xref: /freebsd/sys/kern/kern_rmlock.c (revision 2710751bc309af25c6dea1171781678258e83840) 
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/kdb.h>
45 #include <sys/ktr.h>
46 #include <sys/lock.h>
47 #include <sys/mutex.h>
48 #include <sys/proc.h>
49 #include <sys/rmlock.h>
50 #include <sys/sched.h>
51 #include <sys/smp.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 void	assert_rm(const struct lock_object *lock, int what);
70 static void	lock_rm(struct lock_object *lock, int how);
71 #ifdef KDTRACE_HOOKS
72 static int	owner_rm(const struct lock_object *lock, struct thread **owner);
73 #endif
74 static int	unlock_rm(struct lock_object *lock);
75 
76 struct lock_class lock_class_rm = {
77 	.lc_name = "rm",
78 	.lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
79 	.lc_assert = assert_rm,
80 #if 0
81 #ifdef DDB
82 	.lc_ddb_show = db_show_rwlock,
83 #endif
84 #endif
85 	.lc_lock = lock_rm,
86 	.lc_unlock = unlock_rm,
87 #ifdef KDTRACE_HOOKS
88 	.lc_owner = owner_rm,
89 #endif
90 };
91 
92 static void
93 assert_rm(const struct lock_object *lock, int what)
94 {
95 
96 	panic("assert_rm called");
97 }
98 
99 static void
100 lock_rm(struct lock_object *lock, int how)
101 {
102 
103 	panic("lock_rm called");
104 }
105 
106 static int
107 unlock_rm(struct lock_object *lock)
108 {
109 
110 	panic("unlock_rm called");
111 }
112 
113 #ifdef KDTRACE_HOOKS
114 static int
115 owner_rm(const struct lock_object *lock, struct thread **owner)
116 {
117 
118 	panic("owner_rm called");
119 }
120 #endif
121 
122 static struct mtx rm_spinlock;
123 
124 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
125 
126 /*
127  * Add or remove tracker from per-cpu list.
128  *
129  * The per-cpu list can be traversed at any time in forward direction from an
130  * interrupt on the *local* cpu.
131  */
132 static void inline
133 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
134 {
135 	struct rm_queue *next;
136 
137 	/* Initialize all tracker pointers */
138 	tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
139 	next = pc->pc_rm_queue.rmq_next;
140 	tracker->rmp_cpuQueue.rmq_next = next;
141 
142 	/* rmq_prev is not used during froward traversal. */
143 	next->rmq_prev = &tracker->rmp_cpuQueue;
144 
145 	/* Update pointer to first element. */
146 	pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
147 }
148 
149 static void inline
150 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
151 {
152 	struct rm_queue *next, *prev;
153 
154 	next = tracker->rmp_cpuQueue.rmq_next;
155 	prev = tracker->rmp_cpuQueue.rmq_prev;
156 
157 	/* Not used during forward traversal. */
158 	next->rmq_prev = prev;
159 
160 	/* Remove from list. */
161 	prev->rmq_next = next;
162 }
163 
164 static void
165 rm_cleanIPI(void *arg)
166 {
167 	struct pcpu *pc;
168 	struct rmlock *rm = arg;
169 	struct rm_priotracker *tracker;
170 	struct rm_queue *queue;
171 	pc = pcpu_find(curcpu);
172 
173 	for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
