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: head/sys/kern/kern_sx.c 174629 2007-12-15 23:13:31Z jeff $");
|
| 43__FBSDID("$FreeBSD: head/sys/kern/kern_sx.c 177085 2008-03-12 06:31:06Z jeff $"); |
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
66CTASSERT(((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
106static void assert_sx(struct lock_object *lock, int what);
107#ifdef DDB
108static void db_show_sx(struct lock_object *lock);
109#endif
110static void lock_sx(struct lock_object *lock, int how);
111static int unlock_sx(struct lock_object *lock);
112
113struct lock_class lock_class_sx = {
114 .lc_name = "sx",
115 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
116 .lc_assert = assert_sx,
117#ifdef DDB
118 .lc_ddb_show = db_show_sx,
119#endif
120 .lc_lock = lock_sx,
121 .lc_unlock = unlock_sx,
122};
123
124#ifndef INVARIANTS
125#define _sx_assert(sx, what, file, line)
126#endif
127
128void
129assert_sx(struct lock_object *lock, int what)
130{
131
132 sx_assert((struct sx *)lock, what);
133}
134
135void
136lock_sx(struct lock_object *lock, int how)
137{
138 struct sx *sx;
139
140 sx = (struct sx *)lock;
141 if (how)
142 sx_xlock(sx);
143 else
144 sx_slock(sx);
145}
146
147int
148unlock_sx(struct lock_object *lock)
149{
150 struct sx *sx;
151
152 sx = (struct sx *)lock;
153 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
154 if (sx_xlocked(sx)) {
155 sx_xunlock(sx);
156 return (1);
157 } else {
158 sx_sunlock(sx);
159 return (0);
160 }
161}
162
163void
164sx_sysinit(void *arg)
165{
166 struct sx_args *sargs = arg;
167
168 sx_init(sargs->sa_sx, sargs->sa_desc);
169}
170
171void
172sx_init_flags(struct sx *sx, const char *description, int opts)
173{
174 int flags;
175
176 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
177 SX_NOPROFILE | SX_ADAPTIVESPIN)) == 0);
178
179 flags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE;
180 if (opts & SX_DUPOK)
181 flags |= LO_DUPOK;
182 if (opts & SX_NOPROFILE)
183 flags |= LO_NOPROFILE;
184 if (!(opts & SX_NOWITNESS))
185 flags |= LO_WITNESS;
186 if (opts & SX_QUIET)
187 flags |= LO_QUIET;
188
189 flags |= opts & (SX_ADAPTIVESPIN | SX_RECURSE);
190 sx->sx_lock = SX_LOCK_UNLOCKED;
191 sx->sx_recurse = 0;
192 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
193}
194
195void
196sx_destroy(struct sx *sx)
197{
198
199 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
200 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
201 sx->sx_lock = SX_LOCK_DESTROYED;
202 lock_destroy(&sx->lock_object);
203}
204
205int
206_sx_slock(struct sx *sx, int opts, const char *file, int line)
207{
208 int error = 0;
209
210 MPASS(curthread != NULL);
211 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
212 ("sx_slock() of destroyed sx @ %s:%d", file, line));
213 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line);
214 error = __sx_slock(sx, opts, file, line);
215 if (!error) {
216 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
217 WITNESS_LOCK(&sx->lock_object, 0, file, line);
218 curthread->td_locks++;
219 }
220
221 return (error);
222}
223
224int
225_sx_try_slock(struct sx *sx, const char *file, int line)
226{
227 uintptr_t x;
228
229 for (;;) {
230 x = sx->sx_lock;
231 KASSERT(x != SX_LOCK_DESTROYED,
232 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
233 if (!(x & SX_LOCK_SHARED))
234 break;
235 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
236 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
237 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
238 curthread->td_locks++;
239 return (1);
240 }
241 }
242
243 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
244 return (0);
245}
246
247int
248_sx_xlock(struct sx *sx, int opts, const char *file, int line)
249{
250 int error = 0;
251
252 MPASS(curthread != NULL);
253 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
254 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
255 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
256 line);
257 error = __sx_xlock(sx, curthread, opts, file, line);
258 if (!error) {
259 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
260 file, line);
261 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
262 curthread->td_locks++;
263 }
264
265 return (error);
266}
267
268int
