diff options
Diffstat (limited to 'include/linux/seqlock.h')
| -rw-r--r-- | include/linux/seqlock.h | 398 |
1 files changed, 193 insertions, 205 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index ac5b07f558b0..5ce48eab7a2a 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -17,8 +17,8 @@ #include <linux/kcsan-checks.h> #include <linux/lockdep.h> #include <linux/mutex.h> -#include <linux/ww_mutex.h> #include <linux/preempt.h> +#include <linux/seqlock_types.h> #include <linux/spinlock.h> #include <asm/processor.h> @@ -38,37 +38,6 @@ */ #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) { @@ -133,28 +102,6 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s) */ /* - * 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 @@ -164,7 +111,7 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s) * static initializer or init function. This enables lockdep to validate * that the write side critical section is properly serialized. * - * LOCKNAME: raw_spinlock, spinlock, rwlock, mutex, or ww_mutex. + * LOCKNAME: raw_spinlock, spinlock, rwlock or mutex */ /* @@ -182,9 +129,8 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s) #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); -#define seqcount_ww_mutex_init(s, lock) seqcount_LOCKNAME_init(s, lock, ww_mutex); +#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 @@ -193,39 +139,38 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s) * @lockname: "LOCKNAME" part of seqcount_LOCKNAME_t * @locktype: LOCKNAME canonical C data type * @preemptible: preemptibility of above locktype - * @lockmember: argument for lockdep_assert_held() - * @lockbase: associated lock release function (prefix only) - * @lock_acquire: associated lock acquisition function (full call) + * @lockbase: prefix for associated lock/unlock */ -#define SEQCOUNT_LOCKNAME(lockname, locktype, preemptible, lockmember, lockbase, lock_acquire) \ -typedef struct seqcount_##lockname { \ - seqcount_t seqcount; \ - __SEQ_LOCK(locktype *lock); \ -} seqcount_##lockname##_t; \ - \ +#define SEQCOUNT_LOCKNAME(lockname, locktype, preemptible, lockbase) \ 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); \ + unsigned seq = smp_load_acquire(&s->seqcount.sequence); \ \ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \ return seq; \ \ if (preemptible && unlikely(seq & 1)) { \ - __SEQ_LOCK(lock_acquire); \ + __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); \ + seq = smp_load_acquire(&s->seqcount.sequence); \ } \ \ return seq; \ @@ -244,7 +189,7 @@ __seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s) \ static __always_inline void \ __seqprop_##lockname##_assert(const seqcount_##lockname##_t *s) \ { \ - __SEQ_LOCK(lockdep_assert_held(lockmember)); \ + __SEQ_LOCK(lockdep_assert_held(s->lock)); \ } /* @@ -256,9 +201,14 @@ 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); + return smp_load_acquire(&s->sequence); } static inline bool __seqprop_preemptible(const seqcount_t *s) @@ -273,11 +223,11 @@ static inline void __seqprop_assert(const seqcount_t *s) #define __SEQ_RT IS_ENABLED(CONFIG_PREEMPT_RT) -SEQCOUNT_LOCKNAME(raw_spinlock, raw_spinlock_t, false, s->lock, raw_spin, raw_spin_lock(s->lock)) -SEQCOUNT_LOCKNAME(spinlock, spinlock_t, __SEQ_RT, s->lock, spin, spin_lock(s->lock)) -SEQCOUNT_LOCKNAME(rwlock, rwlock_t, __SEQ_RT, s->lock, read, read_lock(s->lock)) -SEQCOUNT_LOCKNAME(mutex, struct mutex, true, s->lock, mutex, mutex_lock(s->lock)) -SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mutex, ww_mutex_lock(s->lock, NULL)) +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) +#undef SEQCOUNT_LOCKNAME /* * SEQCNT_LOCKNAME_ZERO - static initializer for seqcount_LOCKNAME_t @@ -297,44 +247,36 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu #define SEQCNT_WW_MUTEX_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock) #define __seqprop_case(s, lockname, prop) \ - seqcount_##lockname##_t: __seqprop_##lockname##_##prop((void *)(s)) + seqcount_##lockname##_t: __seqprop_##lockname##_##prop #define __seqprop(s, prop) _Generic(*(s), \ - seqcount_t: __seqprop_##prop((void *)(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), \ - __seqprop_case((s), ww_mutex, prop)) + __seqprop_case((s), mutex, prop)) -#define __seqcount_ptr(s) __seqprop(s, ptr) -#define __seqcount_sequence(s) __seqprop(s, sequence) -#define __seqcount_lock_preemptible(s) __seqprop(s, preemptible) -#define __seqcount_assert_lock_held(s) __seqprop(s, assert) +#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 + * __read_seqcount_begin() - begin a seqcount_t read section * @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; \ + unsigned __seq; \ \ - while ((seq = __seqcount_sequence(s)) & 1) \ + while (unlikely((__seq = seqprop_sequence(s)) & 1)) \ cpu_relax(); \ \ kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \ - seq; \ + __seq; \ }) /** @@ -343,13 +285,7 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu * * Return: count to be passed to read_seqcount_retry() */ -#define raw_read_seqcount_begin(s) \ -({ \ - unsigned seq = __read_seqcount_begin(s); \ - \ - smp_rmb(); \ - seq; \ -}) +#define raw_read_seqcount_begin(s) __read_seqcount_begin(s) /** * read_seqcount_begin() - begin a seqcount_t read critical section @@ -359,7 +295,7 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu */ #define read_seqcount_begin(s) \ ({ \ - seqcount_lockdep_reader_access(__seqcount_ptr(s)); \ + seqcount_lockdep_reader_access(seqprop_const_ptr(s)); \ raw_read_seqcount_begin(s); \ }) @@ -376,11 +312,33 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu */ #define raw_read_seqcount(s) \ ({ \ - unsigned seq = __seqcount_sequence(s); \ + unsigned __seq = seqprop_sequence(s); \ \ - smp_rmb(); \ kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \ - seq; \ + __seq; \ +}) + +/** + * raw_seqcount_try_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 + * @start: count to be passed to read_seqcount_retry() + * + * Similar to raw_seqcount_begin(), except it enables eliding the critical + * section entirely if odd, instead of doing the speculation knowing it will + * fail. + * + * Useful when counter stabilization is more or less equivalent to taking + * the lock and there is a slowpath that does that. + * + * If true, start will be set to the (even) sequence count read. + * + * Return: true when a read critical section is started. + */ +#define raw_seqcount_try_begin(s, start) \ +({ \ + start = raw_read_seqcount(s); \ + !(start & 1); \ }) /** @@ -425,9 +383,9 @@ SEQCOUNT_LOCKNAME(ww_mutex, struct ww_mutex, true, &s->lock->base, ww_mu * Return: true if a read section retry is required, else false */ #define __read_seqcount_retry(s, start) \ - __read_seqcount_t_retry(__seqcount_ptr(s), start) + do___read_seqcount_retry(seqprop_const_ptr(s), start) -static inline int __read_seqcount_t_retry(const seqcount_t *s, unsigned 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); @@ -445,27 +403,29 @@ static inline int __read_seqcount_t_retry(const seqcount_t *s, unsigned start) * Return: true if a read section retry is required, else false */ #define read_seqcount_retry(s, start) \ - read_seqcount_t_retry(__seqcount_ptr(s), start) + do_read_seqcount_retry(seqprop_const_ptr(s), start) -static inline int read_seqcount_t_retry(const seqcount_t *s, unsigned start) +static inline int do_read_seqcount_retry(const seqcount_t *s, unsigned start) { smp_rmb(); - return __read_seqcount_t_retry(s, start); + 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 (__seqcount_lock_preemptible(s)) \ + if (seqprop_preemptible(s)) \ preempt_disable(); \ \ - raw_write_seqcount_t_begin(__seqcount_ptr(s)); \ + do_raw_write_seqcount_begin(seqprop_ptr(s)); \ } while (0) -static inline void raw_write_seqcount_t_begin(seqcount_t *s) +static inline void do_raw_write_seqcount_begin(seqcount_t *s) { kcsan_nestable_atomic_begin(); s->sequence++; @@ -475,16 +435,18 @@ static inline void raw_write_seqcount_t_begin(seqcount_t *s) /** * 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 { \ - raw_write_seqcount_t_end(__seqcount_ptr(s)); \ + do_raw_write_seqcount_end(seqprop_ptr(s)); \ \ - if (__seqcount_lock_preemptible(s)) \ + if (seqprop_preemptible(s)) \ preempt_enable(); \ } while (0) -static inline void raw_write_seqcount_t_end(seqcount_t *s) +static inline void do_raw_write_seqcount_end(seqcount_t *s) { smp_wmb(); s->sequence++; @@ -498,67 +460,68 @@ static inline void raw_write_seqcount_t_end(seqcount_t *s) * @subclass: lockdep nesting level * * See Documentation/locking/lockdep-design.rst + * Context: check write_seqcount_begin() */ #define write_seqcount_begin_nested(s, subclass) \ do { \ - __seqcount_assert_lock_held(s); \ + seqprop_assert(s); \ \ - if (__seqcount_lock_preemptible(s)) \ + if (seqprop_preemptible(s)) \ preempt_disable(); \ \ - write_seqcount_t_begin_nested(__seqcount_ptr(s), subclass); \ + do_write_seqcount_begin_nested(seqprop_ptr(s), subclass); \ } while (0) -static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass) +static inline void do_write_seqcount_begin_nested(seqcount_t *s, int subclass) { - raw_write_seqcount_t_begin(s); 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 * - * write_seqcount_begin opens a write