FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_sx.c
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_adaptive_sx.h"
40 #include "opt_ddb.h"
41
42 #include <sys/cdefs.h>
43 __FBSDID("$FreeBSD$");
44
45 #include <sys/param.h>
46 #include <sys/ktr.h>
47 #include <sys/lock.h>
48 #include <sys/mutex.h>
49 #include <sys/proc.h>
50 #include <sys/sleepqueue.h>
51 #include <sys/sx.h>
52 #include <sys/systm.h>
53
54 #ifdef ADAPTIVE_SX
55 #include <machine/cpu.h>
56 #endif
57
58 #ifdef DDB
59 #include <ddb/ddb.h>
60 #endif
61
62 #if !defined(SMP) && defined(ADAPTIVE_SX)
63 #error "You must have SMP to enable the ADAPTIVE_SX option"
64 #endif
65
66 CTASSERT(((SX_ADAPTIVESPIN | SX_RECURSE) & LO_CLASSFLAGS) ==
67 (SX_ADAPTIVESPIN | SX_RECURSE));
68
69 /* Handy macros for sleep queues. */
70 #define SQ_EXCLUSIVE_QUEUE 0
71 #define SQ_SHARED_QUEUE 1
72
73 /*
74 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
75 * drop Giant anytime we have to sleep or if we adaptively spin.
76 */
77 #define GIANT_DECLARE \
78 int _giantcnt = 0; \
79 WITNESS_SAVE_DECL(Giant) \
80
81 #define GIANT_SAVE() do { \
82 if (mtx_owned(&Giant)) { \
83 WITNESS_SAVE(&Giant.lock_object, Giant); \
84 while (mtx_owned(&Giant)) { \
85 _giantcnt++; \
86 mtx_unlock(&Giant); \
87 } \
88 } \
89 } while (0)
90
91 #define GIANT_RESTORE() do { \
92 if (_giantcnt > 0) { \
93 mtx_assert(&Giant, MA_NOTOWNED); \
94 while (_giantcnt--) \
95 mtx_lock(&Giant); \
96 WITNESS_RESTORE(&Giant.lock_object, Giant); \
97 } \
98 } while (0)
99
100 /*
101 * Returns true if an exclusive lock is recursed. It assumes
102 * curthread currently has an exclusive lock.
103 */
104 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
105
106 #ifdef DDB
107 static void db_show_sx(struct lock_object *lock);
108 #endif
109 static void lock_sx(struct lock_object *lock, int how);
110 static int unlock_sx(struct lock_object *lock);
111
112 struct lock_class lock_class_sx = {
113 .lc_name = "sx",
114 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
115 #ifdef DDB
116 .lc_ddb_show = db_show_sx,
117 #endif
118 .lc_lock = lock_sx,
119 .lc_unlock = unlock_sx,
120 };
121
122 #ifndef INVARIANTS
123 #define _sx_assert(sx, what, file, line)
124 #endif
125
126 void
127 lock_sx(struct lock_object *lock, int how)
128 {
129 struct sx *sx;
130
131 sx = (struct sx *)lock;
132 if (how)
133 sx_xlock(sx);
134 else
135 sx_slock(sx);
136 }
137
138 int
139 unlock_sx(struct lock_object *lock)
140 {
141 struct sx *sx;
142
143 sx = (struct sx *)lock;
144 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
145 if (sx_xlocked(sx)) {
146 sx_xunlock(sx);
147 return (1);
148 } else {
149 sx_sunlock(sx);
150 return (0);
151 }
152 }
153
154 void
155 sx_sysinit(void *arg)
156 {
157 struct sx_args *sargs = arg;
158
159 sx_init(sargs->sa_sx, sargs->sa_desc);
160 }
161
162 void
163 sx_init_flags(struct sx *sx, const char *description, int opts)
164 {
165 int flags;
166
167 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
168 SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0);
169
170 flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE;
171 if (opts & SX_DUPOK)
172 flags |= LO_DUPOK;
173 if (opts & SX_NOPROFILE)
174 flags |= LO_NOPROFILE;
175 if (!(opts & SX_NOWITNESS))
176 flags |= LO_WITNESS;
177 if (opts & SX_QUIET)
178 flags |= LO_QUIET;
179
180 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE);
181 sx->sx_lock = SX_LOCK_UNLOCKED;
182 sx->sx_recurse = 0;
183 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
184 }
185
186 void
187 sx_destroy(struct sx *sx)
188 {
189
190 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
191 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
192 sx->sx_lock = SX_LOCK_DESTROYED;
193 lock_destroy(&sx->lock_object);
194 }
195
196 int
197 _sx_slock(struct sx *sx, int opts, const char *file, int line)
198 {
199 int error = 0;
200
201 MPASS(curthread != NULL);
202 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
203 ("sx_slock() of destroyed sx @ %s:%d", file, line));
204 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line);
205 error = __sx_slock(sx, opts, file, line);
206 if (!error) {
207 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
