1 /*-
2 * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
3 * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
4 * All rights reserved.
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(s), this list of conditions and the following disclaimer as
11 * the first lines of this file unmodified other than the possible
12 * addition of one or more copyright notices.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice(s), this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
16 *
17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
23 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
24 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
27 * DAMAGE.
28 */
29
30 /*
31 * Shared/exclusive locks. This implementation attempts to ensure
32 * deterministic lock granting behavior, so that slocks and xlocks are
33 * interleaved.
34 *
35 * Priority propagation will not generally raise the priority of lock holders,
36 * so should not be relied upon in combination with sx locks.
37 */
38
39 #include "opt_ddb.h"
40 #include "opt_hwpmc_hooks.h"
41 #include "opt_no_adaptive_sx.h"
42
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD$");
45
46 #include <sys/param.h>
47 #include <sys/systm.h>
48 #include <sys/kdb.h>
49 #include <sys/kernel.h>
50 #include <sys/ktr.h>
51 #include <sys/lock.h>
52 #include <sys/mutex.h>
53 #include <sys/proc.h>
54 #include <sys/sched.h>
55 #include <sys/sleepqueue.h>
56 #include <sys/sx.h>
57 #include <sys/smp.h>
58 #include <sys/sysctl.h>
59
60 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
61 #include <machine/cpu.h>
62 #endif
63
64 #ifdef DDB
65 #include <ddb/ddb.h>
66 #endif
67
68 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
69 #define ADAPTIVE_SX
70 #endif
71
72 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
73
74 #ifdef HWPMC_HOOKS
75 #include <sys/pmckern.h>
76 PMC_SOFT_DECLARE( , , lock, failed);
77 #endif
78
79 /* Handy macros for sleep queues. */
80 #define SQ_EXCLUSIVE_QUEUE 0
81 #define SQ_SHARED_QUEUE 1
82
83 /*
84 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
85 * drop Giant anytime we have to sleep or if we adaptively spin.
86 */
87 #define GIANT_DECLARE \
88 int _giantcnt = 0; \
89 WITNESS_SAVE_DECL(Giant) \
90
91 #define GIANT_SAVE(work) do { \
92 if (__predict_false(mtx_owned(&Giant))) { \
93 work++; \
94 WITNESS_SAVE(&Giant.lock_object, Giant); \
95 while (mtx_owned(&Giant)) { \
96 _giantcnt++; \
97 mtx_unlock(&Giant); \
98 } \
99 } \
100 } while (0)
101
102 #define GIANT_RESTORE() do { \
103 if (_giantcnt > 0) { \
104 mtx_assert(&Giant, MA_NOTOWNED); \
105 while (_giantcnt--) \
106 mtx_lock(&Giant); \
107 WITNESS_RESTORE(&Giant.lock_object, Giant); \
108 } \
109 } while (0)
110
111 /*
112 * Returns true if an exclusive lock is recursed. It assumes
113 * curthread currently has an exclusive lock.
114 */
115 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
116
117 static void assert_sx(const struct lock_object *lock, int what);
118 #ifdef DDB
119 static void db_show_sx(const struct lock_object *lock);
120 #endif
121 static void lock_sx(struct lock_object *lock, uintptr_t how);
122 #ifdef KDTRACE_HOOKS
123 static int owner_sx(const struct lock_object *lock, struct thread **owner);
124 #endif
125 static uintptr_t unlock_sx(struct lock_object *lock);
126
127 struct lock_class lock_class_sx = {
128 .lc_name = "sx",
129 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
130 .lc_assert = assert_sx,
131 #ifdef DDB
132 .lc_ddb_show = db_show_sx,
133 #endif
134 .lc_lock = lock_sx,
135 .lc_unlock = unlock_sx,
136 #ifdef KDTRACE_HOOKS
137 .lc_owner = owner_sx,
138 #endif
139 };
140
141 #ifndef INVARIANTS
142 #define _sx_assert(sx, what, file, line)
143 #endif
144
145 #ifdef ADAPTIVE_SX
146 static __read_frequently u_int asx_retries;
147 static __read_frequently u_int asx_loops;
148 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
149 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
150 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
151
152 static struct lock_delay_config __read_frequently sx_delay;
153
154 SYSCTL_INT(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base,
155 0, "");
156 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
157 0, "");
158
159 static void
sx_lock_delay_init(void * arg __unused)160 sx_lock_delay_init(void *arg __unused)
161 {
162
163 lock_delay_default_init(&sx_delay);
164 asx_retries = 10;
165 asx_loops = max(10000, sx_delay.max);
166 }
167 LOCK_DELAY_SYSINIT(sx_lock_delay_init);
168 #endif
169
170 void
assert_sx(const struct lock_object * lock,int what)171 assert_sx(const struct lock_object *lock, int what)
172 {
173
174 sx_assert((const struct sx *)lock, what);
175 }
176
177 void
lock_sx(struct lock_object * lock,uintptr_t how)178 lock_sx(struct lock_object *lock, uintptr_t how)
179 {
180 struct sx *sx;
181
182 sx = (struct sx *)lock;
183 if (how)
184 sx_slock(sx);
185 else
186 sx_xlock(sx);
187 }
188
189 uintptr_t
unlock_sx(struct lock_object * lock)190 unlock_sx(struct lock_object *lock)
191 {
192 struct sx *sx;
193
194 sx = (struct sx *)lock;
195 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
196 if (sx_xlocked(sx)) {
197 sx_xunlock(sx);
198 return (0);
199 } else {
200 sx_sunlock(sx);
201 return (1);
202 }
203 }
204
205 #ifdef KDTRACE_HOOKS
206 int
owner_sx(const struct lock_object * lock,struct thread ** owner)207 owner_sx(const struct lock_object *lock, struct thread **owner)
208 {
209 const struct sx *sx;
210 uintptr_t x;
211
212 sx = (const struct sx *)lock;
213 x = sx->sx_lock;
214 *owner = NULL;
215 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
216 ((*owner = (struct thread *)SX_OWNER(x)) != NULL));
217 }
218 #endif
219
220 void
sx_sysinit(void * arg)221 sx_sysinit(void *arg)
222 {
223 struct sx_args *sargs = arg;
224
225 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
