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