1 /*-
2 * Copyright (c) 2007 Stephan Uphoff <ups@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 * 3. Neither the name of the author nor the names of any co-contributors
14 * may be used to endorse or promote products derived from this software
15 * without specific prior written permission.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
27 * SUCH DAMAGE.
28 */
29
30 /*
31 * Machine independent bits of reader/writer lock implementation.
32 */
33
34 #include <sys/cdefs.h>
35 __FBSDID("$FreeBSD$");
36
37 #include "opt_ddb.h"
38 #include "opt_kdtrace.h"
39
40 #include <sys/param.h>
41 #include <sys/systm.h>
42
43 #include <sys/kernel.h>
44 #include <sys/ktr.h>
45 #include <sys/lock.h>
46 #include <sys/mutex.h>
47 #include <sys/proc.h>
48 #include <sys/rmlock.h>
49 #include <sys/sched.h>
50 #include <sys/smp.h>
51 #include <sys/systm.h>
52 #include <sys/turnstile.h>
53 #include <sys/lock_profile.h>
54 #include <machine/cpu.h>
55
56 #ifdef DDB
57 #include <ddb/ddb.h>
58 #endif
59
60 #define RMPF_ONQUEUE 1
61 #define RMPF_SIGNAL 2
62
63 /*
64 * To support usage of rmlock in CVs and msleep yet another list for the
65 * priority tracker would be needed. Using this lock for cv and msleep also
66 * does not seem very useful
67 */
68
69 static __inline void compiler_memory_barrier(void) {
70 __asm __volatile("":::"memory");
71 }
72
73 static void assert_rm(struct lock_object *lock, int what);
74 static void lock_rm(struct lock_object *lock, int how);
75 #ifdef KDTRACE_HOOKS
76 static int owner_rm(struct lock_object *lock, struct thread **owner);
77 #endif
78 static int unlock_rm(struct lock_object *lock);
79
80 struct lock_class lock_class_rm = {
81 .lc_name = "rm",
82 .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
83 .lc_assert = assert_rm,
84 #if 0
85 #ifdef DDB
86 .lc_ddb_show = db_show_rwlock,
87 #endif
88 #endif
89 .lc_lock = lock_rm,
90 .lc_unlock = unlock_rm,
91 #ifdef KDTRACE_HOOKS
92 .lc_owner = owner_rm,
93 #endif
94 };
95
96 static void
97 assert_rm(struct lock_object *lock, int what)
98 {
99
100 panic("assert_rm called");
101 }
102
103 static void
104 lock_rm(struct lock_object *lock, int how)
105 {
106
107 panic("lock_rm called");
108 }
109
110 static int
111 unlock_rm(struct lock_object *lock)
112 {
113
114 panic("unlock_rm called");
115 }
116
117 #ifdef KDTRACE_HOOKS
118 static int
119 owner_rm(struct lock_object *lock, struct thread **owner)
120 {
121
122 panic("owner_rm called");
123 }
124 #endif
125
126 static struct mtx rm_spinlock;
127
128 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
129
130 /*
131 * Add or remove tracker from per-cpu list.
132 *
133 * The per-cpu list can be traversed at any time in forward direction from an
134 * interrupt on the *local* cpu.
135 */
136 static void inline
137 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
138 {
139 struct rm_queue *next;
140
141 /* Initialize all tracker pointers */
142 tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
143 next = pc->pc_rm_queue.rmq_next;
144 tracker->rmp_cpuQueue.rmq_next = next;
145
146 /* rmq_prev is not used during froward traversal. */
147 next->rmq_prev = &tracker->rmp_cpuQueue;
148
149 /* Update pointer to first element. */
150 pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
151 }
152
153 static void inline
154 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
155 {
156 struct rm_queue *next, *prev;
157
158 next = tracker->rmp_cpuQueue.rmq_next;
159 prev = tracker->rmp_cpuQueue.rmq_prev;
160
161 /* Not used during forward traversal. */
162 next->rmq_prev = prev;
163
164 /* Remove from list. */
165 prev->rmq_next = next;
166 }
167
168 static void
169 rm_cleanIPI(void *arg)
170 {
171 struct pcpu *pc;
172 struct rmlock *rm = arg;
173 struct rm_priotracker *tracker;
174 struct rm_queue *queue;
175 pc = pcpu_find(curcpu);
176
177 for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
