1 /*-
2 * Copyright (c) 2006 John Baldwin <jhb@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 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27 /*
28 * Machine independent bits of reader/writer lock implementation.
29 */
30
31 #include <sys/cdefs.h>
32 __FBSDID("$FreeBSD: releng/11.1/sys/kern/kern_rwlock.c 320241 2017-06-22 18:40:34Z markj $");
33
34 #include "opt_ddb.h"
35 #include "opt_hwpmc_hooks.h"
36 #include "opt_no_adaptive_rwlocks.h"
37
38 #include <sys/param.h>
39 #include <sys/kdb.h>
40 #include <sys/ktr.h>
41 #include <sys/kernel.h>
42 #include <sys/lock.h>
43 #include <sys/mutex.h>
44 #include <sys/proc.h>
45 #include <sys/rwlock.h>
46 #include <sys/sched.h>
47 #include <sys/smp.h>
48 #include <sys/sysctl.h>
49 #include <sys/systm.h>
50 #include <sys/turnstile.h>
51
52 #include <machine/cpu.h>
53
54 #if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS)
55 #define ADAPTIVE_RWLOCKS
56 #endif
57
58 #ifdef HWPMC_HOOKS
59 #include <sys/pmckern.h>
60 PMC_SOFT_DECLARE( , , lock, failed);
61 #endif
62
63 /*
64 * Return the rwlock address when the lock cookie address is provided.
65 * This functionality assumes that struct rwlock* have a member named rw_lock.
66 */
67 #define rwlock2rw(c) (__containerof(c, struct rwlock, rw_lock))
68
69 #ifdef DDB
70 #include <ddb/ddb.h>
71
72 static void db_show_rwlock(const struct lock_object *lock);
73 #endif
74 static void assert_rw(const struct lock_object *lock, int what);
75 static void lock_rw(struct lock_object *lock, uintptr_t how);
76 #ifdef KDTRACE_HOOKS
77 static int owner_rw(const struct lock_object *lock, struct thread **owner);
78 #endif
79 static uintptr_t unlock_rw(struct lock_object *lock);
80
81 struct lock_class lock_class_rw = {
82 .lc_name = "rw",
83 .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE,
84 .lc_assert = assert_rw,
85 #ifdef DDB
86 .lc_ddb_show = db_show_rwlock,
87 #endif
88 .lc_lock = lock_rw,
89 .lc_unlock = unlock_rw,
90 #ifdef KDTRACE_HOOKS
91 .lc_owner = owner_rw,
92 #endif
93 };
94
95 #ifdef ADAPTIVE_RWLOCKS
96 static int rowner_retries = 10;
97 static int rowner_loops = 10000;
98 static SYSCTL_NODE(_debug, OID_AUTO, rwlock, CTLFLAG_RD, NULL,
99 "rwlock debugging");
100 SYSCTL_INT(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
101 SYSCTL_INT(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
102
103 static struct lock_delay_config __read_mostly rw_delay;
104
105 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_base, CTLFLAG_RW, &rw_delay.base,
106 0, "");
107 SYSCTL_INT(_debug_rwlock, OID_AUTO, delay_max, CTLFLAG_RW, &rw_delay.max,
108 0, "");
109
110 LOCK_DELAY_SYSINIT_DEFAULT(rw_delay);
111 #endif
112
113 /*
114 * Return a pointer to the owning thread if the lock is write-locked or
115 * NULL if the lock is unlocked or read-locked.
116 */
117
118 #define lv_rw_wowner(v) \
119 ((v) & RW_LOCK_READ ? NULL : \
120 (struct thread *)RW_OWNER((v)))
121
122 #define rw_wowner(rw) lv_rw_wowner(RW_READ_VALUE(rw))
123
124 /*
125 * Returns if a write owner is recursed. Write ownership is not assured
126 * here and should be previously checked.
127 */
128 #define rw_recursed(rw) ((rw)->rw_recurse != 0)
129
130 /*
131 * Return true if curthread helds the lock.
132 */
133 #define rw_wlocked(rw) (rw_wowner((rw)) == curthread)
134
135 /*
136 * Return a pointer to the owning thread for this lock who should receive
137 * any priority lent by threads that block on this lock. Currently this
138 * is identical to rw_wowner().
