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 64struct 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 73typedef struct { 74 local64_t v; 75} u64_stats_t ; 76 77static inline u64 u64_stats_read(const u64_stats_t *p) 78{ 79 return local64_read(&p->v); 80} 81 82static inline void u64_stats_set(u64_stats_t *p, u64 val) 83{ 84 local64_set(&p->v, val); 85} 86 87static inline void u64_stats_add(u64_stats_t *p, unsigned long val) 88{ 89 local64_add(val, &p->v); 90} 91 92static inline void u64_stats_inc(u64_stats_t *p) 93{ 94 local64_inc(&p->v); 95} 96 97static inline void u64_stats_init(struct u64_stats_sync *syncp) { } 98static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) { } 99static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) { } 100static inline unsigned long __u64_stats_irqsave(void) { return 0; } 101static inline void __u64_stats_irqrestore(unsigned long flags) { } 102static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) 103{ 104 return 0; 105} 106static 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 114typedef struct { 115 u64 v; 116} u64_stats_t; 117 118static inline u64 u64_stats_read(const u64_stats_t *p) 119{ 120 return p->v; 121} 122 123static inline void u64_stats_set(u64_stats_t *p, u64 val) 124{ 125 p->v = val; 126} 127 128static inline void u64_stats_add(u64_stats_t *p, unsigned long val) 129{ 130 p->v += val; 131} 132 133static inline void u64_stats_inc(u64_stats_t *p) 134{ 135 p->v++; 136} 137 138static inline void u64_stats_init(struct u64_stats_sync *syncp) 139{ 140 seqcount_init(&syncp->seq); 141} 142 143static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) 144{ 145 preempt_disable_nested(); 146 write_seqcount_begin(&syncp->seq); 147} 148 149static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) 150{ 151 write_seqcount_end(&syncp->seq); 152 preempt_enable_nested(); 153} 154 155static inline unsigned long __u64_stats_irqsave(void) 156{ 157 unsigned long flags; 158 159 local_irq_save(flags); 160 return flags; 161} 162 163static inline void __u64_stats_irqrestore(unsigned long flags) 164{ 165 local_irq_restore(flags); 166} 167 168static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) 169{ 170 return read_seqcount_begin(&syncp->seq); 171} 172 173static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp, 174 unsigned int start) 175{ 176 return read_seqcount_retry(&syncp->seq, start); 177} 178#endif /* !64 bit */ 179 180static inline void u64_stats_update_begin(struct u64_stats_sync *syncp) 181{ 182 __u64_stats_update_begin(syncp); 183} 184 185static inline void u64_stats_update_end(struct u64_stats_sync *syncp) 186{ 187 __u64_stats_update_end(syncp); 188} 189 190static inline unsigned long u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp) 191{ 192 unsigned long flags = __u64_stats_irqsave(); 193 194 __u64_stats_update_begin(syncp); 195 return flags; 196} 197 198static inline void u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp, 199 unsigned long flags) 200{ 201 __u64_stats_update_end(syncp); 202 __u64_stats_irqrestore(flags); 203} 204 205static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp) 206{ 207 return __u64_stats_fetch_begin(syncp); 208} 209 210static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp, 211 unsigned int start) 212{ 213 return __u64_stats_fetch_retry(syncp, start); 214} 215 216#endif /* _LINUX_U64_STATS_SYNC_H */ 217