178 queue = queue->rmq_next) {
179 tracker = (struct rm_priotracker *)queue;
180 if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
181 tracker->rmp_flags = RMPF_ONQUEUE;
182 mtx_lock_spin(&rm_spinlock);
183 LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
184 rmp_qentry);
185 mtx_unlock_spin(&rm_spinlock);
186 }
187 }
188 }
189
190 void
191 rm_init_flags(struct rmlock *rm, const char *name, int opts)
192 {
193 int liflags;
194
195 liflags = 0;
196 if (!(opts & RM_NOWITNESS))
197 liflags |= LO_WITNESS;
198 if (opts & RM_RECURSE)
199 liflags |= LO_RECURSABLE;
200 rm->rm_noreadtoken = 1;
201 LIST_INIT(&rm->rm_activeReaders);
202 mtx_init(&rm->rm_lock, name, "rmlock_mtx", MTX_NOWITNESS);
203 lock_init(&rm->lock_object, &lock_class_rm, name, NULL, liflags);
204 }
205
206 void
207 rm_init(struct rmlock *rm, const char *name)
208 {
209
210 rm_init_flags(rm, name, 0);
211 }
212
213 void
214 rm_destroy(struct rmlock *rm)
215 {
216
217 mtx_destroy(&rm->rm_lock);
218 lock_destroy(&rm->lock_object);
219 }
220
221 int
222 rm_wowned(struct rmlock *rm)
223 {
224
225 return (mtx_owned(&rm->rm_lock));
226 }
227
228 void
229 rm_sysinit(void *arg)
230 {
231 struct rm_args *args = arg;
232
233 rm_init(args->ra_rm, args->ra_desc);
234 }
235
236 void
237 rm_sysinit_flags(void *arg)
238 {
239 struct rm_args_flags *args = arg;
240
241 rm_init_flags(args->ra_rm, args->ra_desc, args->ra_opts);
242 }
243
244 static void
245 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker)
246 {
247 struct pcpu *pc;
248 struct rm_queue *queue;
249 struct rm_priotracker *atracker;
250
251 critical_enter();
252 pc = pcpu_find(curcpu);
253
254 /* Check if we just need to do a proper critical_exit. */
255 if (0 == rm->rm_noreadtoken) {
256 critical_exit();
257 return;
258 }
259
260 /* Remove our tracker from the per-cpu list. */
261 rm_tracker_remove(pc, tracker);
262
263 /* Check to see if the IPI granted us the lock after all. */
264 if (tracker->rmp_flags) {
265 /* Just add back tracker - we hold the lock. */
266 rm_tracker_add(pc, tracker);
267 critical_exit();
268 return;
269 }
270
271 /*
272 * We allow readers to aquire a lock even if a writer is blocked if
273 * the lock is recursive and the reader already holds the lock.
274 */
275 if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
276 /*
277 * Just grant the lock if this thread already has a tracker
278 * for this lock on the per-cpu queue.
279 */
280 for (queue = pc->pc_rm_queue.rmq_next;
281 queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
282 atracker = (struct rm_priotracker *)queue;
283 if ((atracker->rmp_rmlock == rm) &&
284 (atracker->rmp_thread == tracker->rmp_thread)) {
285 mtx_lock_spin(&rm_spinlock);
286 LIST_INSERT_HEAD(&rm->rm_activeReaders,
287 tracker, rmp_qentry);
288 tracker->rmp_flags = RMPF_ONQUEUE;
289 mtx_unlock_spin(&rm_spinlock);
290 rm_tracker_add(pc, tracker);
291 critical_exit();
292 return;
293 }
294 }
295 }
296
297 sched_unpin();
298 critical_exit();
299
300 mtx_lock(&rm->rm_lock);
301 rm->rm_noreadtoken = 0;
302 critical_enter();
303
304 pc = pcpu_find(curcpu);
305 rm_tracker_add(pc, tracker);
306 sched_pin();
307 critical_exit();
308
309 mtx_unlock(&rm->rm_lock);
310 }
311
312 void
313 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker)
314 {
315 struct thread *td = curthread;
316 struct pcpu *pc;
317
318 if (SCHEDULER_STOPPED())
319 return;
320
321 tracker->rmp_flags = 0;
322 tracker->rmp_thread = td;
323 tracker->rmp_rmlock = rm;
324
325 td->td_critnest++; /* critical_enter(); */
326
327 compiler_memory_barrier();
328
329 pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
330
331 rm_tracker_add(pc, tracker);
332
333 sched_pin();
334
335 compiler_memory_barrier();
336
337 td->td_critnest--;
338
339 /*
340 * Fast path to combine two common conditions into a single
341 * conditional jump.
