1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2006 John Baldwin <[email protected]>
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 /*
29 * Machine independent bits of reader/writer lock implementation.
30 */
31
32 #include <sys/cdefs.h>
33 #include "opt_ddb.h"
34 #include "opt_hwpmc_hooks.h"
35 #include "opt_no_adaptive_rwlocks.h"
36
37 #include <sys/param.h>
38 #include <sys/kdb.h>
39 #include <sys/ktr.h>
40 #include <sys/kernel.h>
41 #include <sys/lock.h>
42 #include <sys/mutex.h>
43 #include <sys/proc.h>
44 #include <sys/rwlock.h>
45 #include <sys/sched.h>
46 #include <sys/smp.h>
47 #include <sys/sysctl.h>
48 #include <sys/systm.h>
49 #include <sys/turnstile.h>
50
51 #include <machine/cpu.h>
52
53 #if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS)
54 #define ADAPTIVE_RWLOCKS
55 #endif
56
57 #ifdef HWPMC_HOOKS
58 #include <sys/pmckern.h>
59 PMC_SOFT_DECLARE( , , lock, failed);
60 #endif
61
62 /*
63 * Return the rwlock address when the lock cookie address is provided.
64 * This functionality assumes that struct rwlock* have a member named rw_lock.
65 */
66 #define rwlock2rw(c) (__containerof(c, struct rwlock, rw_lock))
67
68 #ifdef DDB
69 #include <ddb/ddb.h>
70
71 static void db_show_rwlock(const struct lock_object *lock);
72 #endif
73 static void assert_rw(const struct lock_object *lock, int what);
74 static void lock_rw(struct lock_object *lock, uintptr_t how);
75 #ifdef KDTRACE_HOOKS
76 static int owner_rw(const struct lock_object *lock, struct thread **owner);
77 #endif
78 static uintptr_t unlock_rw(struct lock_object *lock);
79
80 struct lock_class lock_class_rw = {
81 .lc_name = "rw",
82 .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE,
83 .lc_assert = assert_rw,
84 #ifdef DDB
85 .lc_ddb_show = db_show_rwlock,
86 #endif
87 .lc_lock = lock_rw,
88 .lc_unlock = unlock_rw,
89 #ifdef KDTRACE_HOOKS
90 .lc_owner = owner_rw,
91 #endif
92 };
93
94 #ifdef ADAPTIVE_RWLOCKS
95 #ifdef RWLOCK_CUSTOM_BACKOFF
96 static u_short __read_frequently rowner_retries;
97 static u_short __read_frequently rowner_loops;
98 static SYSCTL_NODE(_debug, OID_AUTO, rwlock,
99 CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
100 "rwlock debugging");
101 SYSCTL_U16(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
102 SYSCTL_U16(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
103
104 static struct lock_delay_config __read_frequently rw_delay;
105
106 SYSCTL_U16(_debug_rwlock, OID_AUTO, delay_base, CTLFLAG_RW, &rw_delay.base,
107 0, "");
108 SYSCTL_U16(_debug_rwlock, OID_AUTO, delay_max, CTLFLAG_RW, &rw_delay.max,
109 0, "");
110
111 static void
rw_lock_delay_init(void * arg __unused)112 rw_lock_delay_init(void *arg __unused)
113 {
114
115 lock_delay_default_init(&rw_delay);
116 rowner_retries = 10;
117 rowner_loops = max(10000, rw_delay.max);
118 }
119 LOCK_DELAY_SYSINIT(rw_lock_delay_init);
120 #else
121 #define rw_delay locks_delay
122 #define rowner_retries locks_delay_retries
123 #define rowner_loops locks_delay_loops
124 #endif
125 #endif
126
127 /*
128 * Return a pointer to the owning thread if the lock is write-locked or
129 * NULL if the lock is unlocked or read-locked.
130 */
131
132 #define lv_rw_wowner(v) \
133 ((v) & RW_LOCK_READ ? NULL : \
134 (struct thread *)RW_OWNER((v)))
135
136 #define rw_wowner(rw) lv_rw_wowner(RW_READ_VALUE(rw))
137
138 /*
139 * Returns if a write owner is recursed. Write ownership is not assured
140 * here and should be previously checked.
141 */
142 #define rw_recursed(rw) ((rw)->rw_recurse != 0)
143
144 /*
145 * Return true if curthread helds the lock.
146 */
147 #define rw_wlocked(rw) (rw_wowner((rw)) == curthread)
148
149 /*
150 * Return a pointer to the owning thread for this lock who should receive
151 * any priority lent by threads that block on this lock. Currently this
152 * is identical to rw_wowner().
