diff options
Diffstat (limited to 'include/linux/seqlock.h')
| -rw-r--r-- | include/linux/seqlock.h | 368 |
1 files changed, 285 insertions, 83 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h index 54bc20496392..962d9768945f 100644 --- a/include/linux/seqlock.h +++ b/include/linux/seqlock.h @@ -10,13 +10,16 @@ * * Copyrights: * - Based on x86_64 vsyscall gettimeofday: Keith Owens, Andrea Arcangeli + * - Sequence counters with associated locks, (C) 2020 Linutronix GmbH */ -#include <linux/spinlock.h> -#include <linux/preempt.h> -#include <linux/lockdep.h> #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> /* @@ -48,6 +51,10 @@ * 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_LOCKTYPE_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. @@ -72,17 +79,18 @@ static inline void __seqcount_init(seqcount_t *s, const char *name, } #ifdef CONFIG_DEBUG_LOCK_ALLOC -# define SEQCOUNT_DEP_MAP_INIT(lockname) \ - .dep_map = { .name = #lockname } \ + +# 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); \ +# 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) @@ -108,9 +116,143 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s) */ #define SEQCNT_ZERO(name) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(name) } +/* + * Sequence counters with associated locks (seqcount_LOCKTYPE_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 + */ + +#ifdef CONFIG_LOCKDEP +#define __SEQ_LOCK(expr) expr +#else +#define __SEQ_LOCK(expr) +#endif + +/** + * typedef seqcount_LOCKNAME_t - sequence counter with LOCKTYPR associated + * @seqcount: The real sequence counter + * @lock: Pointer to the associated spinlock + * + * A plain sequence counter with external writer synchronization by a + * spinlock. The spinlock is associated to the sequence count in the + * static initializer or init function. This enables lockdep to validate + * that the write side critical section is properly serialized. + */ + +/** + * seqcount_LOCKNAME_init() - runtime initializer for seqcount_LOCKNAME_t + * @s: Pointer to the seqcount_LOCKNAME_t instance + * @lock: Pointer to the associated LOCKTYPE + */ + +/* + * SEQCOUNT_LOCKTYPE() - Instantiate seqcount_LOCKNAME_t and helpers + * @locktype: actual typename + * @lockname: name + * @preemptible: preemptibility of above locktype + * @lockmember: argument for lockdep_assert_held() + */ +#define SEQCOUNT_LOCKTYPE(locktype, lockname, preemptible, lockmember) \ +typedef struct seqcount_##lockname { \ + seqcount_t seqcount; \ + __SEQ_LOCK(locktype *lock); \ +} seqcount_##lockname##_t; \ + \ +static __always_inline void \ +seqcount_##lockname##_init(seqcount_##lockname##_t *s, locktype *lock) \ +{ \ + seqcount_init(&s->seqcount); \ + __SEQ_LOCK(s->lock = lock); \ +} \ + \ +static __always_inline seqcount_t * \ +__seqcount_##lockname##_ptr(seqcount_##lockname##_t *s) \ +{ \ + return &s->seqcount; \ +} \ + \ +static __always_inline bool \ +__seqcount_##lockname##_preemptible(seqcount_##lockname##_t *s) \ +{ \ + return preemptible; \ +} \ + \ +static __always_inline void \ +__seqcount_##lockname##_assert(seqcount_##lockname##_t *s) \ +{ \ + __SEQ_LOCK(lockdep_assert_held(lockmember)); \ +} + +/* + * __seqprop() for seqcount_t + */ + +static inline seqcount_t *__seqcount_ptr(seqcount_t *s) +{ + return s; +} + +static inline bool __seqcount_preemptible(seqcount_t *s) +{ + return false; +} + +static inline void __seqcount_assert(seqcount_t *s) +{ + lockdep_assert_preemption_disabled(); +} + +SEQCOUNT_LOCKTYPE(raw_spinlock_t, raw_spinlock, false, s->lock) +SEQCOUNT_LOCKTYPE(spinlock_t, spinlock, false, s->lock) +SEQCOUNT_LOCKTYPE(rwlock_t, rwlock, false, s->lock) +SEQCOUNT_LOCKTYPE(struct mutex, mutex, true, s->lock) +SEQCOUNT_LOCKTYPE(struct ww_mutex, ww_mutex, true, &s->lock->base) + +/** + * SEQCNT_LOCKNAME_ZERO - static initializer for seqcount_LOCKNAME_t + * @name: Name of the seqcount_LOCKNAME_t instance + * @lock: Pointer to the associated LOCKTYPE + */ + +#define SEQCOUNT_LOCKTYPE_ZERO(seq_name, assoc_lock) { \ + .seqcount = SEQCNT_ZERO(seq_name.seqcount), \ + __SEQ_LOCK(.lock = (assoc_lock)) \ +} + +#define SEQCNT_SPINLOCK_ZERO(name, lock) SEQCOUNT_LOCKTYPE_ZERO(name, lock) +#define SEQCNT_RAW_SPINLOCK_ZERO(name, lock) SEQCOUNT_LOCKTYPE_ZERO(name, lock) +#define SEQCNT_RWLOCK_ZERO(name, lock) SEQCOUNT_LOCKTYPE_ZERO(name, lock) +#define SEQCNT_MUTEX_ZERO(name, lock) SEQCOUNT_LOCKTYPE_ZERO(name, lock) +#define SEQCNT_WW_MUTEX_ZERO(name, lock) SEQCOUNT_LOCKTYPE_ZERO(name, lock) + + +#define __seqprop_case(s, lockname, prop) \ + seqcount_##lockname##_t: __seqcount_##lockname##_##prop((void *)(s)) + +#define __seqprop(s, prop) _Generic(*(s), \ + seqcount_t: __seqcount_##prop((void *)(s)), \ + __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)) + +#define __seqcount_ptr(s) __seqprop(s, ptr) +#define __seqcount_lock_preemptible(s) __seqprop(s, preemptible) +#define __seqcount_assert_lock_held(s) __seqprop(s, assert) + /** * __read_seqcount_begin() - begin a seqcount_t read section w/o barrier - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_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 @@ -122,7 +264,10 @@ static inline void seqcount_lockdep_reader_access(const seqcount_t *s) * * Return: count to be passed to read_seqcount_retry() */ -static inline unsigned __read_seqcount_begin(const seqcount_t *s) +#define __read_seqcount_begin(s) \ + __read_seqcount_t_begin(__seqcount_ptr(s)) + +static inline unsigned __read_seqcount_t_begin(const seqcount_t *s) { unsigned ret; @@ -138,32 +283,38 @@ repeat: /** * raw_read_seqcount_begin() - begin a seqcount_t read section w/o lockdep - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * Return: count to be passed to read_seqcount_retry() */ -static inline unsigned raw_read_seqcount_begin(const seqcount_t *s) +#define raw_read_seqcount_begin(s) \ + raw_read_seqcount_t_begin(__seqcount_ptr(s)) + +static inline unsigned raw_read_seqcount_t_begin(const seqcount_t *s) { - unsigned ret = __read_seqcount_begin(s); + unsigned ret = __read_seqcount_t_begin(s); smp_rmb(); return ret; } /** * read_seqcount_begin() - begin a seqcount_t read critical section - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * Return: count to be passed to read_seqcount_retry() */ -static inline unsigned read_seqcount_begin(const seqcount_t *s) +#define read_seqcount_begin(s) \ + read_seqcount_t_begin(__seqcount_ptr(s)) + +static inline unsigned read_seqcount_t_begin(const seqcount_t *s) { seqcount_lockdep_reader_access(s); - return raw_read_seqcount_begin(s); + return raw_read_seqcount_t_begin(s); } /** * raw_read_seqcount() - read the raw seqcount_t counter value - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * raw_read_seqcount opens a read critical section of the given * seqcount_t, without any lockdep checking, and without checking or @@ -172,7 +323,10 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s) * * Return: count to be passed to read_seqcount_retry() */ -static inline unsigned raw_read_seqcount(const seqcount_t *s) +#define raw_read_seqcount(s) \ + raw_read_seqcount_t(__seqcount_ptr(s)) + +static inline unsigned raw_read_seqcount_t(const seqcount_t *s) { unsigned ret = READ_ONCE(s->sequence); smp_rmb(); @@ -183,7 +337,7 @@ static inline unsigned raw_read_seqcount(const seqcount_t *s) /** * raw_seqcount_begin() - begin a seqcount_t read critical section w/o * lockdep and w/o counter stabilization - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * raw_seqcount_begin opens a read critical section of the given * seqcount_t. Unlike