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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 | * | |
7 | * This program is free software; you can redistribute it and/or modify | |
8 | * it under the terms of the GNU General Public License as published by | |
9 | * the Free Software Foundation; either version 2 of the License, or | |
10 | * (at your option) any later version. | |
11 | * | |
12 | * This program is distributed in the hope that it will be useful, | |
13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
15 | * GNU General Public License for more details. | |
16 | * | |
17 | * You should have received a copy of the GNU General Public License | |
18 | * along with this program; if not, write to the Free Software | |
19 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
20 | * | |
21 | * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. | |
22 | */ | |
23 | ||
24 | /* Promela validation variables. */ | |
25 | ||
26 | bit removed = 0; /* Has RCU removal happened, e.g., list_del_rcu()? */ | |
27 | bit free = 0; /* Has RCU reclamation happened, e.g., kfree()? */ | |
28 | bit need_mb = 0; /* =1 says need reader mb, =0 for reader response. */ | |
29 | byte reader_progress[4]; | |
30 | /* Count of read-side statement executions. */ | |
31 | ||
32 | /* urcu definitions and variables, taken straight from the algorithm. */ | |
33 | ||
34 | #define RCU_GP_CTR_BIT (1 << 7) | |
35 | #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1) | |
36 | ||
37 | byte urcu_gp_ctr = 1; | |
38 | byte urcu_active_readers = 0; | |
39 | ||
40 | /* Model the RCU read-side critical section. */ | |
41 | ||
42 | proctype urcu_reader() | |
43 | { | |
44 | bit done = 0; | |
45 | bit mbok; | |
46 | byte tmp; | |
47 | byte tmp_removed; | |
48 | byte tmp_free; | |
49 | ||
50 | /* Absorb any early requests for memory barriers. */ | |
51 | do | |
52 | :: need_mb == 1 -> | |
53 | need_mb = 0; | |
54 | :: 1 -> skip; | |
55 | :: 1 -> break; | |
56 | od; | |
57 | ||
58 | /* | |
59 | * Each pass through this loop executes one read-side statement | |
60 | * from the following code fragment: | |
61 | * | |
62 | * rcu_read_lock(); [0a] | |
63 | * rcu_read_lock(); [0b] | |
64 | * p = rcu_dereference(global_p); [1] | |
65 | * x = p->data; [2] | |
66 | * rcu_read_unlock(); [3b] | |
67 | * rcu_read_unlock(); [3a] | |
68 | * | |
69 | * Because we are modeling a weak-memory machine, these statements | |
70 | * can be seen in any order, the only restriction being that | |
71 | * rcu_read_unlock() cannot precede the corresponding rcu_read_lock(). | |
72 | * The placement of the inner rcu_read_lock() and rcu_read_unlock() | |
73 | * is non-deterministic, the above is but one possible placement. | |
74 | * Intestingly enough, this model validates all possible placements | |
75 | * of the inner rcu_read_lock() and rcu_read_unlock() statements, | |
76 | * with the only constraint being that the rcu_read_lock() must | |
77 | * precede the rcu_read_unlock(). | |
78 | * | |
79 | * We also respond to memory-barrier requests, but only if our | |
80 | * execution happens to be ordered. If the current state is | |
81 | * misordered, we ignore memory-barrier requests. | |
82 | */ | |
83 | do | |
84 | :: 1 -> | |
85 | if | |
86 | :: reader_progress[0] < 2 -> /* [0a and 0b] */ | |
87 | tmp = urcu_active_readers; | |
88 | if | |
89 | :: (tmp & RCU_GP_CTR_NEST_MASK) == 0 -> | |
90 | tmp = urcu_gp_ctr; | |
91 | do | |
92 | :: (reader_progress[1] + | |
93 | reader_progress[2] + | |
94 | reader_progress[3] == 0) && need_mb == 1 -> | |
95 | need_mb = 0; | |
96 | :: 1 -> skip; | |
97 | :: 1 -> break; | |
98 | od; | |
99 | urcu_active_readers = tmp; | |
100 | :: else -> | |
101 | urcu_active_readers = tmp + 1; | |
102 | fi; | |
103 | reader_progress[0] = reader_progress[0] + 1; | |
104 | :: reader_progress[1] == 0 -> /* [1] */ | |
105 | tmp_removed = removed; | |
106 | reader_progress[1] = 1; | |
107 | :: reader_progress[2] == 0 -> /* [2] */ | |
108 | tmp_free = free; | |
109 | reader_progress[2] = 1; | |
110 | :: ((reader_progress[0] > reader_progress[3]) && | |
111 | (reader_progress[3] < 2)) -> /* [3a and 3b] */ | |
112 | tmp = urcu_active_readers - 1; | |
113 | urcu_active_readers = tmp; | |
114 | reader_progress[3] = reader_progress[3] + 1; | |
115 | :: else -> break; | |
116 | fi; | |
117 | ||
118 | /* Process memory-barrier requests, if it is safe to do so. */ | |
119 | atomic { | |
120 | mbok = 0; | |
121 | tmp = 0; | |
122 | do | |
123 | :: tmp < 4 && reader_progress[tmp] == 0 -> | |
124 | tmp = tmp + 1; | |
125 | break; | |
126 | :: tmp < 4 && reader_progress[tmp] != 0 -> | |
127 | tmp = tmp + 1; | |
128 | :: tmp >= 4 && | |
129 | reader_progress[0] == reader_progress[3] -> | |
130 | done = 1; | |
131 | break; | |