208 WITNESS_LOCK(&sx->lock_object, 0, file, line);
209 curthread->td_locks++;
210 }
211
212 return (error);
213 }
214
215 int
216 _sx_try_slock(struct sx *sx, const char *file, int line)
217 {
218 uintptr_t x;
219
220 for (;;) {
221 x = sx->sx_lock;
222 KASSERT(x != SX_LOCK_DESTROYED,
223 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
224 if (!(x & SX_LOCK_SHARED))
225 break;
226 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
227 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
228 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
229 curthread->td_locks++;
230 return (1);
231 }
232 }
233
234 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
235 return (0);
236 }
237
238 int
239 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
240 {
241 int error = 0;
242
243 MPASS(curthread != NULL);
244 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
245 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
246 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
247 line);
248 error = __sx_xlock(sx, curthread, opts, file, line);
249 if (!error) {
250 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
251 file, line);
252 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
253 curthread->td_locks++;
254 }
255
256 return (error);
257 }
258
259 int
260 _sx_try_xlock(struct sx *sx, const char *file, int line)
261 {
262 int rval;
263
264 MPASS(curthread != NULL);
265 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
266 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
267
268 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) {
269 sx->sx_recurse++;
270 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
271 rval = 1;
272 } else
273 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
274 (uintptr_t)curthread);
275 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
276 if (rval) {
277 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
278 file, line);
279 curthread->td_locks++;
280 }
281
282 return (rval);
283 }
284
285 void
286 _sx_sunlock(struct sx *sx, const char *file, int line)
287 {
288
289 MPASS(curthread != NULL);
290 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
291 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
292 _sx_assert(sx, SA_SLOCKED, file, line);
293 curthread->td_locks--;
294 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
295 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
296 #ifdef LOCK_PROFILING_SHARED
297 if (SX_SHARERS(sx->sx_lock) == 1)
298 lock_profile_release_lock(&sx->lock_object);
299 #endif
300 __sx_sunlock(sx, file, line);
301 }
302
303 void
304 _sx_xunlock(struct sx *sx, const char *file, int line)
305 {
306
307 MPASS(curthread != NULL);
308 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
309 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
310 _sx_assert(sx, SA_XLOCKED, file, line);
311 curthread->td_locks--;
312 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
313 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
314 line);
315 if (!sx_recursed(sx))
316 lock_profile_release_lock(&sx->lock_object);
317 __sx_xunlock(sx, curthread, file, line);
318 }
319
320 /*
321 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
322 * This will only succeed if this thread holds a single shared lock.
323 * Return 1 if if the upgrade succeed, 0 otherwise.
324 */
325 int
326 _sx_try_upgrade(struct sx *sx, const char *file, int line)
327 {
328 uintptr_t x;
329 int success;
330
331 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
332 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
333 _sx_assert(sx, SA_SLOCKED, file, line);
334
335 /*
336 * Try to switch from one shared lock to an exclusive lock. We need
337 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
338 * we will wake up the exclusive waiters when we drop the lock.
339 */
340 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
341 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
342 (uintptr_t)curthread | x);
343 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
344 if (success)
345 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
346 file, line);
347 return (success);
348 }
349
350 /*
351 * Downgrade an unrecursed exclusive lock into a single shared lock.