read_seqcount_begin(), this function will not wait @@ -197,18 +351,21 @@ static inline unsigned raw_read_seqcount(const seqcount_t *s) * * Return: count to be passed to read_seqcount_retry() */ -static inline unsigned raw_seqcount_begin(const seqcount_t *s) +#define raw_seqcount_begin(s) \ + raw_seqcount_t_begin(__seqcount_ptr(s)) + +static inline unsigned raw_seqcount_t_begin(const seqcount_t *s) { /* * If the counter is odd, let read_seqcount_retry() fail * by decrementing the counter. */ - return raw_read_seqcount(s) & ~1; + return raw_read_seqcount_t(s) & ~1; } /** * __read_seqcount_retry() - end a seqcount_t read section w/o barrier - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * @start: count, from read_seqcount_begin() * * __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb() @@ -221,7 +378,10 @@ static inline unsigned raw_seqcount_begin(const seqcount_t *s) * * Return: true if a read section retry is required, else false */ -static inline int __read_seqcount_retry(const seqcount_t *s, unsigned start) +#define __read_seqcount_retry(s, start) \ + __read_seqcount_t_retry(__seqcount_ptr(s), start) + +static inline int __read_seqcount_t_retry(const seqcount_t *s, unsigned start) { kcsan_atomic_next(0); return unlikely(READ_ONCE(s->sequence) != start); @@ -229,7 +389,7 @@ static inline int __read_seqcount_retry(const seqcount_t *s, unsigned start) /** * read_seqcount_retry() - end a seqcount_t read critical section - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * @start: count, from read_seqcount_begin() * * read_seqcount_retry closes the read critical section of given @@ -238,17 +398,28 @@ static inline int __read_seqcount_retry(const seqcount_t *s, unsigned start) * * Return: true if a read section retry is required, else false */ -static inline int read_seqcount_retry(const seqcount_t *s, unsigned start) +#define read_seqcount_retry(s, start) \ + read_seqcount_t_retry(__seqcount_ptr(s), start) + +static inline int read_seqcount_t_retry(const seqcount_t *s, unsigned start) { smp_rmb(); - return __read_seqcount_retry(s, start); + return __read_seqcount_t_retry(s, start); } /** * raw_write_seqcount_begin() - start a seqcount_t write section w/o lockdep - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants */ -static inline void raw_write_seqcount_begin(seqcount_t *s) +#define raw_write_seqcount_begin(s) \ +do { \ + if (__seqcount_lock_preemptible(s)) \ + preempt_disable(); \ + \ + raw_write_seqcount_t_begin(__seqcount_ptr(s)); \ +} while (0) + +static inline void raw_write_seqcount_t_begin(seqcount_t *s) { kcsan_nestable_atomic_begin(); s->sequence++; @@ -257,49 +428,50 @@ static inline void raw_write_seqcount_begin(seqcount_t *s) /** * raw_write_seqcount_end() - end a seqcount_t write section w/o lockdep - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants */ -static inline void raw_write_seqcount_end(seqcount_t *s) +#define raw_write_seqcount_end(s) \ +do { \ + raw_write_seqcount_t_end(__seqcount_ptr(s)); \ + \ + if (__seqcount_lock_preemptible(s)) \ + preempt_enable(); \ +} while (0) + +static inline void raw_write_seqcount_t_end(seqcount_t *s) { smp_wmb(); s->sequence++; kcsan_nestable_atomic_end(); } -static inline void __write_seqcount_begin_nested(seqcount_t *s, int subclass) -{ - raw_write_seqcount_begin(s); - seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_); -} - /** * write_seqcount_begin_nested() - start a seqcount_t write section with * custom lockdep nesting level - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * @subclass: lockdep nesting level * * See Documentation/locking/lockdep-design.rst */ -static inline void write_seqcount_begin_nested(seqcount_t *s, int subclass) +#define write_seqcount_begin_nested(s, subclass) \ +do { \ + __seqcount_assert_lock_held(s); \ + \ + if (__seqcount_lock_preemptible(s)) \ + preempt_disable(); \ + \ + write_seqcount_t_begin_nested(__seqcount_ptr(s), subclass); \ +} while (0) + +static inline void write_seqcount_t_begin_nested(seqcount_t *s, int subclass) { - lockdep_assert_preemption_disabled(); - __write_seqcount_begin_nested(s, subclass); -} - -/* - * A write_seqcount_begin() variant w/o lockdep non-preemptibility checks. - * - * Use for internal seqlock.h code where it's known that preemption is - * already disabled. For example, seqlock_t write side functions. - */ -static inline void __write_seqcount_begin(seqcount_t *s) -{ - __write_seqcount_begin_nested(s, 0); + raw_write_seqcount_t_begin(s); + seqcount_acquire(&s->dep_map, subclass, 0, _RET_IP_); } /** * write_seqcount_begin() - start a seqcount_t write side critical section - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * write_seqcount_begin opens a write side critical section of the given * seqcount_t. @@ -308,26 +480,44 @@ static inline void __write_seqcount_begin(seqcount_t *s) * non-preemptible. If readers can be invoked from hardirq or softirq * context, interrupts or bottom halves must be respectively disabled. */ -static inline void write_seqcount_begin(seqcount_t *s) +#define write_seqcount_begin(s) \ +do { \ + __seqcount_assert_lock_held(s); \ + \ + if (__seqcount_lock_preemptible(s)) \ + preempt_disable(); \ + \ + write_seqcount_t_begin(__seqcount_ptr(s)); \ +} while (0) + +static inline void write_seqcount_t_begin(seqcount_t *s) { - write_seqcount_begin_nested(s, 0); + write_seqcount_t_begin_nested(s, 0); } /** * write_seqcount_end() - end a seqcount_t write side critical section - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * The write section must've been opened with write_seqcount_begin(). */ -static inline void write_seqcount_end(seqcount_t *s) +#define write_seqcount_end(s) \ +do { \ + write_seqcount_t_end(__seqcount_ptr(s)); \ + \ + if (__seqcount_lock_preemptible(s)) \ + preempt_enable(); \ +} while (0) + +static inline void write_seqcount_t_end(seqcount_t *s) { seqcount_release(&s->dep_map, _RET_IP_); - raw_write_seqcount_end(s); + raw_write_seqcount_t_end(s); } /** * raw_write_seqcount_barrier() - do a seqcount_t write barrier - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_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 @@ -366,7 +556,10 @@ static inline void write_seqcount_end(seqcount_t *s) * WRITE_ONCE(X, false); * } */ -static inline void raw_write_seqcount_barrier(seqcount_t *s) +#define raw_write_seqcount_barrier(s) \ + raw_write_seqcount_t_barrier(__seqcount_ptr(s)) + +static inline void raw_write_seqcount_t_barrier(seqcount_t *s) { kcsan_nestable_atomic_begin(); s->sequence++; @@ -378,12 +571,15 @@ static inline void raw_write_seqcount_barrier(seqcount_t *s) /** * write_seqcount_invalidate() - invalidate in-progress seqcount_t read * side operations - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * After write_seqcount_invalidate, no seqcount_t read side operations * will complete successfully and see data older than this. */ -static inline void write_seqcount_invalidate(seqcount_t *s) +#define write_seqcount_invalidate(s) \ + write_seqcount_t_invalidate(__seqcount_ptr(s)) + +static inline void write_seqcount_t_invalidate(seqcount_t *s) { smp_wmb(); kcsan_nestable_atomic_begin(); @@ -393,7 +589,7 @@ static inline void write_seqcount_invalidate(seqcount_t *s) /** * raw_read_seqcount_latch() - pick even/odd seqcount_t latch data copy - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * Use seqcount_t latching to switch between two storage places protected * by a sequence counter. Doing so allows having interruptible, preemptible, @@ -406,7 +602,10 @@ static inline void