139 */
140 #define rw_owner(rw) rw_wowner(rw)
141
142 #ifndef INVARIANTS
143 #define __rw_assert(c, what, file, line)
144 #endif
145
146 void
147 assert_rw(const struct lock_object *lock, int what)
148 {
149
150 rw_assert((const struct rwlock *)lock, what);
151 }
152
153 void
154 lock_rw(struct lock_object *lock, uintptr_t how)
155 {
156 struct rwlock *rw;
157
158 rw = (struct rwlock *)lock;
159 if (how)
160 rw_rlock(rw);
161 else
162 rw_wlock(rw);
163 }
164
165 uintptr_t
166 unlock_rw(struct lock_object *lock)
167 {
168 struct rwlock *rw;
169
170 rw = (struct rwlock *)lock;
171 rw_assert(rw, RA_LOCKED | LA_NOTRECURSED);
172 if (rw->rw_lock & RW_LOCK_READ) {
173 rw_runlock(rw);
174 return (1);
175 } else {
176 rw_wunlock(rw);
177 return (0);
178 }
179 }
180
181 #ifdef KDTRACE_HOOKS
182 int
183 owner_rw(const struct lock_object *lock, struct thread **owner)
184 {
185 const struct rwlock *rw = (const struct rwlock *)lock;
186 uintptr_t x = rw->rw_lock;
187
188 *owner = rw_wowner(rw);
189 return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) :
190 (*owner != NULL));
191 }
192 #endif
193
194 void
195 _rw_init_flags(volatile uintptr_t *c, const char *name, int opts)
196 {
197 struct rwlock *rw;
198 int flags;
199
200 rw = rwlock2rw(c);
201
202 MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
203 RW_RECURSE | RW_NEW)) == 0);
204 ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
205 ("%s: rw_lock not aligned for %s: %p", __func__, name,
206 &rw->rw_lock));
207
208 flags = LO_UPGRADABLE;
209 if (opts & RW_DUPOK)
210 flags |= LO_DUPOK;
211 if (opts & RW_NOPROFILE)
212 flags |= LO_NOPROFILE;
213 if (!(opts & RW_NOWITNESS))
214 flags |= LO_WITNESS;
215 if (opts & RW_RECURSE)
216 flags |= LO_RECURSABLE;
217 if (opts & RW_QUIET)
218 flags |= LO_QUIET;
219 if (opts & RW_NEW)
220 flags |= LO_NEW;
221
222 lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
223 rw->rw_lock = RW_UNLOCKED;
224 rw->rw_recurse = 0;
225 }
226
227 void
228 _rw_destroy(volatile uintptr_t *c)
229 {
230 struct rwlock *rw;
231
232 rw = rwlock2rw(c);
233
234 KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw));
235 KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw));
236 rw->rw_lock = RW_DESTROYED;
237 lock_destroy(&rw->lock_object);
238 }
239
240 void
241 rw_sysinit(void *arg)
242 {
243 struct rw_args *args = arg;
244
245 rw_init((struct rwlock *)args->ra_rw, args->ra_desc);
246 }
247
248 void
249 rw_sysinit_flags(void *arg)
250 {
251 struct rw_args_flags *args = arg;
252
253 rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc,
254 args->ra_flags);
255 }
256
257 int
258 _rw_wowned(const volatile uintptr_t *c)
259 {
260
261 return (rw_wowner(rwlock2rw(c)) == curthread);
262 }
263
264 void
265 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line)
266 {
267 struct rwlock *rw;
268 uintptr_t tid, v;
269
270 rw = rwlock2rw(c);
271
272 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
273 !TD_IS_IDLETHREAD(curthread),
274 ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d",
275 curthread, rw->lock_object.lo_name, file, line));
276 KASSERT(rw->rw_lock != RW_DESTROYED,
277 ("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
278 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
279 line, NULL);
280 tid = (uintptr_t)curthread;
281 v = RW_UNLOCKED;
282 if (!_rw_write_lock_fetch(rw, &v, tid))
283 _rw_wlock_hard(rw, v, tid, file, line);
284 else
285 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw,
286 0, 0, file, line, LOCKSTAT_WRITER);
287
288 LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
289 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
290 TD_LOCKS_INC(curthread);
291 }
292
293 int
294 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
295 {
296 struct rwlock *rw;
297 struct thread *td;
298 uintptr_t tid, v;
299 int rval;
300 bool recursed;
301
302 td = curthread;
303 tid = (uintptr_t)td;
304 if (SCHEDULER_STOPPED_TD(td))
305 return (1);
306
307 rw = rwlock2rw(c);
308
309 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
310 ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d",
311 curthread, rw->lock_object.lo_name, file, line));
312 KASSERT(rw->rw_lock != RW_DESTROYED,
313 ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
314
315 rval = 1;
316 recursed = false;
317 v = RW_UNLOCKED;
318 for (;;) {
319 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
320 break;
321 if (v == RW_UNLOCKED)
322 continue;
323 if (v == tid && (rw->lock_object.lo_flags & LO_RECURSABLE)) {
324 rw->rw_recurse++;
325 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
326 break;
327 }
328 rval = 0;
329 break;
330 }
331
332 LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
333 if (rval) {
334 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
335 file, line);
336 if (!recursed)
337 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
338 rw, 0, 0, file, line, LOCKSTAT_WRITER);
339 TD_LOCKS_INC(curthread);
340 }
341 return (rval);
342 }
343
344 void
345 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
346 {
347 struct rwlock *rw;
348
349 rw = rwlock2rw(c);
350
351 KASSERT(rw->rw_lock != RW_DESTROYED,
352 ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
353 __rw_assert(c, RA_WLOCKED, file, line);
354 WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
355 LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
356 line);
357
358 #ifdef LOCK_PROFILING
359 _rw_wunlock_hard(rw, (uintptr_t)curthread, file, line);
360 #else
361 __rw_wunlock(rw, curthread, file, line);
362 #endif
363
364 TD_LOCKS_DEC(curthread);
365 }
366
367 /*
368 * Determines whether a new reader can acquire a lock. Succeeds if the
369 * reader already owns a read lock and the lock is locked for read to
370 * prevent deadlock from reader recursion. Also succeeds if the lock
371 * is unlocked and has no writer waiters or spinners. Failing otherwise
372 * prioritizes writers before readers.
373 */
374 #define RW_CAN_READ(td, _rw) \
375 (((td)->td_rw_rlocks && (_rw) & RW_LOCK_READ) || ((_rw) & \
376 (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) == \
377 RW_LOCK_READ)
378
379 static bool __always_inline
380 __rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp,
381 const char *file, int line)
382 {
383
384 /*
385 * Handle the easy case. If no other thread has a write
386 * lock, then try to bump up the count of read locks. Note
387 * that we have to preserve the current state of the
388 * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a
389 * read lock, then rw_lock must have changed, so restart
390 * the loop. Note that this handles the case of a
391 * completely unlocked rwlock since such a lock is encoded
392 * as a read lock with no waiters.
