2 * Copyright (c) 2009 The DragonFly Project. All rights reserved.
4 * This code is derived from software contributed to The DragonFly Project
5 * by Matthew Dillon <dillon@backplane.com>
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
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
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.
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
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.
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
43 * - Exclusive priority over shared to prevent SMP starvation.
44 * - locks can be aborted (async callback, if any, will be made w/ENOLCK).
45 * - locks can be asynchronous.
46 * - synchronous fast path if no blocking occurs (async callback is not
49 * Generally speaking any caller-supplied link state must be properly
50 * initialized before use.
52 * Most of the support is in sys/mutex[2].h. We mostly provide backoff
56 #include <sys/param.h>
57 #include <sys/systm.h>
58 #include <sys/kernel.h>
59 #include <sys/sysctl.h>
60 #include <sys/indefinite.h>
61 #include <sys/thread.h>
63 #include <machine/cpufunc.h>
65 #include <sys/thread2.h>
66 #include <sys/mutex2.h>
67 #include <sys/indefinite2.h>
69 static int mtx_chain_link_ex(mtx_t *mtx, u_int olock);
70 static int mtx_chain_link_sh(mtx_t *mtx, u_int olock);
71 static void mtx_delete_link(mtx_t *mtx, mtx_link_t *link);
74 * Exclusive-lock a mutex, block until acquired unless link is async.
75 * Recursion is allowed.
77 * Returns 0 on success, the tsleep() return code on failure, EINPROGRESS
78 * if async. If immediately successful an async exclusive lock will return 0
79 * and not issue the async callback or link the link structure. The caller
80 * must handle this case (typically this is an optimal code path).
82 * A tsleep() error can only be returned if PCATCH is specified in the flags.
85 __mtx_lock_ex(mtx_t *mtx, mtx_link_t *link, int flags, int to)
98 nlock = MTX_EXCLUSIVE | 1;
99 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
100 mtx->mtx_owner = curthread;
102 link->state = MTX_LINK_ACQUIRED;
108 if ((lock & MTX_EXCLUSIVE) && mtx->mtx_owner == curthread) {
109 KKASSERT((lock & MTX_MASK) != MTX_MASK);
111 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
113 link->state = MTX_LINK_ACQUIRED;
121 * We need MTX_LINKSPIN to manipulate exlink or
124 * We must set MTX_EXWANTED with MTX_LINKSPIN to indicate
125 * pending exclusive requests. It cannot be set as a separate
126 * operation prior to acquiring MTX_LINKSPIN.
128 * To avoid unnecessary cpu cache traffic we poll
129 * for collisions. It is also possible that EXWANTED
130 * state failing the above test was spurious, so all the
131 * tests must be repeated if we cannot obtain LINKSPIN
132 * with the prior state tests intact (i.e. don't reload
133 * the (lock) variable here, for heaven's sake!).
135 if (lock & MTX_LINKSPIN) {
140 nlock = lock | MTX_EXWANTED | MTX_LINKSPIN;
142 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock) == 0) {
148 * Check for early abort.
150 if (link->state == MTX_LINK_ABORTED) {
151 if (mtx->mtx_exlink == NULL) {
152 atomic_clear_int(&mtx->mtx_lock,
156 atomic_clear_int(&mtx->mtx_lock,
160 link->state = MTX_LINK_IDLE;
166 * Add our link to the exlink list and release LINKSPIN.
169 link->state = MTX_LINK_LINKED_EX;
170 if (mtx->mtx_exlink) {
171 link->next = mtx->mtx_exlink;
172 link->prev = link->next->prev;
173 link->next->prev = link;
174 link->prev->next = link;
178 mtx->mtx_exlink = link;
180 isasync = (link->callback != NULL);
181 atomic_clear_int(&mtx->mtx_lock, MTX_LINKSPIN);
185 * If asynchronous lock request return without
186 * blocking, leave link structure linked.
