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_ddb.h"
40 #include "opt_hwpmc_hooks.h"
41 #include "opt_kdtrace.h"
42 #include "opt_no_adaptive_sx.h"
43
44 #include <sys/cdefs.h>
45 __FBSDID("$FreeBSD: releng/9.2/sys/kern/kern_sx.c 250581 2013-05-12 22:01:22Z hiren $");
46
47 #include <sys/param.h>
48 #include <sys/systm.h>
49 #include <sys/ktr.h>
50 #include <sys/lock.h>
51 #include <sys/mutex.h>
52 #include <sys/proc.h>
53 #include <sys/sleepqueue.h>
54 #include <sys/sx.h>
55 #include <sys/sysctl.h>
56
57 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
58 #include <machine/cpu.h>
59 #endif
60
61 #ifdef DDB
62 #include <ddb/ddb.h>
63 #endif
64
65 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
66 #define ADAPTIVE_SX
67 #endif
68
69 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
70
71 #ifdef HWPMC_HOOKS
72 #include <sys/pmckern.h>
73 PMC_SOFT_DECLARE( , , lock, failed);
74 #endif
75
76 /* Handy macros for sleep queues. */
77 #define SQ_EXCLUSIVE_QUEUE 0
78 #define SQ_SHARED_QUEUE 1
79
80 #ifdef ADAPTIVE_SX
81 #define ASX_RETRIES 10
82 #define ASX_LOOPS 10000
83 #endif
84
85 /*
86 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
87 * drop Giant anytime we have to sleep or if we adaptively spin.
88 */
89 #define GIANT_DECLARE \
90 int _giantcnt = 0; \
91 WITNESS_SAVE_DECL(Giant) \
92
93 #define GIANT_SAVE() do { \
94 if (mtx_owned(&Giant)) { \
95 WITNESS_SAVE(&Giant.lock_object, Giant); \
96 while (mtx_owned(&Giant)) { \
97 _giantcnt++; \
98 mtx_unlock(&Giant); \
99 } \
100 } \
101 } while (0)
102
103 #define GIANT_RESTORE() do { \
104 if (_giantcnt > 0) { \
105 mtx_assert(&Giant, MA_NOTOWNED); \
106 while (_giantcnt--) \
107 mtx_lock(&Giant); \
108 WITNESS_RESTORE(&Giant.lock_object, Giant); \
109 } \
110 } while (0)
111
112 /*
113 * Returns true if an exclusive lock is recursed. It assumes
114 * curthread currently has an exclusive lock.
115 */
116 #define sx_recurse lock_object.lo_data
117 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
118
119 static void assert_sx(struct lock_object *lock, int what);
120 #ifdef DDB
121 static void db_show_sx(struct lock_object *lock);
122 #endif
123 static void lock_sx(struct lock_object *lock, int how);
124 #ifdef KDTRACE_HOOKS
125 static int owner_sx(struct lock_object *lock, struct thread **owner);
126 #endif
127 static int unlock_sx(struct lock_object *lock);
128
129 struct lock_class lock_class_sx = {
130 .lc_name = "sx",
131 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
132 .lc_assert = assert_sx,
133 #ifdef DDB
134 .lc_ddb_show = db_show_sx,
135 #endif
136 .lc_lock = lock_sx,
137 .lc_unlock = unlock_sx,
138 #ifdef KDTRACE_HOOKS
139 .lc_owner = owner_sx,
140 #endif
141 };
142
143 #ifndef INVARIANTS
144 #define _sx_assert(sx, what, file, line)
145 #endif
146
147 void
148 assert_sx(struct lock_object *lock, int what)
149 {
150
151 sx_assert((struct sx *)lock, what);
152 }
153
154 void
155 lock_sx(struct lock_object *lock, int how)
156 {
157 struct sx *sx;
158
159 sx = (struct sx *)lock;
160 if (how)
161 sx_xlock(sx);
162 else
163 sx_slock(sx);
164 }
165
166 int
167 unlock_sx(struct lock_object *lock)
168 {
169 struct sx *sx;
170
171 sx = (struct sx *)lock;
172 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
173 if (sx_xlocked(sx)) {
174 sx_xunlock(sx);
175 return (1);
176 } else {
177 sx_sunlock(sx);
178 return (0);
179 }
180 }
181
182 #ifdef KDTRACE_HOOKS
183 int
184 owner_sx(struct lock_object *lock, struct thread **owner)
185 {
186 struct sx *sx = (struct sx *)lock;
187 uintptr_t x = sx->sx_lock;
188
189 *owner = (struct thread *)SX_OWNER(x);
190 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
191 (*owner != NULL));
192 }
193 #endif
194
195 void
196 sx_sysinit(void *arg)
197 {
198 struct sx_args *sargs = arg;
199
200 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
201 }
202
203 void
204 sx_init_flags(struct sx *sx, const char *description, int opts)
205 {
206 int flags;
207
208 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
209 SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
210 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
211 ("%s: sx_lock not aligned for %s: %p", __func__, description,
212 &sx->sx_lock));
213
214 flags = LO_SLEEPABLE | LO_UPGRADABLE;
215 if (opts & SX_DUPOK)
216 flags |= LO_DUPOK;
217 if (opts & SX_NOPROFILE)
218 flags |= LO_NOPROFILE;
