FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_sx.c
1 /*
2 * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice(s), this list of conditions and the following disclaimer as
9 * the first lines of this file unmodified other than the possible
10 * addition of one or more copyright notices.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice(s), this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
16 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
17 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
19 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
20 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
21 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
22 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
25 * DAMAGE.
26 *
27 * $FreeBSD: releng/5.1/sys/kern/kern_sx.c 93812 2002-04-04 20:49:35Z jhb $
28 */
29
30 /*
31 * Shared/exclusive locks. This implementation assures deterministic lock
32 * granting behavior, so that slocks and xlocks are interleaved.
33 *
34 * Priority propagation will not generally raise the priority of lock holders,
35 * so should not be relied upon in combination with sx locks.
36 */
37
38 #include <sys/param.h>
39 #include <sys/systm.h>
40 #include <sys/ktr.h>
41 #include <sys/condvar.h>
42 #include <sys/lock.h>
43 #include <sys/mutex.h>
44 #include <sys/sx.h>
45
46 struct lock_class lock_class_sx = {
47 "sx",
48 LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE
49 };
50
51 #ifndef INVARIANTS
52 #define _sx_assert(sx, what, file, line)
53 #endif
54
55 void
56 sx_sysinit(void *arg)
57 {
58 struct sx_args *sargs = arg;
59
60 sx_init(sargs->sa_sx, sargs->sa_desc);
61 }
62
63 void
64 sx_init(struct sx *sx, const char *description)
65 {
66 struct lock_object *lock;
67
68 lock = &sx->sx_object;
69 KASSERT((lock->lo_flags & LO_INITIALIZED) == 0,
70 ("sx lock %s %p already initialized", description, sx));
71 bzero(sx, sizeof(*sx));
72 lock->lo_class = &lock_class_sx;
73 lock->lo_type = lock->lo_name = description;
74 lock->lo_flags = LO_WITNESS | LO_RECURSABLE | LO_SLEEPABLE |
75 LO_UPGRADABLE;
76 sx->sx_lock = mtx_pool_find(sx);
77 sx->sx_cnt = 0;
78 cv_init(&sx->sx_shrd_cv, description);
79 sx->sx_shrd_wcnt = 0;
80 cv_init(&sx->sx_excl_cv, description);
81 sx->sx_excl_wcnt = 0;
82 sx->sx_xholder = NULL;
83
84 LOCK_LOG_INIT(lock, 0);
85
86 WITNESS_INIT(lock);
87 }
88
89 void
90 sx_destroy(struct sx *sx)
91 {
92
93 LOCK_LOG_DESTROY(&sx->sx_object, 0);
94
95 KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt ==
96 0), ("%s (%s): holders or waiters\n", __func__,
97 sx->sx_object.lo_name));
98
99 sx->sx_lock = NULL;
100 cv_destroy(&sx->sx_shrd_cv);
101 cv_destroy(&sx->sx_excl_cv);
102
103 WITNESS_DESTROY(&sx->sx_object);
104 }
105
106 void
107 _sx_slock(struct sx *sx, const char *file, int line)
108 {
109
110 mtx_lock(sx->sx_lock);
111 KASSERT(sx->sx_xholder != curthread,
112 ("%s (%s): slock while xlock is held @ %s:%d\n", __func__,
113 sx->sx_object.lo_name, file, line));
114
115 /*
116 * Loop in case we lose the race for lock acquisition.