269_sx_try_xlock(struct sx *sx, const char *file, int line)
270{
271 int rval;
272
273 MPASS(curthread != NULL);
274 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
275 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
276
277 if (sx_xlocked(sx) && (sx->lock_object.lo_flags & SX_RECURSE) != 0) {
278 sx->sx_recurse++;
279 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
280 rval = 1;
281 } else
282 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
283 (uintptr_t)curthread);
284 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
285 if (rval) {
286 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
287 file, line);
288 curthread->td_locks++;
289 }
290
291 return (rval);
292}
293
294void
295_sx_sunlock(struct sx *sx, const char *file, int line)
296{
297
298 MPASS(curthread != NULL);
299 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
300 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
301 _sx_assert(sx, SA_SLOCKED, file, line);
302 curthread->td_locks--;
303 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
304 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
305 __sx_sunlock(sx, file, line);
306 lock_profile_release_lock(&sx->lock_object);
307}
308
309void
310_sx_xunlock(struct sx *sx, const char *file, int line)
311{
312
313 MPASS(curthread != NULL);
314 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
315 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
316 _sx_assert(sx, SA_XLOCKED, file, line);
317 curthread->td_locks--;
318 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
319 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
320 line);
321 if (!sx_recursed(sx))
322 lock_profile_release_lock(&sx->lock_object);
323 __sx_xunlock(sx, curthread, file, line);
324}
325
326/*
327 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
328 * This will only succeed if this thread holds a single shared lock.
329 * Return 1 if if the upgrade succeed, 0 otherwise.
330 */
331int
332_sx_try_upgrade(struct sx *sx, const char *file, int line)
333{
334 uintptr_t x;
335 int success;
336
337 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
338 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
339 _sx_assert(sx, SA_SLOCKED, file, line);
340
341 /*
342 * Try to switch from one shared lock to an exclusive lock. We need
343 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
344 * we will wake up the exclusive waiters when we drop the lock.
345 */
346 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
347 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
348 (uintptr_t)curthread | x);
349 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
350 if (success)
351 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
352 file, line);
353 return (success);
354}
355
356/*
357 * Downgrade an unrecursed exclusive lock into a single shared lock.
358 */
359void
360_sx_downgrade(struct sx *sx, const char *file, int line)
361{
362 uintptr_t x;
363
364 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
365 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
366 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
367#ifndef INVARIANTS
368 if (sx_recursed(sx))
369 panic("downgrade of a recursed lock");
370#endif
371
372 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
373
374 /*
375 * Try to switch from an exclusive lock with no shared waiters
376 * to one sharer with no shared waiters. If there are
377 * exclusive waiters, we don't need to lock the sleep queue so
378 * long as we preserve the flag. We do one quick try and if
379 * that fails we grab the sleepq lock to keep the flags from
380 * changing and do it the slow way.
381 *
382 * We have to lock the sleep queue if there are shared waiters
383 * so we can wake them up.
384 */
385 x = sx->sx_lock;
386 if (!(x & SX_LOCK_SHARED_WAITERS) &&
387 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
388 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
389 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
390 return;
391 }
392
393 /*
394 * Lock the sleep queue so we can read the waiters bits
395 * without any races and wakeup any shared waiters.
396 */
397 sleepq_lock(&sx->lock_object);
398
399 /*
400 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
401 * shared lock. If there are any shared waiters, wake them up.