226 }
227
228 void
sx_init_flags(struct sx * sx,const char * description,int opts)229 sx_init_flags(struct sx *sx, const char *description, int opts)
230 {
231 int flags;
232
233 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
234 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0);
235 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
236 ("%s: sx_lock not aligned for %s: %p", __func__, description,
237 &sx->sx_lock));
238
239 flags = LO_SLEEPABLE | LO_UPGRADABLE;
240 if (opts & SX_DUPOK)
241 flags |= LO_DUPOK;
242 if (opts & SX_NOPROFILE)
243 flags |= LO_NOPROFILE;
244 if (!(opts & SX_NOWITNESS))
245 flags |= LO_WITNESS;
246 if (opts & SX_RECURSE)
247 flags |= LO_RECURSABLE;
248 if (opts & SX_QUIET)
249 flags |= LO_QUIET;
250 if (opts & SX_NEW)
251 flags |= LO_NEW;
252
253 flags |= opts & SX_NOADAPTIVE;
254 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
255 sx->sx_lock = SX_LOCK_UNLOCKED;
256 sx->sx_recurse = 0;
257 }
258
259 void
sx_destroy(struct sx * sx)260 sx_destroy(struct sx *sx)
261 {
262
263 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
264 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
265 sx->sx_lock = SX_LOCK_DESTROYED;
266 lock_destroy(&sx->lock_object);
267 }
268
269 int
sx_try_slock_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)270 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
271 {
272 uintptr_t x;
273
274 if (SCHEDULER_STOPPED())
275 return (1);
276
277 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
278 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
279 curthread, sx->lock_object.lo_name, file, line));
280
281 x = sx->sx_lock;
282 for (;;) {
283 KASSERT(x != SX_LOCK_DESTROYED,
284 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
285 if (!(x & SX_LOCK_SHARED))
286 break;
287 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) {
288 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
289 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
290 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
291 sx, 0, 0, file, line, LOCKSTAT_READER);
292 TD_LOCKS_INC(curthread);
293 return (1);
294 }
295 }
296
297 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
298 return (0);
299 }
300
301 int
sx_try_slock_(struct sx * sx,const char * file,int line)302 sx_try_slock_(struct sx *sx, const char *file, int line)
303 {
304
305 return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG));
306 }
307
308 int
_sx_xlock(struct sx * sx,int opts,const char * file,int line)309 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
310 {
311 uintptr_t tid, x;
312 int error = 0;
313
314 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
315 !TD_IS_IDLETHREAD(curthread),
316 ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
317 curthread, sx->lock_object.lo_name, file, line));
318 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
319 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
320 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
321 line, NULL);
322 tid = (uintptr_t)curthread;
323 x = SX_LOCK_UNLOCKED;
324 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
325 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG);
326 else
327 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
328 0, 0, file, line, LOCKSTAT_WRITER);
329 if (!error) {
330 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
331 file, line);
332 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
333 TD_LOCKS_INC(curthread);
334 }
335
336 return (error);
337 }
338
339 int
sx_try_xlock_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)340 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
341 {
342 struct thread *td;
343 uintptr_t tid, x;
344 int rval;
345 bool recursed;
346
347 td = curthread;
348 tid = (uintptr_t)td;
349 if (SCHEDULER_STOPPED_TD(td))
350 return (1);
351
352 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
353 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
354 curthread, sx->lock_object.lo_name, file, line));
355 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
356 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
357
358 rval = 1;
359 recursed = false;
360 x = SX_LOCK_UNLOCKED;
361 for (;;) {
362 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
363 break;
364 if (x == SX_LOCK_UNLOCKED)
365 continue;
366 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
367 sx->sx_recurse++;
368 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
369 break;
370 }
371 rval = 0;
372 break;
373 }
374
375 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
376 if (rval) {
377 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
378 file, line);
379 if (!recursed)
380 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
381 sx, 0, 0, file, line, LOCKSTAT_WRITER);
382 TD_LOCKS_INC(curthread);
383 }
384
385 return (rval);
386 }
387
388 int
sx_try_xlock_(struct sx * sx,const char * file,int line)389 sx_try_xlock_(struct sx *sx, const char *file, int line)
390 {
391
392 return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG));
393 }
394
395 void
_sx_xunlock(struct sx * sx,const char * file,int line)396 _sx_xunlock(struct sx *sx, const char *file, int line)
397 {
398
399 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
400 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
401 _sx_assert(sx, SA_XLOCKED, file, line);
402 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
403 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
404 line);
405 #if LOCK_DEBUG > 0
406 _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line);
407 #else
408 __sx_xunlock(sx, curthread, file, line);
409 #endif
410 TD_LOCKS_DEC(curthread);
411 }
412
413 /*
414 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
415 * This will only succeed if this thread holds a single shared lock.
