From 01573e231f18eb2d99162747186f59511f56b64d Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Fri, 08 Dec 2023 10:40:48 +0000
Subject: [PATCH] 移去rt
---
kernel/include/linux/seqlock.h | 1227 +++++++++++++++++++++++++++++++++++++++++++--------------
1 files changed, 920 insertions(+), 307 deletions(-)
diff --git a/kernel/include/linux/seqlock.h b/kernel/include/linux/seqlock.h
index a42a299..1ac20d7 100644
--- a/kernel/include/linux/seqlock.h
+++ b/kernel/include/linux/seqlock.h
@@ -1,49 +1,66 @@
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __LINUX_SEQLOCK_H
#define __LINUX_SEQLOCK_H
+
/*
- * Reader/writer consistent mechanism without starving writers. This type of
- * lock for data where the reader wants a consistent set of information
- * and is willing to retry if the information changes. There are two types
- * of readers:
- * 1. Sequence readers which never block a writer but they may have to retry
- * if a writer is in progress by detecting change in sequence number.
- * Writers do not wait for a sequence reader.
- * 2. Locking readers which will wait if a writer or another locking reader
- * is in progress. A locking reader in progress will also block a writer
- * from going forward. Unlike the regular rwlock, the read lock here is
- * exclusive so that only one locking reader can get it.
+ * seqcount_t / seqlock_t - a reader-writer consistency mechanism with
+ * lockless readers (read-only retry loops), and no writer starvation.
*
- * This is not as cache friendly as brlock. Also, this may not work well
- * for data that contains pointers, because any writer could
- * invalidate a pointer that a reader was following.
+ * See Documentation/locking/seqlock.rst
*
- * Expected non-blocking reader usage:
- * do {
- * seq = read_seqbegin(&foo);
- * ...
- * } while (read_seqretry(&foo, seq));
- *
- *
- * On non-SMP the spin locks disappear but the writer still needs
- * to increment the sequence variables because an interrupt routine could
- * change the state of the data.
- *
- * Based on x86_64 vsyscall gettimeofday
- * by Keith Owens and Andrea Arcangeli
+ * 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/ww_mutex.h>
+#include <linux/preempt.h>
+#include <linux/spinlock.h>
+
#include <asm/processor.h>
/*
- * Version using sequence counter only.
- * This can be used when code has its own mutex protecting the
- * updating starting before the write_seqcountbeqin() and ending
- * after the write_seqcount_end().
+ * The seqlock seqcount_t interface does not prescribe a precise sequence of
+ * read begin/retry/end. For readers, typically there is a call to
+ * read_seqcount_begin() and read_seqcount_retry(), however, there are more
+ * esoteric cases which do not follow this pattern.
+ *
+ * As a consequence, we take the following best-effort approach for raw usage
+ * via seqcount_t under KCSAN: upon beginning a seq-reader critical section,
+ * pessimistically mark the next KCSAN_SEQLOCK_REGION_MAX memory accesses as
+ * atomics; if there is a matching read_seqcount_retry() call, no following
+ * memory operations are considered atomic. Usage of the seqlock_t interface
+ * is not affected.
+ */
+#define KCSAN_SEQLOCK_REGION_MAX 1000
+
+/*
+ * Sequence counters (seqcount_t)
+ *
+ * This is the raw counting mechanism, without any writer protection.
+ *
+ * Write side critical sections must be serialized and non-preemptible.
+ *
+ * If readers can be invoked from hardirq or softirq contexts,
+ * interrupts or bottom halves must also be respectively disabled before
+ * entering the write section.
+ *
+ * This mechanism can't be used if the protected data contains pointers,
+ * as the writer can invalidate a pointer that a reader is following.
+ *
+ * If the write serialization mechanism is one of the common kernel
+ * locking primitives, use a sequence counter with associated lock
+ * (seqcount_LOCKNAME_t) instead.
+ *
+ * If it's desired to automatically handle the sequence counter writer
+ * serialization and non-preemptibility requirements, use a sequential
+ * lock (seqlock_t) instead.
+ *
+ * See Documentation/locking/seqlock.rst
*/
typedef struct seqcount {
unsigned sequence;
@@ -63,13 +80,18 @@
}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
-# define SEQCOUNT_DEP_MAP_INIT(lockname) \
- .dep_map = { .name = #lockname } \
-# define seqcount_init(s) \
- do { \
- static struct lock_class_key __key; \
- __seqcount_init((s), #s, &__key); \
+# define SEQCOUNT_DEP_MAP_INIT(lockname) \
+ .dep_map = { .name = #lockname }
+
+/**
+ * seqcount_init() - runtime initializer for seqcount_t
+ * @s: Pointer to the seqcount_t instance
+ */
+# define seqcount_init(s) \
+ do { \
+ static struct lock_class_key __key; \
+ __seqcount_init((s), #s, &__key); \
} while (0)
static inline void seqcount_lockdep_reader_access(const seqcount_t *s)
@@ -79,7 +101,7 @@
local_irq_save(flags);
seqcount_acquire_read(&l->dep_map, 0, 0, _RET_IP_);
- seqcount_release(&l->dep_map, 1, _RET_IP_);
+ seqcount_release(&l->dep_map, _RET_IP_);
local_irq_restore(flags);
}
@@ -89,13 +111,210 @@
# define seqcount_lockdep_reader_access(x)
#endif
-#define SEQCNT_ZERO(lockname) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(lockname)}
+/**
+ * SEQCNT_ZERO() - static initializer for seqcount_t
+ * @name: Name of the seqcount_t instance
+ */
+#define SEQCNT_ZERO(name) { .sequence = 0, SEQCOUNT_DEP_MAP_INIT(name) }
+/*
+ * Sequence counters with associated locks (seqcount_LOCKNAME_t)
+ *
+ * A sequence counter which associates the lock used for writer
+ * serialization at initialization time. This enables lockdep to validate
+ * that the write side critical section is properly serialized.
+ *
+ * For associated locks which do not implicitly disable preemption,
+ * preemption protection is enforced in the write side function.
+ *
+ * Lockdep is never used in any for the raw write variants.