174 	    queue = queue->rmq_next) {
175 		tracker = (struct rm_priotracker *)queue;
176 		if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
177 			tracker->rmp_flags = RMPF_ONQUEUE;
178 			mtx_lock_spin(&rm_spinlock);
179 			LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
180 			    rmp_qentry);
181 			mtx_unlock_spin(&rm_spinlock);
182 		}
183 	}
184 }
185 
186 CTASSERT((RM_SLEEPABLE & LO_CLASSFLAGS) == RM_SLEEPABLE);
187 
188 void
189 rm_init_flags(struct rmlock *rm, const char *name, int opts)
190 {
191 	int liflags;
192 
193 	liflags = 0;
194 	if (!(opts & RM_NOWITNESS))
195 		liflags |= LO_WITNESS;
196 	if (opts & RM_RECURSE)
197 		liflags |= LO_RECURSABLE;
198 	rm->rm_writecpus = all_cpus;
199 	LIST_INIT(&rm->rm_activeReaders);
200 	if (opts & RM_SLEEPABLE) {
201 		liflags |= RM_SLEEPABLE;
202 		sx_init_flags(&rm->rm_lock_sx, "rmlock_sx", SX_RECURSE);
203 	} else
204 		mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx", MTX_NOWITNESS);
205 	lock_init(&rm->lock_object, &lock_class_rm, name, NULL, liflags);
206 }
207 
208 void
209 rm_init(struct rmlock *rm, const char *name)
210 {
211 
212 	rm_init_flags(rm, name, 0);
213 }
214 
215 void
216 rm_destroy(struct rmlock *rm)
217 {
218 
219 	if (rm->lock_object.lo_flags & RM_SLEEPABLE)
220 		sx_destroy(&rm->rm_lock_sx);
221 	else
222 		mtx_destroy(&rm->rm_lock_mtx);
223 	lock_destroy(&rm->lock_object);
224 }
225 
226 int
227 rm_wowned(const struct rmlock *rm)
228 {
229 
230 	if (rm->lock_object.lo_flags & RM_SLEEPABLE)
231 		return (sx_xlocked(&rm->rm_lock_sx));
232 	else
233 		return (mtx_owned(&rm->rm_lock_mtx));
234 }
235 
236 void
237 rm_sysinit(void *arg)
238 {
239 	struct rm_args *args = arg;
240 
241 	rm_init(args->ra_rm, args->ra_desc);
242 }
243 
244 void
245 rm_sysinit_flags(void *arg)
246 {
247 	struct rm_args_flags *args = arg;
248 
249 	rm_init_flags(args->ra_rm, args->ra_desc, args->ra_opts);
250 }
251 
252 static int
253 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
254 {
255 	struct pcpu *pc;
256 	struct rm_queue *queue;
257 	struct rm_priotracker *atracker;
258 
259 	critical_enter();
260 	pc = pcpu_find(curcpu);
261 
262 	/* Check if we just need to do a proper critical_exit. */
263 	if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
264 		critical_exit();
265 		return (1);
266 	}
267 
268 	/* Remove our tracker from the per-cpu list. */
269 	rm_tracker_remove(pc, tracker);
270 
271 	/* Check to see if the IPI granted us the lock after all. */
272 	if (tracker->rmp_flags) {
273 		/* Just add back tracker - we hold the lock. */
274 		rm_tracker_add(pc, tracker);
275 		critical_exit();
276 		return (1);
277 	}
278 
279 	/*
280 	 * We allow readers to aquire a lock even if a writer is blocked if
281 	 * the lock is recursive and the reader already holds the lock.
282 	 */
283 	if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
284 		/*
285 		 * Just grant the lock if this thread already has a tracker
286 		 * for this lock on the per-cpu queue.
