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 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
170 ("%s: sx_lock not aligned for %s:%p", __func__, description,
171 &sx->sx_lock));
172
173 flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE;
174 if (opts & SX_DUPOK)
175 flags |= LO_DUPOK;
176 if (opts & SX_NOPROFILE)
177 flags |= LO_NOPROFILE;
178 if (!(opts & SX_NOWITNESS))
179 flags |= LO_WITNESS;
180 if (opts & SX_QUIET)
181 flags |= LO_QUIET;
182
183 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE);
184 sx->sx_lock = SX_LOCK_UNLOCKED;
185 sx->sx_recurse = 0;
186 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
187 }
188
189 void
190 sx_destroy(struct sx *sx)
191 {
192
193 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
194 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
195 sx->sx_lock = SX_LOCK_DESTROYED;
196 lock_destroy(&sx->lock_object);
197 }
198
199 int
200 _sx_slock(struct sx *sx, int opts, const char *file, int line)
201 {
202 int error = 0;
203
204 MPASS(curthread != NULL);
205 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
206 ("sx_slock() of destroyed sx @ %s:%d", file, line));
207 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line);
208 error = __sx_slock(sx, opts, file, line);
209 if (!error) {
210 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
211 WITNESS_LOCK(&sx->lock_object, 0, file, line);
212 curthread->td_locks++;
213 }
214
215 return (error);
216 }
217
218 int
219 _sx_try_slock(struct sx *sx, const char *file, int line)
220 {
221 uintptr_t x;
222
223 for (;;) {
224 x = sx->sx_lock;
225 KASSERT(x != SX_LOCK_DESTROYED,
226 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
227 if (!(x & SX_LOCK_SHARED))
228 break;
229 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
230 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
231 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
232 curthread->td_locks++;
233 return (1);
234 }
235 }
236
237 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
238 return (0);
239 }
240
241 int
242 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
243 {
244 int error = 0;
245
246 MPASS(curthread != NULL);
247 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
248 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
249 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
250 line);
251 error = __sx_xlock(sx, curthread, opts, file, line);
252 if (!error) {
253 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
254 file, line);
255 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
256 curthread->td_locks++;
257 }
258
259 return (error);
260 }
261
262 int
263 _sx_try_xlock(struct sx *sx, const char *file, int line)
264 {
265 int rval;
266
267 MPASS(curthread != NULL);
268 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
269 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
270
271 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) {
272 sx->sx_recurse++;
273 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
274 rval = 1;
275 } else
276 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
277 (uintptr_t)curthread);
278 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
279 if (rval) {
280 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
281 file, line);
282 curthread->td_locks++;
283 }
284
285 return (rval);
286 }
287
288 void
289 _sx_sunlock(struct sx *sx, const char *file, int line)
290 {
291
292 MPASS(curthread != NULL);
293 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
294 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
295 _sx_assert(sx, SA_SLOCKED, file, line);
296 curthread->td_locks--;
297 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
298 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
299 #ifdef LOCK_PROFILING_SHARED
300 if (SX_SHARERS(sx->sx_lock) == 1)
301 lock_profile_release_lock(&sx->lock_object);
302 #endif
303 __sx_sunlock(sx, file, line);
304 }
305
306 void
307 _sx_xunlock(struct sx *sx, const char *file, int line)
308 {
309
310 MPASS(curthread != NULL);
311 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
312 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
313 _sx_assert(sx, SA_XLOCKED, file, line);
314 curthread->td_locks--;
315 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
316 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
317 line);
318 if (!sx_recursed(sx))
319 lock_profile_release_lock(&sx->lock_object);
320 __sx_xunlock(sx, curthread, file, line);
321 }
322
323 /*
324 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
325 * This will only succeed if this thread holds a single shared lock.
326 * Return 1 if if the upgrade succeed, 0 otherwise.
327 */
328 int
329 _sx_try_upgrade(struct sx *sx, const char *file, int line)
330 {
331 uintptr_t x;
332 int success;
333
334 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
335 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
336 _sx_assert(sx, SA_SLOCKED, file, line);
337
338 /*
339 * Try to switch from one shared lock to an exclusive lock. We need
340 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
341 * we will wake up the exclusive waiters when we drop the lock.
