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/sched.h>
51 #include <sys/sleepqueue.h>
52 #include <sys/sx.h>
53 #include <sys/systm.h>
54
55 #ifdef ADAPTIVE_SX
56 #include <machine/cpu.h>
57 #endif
58
59 #ifdef DDB
60 #include <ddb/ddb.h>
61 #endif
62
63 #if !defined(SMP) && defined(ADAPTIVE_SX)
64 #error "You must have SMP to enable the ADAPTIVE_SX option"
65 #endif
66
67 CTASSERT(((SX_ADAPTIVESPIN | SX_RECURSE) & LO_CLASSFLAGS) ==
68 (SX_ADAPTIVESPIN | SX_RECURSE));
69
70 /* Handy macros for sleep queues. */
71 #define SQ_EXCLUSIVE_QUEUE 0
72 #define SQ_SHARED_QUEUE 1
73
74 /*
75 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
76 * drop Giant anytime we have to sleep or if we adaptively spin.
77 */
78 #define GIANT_DECLARE \
79 int _giantcnt = 0; \
80 WITNESS_SAVE_DECL(Giant) \
81
82 #define GIANT_SAVE() do { \
83 if (mtx_owned(&Giant)) { \
84 WITNESS_SAVE(&Giant.mtx_object, Giant); \
85 while (mtx_owned(&Giant)) { \
86 _giantcnt++; \
87 mtx_unlock(&Giant); \
88 } \
89 } \
90 } while (0)
91
92 #define GIANT_RESTORE() do { \
93 if (_giantcnt > 0) { \
94 mtx_assert(&Giant, MA_NOTOWNED); \
95 while (_giantcnt--) \
96 mtx_lock(&Giant); \
97 WITNESS_RESTORE(&Giant.mtx_object, Giant); \
98 } \
99 } while (0)
100
101 /*
102 * Returns true if an exclusive lock is recursed. It assumes
103 * curthread currently has an exclusive lock.
104 */
105 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
106
107 #ifdef DDB
108 static void db_show_sx(struct lock_object *lock);
109 #endif
110
111 struct lock_class lock_class_sx = {
112 .lc_name = "sx",
113 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
114 #ifdef DDB
115 .lc_ddb_show = db_show_sx,
116 #endif
117 };
118
119 #ifndef INVARIANTS
120 #define _sx_assert(sx, what, file, line)
121 #endif
122
123 void
124 sx_sysinit(void *arg)
125 {
126 struct sx_args *sargs = arg;
127
128 sx_init(sargs->sa_sx, sargs->sa_desc);
129 }
130
131 void
132 sx_init(struct sx *sx, const char *description)
133 {
134
135 sx_init_flags(sx, description, 0);
136 }
137
138 void
139 sx_init_flags(struct sx *sx, const char *description, int opts)
140 {
141 int flags;
142
143 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
144 SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0);
145
146 flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE;
147 if (opts & SX_DUPOK)
148 flags |= LO_DUPOK;
149 if (!(opts & SX_NOWITNESS))
150 flags |= LO_WITNESS;
151 if (opts & SX_QUIET)
152 flags |= LO_QUIET;
153
154 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE);
155 sx->sx_lock = SX_LOCK_UNLOCKED;
156 sx->sx_recurse = 0;
157 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
158 }
159
160 void
161 sx_destroy(struct sx *sx)
162 {
163
164 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
165 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
166 sx->sx_lock = SX_LOCK_DESTROYED;
167 lock_destroy(&sx->lock_object);
168 }
169
170 int
171 _sx_slock(struct sx *sx, int opts, const char *file, int line)
172 {
173 int error = 0;
174
175 MPASS(curthread != NULL);
176 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
177 ("sx_slock() of destroyed sx @ %s:%d", file, line));
178 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line);
179 error = __sx_slock(sx, opts, file, line);
180 if (!error) {
181 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
182 WITNESS_LOCK(&sx->lock_object, 0, file, line);
183 curthread->td_locks++;
184 }
185
186 return (error);
187 }
188
189 int
190 _sx_try_slock(struct sx *sx, const char *file, int line)
191 {
192 uintptr_t x;
193
194 x = sx->sx_lock;
195 KASSERT(x != SX_LOCK_DESTROYED,
196 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
197 if ((x & SX_LOCK_SHARED) && atomic_cmpset_acq_ptr(&sx->sx_lock, x,
198 x + SX_ONE_SHARER)) {
199 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
200 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
201 curthread->td_locks++;
202 return (1);
203 }
204
205 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
206 return (0);
207 }
208
209 int
210 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
211 {
212 int error = 0;
213
214 MPASS(curthread != NULL);
215 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
216 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
217 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
218 line);
219 error = __sx_xlock(sx, curthread, opts, file, line);
220 if (!error) {