+ *
+ * See Documentation/locking/seqlock.rst
+ */
+
+/*
+ * For PREEMPT_RT, seqcount_LOCKNAME_t write side critical sections cannot
+ * disable preemption. It can lead to higher latencies, and the write side
+ * sections will not be able to acquire locks which become sleeping locks
+ * (e.g. spinlock_t).
+ *
+ * To remain preemptible while avoiding a possible livelock caused by the
+ * reader preempting the writer, use a different technique: let the reader
+ * detect if a seqcount_LOCKNAME_t writer is in progress. If that is the
+ * case, acquire then release the associated LOCKNAME writer serialization
+ * lock. This will allow any possibly-preempted writer to make progress
+ * until the end of its writer serialization lock critical section.
+ *
+ * This lock-unlock technique must be implemented for all of PREEMPT_RT
+ * sleeping locks. See Documentation/locking/locktypes.rst
+ */
+#if defined(CONFIG_LOCKDEP) || defined(CONFIG_PREEMPT_RT)
+#define __SEQ_LOCK(expr) expr
+#else
+#define __SEQ_LOCK(expr)
+#endif
+
+/*
+ * typedef seqcount_LOCKNAME_t - sequence counter with LOCKNAME associated
+ * @seqcount: The real sequence counter
+ * @lock: Pointer to the associated lock
+ *
+ * A plain sequence counter with external writer synchronization by
+ * LOCKNAME @lock. The lock is associated to the sequence counter in the
+ * static initializer or init function. This enables lockdep to validate
+ * that the write side critical section is properly serialized.
+ *
+ * LOCKNAME: raw_spinlock, spinlock, rwlock, mutex, or ww_mutex.
+ */
+
+/*
+ * seqcount_LOCKNAME_init() - runtime initializer for seqcount_LOCKNAME_t
+ * @s: Pointer to the seqcount_LOCKNAME_t instance
+ * @lock: Pointer to the associated lock
+ */
+
+#define seqcount_LOCKNAME_init(s, _lock, lockname) \
+ do { \
+ seqcount_##lockname##_t *____s = (s); \
+ seqcount_init(&____s->seqcount); \
+ __SEQ_LOCK(____s->lock = (_lock)); \
+ } while (0)
+
+#define seqcount_raw_spinlock_init(s, lock) seqcount_LOCKNAME_init(s, lock, raw_spinlock)
+#define seqcount_spinlock_init(s, lock) seqcount_LOCKNAME_init(s, lock, spinlock)
+#define seqcount_rwlock_init(s, lock) seqcount_LOCKNAME_init(s, lock, rwlock);
+#define seqcount_mutex_init(s, lock) seqcount_LOCKNAME_init(s, lock, mutex);
+#define seqcount_ww_mutex_init(s, lock) seqcount_LOCKNAME_init(s, lock, ww_mutex);
+
+/*
+ * SEQCOUNT_LOCKNAME() - Instantiate seqcount_LOCKNAME_t and helpers
+ * seqprop_LOCKNAME_*() - Property accessors for seqcount_LOCKNAME_t
+ *
+ * @lockname: "LOCKNAME" part of seqcount_LOCKNAME_t
+ * @locktype: LOCKNAME canonical C data type
+ * @preemptible: preemptibility of above locktype
+ * @lockmember: argument for lockdep_assert_held()
+ * @lockbase: associated lock release function (prefix only)
+ * @lock_acquire: associated lock acquisition function (full call)
+ */
+#define SEQCOUNT_LOCKNAME(lockname, locktype, preemptible, lockmember, lockbase, lock_acquire) \
+typedef struct seqcount_##lockname { \
+ seqcount_t seqcount; \
+ __SEQ_LOCK(locktype *lock); \
+} seqcount_##lockname##_t; \
+ \
+static __always_inline seqcount_t * \
+__seqprop_##lockname##_ptr(seqcount_##lockname##_t *s) \
+{ \
+ return &s->seqcount; \
+} \
+ \
+static __always_inline unsigned \
+__seqprop_##lockname##_sequence(const seqcount_##lockname##_t *s) \
+{ \
+ unsigned seq = READ_ONCE(s->seqcount.sequence); \
+ \
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
+ return seq; \
+ \
+ if (preemptible && unlikely(seq & 1)) { \
+ __SEQ_LOCK(lock_acquire); \
+ __SEQ_LOCK(lockbase##_unlock(s->lock)); \
+ \
+ /* \
+ * Re-read the sequence counter since the (possibly \
+ * preempted) writer made progress. \
+ */ \
+ seq = READ_ONCE(s->seqcount.sequence); \
+ } \
+ \
+ return seq; \
+} \
+ \
+static __always_inline bool \
+__seqprop_##lockname##_preemptible(const seqcount_##lockname##_t *s) \
+{ \
+ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) \
+ return preemptible; \
+ \
+ /* PREEMPT_RT relies on the above LOCK+UNLOCK */ \
+ return false; \
+} \
+ \
+static __always_inline void \
+__seqprop_##lockname##_assert(const seqcount_##lockname##_t *s) \
+{ \
+ __SEQ_LOCK(lockdep_assert_held(lockmember)); \
+}
+
+/*
+ * __seqprop() for seqcount_t
+ */
+
+static inline seqcount_t *__seqprop_ptr(seqcount_t *s)
+{
+ return s;
+}
+
+static inline unsigned __seqprop_sequence(const seqcount_t *s)
+{
+ return READ_ONCE(s->sequence);
+}
+
+static inline bool __seqprop_preemptible(const seqcount_t *s)
+{
+ return false;
+}
+
+static inline void __seqprop_assert(const seqcount_t *s)
+{
+ lockdep_assert_preemption_disabled();
+}
+
+#define __SEQ_RT IS_ENABLED(CONFIG_PREEMPT_RT)
+
+SEQCOUNT_LOCKNAME(raw_spinlock, raw_spinlock_t, false, 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))
+
+/*
+ * SEQCNT_LOCKNAME_ZERO - static initializer for seqcount_LOCKNAME_t
+ * @name: Name of the seqcount_LOCKNAME_t instance
+ * @lock: Pointer to the associated LOCKNAME
+ */
+
+#define SEQCOUNT_LOCKNAME_ZERO(seq_name, assoc_lock) { \
+ .seqcount = SEQCNT_ZERO(seq_name.seqcount), \
+ __SEQ_LOCK(.lock = (assoc_lock)) \
+}
+
+#define SEQCNT_RAW_SPINLOCK_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
+#define SEQCNT_SPINLOCK_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
+#define SEQCNT_RWLOCK_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
+#define SEQCNT_MUTEX_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
+#define SEQCNT_WW_MUTEX_ZERO(name, lock) SEQCOUNT_LOCKNAME_ZERO(name, lock)
+
+#define __seqprop_case(s, lockname, prop) \
+ seqcount_##lockname##_t: __seqprop_##lockname##_##prop((void *)(s))
+
+#define __seqprop(s, prop) _Generic(*(s), \
+ seqcount_t: __seqprop_##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_sequence(s) __seqprop(s, sequence)
+#define __seqcount_lock_preemptible(s) __seqprop(s, preemptible)
+#define __seqcount_assert_lock_held(s) __seqprop(s, assert)
/**
- * __read_seqcount_begin - begin a seq-read critical section (without barrier)
- * @s: pointer to seqcount_t
- * Returns: count to be passed to read_seqcount_retry
+ * __read_seqcount_begin() - begin a seqcount_t read section w/o barrier
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
*
* __read_seqcount_begin is like read_seqcount_begin, but has no smp_rmb()
* barrier. Callers should ensure that smp_rmb() or equivalent ordering is
@@ -104,93 +323,96 @@
*
* Use carefully, only in critical code, and comment how the barrier is
* provided.
