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: stable/10/sys/kern/kern_sx.c 323870 2017-09-21 19:24:11Z marius $");
46
47 #include <sys/param.h>
48 #include <sys/systm.h>
49 #include <sys/kdb.h>
50 #include <sys/kernel.h>
51 #include <sys/ktr.h>
52 #include <sys/lock.h>
53 #include <sys/mutex.h>
54 #include <sys/proc.h>
55 #include <sys/sched.h>
56 #include <sys/sleepqueue.h>
57 #include <sys/sx.h>
58 #include <sys/smp.h>
59 #include <sys/sysctl.h>
60
61 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
62 #include <machine/cpu.h>
63 #endif
64
65 #ifdef DDB
66 #include <ddb/ddb.h>
67 #endif
68
69 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
70 #define ADAPTIVE_SX
71 #endif
72
73 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
74
75 #ifdef HWPMC_HOOKS
76 #include <sys/pmckern.h>
77 PMC_SOFT_DECLARE( , , lock, failed);
78 #endif
79
80 /* Handy macros for sleep queues. */
81 #define SQ_EXCLUSIVE_QUEUE 0
82 #define SQ_SHARED_QUEUE 1
83
84 /*
85 * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file. We
86 * drop Giant anytime we have to sleep or if we adaptively spin.
87 */
88 #define GIANT_DECLARE \
89 int _giantcnt = 0; \
90 WITNESS_SAVE_DECL(Giant) \
91
92 #define GIANT_SAVE() do { \
93 if (mtx_owned(&Giant)) { \
94 WITNESS_SAVE(&Giant.lock_object, Giant); \
95 while (mtx_owned(&Giant)) { \
96 _giantcnt++; \
97 mtx_unlock(&Giant); \
98 } \
99 } \
100 } while (0)
101
102 #define GIANT_RESTORE() do { \
103 if (_giantcnt > 0) { \
104 mtx_assert(&Giant, MA_NOTOWNED); \
105 while (_giantcnt--) \
106 mtx_lock(&Giant); \
107 WITNESS_RESTORE(&Giant.lock_object, Giant); \
108 } \
109 } while (0)
110
111 /*
112 * Returns true if an exclusive lock is recursed. It assumes
113 * curthread currently has an exclusive lock.
114 */
115 #define sx_recurse lock_object.lo_data
116 #define sx_recursed(sx) ((sx)->sx_recurse != 0)
117
118 static void assert_sx(const struct lock_object *lock, int what);
119 #ifdef DDB
120 static void db_show_sx(const struct lock_object *lock);
121 #endif
122 static void lock_sx(struct lock_object *lock, uintptr_t how);
123 #ifdef KDTRACE_HOOKS
124 static int owner_sx(const struct lock_object *lock, struct thread **owner);
125 #endif
126 static uintptr_t unlock_sx(struct lock_object *lock);
127
128 struct lock_class lock_class_sx = {
129 .lc_name = "sx",
130 .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
131 .lc_assert = assert_sx,
132 #ifdef DDB
133 .lc_ddb_show = db_show_sx,
134 #endif
135 .lc_lock = lock_sx,
136 .lc_unlock = unlock_sx,
137 #ifdef KDTRACE_HOOKS
138 .lc_owner = owner_sx,
139 #endif
140 };
141
142 #ifndef INVARIANTS
143 #define _sx_assert(sx, what, file, line)
144 #endif
145
146 #ifdef ADAPTIVE_SX
147 static u_int asx_retries = 10;
148 static u_int asx_loops = 10000;
149 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
150 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
151 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
152
153 static struct lock_delay_config sx_delay = {
154 .initial = 1000,
155 .step = 500,
156 .min = 100,
157 .max = 5000,
158 };
159
160 SYSCTL_INT(_debug_sx, OID_AUTO, delay_initial, CTLFLAG_RW, &sx_delay.initial,
161 0, "");
162 SYSCTL_INT(_debug_sx, OID_AUTO, delay_step, CTLFLAG_RW, &sx_delay.step,
163 0, "");
164 SYSCTL_INT(_debug_sx, OID_AUTO, delay_min, CTLFLAG_RW, &sx_delay.min,
165 0, "");
166 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
167 0, "");
168
169 static void
sx_delay_sysinit(void * dummy)170 sx_delay_sysinit(void *dummy)
171 {
172
173 sx_delay.initial = mp_ncpus * 25;
174 sx_delay.step = (mp_ncpus * 25) / 2;
175 sx_delay.min = mp_ncpus * 5;
176 sx_delay.max = mp_ncpus * 25 * 10;
177 }
178 LOCK_DELAY_SYSINIT(sx_delay_sysinit);
179 #endif
180
181 void
assert_sx(const struct lock_object * lock,int what)182 assert_sx(const struct lock_object *lock, int what)
183 {
184
185 sx_assert((const struct sx *)lock, what);
186 }
187
188 void
lock_sx(struct lock_object * lock,uintptr_t how)189 lock_sx(struct lock_object *lock, uintptr_t how)
190 {
191 struct sx *sx;
192
193 sx = (struct sx *)lock;
194 if (how)
195 sx_slock(sx);
196 else
197 sx_xlock(sx);
198 }
199
200 uintptr_t
unlock_sx(struct lock_object * lock)201 unlock_sx(struct lock_object *lock)
202 {
203 struct sx *sx;
204
205 sx = (struct sx *)lock;
206 sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
207 if (sx_xlocked(sx)) {
208 sx_xunlock(sx);
209 return (0);
210 } else {
211 sx_sunlock(sx);
212 return (1);
213 }
214 }
215
216 #ifdef KDTRACE_HOOKS
217 int
owner_sx(const struct lock_object * lock,struct thread ** owner)218 owner_sx(const struct lock_object *lock, struct thread **owner)
219 {
220 const struct sx *sx = (const struct sx *)lock;
221 uintptr_t x = sx->sx_lock;
222
223 *owner = (struct thread *)SX_OWNER(x);
224 return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
225 (*owner != NULL));
226 }
227 #endif
228
229 void
sx_sysinit(void * arg)230 sx_sysinit(void *arg)
231 {
232 struct sx_args *sargs = arg;
233
234 sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
235 }
236
237 void
sx_init_flags(struct sx * sx,const char * description,int opts)238 sx_init_flags(struct sx *sx, const char *description, int opts)
239 {
240 int flags;
241
242 MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
243 SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0);
244 ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
245 ("%s: sx_lock not aligned for %s: %p", __func__, description,
246 &sx->sx_lock));
247
248 flags = LO_SLEEPABLE | LO_UPGRADABLE;
249 if (opts & SX_DUPOK)
250 flags |= LO_DUPOK;
251 if (opts & SX_NOPROFILE)
252 flags |= LO_NOPROFILE;
253 if (!(opts & SX_NOWITNESS))
254 flags |= LO_WITNESS;