219 if (!(opts & SX_NOWITNESS))
220 flags |= LO_WITNESS;
221 if (opts & SX_RECURSE)
222 flags |= LO_RECURSABLE;
223 if (opts & SX_QUIET)
224 flags |= LO_QUIET;
225
226 flags |= opts & SX_NOADAPTIVE;
227 sx->sx_lock = SX_LOCK_UNLOCKED;
228 sx->sx_recurse = 0;
229 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
230 }
231
232 void
233 sx_destroy(struct sx *sx)
234 {
235
236 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
237 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
238 sx->sx_lock = SX_LOCK_DESTROYED;
239 lock_destroy(&sx->lock_object);
240 }
241
242 int
243 _sx_slock(struct sx *sx, int opts, const char *file, int line)
244 {
245 int error = 0;
246
247 if (SCHEDULER_STOPPED())
248 return (0);
249 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
250 ("sx_slock() of destroyed sx @ %s:%d", file, line));
251 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
252 error = __sx_slock(sx, opts, file, line);
253 if (!error) {
254 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
255 WITNESS_LOCK(&sx->lock_object, 0, file, line);
256 curthread->td_locks++;
257 }
258
259 return (error);
260 }
261
262 int
263 _sx_try_slock(struct sx *sx, const char *file, int line)
264 {
265 uintptr_t x;
266
267 if (SCHEDULER_STOPPED())
268 return (1);
269
270 for (;;) {
271 x = sx->sx_lock;
272 KASSERT(x != SX_LOCK_DESTROYED,
273 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
274 if (!(x & SX_LOCK_SHARED))
275 break;
276 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
277 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
278 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
279 curthread->td_locks++;
280 return (1);
281 }
282 }
283
284 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
285 return (0);
286 }
287
288 int
289 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
290 {
291 int error = 0;
292
293 if (SCHEDULER_STOPPED())
294 return (0);
295 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
296 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
297 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
298 line, NULL);
299 error = __sx_xlock(sx, curthread, opts, file, line);
300 if (!error) {
301 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
302 file, line);
303 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
304 curthread->td_locks++;
305 }
306
307 return (error);
308 }
309
310 int
311 _sx_try_xlock(struct sx *sx, const char *file, int line)
312 {
313 int rval;
314
315 if (SCHEDULER_STOPPED())
316 return (1);
317
318 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
319 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
320
321 if (sx_xlocked(sx) &&
322 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
323 sx->sx_recurse++;
324 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
325 rval = 1;
326 } else
327 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
328 (uintptr_t)curthread);
329 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
330 if (rval) {
331 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
332 file, line);
333 curthread->td_locks++;
334 }
335
336 return (rval);
337 }
338
339 void
340 _sx_sunlock(struct sx *sx, const char *file, int line)
341 {
342
343 if (SCHEDULER_STOPPED())
344 return;
345 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
346 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
347 _sx_assert(sx, SA_SLOCKED, file, line);
348 curthread->td_locks--;
349 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
350 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
351 __sx_sunlock(sx, file, line);
352 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
353 }
354
355 void
356 _sx_xunlock(struct sx *sx, const char *file, int line)
357 {
358
359 if (SCHEDULER_STOPPED())
360 return;
361 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
362 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
363 _sx_assert(sx, SA_XLOCKED, file, line);
364 curthread->td_locks--;
365 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
366 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
367 line);
368 if (!sx_recursed(sx))
369 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
370 __sx_xunlock(sx, curthread, file, line);
371 }
372
373 /*
374 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
375 * This will only succeed if this thread holds a single shared lock.