402 */
403 x = sx->sx_lock;
404 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
405 (x & SX_LOCK_EXCLUSIVE_WAITERS));
406 if (x & SX_LOCK_SHARED_WAITERS)
|
407 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1,
|
| 407 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, |
408 SQ_SHARED_QUEUE);
|
409 else
410 sleepq_release(&sx->lock_object);
|
| 409 sleepq_release(&sx->lock_object); |
410
411 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
412}
413
414/*
415 * This function represents the so-called 'hard case' for sx_xlock
416 * operation. All 'easy case' failures are redirected to this. Note
417 * that ideally this would be a static function, but it needs to be
418 * accessible from at least sx.h.
419 */
420int
421_sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
422 int line)
423{
424 GIANT_DECLARE;
425#ifdef ADAPTIVE_SX
426 volatile struct thread *owner;
427#endif
428 uint64_t waittime = 0;
429 uintptr_t x;
430 int contested = 0, error = 0;
431
432 /* If we already hold an exclusive lock, then recurse. */
433 if (sx_xlocked(sx)) {
434 KASSERT((sx->lock_object.lo_flags & SX_RECURSE) != 0,
435 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
436 sx->lock_object.lo_name, file, line));
437 sx->sx_recurse++;
438 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
439 if (LOCK_LOG_TEST(&sx->lock_object, 0))
440 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
441 return (0);
442 }
443
444 if (LOCK_LOG_TEST(&sx->lock_object, 0))
445 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
446 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
447
448 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
449 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
450 &waittime);
451#ifdef ADAPTIVE_SX
452 /*
453 * If the lock is write locked and the owner is
454 * running on another CPU, spin until the owner stops
455 * running or the state of the lock changes.
456 */
457 x = sx->sx_lock;
458 if (!(x & SX_LOCK_SHARED) &&
459 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
460 x = SX_OWNER(x);
461 owner = (struct thread *)x;
462 if (TD_IS_RUNNING(owner)) {
463 if (LOCK_LOG_TEST(&sx->lock_object, 0))
464 CTR3(KTR_LOCK,
465 "%s: spinning on %p held by %p",
466 __func__, sx, owner);
467 GIANT_SAVE();
468 while (SX_OWNER(sx->sx_lock) == x &&
469 TD_IS_RUNNING(owner))
470 cpu_spinwait();
471 continue;
472 }
473 }
474#endif
475
476 sleepq_lock(&sx->lock_object);
477 x = sx->sx_lock;
478
479 /*
480 * If the lock was released while spinning on the
481 * sleep queue chain lock, try again.
482 */
483 if (x == SX_LOCK_UNLOCKED) {
484 sleepq_release(&sx->lock_object);
485 continue;
486 }
487
488#ifdef ADAPTIVE_SX
489 /*
490 * The current lock owner might have started executing
491 * on another CPU (or the lock could have changed
492 * owners) while we were waiting on the sleep queue
493 * chain lock. If so, drop the sleep queue lock and try
494 * again.
495 */
496 if (!(x & SX_LOCK_SHARED) &&
497 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
498 owner = (struct thread *)SX_OWNER(x);
499 if (TD_IS_RUNNING(owner)) {
500 sleepq_release(&sx->lock_object);
501 continue;
502 }
503 }
504#endif
505
506 /*
507 * If an exclusive lock was released with both shared
508 * and exclusive waiters and a shared waiter hasn't
509 * woken up and acquired the lock yet, sx_lock will be
510 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
511 * If we see that value, try to acquire it once. Note
512 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
513 * as there are other exclusive waiters still. If we
514 * fail, restart the loop.
515 */
516 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
517 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
518 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
519 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
520 sleepq_release(&sx->lock_object);
521 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
522 __func__, sx);
523 break;
524 }
525 sleepq_release(&sx->lock_object);
526 continue;
527 }
528
529 /*
530 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
531 * than loop back and retry.
532 */
533 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
534 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
535 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
536 sleepq_release(&sx->lock_object);
537 continue;
538 }
539 if (LOCK_LOG_TEST(&sx->lock_object, 0))
540 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
541 __func__, sx);
542 }
543
544 /*
545 * Since we have been unable to acquire the exclusive
546 * lock and the exclusive waiters flag is set, we have
547 * to sleep.
