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/11.2/sys/kern/kern_rwlock.c 334437 2018-05-31 15:58:28Z mjg $");
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 __read_frequently rowner_retries;
97 static int __read_frequently rowner_loops;
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_frequently 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 static void
111 rw_lock_delay_init(void *arg __unused)
112 {
113
114 lock_delay_default_init(&rw_delay);
115 rowner_retries = 10;
116 rowner_loops = max(10000, rw_delay.max);
117 }
118 LOCK_DELAY_SYSINIT(rw_lock_delay_init);
119 #endif
120
121 /*
122 * Return a pointer to the owning thread if the lock is write-locked or
123 * NULL if the lock is unlocked or read-locked.
124 */
125
126 #define lv_rw_wowner(v) \
127 ((v) & RW_LOCK_READ ? NULL : \
128 (struct thread *)RW_OWNER((v)))
129
130 #define rw_wowner(rw) lv_rw_wowner(RW_READ_VALUE(rw))
131
132 /*
133 * Returns if a write owner is recursed. Write ownership is not assured
134 * here and should be previously checked.
135 */
136 #define rw_recursed(rw) ((rw)->rw_recurse != 0)
137
138 /*
139 * Return true if curthread helds the lock.
140 */
141 #define rw_wlocked(rw) (rw_wowner((rw)) == curthread)
142
143 /*
144 * Return a pointer to the owning thread for this lock who should receive
145 * any priority lent by threads that block on this lock. Currently this
146 * is identical to rw_wowner().
147 */
148 #define rw_owner(rw) rw_wowner(rw)
149
150 #ifndef INVARIANTS
151 #define __rw_assert(c, what, file, line)
152 #endif
153
154 void
155 assert_rw(const struct lock_object *lock, int what)
156 {
157
158 rw_assert((const struct rwlock *)lock, what);
159 }
160
161 void
162 lock_rw(struct lock_object *lock, uintptr_t how)
163 {
164 struct rwlock *rw;
165
166 rw = (struct rwlock *)lock;
167 if (how)
168 rw_rlock(rw);
169 else
170 rw_wlock(rw);
171 }
172
173 uintptr_t
174 unlock_rw(struct lock_object *lock)
175 {
176 struct rwlock *rw;
177
178 rw = (struct rwlock *)lock;
179 rw_assert(rw, RA_LOCKED | LA_NOTRECURSED);
180 if (rw->rw_lock & RW_LOCK_READ) {
181 rw_runlock(rw);
182 return (1);
183 } else {
184 rw_wunlock(rw);
185 return (0);
186 }
187 }
188
189 #ifdef KDTRACE_HOOKS
190 int
191 owner_rw(const struct lock_object *lock, struct thread **owner)
192 {
193 const struct rwlock *rw = (const struct rwlock *)lock;
194 uintptr_t x = rw->rw_lock;
195
196 *owner = rw_wowner(rw);
197 return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) :
198 (*owner != NULL));
199 }
200 #endif
201
202 void
203 _rw_init_flags(volatile uintptr_t *c, const char *name, int opts)
204 {
205 struct rwlock *rw;
206 int flags;
207
208 rw = rwlock2rw(c);
209
210 MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
211 RW_RECURSE | RW_NEW)) == 0);
212 ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
213 ("%s: rw_lock not aligned for %s: %p", __func__, name,
214 &rw->rw_lock));
215
216 flags = LO_UPGRADABLE;
217 if (opts & RW_DUPOK)
218 flags |= LO_DUPOK;
219 if (opts & RW_NOPROFILE)
220 flags |= LO_NOPROFILE;
221 if (!(opts & RW_NOWITNESS))
222 flags |= LO_WITNESS;
223 if (opts & RW_RECURSE)
224 flags |= LO_RECURSABLE;
225 if (opts & RW_QUIET)
226 flags |= LO_QUIET;
227 if (opts & RW_NEW)
228 flags |= LO_NEW;
229
230 lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
231 rw->rw_lock = RW_UNLOCKED;
232 rw->rw_recurse = 0;
233 }
234
235 void
236 _rw_destroy(volatile uintptr_t *c)
237 {
238 struct rwlock *rw;
239
240 rw = rwlock2rw(c);
241
242 KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw));
243 KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw));
244 rw->rw_lock = RW_DESTROYED;
245 lock_destroy(&rw->lock_object);
246 }
247
248 void
249 rw_sysinit(void *arg)
250 {
251 struct rw_args *args;
252
253 args = arg;
254 rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc,
255 args->ra_flags);
256 }
257
258 int
259 _rw_wowned(const volatile uintptr_t *c)
260 {
261
262 return (rw_wowner(rwlock2rw(c)) == curthread);
263 }
264
265 void
266 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line)
267 {
268 struct rwlock *rw;
269 uintptr_t tid, v;
270
271 rw = rwlock2rw(c);
272
273 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
274 !TD_IS_IDLETHREAD(curthread),
275 ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d",
276 curthread, rw->lock_object.lo_name, file, line));
277 KASSERT(rw->rw_lock != RW_DESTROYED,
278 ("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
279 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
280 line, NULL);
281 tid = (uintptr_t)curthread;
282 v = RW_UNLOCKED;
283 if (!_rw_write_lock_fetch(rw, &v, tid))
284 _rw_wlock_hard(rw, v, file, line);
285 else
286 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw,
287 0, 0, file, line, LOCKSTAT_WRITER);
288
289 LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
290 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
291 TD_LOCKS_INC(curthread);
292 }
293
294 int
295 __rw_try_wlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
296 {
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 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
