FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_lock.c
1 /*-
2 * Copyright (c) 2008 Attilio Rao <attilio@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice(s), this list of conditions and the following disclaimer as
10 * the first lines of this file unmodified other than the possible
11 * addition of one or more copyright notices.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice(s), this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
17 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
18 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
19 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
20 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
21 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
22 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
23 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
26 * DAMAGE.
27 */
28
29 #include "opt_ddb.h"
30
31 #include <sys/cdefs.h>
32 __FBSDID("$FreeBSD: src/sys/kern/kern_lock.c,v 1.135 2008/08/05 20:02:31 jhb Exp $");
33
34 #include <sys/param.h>
35 #include <sys/ktr.h>
36 #include <sys/lock.h>
37 #include <sys/lock_profile.h>
38 #include <sys/lockmgr.h>
39 #include <sys/mutex.h>
40 #include <sys/proc.h>
41 #include <sys/sleepqueue.h>
42 #ifdef DEBUG_LOCKS
43 #include <sys/stack.h>
44 #endif
45 #include <sys/systm.h>
46
47 #include <machine/cpu.h>
48
49 #ifdef DDB
50 #include <ddb/ddb.h>
51 #endif
52
53 CTASSERT(((LK_CANRECURSE | LK_NOSHARE) & LO_CLASSFLAGS) ==
54 (LK_CANRECURSE | LK_NOSHARE));
55
56 #define SQ_EXCLUSIVE_QUEUE 0
57 #define SQ_SHARED_QUEUE 1
58
59 #ifndef INVARIANTS
60 #define _lockmgr_assert(lk, what, file, line)
61 #define TD_LOCKS_INC(td)
62 #define TD_LOCKS_DEC(td)
63 #else
64 #define TD_LOCKS_INC(td) ((td)->td_locks++)
65 #define TD_LOCKS_DEC(td) ((td)->td_locks--)
66 #endif
67 #define TD_SLOCKS_INC(td) ((td)->td_lk_slocks++)
68 #define TD_SLOCKS_DEC(td) ((td)->td_lk_slocks--)
69
70 #ifndef DEBUG_LOCKS
71 #define STACK_PRINT(lk)
72 #define STACK_SAVE(lk)
73 #define STACK_ZERO(lk)
74 #else
75 #define STACK_PRINT(lk) stack_print_ddb(&(lk)->lk_stack)
76 #define STACK_SAVE(lk) stack_save(&(lk)->lk_stack)
77 #define STACK_ZERO(lk) stack_zero(&(lk)->lk_stack)
78 #endif
79
80 #define LOCK_LOG2(lk, string, arg1, arg2) \
81 if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \
82 CTR2(KTR_LOCK, (string), (arg1), (arg2))
83 #define LOCK_LOG3(lk, string, arg1, arg2, arg3) \
84 if (LOCK_LOG_TEST(&(lk)->lock_object, 0)) \
85 CTR3(KTR_LOCK, (string), (arg1), (arg2), (arg3))
86
87 #define GIANT_DECLARE \
88 int _i = 0; \
89 WITNESS_SAVE_DECL(Giant)
90 #define GIANT_RESTORE() do { \
91 if (_i > 0) { \
92 while (_i--) \
93 mtx_lock(&Giant); \
94 WITNESS_RESTORE(&Giant.lock_object, Giant); \
95 } \
96 } while (0)
97 #define GIANT_SAVE() do { \
98 if (mtx_owned(&Giant)) { \
99 WITNESS_SAVE(&Giant.lock_object, Giant); \
100 while (mtx_owned(&Giant)) { \
101 _i++; \
102 mtx_unlock(&Giant); \
103 } \
104 } \
105 } while (0)
106
107 #define LK_CAN_SHARE(x) \
108 (((x) & LK_SHARE) && (((x) & LK_EXCLUSIVE_WAITERS) == 0 || \
109 curthread->td_lk_slocks || (curthread->td_pflags & TDP_DEADLKTREAT)))
110 #define LK_TRYOP(x) \