255 if (opts & SX_RECURSE)
256 flags |= LO_RECURSABLE;
257 if (opts & SX_QUIET)
258 flags |= LO_QUIET;
259 if (opts & SX_NEW)
260 flags |= LO_NEW;
261
262 flags |= opts & SX_NOADAPTIVE;
263 lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
264 sx->sx_lock = SX_LOCK_UNLOCKED;
265 sx->sx_recurse = 0;
266 }
267
268 void
sx_destroy(struct sx * sx)269 sx_destroy(struct sx *sx)
270 {
271
272 KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
273 KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
274 sx->sx_lock = SX_LOCK_DESTROYED;
275 lock_destroy(&sx->lock_object);
276 }
277
278 int
_sx_slock(struct sx * sx,int opts,const char * file,int line)279 _sx_slock(struct sx *sx, int opts, const char *file, int line)
280 {
281 int error = 0;
282
283 if (SCHEDULER_STOPPED())
284 return (0);
285 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
286 ("sx_slock() by idle thread %p on sx %s @ %s:%d",
287 curthread, sx->lock_object.lo_name, file, line));
288 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
289 ("sx_slock() of destroyed sx @ %s:%d", file, line));
290 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
291 error = __sx_slock(sx, opts, file, line);
292 if (!error) {
293 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
294 WITNESS_LOCK(&sx->lock_object, 0, file, line);
295 curthread->td_locks++;
296 }
297
298 return (error);
299 }
300
301 int
sx_try_slock_(struct sx * sx,const char * file,int line)302 sx_try_slock_(struct sx *sx, const char *file, int line)
303 {
304 uintptr_t x;
305
306 if (SCHEDULER_STOPPED())
307 return (1);
308
309 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
310 ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
311 curthread, sx->lock_object.lo_name, file, line));
312
313 for (;;) {
314 x = sx->sx_lock;
315 KASSERT(x != SX_LOCK_DESTROYED,
316 ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
317 if (!(x & SX_LOCK_SHARED))
318 break;
319 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x, x + SX_ONE_SHARER)) {
320 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
321 WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
322 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE,
323 sx, 0, 0, file, line);
324 curthread->td_locks++;
325 return (1);
326 }
327 }
328
329 LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
330 return (0);
331 }
332
333 int
_sx_xlock(struct sx * sx,int opts,const char * file,int line)334 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
335 {
336 int error = 0;
337
338 if (SCHEDULER_STOPPED())
339 return (0);
340 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
341 ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
342 curthread, sx->lock_object.lo_name, file, line));
343 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
344 ("sx_xlock() of destroyed sx @ %s:%d", file, line));
345 WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
346 line, NULL);
347 error = __sx_xlock(sx, curthread, opts, file, line);
348 if (!error) {
349 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
350 file, line);
351 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
352 curthread->td_locks++;
353 }
354
355 return (error);
356 }
357
358 int
sx_try_xlock_(struct sx * sx,const char * file,int line)359 sx_try_xlock_(struct sx *sx, const char *file, int line)
360 {
361 int rval;
362
363 if (SCHEDULER_STOPPED())
364 return (1);
365
366 KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
367 ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
368 curthread, sx->lock_object.lo_name, file, line));
369 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
370 ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
371
372 if (sx_xlocked(sx) &&
373 (sx->lock_object.lo_flags & LO_RECURSABLE) != 0) {
374 sx->sx_recurse++;
375 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
376 rval = 1;
377 } else
378 rval = atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED,
379 (uintptr_t)curthread);
380 LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
381 if (rval) {
382 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
383 file, line);
384 if (!sx_recursed(sx))
385 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE,
386 sx, 0, 0, file, line);
387 curthread->td_locks++;
388 }
389
390 return (rval);
391 }
392
393 void
_sx_sunlock(struct sx * sx,const char * file,int line)394 _sx_sunlock(struct sx *sx, const char *file, int line)
395 {
396
397 if (SCHEDULER_STOPPED())
398 return;
399 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
400 ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
401 _sx_assert(sx, SA_SLOCKED, file, line);
402 WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
403 LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
404 __sx_sunlock(sx, file, line);
405 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_SUNLOCK_RELEASE, sx);
406 curthread->td_locks--;
407 }
408
409 void
_sx_xunlock(struct sx * sx,const char * file,int line)410 _sx_xunlock(struct sx *sx, const char *file, int line)
411 {
412
413 if (SCHEDULER_STOPPED())
414 return;
415 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
416 ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
417 _sx_assert(sx, SA_XLOCKED, file, line);
418 WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
419 LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
420 line);
421 if (!sx_recursed(sx))
422 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_SX_XUNLOCK_RELEASE, sx);
423 __sx_xunlock(sx, curthread, file, line);
424 curthread->td_locks--;
425 }
426
427 /*
428 * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
429 * This will only succeed if this thread holds a single shared lock.
