl() - end a seqlock_t locking reader critical section
1019 * @sl: Pointer to seqlock_t
1020 */
1021static inline void read_sequnlock_excl(seqlock_t *sl)
1022 __releases_shared(sl) __no_context_analysis
1023{
1024 spin_unlock(&sl->lock);
1025}
1026
1027/**
1028 * read_seqlock_excl_bh() - start a seqlock_t locking reader section with
1029 * softirqs disabled
1030 * @sl: Pointer to seqlock_t
1031 *
1032 * _bh variant of read_seqlock_excl(). Use this variant only if the
1033 * seqlock_t write side section, *or other read sections*, can be invoked
1034 * from softirq contexts.
1035 */
1036static inline void read_seqlock_excl_bh(seqlock_t *sl)
1037 __acquires_shared(sl) __no_context_analysis
1038{
1039 spin_lock_bh(&sl->lock);
1040}
1041
1042/**
1043 * read_sequnlock_excl_bh() - stop a seqlock_t softirq-disabled locking
1044 * reader section
1045 * @sl: Pointer to seqlock_t
1046 */
1047static inline void read_sequnlock_excl_bh(seqlock_t *sl)
1048 __releases_shared(sl) __no_context_analysis
1049{
1050 spin_unlock_bh(&sl->lock);
1051}
1052
1053/**
1054 * read_seqlock_excl_irq() - start a non-interruptible seqlock_t locking
1055 * reader section
1056 * @sl: Pointer to seqlock_t
1057 *
1058 * _irq variant of read_seqlock_excl(). Use this only if the seqlock_t
1059 * write side section, *or other read sections*, can be invoked from a
1060 * hardirq context.
1061 */
1062static inline void read_seqlock_excl_irq(seqlock_t *sl)
1063 __acquires_shared(sl) __no_context_analysis
1064{
1065 spin_lock_irq(&sl->lock);
1066}
1067
1068/**
1069 * read_sequnlock_excl_irq() - end an interrupts-disabled seqlock_t
1070 * locking reader section
1071 * @sl: Pointer to seqlock_t
1072 */
1073static inline void read_sequnlock_excl_irq(seqlock_t *sl)
1074 __releases_shared(sl) __no_context_analysis
1075{
1076 spin_unlock_irq(&sl->lock);
1077}
1078
1079static inline unsigned long __read_seqlock_excl_irqsave(seqlock_t *sl)
1080 __acquires_shared(sl) __no_context_analysis
1081{
1082 unsigned long flags;
1083
1084 spin_lock_irqsave(&sl->lock, flags);
1085 return flags;
1086}
1087
1088/**
1089 * read_seqlock_excl_irqsave() - start a non-interruptible seqlock_t
1090 * locking reader section
1091 * @lock: Pointer to seqlock_t
1092 * @flags: Stack-allocated storage for saving caller's local interrupt
1093 * state, to be passed to read_sequnlock_excl_irqrestore().
1094 *
1095 * _irqsave variant of read_seqlock_excl(). Use this only if the seqlock_t
1096 * write side section, *or other read sections*, can be invoked from a
1097 * hardirq context.
1098 */
1099#define read_seqlock_excl_irqsave(lock, flags) \
1100 do { flags = __read_seqlock_excl_irqsave(lock); } while (0)
1101
1102/**
1103 * read_sequnlock_excl_irqrestore() - end non-interruptible seqlock_t
1104 * locking reader section
1105 * @sl: Pointer to seqlock_t
1106 * @flags: Caller saved interrupt state, from read_seqlock_excl_irqsave()
1107 */
1108static inline void
1109read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags)
1110 __releases_shared(sl) __no_context_analysis
1111{
1112 spin_unlock_irqrestore(&sl->lock, flags);
1113}
1114
1115/**
1116 * read_seqbegin_or_lock() - begin a seqlock_t lockless or locking reader
1117 * @lock: Pointer to seqlock_t
1118 * @seq : Marker and return parameter. If the passed value is even, the
1119 * reader will become a *lockless* seqlock_t reader as in read_seqbegin().
1120 * If the passed value is odd, the reader will become a *locking* reader
1121 * as in read_seqlock_excl(). In the first call to this function, the
1122 * caller *must* initialize and pass an even value to @seq; this way, a
1123 * lockless read can be optimistically tried first.
1124 *
1125 * read_seqbegin_or_lock is an API designed to optimistically try a normal
1126 * lockless seqlock_t read section first. If an odd counter is found, the
1127 * lockless read trial has failed, and the next read iteration transforms
1128 * itself into a full seqlock_t locking reader.
1129 *
1130 * This is typically used to avoid seqlock_t lockless readers starvation
1131 * (too much retry loops) in the case of a sharp spike in write side
1132 * activity.