221 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
222 file, line);
223 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
224 curthread->td_locks++;
225 }
226
227 return (error);
228 }
229
230 int
231 _sx_try_xlock(struct sx *sx, const char *file, int line)
232 {
233 int rval;
234
235 MPASS(curthread != NULL);
236 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
237 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
238
239 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) {
240 sx->sx_recurse++;
241 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
242 rval = 1;
243 } else
244 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
245 (uintptr_t)curthread);
246 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
247 if (rval) {
248 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
249 file, line);
250 curthread->td_locks++;
251 }
252
253 return (rval);
254 }
255
256 void
257 _sx_sunlock(struct sx *sx, const char *file, int line)
258 {
259
260 MPASS(curthread != NULL);
261 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
262 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
263 _sx_assert(sx, SA_SLOCKED, file, line);
264 curthread->td_locks--;
265 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
266 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
267 #ifdef LOCK_PROFILING_SHARED
268 if (SX_SHARERS(sx->sx_lock) == 1)
269 lock_profile_release_lock(&sx->lock_object);
270 #endif
271 __sx_sunlock(sx, file, line);
272 }
273
274 void
275 _sx_xunlock(struct sx *sx, const char *file, int line)
276 {
277
278 MPASS(curthread != NULL);
279 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
280 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
281 _sx_assert(sx, SA_XLOCKED, file, line);
282 curthread->td_locks--;
283 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
284 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
285 line);
286 if (!sx_recursed(sx))
287 lock_profile_release_lock(&sx->lock_object);
288 __sx_xunlock(sx, curthread, file, line);
289 }
290
291 /*
292 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
293 * This will only succeed if this thread holds a single shared lock.
294 * Return 1 if if the upgrade succeed, 0 otherwise.
295 */
296 int
297 _sx_try_upgrade(struct sx *sx, const char *file, int line)
298 {
299 uintptr_t x;
300 int success;
301
302 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
303 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
304 _sx_assert(sx, SA_SLOCKED, file, line);
305
306 /*
307 * Try to switch from one shared lock to an exclusive lock. We need
308 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
309 * we will wake up the exclusive waiters when we drop the lock.
310 */
311 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
312 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
313 (uintptr_t)curthread | x);
314 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
315 if (success)
316 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
317 file, line);
318 return (success);
319 }
320
321 /*
322 * Downgrade an unrecursed exclusive lock into a single shared lock.
323 */
324 void
325 _sx_downgrade(struct sx *sx, const char *file, int line)
326 {
327 uintptr_t x;
328
329 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
330 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
331 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
332 #ifndef INVARIANTS
333 if (sx_recursed(sx))
334 panic("downgrade of a recursed lock");
335 #endif
336
337 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
338
339 /*
340 * Try to switch from an exclusive lock with no shared waiters
341 * to one sharer with no shared waiters. If there are
342 * exclusive waiters, we don't need to lock the sleep queue so
343 * long as we preserve the flag. We do one quick try and if
344 * that fails we grab the sleepq lock to keep the flags from
345 * changing and do it the slow way.
346 *
347 * We have to lock the sleep queue if there are shared waiters
348 * so we can wake them up.
349 */
350 x = sx->sx_lock;
351 if (!(x & SX_LOCK_SHARED_WAITERS) &&
352 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
353 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
354 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
355 return;
356 }
357
358 /*
359 * Lock the sleep queue so we can read the waiters bits
360 * without any races and wakeup any shared waiters.
