diff options
| -rw-r--r-- | include/asm-generic/qrwlock.h | 166 | ||||
| -rw-r--r-- | include/asm-generic/qrwlock_types.h | 21 | ||||
| -rw-r--r-- | kernel/Kconfig.locks | 7 | ||||
| -rw-r--r-- | kernel/locking/Makefile | 1 | ||||
| -rw-r--r-- | kernel/locking/qrwlock.c | 133 |
5 files changed, 328 insertions, 0 deletions
diff --git a/include/asm-generic/qrwlock.h b/include/asm-generic/qrwlock.h new file mode 100644 index 000000000000..6383d54bf983 --- /dev/null +++ b/include/asm-generic/qrwlock.h @@ -0,0 +1,166 @@ +/* + * Queue read/write lock + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. + * + * Authors: Waiman Long <waiman.long@hp.com> + */ +#ifndef __ASM_GENERIC_QRWLOCK_H +#define __ASM_GENERIC_QRWLOCK_H + +#include <linux/atomic.h> +#include <asm/barrier.h> +#include <asm/processor.h> + +#include <asm-generic/qrwlock_types.h> + +/* + * Writer states & reader shift and bias + */ +#define _QW_WAITING 1 /* A writer is waiting */ +#define _QW_LOCKED 0xff /* A writer holds the lock */ +#define _QW_WMASK 0xff /* Writer mask */ +#define _QR_SHIFT 8 /* Reader count shift */ +#define _QR_BIAS (1U << _QR_SHIFT) + +/* + * External function declarations + */ +extern void queue_read_lock_slowpath(struct qrwlock *lock); +extern void queue_write_lock_slowpath(struct qrwlock *lock); + +/** + * queue_read_can_lock- would read_trylock() succeed? + * @lock: Pointer to queue rwlock structure + */ +static inline int queue_read_can_lock(struct qrwlock *lock) +{ + return !(atomic_read(&lock->cnts) & _QW_WMASK); +} + +/** + * queue_write_can_lock- would write_trylock() succeed? + * @lock: Pointer to queue rwlock structure + */ +static inline int queue_write_can_lock(struct qrwlock *lock) +{ + return !atomic_read(&lock->cnts); +} + +/** + * queue_read_trylock - try to acquire read lock of a queue rwlock + * @lock : Pointer to queue rwlock structure + * Return: 1 if lock acquired, 0 if failed + */ +static inline int queue_read_trylock(struct qrwlock *lock) +{ + u32 cnts; + + cnts = atomic_read(&lock->cnts); + if (likely(!(cnts & _QW_WMASK))) { + cnts = (u32)atomic_add_return(_QR_BIAS, &lock->cnts); + if (likely(!(cnts & _QW_WMASK))) + return 1; + atomic_sub(_QR_BIAS, &lock->cnts); + } + return 0; +} + +/** + * queue_write_trylock - try to acquire write lock of a queue rwlock + * @lock : Pointer to queue rwlock structure + * Return: 1 if lock acquired, 0 if failed + */ +static inline int queue_write_trylock(struct qrwlock *lock) +{ + u32 cnts; + + cnts = atomic_read(&lock->cnts); + if (unlikely(cnts)) + return 0; + + return likely(atomic_cmpxchg(&lock->cnts, + cnts, cnts | _QW_LOCKED) == cnts); +} +/** + * queue_read_lock - acquire read lock of a queue rwlock + * @lock: Pointer to queue rwlock structure + */ +static inline void queue_read_lock(struct qrwlock *lock) +{ + u32 cnts; + + cnts = atomic_add_return(_QR_BIAS, &lock->cnts); + if (likely(!