153 */
154 #define rw_owner(rw) rw_wowner(rw)
155
156 #ifndef INVARIANTS
157 #define __rw_assert(c, what, file, line)
158 #endif
159
160 void
assert_rw(const struct lock_object * lock,int what)161 assert_rw(const struct lock_object *lock, int what)
162 {
163
164 rw_assert((const struct rwlock *)lock, what);
165 }
166
167 void
lock_rw(struct lock_object * lock,uintptr_t how)168 lock_rw(struct lock_object *lock, uintptr_t how)
169 {
170 struct rwlock *rw;
171
172 rw = (struct rwlock *)lock;
173 if (how)
174 rw_rlock(rw);
175 else
176 rw_wlock(rw);
177 }
178
179 uintptr_t
unlock_rw(struct lock_object * lock)180 unlock_rw(struct lock_object *lock)
181 {
182 struct rwlock *rw;
183
184 rw = (struct rwlock *)lock;
185 rw_assert(rw, RA_LOCKED | LA_NOTRECURSED);
186 if (rw->rw_lock & RW_LOCK_READ) {
187 rw_runlock(rw);
188 return (1);
189 } else {
190 rw_wunlock(rw);
191 return (0);
192 }
193 }
194
195 #ifdef KDTRACE_HOOKS
196 int
owner_rw(const struct lock_object * lock,struct thread ** owner)197 owner_rw(const struct lock_object *lock, struct thread **owner)
198 {
199 const struct rwlock *rw = (const struct rwlock *)lock;
200 uintptr_t x = rw->rw_lock;
201
202 *owner = rw_wowner(rw);
203 return ((x & RW_LOCK_READ) != 0 ? (RW_READERS(x) != 0) :
204 (*owner != NULL));
205 }
206 #endif
207
208 void
_rw_init_flags(volatile uintptr_t * c,const char * name,int opts)209 _rw_init_flags(volatile uintptr_t *c, const char *name, int opts)
210 {
211 struct rwlock *rw;
212 int flags;
213
214 rw = rwlock2rw(c);
215
216 MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
217 RW_RECURSE | RW_NEW)) == 0);
218 ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
219 ("%s: rw_lock not aligned for %s: %p", __func__, name,
220 &rw->rw_lock));
221
222 flags = LO_UPGRADABLE;
223 if (opts & RW_DUPOK)
224 flags |= LO_DUPOK;
225 if (opts & RW_NOPROFILE)
226 flags |= LO_NOPROFILE;
227 if (!(opts & RW_NOWITNESS))
228 flags |= LO_WITNESS;
229 if (opts & RW_RECURSE)
230 flags |= LO_RECURSABLE;
231 if (opts & RW_QUIET)
232 flags |= LO_QUIET;
233 if (opts & RW_NEW)
234 flags |= LO_NEW;
235
236 lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
237 rw->rw_lock = RW_UNLOCKED;
238 rw->rw_recurse = 0;
239 }
240
241 void
_rw_destroy(volatile uintptr_t * c)242 _rw_destroy(volatile uintptr_t *c)
243 {
244 struct rwlock *rw;
245
246 rw = rwlock2rw(c);
247
248 KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw));
249 KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw));
250 rw->rw_lock = RW_DESTROYED;
251 lock_destroy(&rw->lock_object);
252 }
253
254 void
rw_sysinit(void * arg)255 rw_sysinit(void *arg)
256 {
257 struct rw_args *args;
258
259 args = arg;
260 rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc,
261 args->ra_flags);
262 }
263
264 int
_rw_wowned(const volatile uintptr_t * c)265 _rw_wowned(const volatile uintptr_t *c)
266 {
267
268 return (rw_wowner(rwlock2rw(c)) == curthread);
269 }
270
271 void
_rw_wlock_cookie(volatile uintptr_t * c,const char * file,int line)272 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line)
273 {
274 struct rwlock *rw;
275 uintptr_t tid, v;
276
277 rw = rwlock2rw(c);
278
279 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
280 !TD_IS_IDLETHREAD(curthread),
281 ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d",
282 curthread, rw->lock_object.lo_name, file, line));
283 KASSERT(rw->rw_lock != RW_DESTROYED,
284 ("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
285 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
286 line, NULL);
287 tid = (uintptr_t)curthread;
288 v = RW_UNLOCKED;
289 if (!_rw_write_lock_fetch(rw, &v, tid))
290 _rw_wlock_hard(rw, v, file, line);
291 else
292 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw,
293 0, 0, file, line, LOCKSTAT_WRITER);
294
295 LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
296 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
297 TD_LOCKS_INC(curthread);
298 }
299
300 int
__rw_try_wlock_int(struct rwlock * rw LOCK_FILE_LINE_ARG_DEF)301 __rw_try_wlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
302 {
303 struct thread *td;
304 uintptr_t tid, v;
305 int rval;
306 bool recursed;
307
308 td = curthread;
309 tid = (uintptr_t)td;
310 if (SCHEDULER_STOPPED_TD(td))
311 return (1);
312
313 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
314 ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d",
315 curthread, rw->lock_object.lo_name, file, line));
316 KASSERT(rw->rw_lock != RW_DESTROYED,
317 ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
318
319 rval = 1;
320 recursed = false;
321 v = RW_UNLOCKED;
322 for (;;) {
323 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
324 break;
325 if (v == RW_UNLOCKED)
326 continue;
327 if (v == tid && (rw->lock_object.lo_flags & LO_RECURSABLE)) {
328 rw->rw_recurse++;
329 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
330 break;
331 }
332 rval = 0;
333 break;
334 }
335
336 LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
337 if (rval) {
338 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
339 file, line);
340 if (!recursed)
341 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
342 rw, 0, 0, file, line, LOCKSTAT_WRITER);
343 TD_LOCKS_INC(curthread);
344 }
345 return (rval);
346 }
347
348 int
__rw_try_wlock(volatile uintptr_t * c,const char * file,int line)349 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
350 {
351 struct rwlock *rw;
352
353 rw = rwlock2rw(c);
354 return (__rw_try_wlock_int(rw LOCK_FILE_LINE_ARG));
355 }
356
357 void
_rw_wunlock_cookie(volatile uintptr_t * c,const char * file,int line)358 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
359 {
360 struct rwlock *rw;
361
362 rw = rwlock2rw(c);
363
364 KASSERT(rw->rw_lock != RW_DESTROYED,
365 ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
366 __rw_assert(c, RA_WLOCKED, file, line);
367 WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
368 LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
369 line);
370
371 #ifdef LOCK_PROFILING
372 _rw_wunlock_hard(rw, (uintptr_t)curthread, file, line);
373 #else
374 __rw_wunlock(rw, curthread, file, line);
375 #endif
376
377 TD_LOCKS_DEC(curthread);
378 }
379
380 /*
381 * Determines whether a new reader can acquire a lock. Succeeds if the
382 * reader already owns a read lock and the lock is locked for read to
383 * prevent deadlock from reader recursion. Also succeeds if the lock
384 * is unlocked and has no writer waiters or spinners. Failing otherwise
385 * prioritizes writers before readers.
386 */
387 static bool __always_inline
__rw_can_read(struct thread * td,uintptr_t v,bool fp)388 __rw_can_read(struct thread *td, uintptr_t v, bool fp)
389 {
390
391 if ((v & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER))
392 == RW_LOCK_READ)
393 return (true);
394 if (!fp && td->td_rw_rlocks && (v & RW_LOCK_READ))
395 return (true);
396 return (false);
397 }
398
399 static bool __always_inline
__rw_rlock_try(struct rwlock * rw,struct thread * td,uintptr_t * vp,bool fp LOCK_FILE_LINE_ARG_DEF)400 __rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp, bool fp
401 LOCK_FILE_LINE_ARG_DEF)
402 {
403
404 /*
405 * Handle the easy case. If no other thread has a write
406 * lock, then try to bump up the count of read locks. Note
407 * that we have to preserve the current state of the
408 * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a
409 * read lock, then rw_lock must have changed, so restart
410 * the loop. Note that this handles the case of a
411 * completely unlocked rwlock since such a lock is encoded
412 * as a read lock with no waiters.