111 ((x) & LK_NOWAIT)
112
113 #define LK_CAN_WITNESS(x) \
114 (((x) & LK_NOWITNESS) == 0 && !LK_TRYOP(x))
115 #define LK_TRYWIT(x) \
116 (LK_TRYOP(x) ? LOP_TRYLOCK : 0)
117
118 #define lockmgr_disowned(lk) \
119 (((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == LK_KERNPROC)
120
121 #define lockmgr_xlocked(lk) \
122 (((lk)->lk_lock & ~(LK_FLAGMASK & ~LK_SHARE)) == (uintptr_t)curthread)
123
124 static void assert_lockmgr(struct lock_object *lock, int how);
125 #ifdef DDB
126 static void db_show_lockmgr(struct lock_object *lock);
127 #endif
128 static void lock_lockmgr(struct lock_object *lock, int how);
129 static int unlock_lockmgr(struct lock_object *lock);
130
131 struct lock_class lock_class_lockmgr = {
132 .lc_name = "lockmgr",
133 .lc_flags = LC_RECURSABLE | LC_SLEEPABLE | LC_SLEEPLOCK | LC_UPGRADABLE,
134 .lc_assert = assert_lockmgr,
135 #ifdef DDB
136 .lc_ddb_show = db_show_lockmgr,
137 #endif
138 .lc_lock = lock_lockmgr,
139 .lc_unlock = unlock_lockmgr
140 };
141
142 static __inline struct thread *
143 lockmgr_xholder(struct lock *lk)
144 {
145 uintptr_t x;
146
147 x = lk->lk_lock;
148 return ((x & LK_SHARE) ? NULL : (struct thread *)LK_HOLDER(x));
149 }
150
151 /*
152 * It assumes sleepq_lock held and returns with this one unheld.
153 * It also assumes the generic interlock is sane and previously checked.
154 * If LK_INTERLOCK is specified the interlock is not reacquired after the
155 * sleep.
156 */
157 static __inline int
158 sleeplk(struct lock *lk, u_int flags, struct lock_object *ilk,
159 const char *wmesg, int pri, int timo, int queue)
160 {
161 GIANT_DECLARE;
162 struct lock_class *class;
163 int catch, error;
164
165 class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
166 catch = pri & PCATCH;
167 pri &= PRIMASK;
168 error = 0;
169
170 LOCK_LOG3(lk, "%s: %p blocking on the %s sleepqueue", __func__, lk,
171 (queue == SQ_EXCLUSIVE_QUEUE) ? "exclusive" : "shared");
172
173 if (flags & LK_INTERLOCK)
174 class->lc_unlock(ilk);
175 GIANT_SAVE();
176 sleepq_add(&lk->lock_object, NULL, wmesg, SLEEPQ_LK | (catch ?
177 SLEEPQ_INTERRUPTIBLE : 0), queue);
178 if ((flags & LK_TIMELOCK) && timo)
179 sleepq_set_timeout(&lk->lock_object, timo);
180
181 /*
182 * Decisional switch for real sleeping.
183 */
184 if ((flags & LK_TIMELOCK) && timo && catch)
185 error = sleepq_timedwait_sig(&lk->lock_object, pri);
186 else if ((flags & LK_TIMELOCK) && timo)
187 error = sleepq_timedwait(&lk->lock_object, pri);
188 else if (catch)
189 error = sleepq_wait_sig(&lk->lock_object, pri);
190 else
191 sleepq_wait(&lk->lock_object, pri);
192 GIANT_RESTORE();
193 if ((flags & LK_SLEEPFAIL) && error == 0)
194 error = ENOLCK;
195
196 return (error);
197 }
198
199 static __inline int
200 wakeupshlk(struct lock *lk, const char *file, int line)
201 {
202 uintptr_t v, x;
203 int queue, wakeup_swapper;
204
205 TD_LOCKS_DEC(curthread);
206 TD_SLOCKS_DEC(curthread);
207 WITNESS_UNLOCK(&lk->lock_object, 0, file, line);
208 LOCK_LOG_LOCK("SUNLOCK", &lk->lock_object, 0, 0, file, line);
209
210 wakeup_swapper = 0;
211 for (;;) {
212 x = lk->lk_lock;
213
214 /*
215 * If there is more than one shared lock held, just drop one
216 * and return.