308 ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d",
309 curthread, rw->lock_object.lo_name, file, line));
310 KASSERT(rw->rw_lock != RW_DESTROYED,
311 ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
312
313 rval = 1;
314 recursed = false;
315 v = RW_UNLOCKED;
316 for (;;) {
317 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
318 break;
319 if (v == RW_UNLOCKED)
320 continue;
321 if (v == tid && (rw->lock_object.lo_flags & LO_RECURSABLE)) {
322 rw->rw_recurse++;
323 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
324 break;
325 }
326 rval = 0;
327 break;
328 }
329
330 LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
331 if (rval) {
332 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
333 file, line);
334 if (!recursed)
335 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
336 rw, 0, 0, file, line, LOCKSTAT_WRITER);
337 TD_LOCKS_INC(curthread);
338 }
339 return (rval);
340 }
341
342 int
343 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
344 {
345 struct rwlock *rw;
346
347 rw = rwlock2rw(c);
348 return (__rw_try_wlock_int(rw LOCK_FILE_LINE_ARG));
349 }
350
351 void
352 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
353 {
354 struct rwlock *rw;
355
356 rw = rwlock2rw(c);
357
358 KASSERT(rw->rw_lock != RW_DESTROYED,
359 ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
360 __rw_assert(c, RA_WLOCKED, file, line);
361 WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
362 LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
363 line);
364
365 #ifdef LOCK_PROFILING
366 _rw_wunlock_hard(rw, (uintptr_t)curthread, file, line);
367 #else
368 __rw_wunlock(rw, curthread, file, line);
369 #endif
370
371 TD_LOCKS_DEC(curthread);
372 }
373
374 /*
375 * Determines whether a new reader can acquire a lock. Succeeds if the
376 * reader already owns a read lock and the lock is locked for read to
377 * prevent deadlock from reader recursion. Also succeeds if the lock
378 * is unlocked and has no writer waiters or spinners. Failing otherwise
379 * prioritizes writers before readers.
380 */
381 static bool __always_inline
382 __rw_can_read(struct thread *td, uintptr_t v, bool fp)
383 {
384
385 if ((v & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER))
386 == RW_LOCK_READ)
387 return (true);
388 if (!fp && td->td_rw_rlocks && (v & RW_LOCK_READ))
389 return (true);
390 return (false);
391 }
392
393 static bool __always_inline
394 __rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp, bool fp
395 LOCK_FILE_LINE_ARG_DEF)
396 {
397
398 /*
399 * Handle the easy case. If no other thread has a write
400 * lock, then try to bump up the count of read locks. Note
401 * that we have to preserve the current state of the
402 * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a
403 * read lock, then rw_lock must have changed, so restart
404 * the loop. Note that this handles the case of a
405 * completely unlocked rwlock since such a lock is encoded
406 * as a read lock with no waiters.
407 */
408 while (__rw_can_read(td, *vp, fp)) {
409 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, vp,
410 *vp + RW_ONE_READER)) {
411 if (LOCK_LOG_TEST(&rw->lock_object, 0))
412 CTR4(KTR_LOCK,
413 "%s: %p succeed %p -> %p", __func__,
414 rw, (void *)*vp,
415 (void *)(*vp + RW_ONE_READER));
416 td->td_rw_rlocks++;
417 return (true);
418 }
419 }
420 return (false);
421 }
422
423 static void __noinline
424 __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
425 LOCK_FILE_LINE_ARG_DEF)
426 {
427 struct turnstile *ts;
428 struct thread *owner;
429 #ifdef ADAPTIVE_RWLOCKS
430 int spintries = 0;
431 int i, n;
432 #endif
433 #ifdef LOCK_PROFILING
434 uint64_t waittime = 0;
435 int contested = 0;
436 #endif
437 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
438 struct lock_delay_arg lda;
439 #endif
440 #ifdef KDTRACE_HOOKS
441 u_int sleep_cnt = 0;
442 int64_t sleep_time = 0;
443 int64_t all_time = 0;
444 #endif
445 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
446 uintptr_t state;
447 int doing_lockprof = 0;
448 #endif
449
450 #ifdef KDTRACE_HOOKS
451 if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
452 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
453 goto out_lockstat;
454 doing_lockprof = 1;
455 all_time -= lockstat_nsecs(&rw->lock_object);
456 state = v;
457 }
458 #endif
459 #ifdef LOCK_PROFILING
460 doing_lockprof = 1;
461 state = v;
462 #endif
463
464 if (SCHEDULER_STOPPED())
465 return;
466
467 #if defined(ADAPTIVE_RWLOCKS)
468 lock_delay_arg_init(&lda, &rw_delay);
469 #elif defined(KDTRACE_HOOKS)
470 lock_delay_arg_init(&lda, NULL);
471 #endif
472
473 #ifdef HWPMC_HOOKS
474 PMC_SOFT_CALL( , , lock, failed);
475 #endif
476 lock_profile_obtain_lock_failed(&rw->lock_object,
477 &contested, &waittime);
478
479 for (;;) {
480 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
481 break;
482 #ifdef KDTRACE_HOOKS
483 lda.spin_cnt++;
484 #endif
485
486 #ifdef ADAPTIVE_RWLOCKS
487 /*
488 * If the owner is running on another CPU, spin until
489 * the owner stops running or the state of the lock
490 * changes.