430 * Return 1 if if the upgrade succeed, 0 otherwise.
431 */
432 int
sx_try_upgrade_(struct sx * sx,const char * file,int line)433 sx_try_upgrade_(struct sx *sx, const char *file, int line)
434 {
435 uintptr_t x;
436 int success;
437
438 if (SCHEDULER_STOPPED())
439 return (1);
440
441 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
442 ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
443 _sx_assert(sx, SA_SLOCKED, file, line);
444
445 /*
446 * Try to switch from one shared lock to an exclusive lock. We need
447 * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
448 * we will wake up the exclusive waiters when we drop the lock.
449 */
450 x = sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS;
451 success = atomic_cmpset_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) | x,
452 (uintptr_t)curthread | x);
453 LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
454 if (success) {
455 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
456 file, line);
457 LOCKSTAT_RECORD0(LS_SX_TRYUPGRADE_UPGRADE, sx);
458 }
459 return (success);
460 }
461
462 /*
463 * Downgrade an unrecursed exclusive lock into a single shared lock.
464 */
465 void
sx_downgrade_(struct sx * sx,const char * file,int line)466 sx_downgrade_(struct sx *sx, const char *file, int line)
467 {
468 uintptr_t x;
469 int wakeup_swapper;
470
471 if (SCHEDULER_STOPPED())
472 return;
473
474 KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
475 ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
476 _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
477 #ifndef INVARIANTS
478 if (sx_recursed(sx))
479 panic("downgrade of a recursed lock");
480 #endif
481
482 WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
483
484 /*
485 * Try to switch from an exclusive lock with no shared waiters
486 * to one sharer with no shared waiters. If there are
487 * exclusive waiters, we don't need to lock the sleep queue so
488 * long as we preserve the flag. We do one quick try and if
489 * that fails we grab the sleepq lock to keep the flags from
490 * changing and do it the slow way.
491 *
492 * We have to lock the sleep queue if there are shared waiters
493 * so we can wake them up.
494 */
495 x = sx->sx_lock;
496 if (!(x & SX_LOCK_SHARED_WAITERS) &&
497 atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
498 (x & SX_LOCK_EXCLUSIVE_WAITERS))) {
499 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
500 return;
501 }
502
503 /*
504 * Lock the sleep queue so we can read the waiters bits
505 * without any races and wakeup any shared waiters.
506 */
507 sleepq_lock(&sx->lock_object);
508
509 /*
510 * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
511 * shared lock. If there are any shared waiters, wake them up.
512 */
513 wakeup_swapper = 0;
514 x = sx->sx_lock;
515 atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
516 (x & SX_LOCK_EXCLUSIVE_WAITERS));
517 if (x & SX_LOCK_SHARED_WAITERS)
518 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
519 0, SQ_SHARED_QUEUE);
520 sleepq_release(&sx->lock_object);
521
522 LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
523 LOCKSTAT_RECORD0(LS_SX_DOWNGRADE_DOWNGRADE, sx);
524
525 if (wakeup_swapper)
526 kick_proc0();
527 }
528
529 /*
530 * This function represents the so-called 'hard case' for sx_xlock
531 * operation. All 'easy case' failures are redirected to this. Note
532 * that ideally this would be a static function, but it needs to be
533 * accessible from at least sx.h.
