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/10.2/sys/kern/kern_sx.c 285759 2015-07-21 17:16:37Z markj $");
46
47 #include <sys/param.h>
48 #include <sys/systm.h>
49 #include <sys/kdb.h>
50 #include <sys/ktr.h>
51 #include <sys/lock.h>
52 #include <sys/mutex.h>
53 #include <sys/proc.h>
54 #include <sys/sched.h>
55 #include <sys/sleepqueue.h>
56 #include <sys/sx.h>
57 #include <sys/sysctl.h>
58
59 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
60 #include <machine/cpu.h>
61 #endif
62
63 #ifdef DDB
64 #include <ddb/ddb.h>
65 #endif
66
67 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
68 #define ADAPTIVE_SX
69 #endif
70
71 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
72
73 #ifdef HWPMC_HOOKS
74 #include <sys/pmckern.h>
75 PMC_SOFT_DECLARE( , , lock, failed);
76 #endif
77
78 /* Handy macros for sleep queues. */
79 #define SQ_EXCLUSIVE_QUEUE 0
80 #define SQ_SHARED_QUEUE 1
81
82 /*
83 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
84 * drop Giant anytime we have to sleep or if we adaptively spin.
85 */
86 #define GIANT_DECLARE \
87 int _giantcnt = 0; \
88 WITNESS_SAVE_DECL(Giant) \
89
90 #define GIANT_SAVE() do { \
91 if (mtx_owned(&Giant)) { \
92 WITNESS_SAVE(&Giant.lock_object, Giant); \
93 while (mtx_owned(&Giant)) { \
94 _giantcnt++; \
95 mtx_unlock(&Giant); \
96 } \
97 } \
98 } while (0)
99
100 #define GIANT_RESTORE() do { \
101 if (_giantcnt > 0) { \
102 mtx_assert(&Giant, MA_NOTOWNED); \
103 while (_giantcnt--) \
104 mtx_lock(&Giant); \
105 WITNESS_RESTORE(&Giant.lock_object, Giant); \
106 } \
107 } while (0)
108
109 /*
110 * Returns true if an exclusive lock is recursed. It assumes
111 * curthread currently has an exclusive lock.
112 */
113 #define sx_recurse lock_object.lo_data
114 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
115
116 static void assert_sx(const struct lock_object *lock, int what);
117 #ifdef DDB
118 static void db_show_sx(const struct lock_object *lock);
119 #endif
120 static void lock_sx(struct lock_object *lock, uintptr_t how);
121 #ifdef KDTRACE_HOOKS
122 static int owner_sx(const struct lock_object *lock, struct thread **owner);
123 #endif
124 static uintptr_t unlock_sx(struct lock_object *lock);
125
126 struct lock_class lock_class_sx = {
127 .lc_name = "sx",
128 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
129 .lc_assert = assert_sx,
130 #ifdef DDB
131 .lc_ddb_show = db_show_sx,
132 #endif
133 .lc_lock = lock_sx,
134 .lc_unlock = unlock_sx,
135 #ifdef KDTRACE_HOOKS
136 .lc_owner = owner_sx,
137 #endif
138 };
139
140 #ifndef INVARIANTS
141 #define _sx_assert(sx, what, file, line)
142 #endif
143
144 #ifdef ADAPTIVE_SX
145 static u_int asx_retries = 10;
146 static u_int asx_loops = 10000;
147 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
148 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
149 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
150 #endif
151
152 void
153 assert_sx(const struct lock_object *lock, int what)
154 {
155
156 sx_assert((const struct sx *)lock, what);
157 }
158
159 void
160 lock_sx(struct lock_object *lock, uintptr_t how)
161 {
162 struct sx *sx;
163
164 sx = (struct sx *)lock;
165 if (how)
166 sx_slock(sx);
167 else
168 sx_xlock(sx);
169 }
170
171 uintptr_t
172 unlock_sx(struct lock_object *lock)
173 {
174 struct sx *sx;
175
176 sx = (struct sx *)lock;
177 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
178 if (sx_xlocked(sx)) {
179 sx_xunlock(sx);
180 return (0);
181 } else {
182 sx_sunlock(sx);
183 return (1);
184 }
185 }
186
187 #ifdef KDTRACE_HOOKS
188 int
189 owner_sx(const struct lock_object *lock, struct thread **owner)
190 {
191 const struct sx *sx = (const struct sx *)lock;
192 uintptr_t x = sx->sx_lock;
193
194 *owner = (struct thread *)SX_OWNER(x);
195 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
196 (*owner != NULL));
197 }
198 #endif
199
200 void
201 sx_sysinit(void *arg)
202 {
203 struct sx_args *sargs = arg;
204
205 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
206 }
207
208 void
209 sx_init_flags(struct sx *sx, const char *description, int opts)
210 {
211 int flags;
212
213 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
214 SX_NOPROFILE | SX_NOADAPTIVE)) == 0);
215 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
216 ("%s: sx_lock not aligned for %s: %p", __func__, description,
217 &sx->sx_lock));
218
219 flags = LO_SLEEPABLE | LO_UPGRADABLE;
220 if (opts & SX_DUPOK)
221 flags |= LO_DUPOK;
222 if (opts & SX_NOPROFILE)
223 flags |= LO_NOPROFILE;
224 if (!(opts & SX_NOWITNESS))
225 flags |= LO_WITNESS;
226 if (opts & SX_RECURSE)
227 flags |= LO_RECURSABLE;
228 if (opts & SX_QUIET)
229 flags |= LO_QUIET;
230
231 flags |= opts & SX_NOADAPTIVE;
232 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
233 sx->sx_lock = SX_LOCK_UNLOCKED;
234 sx->sx_recurse = 0;
235 }
236
237 void
238 sx_destroy(struct sx *sx)
239 {