376 * Return 1 if if the upgrade succeed, 0 otherwise.
377 */
378 int
379 _sx_try_upgrade(struct sx *sx, const char *file, int line)
380 {
381 uintptr_t x;
382 int success;
383
384 if (SCHEDULER_STOPPED())
385 return (1);
386
387 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
388 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
389 _sx_assert(sx, SA_SLOCKED, file, line);
390
391 /*
392 * Try to switch from one shared lock to an exclusive lock. We need
393 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
394 * we will wake up the exclusive waiters when we drop the lock.
395 */
396 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
397 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
398 (uintptr_t)curthread | x);
399 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
400 if (success) {
401 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
402 file, line);
403 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
404 }
405 return (success);
406 }
407
408 /*
409 * Downgrade an unrecursed exclusive lock into a single shared lock.
410 */
411 void
412 _sx_downgrade(struct sx *sx, const char *file, int line)
413 {
414 uintptr_t x;
415 int wakeup_swapper;
416
417 if (SCHEDULER_STOPPED())
418 return;
419
420 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
421 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
422 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
423 #ifndef INVARIANTS
424 if (sx_recursed(sx))
425 panic("downgrade of a recursed lock");
426 #endif
427
428 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
429
430 /*
431 * Try to switch from an exclusive lock with no shared waiters
432 * to one sharer with no shared waiters. If there are
433 * exclusive waiters, we don't need to lock the sleep queue so
434 * long as we preserve the flag. We do one quick try and if
435 * that fails we grab the sleepq lock to keep the flags from
436 * changing and do it the slow way.
437 *
438 * We have to lock the sleep queue if there are shared waiters
439 * so we can wake them up.
440 */
441 x = sx->sx_lock;
442 if (!(x & SX_LOCK_SHARED_WAITERS) &&
443 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
444 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
445 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
446 return;
447 }
448
449 /*
450 * Lock the sleep queue so we can read the waiters bits
451 * without any races and wakeup any shared waiters.
452 */
453 sleepq_lock(&sx->lock_object);
454
455 /*
456 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
457 * shared lock. If there are any shared waiters, wake them up.
458 */
459 wakeup_swapper = 0;
460 x = sx->sx_lock;
461 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
462 (x & SX_LOCK_EXCLUSIVE_WAITERS));
463 if (x & SX_LOCK_SHARED_WAITERS)
464 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
465 0, SQ_SHARED_QUEUE);
466 sleepq_release(&sx->lock_object);
467
468 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
469 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
470
471 if (wakeup_swapper)
472 kick_proc0();
473 }
474
475 /*
476 * This function represents the so-called 'hard case' for sx_xlock
477 * operation. All 'easy case' failures are redirected to this. Note
478 * that ideally this would be a static function, but it needs to be
479 * accessible from at least sx.h.
480 */
481 int
482 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
483 int line)
484 {
485 GIANT_DECLARE;
486 #ifdef ADAPTIVE_SX
487 volatile struct thread *owner;
488 u_int i, spintries = 0;
489 #endif
490 uintptr_t x;
491 #ifdef LOCK_PROFILING
492 uint64_t waittime = 0;
493 int contested = 0;
494 #endif
495 int error = 0;
496 #ifdef KDTRACE_HOOKS
497 uint64_t spin_cnt = 0;
498 uint64_t sleep_cnt = 0;
499 int64_t sleep_time = 0;
500 #endif
501
502 if (SCHEDULER_STOPPED())
503 return (0);
504
505 /* If we already hold an exclusive lock, then recurse. */
506 if (sx_xlocked(sx)) {
507 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
508 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
509 sx->lock_object.lo_name, file, line));
510 sx->sx_recurse++;
511 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
512 if (LOCK_LOG_TEST(&sx->lock_object, 0))
513 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
514 return (0);
515 }
516
517 if (LOCK_LOG_TEST(&sx->lock_object, 0))
518 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
519 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
520
521 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
522 #ifdef KDTRACE_HOOKS
523 spin_cnt++;
524 #endif
525 #ifdef HWPMC_HOOKS
526 PMC_SOFT_CALL( , , lock, failed);
527 #endif
528 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
529 &waittime);
530 #ifdef ADAPTIVE_SX
531 /*
532 * If the lock is write locked and the owner is
533 * running on another CPU, spin until the owner stops
534 * running or the state of the lock changes.
