161 lines
4.9 KiB
C
161 lines
4.9 KiB
C
/*
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* Queued spinlock
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
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* (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
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*
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* Authors: Waiman Long <waiman.long@hpe.com>
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*/
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#ifndef __ASM_GENERIC_QSPINLOCK_H
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#define __ASM_GENERIC_QSPINLOCK_H
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#include <asm-generic/qspinlock_types.h>
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/**
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* queued_spin_is_locked - is the spinlock locked?
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* @lock: Pointer to queued spinlock structure
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* Return: 1 if it is locked, 0 otherwise
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*/
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static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
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{
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/*
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* queued_spin_lock_slowpath() can ACQUIRE the lock before
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* issuing the unordered store that sets _Q_LOCKED_VAL.
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*
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* See both smp_cond_acquire() sites for more detail.
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*
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* This however means that in code like:
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*
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* spin_lock(A) spin_lock(B)
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* spin_unlock_wait(B) spin_is_locked(A)
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* do_something() do_something()
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*
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* Both CPUs can end up running do_something() because the store
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* setting _Q_LOCKED_VAL will pass through the loads in
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* spin_unlock_wait() and/or spin_is_locked().
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*
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* Avoid this by issuing a full memory barrier between the spin_lock()
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* and the loads in spin_unlock_wait() and spin_is_locked().
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*
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* Note that regular mutual exclusion doesn't care about this
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* delayed store.
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*/
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smp_mb();
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return atomic_read(&lock->val) & _Q_LOCKED_MASK;
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}
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/**
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* queued_spin_value_unlocked - is the spinlock structure unlocked?
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* @lock: queued spinlock structure
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* Return: 1 if it is unlocked, 0 otherwise
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*
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* N.B. Whenever there are tasks waiting for the lock, it is considered
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* locked wrt the lockref code to avoid lock stealing by the lockref
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* code and change things underneath the lock. This also allows some
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* optimizations to be applied without conflict with lockref.
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*/
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static __always_inline int queued_spin_value_unlocked(struct qspinlock lock)
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{
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return !atomic_read(&lock.val);
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}
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/**
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* queued_spin_is_contended - check if the lock is contended
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* @lock : Pointer to queued spinlock structure
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* Return: 1 if lock contended, 0 otherwise
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*/
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static __always_inline int queued_spin_is_contended(struct qspinlock *lock)
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{
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return atomic_read(&lock->val) & ~_Q_LOCKED_MASK;
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}
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/**
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* queued_spin_trylock - try to acquire the queued spinlock
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* @lock : Pointer to queued spinlock structure
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* Return: 1 if lock acquired, 0 if failed
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*/
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static __always_inline int queued_spin_trylock(struct qspinlock *lock)
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{
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if (!atomic_read(&lock->val) &&
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(atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL) == 0))
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return 1;
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return 0;
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}
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extern void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
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/**
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* queued_spin_lock - acquire a queued spinlock
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* @lock: Pointer to queued spinlock structure
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*/
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static __always_inline void queued_spin_lock(struct qspinlock *lock)
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{
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u32 val;
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val = atomic_cmpxchg_acquire(&lock->val, 0, _Q_LOCKED_VAL);
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if (likely(val == 0))
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return;
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queued_spin_lock_slowpath(lock, val);
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}
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#ifndef queued_spin_unlock
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/**
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* queued_spin_unlock - release a queued spinlock
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* @lock : Pointer to queued spinlock structure
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*/
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static __always_inline void queued_spin_unlock(struct qspinlock *lock)
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{
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/*
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* smp_mb__before_atomic() in order to guarantee release semantics
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*/
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smp_mb__before_atomic();
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atomic_sub(_Q_LOCKED_VAL, &lock->val);
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}
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#endif
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/**
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* queued_spin_unlock_wait - wait until current lock holder releases the lock
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* @lock : Pointer to queued spinlock structure
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*
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* There is a very slight possibility of live-lock if the lockers keep coming
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* and the waiter is just unfortunate enough to not see any unlock state.
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*/
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static inline void queued_spin_unlock_wait(struct qspinlock *lock)
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{
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/* See queued_spin_is_locked() */
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smp_mb();
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while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
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cpu_relax();
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}
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#ifndef virt_spin_lock
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static __always_inline bool virt_spin_lock(struct qspinlock *lock)
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{
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return false;
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}
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#endif
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/*
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* Remapping spinlock architecture specific functions to the corresponding
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* queued spinlock functions.
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*/
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#define arch_spin_is_locked(l) queued_spin_is_locked(l)
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#define arch_spin_is_contended(l) queued_spin_is_contended(l)
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#define arch_spin_value_unlocked(l) queued_spin_value_unlocked(l)
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#define arch_spin_lock(l) queued_spin_lock(l)
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#define arch_spin_trylock(l) queued_spin_trylock(l)
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#define arch_spin_unlock(l) queued_spin_unlock(l)
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#define arch_spin_lock_flags(l, f) queued_spin_lock(l)
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#define arch_spin_unlock_wait(l) queued_spin_unlock_wait(l)
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#endif /* __ASM_GENERIC_QSPINLOCK_H */
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