352 */
353 void
354 _sx_downgrade(struct sx *sx, const char *file, int line)
355 {
356 uintptr_t x;
357 int wakeup_swapper;
358
359 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
360 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
361 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
362 #ifndef INVARIANTS
363 if (sx_recursed(sx))
364 panic("downgrade of a recursed lock");
365 #endif
366
367 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
368
369 /*
370 * Try to switch from an exclusive lock with no shared waiters
371 * to one sharer with no shared waiters. If there are
372 * exclusive waiters, we don't need to lock the sleep queue so
373 * long as we preserve the flag. We do one quick try and if
374 * that fails we grab the sleepq lock to keep the flags from
375 * changing and do it the slow way.
376 *
377 * We have to lock the sleep queue if there are shared waiters
378 * so we can wake them up.
379 */
380 x = sx->sx_lock;
381 if (!(x & SX_LOCK_SHARED_WAITERS) &&
382 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
383 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
384 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
385 return;
386 }
387
388 /*
389 * Lock the sleep queue so we can read the waiters bits
390 * without any races and wakeup any shared waiters.
391 */
392 sleepq_lock(&sx->lock_object);
393
394 /*
395 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
396 * shared lock. If there are any shared waiters, wake them up.
397 */
398 wakeup_swapper = 0;
399 x = sx->sx_lock;
400 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
401 (x & SX_LOCK_EXCLUSIVE_WAITERS));
402 if (x & SX_LOCK_SHARED_WAITERS)
403 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
404 -1, SQ_SHARED_QUEUE);
405 else
406 sleepq_release(&sx->lock_object);
407
408 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
409
410 if (wakeup_swapper)
411 kick_proc0();
412 }
413
414 /*
415 * This function represents the so-called 'hard case' for sx_xlock
416 * operation. All 'easy case' failures are redirected to this. Note
417 * that ideally this would be a static function, but it needs to be
418 * accessible from at least sx.h.
419 */
420 int
421 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
422 int line)
423 {
424 GIANT_DECLARE;
425 #ifdef ADAPTIVE_SX
426 volatile struct thread *owner;
427 #endif
428 uint64_t waittime = 0;
429 uintptr_t x;
430 int contested = 0, error = 0;
431
432 /* If we already hold an exclusive lock, then recurse. */
433 if (sx_xlocked(sx)) {
434 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0,
435 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
436 sx->lock_object.lo_name, file, line));
437 sx->sx_recurse++;
438 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
439 if (LOCK_LOG_TEST(&sx->lock_object, 0))
440 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
441 return (0);
442 }
443
444 if (LOCK_LOG_TEST(&sx->lock_object, 0))
445 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
446 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
447
448 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
449 #ifdef ADAPTIVE_SX
450 /*
451 * If the lock is write locked and the owner is
452 * running on another CPU, spin until the owner stops
453 * running or the state of the lock changes.
454 */
455 x = sx->sx_lock;
456 if (!(x & SX_LOCK_SHARED) &&
457 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
458 x = SX_OWNER(x);
459 owner = (struct thread *)x;
460 if (TD_IS_RUNNING(owner)) {
461 if (LOCK_LOG_TEST(&sx->lock_object, 0))
462 CTR3(KTR_LOCK,
463 "%s: spinning on %p held by %p",
464 __func__, sx, owner);
465 GIANT_SAVE();
466 lock_profile_obtain_lock_failed(
467 &sx->lock_object, &contested, &waittime);
468 while (SX_OWNER(sx->sx_lock) == x &&
469 TD_IS_RUNNING(owner))
470 cpu_spinwait();
471 continue;
472 }
473 }
474 #endif
475
476 sleepq_lock(&sx->lock_object);
477 x = sx->sx_lock;
478
479 /*
480 * If the lock was released while spinning on the
481 * sleep queue chain lock, try again.
482 */
483 if (x == SX_LOCK_UNLOCKED) {
484 sleepq_release(&sx->lock_object);
485 continue;
486 }
487
488 #ifdef ADAPTIVE_SX
489 /*
490 * The current lock owner might have started executing
491 * on another CPU (or the lock could have changed
492 * owners) while we were waiting on the sleep queue
493 * chain lock. If so, drop the sleep queue lock and try
494 * again.