535 */
536 x = sx->sx_lock;
537 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
538 if ((x & SX_LOCK_SHARED) == 0) {
539 x = SX_OWNER(x);
540 owner = (struct thread *)x;
541 if (TD_IS_RUNNING(owner)) {
542 if (LOCK_LOG_TEST(&sx->lock_object, 0))
543 CTR3(KTR_LOCK,
544 "%s: spinning on %p held by %p",
545 __func__, sx, owner);
546 GIANT_SAVE();
547 while (SX_OWNER(sx->sx_lock) == x &&
548 TD_IS_RUNNING(owner)) {
549 cpu_spinwait();
550 #ifdef KDTRACE_HOOKS
551 spin_cnt++;
552 #endif
553 }
554 continue;
555 }
556 } else if (SX_SHARERS(x) && spintries < ASX_RETRIES) {
557 GIANT_SAVE();
558 spintries++;
559 for (i = 0; i < ASX_LOOPS; i++) {
560 if (LOCK_LOG_TEST(&sx->lock_object, 0))
561 CTR4(KTR_LOCK,
562 "%s: shared spinning on %p with %u and %u",
563 __func__, sx, spintries, i);
564 x = sx->sx_lock;
565 if ((x & SX_LOCK_SHARED) == 0 ||
566 SX_SHARERS(x) == 0)
567 break;
568 cpu_spinwait();
569 #ifdef KDTRACE_HOOKS
570 spin_cnt++;
571 #endif
572 }
573 if (i != ASX_LOOPS)
574 continue;
575 }
576 }
577 #endif
578
579 sleepq_lock(&sx->lock_object);
580 x = sx->sx_lock;
581
582 /*
583 * If the lock was released while spinning on the
584 * sleep queue chain lock, try again.
585 */
586 if (x == SX_LOCK_UNLOCKED) {
587 sleepq_release(&sx->lock_object);
588 continue;
589 }
590
591 #ifdef ADAPTIVE_SX
592 /*
593 * The current lock owner might have started executing
594 * on another CPU (or the lock could have changed
595 * owners) while we were waiting on the sleep queue
596 * chain lock. If so, drop the sleep queue lock and try
597 * again.
598 */
599 if (!(x & SX_LOCK_SHARED) &&
600 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
601 owner = (struct thread *)SX_OWNER(x);
602 if (TD_IS_RUNNING(owner)) {
603 sleepq_release(&sx->lock_object);
604 continue;
605 }
606 }
607 #endif
608
609 /*
610 * If an exclusive lock was released with both shared
611 * and exclusive waiters and a shared waiter hasn't
612 * woken up and acquired the lock yet, sx_lock will be
613 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
614 * If we see that value, try to acquire it once. Note
615 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
616 * as there are other exclusive waiters still. If we
617 * fail, restart the loop.
618 */
619 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
620 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
621 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
622 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
623 sleepq_release(&sx->lock_object);
624 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
625 __func__, sx);
626 break;
627 }
628 sleepq_release(&sx->lock_object);
629 continue;
630 }
631
632 /*
633 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
634 * than loop back and retry.
635 */
636 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
637 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
638 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
639 sleepq_release(&sx->lock_object);
640 continue;
641 }
642 if (LOCK_LOG_TEST(&sx->lock_object, 0))
643 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
644 __func__, sx);
645 }
646
647 /*
648 * Since we have been unable to acquire the exclusive
649 * lock and the exclusive waiters flag is set, we have
650 * to sleep.