491 */
492 if ((v & RW_LOCK_READ) == 0) {
493 owner = (struct thread *)RW_OWNER(v);
494 if (TD_IS_RUNNING(owner)) {
495 if (LOCK_LOG_TEST(&rw->lock_object, 0))
496 CTR3(KTR_LOCK,
497 "%s: spinning on %p held by %p",
498 __func__, rw, owner);
499 KTR_STATE1(KTR_SCHED, "thread",
500 sched_tdname(curthread), "spinning",
501 "lockname:\"%s\"", rw->lock_object.lo_name);
502 do {
503 lock_delay(&lda);
504 v = RW_READ_VALUE(rw);
505 owner = lv_rw_wowner(v);
506 } while (owner != NULL && TD_IS_RUNNING(owner));
507 KTR_STATE0(KTR_SCHED, "thread",
508 sched_tdname(curthread), "running");
509 continue;
510 }
511 } else if (spintries < rowner_retries) {
512 spintries++;
513 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
514 "spinning", "lockname:\"%s\"",
515 rw->lock_object.lo_name);
516 for (i = 0; i < rowner_loops; i += n) {
517 n = RW_READERS(v);
518 lock_delay_spin(n);
519 v = RW_READ_VALUE(rw);
520 if ((v & RW_LOCK_READ) == 0 || __rw_can_read(td, v, false))
521 break;
522 }
523 #ifdef KDTRACE_HOOKS
524 lda.spin_cnt += rowner_loops - i;
525 #endif
526 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
527 "running");
528 if (i < rowner_loops)
529 continue;
530 }
531 #endif
532
533 /*
534 * Okay, now it's the hard case. Some other thread already
535 * has a write lock or there are write waiters present,
536 * acquire the turnstile lock so we can begin the process
537 * of blocking.
538 */
539 ts = turnstile_trywait(&rw->lock_object);
540
541 /*
542 * The lock might have been released while we spun, so
543 * recheck its state and restart the loop if needed.
544 */
545 v = RW_READ_VALUE(rw);
546 retry_ts:
547 if (__rw_can_read(td, v, false)) {
548 turnstile_cancel(ts);
549 continue;
550 }
551
552 owner = lv_rw_wowner(v);
553
554 #ifdef ADAPTIVE_RWLOCKS
555 /*
556 * The current lock owner might have started executing
557 * on another CPU (or the lock could have changed
558 * owners) while we were waiting on the turnstile
559 * chain lock. If so, drop the turnstile lock and try
560 * again.
561 */
562 if (owner != NULL) {
563 if (TD_IS_RUNNING(owner)) {
564 turnstile_cancel(ts);
565 continue;
566 }
567 }
568 #endif
569
570 /*
571 * The lock is held in write mode or it already has waiters.
572 */
573 MPASS(!__rw_can_read(td, v, false));
574
575 /*
576 * If the RW_LOCK_READ_WAITERS flag is already set, then
577 * we can go ahead and block. If it is not set then try
578 * to set it. If we fail to set it drop the turnstile
579 * lock and restart the loop.
580 */
581 if (!(v & RW_LOCK_READ_WAITERS)) {
582 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
583 v | RW_LOCK_READ_WAITERS))
584 goto retry_ts;
585 if (LOCK_LOG_TEST(&rw->lock_object, 0))
586 CTR2(KTR_LOCK, "%s: %p set read waiters flag",
587 __func__, rw);
588 }
589
590 /*
591 * We were unable to acquire the lock and the read waiters
592 * flag is set, so we must block on the turnstile.
593 */
594 if (LOCK_LOG_TEST(&rw->lock_object, 0))
595 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
596 rw);
597 #ifdef KDTRACE_HOOKS
598 sleep_time -= lockstat_nsecs(&rw->lock_object);
599 #endif
600 MPASS(owner == rw_owner(rw));
601 turnstile_wait(ts, owner, TS_SHARED_QUEUE);
602 #ifdef KDTRACE_HOOKS
603 sleep_time += lockstat_nsecs(&rw->lock_object);
604 sleep_cnt++;
605 #endif
606 if (LOCK_LOG_TEST(&rw->lock_object, 0))
607 CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
608 __func__, rw);
609 v = RW_READ_VALUE(rw);
610 }
611 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
612 if (__predict_true(!doing_lockprof))
613 return;
614 #endif
615 #ifdef KDTRACE_HOOKS
616 all_time += lockstat_nsecs(&rw->lock_object);
617 if (sleep_time)
618 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
619 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
620 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
621
622 /* Record only the loops spinning and not sleeping. */
623 if (lda.spin_cnt > sleep_cnt)
624 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
625 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
626 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
627 out_lockstat:
628 #endif
629 /*
630 * TODO: acquire "owner of record" here. Here be turnstile dragons
631 * however. turnstiles don't like owners changing between calls to
632 * turnstile_wait() currently.