416 * Return 1 if if the upgrade succeed, 0 otherwise.
417 */
418 int
sx_try_upgrade_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)419 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
420 {
421 uintptr_t x;
422 uintptr_t waiters;
423 int success;
424
425 if (SCHEDULER_STOPPED())
426 return (1);
427
428 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
429 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
430 _sx_assert(sx, SA_SLOCKED, file, line);
431
432 /*
433 * Try to switch from one shared lock to an exclusive lock. We need
434 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
435 * we will wake up the exclusive waiters when we drop the lock.
436 */
437 success = 0;
438 x = SX_READ_VALUE(sx);
439 for (;;) {
440 if (SX_SHARERS(x) > 1)
441 break;
442 waiters = (x & SX_LOCK_EXCLUSIVE_WAITERS);
443 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
444 (uintptr_t)curthread | waiters)) {
445 success = 1;
446 break;
447 }
448 }
449 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
450 if (success) {
451 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
452 file, line);
453 LOCKSTAT_RECORD0(sx__upgrade, sx);
454 }
455 return (success);
456 }
457
458 int
sx_try_upgrade_(struct sx * sx,const char * file,int line)459 sx_try_upgrade_(struct sx *sx, const char *file, int line)
460 {
461
462 return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG));
463 }
464
465 /*
466 * Downgrade an unrecursed exclusive lock into a single shared lock.
467 */
468 void
sx_downgrade_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)469 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
470 {
471 uintptr_t x;
472 int wakeup_swapper;
473
474 if (SCHEDULER_STOPPED())
475 return;
476
477 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
478 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
479 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
480 #ifndef INVARIANTS
481 if (sx_recursed(sx))
482 panic("downgrade of a recursed lock");
483 #endif
484
485 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
486
487 /*
488 * Try to switch from an exclusive lock with no shared waiters
489 * to one sharer with no shared waiters. If there are
490 * exclusive waiters, we don't need to lock the sleep queue so
491 * long as we preserve the flag. We do one quick try and if
492 * that fails we grab the sleepq lock to keep the flags from
493 * changing and do it the slow way.
494 *
495 * We have to lock the sleep queue if there are shared waiters
496 * so we can wake them up.
497 */
498 x = sx->sx_lock;
499 if (!(x & SX_LOCK_SHARED_WAITERS) &&
500 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
501 (x & SX_LOCK_EXCLUSIVE_WAITERS)))
502 goto out;
503
504 /*
505 * Lock the sleep queue so we can read the waiters bits
506 * without any races and wakeup any shared waiters.
507 */
508 sleepq_lock(&sx->lock_object);
509
510 /*
511 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
512 * shared lock. If there are any shared waiters, wake them up.
513 */
514 wakeup_swapper = 0;
515 x = sx->sx_lock;
516 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
517 (x & SX_LOCK_EXCLUSIVE_WAITERS));
518 if (x & SX_LOCK_SHARED_WAITERS)
519 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
520 0, SQ_SHARED_QUEUE);
521 sleepq_release(&sx->lock_object);
522
523 if (wakeup_swapper)
524 kick_proc0();
525
526 out:
527 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
528 LOCKSTAT_RECORD0(sx__downgrade, sx);
529 }
530
531 void
sx_downgrade_(struct sx * sx,const char * file,int line)532 sx_downgrade_(struct sx *sx, const char *file, int line)
533 {
534
535 sx_downgrade_int(sx LOCK_FILE_LINE_ARG);
536 }
537
538 /*
539 * This function represents the so-called 'hard case' for sx_xlock
540 * operation. All 'easy case' failures are redirected to this. Note
541 * that ideally this would be a static function, but it needs to be
542 * accessible from at least sx.h.
543 */
544 int
_sx_xlock_hard(struct sx * sx,uintptr_t x,int opts LOCK_FILE_LINE_ARG_DEF)545 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
546 {
547 GIANT_DECLARE;
548 uintptr_t tid;
549 #ifdef ADAPTIVE_SX
550 volatile struct thread *owner;
551 u_int i, n, spintries = 0;
552 enum { READERS, WRITER } sleep_reason = READERS;
553 bool adaptive;
554 #endif
555 #ifdef LOCK_PROFILING
556 uint64_t waittime = 0;
557 int contested = 0;
558 #endif
559 int error = 0;
560 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
561 struct lock_delay_arg lda;
562 #endif
563 #ifdef KDTRACE_HOOKS
564 u_int sleep_cnt = 0;
565 int64_t sleep_time = 0;
566 int64_t all_time = 0;
567 #endif
568 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
569 uintptr_t state = 0;
570 #endif
571 int extra_work = 0;
572
573 tid = (uintptr_t)curthread;
574
575 #ifdef KDTRACE_HOOKS
576 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
577 while (x == SX_LOCK_UNLOCKED) {
578 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
579 goto out_lockstat;
580 }
581 extra_work = 1;
582 all_time -= lockstat_nsecs(&sx->lock_object);
583 state = x;
584 }
585 #endif
586 #ifdef LOCK_PROFILING
587 extra_work = 1;
588 state = x;
589 #endif
590
591 if (SCHEDULER_STOPPED())
592 return (0);
593
594 #if defined(ADAPTIVE_SX)
595 lock_delay_arg_init(&lda, &sx_delay);
596 #elif defined(KDTRACE_HOOKS)
597 lock_delay_arg_init(&lda, NULL);
598 #endif
599
600 if (__predict_false(x == SX_LOCK_UNLOCKED))
601 x = SX_READ_VALUE(sx);
602
603 /* If we already hold an exclusive lock, then recurse. */
604 if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) {
605 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
606 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
607 sx->lock_object.lo_name, file, line));
608 sx->sx_recurse++;
609 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
610 if (LOCK_LOG_TEST(&sx->lock_object, 0))
611 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
612 return (0);
613 }
614
615 if (LOCK_LOG_TEST(&sx->lock_object, 0))
616 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
617 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
618
619 #ifdef ADAPTIVE_SX
620 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0);
621 #endif
622
623 #ifdef HWPMC_HOOKS
624 PMC_SOFT_CALL( , , lock, failed);
625 #endif
626 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
627 &waittime);
628
629 #ifndef INVARIANTS
630 GIANT_SAVE(extra_work);
631 #endif
632
633 for (;;) {
634 if (x == SX_LOCK_UNLOCKED) {
635 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
636 break;
637 continue;
638 }
639 #ifdef INVARIANTS
640 GIANT_SAVE(extra_work);
641 #endif
642 #ifdef KDTRACE_HOOKS
643 lda.spin_cnt++;
644 #endif
645 #ifdef ADAPTIVE_SX
646 if (__predict_false(!adaptive))
647 goto sleepq;
648 /*
649 * If the lock is write locked and the owner is
650 * running on another CPU, spin until the owner stops
651 * running or the state of the lock changes.