548 */
549 if (LOCK_LOG_TEST(&sx->lock_object, 0))
550 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
551 __func__, sx);
552
553 GIANT_SAVE();
554 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
555 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
556 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
557 if (!(opts & SX_INTERRUPTIBLE))
|
559 sleepq_wait(&sx->lock_object);
|
| 558 sleepq_wait(&sx->lock_object, 0); |
559 else
|
561 error = sleepq_wait_sig(&sx->lock_object);
|
| 560 error = sleepq_wait_sig(&sx->lock_object, 0); |
561
562 if (error) {
563 if (LOCK_LOG_TEST(&sx->lock_object, 0))
564 CTR2(KTR_LOCK,
565 "%s: interruptible sleep by %p suspended by signal",
566 __func__, sx);
567 break;
568 }
569 if (LOCK_LOG_TEST(&sx->lock_object, 0))
570 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
571 __func__, sx);
572 }
573
574 GIANT_RESTORE();
575 if (!error)
576 lock_profile_obtain_lock_success(&sx->lock_object, contested,
577 waittime, file, line);
578 return (error);
579}
580
581/*
582 * This function represents the so-called 'hard case' for sx_xunlock
583 * operation. All 'easy case' failures are redirected to this. Note
584 * that ideally this would be a static function, but it needs to be
585 * accessible from at least sx.h.
586 */
587void
588_sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
589{
590 uintptr_t x;
591 int queue;
592
593 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
594
595 /* If the lock is recursed, then unrecurse one level. */
596 if (sx_xlocked(sx) && sx_recursed(sx)) {
597 if ((--sx->sx_recurse) == 0)
598 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
599 if (LOCK_LOG_TEST(&sx->lock_object, 0))
600 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
601 return;
602 }
603 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
604 SX_LOCK_EXCLUSIVE_WAITERS));
605 if (LOCK_LOG_TEST(&sx->lock_object, 0))
606 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
607
608 sleepq_lock(&sx->lock_object);
609 x = SX_LOCK_UNLOCKED;
610
611 /*
612 * The wake up algorithm here is quite simple and probably not
613 * ideal. It gives precedence to shared waiters if they are
614 * present. For this condition, we have to preserve the
615 * state of the exclusive waiters flag.
616 */
617 if (sx->sx_lock & SX_LOCK_SHARED_WAITERS) {
618 queue = SQ_SHARED_QUEUE;
619 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
620 } else
621 queue = SQ_EXCLUSIVE_QUEUE;
622
623 /* Wake up all the waiters for the specific queue. */
624 if (LOCK_LOG_TEST(&sx->lock_object, 0))
625 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
626 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
627 "exclusive");
628 atomic_store_rel_ptr(&sx->sx_lock, x);
|
630 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1, queue);
|
629 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, queue);
630 sleepq_release(&sx->lock_object); |
631}
632
633/*
634 * This function represents the so-called 'hard case' for sx_slock
635 * operation. All 'easy case' failures are redirected to this. Note
636 * that ideally this would be a static function, but it needs to be
637 * accessible from at least sx.h.
638 */
639int
640_sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
641{
642 GIANT_DECLARE;
643#ifdef ADAPTIVE_SX
644 volatile struct thread *owner;
645#endif
646 uint64_t waittime = 0;
647 int contested = 0;
648 uintptr_t x;
649 int error = 0;
650
651 /*
652 * As with rwlocks, we don't make any attempt to try to block
653 * shared locks once there is an exclusive waiter.
654 */
655 for (;;) {
656 x = sx->sx_lock;
657
658 /*
659 * If no other thread has an exclusive lock then try to bump up
660 * the count of sharers. Since we have to preserve the state
661 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
662 * shared lock loop back and retry.