534 */
535 int
_sx_xlock_hard(struct sx * sx,uintptr_t tid,int opts,const char * file,int line)536 _sx_xlock_hard(struct sx *sx, uintptr_t tid, int opts, const char *file,
537 int line)
538 {
539 GIANT_DECLARE;
540 #ifdef ADAPTIVE_SX
541 volatile struct thread *owner;
542 u_int i, spintries = 0;
543 #endif
544 uintptr_t x;
545 #ifdef LOCK_PROFILING
546 uint64_t waittime = 0;
547 int contested = 0;
548 #endif
549 int error = 0;
550 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
551 struct lock_delay_arg lda;
552 #endif
553 #ifdef KDTRACE_HOOKS
554 uintptr_t state;
555 u_int sleep_cnt = 0;
556 int64_t sleep_time = 0;
557 int64_t all_time = 0;
558 #endif
559
560 if (SCHEDULER_STOPPED())
561 return (0);
562
563 #if defined(ADAPTIVE_SX)
564 lock_delay_arg_init(&lda, &sx_delay);
565 #elif defined(KDTRACE_HOOKS)
566 lock_delay_arg_init(&lda, NULL);
567 #endif
568
569 /* If we already hold an exclusive lock, then recurse. */
570 if (sx_xlocked(sx)) {
571 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
572 ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
573 sx->lock_object.lo_name, file, line));
574 sx->sx_recurse++;
575 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
576 if (LOCK_LOG_TEST(&sx->lock_object, 0))
577 CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
578 return (0);
579 }
580
581 if (LOCK_LOG_TEST(&sx->lock_object, 0))
582 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
583 sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
584
585 #ifdef KDTRACE_HOOKS
586 all_time -= lockstat_nsecs(&sx->lock_object);
587 state = sx->sx_lock;
588 #endif
589 for (;;) {
590 if (sx->sx_lock == SX_LOCK_UNLOCKED &&
591 atomic_cmpset_acq_ptr(&sx->sx_lock, SX_LOCK_UNLOCKED, tid))
592 break;
593 #ifdef KDTRACE_HOOKS
594 lda.spin_cnt++;
595 #endif
596 #ifdef HWPMC_HOOKS
597 PMC_SOFT_CALL( , , lock, failed);
598 #endif
599 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
600 &waittime);
601 #ifdef ADAPTIVE_SX
602 /*
603 * If the lock is write locked and the owner is
604 * running on another CPU, spin until the owner stops
605 * running or the state of the lock changes.
606 */
607 x = sx->sx_lock;
608 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
609 if ((x & SX_LOCK_SHARED) == 0) {
610 x = SX_OWNER(x);
611 owner = (struct thread *)x;
612 if (TD_IS_RUNNING(owner)) {
613 if (LOCK_LOG_TEST(&sx->lock_object, 0))
614 CTR3(KTR_LOCK,
615 "%s: spinning on %p held by %p",
616 __func__, sx, owner);
617 KTR_STATE1(KTR_SCHED, "thread",
618 sched_tdname(curthread), "spinning",
619 "lockname:\"%s\"",
620 sx->lock_object.lo_name);
621 GIANT_SAVE();
622 while (SX_OWNER(sx->sx_lock) == x &&
623 TD_IS_RUNNING(owner))
624 lock_delay(&lda);
625 KTR_STATE0(KTR_SCHED, "thread",
626 sched_tdname(curthread), "running");
627 continue;
628 }
629 } else if (SX_SHARERS(x) && spintries < asx_retries) {
630 KTR_STATE1(KTR_SCHED, "thread",
631 sched_tdname(curthread), "spinning",
632 "lockname:\"%s\"", sx->lock_object.lo_name);
633 GIANT_SAVE();
634 spintries++;
635 for (i = 0; i < asx_loops; i++) {
636 if (LOCK_LOG_TEST(&sx->lock_object, 0))
637 CTR4(KTR_LOCK,
638 "%s: shared spinning on %p with %u and %u",
639 __func__, sx, spintries, i);
640 x = sx->sx_lock;
641 if ((x & SX_LOCK_SHARED) == 0 ||
642 SX_SHARERS(x) == 0)
643 break;
644 cpu_spinwait();
645 #ifdef KDTRACE_HOOKS
646 lda.spin_cnt++;
647 #endif
648 }
649 KTR_STATE0(KTR_SCHED, "thread",
650 sched_tdname(curthread), "running");
651 if (i != asx_loops)
652 continue;
653 }
654 }
655 #endif
656
657 sleepq_lock(&sx->lock_object);
658 x = sx->sx_lock;
659
660 /*
661 * If the lock was released while spinning on the
662 * sleep queue chain lock, try again.
663 */
664 if (x == SX_LOCK_UNLOCKED) {
665 sleepq_release(&sx->lock_object);
666 continue;
667 }
668
669 #ifdef ADAPTIVE_SX
670 /*
671 * The current lock owner might have started executing
672 * on another CPU (or the lock could have changed
673 * owners) while we were waiting on the sleep queue
674 * chain lock. If so, drop the sleep queue lock and try
675 * again.
676 */
677 if (!(x & SX_LOCK_SHARED) &&
678 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
679 owner = (struct thread *)SX_OWNER(x);
680 if (TD_IS_RUNNING(owner)) {
681 sleepq_release(&sx->lock_object);
682 continue;
683 }
684 }
685 #endif
686
687 /*
688 * If an exclusive lock was released with both shared
689 * and exclusive waiters and a shared waiter hasn't
690 * woken up and acquired the lock yet, sx_lock will be
691 * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
692 * If we see that value, try to acquire it once. Note
693 * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
694 * as there are other exclusive waiters still. If we
695 * fail, restart the loop.