393 */
394 while (RW_CAN_READ(td, *vp)) {
395 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, vp,
396 *vp + RW_ONE_READER)) {
397 if (LOCK_LOG_TEST(&rw->lock_object, 0))
398 CTR4(KTR_LOCK,
399 "%s: %p succeed %p -> %p", __func__,
400 rw, (void *)*vp,
401 (void *)(*vp + RW_ONE_READER));
402 td->td_rw_rlocks++;
403 return (true);
404 }
405 }
406 return (false);
407 }
408
409 static void __noinline
410 __rw_rlock_hard(volatile uintptr_t *c, struct thread *td, uintptr_t v,
411 const char *file, int line)
412 {
413 struct rwlock *rw;
414 struct turnstile *ts;
415 #ifdef ADAPTIVE_RWLOCKS
416 volatile struct thread *owner;
417 int spintries = 0;
418 int i;
419 #endif
420 #ifdef LOCK_PROFILING
421 uint64_t waittime = 0;
422 int contested = 0;
423 #endif
424 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
425 struct lock_delay_arg lda;
426 #endif
427 #ifdef KDTRACE_HOOKS
428 uintptr_t state;
429 u_int sleep_cnt = 0;
430 int64_t sleep_time = 0;
431 int64_t all_time = 0;
432 #endif
433
434 if (SCHEDULER_STOPPED())
435 return;
436
437 #if defined(ADAPTIVE_RWLOCKS)
438 lock_delay_arg_init(&lda, &rw_delay);
439 #elif defined(KDTRACE_HOOKS)
440 lock_delay_arg_init(&lda, NULL);
441 #endif
442 rw = rwlock2rw(c);
443
444 #ifdef KDTRACE_HOOKS
445 all_time -= lockstat_nsecs(&rw->lock_object);
446 #endif
447 #ifdef KDTRACE_HOOKS
448 state = v;
449 #endif
450 for (;;) {
451 if (__rw_rlock_try(rw, td, &v, file, line))
452 break;
453 #ifdef KDTRACE_HOOKS
454 lda.spin_cnt++;
455 #endif
456 #ifdef HWPMC_HOOKS
457 PMC_SOFT_CALL( , , lock, failed);
458 #endif
459 lock_profile_obtain_lock_failed(&rw->lock_object,
460 &contested, &waittime);
461
462 #ifdef ADAPTIVE_RWLOCKS
463 /*
464 * If the owner is running on another CPU, spin until
465 * the owner stops running or the state of the lock
466 * changes.
467 */
468 if ((v & RW_LOCK_READ) == 0) {
469 owner = (struct thread *)RW_OWNER(v);
470 if (TD_IS_RUNNING(owner)) {
471 if (LOCK_LOG_TEST(&rw->lock_object, 0))
472 CTR3(KTR_LOCK,
473 "%s: spinning on %p held by %p",
474 __func__, rw, owner);
475 KTR_STATE1(KTR_SCHED, "thread",
476 sched_tdname(curthread), "spinning",
477 "lockname:\"%s\"", rw->lock_object.lo_name);
478 do {
479 lock_delay(&lda);
480 v = RW_READ_VALUE(rw);
481 owner = lv_rw_wowner(v);
482 } while (owner != NULL && TD_IS_RUNNING(owner));
483 KTR_STATE0(KTR_SCHED, "thread",
484 sched_tdname(curthread), "running");
485 continue;
486 }
487 } else if (spintries < rowner_retries) {
488 spintries++;
489 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
490 "spinning", "lockname:\"%s\"",
491 rw->lock_object.lo_name);
492 for (i = 0; i < rowner_loops; i++) {
493 v = RW_READ_VALUE(rw);
494 if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(td, v))
495 break;
496 cpu_spinwait();
497 }
498 v = RW_READ_VALUE(rw);
499 #ifdef KDTRACE_HOOKS
500 lda.spin_cnt += rowner_loops - i;
501 #endif
502 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
503 "running");
504 if (i != rowner_loops)
505 continue;
506 }
507 #endif
508
509 /*
510 * Okay, now it's the hard case. Some other thread already
511 * has a write lock or there are write waiters present,
512 * acquire the turnstile lock so we can begin the process
513 * of blocking.
514 */
515 ts = turnstile_trywait(&rw->lock_object);
516
517 /*
518 * The lock might have been released while we spun, so
519 * recheck its state and restart the loop if needed.
520 */
521 v = RW_READ_VALUE(rw);
522 if (RW_CAN_READ(td, v)) {
523 turnstile_cancel(ts);
524 continue;
525 }
526
527 #ifdef ADAPTIVE_RWLOCKS
528 /*
529 * The current lock owner might have started executing
530 * on another CPU (or the lock could have changed
531 * owners) while we were waiting on the turnstile
532 * chain lock. If so, drop the turnstile lock and try
533 * again.
534 */
535 if ((v & RW_LOCK_READ) == 0) {
536 owner = (struct thread *)RW_OWNER(v);
537 if (TD_IS_RUNNING(owner)) {
538 turnstile_cancel(ts);
539 continue;
540 }
541 }
542 #endif
543
544 /*
545 * The lock is held in write mode or it already has waiters.
546 */
547 MPASS(!RW_CAN_READ(td, v));
548
549 /*
550 * If the RW_LOCK_READ_WAITERS flag is already set, then
551 * we can go ahead and block. If it is not set then try
552 * to set it. If we fail to set it drop the turnstile
553 * lock and restart the loop.
