Home | History | Annotate | Line # | Download | only in linux 
      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