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 * $FreeBSD$ 26 */ 27 28 #ifndef _SYS_SEQC_H_ 29 #define _SYS_SEQC_H_ 30 31 #ifdef _KERNEL 32 #include <sys/systm.h> 33 #endif 34 #include <sys/types.h> 35 36 /* 37 * seqc_t may be included in structs visible to userspace 38 */ 39 #include <sys/_seqc.h> 40 41 #ifdef _KERNEL 42 43 /* A hack to get MPASS macro */ 44 #include <sys/lock.h> 45 46 #include <machine/cpu.h> 47 48 #define SEQC_MOD 1 49 50 /* 51 * Predicts from inline functions are not honored by clang. 52 */ 53 #define seqc_in_modify(seqc) ({ \ 54 seqc_t __seqc = (seqc); \ 55 \ 56 __predict_false(__seqc & SEQC_MOD); \ 57 }) 58 59 static __inline void 60 seqc_write_begin(seqc_t *seqcp) 61 { 62 63 critical_enter(); 64 MPASS(!seqc_in_modify(*seqcp)); 65 *seqcp += SEQC_MOD; 66 atomic_thread_fence_rel(); 67 } 68 69 static __inline void 70 seqc_write_end(seqc_t *seqcp) 71 { 72 73 atomic_thread_fence_rel(); 74 *seqcp += SEQC_MOD; 75 MPASS(!seqc_in_modify(*seqcp)); 76 critical_exit(); 77 } 78 79 static __inline seqc_t 80 seqc_read_any(const seqc_t *seqcp) 81 { 82 83 return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp))); 84 } 85 86 static __inline seqc_t 87 seqc_read_notmodify(const seqc_t *seqcp) 88 { 89 90 return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)) & ~SEQC_MOD); 91 } 92 93 static __inline seqc_t 94 seqc_read(const seqc_t *seqcp) 95 { 96 seqc_t ret; 97 98 for (;;) { 99 ret = seqc_read_any(seqcp); 100 if (seqc_in_modify(ret)) { 101 cpu_spinwait(); 102 continue; 103 } 104 break; 105 } 106 107 return (ret); 108 } 109 110 #define seqc_consistent_nomb(seqcp, oldseqc) ({ \ 111 const seqc_t *__seqcp = (seqcp); \ 112 seqc_t __oldseqc = (oldseqc); \ 113 \ 114 MPASS(!(seqc_in_modify(__oldseqc))); \ 115 __predict_true(*__seqcp == __oldseqc); \ 116 }) 117 118 #define seqc_consistent(seqcp, oldseqc) ({ \ 119 atomic_thread_fence_acq(); \ 120 seqc_consistent_nomb(seqcp, oldseqc); \ 121 }) 122 123 /* 124 * Variant which does not critical enter/exit. 125 */ 126 static __inline void 127 seqc_sleepable_write_begin(seqc_t *seqcp) 128 { 129 130 MPASS(!seqc_in_modify(*seqcp)); 131 *seqcp += SEQC_MOD; 132 atomic_thread_fence_rel(); 133 } 134 135 static __inline void 136 seqc_sleepable_write_end(seqc_t *seqcp) 137 { 138 139 atomic_thread_fence_rel(); 140 *seqcp += SEQC_MOD; 141 MPASS(!seqc_in_modify(*seqcp)); 142 } 143 144 #endif /* _KERNEL */ 145 #endif /* _SYS_SEQC_H_ */ 146