696 */
697 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
698 if (atomic_cmpset_acq_ptr(&sx->sx_lock,
699 SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS,
700 tid | SX_LOCK_EXCLUSIVE_WAITERS)) {
701 sleepq_release(&sx->lock_object);
702 CTR2(KTR_LOCK, "%s: %p claimed by new writer",
703 __func__, sx);
704 break;
705 }
706 sleepq_release(&sx->lock_object);
707 continue;
708 }
709
710 /*
711 * Try to set the SX_LOCK_EXCLUSIVE_WAITERS. If we fail,
712 * than loop back and retry.
713 */
714 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
715 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
716 x | SX_LOCK_EXCLUSIVE_WAITERS)) {
717 sleepq_release(&sx->lock_object);
718 continue;
719 }
720 if (LOCK_LOG_TEST(&sx->lock_object, 0))
721 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
722 __func__, sx);
723 }
724
725 /*
726 * Since we have been unable to acquire the exclusive
727 * lock and the exclusive waiters flag is set, we have
728 * to sleep.
729 */
730 if (LOCK_LOG_TEST(&sx->lock_object, 0))
731 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
732 __func__, sx);
733
734 #ifdef KDTRACE_HOOKS
735 sleep_time -= lockstat_nsecs(&sx->lock_object);
736 #endif
737 GIANT_SAVE();
738 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
739 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
740 SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
741 if (!(opts & SX_INTERRUPTIBLE))
742 sleepq_wait(&sx->lock_object, 0);
743 else
744 error = sleepq_wait_sig(&sx->lock_object, 0);
745 #ifdef KDTRACE_HOOKS
746 sleep_time += lockstat_nsecs(&sx->lock_object);
747 sleep_cnt++;
748 #endif
749 if (error) {
750 if (LOCK_LOG_TEST(&sx->lock_object, 0))
751 CTR2(KTR_LOCK,
752 "%s: interruptible sleep by %p suspended by signal",
753 __func__, sx);
754 break;
755 }
756 if (LOCK_LOG_TEST(&sx->lock_object, 0))
757 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
758 __func__, sx);
759 }
760 #ifdef KDTRACE_HOOKS
761 all_time += lockstat_nsecs(&sx->lock_object);
762 if (sleep_time)
763 LOCKSTAT_RECORD4(LS_SX_XLOCK_BLOCK, sx, sleep_time,
764 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
765 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
766 if (lda.spin_cnt > sleep_cnt)
767 LOCKSTAT_RECORD4(LS_SX_XLOCK_SPIN, sx, all_time - sleep_time,
768 LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
769 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
770 #endif
771 if (!error)
772 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_XLOCK_ACQUIRE, sx,
773 contested, waittime, file, line);
774 GIANT_RESTORE();
775 return (error);
776 }
777
778 /*
779 * This function represents the so-called 'hard case' for sx_xunlock
780 * operation. All 'easy case' failures are redirected to this. Note
781 * that ideally this would be a static function, but it needs to be
782 * accessible from at least sx.h.
783 */
784 void
_sx_xunlock_hard(struct sx * sx,uintptr_t tid,const char * file,int line)785 _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
786 {
787 uintptr_t x;
788 int queue, wakeup_swapper;
789
790 if (SCHEDULER_STOPPED())
791 return;
792
793 MPASS(!(sx->sx_lock & SX_LOCK_SHARED));
794
795 /* If the lock is recursed, then unrecurse one level. */
796 if (sx_xlocked(sx) && sx_recursed(sx)) {
797 if ((--sx->sx_recurse) == 0)
798 atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
799 if (LOCK_LOG_TEST(&sx->lock_object, 0))
800 CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
801 return;
802 }
803 MPASS(sx->sx_lock & (SX_LOCK_SHARED_WAITERS |
804 SX_LOCK_EXCLUSIVE_WAITERS));
805 if (LOCK_LOG_TEST(&sx->lock_object, 0))
806 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
807
808 sleepq_lock(&sx->lock_object);
809 x = SX_LOCK_UNLOCKED;
810
811 /*
812 * The wake up algorithm here is quite simple and probably not
813 * ideal. It gives precedence to shared waiters if they are
814 * present. For this condition, we have to preserve the
815 * state of the exclusive waiters flag.
816 * If interruptible sleeps left the shared queue empty avoid a
817 * starvation for the threads sleeping on the exclusive queue by giving
818 * them precedence and cleaning up the shared waiters bit anyway.
819 */
820 if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
821 sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
822 queue = SQ_SHARED_QUEUE;
823 x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
824 } else
825 queue = SQ_EXCLUSIVE_QUEUE;
826
827 /* Wake up all the waiters for the specific queue. */
828 if (LOCK_LOG_TEST(&sx->lock_object, 0))
829 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
830 __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
831 "exclusive");
832 atomic_store_rel_ptr(&sx->sx_lock, x);
833 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
834 queue);
835 sleepq_release(&sx->lock_object);
836 if (wakeup_swapper)
837 kick_proc0();
838 }
839
840 /*
841 * This function represents the so-called 'hard case' for sx_slock
842 * operation. All 'easy case' failures are redirected to this. Note
843 * that ideally this would be a static function, but it needs to be
844 * accessible from at least sx.h.
