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