287 		 */
288 		for (queue = pc->pc_rm_queue.rmq_next;
289 		    queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
290 			atracker = (struct rm_priotracker *)queue;
291 			if ((atracker->rmp_rmlock == rm) &&
292 			    (atracker->rmp_thread == tracker->rmp_thread)) {
293 				mtx_lock_spin(&rm_spinlock);
294 				LIST_INSERT_HEAD(&rm->rm_activeReaders,
295 				    tracker, rmp_qentry);
296 				tracker->rmp_flags = RMPF_ONQUEUE;
297 				mtx_unlock_spin(&rm_spinlock);
298 				rm_tracker_add(pc, tracker);
299 				critical_exit();
300 				return (1);
301 			}
302 		}
303 	}
304 
305 	sched_unpin();
306 	critical_exit();
307 
308 	if (trylock) {
309 		if (rm->lock_object.lo_flags & RM_SLEEPABLE) {
310 			if (!sx_try_xlock(&rm->rm_lock_sx))
311 				return (0);
312 		} else {
313 			if (!mtx_trylock(&rm->rm_lock_mtx))
314 				return (0);
315 		}
316 	} else {
317 		if (rm->lock_object.lo_flags & RM_SLEEPABLE)
318 			sx_xlock(&rm->rm_lock_sx);
319 		else
320 			mtx_lock(&rm->rm_lock_mtx);
321 	}
322 
323 	critical_enter();
324 	pc = pcpu_find(curcpu);
325 	CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
326 	rm_tracker_add(pc, tracker);
327 	sched_pin();
328 	critical_exit();
329 
330 	if (rm->lock_object.lo_flags & RM_SLEEPABLE)
331 		sx_xunlock(&rm->rm_lock_sx);
332 	else
333 		mtx_unlock(&rm->rm_lock_mtx);
334 
335 	return (1);
336 }
337 
338 int
339 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
340 {
341 	struct thread *td = curthread;
342 	struct pcpu *pc;
343 
344 	if (SCHEDULER_STOPPED())
345 		return (1);
346 
347 	tracker->rmp_flags  = 0;
348 	tracker->rmp_thread = td;
349 	tracker->rmp_rmlock = rm;
350 
351 	td->td_critnest++;	/* critical_enter(); */
352 
353 	__compiler_membar();
354 
355 	pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
356 
357 	rm_tracker_add(pc, tracker);
358 
359 	sched_pin();
360 
361 	__compiler_membar();
362 
363 	td->td_critnest--;
364 
365 	/*
366 	 * Fast path to combine two common conditions into a single
367 	 * conditional jump.
368 	 */
369 	if (0 == (td->td_owepreempt |
370 	    CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)))
371 		return (1);
372 
373 	/* We do not have a read token and need to acquire one. */
374 	return _rm_rlock_hard(rm, tracker, trylock);
375 }
376 
377 static void
378 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
379 {
380 
381 	if (td->td_owepreempt) {
382 		td->td_critnest++;
383 		critical_exit();
384 	}
385 
386 	if (!tracker->rmp_flags)
387 		return;
388 
389 	mtx_lock_spin(&rm_spinlock);
390 	LIST_REMOVE(tracker, rmp_qentry);
391 
392 	if (tracker->rmp_flags & RMPF_SIGNAL) {
393 		struct rmlock *rm;
394 		struct turnstile *ts;
395 
396 		rm = tracker->rmp_rmlock;
397 
398 		turnstile_chain_lock(&rm->lock_object);
399 		mtx_unlock_spin(&rm_spinlock);
400 
401 		ts = turnstile_lookup(&rm->lock_object);
402 
403 		turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
404 		turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
405 		turnstile_chain_unlock(&rm->lock_object);
406 	} else
407 		mtx_unlock_spin(&rm_spinlock);
408 }
409 
410 void
411 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
412 {
413 	struct pcpu *pc;
414 	struct thread *td = tracker->rmp_thread;
415 
416 	if (SCHEDULER_STOPPED())
417 		return;
418 
419 	td->td_critnest++;	/* critical_enter(); */
420 	pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
421 	rm_tracker_remove(pc, tracker);
422 	td->td_critnest--;
423 	sched_unpin();
424 
425 	if (0 == (td->td_owepreempt | tracker->rmp_flags))
426 		return;
427 
428 	_rm_unlock_hard(td, tracker);
429 }
430 
431 void
432 _rm_wlock(struct rmlock *rm)
433 {
434 	struct rm_priotracker *prio;
435 	struct turnstile *ts;
436 	cpuset_t readcpus;
437 
438 	if (SCHEDULER_STOPPED())
439 		return;
440 
441 	if (rm->lock_object.lo_flags & RM_SLEEPABLE)
442 		sx_xlock(&rm->rm_lock_sx);
443 	else
444 		mtx_lock(&rm->rm_lock_mtx);
445 
446 	if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
447 		/* Get all read tokens back */
448 		readcpus = all_cpus;
449 		CPU_NAND(&readcpus, &rm->rm_writecpus);
450 		rm->rm_writecpus = all_cpus;
451 
452 		/*
453 		 * Assumes rm->rm_writecpus update is visible on other CPUs
454 		 * before rm_cleanIPI is called.