217 */
218 if (LK_SHARERS(x) > 1) {
219 if (atomic_cmpset_ptr(&lk->lk_lock, x,
220 x - LK_ONE_SHARER))
221 break;
222 continue;
223 }
224
225 /*
226 * If there are not waiters on the exclusive queue, drop the
227 * lock quickly.
228 */
229 if ((x & LK_ALL_WAITERS) == 0) {
230 MPASS(x == LK_SHARERS_LOCK(1));
231 if (atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1),
232 LK_UNLOCKED))
233 break;
234 continue;
235 }
236
237 /*
238 * We should have a sharer with waiters, so enter the hard
239 * path in order to handle wakeups correctly.
240 */
241 sleepq_lock(&lk->lock_object);
242 x = lk->lk_lock & LK_ALL_WAITERS;
243 v = LK_UNLOCKED;
244
245 /*
246 * If the lock has exclusive waiters, give them preference in
247 * order to avoid deadlock with shared runners up.
248 */
249 if (x & LK_EXCLUSIVE_WAITERS) {
250 queue = SQ_EXCLUSIVE_QUEUE;
251 v |= (x & LK_SHARED_WAITERS);
252 } else {
253 MPASS(x == LK_SHARED_WAITERS);
254 queue = SQ_SHARED_QUEUE;
255 }
256
257 if (!atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x,
258 v)) {
259 sleepq_release(&lk->lock_object);
260 continue;
261 }
262 LOCK_LOG3(lk, "%s: %p waking up threads on the %s queue",
263 __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
264 "exclusive");
265 wakeup_swapper = sleepq_broadcast(&lk->lock_object, SLEEPQ_LK,
266 0, queue);
267 sleepq_release(&lk->lock_object);
268 break;
269 }
270
271 lock_profile_release_lock(&lk->lock_object);
272 return (wakeup_swapper);
273 }
274
275 static void
276 assert_lockmgr(struct lock_object *lock, int what)
277 {
278
279 panic("lockmgr locks do not support assertions");
280 }
281
282 static void
283 lock_lockmgr(struct lock_object *lock, int how)
284 {
285
286 panic("lockmgr locks do not support sleep interlocking");
287 }
288
289 static int
290 unlock_lockmgr(struct lock_object *lock)
291 {
292
293 panic("lockmgr locks do not support sleep interlocking");
294 }
295
296 void
297 lockinit(struct lock *lk, int pri, const char *wmesg, int timo, int flags)
298 {
299 int iflags;
300
301 MPASS((flags & ~LK_INIT_MASK) == 0);
302
303 iflags = LO_RECURSABLE | LO_SLEEPABLE | LO_UPGRADABLE;
304 if ((flags & LK_NODUP) == 0)
305 iflags |= LO_DUPOK;
306 if (flags & LK_NOPROFILE)
307 iflags |= LO_NOPROFILE;
308 if ((flags & LK_NOWITNESS) == 0)
309 iflags |= LO_WITNESS;
310 if (flags & LK_QUIET)
311 iflags |= LO_QUIET;
312 iflags |= flags & (LK_CANRECURSE | LK_NOSHARE);
313
314 lk->lk_lock = LK_UNLOCKED;
315 lk->lk_recurse = 0;
316 lk->lk_timo = timo;
317 lk->lk_pri = pri;
318 lock_init(&lk->lock_object, &lock_class_lockmgr, wmesg, NULL, iflags);
319 STACK_ZERO(lk);
320 }
321
322 void
323 lockdestroy(struct lock *lk)
324 {
325
326 KASSERT(lk->lk_lock == LK_UNLOCKED, ("lockmgr still held"));
327 KASSERT(lk->lk_recurse == 0, ("lockmgr still recursed"));
328 lock_destroy(&lk->lock_object);
329 }
330
331 int
332 __lockmgr_args(struct lock *lk, u_int flags, struct lock_object *ilk,
333 const char *wmesg, int pri, int timo, const char *file, int line)
334 {
335 GIANT_DECLARE;
336 uint64_t waittime;
337 struct lock_class *class;
338 const char *iwmesg;
339 uintptr_t tid, v, x;
340 u_int op;