117 */
118 while (sx->sx_cnt < 0) {
119 sx->sx_shrd_wcnt++;
120 cv_wait(&sx->sx_shrd_cv, sx->sx_lock);
121 sx->sx_shrd_wcnt--;
122 }
123
124 /* Acquire a shared lock. */
125 sx->sx_cnt++;
126
127 LOCK_LOG_LOCK("SLOCK", &sx->sx_object, 0, 0, file, line);
128 WITNESS_LOCK(&sx->sx_object, 0, file, line);
129
130 mtx_unlock(sx->sx_lock);
131 }
132
133 int
134 _sx_try_slock(struct sx *sx, const char *file, int line)
135 {
136
137 mtx_lock(sx->sx_lock);
138 if (sx->sx_cnt >= 0) {
139 sx->sx_cnt++;
140 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 1, file, line);
141 WITNESS_LOCK(&sx->sx_object, LOP_TRYLOCK, file, line);
142 mtx_unlock(sx->sx_lock);
143 return (1);
144 } else {
145 LOCK_LOG_TRY("SLOCK", &sx->sx_object, 0, 0, file, line);
146 mtx_unlock(sx->sx_lock);
147 return (0);
148 }
149 }
150
151 void
152 _sx_xlock(struct sx *sx, const char *file, int line)
153 {
154
155 mtx_lock(sx->sx_lock);
156
157 /*
158 * With sx locks, we're absolutely not permitted to recurse on
159 * xlocks, as it is fatal (deadlock). Normally, recursion is handled
160 * by WITNESS, but as it is not semantically correct to hold the
161 * xlock while in here, we consider it API abuse and put it under
162 * INVARIANTS.
163 */
164 KASSERT(sx->sx_xholder != curthread,
165 ("%s (%s): xlock already held @ %s:%d", __func__,
166 sx->sx_object.lo_name, file, line));
167
168 /* Loop in case we lose the race for lock acquisition. */
169 while (sx->sx_cnt != 0) {
170 sx->sx_excl_wcnt++;
171 cv_wait(&sx->sx_excl_cv, sx->sx_lock);
172 sx->sx_excl_wcnt--;
173 }
174
175 MPASS(sx->sx_cnt == 0);
176
177 /* Acquire an exclusive lock. */
178 sx->sx_cnt--;
179 sx->sx_xholder = curthread;
180
181 LOCK_LOG_LOCK("XLOCK", &sx->sx_object, 0, 0, file, line);
182 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
183
184 mtx_unlock(sx->sx_lock);
185 }
186
187 int
188 _sx_try_xlock(struct sx *sx, const char *file, int line)
189 {
190
191 mtx_lock(sx->sx_lock);
192 if (sx->sx_cnt == 0) {
193 sx->sx_cnt--;
194 sx->sx_xholder = curthread;
195 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 1, file, line);
196 WITNESS_LOCK(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK, file,
197 line);
198 mtx_unlock(sx->sx_lock);
199 return (1);
200 } else {
201 LOCK_LOG_TRY("XLOCK", &sx->sx_object, 0, 0, file, line);
202 mtx_unlock(sx->sx_lock);
203 return (0);
204 }
205 }
206
207 void
208 _sx_sunlock(struct sx *sx, const char *file, int line)
209 {
210
211 _sx_assert(sx, SX_SLOCKED, file, line);
212 mtx_lock(sx->sx_lock);
213
214 WITNESS_UNLOCK(&sx->sx_object, 0, file, line);
215
216 /* Release. */
217 sx->sx_cnt--;
218
219 /*
220 * If we just released the last shared lock, wake any waiters up, giving
221 * exclusive lockers precedence. In order to make sure that exclusive
222 * lockers won't be blocked forever, don't wake shared lock waiters if
223 * there are exclusive lock waiters.
224 */
225 if (sx->sx_excl_wcnt > 0) {
226 if (sx->sx_cnt == 0)
227 cv_signal(&sx->sx_excl_cv);
228 } else if (sx->sx_shrd_wcnt > 0)
229 cv_broadcast(&sx->sx_shrd_cv);
230
231 LOCK_LOG_LOCK("SUNLOCK", &sx->sx_object, 0, 0, file, line);
232
233 mtx_unlock(sx->sx_lock);
234 }
235
236 void
237 _sx_xunlock(struct sx *sx, const char *file, int line)
238 {
239
240 _sx_assert(sx, SX_XLOCKED, file, line);
241 mtx_lock(sx->sx_lock);
242 MPASS(sx->sx_cnt == -1);
243
244 WITNESS_UNLOCK(&sx->sx_object, LOP_EXCLUSIVE, file, line);
245
246 /* Release. */
247 sx->sx_cnt++;
248 sx->sx_xholder = NULL;
249
250 /*
251 * Wake up waiters if there are any. Give precedence to slock waiters.