633 */
634 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
635 waittime, file, line, LOCKSTAT_READER);
636 }
637
638 void
639 __rw_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
640 {
641 struct thread *td;
642 uintptr_t v;
643
644 td = curthread;
645
646 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED_TD(td) ||
647 !TD_IS_IDLETHREAD(td),
648 ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d",
649 td, rw->lock_object.lo_name, file, line));
650 KASSERT(rw->rw_lock != RW_DESTROYED,
651 ("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
652 KASSERT(rw_wowner(rw) != td,
653 ("rw_rlock: wlock already held for %s @ %s:%d",
654 rw->lock_object.lo_name, file, line));
655 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
656
657 v = RW_READ_VALUE(rw);
658 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__acquire) ||
659 !__rw_rlock_try(rw, td, &v, true LOCK_FILE_LINE_ARG)))
660 __rw_rlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
661 else
662 lock_profile_obtain_lock_success(&rw->lock_object, 0, 0,
663 file, line);
664
665 LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
666 WITNESS_LOCK(&rw->lock_object, 0, file, line);
667 TD_LOCKS_INC(curthread);
668 }
669
670 void
671 __rw_rlock(volatile uintptr_t *c, const char *file, int line)
672 {
673 struct rwlock *rw;
674
675 rw = rwlock2rw(c);
676 __rw_rlock_int(rw LOCK_FILE_LINE_ARG);
677 }
678
679 int
680 __rw_try_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
681 {
682 uintptr_t x;
683
684 if (SCHEDULER_STOPPED())
685 return (1);
686
687 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
688 ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
689 curthread, rw->lock_object.lo_name, file, line));
690
691 x = rw->rw_lock;
692 for (;;) {
693 KASSERT(rw->rw_lock != RW_DESTROYED,
694 ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
695 if (!(x & RW_LOCK_READ))
696 break;
697 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &x, x + RW_ONE_READER)) {
698 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
699 line);
700 WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
701 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
702 rw, 0, 0, file, line, LOCKSTAT_READER);
703 TD_LOCKS_INC(curthread);
704 curthread->td_rw_rlocks++;
705 return (1);
706 }
707 }
708
709 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
710 return (0);
711 }
712
713 int
714 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
715 {
716 struct rwlock *rw;
717
718 rw = rwlock2rw(c);
719 return (__rw_try_rlock_int(rw LOCK_FILE_LINE_ARG));
720 }
721
722 static bool __always_inline
723 __rw_runlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp)
724 {
725
726 for (;;) {
727 /*
728 * See if there is more than one read lock held. If so,
729 * just drop one and return.
730 */
731 if (RW_READERS(*vp) > 1) {
732 if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp,
733 *vp - RW_ONE_READER)) {
734 if (LOCK_LOG_TEST(&rw->lock_object, 0))
735 CTR4(KTR_LOCK,
736 "%s: %p succeeded %p -> %p",
737 __func__, rw, (void *)*vp,
738 (void *)(*vp - RW_ONE_READER));
739 td->td_rw_rlocks--;
740 return (true);
741 }
742 continue;
743 }
744 /*
745 * If there aren't any waiters for a write lock, then try
746 * to drop it quickly.
747 */
748 if (!(*vp & RW_LOCK_WAITERS)) {
749 MPASS((*vp & ~RW_LOCK_WRITE_SPINNER) ==
750 RW_READERS_LOCK(1));
751 if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp,
752 RW_UNLOCKED)) {
753 if (LOCK_LOG_TEST(&rw->lock_object, 0))
754 CTR2(KTR_LOCK, "%s: %p last succeeded",
755 __func__, rw);
756 td->td_rw_rlocks--;
757 return (true);
758 }
759 continue;
760 }
761 break;
762 }
763 return (false);
764 }
765
766 static void __noinline
767 __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
768 LOCK_FILE_LINE_ARG_DEF)
769 {
770 struct turnstile *ts;
771 uintptr_t setv, queue;
772
773 if (SCHEDULER_STOPPED())
774 return;
775
776 if (__rw_runlock_try(rw, td, &v))
777 goto out_lockstat;
778
779 /*
780 * Ok, we know we have waiters and we think we are the
781 * last reader, so grab the turnstile lock.
782 */
783 turnstile_chain_lock(&rw->lock_object);
784 v = RW_READ_VALUE(rw);
785 for (;;) {
786 if (__rw_runlock_try(rw, td, &v))
787 break;
788
789 v &= (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
790 MPASS(v & RW_LOCK_WAITERS);
791
792 /*
793 * Try to drop our lock leaving the lock in a unlocked
794 * state.
795 *
796 * If you wanted to do explicit lock handoff you'd have to
797 * do it here. You'd also want to use turnstile_signal()
798 * and you'd have to handle the race where a higher
799 * priority thread blocks on the write lock before the
800 * thread you wakeup actually runs and have the new thread
801 * "steal" the lock. For now it's a lot simpler to just
802 * wakeup all of the waiters.
803 *
804 * As above, if we fail, then another thread might have
805 * acquired a read lock, so drop the turnstile lock and
806 * restart.
807 */
808 setv = RW_UNLOCKED;
809 queue = TS_SHARED_QUEUE;
810 if (v & RW_LOCK_WRITE_WAITERS) {
811 queue = TS_EXCLUSIVE_QUEUE;
812 setv |= (v & RW_LOCK_READ_WAITERS);
813 }
814 v |= RW_READERS_LOCK(1);
815 if (!atomic_fcmpset_rel_ptr(&rw->rw_lock, &v, setv))
816 continue;
817 if (LOCK_LOG_TEST(&rw->lock_object, 0))
818 CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
819 __func__, rw);
820
821 /*
822 * Ok. The lock is released and all that's left is to
823 * wake up the waiters. Note that the lock might not be
824 * free anymore, but in that case the writers will just
825 * block again if they run before the new lock holder(s)
826 * release the lock.
