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3162dfe1 MD |
1 | /* |
2 | * urcu_mbmin.spin: Promela code to validate urcu. See commit number | |
3 | * 3a9e6e9df706b8d39af94d2f027210e2e7d4106e of Mathieu Desnoyer's | |
4 | * git archive at git://lttng.org/userspace-rcu.git, but with | |
5 | * memory barriers removed. | |
6 | * | |
c7bc0baa PM |
7 | * This validates a single reader against a single updater. The |
8 | * updater is assumed to have smp_mb() barriers between each pair | |
9 | * of operations, and this model validates that a signal-mediated | |
10 | * broadcast barrier is required only at the beginning and end of | |
11 | * the synchronize_rcu(). | |
12 | * | |
13 | * Note that the second half of a prior synchronize_rcu() is modelled | |
14 | * as well as the current synchronize_rcu(). | |
15 | * | |
3162dfe1 MD |
16 | * This program is free software; you can redistribute it and/or modify |
17 | * it under the terms of the GNU General Public License as published by | |
18 | * the Free Software Foundation; either version 2 of the License, or | |
19 | * (at your option) any later version. | |
20 | * | |
21 | * This program is distributed in the hope that it will be useful, | |
22 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
23 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
24 | * GNU General Public License for more details. | |
25 | * | |
26 | * You should have received a copy of the GNU General Public License | |
27 | * along with this program; if not, write to the Free Software | |
28 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
29 | * | |
30 | * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. | |
31 | */ | |
32 | ||
33 | /* Promela validation variables. */ | |
34 | ||
c7bc0baa PM |
35 | bit removed = 0; /* Has RCU removal happened, e.g., list_del_rcu()? */ |
36 | bit free = 0; /* Has RCU reclamation happened, e.g., kfree()? */ | |
37 | bit need_mb = 0; /* =1 says need reader mb, =0 for reader response. */ | |
38 | byte reader_progress[4]; /* Count of read-side statement executions. */ | |
39 | bit reader_done = 0; /* =0 says reader still running, =1 says done. */ | |
40 | bit updater_done = 0; /* =0 says updater still running, =1 says done. */ | |
41 | ||
42 | /* Broadcast memory barriers to enable, prior synchronize_rcu() instance. */ | |
43 | ||
44 | /* #define MB_A */ /* Not required for correctness. */ | |
45 | /* #define MB_B */ /* Not required for correctness. */ | |
46 | /* #define MB_C */ /* Not required for correctness. */ | |
47 | ||
48 | /* Broadcast memory barriers to enable, current synchronize_rcu() instance. */ | |
49 | ||
50 | #define MB_D /* First broadcast barrier in synchronize_rcu(). */ | |
51 | /* #define MB_E */ /* Not required for correctness. */ | |
52 | /* #define MB_F */ /* Not required for correctness. */ | |
53 | #define MB_G /* Last broadcast barrier in synchronize_rcu(). */ | |
3162dfe1 MD |
54 | |
55 | /* urcu definitions and variables, taken straight from the algorithm. */ | |
56 | ||
57 | #define RCU_GP_CTR_BIT (1 << 7) | |
58 | #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1) | |
59 | ||
60 | byte urcu_gp_ctr = 1; | |
61 | byte urcu_active_readers = 0; | |
62 | ||
63 | /* Model the RCU read-side critical section. */ | |
64 | ||
65 | proctype urcu_reader() | |
66 | { | |
67 | bit done = 0; | |
68 | bit mbok; | |
69 | byte tmp; | |
70 | byte tmp_removed; | |