663 */
664 if (x & SX_LOCK_SHARED) {
665 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
666 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
667 x + SX_ONE_SHARER)) {
668 if (LOCK_LOG_TEST(&sx->lock_object, 0))
669 CTR4(KTR_LOCK,
670 "%s: %p succeed %p -> %p", __func__,
671 sx, (void *)x,
672 (void *)(x + SX_ONE_SHARER));
673 break;
674 }
675 continue;
676 }
677 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
678 &waittime);
679
680#ifdef ADAPTIVE_SX
681 /*
682 * If the owner is running on another CPU, spin until
683 * the owner stops running or the state of the lock
684 * changes.
685 */
686 if (sx->lock_object.lo_flags & SX_ADAPTIVESPIN) {
687 x = SX_OWNER(x);
688 owner = (struct thread *)x;
689 if (TD_IS_RUNNING(owner)) {
690 if (LOCK_LOG_TEST(&sx->lock_object, 0))
691 CTR3(KTR_LOCK,
692 "%s: spinning on %p held by %p",
693 __func__, sx, owner);
694 GIANT_SAVE();
695 while (SX_OWNER(sx->sx_lock) == x &&
696 TD_IS_RUNNING(owner))
697 cpu_spinwait();
698 continue;
699 }
700 }
701#endif
702
703 /*
704 * Some other thread already has an exclusive lock, so
705 * start the process of blocking.
706 */
707 sleepq_lock(&sx->lock_object);
708 x = sx->sx_lock;
709
710 /*
711 * The lock could have been released while we spun.
712 * In this case loop back and retry.
713 */
714 if (x & SX_LOCK_SHARED) {
715 sleepq_release(&sx->lock_object);
716 continue;
717 }
718
719#ifdef ADAPTIVE_SX
720 /*
721 * If the owner is running on another CPU, spin until
722 * the owner stops running or the state of the lock
723 * changes.
724 */
725 if (!(x & SX_LOCK_SHARED) &&
726 (sx->lock_object.lo_flags & SX_ADAPTIVESPIN)) {
727 owner = (struct thread *)SX_OWNER(x);
728 if (TD_IS_RUNNING(owner)) {
729 sleepq_release(&sx->lock_object);
730 continue;
731 }
732 }
733#endif
734
735 /*
736 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
737 * fail to set it drop the sleep queue lock and loop
738 * back.
739 */
740 if (!(x & SX_LOCK_SHARED_WAITERS)) {
741 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
742 x | SX_LOCK_SHARED_WAITERS)) {
743 sleepq_release(&sx->lock_object);
744 continue;
745 }
746 if (LOCK_LOG_TEST(&sx->lock_object, 0))
747 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
748 __func__, sx);
749 }
750
751 /*
752 * Since we have been unable to acquire the shared lock,
753 * we have to sleep.
754 */
755 if (LOCK_LOG_TEST(&sx->lock_object, 0))
756 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
757 __func__, sx);
758
759 GIANT_SAVE();
760 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
761 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
762 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
763 if (!(opts & SX_INTERRUPTIBLE))
|
764 sleepq_wait(&sx->lock_object);
|
| 764 sleepq_wait(&sx->lock_object, 0); |
765 else
|
766 error = sleepq_wait_sig(&sx->lock_object);
|
| 766 error = sleepq_wait_sig(&sx->lock_object, 0); |
767
768 if (error) {
769 if (LOCK_LOG_TEST(&sx->lock_object, 0))
770 CTR2(KTR_LOCK,
771 "%s: interruptible sleep by %p suspended by signal",
772 __func__, sx);
773 break;
774 }
775 if (LOCK_LOG_TEST(&sx->lock_object, 0))
776 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
777 __func__, sx);
778 }
779 if (error == 0)
780 lock_profile_obtain_lock_success(&sx->lock_object, contested,
781 waittime, file, line);
782
783 GIANT_RESTORE();
784 return (error);
785}
786
787/*
788 * This function represents the so-called 'hard case' for sx_sunlock
789 * operation. All 'easy case' failures are redirected to this. Note
790 * that ideally this would be a static function, but it needs to be
791 * accessible from at least sx.h.
