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linprocfs - Introduce /proc/mounts
[dragonfly.git] / sys / kern / kern_mutex.c
blobd7895cae20810acfb493cadaaf0a3d1041946270
1 /*
2 * Copyright (c) 2009 The DragonFly Project. All rights reserved.
3 *
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
6 *
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
9 * are met:
10 *
11 * 1. Redistributions of source code must retain the above copyright
12 * notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice, this list of conditions and the following disclaimer in
15 * the documentation and/or other materials provided with the
16 * distribution.
17 * 3. Neither the name of The DragonFly Project nor the names of its
18 * contributors may be used to endorse or promote products derived
19 * from this software without specific, prior written permission.
20 *
21 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
22 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
23 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
24 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
25 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
26 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
27 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
28 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
29 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
30 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
31 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
32 * SUCH DAMAGE.
33 */
34 /*
35 * Implement fast persistent locks based on atomic_cmpset_int() with
36 * semantics similar to lockmgr locks but faster and taking up much less
37 * space. Taken from HAMMER's lock implementation.
38 *
39 * These are meant to complement our LWKT tokens. Tokens are only held
40 * while the thread is running. Mutexes can be held across blocking
41 * conditions.
42 *
43 * Most of the support is in sys/mutex[2].h. We mostly provide backoff
44 * functions here.
45 */
46
47 #include <sys/param.h>
48 #include <sys/systm.h>
49 #include <sys/kernel.h>
50 #include <sys/sysctl.h>
51 #include <sys/thread.h>
52 #include <sys/mutex.h>
53
54 #include <machine/cpufunc.h>
55
56 #include <sys/thread2.h>
57 #include <sys/mutex2.h>
58
59 static __int64_t mtx_contention_count;
60 static __int64_t mtx_collision_count;
61 static __int64_t mtx_wakeup_count;
62
63 SYSCTL_QUAD(_kern, OID_AUTO, mtx_contention_count, CTLFLAG_RW,
64 &mtx_contention_count, 0, "");
65 SYSCTL_QUAD(_kern, OID_AUTO, mtx_collision_count, CTLFLAG_RW,
66 &mtx_collision_count, 0, "");
67 SYSCTL_QUAD(_kern, OID_AUTO, mtx_wakeup_count, CTLFLAG_RW,
68 &mtx_wakeup_count, 0, "");
69
70 static void mtx_chain_link(mtx_t mtx);
71 static void mtx_delete_link(mtx_t mtx, mtx_link_t link);
72
73 /*
74 * Exclusive-lock a mutex, block until acquired. Recursion is allowed.
75 *
76 * Returns 0 on success, or the tsleep() return code on failure.
77 * An error can only be returned if PCATCH is specified in the flags.
78 */
79 static __inline int
80 __mtx_lock_ex(mtx_t mtx, mtx_link_t link, const char *ident, int flags, int to)
81 {
82 u_int lock;
83 u_int nlock;
84 int error;
85
86 for (;;) {
87 lock = mtx->mtx_lock;
88 if (lock == 0) {
89 nlock = MTX_EXCLUSIVE | 1;
90 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
91 mtx->mtx_owner = curthread;
92 error = 0;
93 break;
94 }
95 } else if ((lock & MTX_EXCLUSIVE) &&
96 mtx->mtx_owner == curthread) {
97 KKASSERT((lock & MTX_MASK) != MTX_MASK);
98 nlock = lock + 1;
99 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
100 error = 0;
101 break;
102 }
103 } else {
104 /*
105 * Clearing MTX_EXLINK in lock causes us to loop until
106 * MTX_EXLINK is available. However, to avoid
107 * unnecessary cpu cache traffic we poll instead.
108 *
109 * Setting MTX_EXLINK in nlock causes us to loop until
110 * we can acquire MTX_EXLINK.
111 *
112 * Also set MTX_EXWANTED coincident with EXLINK, if
113 * not already set.
114 */
115 if (lock & MTX_EXLINK) {
116 cpu_pause();
117 ++mtx_collision_count;
118 continue;
119 }
120 /*lock &= ~MTX_EXLINK;*/
121 nlock = lock | MTX_EXWANTED | MTX_EXLINK;
122 ++mycpu->gd_spinlocks_wr;
123 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
124 /*
125 * Check for early abort
126 */
127 if (link->state == MTX_LINK_ABORTED) {
128 atomic_clear_int(&mtx->mtx_lock,
129 MTX_EXLINK);
130 --mycpu->gd_spinlocks_wr;
131 error = ENOLCK;
132 if (mtx->mtx_link == NULL) {
133 atomic_clear_int(&mtx->mtx_lock,
134 MTX_EXWANTED);
135 }
136 break;
137 }
138
139 /*
140 * Success. Link in our structure then
141 * release EXLINK and sleep.