196 error = mtx_wait_link(mtx, link, flags, to);
203 _mtx_lock_ex_link(mtx_t *mtx, mtx_link_t *link, int flags, int to)
205 return(__mtx_lock_ex(mtx, link, flags, to));
209 _mtx_lock_ex(mtx_t *mtx, int flags, int to)
213 mtx_link_init(&link);
214 return(__mtx_lock_ex(mtx, &link, flags, to));
218 _mtx_lock_ex_quick(mtx_t *mtx)
222 mtx_link_init(&link);
223 return(__mtx_lock_ex(mtx, &link, 0, 0));
227 * Share-lock a mutex, block until acquired. Recursion is allowed.
229 * Returns 0 on success, or the tsleep() return code on failure.
230 * An error can only be returned if PCATCH is specified in the flags.
232 * NOTE: Shared locks get a mass-wakeup so if the tsleep fails we
233 * do not have to chain the wakeup().
236 __mtx_lock_sh(mtx_t *mtx, mtx_link_t *link, int flags, int to)
245 lock = mtx->mtx_lock;
250 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
253 link->state = MTX_LINK_ACQUIRED;
258 if ((lock & (MTX_EXCLUSIVE | MTX_EXWANTED)) == 0) {
259 KKASSERT((lock & MTX_MASK) != MTX_MASK);
261 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
264 link->state = MTX_LINK_ACQUIRED;
271 * We need MTX_LINKSPIN to manipulate exlink or
274 * We must set MTX_SHWANTED with MTX_LINKSPIN to indicate
275 * pending shared requests. It cannot be set as a separate
276 * operation prior to acquiring MTX_LINKSPIN.
278 * To avoid unnecessary cpu cache traffic we poll
279 * for collisions. It is also possible that EXWANTED
280 * state failing the above test was spurious, so all the
281 * tests must be repeated if we cannot obtain LINKSPIN
282 * with the prior state tests intact (i.e. don't reload
283 * the (lock) variable here, for heaven's sake!).
285 if (lock & MTX_LINKSPIN) {
290 nlock = lock | MTX_SHWANTED | MTX_LINKSPIN;
292 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock) == 0) {
298 * Check for early abort. Other shared lock requestors
299 * could have sneaked in before we set LINKSPIN so make
300 * sure we undo the state properly.
302 if (link->state == MTX_LINK_ABORTED) {
303 if (mtx->mtx_shlink) {
304 atomic_clear_int(&mtx->mtx_lock,
307 atomic_clear_int(&mtx->mtx_lock,
312 link->state = MTX_LINK_IDLE;
318 * Add our link to the shlink list and release LINKSPIN.
321 link->state = MTX_LINK_LINKED_SH;
322 if (mtx->mtx_shlink) {
323 link->next = mtx->mtx_shlink;
324 link->prev = link->next->prev;
325 link->next->prev = link;
326 link->prev->next = link;
330 mtx->mtx_shlink = link;
332 isasync = (link->callback != NULL);
333 atomic_clear_int(&mtx->mtx_lock, MTX_LINKSPIN);
337 * If asynchronous lock request return without
338 * blocking, leave link structure linked.
348 error = mtx_wait_link(mtx, link, flags, to);
355 _mtx_lock_sh_link(mtx_t *mtx, mtx_link_t *link, int flags, int to)
357 return(__mtx_lock_sh(mtx, link, flags, to));
361 _mtx_lock_sh(mtx_t *mtx, int flags, int to)
365 mtx_link_init(&link);
366 return(__mtx_lock_sh(mtx, &link, flags, to));
370 _mtx_lock_sh_quick(mtx_t *mtx)
374 mtx_link_init(&link);
375 return(__mtx_lock_sh(mtx, &link, 0, 0));
379 * Get an exclusive spinlock the hard way.
382 _mtx_spinlock(mtx_t *mtx)
390 lock = mtx->mtx_lock;
392 nlock = MTX_EXCLUSIVE | 1;
393 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
394 mtx->mtx_owner = curthread;
397 } else if ((lock & MTX_EXCLUSIVE) &&
398 mtx->mtx_owner == curthread) {
399 KKASSERT((lock & MTX_MASK) != MTX_MASK);
401 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
408 for (bo = 0; bo < bb; ++bo)
416 * Attempt to acquire a spinlock, if we fail we must undo the
417 * gd->gd_spinlocks/gd->gd_curthead->td_critcount predisposition.