554 */
555 if (!(v & RW_LOCK_READ_WAITERS)) {
556 if (!atomic_cmpset_ptr(&rw->rw_lock, v,
557 v | RW_LOCK_READ_WAITERS)) {
558 turnstile_cancel(ts);
559 v = RW_READ_VALUE(rw);
560 continue;
561 }
562 if (LOCK_LOG_TEST(&rw->lock_object, 0))
563 CTR2(KTR_LOCK, "%s: %p set read waiters flag",
564 __func__, rw);
565 }
566
567 /*
568 * We were unable to acquire the lock and the read waiters
569 * flag is set, so we must block on the turnstile.
570 */
571 if (LOCK_LOG_TEST(&rw->lock_object, 0))
572 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
573 rw);
574 #ifdef KDTRACE_HOOKS
575 sleep_time -= lockstat_nsecs(&rw->lock_object);
576 #endif
577 turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE);
578 #ifdef KDTRACE_HOOKS
579 sleep_time += lockstat_nsecs(&rw->lock_object);
580 sleep_cnt++;
581 #endif
582 if (LOCK_LOG_TEST(&rw->lock_object, 0))
583 CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
584 __func__, rw);
585 v = RW_READ_VALUE(rw);
586 }
587 #ifdef KDTRACE_HOOKS
588 all_time += lockstat_nsecs(&rw->lock_object);
589 if (sleep_time)
590 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
591 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
592 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
593
594 /* Record only the loops spinning and not sleeping. */
595 if (lda.spin_cnt > sleep_cnt)
596 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
597 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
598 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
599 #endif
600 /*
601 * TODO: acquire "owner of record" here. Here be turnstile dragons
602 * however. turnstiles don't like owners changing between calls to
603 * turnstile_wait() currently.
604 */
605 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
606 waittime, file, line, LOCKSTAT_READER);
607 }
608
609 void
610 __rw_rlock(volatile uintptr_t *c, const char *file, int line)
611 {
612 struct rwlock *rw;
613 struct thread *td;
614 uintptr_t v;
615
616 td = curthread;
617 rw = rwlock2rw(c);
618
619 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED_TD(td) ||
620 !TD_IS_IDLETHREAD(td),
621 ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d",
622 td, rw->lock_object.lo_name, file, line));
623 KASSERT(rw->rw_lock != RW_DESTROYED,
624 ("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
625 KASSERT(rw_wowner(rw) != td,
626 ("rw_rlock: wlock already held for %s @ %s:%d",
627 rw->lock_object.lo_name, file, line));
628 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
629
630 v = RW_READ_VALUE(rw);
631 if (__predict_false(LOCKSTAT_OOL_PROFILE_ENABLED(rw__acquire) ||
632 !__rw_rlock_try(rw, td, &v, file, line)))
633 __rw_rlock_hard(c, td, v, file, line);
634
635 LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
636 WITNESS_LOCK(&rw->lock_object, 0, file, line);
637 TD_LOCKS_INC(curthread);
638 }
639
640 int
641 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
642 {
643 struct rwlock *rw;
644 uintptr_t x;
645
646 if (SCHEDULER_STOPPED())
647 return (1);
648
649 rw = rwlock2rw(c);
650
651 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
652 ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
653 curthread, rw->lock_object.lo_name, file, line));
654
655 x = rw->rw_lock;
656 for (;;) {
657 KASSERT(rw->rw_lock != RW_DESTROYED,
658 ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
659 if (!(x & RW_LOCK_READ))
660 break;
661 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &x, x + RW_ONE_READER)) {
662 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
663 line);
664 WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
665 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
666 rw, 0, 0, file, line, LOCKSTAT_READER);
667 TD_LOCKS_INC(curthread);
668 curthread->td_rw_rlocks++;
669 return (1);
670 }
671 }
672
673 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
674 return (0);
675 }
676
677 static bool __always_inline
678 __rw_runlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp)
679 {
680
681 for (;;) {
682 /*
683 * See if there is more than one read lock held. If so,
684 * just drop one and return.
685 */
686 if (RW_READERS(*vp) > 1) {
687 if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp,
688 *vp - RW_ONE_READER)) {
689 if (LOCK_LOG_TEST(&rw->lock_object, 0))
690 CTR4(KTR_LOCK,
691 "%s: %p succeeded %p -> %p",
692 __func__, rw, (void *)*vp,
693 (void *)(*vp - RW_ONE_READER));
694 td->td_rw_rlocks--;
695 return (true);
696 }
697 continue;
698 }
699 /*
700 * If there aren't any waiters for a write lock, then try
701 * to drop it quickly.
702 */
703 if (!(*vp & RW_LOCK_WAITERS)) {
704 MPASS((*vp & ~RW_LOCK_WRITE_SPINNER) ==
705 RW_READERS_LOCK(1));
706 if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp,
707 RW_UNLOCKED)) {
708 if (LOCK_LOG_TEST(&rw->lock_object, 0))
709 CTR2(KTR_LOCK, "%s: %p last succeeded",
710 __func__, rw);
711 td->td_rw_rlocks--;
712 return (true);
713 }
714 continue;
715 }
716 break;
717 }
718 return (false);
719 }
720
721 static void __noinline
722 __rw_runlock_hard(volatile uintptr_t *c, struct thread *td, uintptr_t v,
723 const char *file, int line)
724 {
725 struct rwlock *rw;
726 struct turnstile *ts;
727 uintptr_t x, queue;
728
729 if (SCHEDULER_STOPPED())
730 return;
731
732 rw = rwlock2rw(c);
733
734 for (;;) {
735 if (__rw_runlock_try(rw, td, &v))
736 break;
737
738 /*
739 * Ok, we know we have waiters and we think we are the
740 * last reader, so grab the turnstile lock.
