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 * | +0 | +1 | +2 | +3 | 31 * ----+----+----+----+----+ 32 * LE | 78 | 56 | 34 | 12 | 0x12345678 33 * ----+----+----+----+----+ 34 * | wr | rd | 35 * +----+----+----+----+ 36 * 37 * ----+----+----+----+----+ 38 * BE | 12 | 34 | 56 | 78 | 0x12345678 39 * ----+----+----+----+----+ 40 * | rd | wr | 41 * +----+----+----+----+ 42 */ 43 #define _QW_WAITING 1 /* A writer is waiting */ 44 #define _QW_LOCKED 0xff /* A writer holds the lock */ 45 #define _QW_WMASK 0xff /* Writer mask */ 46 #define _QR_SHIFT 8 /* Reader count shift */ 47 #define _QR_BIAS (1U << _QR_SHIFT) 48 49 /* 50 * External function declarations 51 */ 52 extern void queued_read_lock_slowpath(struct qrwlock *lock, u32 cnts); 53 extern void queued_write_lock_slowpath(struct qrwlock *lock); 54 55 /** 56 * queued_read_trylock - try to acquire read lock of a queue rwlock 57 * @lock : Pointer to queue rwlock structure 58 * Return: 1 if lock acquired, 0 if failed 59 */ 60 static inline int queued_read_trylock(struct qrwlock *lock) 61 { 62 u32 cnts; 63 64 cnts = atomic_read(&lock->cnts); 65 if (likely(!(cnts & _QW_WMASK))) { 66 cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts); 67 if (likely(!(cnts & _QW_WMASK))) 68 return 1; 69 atomic_sub(_QR_BIAS, &lock->cnts); 70 } 71 return 0; 72 } 73 74 /** 75 * queued_write_trylock - try to acquire write lock of a queue rwlock 76 * @lock : Pointer to queue rwlock structure 77 * Return: 1 if lock acquired, 0 if failed 78 */ 79 static inline int queued_write_trylock(struct qrwlock *lock) 80 { 81 u32 cnts; 82 83 cnts = atomic_read(&lock->cnts); 84 if (unlikely(cnts)) 85 return 0; 86 87 return likely(atomic_cmpxchg_acquire(&lock->cnts, 88 cnts, cnts | _QW_LOCKED) == cnts); 89 } 90 /** 91 * queued_read_lock - acquire read lock of a queue rwlock 92 * @lock: Pointer to queue rwlock structure 93 */ 94 static inline void queued_read_lock(struct qrwlock *lock) 95 { 96 u32 cnts; 97 98 cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts); 99 if (likely(!(cnts & _QW_WMASK))) 100 return; 101 102 /* The slowpath will decrement the reader count, if necessary. */ 103 queued_read_lock_slowpath(lock, cnts); 104 } 105 106 /** 107 * queued_write_lock - acquire write lock of a queue rwlock 108 * @lock : Pointer to queue rwlock structure 109 */ 110 static inline void queued_write_lock(struct qrwlock *lock) 111 { 112 /* Optimize for the unfair lock case where the fair flag is 0. */ 113 if (atomic_cmpxchg_acquire(&lock->cnts, 0, _QW_LOCKED) == 0) 114 return; 115 116 queued_write_lock_slowpath(lock); 117 } 118 119 /** 120 * queued_read_unlock - release read lock of a queue rwlock 121 * @lock : Pointer to queue rwlock structure 122 */ 123 static inline void queued_read_unlock(struct qrwlock *lock) 124 { 125 /* 126 * Atomically decrement the reader count 127 */ 128 (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts); 129 } 130 131 /** 132 * queued_write_unlock - release write lock of a queue rwlock 133 * @lock : Pointer to queue rwlock structure 134 */ 135 static inline void queued_write_unlock(struct qrwlock *lock) 136 { 137 smp_store_release(&lock->wmode, 0); 138 } 139 140 /* 141 * Remapping rwlock architecture specific functions to the corresponding 142 * queue rwlock functions. 143 */ 144 #define arch_read_lock(l) queued_read_lock(l) 145 #define arch_write_lock(l) queued_write_lock(l) 146 #define arch_read_trylock(l) queued_read_trylock(l) 147 #define arch_write_trylock(l) queued_write_trylock(l) 148 #define arch_read_unlock(l) queued_read_unlock(l) 149 #define arch_write_unlock(l) queued_write_unlock(l) 150 151 #endif /* __ASM_GENERIC_QRWLOCK_H */ 152