1 /* 2 * Queued spinlock 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 2013-2015 Hewlett-Packard Development Company, L.P. 15 * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP 16 * 17 * Authors: Waiman Long <waiman.long@hpe.com> 18 */ 19 #ifndef __ASM_GENERIC_QSPINLOCK_H 20 #define __ASM_GENERIC_QSPINLOCK_H 21 22 #include <asm-generic/qspinlock_types.h> 23 24 /** 25 * queued_spin_unlock_wait - wait until the _current_ lock holder releases the lock 26 * @lock : Pointer to queued spinlock structure 27 * 28 * There is a very slight possibility of live-lock if the lockers keep coming 29 * and the waiter is just unfortunate enough to not see any unlock state. 30 */ 31 #ifndef queued_spin_unlock_wait 32 extern void queued_spin_unlock_wait(struct qspinlock *lock); 33 #endif 34 35 /** 36 * queued_spin_is_locked - is the spinlock locked? 37 * @lock: Pointer to queued spinlock structure 38 * Return: 1 if it is locked, 0 otherwise 39 */ 40 #ifndef queued_spin_is_locked 41 static __always_inline int queued_spin_is_locked(struct qspinlock *lock) 42 { 43 /* 44 * See queued_spin_unlock_wait(). 45 * 46 * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL 47 * isn't immediately observable. 48 */ 49 return atomic_read(&lock->val); 50 } 51 #endif 52 53 /** 54 * queued_spin_value_unlocked - is the spinlock structure unlocked? 55 * @lock: queued spinlock structure 56 * Return: 1 if it is unlocked, 0 otherwise 57 * 58 * N.B. Whenever there are tasks waiting for the lock, it is considered 59 * locked wrt the lockref code to avoid lock stealing by the lockref 60 * code and change things underneath the lock. This also allows some 61 * optimizations to be applied without conflict with lockref. 62 */ 63 static __always_inline int queued_spin_value_unlocked(struct qspinlock lock) 64 { 65 return !atomic_read(&lock.val); 66 } 67 68 /** 69 * queued_spin_is_contended - check if the lock is contended 70 * @lock : Pointer to queued spinlock structure 71 * Return: 1 if lock contended, 0 otherwise 72 */ 73 static __always_inline int queued_spin_is_contended(struct qspinlock *lock) 74 { 75 return atomic_read(&lock->val) & ~_Q_LOCKED_MASK; 76 } 77 /** 78 * queued_spin_trylock - try to acquire the queued spinlock 79 * @lock : Pointer to queued spinlock structure 80 * Return: 1 if lock acquired, 0 if failed 81 */ 82 static __always_inline int queued_spin_trylock(struct qspinlock *lock) 83 { 84 if (!atomic_read(&lock->val) && 85 (atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) == 0)) 86 return 1; 87 return 0; 88 } 89 90 extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); 91 92 /** 93 * queued_spin_lock - acquire a queued spinlock 94 * @lock: Pointer to queued spinlock structure 95 */ 96 static __always_inline void queued_spin_lock(struct qspinlock *lock) 97 { 98 u32 val; 99 100 val = atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL); 101 if (likely(val == 0)) 102 return; 103 queued_spin_lock_slowpath(lock, val); 104 } 105 106 #ifndef queued_spin_unlock 107 /** 108 * queued_spin_unlock - release a queued spinlock 109 * @lock : Pointer to queued spinlock structure 110 */ 111 static __always_inline void queued_spin_unlock(struct qspinlock *lock) 112 { 113 /* 114 * smp_mb__before_atomic() in order to guarantee release semantics 115 */ 116 smp_mb__before_atomic(); 117 atomic_sub(_Q_LOCKED_VAL, &lock->val); 118 } 119 #endif 120 121 #ifndef virt_spin_lock 122 static __always_inline bool virt_spin_lock(struct qspinlock *lock) 123 { 124 return false; 125 } 126 #endif 127 128 /* 129 * Remapping spinlock architecture specific functions to the corresponding 130 * queued spinlock functions. 131 */ 132 #define arch_spin_is_locked(l) queued_spin_is_locked(l) 133 #define arch_spin_is_contended(l) queued_spin_is_contended(l) 134 #define arch_spin_value_unlocked(l) queued_spin_value_unlocked(l) 135 #define arch_spin_lock(l) queued_spin_lock(l) 136 #define arch_spin_trylock(l) queued_spin_trylock(l) 137 #define arch_spin_unlock(l) queued_spin_unlock(l) 138 #define arch_spin_lock_flags(l, f) queued_spin_lock(l) 139 #define arch_spin_unlock_wait(l) queued_spin_unlock_wait(l) 140 141 #endif /* __ASM_GENERIC_QSPINLOCK_H */ 142