1/*-
2 * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
--- 43 unchanged lines hidden (view full) ---
52 * already has a turnstile, then it gives its turnstile to the lock's
53 * turnstile's free list. When a thread is woken up, it takes a turnstile from
54 * the free list if there are any other waiters. If it is the only thread
55 * blocked on the lock, then it reclaims the turnstile associated with the lock
56 * and removes it from the hash table.
57 */
58
59#include <sys/cdefs.h>
60__FBSDID("$FreeBSD: head/sys/kern/subr_turnstile.c 170295 2007-06-04 23:51:44Z jeff $");
61
62#include "opt_ddb.h"
63#include "opt_turnstile_profiling.h"
64
65#include <sys/param.h>
66#include <sys/systm.h>
67#include <sys/kernel.h>
68#include <sys/ktr.h>
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111 * turnstile_signal() or turnstile_wait() that are waiting to be put on
112 * the run queue.
113 *
114 * Locking key:
115 * c - turnstile chain lock
116 * q - td_contested lock
117 */
118struct turnstile {
119 struct mtx ts_lock; /* Spin lock for self. */
120 struct threadqueue ts_blocked[2]; /* (c + q) Blocked threads. */
121 struct threadqueue ts_pending; /* (c) Pending threads. */
122 LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */
123 LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */
124 LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */
125 struct lock_object *ts_lockobj; /* (c) Lock we reference. */
126 struct thread *ts_owner; /* (c + q) Who owns the lock. */
127};
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158static int turnstile_adjust_thread(struct turnstile *ts,
159 struct thread *td);
160static struct thread *turnstile_first_waiter(struct turnstile *ts);
161static void turnstile_setowner(struct turnstile *ts, struct thread *owner);
162#ifdef INVARIANTS
163static void turnstile_dtor(void *mem, int size, void *arg);
164#endif
165static int turnstile_init(void *mem, int size, int flags);
166static void turnstile_fini(void *mem, int size);
167
168/*
169 * Walks the chain of turnstiles and their owners to propagate the priority
170 * of the thread being blocked to all the threads holding locks that have to
171 * release their locks before this thread can run again.
172 */
173static void
174propagate_priority(struct thread *td)
175{
176 struct turnstile *ts;
177 int pri;
178
179 THREAD_LOCK_ASSERT(td, MA_OWNED);
180 pri = td->td_priority;
181 ts = td->td_blocked;
182 MPASS(td->td_lock == &ts->ts_lock);
183 /*
184 * Grab a recursive lock on this turnstile chain so it stays locked
185 * for the whole operation. The caller expects us to return with
186 * the original lock held. We only ever lock down the chain so
187 * the lock order is constant.
188 */
189 mtx_lock_spin(&ts->ts_lock);
190 for (;;) {
191 td = ts->ts_owner;
192
193 if (td == NULL) {
194 /*
195 * This might be a read lock with no owner. There's
196 * not much we can do, so just bail.
197 */
198 mtx_unlock_spin(&ts->ts_lock);
199 return;
200 }
201
202 thread_lock_flags(td, MTX_DUPOK);
203 mtx_unlock_spin(&ts->ts_lock);
204 MPASS(td->td_proc != NULL);
205 MPASS(td->td_proc->p_magic == P_MAGIC);
206
207 /*
208 * If the thread is asleep, then we are probably about
209 * to deadlock. To make debugging this easier, just
210 * panic and tell the user which thread misbehaved so
211 * they can hopefully get a stack trace from the truly
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220#endif
221 panic("sleeping thread");
222 }
223
224 /*
225 * If this thread already has higher priority than the
226 * thread that is being blocked, we are finished.
227 */
228 if (td->td_priority <= pri) {
229 thread_unlock(td);
230 return;
231 }
232
233 /*
234 * Bump this thread's priority.
235 */
236 sched_lend_prio(td, pri);
237
238 /*
239 * If lock holder is actually running or on the run queue
240 * then we are done.
241 */
242 if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) {
243 MPASS(td->td_blocked == NULL);
244 thread_unlock(td);
245 return;
246 }
247
248#ifndef SMP
249 /*
250 * For UP, we check to see if td is curthread (this shouldn't
251 * ever happen however as it would mean we are in a deadlock.)