342 */
343 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
344 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
345 (uintptr_t)curthread | x);
346 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
347 if (success)
348 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
349 file, line);
350 return (success);
351 }
352
353 /*
354 * Downgrade an unrecursed exclusive lock into a single shared lock.
355 */
356 void
357 _sx_downgrade(struct sx *sx, const char *file, int line)
358 {
359 uintptr_t x;
360 int wakeup_swapper;
361
362 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
363 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
364 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
365 #ifndef INVARIANTS
366 if (sx_recursed(sx))
367 panic("downgrade of a recursed lock");
368 #endif
369
370 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
371
372 /*
373 * Try to switch from an exclusive lock with no shared waiters
374 * to one sharer with no shared waiters. If there are
375 * exclusive waiters, we don't need to lock the sleep queue so
376 * long as we preserve the flag. We do one quick try and if
377 * that fails we grab the sleepq lock to keep the flags from
378 * changing and do it the slow way.
379 *
380 * We have to lock the sleep queue if there are shared waiters
381 * so we can wake them up.
382 */
383 x = sx->sx_lock;
384 if (!(x & SX_LOCK_SHARED_WAITERS) &&
385 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
386 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
387 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
388 return;
389 }
390
391 /*
392 * Lock the sleep queue so we can read the waiters bits
393 * without any races and wakeup any shared waiters.
394 */
395 sleepq_lock(&sx->lock_object);
396
397 /*
398 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
399 * shared lock. If there are any shared waiters, wake them up.
400 */
401 wakeup_swapper = 0;
402 x = sx->sx_lock;
403 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
404 (x & SX_LOCK_EXCLUSIVE_WAITERS));
405 if (x & SX_LOCK_SHARED_WAITERS)
406 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
407 -1, SQ_SHARED_QUEUE);
408 else
409 sleepq_release(&sx->lock_object);
410
411 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
412
413 if (wakeup_swapper)
414 kick_proc0();
415 }
416
417 /*
418 * This function represents the so-called 'hard case' for sx_xlock
419 * operation. All 'easy case' failures are redirected to this. Note
420 * that ideally this would be a static function, but it needs to be
421 * accessible from at least sx.h.
422 */
423 int
424 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
425 int line)
426 {
427 GIANT_DECLARE;
428 #ifdef ADAPTIVE_SX
429 volatile struct thread *owner;
430 #endif
431 uint64_t waittime = 0;
432 uintptr_t x;
433 int contested = 0, error = 0;
434
435 /* If we already hold an exclusive lock, then recurse. */
436 if (sx_xlocked(sx)) {
437 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0,
438 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
439 sx->lock_object.lo_name, file, line));
440 sx->sx_recurse++;
441 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
442 if (LOCK_LOG_TEST(&sx->lock_object, 0))
443 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
444 return (0);
445 }
446
447 if (LOCK_LOG_TEST(&sx->lock_object, 0))
448 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
449 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
450
451 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
452 #ifdef ADAPTIVE_SX
453 /*
454 * If the lock is write locked and the owner is
455 * running on another CPU, spin until the owner stops
456 * running or the state of the lock changes.
457 */
458 x = sx->sx_lock;
459 if (!(x & SX_LOCK_SHARED) &&
460 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
461 x = SX_OWNER(x);
462 owner = (struct thread *)x;
463 if (TD_IS_RUNNING(owner)) {
464 if (LOCK_LOG_TEST(&sx->lock_object, 0))
465 CTR3(KTR_LOCK,
466 "%s: spinning on %p held by %p",
467 __func__, sx, owner);
468 GIANT_SAVE();
469 lock_profile_obtain_lock_failed(
470 &sx->lock_object, &contested, &waittime);
471 while (SX_OWNER(sx->sx_lock) == x &&
472 TD_IS_RUNNING(owner))
473 cpu_spinwait();
474 continue;
475 }
476 }
477 #endif
478
479 sleepq_lock(&sx->lock_object);
480 x = sx->sx_lock;
481
482 /*
483 * If the lock was released while spinning on the
484 * sleep queue chain lock, try again.
