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Diffstat (limited to 'include/linux/rcuref.h')
| -rw-r--r-- | include/linux/rcuref.h | 220 |
1 files changed, 220 insertions, 0 deletions
diff --git a/include/linux/rcuref.h b/include/linux/rcuref.h new file mode 100644 index 000000000000..e1adbba14b67 --- /dev/null +++ b/include/linux/rcuref.h @@ -0,0 +1,220 @@ +/* + * 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_ */ |