792 */
793void
794_sx_sunlock_hard(struct sx *sx, const char *file, int line)
795{
796 uintptr_t x;
797
798 for (;;) {
799 x = sx->sx_lock;
800
801 /*
802 * We should never have sharers while at least one thread
803 * holds a shared lock.
804 */
805 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
806 ("%s: waiting sharers", __func__));
807
808 /*
809 * See if there is more than one shared lock held. If
810 * so, just drop one and return.
811 */
812 if (SX_SHARERS(x) > 1) {
813 if (atomic_cmpset_ptr(&sx->sx_lock, x,
814 x - SX_ONE_SHARER)) {
815 if (LOCK_LOG_TEST(&sx->lock_object, 0))
816 CTR4(KTR_LOCK,
817 "%s: %p succeeded %p -> %p",
818 __func__, sx, (void *)x,
819 (void *)(x - SX_ONE_SHARER));
820 break;
821 }
822 continue;
823 }
824
825 /*
826 * If there aren't any waiters for an exclusive lock,
827 * then try to drop it quickly.
828 */
829 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
830 MPASS(x == SX_SHARERS_LOCK(1));
831 if (atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1),
832 SX_LOCK_UNLOCKED)) {
833 if (LOCK_LOG_TEST(&sx->lock_object, 0))
834 CTR2(KTR_LOCK, "%s: %p last succeeded",
835 __func__, sx);
836 break;
837 }
838 continue;
839 }
840
841 /*
842 * At this point, there should just be one sharer with
843 * exclusive waiters.
844 */
845 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
846
847 sleepq_lock(&sx->lock_object);
848
849 /*
850 * Wake up semantic here is quite simple:
851 * Just wake up all the exclusive waiters.
852 * Note that the state of the lock could have changed,
853 * so if it fails loop back and retry.
854 */
855 if (!atomic_cmpset_ptr(&sx->sx_lock,
856 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
857 SX_LOCK_UNLOCKED)) {
858 sleepq_release(&sx->lock_object);
859 continue;
860 }
861 if (LOCK_LOG_TEST(&sx->lock_object, 0))
862 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
863 "exclusive queue", __func__, sx);
|
864 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, -1,
|
| 864 sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0, |
865 SQ_EXCLUSIVE_QUEUE);
|
| 866 sleepq_release(&sx->lock_object); |
867 break;
868 }
869}
870
871#ifdef INVARIANT_SUPPORT
872#ifndef INVARIANTS
873#undef _sx_assert
874#endif
875
876/*
877 * In the non-WITNESS case, sx_assert() can only detect that at least
878 * *some* thread owns an slock, but it cannot guarantee that *this*
879 * thread owns an slock.
880 */
881void
882_sx_assert(struct sx *sx, int what, const char *file, int line)
883{
884#ifndef WITNESS
885 int slocked = 0;
886#endif
887
888 if (panicstr != NULL)
889 return;
890 switch (what) {
891 case SA_SLOCKED:
892 case SA_SLOCKED | SA_NOTRECURSED:
893 case SA_SLOCKED | SA_RECURSED:
894#ifndef WITNESS
895 slocked = 1;
896 /* FALLTHROUGH */
897#endif
898 case SA_LOCKED:
899 case SA_LOCKED | SA_NOTRECURSED:
900 case SA_LOCKED | SA_RECURSED:
901#ifdef WITNESS
902 witness_assert(&sx->lock_object, what, file, line);
903#else
904 /*
905 * If some other thread has an exclusive lock or we
906 * have one and are asserting a shared lock, fail.
907 * Also, if no one has a lock at all, fail.