652 */
653 if ((x & SX_LOCK_SHARED) == 0) {
654 sleep_reason = WRITER;
655 owner = lv_sx_owner(x);
656 if (!TD_IS_RUNNING(owner))
657 goto sleepq;
658 if (LOCK_LOG_TEST(&sx->lock_object, 0))
659 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
660 __func__, sx, owner);
661 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
662 "spinning", "lockname:\"%s\"",
663 sx->lock_object.lo_name);
664 do {
665 lock_delay(&lda);
666 x = SX_READ_VALUE(sx);
667 owner = lv_sx_owner(x);
668 } while (owner != NULL && TD_IS_RUNNING(owner));
669 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
670 "running");
671 continue;
672 } else if (SX_SHARERS(x) > 0) {
673 sleep_reason = READERS;
674 if (spintries == asx_retries)
675 goto sleepq;
676 spintries++;
677 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
678 "spinning", "lockname:\"%s\"",
679 sx->lock_object.lo_name);
680 for (i = 0; i < asx_loops; i += n) {
681 n = SX_SHARERS(x);
682 lock_delay_spin(n);
683 x = SX_READ_VALUE(sx);
684 if ((x & SX_LOCK_SHARED) == 0 ||
685 SX_SHARERS(x) == 0)
686 break;
687 }
688 #ifdef KDTRACE_HOOKS
689 lda.spin_cnt += i;
690 #endif
691 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
692 "running");
693 if (i < asx_loops)
694 continue;
695 }
696 sleepq:
697 #endif
698 sleepq_lock(&sx->lock_object);
699 x = SX_READ_VALUE(sx);
700 retry_sleepq:
701
702 /*
703 * If the lock was released while spinning on the
704 * sleep queue chain lock, try again.
705 */
706 if (x == SX_LOCK_UNLOCKED) {
707 sleepq_release(&sx->lock_object);
708 continue;
709 }
710
711 #ifdef ADAPTIVE_SX
712 /*
713 * The current lock owner might have started executing
714 * on another CPU (or the lock could have changed
715 * owners) while we were waiting on the sleep queue
716 * chain lock. If so, drop the sleep queue lock and try
717 * again.
718 */
719 if (adaptive) {
720 if (!(x & SX_LOCK_SHARED)) {
721 owner = (struct thread *)SX_OWNER(x);
722 if (TD_IS_RUNNING(owner)) {
723 sleepq_release(&sx->lock_object);
724 continue;
725 }
726 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) {
727 sleepq_release(&sx->lock_object);
728 continue;
729 }
730 }
731 #endif
732
733 /*
734 * If an exclusive lock was released with both shared
735 * and exclusive waiters and a shared waiter hasn't
736 * woken up and acquired the lock yet, sx_lock will be
737 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
738 * If we see that value, try to acquire it once. Note
739 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
740 * as there are other exclusive waiters still. If we
741 * fail, restart the loop.
742 */
743 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
744 if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
745 tid | SX_LOCK_EXCLUSIVE_WAITERS))
746 goto retry_sleepq;
747 sleepq_release(&sx->lock_object);
748 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
749 __func__, sx);
750 break;
751 }
752
753 /*
754 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
755 * than loop back and retry.
756 */
757 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
758 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
759 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
760 goto retry_sleepq;
761 }
762 if (LOCK_LOG_TEST(&sx->lock_object, 0))
763 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
764 __func__, sx);
765 }
766
767 /*
768 * Since we have been unable to acquire the exclusive
769 * lock and the exclusive waiters flag is set, we have
770 * to sleep.
