1/* 2 * Queue read/write lock 3 * 4 * This program is free software; you can redistribute it and/or modify 5 * it under the terms of the GNU General Public License as published by 6 * the Free Software Foundation; either version 2 of the License, or 7 * (at your option) any later version. 8 * 9 * This program is distributed in the hope that it will be useful, 10 * but WITHOUT ANY WARRANTY; without even the implied warranty of 11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 12 * GNU General Public License for more details. 13 * 14 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. 15 * 16 * Authors: Waiman Long <waiman.long@hp.com> 17 */ 18#ifndef __ASM_GENERIC_QRWLOCK_H 19#define __ASM_GENERIC_QRWLOCK_H 20 21#include <linux/atomic.h> 22#include <asm/barrier.h> 23#include <asm/processor.h> 24 25#include <asm-generic/qrwlock_types.h> 26 27/* 28 * Writer states & reader shift and bias 29 */ 30#define _QW_WAITING 1 /* A writer is waiting */ 31#define _QW_LOCKED 0xff /* A writer holds the lock */ 32#define _QW_WMASK 0xff /* Writer mask */ 33#define _QR_SHIFT 8 /* Reader count shift */ 34#define _QR_BIAS (1U << _QR_SHIFT) 35 36/* 37 * External function declarations 38 */ 39extern void queue_read_lock_slowpath(struct qrwlock *lock); 40extern void queue_write_lock_slowpath(struct qrwlock *lock); 41 42/** 43 * queue_read_can_lock- would read_trylock() succeed? 44 * @lock: Pointer to queue rwlock structure 45 */ 46static inline int queue_read_can_lock(struct qrwlock *lock) 47{ 48 return !(atomic_read(&lock->cnts) & _QW_WMASK); 49} 50 51/** 52 * queue_write_can_lock- would write_trylock() succeed? 53 * @lock: Pointer to queue rwlock structure 54 */ 55static inline int queue_write_can_lock(struct qrwlock *lock) 56{ 57 return !atomic_read(&lock->cnts); 58} 59 60/** 61 * queue_read_trylock - try to acquire read lock of a queue rwlock 62 * @lock : Pointer to queue rwlock structure 63 * Return: 1 if lock acquired, 0 if failed 64 */ 65static inline int queue_read_trylock(struct qrwlock *lock) 66{ 67 u32 cnts; 68 69 cnts = atomic_read(&lock->cnts); 70 if (likely(!(cnts & _QW_WMASK))) { 71 cnts = (u32)atomic_add_return(_QR_BIAS, &lock->cnts); 72 if (likely(!(cnts & _QW_WMASK))) 73 return 1; 74 atomic_sub(_QR_BIAS, &lock->cnts); 75 } 76 return 0; 77} 78 79/** 80 * queue_write_trylock - try to acquire write lock of a queue rwlock 81 * @lock : Pointer to queue rwlock structure 82 * Return: 1 if lock acquired, 0 if failed 83 */ 84static inline int queue_write_trylock(struct qrwlock *lock) 85{ 86 u32 cnts; 87 88 cnts = atomic_read(&lock->cnts); 89 if (unlikely(cnts)) 90 return 0; 91 92 return likely(atomic_cmpxchg(&lock->cnts, 93 cnts, cnts | _QW_LOCKED) == cnts); 94} 95/** 96 * queue_read_lock - acquire read lock of a queue rwlock 97 * @lock: Pointer to queue rwlock structure 98 */ 99static inline void queue_read_lock(struct qrwlock *lock) 100{ 101 u32 cnts; 102 103 cnts = atomic_add_return(_QR_BIAS, &lock->cnts); 104 if (likely(!(cnts & _QW_WMASK))) 105 return; 106 107 /* The slowpath will decrement the reader count, if necessary. */ 108 queue_read_lock_slowpath(lock); 109} 110 111/** 112 * queue_write_lock - acquire write lock of a queue rwlock 113 * @lock : Pointer to queue rwlock structure 114 */ 115static inline void queue_write_lock(struct qrwlock *lock) 116{ 117 /* Optimize for the unfair lock case where the fair flag is 0. */ 118 if (atomic_cmpxchg(&lock->cnts, 0, _QW_LOCKED) == 0) 119 return; 120 121 queue_write_lock_slowpath(lock); 122} 123 124/** 125 * queue_read_unlock - release read lock of a queue rwlock 126 * @lock : Pointer to queue rwlock structure 127 */ 128static inline void queue_read_unlock(struct qrwlock *lock) 129{ 130 /* 131 * Atomically decrement the reader count 132 */ 133 smp_mb__before_atomic(); 134 atomic_sub(_QR_BIAS, &lock->cnts); 135} 136 137#ifndef queue_write_unlock 138/** 139 * queue_write_unlock - release write lock of a queue rwlock 140 * @lock : Pointer to queue rwlock structure 141 */ 142static inline void queue_write_unlock(struct qrwlock *lock) 143{ 144 /* 145 * If the writer field is atomic, it can be cleared directly. 146 * Otherwise, an atomic subtraction will be used to clear it. 147 */ 148 smp_mb__before_atomic(); 149 atomic_sub(_QW_LOCKED, &lock->cnts); 150} 151#endif 152 153/* 154 * Remapping rwlock architecture specific functions to the corresponding 155 * queue rwlock functions. 156 */ 157#define arch_read_can_lock(l) queue_read_can_lock(l) 158#define arch_write_can_lock(l) queue_write_can_lock(l) 159#define arch_read_lock(l) queue_read_lock(l) 160#define arch_write_lock(l) queue_write_lock(l) 161#define arch_read_trylock(l) queue_read_trylock(l) 162#define arch_write_trylock(l) queue_write_trylock(l) 163#define arch_read_unlock(l) queue_read_unlock(l) 164#define arch_write_unlock(l) queue_write_unlock(l) 165 166#endif /* __ASM_GENERIC_QRWLOCK_H */ 167