827 */
828 ts = turnstile_lookup(&rw->lock_object);
829 MPASS(ts != NULL);
830 turnstile_broadcast(ts, queue);
831 turnstile_unpend(ts, TS_SHARED_LOCK);
832 td->td_rw_rlocks--;
833 break;
834 }
835 turnstile_chain_unlock(&rw->lock_object);
836 out_lockstat:
837 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER);
838 }
839
840 void
841 _rw_runlock_cookie_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
842 {
843 struct thread *td;
844 uintptr_t v;
845
846 KASSERT(rw->rw_lock != RW_DESTROYED,
847 ("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
848 __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
849 WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
850 LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
851
852 td = curthread;
853 v = RW_READ_VALUE(rw);
854
855 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__release) ||
856 !__rw_runlock_try(rw, td, &v)))
857 __rw_runlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
858 else
859 lock_profile_release_lock(&rw->lock_object);
860
861 TD_LOCKS_DEC(curthread);
862 }
863
864 void
865 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
866 {
867 struct rwlock *rw;
868
869 rw = rwlock2rw(c);
870 _rw_runlock_cookie_int(rw LOCK_FILE_LINE_ARG);
871 }
872
873 /*
874 * This function is called when we are unable to obtain a write lock on the
875 * first try. This means that at least one other thread holds either a
876 * read or write lock.
877 */
878 void
879 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
880 {
881 uintptr_t tid;
882 struct rwlock *rw;
883 struct turnstile *ts;
884 struct thread *owner;
885 #ifdef ADAPTIVE_RWLOCKS
886 int spintries = 0;
887 int i, n;
888 enum { READERS, WRITER } sleep_reason = READERS;
889 #endif
890 uintptr_t x;
891 #ifdef LOCK_PROFILING
892 uint64_t waittime = 0;
893 int contested = 0;
894 #endif
895 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
896 struct lock_delay_arg lda;
897 #endif
898 #ifdef KDTRACE_HOOKS
899 u_int sleep_cnt = 0;
900 int64_t sleep_time = 0;
901 int64_t all_time = 0;
902 #endif
903 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
904 uintptr_t state;
905 int doing_lockprof = 0;
906 #endif
907
908 tid = (uintptr_t)curthread;
909 rw = rwlock2rw(c);
910
911 #ifdef KDTRACE_HOOKS
912 if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
913 while (v == RW_UNLOCKED) {
914 if (_rw_write_lock_fetch(rw, &v, tid))
915 goto out_lockstat;
916 }
917 doing_lockprof = 1;
918 all_time -= lockstat_nsecs(&rw->lock_object);
919 state = v;
920 }
921 #endif
922 #ifdef LOCK_PROFILING
923 doing_lockprof = 1;
924 state = v;
925 #endif
926
927 if (SCHEDULER_STOPPED())
928 return;
929
930 #if defined(ADAPTIVE_RWLOCKS)
931 lock_delay_arg_init(&lda, &rw_delay);
932 #elif defined(KDTRACE_HOOKS)
933 lock_delay_arg_init(&lda, NULL);
934 #endif
935 if (__predict_false(v == RW_UNLOCKED))
936 v = RW_READ_VALUE(rw);
937
938 if (__predict_false(lv_rw_wowner(v) == (struct thread *)tid)) {
939 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
940 ("%s: recursing but non-recursive rw %s @ %s:%d\n",
941 __func__, rw->lock_object.lo_name, file, line));
942 rw->rw_recurse++;
943 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
944 if (LOCK_LOG_TEST(&rw->lock_object, 0))
945 CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
946 return;
947 }
948
949 if (LOCK_LOG_TEST(&rw->lock_object, 0))
950 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
951 rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
952
953 #ifdef HWPMC_HOOKS
954 PMC_SOFT_CALL( , , lock, failed);
955 #endif
956 lock_profile_obtain_lock_failed(&rw->lock_object,
957 &contested, &waittime);
958
959 for (;;) {
960 if (v == RW_UNLOCKED) {
961 if (_rw_write_lock_fetch(rw, &v, tid))
962 break;
963 continue;
964 }
965 #ifdef KDTRACE_HOOKS
966 lda.spin_cnt++;
967 #endif
968
969 #ifdef ADAPTIVE_RWLOCKS
970 /*
971 * If the lock is write locked and the owner is
972 * running on another CPU, spin until the owner stops
973 * running or the state of the lock changes.
974 */
975 if (!(v & RW_LOCK_READ)) {
976 sleep_reason = WRITER;
977 owner = lv_rw_wowner(v);
978 if (!TD_IS_RUNNING(owner))
979 goto ts;
980 if (LOCK_LOG_TEST(&rw->lock_object, 0))
981 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
982 __func__, rw, owner);
983 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
984 "spinning", "lockname:\"%s\"",
985 rw->lock_object.lo_name);
986 do {
987 lock_delay(&lda);
988 v = RW_READ_VALUE(rw);
989 owner = lv_rw_wowner(v);
990 } while (owner != NULL && TD_IS_RUNNING(owner));
991 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
992 "running");
993 continue;
994 } else if (RW_READERS(v) > 0) {
995 sleep_reason = READERS;
996 if (spintries == rowner_retries)
997 goto ts;
998 if (!(v & RW_LOCK_WRITE_SPINNER)) {
999 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
1000 v | RW_LOCK_WRITE_SPINNER)) {
1001 continue;
1002 }
1003 }
1004 spintries++;
1005 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1006 "spinning", "lockname:\"%s\"",
1007 rw->lock_object.lo_name);
1008 for (i = 0; i < rowner_loops; i += n) {
1009 n = RW_READERS(v);
1010 lock_delay_spin(n);
1011 v = RW_READ_VALUE(rw);
1012 if ((v & RW_LOCK_WRITE_SPINNER) == 0)
1013 break;
1014 }
1015 #ifdef KDTRACE_HOOKS
1016 lda.spin_cnt += i;
1017 #endif
1018 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1019 "running");
1020 if (i < rowner_loops)
1021 continue;
1022 }
1023 ts:
1024 #endif
1025 ts = turnstile_trywait(&rw->lock_object);
1026 v = RW_READ_VALUE(rw);
1027 retry_ts:
1028 owner = lv_rw_wowner(v);
1029
1030 #ifdef ADAPTIVE_RWLOCKS
1031 /*
1032 * The current lock owner might have started executing
1033 * on another CPU (or the lock could have changed
1034 * owners) while we were waiting on the turnstile
1035 * chain lock. If so, drop the turnstile lock and try
1036 * again.