252 */
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261 td->td_tid, td->td_proc->p_comm, td->td_state,
262 ts->ts_lockobj->lo_name));
263
264 /*
265 * Pick up the lock that td is blocked on.
266 */
267 ts = td->td_blocked;
268 MPASS(ts != NULL);
269 MPASS(td->td_lock == &ts->ts_lock);
270 /* Resort td on the list if needed. */
271 if (!turnstile_adjust_thread(ts, td)) {
272 mtx_unlock_spin(&ts->ts_lock);
273 return;
274 }
275 /* The thread lock is released as ts lock above. */
276 }
277}
278
279/*
280 * Adjust the thread's position on a turnstile after its priority has been
281 * changed.
282 */
283static int
284turnstile_adjust_thread(struct turnstile *ts, struct thread *td)
285{
286 struct thread *td1, *td2;
287 int queue;
288
289 THREAD_LOCK_ASSERT(td, MA_OWNED);
290 MPASS(TD_ON_LOCK(td));
291
292 /*
293 * This thread may not be blocked on this turnstile anymore
294 * but instead might already be woken up on another CPU
295 * that is waiting on the thread lock in turnstile_unpend() to
296 * finish waking this thread up. We can detect this case
297 * by checking to see if this thread has been given a
298 * turnstile by either turnstile_signal() or
299 * turnstile_broadcast(). In this case, treat the thread as
300 * if it was already running.
301 */
302 if (td->td_turnstile != NULL)
303 return (0);
304
305 /*
306 * Check if the thread needs to be moved on the blocked chain.
307 * It needs to be moved if either its priority is lower than
308 * the previous thread or higher than the next thread.
309 */
310 MPASS(td->td_lock == &ts->ts_lock);
311 td1 = TAILQ_PREV(td, threadqueue, td_lockq);
312 td2 = TAILQ_NEXT(td, td_lockq);
313 if ((td1 != NULL && td->td_priority < td1->td_priority) ||
314 (td2 != NULL && td->td_priority > td2->td_priority)) {
315
316 /*
317 * Remove thread from blocked chain and determine where
318 * it should be moved to.
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391#endif
392
393static void
394init_turnstile0(void *dummy)
395{
396
397 turnstile_zone = uma_zcreate("TURNSTILE", sizeof(struct turnstile),
398#ifdef INVARIANTS
399 NULL, turnstile_dtor, turnstile_init, turnstile_fini,
400 UMA_ALIGN_CACHE, 0);
401#else
402 NULL, NULL, turnstile_init, turnstile_fini, UMA_ALIGN_CACHE, 0);
403#endif
404 thread0.td_turnstile = turnstile_alloc();
405}
406SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
407
408/*
409 * Update a thread on the turnstile list after it's priority has been changed.
410 * The old priority is passed in as an argument.
411 */
412void
413turnstile_adjust(struct thread *td, u_char oldpri)
414{
415 struct turnstile *ts;
416
417 MPASS(TD_ON_LOCK(td));
418
419 /*
420 * Pick up the lock that td is blocked on.
421 */
422 ts = td->td_blocked;
423 MPASS(ts != NULL);
424 MPASS(td->td_lock == &ts->ts_lock);
425 mtx_assert(&ts->ts_lock, MA_OWNED);
426
427 /* Resort the turnstile on the list. */
428 if (!turnstile_adjust_thread(ts, td))
429 return;
430 /*
431 * If our priority was lowered and we are at the head of the
432 * turnstile, then propagate our new priority up the chain.
433 * Note that we currently don't try to revoke lent priorities
434 * when our priority goes up.
435 */
436 MPASS(td->td_tsqueue == TS_EXCLUSIVE_QUEUE ||
437 td->td_tsqueue == TS_SHARED_QUEUE);
438 if (td == TAILQ_FIRST(&ts->ts_blocked[td->td_tsqueue]) &&
439 td->td_priority < oldpri) {
440 propagate_priority(td);
441 }
442}
443
444/*
445 * Set the owner of the lock this turnstile is attached to.