485 */
486 if (x == SX_LOCK_UNLOCKED) {
487 sleepq_release(&sx->lock_object);
488 continue;
489 }
490
491 #ifdef ADAPTIVE_SX
492 /*
493 * The current lock owner might have started executing
494 * on another CPU (or the lock could have changed
495 * owners) while we were waiting on the sleep queue
496 * chain lock. If so, drop the sleep queue lock and try
497 * again.
498 */
499 if (!(x & SX_LOCK_SHARED) &&
500 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
501 owner = (struct thread *)SX_OWNER(x);
502 if (TD_IS_RUNNING(owner)) {
503 sleepq_release(&sx->lock_object);
504 continue;
505 }
506 }
507 #endif
508
509 /*
510 * If an exclusive lock was released with both shared
511 * and exclusive waiters and a shared waiter hasn't
512 * woken up and acquired the lock yet, sx_lock will be
513 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
514 * If we see that value, try to acquire it once. Note
515 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
516 * as there are other exclusive waiters still. If we
517 * fail, restart the loop.
518 */
519 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
520 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
521 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
522 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
523 sleepq_release(&sx->lock_object);
524 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
525 __func__, sx);
526 break;
527 }
528 sleepq_release(&sx->lock_object);
529 continue;
530 }
531
532 /*
533 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
534 * than loop back and retry.
535 */
536 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
537 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
538 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
539 sleepq_release(&sx->lock_object);
540 continue;
541 }
542 if (LOCK_LOG_TEST(&sx->lock_object, 0))
543 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
544 __func__, sx);
545 }
546
547 /*
548 * Since we have been unable to acquire the exclusive
549 * lock and the exclusive waiters flag is set, we have
550 * to sleep.
551 */
552 if (LOCK_LOG_TEST(&sx->lock_object, 0))
553 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
554 __func__, sx);
555
556 GIANT_SAVE();
557 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
558 &waittime);
559 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
560 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
561 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
562 if (!(opts & SX_INTERRUPTIBLE))
563 sleepq_wait(&sx->lock_object);
564 else
565 error = sleepq_wait_sig(&sx->lock_object);
566
567 if (error) {
568 if (LOCK_LOG_TEST(&sx->lock_object, 0))
569 CTR2(KTR_LOCK,
570 "%s: interruptible sleep by %p suspended by signal",
571 __func__, sx);
572 break;
573 }
574 if (LOCK_LOG_TEST(&sx->lock_object, 0))
575 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
576 __func__, sx);
577 }
578
579 GIANT_RESTORE();
580 if (!error)
581 lock_profile_obtain_lock_success(&sx->lock_object, contested,
582 waittime, file, line);
583 return (error);
584 }
585
586 /*
587 * This function represents the so-called 'hard case' for sx_xunlock
588 * operation. All 'easy case' failures are redirected to this. Note
589 * that ideally this would be a static function, but it needs to be
590 * accessible from at least sx.h.
591 */
592 void
593 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
594 {
595 uintptr_t x;
596 int queue, wakeup_swapper;
597
598 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
599
600 /* If the lock is recursed, then unrecurse one level. */
601 if (sx_xlocked(sx) && sx_recursed(sx)) {
602 if ((--sx->sx_recurse) == 0)
603 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
604 if (LOCK_LOG_TEST(&sx->lock_object, 0))
605 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
606 return;
607 }
608 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
609 SX_LOCK_EXCLUSIVE_WAITERS));
610 if (LOCK_LOG_TEST(&sx->lock_object, 0))
611 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
612
613 sleepq_lock(&sx->lock_object);
614 x = SX_LOCK_UNLOCKED;
615
616 /*
617 * The wake up algorithm here is quite simple and probably not
618 * ideal. It gives precedence to shared waiters if they are
619 * present. For this condition, we have to preserve the
620 * state of the exclusive waiters flag.
621 */
622 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) {
623 queue = SQ_SHARED_QUEUE;
624 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
625 } else
626 queue = SQ_EXCLUSIVE_QUEUE;
627
628 /* Wake up all the waiters for the specific queue. */
629 if (LOCK_LOG_TEST(&sx->lock_object, 0))
630 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
631 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
632 "exclusive");
633 atomic_store_rel_ptr(&sx->sx_lock, x);
634 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1,
635 queue);
636 if (wakeup_swapper)
637 kick_proc0();
638 }
639
640 /*
641 * This function represents the so-called 'hard case' for sx_slock
642 * operation. All 'easy case' failures are redirected to this. Note
643 * that ideally this would be a static function, but it needs to be
644 * accessible from at least sx.h.