495 */
496 if (!(x & SX_LOCK_SHARED) &&
497 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
498 owner = (struct thread *)SX_OWNER(x);
499 if (TD_IS_RUNNING(owner)) {
500 sleepq_release(&sx->lock_object);
501 continue;
502 }
503 }
504 #endif
505
506 /*
507 * If an exclusive lock was released with both shared
508 * and exclusive waiters and a shared waiter hasn't
509 * woken up and acquired the lock yet, sx_lock will be
510 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
511 * If we see that value, try to acquire it once. Note
512 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
513 * as there are other exclusive waiters still. If we
514 * fail, restart the loop.
515 */
516 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
517 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
518 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
519 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
520 sleepq_release(&sx->lock_object);
521 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
522 __func__, sx);
523 break;
524 }
525 sleepq_release(&sx->lock_object);
526 continue;
527 }
528
529 /*
530 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
531 * than loop back and retry.
532 */
533 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
534 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
535 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
536 sleepq_release(&sx->lock_object);
537 continue;
538 }
539 if (LOCK_LOG_TEST(&sx->lock_object, 0))
540 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
541 __func__, sx);
542 }
543
544 /*
545 * Since we have been unable to acquire the exclusive
546 * lock and the exclusive waiters flag is set, we have
547 * to sleep.
548 */
549 if (LOCK_LOG_TEST(&sx->lock_object, 0))
550 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
551 __func__, sx);
552
553 GIANT_SAVE();
554 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
555 &waittime);
556 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
557 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
558 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
559 if (!(opts & SX_INTERRUPTIBLE))
560 sleepq_wait(&sx->lock_object);
561 else
562 error = sleepq_wait_sig(&sx->lock_object);
563
564 if (error) {
565 if (LOCK_LOG_TEST(&sx->lock_object, 0))
566 CTR2(KTR_LOCK,
567 "%s: interruptible sleep by %p suspended by signal",
568 __func__, sx);
569 break;
570 }
571 if (LOCK_LOG_TEST(&sx->lock_object, 0))
572 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
573 __func__, sx);
574 }
575
576 GIANT_RESTORE();
577 if (!error)
578 lock_profile_obtain_lock_success(&sx->lock_object, contested,
579 waittime, file, line);
580 return (error);
581 }
582
583 /*
584 * This function represents the so-called 'hard case' for sx_xunlock
585 * operation. All 'easy case' failures are redirected to this. Note
586 * that ideally this would be a static function, but it needs to be
587 * accessible from at least sx.h.
588 */
589 void
590 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
591 {
592 uintptr_t x;
593 int queue, wakeup_swapper;
594
595 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
596
597 /* If the lock is recursed, then unrecurse one level. */
598 if (sx_xlocked(sx) && sx_recursed(sx)) {
599 if ((--sx->sx_recurse) == 0)
600 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
601 if (LOCK_LOG_TEST(&sx->lock_object, 0))
602 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
603 return;
604 }
605 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
606 SX_LOCK_EXCLUSIVE_WAITERS));
607 if (LOCK_LOG_TEST(&sx->lock_object, 0))
608 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
609
610 sleepq_lock(&sx->lock_object);
611 x = SX_LOCK_UNLOCKED;
612
613 /*
614 * The wake up algorithm here is quite simple and probably not
615 * ideal. It gives precedence to shared waiters if they are
616 * present. For this condition, we have to preserve the
617 * state of the exclusive waiters flag.
618 */
619 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) {
620 queue = SQ_SHARED_QUEUE;
621 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
622 } else
623 queue = SQ_EXCLUSIVE_QUEUE;
624
625 /* Wake up all the waiters for the specific queue. */
626 if (LOCK_LOG_TEST(&sx->lock_object, 0))
627 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
628 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
629 "exclusive");
630 atomic_store_rel_ptr(&sx->sx_lock, x);
631 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1,
632 queue);
633 if (wakeup_swapper)
634 kick_proc0();
635 }
636
637 /*
638 * This function represents the so-called 'hard case' for sx_slock
639 * operation. All 'easy case' failures are redirected to this. Note
640 * that ideally this would be a static function, but it needs to be
641 * accessible from at least sx.h.