361 */
362 sleepq_lock(&sx->lock_object);
363
364 /*
365 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
366 * shared lock. If there are any shared waiters, wake them up.
367 */
368 x = sx->sx_lock;
369 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
370 (x & SX_LOCK_EXCLUSIVE_WAITERS));
371 if (x & SX_LOCK_SHARED_WAITERS)
372 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1,
373 SQ_SHARED_QUEUE);
374 else
375 sleepq_release(&sx->lock_object);
376
377 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
378 }
379
380 /*
381 * This function represents the so-called 'hard case' for sx_xlock
382 * operation. All 'easy case' failures are redirected to this. Note
383 * that ideally this would be a static function, but it needs to be
384 * accessible from at least sx.h.
385 */
386 int
387 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
388 int line)
389 {
390 GIANT_DECLARE;
391 #ifdef ADAPTIVE_SX
392 volatile struct thread *owner;
393 #endif
394 /* uint64_t waittime = 0; */
395 uintptr_t x;
396 int /* contested = 0, */error = 0;
397
398 /* If we already hold an exclusive lock, then recurse. */
399 if (sx_xlocked(sx)) {
400 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0,
401 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
402 sx->lock_object.lo_name, file, line));
403 sx->sx_recurse++;
404 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
405 if (LOCK_LOG_TEST(&sx->lock_object, 0))
406 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
407 return (0);
408 }
409
410 if (LOCK_LOG_TEST(&sx->lock_object, 0))
411 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
412 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
413
414 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
415 #ifdef ADAPTIVE_SX
416 /*
417 * If the lock is write locked and the owner is
418 * running on another CPU, spin until the owner stops
419 * running or the state of the lock changes.
420 */
421 x = sx->sx_lock;
422 if (!(x & SX_LOCK_SHARED) &&
423 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
424 x = SX_OWNER(x);
425 owner = (struct thread *)x;
426 if (TD_IS_RUNNING(owner)) {
427 if (LOCK_LOG_TEST(&sx->lock_object, 0))
428 CTR3(KTR_LOCK,
429 "%s: spinning on %p held by %p",
430 __func__, sx, owner);
431 GIANT_SAVE();
432 lock_profile_obtain_lock_failed(
433 &sx->lock_object, &contested, &waittime);
434 while (SX_OWNER(sx->sx_lock) == x &&
435 TD_IS_RUNNING(owner))
436 cpu_spinwait();
437 continue;
438 }
439 }
440 #endif
441
442 sleepq_lock(&sx->lock_object);
443 x = sx->sx_lock;
444
445 /*
446 * If the lock was released while spinning on the
447 * sleep queue chain lock, try again.
448 */
449 if (x == SX_LOCK_UNLOCKED) {
450 sleepq_release(&sx->lock_object);
451 continue;
452 }
453
454 #ifdef ADAPTIVE_SX
455 /*
456 * The current lock owner might have started executing
457 * on another CPU (or the lock could have changed
458 * owners) while we were waiting on the sleep queue
459 * chain lock. If so, drop the sleep queue lock and try
460 * again.
461 */
462 if (!(x & SX_LOCK_SHARED) &&
463 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
464 owner = (struct thread *)SX_OWNER(x);
465 if (TD_IS_RUNNING(owner)) {
466 sleepq_release(&sx->lock_object);
467 continue;
468 }
469 }
470 #endif
471
472 /*
473 * If an exclusive lock was released with both shared
474 * and exclusive waiters and a shared waiter hasn't
475 * woken up and acquired the lock yet, sx_lock will be
476 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
477 * If we see that value, try to acquire it once. Note
478 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
479 * as there are other exclusive waiters still. If we
480 * fail, restart the loop.
481 */
482 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
483 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
484 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
485 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
486 sleepq_release(&sx->lock_object);
487 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
488 __func__, sx);
489 break;
490 }
491 sleepq_release(&sx->lock_object);
492 continue;
493 }
494
495 /*
496 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
497 * than loop back and retry.