142 */
143 link->owner = curthread;
144 link->state = MTX_LINK_LINKED;
145 if (mtx->mtx_link) {
146 link->next = mtx->mtx_link;
147 link->prev = link->next->prev;
148 link->next->prev = link;
149 link->prev->next = link;
150 } else {
151 link->next = link;
152 link->prev = link;
153 mtx->mtx_link = link;
154 }
155 tsleep_interlock(link, 0);
156 atomic_clear_int(&mtx->mtx_lock, MTX_EXLINK);
157 --mycpu->gd_spinlocks_wr;
158
159 error = tsleep(link, flags, ident, to);
160 ++mtx_contention_count;
161
162 /*
163 * Normal unlink, we should own the exclusive
164 * lock now.
165 */
166 if (link->state == MTX_LINK_LINKED)
167 mtx_delete_link(mtx, link);
168 if (link->state == MTX_LINK_ACQUIRED) {
169 KKASSERT(mtx->mtx_owner == link->owner);
170 error = 0;
171 break;
172 }
173
174 /*
175 * Aborted lock (mtx_abort_ex called).
176 */
177 if (link->state == MTX_LINK_ABORTED) {
178 error = ENOLCK;
179 break;
180 }
181
182 /*
183 * tsleep error, else retry.
184 */
185 if (error)
186 break;
187 } else {
188 --mycpu->gd_spinlocks_wr;
189 }
190 }
191 ++mtx_collision_count;
192 }
193 return (error);
194 }
195
196 int
197 _mtx_lock_ex_link(mtx_t mtx, mtx_link_t link,
198 const char *ident, int flags, int to)
199 {
200 return(__mtx_lock_ex(mtx, link, ident, flags, to));
201 }
202
203 int
204 _mtx_lock_ex(mtx_t mtx, const char *ident, int flags, int to)
205 {
206 struct mtx_link link;
207
208 mtx_link_init(&link);
209 return(__mtx_lock_ex(mtx, &link, ident, flags, to));
210 }
211
212 int
213 _mtx_lock_ex_quick(mtx_t mtx, const char *ident)
214 {
215 struct mtx_link link;
216
217 mtx_link_init(&link);
218 return(__mtx_lock_ex(mtx, &link, ident, 0, 0));
219 }
220
221 /*
222 * Share-lock a mutex, block until acquired. Recursion is allowed.
223 *
224 * Returns 0 on success, or the tsleep() return code on failure.
225 * An error can only be returned if PCATCH is specified in the flags.
226 *
227 * NOTE: Shared locks get a mass-wakeup so if the tsleep fails we
228 * do not have to chain the wakeup().
229 */
230 static __inline int
231 __mtx_lock_sh(mtx_t mtx, const char *ident, int flags, int to)
232 {
233 u_int lock;
234 u_int nlock;
235 int error;
236
237 for (;;) {
238 lock = mtx->mtx_lock;
239 if ((lock & MTX_EXCLUSIVE) == 0) {
240 KKASSERT((lock & MTX_MASK) != MTX_MASK);
241 nlock = lock + 1;
242 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
243 error = 0;
244 break;
245 }
246 } else {
247 nlock = lock | MTX_SHWANTED;
248 tsleep_interlock(mtx, 0);
249 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
250 error = tsleep(mtx, flags, ident, to);
251 if (error)
252 break;
253 ++mtx_contention_count;
254 /* retry */
255 } else {
256 tsleep_remove(curthread);
257 }
258 }
259 ++mtx_collision_count;
260 }
261 return (error);
262 }
263
264 int
265 _mtx_lock_sh(mtx_t mtx, const char *ident, int flags, int to)
266 {
267 return (__mtx_lock_sh(mtx, ident, flags, to));
268 }
269
270 int
271 _mtx_lock_sh_quick(mtx_t mtx, const char *ident)
272 {
273 return (__mtx_lock_sh(mtx, ident, 0, 0));
274 }
275
276 void
277 _mtx_spinlock_ex(mtx_t mtx)
278 {
279 u_int lock;
280 u_int nlock;
281 int bb = 1;
282 int bo;
283
284 for (;;) {
285 lock = mtx->mtx_lock;
286 if (lock == 0) {
287 nlock = MTX_EXCLUSIVE | 1;
288 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
289 mtx->mtx_owner = curthread;
290 break;
291 }
292 } else if ((lock & MTX_EXCLUSIVE) &&
293 mtx->mtx_owner == curthread) {
294 KKASSERT((lock & MTX_MASK) != MTX_MASK);
295 nlock = lock + 1;
296 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
297 break;
298 } else {
299 /* MWAIT here */
300 if (bb < 1000)
301 ++bb;
302 cpu_pause();
303 for (bo = 0; bo < bb; ++bo)
304 ;