71 | byte tmp_free; | |
72 | ||
73 | /* Absorb any early requests for memory barriers. */ | |
74 | do | |
75 | :: need_mb == 1 -> | |
76 | need_mb = 0; | |
3162dfe1 MD |
77 | :: 1 -> break; |
78 | od; | |
79 | ||
80 | /* | |
81 | * Each pass through this loop executes one read-side statement | |
82 | * from the following code fragment: | |
83 | * | |
84 | * rcu_read_lock(); [0a] | |
85 | * rcu_read_lock(); [0b] | |
86 | * p = rcu_dereference(global_p); [1] | |
87 | * x = p->data; [2] | |
88 | * rcu_read_unlock(); [3b] | |
89 | * rcu_read_unlock(); [3a] | |
90 | * | |
91 | * Because we are modeling a weak-memory machine, these statements | |
92 | * can be seen in any order, the only restriction being that | |
93 | * rcu_read_unlock() cannot precede the corresponding rcu_read_lock(). | |
94 | * The placement of the inner rcu_read_lock() and rcu_read_unlock() | |
95 | * is non-deterministic, the above is but one possible placement. | |
96 | * Intestingly enough, this model validates all possible placements | |
97 | * of the inner rcu_read_lock() and rcu_read_unlock() statements, | |
98 | * with the only constraint being that the rcu_read_lock() must | |
99 | * precede the rcu_read_unlock(). | |
100 | * | |
101 | * We also respond to memory-barrier requests, but only if our | |
102 | * execution happens to be ordered. If the current state is | |
103 | * misordered, we ignore memory-barrier requests. | |
104 | */ | |
105 | do | |
106 | :: 1 -> | |
107 | if | |
108 | :: reader_progress[0] < 2 -> /* [0a and 0b] */ | |
109 | tmp = urcu_active_readers; | |
110 | if | |
111 | :: (tmp & RCU_GP_CTR_NEST_MASK) == 0 -> | |
112 | tmp = urcu_gp_ctr; | |
113 | do | |
114 | :: (reader_progress[1] + | |
115 | reader_progress[2] + | |
116 | reader_progress[3] == 0) && need_mb == 1 -> | |
117 | need_mb = 0; | |
c7bc0baa | 118 | :: need_mb == 0 && !updater_done -> skip; |
3162dfe1 MD |
119 | :: 1 -> break; |
120 | od; | |
121 | urcu_active_readers = tmp; | |
122 | :: else -> | |
123 | urcu_active_readers = tmp + 1; | |
124 | fi; | |
125 | reader_progress[0] = reader_progress[0] + 1; | |
126 | :: reader_progress[1] == 0 -> /* [1] */ | |
127 | tmp_removed = removed; | |
128 | reader_progress[1] = 1; | |
129 | :: reader_progress[2] == 0 -> /* [2] */ | |
130 | tmp_free = free; | |
131 | reader_progress[2] = 1; | |
132 | :: ((reader_progress[0] > reader_progress[3]) && | |
133 | (reader_progress[3] < 2)) -> /* [3a and 3b] */ | |
134 | tmp = urcu_active_readers - 1; | |
135 | urcu_active_readers = tmp; | |
136 | reader_progress[3] = reader_progress[3] + 1; | |
137 | :: else -> break; | |
138 | fi; | |
139 | ||
140 | /* Process memory-barrier requests, if it is safe to do so. */ | |
141 | atomic { | |
142 | mbok = 0; | |
143 | tmp = 0; | |
144 | do | |
145 | :: tmp < 4 && reader_progress[tmp] == 0 -> | |
146 | tmp = tmp + 1; | |
147 | break; | |
148 | :: tmp < 4 && reader_progress[tmp] != 0 -> | |
149 | tmp = tmp + 1; | |
150 | :: tmp >= 4 && | |
151 | reader_progress[0] == reader_progress[3] -> | |
152 | done = 1; | |
153 | break; | |
154 | :: tmp >= 4 && | |
155 | reader_progress[0] != reader_progress[3] -> | |
156 | break; | |
157 | od; | |
158 | do | |
159 | :: tmp < 4 && reader_progress[tmp] == 0 -> | |
160 | tmp = tmp + 1; | |
161 | :: tmp < 4 && reader_progress[tmp] != 0 -> | |
162 | break; | |
163 | :: tmp >= 4 -> | |
164 | mbok = 1; | |
165 | break; | |