342 */
343 if (0 == (td->td_owepreempt | rm->rm_noreadtoken))
344 return;
345
346 /* We do not have a read token and need to acquire one. */
347 _rm_rlock_hard(rm, tracker);
348 }
349
350 static void
351 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
352 {
353
354 if (td->td_owepreempt) {
355 td->td_critnest++;
356 critical_exit();
357 }
358
359 if (!tracker->rmp_flags)
360 return;
361
362 mtx_lock_spin(&rm_spinlock);
363 LIST_REMOVE(tracker, rmp_qentry);
364
365 if (tracker->rmp_flags & RMPF_SIGNAL) {
366 struct rmlock *rm;
367 struct turnstile *ts;
368
369 rm = tracker->rmp_rmlock;
370
371 turnstile_chain_lock(&rm->lock_object);
372 mtx_unlock_spin(&rm_spinlock);
373
374 ts = turnstile_lookup(&rm->lock_object);
375
376 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
377 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
378 turnstile_chain_unlock(&rm->lock_object);
379 } else
380 mtx_unlock_spin(&rm_spinlock);
381 }
382
383 void
384 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
385 {
386 struct pcpu *pc;
387 struct thread *td = tracker->rmp_thread;
388
389 if (SCHEDULER_STOPPED())
390 return;
391
392 td->td_critnest++; /* critical_enter(); */
393 pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
394 rm_tracker_remove(pc, tracker);
395 td->td_critnest--;
396 sched_unpin();
397
398 if (0 == (td->td_owepreempt | tracker->rmp_flags))
399 return;
400
401 _rm_unlock_hard(td, tracker);
402 }
403
404 void
405 _rm_wlock(struct rmlock *rm)
406 {
407 struct rm_priotracker *prio;
408 struct turnstile *ts;
409
410 if (SCHEDULER_STOPPED())
411 return;
412
413 mtx_lock(&rm->rm_lock);
414
415 if (rm->rm_noreadtoken == 0) {
416 /* Get all read tokens back */
417
418 rm->rm_noreadtoken = 1;
419
420 /*
421 * Assumes rm->rm_noreadtoken update is visible on other CPUs
422 * before rm_cleanIPI is called.
423 */
424 #ifdef SMP
425 smp_rendezvous(smp_no_rendevous_barrier,
426 rm_cleanIPI,
427 smp_no_rendevous_barrier,
428 rm);
429
430 #else
431 rm_cleanIPI(rm);
432 #endif
433
434 mtx_lock_spin(&rm_spinlock);
435 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
436 ts = turnstile_trywait(&rm->lock_object);
437 prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
438 mtx_unlock_spin(&rm_spinlock);
439 turnstile_wait(ts, prio->rmp_thread,
440 TS_EXCLUSIVE_QUEUE);
441 mtx_lock_spin(&rm_spinlock);
442 }
443 mtx_unlock_spin(&rm_spinlock);
444 }
445 }
446
447 void
448 _rm_wunlock(struct rmlock *rm)
449 {
450
451 mtx_unlock(&rm->rm_lock);
452 }
453
454 #ifdef LOCK_DEBUG
455
456 void _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
457 {
458
459 if (SCHEDULER_STOPPED())
460 return;
461
462 WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
463 file, line, NULL);
464
465 _rm_wlock(rm);
466
467 LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
468
469 WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
470
471 curthread->td_locks++;
472
473 }
474
475 void
476 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
477 {
478
479 if (SCHEDULER_STOPPED())
480 return;
481
482 curthread->td_locks--;
483 WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
484 LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
485 _rm_wunlock(rm);
486 }
487
488 void
489 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
490 const char *file, int line)
491 {
492
493 if (SCHEDULER_STOPPED())
494 return;
495
496 WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER, file, line, NULL);
497
498 _rm_rlock(rm, tracker);
499
500 LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file, line);
501
502 WITNESS_LOCK(&rm->lock_object, 0, file, line);
503
504 curthread->td_locks++;
505 }
506
507 void
508 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
509 const char *file, int line)
510 {
511
512 if (SCHEDULER_STOPPED())
513 return;
514
515 curthread->td_locks--;
516 WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
517 LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
518 _rm_runlock(rm, tracker);
519 }
520
521 #else
522
523 /*
524 * Just strip out file and line arguments if no lock debugging is enabled in
525 * the kernel - we are called from a kernel module.
526 */
527 void
528 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
529 {
530
531 _rm_wlock(rm);
532 }
533
534 void
535 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
536 {
537
538 _rm_wunlock(rm);
539 }
540
541 void
542 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
543 const char *file, int line)
544 {
545
546 _rm_rlock(rm, tracker);
547 }
548
549 void
550 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
551 const char *file, int line)
552 {
553
554 _rm_runlock(rm, tracker);
555 }
556
557 #endif
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