1 /* SPDX-License-Identifier: GPL-2.0 */ 2 #ifndef _LINUX_U64_STATS_SYNC_H 3 #define _LINUX_U64_STATS_SYNC_H 4 5 /* 6 * Protect against 64-bit values tearing on 32-bit architectures. This is 7 * typically used for statistics read/update in different subsystems. 8 * 9 * Key points : 10 * 11 * - Use a seqcount on 32-bit 12 * - The whole thing is a no-op on 64-bit architectures. 13 * 14 * Usage constraints: 15 * 16 * 1) Write side must ensure mutual exclusion, or one seqcount update could 17 * be lost, thus blocking readers forever. 18 * 19 * 2) Write side must disable preemption, or a seqcount reader can preempt the 20 * writer and also spin forever. 21 * 22 * 3) Write side must use the _irqsave() variant if other writers, or a reader, 23 * can be invoked from an IRQ context. On 64bit systems this variant does not 24 * disable interrupts. 25 * 26 * 4) If reader fetches several counters, there is no guarantee the whole values 27 * are consistent w.r.t. each other (remember point #2: seqcounts are not 28 * used for 64bit architectures). 29 * 30 * 5) Readers are allowed to sleep or be preempted/interrupted: they perform 31 * pure reads. 32 * 33 * Usage : 34 * 35 * Stats producer (writer) should use following template granted it already got 36 * an exclusive access to counters (a lock is already taken, or per cpu 37 * data is used [in a non preemptable context]) 38 * 39 * spin_lock_bh(...) or other synchronization to get exclusive access 40 * ... 41 * u64_stats_update_begin(&stats->syncp); 42 * u64_stats_add(&stats->bytes64, len); // non atomic operation 43 * u64_stats_inc(&stats->packets64); // non atomic operation 44 * u64_stats_update_end(&stats->syncp); 45 * 46 * While a consumer (reader) should use following template to get consistent 47 * snapshot for each variable (but no guarantee on several ones) 48 * 49 * u64 tbytes, tpackets; 50 * unsigned int start; 51 * 52 * do { 53 * start = u64_stats_fetch_begin(&stats->syncp); 54 * tbytes = u64_stats_read(&stats->bytes64); // non atomic operation 55 * tpackets = u64_stats_read(&stats->packets64); // non atomic operation 56 * } while (u64_stats_fetch_retry(&stats->syncp, start)); 57 * 58 * 59 * Example of use in drivers/net/loopback.c, using per_cpu containers, 60 * in BH disabled context. 61 */ 62 #include <linux/seqlock.h> 63 64 struct u64_stats_sync { 65 #if BITS_PER_LONG == 32 66 seqcount_t seq; 67 #endif 68 }; 69 70 #if BITS_PER_LONG == 64 71 #include <asm/local64.h> 72 73 typedef struct { 74 local64_t v; 75 } u64_stats_t ; 76 77 static inline u64 u64_stats_read(const u64_stats_t *p) 78 { 79 return local64_read(&p->v); 80 } 81 82 static inline void *u64_stats_copy(void *dst, const void *src, size_t len) 83 { 84 BUILD_BUG_ON(len % sizeof(u64_stats_t)); 85 for (size_t i = 0; i < len / sizeof(u64_stats_t); i++) 86 ((u64 *)dst)[i] = local64_read(&((local64_t *)src)[i]); 87 return dst; 88 } 89 90 static inline void u64_stats_set(u64_stats_t *p, u64 val) 91 { 92 local64_set(&p->v, val); 93 } 94 95 static inline void u64_stats_add(u64_stats_t *p, unsigned long val) 96 { 97 local64_add(val, &p->v); 98 } 99 100 static inline void u64_stats_sub(u64_stats_t *p, s64 val) 101 { 102 local64_sub(val, &p->v); 103 } 104 105 static inline void u64_stats_inc(u64_stats_t *p) 106 { 107 local64_inc(&p->v); 108 } 109 110 static inline void u64_stats_init(struct u64_stats_sync *syncp) { } 111 static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) { } 112 static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) { } 113 static inline unsigned long __u64_stats_irqsave(void) { return 0; } 114 static inline void __u64_stats_irqrestore(unsigned long flags) { } 115 static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) 116 { 117 return 0; 118 } 119 static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp, 120 unsigned int start) 121 { 122 return false; 123 } 124 125 #else /* 64 bit */ 126 #include <linux/string.h> 127 128 typedef struct { 129 u64 v; 130 } u64_stats_t; 131 132 static inline u64 u64_stats_read(const u64_stats_t *p) 133 { 134 return p->v; 135 } 136 137 static inline void *u64_stats_copy(void *dst, const void *src, size_t len) 138 { 139 BUILD_BUG_ON(len % sizeof(u64_stats_t)); 140 return memcpy(dst, src, len); 141 } 142 143 static inline void u64_stats_set(u64_stats_t *p, u64 val) 144 { 145 p->v = val; 146 } 147 148 static inline void u64_stats_add(u64_stats_t *p, unsigned long val) 149 { 150 p->v += val; 151 } 152 153 static inline void u64_stats_sub(u64_stats_t *p, s64 val) 154 { 155 p->v -= val; 156 } 157 158 static inline void u64_stats_inc(u64_stats_t *p) 159 { 160 p->v++; 161 } 162 163 #define u64_stats_init(syncp) \ 164 do { \ 165 struct u64_stats_sync *__s = (syncp); \ 166 seqcount_init(&__s->seq); \ 167 } while (0) 168 169 static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) 170 { 171 preempt_disable_nested(); 172 write_seqcount_begin(&syncp->seq); 173 } 174 175 static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) 176 { 177 write_seqcount_end(&syncp->seq); 178 preempt_enable_nested(); 179 } 180 181 static inline unsigned long __u64_stats_irqsave(void) 182 { 183 unsigned long flags; 184 185 local_irq_save(flags); 186 return flags; 187 } 188 189 static inline void __u64_stats_irqrestore(unsigned long flags) 190 { 191 local_irq_restore(flags); 192 } 193 194 static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) 195 { 196 return read_seqcount_begin(&syncp->seq); 197 } 198 199 static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp, 200 unsigned int start) 201 { 202 return read_seqcount_retry(&syncp->seq, start); 203 } 204 #endif /* !64 bit */ 205 206 static inline void u64_stats_update_begin(struct u64_stats_sync *syncp) 207 { 208 __u64_stats_update_begin(syncp); 209 } 210 211 static inline void u64_stats_update_end(struct u64_stats_sync *syncp) 212 { 213 __u64_stats_update_end(syncp); 214 } 215 216 static inline unsigned long u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp) 217 { 218 unsigned long flags = __u64_stats_irqsave(); 219 220 __u64_stats_update_begin(syncp); 221 return flags; 222 } 223 224 static inline void u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp, 225 unsigned long flags) 226 { 227 __u64_stats_update_end(syncp); 228 __u64_stats_irqrestore(flags); 229 } 230 231 static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp) 232 { 233 return __u64_stats_fetch_begin(syncp); 234 } 235 236 static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp, 237 unsigned int start) 238 { 239 return __u64_stats_fetch_retry(syncp, start); 240 } 241 242 #endif /* _LINUX_U64_STATS_SYNC_H */ 243