305 ++mtx_contention_count;
306 }
307 cpu_pause();
308 ++mtx_collision_count;
309 }
310 }
311
312 void
313 _mtx_spinlock_sh(mtx_t mtx)
314 {
315 u_int lock;
316 u_int nlock;
317 int bb = 1;
318 int bo;
319
320 for (;;) {
321 lock = mtx->mtx_lock;
322 if ((lock & MTX_EXCLUSIVE) == 0) {
323 KKASSERT((lock & MTX_MASK) != MTX_MASK);
324 nlock = lock + 1;
325 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
326 break;
327 } else {
328 /* MWAIT here */
329 if (bb < 1000)
330 ++bb;
331 cpu_pause();
332 for (bo = 0; bo < bb; ++bo)
333 ;
334 ++mtx_contention_count;
335 }
336 cpu_pause();
337 ++mtx_collision_count;
338 }
339 }
340
341 int
342 _mtx_lock_ex_try(mtx_t mtx)
343 {
344 u_int lock;
345 u_int nlock;
346 int error = 0;
347
348 for (;;) {
349 lock = mtx->mtx_lock;
350 if (lock == 0) {
351 nlock = MTX_EXCLUSIVE | 1;
352 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
353 mtx->mtx_owner = curthread;
354 break;
355 }
356 } else if ((lock & MTX_EXCLUSIVE) &&
357 mtx->mtx_owner == curthread) {
358 KKASSERT((lock & MTX_MASK) != MTX_MASK);
359 nlock = lock + 1;
360 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
361 break;
362 } else {
363 error = EAGAIN;
364 break;
365 }
366 cpu_pause();
367 ++mtx_collision_count;
368 }
369 return (error);
370 }
371
372 int
373 _mtx_lock_sh_try(mtx_t mtx)
374 {
375 u_int lock;
376 u_int nlock;
377 int error = 0;
378
379 for (;;) {
380 lock = mtx->mtx_lock;
381 if ((lock & MTX_EXCLUSIVE) == 0) {
382 KKASSERT((lock & MTX_MASK) != MTX_MASK);
383 nlock = lock + 1;
384 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
385 break;
386 } else {
387 error = EAGAIN;
388 break;
389 }
390 cpu_pause();
391 ++mtx_collision_count;
392 }
393 return (error);
394 }
395
396 /*
397 * If the lock is held exclusively it must be owned by the caller. If the
398 * lock is already a shared lock this operation is a NOP. A panic will
399 * occur if the lock is not held either shared or exclusive.
400 *
401 * The exclusive count is converted to a shared count.
402 */
403 void
404 _mtx_downgrade(mtx_t mtx)
405 {
406 u_int lock;
407 u_int nlock;
408
409 for (;;) {
410 lock = mtx->mtx_lock;
411 if ((lock & MTX_EXCLUSIVE) == 0) {
412 KKASSERT((lock & MTX_MASK) > 0);
413 break;
414 }
415 KKASSERT(mtx->mtx_owner == curthread);
416 nlock = lock & ~(MTX_EXCLUSIVE | MTX_SHWANTED);
417 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
418 if (lock & MTX_SHWANTED) {
419 wakeup(mtx);
420 ++mtx_wakeup_count;
421 }
422 break;
423 }
424 cpu_pause();
425 ++mtx_collision_count;
426 }
427 }
428
429 /*
430 * Upgrade a shared lock to an exclusive lock. The upgrade will fail if
431 * the shared lock has a count other then 1. Optimize the most likely case
432 * but note that a single cmpset can fail due to WANTED races.
433 *
434 * If the lock is held exclusively it must be owned by the caller and
435 * this function will simply return without doing anything. A panic will
436 * occur if the lock is held exclusively by someone other then the caller.
437 *
438 * Returns 0 on success, EDEADLK on failure.
439 */
440 int
441 _mtx_upgrade_try(mtx_t mtx)
442 {
443 u_int lock;
444 u_int nlock;
445 int error = 0;
446
447 for (;;) {
448 lock = mtx->mtx_lock;
449
450 if ((lock & ~MTX_EXWANTED) == 1) {
451 nlock = lock | MTX_EXCLUSIVE;
452 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
453 mtx->mtx_owner = curthread;
454 break;
455 }
456 } else if (lock & MTX_EXCLUSIVE) {
457 KKASSERT(mtx->mtx_owner == curthread);
458 break;
459 } else {
460 error = EDEADLK;
461 break;
462 }
463 cpu_pause();
464 ++mtx_collision_count;
465 }
466 return (error);
467 }
468
469 /*
470 * Unlock a lock. The caller must hold the lock either shared or exclusive.
