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27b012e2 MD |
1 | #ifndef _URCU_H |
2 | #define _URCU_H | |
3 | ||
b257a10b MD |
4 | /* |
5 | * urcu.h | |
6 | * | |
7 | * Userspace RCU header | |
8 | * | |
9 | * Copyright February 2009 - Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | |
10 | * | |
5e7e64b9 MD |
11 | * Credits for Paul e. McKenney <paulmck@linux.vnet.ibm.com> |
12 | * for inspiration coming from the Linux kernel RCU and rcu-preempt. | |
13 | * | |
14 | * The barrier, mb, rmb, wmb, atomic_inc, smp_read_barrier_depends, ACCESS_ONCE | |
15 | * and rcu_dereference primitives come from the Linux kernel. | |
16 | * | |
b257a10b MD |
17 | * Distributed under GPLv2 |
18 | */ | |
19 | ||
9b171f46 | 20 | #define __USE_GNU |
1430ee0b MD |
21 | #include <stdlib.h> |
22 | ||
27b012e2 MD |
23 | /* The "volatile" is due to gcc bugs */ |
24 | #define barrier() __asm__ __volatile__("": : :"memory") | |
25 | ||
26 | /* x86 32/64 specific */ | |
27 | #define mb() asm volatile("mfence":::"memory") | |
28 | #define rmb() asm volatile("lfence":::"memory") | |
29 | #define wmb() asm volatile("sfence" ::: "memory") | |
30 | ||
27b012e2 MD |
31 | static inline void atomic_inc(int *v) |
32 | { | |
33 | asm volatile("lock; incl %0" | |
f69f195a | 34 | : "+m" (*v)); |
27b012e2 MD |
35 | } |
36 | ||
f4a486ac MD |
37 | #define xchg(ptr, v) \ |
38 | ((__typeof__(*(ptr)))__xchg((unsigned long)(v), (ptr), sizeof(*(ptr)))) | |
39 | ||
40 | struct __xchg_dummy { | |
41 | unsigned long a[100]; | |
42 | }; | |
43 | #define __xg(x) ((struct __xchg_dummy *)(x)) | |
44 | ||
45 | /* | |
46 | * Note: no "lock" prefix even on SMP: xchg always implies lock anyway | |
47 | * Note 2: xchg has side effect, so that attribute volatile is necessary, | |
48 | * but generally the primitive is invalid, *ptr is output argument. --ANK | |
49 | */ | |
50 | static inline unsigned long __xchg(unsigned long x, volatile void *ptr, | |
51 | int size) | |
52 | { | |
53 | switch (size) { | |
54 | case 1: | |
55 | asm volatile("xchgb %b0,%1" | |
56 | : "=q" (x) | |
57 | : "m" (*__xg(ptr)), "0" (x) | |
58 | : "memory"); | |
59 | break; | |
60 | case 2: | |
61 | asm volatile("xchgw %w0,%1" | |
62 | : "=r" (x) | |
63 | : "m" (*__xg(ptr)), "0" (x) | |
64 | : "memory"); | |
65 | break; | |
66 | case 4: | |
67 | asm volatile("xchgl %0,%1" | |
68 | : "=r" (x) | |
69 | : "m" (*__xg(ptr)), "0" (x) | |
70 | : "memory"); | |
71 | break; | |
72 | } | |
73 | return x; | |
74 | } | |
75 | ||
27b012e2 MD |
76 | /* Nop everywhere except on alpha. */ |
77 | #define smp_read_barrier_depends() | |
78 | ||
41718ff9 MD |
79 | /* |
80 | * Prevent the compiler from merging or refetching accesses. The compiler | |
81 | * is also forbidden from reordering successive instances of ACCESS_ONCE(), | |
82 | * but only when the compiler is aware of some particular ordering. One way | |
83 | * to make the compiler aware of ordering is to put the two invocations of | |
84 | * ACCESS_ONCE() in different C statements. | |
85 | * | |