419 * Returns 0 on success, EAGAIN on failure.
422 _mtx_spinlock_try(mtx_t *mtx)
424 globaldata_t gd = mycpu;
430 lock = mtx->mtx_lock;
432 nlock = MTX_EXCLUSIVE | 1;
433 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
434 mtx->mtx_owner = gd->gd_curthread;
437 } else if ((lock & MTX_EXCLUSIVE) &&
438 mtx->mtx_owner == gd->gd_curthread) {
439 KKASSERT((lock & MTX_MASK) != MTX_MASK);
441 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
446 crit_exit_raw(gd->gd_curthread);
458 _mtx_spinlock_sh(mtx_t *mtx)
466 lock = mtx->mtx_lock;
467 if ((lock & MTX_EXCLUSIVE) == 0) {
468 KKASSERT((lock & MTX_MASK) != MTX_MASK);
470 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
477 for (bo = 0; bo < bb; ++bo)
487 _mtx_lock_ex_try(mtx_t *mtx)
494 lock = mtx->mtx_lock;
496 nlock = MTX_EXCLUSIVE | 1;
497 if (atomic_cmpset_int(&mtx->mtx_lock, 0, nlock)) {
498 mtx->mtx_owner = curthread;
502 } else if ((lock & MTX_EXCLUSIVE) &&
503 mtx->mtx_owner == curthread) {
504 KKASSERT((lock & MTX_MASK) != MTX_MASK);
506 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
520 _mtx_lock_sh_try(mtx_t *mtx)
527 lock = mtx->mtx_lock;
528 if ((lock & MTX_EXCLUSIVE) == 0) {
529 KKASSERT((lock & MTX_MASK) != MTX_MASK);
531 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
543 * If the lock is held exclusively it must be owned by the caller. If the
544 * lock is already a shared lock this operation is a NOP. A panic will
545 * occur if the lock is not held either shared or exclusive.
547 * The exclusive count is converted to a shared count.
550 _mtx_downgrade(mtx_t *mtx)
556 lock = mtx->mtx_lock;
560 * NOP if already shared.
562 if ((lock & MTX_EXCLUSIVE) == 0) {
563 KKASSERT((lock & MTX_MASK) > 0);
568 * Transfer count to shared. Any additional pending shared
569 * waiters must be woken up.
571 if (lock & MTX_SHWANTED) {
572 if (mtx_chain_link_sh(mtx, lock))
576 nlock = lock & ~MTX_EXCLUSIVE;
577 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
586 * Upgrade a shared lock to an exclusive lock. The upgrade will fail if
587 * the shared lock has a count other then 1. Optimize the most likely case
588 * but note that a single cmpset can fail due to WANTED races.
590 * If the lock is held exclusively it must be owned by the caller and
591 * this function will simply return without doing anything. A panic will
592 * occur if the lock is held exclusively by someone other then the caller.
594 * Returns 0 on success, EDEADLK on failure.
597 _mtx_upgrade_try(mtx_t *mtx)
604 lock = mtx->mtx_lock;
607 if ((lock & ~MTX_EXWANTED) == 1) {
608 nlock = lock | MTX_EXCLUSIVE;
609 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock)) {
610 mtx->mtx_owner = curthread;
613 } else if (lock & MTX_EXCLUSIVE) {
614 KKASSERT(mtx->mtx_owner == curthread);
626 * Unlock a lock. The caller must hold the lock either shared or exclusive.
628 * On the last release we handle any pending chains.
631 _mtx_unlock(mtx_t *mtx)
633 thread_t td __debugvar = curthread;
638 lock = mtx->mtx_lock;
642 case MTX_EXCLUSIVE | 1:
644 * Last release, exclusive lock.
645 * No exclusive or shared requests pending.
647 KKASSERT(mtx->mtx_owner == td ||
648 mtx->mtx_owner == NULL);
649 mtx->mtx_owner = NULL;
651 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
654 case MTX_EXCLUSIVE | MTX_EXWANTED | 1:
655 case MTX_EXCLUSIVE | MTX_EXWANTED | MTX_SHWANTED | 1:
657 * Last release, exclusive lock.
