1 /* $NetBSD: mutex.h,v 1.6 2007/11/21 10:19:08 yamt 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 _SPARC_MUTEX_H_ 40 #define _SPARC_MUTEX_H_ 41 42 /* 43 * There sparc mutex implementation is troublesome, because sparc (v7 and 44 * v8) lacks a compare-and-set operation, yet there are many SMP sparc 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. 48 * 49 * The locked byte set by the sparc 'ldstub' instruction is 0xff. sparc 50 * kernels are always loaded above 0xe0000000, and the low 5 bits of any 51 * "struct lwp *" are always zero. So, to record the lock owner, we only 52 * need 23 bits of space. mtxa_owner contains the mutex owner's address 53 * shifted right by 5: the top three bits of which will always be 0xe, 54 * overlapping with the interlock at the top byte, which is always 0xff 55 * when the mutex is held. 56 * 57 * For a mutex acquisition, the owner field is set in two steps: first, 58 * acquire the interlock (top byte), and second OR in the owner's address. 59 * Once the owner field is non zero, it will appear that the mutex is held, 60 * by which LWP it does not matter: other LWPs competing for the lock will 61 * fall through to mutex_vector_enter(), and either spin or sleep. 62 * 63 * As a result there is no space for a waiters bit in the owner field. No 64 * problem, because it would be hard to synchronise using one without a CAS 65 * operation. Note that in order to do unlocked release of adaptive 66 * mutexes, we need the effect of MUTEX_SET_WAITERS() to be immediatley 67 * visible on the bus. So, adaptive mutexes share the spin lock byte with 68 * spin mutexes (set with ldstub), but it is not treated as a lock in its 69 * own right, rather as a flag that can be atomically set or cleared. 70 * 71 * When releasing an adaptive mutex, we first clear the owners field, and 72 * then check to see if the waiters byte is set. This ensures that there 73 * will always be someone to wake any sleeping waiters up (even it the mutex 74 * is acquired immediately after we release it, or if we are preempted 75 * immediatley after clearing the owners field). The setting or clearing of 76 * the waiters byte is serialized by the turnstile chain lock associated 77 * with the mutex. 78 * 79 * See comments in kern_mutex.c about releasing adaptive mutexes without 80 * an interlocking step. 81 */ 82 83 #ifndef __MUTEX_PRIVATE 84 85 struct kmutex { 86 uintptr_t mtx_pad1; 87 uint32_t mtx_pad2; 88 }; 89 90 #else /* __MUTEX_PRIVATE */ 91 92 struct kmutex { 93 union { 94 /* Adaptive mutex */ 95 volatile uintptr_t mtxu_owner; /* 0-3 */ 96 __cpu_simple_lock_t mtxu_interlock; /* 0 */ 97 98 /* Spin mutex. */ 99 struct { 100 uint8_t mtxs_dummy; /* 0 */ 101 uint8_t mtxs_unused1; /* 1 */ 102 ipl_cookie_t mtxs_ipl; /* 2 */ 103 uint8_t mtxs_unused2; /* 3 */ 104 } s; 105 } u; 106 __cpu_simple_lock_t mtx_lock; /* 4 */ 107 uint8_t mtx_dodebug; /* 5 */ 108 uint8_t mtx_isspin; /* 6 */ 109 uint8_t mtx_pad[1]; /* 7 */ 110 }; 111 112 #define __HAVE_MUTEX_STUBS 1 113 #if 0 /* does not work for MP yet */ 114 #define __HAVE_SPIN_MUTEX_STUBS 1 115 #endif 116 117 #define mtx_owner u.mtxu_owner 118 #define mtx_interlock u.mtxu_interlock 119 #define mtx_dummy u.s.mtxs_dummy 120 #define mtx_ipl u.s.mtxs_ipl 121 122 static inline uintptr_t 123 MUTEX_OWNER(uintptr_t owner) 124 { 125 return owner << 5; 126 } 127 128 static inline int 129 MUTEX_OWNED(uintptr_t owner) 130 { 131 return owner != 0; 132 } 133 134 static inline int 135 MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner) 136 { 137 (void)__cpu_simple_lock_try(&mtx->mtx_lock); 138 return mtx->mtx_owner != 0; 139 } 140 141 static inline int 142 MUTEX_HAS_WAITERS(volatile kmutex_t *mtx) 143 { 144 if (mtx->mtx_owner == 0) 145 return 0; 146 return mtx->mtx_lock == __SIMPLELOCK_LOCKED; 147 } 148 149 static inline void 150 MUTEX_INITIALIZE_SPIN(kmutex_t *mtx, bool dodebug, int ipl) 151 { 152 mtx->mtx_dodebug = dodebug; 153 mtx->mtx_isspin = 1; 154 mtx->mtx_ipl = makeiplcookie(ipl); 155 mtx->mtx_interlock = __SIMPLELOCK_LOCKED; 156 __cpu_simple_lock_init(&mtx->mtx_lock); 157 } 158 159 static inline void 160 MUTEX_INITIALIZE_ADAPTIVE(kmutex_t *mtx, bool dodebug) 161 { 162 mtx->mtx_dodebug = dodebug; 163 mtx->mtx_isspin = 0; 164 __cpu_simple_lock_init(&mtx->mtx_lock); 165 } 166 167 static inline void 168 MUTEX_DESTROY(kmutex_t *mtx) 169 { 170 mtx->mtx_owner = (uintptr_t)-1L; 171 } 172 173 static inline bool 174 MUTEX_DEBUG_P(kmutex_t *mtx) 175 { 176 return mtx->mtx_dodebug != 0; 177 } 178 179 static inline int 180 MUTEX_SPIN_P(volatile kmutex_t *mtx) 181 { 182 return mtx->mtx_isspin != 0; 183 } 184 185 static inline int 186 MUTEX_ADAPTIVE_P(volatile kmutex_t *mtx) 187 { 188 return mtx->mtx_isspin == 0; 189 } 190 191 static inline int 192 MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread) 193 { 194 if (!__cpu_simple_lock_try(&mtx->mtx_interlock)) 195 return 0; 196 mtx->mtx_owner = (curthread >> 5) | 0xf8000000; 197 return 1; 198 } 199 200 static inline void 201 MUTEX_RELEASE(kmutex_t *mtx) 202 { 203 mtx->mtx_owner = 0; 204 __cpu_simple_unlock(&mtx->mtx_lock); 205 } 206 207 static inline void 208 MUTEX_CLEAR_WAITERS(kmutex_t *mtx) 209 { 210 __cpu_simple_unlock(&mtx->mtx_lock); 211 } 212 213 #endif /* __MUTEX_PRIVATE */ 214 215 #endif /* _SPARC_MUTEX_H_ */ 216