642 */
643 int
644 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
645 {
646 GIANT_DECLARE;
647 #ifdef ADAPTIVE_SX
648 volatile struct thread *owner;
649 #endif
650 #ifdef LOCK_PROFILING_SHARED
651 uint64_t waittime = 0;
652 int contested = 0;
653 #endif
654 uintptr_t x;
655 int error = 0;
656
657 /*
658 * As with rwlocks, we don't make any attempt to try to block
659 * shared locks once there is an exclusive waiter.
660 */
661 for (;;) {
662 x = sx->sx_lock;
663
664 /*
665 * If no other thread has an exclusive lock then try to bump up
666 * the count of sharers. Since we have to preserve the state
667 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
668 * shared lock loop back and retry.
669 */
670 if (x & SX_LOCK_SHARED) {
671 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
672 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
673 x + SX_ONE_SHARER)) {
674 #ifdef LOCK_PROFILING_SHARED
675 if (SX_SHARERS(x) == 0)
676 lock_profile_obtain_lock_success(
677 &sx->lock_object, contested,
678 waittime, file, line);
679 #endif
680 if (LOCK_LOG_TEST(&sx->lock_object, 0))
681 CTR4(KTR_LOCK,
682 "%s: %p succeed %p -> %p", __func__,
683 sx, (void *)x,
684 (void *)(x + SX_ONE_SHARER));
685 break;
686 }
687 continue;
688 }
689
690 #ifdef ADAPTIVE_SX
691 /*
692 * If the owner is running on another CPU, spin until
693 * the owner stops running or the state of the lock
694 * changes.
695 */
696 else if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) {
697 x = SX_OWNER(x);
698 owner = (struct thread *)x;
699 if (TD_IS_RUNNING(owner)) {
700 if (LOCK_LOG_TEST(&sx->lock_object, 0))
701 CTR3(KTR_LOCK,
702 "%s: spinning on %p held by %p",
703 __func__, sx, owner);
704 GIANT_SAVE();
705 #ifdef LOCK_PROFILING_SHARED
706 lock_profile_obtain_lock_failed(
707 &sx->lock_object, &contested, &waittime);
708 #endif
709 while (SX_OWNER(sx->sx_lock) == x &&
710 TD_IS_RUNNING(owner))
711 cpu_spinwait();
712 continue;
713 }
714 }
715 #endif
716
717 /*
718 * Some other thread already has an exclusive lock, so
719 * start the process of blocking.
720 */
721 sleepq_lock(&sx->lock_object);
722 x = sx->sx_lock;
723
724 /*
725 * The lock could have been released while we spun.
726 * In this case loop back and retry.
727 */
728 if (x & SX_LOCK_SHARED) {
729 sleepq_release(&sx->lock_object);
730 continue;
731 }
732
733 #ifdef ADAPTIVE_SX
734 /*
735 * If the owner is running on another CPU, spin until
736 * the owner stops running or the state of the lock
737 * changes.
738 */
739 if (!(x & SX_LOCK_SHARED) &&
740 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
741 owner = (struct thread *)SX_OWNER(x);
742 if (TD_IS_RUNNING(owner)) {
743 sleepq_release(&sx->lock_object);
744 continue;
745 }
746 }
747 #endif
748
749 /*
750 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
751 * fail to set it drop the sleep queue lock and loop
752 * back.
753 */
754 if (!(x & SX_LOCK_SHARED_WAITERS)) {
755 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
756 x | SX_LOCK_SHARED_WAITERS)) {
757 sleepq_release(&sx->lock_object);
758 continue;
759 }
760 if (LOCK_LOG_TEST(&sx->lock_object, 0))
761 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
762 __func__, sx);
763 }
764
765 /*
766 * Since we have been unable to acquire the shared lock,
767 * we have to sleep.
768 */
769 if (LOCK_LOG_TEST(&sx->lock_object, 0))
770 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
771 __func__, sx);
772
773 GIANT_SAVE();
774 #ifdef LOCK_PROFILING_SHARED
775 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
776 &waittime);
777 #endif
778 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
779 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
780 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
781 if (!(opts & SX_INTERRUPTIBLE))
782 sleepq_wait(&sx->lock_object);
783 else
784 error = sleepq_wait_sig(&sx->lock_object);
785
786 if (error) {
787 if (LOCK_LOG_TEST(&sx->lock_object, 0))
788 CTR2(KTR_LOCK,
789 "%s: interruptible sleep by %p suspended by signal",
790 __func__, sx);
791 break;
792 }
793 if (LOCK_LOG_TEST(&sx->lock_object, 0))
794 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
795 __func__, sx);
796 }
797
798 GIANT_RESTORE();
799 return (error);
800 }
801
802 /*
803 * This function represents the so-called 'hard case' for sx_sunlock
804 * operation. All 'easy case' failures are redirected to this. Note
805 * that ideally this would be a static function, but it needs to be
806 * accessible from at least sx.h.