1133 *
1134 * Context: if the seqlock_t write section, *or other read sections*, can
1135 * be invoked from hardirq or softirq contexts, use the _irqsave or _bh
1136 * variant of this function instead.
1137 *
1138 * Check Documentation/locking/seqlock.rst for template example code.
1139 *
1140 * Return: the encountered sequence counter value, through the @seq
1141 * parameter, which is overloaded as a return parameter. This returned
1142 * value must be checked with need_seqretry(). If the read section need to
1143 * be retried, this returned value must also be passed as the @seq
1144 * parameter of the next read_seqbegin_or_lock() iteration.
1145 */
1146static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
1147 __acquires_shared(lock) __no_context_analysis
1148{
1149 if (!(*seq & 1)) /* Even */
1150 *seq = read_seqbegin(lock);
1151 else /* Odd */
1152 read_seqlock_excl(lock);
1153}
1154
1155/**
1156 * need_seqretry() - validate seqlock_t "locking or lockless" read section
1157 * @lock: Pointer to seqlock_t
1158 * @seq: sequence count, from read_seqbegin_or_lock()
1159 *
1160 * Return: true if a read section retry is required, false otherwise
1161 */
1162static inline int need_seqretry(seqlock_t *lock, int seq)
1163 __releases_shared(lock) __no_context_analysis
1164{
1165 return !(seq & 1) && read_seqretry(lock, seq);
1166}
1167
1168/**
1169 * done_seqretry() - end seqlock_t "locking or lockless" reader section
1170 * @lock: Pointer to seqlock_t
1171 * @seq: count, from read_seqbegin_or_lock()
1172 *
1173 * done_seqretry finishes the seqlock_t read side critical section started
1174 * with read_seqbegin_or_lock() and validated by need_seqretry().
1175 */
1176static inline void done_seqretry(seqlock_t *lock, int seq)
1177 __no_context_analysis
1178{
1179 if (seq & 1)
1180 read_sequnlock_excl(lock);
1181}
1182
1183/**
1184 * read_seqbegin_or_lock_irqsave() - begin a seqlock_t lockless reader, or
1185 * a non-interruptible locking reader
1186 * @lock: Pointer to seqlock_t
1187 * @seq: Marker and return parameter. Check read_seqbegin_or_lock().
1188 *
1189 * This is the _irqsave variant of read_seqbegin_or_lock(). Use it only if
1190 * the seqlock_t write section, *or other read sections*, can be invoked
1191 * from hardirq context.
1192 *
1193 * Note: Interrupts will be disabled only for "locking reader" mode.
1194 *
1195 * Return:
1196 *
1197 * 1. The saved local interrupts state in case of a locking reader, to
1198 * be passed to done_seqretry_irqrestore().
1199 *
1200 * 2. The encountered sequence counter value, returned through @seq
1201 * overloaded as a return parameter. Check read_seqbegin_or_lock().
1202 */
1203static inline unsigned long
1204read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq)
1205 __acquires_shared(lock) __no_context_analysis
1206{
1207 unsigned long flags = 0;
1208
1209 if (!(*seq & 1)) /* Even */
1210 *seq = read_seqbegin(lock);
1211 else /* Odd */
1212 read_seqlock_excl_irqsave(lock, flags);
1213
1214 return flags;
1215}
1216
1217/**
1218 * done_seqretry_irqrestore() - end a seqlock_t lockless reader, or a
1219 * non-interruptible locking reader section
1220 * @lock: Pointer to seqlock_t
1221 * @seq: Count, from read_seqbegin_or_lock_irqsave()
1222 * @flags: Caller's saved local interrupt state in case of a locking
1223 * reader, also from read_seqbegin_or_lock_irqsave()
1224 *
1225 * This is the _irqrestore variant of done_seqretry(). The read section
1226 * must've been opened with read_seqbegin_or_lock_irqsave(), and validated
1227 * by need_seqretry().
1228 */
1229static inline void
1230done_seqretry_irqrestore(seqlock_t *lock, int seq, unsigned long flags)
1231 __no_context_analysis
1232{
1233 if (seq & 1)
1234 read_sequnlock_excl_irqrestore(lock, flags);
1235}
1236
1237enum ss_state {
1238 ss_done = 0,
1239 ss_lock,
1240 ss_lock_irqsave,
1241 ss_lockless,
1242};
1243
1244struct ss_tmp {
1245 enum ss_state state;
1246 unsigned long data;
1247 spinlock_t *lock;
1248 spinlock_t *lock_irqsave;
1249};
1250
1251static __always_inline void __scoped_seqlock_cleanup(struct ss_tmp *sst)
1252 __no_context_analysis
1253{
1254 if (sst->lock)
1255 spin_unlock(sst->lock);
1256 if (sst->lock_irqsave)
1257 spin_unlock_irqrestore(sst->lock_irqsave, sst->data);
1258}
1259
1260extern void __scoped_seqlock_invalid_target(void);
1261
1262#if (defined(CONFIG_CC_IS_GCC) && CONFIG_GCC_VERSION < 90000) || \
1263 defined(CONFIG_KASAN) || defined(CONFIG_UBSAN_ALIGNMENT)
1264/*
1265 * For some reason some GCC-8 architectures (nios2, alpha) have trouble
1266 * determining that the ss_done state is impossible in __scoped_seqlock_next()
1267 * below.