446 */
447static void
448turnstile_setowner(struct turnstile *ts, struct thread *owner)
449{
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485 struct turnstile *ts;
486
487 bzero(mem, size);
488 ts = mem;
489 TAILQ_INIT(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]);
490 TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]);
491 TAILQ_INIT(&ts->ts_pending);
492 LIST_INIT(&ts->ts_free);
493 mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN | MTX_RECURSE);
494 return (0);
495}
496
497static void
498turnstile_fini(void *mem, int size)
499{
500 struct turnstile *ts;
501
502 ts = mem;
503 mtx_destroy(&ts->ts_lock);
504}
505
506/*
507 * Get a turnstile for a new thread.
508 */
509struct turnstile *
510turnstile_alloc(void)
511{
512
513 return (uma_zalloc(turnstile_zone, M_WAITOK));
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522
523 uma_zfree(turnstile_zone, ts);
524}
525
526/*
527 * Lock the turnstile chain associated with the specified lock.
528 */
529void
530turnstile_chain_lock(struct lock_object *lock)
531{
532 struct turnstile_chain *tc;
533
534 tc = TC_LOOKUP(lock);
535 mtx_lock_spin(&tc->tc_lock);
536}
537
538struct turnstile *
539turnstile_trywait(struct lock_object *lock)
540{
541 struct turnstile_chain *tc;
542 struct turnstile *ts;
543
544 tc = TC_LOOKUP(lock);
545 mtx_lock_spin(&tc->tc_lock);
546 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
547 if (ts->ts_lockobj == lock) {
548 mtx_lock_spin(&ts->ts_lock);
549 return (ts);
550 }
551
552 ts = curthread->td_turnstile;
553 MPASS(ts != NULL);
554 mtx_lock_spin(&ts->ts_lock);
555 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
556 ts->ts_lockobj = lock;
557
558 return (ts);
559}
560
561void
562turnstile_cancel(struct turnstile *ts)
563{
564 struct turnstile_chain *tc;
565 struct lock_object *lock;
566
567 mtx_assert(&ts->ts_lock, MA_OWNED);
568
569 mtx_unlock_spin(&ts->ts_lock);
570 lock = ts->ts_lockobj;
571 if (ts == curthread->td_turnstile)
572 ts->ts_lockobj = NULL;
573 tc = TC_LOOKUP(lock);
574 mtx_unlock_spin(&tc->tc_lock);
575}
576
577/*
578 * Look up the turnstile for a lock in the hash table locking the associated
579 * turnstile chain along the way. If no turnstile is found in the hash
580 * table, NULL is returned.
581 */
582struct turnstile *
583turnstile_lookup(struct lock_object *lock)
584{
585 struct turnstile_chain *tc;
586 struct turnstile *ts;
587
588 tc = TC_LOOKUP(lock);
589 mtx_assert(&tc->tc_lock, MA_OWNED);
590 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
591 if (ts->ts_lockobj == lock) {
592 mtx_lock_spin(&ts->ts_lock);
593 return (ts);
594 }
595 return (NULL);
596}
597
598/*
599 * Unlock the turnstile chain associated with a given lock.
600 */
601void
602turnstile_chain_unlock(struct lock_object *lock)
603{
604 struct turnstile_chain *tc;
605
606 tc = TC_LOOKUP(lock);
607 mtx_unlock_spin(&tc->tc_lock);
608}
609
610/*
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623 return (xtd);
624}
625
626/*
627 * Take ownership of a turnstile and adjust the priority of the new
628 * owner appropriately.
629 */
630void
631turnstile_claim(struct turnstile *ts)
632{
633 struct thread *td, *owner;
634 struct turnstile_chain *tc;
635
636 mtx_assert(&ts->ts_lock, MA_OWNED);
637 MPASS(ts != curthread->td_turnstile);
638
639 owner = curthread;
640 mtx_lock_spin(&td_contested_lock);
641 turnstile_setowner(ts, owner);
642 mtx_unlock_spin(&td_contested_lock);
643
644 td = turnstile_first_waiter(ts);
645 MPASS(td != NULL);
646 MPASS(td->td_proc->p_magic == P_MAGIC);
647 MPASS(td->td_lock == &ts->ts_lock);
648
649 /*
650 * Update the priority of the new owner if needed.
