1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_U64_STATS_SYNC_H
3 #define _LINUX_U64_STATS_SYNC_H
6 * Protect against 64-bit values tearing on 32-bit architectures. This is
7 * typically used for statistics read/update in different subsystems.
11 * - Use a seqcount on 32-bit
12 * - The whole thing is a no-op on 64-bit architectures.
16 * 1) Write side must ensure mutual exclusion, or one seqcount update could
17 * be lost, thus blocking readers forever.
19 * 2) Write side must disable preemption, or a seqcount reader can preempt the
20 * writer and also spin forever.
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
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).
30 * 5) Readers are allowed to sleep or be preempted/interrupted: they perform
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])
39 * spin_lock_bh(...) or other synchronization to get exclusive access
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);
46 * While a consumer (reader) should use following template to get consistent
47 * snapshot for each variable (but no guarantee on several ones)
49 * u64 tbytes, tpackets;
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));
59 * Example of use in drivers/net/loopback.c, using per_cpu containers,
60 * in BH disabled context.
62 #include <linux/seqlock.h>
64 struct u64_stats_sync {
65 #if BITS_PER_LONG == 32
70 #if BITS_PER_LONG == 64
71 #include <asm/local64.h>
77 static inline u64 u64_stats_read(const u64_stats_t *p)
79 return local64_read(&p->v);
82 static inline void u64_stats_set(u64_stats_t *p, u64 val)
84 local64_set(&p->v, val);
87 static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
89 local64_add(val, &p->v);
92 static inline void u64_stats_inc(u64_stats_t *p)
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)
106 static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
118 static inline u64 u64_stats_read(const u64_stats_t *p)
123 static inline void u64_stats_set(u64_stats_t *p, u64 val)
128 static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
133 static inline void u64_stats_inc(u64_stats_t *p)
138 static inline void u64_stats_init(struct u64_stats_sync *syncp)
140 seqcount_init(&syncp->seq);
143 static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp)
145 preempt_disable_nested();
146 write_seqcount_begin(&syncp->seq);
149 static inline void __u64_stats_update_end(struct u64_stats_sync *syncp)
151 write_seqcount_end(&syncp->seq);
152 preempt_enable_nested();
155 static inline unsigned long __u64_stats_irqsave(void)
159 local_irq_save(flags);
163 static inline void __u64_stats_irqrestore(unsigned long flags)
165 local_irq_restore(flags);
168 static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
170 return read_seqcount_begin(&syncp->seq);
173 static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
176 return read_seqcount_retry(&syncp->seq, start);
180 static inline void u64_stats_update_begin(struct u64_stats_sync *syncp)
182 __u64_stats_update_begin(syncp);
185 static inline void u64_stats_update_end(struct u64_stats_sync *syncp)
187 __u64_stats_update_end(syncp);
190 static inline unsigned long u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp)
192 unsigned long flags = __u64_stats_irqsave();
194 __u64_stats_update_begin(syncp);
198 static inline void u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp,
201 __u64_stats_update_end(syncp);
202 __u64_stats_irqrestore(flags);
205 static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
207 return __u64_stats_fetch_begin(syncp);
210 static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
213 return __u64_stats_fetch_retry(syncp, start);
216 /* Obsolete interfaces */
217 static inline unsigned int u64_stats_fetch_begin_irq(const struct u64_stats_sync *syncp)
219 return u64_stats_fetch_begin(syncp);
222 static inline bool u64_stats_fetch_retry_irq(const struct u64_stats_sync *syncp,
225 return u64_stats_fetch_retry(syncp, start);
228 #endif /* _LINUX_U64_STATS_SYNC_H */