413 */
414 while (__rw_can_read(td, *vp, fp)) {
415 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, vp,
416 *vp + RW_ONE_READER)) {
417 if (LOCK_LOG_TEST(&rw->lock_object, 0))
418 CTR4(KTR_LOCK,
419 "%s: %p succeed %p -> %p", __func__,
420 rw, (void *)*vp,
421 (void *)(*vp + RW_ONE_READER));
422 td->td_rw_rlocks++;
423 return (true);
424 }
425 }
426 return (false);
427 }
428
429 static void __noinline
__rw_rlock_hard(struct rwlock * rw,struct thread * td,uintptr_t v LOCK_FILE_LINE_ARG_DEF)430 __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
431 LOCK_FILE_LINE_ARG_DEF)
432 {
433 struct turnstile *ts;
434 struct thread *owner;
435 #ifdef ADAPTIVE_RWLOCKS
436 int spintries = 0;
437 int i, n;
438 #endif
439 #ifdef LOCK_PROFILING
440 uint64_t waittime = 0;
441 int contested = 0;
442 #endif
443 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
444 struct lock_delay_arg lda;
445 #endif
446 #ifdef KDTRACE_HOOKS
447 u_int sleep_cnt = 0;
448 int64_t sleep_time = 0;
449 int64_t all_time = 0;
450 #endif
451 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
452 uintptr_t state = 0;
453 int doing_lockprof = 0;
454 #endif
455
456 #ifdef KDTRACE_HOOKS
457 if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
458 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
459 goto out_lockstat;
460 doing_lockprof = 1;
461 all_time -= lockstat_nsecs(&rw->lock_object);
462 state = v;
463 }
464 #endif
465 #ifdef LOCK_PROFILING
466 doing_lockprof = 1;
467 state = v;
468 #endif
469
470 if (SCHEDULER_STOPPED())
471 return;
472
473 #if defined(ADAPTIVE_RWLOCKS)
474 lock_delay_arg_init(&lda, &rw_delay);
475 #elif defined(KDTRACE_HOOKS)
476 lock_delay_arg_init_noadapt(&lda);
477 #endif
478
479 #ifdef HWPMC_HOOKS
480 PMC_SOFT_CALL( , , lock, failed);
481 #endif
482 lock_profile_obtain_lock_failed(&rw->lock_object, false,
483 &contested, &waittime);
484
485 for (;;) {
486 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
487 break;
488 #ifdef KDTRACE_HOOKS
489 lda.spin_cnt++;
490 #endif
491
492 #ifdef ADAPTIVE_RWLOCKS
493 /*
494 * If the owner is running on another CPU, spin until
495 * the owner stops running or the state of the lock
496 * changes.
497 */
498 if ((v & RW_LOCK_READ) == 0) {
499 owner = (struct thread *)RW_OWNER(v);
500 if (TD_IS_RUNNING(owner)) {
501 if (LOCK_LOG_TEST(&rw->lock_object, 0))
502 CTR3(KTR_LOCK,
503 "%s: spinning on %p held by %p",
504 __func__, rw, owner);
505 KTR_STATE1(KTR_SCHED, "thread",
506 sched_tdname(curthread), "spinning",
507 "lockname:\"%s\"", rw->lock_object.lo_name);
508 do {
509 lock_delay(&lda);
510 v = RW_READ_VALUE(rw);
511 owner = lv_rw_wowner(v);
512 } while (owner != NULL && TD_IS_RUNNING(owner));
513 KTR_STATE0(KTR_SCHED, "thread",
514 sched_tdname(curthread), "running");
515 continue;
516 }
517 } else {
518 if ((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) {
519 MPASS(!__rw_can_read(td, v, false));
520 lock_delay_spin(2);
521 v = RW_READ_VALUE(rw);
522 continue;
523 }
524 if (spintries < rowner_retries) {
525 spintries++;
526 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
527 "spinning", "lockname:\"%s\"",
528 rw->lock_object.lo_name);
529 n = RW_READERS(v);
530 for (i = 0; i < rowner_loops; i += n) {
531 lock_delay_spin(n);
532 v = RW_READ_VALUE(rw);
533 if (!(v & RW_LOCK_READ))
534 break;
535 n = RW_READERS(v);
536 if (n == 0)
537 break;
538 if (__rw_can_read(td, v, false))
539 break;
540 }
541 #ifdef KDTRACE_HOOKS
542 lda.spin_cnt += rowner_loops - i;
543 #endif
544 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
545 "running");
546 if (i < rowner_loops)
547 continue;
548 }
549 }
550 #endif
551
552 /*
553 * Okay, now it's the hard case. Some other thread already
554 * has a write lock or there are write waiters present,
555 * acquire the turnstile lock so we can begin the process
556 * of blocking.
557 */
558 ts = turnstile_trywait(&rw->lock_object);
559
560 /*
561 * The lock might have been released while we spun, so
562 * recheck its state and restart the loop if needed.
563 */
564 v = RW_READ_VALUE(rw);
565 retry_ts:
566 if (((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) ||
567 __rw_can_read(td, v, false)) {
568 turnstile_cancel(ts);
569 continue;
570 }
571
572 owner = lv_rw_wowner(v);
573
574 #ifdef ADAPTIVE_RWLOCKS
575 /*
576 * The current lock owner might have started executing
577 * on another CPU (or the lock could have changed
578 * owners) while we were waiting on the turnstile
579 * chain lock. If so, drop the turnstile lock and try
580 * again.
581 */
582 if (owner != NULL) {
583 if (TD_IS_RUNNING(owner)) {
584 turnstile_cancel(ts);
585 continue;
586 }
587 }
588 #endif
589
590 /*
591 * The lock is held in write mode or it already has waiters.
592 */
593 MPASS(!__rw_can_read(td, v, false));
594
595 /*
596 * If the RW_LOCK_READ_WAITERS flag is already set, then
597 * we can go ahead and block. If it is not set then try
598 * to set it. If we fail to set it drop the turnstile
599 * lock and restart the loop.
600 */
601 if (!(v & RW_LOCK_READ_WAITERS)) {
602 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
603 v | RW_LOCK_READ_WAITERS))
604 goto retry_ts;
605 if (LOCK_LOG_TEST(&rw->lock_object, 0))
606 CTR2(KTR_LOCK, "%s: %p set read waiters flag",
607 __func__, rw);
608 }
609
610 /*
611 * We were unable to acquire the lock and the read waiters
612 * flag is set, so we must block on the turnstile.
