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 /* 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 & 1); \ 55 }) 56 57 static __inline void 58 seqc_write_begin(seqc_t *seqcp) 59 { 60 61 critical_enter(); 62 MPASS(!seqc_in_modify(*seqcp)); 63 *seqcp += 1; 64 atomic_thread_fence_rel(); 65 } 66 67 static __inline void 68 seqc_write_end(seqc_t *seqcp) 69 { 70 71 atomic_thread_fence_rel(); 72 *seqcp += 1; 73 MPASS(!seqc_in_modify(*seqcp)); 74 critical_exit(); 75 } 76 77 static __inline seqc_t 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 85 seqc_read_notmodify(const seqc_t *seqcp) 86 { 87 88 return (atomic_load_acq_int(__DECONST(seqc_t *, seqcp)) & ~1); 89 } 90 91 static __inline seqc_t 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_nomb(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_nomb(seqcp, oldseqc); \ 119 }) 120 121 /* 122 * Variant which does not critical enter/exit. 123 */ 124 static __inline void 125 seqc_sleepable_write_begin(seqc_t *seqcp) 126 { 127 128 MPASS(!seqc_in_modify(*seqcp)); 129 *seqcp += 1; 130 atomic_thread_fence_rel(); 131 } 132 133 static __inline void 134 seqc_sleepable_write_end(seqc_t *seqcp) 135 { 136 137 atomic_thread_fence_rel(); 138 *seqcp += 1; 139 MPASS(!seqc_in_modify(*seqcp)); 140 } 141 142 #endif /* _KERNEL */ 143 #endif /* _SYS_SEQC_H_ */ 144