1 /*-
2 * Copyright (c) 2014 Mateusz Guzik <mjg@FreeBSD.org>
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
14 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
16 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
17 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
18 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
19 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
20 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
21 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
22 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
23 * SUCH DAMAGE.
24 */
25
26 #ifndef _SYS_SEQC_H_
27 #define _SYS_SEQC_H_
28
29 #ifdef _KERNEL
30 #include <sys/systm.h>
31 #endif
32 #include <sys/types.h>
33
34 /*
35 * seqc_t may be included in structs visible to userspace
36 */
37 #include <sys/_seqc.h>
38
39 #ifdef _KERNEL
40
41 /* A hack to get MPASS macro */
42 #include <sys/lock.h>
43
44 #include <machine/cpu.h>
45
46 #define SEQC_MOD 1
47
48 /*
49 * Predicts from inline functions are not honored by clang.
50 */
51 #define seqc_in_modify(seqc) ({ \
52 seqc_t __seqc = (seqc); \
53 \
54 __predict_false(__seqc & SEQC_MOD); \
55 })
56
57 static __inline void
seqc_write_begin(seqc_t * seqcp)58 seqc_write_begin(seqc_t *seqcp)
59 {
60
61 critical_enter();
62 MPASS(!seqc_in_modify(*seqcp));
63 *seqcp += SEQC_MOD;
64 atomic_thread_fence_rel();
65 }
66
67 static __inline void
seqc_write_end(seqc_t * seqcp)68 seqc_write_end(seqc_t *seqcp)
69 {
70
71 atomic_thread_fence_rel();
72 *seqcp += SEQC_MOD;
73 MPASS(!seqc_in_modify(*seqcp));
74 critical_exit();
75 }
76
77 static __inline seqc_t
seqc_read_any(const seqc_t * seqcp)78 seqc_read_any(const seqc_t *seqcp)
79 {
80
81 return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)));
82 }
83
84 static __inline seqc_t
seqc_read_notmodify(const seqc_t * seqcp)85 seqc_read_notmodify(const seqc_t *seqcp)
86 {
87
88 return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)) & ~SEQC_MOD);
89 }
90
91 static __inline seqc_t
seqc_read(const seqc_t * seqcp)92 seqc_read(const seqc_t *seqcp)
93 {
94 seqc_t ret;
95
96 for (;;) {
97 ret = seqc_read_any(seqcp);
98 if (seqc_in_modify(ret)) {
99 cpu_spinwait();
100 continue;
101 }
102 break;
103 }
104
105 return (ret);
106 }
107
108 #define seqc_consistent_no_fence(seqcp, oldseqc)({ \
109 const seqc_t *__seqcp = (seqcp); \
110 seqc_t __oldseqc = (oldseqc); \
111 \
112 MPASS(!(seqc_in_modify(__oldseqc))); \
113 __predict_true(*__seqcp == __oldseqc); \
114 })
115
116 #define seqc_consistent(seqcp, oldseqc) ({ \
117 atomic_thread_fence_acq(); \
118 seqc_consistent_no_fence(seqcp, oldseqc); \
119 })
120
121 /*
122 * Variant which does not critical enter/exit.
123 */
124 static __inline void
seqc_sleepable_write_begin(seqc_t * seqcp)125 seqc_sleepable_write_begin(seqc_t *seqcp)
126 {
127
128 MPASS(!seqc_in_modify(*seqcp));
129 *seqcp += SEQC_MOD;
130 atomic_thread_fence_rel();
131 }
132
133 static __inline void
seqc_sleepable_write_end(seqc_t * seqcp)134 seqc_sleepable_write_end(seqc_t *seqcp)
135 {
136
137 atomic_thread_fence_rel();
138 *seqcp += SEQC_MOD;
139 MPASS(!seqc_in_modify(*seqcp));
140 }
141
142 #endif /* _KERNEL */
143 #endif /* _SYS_SEQC_H_ */
144