86 | * This macro does absolutely -nothing- to prevent the CPU from reordering, | |
87 | * merging, or refetching absolutely anything at any time. Its main intended | |
88 | * use is to mediate communication between process-level code and irq/NMI | |
89 | * handlers, all running on the same CPU. | |
90 | */ | |
91 | #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) | |
92 | ||
93 | /** | |
94 | * rcu_dereference - fetch an RCU-protected pointer in an | |
95 | * RCU read-side critical section. This pointer may later | |
96 | * be safely dereferenced. | |
97 | * | |
98 | * Inserts memory barriers on architectures that require them | |
99 | * (currently only the Alpha), and, more importantly, documents | |
100 | * exactly which pointers are protected by RCU. | |
101 | */ | |
102 | ||
103 | #define rcu_dereference(p) ({ \ | |
104 | typeof(p) _________p1 = ACCESS_ONCE(p); \ | |
105 | smp_read_barrier_depends(); \ | |
106 | (_________p1); \ | |
107 | }) | |
108 | ||
27b012e2 MD |
109 | #define SIGURCU SIGUSR1 |
110 | ||
cf380c2f MD |
111 | #ifdef DEBUG_YIELD |
112 | #include <sched.h> | |
9b171f46 MD |
113 | #include <time.h> |
114 | #include <pthread.h> | |
cf380c2f MD |
115 | |
116 | #define YIELD_READ (1 << 0) | |
117 | #define YIELD_WRITE (1 << 1) | |
118 | ||
9d335088 MD |
119 | extern unsigned int yield_active; |
120 | extern unsigned int __thread rand_yield; | |
cf380c2f MD |
121 | |
122 | static inline void debug_yield_read(void) | |
123 | { | |
124 | if (yield_active & YIELD_READ) | |
9d335088 MD |
125 | if (rand_r(&rand_yield) & 0x1) |
126 | sched_yield(); | |
cf380c2f MD |
127 | } |
128 | ||
129 | static inline void debug_yield_write(void) | |
130 | { | |
131 | if (yield_active & YIELD_WRITE) | |
9d335088 MD |
132 | if (rand_r(&rand_yield) & 0x1) |
133 | sched_yield(); | |
134 | } | |
135 | ||
136 | static inline void debug_yield_init(void) | |
137 | { | |
138 | rand_yield = time(NULL) ^ pthread_self(); | |
cf380c2f MD |
139 | } |
140 | #else | |
141 | static inline void debug_yield_read(void) | |
142 | { | |
143 | } | |
144 | ||
145 | static inline void debug_yield_write(void) | |
146 | { | |
9d335088 MD |
147 | } |
148 | ||
149 | static inline void debug_yield_init(void) | |
150 | { | |
151 | ||
cf380c2f MD |
152 | } |
153 | #endif | |
154 | ||
1430ee0b MD |
155 | /* |
156 | * Limiting the nesting level to 256 to keep instructions small in the read | |
157 | * fast-path. | |
158 | */ | |
159 | #define RCU_GP_COUNT (1U << 0) | |
160 | #define RCU_GP_CTR_BIT (1U << 8) | |
161 | #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1) | |
162 | ||
163 | /* Global quiescent period counter with low-order bits unused. */ | |
164 | extern int urcu_gp_ctr; | |
27b012e2 | 165 | |
1430ee0b | 166 | extern int __thread urcu_active_readers; |
27b012e2 | 167 | |
1430ee0b | 168 | static inline int rcu_old_gp_ongoing(int *value) |
27b012e2 | 169 | { |
1430ee0b MD |
170 | int v; |
171 | ||
172 | if (value == NULL) | |
173 | return 0; | |
174 | debug_yield_write(); | |
175 | v = ACCESS_ONCE(*value); | |
176 | debug_yield_write(); | |