341 int contested, error, ipri, itimo, queue, wakeup_swapper;
342
343 contested = 0;
344 error = 0;
345 waittime = 0;
346 tid = (uintptr_t)curthread;
347 op = (flags & LK_TYPE_MASK);
348 iwmesg = (wmesg == LK_WMESG_DEFAULT) ? lk->lock_object.lo_name : wmesg;
349 ipri = (pri == LK_PRIO_DEFAULT) ? lk->lk_pri : pri;
350 itimo = (timo == LK_TIMO_DEFAULT) ? lk->lk_timo : timo;
351
352 MPASS((flags & ~LK_TOTAL_MASK) == 0);
353 KASSERT((op & (op - 1)) == 0,
354 ("%s: Invalid requested operation @ %s:%d", __func__, file, line));
355 KASSERT((flags & (LK_NOWAIT | LK_SLEEPFAIL)) == 0 ||
356 (op != LK_DOWNGRADE && op != LK_RELEASE),
357 ("%s: Invalid flags in regard of the operation desired @ %s:%d",
358 __func__, file, line));
359 KASSERT((flags & LK_INTERLOCK) == 0 || ilk != NULL,
360 ("%s: LK_INTERLOCK passed without valid interlock @ %s:%d",
361 __func__, file, line));
362
363 class = (flags & LK_INTERLOCK) ? LOCK_CLASS(ilk) : NULL;
364 if (panicstr != NULL) {
365 if (flags & LK_INTERLOCK)
366 class->lc_unlock(ilk);
367 return (0);
368 }
369
370 if (op == LK_SHARED && (lk->lock_object.lo_flags & LK_NOSHARE))
371 op = LK_EXCLUSIVE;
372
373 wakeup_swapper = 0;
374 switch (op) {
375 case LK_SHARED:
376 if (LK_CAN_WITNESS(flags))
377 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER,
378 file, line);
379 for (;;) {
380 x = lk->lk_lock;
381
382 /*
383 * If no other thread has an exclusive lock, or
384 * no exclusive waiter is present, bump the count of
385 * sharers. Since we have to preserve the state of
386 * waiters, if we fail to acquire the shared lock
387 * loop back and retry.
388 */
389 if (LK_CAN_SHARE(x)) {
390 if (atomic_cmpset_acq_ptr(&lk->lk_lock, x,
391 x + LK_ONE_SHARER))
392 break;
393 continue;
394 }
395 lock_profile_obtain_lock_failed(&lk->lock_object,
396 &contested, &waittime);
397
398 /*
399 * If the lock is already held by curthread in
400 * exclusive way avoid a deadlock.
401 */
402 if (LK_HOLDER(x) == tid) {
403 LOCK_LOG2(lk,
404 "%s: %p already held in exclusive mode",
405 __func__, lk);
406 error = EDEADLK;
407 break;
408 }
409
410 /*
411 * If the lock is expected to not sleep just give up
412 * and return.
413 */
414 if (LK_TRYOP(flags)) {
415 LOCK_LOG2(lk, "%s: %p fails the try operation",
416 __func__, lk);
417 error = EBUSY;
418 break;
419 }
420
421 /*
422 * Acquire the sleepqueue chain lock because we
423 * probabilly will need to manipulate waiters flags.
424 */
425 sleepq_lock(&lk->lock_object);
426 x = lk->lk_lock;
427
428 /*
429 * if the lock can be acquired in shared mode, try
430 * again.
431 */
432 if (LK_CAN_SHARE(x)) {
433 sleepq_release(&lk->lock_object);
434 continue;
435 }
436
437 /*
438 * Try to set the LK_SHARED_WAITERS flag. If we fail,
439 * loop back and retry.
440 */
441 if ((x & LK_SHARED_WAITERS) == 0) {
442 if (!atomic_cmpset_acq_ptr(&lk->lk_lock, x,
443 x | LK_SHARED_WAITERS)) {
444 sleepq_release(&lk->lock_object);
445 continue;
446 }
447 LOCK_LOG2(lk, "%s: %p set shared waiters flag",
448 __func__, lk);
449 }
450
451 /*
452 * As far as we have been unable to acquire the
453 * shared lock and the shared waiters flag is set,
454 * we will sleep.