651 */
652 thread_lock(owner);
653 if (td->td_priority < owner->td_priority)
654 sched_lend_prio(owner, td->td_priority);
655 thread_unlock(owner);
656 tc = TC_LOOKUP(ts->ts_lockobj);
657 mtx_unlock_spin(&ts->ts_lock);
658 mtx_unlock_spin(&tc->tc_lock);
659}
660
661/*
662 * Block the current thread on the turnstile assicated with 'lock'. This
663 * function will context switch and not return until this thread has been
664 * woken back up. This function must be called with the appropriate
665 * turnstile chain locked and will return with it unlocked.
666 */
667void
668turnstile_wait(struct turnstile *ts, struct thread *owner, int queue)
669{
670 struct turnstile_chain *tc;
671 struct thread *td, *td1;
672 struct lock_object *lock;
673
674 td = curthread;
675 mtx_assert(&ts->ts_lock, MA_OWNED);
676 if (queue == TS_SHARED_QUEUE)
677 MPASS(owner != NULL);
678 if (owner)
679 MPASS(owner->td_proc->p_magic == P_MAGIC);
680 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
681
682 /*
683 * If the lock does not already have a turnstile, use this thread's
684 * turnstile. Otherwise insert the current thread into the
685 * turnstile already in use by this lock.
686 */
687 tc = TC_LOOKUP(ts->ts_lockobj);
688 if (ts == td->td_turnstile) {
689 mtx_assert(&tc->tc_lock, MA_OWNED);
690#ifdef TURNSTILE_PROFILING
691 tc->tc_depth++;
692 if (tc->tc_depth > tc->tc_max_depth) {
693 tc->tc_max_depth = tc->tc_depth;
694 if (tc->tc_max_depth > turnstile_max_depth)
695 turnstile_max_depth = tc->tc_max_depth;
696 }
697#endif
698 tc = TC_LOOKUP(ts->ts_lockobj);
699 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash);
700 KASSERT(TAILQ_EMPTY(&ts->ts_pending),
701 ("thread's turnstile has pending threads"));
702 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]),
703 ("thread's turnstile has exclusive waiters"));
704 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]),
705 ("thread's turnstile has shared waiters"));
706 KASSERT(LIST_EMPTY(&ts->ts_free),
707 ("thread's turnstile has a non-empty free list"));
708 MPASS(ts->ts_lockobj != NULL);
709 mtx_lock_spin(&td_contested_lock);
710 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
711 turnstile_setowner(ts, owner);
712 mtx_unlock_spin(&td_contested_lock);
713 } else {
714 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq)
715 if (td1->td_priority > td->td_priority)
716 break;
717 mtx_lock_spin(&td_contested_lock);
718 if (td1 != NULL)
719 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
720 else
721 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
722 MPASS(owner == ts->ts_owner);
723 mtx_unlock_spin(&td_contested_lock);
724 MPASS(td->td_turnstile != NULL);
725 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
726 }
727 thread_lock(td);
728 thread_lock_set(td, &ts->ts_lock);
729 td->td_turnstile = NULL;
730
731 /* Save who we are blocked on and switch. */
732 lock = ts->ts_lockobj;
733 td->td_tsqueue = queue;
734 td->td_blocked = ts;
735 td->td_lockname = lock->lo_name;
736 TD_SET_LOCK(td);
737 mtx_unlock_spin(&tc->tc_lock);
738 propagate_priority(td);
739
740 if (LOCK_LOG_TEST(lock, 0))
741 CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__,
742 td->td_tid, lock, lock->lo_name);
743
744 MPASS(td->td_lock == &ts->ts_lock);
745 SCHED_STAT_INC(switch_turnstile);
746 mi_switch(SW_VOL, NULL);
747
748 if (LOCK_LOG_TEST(lock, 0))
749 CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s",
750 __func__, td->td_tid, lock, lock->lo_name);
751 thread_unlock(td);
752}
753
754/*
755 * Pick the highest priority thread on this turnstile and put it on the
756 * pending list. This must be called with the turnstile chain locked.