771 */
772 if (LOCK_LOG_TEST(&sx->lock_object, 0))
773 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
774 __func__, sx);
775
776 #ifdef KDTRACE_HOOKS
777 sleep_time -= lockstat_nsecs(&sx->lock_object);
778 #endif
779 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
780 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
781 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
782 if (!(opts & SX_INTERRUPTIBLE))
783 sleepq_wait(&sx->lock_object, 0);
784 else
785 error = sleepq_wait_sig(&sx->lock_object, 0);
786 #ifdef KDTRACE_HOOKS
787 sleep_time += lockstat_nsecs(&sx->lock_object);
788 sleep_cnt++;
789 #endif
790 if (error) {
791 if (LOCK_LOG_TEST(&sx->lock_object, 0))
792 CTR2(KTR_LOCK,
793 "%s: interruptible sleep by %p suspended by signal",
794 __func__, sx);
795 break;
796 }
797 if (LOCK_LOG_TEST(&sx->lock_object, 0))
798 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
799 __func__, sx);
800 x = SX_READ_VALUE(sx);
801 }
802 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
803 if (__predict_true(!extra_work))
804 return (error);
805 #endif
806 #ifdef KDTRACE_HOOKS
807 all_time += lockstat_nsecs(&sx->lock_object);
808 if (sleep_time)
809 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
810 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
811 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
812 if (lda.spin_cnt > sleep_cnt)
813 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
814 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
815 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
816 out_lockstat:
817 #endif
818 if (!error)
819 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
820 contested, waittime, file, line, LOCKSTAT_WRITER);
821 GIANT_RESTORE();
822 return (error);
823 }
824
825 /*
826 * This function represents the so-called 'hard case' for sx_xunlock
827 * operation. All 'easy case' failures are redirected to this. Note
828 * that ideally this would be a static function, but it needs to be
829 * accessible from at least sx.h.
830 */
831 void
_sx_xunlock_hard(struct sx * sx,uintptr_t x LOCK_FILE_LINE_ARG_DEF)832 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
833 {
834 uintptr_t tid, setx;
835 int queue, wakeup_swapper;
836
837 if (SCHEDULER_STOPPED())
838 return;
839
840 tid = (uintptr_t)curthread;
841
842 if (__predict_false(x == tid))
843 x = SX_READ_VALUE(sx);
844
845 MPASS(!(x & SX_LOCK_SHARED));
846
847 if (__predict_false(x & SX_LOCK_RECURSED)) {
848 /* The lock is recursed, unrecurse one level. */
849 if ((--sx->sx_recurse) == 0)
850 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
851 if (LOCK_LOG_TEST(&sx->lock_object, 0))
852 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
853 return;
854 }
855
856 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
857 if (x == tid &&
858 atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
859 return;
860
861 if (LOCK_LOG_TEST(&sx->lock_object, 0))
862 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
863
864 sleepq_lock(&sx->lock_object);
865 x = SX_READ_VALUE(sx);
866 MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS));
867
868 /*
869 * The wake up algorithm here is quite simple and probably not
870 * ideal. It gives precedence to shared waiters if they are
871 * present. For this condition, we have to preserve the
872 * state of the exclusive waiters flag.
873 * If interruptible sleeps left the shared queue empty avoid a
874 * starvation for the threads sleeping on the exclusive queue by giving
875 * them precedence and cleaning up the shared waiters bit anyway.
876 */
877 setx = SX_LOCK_UNLOCKED;
878 queue = SQ_EXCLUSIVE_QUEUE;
879 if ((x & SX_LOCK_SHARED_WAITERS) != 0 &&
880 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
881 queue = SQ_SHARED_QUEUE;
882 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS);
883 }
884 atomic_store_rel_ptr(&sx->sx_lock, setx);
885
886 /* Wake up all the waiters for the specific queue. */
887 if (LOCK_LOG_TEST(&sx->lock_object, 0))
888 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
889 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
890 "exclusive");
891
892 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
893 queue);
894 sleepq_release(&sx->lock_object);
895 if (wakeup_swapper)
896 kick_proc0();
897 }
898
899 static bool __always_inline
__sx_slock_try(struct sx * sx,uintptr_t * xp LOCK_FILE_LINE_ARG_DEF)900 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF)
901 {
902
903 /*
904 * If no other thread has an exclusive lock then try to bump up
905 * the count of sharers. Since we have to preserve the state
906 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
907 * shared lock loop back and retry.
908 */
909 while (*xp & SX_LOCK_SHARED) {
910 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS));
911 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp,
912 *xp + SX_ONE_SHARER)) {
913 if (LOCK_LOG_TEST(&sx->lock_object, 0))
914 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p",
915 __func__, sx, (void *)*xp,
916 (void *)(*xp + SX_ONE_SHARER));
917 return (true);
918 }
919 }
920 return (false);
921 }
922
923 static int __noinline
_sx_slock_hard(struct sx * sx,int opts,uintptr_t x LOCK_FILE_LINE_ARG_DEF)924 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
925 {
926 GIANT_DECLARE;
927 #ifdef ADAPTIVE_SX
928 volatile struct thread *owner;
929 bool adaptive;
930 #endif
931 #ifdef LOCK_PROFILING
932 uint64_t waittime = 0;
933 int contested = 0;
934 #endif
935 int error = 0;
936 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
937 struct lock_delay_arg lda;
938 #endif
939 #ifdef KDTRACE_HOOKS
940 u_int sleep_cnt = 0;
941 int64_t sleep_time = 0;
942 int64_t all_time = 0;
943 #endif
944 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
945 uintptr_t state = 0;
946 #endif
947 int extra_work = 0;
948
949 #ifdef KDTRACE_HOOKS
950 if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
951 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))
952 goto out_lockstat;
953 extra_work = 1;
954 all_time -= lockstat_nsecs(&sx->lock_object);
955 state = x;
956 }
957 #endif
958 #ifdef LOCK_PROFILING
959 extra_work = 1;
960 state = x;
961 #endif
962
963 if (SCHEDULER_STOPPED())
964 return (0);
965
966 #if defined(ADAPTIVE_SX)
967 lock_delay_arg_init(&lda, &sx_delay);
968 #elif defined(KDTRACE_HOOKS)
969 lock_delay_arg_init(&lda, NULL);
970 #endif
971
972 #ifdef ADAPTIVE_SX
973 adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0);
974 #endif
975
976 #ifdef HWPMC_HOOKS
977 PMC_SOFT_CALL( , , lock, failed);
978 #endif
979 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
980 &waittime);
981
982 #ifndef INVARIANTS
983 GIANT_SAVE(extra_work);
984 #endif
985
986 /*
987 * As with rwlocks, we don't make any attempt to try to block
988 * shared locks once there is an exclusive waiter.
