1 /* SPDX-License-Identifier: GPL-2.0-or-later */ 2 /* 3 * Queue read/write lock 4 * 5 * (C) Copyright 2013-2014 Hewlett-Packard Development Company, L.P. 6 * 7 * Authors: Waiman Long <waiman.long@hp.com> 8 */ 9 #ifndef __ASM_GENERIC_QRWLOCK_H 10 #define __ASM_GENERIC_QRWLOCK_H 11 12 #include <linux/atomic.h> 13 #include <asm/barrier.h> 14 #include <asm/processor.h> 15 16 #include <asm-generic/qrwlock_types.h> 17 18 /* Must be included from asm/spinlock.h after defining arch_spin_is_locked. */ 19 20 /* 21 * Writer states & reader shift and bias. 22 */ 23 #define _QW_WAITING 0x100 /* A writer is waiting */ 24 #define _QW_LOCKED 0x0ff /* A writer holds the lock */ 25 #define _QW_WMASK 0x1ff /* Writer mask */ 26 #define _QR_SHIFT 9 /* Reader count shift */ 27 #define _QR_BIAS (1U << _QR_SHIFT) 28 29 /* 30 * External function declarations 31 */ 32 extern void queued_read_lock_slowpath(struct qrwlock *lock); 33 extern void queued_write_lock_slowpath(struct qrwlock *lock); 34 35 /** 36 * queued_read_trylock - try to acquire read lock of a queue rwlock 37 * @lock : Pointer to queue rwlock structure 38 * Return: 1 if lock acquired, 0 if failed 39 */ 40 static inline int queued_read_trylock(struct qrwlock *lock) 41 { 42 int cnts; 43 44 cnts = atomic_read(&lock->cnts); 45 if (likely(!(cnts & _QW_WMASK))) { 46 cnts = (u32)atomic_add_return_acquire(_QR_BIAS, &lock->cnts); 47 if (likely(!(cnts & _QW_WMASK))) 48 return 1; 49 atomic_sub(_QR_BIAS, &lock->cnts); 50 } 51 return 0; 52 } 53 54 /** 55 * queued_write_trylock - try to acquire write lock of a queue rwlock 56 * @lock : Pointer to queue rwlock structure 57 * Return: 1 if lock acquired, 0 if failed 58 */ 59 static inline int queued_write_trylock(struct qrwlock *lock) 60 { 61 int cnts; 62 63 cnts = atomic_read(&lock->cnts); 64 if (unlikely(cnts)) 65 return 0; 66 67 return likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, 68 _QW_LOCKED)); 69 } 70 /** 71 * queued_read_lock - acquire read lock of a queue rwlock 72 * @lock: Pointer to queue rwlock structure 73 */ 74 static inline void queued_read_lock(struct qrwlock *lock) 75 { 76 int cnts; 77 78 cnts = atomic_add_return_acquire(_QR_BIAS, &lock->cnts); 79 if (likely(!(cnts & _QW_WMASK))) 80 return; 81 82 /* The slowpath will decrement the reader count, if necessary. */ 83 queued_read_lock_slowpath(lock); 84 } 85 86 /** 87 * queued_write_lock - acquire write lock of a queue rwlock 88 * @lock : Pointer to queue rwlock structure 89 */ 90 static inline void queued_write_lock(struct qrwlock *lock) 91 { 92 int cnts = 0; 93 /* Optimize for the unfair lock case where the fair flag is 0. */ 94 if (likely(atomic_try_cmpxchg_acquire(&lock->cnts, &cnts, _QW_LOCKED))) 95 return; 96 97 queued_write_lock_slowpath(lock); 98 } 99 100 /** 101 * queued_read_unlock - release read lock of a queue rwlock 102 * @lock : Pointer to queue rwlock structure 103 */ 104 static inline void queued_read_unlock(struct qrwlock *lock) 105 { 106 /* 107 * Atomically decrement the reader count 108 */ 109 (void)atomic_sub_return_release(_QR_BIAS, &lock->cnts); 110 } 111 112 /** 113 * queued_write_unlock - release write lock of a queue rwlock 114 * @lock : Pointer to queue rwlock structure 115 */ 116 static inline void queued_write_unlock(struct qrwlock *lock) 117 { 118 smp_store_release(&lock->wlocked, 0); 119 } 120 121 /** 122 * queued_rwlock_is_contended - check if the lock is contended 123 * @lock : Pointer to queue rwlock structure 124 * Return: 1 if lock contended, 0 otherwise 125 */ 126 static inline int queued_rwlock_is_contended(struct qrwlock *lock) 127 { 128 return arch_spin_is_locked(&lock->wait_lock); 129 } 130 131 /* 132 * Remapping rwlock architecture specific functions to the corresponding 133 * queue rwlock functions. 134 */ 135 #define arch_read_lock(l) queued_read_lock(l) 136 #define arch_write_lock(l) queued_write_lock(l) 137 #define arch_read_trylock(l) queued_read_trylock(l) 138 #define arch_write_trylock(l) queued_write_trylock(l) 139 #define arch_read_unlock(l) queued_read_unlock(l) 140 #define arch_write_unlock(l) queued_write_unlock(l) 141 #define arch_rwlock_is_contended(l) queued_rwlock_is_contended(l) 142 143 #endif /* __ASM_GENERIC_QRWLOCK_H */ 144