240
241 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
242 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
243 sx->sx_lock = SX_LOCK_DESTROYED;
244 lock_destroy(&sx->lock_object);
245 }
246
247 int
248 _sx_slock(struct sx *sx, int opts, const char *file, int line)
249 {
250 int error = 0;
251
252 if (SCHEDULER_STOPPED())
253 return (0);
254 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
255 ("sx_slock() by idle thread %p on sx %s @ %s:%d",
256 curthread, sx->lock_object.lo_name, file, line));
257 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
258 ("sx_slock() of destroyed sx @ %s:%d", file, line));
259 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
260 error = __sx_slock(sx, opts, file, line);
261 if (!error) {
262 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
263 WITNESS_LOCK(&sx->lock_object, 0, file, line);
264 curthread->td_locks++;
265 }
266
267 return (error);
268 }
269
270 int
271 sx_try_slock_(struct sx *sx, const char *file, int line)
272 {
273 uintptr_t x;
274
275 if (SCHEDULER_STOPPED())
276 return (1);
277
278 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
279 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
280 curthread, sx->lock_object.lo_name, file, line));
281
282 for (;;) {
283 x = sx->sx_lock;
284 KASSERT(x != SX_LOCK_DESTROYED,
285 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
286 if (!(x & SX_LOCK_SHARED))
287 break;
288 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
289 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
290 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
291 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE,
292 sx, 0, 0, file, line);
293 curthread->td_locks++;
294 return (1);
295 }
296 }
297
298 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
299 return (0);
300 }
301
302 int
303 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
304 {
305 int error = 0;
306
307 if (SCHEDULER_STOPPED())
308 return (0);
309 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
310 ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
311 curthread, sx->lock_object.lo_name, file, line));
312 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
313 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
314 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
315 line, NULL);
316 error = __sx_xlock(sx, curthread, opts, file, line);
317 if (!error) {
318 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
319 file, line);
320 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
321 curthread->td_locks++;
322 }
323
324 return (error);
325 }
326
327 int
328 sx_try_xlock_(struct sx *sx, const char *file, int line)
329 {
330 int rval;
331
332 if (SCHEDULER_STOPPED())
333 return (1);
334
335 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
336 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
337 curthread, sx->lock_object.lo_name, file, line));
338 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
339 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
340
341 if (sx_xlocked(sx) &&
342 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
343 sx->sx_recurse++;
344 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
345 rval = 1;
346 } else
347 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
348 (uintptr_t)curthread);
349 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
350 if (rval) {
351 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
352 file, line);
353 if (!sx_recursed(sx))
354 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE,
355 sx, 0, 0, file, line);
356 curthread->td_locks++;
357 }
358
359 return (rval);
360 }
361
362 void
363 _sx_sunlock(struct sx *sx, const char *file, int line)
364 {
365
366 if (SCHEDULER_STOPPED())
367 return;
368 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
369 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
370 _sx_assert(sx, SA_SLOCKED, file, line);
371 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
372 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
373 __sx_sunlock(sx, file, line);
374 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
375 curthread->td_locks--;
376 }
377
378 void
379 _sx_xunlock(struct sx *sx, const char *file, int line)
380 {
381
382 if (SCHEDULER_STOPPED())
383 return;
384 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
385 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
386 _sx_assert(sx, SA_XLOCKED, file, line);
387 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
388 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
389 line);
390 if (!sx_recursed(sx))
391 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
392 __sx_xunlock(sx, curthread, file, line);
393 curthread->td_locks--;
394 }
395
396 /*
397 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
398 * This will only succeed if this thread holds a single shared lock.