613 */
614 if (LOCK_LOG_TEST(&rw->lock_object, 0))
615 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
616 rw);
617 #ifdef KDTRACE_HOOKS
618 sleep_time -= lockstat_nsecs(&rw->lock_object);
619 #endif
620 MPASS(owner == rw_owner(rw));
621 turnstile_wait(ts, owner, TS_SHARED_QUEUE);
622 #ifdef KDTRACE_HOOKS
623 sleep_time += lockstat_nsecs(&rw->lock_object);
624 sleep_cnt++;
625 #endif
626 if (LOCK_LOG_TEST(&rw->lock_object, 0))
627 CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
628 __func__, rw);
629 v = RW_READ_VALUE(rw);
630 }
631 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
632 if (__predict_true(!doing_lockprof))
633 return;
634 #endif
635 #ifdef KDTRACE_HOOKS
636 all_time += lockstat_nsecs(&rw->lock_object);
637 if (sleep_time)
638 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
639 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
640 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
641
642 /* Record only the loops spinning and not sleeping. */
643 if (lda.spin_cnt > sleep_cnt)
644 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
645 LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
646 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
647 out_lockstat:
648 #endif
649 /*
650 * TODO: acquire "owner of record" here. Here be turnstile dragons
651 * however. turnstiles don't like owners changing between calls to
652 * turnstile_wait() currently.
653 */
654 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
655 waittime, file, line, LOCKSTAT_READER);
656 }
657
658 void
__rw_rlock_int(struct rwlock * rw LOCK_FILE_LINE_ARG_DEF)659 __rw_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
660 {
661 struct thread *td;
662 uintptr_t v;
663
664 td = curthread;
665
666 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED_TD(td) ||
667 !TD_IS_IDLETHREAD(td),
668 ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d",
669 td, rw->lock_object.lo_name, file, line));
670 KASSERT(rw->rw_lock != RW_DESTROYED,
671 ("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
672 KASSERT(rw_wowner(rw) != td,
673 ("rw_rlock: wlock already held for %s @ %s:%d",
674 rw->lock_object.lo_name, file, line));
675 WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
676
677 v = RW_READ_VALUE(rw);
678 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__acquire) ||
679 !__rw_rlock_try(rw, td, &v, true LOCK_FILE_LINE_ARG)))
680 __rw_rlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
681 else
682 lock_profile_obtain_lock_success(&rw->lock_object, false, 0, 0,
683 file, line);
684
685 LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
686 WITNESS_LOCK(&rw->lock_object, 0, file, line);
687 TD_LOCKS_INC(curthread);
688 }
689
690 void
__rw_rlock(volatile uintptr_t * c,const char * file,int line)691 __rw_rlock(volatile uintptr_t *c, const char *file, int line)
692 {
693 struct rwlock *rw;
694
695 rw = rwlock2rw(c);
696 __rw_rlock_int(rw LOCK_FILE_LINE_ARG);
697 }
698
699 int
__rw_try_rlock_int(struct rwlock * rw LOCK_FILE_LINE_ARG_DEF)700 __rw_try_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
701 {
702 uintptr_t x;
703
704 if (SCHEDULER_STOPPED())
705 return (1);
706
707 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
708 ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
709 curthread, rw->lock_object.lo_name, file, line));
710
711 x = rw->rw_lock;
712 for (;;) {
713 KASSERT(rw->rw_lock != RW_DESTROYED,
714 ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
715 if (!(x & RW_LOCK_READ))
716 break;
717 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &x, x + RW_ONE_READER)) {
718 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
719 line);
720 WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
721 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
722 rw, 0, 0, file, line, LOCKSTAT_READER);
723 TD_LOCKS_INC(curthread);
724 curthread->td_rw_rlocks++;
725 return (1);
726 }
727 }
728
729 LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
730 return (0);
731 }
732
733 int
__rw_try_rlock(volatile uintptr_t * c,const char * file,int line)734 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
735 {
736 struct rwlock *rw;
737
738 rw = rwlock2rw(c);
739 return (__rw_try_rlock_int(rw LOCK_FILE_LINE_ARG));
740 }
741
742 static bool __always_inline
__rw_runlock_try(struct rwlock * rw,struct thread * td,uintptr_t * vp)743 __rw_runlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp)
744 {
745
746 for (;;) {
747 if (RW_READERS(*vp) > 1 || !(*vp & RW_LOCK_WAITERS)) {
748 if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp,
749 *vp - RW_ONE_READER)) {
750 if (LOCK_LOG_TEST(&rw->lock_object, 0))
751 CTR4(KTR_LOCK,
752 "%s: %p succeeded %p -> %p",
753 __func__, rw, (void *)*vp,
754 (void *)(*vp - RW_ONE_READER));
755 td->td_rw_rlocks--;
756 return (true);
757 }
758 continue;
759 }
760 break;
761 }
762 return (false);
763 }
764
765 static void __noinline
__rw_runlock_hard(struct rwlock * rw,struct thread * td,uintptr_t v LOCK_FILE_LINE_ARG_DEF)766 __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
767 LOCK_FILE_LINE_ARG_DEF)
768 {
769 struct turnstile *ts;
770 uintptr_t setv, queue;
771
772 if (SCHEDULER_STOPPED())
773 return;
774
775 if (__rw_runlock_try(rw, td, &v))
776 goto out_lockstat;
777
778 /*
779 * Ok, we know we have waiters and we think we are the
780 * last reader, so grab the turnstile lock.
781 */
782 turnstile_chain_lock(&rw->lock_object);
783 v = RW_READ_VALUE(rw);
784 for (;;) {
785 if (__rw_runlock_try(rw, td, &v))
786 break;
787
788 MPASS(v & RW_LOCK_WAITERS);
789
790 /*
791 * Try to drop our lock leaving the lock in a unlocked
792 * state.
793 *
794 * If you wanted to do explicit lock handoff you'd have to
795 * do it here. You'd also want to use turnstile_signal()
796 * and you'd have to handle the race where a higher
797 * priority thread blocks on the write lock before the
798 * thread you wakeup actually runs and have the new thread
799 * "steal" the lock. For now it's a lot simpler to just
800 * wakeup all of the waiters.
801 *
802 * As above, if we fail, then another thread might have
803 * acquired a read lock, so drop the turnstile lock and
804 * restart.
