/*
* rcuref.h
*
* Reference counting for elements of lists/arrays protected by
* RCU.
*
* 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.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) IBM Corporation, 2005
*
* Author: Dipankar Sarma <dipankar@in.ibm.com>
* Ravikiran Thirumalai <kiran_th@gmail.com>
*
* See Documentation/RCU/rcuref.txt for detailed user guide.
*
*/
#ifndef _RCUREF_H_
#define _RCUREF_H_
#ifdef __KERNEL__
#include <linux/types.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
/*
* These APIs work on traditional atomic_t counters used in the
* kernel for reference counting. Under special circumstances
* where a lock-free get() operation races with a put() operation
* these APIs can be used. See Documentation/RCU/rcuref.txt.
*/
#ifdef __HAVE_ARCH_CMPXCHG
/**
* rcuref_inc - increment refcount for object.
* @rcuref: reference counter in the object in question.
*
* This should be used only for objects where we use RCU and
* use the rcuref_inc_lf() api to acquire a reference
* in a lock-free reader-side critical section.
*/
static inline void rcuref_inc(atomic_t *rcuref)
{
atomic_inc(rcuref);
}
/**
* rcuref_dec - decrement refcount for object.
* @rcuref: reference counter in the object in question.
*
* This should be used only for objects where we use RCU and
* use the rcuref_inc_lf() api to acquire a reference
* in a lock-free reader-side critical section.
*/
static inline void rcuref_dec(atomic_t *rcuref)
{
atomic_dec(rcuref);
}
/**
* rcuref_dec_and_test - decrement refcount for object and test
* @rcuref: reference counter in the object.
* @release: pointer to the function that will clean up the object
* when the last reference to the object is released.
* This pointer is required.
*
* Decrement the refcount, and if 0, return 1. Else return 0.
*
* This should be used only for objects where we use RCU and
* use the rcuref_inc_lf() api to acquire a reference
* in a lock-free reader-side critical section.
*/
static inline int rcuref_dec_and_test(atomic_t *rcuref)
{
return atomic_dec_and_test(rcuref);
}
/*
* cmpxchg is needed on UP too, if deletions to the list/array can happen
* in interrupt context.
*/
/**
* rcuref_inc_lf - Take reference to an object in a read-side
* critical section protected by RCU.
* @rcuref: reference counter in the object in question.
*
* Try and increment the refcount by 1. The increment might fail if
* the reference counter has been through a 1 to 0 transition and
* is no longer part of the lock-free list.
* Returns non-zero on successful increment and zero otherwise.
*/
static inline int rcuref_inc_lf(atomic_t *rcuref)
{
int c, old;
c = atomic_read(rcuref);
while (c && (old = cmpxchg(&rcuref->counter, c, c + 1)) != c)
c = old;
return c;
}
#else /* !__HAVE_ARCH_CMPXCHG */
extern spinlock_t __rcuref_hash[];
/*
* Use a hash table of locks to protect the reference count
* since cmpxchg is not available in this arch.
*/
#ifdef CONFIG_SMP
#define RCUREF_HASH_SIZE 4
#define RCUREF_HASH(k) \
(&__rcuref_hash[(((unsigned long)k)>>8) & (RCUREF_HASH_SIZE-1)])
#else
#define RCUREF_HASH_SIZE 1
#define RCUREF_HASH(k) &__rcuref_hash[0]
#endif /* CONFIG_SMP */
/**
* rcuref_inc - increment refcount for object.
* @rcuref: reference counter in the object in question.
*
* This should be used only for objects where we use RCU and
* use the rcuref_inc_lf() api to acquire a reference in a lock-free
* reader-side critical section.
*/
static inline void rcuref_inc(atomic_t *rcuref)
{
unsigned long flags;
spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
rcuref->counter += 1;
spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
}
/**
* rcuref_dec - decrement refcount for object.
* @rcuref: reference counter in the object in question.
*
* This should be used only for objects where we use RCU and
* use the rcuref_inc_lf() api to acquire a reference in a lock-free
* reader-side critical section.
*/
static inline void rcuref_dec(atomic_t *rcuref)
{
unsigned long flags;
spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
rcuref->counter -= 1;
spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
}
/**
* rcuref_dec_and_test - decrement refcount for object and test
* @rcuref: reference counter in the object.
* @release: pointer to the function that will clean up the object
* when the last reference to the object is released.
* This pointer is required.
*
* Decrement the refcount, and if 0, return 1. Else return 0.
*
* This should be used only for objects where we use RCU and
* use the rcuref_inc_lf() api to acquire a reference in a lock-free
* reader-side critical section.
*/
static inline int rcuref_dec_and_test(atomic_t *rcuref)
{
unsigned long flags;
spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
rcuref->counter--;
if (!rcuref->counter) {
spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
return 1;
} else {
spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
return 0;
}
}
/**
* rcuref_inc_lf - Take reference to an object of a lock-free collection
* by traversing a lock-free list/array.
* @rcuref: reference counter in the object in question.
*
* Try and increment the refcount by 1. The increment might fail if
* the reference counter has been through a 1 to 0 transition and
* object is no longer part of the lock-free list.
* Returns non-zero on successful increment and zero otherwise.
*/
static inline int rcuref_inc_lf(atomic_t *rcuref)
{
int ret;
unsigned long flags;
spin_lock_irqsave(RCUREF_HASH(rcuref), flags);
if (rcuref->counter)
ret = rcuref->counter++;
else
ret = 0;
spin_unlock_irqrestore(RCUREF_HASH(rcuref), flags);
return ret;
}
#endif /* !__HAVE_ARCH_CMPXCHG */
#endif /* __KERNEL__ */
#endif /* _RCUREF_H_ */
