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.
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.
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.
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.
21 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
24 /* Promela validation variables. */
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. */
32 /* urcu definitions and variables, taken straight from the algorithm. */
34 #define RCU_GP_CTR_BIT (1 << 7)
35 #define RCU_GP_CTR_NEST_MASK (RCU_GP_CTR_BIT - 1)
38 byte urcu_active_readers = 0;
40 /* Model the RCU read-side critical section. */
42 proctype urcu_reader()
50 /* Absorb any early requests for memory barriers. */
59 * Each pass through this loop executes one read-side statement
60 * from the following code fragment:
62 * rcu_read_lock(); [0a]
63 * rcu_read_lock(); [0b]
64 * p = rcu_dereference(global_p); [1]
66 * rcu_read_unlock(); [3b]
67 * rcu_read_unlock(); [3a]
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().
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.
86 :: reader_progress[0] < 2 -> /* [0a and 0b] */
87 tmp = urcu_active_readers;
89 :: (tmp & RCU_GP_CTR_NEST_MASK) == 0 ->
92 :: (reader_progress[1] +
94 reader_progress[3] == 0) && need_mb == 1 ->
99 urcu_active_readers = tmp;
101 urcu_active_readers = tmp + 1;
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] */
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;
118 /* Process memory-barrier requests, if it is safe to do so. */
123 :: tmp < 4 && reader_progress[tmp] == 0 ->
126 :: tmp < 4 && reader_progress[tmp] != 0 ->
129 reader_progress[0] == reader_progress[3] ->
133 reader_progress[0] != reader_progress[3] ->
137 :: tmp < 4 && reader_progress[tmp] == 0 ->
139 :: tmp < 4 && reader_progress[tmp] != 0 ->
150 /* We get here if mb processing is safe. */
161 * Check to see if we have modeled the entire RCU read-side
162 * critical section, and leave if so.
165 :: done == 1 -> break;
169 assert((tmp_free == 0) || (tmp_removed == 1));
171 /* Process any late-arriving memory-barrier requests. */
180 /* Model the RCU update process. */
182 proctype urcu_updater()
186 /* prior synchronize_rcu(), second counter flip. */
187 need_mb = 1; /* mb() A */
189 :: need_mb == 1 -> skip;
190 :: need_mb == 0 -> break;
192 urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
193 need_mb = 1; /* mb() B */
195 :: need_mb == 1 -> skip;
196 :: need_mb == 0 -> break;
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) ->
208 need_mb = 1; /* mb() C absolutely required by analogy with G */
210 :: need_mb == 1 -> skip;
211 :: need_mb == 0 -> break;
214 /* Removal statement, e.g., list_del_rcu(). */
217 /* current synchronize_rcu(), first counter flip. */
218 need_mb = 1; /* mb() D suggested */
220 :: need_mb == 1 -> skip;
221 :: need_mb == 0 -> break;
223 urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
224 need_mb = 1; /* mb() E required if D not present */
226 :: need_mb == 1 -> skip;
227 :: need_mb == 0 -> break;
230 /* current synchronize_rcu(), first-flip check plus second flip. */
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) ->
243 urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
246 urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
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) ->
259 /* current synchronize_rcu(), second counter flip check. */
260 need_mb = 1; /* mb() F not required */
262 :: need_mb == 1 -> skip;
263 :: need_mb == 0 -> break;
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) ->
275 need_mb = 1; /* mb() G absolutely required */
277 :: need_mb == 1 -> skip;
278 :: need_mb == 0 -> break;
281 /* free-up step, e.g., kfree(). */
286 * Initialize the array, spawn a reader and an updater. Because readers
287 * are independent of each other, only one reader is needed.
292 reader_progress[0] = 0;
293 reader_progress[1] = 0;
294 reader_progress[2] = 0;
295 reader_progress[3] = 0;