471 *
472 * Any release which makes the lock available when others want an exclusive
473 * lock causes us to chain the owner to the next exclusive lock instead of
474 * releasing the lock.
475 */
476 void
477 _mtx_unlock(mtx_t mtx)
478 {
479 u_int lock;
480 u_int nlock;
481
482 for (;;) {
483 lock = mtx->mtx_lock;
484 nlock = lock & ~(MTX_SHWANTED | MTX_EXLINK);
485
486 if (nlock == 1) {
487 /*
488 * Last release, shared lock, no exclusive waiters.
489 */
490 nlock = lock & MTX_EXLINK;
491 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
492 break;
493 } else if (nlock == (MTX_EXCLUSIVE | 1)) {
494 /*
495 * Last release, exclusive lock, no exclusive waiters.
496 * Wake up any shared waiters.
497 */
498 mtx->mtx_owner = NULL;
499 nlock = lock & MTX_EXLINK;
500 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
501 if (lock & MTX_SHWANTED) {
502 wakeup(mtx);
503 ++mtx_wakeup_count;
504 }
505 break;
506 }
507 } else if (nlock == (MTX_EXWANTED | 1)) {
508 /*
509 * Last release, shared lock, with exclusive
510 * waiters.
511 *
512 * Wait for EXLINK to clear, then acquire it.
513 * We could use the cmpset for this but polling
514 * is better on the cpu caches.
515 *
516 * Acquire an exclusive lock leaving the lockcount
517 * set to 1, and get EXLINK for access to mtx_link.
518 */
519 if (lock & MTX_EXLINK) {
520 cpu_pause();
521 ++mtx_collision_count;
522 continue;
523 }
524 /*lock &= ~MTX_EXLINK;*/
525 nlock |= MTX_EXLINK | MTX_EXCLUSIVE;
526 nlock |= (lock & MTX_SHWANTED);
527 ++mycpu->gd_spinlocks_wr;
528 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
529 mtx_chain_link(mtx);
530 --mycpu->gd_spinlocks_wr;
531 break;
532 }
533 --mycpu->gd_spinlocks_wr;
534 } else if (nlock == (MTX_EXCLUSIVE | MTX_EXWANTED | 1)) {
535 /*
536 * Last release, exclusive lock, with exclusive
537 * waiters.
538 *
539 * leave the exclusive lock intact and the lockcount
540 * set to 1, and get EXLINK for access to mtx_link.
541 */
542 if (lock & MTX_EXLINK) {
543 cpu_pause();
544 ++mtx_collision_count;
545 continue;
546 }
547 /*lock &= ~MTX_EXLINK;*/
548 nlock |= MTX_EXLINK;
549 nlock |= (lock & MTX_SHWANTED);
550 ++mycpu->gd_spinlocks_wr;
551 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
552 mtx_chain_link(mtx);
553 --mycpu->gd_spinlocks_wr;
554 break;
555 }
556 --mycpu->gd_spinlocks_wr;
557 } else {
558 /*
559 * Not the last release (shared or exclusive)
560 */
561 nlock = lock - 1;
562 KKASSERT((nlock & MTX_MASK) != MTX_MASK);
563 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
564 break;
565 }
566 cpu_pause();
567 ++mtx_collision_count;
568 }
569 }
570
571 /*
572 * Chain mtx_chain_link. Called with the lock held exclusively with a
573 * single ref count, and also with MTX_EXLINK held.
574 */
575 static void
576 mtx_chain_link(mtx_t mtx)
577 {
578 mtx_link_t link;
579 u_int lock;
580 u_int nlock;
581 u_int clock; /* bits we own and want to clear */
582
583 /*
584 * Chain the exclusive lock to the next link. The caller cleared
585 * SHWANTED so if there is no link we have to wake up any shared
586 * waiters.
587 */
588 clock = MTX_EXLINK;
589 if ((link = mtx->mtx_link) != NULL) {
590 KKASSERT(link->state == MTX_LINK_LINKED);
591 if (link->next == link) {
592 mtx->mtx_link = NULL;
593 clock |= MTX_EXWANTED;
594 } else {
595 mtx->mtx_link = link->next;
596 link->next->prev = link->prev;
597 link->prev->next = link->next;
598 }
599 link->state = MTX_LINK_ACQUIRED;
600 mtx->mtx_owner = link->owner;
601 } else {
602 /*
603 * Chain was empty, release the exclusive lock's last count
604 * as well the bits shown.