757 */
758int
759turnstile_signal(struct turnstile *ts, int queue)
760{
761 struct turnstile_chain *tc;
762 struct thread *td;
763 int empty;
764
765 MPASS(ts != NULL);
766 mtx_assert(&ts->ts_lock, MA_OWNED);
767 MPASS(curthread->td_proc->p_magic == P_MAGIC);
768 MPASS(ts->ts_owner == curthread ||
769 (queue == TS_EXCLUSIVE_QUEUE && ts->ts_owner == NULL));
770 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
771
772 /*
773 * Pick the highest priority thread blocked on this lock and
774 * move it to the pending list.
775 */
776 td = TAILQ_FIRST(&ts->ts_blocked[queue]);
777 MPASS(td->td_proc->p_magic == P_MAGIC);
--- 5 unchanged lines hidden (view full) ---
783 /*
784 * If the turnstile is now empty, remove it from its chain and
785 * give it to the about-to-be-woken thread. Otherwise take a
786 * turnstile from the free list and give it to the thread.
787 */
788 empty = TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) &&
789 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]);
790 if (empty) {
791 tc = TC_LOOKUP(ts->ts_lockobj);
792 mtx_assert(&tc->tc_lock, MA_OWNED);
793 MPASS(LIST_EMPTY(&ts->ts_free));
794#ifdef TURNSTILE_PROFILING
795 tc->tc_depth--;
796#endif
797 } else
798 ts = LIST_FIRST(&ts->ts_free);
799 MPASS(ts != NULL);
800 LIST_REMOVE(ts, ts_hash);
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810void
811turnstile_broadcast(struct turnstile *ts, int queue)
812{
813 struct turnstile_chain *tc;
814 struct turnstile *ts1;
815 struct thread *td;
816
817 MPASS(ts != NULL);
818 mtx_assert(&ts->ts_lock, MA_OWNED);
819 MPASS(curthread->td_proc->p_magic == P_MAGIC);
820 MPASS(ts->ts_owner == curthread ||
821 (queue == TS_EXCLUSIVE_QUEUE && ts->ts_owner == NULL));
822 /*
823 * We must have the chain locked so that we can remove the empty
824 * turnstile from the hash queue.
825 */
826 tc = TC_LOOKUP(ts->ts_lockobj);
827 mtx_assert(&tc->tc_lock, MA_OWNED);
828 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
829
830 /*
831 * Transfer the blocked list to the pending list.
832 */
833 mtx_lock_spin(&td_contested_lock);
--- 23 unchanged lines hidden (view full) ---
857 * Wakeup all threads on the pending list and adjust the priority of the
858 * current thread appropriately. This must be called with the turnstile
859 * chain locked.
860 */
861void
862turnstile_unpend(struct turnstile *ts, int owner_type)
863{
864 TAILQ_HEAD( ,thread) pending_threads;
865 struct turnstile *nts;
866 struct thread *td;
867 u_char cp, pri;
868
869 MPASS(ts != NULL);
870 mtx_assert(&ts->ts_lock, MA_OWNED);
871 MPASS(ts->ts_owner == curthread ||
872 (owner_type == TS_SHARED_LOCK && ts->ts_owner == NULL));
873 MPASS(!TAILQ_EMPTY(&ts->ts_pending));
874
875 /*
876 * Move the list of pending threads out of the turnstile and
877 * into a local variable.
878 */
879 TAILQ_INIT(&pending_threads);
880 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq);
881#ifdef INVARIANTS
882 if (TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) &&
883 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]))
884 ts->ts_lockobj = NULL;
885#endif
886 /*
887 * Adjust the priority of curthread based on other contested
888 * locks it owns. Don't lower the priority below the base
889 * priority however.
890 */
891 td = curthread;
892 pri = PRI_MAX;
893 thread_lock(td);
894 mtx_lock_spin(&td_contested_lock);
895 /*
896 * Remove the turnstile from this thread's list of contested locks
897 * since this thread doesn't own it anymore. New threads will
898 * not be blocking on the turnstile until it is claimed by a new
899 * owner. There might not be a current owner if this is a shared
900 * lock.