845 */
846 int
_sx_slock_hard(struct sx * sx,int opts,const char * file,int line)847 _sx_slock_hard(struct sx *sx, int opts, const char *file, int line)
848 {
849 GIANT_DECLARE;
850 #ifdef ADAPTIVE_SX
851 volatile struct thread *owner;
852 #endif
853 #ifdef LOCK_PROFILING
854 uint64_t waittime = 0;
855 int contested = 0;
856 #endif
857 uintptr_t x;
858 int error = 0;
859 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
860 struct lock_delay_arg lda;
861 #endif
862 #ifdef KDTRACE_HOOKS
863 uintptr_t state;
864 u_int sleep_cnt = 0;
865 int64_t sleep_time = 0;
866 int64_t all_time = 0;
867 #endif
868
869 if (SCHEDULER_STOPPED())
870 return (0);
871
872 #if defined(ADAPTIVE_SX)
873 lock_delay_arg_init(&lda, &sx_delay);
874 #elif defined(KDTRACE_HOOKS)
875 lock_delay_arg_init(&lda, NULL);
876 #endif
877 #ifdef KDTRACE_HOOKS
878 state = sx->sx_lock;
879 all_time -= lockstat_nsecs(&sx->lock_object);
880 #endif
881
882 /*
883 * As with rwlocks, we don't make any attempt to try to block
884 * shared locks once there is an exclusive waiter.
885 */
886 for (;;) {
887 #ifdef KDTRACE_HOOKS
888 lda.spin_cnt++;
889 #endif
890 x = sx->sx_lock;
891
892 /*
893 * If no other thread has an exclusive lock then try to bump up
894 * the count of sharers. Since we have to preserve the state
895 * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
896 * shared lock loop back and retry.
897 */
898 if (x & SX_LOCK_SHARED) {
899 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
900 if (atomic_cmpset_acq_ptr(&sx->sx_lock, x,
901 x + SX_ONE_SHARER)) {
902 if (LOCK_LOG_TEST(&sx->lock_object, 0))
903 CTR4(KTR_LOCK,
904 "%s: %p succeed %p -> %p", __func__,
905 sx, (void *)x,
906 (void *)(x + SX_ONE_SHARER));
907 break;
908 }
909 continue;
910 }
911 #ifdef HWPMC_HOOKS
912 PMC_SOFT_CALL( , , lock, failed);
913 #endif
914 lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
915 &waittime);
916
917 #ifdef ADAPTIVE_SX
918 /*
919 * If the owner is running on another CPU, spin until
920 * the owner stops running or the state of the lock
921 * changes.
922 */
923 if ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
924 x = SX_OWNER(x);
925 owner = (struct thread *)x;
926 if (TD_IS_RUNNING(owner)) {
927 if (LOCK_LOG_TEST(&sx->lock_object, 0))
928 CTR3(KTR_LOCK,
929 "%s: spinning on %p held by %p",
930 __func__, sx, owner);
931 KTR_STATE1(KTR_SCHED, "thread",
932 sched_tdname(curthread), "spinning",
933 "lockname:\"%s\"", sx->lock_object.lo_name);
934 GIANT_SAVE();
935 while (SX_OWNER(sx->sx_lock) == x &&
936 TD_IS_RUNNING(owner))
937 lock_delay(&lda);
938 KTR_STATE0(KTR_SCHED, "thread",
939 sched_tdname(curthread), "running");
940 continue;
941 }
942 }
943 #endif
944
945 /*
946 * Some other thread already has an exclusive lock, so
947 * start the process of blocking.
948 */
949 sleepq_lock(&sx->lock_object);
950 x = sx->sx_lock;
951
952 /*
953 * The lock could have been released while we spun.
954 * In this case loop back and retry.
955 */
956 if (x & SX_LOCK_SHARED) {
957 sleepq_release(&sx->lock_object);
958 continue;
959 }
960
961 #ifdef ADAPTIVE_SX
962 /*
963 * If the owner is running on another CPU, spin until
964 * the owner stops running or the state of the lock
965 * changes.
966 */
967 if (!(x & SX_LOCK_SHARED) &&
968 (sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0) {
969 owner = (struct thread *)SX_OWNER(x);
970 if (TD_IS_RUNNING(owner)) {
971 sleepq_release(&sx->lock_object);
972 continue;
973 }
974 }
975 #endif
976
977 /*
978 * Try to set the SX_LOCK_SHARED_WAITERS flag. If we
979 * fail to set it drop the sleep queue lock and loop
980 * back.
981 */
982 if (!(x & SX_LOCK_SHARED_WAITERS)) {
983 if (!atomic_cmpset_ptr(&sx->sx_lock, x,
984 x | SX_LOCK_SHARED_WAITERS)) {
985 sleepq_release(&sx->lock_object);
986 continue;
987 }
988 if (LOCK_LOG_TEST(&sx->lock_object, 0))
989 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
990 __func__, sx);
991 }
992
993 /*
994 * Since we have been unable to acquire the shared lock,
995 * we have to sleep.