989 */
990 for (;;) {
991 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))
992 break;
993 #ifdef INVARIANTS
994 GIANT_SAVE(extra_work);
995 #endif
996 #ifdef KDTRACE_HOOKS
997 lda.spin_cnt++;
998 #endif
999
1000 #ifdef ADAPTIVE_SX
1001 if (__predict_false(!adaptive))
1002 goto sleepq;
1003 /*
1004 * If the owner is running on another CPU, spin until
1005 * the owner stops running or the state of the lock
1006 * changes.
1007 */
1008 owner = lv_sx_owner(x);
1009 if (TD_IS_RUNNING(owner)) {
1010 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1011 CTR3(KTR_LOCK,
1012 "%s: spinning on %p held by %p",
1013 __func__, sx, owner);
1014 KTR_STATE1(KTR_SCHED, "thread",
1015 sched_tdname(curthread), "spinning",
1016 "lockname:\"%s\"", sx->lock_object.lo_name);
1017 do {
1018 lock_delay(&lda);
1019 x = SX_READ_VALUE(sx);
1020 owner = lv_sx_owner(x);
1021 } while (owner != NULL && TD_IS_RUNNING(owner));
1022 KTR_STATE0(KTR_SCHED, "thread",
1023 sched_tdname(curthread), "running");
1024 continue;
1025 }
1026 sleepq:
1027 #endif
1028
1029 /*
1030 * Some other thread already has an exclusive lock, so
1031 * start the process of blocking.
1032 */
1033 sleepq_lock(&sx->lock_object);
1034 x = SX_READ_VALUE(sx);
1035 retry_sleepq:
1036 /*
1037 * The lock could have been released while we spun.
1038 * In this case loop back and retry.
1039 */
1040 if (x & SX_LOCK_SHARED) {
1041 sleepq_release(&sx->lock_object);
1042 continue;
1043 }
1044
1045 #ifdef ADAPTIVE_SX
1046 /*
1047 * If the owner is running on another CPU, spin until
1048 * the owner stops running or the state of the lock
1049 * changes.
1050 */
1051 if (!(x & SX_LOCK_SHARED) && adaptive) {
1052 owner = (struct thread *)SX_OWNER(x);
1053 if (TD_IS_RUNNING(owner)) {
1054 sleepq_release(&sx->lock_object);
1055 x = SX_READ_VALUE(sx);
1056 continue;
1057 }
1058 }
1059 #endif
1060
1061 /*
1062 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
1063 * fail to set it drop the sleep queue lock and loop
1064 * back.
1065 */
1066 if (!(x & SX_LOCK_SHARED_WAITERS)) {
1067 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
1068 x | SX_LOCK_SHARED_WAITERS))
1069 goto retry_sleepq;
1070 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1071 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
1072 __func__, sx);
1073 }
1074
1075 /*
1076 * Since we have been unable to acquire the shared lock,
1077 * we have to sleep.
1078 */
1079 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1080 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
1081 __func__, sx);
1082
1083 #ifdef KDTRACE_HOOKS
1084 sleep_time -= lockstat_nsecs(&sx->lock_object);
1085 #endif
1086 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1087 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1088 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1089 if (!(opts & SX_INTERRUPTIBLE))
1090 sleepq_wait(&sx->lock_object, 0);
1091 else
1092 error = sleepq_wait_sig(&sx->lock_object, 0);
1093 #ifdef KDTRACE_HOOKS
1094 sleep_time += lockstat_nsecs(&sx->lock_object);
1095 sleep_cnt++;
1096 #endif
1097 if (error) {
1098 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1099 CTR2(KTR_LOCK,
1100 "%s: interruptible sleep by %p suspended by signal",
1101 __func__, sx);
1102 break;
1103 }
1104 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1105 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1106 __func__, sx);
1107 x = SX_READ_VALUE(sx);
1108 }
1109 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1110 if (__predict_true(!extra_work))
1111 return (error);
1112 #endif
1113 #ifdef KDTRACE_HOOKS
1114 all_time += lockstat_nsecs(&sx->lock_object);
1115 if (sleep_time)
1116 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
1117 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1118 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1119 if (lda.spin_cnt > sleep_cnt)
1120 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
1121 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1122 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1123 out_lockstat:
1124 #endif
1125 if (error == 0) {
1126 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
1127 contested, waittime, file, line, LOCKSTAT_READER);
1128 }
1129 GIANT_RESTORE();
1130 return (error);
1131 }
1132
1133 int
_sx_slock_int(struct sx * sx,int opts LOCK_FILE_LINE_ARG_DEF)1134 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF)
1135 {
1136 uintptr_t x;
1137 int error;
1138
1139 KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
1140 !TD_IS_IDLETHREAD(curthread),
1141 ("sx_slock() by idle thread %p on sx %s @ %s:%d",
1142 curthread, sx->lock_object.lo_name, file, line));
1143 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1144 ("sx_slock() of destroyed sx @ %s:%d", file, line));
1145 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
1146
1147 error = 0;
1148 x = SX_READ_VALUE(sx);
1149 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) ||
1150 !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)))
1151 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG);
1152 else
1153 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0,
1154 file, line);
1155 if (error == 0) {
1156 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
1157 WITNESS_LOCK(&sx->lock_object, 0, file, line);
1158 TD_LOCKS_INC(curthread);
1159 }
1160 return (error);
1161 }
1162
1163 int
_sx_slock(struct sx * sx,int opts,const char * file,int line)1164 _sx_slock(struct sx *sx, int opts, const char *file, int line)
1165 {
1166
1167 return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG));
1168 }
1169
1170 static bool __always_inline
_sx_sunlock_try(struct sx * sx,uintptr_t * xp)1171 _sx_sunlock_try(struct sx *sx, uintptr_t *xp)
1172 {
1173
1174 for (;;) {
1175 /*
1176 * We should never have sharers while at least one thread
1177 * holds a shared lock.