901 */
902 if (ts->ts_owner != NULL) {
903 ts->ts_owner = NULL;
904 LIST_REMOVE(ts, ts_link);
905 }
906 LIST_FOREACH(nts, &td->td_contested, ts_link) {
907 cp = turnstile_first_waiter(nts)->td_priority;
908 if (cp < pri)
909 pri = cp;
910 }
911 mtx_unlock_spin(&td_contested_lock);
912 sched_unlend_prio(td, pri);
913 thread_unlock(td);
914 /*
915 * Wake up all the pending threads. If a thread is not blocked
916 * on a lock, then it is currently executing on another CPU in
917 * turnstile_wait() or sitting on a run queue waiting to resume
918 * in turnstile_wait(). Set a flag to force it to try to acquire
919 * the lock again instead of blocking.
920 */
921 while (!TAILQ_EMPTY(&pending_threads)) {
922 td = TAILQ_FIRST(&pending_threads);
923 TAILQ_REMOVE(&pending_threads, td, td_lockq);
924 thread_lock(td);
925 MPASS(td->td_lock == &ts->ts_lock);
926 MPASS(td->td_proc->p_magic == P_MAGIC);
927 MPASS(TD_ON_LOCK(td));
928 TD_CLR_LOCK(td);
929 MPASS(TD_CAN_RUN(td));
930 td->td_blocked = NULL;
931 td->td_lockname = NULL;
932#ifdef INVARIANTS
933 td->td_tsqueue = 0xff;
934#endif
935 sched_add(td, SRQ_BORING);
936 thread_unlock(td);
937 }
938 mtx_unlock_spin(&ts->ts_lock);
939}
940
941/*
942 * Give up ownership of a turnstile. This must be called with the
943 * turnstile chain locked.
944 */
945void
946turnstile_disown(struct turnstile *ts)
947{
948 struct thread *td;
949 u_char cp, pri;
950
951 MPASS(ts != NULL);
952 mtx_assert(&ts->ts_lock, MA_OWNED);
953 MPASS(ts->ts_owner == curthread);
954 MPASS(TAILQ_EMPTY(&ts->ts_pending));
955 MPASS(!TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) ||
956 !TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]));
957
958 /*
959 * Remove the turnstile from this thread's list of contested locks
960 * since this thread doesn't own it anymore. New threads will
961 * not be blocking on the turnstile until it is claimed by a new
962 * owner.
963 */
964 mtx_lock_spin(&td_contested_lock);
965 ts->ts_owner = NULL;
966 LIST_REMOVE(ts, ts_link);
967 mtx_unlock_spin(&td_contested_lock);
968
969 /*
970 * Adjust the priority of curthread based on other contested
971 * locks it owns. Don't lower the priority below the base
972 * priority however.
973 */
974 td = curthread;
975 pri = PRI_MAX;
976 thread_lock(td);
977 mtx_unlock_spin(&ts->ts_lock);
978 mtx_lock_spin(&td_contested_lock);
979 LIST_FOREACH(ts, &td->td_contested, ts_link) {
980 cp = turnstile_first_waiter(ts)->td_priority;
981 if (cp < pri)
982 pri = cp;
983 }
984 mtx_unlock_spin(&td_contested_lock);
985 sched_unlend_prio(td, pri);
986 thread_unlock(td);
987}
988
989/*
990 * Return the first thread in a turnstile.
991 */
992struct thread *
993turnstile_head(struct turnstile *ts, int queue)
994{
995#ifdef INVARIANTS
996
997 MPASS(ts != NULL);
998 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
999 mtx_assert(&ts->ts_lock, MA_OWNED);
1000#endif
1001 return (TAILQ_FIRST(&ts->ts_blocked[queue]));
1002}
1003
1004/*
1005 * Returns true if a sub-queue of a turnstile is empty.
1006 */
1007int
1008turnstile_empty(struct turnstile *ts, int queue)
1009{
1010#ifdef INVARIANTS
1011
1012 MPASS(ts != NULL);
1013 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
1014 mtx_assert(&ts->ts_lock, MA_OWNED);
1015#endif
1016 return (TAILQ_EMPTY(&ts->ts_blocked[queue]));
1017}
1018
1019#ifdef DDB
1020static void
1021print_thread(struct thread *td, const char *prefix)
1022{
--- 280 unchanged lines hidden ---
2 * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
--- 43 unchanged lines hidden (view full) ---
52 * already has a turnstile, then it gives its turnstile to the lock's
53 * turnstile's free list. When a thread is woken up, it takes a turnstile from
54 * the free list if there are any other waiters. If it is the only thread
55 * blocked on the lock, then it reclaims the turnstile associated with the lock
56 * and removes it from the hash table.
