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Previously Solaris style atomic primitives were implemented simply by wrapping the desired operation in a global spinlock. This was easy to implement at the time when I wasn't 100% sure I could safely layer the Solaris atomic primatives on the Linux counterparts. It however was likely not good for performance. After more investigation however it does appear the Solaris primitives can be layered on Linux's fairly safely. The Linux atomic_t type really just wraps a long so we can simply cast the Solaris unsigned value to either a atomic_t or atomic64_t. The only lingering problem for both implementations is that Solaris provides no atomic read function. This means reading a 64-bit value on a 32-bit arch can (and will) result in word breaking. I was very concerned about this initially, but upon further reflection it is a limitation of the Solaris API. So really we are just being bug-for-bug compatible here. With this change the default implementation is layered on top of Linux atomic types. However, because we're assuming a lot about the internal implementation of those types I've made it easy to fall-back to the generic approach. Simply build with --enable-atomic_spinlocks if issues are encountered with the new implementation.
227 lines
6.0 KiB
C
227 lines
6.0 KiB
C
/*
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* This file is part of the SPL: Solaris Porting Layer.
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*
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* Copyright (c) 2008 Lawrence Livermore National Security, LLC.
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* Produced at Lawrence Livermore National Laboratory
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* Written by:
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* Brian Behlendorf <behlendorf1@llnl.gov>,
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* Herb Wartens <wartens2@llnl.gov>,
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* Jim Garlick <garlick@llnl.gov>
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* UCRL-CODE-235197
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*
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* This is free software; you can redistribute it and/or modify it
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* 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 is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#ifndef _SPL_ATOMIC_H
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#define _SPL_ATOMIC_H
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#include <linux/module.h>
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#include <linux/spinlock.h>
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#include <sys/types.h>
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/*
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* Two approaches to atomic operations are implemented each with its
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* own benefits are drawbacks imposed by the Solaris API. Neither
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* approach handles the issue of word breaking when using a 64-bit
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* atomic variable on a 32-bit arch. The Solaris API would need to
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* add an atomic read call to correctly support this.
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*
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* When ATOMIC_SPINLOCK is defined all atomic operations will be
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* serialized through global spin locks. This is bad for performance
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* but it does allow a simple generic implementation.
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*
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* When ATOMIC_SPINLOCK is not defined the Linux atomic operations
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* are used. This is safe as long as the core Linux implementation
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* doesn't change because we are relying on the fact that an atomic
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* type is really just a uint32 or uint64. If this changes at some
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* point in the future we need to fall-back to the spin approach.
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*/
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#ifdef ATOMIC_SPINLOCK
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extern spinlock_t atomic32_lock;
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extern spinlock_t atomic64_lock;
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static __inline__ void
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atomic_inc_32(volatile uint32_t *target)
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{
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spin_lock(&atomic32_lock);
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(*target)++;
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spin_unlock(&atomic32_lock);
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}
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static __inline__ void
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atomic_dec_32(volatile uint32_t *target)
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{
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spin_lock(&atomic32_lock);
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(*target)--;
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spin_unlock(&atomic32_lock);
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}
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static __inline__ void
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atomic_add_32(volatile uint32_t *target, int32_t delta)
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{
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spin_lock(&atomic32_lock);
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*target += delta;
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spin_unlock(&atomic32_lock);
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}
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static __inline__ void
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atomic_sub_32(volatile uint32_t *target, int32_t delta)
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{
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spin_lock(&atomic32_lock);
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*target -= delta;
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spin_unlock(&atomic32_lock);
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}
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static __inline__ uint32_t
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atomic_add_32_nv(volatile uint32_t *target, uint32_t delta)
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{
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spin_lock(&atomic32_lock);
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*target += delta;
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spin_unlock(&atomic32_lock);
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return *target;
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}
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static __inline__ uint32_t
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atomic_sub_32_nv(volatile uint32_t *target, uint32_t delta)
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{
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spin_lock(&atomic32_lock);
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*target -= delta;
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spin_unlock(&atomic32_lock);
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return *target;
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}
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static __inline__ uint32_t