455 */
456 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
457 SQ_SHARED_QUEUE);
458 flags &= ~LK_INTERLOCK;
459 if (error) {
460 LOCK_LOG3(lk,
461 "%s: interrupted sleep for %p with %d",
462 __func__, lk, error);
463 break;
464 }
465 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
466 __func__, lk);
467 }
468 if (error == 0) {
469 lock_profile_obtain_lock_success(&lk->lock_object,
470 contested, waittime, file, line);
471 LOCK_LOG_LOCK("SLOCK", &lk->lock_object, 0, 0, file,
472 line);
473 WITNESS_LOCK(&lk->lock_object, LK_TRYWIT(flags), file,
474 line);
475 TD_LOCKS_INC(curthread);
476 TD_SLOCKS_INC(curthread);
477 STACK_SAVE(lk);
478 }
479 break;
480 case LK_UPGRADE:
481 _lockmgr_assert(lk, KA_SLOCKED, file, line);
482 x = lk->lk_lock & LK_ALL_WAITERS;
483
484 /*
485 * Try to switch from one shared lock to an exclusive one.
486 * We need to preserve waiters flags during the operation.
487 */
488 if (atomic_cmpset_ptr(&lk->lk_lock, LK_SHARERS_LOCK(1) | x,
489 tid | x)) {
490 LOCK_LOG_LOCK("XUPGRADE", &lk->lock_object, 0, 0, file,
491 line);
492 WITNESS_UPGRADE(&lk->lock_object, LOP_EXCLUSIVE |
493 LK_TRYWIT(flags), file, line);
494 TD_SLOCKS_DEC(curthread);
495 break;
496 }
497
498 /*
499 * We have been unable to succeed in upgrading, so just
500 * give up the shared lock.
501 */
502 wakeup_swapper += wakeupshlk(lk, file, line);
503
504 /* FALLTHROUGH */
505 case LK_EXCLUSIVE:
506 if (LK_CAN_WITNESS(flags))
507 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
508 LOP_EXCLUSIVE, file, line);
509
510 /*
511 * If curthread already holds the lock and this one is
512 * allowed to recurse, simply recurse on it.
513 */
514 if (lockmgr_xlocked(lk)) {
515 if ((flags & LK_CANRECURSE) == 0 &&
516 (lk->lock_object.lo_flags & LK_CANRECURSE) == 0) {
517
518 /*
519 * If the lock is expected to not panic just
520 * give up and return.
521 */
522 if (LK_TRYOP(flags)) {
523 LOCK_LOG2(lk,
524 "%s: %p fails the try operation",
525 __func__, lk);
526 error = EBUSY;
527 break;
528 }
529 if (flags & LK_INTERLOCK)
530 class->lc_unlock(ilk);
531 panic("%s: recursing on non recursive lockmgr %s @ %s:%d\n",
532 __func__, iwmesg, file, line);
533 }
534 lk->lk_recurse++;
535 LOCK_LOG2(lk, "%s: %p recursing", __func__, lk);
536 LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0,
537 lk->lk_recurse, file, line);
538 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
539 LK_TRYWIT(flags), file, line);
540 TD_LOCKS_INC(curthread);
541 break;
542 }
543
544 while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED,
545 tid)) {
546 lock_profile_obtain_lock_failed(&lk->lock_object,
547 &contested, &waittime);
548
549 /*
550 * If the lock is expected to not sleep just give up
551 * and return.
552 */
553 if (LK_TRYOP(flags)) {
554 LOCK_LOG2(lk, "%s: %p fails the try operation",
555 __func__, lk);
556 error = EBUSY;
557 break;
558 }
559
560 /*
561 * Acquire the sleepqueue chain lock because we
562 * probabilly will need to manipulate waiters flags.
563 */
564 sleepq_lock(&lk->lock_object);
565 x = lk->lk_lock;
566 v = x & LK_ALL_WAITERS;
567
568 /*
569 * if the lock has been released while we spun on
570 * the sleepqueue chain lock just try again.