+ *
+ * Return: count to be passed to read_seqcount_retry()
*/
-static inline unsigned __read_seqcount_begin(const seqcount_t *s)
-{
- unsigned ret;
-
-repeat:
- ret = READ_ONCE(s->sequence);
- if (unlikely(ret & 1)) {
- cpu_relax();
- goto repeat;
- }
- return ret;
-}
+#define __read_seqcount_begin(s) \
+({ \
+ unsigned seq; \
+ \
+ while ((seq = __seqcount_sequence(s)) & 1) \
+ cpu_relax(); \
+ \
+ kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
+ seq; \
+})
/**
- * raw_read_seqcount - Read the raw seqcount
- * @s: pointer to seqcount_t
- * Returns: count to be passed to read_seqcount_retry
+ * raw_read_seqcount_begin() - begin a seqcount_t read section w/o lockdep
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ *
+ * Return: count to be passed to read_seqcount_retry()
+ */
+#define raw_read_seqcount_begin(s) \
+({ \
+ unsigned seq = __read_seqcount_begin(s); \
+ \
+ smp_rmb(); \
+ seq; \
+})
+
+/**
+ * read_seqcount_begin() - begin a seqcount_t read critical section
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ *
+ * Return: count to be passed to read_seqcount_retry()
+ */
+#define read_seqcount_begin(s) \
+({ \
+ seqcount_lockdep_reader_access(__seqcount_ptr(s)); \
+ raw_read_seqcount_begin(s); \
+})
+
+/**
+ * raw_read_seqcount() - read the raw seqcount_t counter value
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
*
* raw_read_seqcount opens a read critical section of the given
- * seqcount without any lockdep checking and without checking or
- * masking the LSB. Calling code is responsible for handling that.
+ * seqcount_t, without any lockdep checking, and without checking or
+ * masking the sequence counter LSB. Calling code is responsible for
+ * handling that.
+ *
+ * Return: count to be passed to read_seqcount_retry()
*/
-static inline unsigned raw_read_seqcount(const seqcount_t *s)
-{
- unsigned ret = READ_ONCE(s->sequence);
- smp_rmb();
- return ret;
-}
+#define raw_read_seqcount(s) \
+({ \
+ unsigned seq = __seqcount_sequence(s); \
+ \
+ smp_rmb(); \
+ kcsan_atomic_next(KCSAN_SEQLOCK_REGION_MAX); \
+ seq; \
+})
/**
- * raw_read_seqcount_begin - start seq-read critical section w/o lockdep
- * @s: pointer to seqcount_t
- * Returns: count to be passed to read_seqcount_retry
+ * raw_seqcount_begin() - begin a seqcount_t read critical section w/o
+ * lockdep and w/o counter stabilization
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
*
- * raw_read_seqcount_begin opens a read critical section of the given
- * seqcount, but without any lockdep checking. Validity of the critical
- * section is tested by checking read_seqcount_retry function.
+ * raw_seqcount_begin opens a read critical section of the given
+ * seqcount_t. Unlike read_seqcount_begin(), this function will not wait
+ * for the count to stabilize. If a writer is active when it begins, it
+ * will fail the read_seqcount_retry() at the end of the read critical
+ * section instead of stabilizing at the beginning of it.
+ *
+ * Use this only in special kernel hot paths where the read section is
+ * small and has a high probability of success through other external
+ * means. It will save a single branching instruction.
+ *
+ * Return: count to be passed to read_seqcount_retry()
*/
-static inline unsigned raw_read_seqcount_begin(const seqcount_t *s)
-{
- unsigned ret = __read_seqcount_begin(s);
- smp_rmb();
- return ret;
-}
+#define raw_seqcount_begin(s) \
+({ \
+ /* \
+ * If the counter is odd, let read_seqcount_retry() fail \
+ * by decrementing the counter. \
+ */ \
+ raw_read_seqcount(s) & ~1; \
+})
/**
- * read_seqcount_begin - begin a seq-read critical section
- * @s: pointer to seqcount_t
- * Returns: count to be passed to read_seqcount_retry
- *
- * read_seqcount_begin opens a read critical section of the given seqcount.
- * Validity of the critical section is tested by checking read_seqcount_retry
- * function.
- */
-static inline unsigned read_seqcount_begin(const seqcount_t *s)
-{
- seqcount_lockdep_reader_access(s);
- return raw_read_seqcount_begin(s);
-}
-
-/**
- * raw_seqcount_begin - begin a seq-read critical section
- * @s: pointer to seqcount_t
- * Returns: count to be passed to read_seqcount_retry
- *
- * raw_seqcount_begin opens a read critical section of the given seqcount.