996 */
997 if (LOCK_LOG_TEST(&sx->lock_object, 0))
998 CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
999 __func__, sx);
1000
1001 #ifdef KDTRACE_HOOKS
1002 sleep_time -= lockstat_nsecs(&sx->lock_object);
1003 #endif
1004 GIANT_SAVE();
1005 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1006 SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1007 SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1008 if (!(opts & SX_INTERRUPTIBLE))
1009 sleepq_wait(&sx->lock_object, 0);
1010 else
1011 error = sleepq_wait_sig(&sx->lock_object, 0);
1012 #ifdef KDTRACE_HOOKS
1013 sleep_time += lockstat_nsecs(&sx->lock_object);
1014 sleep_cnt++;
1015 #endif
1016 if (error) {
1017 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1018 CTR2(KTR_LOCK,
1019 "%s: interruptible sleep by %p suspended by signal",
1020 __func__, sx);
1021 break;
1022 }
1023 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1024 CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1025 __func__, sx);
1026 }
1027 #ifdef KDTRACE_HOOKS
1028 all_time += lockstat_nsecs(&sx->lock_object);
1029 if (sleep_time)
1030 LOCKSTAT_RECORD4(LS_SX_SLOCK_BLOCK, sx, sleep_time,
1031 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1032 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1033 if (lda.spin_cnt > sleep_cnt)
1034 LOCKSTAT_RECORD4(LS_SX_SLOCK_SPIN, sx, all_time - sleep_time,
1035 LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1036 (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1037 #endif
1038 if (error == 0)
1039 LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_SX_SLOCK_ACQUIRE, sx,
1040 contested, waittime, file, line);
1041 GIANT_RESTORE();
1042 return (error);
1043 }
1044
1045 /*
1046 * This function represents the so-called 'hard case' for sx_sunlock
1047 * operation. All 'easy case' failures are redirected to this. Note
1048 * that ideally this would be a static function, but it needs to be
1049 * accessible from at least sx.h.
1050 */
1051 void
_sx_sunlock_hard(struct sx * sx,const char * file,int line)1052 _sx_sunlock_hard(struct sx *sx, const char *file, int line)
1053 {
1054 uintptr_t x;
1055 int wakeup_swapper;
1056
1057 if (SCHEDULER_STOPPED())
1058 return;
1059
1060 for (;;) {
1061 x = sx->sx_lock;
1062
1063 /*
1064 * We should never have sharers while at least one thread
1065 * holds a shared lock.
1066 */
1067 KASSERT(!(x & SX_LOCK_SHARED_WAITERS),
1068 ("%s: waiting sharers", __func__));
1069
1070 /*
1071 * See if there is more than one shared lock held. If
1072 * so, just drop one and return.
1073 */
1074 if (SX_SHARERS(x) > 1) {
1075 if (atomic_cmpset_rel_ptr(&sx->sx_lock, x,
1076 x - SX_ONE_SHARER)) {
1077 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1078 CTR4(KTR_LOCK,
1079 "%s: %p succeeded %p -> %p",
1080 __func__, sx, (void *)x,
1081 (void *)(x - SX_ONE_SHARER));
1082 break;
1083 }
1084 continue;
1085 }
1086
1087 /*
1088 * If there aren't any waiters for an exclusive lock,
1089 * then try to drop it quickly.
1090 */
1091 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
1092 MPASS(x == SX_SHARERS_LOCK(1));
1093 if (atomic_cmpset_rel_ptr(&sx->sx_lock,
1094 SX_SHARERS_LOCK(1), SX_LOCK_UNLOCKED)) {
1095 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1096 CTR2(KTR_LOCK, "%s: %p last succeeded",
1097 __func__, sx);
1098 break;
1099 }
1100 continue;
1101 }
1102
1103 /*
1104 * At this point, there should just be one sharer with
1105 * exclusive waiters.
1106 */
1107 MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1108
1109 sleepq_lock(&sx->lock_object);
1110
1111 /*
1112 * Wake up semantic here is quite simple:
1113 * Just wake up all the exclusive waiters.
1114 * Note that the state of the lock could have changed,
1115 * so if it fails loop back and retry.
1116 */
1117 if (!atomic_cmpset_rel_ptr(&sx->sx_lock,
1118 SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS,
1119 SX_LOCK_UNLOCKED)) {
1120 sleepq_release(&sx->lock_object);
1121 continue;
1122 }
1123 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1124 CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1125 "exclusive queue", __func__, sx);
1126 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1127 0, SQ_EXCLUSIVE_QUEUE);
1128 sleepq_release(&sx->lock_object);
1129 if (wakeup_swapper)
1130 kick_proc0();
1131 break;
1132 }
1133 }
1134
1135 #ifdef INVARIANT_SUPPORT
1136 #ifndef INVARIANTS
1137 #undef _sx_assert
1138 #endif
1139
1140 /*
1141 * In the non-WITNESS case, sx_assert() can only detect that at least
1142 * *some* thread owns an slock, but it cannot guarantee that *this*
1143 * thread owns an slock.
