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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153/* SPDX-License-Identifier: GPL-2.0-or-later *//* * Queued spinlock * * A 'generic' spinlock implementation that is based on MCS locks. For an * architecture that's looking for a 'generic' spinlock, please first consider * ticket-lock.h and only come looking here when you've considered all the * constraints below and can show your hardware does actually perform better * with qspinlock. * * qspinlock relies on atomic_*_release()/atomic_*_acquire() to be RCsc (or no * weaker than RCtso if you're power), where regular code only expects atomic_t * to be RCpc. * * qspinlock relies on a far greater (compared to asm-generic/spinlock.h) set * of atomic operations to behave well together, please audit them carefully to * ensure they all have forward progress. Many atomic operations may default to * cmpxchg() loops which will not have good forward progress properties on * LL/SC architectures. * * One notable example is atomic_fetch_or_acquire(), which x86 cannot (cheaply) * do. Carefully read the patches that introduced * queued_fetch_set_pending_acquire(). * * qspinlock also heavily relies on mixed size atomic operations, in specific * it requires architectures to have xchg16; something which many LL/SC * architectures need to implement as a 32bit and+or in order to satisfy the * forward progress guarantees mentioned above. * * Further reading on mixed size atomics that might be relevant: * * http://www.cl.cam.ac.uk/~pes20/popl17/mixed-size.pdf * * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P. * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP * * Authors: Waiman Long <waiman.long@hpe.com> */#ifndef __ASM_GENERIC_QSPINLOCK_H#define __ASM_GENERIC_QSPINLOCK_H
#include <asm-generic/qspinlock_types.h>#include <linux/atomic.h>
#ifndef queued_spin_is_locked/** * 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){ /* * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL * isn't immediately observable. */ return atomic_read(&lock->val);}#endif
/** * 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 !lock.val.counter;}
/** * 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){ int val = atomic_read(&lock->val);
if (unlikely(val)) return 0;
return likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL));}
extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
#ifndef queued_spin_lock/** * queued_spin_lock - acquire a queued spinlock * @lock: Pointer to queued spinlock structure */static __always_inline void queued_spin_lock(struct qspinlock *lock){ int val = 0;
if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL))) return;
queued_spin_lock_slowpath(lock, val);}#endif
#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){ /* * unlock() needs release semantics: */ smp_store_release(&lock->locked, 0);}#endif
#ifndef virt_spin_lockstatic __always_inline bool virt_spin_lock(struct qspinlock *lock){ return false;}#endif
#ifndef __no_arch_spinlock_redefine/* * 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)#endif
#endif /* __ASM_GENERIC_QSPINLOCK_H */