645 */
646 int
647 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
648 {
649 GIANT_DECLARE;
650 #ifdef ADAPTIVE_SX
651 volatile struct thread *owner;
652 #endif
653 #ifdef LOCK_PROFILING_SHARED
654 uint64_t waittime = 0;
655 int contested = 0;
656 #endif
657 uintptr_t x;
658 int error = 0;
659
660 /*
661 * As with rwlocks, we don't make any attempt to try to block
662 * shared locks once there is an exclusive waiter.
663 */
664 for (;;) {
665 x = sx->sx_lock;
666
667 /*
668 * If no other thread has an exclusive lock then try to bump up
669 * the count of sharers. Since we have to preserve the state
670 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
671 * shared lock loop back and retry.
672 */
673 if (x & SX_LOCK_SHARED) {
674 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
675 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
676 x + SX_ONE_SHARER)) {
677 #ifdef LOCK_PROFILING_SHARED
678 if (SX_SHARERS(x) == 0)
679 lock_profile_obtain_lock_success(
680 &sx->lock_object, contested,
681 waittime, file, line);
682 #endif
683 if (LOCK_LOG_TEST(&sx->lock_object, 0))
684 CTR4(KTR_LOCK,
685 "%s: %p succeed %p -> %p", __func__,
686 sx, (void *)x,
687 (void *)(x + SX_ONE_SHARER));
688 break;
689 }
690 continue;
691 }
692
693 #ifdef ADAPTIVE_SX
694 /*
695 * If the owner is running on another CPU, spin until
696 * the owner stops running or the state of the lock
697 * changes.
698 */
699 else if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) {
700 x = SX_OWNER(x);
701 owner = (struct thread *)x;
702 if (TD_IS_RUNNING(owner)) {
703 if (LOCK_LOG_TEST(&sx->lock_object, 0))
704 CTR3(KTR_LOCK,
705 "%s: spinning on %p held by %p",
706 __func__, sx, owner);
707 GIANT_SAVE();
708 #ifdef LOCK_PROFILING_SHARED
709 lock_profile_obtain_lock_failed(
710 &sx->lock_object, &contested, &waittime);
711 #endif
712 while (SX_OWNER(sx->sx_lock) == x &&
713 TD_IS_RUNNING(owner))
714 cpu_spinwait();
715 continue;
716 }
717 }
718 #endif
719
720 /*
721 * Some other thread already has an exclusive lock, so
722 * start the process of blocking.
723 */
724 sleepq_lock(&sx->lock_object);
725 x = sx->sx_lock;
726
727 /*
728 * The lock could have been released while we spun.
729 * In this case loop back and retry.
730 */
731 if (x & SX_LOCK_SHARED) {
732 sleepq_release(&sx->lock_object);
733 continue;
734 }
735
736 #ifdef ADAPTIVE_SX
737 /*
738 * If the owner is running on another CPU, spin until
739 * the owner stops running or the state of the lock
740 * changes.
741 */
742 if (!(x & SX_LOCK_SHARED) &&
743 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
744 owner = (struct thread *)SX_OWNER(x);
745 if (TD_IS_RUNNING(owner)) {
746 sleepq_release(&sx->lock_object);
747 continue;
748 }
749 }
750 #endif
751
752 /*
753 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
754 * fail to set it drop the sleep queue lock and loop
755 * back.