455 		 */
456 #ifdef SMP
457 		smp_rendezvous_cpus(readcpus,
458 		    smp_no_rendevous_barrier,
459 		    rm_cleanIPI,
460 		    smp_no_rendevous_barrier,
461 		    rm);
462 
463 #else
464 		rm_cleanIPI(rm);
465 #endif
466 
467 		mtx_lock_spin(&rm_spinlock);
468 		while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
469 			ts = turnstile_trywait(&rm->lock_object);
470 			prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
471 			mtx_unlock_spin(&rm_spinlock);
472 			turnstile_wait(ts, prio->rmp_thread,
473 			    TS_EXCLUSIVE_QUEUE);
474 			mtx_lock_spin(&rm_spinlock);
475 		}
476 		mtx_unlock_spin(&rm_spinlock);
477 	}
478 }
479 
480 void
481 _rm_wunlock(struct rmlock *rm)
482 {
483 
484 	if (rm->lock_object.lo_flags & RM_SLEEPABLE)
485 		sx_xunlock(&rm->rm_lock_sx);
486 	else
487 		mtx_unlock(&rm->rm_lock_mtx);
488 }
489 
490 #ifdef LOCK_DEBUG
491 
492 void _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
493 {
494 
495 	if (SCHEDULER_STOPPED())
496 		return;
497 
498 	KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
499 	    ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
500 	    curthread, rm->lock_object.lo_name, file, line));
501 	WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
502 	    file, line, NULL);
503 
504 	_rm_wlock(rm);
505 
506 	LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
507 
508 	if (rm->lock_object.lo_flags & RM_SLEEPABLE)
509 		WITNESS_LOCK(&rm->rm_lock_sx.lock_object, LOP_EXCLUSIVE,
510 		    file, line);
511 	else
512 		WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
513 
514 	curthread->td_locks++;
515 
516 }
517 
518 void
519 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
520 {
521 
522 	if (SCHEDULER_STOPPED())
523 		return;
524 
525 	curthread->td_locks--;
526 	if (rm->lock_object.lo_flags & RM_SLEEPABLE)
527 		WITNESS_UNLOCK(&rm->rm_lock_sx.lock_object, LOP_EXCLUSIVE,
528 		    file, line);
529 	else
530 		WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
531 	LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
532 	_rm_wunlock(rm);
533 }
534 
535 int
536 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
537     int trylock, const char *file, int line)
538 {
539 
540 	if (SCHEDULER_STOPPED())
541 		return (1);
542 
543 	KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
544 	    ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
545 	    curthread, rm->lock_object.lo_name, file, line));
546 	if (!trylock && (rm->lock_object.lo_flags & RM_SLEEPABLE))
547 		WITNESS_CHECKORDER(&rm->rm_lock_sx.lock_object, LOP_NEWORDER,
548 		    file, line, NULL);
549 	WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER, file, line, NULL);
550 
551 	if (_rm_rlock(rm, tracker, trylock)) {
552 		LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file, line);
553 
554 		WITNESS_LOCK(&rm->lock_object, 0, file, line);
555 
556 		curthread->td_locks++;
557 
558 		return (1);
559 	}
560 
561 	return (0);
562 }
563 
564 void
565 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
566     const char *file, int line)
567 {
568 
569 	if (SCHEDULER_STOPPED())
570 		return;
571 
572 	curthread->td_locks--;
573 	WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
574 	LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
575 	_rm_runlock(rm, tracker);
576 }
577 
578 #else
579 
580 /*
581  * Just strip out file and line arguments if no lock debugging is enabled in
582  * the kernel - we are called from a kernel module.
583  */
584 void
585 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
586 {
587 
588 	_rm_wlock(rm);
589 }
590 
591 void
592 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
593 {
594 
595 	_rm_wunlock(rm);
596 }
597 
598 int
599 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
600     int trylock, const char *file, int line)
601 {
602 
603 	return _rm_rlock(rm, tracker, trylock);
604 }
605 
606 void
607 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
608     const char *file, int line)
609 {
610 
611 	_rm_runlock(rm, tracker);
612 }
613 
614 #endif
615