571 */
572 if (x == LK_UNLOCKED) {
573 sleepq_release(&lk->lock_object);
574 continue;
575 }
576
577 /*
578 * The lock can be in the state where there is a
579 * pending queue of waiters, but still no owner.
580 * This happens when the lock is contested and an
581 * owner is going to claim the lock.
582 * If curthread is the one successfully acquiring it
583 * claim lock ownership and return, preserving waiters
584 * flags.
585 */
586 if (x == (LK_UNLOCKED | v)) {
587 if (atomic_cmpset_acq_ptr(&lk->lk_lock, x,
588 tid | v)) {
589 sleepq_release(&lk->lock_object);
590 LOCK_LOG2(lk,
591 "%s: %p claimed by a new writer",
592 __func__, lk);
593 break;
594 }
595 sleepq_release(&lk->lock_object);
596 continue;
597 }
598
599 /*
600 * Try to set the LK_EXCLUSIVE_WAITERS flag. If we
601 * fail, loop back and retry.
602 */
603 if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
604 if (!atomic_cmpset_ptr(&lk->lk_lock, x,
605 x | LK_EXCLUSIVE_WAITERS)) {
606 sleepq_release(&lk->lock_object);
607 continue;
608 }
609 LOCK_LOG2(lk, "%s: %p set excl waiters flag",
610 __func__, lk);
611 }
612
613 /*
614 * As far as we have been unable to acquire the
615 * exclusive lock and the exclusive waiters flag
616 * is set, we will sleep.
617 */
618 error = sleeplk(lk, flags, ilk, iwmesg, ipri, itimo,
619 SQ_EXCLUSIVE_QUEUE);
620 flags &= ~LK_INTERLOCK;
621 if (error) {
622 LOCK_LOG3(lk,
623 "%s: interrupted sleep for %p with %d",
624 __func__, lk, error);
625 break;
626 }
627 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
628 __func__, lk);
629 }
630 if (error == 0) {
631 lock_profile_obtain_lock_success(&lk->lock_object,
632 contested, waittime, file, line);
633 LOCK_LOG_LOCK("XLOCK", &lk->lock_object, 0,
634 lk->lk_recurse, file, line);
635 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
636 LK_TRYWIT(flags), file, line);
637 TD_LOCKS_INC(curthread);
638 STACK_SAVE(lk);
639 }
640 break;
641 case LK_DOWNGRADE:
642 _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, file, line);
643 LOCK_LOG_LOCK("XDOWNGRADE", &lk->lock_object, 0, 0, file, line);
644 WITNESS_DOWNGRADE(&lk->lock_object, 0, file, line);
645 TD_SLOCKS_INC(curthread);
646
647 /*
648 * In order to preserve waiters flags, just spin.
649 */
650 for (;;) {
651 x = lk->lk_lock & LK_ALL_WAITERS;
652 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
653 LK_SHARERS_LOCK(1) | x))
654 break;
655 cpu_spinwait();
656 }
657 break;
658 case LK_RELEASE:
659 _lockmgr_assert(lk, KA_LOCKED, file, line);
660 x = lk->lk_lock;
661
662 if ((x & LK_SHARE) == 0) {
663
664 /*
665 * As first option, treact the lock as if it has not
666 * any waiter.
667 * Fix-up the tid var if the lock has been disowned.
668 */
669 if (LK_HOLDER(x) == LK_KERNPROC)
670 tid = LK_KERNPROC;
671 else {
672 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE,
673 file, line);
674 TD_LOCKS_DEC(curthread);
675 }
676 LOCK_LOG_LOCK("XUNLOCK", &lk->lock_object, 0,
677 lk->lk_recurse, file, line);
678
679 /*
680 * The lock is held in exclusive mode.
681 * If the lock is recursed also, then unrecurse it.