399 * Return 1 if if the upgrade succeed, 0 otherwise.
400 */
401 int
402 sx_try_upgrade_(struct sx *sx, const char *file, int line)
403 {
404 uintptr_t x;
405 int success;
406
407 if (SCHEDULER_STOPPED())
408 return (1);
409
410 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
411 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
412 _sx_assert(sx, SA_SLOCKED, file, line);
413
414 /*
415 * Try to switch from one shared lock to an exclusive lock. We need
416 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
417 * we will wake up the exclusive waiters when we drop the lock.
418 */
419 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
420 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
421 (uintptr_t)curthread | x);
422 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
423 if (success) {
424 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
425 file, line);
426 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
427 }
428 return (success);
429 }
430
431 /*
432 * Downgrade an unrecursed exclusive lock into a single shared lock.
433 */
434 void
435 sx_downgrade_(struct sx *sx, const char *file, int line)
436 {
437 uintptr_t x;
438 int wakeup_swapper;
439
440 if (SCHEDULER_STOPPED())
441 return;
442
443 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
444 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
445 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
446 #ifndef INVARIANTS
447 if (sx_recursed(sx))
448 panic("downgrade of a recursed lock");
449 #endif
450
451 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
452
453 /*
454 * Try to switch from an exclusive lock with no shared waiters
455 * to one sharer with no shared waiters. If there are
456 * exclusive waiters, we don't need to lock the sleep queue so
457 * long as we preserve the flag. We do one quick try and if
458 * that fails we grab the sleepq lock to keep the flags from
459 * changing and do it the slow way.
460 *
461 * We have to lock the sleep queue if there are shared waiters
462 * so we can wake them up.
463 */
464 x = sx->sx_lock;
465 if (!(x & SX_LOCK_SHARED_WAITERS) &&
466 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
467 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
468 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
469 return;
470 }
471
472 /*
473 * Lock the sleep queue so we can read the waiters bits
474 * without any races and wakeup any shared waiters.
475 */
476 sleepq_lock(&sx->lock_object);
477
478 /*
479 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
480 * shared lock. If there are any shared waiters, wake them up.
481 */
482 wakeup_swapper = 0;
483 x = sx->sx_lock;
484 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
485 (x & SX_LOCK_EXCLUSIVE_WAITERS));
486 if (x & SX_LOCK_SHARED_WAITERS)
487 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
488 0, SQ_SHARED_QUEUE);
489 sleepq_release(&sx->lock_object);
490
491 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
492 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
493
494 if (wakeup_swapper)
495 kick_proc0();
496 }
497
498 /*
499 * This function represents the so-called 'hard case' for sx_xlock
500 * operation. All 'easy case' failures are redirected to this. Note
501 * that ideally this would be a static function, but it needs to be
502 * accessible from at least sx.h.
503 */
504 int
505 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
506 int line)
507 {
508 GIANT_DECLARE;
509 #ifdef ADAPTIVE_SX
510 volatile struct thread *owner;
511 u_int i, spintries = 0;
512 #endif
513 uintptr_t x;
514 #ifdef LOCK_PROFILING
515 uint64_t waittime = 0;
516 int contested = 0;
517 #endif
518 int error = 0;
519 #ifdef KDTRACE_HOOKS
520 uintptr_t state;
521 uint64_t spin_cnt = 0;
522 uint64_t sleep_cnt = 0;
523 int64_t sleep_time = 0;
524 int64_t all_time = 0;
525 #endif
526
527 if (SCHEDULER_STOPPED())
528 return (0);
529
530 /* If we already hold an exclusive lock, then recurse. */
531 if (sx_xlocked(sx)) {
532 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
533 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
534 sx->lock_object.lo_name, file, line));
535 sx->sx_recurse++;
536 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
537 if (LOCK_LOG_TEST(&sx->lock_object, 0))
538 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
539 return (0);
540 }
541
542 if (LOCK_LOG_TEST(&sx->lock_object, 0))
543 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
544 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
545
546 #ifdef KDTRACE_HOOKS
547 all_time -= lockstat_nsecs(&sx->lock_object);
548 state = sx->sx_lock;
549 #endif
550 while (!atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid)) {
551 #ifdef KDTRACE_HOOKS
552 spin_cnt++;
553 #endif
554 #ifdef HWPMC_HOOKS
555 PMC_SOFT_CALL( , , lock, failed);
556 #endif
557 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
558 &waittime);
559 #ifdef ADAPTIVE_SX
560 /*
561 * If the lock is write locked and the owner is
562 * running on another CPU, spin until the owner stops
563 * running or the state of the lock changes.