805 */
806 setv = RW_UNLOCKED;
807 queue = TS_SHARED_QUEUE;
808 if (v & RW_LOCK_WRITE_WAITERS) {
809 queue = TS_EXCLUSIVE_QUEUE;
810 setv |= (v & RW_LOCK_READ_WAITERS);
811 }
812 setv |= (v & RW_LOCK_WRITE_SPINNER);
813 if (!atomic_fcmpset_rel_ptr(&rw->rw_lock, &v, setv))
814 continue;
815 if (LOCK_LOG_TEST(&rw->lock_object, 0))
816 CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
817 __func__, rw);
818
819 /*
820 * Ok. The lock is released and all that's left is to
821 * wake up the waiters. Note that the lock might not be
822 * free anymore, but in that case the writers will just
823 * block again if they run before the new lock holder(s)
824 * release the lock.
825 */
826 ts = turnstile_lookup(&rw->lock_object);
827 MPASS(ts != NULL);
828 turnstile_broadcast(ts, queue);
829 turnstile_unpend(ts);
830 td->td_rw_rlocks--;
831 break;
832 }
833 turnstile_chain_unlock(&rw->lock_object);
834 out_lockstat:
835 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER);
836 }
837
838 void
_rw_runlock_cookie_int(struct rwlock * rw LOCK_FILE_LINE_ARG_DEF)839 _rw_runlock_cookie_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
840 {
841 struct thread *td;
842 uintptr_t v;
843
844 KASSERT(rw->rw_lock != RW_DESTROYED,
845 ("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
846 __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
847 WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
848 LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
849
850 td = curthread;
851 v = RW_READ_VALUE(rw);
852
853 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__release) ||
854 !__rw_runlock_try(rw, td, &v)))
855 __rw_runlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
856 else
857 lock_profile_release_lock(&rw->lock_object, false);
858
859 TD_LOCKS_DEC(curthread);
860 }
861
862 void
_rw_runlock_cookie(volatile uintptr_t * c,const char * file,int line)863 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
864 {
865 struct rwlock *rw;
866
867 rw = rwlock2rw(c);
868 _rw_runlock_cookie_int(rw LOCK_FILE_LINE_ARG);
869 }
870
871 #ifdef ADAPTIVE_RWLOCKS
872 static inline void
rw_drop_critical(uintptr_t v,bool * in_critical,int * extra_work)873 rw_drop_critical(uintptr_t v, bool *in_critical, int *extra_work)
874 {
875
876 if (v & RW_LOCK_WRITE_SPINNER)
877 return;
878 if (*in_critical) {
879 critical_exit();
880 *in_critical = false;
881 (*extra_work)--;
882 }
883 }
884 #else
885 #define rw_drop_critical(v, in_critical, extra_work) do { } while (0)
886 #endif
887
888 /*
889 * This function is called when we are unable to obtain a write lock on the
890 * first try. This means that at least one other thread holds either a
891 * read or write lock.
892 */
893 void
__rw_wlock_hard(volatile uintptr_t * c,uintptr_t v LOCK_FILE_LINE_ARG_DEF)894 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
895 {
896 uintptr_t tid;
897 struct rwlock *rw;
898 struct turnstile *ts;
899 struct thread *owner;
900 #ifdef ADAPTIVE_RWLOCKS
901 int spintries = 0;
902 int i, n;
903 enum { READERS, WRITER } sleep_reason = READERS;
904 bool in_critical = false;
905 #endif
906 uintptr_t setv;
907 #ifdef LOCK_PROFILING
908 uint64_t waittime = 0;
909 int contested = 0;
910 #endif
911 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
912 struct lock_delay_arg lda;
913 #endif
914 #ifdef KDTRACE_HOOKS
915 u_int sleep_cnt = 0;
916 int64_t sleep_time = 0;
917 int64_t all_time = 0;
918 #endif
919 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
920 uintptr_t state = 0;
921 int doing_lockprof = 0;
922 #endif
923 int extra_work = 0;
924
925 tid = (uintptr_t)curthread;
926 rw = rwlock2rw(c);
927
928 #ifdef KDTRACE_HOOKS
929 if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
930 while (v == RW_UNLOCKED) {
931 if (_rw_write_lock_fetch(rw, &v, tid))
932 goto out_lockstat;
933 }
934 extra_work = 1;
935 doing_lockprof = 1;
936 all_time -= lockstat_nsecs(&rw->lock_object);
937 state = v;
938 }
939 #endif
940 #ifdef LOCK_PROFILING
941 extra_work = 1;
942 doing_lockprof = 1;
943 state = v;
944 #endif
945
946 if (SCHEDULER_STOPPED())
947 return;
948
949 if (__predict_false(v == RW_UNLOCKED))
950 v = RW_READ_VALUE(rw);
951
952 if (__predict_false(lv_rw_wowner(v) == (struct thread *)tid)) {
953 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
954 ("%s: recursing but non-recursive rw %s @ %s:%d\n",
955 __func__, rw->lock_object.lo_name, file, line));
956 rw->rw_recurse++;
957 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
958 if (LOCK_LOG_TEST(&rw->lock_object, 0))
959 CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
960 return;
961 }
962
963 if (LOCK_LOG_TEST(&rw->lock_object, 0))
964 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
965 rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
966
967 #if defined(ADAPTIVE_RWLOCKS)
968 lock_delay_arg_init(&lda, &rw_delay);
969 #elif defined(KDTRACE_HOOKS)
970 lock_delay_arg_init_noadapt(&lda);
971 #endif
972
973 #ifdef HWPMC_HOOKS
974 PMC_SOFT_CALL( , , lock, failed);
975 #endif
976 lock_profile_obtain_lock_failed(&rw->lock_object, false,
977 &contested, &waittime);
978
979 for (;;) {
980 if (v == RW_UNLOCKED) {
981 if (_rw_write_lock_fetch(rw, &v, tid))
982 break;
983 continue;
984 }
985 #ifdef KDTRACE_HOOKS
986 lda.spin_cnt++;
987 #endif
988
989 #ifdef ADAPTIVE_RWLOCKS
990 if (v == (RW_LOCK_READ | RW_LOCK_WRITE_SPINNER)) {
991 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
992 break;
993 continue;
994 }
995
996 /*
997 * If the lock is write locked and the owner is
998 * running on another CPU, spin until the owner stops
999 * running or the state of the lock changes.