write_seqcount_invalidate(seqcount_t *s) * picking which data copy to read. The full counter value must then be * checked with read_seqcount_retry(). */ -static inline int raw_read_seqcount_latch(seqcount_t *s) +#define raw_read_seqcount_latch(s) \ + raw_read_seqcount_t_latch(__seqcount_ptr(s)) + +static inline int raw_read_seqcount_t_latch(seqcount_t *s) { /* Pairs with the first smp_wmb() in raw_write_seqcount_latch() */ int seq = READ_ONCE(s->sequence); /* ^^^ */ @@ -415,7 +614,7 @@ static inline int raw_read_seqcount_latch(seqcount_t *s) /** * raw_write_seqcount_latch() - redirect readers to even/odd copy - * @s: Pointer to seqcount_t + * @s: Pointer to seqcount_t or any of the seqcount_locktype_t variants * * The latch technique is a multiversion concurrency control method that allows * queries during non-atomic modifications. If you can guarantee queries never @@ -494,7 +693,10 @@ static inline int raw_read_seqcount_latch(seqcount_t *s) * 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_t *s) +#define raw_write_seqcount_latch(s) \ + raw_write_seqcount_t_latch(__seqcount_ptr(s)) + +static inline void raw_write_seqcount_t_latch(seqcount_t *s) { smp_wmb(); /* prior stores before incrementing "sequence" */ s->sequence++; @@ -516,20 +718,20 @@ typedef struct { spinlock_t lock; } seqlock_t; -#define __SEQLOCK_UNLOCKED(lockname) \ - { \ - .seqcount = SEQCNT_ZERO(lockname), \ - .lock = __SPIN_LOCK_UNLOCKED(lockname) \ +#define __SEQLOCK_UNLOCKED(lockname) \ + { \ + .seqcount = SEQCNT_ZERO(lockname), \ + .lock = __SPIN_LOCK_UNLOCKED(lockname) \ } /** * seqlock_init() - dynamic initializer for seqlock_t * @sl: Pointer to the seqlock_t instance */ -#define seqlock_init(sl) \ - do { \ - seqcount_init(&(sl)->seqcount); \ - spin_lock_init(&(sl)->lock); \ +#define seqlock_init(sl) \ + do { \ + seqcount_init(&(sl)->seqcount); \ + spin_lock_init(&(sl)->lock); \ } while (0) /** @@ -592,7 +794,7 @@ 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_begin(&sl->seqcount); + write_seqcount_t_begin(&sl->seqcount); } /** @@ -604,7 +806,7 @@ static inline void write_seqlock(seqlock_t *sl) */ static inline void write_sequnlock(seqlock_t *sl) { - write_seqcount_end(&sl->seqcount); + write_seqcount_t_end(&sl->seqcount); spin_unlock(&sl->lock); } @@ -618,7 +820,7 @@ static inline void write_sequnlock(seqlock_t *sl) static inline void write_seqlock_bh(seqlock_t *sl) { spin_lock_bh(&sl->lock); - __write_seqcount_begin(&sl->seqcount); + write_seqcount_t_begin(&sl->seqcount); } /** @@ -631,7 +833,7 @@ static inline void write_seqlock_bh(seqlock_t *sl) */ static inline void write_sequnlock_bh(seqlock_t *sl) { - write_seqcount_end(&sl->seqcount); + write_seqcount_t_end(&sl->seqcount); spin_unlock_bh(&sl->lock); } @@ -645,7 +847,7 @@ 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_begin(&sl->seqcount); + write_seqcount_t_begin(&sl->seqcount); } /** @@ -657,7 +859,7 @@ static inline void write_seqlock_irq(seqlock_t *sl) */ static inline void write_sequnlock_irq(seqlock_t *sl) { - write_seqcount_end(&sl->seqcount); + write_seqcount_t_end(&sl->seqcount); spin_unlock_irq(&sl->lock); } @@ -666,7 +868,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl) unsigned long flags; spin_lock_irqsave(&sl->lock, flags); - __write_seqcount_begin(&sl->seqcount); + write_seqcount_t_begin(&sl->seqcount); return flags; } @@ -695,13 +897,13 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl) static inline void write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags) { - write_seqcount_end(&sl->seqcount); + write_seqcount_t_end(&sl->seqcount); spin_unlock_irqrestore(&sl->lock, flags); } /** * read_seqlock_excl() - begin a seqlock_t locking reader section - * @sl: Pointer to seqlock_t + * @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 |