Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
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_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
90static inline void u64_stats_set(u64_stats_t *p, u64 val)
91{
92 local64_set(&p->v, val);
93}
94
95static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
96{
97 local64_add(val, &p->v);
98}
99
100static inline void u64_stats_sub(u64_stats_t *p, s64 val)
101{
102 local64_sub(val, &p->v);
103}
104
105static inline void u64_stats_inc(u64_stats_t *p)
106{
107 local64_inc(&p->v);
108}
109
110static inline void u64_stats_init(struct u64_stats_sync *syncp) { }
111static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) { }
112static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) { }
113static inline unsigned long __u64_stats_irqsave(void) { return 0; }
114static inline void __u64_stats_irqrestore(unsigned long flags) { }
115static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
116{
117 return 0;
118}
119static 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
128typedef struct {
129 u64 v;
130} u64_stats_t;
131
132static inline u64 u64_stats_read(const u64_stats_t *p)
133{
134 return p->v;
135}
136
137static 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
143static inline void u64_stats_set(u64_stats_t *p, u64 val)
144{
145 p->v = val;
146}
147
148static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
149{
150 p->v += val;
151}
152
153static inline void u64_stats_sub(u64_stats_t *p, s64 val)
154{
155 p->v -= val;
156}
157
158static 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
169static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp)
170{
171 preempt_disable_nested();
172 write_seqcount_begin(&syncp->seq);
173}
174
175static inline void __u64_stats_update_end(struct u64_stats_sync *syncp)
176{
177 write_seqcount_end(&syncp->seq);
178 preempt_enable_nested();
179}
180
181static inline unsigned long __u64_stats_irqsave(void)
182{
183 unsigned long flags;
184
185 local_irq_save(flags);
186 return flags;
187}
188
189static inline void __u64_stats_irqrestore(unsigned long flags)
190{
191 local_irq_restore(flags);
192}
193
194static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
195{
196 return read_seqcount_begin(&syncp->seq);
197}
198
199static 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
206static inline void u64_stats_update_begin(struct u64_stats_sync *syncp)
207{
208 __u64_stats_update_begin(syncp);
209}
210
211static inline void u64_stats_update_end(struct u64_stats_sync *syncp)
212{
213 __u64_stats_update_end(syncp);
214}
215
216static 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
224static 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
231static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
232{
233 return __u64_stats_fetch_begin(syncp);
234}
235
236static 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 */