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atomic_cas_32(volatile uint32_t *target, uint32_t cmp,
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uint32_t newval)
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{
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uint32_t rc;
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spin_lock(&atomic32_lock);
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rc = *target;
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if (*target == cmp)
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*target = newval;
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spin_unlock(&atomic32_lock);
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return rc;
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}
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static __inline__ void
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atomic_inc_64(volatile uint64_t *target)
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{
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spin_lock(&atomic64_lock);
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(*target)++;
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spin_unlock(&atomic64_lock);
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}
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static __inline__ void
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atomic_dec_64(volatile uint64_t *target)
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{
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spin_lock(&atomic64_lock);
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(*target)--;
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spin_unlock(&atomic64_lock);
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}
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static __inline__ void
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atomic_add_64(volatile uint64_t *target, uint64_t delta)
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{
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spin_lock(&atomic64_lock);
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*target += delta;
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spin_unlock(&atomic64_lock);
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}
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static __inline__ void
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atomic_sub_64(volatile uint64_t *target, uint64_t delta)
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{
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spin_lock(&atomic64_lock);
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*target -= delta;
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spin_unlock(&atomic64_lock);
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}
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static __inline__ uint64_t
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atomic_add_64_nv(volatile uint64_t *target, uint64_t delta)
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{
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spin_lock(&atomic64_lock);
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*target += delta;
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spin_unlock(&atomic64_lock);
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return *target;
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}
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static __inline__ uint64_t
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atomic_sub_64_nv(volatile uint64_t *target, uint64_t delta)
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{
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spin_lock(&atomic64_lock);
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*target -= delta;
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spin_unlock(&atomic64_lock);
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return *target;
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}
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static __inline__ uint64_t
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atomic_cas_64(volatile uint64_t *target, uint64_t cmp,
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uint64_t newval)
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{
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uint64_t rc;
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spin_lock(&atomic64_lock);
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rc = *target;
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if (*target == cmp)
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*target = newval;
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spin_unlock(&atomic64_lock);
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return rc;
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}
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#else /* ATOMIC_SPINLOCK */
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#define atomic_inc_32(v) atomic_inc((atomic_t *)(v))
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#define atomic_dec_32(v) atomic_dec((atomic_t *)(v))
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#define atomic_add_32(v, i) atomic_add((i), (atomic_t *)(v))
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#define atomic_sub_32(v, i) atomic_sub((i), (atomic_t *)(v))
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#define atomic_add_32_nv(v, i) atomic_add_return((i), (atomic_t *)(v))
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#define atomic_sub_32_nv(v, i) atomic_sub_return((i), (atomic_t *)(v))
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#define atomic_cas_32(v, x, y) atomic_cmpxchg((atomic_t *)(v), x, y)
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#define atomic_inc_64(v) atomic64_inc((atomic64_t *)(v))
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#define atomic_dec_64(v) atomic64_dec((atomic64_t *)(v))
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#define atomic_add_64(v, i) atomic64_add((i), (atomic64_t *)(v))
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#define atomic_sub_64(v, i) atomic64_sub((i), (atomic64_t *)(v))
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#define atomic_add_64_nv(v, i) atomic64_add_return((i), (atomic64_t *)(v))
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#define atomic_sub_64_nv(v, i) atomic64_sub_return((i), (atomic64_t *)(v))
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#define atomic_cas_64(v, x, y) atomic64_cmpxchg((atomic64_t *)(v), x, y)
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#endif /* ATOMIC_SPINLOCK */
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#ifdef _LP64
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static __inline__ void *
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atomic_cas_ptr(volatile void *target, void *cmp, void *newval)
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{
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return (void *)atomic_cas_64((volatile uint64_t *)target,
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(uint64_t)cmp, (uint64_t)newval);
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}
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#else /* _LP64 */
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static __inline__ void *
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atomic_cas_ptr(volatile void *target, void *cmp, void *newval)
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{
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return (void *)atomic_cas_32((volatile uint32_t *)target,
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(uint32_t)cmp, (uint32_t)newval);
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}
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#endif /* _LP64 */
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#endif /* _SPL_ATOMIC_H */
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