166 | od | |
167 | ||
168 | } | |
169 | ||
170 | if | |
171 | :: mbok == 1 -> | |
172 | /* We get here if mb processing is safe. */ | |
173 | do | |
174 | :: need_mb == 1 -> | |
175 | need_mb = 0; | |
3162dfe1 MD |
176 | :: 1 -> break; |
177 | od; | |
178 | :: else -> skip; | |
179 | fi; | |
180 | ||
181 | /* | |
182 | * Check to see if we have modeled the entire RCU read-side | |
183 | * critical section, and leave if so. | |
184 | */ | |
185 | if | |
186 | :: done == 1 -> break; | |
187 | :: else -> skip; | |
188 | fi | |
189 | od; | |
190 | assert((tmp_free == 0) || (tmp_removed == 1)); | |
191 | ||
c7bc0baa PM |
192 | /* Reader has completed. */ |
193 | reader_done = 1; | |
194 | ||
195 | /* | |
196 | * Process any late-arriving memory-barrier requests, and | |
197 | * in addition create a progress cycle. | |
198 | */ | |
199 | reader_done = 1; | |
200 | ||
3162dfe1 MD |
201 | do |
202 | :: need_mb == 1 -> | |
203 | need_mb = 0; | |
c7bc0baa PM |
204 | :: 1 -> |
205 | progress_reader: | |
206 | skip; | |
3162dfe1 MD |
207 | :: 1 -> break; |
208 | od; | |
209 | } | |
210 | ||
211 | /* Model the RCU update process. */ | |
212 | ||
213 | proctype urcu_updater() | |
214 | { | |
215 | byte tmp; | |
216 | ||
c7bc0baa PM |
217 | /* |
218 | * ---------------------------------------------------------------- | |
219 | * prior synchronize_rcu(). | |
220 | */ | |
221 | ||
3162dfe1 | 222 | /* prior synchronize_rcu(), second counter flip. */ |
c7bc0baa PM |
223 | #ifdef MB_A |
224 | need_mb = 1; /* mb() A (analogous to omitted barrier between E and F) */ | |
3162dfe1 | 225 | do |
c7bc0baa PM |
226 | :: need_mb == 1 && !reader_done -> skip; |
227 | :: need_mb == 0 || reader_done -> break; | |
3162dfe1 | 228 | od; |
c7bc0baa | 229 | #endif /* #ifdef MB_A */ |
3162dfe1 | 230 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; |
c7bc0baa PM |
231 | #ifdef MB_B |
232 | need_mb = 1; /* mb() B (analogous to F) */ | |
3162dfe1 | 233 | do |
c7bc0baa PM |
234 | :: need_mb == 1 && !reader_done -> skip; |
235 | :: need_mb == 0 || reader_done -> break; | |
3162dfe1 | 236 | od; |
c7bc0baa | 237 | #endif /* #ifdef MB_B */ |
3162dfe1 MD |
238 | do |
239 | :: 1 -> | |
240 | if | |
241 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
242 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
243 | (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) -> | |
244 | skip; | |
245 | :: else -> break; | |
246 | fi | |
247 | od; | |
c7bc0baa | 248 | #ifdef MB_C |
3162dfe1 MD |
249 | need_mb = 1; /* mb() C absolutely required by analogy with G */ |
250 | do | |
c7bc0baa PM |
251 | :: need_mb == 1 && !reader_done -> skip; |
252 | :: need_mb == 0 || reader_done -> break; | |
3162dfe1 | 253 | od; |
c7bc0baa | 254 | #endif /* #ifdef MB_C */ |
3162dfe1 MD |
255 | |
256 | /* Removal statement, e.g., list_del_rcu(). */ | |
257 | removed = 1; | |
258 | ||
c7bc0baa PM |
259 | /* |
260 | * prior synchronize_rcu(). | |
261 | * ---------------------------------------------------------------- | |
262 | */ | |
263 | ||
264 | /* | |
265 | * ---------------------------------------------------------------- | |
266 | * current synchronize_rcu(). | |
267 | */ | |
268 | ||
3162dfe1 | 269 | /* current synchronize_rcu(), first counter flip. */ |
c7bc0baa | 270 | #ifdef MB_D |
3162dfe1 MD |
271 | need_mb = 1; /* mb() D suggested */ |
272 | do | |
c7bc0baa PM |
273 | :: need_mb == 1 && !reader_done -> skip; |