132 | :: tmp >= 4 && | |
133 | reader_progress[0] != reader_progress[3] -> | |
134 | break; | |
135 | od; | |
136 | do | |
137 | :: tmp < 4 && reader_progress[tmp] == 0 -> | |
138 | tmp = tmp + 1; | |
139 | :: tmp < 4 && reader_progress[tmp] != 0 -> | |
140 | break; | |
141 | :: tmp >= 4 -> | |
142 | mbok = 1; | |
143 | break; | |
144 | od | |
145 | ||
146 | } | |
147 | ||
148 | if | |
149 | :: mbok == 1 -> | |
150 | /* We get here if mb processing is safe. */ | |
151 | do | |
152 | :: need_mb == 1 -> | |
153 | need_mb = 0; | |
154 | :: 1 -> skip; | |
155 | :: 1 -> break; | |
156 | od; | |
157 | :: else -> skip; | |
158 | fi; | |
159 | ||
160 | /* | |
161 | * Check to see if we have modeled the entire RCU read-side | |
162 | * critical section, and leave if so. | |
163 | */ | |
164 | if | |
165 | :: done == 1 -> break; | |
166 | :: else -> skip; | |
167 | fi | |
168 | od; | |
169 | assert((tmp_free == 0) || (tmp_removed == 1)); | |
170 | ||
171 | /* Process any late-arriving memory-barrier requests. */ | |
172 | do | |
173 | :: need_mb == 1 -> | |
174 | need_mb = 0; | |
175 | :: 1 -> skip; | |
176 | :: 1 -> break; | |
177 | od; | |
178 | } | |
179 | ||
180 | /* Model the RCU update process. */ | |
181 | ||
182 | proctype urcu_updater() | |
183 | { | |
184 | byte tmp; | |
185 | ||
186 | /* prior synchronize_rcu(), second counter flip. */ | |
187 | need_mb = 1; /* mb() A */ | |
188 | do | |
189 | :: need_mb == 1 -> skip; | |
190 | :: need_mb == 0 -> break; | |
191 | od; | |
192 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; | |
193 | need_mb = 1; /* mb() B */ | |
194 | do | |
195 | :: need_mb == 1 -> skip; | |
196 | :: need_mb == 0 -> break; | |
197 | od; | |
198 | do | |
199 | :: 1 -> | |
200 | if | |
201 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
202 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
203 | (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) -> | |
204 | skip; | |
205 | :: else -> break; | |
206 | fi | |
207 | od; | |
208 | need_mb = 1; /* mb() C absolutely required by analogy with G */ | |
209 | do | |
210 | :: need_mb == 1 -> skip; | |
211 | :: need_mb == 0 -> break; | |
212 | od; | |
213 | ||
214 | /* Removal statement, e.g., list_del_rcu(). */ | |
215 | removed = 1; | |
216 | ||
217 | /* current synchronize_rcu(), first counter flip. */ | |
218 | need_mb = 1; /* mb() D suggested */ | |
219 | do | |
220 | :: need_mb == 1 -> skip; | |
221 | :: need_mb == 0 -> break; | |
222 | od; | |
223 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; | |
224 | need_mb = 1; /* mb() E required if D not present */ | |
225 | do | |
226 | :: need_mb == 1 -> skip; | |
227 | :: need_mb == 0 -> break; | |
228 | od; | |
229 | ||
230 | /* current synchronize_rcu(), first-flip check plus second flip. */ | |
231 | if | |
232 | :: 1 -> | |
233 | do | |
234 | :: 1 -> | |
235 | if | |
236 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
237 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
238 | (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) -> | |
239 | skip; | |
240 | :: else -> break; | |
241 | fi; | |
242 | od; | |
243 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; | |
244 | :: 1 -> | |
245 | tmp = urcu_gp_ctr; | |
246 | urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT; | |
247 | do | |
248 | :: 1 -> | |
249 | if | |
250 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
251 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
252 | (tmp & ~RCU_GP_CTR_NEST_MASK) -> | |
253 | skip; | |
254 | :: else -> break; | |
255 | fi; | |
256 | od; | |
257 | fi; | |
258 | ||
259 | /* current synchronize_rcu(), second counter flip check. */ | |
260 | need_mb = 1; /* mb() F not required */ | |
261 | do | |
262 | :: need_mb == 1 -> skip; | |
263 | :: need_mb == 0 -> break; | |
264 | od; | |
265 | do | |
266 | :: 1 -> | |
267 | if | |
268 | :: (urcu_active_readers & RCU_GP_CTR_NEST_MASK) != 0 && | |
269 | (urcu_active_readers & ~RCU_GP_CTR_NEST_MASK) != | |
270 | (urcu_gp_ctr & ~RCU_GP_CTR_NEST_MASK) -> | |
271 | skip; | |
272 | :: else -> break; | |
273 | fi; | |
274 | od; | |
275 | need_mb = 1; /* mb() G absolutely required */ | |
276 | do | |
277 | :: need_mb == 1 -> skip; | |
278 | :: need_mb == 0 -> break; | |
279 | od; | |
280 | ||
281 | /* free-up step, e.g., kfree(). */ | |
282 | free = 1; | |
283 | } | |
284 | ||
285 | /* | |
286 | * Initialize the array, spawn a reader and an updater. Because readers | |
287 | * are independent of each other, only one reader is needed. | |
288 | */ | |
289 | ||
290 | init { | |
291 | atomic { | |
292 | reader_progress[0] = 0; | |
293 | reader_progress[1] = 0; | |
294 | reader_progress[2] = 0; | |
295 | reader_progress[3] = 0; | |
296 | run urcu_reader(); | |
297 | run urcu_updater(); | |
298 | } | |
299 | } |