605 */
606 clock |= MTX_EXCLUSIVE | MTX_EXWANTED | MTX_SHWANTED | 1;
607 }
608
609 /*
610 * We have to uset cmpset here to deal with MTX_SHWANTED. If
611 * we just clear the bits we can miss a wakeup or, worse,
612 * leave mtx_lock unlocked with MTX_SHWANTED still set.
613 */
614 for (;;) {
615 lock = mtx->mtx_lock;
616 nlock = lock & ~clock;
617
618 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
619 if (link) {
620 /*
621 * Wakeup new exclusive holder. Leave
622 * SHWANTED intact.
623 */
624 wakeup(link);
625 } else if (lock & MTX_SHWANTED) {
626 /*
627 * Signal any shared waiters (and we also
628 * clear SHWANTED).
629 */
630 mtx->mtx_owner = NULL;
631 wakeup(mtx);
632 ++mtx_wakeup_count;
633 }
634 break;
635 }
636 cpu_pause();
637 ++mtx_collision_count;
638 }
639 }
640
641 /*
642 * Delete a link structure after tsleep has failed. This code is not
643 * in the critical path as most exclusive waits are chained.
644 */
645 static
646 void
647 mtx_delete_link(mtx_t mtx, mtx_link_t link)
648 {
649 u_int lock;
650 u_int nlock;
651
652 /*
653 * Acquire MTX_EXLINK.
654 *
655 * Do not use cmpxchg to wait for EXLINK to clear as this might
656 * result in too much cpu cache traffic.
657 */
658 ++mycpu->gd_spinlocks_wr;
659 for (;;) {
660 lock = mtx->mtx_lock;
661 if (lock & MTX_EXLINK) {
662 cpu_pause();
663 ++mtx_collision_count;
664 continue;
665 }
666 /* lock &= ~MTX_EXLINK; */
667 nlock = lock | MTX_EXLINK;
668 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
669 break;
670 cpu_pause();
671 ++mtx_collision_count;
672 }
673
674 /*
675 * Delete the link and release EXLINK.
676 */
677 if (link->state == MTX_LINK_LINKED) {
678 if (link->next == link) {
679 mtx->mtx_link = NULL;
680 } else {
681 mtx->mtx_link = link->next;
682 link->next->prev = link->prev;
683 link->prev->next = link->next;
684 }
685 link->state = MTX_LINK_IDLE;
686 }
687 atomic_clear_int(&mtx->mtx_lock, MTX_EXLINK);
688 --mycpu->gd_spinlocks_wr;
689 }
690
691 /*
692 * Abort a mutex locking operation, causing mtx_lock_ex_link() to
693 * return ENOLCK. This may be called at any time after the
694 * mtx_link is initialized, including both before and after the call
695 * to mtx_lock_ex_link().
696 */
697 void
698 mtx_abort_ex_link(mtx_t mtx, mtx_link_t link)
699 {
700 u_int lock;
701 u_int nlock;
702
703 /*
704 * Acquire MTX_EXLINK
705 */
706 ++mycpu->gd_spinlocks_wr;
707 for (;;) {
708 lock = mtx->mtx_lock;
709 if (lock & MTX_EXLINK) {
710 cpu_pause();
711 ++mtx_collision_count;
712 continue;
713 }
714 /* lock &= ~MTX_EXLINK; */
715 nlock = lock | MTX_EXLINK;
716 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
717 break;
718 cpu_pause();
719 ++mtx_collision_count;
720 }
721
722 /*
723 * Do the abort
724 */
725 switch(link->state) {
726 case MTX_LINK_IDLE:
727 /*
728 * Link not started yet
729 */
730 link->state = MTX_LINK_ABORTED;
731 break;
732 case MTX_LINK_LINKED:
733 /*
734 * de-link, mark aborted, and wakeup the thread.
735 */
736 if (link->next == link) {
737 mtx->mtx_link = NULL;
738 } else {
739 mtx->mtx_link = link->next;
740 link->next->prev = link->prev;
741 link->prev->next = link->next;
742 }
743 link->state = MTX_LINK_ABORTED;
744 wakeup(link);
745 break;
746 case MTX_LINK_ACQUIRED:
747 /*
748 * Too late, the lock was acquired. Let it complete.
749 */
750 break;
751 default:
752 /*
753 * link already aborted, do nothing.
754 */
755 break;
756 }
757 atomic_clear_int(&mtx->mtx_lock, MTX_EXLINK);
758 --mycpu->gd_spinlocks_wr;
759 }
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