741 */
742 turnstile_chain_lock(&rw->lock_object);
743 v = rw->rw_lock & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
744 MPASS(v & RW_LOCK_WAITERS);
745
746 /*
747 * Try to drop our lock leaving the lock in a unlocked
748 * state.
749 *
750 * If you wanted to do explicit lock handoff you'd have to
751 * do it here. You'd also want to use turnstile_signal()
752 * and you'd have to handle the race where a higher
753 * priority thread blocks on the write lock before the
754 * thread you wakeup actually runs and have the new thread
755 * "steal" the lock. For now it's a lot simpler to just
756 * wakeup all of the waiters.
757 *
758 * As above, if we fail, then another thread might have
759 * acquired a read lock, so drop the turnstile lock and
760 * restart.
761 */
762 x = RW_UNLOCKED;
763 if (v & RW_LOCK_WRITE_WAITERS) {
764 queue = TS_EXCLUSIVE_QUEUE;
765 x |= (v & RW_LOCK_READ_WAITERS);
766 } else
767 queue = TS_SHARED_QUEUE;
768 if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v,
769 x)) {
770 turnstile_chain_unlock(&rw->lock_object);
771 v = RW_READ_VALUE(rw);
772 continue;
773 }
774 if (LOCK_LOG_TEST(&rw->lock_object, 0))
775 CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
776 __func__, rw);
777
778 /*
779 * Ok. The lock is released and all that's left is to
780 * wake up the waiters. Note that the lock might not be
781 * free anymore, but in that case the writers will just
782 * block again if they run before the new lock holder(s)
783 * release the lock.
784 */
785 ts = turnstile_lookup(&rw->lock_object);
786 MPASS(ts != NULL);
787 turnstile_broadcast(ts, queue);
788 turnstile_unpend(ts, TS_SHARED_LOCK);
789 turnstile_chain_unlock(&rw->lock_object);
790 td->td_rw_rlocks--;
791 break;
792 }
793 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER);
794 }
795
796 void
797 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
798 {
799 struct rwlock *rw;
800 struct thread *td;
801 uintptr_t v;
802
803 rw = rwlock2rw(c);
804
805 KASSERT(rw->rw_lock != RW_DESTROYED,
806 ("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
807 __rw_assert(c, RA_RLOCKED, file, line);
808 WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
809 LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
810
811 td = curthread;
812 v = RW_READ_VALUE(rw);
813
814 if (__predict_false(LOCKSTAT_OOL_PROFILE_ENABLED(rw__release) ||
815 !__rw_runlock_try(rw, td, &v)))
816 __rw_runlock_hard(c, td, v, file, line);
817
818 TD_LOCKS_DEC(curthread);
819 }
820
821 /*
822 * This function is called when we are unable to obtain a write lock on the
823 * first try. This means that at least one other thread holds either a
824 * read or write lock.
825 */
826 void
827 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v, uintptr_t tid,
828 const char *file, int line)
829 {
830 struct rwlock *rw;
831 struct turnstile *ts;
832 #ifdef ADAPTIVE_RWLOCKS
833 volatile struct thread *owner;
834 int spintries = 0;
835 int i;
836 #endif
837 uintptr_t x;
838 #ifdef LOCK_PROFILING
839 uint64_t waittime = 0;
840 int contested = 0;
841 #endif
842 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
843 struct lock_delay_arg lda;
844 #endif
845 #ifdef KDTRACE_HOOKS
846 uintptr_t state;
847 u_int sleep_cnt = 0;
848 int64_t sleep_time = 0;
849 int64_t all_time = 0;
850 #endif
851
852 if (SCHEDULER_STOPPED())
853 return;
854
855 #if defined(ADAPTIVE_RWLOCKS)
856 lock_delay_arg_init(&lda, &rw_delay);
857 #elif defined(KDTRACE_HOOKS)
858 lock_delay_arg_init(&lda, NULL);
859 #endif
860 rw = rwlock2rw(c);
861 if (__predict_false(v == RW_UNLOCKED))
862 v = RW_READ_VALUE(rw);
863
864 if (__predict_false(lv_rw_wowner(v) == (struct thread *)tid)) {
865 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
866 ("%s: recursing but non-recursive rw %s @ %s:%d\n",
867 __func__, rw->lock_object.lo_name, file, line));
868 rw->rw_recurse++;
869 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
870 if (LOCK_LOG_TEST(&rw->lock_object, 0))
871 CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
872 return;
873 }
874
875 if (LOCK_LOG_TEST(&rw->lock_object, 0))
876 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
877 rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
878
879 #ifdef KDTRACE_HOOKS
880 all_time -= lockstat_nsecs(&rw->lock_object);
881 state = v;
882 #endif
883 for (;;) {
884 if (v == RW_UNLOCKED) {
885 if (_rw_write_lock_fetch(rw, &v, tid))
886 break;
887 continue;
888 }
889 #ifdef KDTRACE_HOOKS
890 lda.spin_cnt++;
891 #endif
892 #ifdef HWPMC_HOOKS
893 PMC_SOFT_CALL( , , lock, failed);
894 #endif
895 lock_profile_obtain_lock_failed(&rw->lock_object,
896 &contested, &waittime);
897 #ifdef ADAPTIVE_RWLOCKS
898 /*
899 * If the lock is write locked and the owner is
900 * running on another CPU, spin until the owner stops
901 * running or the state of the lock changes.