1178 */
1179 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS),
1180 ("%s: waiting sharers", __func__));
1181
1182 /*
1183 * See if there is more than one shared lock held. If
1184 * so, just drop one and return.
1185 */
1186 if (SX_SHARERS(*xp) > 1) {
1187 if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp,
1188 *xp - SX_ONE_SHARER)) {
1189 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1190 CTR4(KTR_LOCK,
1191 "%s: %p succeeded %p -> %p",
1192 __func__, sx, (void *)*xp,
1193 (void *)(*xp - SX_ONE_SHARER));
1194 return (true);
1195 }
1196 continue;
1197 }
1198
1199 /*
1200 * If there aren't any waiters for an exclusive lock,
1201 * then try to drop it quickly.
1202 */
1203 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) {
1204 MPASS(*xp == SX_SHARERS_LOCK(1));
1205 *xp = SX_SHARERS_LOCK(1);
1206 if (atomic_fcmpset_rel_ptr(&sx->sx_lock,
1207 xp, SX_LOCK_UNLOCKED)) {
1208 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1209 CTR2(KTR_LOCK, "%s: %p last succeeded",
1210 __func__, sx);
1211 return (true);
1212 }
1213 continue;
1214 }
1215 break;
1216 }
1217 return (false);
1218 }
1219
1220 static void __noinline
_sx_sunlock_hard(struct sx * sx,uintptr_t x LOCK_FILE_LINE_ARG_DEF)1221 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
1222 {
1223 int wakeup_swapper = 0;
1224 uintptr_t setx;
1225
1226 if (SCHEDULER_STOPPED())
1227 return;
1228
1229 if (_sx_sunlock_try(sx, &x))
1230 goto out_lockstat;
1231
1232 /*
1233 * At this point, there should just be one sharer with
1234 * exclusive waiters.
1235 */
1236 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1237
1238 sleepq_lock(&sx->lock_object);
1239 x = SX_READ_VALUE(sx);
1240 for (;;) {
1241 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS);
1242 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
1243 if (_sx_sunlock_try(sx, &x))
1244 break;
1245
1246 /*
1247 * Wake up semantic here is quite simple:
1248 * Just wake up all the exclusive waiters.
1249 * Note that the state of the lock could have changed,
1250 * so if it fails loop back and retry.
1251 */
1252 setx = x - SX_ONE_SHARER;
1253 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS;
1254 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx))
1255 continue;
1256 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1257 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1258 "exclusive queue", __func__, sx);
1259 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1260 0, SQ_EXCLUSIVE_QUEUE);
1261 break;
1262 }
1263 sleepq_release(&sx->lock_object);
1264 if (wakeup_swapper)
1265 kick_proc0();
1266 out_lockstat:
1267 LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
1268 }
1269
1270 void
_sx_sunlock_int(struct sx * sx LOCK_FILE_LINE_ARG_DEF)1271 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
1272 {
1273 uintptr_t x;
1274
1275 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1276 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
1277 _sx_assert(sx, SA_SLOCKED, file, line);
1278 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
1279 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
1280
1281 x = SX_READ_VALUE(sx);
1282 if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) ||
1283 !_sx_sunlock_try(sx, &x)))
1284 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG);
1285 else
1286 lock_profile_release_lock(&sx->lock_object);
1287
1288 TD_LOCKS_DEC(curthread);
1289 }
1290
1291 void
_sx_sunlock(struct sx * sx,const char * file,int line)1292 _sx_sunlock(struct sx *sx, const char *file, int line)
1293 {
1294
1295 _sx_sunlock_int(sx LOCK_FILE_LINE_ARG);
1296 }
1297
1298 #ifdef INVARIANT_SUPPORT
1299 #ifndef INVARIANTS
1300 #undef _sx_assert
1301 #endif
1302
1303 /*
1304 * In the non-WITNESS case, sx_assert() can only detect that at least
1305 * *some* thread owns an slock, but it cannot guarantee that *this*
1306 * thread owns an slock.