498 */
499 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
500 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
501 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
502 sleepq_release(&sx->lock_object);
503 continue;
504 }
505 if (LOCK_LOG_TEST(&sx->lock_object, 0))
506 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
507 __func__, sx);
508 }
509
510 /*
511 * Since we have been unable to acquire the exclusive
512 * lock and the exclusive waiters flag is set, we have
513 * to sleep.
514 */
515 if (LOCK_LOG_TEST(&sx->lock_object, 0))
516 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
517 __func__, sx);
518
519 GIANT_SAVE();
520 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
521 &waittime);
522 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
523 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
524 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
525 if (!(opts & SX_INTERRUPTIBLE))
526 sleepq_wait(&sx->lock_object);
527 else
528 error = sleepq_wait_sig(&sx->lock_object);
529
530 if (error) {
531 if (LOCK_LOG_TEST(&sx->lock_object, 0))
532 CTR2(KTR_LOCK,
533 "%s: interruptible sleep by %p suspended by signal",
534 __func__, sx);
535 break;
536 }
537 if (LOCK_LOG_TEST(&sx->lock_object, 0))
538 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
539 __func__, sx);
540 }
541
542 GIANT_RESTORE();
543 if (!error)
544 lock_profile_obtain_lock_success(&sx->lock_object, contested,
545 waittime, file, line);
546 return (error);
547 }
548
549 /*
550 * This function represents the so-called 'hard case' for sx_xunlock
551 * operation. All 'easy case' failures are redirected to this. Note
552 * that ideally this would be a static function, but it needs to be
553 * accessible from at least sx.h.
554 */
555 void
556 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
557 {
558 uintptr_t x;
559 int queue;
560
561 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
562
563 /* If the lock is recursed, then unrecurse one level. */
564 if (sx_xlocked(sx) && sx_recursed(sx)) {
565 if ((--sx->sx_recurse) == 0)
566 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
567 if (LOCK_LOG_TEST(&sx->lock_object, 0))
568 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
569 return;
570 }
571 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
572 SX_LOCK_EXCLUSIVE_WAITERS));
573 if (LOCK_LOG_TEST(&sx->lock_object, 0))
574 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
575
576 sleepq_lock(&sx->lock_object);
577 x = SX_LOCK_UNLOCKED;
578
579 /*
580 * The wake up algorithm here is quite simple and probably not
581 * ideal. It gives precedence to shared waiters if they are
582 * present. For this condition, we have to preserve the
583 * state of the exclusive waiters flag.
584 */
585 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) {
586 queue = SQ_SHARED_QUEUE;
587 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
588 } else
589 queue = SQ_EXCLUSIVE_QUEUE;
590
591 /* Wake up all the waiters for the specific queue. */
592 if (LOCK_LOG_TEST(&sx->lock_object, 0))
593 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
594 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
595 "exclusive");
596 atomic_store_rel_ptr(&sx->sx_lock, x);
597 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, queue);
598 }
599
600 /*
601 * This function represents the so-called 'hard case' for sx_slock
602 * operation. All 'easy case' failures are redirected to this. Note
603 * that ideally this would be a static function, but it needs to be
604 * accessible from at least sx.h.
605 */
606 int
607 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
608 {
609 GIANT_DECLARE;
610 #ifdef ADAPTIVE_SX
611 volatile struct thread *owner;
612 #endif
613 #ifdef LOCK_PROFILING_SHARED
614 uint64_t waittime = 0;
615 int contested = 0;
616 #endif
617 uintptr_t x;
618 int error = 0;
619
620 /*
621 * As with rwlocks, we don't make any attempt to try to block
622 * shared locks once there is an exclusive waiter.
623 */
624 for (;;) {
625 x = sx->sx_lock;
626
627 /*
628 * If no other thread has an exclusive lock then try to bump up
629 * the count of sharers. Since we have to preserve the state
630 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
631 * shared lock loop back and retry.