- * Validity of the critical section is tested by checking read_seqcount_retry
- * function.
- *
- * Unlike read_seqcount_begin(), this function will not wait for the count
- * to stabilize. If a writer is active when we begin, we will fail the
- * read_seqcount_retry() instead of stabilizing at the beginning of the
- * critical section.
- */
-static inline unsigned raw_seqcount_begin(const seqcount_t *s)
-{
- unsigned ret = READ_ONCE(s->sequence);
- smp_rmb();
- return ret & ~1;
-}
-
-/**
- * __read_seqcount_retry - end a seq-read critical section (without barrier)
- * @s: pointer to seqcount_t
- * @start: count, from read_seqcount_begin
- * Returns: 1 if retry is required, else 0
+ * __read_seqcount_retry() - end a seqcount_t read section w/o barrier
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ * @start: count, from read_seqcount_begin()
*
* __read_seqcount_retry is like read_seqcount_retry, but has no smp_rmb()
* barrier. Callers should ensure that smp_rmb() or equivalent ordering is
@@ -199,100 +421,282 @@
*
* Use carefully, only in critical code, and comment how the barrier is
* provided.
+ *
+ * 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)
{
- return unlikely(s->sequence != start);
+ kcsan_atomic_next(0);
+ return unlikely(READ_ONCE(s->sequence) != start);
}
/**
- * read_seqcount_retry - end a seq-read critical section
- * @s: pointer to seqcount_t
- * @start: count, from read_seqcount_begin
- * Returns: 1 if retry is required, else 0
+ * read_seqcount_retry() - end a seqcount_t read critical section
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ * @start: count, from read_seqcount_begin()
*
- * read_seqcount_retry closes a read critical section of the given seqcount.
- * If the critical section was invalid, it must be ignored (and typically
- * retried).
+ * read_seqcount_retry closes the read critical section of given
+ * seqcount_t. If the critical section was invalid, it must be ignored
+ * (and typically retried).
+ *
+ * Return: true if a read section retry is required, else false
*/
-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);
-}
-
-
-
-static inline void raw_write_seqcount_begin(seqcount_t *s)
-{
- s->sequence++;
- smp_wmb();
-}
-
-static inline void raw_write_seqcount_end(seqcount_t *s)
-{
- smp_wmb();
- s->sequence++;
+ return __read_seqcount_t_retry(s, start);
}
/**
- * raw_write_seqcount_barrier - do a seq write barrier
- * @s: pointer to seqcount_t
+ * 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
+ */
+#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++;
+ smp_wmb();
+}
+
+/**
+ * raw_write_seqcount_end() - end a seqcount_t write section w/o lockdep
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ */
+#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();
+}
+
+/**
+ * write_seqcount_begin_nested() - start a seqcount_t write section with
+ * custom lockdep nesting level
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ * @subclass: lockdep nesting level
*
- * This can be used to provide an ordering guarantee instead of the
- * usual consistency guarantee. It is one wmb cheaper, because we can
- * collapse the two back-to-back wmb()s.
+ * See Documentation/locking/lockdep-design.rst
+ */
+#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)
+{
+ 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 or any of the seqcount_LOCKNAME_t variants
*
- * Note that, writes surrounding the barrier should be declared atomic (e.g.
+ * 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, interrupts or bottom halves must be respectively disabled.
+ */
+#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_t_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().
+ */
+#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_t_end(s);
+}
+
+/**
+ * raw_write_seqcount_barrier() - do a seqcount_t write barrier
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ *
+ * This can be used to provide an ordering guarantee instead of the usual
+ * consistency guarantee. It is one wmb cheaper, because it can collapse
+ * the two back-to-back wmb()s.
+ *
+ * Note that writes surrounding the barrier should be declared atomic (e.g.
* via WRITE_ONCE): a) to ensure the writes become visible to other threads
* atomically, avoiding compiler optimizations; b) to document which writes are
* meant to propagate to the reader critical section. This is necessary because
* neither writes before and after the barrier are enclosed in a seq-writer
- * critical section that would ensure readers are aware of ongoing writes.
+ * critical section that would ensure readers are aware of ongoing writes::
*
- * seqcount_t seq;
- * bool X = true, Y = false;
+ * seqcount_t seq;
+ * bool X = true, Y = false;
*
- * void read(void)
- * {
- * bool x, y;
+ * void read(void)
+ * {
+ * bool x, y;
*
- * do {
- * int s = read_seqcount_begin(&seq);
+ * do {
+ * int s = read_seqcount_begin(&seq);
*
- * x = X; y = Y;
+ * x = X; y = Y;
*
- * } while (read_seqcount_retry(&seq, s));
+ * } while (read_seqcount_retry(&seq, s));
*
- * BUG_ON(!x && !y);
+ * BUG_ON(!x && !y);
* }
*
* void write(void)
* {
- * WRITE_ONCE(Y, true);
+ * WRITE_ONCE(Y, true);
*
- * raw_write_seqcount_barrier(seq);
+ * raw_write_seqcount_barrier(seq);
*
- * WRITE_ONCE(X, false);
+ * 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++;
smp_wmb();
s->sequence++;
-}
-
-static inline int raw_read_seqcount_latch(seqcount_t *s)
-{
- /* Pairs with the first smp_wmb() in raw_write_seqcount_latch() */
- int seq = READ_ONCE(s->sequence); /* ^^^ */
- return seq;
+ kcsan_nestable_atomic_end();
}
/**
- * raw_write_seqcount_latch - redirect readers to even/odd copy
- * @s: pointer to seqcount_t
+ * write_seqcount_invalidate() - invalidate in-progress seqcount_t read
+ * side operations
+ * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
+ *
+ * After write_seqcount_invalidate, no seqcount_t read side operations
+ * will complete successfully and see data older than this.