1000 */
1001 if (!(v & RW_LOCK_READ)) {
1002 rw_drop_critical(v, &in_critical, &extra_work);
1003 sleep_reason = WRITER;
1004 owner = lv_rw_wowner(v);
1005 if (!TD_IS_RUNNING(owner))
1006 goto ts;
1007 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1008 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
1009 __func__, rw, owner);
1010 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1011 "spinning", "lockname:\"%s\"",
1012 rw->lock_object.lo_name);
1013 do {
1014 lock_delay(&lda);
1015 v = RW_READ_VALUE(rw);
1016 owner = lv_rw_wowner(v);
1017 } while (owner != NULL && TD_IS_RUNNING(owner));
1018 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1019 "running");
1020 continue;
1021 } else if (RW_READERS(v) > 0) {
1022 sleep_reason = READERS;
1023 if (spintries == rowner_retries)
1024 goto ts;
1025 if (!(v & RW_LOCK_WRITE_SPINNER)) {
1026 if (!in_critical) {
1027 critical_enter();
1028 in_critical = true;
1029 extra_work++;
1030 }
1031 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
1032 v | RW_LOCK_WRITE_SPINNER)) {
1033 critical_exit();
1034 in_critical = false;
1035 extra_work--;
1036 continue;
1037 }
1038 }
1039 spintries++;
1040 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1041 "spinning", "lockname:\"%s\"",
1042 rw->lock_object.lo_name);
1043 n = RW_READERS(v);
1044 for (i = 0; i < rowner_loops; i += n) {
1045 lock_delay_spin(n);
1046 v = RW_READ_VALUE(rw);
1047 if (!(v & RW_LOCK_WRITE_SPINNER))
1048 break;
1049 if (!(v & RW_LOCK_READ))
1050 break;
1051 n = RW_READERS(v);
1052 if (n == 0)
1053 break;
1054 }
1055 #ifdef KDTRACE_HOOKS
1056 lda.spin_cnt += i;
1057 #endif
1058 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1059 "running");
1060 if (i < rowner_loops)
1061 continue;
1062 }
1063 ts:
1064 #endif
1065 ts = turnstile_trywait(&rw->lock_object);
1066 v = RW_READ_VALUE(rw);
1067 retry_ts:
1068 owner = lv_rw_wowner(v);
1069
1070 #ifdef ADAPTIVE_RWLOCKS
1071 /*
1072 * The current lock owner might have started executing
1073 * on another CPU (or the lock could have changed
1074 * owners) while we were waiting on the turnstile
1075 * chain lock. If so, drop the turnstile lock and try
1076 * again.
1077 */
1078 if (owner != NULL) {
1079 if (TD_IS_RUNNING(owner)) {
1080 turnstile_cancel(ts);
1081 rw_drop_critical(v, &in_critical, &extra_work);
1082 continue;
1083 }
1084 } else if (RW_READERS(v) > 0 && sleep_reason == WRITER) {
1085 turnstile_cancel(ts);
1086 rw_drop_critical(v, &in_critical, &extra_work);
1087 continue;
1088 }
1089 #endif
1090 /*
1091 * Check for the waiters flags about this rwlock.
1092 * If the lock was released, without maintain any pending
1093 * waiters queue, simply try to acquire it.
1094 * If a pending waiters queue is present, claim the lock
1095 * ownership and maintain the pending queue.
1096 */
1097 setv = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
1098 if ((v & ~setv) == RW_UNLOCKED) {
1099 setv &= ~RW_LOCK_WRITE_SPINNER;
1100 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid | setv)) {
1101 if (setv)
1102 turnstile_claim(ts);
1103 else
1104 turnstile_cancel(ts);
1105 break;
1106 }
1107 goto retry_ts;
1108 }
1109
1110 #ifdef ADAPTIVE_RWLOCKS
1111 if (in_critical) {
1112 if ((v & RW_LOCK_WRITE_SPINNER) ||
1113 !((v & RW_LOCK_WRITE_WAITERS))) {
1114 setv = v & ~RW_LOCK_WRITE_SPINNER;
1115 setv |= RW_LOCK_WRITE_WAITERS;
1116 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v, setv))
1117 goto retry_ts;
1118 }
1119 critical_exit();
1120 in_critical = false;
1121 extra_work--;
1122 } else {
1123 #endif
1124 /*
1125 * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
1126 * set it. If we fail to set it, then loop back and try
1127 * again.
1128 */
1129 if (!(v & RW_LOCK_WRITE_WAITERS)) {
1130 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
1131 v | RW_LOCK_WRITE_WAITERS))
1132 goto retry_ts;
1133 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1134 CTR2(KTR_LOCK, "%s: %p set write waiters flag",
1135 __func__, rw);
1136 }
1137 #ifdef ADAPTIVE_RWLOCKS
1138 }
1139 #endif
1140 /*
1141 * We were unable to acquire the lock and the write waiters
1142 * flag is set, so we must block on the turnstile.
1143 */
1144 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1145 CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
1146 rw);
1147 #ifdef KDTRACE_HOOKS
1148 sleep_time -= lockstat_nsecs(&rw->lock_object);
1149 #endif
1150 MPASS(owner == rw_owner(rw));
1151 turnstile_wait(ts, owner, TS_EXCLUSIVE_QUEUE);
1152 #ifdef KDTRACE_HOOKS
1153 sleep_time += lockstat_nsecs(&rw->lock_object);
1154 sleep_cnt++;
1155 #endif
1156 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1157 CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
1158 __func__, rw);
1159 #ifdef ADAPTIVE_RWLOCKS
1160 spintries = 0;
1161 #endif
1162 v = RW_READ_VALUE(rw);
1163 }
1164 if (__predict_true(!extra_work))
1165 return;
1166 #ifdef ADAPTIVE_RWLOCKS
1167 if (in_critical)
1168 critical_exit();
1169 #endif
1170 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1171 if (__predict_true(!doing_lockprof))
1172 return;
1173 #endif
1174 #ifdef KDTRACE_HOOKS
1175 all_time += lockstat_nsecs(&rw->lock_object);
1176 if (sleep_time)
1177 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
1178 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1179 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1180
1181 /* Record only the loops spinning and not sleeping. */
1182 if (lda.spin_cnt > sleep_cnt)
1183 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
1184 LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1185 (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1186 out_lockstat:
1187 #endif
1188 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
1189 waittime, file, line, LOCKSTAT_WRITER);
1190 }
1191
1192 /*
1193 * This function is called if lockstat is active or the first try at releasing
1194 * a write lock failed. The latter means that the lock is recursed or one of
1195 * the 2 waiter bits must be set indicating that at least one thread is waiting
1196 * on this lock.