1037 */
1038 if (owner != NULL) {
1039 if (TD_IS_RUNNING(owner)) {
1040 turnstile_cancel(ts);
1041 continue;
1042 }
1043 } else if (RW_READERS(v) > 0 && sleep_reason == WRITER) {
1044 turnstile_cancel(ts);
1045 continue;
1046 }
1047 #endif
1048 /*
1049 * Check for the waiters flags about this rwlock.
1050 * If the lock was released, without maintain any pending
1051 * waiters queue, simply try to acquire it.
1052 * If a pending waiters queue is present, claim the lock
1053 * ownership and maintain the pending queue.
1054 */
1055 x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
1056 if ((v & ~x) == RW_UNLOCKED) {
1057 x &= ~RW_LOCK_WRITE_SPINNER;
1058 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid | x)) {
1059 if (x)
1060 turnstile_claim(ts);
1061 else
1062 turnstile_cancel(ts);
1063 break;
1064 }
1065 goto retry_ts;
1066 }
1067 /*
1068 * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
1069 * set it. If we fail to set it, then loop back and try
1070 * again.
1071 */
1072 if (!(v & RW_LOCK_WRITE_WAITERS)) {
1073 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
1074 v | RW_LOCK_WRITE_WAITERS))
1075 goto retry_ts;
1076 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1077 CTR2(KTR_LOCK, "%s: %p set write waiters flag",
1078 __func__, rw);
1079 }
1080 /*
1081 * We were unable to acquire the lock and the write waiters
1082 * flag is set, so we must block on the turnstile.
1083 */
1084 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1085 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
1086 rw);
1087 #ifdef KDTRACE_HOOKS
1088 sleep_time -= lockstat_nsecs(&rw->lock_object);
1089 #endif
1090 MPASS(owner == rw_owner(rw));
1091 turnstile_wait(ts, owner, TS_EXCLUSIVE_QUEUE);
1092 #ifdef KDTRACE_HOOKS
1093 sleep_time += lockstat_nsecs(&rw->lock_object);
1094 sleep_cnt++;
1095 #endif
1096 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1097 CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
1098 __func__, rw);
1099 #ifdef ADAPTIVE_RWLOCKS
1100 spintries = 0;
1101 #endif
1102 v = RW_READ_VALUE(rw);
1103 }
1104 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1105 if (__predict_true(!doing_lockprof))
1106 return;
1107 #endif
1108 #ifdef KDTRACE_HOOKS
1109 all_time += lockstat_nsecs(&rw->lock_object);
1110 if (sleep_time)
1111 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
1112 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1113 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1114
1115 /* Record only the loops spinning and not sleeping. */
1116 if (lda.spin_cnt > sleep_cnt)
1117 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
1118 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1119 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1120 out_lockstat:
1121 #endif
1122 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
1123 waittime, file, line, LOCKSTAT_WRITER);
1124 }
1125
1126 /*
1127 * This function is called if lockstat is active or the first try at releasing
1128 * a write lock failed. The latter means that the lock is recursed or one of
1129 * the 2 waiter bits must be set indicating that at least one thread is waiting
1130 * on this lock.
1131 */
1132 void
1133 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
1134 {
1135 struct rwlock *rw;
1136 struct turnstile *ts;
1137 uintptr_t tid, setv;
1138 int queue;
1139
1140 tid = (uintptr_t)curthread;
1141 if (SCHEDULER_STOPPED())
1142 return;
1143
1144 rw = rwlock2rw(c);
1145 if (__predict_false(v == tid))
1146 v = RW_READ_VALUE(rw);
1147
1148 if (v & RW_LOCK_WRITER_RECURSED) {
1149 if (--(rw->rw_recurse) == 0)
1150 atomic_clear_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
1151 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1152 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
1153 return;
1154 }
1155
1156 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_WRITER);
1157 if (v == tid && _rw_write_unlock(rw, tid))
1158 return;
1159
1160 KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
1161 ("%s: neither of the waiter flags are set", __func__));
1162
1163 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1164 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
1165
1166 turnstile_chain_lock(&rw->lock_object);
1167
1168 /*
1169 * Use the same algo as sx locks for now. Prefer waking up shared
1170 * waiters if we have any over writers. This is probably not ideal.
1171 *
1172 * 'v' is the value we are going to write back to rw_lock. If we
1173 * have waiters on both queues, we need to preserve the state of
1174 * the waiter flag for the queue we don't wake up. For now this is
1175 * hardcoded for the algorithm mentioned above.
1176 *
1177 * In the case of both readers and writers waiting we wakeup the
1178 * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a
1179 * new writer comes in before a reader it will claim the lock up
1180 * above. There is probably a potential priority inversion in
1181 * there that could be worked around either by waking both queues
1182 * of waiters or doing some complicated lock handoff gymnastics.