1268 *
1269 * Similarly KASAN and UBSAN_ALIGNMENT are known to confuse compilers enough
1270 * to break this. But we don't care about code quality for such builds anyway.
1271 */
1272static inline void __scoped_seqlock_bug(void) { }
1273#else
1274/*
1275 * Canary for compiler optimization -- if the compiler doesn't realize this is
1276 * an impossible state, it very likely generates sub-optimal code here.
1277 */
1278extern void __scoped_seqlock_bug(void);
1279#endif
1280
1281static __always_inline void
1282__scoped_seqlock_next(struct ss_tmp *sst, seqlock_t *lock, enum ss_state target)
1283 __no_context_analysis
1284{
1285 switch (sst->state) {
1286 case ss_done:
1287 __scoped_seqlock_bug();
1288 return;
1289
1290 case ss_lock:
1291 case ss_lock_irqsave:
1292 sst->state = ss_done;
1293 return;
1294
1295 case ss_lockless:
1296 if (!read_seqretry(lock, sst->data)) {
1297 sst->state = ss_done;
1298 return;
1299 }
1300 break;
1301 }
1302
1303 switch (target) {
1304 case ss_done:
1305 __scoped_seqlock_invalid_target();
1306 return;
1307
1308 case ss_lock:
1309 sst->lock = &lock->lock;
1310 spin_lock(sst->lock);
1311 sst->state = ss_lock;
1312 return;
1313
1314 case ss_lock_irqsave:
1315 sst->lock_irqsave = &lock->lock;
1316 spin_lock_irqsave(sst->lock_irqsave, sst->data);
1317 sst->state = ss_lock_irqsave;
1318 return;
1319
1320 case ss_lockless:
1321 sst->data = read_seqbegin(lock);
1322 return;
1323 }
1324}
1325
1326/*
1327 * Context analysis no-op helper to release seqlock at the end of the for-scope;
1328 * the alias analysis of the compiler will recognize that the pointer @s is an
1329 * alias to @_seqlock passed to read_seqbegin(_seqlock) below.
1330 */
1331static __always_inline void __scoped_seqlock_cleanup_ctx(struct ss_tmp **s)
1332 __releases_shared(*((seqlock_t **)s)) __no_context_analysis {}
1333
1334#define __scoped_seqlock_read(_seqlock, _target, _s) \
1335 for (struct ss_tmp _s __cleanup(__scoped_seqlock_cleanup) = \
1336 { .state = ss_lockless, .data = read_seqbegin(_seqlock) }, \
1337 *__UNIQUE_ID(ctx) __cleanup(__scoped_seqlock_cleanup_ctx) =\
1338 (struct ss_tmp *)_seqlock; \
1339 _s.state != ss_done; \
1340 __scoped_seqlock_next(&_s, _seqlock, _target))
1341
1342/**
1343 * scoped_seqlock_read() - execute the read-side critical section
1344 * without manual sequence counter handling
1345 * or calls to other helpers
1346 * @_seqlock: pointer to seqlock_t protecting the data
1347 * @_target: an enum ss_state: one of {ss_lock, ss_lock_irqsave, ss_lockless}
1348 * indicating the type of critical read section
1349 *
1350 * Example::
1351 *
1352 * scoped_seqlock_read (&lock, ss_lock) {
1353 * // read-side critical section
1354 * }
1355 *
1356 * Starts with a lockess pass first. If it fails, restarts the critical
1357 * section with the lock held.
1358 */
1359#define scoped_seqlock_read(_seqlock, _target) \
1360 __scoped_seqlock_read(_seqlock, _target, __UNIQUE_ID(seqlock))
1361
1362DEFINE_LOCK_GUARD_1(seqlock_init, seqlock_t, seqlock_init(_T->lock), /* */)
1363DECLARE_LOCK_GUARD_1_ATTRS(seqlock_init, __acquires(_T), __releases(*(seqlock_t **)_T))
1364#define class_seqlock_init_constructor(_T) WITH_LOCK_GUARD_1_ATTRS(seqlock_init, _T)
1365
1366#endif /* __LINUX_SEQLOCK_H */