682 */
683 if (lockmgr_xlocked(lk) && lockmgr_recursed(lk)) {
684 LOCK_LOG2(lk, "%s: %p unrecursing", __func__,
685 lk);
686 lk->lk_recurse--;
687 break;
688 }
689 lock_profile_release_lock(&lk->lock_object);
690
691 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid,
692 LK_UNLOCKED))
693 break;
694
695 sleepq_lock(&lk->lock_object);
696 x = lk->lk_lock & LK_ALL_WAITERS;
697 v = LK_UNLOCKED;
698
699 /*
700 * If the lock has exclusive waiters, give them
701 * preference in order to avoid deadlock with
702 * shared runners up.
703 */
704 if (x & LK_EXCLUSIVE_WAITERS) {
705 queue = SQ_EXCLUSIVE_QUEUE;
706 v |= (x & LK_SHARED_WAITERS);
707 } else {
708 MPASS(x == LK_SHARED_WAITERS);
709 queue = SQ_SHARED_QUEUE;
710 }
711
712 LOCK_LOG3(lk,
713 "%s: %p waking up threads on the %s queue",
714 __func__, lk, queue == SQ_SHARED_QUEUE ? "shared" :
715 "exclusive");
716 atomic_store_rel_ptr(&lk->lk_lock, v);
717 wakeup_swapper = sleepq_broadcast(&lk->lock_object,
718 SLEEPQ_LK, 0, queue);
719 sleepq_release(&lk->lock_object);
720 break;
721 } else
722 wakeup_swapper = wakeupshlk(lk, file, line);
723 break;
724 case LK_DRAIN:
725 if (LK_CAN_WITNESS(flags))
726 WITNESS_CHECKORDER(&lk->lock_object, LOP_NEWORDER |
727 LOP_EXCLUSIVE, file, line);
728
729 /*
730 * Trying to drain a lock we already own will result in a
731 * deadlock.
732 */
733 if (lockmgr_xlocked(lk)) {
734 if (flags & LK_INTERLOCK)
735 class->lc_unlock(ilk);
736 panic("%s: draining %s with the lock held @ %s:%d\n",
737 __func__, iwmesg, file, line);
738 }
739
740 while (!atomic_cmpset_acq_ptr(&lk->lk_lock, LK_UNLOCKED, tid)) {
741 lock_profile_obtain_lock_failed(&lk->lock_object,
742 &contested, &waittime);
743
744 /*
745 * If the lock is expected to not sleep just give up
746 * and return.
747 */
748 if (LK_TRYOP(flags)) {
749 LOCK_LOG2(lk, "%s: %p fails the try operation",
750 __func__, lk);
751 error = EBUSY;
752 break;
753 }
754
755 /*
756 * Acquire the sleepqueue chain lock because we
757 * probabilly will need to manipulate waiters flags.
758 */
759 sleepq_lock(&lk->lock_object);
760 x = lk->lk_lock;
761 v = x & LK_ALL_WAITERS;
762
763 /*
764 * if the lock has been released while we spun on
765 * the sleepqueue chain lock just try again.
766 */
767 if (x == LK_UNLOCKED) {
768 sleepq_release(&lk->lock_object);
769 continue;
770 }
771
772 if (x == (LK_UNLOCKED | v)) {
773 v = x;
774 if (v & LK_EXCLUSIVE_WAITERS) {
775 queue = SQ_EXCLUSIVE_QUEUE;
776 v &= ~LK_EXCLUSIVE_WAITERS;
777 } else {
778 MPASS(v & LK_SHARED_WAITERS);
779 queue = SQ_SHARED_QUEUE;
780 v &= ~LK_SHARED_WAITERS;
781 }
782 if (!atomic_cmpset_ptr(&lk->lk_lock, x, v)) {
783 sleepq_release(&lk->lock_object);
784 continue;
785 }
786 LOCK_LOG3(lk,
787 "%s: %p waking up all threads on the %s queue",
788 __func__, lk, queue == SQ_SHARED_QUEUE ?
789 "shared" : "exclusive");
790 wakeup_swapper += sleepq_broadcast(
791 &lk->lock_object, SLEEPQ_LK, 0, queue);
792
793 /*
794 * If shared waiters have been woken up we need
795 * to wait for one of them to acquire the lock
796 * before to set the exclusive waiters in
797 * order to avoid a deadlock.
