1 /* $NetBSD: seqlock.h,v 1.5 2021/12/19 01:50:10 riastradh Exp $ */ 2 3 /*- 4 * Copyright (c) 2018 The NetBSD Foundation, Inc. 5 * All rights reserved. 6 * 7 * This code is derived from software contributed to The NetBSD Foundation 8 * by Taylor R. Campbell. 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 * 19 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 20 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 21 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 22 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 23 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 24 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 25 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 26 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 27 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 28 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 29 * POSSIBILITY OF SUCH DAMAGE. 30 */ 31 32 #ifndef _LINUX_SEQLOCK_H_ 33 #define _LINUX_SEQLOCK_H_ 34 35 #include <sys/types.h> 36 #include <sys/atomic.h> 37 #include <sys/lock.h> 38 39 #include <lib/libkern/libkern.h> 40 41 struct seqcount { 42 unsigned sqc_gen; 43 }; 44 45 typedef struct seqcount seqcount_t; 46 47 static inline void 48 seqcount_init(struct seqcount *seqcount) 49 { 50 51 seqcount->sqc_gen = 0; 52 } 53 54 static inline void 55 seqcount_destroy(struct seqcount *seqcount) 56 { 57 58 KASSERT((seqcount->sqc_gen & 1) == 0); 59 seqcount->sqc_gen = -1; 60 } 61 62 static inline void 63 write_seqcount_begin(struct seqcount *seqcount) 64 { 65 66 KASSERT((seqcount->sqc_gen & 1) == 0); 67 seqcount->sqc_gen |= 1; 68 membar_producer(); 69 } 70 71 static inline void 72 write_seqcount_end(struct seqcount *seqcount) 73 { 74 75 KASSERT((seqcount->sqc_gen & 1) == 1); 76 membar_producer(); 77 seqcount->sqc_gen |= 1; /* paranoia */ 78 seqcount->sqc_gen++; 79 } 80 81 static inline unsigned 82 __read_seqcount_begin(const struct seqcount *seqcount) 83 { 84 unsigned gen; 85 86 while (__predict_false((gen = seqcount->sqc_gen) & 1)) 87 SPINLOCK_BACKOFF_HOOK; 88 __insn_barrier(); 89 90 return gen; 91 } 92 93 static inline bool 94 __read_seqcount_retry(const struct seqcount *seqcount, unsigned gen) 95 { 96 97 __insn_barrier(); 98 return __predict_false(seqcount->sqc_gen != gen); 99 } 100 101 static inline unsigned 102 read_seqcount_begin(const struct seqcount *seqcount) 103 { 104 unsigned gen; 105 106 gen = __read_seqcount_begin(seqcount); 107 membar_consumer(); 108 109 return gen; 110 } 111 112 static inline bool 113 read_seqcount_retry(const struct seqcount *seqcount, unsigned gen) 114 { 115 116 membar_consumer(); 117 return __read_seqcount_retry(seqcount, gen); 118 } 119 120 static inline unsigned 121 raw_read_seqcount(const struct seqcount *seqcount) 122 { 123 unsigned gen; 124 125 gen = seqcount->sqc_gen; 126 membar_consumer(); 127 128 return gen; 129 } 130 131 struct seqlock { 132 kmutex_t sql_lock; 133 struct seqcount sql_count; 134 }; 135 136 typedef struct seqlock seqlock_t; 137 138 static inline void 139 seqlock_init(struct seqlock *seqlock) 140 { 141 142 mutex_init(&seqlock->sql_lock, MUTEX_DEFAULT, IPL_VM); 143 seqcount_init(&seqlock->sql_count); 144 } 145 146 static inline void 147 seqlock_destroy(struct seqlock *seqlock) 148 { 149 150 seqcount_destroy(&seqlock->sql_count); 151 mutex_destroy(&seqlock->sql_lock); 152 } 153 154 static inline void 155 write_seqlock(struct seqlock *seqlock) 156 { 157 158 mutex_spin_enter(&seqlock->sql_lock); 159 write_seqcount_begin(&seqlock->sql_count); 160 } 161 162 static inline void 163 write_sequnlock(struct seqlock *seqlock) 164 { 165 166 write_seqcount_end(&seqlock->sql_count); 167 mutex_spin_exit(&seqlock->sql_lock); 168 } 169 170 #define write_seqlock_irqsave(SEQLOCK, FLAGS) do { \ 171 (FLAGS) = (unsigned long)splvm(); \ 172 write_seqlock(SEQLOCK); \ 173 } while (0) 174 175 #define write_sequnlock_irqrestore(SEQLOCK, FLAGS) do { \ 176 write_sequnlock(SEQLOCK); \ 177 splx((int)(FLAGS)); \ 178 } while (0) 179 180 static inline unsigned 181 read_seqbegin(const struct seqlock *seqlock) 182 { 183 184 return read_seqcount_begin(&seqlock->sql_count); 185 } 186 187 static inline bool 188 read_seqretry(const struct seqlock *seqlock, unsigned gen) 189 { 190 191 return read_seqcount_retry(&seqlock->sql_count, gen); 192 } 193 194 #endif /* _LINUX_SEQLOCK_H_ */ 195