atomic64.c
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/*
* Generic implementation of 64-bit atomics using spinlocks,
* useful on processors that don't have 64-bit atomic instructions.
*
* Copyright © 2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
*
* 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.
*/
#include <linux/types.h>
#include <linux/cache.h>
#include <linux/spinlock.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/atomic.h>
/*
* We use a hashed array of spinlocks to provide exclusive access
* to each atomic64_t variable. Since this is expected to used on
* systems with small numbers of CPUs (<= 4 or so), we use a
* relatively small array of 16 spinlocks to avoid wasting too much
* memory on the spinlock array.
*/
#define NR_LOCKS 16
/*
* Ensure each lock is in a separate cacheline.
*/
static union {
raw_spinlock_t lock;
char pad[L1_CACHE_BYTES];
} atomic64_lock[NR_LOCKS] __cacheline_aligned_in_smp;
static inline raw_spinlock_t *lock_addr(const atomic64_t *v)
{
unsigned long addr = (unsigned long) v;
addr >>= L1_CACHE_SHIFT;
addr ^= (addr >> 8) ^ (addr >> 16);
return &atomic64_lock[addr & (NR_LOCKS - 1)].lock;
}
long long atomic64_read(const atomic64_t *v)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
long long val;
raw_spin_lock_irqsave(lock, flags);
val = v->counter;
raw_spin_unlock_irqrestore(lock, flags);
return val;
}
EXPORT_SYMBOL(atomic64_read);
void atomic64_set(atomic64_t *v, long long i)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
raw_spin_lock_irqsave(lock, flags);
v->counter = i;
raw_spin_unlock_irqrestore(lock, flags);
}
EXPORT_SYMBOL(atomic64_set);
void atomic64_add(long long a, atomic64_t *v)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
raw_spin_lock_irqsave(lock, flags);
v->counter += a;
raw_spin_unlock_irqrestore(lock, flags);
}
EXPORT_SYMBOL(atomic64_add);
long long atomic64_add_return(long long a, atomic64_t *v)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
long long val;
raw_spin_lock_irqsave(lock, flags);
val = v->counter += a;
raw_spin_unlock_irqrestore(lock, flags);
return val;
}
EXPORT_SYMBOL(atomic64_add_return);
void atomic64_sub(long long a, atomic64_t *v)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
raw_spin_lock_irqsave(lock, flags);
v->counter -= a;
raw_spin_unlock_irqrestore(lock, flags);
}
EXPORT_SYMBOL(atomic64_sub);
long long atomic64_sub_return(long long a, atomic64_t *v)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
long long val;
raw_spin_lock_irqsave(lock, flags);
val = v->counter -= a;
raw_spin_unlock_irqrestore(lock, flags);
return val;
}
EXPORT_SYMBOL(atomic64_sub_return);
long long atomic64_dec_if_positive(atomic64_t *v)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
long long val;
raw_spin_lock_irqsave(lock, flags);
val = v->counter - 1;
if (val >= 0)
v->counter = val;
raw_spin_unlock_irqrestore(lock, flags);
return val;
}
EXPORT_SYMBOL(atomic64_dec_if_positive);
long long atomic64_cmpxchg(atomic64_t *v, long long o, long long n)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
long long val;
raw_spin_lock_irqsave(lock, flags);
val = v->counter;
if (val == o)
v->counter = n;
raw_spin_unlock_irqrestore(lock, flags);
return val;
}
EXPORT_SYMBOL(atomic64_cmpxchg);
long long atomic64_xchg(atomic64_t *v, long long new)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
long long val;
raw_spin_lock_irqsave(lock, flags);
val = v->counter;
v->counter = new;
raw_spin_unlock_irqrestore(lock, flags);
return val;
}
EXPORT_SYMBOL(atomic64_xchg);
int atomic64_add_unless(atomic64_t *v, long long a, long long u)
{
unsigned long flags;
raw_spinlock_t *lock = lock_addr(v);
int ret = 0;
raw_spin_lock_irqsave(lock, flags);
if (v->counter != u) {
v->counter += a;
ret = 1;
}
raw_spin_unlock_irqrestore(lock, flags);
return ret;
}
EXPORT_SYMBOL(atomic64_add_unless);
static int init_atomic64_lock(void)
{
int i;
for (i = 0; i < NR_LOCKS; ++i)
raw_spin_lock_init(&atomic64_lock[i].lock);
return 0;
}
pure_initcall(init_atomic64_lock);