564 */
565 x = sx->sx_lock;
566 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
567 if ((x & SX_LOCK_SHARED) == 0) {
568 x = SX_OWNER(x);
569 owner = (struct thread *)x;
570 if (TD_IS_RUNNING(owner)) {
571 if (LOCK_LOG_TEST(&sx->lock_object, 0))
572 CTR3(KTR_LOCK,
573 "%s: spinning on %p held by %p",
574 __func__, sx, owner);
575 KTR_STATE1(KTR_SCHED, "thread",
576 sched_tdname(curthread), "spinning",
577 "lockname:\"%s\"",
578 sx->lock_object.lo_name);
579 GIANT_SAVE();
580 while (SX_OWNER(sx->sx_lock) == x &&
581 TD_IS_RUNNING(owner)) {
582 cpu_spinwait();
583 #ifdef KDTRACE_HOOKS
584 spin_cnt++;
585 #endif
586 }
587 KTR_STATE0(KTR_SCHED, "thread",
588 sched_tdname(curthread), "running");
589 continue;
590 }
591 } else if (SX_SHARERS(x) && spintries < asx_retries) {
592 KTR_STATE1(KTR_SCHED, "thread",
593 sched_tdname(curthread), "spinning",
594 "lockname:\"%s\"", sx->lock_object.lo_name);
595 GIANT_SAVE();
596 spintries++;
597 for (i = 0; i < asx_loops; i++) {
598 if (LOCK_LOG_TEST(&sx->lock_object, 0))
599 CTR4(KTR_LOCK,
600 "%s: shared spinning on %p with %u and %u",
601 __func__, sx, spintries, i);
602 x = sx->sx_lock;
603 if ((x & SX_LOCK_SHARED) == 0 ||
604 SX_SHARERS(x) == 0)
605 break;
606 cpu_spinwait();
607 #ifdef KDTRACE_HOOKS
608 spin_cnt++;
609 #endif
610 }
611 KTR_STATE0(KTR_SCHED, "thread",
612 sched_tdname(curthread), "running");
613 if (i != asx_loops)
614 continue;
615 }
616 }
617 #endif
618
619 sleepq_lock(&sx->lock_object);
620 x = sx->sx_lock;
621
622 /*
623 * If the lock was released while spinning on the
624 * sleep queue chain lock, try again.
625 */
626 if (x == SX_LOCK_UNLOCKED) {
627 sleepq_release(&sx->lock_object);
628 continue;
629 }
630
631 #ifdef ADAPTIVE_SX
632 /*
633 * The current lock owner might have started executing
634 * on another CPU (or the lock could have changed
635 * owners) while we were waiting on the sleep queue
636 * chain lock. If so, drop the sleep queue lock and try
637 * again.
638 */
639 if (!(x & SX_LOCK_SHARED) &&
640 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
641 owner = (struct thread *)SX_OWNER(x);
642 if (TD_IS_RUNNING(owner)) {
643 sleepq_release(&sx->lock_object);
644 continue;
645 }
646 }
647 #endif
648
649 /*
650 * If an exclusive lock was released with both shared
651 * and exclusive waiters and a shared waiter hasn't
652 * woken up and acquired the lock yet, sx_lock will be
653 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
654 * If we see that value, try to acquire it once. Note
655 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
656 * as there are other exclusive waiters still. If we
657 * fail, restart the loop.
658 */
659 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
660 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
661 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
662 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
663 sleepq_release(&sx->lock_object);
664 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
665 __func__, sx);
666 break;
667 }
668 sleepq_release(&sx->lock_object);
669 continue;
670 }
671
672 /*
673 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
674 * than loop back and retry.
675 */
676 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
677 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
678 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
679 sleepq_release(&sx->lock_object);
680 continue;
681 }
682 if (LOCK_LOG_TEST(&sx->lock_object, 0))
683 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
684 __func__, sx);
685 }
686
687 /*
688 * Since we have been unable to acquire the exclusive
689 * lock and the exclusive waiters flag is set, we have
690 * to sleep.
