Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 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. |
Waiman Long | 64d816c | 2015-11-09 19:09:21 -0500 | [diff] [blame] | 15 | * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 16 | * |
Waiman Long | 64d816c | 2015-11-09 19:09:21 -0500 | [diff] [blame] | 17 | * Authors: Waiman Long <waiman.long@hpe.com> |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 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 | { |
Peter Zijlstra | 54cf809 | 2016-05-20 18:04:36 +0200 | [diff] [blame^] | 31 | /* |
| 32 | * queued_spin_lock_slowpath() can ACQUIRE the lock before |
| 33 | * issuing the unordered store that sets _Q_LOCKED_VAL. |
| 34 | * |
| 35 | * See both smp_cond_acquire() sites for more detail. |
| 36 | * |
| 37 | * This however means that in code like: |
| 38 | * |
| 39 | * spin_lock(A) spin_lock(B) |
| 40 | * spin_unlock_wait(B) spin_is_locked(A) |
| 41 | * do_something() do_something() |
| 42 | * |
| 43 | * Both CPUs can end up running do_something() because the store |
| 44 | * setting _Q_LOCKED_VAL will pass through the loads in |
| 45 | * spin_unlock_wait() and/or spin_is_locked(). |
| 46 | * |
| 47 | * Avoid this by issuing a full memory barrier between the spin_lock() |
| 48 | * and the loads in spin_unlock_wait() and spin_is_locked(). |
| 49 | * |
| 50 | * Note that regular mutual exclusion doesn't care about this |
| 51 | * delayed store. |
| 52 | */ |
| 53 | smp_mb(); |
| 54 | return atomic_read(&lock->val) & _Q_LOCKED_MASK; |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 55 | } |
| 56 | |
| 57 | /** |
| 58 | * queued_spin_value_unlocked - is the spinlock structure unlocked? |
| 59 | * @lock: queued spinlock structure |
| 60 | * Return: 1 if it is unlocked, 0 otherwise |
| 61 | * |
| 62 | * N.B. Whenever there are tasks waiting for the lock, it is considered |
| 63 | * locked wrt the lockref code to avoid lock stealing by the lockref |
| 64 | * code and change things underneath the lock. This also allows some |
| 65 | * optimizations to be applied without conflict with lockref. |
| 66 | */ |
| 67 | static __always_inline int queued_spin_value_unlocked(struct qspinlock lock) |
| 68 | { |
| 69 | return !atomic_read(&lock.val); |
| 70 | } |
| 71 | |
| 72 | /** |
| 73 | * queued_spin_is_contended - check if the lock is contended |
| 74 | * @lock : Pointer to queued spinlock structure |
| 75 | * Return: 1 if lock contended, 0 otherwise |
| 76 | */ |
| 77 | static __always_inline int queued_spin_is_contended(struct qspinlock *lock) |
| 78 | { |
| 79 | return atomic_read(&lock->val) & ~_Q_LOCKED_MASK; |
| 80 | } |
| 81 | /** |
| 82 | * queued_spin_trylock - try to acquire the queued spinlock |
| 83 | * @lock : Pointer to queued spinlock structure |
| 84 | * Return: 1 if lock acquired, 0 if failed |
| 85 | */ |
| 86 | static __always_inline int queued_spin_trylock(struct qspinlock *lock) |
| 87 | { |
| 88 | if (!atomic_read(&lock->val) && |
Waiman Long | 64d816c | 2015-11-09 19:09:21 -0500 | [diff] [blame] | 89 | (atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) == 0)) |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 90 | return 1; |
| 91 | return 0; |
| 92 | } |
| 93 | |
| 94 | extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); |
| 95 | |
| 96 | /** |
| 97 | * queued_spin_lock - acquire a queued spinlock |
| 98 | * @lock: Pointer to queued spinlock structure |
| 99 | */ |
| 100 | static __always_inline void queued_spin_lock(struct qspinlock *lock) |
| 101 | { |
| 102 | u32 val; |
| 103 | |
Waiman Long | 64d816c | 2015-11-09 19:09:21 -0500 | [diff] [blame] | 104 | val = atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL); |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 105 | if (likely(val == 0)) |
| 106 | return; |
| 107 | queued_spin_lock_slowpath(lock, val); |
| 108 | } |
| 109 | |
| 110 | #ifndef queued_spin_unlock |
| 111 | /** |
| 112 | * queued_spin_unlock - release a queued spinlock |
| 113 | * @lock : Pointer to queued spinlock structure |
| 114 | */ |
| 115 | static __always_inline void queued_spin_unlock(struct qspinlock *lock) |
| 116 | { |
| 117 | /* |
| 118 | * smp_mb__before_atomic() in order to guarantee release semantics |
| 119 | */ |
Waiman Long | 64d816c | 2015-11-09 19:09:21 -0500 | [diff] [blame] | 120 | smp_mb__before_atomic(); |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 121 | atomic_sub(_Q_LOCKED_VAL, &lock->val); |
| 122 | } |
| 123 | #endif |
| 124 | |
| 125 | /** |
| 126 | * queued_spin_unlock_wait - wait until current lock holder releases the lock |
| 127 | * @lock : Pointer to queued spinlock structure |
| 128 | * |
| 129 | * There is a very slight possibility of live-lock if the lockers keep coming |
| 130 | * and the waiter is just unfortunate enough to not see any unlock state. |
| 131 | */ |
| 132 | static inline void queued_spin_unlock_wait(struct qspinlock *lock) |
| 133 | { |
Peter Zijlstra | 54cf809 | 2016-05-20 18:04:36 +0200 | [diff] [blame^] | 134 | /* See queued_spin_is_locked() */ |
| 135 | smp_mb(); |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 136 | while (atomic_read(&lock->val) & _Q_LOCKED_MASK) |
| 137 | cpu_relax(); |
| 138 | } |
| 139 | |
Peter Zijlstra | 43b3f02 | 2015-09-04 17:25:23 +0200 | [diff] [blame] | 140 | #ifndef virt_spin_lock |
| 141 | static __always_inline bool virt_spin_lock(struct qspinlock *lock) |
Peter Zijlstra (Intel) | 2aa79af | 2015-04-24 14:56:36 -0400 | [diff] [blame] | 142 | { |
| 143 | return false; |
| 144 | } |
| 145 | #endif |
| 146 | |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 147 | /* |
Waiman Long | a33fda3 | 2015-04-24 14:56:30 -0400 | [diff] [blame] | 148 | * Remapping spinlock architecture specific functions to the corresponding |
| 149 | * queued spinlock functions. |
| 150 | */ |
| 151 | #define arch_spin_is_locked(l) queued_spin_is_locked(l) |
| 152 | #define arch_spin_is_contended(l) queued_spin_is_contended(l) |
| 153 | #define arch_spin_value_unlocked(l) queued_spin_value_unlocked(l) |
| 154 | #define arch_spin_lock(l) queued_spin_lock(l) |
| 155 | #define arch_spin_trylock(l) queued_spin_trylock(l) |
| 156 | #define arch_spin_unlock(l) queued_spin_unlock(l) |
| 157 | #define arch_spin_lock_flags(l, f) queued_spin_lock(l) |
| 158 | #define arch_spin_unlock_wait(l) queued_spin_unlock_wait(l) |
| 159 | |
| 160 | #endif /* __ASM_GENERIC_QSPINLOCK_H */ |