209 lines
6.4 KiB
C
209 lines
6.4 KiB
C
/* $NetBSD: mutex.h,v 1.1 2007/02/16 01:34:03 matt Exp $ */
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/*-
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* Copyright (c) 2002, 2007 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Jason R. Thorpe and Andrew Doran.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the NetBSD
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* Foundation, Inc. and its contributors.
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* 4. Neither the name of The NetBSD Foundation nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef _VAX_MUTEX_H_
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#define _VAX_MUTEX_H_
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/*
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* The VAX mutex implementation is troublesome, because the VAX architecture
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* lacks a compare-and-set operation, yet there are many SMP VAX
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* machines in circulation. SMP for spin mutexes is easy - we don't need
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* to know who owns the lock. For adaptive mutexes, we need an aditional
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* interlock. However, since we know that owners will be kernel addresses
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* and all kernel addresses have the high bit set, we can use the high bit
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* as an interlock.
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*
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* So we test the high bit with BBSSI and if clear
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* kernels are always loaded above 0xe0000000, and the low 5 bits of any
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* "struct lwp *" are always zero. So, to record the lock owner, we only
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* need 23 bits of space. mtxa_owner contains the mutex owner's address
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* shifted right by 5: the top three bits of which will always be 0xe,
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* overlapping with the interlock at the top byte, which is always 0xff
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* when the mutex is held.
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*
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* For a mutex acquisition, the owner field is set in two steps: first,
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* acquire the interlock (top bit), and second OR in the owner's address.
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* Once the owner field is non zero, it will appear that the mutex is held,
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* by which LWP it does not matter: other LWPs competing for the lock will
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* fall through to mutex_vector_enter(), and either spin or sleep.
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*
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* As a result there is no space for a waiters bit in the owner field. No
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* problem, because it would be hard to synchronise using one without a CAS
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* operation. Note that in order to do unlocked release of adaptive
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* mutexes, we need the effect of MUTEX_SET_WAITERS() to be immediatley
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* visible on the bus. So, adaptive mutexes share the spin lock byte with
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* spin mutexes (set with bb{cc,ss}i), but it is not treated as a lock in its
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* own right, rather as a flag that can be atomically set or cleared.
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*
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* When releasing an adaptive mutex, we first clear the owners field, and
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* then check to see if the waiters byte is set. This ensures that there
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* will always be someone to wake any sleeping waiters up (even it the mutex
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* is acquired immediately after we release it, or if we are preempted
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* immediatley after clearing the owners field). The setting or clearing of
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* the waiters byte is serialized by the turnstile chain lock associated
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* with the mutex.
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*
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* See comments in kern_mutex.c about releasing adaptive mutexes without
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* an interlocking step.
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*/
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#ifndef __MUTEX_PRIVATE
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struct kmutex {
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uintptr_t mtx_pad1;
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uint32_t mtx_pad2[2];
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};
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#else /* __MUTEX_PRIVATE */
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struct kmutex {
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/* Adaptive mutex */
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union {
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volatile uintptr_t mtxu_owner; /* 0-3 */
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__cpu_simple_lock_t mtxu_lock; /* 0 */
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} mtx_u;
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ipl_cookie_t mtx_ipl; /* 4-7 */
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uint32_t mtx_id; /* 8-11 */
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};
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#define mtx_owner mtx_u.mtxu_owner
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#define mtx_lock mtx_u.mtxu_lock
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#define __HAVE_MUTEX_STUBS 1
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#define __HAVE_SPIN_MUTEX_STUBS 1
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static inline uintptr_t
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MUTEX_OWNER(uintptr_t owner)
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{
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return owner & ~1;
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}
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static inline bool
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MUTEX_OWNED(uintptr_t owner)
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{
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return owner != 0;
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}
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static inline bool
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MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
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{
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mtx->mtx_owner |= 1;
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return mtx->mtx_owner != 0;
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}
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static inline bool
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MUTEX_HAS_WAITERS(volatile kmutex_t *mtx)
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{
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return (mtx->mtx_owner & 1) != 0;
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}
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static inline void
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MUTEX_CLEAR_WAITERS(volatile kmutex_t *mtx)
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{
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mtx->mtx_owner &= ~1;
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}
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static inline void
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MUTEX_INITIALIZE_SPIN(kmutex_t *mtx, u_int id, int ipl)
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{
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mtx->mtx_id = (id << 1) | 1;
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mtx->mtx_ipl = makeiplcookie(ipl);
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mtx->mtx_lock = 0;
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}
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static inline void
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MUTEX_INITIALIZE_ADAPTIVE(kmutex_t *mtx, u_int id)
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{
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mtx->mtx_id = id << 1;
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mtx->mtx_ipl = makeiplcookie(-1);
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mtx->mtx_owner = 0;
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}
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static inline void
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MUTEX_DESTROY(kmutex_t *mtx)
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{
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mtx->mtx_owner = (uintptr_t)-1L;
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mtx->mtx_id = 0xdeadface << 1;
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}
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static inline u_int
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MUTEX_GETID(volatile kmutex_t *mtx)
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{
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return (mtx)->mtx_id >> 1;
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}
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static inline bool
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MUTEX_SPIN_P(volatile kmutex_t *mtx)
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{
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return (mtx->mtx_id & 1) != 0;
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}
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static inline bool
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MUTEX_ADAPTIVE_P(volatile kmutex_t *mtx)
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{
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return (mtx->mtx_id & 1) == 0;
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}
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static inline bool
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MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
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{
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int rv;
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__asm __volatile(
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"clrl %1;"
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"bbssi $31,%0,1f;"
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"incl %1;"
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"insv %2,%0,$31,%0;"
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"1:"
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: "=m"(mtx->mtx_owner), "=r"(rv)
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: "g"(curthread));
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return 1;
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}
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static inline void
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MUTEX_RELEASE(kmutex_t *mtx)
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{
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__asm __volatile(
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"insv $0,$0,$31,%0;"
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"bbcci $31,%0,1f;"
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"1:"
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: "=m" (mtx->mtx_owner));
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}
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#endif /* __MUTEX_PRIVATE */
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#endif /* _VAX_MUTEX_H_ */
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