(cnts & _QW_WMASK))) + return; + + /* The slowpath will decrement the reader count, if necessary. */ + queue_read_lock_slowpath(lock); +} + +/** + * queue_write_lock - acquire write lock of a queue rwlock + * @lock : Pointer to queue rwlock structure + */ +static inline void queue_write_lock(struct qrwlock *lock) +{ + /* Optimize for the unfair lock case where the fair flag is 0. */ + if (atomic_cmpxchg(&lock->cnts, 0, _QW_LOCKED) == 0) + return; + + queue_write_lock_slowpath(lock); +} + +/** + * queue_read_unlock - release read lock of a queue rwlock + * @lock : Pointer to queue rwlock structure + */ +static inline void queue_read_unlock(struct qrwlock *lock) +{ + /* + * Atomically decrement the reader count + */ + smp_mb__before_atomic(); + atomic_sub(_QR_BIAS, &lock->cnts); +} + +#ifndef queue_write_unlock +/** + * queue_write_unlock - release write lock of a queue rwlock + * @lock : Pointer to queue rwlock structure + */ +static inline void queue_write_unlock(struct qrwlock *lock) +{ + /* + * If the writer field is atomic, it can be cleared directly. + * Otherwise, an atomic subtraction will be used to clear it. + */ + smp_mb__before_atomic(); + atomic_sub(_QW_LOCKED, &lock->cnts); +} +#endif + +/* + * Remapping rwlock architecture specific functions to the corresponding + * queue rwlock functions. + */ +#define arch_read_can_lock(l) queue_read_can_lock(l) +#define arch_write_can_lock(l) queue_write_can_lock(l) +#define arch_read_lock(l) queue_read_lock(l) +#define arch_write_lock(l) queue_write_lock(l) +#define arch_read_trylock(l) queue_read_trylock(l) +#define arch_write_trylock(l) queue_write_trylock(l) +#define arch_read_unlock(l) queue_read_unlock(l) +#define arch_write_unlock(l) queue_write_unlock(l) + +#endif /* __ASM_GENERIC_QRWLOCK_H */ diff --git a/include/asm-generic/qrwlock_types.h b/include/asm-generic/qrwlock_types.h new file mode 100644 index 000000000000..4d76f24df518 --- /dev/null +++ b/include/asm-generic/qrwlock_types.h @@ -0,0 +1,21 @@ +#ifndef __ASM_GENERIC_QRWLOCK_TYPES_H +#define __ASM_GENERIC_QRWLOCK_TYPES_H + +#include <linux/types.h> +#include <asm/spinlock_types.h> + +/* + * The queue read/write lock data structure + */ + +typedef struct qrwlock { + atomic_t cnts; + arch_spinlock_t lock; +} arch_rwlock_t; + +#define __ARCH_RW_LOCK_UNLOCKED { \ + .cnts = ATOMIC_INIT(0), \ + .lock = __ARCH_SPIN_LOCK_UNLOCKED, \ +} + +#endif /* __ASM_GENERIC_QRWLOCK_TYPES_H */ diff --git a/kernel/Kconfig.locks b/kernel/Kconfig.locks index d2b32ac27a39..35536d9c0964 100644 --- a/kernel/Kconfig.locks +++ b/kernel/Kconfig.locks @@ -223,3 +223,10 @@ endif config MUTEX_SPIN_ON_OWNER def_bool y depends on SMP && !DEBUG_MUTEXES + +config ARCH_USE_QUEUE_RWLOCK + bool + +config QUEUE_RWLOCK + def_bool y if ARCH_USE_QUEUE_RWLOCK + depends on SMP diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile index b8bdcd4785b7..8541bfdfd232 100644 --- a/kernel/locking/Makefile +++ b/kernel/locking/Makefile @@ -24,4 +24,5 @@ obj-$(CONFIG_DEBUG_SPINLOCK) += spinlock_debug.o obj-$(CONFIG_RWSEM_GENERIC_SPINLOCK) += rwsem-spinlock.o obj-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem-xadd.o obj-$(CONFIG_PERCPU_RWSEM) += percpu-rwsem.o +obj-$(CONFIG_QUEUE_RWLOCK) += qrwlock.o obj-$(CONFIG_LOCK_TORTURE_TEST) += locktorture.o diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c new file mode 100644 index 000000000000..fb5b8ac411a5 --- /dev/null +++ b/kernel/locking/qrwlock.c @@ -0,0 +1,133 @@ +/* + * Queue read/write lock + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. + * + * Authors: Waiman Long <waiman.long@hp.com> + */ +#include <linux/smp.h> +#include <linux/bug.h> +#include <linux/cpumask.h> +#include <linux/percpu.h> +#include <linux/hardirq.h> +#include <linux/mutex.h> +#include <asm/qrwlock.h> + +/** + * rspin_until_writer_unlock - inc reader count & spin until writer is gone + * @lock : Pointer to queue rwlock structure + * @writer: Current queue rwlock writer status byte + * + * In interrupt context or at the head of the queue, the reader will just + * increment the reader count & wait until the writer releases the lock. + */ +static __always_inline void +rspin_until_writer_unlock(struct qrwlock *lock, u32 cnts) +{ + while ((cnts & _QW_WMASK) == _QW_LOCKED) { + arch_mutex_cpu_relax(); + cnts = smp_load_acquire((u32 *)&lock->cnts); + } +} + +/** + * queue_read_lock_slowpath - acquire read lock of a queue rwlock + * @lock: Pointer to queue rwlock structure + */ +void queue_read_lock_slowpath(struct qrwlock *lock) +{ + u32 cnts; + + /* + * Readers come here when they cannot get the lock without waiting + */ + if (unlikely(in_interrupt())) { + /* + * Readers in interrupt context will spin until the lock is + * available without waiting in the queue. + */ + cnts = smp_load_acquire((u32 *)&lock->cnts); + rspin_until_writer_unlock(lock, cnts); + return; + } + atomic_sub(_QR_BIAS, &lock->cnts); + + /* + * Put the reader into the wait queue + */ + arch_spin_lock(&lock->lock); + + /* + * At the head of the wait queue now, wait until the writer state + * goes to 0 and then try to increment the reader count and get + * the lock. It is possible that an incoming writer may steal the + * lock in the interim, so it is necessary to check the writer byte + * to make sure that the write lock isn't taken. + */ + while (atomic_read(&lock->cnts) & _QW_WMASK) + arch_mutex_cpu_relax(); + + cnts = atomic_add_return(_QR_BIAS, &lock->cnts) - _QR_BIAS; + rspin_until_writer_unlock(lock, cnts); + + /* + * Signal the next one in queue to become queue head + */ + arch_spin_unlock(&lock->lock); +} +EXPORT_SYMBOL(queue_read_lock_slowpath); + +/** + * queue_write_lock_slowpath - acquire write lock of a queue rwlock + * @lock : Pointer to queue rwlock structure + */ +void queue_write_lock_slowpath(struct qrwlock *lock) +{ + u32 cnts; + + /* Put the writer into the wait queue */ + arch_spin_lock(&lock->lock); + + /* Try to acquire the lock directly if no reader is present */ + if (!atomic_read(&lock->cnts) && + (atomic_cmpxchg(&lock->cnts, 0, _QW_LOCKED) == 0)) + goto unlock; + + /* + * Set the waiting flag to notify readers that a writer is pending, + * or wait for a previous writer to go away. + */ + for (;;) { + cnts = atomic_read(&lock->cnts); + if (!(cnts & _QW_WMASK) && + (atomic_cmpxchg(&lock->cnts, cnts, + cnts | _QW_WAITING) == cnts)) + break; + + arch_mutex_cpu_relax(); + } + + /* When no more readers, set the locked flag */ + for (;;) { + cnts = atomic_read(&lock->cnts); + if ((cnts == _QW_WAITING) && + (atomic_cmpxchg(&lock->cnts, _QW_WAITING, + _QW_LOCKED) == _QW_WAITING)) + break; + + arch_mutex_cpu_relax(); + } +unlock: + arch_spin_unlock(&lock->lock); +} +EXPORT_SYMBOL(queue_write_lock_slowpath); |