274 | :: need_mb == 0 || reader_done -> break; | |
3162dfe1 | 275 | od; |
c7bc0baa | 276 | #endif /* #ifdef MB_D */ |
3162dfe1 | 277 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; |
c7bc0baa | 278 | #ifdef MB_E |
3162dfe1 MD |
279 | need_mb = 1; /* mb() E required if D not present */ |
280 | do | |
c7bc0baa PM |
281 | :: need_mb == 1 && !reader_done -> skip; |
282 | :: need_mb == 0 || reader_done -> break; | |
3162dfe1 | 283 | od; |
c7bc0baa | 284 | #endif /* #ifdef MB_E */ |
3162dfe1 MD |
285 | |
286 | /* current synchronize_rcu(), first-flip check plus second flip. */ | |
287 | if | |
288 | :: 1 -> | |
289 | do | |
290 | :: 1 -> | |
291 | if | |
292 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
293 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
294 | (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) -> | |
295 | skip; | |
296 | :: else -> break; | |
297 | fi; | |
298 | od; | |
299 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; | |
300 | :: 1 -> | |
301 | tmp = urcu_gp_ctr; | |
302 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; | |
303 | do | |
304 | :: 1 -> | |
305 | if | |
306 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
307 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
308 | (tmp & ~RCU_GP_CTR_NEST_MASK) -> | |
309 | skip; | |
310 | :: else -> break; | |
311 | fi; | |
312 | od; | |
313 | fi; | |
314 | ||
315 | /* current synchronize_rcu(), second counter flip check. */ | |
c7bc0baa | 316 | #ifdef MB_F |
3162dfe1 MD |
317 | need_mb = 1; /* mb() F not required */ |
318 | do | |
c7bc0baa PM |
319 | :: need_mb == 1 && !reader_done -> skip; |
320 | :: need_mb == 0 || reader_done -> break; | |
3162dfe1 | 321 | od; |
c7bc0baa | 322 | #endif /* #ifdef MB_F */ |
3162dfe1 MD |
323 | do |
324 | :: 1 -> | |
325 | if | |
326 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
327 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
328 | (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) -> | |
329 | skip; | |
330 | :: else -> break; | |
331 | fi; | |
332 | od; | |
c7bc0baa | 333 | #ifdef MB_G |
3162dfe1 MD |
334 | need_mb = 1; /* mb() G absolutely required */ |
335 | do | |
c7bc0baa PM |
336 | :: need_mb == 1 && !reader_done -> skip; |
337 | :: need_mb == 0 || reader_done -> break; | |
3162dfe1 | 338 | od; |
c7bc0baa PM |
339 | #endif /* #ifdef MB_G */ |
340 | ||
341 | /* | |
342 | * current synchronize_rcu(). | |
343 | * ---------------------------------------------------------------- | |
344 | */ | |
3162dfe1 MD |
345 | |
346 | /* free-up step, e.g., kfree(). */ | |
347 | free = 1; | |
c7bc0baa PM |
348 | |
349 | /* We are done, so kill all the infinite loops in the reader. */ | |
350 | updater_done = 1; | |
351 | ||
352 | /* Create a progress cycle. Correctness requires we get here. */ | |
353 | do | |
354 | :: 1 -> | |
355 | progress_updater: | |
356 | skip; | |
357 | :: 1 -> break; | |
358 | od; | |
3162dfe1 MD |
359 | } |
360 | ||
361 | /* | |
362 | * Initialize the array, spawn a reader and an updater. Because readers | |
363 | * are independent of each other, only one reader is needed. | |
364 | */ | |
365 | ||
366 | init { | |
367 | atomic { | |
368 | reader_progress[0] = 0; | |
369 | reader_progress[1] = 0; | |
370 | reader_progress[2] = 0; | |
371 | reader_progress[3] = 0; | |
372 | run urcu_reader(); | |
373 | run urcu_updater(); | |
374 | } | |
375 | } |