632 */
633 if (x & SX_LOCK_SHARED) {
634 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
635 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
636 x + SX_ONE_SHARER)) {
637 #ifdef LOCK_PROFILING_SHARED
638 if (SX_SHARERS(x) == 0)
639 lock_profile_obtain_lock_success(
640 &sx->lock_object, contested,
641 waittime, file, line);
642 #endif
643 if (LOCK_LOG_TEST(&sx->lock_object, 0))
644 CTR4(KTR_LOCK,
645 "%s: %p succeed %p -> %p", __func__,
646 sx, (void *)x,
647 (void *)(x + SX_ONE_SHARER));
648 break;
649 }
650 continue;
651 }
652
653 #ifdef ADAPTIVE_SX
654 /*
655 * If the owner is running on another CPU, spin until
656 * the owner stops running or the state of the lock
657 * changes.
658 */
659 else if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) {
660 x = SX_OWNER(x);
661 owner = (struct thread *)x;
662 if (TD_IS_RUNNING(owner)) {
663 if (LOCK_LOG_TEST(&sx->lock_object, 0))
664 CTR3(KTR_LOCK,
665 "%s: spinning on %p held by %p",
666 __func__, sx, owner);
667 GIANT_SAVE();
668 #ifdef LOCK_PROFILING_SHARED
669 lock_profile_obtain_lock_failed(
670 &sx->lock_object, &contested, &waittime);
671 #endif
672 while (SX_OWNER(sx->sx_lock) == x &&
673 TD_IS_RUNNING(owner))
674 cpu_spinwait();
675 continue;
676 }
677 }
678 #endif
679
680 /*
681 * Some other thread already has an exclusive lock, so
682 * start the process of blocking.
683 */
684 sleepq_lock(&sx->lock_object);
685 x = sx->sx_lock;
686
687 /*
688 * The lock could have been released while we spun.
689 * In this case loop back and retry.
690 */
691 if (x & SX_LOCK_SHARED) {
692 sleepq_release(&sx->lock_object);
693 continue;
694 }
695
696 #ifdef ADAPTIVE_SX
697 /*
698 * If the owner is running on another CPU, spin until
699 * the owner stops running or the state of the lock
700 * changes.
701 */
702 if (!(x & SX_LOCK_SHARED) &&
703 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
704 owner = (struct thread *)SX_OWNER(x);
705 if (TD_IS_RUNNING(owner)) {
706 sleepq_release(&sx->lock_object);
707 continue;
708 }
709 }
710 #endif
711
712 /*
713 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
714 * fail to set it drop the sleep queue lock and loop
715 * back.
716 */
717 if (!(x & SX_LOCK_SHARED_WAITERS)) {
718 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
719 x | SX_LOCK_SHARED_WAITERS)) {
720 sleepq_release(&sx->lock_object);
721 continue;
722 }
723 if (LOCK_LOG_TEST(&sx->lock_object, 0))
724 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
725 __func__, sx);
726 }
727
728 /*
729 * Since we have been unable to acquire the shared lock,
730 * we have to sleep.
731 */
732 if (LOCK_LOG_TEST(&sx->lock_object, 0))
733 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
734 __func__, sx);
735
736 GIANT_SAVE();
737 #ifdef LOCK_PROFILING_SHARED
738 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
739 &waittime);
740 #endif
741 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
742 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
743 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
744 if (!(opts & SX_INTERRUPTIBLE))
745 sleepq_wait(&sx->lock_object);
746 else
747 error = sleepq_wait_sig(&sx->lock_object);
748
749 if (error) {
750 if (LOCK_LOG_TEST(&sx->lock_object, 0))
751 CTR2(KTR_LOCK,
752 "%s: interruptible sleep by %p suspended by signal",
753 __func__, sx);
754 break;
755 }
756 if (LOCK_LOG_TEST(&sx->lock_object, 0))
757 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
758 __func__, sx);
759 }
760
761 GIANT_RESTORE();
762 return (error);
763 }
764
765 /*
766 * This function represents the so-called 'hard case' for sx_sunlock
767 * operation. All 'easy case' failures are redirected to this. Note
768 * that ideally this would be a static function, but it needs to be
769 * accessible from at least sx.h.