side critical section of the given - * seqcount_t. - * - * Context: seqcount_t write side critical sections must be serialized and - * non-preemptible. If readers can be invoked from hardirq or softirq + * 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 { \ - __seqcount_assert_lock_held(s); \ + seqprop_assert(s); \ \ - if (__seqcount_lock_preemptible(s)) \ + if (seqprop_preemptible(s)) \ preempt_disable(); \ \ - write_seqcount_t_begin(__seqcount_ptr(s)); \ + do_write_seqcount_begin(seqprop_ptr(s)); \ } while (0) -static inline void write_seqcount_t_begin(seqcount_t *s) +static inline void do_write_seqcount_begin(seqcount_t *s) { - write_seqcount_t_begin_nested(s, 0); + 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 * - * The write section must've been opened with write_seqcount_begin(). + * 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 { \ - write_seqcount_t_end(__seqcount_ptr(s)); \ + do_write_seqcount_end(seqprop_ptr(s)); \ \ - if (__seqcount_lock_preemptible(s)) \ + if (seqprop_preemptible(s)) \ preempt_enable(); \ } while (0) -static inline void write_seqcount_t_end(seqcount_t *s) +static inline void do_write_seqcount_end(seqcount_t *s) { seqcount_release(&s->dep_map, _RET_IP_); - raw_write_seqcount_t_end(s); + do_raw_write_seqcount_end(s); } /** @@ -573,7 +536,7 @@ static inline void write_seqcount_t_end(seqcount_t *s) * 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 and after the barrier are enclosed in a seq-writer + * 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; @@ -603,9 +566,9 @@ static inline void write_seqcount_t_end(seqcount_t *s) * } */ #define raw_write_seqcount_barrier(s) \ - raw_write_seqcount_t_barrier(__seqcount_ptr(s)) + do_raw_write_seqcount_barrier(seqprop_ptr(s)) -static inline void raw_write_seqcount_t_barrier(seqcount_t *s) +static inline void do_raw_write_seqcount_barrier(seqcount_t *s) { kcsan_nestable_atomic_begin(); s->sequence++; @@ -623,9 +586,9 @@ static inline void raw_write_seqcount_t_barrier(seqcount_t *s) * will complete successfully and see data older than this. */ #define write_seqcount_invalidate(s) \ - write_seqcount_t_invalidate(__seqcount_ptr(s)) + do_write_seqcount_invalidate(seqprop_ptr(s)) -static inline void write_seqcount_t_invalidate(seqcount_t *s) +static inline void do_write_seqcount_invalidate(seqcount_t *s) { smp_wmb(); kcsan_nestable_atomic_begin(); @@ -659,10 +622,7 @@ typedef struct { * seqcount_latch_init() - runtime initializer for seqcount_latch_t * @s: Pointer to the seqcount_latch_t instance */ -static inline void seqcount_latch_init(seqcount_latch_t *s) -{ - seqcount_init(&s->seqcount); -} +#define seqcount_latch_init(s) seqcount_init(&(s)->seqcount) /** * raw_read_seqcount_latch() - pick even/odd latch data copy @@ -673,9 +633,9 @@ static inline void seqcount_latch_init(seqcount_latch_t *s) * * 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 read_seqcount_latch_retry(). + * with raw_read_seqcount_latch_retry(). */ -static inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s) +static __always_inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s) { /* * Pairs with the first smp_wmb() in raw_write_seqcount_latch(). @@ -685,21 +645,64 @@ static inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s) } /** - * read_seqcount_latch_retry() - end a seqcount_latch_t read section + * read_seqcount_latch() - pick even/odd latch data copy + * @s: Pointer to seqcount_latch_t + * + * See 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 read_seqcount_latch_retry(). + */ +static __always_inline unsigned read_seqcount_latch(const seqcount_latch_t *s) +{ + kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); + return raw_read_seqcount_latch(s); +} + +/** + * 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 inline int +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); +} + +/** + * read_seqcount_latch_retry() - end a seqcount_latch_t read section + * @s: Pointer to seqcount_latch_t + * @start: count, from read_seqcount_latch() + * + * Return: true if a read section retry is required, else false + */ +static __always_inline int read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) { - return read_seqcount_retry(&s->seqcount, start); + kcsan_atomic_next(0); + return raw_read_seqcount_latch_retry(s, start); } /** * raw_write_seqcount_latch() - redirect latch readers to even/odd copy * @s: Pointer to seqcount_latch_t + */ +static __always_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 */ +} + +/** + * write_seqcount_latch_begin() - redirect latch readers to 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 @@ -727,17 +730,11 @@ read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) * * 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 - * + * write_seqcount_latch_begin(&latch->seq); * 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 - * + * write_seqcount_latch(&latch->seq); * modify(latch->data[1], ...); + * write_seqcount_latch_end(&latch->seq); * } * * The query will have a form like:: @@ -748,7 +745,7 @@ read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) * unsigned seq, idx; * * do { - * seq = raw_read_seqcount_latch(&latch->seq); + * seq = read_seqcount_latch(&latch->seq); * * idx = seq & 0x01; * entry = data_query(latch->data[idx], ...); @@ -778,31 +775,32 @@ read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start) * 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) +static __always_inline void write_seqcount_latch_begin(seqcount_latch_t *s) { - smp_wmb(); /* prior stores before incrementing "sequence" */ - s->seqcount.sequence++; - smp_wmb(); /* increment "sequence" before following stores */ + kcsan_nestable_atomic_begin(); + raw_write_seqcount_latch(s); } -/* - * Sequential locks (seqlock_t) - * - * Sequence counters with an embedded spinlock for writer serialization - * and non-preemptibility. +/** + * write_seqcount_latch() - redirect latch readers to even copy + * @s: Pointer to seqcount_latch_t + */ +static __always_inline void write_seqcount_latch(seqcount_latch_t *s) +{ + raw_write_seqcount_latch(s); +} + +/** + * write_seqcount_latch_end() - end a seqcount_latch_t write section + * @s: Pointer to seqcount_latch_t * - * For more info, see: - * - Comments on top of seqcount_t - * - Documentation/locking/seqlock.rst + * Marks the end of a seqcount_latch_t writer section, after all copies of the + * latch-protected data have been updated. */ -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; +static __always_inline void write_seqcount_latch_end(seqcount_latch_t *s) +{ + kcsan_nestable_atomic_end(); +} #define __SEQLOCK_UNLOCKED(lockname) \ { \ @@ -835,11 +833,7 @@ typedef struct { */ 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; + return read_seqcount_begin(&sl->seqcount); } /** @@ -855,19 +849,13 @@ static inline unsigned read_seqbegin(const seqlock_t *sl) */ 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 write_seqcount_*t*_begin() - * instead of the generic write_seqcount_begin(). This way, no redundant - * lockdep_assert_held() checks are added. + * 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. */ /** @@ -886,7 +874,7 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start) static inline void write_seqlock(seqlock_t *sl) { spin_lock(&sl->lock); - write_seqcount_t_begin(&sl->seqcount.seqcount); + do_write_seqcount_begin(&sl->seqcount.seqcount); } /** @@ -898,7 +886,7 @@ static inline void write_seqlock(seqlock_t *sl) */ static inline void write_sequnlock(seqlock_t *sl) { - write_seqcount_t_end(&sl->seqcount.seqcount); + do_write_seqcount_end(&sl->seqcount.seqcount); spin_unlock(&sl->lock); } @@ -912,7 +900,7 @@ static inline void write_sequnlock(seqlock_t *sl) static inline void write_seqlock_bh(seqlock_t *sl) { spin_lock_bh(&sl->lock); - write_seqcount_t_begin(&sl->seqcount.seqcount); + do_write_seqcount_begin(&sl->seqcount.seqcount); } /** @@ -925,7 +913,7 @@ static inline void write_seqlock_bh(seqlock_t *sl) */ static inline void write_sequnlock_bh(seqlock_t *sl) { - write_seqcount_t_end(&sl->seqcount.seqcount); + do_write_seqcount_end(&sl->seqcount.seqcount); spin_unlock_bh(&sl->lock); } @@ -939,7 +927,7 @@ static inline void write_sequnlock_bh(seqlock_t *sl) static inline void write_seqlock_irq(seqlock_t *sl) { spin_lock_irq(&sl->lock); - write_seqcount_t_begin(&sl->seqcount.seqcount); + do_write_seqcount_begin(&sl->seqcount.seqcount); } /** @@ -951,7 +939,7 @@ static inline void write_seqlock_irq(seqlock_t *sl) */ static inline void write_sequnlock_irq(seqlock_t *sl) { - write_seqcount_t_end(&sl->seqcount.seqcount); + do_write_seqcount_end(&sl->seqcount.seqcount); spin_unlock_irq(&sl->lock); } @@ -960,7 +948,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl) unsigned long flags; spin_lock_irqsave(&sl->lock, flags); - write_seqcount_t_begin(&sl->seqcount.seqcount); + do_write_seqcount_begin(&sl->seqcount.seqcount); return flags; } @@ -989,7 +977,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl) static inline void write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags) { - write_seqcount_t_end(&sl->seqcount.seqcount); + do_write_seqcount_end(&sl->seqcount.seqcount); spin_unlock_irqrestore(&sl->lock, flags); } |