658 * Exclusive requests pending.
659 * Exclusive requests have priority over shared reqs.
661 KKASSERT(mtx->mtx_owner == td ||
662 mtx->mtx_owner == NULL);
663 mtx->mtx_owner = NULL;
664 if (mtx_chain_link_ex(mtx, lock))
667 case MTX_EXCLUSIVE | MTX_SHWANTED | 1:
669 * Last release, exclusive lock.
671 * Shared requests are pending. Transfer our count (1)
672 * to the first shared request, wakeup all shared reqs.
674 KKASSERT(mtx->mtx_owner == td ||
675 mtx->mtx_owner == NULL);
676 mtx->mtx_owner = NULL;
677 if (mtx_chain_link_sh(mtx, lock))
682 * Last release, shared lock.
683 * No exclusive or shared requests pending.
686 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
689 case MTX_EXWANTED | 1:
690 case MTX_EXWANTED | MTX_SHWANTED | 1:
692 * Last release, shared lock.
694 * Exclusive requests are pending. Upgrade this
695 * final shared lock to exclusive and transfer our
696 * count (1) to the next exclusive request.
698 * Exclusive requests have priority over shared reqs.
700 if (mtx_chain_link_ex(mtx, lock))
703 case MTX_SHWANTED | 1:
705 * Last release, shared lock.
706 * Shared requests pending.
708 if (mtx_chain_link_sh(mtx, lock))
713 * We have to loop if this is the last release but
714 * someone is fiddling with LINKSPIN.
716 if ((lock & MTX_MASK) == 1) {
717 KKASSERT(lock & MTX_LINKSPIN);
722 * Not the last release (shared or exclusive)
725 KKASSERT((nlock & MTX_MASK) != MTX_MASK);
726 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
738 * Chain pending links. Called on the last release of an exclusive or
739 * shared lock when the appropriate WANTED bit is set. mtx_lock old state
740 * is passed in with the count left at 1, which we can inherit, and other
741 * bits which we must adjust in a single atomic operation.
743 * Return non-zero on success, 0 if caller needs to retry.
745 * NOTE: It's ok if MTX_EXWANTED is in an indeterminant state while we are
746 * acquiring LINKSPIN as all other cases will also need to acquire
747 * LINKSPIN when handling the EXWANTED case.
750 mtx_chain_link_ex(mtx_t *mtx, u_int olock)
752 thread_t td = curthread;
756 olock &= ~MTX_LINKSPIN;
757 nlock = olock | MTX_LINKSPIN | MTX_EXCLUSIVE; /* upgrade if necc */
759 if (atomic_cmpset_int(&mtx->mtx_lock, olock, nlock)) {
760 link = mtx->mtx_exlink;
761 KKASSERT(link != NULL);
762 if (link->next == link) {
763 mtx->mtx_exlink = NULL;
764 nlock = MTX_LINKSPIN | MTX_EXWANTED; /* to clear */
766 mtx->mtx_exlink = link->next;
767 link->next->prev = link->prev;
768 link->prev->next = link->next;
769 nlock = MTX_LINKSPIN; /* to clear */
771 KKASSERT(link->state == MTX_LINK_LINKED_EX);
772 mtx->mtx_owner = link->owner;
776 * WARNING! The callback can only be safely
777 * made with LINKSPIN still held
778 * and in a critical section.
780 * WARNING! The link can go away after the
781 * state is set, or after the
784 if (link->callback) {
785 link->state = MTX_LINK_CALLEDBACK;
786 link->callback(link, link->arg, 0);
788 link->state = MTX_LINK_ACQUIRED;
791 atomic_clear_int(&mtx->mtx_lock, nlock);
802 * Flush waiting shared locks. The lock's prior state is passed in and must
803 * be adjusted atomically only if it matches and LINKSPIN is not set.
805 * IMPORTANT! The caller has left one active count on the lock for us to
806 * consume. We will apply this to the first link, but must add
807 * additional counts for any other links.
