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 | static inline void u64_stats_init(struct u64_stats_sync *syncp) |
139 | { |
140 | seqcount_init(&syncp->seq); |
141 | } |
142 | |
143 | static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) |
144 | { |
145 | preempt_disable_nested(); |
146 | write_seqcount_begin(&syncp->seq); |
147 | } |
148 | |
149 | static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) |
150 | { |
151 | write_seqcount_end(&syncp->seq); |
152 | preempt_enable_nested(); |
153 | } |
154 | |
155 | static inline unsigned long __u64_stats_irqsave(void) |
156 | { |
157 | unsigned long flags; |
158 | |
159 | local_irq_save(flags); |
160 | return flags; |
161 | } |
162 | |
163 | static inline void __u64_stats_irqrestore(unsigned long flags) |
164 | { |
165 | local_irq_restore(flags); |
166 | } |
167 | |
168 | static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp) |
169 | { |
170 | return read_seqcount_begin(&syncp->seq); |
171 | } |
172 | |
173 | static 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 | |
180 | static inline void u64_stats_update_begin(struct u64_stats_sync *syncp) |
181 | { |
182 | __u64_stats_update_begin(syncp); |
183 | } |
184 | |
185 | static inline void u64_stats_update_end(struct u64_stats_sync *syncp) |
186 | { |
187 | __u64_stats_update_end(syncp); |
188 | } |
189 | |
190 | static 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 | |
198 | static 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 | |
205 | static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp) |
206 | { |
207 | return __u64_stats_fetch_begin(syncp); |
208 | } |
209 | |
210 | static 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 | |