+ */
+#define write_seqcount_invalidate(s) \
+ write_seqcount_t_invalidate(__seqcount_ptr(s))
+
+static inline void write_seqcount_t_invalidate(seqcount_t *s)
+{
+ smp_wmb();
+ kcsan_nestable_atomic_begin();
+ s->sequence+=2;
+ kcsan_nestable_atomic_end();
+}
+
+/*
+ * Latch sequence counters (seqcount_latch_t)
+ *
+ * A sequence counter variant where the counter even/odd value is used to
+ * switch between two copies of protected data. This allows the read path,
+ * typically NMIs, to safely interrupt the write side critical section.
+ *
+ * As the write sections are fully preemptible, no special handling for
+ * PREEMPT_RT is needed.
+ */
+typedef struct {
+ seqcount_t seqcount;
+} seqcount_latch_t;
+
+/**
+ * SEQCNT_LATCH_ZERO() - static initializer for seqcount_latch_t
+ * @seq_name: Name of the seqcount_latch_t instance
+ */
+#define SEQCNT_LATCH_ZERO(seq_name) { \
+ .seqcount = SEQCNT_ZERO(seq_name.seqcount), \
+}
+
+/**
+ * seqcount_latch_init() - runtime initializer for seqcount_latch_t
+ * @s: Pointer to the seqcount_latch_t instance
+ */
+#define seqcount_latch_init(s) seqcount_init(&(s)->seqcount)
+
+/**
+ * raw_read_seqcount_latch() - pick even/odd latch data copy
+ * @s: Pointer to seqcount_latch_t
+ *
+ * See raw_write_seqcount_latch() for details and a full reader/writer
+ * usage example.
+ *
+ * Return: sequence counter raw value. Use the lowest bit as an index for
+ * picking which data copy to read. The full counter must then be checked
+ * with read_seqcount_latch_retry().
+ */
+static inline unsigned raw_read_seqcount_latch(const seqcount_latch_t *s)
+{
+ /*
+ * Pairs with the first smp_wmb() in raw_write_seqcount_latch().
+ * Due to the dependent load, a full smp_rmb() is not needed.
+ */
+ return READ_ONCE(s->seqcount.sequence);
+}
+
+/**
+ * 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
+read_seqcount_latch_retry(const seqcount_latch_t *s, unsigned start)
+{
+ return read_seqcount_retry(&s->seqcount, start);
+}
+
+/**
+ * raw_write_seqcount_latch() - redirect latch readers to even/odd copy
+ * @s: Pointer to seqcount_latch_t
*
* The latch technique is a multiversion concurrency control method that allows
* queries during non-atomic modifications. If you can guarantee queries never
@@ -308,181 +712,243 @@
* Very simply put: we first modify one copy and then the other. This ensures
* there is always one copy in a stable state, ready to give us an answer.
*
- * The basic form is a data structure like:
+ * The basic form is a data structure like::
*
- * struct latch_struct {
- * seqcount_t seq;
- * struct data_struct data[2];
- * };
+ * struct latch_struct {
+ * seqcount_latch_t seq;
+ * struct data_struct data[2];
+ * };
*
* Where a modification, which is assumed to be externally serialized, does the
- * following:
+ * following::
*
- * void latch_modify(struct latch_struct *latch, ...)
- * {
- * smp_wmb(); <- Ensure that the last data[1] update is visible
- * latch->seq++;
- * smp_wmb(); <- Ensure that the seqcount update is visible
+ * void latch_modify(struct latch_struct *latch, ...)
+ * {
+ * smp_wmb(); // Ensure that the last data[1] update is visible
+ * latch->seq.sequence++;
+ * smp_wmb(); // Ensure that the seqcount update is visible
*
- * modify(latch->data[0], ...);
+ * modify(latch->data[0], ...);
*
- * smp_wmb(); <- Ensure that the data[0] update is visible
- * latch->seq++;
- * smp_wmb(); <- Ensure that the seqcount update is visible
+ * smp_wmb(); // Ensure that the data[0] update is visible
+ * latch->seq.sequence++;
+ * smp_wmb(); // Ensure that the seqcount update is visible
*
- * modify(latch->data[1], ...);
- * }
+ * modify(latch->data[1], ...);
+ * }
*
- * The query will have a form like:
+ * The query will have a form like::
*
- * struct entry *latch_query(struct latch_struct *latch, ...)
- * {
- * struct entry *entry;
- * unsigned seq, idx;
+ * struct entry *latch_query(struct latch_struct *latch, ...)
+ * {
+ * struct entry *entry;
+ * unsigned seq, idx;
*
- * do {
- * seq = raw_read_seqcount_latch(&latch->seq);
+ * do {
+ * seq = raw_read_seqcount_latch(&latch->seq);
*
- * idx = seq & 0x01;
- * entry = data_query(latch->data[idx], ...);
+ * idx = seq & 0x01;
+ * entry = data_query(latch->data[idx], ...);
*
- * smp_rmb();
- * } while (seq != latch->seq);
+ * // This includes needed smp_rmb()
+ * } while (read_seqcount_latch_retry(&latch->seq, seq));
*
- * return entry;
- * }
+ * return entry;
+ * }
*
* So during the modification, queries are first redirected to data[1]. Then we
* modify data[0]. When that is complete, we redirect queries back to data[0]
* and we can modify data[1].
*
- * NOTE: The non-requirement for atomic modifications does _NOT_ include
- * the publishing of new entries in the case where data is a dynamic
- * data structure.
+ * NOTE:
*
- * An iteration might start in data[0] and get suspended long enough
- * to miss an entire modification sequence, once it resumes it might
- * observe the new entry.
+ * The non-requirement for atomic modifications does _NOT_ include
+ * the publishing of new entries in the case where data is a dynamic
+ * data structure.
*
- * NOTE: When data is a dynamic data structure; one should use regular RCU
- * patterns to manage the lifetimes of the objects within.
+ * An iteration might start in data[0] and get suspended long enough
+ * to miss an entire modification sequence, once it resumes it might
+ * observe the new entry.
+ *
+ * NOTE2:
+ *
+ * When data is a dynamic data structure; one should use regular RCU
+ * patterns to manage the lifetimes of the objects within.