810 mtx_chain_link_sh(mtx_t *mtx, u_int olock)
812 thread_t td = curthread;
817 olock &= ~MTX_LINKSPIN;
818 nlock = olock | MTX_LINKSPIN;
819 nlock &= ~MTX_EXCLUSIVE;
821 if (atomic_cmpset_int(&mtx->mtx_lock, olock, nlock)) {
823 * It should not be possible for SHWANTED to be set without
826 KKASSERT(mtx->mtx_shlink != NULL);
829 * We have to process the count for all shared locks before
830 * we process any of the links. Count the additional shared
831 * locks beyond the first link (which is already accounted
832 * for) and associate the full count with the lock
836 for (link = mtx->mtx_shlink->next; link != mtx->mtx_shlink;
841 atomic_add_int(&mtx->mtx_lock, addcount);
844 * We can wakeup all waiting shared locks.
846 while ((link = mtx->mtx_shlink) != NULL) {
847 KKASSERT(link->state == MTX_LINK_LINKED_SH);
848 if (link->next == link) {
849 mtx->mtx_shlink = NULL;
851 mtx->mtx_shlink = link->next;
852 link->next->prev = link->prev;
853 link->prev->next = link->next;
858 if (link->callback) {
859 link->state = MTX_LINK_CALLEDBACK;
860 link->callback(link, link->arg, 0);
863 link->state = MTX_LINK_ACQUIRED;
867 atomic_clear_int(&mtx->mtx_lock, MTX_LINKSPIN |
879 * Delete a link structure after tsleep has failed. This code is not
880 * in the critical path as most exclusive waits are chained.
884 mtx_delete_link(mtx_t *mtx, mtx_link_t *link)
886 thread_t td = curthread;
891 * Acquire MTX_LINKSPIN.
893 * Do not use cmpxchg to wait for LINKSPIN to clear as this might
894 * result in too much cpu cache traffic.
898 lock = mtx->mtx_lock;
899 if (lock & MTX_LINKSPIN) {
903 nlock = lock | MTX_LINKSPIN;
904 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
910 * Delete the link and release LINKSPIN.
912 nlock = MTX_LINKSPIN; /* to clear */
914 switch(link->state) {
915 case MTX_LINK_LINKED_EX:
916 if (link->next == link) {
917 mtx->mtx_exlink = NULL;
918 nlock |= MTX_EXWANTED; /* to clear */
920 mtx->mtx_exlink = link->next;
921 link->next->prev = link->prev;
922 link->prev->next = link->next;
925 case MTX_LINK_LINKED_SH:
926 if (link->next == link) {
927 mtx->mtx_shlink = NULL;
928 nlock |= MTX_SHWANTED; /* to clear */
930 mtx->mtx_shlink = link->next;
931 link->next->prev = link->prev;
932 link->prev->next = link->next;
939 atomic_clear_int(&mtx->mtx_lock, nlock);
944 * Wait for async lock completion or abort. Returns ENOLCK if an abort
948 mtx_wait_link(mtx_t *mtx, mtx_link_t *link, int flags, int to)
950 indefinite_info_t info;
953 indefinite_init(&info, mtx->mtx_ident, 1,
954 ((link->state & MTX_LINK_LINKED_SH) ? 'm' : 'M'));
957 * Sleep. Handle false wakeups, interruptions, etc.
958 * The link may also have been aborted. The LINKED
959 * bit was set by this cpu so we can test it without
963 while (link->state & MTX_LINK_LINKED) {
964 tsleep_interlock(link, 0);
966 if (link->state & MTX_LINK_LINKED) {
967 error = tsleep(link, flags | PINTERLOCKED,
972 if ((mtx->mtx_flags & MTXF_NOCOLLSTATS) == 0)
973 indefinite_check(&info);
977 * We need at least a lfence (load fence) to ensure our cpu does not
978 * reorder loads (of data outside the lock structure) prior to the
979 * remote cpu's release, since the above test may have run without
980 * any atomic interactions.
982 * If we do not do this then state updated by the other cpu before
983 * releasing its lock may not be read cleanly by our cpu when this
984 * function returns. Even though the other cpu ordered its stores,
985 * our loads can still be out of order.
990 * We are done, make sure the link structure is unlinked.
991 * It may still be on the list due to e.g. EINTR or
994 * It is possible for the tsleep to race an ABORT and cause
997 * The tsleep() can be woken up for numerous reasons and error
998 * might be zero in situations where we intend to return an error.