770 */
771 void
772 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
773 {
774 uintptr_t x;
775
776 for (;;) {
777 x = sx->sx_lock;
778
779 /*
780 * We should never have sharers while at least one thread
781 * holds a shared lock.
782 */
783 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
784 ("%s: waiting sharers", __func__));
785
786 /*
787 * See if there is more than one shared lock held. If
788 * so, just drop one and return.
789 */
790 if (SX_SHARERS(x) > 1) {
791 if (atomic_cmpset_ptr(&sx->sx_lock, x,
792 x - SX_ONE_SHARER)) {
793 if (LOCK_LOG_TEST(&sx->lock_object, 0))
794 CTR4(KTR_LOCK,
795 "%s: %p succeeded %p -> %p",
796 __func__, sx, (void *)x,
797 (void *)(x - SX_ONE_SHARER));
798 break;
799 }
800 continue;
801 }
802
803 /*
804 * If there aren't any waiters for an exclusive lock,
805 * then try to drop it quickly.
806 */
807 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
808 MPASS(x == SX_SHARERS_LOCK(1));
809 if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1),
810 SX_LOCK_UNLOCKED)) {
811 if (LOCK_LOG_TEST(&sx->lock_object, 0))
812 CTR2(KTR_LOCK, "%s: %p last succeeded",
813 __func__, sx);
814 break;
815 }
816 continue;
817 }
818
819 /*
820 * At this point, there should just be one sharer with
821 * exclusive waiters.
822 */
823 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
824
825 sleepq_lock(&sx->lock_object);
826
827 /*
828 * Wake up semantic here is quite simple:
829 * Just wake up all the exclusive waiters.
830 * Note that the state of the lock could have changed,
831 * so if it fails loop back and retry.
832 */
833 if (!atomic_cmpset_ptr(&sx->sx_lock,
834 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
835 SX_LOCK_UNLOCKED)) {
836 sleepq_release(&sx->lock_object);
837 continue;
838 }
839 if (LOCK_LOG_TEST(&sx->lock_object, 0))
840 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
841 "exclusive queue", __func__, sx);
842 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1,
843 SQ_EXCLUSIVE_QUEUE);
844 break;
845 }
846 }
847
848 /*
849 * Atomically drop an sx lock while going to sleep. This is just a hack
850 * for 6.x. In 7.0 and later this is done more cleanly.
851 */
852 int
853 sx_sleep(void *ident, struct sx *sx, int priority, const char *wmesg, int timo)
854 {
855 struct thread *td;
856 struct proc *p;
857 int catch, rval, flags, xlocked;
858 WITNESS_SAVE_DECL(sx_witness);
859
860 td = curthread;
861 p = td->td_proc;
862 #ifdef KTRACE
863 if (KTRPOINT(td, KTR_CSW))
864 ktrcsw(1, 0);
865 #endif
866 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL,
867 "Sleeping on \"%s\"", wmesg);
868 KASSERT(sx != NULL, ("sx_sleep w/o an sx lock"));
869 KASSERT(ident != NULL && TD_IS_RUNNING(td), ("sx_sleep"));
870
871 if (cold) {
872 /*
873 * During autoconfiguration, just return;
874 * don't run any other threads or panic below,
875 * in case this is the idle thread and already asleep.
876 * XXX: this used to do "s = splhigh(); splx(safepri);
877 * splx(s);" to give interrupts a chance, but there is
878 * no way to give interrupts a chance now.
879 */
880 if (priority & PDROP)
881 sx_unlock(sx);
882 return (0);
883 }
884 catch = priority & PCATCH;
885 rval = 0;
886
887 /*
888 * If we are already on a sleep queue, then remove us from that
889 * sleep queue first. We have to do this to handle recursive
890 * sleeps.