651 */
652 if (LOCK_LOG_TEST(&sx->lock_object, 0))
653 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
654 __func__, sx);
655
656 #ifdef KDTRACE_HOOKS
657 sleep_time -= lockstat_nsecs();
658 #endif
659 GIANT_SAVE();
660 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
661 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
662 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
663 if (!(opts & SX_INTERRUPTIBLE))
664 sleepq_wait(&sx->lock_object, 0);
665 else
666 error = sleepq_wait_sig(&sx->lock_object, 0);
667 #ifdef KDTRACE_HOOKS
668 sleep_time += lockstat_nsecs();
669 sleep_cnt++;
670 #endif
671 if (error) {
672 if (LOCK_LOG_TEST(&sx->lock_object, 0))
673 CTR2(KTR_LOCK,
674 "%s: interruptible sleep by %p suspended by signal",
675 __func__, sx);
676 break;
677 }
678 if (LOCK_LOG_TEST(&sx->lock_object, 0))
679 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
680 __func__, sx);
681 }
682
683 GIANT_RESTORE();
684 if (!error)
685 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
686 contested, waittime, file, line);
687 #ifdef KDTRACE_HOOKS
688 if (sleep_time)
689 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
690 if (spin_cnt > sleep_cnt)
691 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
692 #endif
693 return (error);
694 }
695
696 /*
697 * This function represents the so-called 'hard case' for sx_xunlock
698 * operation. All 'easy case' failures are redirected to this. Note
699 * that ideally this would be a static function, but it needs to be
700 * accessible from at least sx.h.
701 */
702 void
703 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
704 {
705 uintptr_t x;
706 int queue, wakeup_swapper;
707
708 if (SCHEDULER_STOPPED())
709 return;
710
711 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
712
713 /* If the lock is recursed, then unrecurse one level. */
714 if (sx_xlocked(sx) && sx_recursed(sx)) {
715 if ((--sx->sx_recurse) == 0)
716 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
717 if (LOCK_LOG_TEST(&sx->lock_object, 0))
718 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
719 return;
720 }
721 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
722 SX_LOCK_EXCLUSIVE_WAITERS));
723 if (LOCK_LOG_TEST(&sx->lock_object, 0))
724 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
725
726 sleepq_lock(&sx->lock_object);
727 x = SX_LOCK_UNLOCKED;
728
729 /*
730 * The wake up algorithm here is quite simple and probably not
731 * ideal. It gives precedence to shared waiters if they are
732 * present. For this condition, we have to preserve the
733 * state of the exclusive waiters flag.
734 * If interruptible sleeps left the shared queue empty avoid a
735 * starvation for the threads sleeping on the exclusive queue by giving
736 * them precedence and cleaning up the shared waiters bit anyway.
737 */
738 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
739 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
740 queue = SQ_SHARED_QUEUE;
741 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
742 } else
743 queue = SQ_EXCLUSIVE_QUEUE;
744
745 /* Wake up all the waiters for the specific queue. */
746 if (LOCK_LOG_TEST(&sx->lock_object, 0))
747 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
748 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
749 "exclusive");
750 atomic_store_rel_ptr(&sx->sx_lock, x);
751 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
752 queue);
753 sleepq_release(&sx->lock_object);
754 if (wakeup_swapper)
755 kick_proc0();
756 }
757
758 /*
759 * This function represents the so-called 'hard case' for sx_slock
760 * operation. All 'easy case' failures are redirected to this. Note
761 * that ideally this would be a static function, but it needs to be
762 * accessible from at least sx.h.
763 */
764 int
765 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
766 {
767 GIANT_DECLARE;
768 #ifdef ADAPTIVE_SX
769 volatile struct thread *owner;
770 #endif
771 #ifdef LOCK_PROFILING
772 uint64_t waittime = 0;
773 int contested = 0;
774 #endif
775 uintptr_t x;
776 int error = 0;
777 #ifdef KDTRACE_HOOKS
778 uint64_t spin_cnt = 0;
779 uint64_t sleep_cnt = 0;
780 int64_t sleep_time = 0;
781 #endif
782
783 if (SCHEDULER_STOPPED())
784 return (0);
785
786 /*
787 * As with rwlocks, we don't make any attempt to try to block
788 * shared locks once there is an exclusive waiter.
789 */
790 for (;;) {
791 #ifdef KDTRACE_HOOKS
792 spin_cnt++;
793 #endif
794 x = sx->sx_lock;
795
796 /*
797 * If no other thread has an exclusive lock then try to bump up
798 * the count of sharers. Since we have to preserve the state
799 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
800 * shared lock loop back and retry.