1307 */
1308 void
_sx_assert(const struct sx * sx,int what,const char * file,int line)1309 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1310 {
1311 #ifndef WITNESS
1312 int slocked = 0;
1313 #endif
1314
1315 if (SCHEDULER_STOPPED())
1316 return;
1317 switch (what) {
1318 case SA_SLOCKED:
1319 case SA_SLOCKED | SA_NOTRECURSED:
1320 case SA_SLOCKED | SA_RECURSED:
1321 #ifndef WITNESS
1322 slocked = 1;
1323 /* FALLTHROUGH */
1324 #endif
1325 case SA_LOCKED:
1326 case SA_LOCKED | SA_NOTRECURSED:
1327 case SA_LOCKED | SA_RECURSED:
1328 #ifdef WITNESS
1329 witness_assert(&sx->lock_object, what, file, line);
1330 #else
1331 /*
1332 * If some other thread has an exclusive lock or we
1333 * have one and are asserting a shared lock, fail.
1334 * Also, if no one has a lock at all, fail.
1335 */
1336 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1337 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1338 sx_xholder(sx) != curthread)))
1339 panic("Lock %s not %slocked @ %s:%d\n",
1340 sx->lock_object.lo_name, slocked ? "share " : "",
1341 file, line);
1342
1343 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1344 if (sx_recursed(sx)) {
1345 if (what & SA_NOTRECURSED)
1346 panic("Lock %s recursed @ %s:%d\n",
1347 sx->lock_object.lo_name, file,
1348 line);
1349 } else if (what & SA_RECURSED)
1350 panic("Lock %s not recursed @ %s:%d\n",
1351 sx->lock_object.lo_name, file, line);
1352 }
1353 #endif
1354 break;
1355 case SA_XLOCKED:
1356 case SA_XLOCKED | SA_NOTRECURSED:
1357 case SA_XLOCKED | SA_RECURSED:
1358 if (sx_xholder(sx) != curthread)
1359 panic("Lock %s not exclusively locked @ %s:%d\n",
1360 sx->lock_object.lo_name, file, line);
1361 if (sx_recursed(sx)) {
1362 if (what & SA_NOTRECURSED)
1363 panic("Lock %s recursed @ %s:%d\n",
1364 sx->lock_object.lo_name, file, line);
1365 } else if (what & SA_RECURSED)
1366 panic("Lock %s not recursed @ %s:%d\n",
1367 sx->lock_object.lo_name, file, line);
1368 break;
1369 case SA_UNLOCKED:
1370 #ifdef WITNESS
1371 witness_assert(&sx->lock_object, what, file, line);
1372 #else
1373 /*
1374 * If we hold an exclusve lock fail. We can't
1375 * reliably check to see if we hold a shared lock or
1376 * not.
1377 */
1378 if (sx_xholder(sx) == curthread)
1379 panic("Lock %s exclusively locked @ %s:%d\n",
1380 sx->lock_object.lo_name, file, line);
1381 #endif
1382 break;
1383 default:
1384 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1385 line);
1386 }
1387 }
1388 #endif /* INVARIANT_SUPPORT */
1389
1390 #ifdef DDB
1391 static void
db_show_sx(const struct lock_object * lock)1392 db_show_sx(const struct lock_object *lock)
1393 {
1394 struct thread *td;
1395 const struct sx *sx;
1396
1397 sx = (const struct sx *)lock;
1398
1399 db_printf(" state: ");
1400 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1401 db_printf("UNLOCKED\n");
1402 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1403 db_printf("DESTROYED\n");
1404 return;
1405 } else if (sx->sx_lock & SX_LOCK_SHARED)
1406 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1407 else {
1408 td = sx_xholder(sx);
1409 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1410 td->td_tid, td->td_proc->p_pid, td->td_name);
1411 if (sx_recursed(sx))
1412 db_printf(" recursed: %d\n", sx->sx_recurse);
1413 }
1414
1415 db_printf(" waiters: ");
1416 switch(sx->sx_lock &
1417 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1418 case SX_LOCK_SHARED_WAITERS:
1419 db_printf("shared\n");
1420 break;
1421 case SX_LOCK_EXCLUSIVE_WAITERS:
1422 db_printf("exclusive\n");
1423 break;
1424 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1425 db_printf("exclusive and shared\n");
1426 break;
1427 default:
1428 db_printf("none\n");
1429 }
1430 }
1431
1432 /*
1433 * Check to see if a thread that is blocked on a sleep queue is actually
1434 * blocked on an sx lock. If so, output some details and return true.
1435 * If the lock has an exclusive owner, return that in *ownerp.
1436 */
1437 int
sx_chain(struct thread * td,struct thread ** ownerp)1438 sx_chain(struct thread *td, struct thread **ownerp)
1439 {
1440 struct sx *sx;
1441
1442 /*
1443 * Check to see if this thread is blocked on an sx lock.
1444 * First, we check the lock class. If that is ok, then we
1445 * compare the lock name against the wait message.
1446 */
1447 sx = td->td_wchan;
1448 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1449 sx->lock_object.lo_name != td->td_wmesg)
1450 return (0);
1451
1452 /* We think we have an sx lock, so output some details. */
1453 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1454 *ownerp = sx_xholder(sx);
1455 if (sx->sx_lock & SX_LOCK_SHARED)
1456 db_printf("SLOCK (count %ju)\n",
1457 (uintmax_t)SX_SHARERS(sx->sx_lock));
1458 else
1459 db_printf("XLOCK\n");
1460 return (1);
1461 }
1462 #endif
1463