902 */
903 owner = lv_rw_wowner(v);
904 if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) {
905 if (LOCK_LOG_TEST(&rw->lock_object, 0))
906 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
907 __func__, rw, owner);
908 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
909 "spinning", "lockname:\"%s\"",
910 rw->lock_object.lo_name);
911 do {
912 lock_delay(&lda);
913 v = RW_READ_VALUE(rw);
914 owner = lv_rw_wowner(v);
915 } while (owner != NULL && TD_IS_RUNNING(owner));
916 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
917 "running");
918 continue;
919 }
920 if ((v & RW_LOCK_READ) && RW_READERS(v) &&
921 spintries < rowner_retries) {
922 if (!(v & RW_LOCK_WRITE_SPINNER)) {
923 if (!atomic_cmpset_ptr(&rw->rw_lock, v,
924 v | RW_LOCK_WRITE_SPINNER)) {
925 v = RW_READ_VALUE(rw);
926 continue;
927 }
928 }
929 spintries++;
930 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
931 "spinning", "lockname:\"%s\"",
932 rw->lock_object.lo_name);
933 for (i = 0; i < rowner_loops; i++) {
934 if ((rw->rw_lock & RW_LOCK_WRITE_SPINNER) == 0)
935 break;
936 cpu_spinwait();
937 }
938 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
939 "running");
940 v = RW_READ_VALUE(rw);
941 #ifdef KDTRACE_HOOKS
942 lda.spin_cnt += rowner_loops - i;
943 #endif
944 if (i != rowner_loops)
945 continue;
946 }
947 #endif
948 ts = turnstile_trywait(&rw->lock_object);
949 v = RW_READ_VALUE(rw);
950
951 #ifdef ADAPTIVE_RWLOCKS
952 /*
953 * The current lock owner might have started executing
954 * on another CPU (or the lock could have changed
955 * owners) while we were waiting on the turnstile
956 * chain lock. If so, drop the turnstile lock and try
957 * again.
958 */
959 if (!(v & RW_LOCK_READ)) {
960 owner = (struct thread *)RW_OWNER(v);
961 if (TD_IS_RUNNING(owner)) {
962 turnstile_cancel(ts);
963 continue;
964 }
965 }
966 #endif
967 /*
968 * Check for the waiters flags about this rwlock.
969 * If the lock was released, without maintain any pending
970 * waiters queue, simply try to acquire it.
971 * If a pending waiters queue is present, claim the lock
972 * ownership and maintain the pending queue.
973 */
974 x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
975 if ((v & ~x) == RW_UNLOCKED) {
976 x &= ~RW_LOCK_WRITE_SPINNER;
977 if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid | x)) {
978 if (x)
979 turnstile_claim(ts);
980 else
981 turnstile_cancel(ts);
982 break;
983 }
984 turnstile_cancel(ts);
985 v = RW_READ_VALUE(rw);
986 continue;
987 }
988 /*
989 * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
990 * set it. If we fail to set it, then loop back and try
991 * again.
992 */
993 if (!(v & RW_LOCK_WRITE_WAITERS)) {
994 if (!atomic_cmpset_ptr(&rw->rw_lock, v,
995 v | RW_LOCK_WRITE_WAITERS)) {
996 turnstile_cancel(ts);
997 v = RW_READ_VALUE(rw);
998 continue;
999 }
1000 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1001 CTR2(KTR_LOCK, "%s: %p set write waiters flag",
1002 __func__, rw);
1003 }
1004 /*
1005 * We were unable to acquire the lock and the write waiters
1006 * flag is set, so we must block on the turnstile.
1007 */
1008 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1009 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
1010 rw);
1011 #ifdef KDTRACE_HOOKS
1012 sleep_time -= lockstat_nsecs(&rw->lock_object);
1013 #endif
1014 turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE);
1015 #ifdef KDTRACE_HOOKS
1016 sleep_time += lockstat_nsecs(&rw->lock_object);
1017 sleep_cnt++;
1018 #endif
1019 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1020 CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
1021 __func__, rw);
1022 #ifdef ADAPTIVE_RWLOCKS
1023 spintries = 0;
1024 #endif
1025 v = RW_READ_VALUE(rw);
1026 }
1027 #ifdef KDTRACE_HOOKS
1028 all_time += lockstat_nsecs(&rw->lock_object);
1029 if (sleep_time)
1030 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
1031 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1032 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1033
1034 /* Record only the loops spinning and not sleeping. */
1035 if (lda.spin_cnt > sleep_cnt)
1036 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
1037 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1038 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1039 #endif
1040 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
1041 waittime, file, line, LOCKSTAT_WRITER);
1042 }
1043
1044 /*
1045 * This function is called if lockstat is active or the first try at releasing
1046 * a write lock failed. The latter means that the lock is recursed or one of
1047 * the 2 waiter bits must be set indicating that at least one thread is waiting
1048 * on this lock.
1049 */
1050 void
1051 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
1052 int line)
1053 {
1054 struct rwlock *rw;
1055 struct turnstile *ts;
1056 uintptr_t v;
1057 int queue;
1058
1059 if (SCHEDULER_STOPPED())
1060 return;
1061
1062 rw = rwlock2rw(c);
1063 v = RW_READ_VALUE(rw);
1064 if (v & RW_LOCK_WRITER_RECURSED) {
1065 if (--(rw->rw_recurse) == 0)
1066 atomic_clear_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
1067 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1068 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
1069 return;
1070 }
1071
1072 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_WRITER);
1073 if (v == tid && _rw_write_unlock(rw, tid))
1074 return;
1075
1076 KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
1077 ("%s: neither of the waiter flags are set", __func__));
1078
1079 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1080 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
1081
1082 turnstile_chain_lock(&rw->lock_object);
1083 ts = turnstile_lookup(&rw->lock_object);
1084 MPASS(ts != NULL);
1085
1086 /*
1087 * Use the same algo as sx locks for now. Prefer waking up shared
1088 * waiters if we have any over writers. This is probably not ideal.