801 */
802 if (x & SX_LOCK_SHARED) {
803 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
804 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
805 x + SX_ONE_SHARER)) {
806 if (LOCK_LOG_TEST(&sx->lock_object, 0))
807 CTR4(KTR_LOCK,
808 "%s: %p succeed %p -> %p", __func__,
809 sx, (void *)x,
810 (void *)(x + SX_ONE_SHARER));
811 break;
812 }
813 continue;
814 }
815 #ifdef HWPMC_HOOKS
816 PMC_SOFT_CALL( , , lock, failed);
817 #endif
818 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
819 &waittime);
820
821 #ifdef ADAPTIVE_SX
822 /*
823 * If the owner is running on another CPU, spin until
824 * the owner stops running or the state of the lock
825 * changes.
826 */
827 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
828 x = SX_OWNER(x);
829 owner = (struct thread *)x;
830 if (TD_IS_RUNNING(owner)) {
831 if (LOCK_LOG_TEST(&sx->lock_object, 0))
832 CTR3(KTR_LOCK,
833 "%s: spinning on %p held by %p",
834 __func__, sx, owner);
835 GIANT_SAVE();
836 while (SX_OWNER(sx->sx_lock) == x &&
837 TD_IS_RUNNING(owner)) {
838 #ifdef KDTRACE_HOOKS
839 spin_cnt++;
840 #endif
841 cpu_spinwait();
842 }
843 continue;
844 }
845 }
846 #endif
847
848 /*
849 * Some other thread already has an exclusive lock, so
850 * start the process of blocking.
851 */
852 sleepq_lock(&sx->lock_object);
853 x = sx->sx_lock;
854
855 /*
856 * The lock could have been released while we spun.
857 * In this case loop back and retry.
858 */
859 if (x & SX_LOCK_SHARED) {
860 sleepq_release(&sx->lock_object);
861 continue;
862 }
863
864 #ifdef ADAPTIVE_SX
865 /*
866 * If the owner is running on another CPU, spin until
867 * the owner stops running or the state of the lock
868 * changes.
869 */
870 if (!(x & SX_LOCK_SHARED) &&
871 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
872 owner = (struct thread *)SX_OWNER(x);
873 if (TD_IS_RUNNING(owner)) {
874 sleepq_release(&sx->lock_object);
875 continue;
876 }
877 }
878 #endif
879
880 /*
881 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
882 * fail to set it drop the sleep queue lock and loop
883 * back.
884 */
885 if (!(x & SX_LOCK_SHARED_WAITERS)) {
886 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
887 x | SX_LOCK_SHARED_WAITERS)) {
888 sleepq_release(&sx->lock_object);
889 continue;
890 }
891 if (LOCK_LOG_TEST(&sx->lock_object, 0))
892 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
893 __func__, sx);
894 }
895
896 /*
897 * Since we have been unable to acquire the shared lock,
898 * we have to sleep.
899 */
900 if (LOCK_LOG_TEST(&sx->lock_object, 0))
901 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
902 __func__, sx);
903
904 #ifdef KDTRACE_HOOKS
905 sleep_time -= lockstat_nsecs();
906 #endif
907 GIANT_SAVE();
908 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
909 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
910 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
911 if (!(opts & SX_INTERRUPTIBLE))
912 sleepq_wait(&sx->lock_object, 0);
913 else
914 error = sleepq_wait_sig(&sx->lock_object, 0);
915 #ifdef KDTRACE_HOOKS
916 sleep_time += lockstat_nsecs();
917 sleep_cnt++;
918 #endif
919 if (error) {
920 if (LOCK_LOG_TEST(&sx->lock_object, 0))
921 CTR2(KTR_LOCK,
922 "%s: interruptible sleep by %p suspended by signal",
923 __func__, sx);
924 break;
925 }
926 if (LOCK_LOG_TEST(&sx->lock_object, 0))
927 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
928 __func__, sx);
929 }
930 if (error == 0)
931 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
932 contested, waittime, file, line);
933 #ifdef KDTRACE_HOOKS
934 if (sleep_time)
935 LOCKSTAT_RECORD1(LS_SX_XLOCK_BLOCK, sx, sleep_time);
936 if (spin_cnt > sleep_cnt)
937 LOCKSTAT_RECORD1(LS_SX_XLOCK_SPIN, sx, (spin_cnt - sleep_cnt));
938 #endif
939 GIANT_RESTORE();
940 return (error);
941 }
942
943 /*
944 * This function represents the so-called 'hard case' for sx_sunlock
945 * operation. All 'easy case' failures are redirected to this. Note
946 * that ideally this would be a static function, but it needs to be
947 * accessible from at least sx.h.