*/
-static inline void raw_write_seqcount_latch(seqcount_t *s)
+static inline void raw_write_seqcount_latch(seqcount_latch_t *s)
{
- smp_wmb(); /* prior stores before incrementing "sequence" */
- s->sequence++;
- smp_wmb(); /* increment "sequence" before following stores */
+ smp_wmb(); /* prior stores before incrementing "sequence" */
+ s->seqcount.sequence++;
+ smp_wmb(); /* increment "sequence" before following stores */
}
/*
- * Sequence counter only version assumes that callers are using their
- * own mutexing.
- */
-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_);
-}
-
-static inline void write_seqcount_begin(seqcount_t *s)
-{
- write_seqcount_begin_nested(s, 0);
-}
-
-static inline void write_seqcount_end(seqcount_t *s)
-{
- seqcount_release(&s->dep_map, 1, _RET_IP_);
- raw_write_seqcount_end(s);
-}
-
-/**
- * write_seqcount_invalidate - invalidate in-progress read-side seq operations
- * @s: pointer to seqcount_t
+ * Sequential locks (seqlock_t)
*
- * After write_seqcount_invalidate, no read-side seq operations will complete
- * successfully and see data older than this.
+ * Sequence counters with an embedded spinlock for writer serialization
+ * and non-preemptibility.
+ *
+ * For more info, see:
+ * - Comments on top of seqcount_t
+ * - Documentation/locking/seqlock.rst
*/
-static inline void write_seqcount_invalidate(seqcount_t *s)
-{
- smp_wmb();
- s->sequence+=2;
-}
-
typedef struct {
- struct seqcount seqcount;
+ /*
+ * 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;
-/*
- * These macros triggered gcc-3.x compile-time problems. We think these are
- * OK now. Be cautious.
- */
-#define __SEQLOCK_UNLOCKED(lockname) \
- { \
- .seqcount = SEQCNT_ZERO(lockname), \
- .lock = __SPIN_LOCK_UNLOCKED(lockname) \
+#define __SEQLOCK_UNLOCKED(lockname) \
+ { \
+ .seqcount = SEQCNT_SPINLOCK_ZERO(lockname, &(lockname).lock), \
+ .lock = __SPIN_LOCK_UNLOCKED(lockname) \
}
-#define seqlock_init(x) \
- do { \
- seqcount_init(&(x)->seqcount); \
- spin_lock_init(&(x)->lock); \
+/**
+ * seqlock_init() - dynamic initializer for seqlock_t
+ * @sl: Pointer to the seqlock_t instance
+ */
+#define seqlock_init(sl) \
+ do { \
+ spin_lock_init(&(sl)->lock); \
+ seqcount_spinlock_init(&(sl)->seqcount, &(sl)->lock); \
} while (0)
-#define DEFINE_SEQLOCK(x) \
- seqlock_t x = __SEQLOCK_UNLOCKED(x)
+/**
+ * DEFINE_SEQLOCK(sl) - Define a statically allocated seqlock_t
+ * @sl: Name of the seqlock_t instance
+ */
+#define DEFINE_SEQLOCK(sl) \
+ seqlock_t sl = __SEQLOCK_UNLOCKED(sl)
-/*
- * Read side functions for starting and finalizing a read side section.
+/**
+ * read_seqbegin() - start a seqlock_t read side critical section
+ * @sl: Pointer to seqlock_t
+ *
+ * Return: count, to be passed to read_seqretry()
*/
static inline unsigned read_seqbegin(const seqlock_t *sl)
{
- return read_seqcount_begin(&sl->seqcount);
+ unsigned ret = read_seqcount_begin(&sl->seqcount);
+
+ kcsan_atomic_next(0); /* non-raw usage, assume closing read_seqretry() */
+ kcsan_flat_atomic_begin();
+ return ret;
}
+/**
+ * read_seqretry() - end a seqlock_t read side section
+ * @sl: Pointer to seqlock_t
+ * @start: count, from read_seqbegin()
+ *
+ * read_seqretry closes the read side critical section of given seqlock_t.
+ * If the critical section was invalid, it must be ignored (and typically
+ * retried).
+ *
+ * Return: true if a read section retry is required, else false
+ */
static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
{
+ /*
+ * Assume not nested: read_seqretry() may be called multiple times when
+ * completing read critical section.
+ */
+ kcsan_flat_atomic_end();
+
return read_seqcount_retry(&sl->seqcount, start);
}
/*
- * Lock out other writers and update the count.
- * Acts like a normal spin_lock/unlock.
- * Don't need preempt_disable() because that is in the spin_lock already.
+ * 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.
+ */
+
+/**
+ * write_seqlock() - start a seqlock_t write side critical section
+ * @sl: Pointer to seqlock_t
+ *
+ * write_seqlock opens a write side critical section for the given
+ * seqlock_t. It also implicitly acquires the spinlock_t embedded inside
+ * that sequential lock. All seqlock_t write side sections are thus
+ * automatically serialized and non-preemptible.
+ *
+ * Context: if the seqlock_t read section, or other write side critical
+ * sections, can be invoked from hardirq or softirq contexts, use the
+ * _irqsave or _bh variants of this function instead.
*/
static inline void write_seqlock(seqlock_t *sl)
{
spin_lock(&sl->lock);
- write_seqcount_begin(&sl->seqcount);
+ write_seqcount_t_begin(&sl->seqcount.seqcount);
}
+/**
+ * write_sequnlock() - end a seqlock_t write side critical section
+ * @sl: Pointer to seqlock_t
+ *
+ * write_sequnlock closes the (serialized and non-preemptible) write side
+ * critical section of given seqlock_t.
+ */
static inline void write_sequnlock(seqlock_t *sl)
{
- write_seqcount_end(&sl->seqcount);
+ write_seqcount_t_end(&sl->seqcount.seqcount);
spin_unlock(&sl->lock);
}
+/**
+ * write_seqlock_bh() - start a softirqs-disabled seqlock_t write section
+ * @sl: Pointer to seqlock_t
+ *
+ * _bh variant of write_seqlock(). Use only if the read side section, or
+ * other write side sections, can be invoked from softirq contexts.