1089 *
1090 * 'v' is the value we are going to write back to rw_lock. If we
1091 * have waiters on both queues, we need to preserve the state of
1092 * the waiter flag for the queue we don't wake up. For now this is
1093 * hardcoded for the algorithm mentioned above.
1094 *
1095 * In the case of both readers and writers waiting we wakeup the
1096 * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a
1097 * new writer comes in before a reader it will claim the lock up
1098 * above. There is probably a potential priority inversion in
1099 * there that could be worked around either by waking both queues
1100 * of waiters or doing some complicated lock handoff gymnastics.
1101 */
1102 v = RW_UNLOCKED;
1103 if (rw->rw_lock & RW_LOCK_WRITE_WAITERS) {
1104 queue = TS_EXCLUSIVE_QUEUE;
1105 v |= (rw->rw_lock & RW_LOCK_READ_WAITERS);
1106 } else
1107 queue = TS_SHARED_QUEUE;
1108
1109 /* Wake up all waiters for the specific queue. */
1110 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1111 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
1112 queue == TS_SHARED_QUEUE ? "read" : "write");
1113 turnstile_broadcast(ts, queue);
1114 atomic_store_rel_ptr(&rw->rw_lock, v);
1115 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
1116 turnstile_chain_unlock(&rw->lock_object);
1117 }
1118
1119 /*
1120 * Attempt to do a non-blocking upgrade from a read lock to a write
1121 * lock. This will only succeed if this thread holds a single read
1122 * lock. Returns true if the upgrade succeeded and false otherwise.
1123 */
1124 int
1125 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
1126 {
1127 struct rwlock *rw;
1128 uintptr_t v, x, tid;
1129 struct turnstile *ts;
1130 int success;
1131
1132 if (SCHEDULER_STOPPED())
1133 return (1);
1134
1135 rw = rwlock2rw(c);
1136
1137 KASSERT(rw->rw_lock != RW_DESTROYED,
1138 ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
1139 __rw_assert(c, RA_RLOCKED, file, line);
1140
1141 /*
1142 * Attempt to switch from one reader to a writer. If there
1143 * are any write waiters, then we will have to lock the
1144 * turnstile first to prevent races with another writer
1145 * calling turnstile_wait() before we have claimed this
1146 * turnstile. So, do the simple case of no waiters first.
1147 */
1148 tid = (uintptr_t)curthread;
1149 success = 0;
1150 for (;;) {
1151 v = rw->rw_lock;
1152 if (RW_READERS(v) > 1)
1153 break;
1154 if (!(v & RW_LOCK_WAITERS)) {
1155 success = atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid);
1156 if (!success)
1157 continue;
1158 break;
1159 }
1160
1161 /*
1162 * Ok, we think we have waiters, so lock the turnstile.
1163 */
1164 ts = turnstile_trywait(&rw->lock_object);
1165 v = rw->rw_lock;
1166 if (RW_READERS(v) > 1) {
1167 turnstile_cancel(ts);
1168 break;
1169 }
1170 /*
1171 * Try to switch from one reader to a writer again. This time
1172 * we honor the current state of the waiters flags.
1173 * If we obtain the lock with the flags set, then claim
1174 * ownership of the turnstile.
1175 */
1176 x = rw->rw_lock & RW_LOCK_WAITERS;
1177 success = atomic_cmpset_ptr(&rw->rw_lock, v, tid | x);
1178 if (success) {
1179 if (x)
1180 turnstile_claim(ts);
1181 else
1182 turnstile_cancel(ts);
1183 break;
1184 }
1185 turnstile_cancel(ts);
1186 }
1187 LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
1188 if (success) {
1189 curthread->td_rw_rlocks--;
1190 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
1191 file, line);
1192 LOCKSTAT_RECORD0(rw__upgrade, rw);
1193 }
1194 return (success);
1195 }
1196
1197 /*
1198 * Downgrade a write lock into a single read lock.
1199 */
1200 void
1201 __rw_downgrade(volatile uintptr_t *c, const char *file, int line)
1202 {
1203 struct rwlock *rw;
1204 struct turnstile *ts;
1205 uintptr_t tid, v;
1206 int rwait, wwait;
1207
1208 if (SCHEDULER_STOPPED())
1209 return;
1210
1211 rw = rwlock2rw(c);
1212
1213 KASSERT(rw->rw_lock != RW_DESTROYED,
1214 ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
1215 __rw_assert(c, RA_WLOCKED | RA_NOTRECURSED, file, line);
1216 #ifndef INVARIANTS
1217 if (rw_recursed(rw))
1218 panic("downgrade of a recursed lock");
1219 #endif
1220
1221 WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
1222
1223 /*
1224 * Convert from a writer to a single reader. First we handle
1225 * the easy case with no waiters. If there are any waiters, we
1226 * lock the turnstile and "disown" the lock.
1227 */
1228 tid = (uintptr_t)curthread;
1229 if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
1230 goto out;
1231
1232 /*
1233 * Ok, we think we have waiters, so lock the turnstile so we can
1234 * read the waiter flags without any races.
1235 */
1236 turnstile_chain_lock(&rw->lock_object);
1237 v = rw->rw_lock & RW_LOCK_WAITERS;
1238 rwait = v & RW_LOCK_READ_WAITERS;
1239 wwait = v & RW_LOCK_WRITE_WAITERS;
1240 MPASS(rwait | wwait);
1241
1242 /*
1243 * Downgrade from a write lock while preserving waiters flag
1244 * and give up ownership of the turnstile.