948 */
949 void
950 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
951 {
952 uintptr_t x;
953 int wakeup_swapper;
954
955 if (SCHEDULER_STOPPED())
956 return;
957
958 for (;;) {
959 x = sx->sx_lock;
960
961 /*
962 * We should never have sharers while at least one thread
963 * holds a shared lock.
964 */
965 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
966 ("%s: waiting sharers", __func__));
967
968 /*
969 * See if there is more than one shared lock held. If
970 * so, just drop one and return.
971 */
972 if (SX_SHARERS(x) > 1) {
973 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
974 x - SX_ONE_SHARER)) {
975 if (LOCK_LOG_TEST(&sx->lock_object, 0))
976 CTR4(KTR_LOCK,
977 "%s: %p succeeded %p -> %p",
978 __func__, sx, (void *)x,
979 (void *)(x - SX_ONE_SHARER));
980 break;
981 }
982 continue;
983 }
984
985 /*
986 * If there aren't any waiters for an exclusive lock,
987 * then try to drop it quickly.
988 */
989 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
990 MPASS(x == SX_SHARERS_LOCK(1));
991 if (atomic_cmpset_rel_ptr(&sx->sx_lock,
992 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
993 if (LOCK_LOG_TEST(&sx->lock_object, 0))
994 CTR2(KTR_LOCK, "%s: %p last succeeded",
995 __func__, sx);
996 break;
997 }
998 continue;
999 }
1000
1001 /*
1002 * At this point, there should just be one sharer with
1003 * exclusive waiters.
1004 */
1005 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1006
1007 sleepq_lock(&sx->lock_object);
1008
1009 /*
1010 * Wake up semantic here is quite simple:
1011 * Just wake up all the exclusive waiters.
1012 * Note that the state of the lock could have changed,
1013 * so if it fails loop back and retry.
1014 */
1015 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1016 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1017 SX_LOCK_UNLOCKED)) {
1018 sleepq_release(&sx->lock_object);
1019 continue;
1020 }
1021 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1022 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1023 "exclusive queue", __func__, sx);
1024 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1025 0, SQ_EXCLUSIVE_QUEUE);
1026 sleepq_release(&sx->lock_object);
1027 if (wakeup_swapper)
1028 kick_proc0();
1029 break;
1030 }
1031 }
1032
1033 #ifdef INVARIANT_SUPPORT
1034 #ifndef INVARIANTS
1035 #undef _sx_assert
1036 #endif
1037
1038 /*
1039 * In the non-WITNESS case, sx_assert() can only detect that at least
1040 * *some* thread owns an slock, but it cannot guarantee that *this*
1041 * thread owns an slock.
1042 */
1043 void
1044 _sx_assert(struct sx *sx, int what, const char *file, int line)
1045 {
1046 #ifndef WITNESS
1047 int slocked = 0;
1048 #endif
1049
1050 if (panicstr != NULL)
1051 return;
1052 switch (what) {
1053 case SA_SLOCKED:
1054 case SA_SLOCKED | SA_NOTRECURSED:
1055 case SA_SLOCKED | SA_RECURSED:
1056 #ifndef WITNESS
1057 slocked = 1;
1058 /* FALLTHROUGH */
1059 #endif
1060 case SA_LOCKED:
1061 case SA_LOCKED | SA_NOTRECURSED:
1062 case SA_LOCKED | SA_RECURSED:
1063 #ifdef WITNESS
1064 witness_assert(&sx->lock_object, what, file, line);
1065 #else
1066 /*
1067 * If some other thread has an exclusive lock or we
1068 * have one and are asserting a shared lock, fail.
1069 * Also, if no one has a lock at all, fail.