691 */
692 if (LOCK_LOG_TEST(&sx->lock_object, 0))
693 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
694 __func__, sx);
695
696 #ifdef KDTRACE_HOOKS
697 sleep_time -= lockstat_nsecs(&sx->lock_object);
698 #endif
699 GIANT_SAVE();
700 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
701 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
702 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
703 if (!(opts & SX_INTERRUPTIBLE))
704 sleepq_wait(&sx->lock_object, 0);
705 else
706 error = sleepq_wait_sig(&sx->lock_object, 0);
707 #ifdef KDTRACE_HOOKS
708 sleep_time += lockstat_nsecs(&sx->lock_object);
709 sleep_cnt++;
710 #endif
711 if (error) {
712 if (LOCK_LOG_TEST(&sx->lock_object, 0))
713 CTR2(KTR_LOCK,
714 "%s: interruptible sleep by %p suspended by signal",
715 __func__, sx);
716 break;
717 }
718 if (LOCK_LOG_TEST(&sx->lock_object, 0))
719 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
720 __func__, sx);
721 }
722 #ifdef KDTRACE_HOOKS
723 all_time += lockstat_nsecs(&sx->lock_object);
724 if (sleep_time)
725 LOCKSTAT_RECORD4(LS_SX_XLOCK_BLOCK, sx, sleep_time,
726 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
727 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
728 if (spin_cnt > sleep_cnt)
729 LOCKSTAT_RECORD4(LS_SX_XLOCK_SPIN, sx, all_time - sleep_time,
730 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
731 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
732 #endif
733 if (!error)
734 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
735 contested, waittime, file, line);
736 GIANT_RESTORE();
737 return (error);
738 }
739
740 /*
741 * This function represents the so-called 'hard case' for sx_xunlock
742 * operation. All 'easy case' failures are redirected to this. Note
743 * that ideally this would be a static function, but it needs to be
744 * accessible from at least sx.h.
745 */
746 void
747 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
748 {
749 uintptr_t x;
750 int queue, wakeup_swapper;
751
752 if (SCHEDULER_STOPPED())
753 return;
754
755 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
756
757 /* If the lock is recursed, then unrecurse one level. */
758 if (sx_xlocked(sx) && sx_recursed(sx)) {
759 if ((--sx->sx_recurse) == 0)
760 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
761 if (LOCK_LOG_TEST(&sx->lock_object, 0))
762 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
763 return;
764 }
765 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
766 SX_LOCK_EXCLUSIVE_WAITERS));
767 if (LOCK_LOG_TEST(&sx->lock_object, 0))
768 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
769
770 sleepq_lock(&sx->lock_object);
771 x = SX_LOCK_UNLOCKED;
772
773 /*
774 * The wake up algorithm here is quite simple and probably not
775 * ideal. It gives precedence to shared waiters if they are
776 * present. For this condition, we have to preserve the
777 * state of the exclusive waiters flag.
778 * If interruptible sleeps left the shared queue empty avoid a
779 * starvation for the threads sleeping on the exclusive queue by giving
780 * them precedence and cleaning up the shared waiters bit anyway.
781 */
782 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
783 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
784 queue = SQ_SHARED_QUEUE;
785 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
786 } else
787 queue = SQ_EXCLUSIVE_QUEUE;
788
789 /* Wake up all the waiters for the specific queue. */
790 if (LOCK_LOG_TEST(&sx->lock_object, 0))
791 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
792 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
793 "exclusive");
794 atomic_store_rel_ptr(&sx->sx_lock, x);
795 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
796 queue);
797 sleepq_release(&sx->lock_object);
798 if (wakeup_swapper)
799 kick_proc0();
800 }
801
802 /*
803 * This function represents the so-called 'hard case' for sx_slock
804 * operation. All 'easy case' failures are redirected to this. Note
805 * that ideally this would be a static function, but it needs to be
806 * accessible from at least sx.h.
807 */
808 int
809 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
810 {
811 GIANT_DECLARE;
812 #ifdef ADAPTIVE_SX
813 volatile struct thread *owner;
814 #endif
815 #ifdef LOCK_PROFILING
816 uint64_t waittime = 0;
817 int contested = 0;
818 #endif
819 uintptr_t x;
820 int error = 0;
821 #ifdef KDTRACE_HOOKS
822 uintptr_t state;
823 uint64_t spin_cnt = 0;
824 uint64_t sleep_cnt = 0;
825 int64_t sleep_time = 0;
826 int64_t all_time = 0;
827 #endif
828
829 if (SCHEDULER_STOPPED())
830 return (0);
831
832 #ifdef KDTRACE_HOOKS
833 state = sx->sx_lock;
834 all_time -= lockstat_nsecs(&sx->lock_object);
835 #endif
836
837 /*
838 * As with rwlocks, we don't make any attempt to try to block
839 * shared locks once there is an exclusive waiter.