756 */
757 if (!(x & SX_LOCK_SHARED_WAITERS)) {
758 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
759 x | SX_LOCK_SHARED_WAITERS)) {
760 sleepq_release(&sx->lock_object);
761 continue;
762 }
763 if (LOCK_LOG_TEST(&sx->lock_object, 0))
764 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
765 __func__, sx);
766 }
767
768 /*
769 * Since we have been unable to acquire the shared lock,
770 * we have 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 GIANT_SAVE();
777 #ifdef LOCK_PROFILING_SHARED
778 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
779 &waittime);
780 #endif
781 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
782 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
783 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
784 if (!(opts & SX_INTERRUPTIBLE))
785 sleepq_wait(&sx->lock_object);
786 else
787 error = sleepq_wait_sig(&sx->lock_object);
788
789 if (error) {
790 if (LOCK_LOG_TEST(&sx->lock_object, 0))
791 CTR2(KTR_LOCK,
792 "%s: interruptible sleep by %p suspended by signal",
793 __func__, sx);
794 break;
795 }
796 if (LOCK_LOG_TEST(&sx->lock_object, 0))
797 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
798 __func__, sx);
799 }
800
801 GIANT_RESTORE();
802 return (error);
803 }
804
805 /*
806 * This function represents the so-called 'hard case' for sx_sunlock
807 * operation. All 'easy case' failures are redirected to this. Note
808 * that ideally this would be a static function, but it needs to be
809 * accessible from at least sx.h.
810 */
811 void
812 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
813 {
814 uintptr_t x;
815 int wakeup_swapper;
816
817 for (;;) {
818 x = sx->sx_lock;
819
820 /*
821 * We should never have sharers while at least one thread
822 * holds a shared lock.
823 */
824 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
825 ("%s: waiting sharers", __func__));
826
827 /*
828 * See if there is more than one shared lock held. If
829 * so, just drop one and return.
830 */
831 if (SX_SHARERS(x) > 1) {
832 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
833 x - SX_ONE_SHARER)) {
834 if (LOCK_LOG_TEST(&sx->lock_object, 0))
835 CTR4(KTR_LOCK,
836 "%s: %p succeeded %p -> %p",
837 __func__, sx, (void *)x,
838 (void *)(x - SX_ONE_SHARER));
839 break;
840 }
841 continue;
842 }
843
844 /*
845 * If there aren't any waiters for an exclusive lock,
846 * then try to drop it quickly.
847 */
848 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
849 MPASS(x == SX_SHARERS_LOCK(1));
850 if (atomic_cmpset_rel_ptr(&sx->sx_lock,
851 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
852 if (LOCK_LOG_TEST(&sx->lock_object, 0))
853 CTR2(KTR_LOCK, "%s: %p last succeeded",
854 __func__, sx);
855 break;
856 }
857 continue;
858 }
859
860 /*
861 * At this point, there should just be one sharer with
862 * exclusive waiters.
863 */
864 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
865
866 sleepq_lock(&sx->lock_object);
867
868 /*
869 * Wake up semantic here is quite simple:
870 * Just wake up all the exclusive waiters.
871 * Note that the state of the lock could have changed,
872 * so if it fails loop back and retry.
873 */
874 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
875 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
876 SX_LOCK_UNLOCKED)) {
877 sleepq_release(&sx->lock_object);
878 continue;
879 }
880 if (LOCK_LOG_TEST(&sx->lock_object, 0))
881 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
882 "exclusive queue", __func__, sx);
883 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
884 -1, SQ_EXCLUSIVE_QUEUE);
885 if (wakeup_swapper)
886 kick_proc0();
887 break;
888 }
889 }
890
891 #ifdef INVARIANT_SUPPORT
892 #ifndef INVARIANTS
893 #undef _sx_assert
894 #endif
895
896 /*
897 * In the non-WITNESS case, sx_assert() can only detect that at least
898 * *some* thread owns an slock, but it cannot guarantee that *this*
899 * thread owns an slock.
900 */
901 void
902 _sx_assert(struct sx *sx, int what, const char *file, int line)
903 {
904 #ifndef WITNESS
905 int slocked = 0;
906 #endif
907
908 if (panicstr != NULL)
909 return;
910 switch (what) {
911 case SA_SLOCKED:
912 case SA_SLOCKED | SA_NOTRECURSED:
913 case SA_SLOCKED | SA_RECURSED:
914 #ifndef WITNESS
915 slocked = 1;
916 /* FALLTHROUGH */
917 #endif
918 case SA_LOCKED:
919 case SA_LOCKED | SA_NOTRECURSED:
920 case SA_LOCKED | SA_RECURSED:
921 #ifdef WITNESS
922 witness_assert(&sx->lock_object, what, file, line);
923 #else
924 /*
925 * If some other thread has an exclusive lock or we
926 * have one and are asserting a shared lock, fail.
927 * Also, if no one has a lock at all, fail.