252 */
253 if (sx->sx_shrd_wcnt > 0)
254 cv_broadcast(&sx->sx_shrd_cv);
255 else if (sx->sx_excl_wcnt > 0)
256 cv_signal(&sx->sx_excl_cv);
257
258 LOCK_LOG_LOCK("XUNLOCK", &sx->sx_object, 0, 0, file, line);
259
260 mtx_unlock(sx->sx_lock);
261 }
262
263 int
264 _sx_try_upgrade(struct sx *sx, const char *file, int line)
265 {
266
267 _sx_assert(sx, SX_SLOCKED, file, line);
268 mtx_lock(sx->sx_lock);
269
270 if (sx->sx_cnt == 1) {
271 sx->sx_cnt = -1;
272 sx->sx_xholder = curthread;
273
274 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 1, file, line);
275 WITNESS_UPGRADE(&sx->sx_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
276 file, line);
277
278 mtx_unlock(sx->sx_lock);
279 return (1);
280 } else {
281 LOCK_LOG_TRY("XUPGRADE", &sx->sx_object, 0, 0, file, line);
282 mtx_unlock(sx->sx_lock);
283 return (0);
284 }
285 }
286
287 void
288 _sx_downgrade(struct sx *sx, const char *file, int line)
289 {
290
291 _sx_assert(sx, SX_XLOCKED, file, line);
292 mtx_lock(sx->sx_lock);
293 MPASS(sx->sx_cnt == -1);
294
295 WITNESS_DOWNGRADE(&sx->sx_object, 0, file, line);
296
297 sx->sx_cnt = 1;
298 sx->sx_xholder = NULL;
299 if (sx->sx_shrd_wcnt > 0)
300 cv_broadcast(&sx->sx_shrd_cv);
301
302 LOCK_LOG_LOCK("XDOWNGRADE", &sx->sx_object, 0, 0, file, line);
303
304 mtx_unlock(sx->sx_lock);
305 }
306
307 #ifdef INVARIANT_SUPPORT
308 #ifndef INVARIANTS
309 #undef _sx_assert
310 #endif
311
312 /*
313 * In the non-WITNESS case, sx_assert() can only detect that at least
314 * *some* thread owns an slock, but it cannot guarantee that *this*
315 * thread owns an slock.
316 */
317 void
318 _sx_assert(struct sx *sx, int what, const char *file, int line)
319 {
320
321 switch (what) {
322 case SX_LOCKED:
323 case SX_SLOCKED:
324 #ifdef WITNESS
325 witness_assert(&sx->sx_object, what, file, line);
326 #else
327 mtx_lock(sx->sx_lock);
328 if (sx->sx_cnt <= 0 &&
329 (what == SX_SLOCKED || sx->sx_xholder != curthread))
330 printf("Lock %s not %slocked @ %s:%d\n",
331 sx->sx_object.lo_name, (what == SX_SLOCKED) ?
332 "share " : "", file, line);
333 mtx_unlock(sx->sx_lock);
334 #endif
335 break;
336 case SX_XLOCKED:
337 mtx_lock(sx->sx_lock);
338 if (sx->sx_xholder != curthread)
339 printf("Lock %s not exclusively locked @ %s:%d\n",
340 sx->sx_object.lo_name, file, line);
341 mtx_unlock(sx->sx_lock);
342 break;
343 default:
344 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
345 line);
346 }
347 }
348 #endif /* INVARIANT_SUPPORT */
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