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 0x100 /* A writer is waiting */ 31 #define _QW_LOCKED 0x0ff /* A writer holds the lock */ 32 #define _QW_WMASK 0x1ff /* Writer mask */ 33 #define _QR_SHIFT 9 /* Reader count shift */ 34 #define _QR_BIAS (1U << _QR_SHIFT) 35 36 /* 37 * External function declarations 38 */ 39 extern void queued_read_lock_slowpath(struct qrwlock *lock); 40 extern void queued_write_lock_slowpath(struct qrwlock *lock); 41 42 /** 43 * queued_read_trylock - try to acquire read lock of a queue rwlock 44 * @lock : Pointer to queue rwlock structure 45 * Return: 1 if lock acquired, 0 if failed 46 */ 47 static inline int queued_read_trylock(struct qrwlock *lock) 48 { 49 u32 cnts; 50 51 cnts = atomic_read(&lock->cnts); 52 if (likely(!(cnts & _QW_WMASK))) { 53 cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts); 54 if (likely(!(cnts & _QW_WMASK))) 55 return 1; 56 atomic_sub(_QR_BIAS, &lock->cnts); 57 } 58 return 0; 59 } 60 61 /** 62 * queued_write_trylock - try to acquire write lock of a queue rwlock 63 * @lock : Pointer to queue rwlock structure 64 * Return: 1 if lock acquired, 0 if failed 65 */ 66 static inline int queued_write_trylock(struct qrwlock *lock) 67 { 68 u32 cnts; 69 70 cnts = atomic_read(&lock->cnts); 71 if (unlikely(cnts)) 72 return 0; 73 74 return likely(atomic_cmpxchg_acquire(&lock->cnts, 75 cnts, cnts | _QW_LOCKED) == cnts); 76 } 77 /** 78 * queued_read_lock - acquire read lock of a queue rwlock 79 * @lock: Pointer to queue rwlock structure 80 */ 81 static inline void queued_read_lock(struct qrwlock *lock) 82 { 83 u32 cnts; 84 85 cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts); 86 if (likely(!(cnts & _QW_WMASK))) 87 return; 88 89 /* The slowpath will decrement the reader count, if necessary. */ 90 queued_read_lock_slowpath(lock); 91 } 92 93 /** 94 * queued_write_lock - acquire write lock of a queue rwlock 95 * @lock : Pointer to queue rwlock structure 96 */ 97 static inline void queued_write_lock(struct qrwlock *lock) 98 { 99 /* Optimize for the unfair lock case where the fair flag is 0. */ 100 if (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0) 101 return; 102 103 queued_write_lock_slowpath(lock); 104 } 105 106 /** 107 * queued_read_unlock - release read lock of a queue rwlock 108 * @lock : Pointer to queue rwlock structure 109 */ 110 static inline void queued_read_unlock(struct qrwlock *lock) 111 { 112 /* 113 * Atomically decrement the reader count 114 */ 115 (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts); 116 } 117 118 /** 119 * queued_write_unlock - release write lock of a queue rwlock 120 * @lock : Pointer to queue rwlock structure 121 */ 122 static inline void queued_write_unlock(struct qrwlock *lock) 123 { 124 smp_store_release(&lock->wlocked, 0); 125 } 126 127 /* 128 * Remapping rwlock architecture specific functions to the corresponding 129 * queue rwlock functions. 130 */ 131 #define arch_read_lock(l) queued_read_lock(l) 132 #define arch_write_lock(l) queued_write_lock(l) 133 #define arch_read_trylock(l) queued_read_trylock(l) 134 #define arch_write_trylock(l) queued_write_trylock(l) 135 #define arch_read_unlock(l) queued_read_unlock(l) 136 #define arch_write_unlock(l) queued_write_unlock(l) 137 138 #endif /* __ASM_GENERIC_QRWLOCK_H */ 139