177 | return (v & RCU_GP_CTR_NEST_MASK) && | |
178 | ((v ^ ACCESS_ONCE(urcu_gp_ctr)) & RCU_GP_CTR_BIT); | |
27b012e2 MD |
179 | } |
180 | ||
1430ee0b | 181 | static inline void rcu_read_lock(void) |
27b012e2 | 182 | { |
1430ee0b MD |
183 | int tmp; |
184 | ||
cf380c2f | 185 | debug_yield_read(); |
1430ee0b | 186 | tmp = urcu_active_readers; |
cf380c2f | 187 | debug_yield_read(); |
1430ee0b MD |
188 | if (!(tmp & RCU_GP_CTR_NEST_MASK)) |
189 | urcu_active_readers = urcu_gp_ctr + RCU_GP_COUNT; | |
190 | else | |
191 | urcu_active_readers = tmp + RCU_GP_COUNT; | |
cf380c2f | 192 | debug_yield_read(); |
27b012e2 MD |
193 | /* |
194 | * Increment active readers count before accessing the pointer. | |
195 | * See force_mb_all_threads(). | |
196 | */ | |
197 | barrier(); | |
cf380c2f | 198 | debug_yield_read(); |
27b012e2 MD |
199 | } |
200 | ||
1430ee0b | 201 | static inline void rcu_read_unlock(void) |
27b012e2 | 202 | { |
cf380c2f | 203 | debug_yield_read(); |
27b012e2 | 204 | barrier(); |
cf380c2f | 205 | debug_yield_read(); |
27b012e2 MD |
206 | /* |
207 | * Finish using rcu before decrementing the pointer. | |
208 | * See force_mb_all_threads(). | |
209 | */ | |
1430ee0b | 210 | urcu_active_readers -= RCU_GP_COUNT; |
cf380c2f | 211 | debug_yield_read(); |
27b012e2 MD |
212 | } |
213 | ||
e462817e MD |
214 | /** |
215 | * rcu_assign_pointer - assign (publicize) a pointer to a newly | |
216 | * initialized structure that will be dereferenced by RCU read-side | |
217 | * critical sections. Returns the value assigned. | |
218 | * | |
219 | * Inserts memory barriers on architectures that require them | |
220 | * (pretty much all of them other than x86), and also prevents | |
221 | * the compiler from reordering the code that initializes the | |
222 | * structure after the pointer assignment. More importantly, this | |
223 | * call documents which pointers will be dereferenced by RCU read-side | |
224 | * code. | |
225 | */ | |
226 | ||
227 | #define rcu_assign_pointer(p, v) \ | |
228 | ({ \ | |
229 | if (!__builtin_constant_p(v) || \ | |
230 | ((v) != NULL)) \ | |
231 | wmb(); \ | |
232 | (p) = (v); \ | |
233 | }) | |
234 | ||
f4a486ac MD |
235 | #define rcu_xchg_pointer(p, v) \ |
236 | ({ \ | |
237 | if (!__builtin_constant_p(v) || \ | |
238 | ((v) != NULL)) \ | |
239 | wmb(); \ | |
240 | xchg(p, v); \ | |
241 | }) | |
242 | ||
e462817e | 243 | extern void synchronize_rcu(void); |
27b012e2 | 244 | |
f4a486ac MD |
245 | /* |
246 | * Exchanges the pointer and waits for quiescent state. | |
247 | * The pointer returned can be freed. | |
248 | */ | |
249 | #define urcu_publish_content(p, v) \ | |
250 | ({ \ | |
251 | void *oldptr; \ | |
252 | debug_yield_write(); \ | |
253 | oldptr = rcu_xchg_pointer(p, v); \ | |
254 | synchronize_rcu(); \ | |
255 | oldptr; \ | |
256 | }) | |
257 | ||
27b012e2 MD |
258 | /* |
259 | * Reader thread registration. | |
260 | */ | |
261 | extern void urcu_register_thread(void); | |
5e7e64b9 | 262 | extern void urcu_unregister_thread(void); |
27b012e2 MD |
263 | |
264 | #endif /* _URCU_H */ |