891 */
892 if (TD_ON_SLEEPQ(td))
893 sleepq_remove(td, td->td_wchan);
894
895 flags = SLEEPQ_MSLEEP;
896 if (catch)
897 flags |= SLEEPQ_INTERRUPTIBLE;
898
899 sleepq_lock(ident);
900 CTR5(KTR_PROC, "sx_sleep: thread %p (pid %ld, %s) on %s (%p)",
901 (void *)td, (long)p->p_pid, p->p_comm, wmesg, ident);
902
903 DROP_GIANT();
904
905 /*
906 * We put ourselves on the sleep queue and start our timeout
907 * before calling thread_suspend_check, as we could stop there,
908 * and a wakeup or a SIGCONT (or both) could occur while we were
909 * stopped without resuming us. Thus, we must be ready for sleep
910 * when cursig() is called. If the wakeup happens while we're
911 * stopped, then td will no longer be on a sleep queue upon
912 * return from cursig().
913 */
914 sleepq_add(ident, &sx->lock_object, wmesg, flags, 0);
915 if (timo)
916 sleepq_set_timeout(ident, timo);
917
918 /*
919 * Now that we are on the queue, drop the sleepq lock so we
920 * can safely unlock the sx lock.
921 */
922 sleepq_release(ident);
923 WITNESS_SAVE(&sx->lock_object, sx_witness);
924 xlocked = sx_xlocked(sx);
925 if (xlocked)
926 sx_xunlock(sx);
927 else
928 sx_sunlock(sx);
929 sleepq_lock(ident);
930
931 /*
932 * Adjust this thread's priority.
933 */
934 if ((priority & PRIMASK) != 0) {
935 mtx_lock_spin(&sched_lock);
936 sched_prio(td, priority & PRIMASK);
937 mtx_unlock_spin(&sched_lock);
938 }
939
940 if (timo && catch)
941 rval = sleepq_timedwait_sig(ident);
942 else if (timo)
943 rval = sleepq_timedwait(ident);
944 else if (catch)
945 rval = sleepq_wait_sig(ident);
946 else {
947 sleepq_wait(ident);
948 rval = 0;
949 }
950 #ifdef KTRACE
951 if (KTRPOINT(td, KTR_CSW))
952 ktrcsw(0, 0);
953 #endif
954 PICKUP_GIANT();
955 if (!(priority & PDROP)) {
956 if (xlocked)
957 sx_xlock(sx);
958 else
959 sx_slock(sx);
960 WITNESS_RESTORE(&sx->lock_object, sx_witness);
961 }
962 return (rval);
963 }
964
965 #ifdef INVARIANT_SUPPORT
966 #ifndef INVARIANTS
967 #undef _sx_assert
968 #endif
969
970 /*
971 * In the non-WITNESS case, sx_assert() can only detect that at least
972 * *some* thread owns an slock, but it cannot guarantee that *this*
973 * thread owns an slock.
974 */
975 void
976 _sx_assert(struct sx *sx, int what, const char *file, int line)
977 {
978 #ifndef WITNESS
979 int slocked = 0;
980 #endif
981
982 if (panicstr != NULL)
983 return;
984 switch (what) {
985 case SA_SLOCKED:
986 case SA_SLOCKED | SA_NOTRECURSED:
987 case SA_SLOCKED | SA_RECURSED:
988 #ifndef WITNESS
989 slocked = 1;
990 /* FALLTHROUGH */
991 #endif
992 case SA_LOCKED:
993 case SA_LOCKED | SA_NOTRECURSED:
994 case SA_LOCKED | SA_RECURSED:
995 #ifdef WITNESS
996 witness_assert(&sx->lock_object, what, file, line);
997 #else
998 /*
999 * If some other thread has an exclusive lock or we
1000 * have one and are asserting a shared lock, fail.
1001 * Also, if no one has a lock at all, fail.