840 */
841 for (;;) {
842 #ifdef KDTRACE_HOOKS
843 spin_cnt++;
844 #endif
845 x = sx->sx_lock;
846
847 /*
848 * If no other thread has an exclusive lock then try to bump up
849 * the count of sharers. Since we have to preserve the state
850 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
851 * shared lock loop back and retry.
852 */
853 if (x & SX_LOCK_SHARED) {
854 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
855 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
856 x + SX_ONE_SHARER)) {
857 if (LOCK_LOG_TEST(&sx->lock_object, 0))
858 CTR4(KTR_LOCK,
859 "%s: %p succeed %p -> %p", __func__,
860 sx, (void *)x,
861 (void *)(x + SX_ONE_SHARER));
862 break;
863 }
864 continue;
865 }
866 #ifdef HWPMC_HOOKS
867 PMC_SOFT_CALL( , , lock, failed);
868 #endif
869 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
870 &waittime);
871
872 #ifdef ADAPTIVE_SX
873 /*
874 * If the owner is running on another CPU, spin until
875 * the owner stops running or the state of the lock
876 * changes.
877 */
878 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
879 x = SX_OWNER(x);
880 owner = (struct thread *)x;
881 if (TD_IS_RUNNING(owner)) {
882 if (LOCK_LOG_TEST(&sx->lock_object, 0))
883 CTR3(KTR_LOCK,
884 "%s: spinning on %p held by %p",
885 __func__, sx, owner);
886 KTR_STATE1(KTR_SCHED, "thread",
887 sched_tdname(curthread), "spinning",
888 "lockname:\"%s\"", sx->lock_object.lo_name);
889 GIANT_SAVE();
890 while (SX_OWNER(sx->sx_lock) == x &&
891 TD_IS_RUNNING(owner)) {
892 #ifdef KDTRACE_HOOKS
893 spin_cnt++;
894 #endif
895 cpu_spinwait();
896 }
897 KTR_STATE0(KTR_SCHED, "thread",
898 sched_tdname(curthread), "running");
899 continue;
900 }
901 }
902 #endif
903
904 /*
905 * Some other thread already has an exclusive lock, so
906 * start the process of blocking.
907 */
908 sleepq_lock(&sx->lock_object);
909 x = sx->sx_lock;
910
911 /*
912 * The lock could have been released while we spun.
913 * In this case loop back and retry.
914 */
915 if (x & SX_LOCK_SHARED) {
916 sleepq_release(&sx->lock_object);
917 continue;
918 }
919
920 #ifdef ADAPTIVE_SX
921 /*
922 * If the owner is running on another CPU, spin until
923 * the owner stops running or the state of the lock
924 * changes.
925 */
926 if (!(x & SX_LOCK_SHARED) &&
927 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
928 owner = (struct thread *)SX_OWNER(x);
929 if (TD_IS_RUNNING(owner)) {
930 sleepq_release(&sx->lock_object);
931 continue;
932 }
933 }
934 #endif
935
936 /*
937 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
938 * fail to set it drop the sleep queue lock and loop
939 * back.
940 */
941 if (!(x & SX_LOCK_SHARED_WAITERS)) {
942 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
943 x | SX_LOCK_SHARED_WAITERS)) {
944 sleepq_release(&sx->lock_object);
945 continue;
946 }
947 if (LOCK_LOG_TEST(&sx->lock_object, 0))
948 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
949 __func__, sx);
950 }
951
952 /*
953 * Since we have been unable to acquire the shared lock,
954 * we have to sleep.
