1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
|
/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_U64_STATS_SYNC_H
#define _LINUX_U64_STATS_SYNC_H
/*
* Protect against 64-bit values tearing on 32-bit architectures. This is
* typically used for statistics read/update in different subsystems.
*
* Key points :
*
* - Use a seqcount on 32-bit
* - The whole thing is a no-op on 64-bit architectures.
*
* Usage constraints:
*
* 1) Write side must ensure mutual exclusion, or one seqcount update could
* be lost, thus blocking readers forever.
*
* 2) Write side must disable preemption, or a seqcount reader can preempt the
* writer and also spin forever.
*
* 3) Write side must use the _irqsave() variant if other writers, or a reader,
* can be invoked from an IRQ context. On 64bit systems this variant does not
* disable interrupts.
*
* 4) If reader fetches several counters, there is no guarantee the whole values
* are consistent w.r.t. each other (remember point #2: seqcounts are not
* used for 64bit architectures).
*
* 5) Readers are allowed to sleep or be preempted/interrupted: they perform
* pure reads.
*
* Usage :
*
* Stats producer (writer) should use following template granted it already got
* an exclusive access to counters (a lock is already taken, or per cpu
* data is used [in a non preemptable context])
*
* spin_lock_bh(...) or other synchronization to get exclusive access
* ...
* u64_stats_update_begin(&stats->syncp);
* u64_stats_add(&stats->bytes64, len); // non atomic operation
* u64_stats_inc(&stats->packets64); // non atomic operation
* u64_stats_update_end(&stats->syncp);
*
* While a consumer (reader) should use following template to get consistent
* snapshot for each variable (but no guarantee on several ones)
*
* u64 tbytes, tpackets;
* unsigned int start;
*
* do {
* start = u64_stats_fetch_begin(&stats->syncp);
* tbytes = u64_stats_read(&stats->bytes64); // non atomic operation
* tpackets = u64_stats_read(&stats->packets64); // non atomic operation
* } while (u64_stats_fetch_retry(&stats->syncp, start));
*
*
* Example of use in drivers/net/loopback.c, using per_cpu containers,
* in BH disabled context.
*/
#include <linux/seqlock.h>
struct u64_stats_sync {
#if BITS_PER_LONG == 32
seqcount_t seq;
#endif
};
#if BITS_PER_LONG == 64
#include <asm/local64.h>
typedef struct {
local64_t v;
} u64_stats_t ;
static inline u64 u64_stats_read(const u64_stats_t *p)
{
return local64_read(&p->v);
}
static inline void u64_stats_set(u64_stats_t *p, u64 val)
{
local64_set(&p->v, val);
}
static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
{
local64_add(val, &p->v);
}
static inline void u64_stats_inc(u64_stats_t *p)
{
local64_inc(&p->v);
}
static inline void u64_stats_init(struct u64_stats_sync *syncp) { }
static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp) { }
static inline void __u64_stats_update_end(struct u64_stats_sync *syncp) { }
static inline unsigned long __u64_stats_irqsave(void) { return 0; }
static inline void __u64_stats_irqrestore(unsigned long flags) { }
static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
{
return 0;
}
static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
unsigned int start)
{
return false;
}
#else /* 64 bit */
typedef struct {
u64 v;
} u64_stats_t;
static inline u64 u64_stats_read(const u64_stats_t *p)
{
return p->v;
}
static inline void u64_stats_set(u64_stats_t *p, u64 val)
{
p->v = val;
}
static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
{
p->v += val;
}
static inline void u64_stats_inc(u64_stats_t *p)
{
p->v++;
}
#define u64_stats_init(syncp) \
do { \
struct u64_stats_sync *__s = (syncp); \
seqcount_init(&__s->seq); \
} while (0)
static inline void __u64_stats_update_begin(struct u64_stats_sync *syncp)
{
preempt_disable_nested();
write_seqcount_begin(&syncp->seq);
}
static inline void __u64_stats_update_end(struct u64_stats_sync *syncp)
{
write_seqcount_end(&syncp->seq);
preempt_enable_nested();
}
static inline unsigned long __u64_stats_irqsave(void)
{
unsigned long flags;
local_irq_save(flags);
return flags;
}
static inline void __u64_stats_irqrestore(unsigned long flags)
{
local_irq_restore(flags);
}
static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
{
return read_seqcount_begin(&syncp->seq);
}
static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
unsigned int start)
{
return read_seqcount_retry(&syncp->seq, start);
}
#endif /* !64 bit */
static inline void u64_stats_update_begin(struct u64_stats_sync *syncp)
{
__u64_stats_update_begin(syncp);
}
static inline void u64_stats_update_end(struct u64_stats_sync *syncp)
{
__u64_stats_update_end(syncp);
}
static inline unsigned long u64_stats_update_begin_irqsave(struct u64_stats_sync *syncp)
{
unsigned long flags = __u64_stats_irqsave();
__u64_stats_update_begin(syncp);
return flags;
}
static inline void u64_stats_update_end_irqrestore(struct u64_stats_sync *syncp,
unsigned long flags)
{
__u64_stats_update_end(syncp);
__u64_stats_irqrestore(flags);
}
static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
{
return __u64_stats_fetch_begin(syncp);
}
static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
unsigned int start)
{
return __u64_stats_fetch_retry(syncp, start);
}
#endif /* _LINUX_U64_STATS_SYNC_H */
|