1070 */
1071 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1072 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1073 sx_xholder(sx) != curthread)))
1074 panic("Lock %s not %slocked @ %s:%d\n",
1075 sx->lock_object.lo_name, slocked ? "share " : "",
1076 file, line);
1077
1078 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1079 if (sx_recursed(sx)) {
1080 if (what & SA_NOTRECURSED)
1081 panic("Lock %s recursed @ %s:%d\n",
1082 sx->lock_object.lo_name, file,
1083 line);
1084 } else if (what & SA_RECURSED)
1085 panic("Lock %s not recursed @ %s:%d\n",
1086 sx->lock_object.lo_name, file, line);
1087 }
1088 #endif
1089 break;
1090 case SA_XLOCKED:
1091 case SA_XLOCKED | SA_NOTRECURSED:
1092 case SA_XLOCKED | SA_RECURSED:
1093 if (sx_xholder(sx) != curthread)
1094 panic("Lock %s not exclusively locked @ %s:%d\n",
1095 sx->lock_object.lo_name, file, line);
1096 if (sx_recursed(sx)) {
1097 if (what & SA_NOTRECURSED)
1098 panic("Lock %s recursed @ %s:%d\n",
1099 sx->lock_object.lo_name, file, line);
1100 } else if (what & SA_RECURSED)
1101 panic("Lock %s not recursed @ %s:%d\n",
1102 sx->lock_object.lo_name, file, line);
1103 break;
1104 case SA_UNLOCKED:
1105 #ifdef WITNESS
1106 witness_assert(&sx->lock_object, what, file, line);
1107 #else
1108 /*
1109 * If we hold an exclusve lock fail. We can't
1110 * reliably check to see if we hold a shared lock or
1111 * not.
1112 */
1113 if (sx_xholder(sx) == curthread)
1114 panic("Lock %s exclusively locked @ %s:%d\n",
1115 sx->lock_object.lo_name, file, line);
1116 #endif
1117 break;
1118 default:
1119 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1120 line);
1121 }
1122 }
1123 #endif /* INVARIANT_SUPPORT */
1124
1125 #ifdef DDB
1126 static void
1127 db_show_sx(struct lock_object *lock)
1128 {
1129 struct thread *td;
1130 struct sx *sx;
1131
1132 sx = (struct sx *)lock;
1133
1134 db_printf(" state: ");
1135 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1136 db_printf("UNLOCKED\n");
1137 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1138 db_printf("DESTROYED\n");
1139 return;
1140 } else if (sx->sx_lock & SX_LOCK_SHARED)
1141 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1142 else {
1143 td = sx_xholder(sx);
1144 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1145 td->td_tid, td->td_proc->p_pid, td->td_name);
1146 if (sx_recursed(sx))
1147 db_printf(" recursed: %d\n", sx->sx_recurse);
1148 }
1149
1150 db_printf(" waiters: ");
1151 switch(sx->sx_lock &
1152 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1153 case SX_LOCK_SHARED_WAITERS:
1154 db_printf("shared\n");
1155 break;
1156 case SX_LOCK_EXCLUSIVE_WAITERS:
1157 db_printf("exclusive\n");
1158 break;
1159 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1160 db_printf("exclusive and shared\n");
1161 break;
1162 default:
1163 db_printf("none\n");
1164 }
1165 }
1166
1167 /*
1168 * Check to see if a thread that is blocked on a sleep queue is actually
1169 * blocked on an sx lock. If so, output some details and return true.
1170 * If the lock has an exclusive owner, return that in *ownerp.
1171 */
1172 int
1173 sx_chain(struct thread *td, struct thread **ownerp)
1174 {
1175 struct sx *sx;
1176
1177 /*
1178 * Check to see if this thread is blocked on an sx lock.
1179 * First, we check the lock class. If that is ok, then we
1180 * compare the lock name against the wait message.
1181 */
1182 sx = td->td_wchan;
1183 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1184 sx->lock_object.lo_name != td->td_wmesg)
1185 return (0);
1186
1187 /* We think we have an sx lock, so output some details. */
1188 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1189 *ownerp = sx_xholder(sx);
1190 if (sx->sx_lock & SX_LOCK_SHARED)
1191 db_printf("SLOCK (count %ju)\n",
1192 (uintmax_t)SX_SHARERS(sx->sx_lock));
1193 else
1194 db_printf("XLOCK\n");
1195 return (1);
1196 }
1197 #endif
Cache object: bcc317416132f0838a74871016bfd5df
|