| 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_set(u64_stats_t *p, u64 val) |
| 83 | { |
| 84 | local64_set(&p->v, val); |
| 85 | } |
| 86 | |
| 87 | static inline void u64_stats_add(u64_stats_t *p, unsigned long val) |
| 88 | { |
| 89 | local64_add(val, &p->v); |
| 90 | } |
| 91 | |
| 92 | static inline void u64_stats_inc(u64_stats_t *p) |
| 93 | { |
| 94 | local64_inc(&p->v); |
| 95 | } |
| 96 | |
| 97 | static inline void u64_stats_init(struct u64_stats_sync *syncp) { } |
| 98 | static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) { } |
| 99 | static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) { } |
| 100 | static inline unsigned long __u64_stats_irqsave(void) { return 0; } |
| 101 | static inline void __u64_stats_irqrestore(unsigned long flags) { } |
| 102 | static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) |
| 103 | { |
| 104 | return 0; |
| 105 | } |
| 106 | static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp, |
| 107 | unsigned int start) |
| 108 | { |
| 109 | return false; |
| 110 | } |
| 111 | |
| 112 | #else /* 64 bit */ |
| 113 | |
| 114 | typedef struct { |
| 115 | u64 v; |
| 116 | } u64_stats_t; |
| 117 | |
| 118 | static inline u64 u64_stats_read(const u64_stats_t *p) |
| 119 | { |
| 120 | return p->v; |
| 121 | } |
| 122 | |
| 123 | static inline void u64_stats_set(u64_stats_t *p, u64 val) |
| 124 | { |
| 125 | p->v = val; |
| 126 | } |
| 127 | |
| 128 | static inline void u64_stats_add(u64_stats_t *p, unsigned long val) |
| 129 | { |
| 130 | p->v += val; |
| 131 | } |
| 132 | |
| 133 | static inline void u64_stats_inc(u64_stats_t *p) |
| 134 | { |
| 135 | p->v++; |
| 136 | } |
| 137 | |
| 138 | #define u64_stats_init(syncp) \ |
| 139 | do { \ |
| 140 | struct u64_stats_sync *__s = (syncp); \ |
| 141 | seqcount_init(&__s->seq); \ |
| 142 | } while (0) |
| 143 | |
| 144 | static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) |
| 145 | { |
| 146 | preempt_disable_nested(); |
| 147 | write_seqcount_begin(&syncp->seq); |
| 148 | } |
| 149 | |
| 150 | static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) |
| 151 | { |
| 152 | write_seqcount_end(&syncp->seq); |
| 153 | preempt_enable_nested(); |
| 154 | } |
| 155 | |
| 156 | static inline unsigned long __u64_stats_irqsave(void) |
| 157 | { |
| 158 | unsigned long flags; |
| 159 | |
| 160 | local_irq_save(flags); |
| 161 | return flags; |
| 162 | } |
| 163 | |
| 164 | static inline void __u64_stats_irqrestore(unsigned long flags) |
| 165 | { |
| 166 | local_irq_restore(flags); |
| 167 | } |
| 168 | |
| 169 | static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) |
| 170 | { |
| 171 | return read_seqcount_begin(&syncp->seq); |
| 172 | } |
| 173 | |
| 174 | static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp, |
| 175 | unsigned int start) |
| 176 | { |
| 177 | return read_seqcount_retry(&syncp->seq, start); |
| 178 | } |
| 179 | #endif /* !64 bit */ |
| 180 | |
| 181 | static inline void u64_stats_update_begin(struct u64_stats_sync *syncp) |
| 182 | { |
| 183 | __u64_stats_update_begin(syncp); |
| 184 | } |
| 185 | |
| 186 | static inline void u64_stats_update_end(struct u64_stats_sync *syncp) |
| 187 | { |
| 188 | __u64_stats_update_end(syncp); |
| 189 | } |
| 190 | |
| 191 | static inline unsigned long u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp) |
| 192 | { |
| 193 | unsigned long flags = __u64_stats_irqsave(); |
| 194 | |
| 195 | __u64_stats_update_begin(syncp); |
| 196 | return flags; |
| 197 | } |
| 198 | |
| 199 | static inline void u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp, |
| 200 | unsigned long flags) |
| 201 | { |
| 202 | __u64_stats_update_end(syncp); |
| 203 | __u64_stats_irqrestore(flags); |
| 204 | } |
| 205 | |
| 206 | static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp) |
| 207 | { |
| 208 | return __u64_stats_fetch_begin(syncp); |
| 209 | } |
| 210 | |
| 211 | static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp, |
| 212 | unsigned int start) |
| 213 | { |
| 214 | return __u64_stats_fetch_retry(syncp, start); |
| 215 | } |
| 216 | |
| 217 | #endif /* _LINUX_U64_STATS_SYNC_H */ |