1245 */
1246 ts = turnstile_lookup(&rw->lock_object);
1247 MPASS(ts != NULL);
1248 if (!wwait)
1249 v &= ~RW_LOCK_READ_WAITERS;
1250 atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
1251 /*
1252 * Wake other readers if there are no writers pending. Otherwise they
1253 * won't be able to acquire the lock anyway.
1254 */
1255 if (rwait && !wwait) {
1256 turnstile_broadcast(ts, TS_SHARED_QUEUE);
1257 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
1258 } else
1259 turnstile_disown(ts);
1260 turnstile_chain_unlock(&rw->lock_object);
1261 out:
1262 curthread->td_rw_rlocks++;
1263 LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
1264 LOCKSTAT_RECORD0(rw__downgrade, rw);
1265 }
1266
1267 #ifdef INVARIANT_SUPPORT
1268 #ifndef INVARIANTS
1269 #undef __rw_assert
1270 #endif
1271
1272 /*
1273 * In the non-WITNESS case, rw_assert() can only detect that at least
1274 * *some* thread owns an rlock, but it cannot guarantee that *this*
1275 * thread owns an rlock.
1276 */
1277 void
1278 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
1279 {
1280 const struct rwlock *rw;
1281
1282 if (panicstr != NULL)
1283 return;
1284
1285 rw = rwlock2rw(c);
1286
1287 switch (what) {
1288 case RA_LOCKED:
1289 case RA_LOCKED | RA_RECURSED:
1290 case RA_LOCKED | RA_NOTRECURSED:
1291 case RA_RLOCKED:
1292 case RA_RLOCKED | RA_RECURSED:
1293 case RA_RLOCKED | RA_NOTRECURSED:
1294 #ifdef WITNESS
1295 witness_assert(&rw->lock_object, what, file, line);
1296 #else
1297 /*
1298 * If some other thread has a write lock or we have one
1299 * and are asserting a read lock, fail. Also, if no one
1300 * has a lock at all, fail.
1301 */
1302 if (rw->rw_lock == RW_UNLOCKED ||
1303 (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
1304 rw_wowner(rw) != curthread)))
1305 panic("Lock %s not %slocked @ %s:%d\n",
1306 rw->lock_object.lo_name, (what & RA_RLOCKED) ?
1307 "read " : "", file, line);
1308
1309 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
1310 if (rw_recursed(rw)) {
1311 if (what & RA_NOTRECURSED)
1312 panic("Lock %s recursed @ %s:%d\n",
1313 rw->lock_object.lo_name, file,
1314 line);
1315 } else if (what & RA_RECURSED)
1316 panic("Lock %s not recursed @ %s:%d\n",
1317 rw->lock_object.lo_name, file, line);
1318 }
1319 #endif
1320 break;
1321 case RA_WLOCKED:
1322 case RA_WLOCKED | RA_RECURSED:
1323 case RA_WLOCKED | RA_NOTRECURSED:
1324 if (rw_wowner(rw) != curthread)
1325 panic("Lock %s not exclusively locked @ %s:%d\n",
1326 rw->lock_object.lo_name, file, line);
1327 if (rw_recursed(rw)) {
1328 if (what & RA_NOTRECURSED)
1329 panic("Lock %s recursed @ %s:%d\n",
1330 rw->lock_object.lo_name, file, line);
1331 } else if (what & RA_RECURSED)
1332 panic("Lock %s not recursed @ %s:%d\n",
1333 rw->lock_object.lo_name, file, line);
1334 break;
1335 case RA_UNLOCKED:
1336 #ifdef WITNESS
1337 witness_assert(&rw->lock_object, what, file, line);
1338 #else
1339 /*
1340 * If we hold a write lock fail. We can't reliably check
1341 * to see if we hold a read lock or not.
1342 */
1343 if (rw_wowner(rw) == curthread)
1344 panic("Lock %s exclusively locked @ %s:%d\n",
1345 rw->lock_object.lo_name, file, line);
1346 #endif
1347 break;
1348 default:
1349 panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
1350 line);
1351 }
1352 }
1353 #endif /* INVARIANT_SUPPORT */
1354
1355 #ifdef DDB
1356 void
1357 db_show_rwlock(const struct lock_object *lock)
1358 {
1359 const struct rwlock *rw;
1360 struct thread *td;
1361
1362 rw = (const struct rwlock *)lock;
1363
1364 db_printf(" state: ");
1365 if (rw->rw_lock == RW_UNLOCKED)
1366 db_printf("UNLOCKED\n");
1367 else if (rw->rw_lock == RW_DESTROYED) {
1368 db_printf("DESTROYED\n");
1369 return;
1370 } else if (rw->rw_lock & RW_LOCK_READ)
1371 db_printf("RLOCK: %ju locks\n",
1372 (uintmax_t)(RW_READERS(rw->rw_lock)));
1373 else {
1374 td = rw_wowner(rw);
1375 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1376 td->td_tid, td->td_proc->p_pid, td->td_name);
1377 if (rw_recursed(rw))
1378 db_printf(" recursed: %u\n", rw->rw_recurse);
1379 }
1380 db_printf(" waiters: ");
1381 switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
1382 case RW_LOCK_READ_WAITERS:
1383 db_printf("readers\n");
1384 break;
1385 case RW_LOCK_WRITE_WAITERS:
1386 db_printf("writers\n");
1387 break;
1388 case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
1389 db_printf("readers and writers\n");
1390 break;
1391 default:
1392 db_printf("none\n");
1393 break;
1394 }
1395 }
1396
1397 #endif
Cache object: 29311ef31354668f717db2c5f7c881c4
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