+ */
static inline void write_seqlock_bh(seqlock_t *sl)
{
spin_lock_bh(&sl->lock);
- write_seqcount_begin(&sl->seqcount);
+ write_seqcount_t_begin(&sl->seqcount.seqcount);
}
+/**
+ * write_sequnlock_bh() - end a softirqs-disabled seqlock_t write section
+ * @sl: Pointer to seqlock_t
+ *
+ * write_sequnlock_bh closes the serialized, non-preemptible, and
+ * softirqs-disabled, seqlock_t write side critical section opened with
+ * write_seqlock_bh().
+ */
static inline void write_sequnlock_bh(seqlock_t *sl)
{
- write_seqcount_end(&sl->seqcount);
+ write_seqcount_t_end(&sl->seqcount.seqcount);
spin_unlock_bh(&sl->lock);
}
+/**
+ * write_seqlock_irq() - start a non-interruptible seqlock_t write section
+ * @sl: Pointer to seqlock_t
+ *
+ * _irq variant of write_seqlock(). Use only if the read side section, or
+ * other write sections, can be invoked from hardirq contexts.
+ */
static inline void write_seqlock_irq(seqlock_t *sl)
{
spin_lock_irq(&sl->lock);
- write_seqcount_begin(&sl->seqcount);
+ write_seqcount_t_begin(&sl->seqcount.seqcount);
}
+/**
+ * write_sequnlock_irq() - end a non-interruptible seqlock_t write section
+ * @sl: Pointer to seqlock_t
+ *
+ * write_sequnlock_irq closes the serialized and non-interruptible
+ * seqlock_t write side section opened with write_seqlock_irq().
+ */
static inline void write_sequnlock_irq(seqlock_t *sl)
{
- write_seqcount_end(&sl->seqcount);
+ write_seqcount_t_end(&sl->seqcount.seqcount);
spin_unlock_irq(&sl->lock);
}
@@ -491,79 +957,112 @@
unsigned long flags;
spin_lock_irqsave(&sl->lock, flags);
- write_seqcount_begin(&sl->seqcount);
+ write_seqcount_t_begin(&sl->seqcount.seqcount);
return flags;
}
+/**
+ * write_seqlock_irqsave() - start a non-interruptible seqlock_t write
+ * section
+ * @lock: Pointer to seqlock_t
+ * @flags: Stack-allocated storage for saving caller's local interrupt
+ * state, to be passed to write_sequnlock_irqrestore().
+ *
+ * _irqsave variant of write_seqlock(). Use it only if the read side
+ * section, or other write sections, can be invoked from hardirq context.
+ */
#define write_seqlock_irqsave(lock, flags) \
do { flags = __write_seqlock_irqsave(lock); } while (0)
+/**
+ * write_sequnlock_irqrestore() - end non-interruptible seqlock_t write
+ * section
+ * @sl: Pointer to seqlock_t
+ * @flags: Caller's saved interrupt state, from write_seqlock_irqsave()
+ *
+ * write_sequnlock_irqrestore closes the serialized and non-interruptible
+ * seqlock_t write section previously opened with write_seqlock_irqsave().
+ */
static inline void
write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
{
- write_seqcount_end(&sl->seqcount);
+ write_seqcount_t_end(&sl->seqcount.seqcount);
spin_unlock_irqrestore(&sl->lock, flags);
}
-/*
- * A locking reader exclusively locks out other writers and locking readers,
- * but doesn't update the sequence number. Acts like a normal spin_lock/unlock.
- * Don't need preempt_disable() because that is in the spin_lock already.
+/**
+ * read_seqlock_excl() - begin a seqlock_t locking reader section
+ * @sl: Pointer to seqlock_t
+ *
+ * read_seqlock_excl opens a seqlock_t locking reader critical section. A
+ * locking reader exclusively locks out *both* other writers *and* other
+ * locking readers, but it does not update the embedded sequence number.
+ *
+ * Locking readers act like a normal spin_lock()/spin_unlock().
+ *
+ * Context: if the seqlock_t write section, *or other read sections*, can
+ * be invoked from hardirq or softirq contexts, use the _irqsave or _bh
+ * variant of this function instead.
+ *
+ * The opened read section must be closed with read_sequnlock_excl().
*/
static inline void read_seqlock_excl(seqlock_t *sl)
{
spin_lock(&sl->lock);
}
+/**
+ * read_sequnlock_excl() - end a seqlock_t locking reader critical section
+ * @sl: Pointer to seqlock_t
+ */
static inline void read_sequnlock_excl(seqlock_t *sl)
{
spin_unlock(&sl->lock);
}
/**
- * read_seqbegin_or_lock - begin a sequence number check or locking block
- * @lock: sequence lock
- * @seq : sequence number to be checked
+ * read_seqlock_excl_bh() - start a seqlock_t locking reader section with
+ * softirqs disabled
+ * @sl: Pointer to seqlock_t
*
- * First try it once optimistically without taking the lock. If that fails,
- * take the lock. The sequence number is also used as a marker for deciding
- * whether to be a reader (even) or writer (odd).
- * N.B. seq must be initialized to an even number to begin with.
+ * _bh variant of read_seqlock_excl(). Use this variant only if the
+ * seqlock_t write side section, *or other read sections*, can be invoked
+ * from softirq contexts.
*/
-static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
-{
- if (!(*seq & 1)) /* Even */
- *seq = read_seqbegin(lock);
- else /* Odd */
- read_seqlock_excl(lock);
-}
-
-static inline int need_seqretry(seqlock_t *lock, int seq)
-{
- return !(seq & 1) && read_seqretry(lock, seq);
-}
-
-static inline void done_seqretry(seqlock_t *lock, int seq)
-{
- if (seq & 1)
- read_sequnlock_excl(lock);
-}
-
static inline void read_seqlock_excl_bh(seqlock_t *sl)
{
spin_lock_bh(&sl->lock);
}
+/**
+ * read_sequnlock_excl_bh() - stop a seqlock_t softirq-disabled locking
+ * reader section
+ * @sl: Pointer to seqlock_t
+ */
static inline void read_sequnlock_excl_bh(seqlock_t *sl)
{
spin_unlock_bh(&sl->lock);
}
+/**
+ * read_seqlock_excl_irq() - start a non-interruptible seqlock_t locking
+ * reader section
+ * @sl: Pointer to seqlock_t
+ *
+ * _irq variant of read_seqlock_excl(). Use this only if the seqlock_t
+ * write side section, *or other read sections*, can be invoked from a
+ * hardirq context.