955 */
956 if (LOCK_LOG_TEST(&sx->lock_object, 0))
957 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
958 __func__, sx);
959
960 #ifdef KDTRACE_HOOKS
961 sleep_time -= lockstat_nsecs(&sx->lock_object);
962 #endif
963 GIANT_SAVE();
964 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
965 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
966 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
967 if (!(opts & SX_INTERRUPTIBLE))
968 sleepq_wait(&sx->lock_object, 0);
969 else
970 error = sleepq_wait_sig(&sx->lock_object, 0);
971 #ifdef KDTRACE_HOOKS
972 sleep_time += lockstat_nsecs(&sx->lock_object);
973 sleep_cnt++;
974 #endif
975 if (error) {
976 if (LOCK_LOG_TEST(&sx->lock_object, 0))
977 CTR2(KTR_LOCK,
978 "%s: interruptible sleep by %p suspended by signal",
979 __func__, sx);
980 break;
981 }
982 if (LOCK_LOG_TEST(&sx->lock_object, 0))
983 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
984 __func__, sx);
985 }
986 #ifdef KDTRACE_HOOKS
987 all_time += lockstat_nsecs(&sx->lock_object);
988 if (sleep_time)
989 LOCKSTAT_RECORD4(LS_SX_SLOCK_BLOCK, sx, sleep_time,
990 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
991 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
992 if (spin_cnt > sleep_cnt)
993 LOCKSTAT_RECORD4(LS_SX_SLOCK_SPIN, sx, all_time - sleep_time,
994 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
995 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
996 #endif
997 if (error == 0)
998 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
999 contested, waittime, file, line);
1000 GIANT_RESTORE();
1001 return (error);
1002 }
1003
1004 /*
1005 * This function represents the so-called 'hard case' for sx_sunlock
1006 * operation. All 'easy case' failures are redirected to this. Note
1007 * that ideally this would be a static function, but it needs to be
1008 * accessible from at least sx.h.
1009 */
1010 void
1011 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
1012 {
1013 uintptr_t x;
1014 int wakeup_swapper;
1015
1016 if (SCHEDULER_STOPPED())
1017 return;
1018
1019 for (;;) {
1020 x = sx->sx_lock;
1021
1022 /*
1023 * We should never have sharers while at least one thread
1024 * holds a shared lock.
1025 */
1026 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
1027 ("%s: waiting sharers", __func__));
1028
1029 /*
1030 * See if there is more than one shared lock held. If
1031 * so, just drop one and return.
1032 */
1033 if (SX_SHARERS(x) > 1) {
1034 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
1035 x - SX_ONE_SHARER)) {
1036 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1037 CTR4(KTR_LOCK,
1038 "%s: %p succeeded %p -> %p",
1039 __func__, sx, (void *)x,
1040 (void *)(x - SX_ONE_SHARER));
1041 break;
1042 }
1043 continue;
1044 }
1045
1046 /*
1047 * If there aren't any waiters for an exclusive lock,
1048 * then try to drop it quickly.
1049 */
1050 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
1051 MPASS(x == SX_SHARERS_LOCK(1));
1052 if (atomic_cmpset_rel_ptr(&sx->sx_lock,
1053 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
1054 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1055 CTR2(KTR_LOCK, "%s: %p last succeeded",
1056 __func__, sx);
1057 break;
1058 }
1059 continue;
1060 }
1061
1062 /*
1063 * At this point, there should just be one sharer with
1064 * exclusive waiters.
1065 */
1066 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1067
1068 sleepq_lock(&sx->lock_object);
1069
1070 /*
1071 * Wake up semantic here is quite simple:
1072 * Just wake up all the exclusive waiters.
1073 * Note that the state of the lock could have changed,
1074 * so if it fails loop back and retry.
1075 */
1076 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1077 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1078 SX_LOCK_UNLOCKED)) {
1079 sleepq_release(&sx->lock_object);
1080 continue;
1081 }
1082 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1083 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1084 "exclusive queue", __func__, sx);
1085 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1086 0, SQ_EXCLUSIVE_QUEUE);
1087 sleepq_release(&sx->lock_object);
1088 if (wakeup_swapper)
1089 kick_proc0();
1090 break;
1091 }
1092 }
1093
1094 #ifdef INVARIANT_SUPPORT
1095 #ifndef INVARIANTS
1096 #undef _sx_assert
1097 #endif
1098
1099 /*
1100 * In the non-WITNESS case, sx_assert() can only detect that at least
1101 * *some* thread owns an slock, but it cannot guarantee that *this*
1102 * thread owns an slock.
1103 */
1104 void
1105 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1106 {
1107 #ifndef WITNESS
1108 int slocked = 0;
1109 #endif
1110
1111 if (panicstr != NULL)
1112 return;
1113 switch (what) {
1114 case SA_SLOCKED:
1115 case SA_SLOCKED | SA_NOTRECURSED:
1116 case SA_SLOCKED | SA_RECURSED:
1117 #ifndef WITNESS
1118 slocked = 1;
1119 /* FALLTHROUGH */
1120 #endif
1121 case SA_LOCKED:
1122 case SA_LOCKED | SA_NOTRECURSED:
1123 case SA_LOCKED | SA_RECURSED:
1124 #ifdef WITNESS
1125 witness_assert(&sx->lock_object, what, file, line);
1126 #else
1127 /*
1128 * If some other thread has an exclusive lock or we
1129 * have one and are asserting a shared lock, fail.