1197 */
1198 void
__rw_wunlock_hard(volatile uintptr_t * c,uintptr_t v LOCK_FILE_LINE_ARG_DEF)1199 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
1200 {
1201 struct rwlock *rw;
1202 struct turnstile *ts;
1203 uintptr_t tid, setv;
1204 int queue;
1205
1206 tid = (uintptr_t)curthread;
1207 if (SCHEDULER_STOPPED())
1208 return;
1209
1210 rw = rwlock2rw(c);
1211 if (__predict_false(v == tid))
1212 v = RW_READ_VALUE(rw);
1213
1214 if (v & RW_LOCK_WRITER_RECURSED) {
1215 if (--(rw->rw_recurse) == 0)
1216 atomic_clear_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
1217 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1218 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
1219 return;
1220 }
1221
1222 LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_WRITER);
1223 if (v == tid && _rw_write_unlock(rw, tid))
1224 return;
1225
1226 KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
1227 ("%s: neither of the waiter flags are set", __func__));
1228
1229 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1230 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
1231
1232 turnstile_chain_lock(&rw->lock_object);
1233
1234 /*
1235 * Use the same algo as sx locks for now. Prefer waking up shared
1236 * waiters if we have any over writers. This is probably not ideal.
1237 *
1238 * 'v' is the value we are going to write back to rw_lock. If we
1239 * have waiters on both queues, we need to preserve the state of
1240 * the waiter flag for the queue we don't wake up. For now this is
1241 * hardcoded for the algorithm mentioned above.
1242 *
1243 * In the case of both readers and writers waiting we wakeup the
1244 * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a
1245 * new writer comes in before a reader it will claim the lock up
1246 * above. There is probably a potential priority inversion in
1247 * there that could be worked around either by waking both queues
1248 * of waiters or doing some complicated lock handoff gymnastics.
1249 */
1250 setv = RW_UNLOCKED;
1251 v = RW_READ_VALUE(rw);
1252 queue = TS_SHARED_QUEUE;
1253 if (v & RW_LOCK_WRITE_WAITERS) {
1254 queue = TS_EXCLUSIVE_QUEUE;
1255 setv |= (v & RW_LOCK_READ_WAITERS);
1256 }
1257 atomic_store_rel_ptr(&rw->rw_lock, setv);
1258
1259 /* Wake up all waiters for the specific queue. */
1260 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1261 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
1262 queue == TS_SHARED_QUEUE ? "read" : "write");
1263
1264 ts = turnstile_lookup(&rw->lock_object);
1265 MPASS(ts != NULL);
1266 turnstile_broadcast(ts, queue);
1267 turnstile_unpend(ts);
1268 turnstile_chain_unlock(&rw->lock_object);
1269 }
1270
1271 /*
1272 * Attempt to do a non-blocking upgrade from a read lock to a write
1273 * lock. This will only succeed if this thread holds a single read
1274 * lock. Returns true if the upgrade succeeded and false otherwise.
1275 */
1276 int
__rw_try_upgrade_int(struct rwlock * rw LOCK_FILE_LINE_ARG_DEF)1277 __rw_try_upgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
1278 {
1279 uintptr_t v, setv, tid;
1280 struct turnstile *ts;
1281 int success;
1282
1283 if (SCHEDULER_STOPPED())
1284 return (1);
1285
1286 KASSERT(rw->rw_lock != RW_DESTROYED,
1287 ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
1288 __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
1289
1290 /*
1291 * Attempt to switch from one reader to a writer. If there
1292 * are any write waiters, then we will have to lock the
1293 * turnstile first to prevent races with another writer
1294 * calling turnstile_wait() before we have claimed this
1295 * turnstile. So, do the simple case of no waiters first.
1296 */
1297 tid = (uintptr_t)curthread;
1298 success = 0;
1299 v = RW_READ_VALUE(rw);
1300 for (;;) {
1301 if (RW_READERS(v) > 1)
1302 break;
1303 if (!(v & RW_LOCK_WAITERS)) {
1304 success = atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid);
1305 if (!success)
1306 continue;
1307 break;
1308 }
1309
1310 /*
1311 * Ok, we think we have waiters, so lock the turnstile.
1312 */
1313 ts = turnstile_trywait(&rw->lock_object);
1314 v = RW_READ_VALUE(rw);
1315 retry_ts:
1316 if (RW_READERS(v) > 1) {
1317 turnstile_cancel(ts);
1318 break;
1319 }
1320 /*
1321 * Try to switch from one reader to a writer again. This time
1322 * we honor the current state of the waiters flags.
1323 * If we obtain the lock with the flags set, then claim
1324 * ownership of the turnstile.
1325 */
1326 setv = tid | (v & RW_LOCK_WAITERS);
1327 success = atomic_fcmpset_ptr(&rw->rw_lock, &v, setv);
1328 if (success) {
1329 if (v & RW_LOCK_WAITERS)
1330 turnstile_claim(ts);
1331 else
1332 turnstile_cancel(ts);
1333 break;
1334 }
1335 goto retry_ts;
1336 }
1337 LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
1338 if (success) {
1339 curthread->td_rw_rlocks--;
1340 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
1341 file, line);
1342 LOCKSTAT_RECORD0(rw__upgrade, rw);
1343 }
1344 return (success);
1345 }
1346
1347 int
__rw_try_upgrade(volatile uintptr_t * c,const char * file,int line)1348 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
1349 {
1350 struct rwlock *rw;
1351
1352 rw = rwlock2rw(c);
1353 return (__rw_try_upgrade_int(rw LOCK_FILE_LINE_ARG));
1354 }
1355
1356 /*
1357 * Downgrade a write lock into a single read lock.
1358 */
1359 void
__rw_downgrade_int(struct rwlock * rw LOCK_FILE_LINE_ARG_DEF)1360 __rw_downgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
1361 {
1362 struct turnstile *ts;
1363 uintptr_t tid, v;
1364 int rwait, wwait;
1365
1366 if (SCHEDULER_STOPPED())
1367 return;
1368
1369 KASSERT(rw->rw_lock != RW_DESTROYED,
1370 ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
1371 __rw_assert(&rw->rw_lock, RA_WLOCKED | RA_NOTRECURSED, file, line);
1372 #ifndef INVARIANTS
1373 if (rw_recursed(rw))
1374 panic("downgrade of a recursed lock");
1375 #endif
1376
1377 WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
1378
1379 /*
1380 * Convert from a writer to a single reader. First we handle
1381 * the easy case with no waiters. If there are any waiters, we
1382 * lock the turnstile and "disown" the lock.
1383 */
1384 tid = (uintptr_t)curthread;
1385 if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
1386 goto out;
1387
1388 /*
1389 * Ok, we think we have waiters, so lock the turnstile so we can
1390 * read the waiter flags without any races.