908 */
909 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
910 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
911 sx_xholder(sx) != curthread)))
912 panic("Lock %s not %slocked @ %s:%d\n",
913 sx->lock_object.lo_name, slocked ? "share " : "",
914 file, line);
915
916 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
917 if (sx_recursed(sx)) {
918 if (what & SA_NOTRECURSED)
919 panic("Lock %s recursed @ %s:%d\n",
920 sx->lock_object.lo_name, file,
921 line);
922 } else if (what & SA_RECURSED)
923 panic("Lock %s not recursed @ %s:%d\n",
924 sx->lock_object.lo_name, file, line);
925 }
926#endif
927 break;
928 case SA_XLOCKED:
929 case SA_XLOCKED | SA_NOTRECURSED:
930 case SA_XLOCKED | SA_RECURSED:
931 if (sx_xholder(sx) != curthread)
932 panic("Lock %s not exclusively locked @ %s:%d\n",
933 sx->lock_object.lo_name, file, line);
934 if (sx_recursed(sx)) {
935 if (what & SA_NOTRECURSED)
936 panic("Lock %s recursed @ %s:%d\n",
937 sx->lock_object.lo_name, file, line);
938 } else if (what & SA_RECURSED)
939 panic("Lock %s not recursed @ %s:%d\n",
940 sx->lock_object.lo_name, file, line);
941 break;
942 case SA_UNLOCKED:
943#ifdef WITNESS
944 witness_assert(&sx->lock_object, what, file, line);
945#else
946 /*
947 * If we hold an exclusve lock fail. We can't
948 * reliably check to see if we hold a shared lock or
949 * not.
950 */
951 if (sx_xholder(sx) == curthread)
952 panic("Lock %s exclusively locked @ %s:%d\n",
953 sx->lock_object.lo_name, file, line);
954#endif
955 break;
956 default:
957 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
958 line);
959 }
960}
961#endif /* INVARIANT_SUPPORT */
962
963#ifdef DDB
964static void
965db_show_sx(struct lock_object *lock)
966{
967 struct thread *td;
968 struct sx *sx;
969
970 sx = (struct sx *)lock;
971
972 db_printf(" state: ");
973 if (sx->sx_lock == SX_LOCK_UNLOCKED)
974 db_printf("UNLOCKED\n");
975 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
976 db_printf("DESTROYED\n");
977 return;
978 } else if (sx->sx_lock & SX_LOCK_SHARED)
979 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
980 else {
981 td = sx_xholder(sx);
982 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
983 td->td_tid, td->td_proc->p_pid, td->td_name);
984 if (sx_recursed(sx))
985 db_printf(" recursed: %d\n", sx->sx_recurse);
986 }
987
988 db_printf(" waiters: ");
989 switch(sx->sx_lock &
990 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
991 case SX_LOCK_SHARED_WAITERS:
992 db_printf("shared\n");
993 break;
994 case SX_LOCK_EXCLUSIVE_WAITERS:
995 db_printf("exclusive\n");
996 break;
997 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
998 db_printf("exclusive and shared\n");
999 break;
1000 default:
1001 db_printf("none\n");
1002 }
1003}
1004
1005/*
1006 * Check to see if a thread that is blocked on a sleep queue is actually
1007 * blocked on an sx lock. If so, output some details and return true.
1008 * If the lock has an exclusive owner, return that in *ownerp.
1009 */
1010int
1011sx_chain(struct thread *td, struct thread **ownerp)
1012{
1013 struct sx *sx;
1014
1015 /*
1016 * Check to see if this thread is blocked on an sx lock.
1017 * First, we check the lock class. If that is ok, then we
1018 * compare the lock name against the wait message.
1019 */
1020 sx = td->td_wchan;
1021 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1022 sx->lock_object.lo_name != td->td_wmesg)
1023 return (0);
1024
1025 /* We think we have an sx lock, so output some details. */
1026 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1027 *ownerp = sx_xholder(sx);
1028 if (sx->sx_lock & SX_LOCK_SHARED)
1029 db_printf("SLOCK (count %ju)\n",
1030 (uintmax_t)SX_SHARERS(sx->sx_lock));
1031 else
1032 db_printf("XLOCK\n");
1033 return (1);
1034}
1035#endif
|