1130 * Also, if no one has a lock at all, fail.
1131 */
1132 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1133 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1134 sx_xholder(sx) != curthread)))
1135 panic("Lock %s not %slocked @ %s:%d\n",
1136 sx->lock_object.lo_name, slocked ? "share " : "",
1137 file, line);
1138
1139 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1140 if (sx_recursed(sx)) {
1141 if (what & SA_NOTRECURSED)
1142 panic("Lock %s recursed @ %s:%d\n",
1143 sx->lock_object.lo_name, file,
1144 line);
1145 } else if (what & SA_RECURSED)
1146 panic("Lock %s not recursed @ %s:%d\n",
1147 sx->lock_object.lo_name, file, line);
1148 }
1149 #endif
1150 break;
1151 case SA_XLOCKED:
1152 case SA_XLOCKED | SA_NOTRECURSED:
1153 case SA_XLOCKED | SA_RECURSED:
1154 if (sx_xholder(sx) != curthread)
1155 panic("Lock %s not exclusively locked @ %s:%d\n",
1156 sx->lock_object.lo_name, file, line);
1157 if (sx_recursed(sx)) {
1158 if (what & SA_NOTRECURSED)
1159 panic("Lock %s recursed @ %s:%d\n",
1160 sx->lock_object.lo_name, file, line);
1161 } else if (what & SA_RECURSED)
1162 panic("Lock %s not recursed @ %s:%d\n",
1163 sx->lock_object.lo_name, file, line);
1164 break;
1165 case SA_UNLOCKED:
1166 #ifdef WITNESS
1167 witness_assert(&sx->lock_object, what, file, line);
1168 #else
1169 /*
1170 * If we hold an exclusve lock fail. We can't
1171 * reliably check to see if we hold a shared lock or
1172 * not.
1173 */
1174 if (sx_xholder(sx) == curthread)
1175 panic("Lock %s exclusively locked @ %s:%d\n",
1176 sx->lock_object.lo_name, file, line);
1177 #endif
1178 break;
1179 default:
1180 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1181 line);
1182 }
1183 }
1184 #endif /* INVARIANT_SUPPORT */
1185
1186 #ifdef DDB
1187 static void
1188 db_show_sx(const struct lock_object *lock)
1189 {
1190 struct thread *td;
1191 const struct sx *sx;
1192
1193 sx = (const struct sx *)lock;
1194
1195 db_printf(" state: ");
1196 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1197 db_printf("UNLOCKED\n");
1198 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1199 db_printf("DESTROYED\n");
1200 return;
1201 } else if (sx->sx_lock & SX_LOCK_SHARED)
1202 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1203 else {
1204 td = sx_xholder(sx);
1205 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1206 td->td_tid, td->td_proc->p_pid, td->td_name);
1207 if (sx_recursed(sx))
1208 db_printf(" recursed: %d\n", sx->sx_recurse);
1209 }
1210
1211 db_printf(" waiters: ");
1212 switch(sx->sx_lock &
1213 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1214 case SX_LOCK_SHARED_WAITERS:
1215 db_printf("shared\n");
1216 break;
1217 case SX_LOCK_EXCLUSIVE_WAITERS:
1218 db_printf("exclusive\n");
1219 break;
1220 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1221 db_printf("exclusive and shared\n");
1222 break;
1223 default:
1224 db_printf("none\n");
1225 }
1226 }
1227
1228 /*
1229 * Check to see if a thread that is blocked on a sleep queue is actually
1230 * blocked on an sx lock. If so, output some details and return true.
1231 * If the lock has an exclusive owner, return that in *ownerp.
1232 */
1233 int
1234 sx_chain(struct thread *td, struct thread **ownerp)
1235 {
1236 struct sx *sx;
1237
1238 /*
1239 * Check to see if this thread is blocked on an sx lock.
1240 * First, we check the lock class. If that is ok, then we
1241 * compare the lock name against the wait message.
1242 */
1243 sx = td->td_wchan;
1244 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1245 sx->lock_object.lo_name != td->td_wmesg)
1246 return (0);
1247
1248 /* We think we have an sx lock, so output some details. */
1249 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1250 *ownerp = sx_xholder(sx);
1251 if (sx->sx_lock & SX_LOCK_SHARED)
1252 db_printf("SLOCK (count %ju)\n",
1253 (uintmax_t)SX_SHARERS(sx->sx_lock));
1254 else
1255 db_printf("XLOCK\n");
1256 return (1);
1257 }
1258 #endif
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