1002 */
1003 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1004 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1005 sx_xholder(sx) != curthread)))
1006 panic("Lock %s not %slocked @ %s:%d\n",
1007 sx->lock_object.lo_name, slocked ? "share " : "",
1008 file, line);
1009
1010 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1011 if (sx_recursed(sx)) {
1012 if (what & SA_NOTRECURSED)
1013 panic("Lock %s recursed @ %s:%d\n",
1014 sx->lock_object.lo_name, file,
1015 line);
1016 } else if (what & SA_RECURSED)
1017 panic("Lock %s not recursed @ %s:%d\n",
1018 sx->lock_object.lo_name, file, line);
1019 }
1020 #endif
1021 break;
1022 case SA_XLOCKED:
1023 case SA_XLOCKED | SA_NOTRECURSED:
1024 case SA_XLOCKED | SA_RECURSED:
1025 if (sx_xholder(sx) != curthread)
1026 panic("Lock %s not exclusively locked @ %s:%d\n",
1027 sx->lock_object.lo_name, file, line);
1028 if (sx_recursed(sx)) {
1029 if (what & SA_NOTRECURSED)
1030 panic("Lock %s recursed @ %s:%d\n",
1031 sx->lock_object.lo_name, file, line);
1032 } else if (what & SA_RECURSED)
1033 panic("Lock %s not recursed @ %s:%d\n",
1034 sx->lock_object.lo_name, file, line);
1035 break;
1036 case SA_UNLOCKED:
1037 #ifdef WITNESS
1038 witness_assert(&sx->lock_object, what, file, line);
1039 #else
1040 /*
1041 * If we hold an exclusve lock fail. We can't
1042 * reliably check to see if we hold a shared lock or
1043 * not.
1044 */
1045 if (sx_xholder(sx) == curthread)
1046 panic("Lock %s exclusively locked @ %s:%d\n",
1047 sx->lock_object.lo_name, file, line);
1048 #endif
1049 break;
1050 default:
1051 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1052 line);
1053 }
1054 }
1055 #endif /* INVARIANT_SUPPORT */
1056
1057 #ifdef DDB
1058 static void
1059 db_show_sx(struct lock_object *lock)
1060 {
1061 struct thread *td;
1062 struct sx *sx;
1063
1064 sx = (struct sx *)lock;
1065
1066 db_printf(" state: ");
1067 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1068 db_printf("UNLOCKED\n");
1069 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1070 db_printf("DESTROYED\n");
1071 return;
1072 } else if (sx->sx_lock & SX_LOCK_SHARED)
1073 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1074 else {
1075 td = sx_xholder(sx);
1076 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1077 td->td_tid, td->td_proc->p_pid, td->td_proc->p_comm);
1078 if (sx_recursed(sx))
1079 db_printf(" recursed: %d\n", sx->sx_recurse);
1080 }
1081
1082 db_printf(" waiters: ");
1083 switch(sx->sx_lock &
1084 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1085 case SX_LOCK_SHARED_WAITERS:
1086 db_printf("shared\n");
1087 break;
1088 case SX_LOCK_EXCLUSIVE_WAITERS:
1089 db_printf("exclusive\n");
1090 break;
1091 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1092 db_printf("exclusive and shared\n");
1093 break;
1094 default:
1095 db_printf("none\n");
1096 }
1097 }
1098
1099 /*
1100 * Check to see if a thread that is blocked on a sleep queue is actually
1101 * blocked on an sx lock. If so, output some details and return true.
1102 * If the lock has an exclusive owner, return that in *ownerp.
1103 */
1104 int
1105 sx_chain(struct thread *td, struct thread **ownerp)
1106 {
1107 struct sx *sx;
1108
1109 /*
1110 * Check to see if this thread is blocked on an sx lock.
1111 * First, we check the lock class. If that is ok, then we
1112 * compare the lock name against the wait message.
1113 */
1114 sx = td->td_wchan;
1115 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1116 sx->lock_object.lo_name != td->td_wmesg)
1117 return (0);
1118
1119 /* We think we have an sx lock, so output some details. */
1120 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1121 *ownerp = sx_xholder(sx);
1122 if (sx->sx_lock & SX_LOCK_SHARED)
1123 db_printf("SLOCK (count %ju)\n",
1124 (uintmax_t)SX_SHARERS(sx->sx_lock));
1125 else
1126 db_printf("XLOCK\n");
1127 return (1);
1128 }
1129 #endif
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