798 */
799 if (queue == SQ_SHARED_QUEUE) {
800 for (v = lk->lk_lock;
801 (v & LK_SHARE) && !LK_SHARERS(v);
802 v = lk->lk_lock)
803 cpu_spinwait();
804 }
805 }
806
807 /*
808 * Try to set the LK_EXCLUSIVE_WAITERS flag. If we
809 * fail, loop back and retry.
810 */
811 if ((x & LK_EXCLUSIVE_WAITERS) == 0) {
812 if (!atomic_cmpset_ptr(&lk->lk_lock, x,
813 x | LK_EXCLUSIVE_WAITERS)) {
814 sleepq_release(&lk->lock_object);
815 continue;
816 }
817 LOCK_LOG2(lk, "%s: %p set drain waiters flag",
818 __func__, lk);
819 }
820
821 /*
822 * As far as we have been unable to acquire the
823 * exclusive lock and the exclusive waiters flag
824 * is set, we will sleep.
825 */
826 if (flags & LK_INTERLOCK) {
827 class->lc_unlock(ilk);
828 flags &= ~LK_INTERLOCK;
829 }
830 GIANT_SAVE();
831 sleepq_add(&lk->lock_object, NULL, iwmesg, SLEEPQ_LK,
832 SQ_EXCLUSIVE_QUEUE);
833 sleepq_wait(&lk->lock_object, ipri & PRIMASK);
834 GIANT_RESTORE();
835 LOCK_LOG2(lk, "%s: %p resuming from the sleep queue",
836 __func__, lk);
837 }
838
839 if (error == 0) {
840 lock_profile_obtain_lock_success(&lk->lock_object,
841 contested, waittime, file, line);
842 LOCK_LOG_LOCK("DRAIN", &lk->lock_object, 0,
843 lk->lk_recurse, file, line);
844 WITNESS_LOCK(&lk->lock_object, LOP_EXCLUSIVE |
845 LK_TRYWIT(flags), file, line);
846 TD_LOCKS_INC(curthread);
847 STACK_SAVE(lk);
848 }
849 break;
850 default:
851 if (flags & LK_INTERLOCK)
852 class->lc_unlock(ilk);
853 panic("%s: unknown lockmgr request 0x%x\n", __func__, op);
854 }
855
856 if (flags & LK_INTERLOCK)
857 class->lc_unlock(ilk);
858 if (wakeup_swapper)
859 kick_proc0();
860
861 return (error);
862 }
863
864 void
865 _lockmgr_disown(struct lock *lk, const char *file, int line)
866 {
867 uintptr_t tid, x;
868
869 tid = (uintptr_t)curthread;
870 _lockmgr_assert(lk, KA_XLOCKED | KA_NOTRECURSED, file, line);
871
872 /*
873 * If the owner is already LK_KERNPROC just skip the whole operation.
874 */
875 if (LK_HOLDER(lk->lk_lock) != tid)
876 return;
877 LOCK_LOG_LOCK("XDISOWN", &lk->lock_object, 0, 0, file, line);
878 WITNESS_UNLOCK(&lk->lock_object, LOP_EXCLUSIVE, file, line);
879 TD_LOCKS_DEC(curthread);
880
881 /*
882 * In order to preserve waiters flags, just spin.
883 */
884 for (;;) {
885 x = lk->lk_lock & LK_ALL_WAITERS;
886 if (atomic_cmpset_rel_ptr(&lk->lk_lock, tid | x,
887 LK_KERNPROC | x))
888 return;
889 cpu_spinwait();
890 }
891 }
892
893 void
894 lockmgr_printinfo(struct lock *lk)
895 {
896 struct thread *td;
897 uintptr_t x;
898
899 if (lk->lk_lock == LK_UNLOCKED)
900 printf(" lock type %s: UNLOCKED\n", lk->lock_object.lo_name);
901 else if (lk->lk_lock & LK_SHARE)
902 printf(" lock type %s: SHARED (count %ju)\n",
903 lk->lock_object.lo_name,
904 (uintmax_t)LK_SHARERS(lk->lk_lock));
905 else {
|