Root/
1 | #ifndef __LINUX_SEQLOCK_H |
2 | #define __LINUX_SEQLOCK_H |
3 | /* |
4 | * Reader/writer consistent mechanism without starving writers. This type of |
5 | * lock for data where the reader wants a consistent set of information |
6 | * and is willing to retry if the information changes. Readers never |
7 | * block but they may have to retry if a writer is in |
8 | * progress. Writers do not wait for readers. |
9 | * |
10 | * This is not as cache friendly as brlock. Also, this will not work |
11 | * for data that contains pointers, because any writer could |
12 | * invalidate a pointer that a reader was following. |
13 | * |
14 | * Expected reader usage: |
15 | * do { |
16 | * seq = read_seqbegin(&foo); |
17 | * ... |
18 | * } while (read_seqretry(&foo, seq)); |
19 | * |
20 | * |
21 | * On non-SMP the spin locks disappear but the writer still needs |
22 | * to increment the sequence variables because an interrupt routine could |
23 | * change the state of the data. |
24 | * |
25 | * Based on x86_64 vsyscall gettimeofday |
26 | * by Keith Owens and Andrea Arcangeli |
27 | */ |
28 | |
29 | #include <linux/spinlock.h> |
30 | #include <linux/preempt.h> |
31 | |
32 | typedef struct { |
33 | unsigned sequence; |
34 | spinlock_t lock; |
35 | } seqlock_t; |
36 | |
37 | /* |
38 | * These macros triggered gcc-3.x compile-time problems. We think these are |
39 | * OK now. Be cautious. |
40 | */ |
41 | #define __SEQLOCK_UNLOCKED(lockname) \ |
42 | { 0, __SPIN_LOCK_UNLOCKED(lockname) } |
43 | |
44 | #define SEQLOCK_UNLOCKED \ |
45 | __SEQLOCK_UNLOCKED(old_style_seqlock_init) |
46 | |
47 | #define seqlock_init(x) \ |
48 | do { \ |
49 | (x)->sequence = 0; \ |
50 | spin_lock_init(&(x)->lock); \ |
51 | } while (0) |
52 | |
53 | #define DEFINE_SEQLOCK(x) \ |
54 | seqlock_t x = __SEQLOCK_UNLOCKED(x) |
55 | |
56 | /* Lock out other writers and update the count. |
57 | * Acts like a normal spin_lock/unlock. |
58 | * Don't need preempt_disable() because that is in the spin_lock already. |
59 | */ |
60 | static inline void write_seqlock(seqlock_t *sl) |
61 | { |
62 | spin_lock(&sl->lock); |
63 | ++sl->sequence; |
64 | smp_wmb(); |
65 | } |
66 | |
67 | static inline void write_sequnlock(seqlock_t *sl) |
68 | { |
69 | smp_wmb(); |
70 | sl->sequence++; |
71 | spin_unlock(&sl->lock); |
72 | } |
73 | |
74 | static inline int write_tryseqlock(seqlock_t *sl) |
75 | { |
76 | int ret = spin_trylock(&sl->lock); |
77 | |
78 | if (ret) { |
79 | ++sl->sequence; |
80 | smp_wmb(); |
81 | } |
82 | return ret; |
83 | } |
84 | |
85 | /* Start of read calculation -- fetch last complete writer token */ |
86 | static __always_inline unsigned read_seqbegin(const seqlock_t *sl) |
87 | { |
88 | unsigned ret; |
89 | |
90 | repeat: |
91 | ret = sl->sequence; |
92 | smp_rmb(); |
93 | if (unlikely(ret & 1)) { |
94 | cpu_relax(); |
95 | goto repeat; |
96 | } |
97 | |
98 | return ret; |
99 | } |
100 | |
101 | /* |
102 | * Test if reader processed invalid data. |
103 | * |
104 | * If sequence value changed then writer changed data while in section. |
105 | */ |
106 | static __always_inline int read_seqretry(const seqlock_t *sl, unsigned start) |
107 | { |
108 | smp_rmb(); |
109 | |
110 | return (sl->sequence != start); |
111 | } |
112 | |
113 | |
114 | /* |
115 | * Version using sequence counter only. |
116 | * This can be used when code has its own mutex protecting the |
117 | * updating starting before the write_seqcountbeqin() and ending |
118 | * after the write_seqcount_end(). |
119 | */ |
120 | |
121 | typedef struct seqcount { |
122 | unsigned sequence; |
123 | } seqcount_t; |
124 | |
125 | #define SEQCNT_ZERO { 0 } |
126 | #define seqcount_init(x) do { *(x) = (seqcount_t) SEQCNT_ZERO; } while (0) |
127 | |
128 | /* Start of read using pointer to a sequence counter only. */ |
129 | static inline unsigned read_seqcount_begin(const seqcount_t *s) |
130 | { |
131 | unsigned ret; |
132 | |
133 | repeat: |
134 | ret = s->sequence; |
135 | smp_rmb(); |
136 | if (unlikely(ret & 1)) { |
137 | cpu_relax(); |
138 | goto repeat; |
139 | } |
140 | return ret; |
141 | } |
142 | |
143 | /* |
144 | * Test if reader processed invalid data because sequence number has changed. |
145 | */ |
146 | static inline int read_seqcount_retry(const seqcount_t *s, unsigned start) |
147 | { |
148 | smp_rmb(); |
149 | |
150 | return s->sequence != start; |
151 | } |
152 | |
153 | |
154 | /* |
155 | * Sequence counter only version assumes that callers are using their |
156 | * own mutexing. |
157 | */ |
158 | static inline void write_seqcount_begin(seqcount_t *s) |
159 | { |
160 | s->sequence++; |
161 | smp_wmb(); |
162 | } |
163 | |
164 | static inline void write_seqcount_end(seqcount_t *s) |
165 | { |
166 | smp_wmb(); |
167 | s->sequence++; |
168 | } |
169 | |
170 | /* |
171 | * Possible sw/hw IRQ protected versions of the interfaces. |
172 | */ |
173 | #define write_seqlock_irqsave(lock, flags) \ |
174 | do { local_irq_save(flags); write_seqlock(lock); } while (0) |
175 | #define write_seqlock_irq(lock) \ |
176 | do { local_irq_disable(); write_seqlock(lock); } while (0) |
177 | #define write_seqlock_bh(lock) \ |
178 | do { local_bh_disable(); write_seqlock(lock); } while (0) |
179 | |
180 | #define write_sequnlock_irqrestore(lock, flags) \ |
181 | do { write_sequnlock(lock); local_irq_restore(flags); } while(0) |
182 | #define write_sequnlock_irq(lock) \ |
183 | do { write_sequnlock(lock); local_irq_enable(); } while(0) |
184 | #define write_sequnlock_bh(lock) \ |
185 | do { write_sequnlock(lock); local_bh_enable(); } while(0) |
186 | |
187 | #define read_seqbegin_irqsave(lock, flags) \ |
188 | ({ local_irq_save(flags); read_seqbegin(lock); }) |
189 | |
190 | #define read_seqretry_irqrestore(lock, iv, flags) \ |
191 | ({ \ |
192 | int ret = read_seqretry(lock, iv); \ |
193 | local_irq_restore(flags); \ |
194 | ret; \ |
195 | }) |
196 | |
197 | #endif /* __LINUX_SEQLOCK_H */ |
198 |
Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.11
jz-3.12
jz-3.13
jz-3.15
jz-3.16
jz-3.18-dt
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-clk
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master
Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9