807 */
808 void
809 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
810 {
811 uintptr_t x;
812 int wakeup_swapper;
813
814 for (;;) {
815 x = sx->sx_lock;
816
817 /*
818 * We should never have sharers while at least one thread
819 * holds a shared lock.
820 */
821 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
822 ("%s: waiting sharers", __func__));
823
824 /*
825 * See if there is more than one shared lock held. If
826 * so, just drop one and return.
827 */
828 if (SX_SHARERS(x) > 1) {
829 if (atomic_cmpset_ptr(&sx->sx_lock, x,
830 x - SX_ONE_SHARER)) {
831 if (LOCK_LOG_TEST(&sx->lock_object, 0))
832 CTR4(KTR_LOCK,
833 "%s: %p succeeded %p -> %p",
834 __func__, sx, (void *)x,
835 (void *)(x - SX_ONE_SHARER));
836 break;
837 }
838 continue;
839 }
840
841 /*
842 * If there aren't any waiters for an exclusive lock,
843 * then try to drop it quickly.
844 */
845 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
846 MPASS(x == SX_SHARERS_LOCK(1));
847 if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1),
848 SX_LOCK_UNLOCKED)) {
849 if (LOCK_LOG_TEST(&sx->lock_object, 0))
850 CTR2(KTR_LOCK, "%s: %p last succeeded",
851 __func__, sx);
852 break;
853 }
854 continue;
855 }
856
857 /*
858 * At this point, there should just be one sharer with
859 * exclusive waiters.
860 */
861 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
862
863 sleepq_lock(&sx->lock_object);
864
865 /*
866 * Wake up semantic here is quite simple:
867 * Just wake up all the exclusive waiters.
868 * Note that the state of the lock could have changed,
869 * so if it fails loop back and retry.
870 */
871 if (!atomic_cmpset_ptr(&sx->sx_lock,
872 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
873 SX_LOCK_UNLOCKED)) {
874 sleepq_release(&sx->lock_object);
875 continue;
876 }
877 if (LOCK_LOG_TEST(&sx->lock_object, 0))
878 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
879 "exclusive queue", __func__, sx);
880 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
881 -1, SQ_EXCLUSIVE_QUEUE);
882 if (wakeup_swapper)
883 kick_proc0();
884 break;
885 }
886 }
887
888 #ifdef INVARIANT_SUPPORT
889 #ifndef INVARIANTS
890 #undef _sx_assert
891 #endif
892
893 /*
894 * In the non-WITNESS case, sx_assert() can only detect that at least
895 * *some* thread owns an slock, but it cannot guarantee that *this*
896 * thread owns an slock.
897 */
898 void
899 _sx_assert(struct sx *sx, int what, const char *file, int line)
900 {
901 #ifndef WITNESS
902 int slocked = 0;
903 #endif
904
905 if (panicstr != NULL)
906 return;
907 switch (what) {
908 case SA_SLOCKED:
909 case SA_SLOCKED | SA_NOTRECURSED:
910 case SA_SLOCKED | SA_RECURSED:
911 #ifndef WITNESS
912 slocked = 1;
913 /* FALLTHROUGH */
914 #endif
915 case SA_LOCKED:
916 case SA_LOCKED | SA_NOTRECURSED:
917 case SA_LOCKED | SA_RECURSED:
918 #ifdef WITNESS
919 witness_assert(&sx->lock_object, what, file, line);
920 #else
921 /*
922 * If some other thread has an exclusive lock or we
923 * have one and are asserting a shared lock, fail.
924 * Also, if no one has a lock at all, fail.