928 */
929 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
930 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
931 sx_xholder(sx) != curthread)))
932 panic("Lock %s not %slocked @ %s:%d\n",
933 sx->lock_object.lo_name, slocked ? "share " : "",
934 file, line);
935
936 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
937 if (sx_recursed(sx)) {
938 if (what & SA_NOTRECURSED)
939 panic("Lock %s recursed @ %s:%d\n",
940 sx->lock_object.lo_name, file,
941 line);
942 } else if (what & SA_RECURSED)
943 panic("Lock %s not recursed @ %s:%d\n",
944 sx->lock_object.lo_name, file, line);
945 }
946 #endif
947 break;
948 case SA_XLOCKED:
949 case SA_XLOCKED | SA_NOTRECURSED:
950 case SA_XLOCKED | SA_RECURSED:
951 if (sx_xholder(sx) != curthread)
952 panic("Lock %s not exclusively locked @ %s:%d\n",
953 sx->lock_object.lo_name, file, line);
954 if (sx_recursed(sx)) {
955 if (what & SA_NOTRECURSED)
956 panic("Lock %s recursed @ %s:%d\n",
957 sx->lock_object.lo_name, file, line);
958 } else if (what & SA_RECURSED)
959 panic("Lock %s not recursed @ %s:%d\n",
960 sx->lock_object.lo_name, file, line);
961 break;
962 case SA_UNLOCKED:
963 #ifdef WITNESS
964 witness_assert(&sx->lock_object, what, file, line);
965 #else
966 /*
967 * If we hold an exclusve lock fail. We can't
968 * reliably check to see if we hold a shared lock or
969 * not.
970 */
971 if (sx_xholder(sx) == curthread)
972 panic("Lock %s exclusively locked @ %s:%d\n",
973 sx->lock_object.lo_name, file, line);
974 #endif
975 break;
976 default:
977 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
978 line);
979 }
980 }
981 #endif /* INVARIANT_SUPPORT */
982
983 #ifdef DDB
984 static void
985 db_show_sx(struct lock_object *lock)
986 {
987 struct thread *td;
988 struct sx *sx;
989
990 sx = (struct sx *)lock;
991
992 db_printf(" state: ");
993 if (sx->sx_lock == SX_LOCK_UNLOCKED)
994 db_printf("UNLOCKED\n");
995 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
996 db_printf("DESTROYED\n");
997 return;
998 } else if (sx->sx_lock & SX_LOCK_SHARED)
999 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1000 else {
1001 td = sx_xholder(sx);
1002 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1003 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm);
1004 if (sx_recursed(sx))
1005 db_printf(" recursed: %d\n", sx->sx_recurse);
1006 }
1007
1008 db_printf(" waiters: ");
1009 switch(sx->sx_lock &
1010 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1011 case SX_LOCK_SHARED_WAITERS:
1012 db_printf("shared\n");
1013 break;
1014 case SX_LOCK_EXCLUSIVE_WAITERS:
1015 db_printf("exclusive\n");
1016 break;
1017 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1018 db_printf("exclusive and shared\n");
1019 break;
1020 default:
1021 db_printf("none\n");
1022 }
1023 }
1024
1025 /*
1026 * Check to see if a thread that is blocked on a sleep queue is actually
1027 * blocked on an sx lock. If so, output some details and return true.
1028 * If the lock has an exclusive owner, return that in *ownerp.
1029 */
1030 int
1031 sx_chain(struct thread *td, struct thread **ownerp)
1032 {
1033 struct sx *sx;
1034
1035 /*
1036 * Check to see if this thread is blocked on an sx lock.
1037 * First, we check the lock class. If that is ok, then we
1038 * compare the lock name against the wait message.
1039 */
1040 sx = td->td_wchan;
1041 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1042 sx->lock_object.lo_name != td->td_wmesg)
1043 return (0);
1044
1045 /* We think we have an sx lock, so output some details. */
1046 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1047 *ownerp = sx_xholder(sx);
1048 if (sx->sx_lock & SX_LOCK_SHARED)
1049 db_printf("SLOCK (count %ju)\n",
1050 (uintmax_t)SX_SHARERS(sx->sx_lock));
1051 else
1052 db_printf("XLOCK\n");
1053 return (1);
1054 }
1055 #endif
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