mutex.h revision 1.3
1/* $NetBSD: mutex.h,v 1.3 2007/02/17 05:34:07 matt Exp $ */ 2 3/*- 4 * Copyright (c) 2002, 2007 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Jason R. Thorpe and Andrew Doran. 9 * 10 * Redistribution and use in source and binary forms, with or without 11 * modification, are permitted provided that the following conditions 12 * are met: 13 * 1. Redistributions of source code must retain the above copyright 14 * notice, this list of conditions and the following disclaimer. 15 * 2. Redistributions in binary form must reproduce the above copyright 16 * notice, this list of conditions and the following disclaimer in the 17 * documentation and/or other materials provided with the distribution. 18 * 3. All advertising materials mentioning features or use of this software 19 * must display the following acknowledgement: 20 * This product includes software developed by the NetBSD 21 * Foundation, Inc. and its contributors. 22 * 4. Neither the name of The NetBSD Foundation nor the names of its 23 * contributors may be used to endorse or promote products derived 24 * from this software without specific prior written permission. 25 * 26 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 27 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 28 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 29 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 30 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 31 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 32 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 33 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 34 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 35 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 36 * POSSIBILITY OF SUCH DAMAGE. 37 */ 38 39#ifndef _VAX_MUTEX_H_ 40#define _VAX_MUTEX_H_ 41 42/* 43 * The VAX mutex implementation is troublesome, because the VAX architecture 44 * lacks a compare-and-set operation, yet there are many SMP VAX 45 * machines in circulation. SMP for spin mutexes is easy - we don't need 46 * to know who owns the lock. For adaptive mutexes, we need an aditional 47 * interlock. However, since we know that owners will be kernel addresses 48 * and all kernel addresses have the high bit set, we can use the high bit 49 * as an interlock. 50 * 51 * So we test the high bit with BBSSI and if clear 52 * kernels are always loaded above 0xe0000000, and the low 5 bits of any 53 * "struct lwp *" are always zero. So, to record the lock owner, we only 54 * need 23 bits of space. mtxa_owner contains the mutex owner's address 55 * shifted right by 5: the top three bits of which will always be 0xe, 56 * overlapping with the interlock at the top byte, which is always 0xff 57 * when the mutex is held. 58 * 59 * For a mutex acquisition, the owner field is set in two steps: first, 60 * acquire the interlock (top bit), and second OR in the owner's address. 61 * Once the owner field is non zero, it will appear that the mutex is held, 62 * by which LWP it does not matter: other LWPs competing for the lock will 63 * fall through to mutex_vector_enter(), and either spin or sleep. 64 * 65 * As a result there is no space for a waiters bit in the owner field. No 66 * problem, because it would be hard to synchronise using one without a CAS 67 * operation. Note that in order to do unlocked release of adaptive 68 * mutexes, we need the effect of MUTEX_SET_WAITERS() to be immediatley 69 * visible on the bus. So, adaptive mutexes share the spin lock byte with 70 * spin mutexes (set with bb{cc,ss}i), but it is not treated as a lock in its 71 * own right, rather as a flag that can be atomically set or cleared. 72 * 73 * When releasing an adaptive mutex, we first clear the owners field, and 74 * then check to see if the waiters byte is set. This ensures that there 75 * will always be someone to wake any sleeping waiters up (even it the mutex 76 * is acquired immediately after we release it, or if we are preempted 77 * immediatley after clearing the owners field). The setting or clearing of 78 * the waiters byte is serialized by the turnstile chain lock associated 79 * with the mutex. 80 * 81 * See comments in kern_mutex.c about releasing adaptive mutexes without 82 * an interlocking step. 83 */ 84 85#ifndef __MUTEX_PRIVATE 86 87struct kmutex { 88 uintptr_t mtx_pad1; 89 uint32_t mtx_pad2[2]; 90}; 91 92#else /* __MUTEX_PRIVATE */ 93 94struct kmutex { 95 /* Adaptive mutex */ 96 union { 97 volatile uintptr_t mtxu_owner; /* 0-3 */ 98 __cpu_simple_lock_t mtxu_lock; /* 0 */ 99 } mtx_u; 100 ipl_cookie_t mtx_ipl; /* 4-7 */ 101 uint32_t mtx_id; /* 8-11 */ 102}; 103#define mtx_owner mtx_u.mtxu_owner 104#define mtx_lock mtx_u.mtxu_lock 105 106#define __HAVE_MUTEX_STUBS 1 107#define __HAVE_SPIN_MUTEX_STUBS 1 108#define __HAVE_MUTEX_NO_SPIN_ACTIVE_P 1 109 110static inline uintptr_t 111MUTEX_OWNER(uintptr_t owner) 112{ 113 return owner & ~1; 114} 115 116static inline bool 117MUTEX_OWNED(uintptr_t owner) 118{ 119 return owner != 0; 120} 121 122static inline bool 123MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner) 124{ 125 mtx->mtx_owner |= 1; 126 return (mtx->mtx_owner & ~1) != 0; 127} 128 129static inline bool 130MUTEX_HAS_WAITERS(volatile kmutex_t *mtx) 131{ 132 return (mtx->mtx_owner & 1) != 0; 133} 134 135static inline void 136MUTEX_CLEAR_WAITERS(volatile kmutex_t *mtx) 137{ 138 mtx->mtx_owner &= ~1; 139} 140 141static inline void 142MUTEX_INITIALIZE_SPIN(kmutex_t *mtx, u_int id, int ipl) 143{ 144 mtx->mtx_id = (id << 1) | 1; 145 mtx->mtx_ipl = makeiplcookie(ipl); 146 mtx->mtx_lock = 0; 147} 148 149static inline void 150MUTEX_INITIALIZE_ADAPTIVE(kmutex_t *mtx, u_int id) 151{ 152 mtx->mtx_id = id << 1; 153 mtx->mtx_ipl = makeiplcookie(-1); 154 mtx->mtx_owner = 0; 155} 156 157static inline void 158MUTEX_DESTROY(kmutex_t *mtx) 159{ 160 mtx->mtx_owner = (uintptr_t)-1L; 161 mtx->mtx_id = 0xdeadface << 1; 162} 163 164static inline u_int 165MUTEX_GETID(volatile kmutex_t *mtx) 166{ 167 return (mtx)->mtx_id >> 1; 168} 169 170static inline bool 171MUTEX_SPIN_P(volatile kmutex_t *mtx) 172{ 173 return (mtx->mtx_id & 1) != 0; 174} 175 176static inline bool 177MUTEX_ADAPTIVE_P(volatile kmutex_t *mtx) 178{ 179 return (mtx->mtx_id & 1) == 0; 180} 181 182static inline bool 183MUTEX_NO_SPIN_ACTIVE_P(struct cpu_info *ci) 184{ 185 return ci->ci_mtx_count == 1; 186} 187 188static inline bool 189MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread) 190{ 191 int rv; 192 __asm __volatile( 193 "clrl %1;" 194 "bbssi $31,%0,1f;" 195 "incl %1;" 196 "insv %2,%0,$31,%0;" 197 "1:" 198 : "=m"(mtx->mtx_owner), "=r"(rv) 199 : "g"(curthread)); 200 return 1; 201} 202 203static inline void 204MUTEX_RELEASE(kmutex_t *mtx) 205{ 206 __asm __volatile( 207 "insv $0,$0,$31,%0;" 208 "bbcci $31,%0,1f;" 209 "1:" 210 : "=m" (mtx->mtx_owner)); 211} 212 213#endif /* __MUTEX_PRIVATE */ 214 215#endif /* _VAX_MUTEX_H_ */ 216