1183 */
1184 setv = RW_UNLOCKED;
1185 v = RW_READ_VALUE(rw);
1186 queue = TS_SHARED_QUEUE;
1187 if (v & RW_LOCK_WRITE_WAITERS) {
1188 queue = TS_EXCLUSIVE_QUEUE;
1189 setv |= (v & RW_LOCK_READ_WAITERS);
1190 }
1191 atomic_store_rel_ptr(&rw->rw_lock, setv);
1192
1193 /* Wake up all waiters for the specific queue. */
1194 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1195 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
1196 queue == TS_SHARED_QUEUE ? "read" : "write");
1197
1198 ts = turnstile_lookup(&rw->lock_object);
1199 MPASS(ts != NULL);
1200 turnstile_broadcast(ts, queue);
1201 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
1202 turnstile_chain_unlock(&rw->lock_object);
1203 }
1204
1205 /*
1206 * Attempt to do a non-blocking upgrade from a read lock to a write
1207 * lock. This will only succeed if this thread holds a single read
1208 * lock. Returns true if the upgrade succeeded and false otherwise.
1209 */
1210 int
1211 __rw_try_upgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
1212 {
1213 uintptr_t v, setv, tid;
1214 struct turnstile *ts;
1215 int success;
1216
1217 if (SCHEDULER_STOPPED())
1218 return (1);
1219
1220 KASSERT(rw->rw_lock != RW_DESTROYED,
1221 ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
1222 __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
1223
1224 /*
1225 * Attempt to switch from one reader to a writer. If there
1226 * are any write waiters, then we will have to lock the
1227 * turnstile first to prevent races with another writer
1228 * calling turnstile_wait() before we have claimed this
1229 * turnstile. So, do the simple case of no waiters first.
1230 */
1231 tid = (uintptr_t)curthread;
1232 success = 0;
1233 v = RW_READ_VALUE(rw);
1234 for (;;) {
1235 if (RW_READERS(v) > 1)
1236 break;
1237 if (!(v & RW_LOCK_WAITERS)) {
1238 success = atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid);
1239 if (!success)
1240 continue;
1241 break;
1242 }
1243
1244 /*
1245 * Ok, we think we have waiters, so lock the turnstile.
1246 */
1247 ts = turnstile_trywait(&rw->lock_object);
1248 v = RW_READ_VALUE(rw);
1249 retry_ts:
1250 if (RW_READERS(v) > 1) {
1251 turnstile_cancel(ts);
1252 break;
1253 }
1254 /*
1255 * Try to switch from one reader to a writer again. This time
1256 * we honor the current state of the waiters flags.
1257 * If we obtain the lock with the flags set, then claim
1258 * ownership of the turnstile.
1259 */
1260 setv = tid | (v & RW_LOCK_WAITERS);
1261 success = atomic_fcmpset_ptr(&rw->rw_lock, &v, setv);
1262 if (success) {
1263 if (v & RW_LOCK_WAITERS)
1264 turnstile_claim(ts);
1265 else
1266 turnstile_cancel(ts);
1267 break;
1268 }
1269 goto retry_ts;
1270 }
1271 LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
1272 if (success) {
1273 curthread->td_rw_rlocks--;
1274 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
1275 file, line);
1276 LOCKSTAT_RECORD0(rw__upgrade, rw);
1277 }
1278 return (success);
1279 }
1280
1281 int
1282 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
1283 {
1284 struct rwlock *rw;
1285
1286 rw = rwlock2rw(c);
1287 return (__rw_try_upgrade_int(rw LOCK_FILE_LINE_ARG));
1288 }
1289
1290 /*
1291 * Downgrade a write lock into a single read lock.
1292 */
1293 void
1294 __rw_downgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
1295 {
1296 struct turnstile *ts;
1297 uintptr_t tid, v;
1298 int rwait, wwait;
1299
1300 if (SCHEDULER_STOPPED())
1301 return;
1302
1303 KASSERT(rw->rw_lock != RW_DESTROYED,
1304 ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
1305 __rw_assert(&rw->rw_lock, RA_WLOCKED | RA_NOTRECURSED, file, line);
1306 #ifndef INVARIANTS
1307 if (rw_recursed(rw))
1308 panic("downgrade of a recursed lock");
1309 #endif
1310
1311 WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
1312
1313 /*
1314 * Convert from a writer to a single reader. First we handle
1315 * the easy case with no waiters. If there are any waiters, we
1316 * lock the turnstile and "disown" the lock.
1317 */
1318 tid = (uintptr_t)curthread;
1319 if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
1320 goto out;
1321
1322 /*
1323 * Ok, we think we have waiters, so lock the turnstile so we can
1324 * read the waiter flags without any races.
1325 */
1326 turnstile_chain_lock(&rw->lock_object);
1327 v = rw->rw_lock & RW_LOCK_WAITERS;
1328 rwait = v & RW_LOCK_READ_WAITERS;
1329 wwait = v & RW_LOCK_WRITE_WAITERS;
1330 MPASS(rwait | wwait);
1331
1332 /*
1333 * Downgrade from a write lock while preserving waiters flag
1334 * and give up ownership of the turnstile.
1335 */
1336 ts = turnstile_lookup(&rw->lock_object);
1337 MPASS(ts != NULL);
1338 if (!wwait)
1339 v &= ~RW_LOCK_READ_WAITERS;
1340 atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
1341 /*
1342 * Wake other readers if there are no writers pending. Otherwise they
1343 * won't be able to acquire the lock anyway.