1000 * (This is the synchronous case so state cannot be CALLEDBACK)
1002 switch(link->state) {
1003 case MTX_LINK_ACQUIRED:
1004 case MTX_LINK_CALLEDBACK:
1007 case MTX_LINK_ABORTED:
1010 case MTX_LINK_LINKED_EX:
1011 case MTX_LINK_LINKED_SH:
1012 mtx_delete_link(mtx, link);
1016 error = EWOULDBLOCK;
1021 * Clear state on status returned.
1023 link->state = MTX_LINK_IDLE;
1025 if ((mtx->mtx_flags & MTXF_NOCOLLSTATS) == 0)
1026 indefinite_done(&info);
1032 * Abort a mutex locking operation, causing mtx_lock_ex_link() to
1033 * return ENOLCK. This may be called at any time after the mtx_link
1034 * is initialized or the status from a previous lock has been
1035 * returned. If called prior to the next (non-try) lock attempt, the
1036 * next lock attempt using this link structure will abort instantly.
1038 * Caller must still wait for the operation to complete, either from a
1039 * blocking call that is still in progress or by calling mtx_wait_link().
1041 * If an asynchronous lock request is possibly in-progress, the caller
1042 * should call mtx_wait_link() synchronously. Note that the asynchronous
1043 * lock callback will NOT be called if a successful abort occurred. XXX
1046 mtx_abort_link(mtx_t *mtx, mtx_link_t *link)
1048 thread_t td = curthread;
1053 * Acquire MTX_LINKSPIN
1057 lock = mtx->mtx_lock;
1058 if (lock & MTX_LINKSPIN) {
1062 nlock = lock | MTX_LINKSPIN;
1063 if (atomic_cmpset_int(&mtx->mtx_lock, lock, nlock))
1071 * WARNING! Link structure can disappear once link->state is set.
1073 nlock = MTX_LINKSPIN; /* to clear */
1075 switch(link->state) {
1078 * Link not started yet
1080 link->state = MTX_LINK_ABORTED;
1082 case MTX_LINK_LINKED_EX:
1084 * de-link, mark aborted, and potentially wakeup the thread
1085 * or issue the callback.
1087 if (link->next == link) {
1088 if (mtx->mtx_exlink == link) {
1089 mtx->mtx_exlink = NULL;
1090 nlock |= MTX_EXWANTED; /* to clear */
1093 if (mtx->mtx_exlink == link)
1094 mtx->mtx_exlink = link->next;
1095 link->next->prev = link->prev;
1096 link->prev->next = link->next;
1100 * When aborting the async callback is still made. We must
1101 * not set the link status to ABORTED in the callback case
1102 * since there is nothing else to clear its status if the
1105 if (link->callback) {
1106 link->state = MTX_LINK_CALLEDBACK;
1107 link->callback(link, link->arg, ENOLCK);
1109 link->state = MTX_LINK_ABORTED;
1113 case MTX_LINK_LINKED_SH:
1115 * de-link, mark aborted, and potentially wakeup the thread
1116 * or issue the callback.
1118 if (link->next == link) {
1119 if (mtx->mtx_shlink == link) {
1120 mtx->mtx_shlink = NULL;
1121 nlock |= MTX_SHWANTED; /* to clear */
1124 if (mtx->mtx_shlink == link)
1125 mtx->mtx_shlink = link->next;
1126 link->next->prev = link->prev;
1127 link->prev->next = link->next;
1131 * When aborting the async callback is still made. We must
1132 * not set the link status to ABORTED in the callback case
1133 * since there is nothing else to clear its status if the
1136 if (link->callback) {
1137 link->state = MTX_LINK_CALLEDBACK;
1138 link->callback(link, link->arg, ENOLCK);
1140 link->state = MTX_LINK_ABORTED;
1144 case MTX_LINK_ACQUIRED:
1145 case MTX_LINK_CALLEDBACK:
1147 * Too late, the lock was acquired. Let it complete.
1152 * link already aborted, do nothing.
1156 atomic_clear_int(&mtx->mtx_lock, nlock);