1391 */
1392 turnstile_chain_lock(&rw->lock_object);
1393 v = rw->rw_lock & RW_LOCK_WAITERS;
1394 rwait = v & RW_LOCK_READ_WAITERS;
1395 wwait = v & RW_LOCK_WRITE_WAITERS;
1396 MPASS(rwait | wwait);
1397
1398 /*
1399 * Downgrade from a write lock while preserving waiters flag
1400 * and give up ownership of the turnstile.
1401 */
1402 ts = turnstile_lookup(&rw->lock_object);
1403 MPASS(ts != NULL);
1404 if (!wwait)
1405 v &= ~RW_LOCK_READ_WAITERS;
1406 atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
1407 /*
1408 * Wake other readers if there are no writers pending. Otherwise they
1409 * won't be able to acquire the lock anyway.
1410 */
1411 if (rwait && !wwait) {
1412 turnstile_broadcast(ts, TS_SHARED_QUEUE);
1413 turnstile_unpend(ts);
1414 } else
1415 turnstile_disown(ts);
1416 turnstile_chain_unlock(&rw->lock_object);
1417 out:
1418 curthread->td_rw_rlocks++;
1419 LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
1420 LOCKSTAT_RECORD0(rw__downgrade, rw);
1421 }
1422
1423 void
__rw_downgrade(volatile uintptr_t * c,const char * file,int line)1424 __rw_downgrade(volatile uintptr_t *c, const char *file, int line)
1425 {
1426 struct rwlock *rw;
1427
1428 rw = rwlock2rw(c);
1429 __rw_downgrade_int(rw LOCK_FILE_LINE_ARG);
1430 }
1431
1432 #ifdef INVARIANT_SUPPORT
1433 #ifndef INVARIANTS
1434 #undef __rw_assert
1435 #endif
1436
1437 /*
1438 * In the non-WITNESS case, rw_assert() can only detect that at least
1439 * *some* thread owns an rlock, but it cannot guarantee that *this*
1440 * thread owns an rlock.
1441 */
1442 void
__rw_assert(const volatile uintptr_t * c,int what,const char * file,int line)1443 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
1444 {
1445 const struct rwlock *rw;
1446
1447 if (SCHEDULER_STOPPED())
1448 return;
1449
1450 rw = rwlock2rw(c);
1451
1452 switch (what) {
1453 case RA_LOCKED:
1454 case RA_LOCKED | RA_RECURSED:
1455 case RA_LOCKED | RA_NOTRECURSED:
1456 case RA_RLOCKED:
1457 case RA_RLOCKED | RA_RECURSED:
1458 case RA_RLOCKED | RA_NOTRECURSED:
1459 #ifdef WITNESS
1460 witness_assert(&rw->lock_object, what, file, line);
1461 #else
1462 /*
1463 * If some other thread has a write lock or we have one
1464 * and are asserting a read lock, fail. Also, if no one
1465 * has a lock at all, fail.
1466 */
1467 if (rw->rw_lock == RW_UNLOCKED ||
1468 (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
1469 rw_wowner(rw) != curthread)))
1470 panic("Lock %s not %slocked @ %s:%d\n",
1471 rw->lock_object.lo_name, (what & RA_RLOCKED) ?
1472 "read " : "", file, line);
1473
1474 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
1475 if (rw_recursed(rw)) {
1476 if (what & RA_NOTRECURSED)
1477 panic("Lock %s recursed @ %s:%d\n",
1478 rw->lock_object.lo_name, file,
1479 line);
1480 } else if (what & RA_RECURSED)
1481 panic("Lock %s not recursed @ %s:%d\n",
1482 rw->lock_object.lo_name, file, line);
1483 }
1484 #endif
1485 break;
1486 case RA_WLOCKED:
1487 case RA_WLOCKED | RA_RECURSED:
1488 case RA_WLOCKED | RA_NOTRECURSED:
1489 if (rw_wowner(rw) != curthread)
1490 panic("Lock %s not exclusively locked @ %s:%d\n",
1491 rw->lock_object.lo_name, file, line);
1492 if (rw_recursed(rw)) {
1493 if (what & RA_NOTRECURSED)
1494 panic("Lock %s recursed @ %s:%d\n",
1495 rw->lock_object.lo_name, file, line);
1496 } else if (what & RA_RECURSED)
1497 panic("Lock %s not recursed @ %s:%d\n",
1498 rw->lock_object.lo_name, file, line);
1499 break;
1500 case RA_UNLOCKED:
1501 #ifdef WITNESS
1502 witness_assert(&rw->lock_object, what, file, line);
1503 #else
1504 /*
1505 * If we hold a write lock fail. We can't reliably check
1506 * to see if we hold a read lock or not.
1507 */
1508 if (rw_wowner(rw) == curthread)
1509 panic("Lock %s exclusively locked @ %s:%d\n",
1510 rw->lock_object.lo_name, file, line);
1511 #endif
1512 break;
1513 default:
1514 panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
1515 line);
1516 }
1517 }
1518 #endif /* INVARIANT_SUPPORT */
1519
1520 #ifdef DDB
1521 void
db_show_rwlock(const struct lock_object * lock)1522 db_show_rwlock(const struct lock_object *lock)
1523 {
1524 const struct rwlock *rw;
1525 struct thread *td;
1526
1527 rw = (const struct rwlock *)lock;
1528
1529 db_printf(" state: ");
1530 if (rw->rw_lock == RW_UNLOCKED)
1531 db_printf("UNLOCKED\n");
1532 else if (rw->rw_lock == RW_DESTROYED) {
1533 db_printf("DESTROYED\n");
1534 return;
1535 } else if (rw->rw_lock & RW_LOCK_READ)
1536 db_printf("RLOCK: %ju locks\n",
1537 (uintmax_t)(RW_READERS(rw->rw_lock)));
1538 else {
1539 td = rw_wowner(rw);
1540 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1541 td->td_tid, td->td_proc->p_pid, td->td_name);
1542 if (rw_recursed(rw))
1543 db_printf(" recursed: %u\n", rw->rw_recurse);
1544 }
1545 db_printf(" waiters: ");
1546 switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
1547 case RW_LOCK_READ_WAITERS:
1548 db_printf("readers\n");
1549 break;
1550 case RW_LOCK_WRITE_WAITERS:
1551 db_printf("writers\n");
1552 break;
1553 case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
1554 db_printf("readers and writers\n");
1555 break;
1556 default:
1557 db_printf("none\n");
1558 break;
1559 }
1560 }
1561
1562 #endif
1563