925 */
926 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
927 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
928 sx_xholder(sx) != curthread)))
929 panic("Lock %s not %slocked @ %s:%d\n",
930 sx->lock_object.lo_name, slocked ? "share " : "",
931 file, line);
932
933 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
934 if (sx_recursed(sx)) {
935 if (what & SA_NOTRECURSED)
936 panic("Lock %s recursed @ %s:%d\n",
937 sx->lock_object.lo_name, file,
938 line);
939 } else if (what & SA_RECURSED)
940 panic("Lock %s not recursed @ %s:%d\n",
941 sx->lock_object.lo_name, file, line);
942 }
943 #endif
944 break;
945 case SA_XLOCKED:
946 case SA_XLOCKED | SA_NOTRECURSED:
947 case SA_XLOCKED | SA_RECURSED:
948 if (sx_xholder(sx) != curthread)
949 panic("Lock %s not exclusively locked @ %s:%d\n",
950 sx->lock_object.lo_name, file, line);
951 if (sx_recursed(sx)) {
952 if (what & SA_NOTRECURSED)
953 panic("Lock %s recursed @ %s:%d\n",
954 sx->lock_object.lo_name, file, line);
955 } else if (what & SA_RECURSED)
956 panic("Lock %s not recursed @ %s:%d\n",
957 sx->lock_object.lo_name, file, line);
958 break;
959 case SA_UNLOCKED:
960 #ifdef WITNESS
961 witness_assert(&sx->lock_object, what, file, line);
962 #else
963 /*
964 * If we hold an exclusve lock fail. We can't
965 * reliably check to see if we hold a shared lock or
966 * not.
967 */
968 if (sx_xholder(sx) == curthread)
969 panic("Lock %s exclusively locked @ %s:%d\n",
970 sx->lock_object.lo_name, file, line);
971 #endif
972 break;
973 default:
974 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
975 line);
976 }
977 }
978 #endif /* INVARIANT_SUPPORT */
979
980 #ifdef DDB
981 static void
982 db_show_sx(struct lock_object *lock)
983 {
984 struct thread *td;
985 struct sx *sx;
986
987 sx = (struct sx *)lock;
988
989 db_printf(" state: ");
990 if (sx->sx_lock == SX_LOCK_UNLOCKED)
991 db_printf("UNLOCKED\n");
992 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
993 db_printf("DESTROYED\n");
994 return;
995 } else if (sx->sx_lock & SX_LOCK_SHARED)
996 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
997 else {
998 td = sx_xholder(sx);
999 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1000 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm);
1001 if (sx_recursed(sx))
1002 db_printf(" recursed: %d\n", sx->sx_recurse);
1003 }
1004
1005 db_printf(" waiters: ");
1006 switch(sx->sx_lock &
1007 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1008 case SX_LOCK_SHARED_WAITERS:
1009 db_printf("shared\n");
1010 break;
1011 case SX_LOCK_EXCLUSIVE_WAITERS:
1012 db_printf("exclusive\n");
1013 break;
1014 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1015 db_printf("exclusive and shared\n");
1016 break;
1017 default:
1018 db_printf("none\n");
1019 }
1020 }
1021
1022 /*
1023 * Check to see if a thread that is blocked on a sleep queue is actually
1024 * blocked on an sx lock. If so, output some details and return true.
1025 * If the lock has an exclusive owner, return that in *ownerp.
1026 */
1027 int
1028 sx_chain(struct thread *td, struct thread **ownerp)
1029 {
1030 struct sx *sx;
1031
1032 /*
1033 * Check to see if this thread is blocked on an sx lock.
1034 * First, we check the lock class. If that is ok, then we
1035 * compare the lock name against the wait message.
1036 */
1037 sx = td->td_wchan;
1038 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1039 sx->lock_object.lo_name != td->td_wmesg)
1040 return (0);
1041
1042 /* We think we have an sx lock, so output some details. */
1043 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1044 *ownerp = sx_xholder(sx);
1045 if (sx->sx_lock & SX_LOCK_SHARED)
1046 db_printf("SLOCK (count %ju)\n",
1047 (uintmax_t)SX_SHARERS(sx->sx_lock));
1048 else
1049 db_printf("XLOCK\n");
1050 return (1);
1051 }
1052 #endif
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