+ */
static inline void read_seqlock_excl_irq(seqlock_t *sl)
{
spin_lock_irq(&sl->lock);
}
+/**
+ * read_sequnlock_excl_irq() - end an interrupts-disabled seqlock_t
+ * locking reader section
+ * @sl: Pointer to seqlock_t
+ */
static inline void read_sequnlock_excl_irq(seqlock_t *sl)
{
spin_unlock_irq(&sl->lock);
@@ -577,15 +1076,117 @@
return flags;
}
+/**
+ * read_seqlock_excl_irqsave() - start a non-interruptible seqlock_t
+ * locking reader section
+ * @lock: Pointer to seqlock_t
+ * @flags: Stack-allocated storage for saving caller's local interrupt
+ * state, to be passed to read_sequnlock_excl_irqrestore().
+ *
+ * _irqsave variant of read_seqlock_excl(). Use this only if the seqlock_t
+ * write side section, *or other read sections*, can be invoked from a
+ * hardirq context.
+ */
#define read_seqlock_excl_irqsave(lock, flags) \
do { flags = __read_seqlock_excl_irqsave(lock); } while (0)
+/**
+ * read_sequnlock_excl_irqrestore() - end non-interruptible seqlock_t
+ * locking reader section
+ * @sl: Pointer to seqlock_t
+ * @flags: Caller saved interrupt state, from read_seqlock_excl_irqsave()
+ */
static inline void
read_sequnlock_excl_irqrestore(seqlock_t *sl, unsigned long flags)
{
spin_unlock_irqrestore(&sl->lock, flags);
}
+/**
+ * read_seqbegin_or_lock() - begin a seqlock_t lockless or locking reader
+ * @lock: Pointer to seqlock_t
+ * @seq : Marker and return parameter. If the passed value is even, the
+ * reader will become a *lockless* seqlock_t reader as in read_seqbegin().
+ * If the passed value is odd, the reader will become a *locking* reader
+ * as in read_seqlock_excl(). In the first call to this function, the
+ * caller *must* initialize and pass an even value to @seq; this way, a
+ * lockless read can be optimistically tried first.
+ *
+ * read_seqbegin_or_lock is an API designed to optimistically try a normal
+ * lockless seqlock_t read section first. If an odd counter is found, the
+ * lockless read trial has failed, and the next read iteration transforms
+ * itself into a full seqlock_t locking reader.
+ *
+ * This is typically used to avoid seqlock_t lockless readers starvation
+ * (too much retry loops) in the case of a sharp spike in write side
+ * activity.
+ *
+ * Context: if the seqlock_t write section, *or other read sections*, can
+ * be invoked from hardirq or softirq contexts, use the _irqsave or _bh
+ * variant of this function instead.
+ *
+ * Check Documentation/locking/seqlock.rst for template example code.
+ *
+ * Return: the encountered sequence counter value, through the @seq
+ * parameter, which is overloaded as a return parameter. This returned
+ * value must be checked with need_seqretry(). If the read section need to
+ * be retried, this returned value must also be passed as the @seq
+ * parameter of the next read_seqbegin_or_lock() iteration.
+ */
+static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
+{
+ if (!(*seq & 1)) /* Even */
+ *seq = read_seqbegin(lock);
+ else /* Odd */
+ read_seqlock_excl(lock);
+}
+
+/**
+ * need_seqretry() - validate seqlock_t "locking or lockless" read section
+ * @lock: Pointer to seqlock_t
+ * @seq: sequence count, from read_seqbegin_or_lock()
+ *
+ * Return: true if a read section retry is required, false otherwise
+ */
+static inline int need_seqretry(seqlock_t *lock, int seq)
+{
+ return !(seq & 1) && read_seqretry(lock, seq);
+}
+
+/**
+ * done_seqretry() - end seqlock_t "locking or lockless" reader section
+ * @lock: Pointer to seqlock_t
+ * @seq: count, from read_seqbegin_or_lock()
+ *
+ * done_seqretry finishes the seqlock_t read side critical section started
+ * with read_seqbegin_or_lock() and validated by need_seqretry().
+ */
+static inline void done_seqretry(seqlock_t *lock, int seq)
+{
+ if (seq & 1)
+ read_sequnlock_excl(lock);
+}
+
+/**
+ * read_seqbegin_or_lock_irqsave() - begin a seqlock_t lockless reader, or
+ * a non-interruptible locking reader
+ * @lock: Pointer to seqlock_t
+ * @seq: Marker and return parameter. Check read_seqbegin_or_lock().
+ *
+ * This is the _irqsave variant of read_seqbegin_or_lock(). Use it only if
+ * the seqlock_t write section, *or other read sections*, can be invoked
+ * from hardirq context.
+ *
+ * Note: Interrupts will be disabled only for "locking reader" mode.
+ *
+ * Return:
+ *
+ * 1. The saved local interrupts state in case of a locking reader, to
+ * be passed to done_seqretry_irqrestore().
+ *
+ * 2. The encountered sequence counter value, returned through @seq
+ * overloaded as a return parameter. Check read_seqbegin_or_lock().
+ */
static inline unsigned long
read_seqbegin_or_lock_irqsave(seqlock_t *lock, int *seq)
{
@@ -599,6 +1200,18 @@
return flags;
}
+/**
+ * done_seqretry_irqrestore() - end a seqlock_t lockless reader, or a
+ * non-interruptible locking reader section
+ * @lock: Pointer to seqlock_t
+ * @seq: Count, from read_seqbegin_or_lock_irqsave()
+ * @flags: Caller's saved local interrupt state in case of a locking
+ * reader, also from read_seqbegin_or_lock_irqsave()
+ *
+ * This is the _irqrestore variant of done_seqretry(). The read section
+ * must've been opened with read_seqbegin_or_lock_irqsave(), and validated
+ * by need_seqretry().
+ */
static inline void
done_seqretry_irqrestore(seqlock_t *lock, int seq, unsigned long flags)
{
--
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