1144 */
1145 void
_sx_assert(const struct sx * sx,int what,const char * file,int line)1146 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1147 {
1148 #ifndef WITNESS
1149 int slocked = 0;
1150 #endif
1151
1152 if (panicstr != NULL)
1153 return;
1154 switch (what) {
1155 case SA_SLOCKED:
1156 case SA_SLOCKED | SA_NOTRECURSED:
1157 case SA_SLOCKED | SA_RECURSED:
1158 #ifndef WITNESS
1159 slocked = 1;
1160 /* FALLTHROUGH */
1161 #endif
1162 case SA_LOCKED:
1163 case SA_LOCKED | SA_NOTRECURSED:
1164 case SA_LOCKED | SA_RECURSED:
1165 #ifdef WITNESS
1166 witness_assert(&sx->lock_object, what, file, line);
1167 #else
1168 /*
1169 * If some other thread has an exclusive lock or we
1170 * have one and are asserting a shared lock, fail.
1171 * Also, if no one has a lock at all, fail.
1172 */
1173 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1174 (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1175 sx_xholder(sx) != curthread)))
1176 panic("Lock %s not %slocked @ %s:%d\n",
1177 sx->lock_object.lo_name, slocked ? "share " : "",
1178 file, line);
1179
1180 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1181 if (sx_recursed(sx)) {
1182 if (what & SA_NOTRECURSED)
1183 panic("Lock %s recursed @ %s:%d\n",
1184 sx->lock_object.lo_name, file,
1185 line);
1186 } else if (what & SA_RECURSED)
1187 panic("Lock %s not recursed @ %s:%d\n",
1188 sx->lock_object.lo_name, file, line);
1189 }
1190 #endif
1191 break;
1192 case SA_XLOCKED:
1193 case SA_XLOCKED | SA_NOTRECURSED:
1194 case SA_XLOCKED | SA_RECURSED:
1195 if (sx_xholder(sx) != curthread)
1196 panic("Lock %s not exclusively locked @ %s:%d\n",
1197 sx->lock_object.lo_name, file, line);
1198 if (sx_recursed(sx)) {
1199 if (what & SA_NOTRECURSED)
1200 panic("Lock %s recursed @ %s:%d\n",
1201 sx->lock_object.lo_name, file, line);
1202 } else if (what & SA_RECURSED)
1203 panic("Lock %s not recursed @ %s:%d\n",
1204 sx->lock_object.lo_name, file, line);
1205 break;
1206 case SA_UNLOCKED:
1207 #ifdef WITNESS
1208 witness_assert(&sx->lock_object, what, file, line);
1209 #else
1210 /*
1211 * If we hold an exclusve lock fail. We can't
1212 * reliably check to see if we hold a shared lock or
1213 * not.
1214 */
1215 if (sx_xholder(sx) == curthread)
1216 panic("Lock %s exclusively locked @ %s:%d\n",
1217 sx->lock_object.lo_name, file, line);
1218 #endif
1219 break;
1220 default:
1221 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1222 line);
1223 }
1224 }
1225 #endif /* INVARIANT_SUPPORT */
1226
1227 #ifdef DDB
1228 static void
db_show_sx(const struct lock_object * lock)1229 db_show_sx(const struct lock_object *lock)
1230 {
1231 struct thread *td;
1232 const struct sx *sx;
1233
1234 sx = (const struct sx *)lock;
1235
1236 db_printf(" state: ");
1237 if (sx->sx_lock == SX_LOCK_UNLOCKED)
1238 db_printf("UNLOCKED\n");
1239 else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1240 db_printf("DESTROYED\n");
1241 return;
1242 } else if (sx->sx_lock & SX_LOCK_SHARED)
1243 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1244 else {
1245 td = sx_xholder(sx);
1246 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1247 td->td_tid, td->td_proc->p_pid, td->td_name);
1248 if (sx_recursed(sx))
1249 db_printf(" recursed: %d\n", sx->sx_recurse);
1250 }
1251
1252 db_printf(" waiters: ");
1253 switch(sx->sx_lock &
1254 (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1255 case SX_LOCK_SHARED_WAITERS:
1256 db_printf("shared\n");
1257 break;
1258 case SX_LOCK_EXCLUSIVE_WAITERS:
1259 db_printf("exclusive\n");
1260 break;
1261 case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1262 db_printf("exclusive and shared\n");
1263 break;
1264 default:
1265 db_printf("none\n");
1266 }
1267 }
1268
1269 /*
1270 * Check to see if a thread that is blocked on a sleep queue is actually
1271 * blocked on an sx lock. If so, output some details and return true.
1272 * If the lock has an exclusive owner, return that in *ownerp.
1273 */
1274 int
sx_chain(struct thread * td,struct thread ** ownerp)1275 sx_chain(struct thread *td, struct thread **ownerp)
1276 {
1277 struct sx *sx;
1278
1279 /*
1280 * Check to see if this thread is blocked on an sx lock.
1281 * First, we check the lock class. If that is ok, then we
1282 * compare the lock name against the wait message.
1283 */
1284 sx = td->td_wchan;
1285 if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1286 sx->lock_object.lo_name != td->td_wmesg)
1287 return (0);
1288
1289 /* We think we have an sx lock, so output some details. */
1290 db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1291 *ownerp = sx_xholder(sx);
1292 if (sx->sx_lock & SX_LOCK_SHARED)
1293 db_printf("SLOCK (count %ju)\n",
1294 (uintmax_t)SX_SHARERS(sx->sx_lock));
1295 else
1296 db_printf("XLOCK\n");
1297 return (1);
1298 }
1299 #endif
1300