1344 */
1345 if (rwait && !wwait) {
1346 turnstile_broadcast(ts, TS_SHARED_QUEUE);
1347 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
1348 } else
1349 turnstile_disown(ts);
1350 turnstile_chain_unlock(&rw->lock_object);
1351 out:
1352 curthread->td_rw_rlocks++;
1353 LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
1354 LOCKSTAT_RECORD0(rw__downgrade, rw);
1355 }
1356
1357 void
1358 __rw_downgrade(volatile uintptr_t *c, const char *file, int line)
1359 {
1360 struct rwlock *rw;
1361
1362 rw = rwlock2rw(c);
1363 __rw_downgrade_int(rw LOCK_FILE_LINE_ARG);
1364 }
1365
1366 #ifdef INVARIANT_SUPPORT
1367 #ifndef INVARIANTS
1368 #undef __rw_assert
1369 #endif
1370
1371 /*
1372 * In the non-WITNESS case, rw_assert() can only detect that at least
1373 * *some* thread owns an rlock, but it cannot guarantee that *this*
1374 * thread owns an rlock.
1375 */
1376 void
1377 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
1378 {
1379 const struct rwlock *rw;
1380
1381 if (panicstr != NULL)
1382 return;
1383
1384 rw = rwlock2rw(c);
1385
1386 switch (what) {
1387 case RA_LOCKED:
1388 case RA_LOCKED | RA_RECURSED:
1389 case RA_LOCKED | RA_NOTRECURSED:
1390 case RA_RLOCKED:
1391 case RA_RLOCKED | RA_RECURSED:
1392 case RA_RLOCKED | RA_NOTRECURSED:
1393 #ifdef WITNESS
1394 witness_assert(&rw->lock_object, what, file, line);
1395 #else
1396 /*
1397 * If some other thread has a write lock or we have one
1398 * and are asserting a read lock, fail. Also, if no one
1399 * has a lock at all, fail.
1400 */
1401 if (rw->rw_lock == RW_UNLOCKED ||
1402 (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
1403 rw_wowner(rw) != curthread)))
1404 panic("Lock %s not %slocked @ %s:%d\n",
1405 rw->lock_object.lo_name, (what & RA_RLOCKED) ?
1406 "read " : "", file, line);
1407
1408 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
1409 if (rw_recursed(rw)) {
1410 if (what & RA_NOTRECURSED)
1411 panic("Lock %s recursed @ %s:%d\n",
1412 rw->lock_object.lo_name, file,
1413 line);
1414 } else if (what & RA_RECURSED)
1415 panic("Lock %s not recursed @ %s:%d\n",
1416 rw->lock_object.lo_name, file, line);
1417 }
1418 #endif
1419 break;
1420 case RA_WLOCKED:
1421 case RA_WLOCKED | RA_RECURSED:
1422 case RA_WLOCKED | RA_NOTRECURSED:
1423 if (rw_wowner(rw) != curthread)
1424 panic("Lock %s not exclusively locked @ %s:%d\n",
1425 rw->lock_object.lo_name, file, line);
1426 if (rw_recursed(rw)) {
1427 if (what & RA_NOTRECURSED)
1428 panic("Lock %s recursed @ %s:%d\n",
1429 rw->lock_object.lo_name, file, line);
1430 } else if (what & RA_RECURSED)
1431 panic("Lock %s not recursed @ %s:%d\n",
1432 rw->lock_object.lo_name, file, line);
1433 break;
1434 case RA_UNLOCKED:
1435 #ifdef WITNESS
1436 witness_assert(&rw->lock_object, what, file, line);
1437 #else
1438 /*
1439 * If we hold a write lock fail. We can't reliably check
1440 * to see if we hold a read lock or not.
1441 */
1442 if (rw_wowner(rw) == curthread)
1443 panic("Lock %s exclusively locked @ %s:%d\n",
1444 rw->lock_object.lo_name, file, line);
1445 #endif
1446 break;
1447 default:
1448 panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
1449 line);
1450 }
1451 }
1452 #endif /* INVARIANT_SUPPORT */
1453
1454 #ifdef DDB
1455 void
1456 db_show_rwlock(const struct lock_object *lock)
1457 {
1458 const struct rwlock *rw;
1459 struct thread *td;
1460
1461 rw = (const struct rwlock *)lock;
1462
1463 db_printf(" state: ");
1464 if (rw->rw_lock == RW_UNLOCKED)
1465 db_printf("UNLOCKED\n");
1466 else if (rw->rw_lock == RW_DESTROYED) {
1467 db_printf("DESTROYED\n");
1468 return;
1469 } else if (rw->rw_lock & RW_LOCK_READ)
1470 db_printf("RLOCK: %ju locks\n",
1471 (uintmax_t)(RW_READERS(rw->rw_lock)));
1472 else {
1473 td = rw_wowner(rw);
1474 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1475 td->td_tid, td->td_proc->p_pid, td->td_name);
1476 if (rw_recursed(rw))
1477 db_printf(" recursed: %u\n", rw->rw_recurse);
1478 }
1479 db_printf(" waiters: ");
1480 switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
1481 case RW_LOCK_READ_WAITERS:
1482 db_printf("readers\n");
1483 break;
1484 case RW_LOCK_WRITE_WAITERS:
1485 db_printf("writers\n");
1486 break;
1487 case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
1488 db_printf("readers and writers\n");
1489 break;
1490 default:
1491 db_printf("none\n");
1492 break;
1493 }
1494 }
1495
1496 #endif
Cache object: 4ee859eba64a628a59b4dbdb39a53ade
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