diff options
Diffstat (limited to 'include/asm-generic/qspinlock.h')
| -rw-r--r-- | include/asm-generic/qspinlock.h | 132 |
1 files changed, 132 insertions, 0 deletions
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h new file mode 100644 index 000000000000..569abcd47a9a --- /dev/null +++ b/include/asm-generic/qspinlock.h @@ -0,0 +1,132 @@ +/* + * Queued spinlock + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P. + * + * Authors: Waiman Long <waiman.long@hp.com> + */ +#ifndef __ASM_GENERIC_QSPINLOCK_H +#define __ASM_GENERIC_QSPINLOCK_H + +#include <asm-generic/qspinlock_types.h> + +/** + * queued_spin_is_locked - is the spinlock locked? + * @lock: Pointer to queued spinlock structure + * Return: 1 if it is locked, 0 otherwise + */ +static __always_inline int queued_spin_is_locked(struct qspinlock *lock) +{ + return atomic_read(&lock->val); +} + +/** + * queued_spin_value_unlocked - is the spinlock structure unlocked? + * @lock: queued spinlock structure + * Return: 1 if it is unlocked, 0 otherwise + * + * N.B. Whenever there are tasks waiting for the lock, it is considered + * locked wrt the lockref code to avoid lock stealing by the lockref + * code and change things underneath the lock. This also allows some + * optimizations to be applied without conflict with lockref. + */ +static __always_inline int queued_spin_value_unlocked(struct qspinlock lock) +{ + return !atomic_read(&lock.val); +} + +/** + * queued_spin_is_contended - check if the lock is contended + * @lock : Pointer to queued spinlock structure + * Return: 1 if lock contended, 0 otherwise + */ +static __always_inline int queued_spin_is_contended(struct qspinlock *lock) +{ + return atomic_read(&lock->val) & ~_Q_LOCKED_MASK; +} +/** + * queued_spin_trylock - try to acquire the queued spinlock + * @lock : Pointer to queued spinlock structure + * Return: 1 if lock acquired, 0 if failed + */ +static __always_inline int queued_spin_trylock(struct qspinlock *lock) +{ + if (!atomic_read(&lock->val) && + (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) == 0)) + return 1; + return 0; +} + +extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); + +/** + * queued_spin_lock - acquire a queued spinlock + * @lock: Pointer to queued spinlock structure + */ +static __always_inline void queued_spin_lock(struct qspinlock *lock) +{ + u32 val; + + val = atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL); + if (likely(val == 0)) + return; + queued_spin_lock_slowpath(lock, val); +} + +#ifndef queued_spin_unlock +/** + * queued_spin_unlock - release a queued spinlock + * @lock : Pointer to queued spinlock structure + */ +static __always_inline void queued_spin_unlock(struct qspinlock *lock) +{ + /* + * smp_mb__before_atomic() in order to guarantee release semantics + */ + smp_mb__before_atomic_dec(); + atomic_sub(_Q_LOCKED_VAL, &lock->val); +} +#endif + +/** + * queued_spin_unlock_wait - wait until current lock holder releases the lock + * @lock : Pointer to queued spinlock structure + * + * There is a very slight possibility of live-lock if the lockers keep coming + * and the waiter is just unfortunate enough to not see any unlock state. + */ +static inline void queued_spin_unlock_wait(struct qspinlock *lock) +{ + while (atomic_read(&lock->val) & _Q_LOCKED_MASK) + cpu_relax(); +} + +/* + * Initializier + */ +#define __ARCH_SPIN_LOCK_UNLOCKED { ATOMIC_INIT(0) } + +/* + * Remapping spinlock architecture specific functions to the corresponding + * queued spinlock functions. + */ +#define arch_spin_is_locked(l) queued_spin_is_locked(l) +#define arch_spin_is_contended(l) queued_spin_is_contended(l) +#define arch_spin_value_unlocked(l) queued_spin_value_unlocked(l) +#define arch_spin_lock(l) queued_spin_lock(l) +#define arch_spin_trylock(l) queued_spin_trylock(l) +#define arch_spin_unlock(l) queued_spin_unlock(l) +#define arch_spin_lock_flags(l, f) queued_spin_lock(l) +#define arch_spin_unlock_wait(l) queued_spin_unlock_wait(l) + +#endif /* __ASM_GENERIC_QSPINLOCK_H */ |