57 */
58
59#include <sys/cdefs.h>
60__FBSDID("$FreeBSD: head/sys/kern/subr_turnstile.c 170295 2007-06-04 23:51:44Z jeff $");
61
62#include "opt_ddb.h"
63#include "opt_turnstile_profiling.h"
64
65#include <sys/param.h>
66#include <sys/systm.h>
67#include <sys/kernel.h>
68#include <sys/ktr.h>
--- 42 unchanged lines hidden (view full) ---
111 * turnstile_signal() or turnstile_wait() that are waiting to be put on
112 * the run queue.
113 *
114 * Locking key:
115 * c - turnstile chain lock
116 * q - td_contested lock
117 */
118struct turnstile {
119 struct mtx ts_lock; /* Spin lock for self. */
120 struct threadqueue ts_blocked[2]; /* (c + q) Blocked threads. */
121 struct threadqueue ts_pending; /* (c) Pending threads. */
122 LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */
123 LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */
124 LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */
125 struct lock_object *ts_lockobj; /* (c) Lock we reference. */
126 struct thread *ts_owner; /* (c + q) Who owns the lock. */
127};
--- 30 unchanged lines hidden (view full) ---
158static int turnstile_adjust_thread(struct turnstile *ts,
159 struct thread *td);
160static struct thread *turnstile_first_waiter(struct turnstile *ts);
161static void turnstile_setowner(struct turnstile *ts, struct thread *owner);
162#ifdef INVARIANTS
163static void turnstile_dtor(void *mem, int size, void *arg);
164#endif
165static int turnstile_init(void *mem, int size, int flags);
166static void turnstile_fini(void *mem, int size);
167
168/*
169 * Walks the chain of turnstiles and their owners to propagate the priority
170 * of the thread being blocked to all the threads holding locks that have to
171 * release their locks before this thread can run again.
172 */
173static void
174propagate_priority(struct thread *td)
175{
176 struct turnstile *ts;
177 int pri;
178
179 THREAD_LOCK_ASSERT(td, MA_OWNED);
180 pri = td->td_priority;
181 ts = td->td_blocked;
182 MPASS(td->td_lock == &ts->ts_lock);
183 /*
184 * Grab a recursive lock on this turnstile chain so it stays locked
185 * for the whole operation. The caller expects us to return with
186 * the original lock held. We only ever lock down the chain so
187 * the lock order is constant.
188 */
189 mtx_lock_spin(&ts->ts_lock);
190 for (;;) {
191 td = ts->ts_owner;
192
193 if (td == NULL) {
194 /*
195 * This might be a read lock with no owner. There's
196 * not much we can do, so just bail.
197 */
198 mtx_unlock_spin(&ts->ts_lock);
199 return;
200 }
201
202 thread_lock_flags(td, MTX_DUPOK);
203 mtx_unlock_spin(&ts->ts_lock);
204 MPASS(td->td_proc != NULL);
205 MPASS(td->td_proc->p_magic == P_MAGIC);
206
207 /*
208 * If the thread is asleep, then we are probably about
209 * to deadlock. To make debugging this easier, just
210 * panic and tell the user which thread misbehaved so
211 * they can hopefully get a stack trace from the truly
--- 8 unchanged lines hidden (view full) ---
220#endif
221 panic("sleeping thread");
222 }
223
224 /*
225 * If this thread already has higher priority than the
226 * thread that is being blocked, we are finished.
227 */
228 if (td->td_priority <= pri) {
229 thread_unlock(td);
230 return;
231 }
232
233 /*
234 * Bump this thread's priority.
235 */
236 sched_lend_prio(td, pri);
237
238 /*
239 * If lock holder is actually running or on the run queue
240 * then we are done.
241 */
242 if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) {
243 MPASS(td->td_blocked == NULL);
244 thread_unlock(td);
245 return;
246 }
247
248#ifndef SMP
249 /*
250 * For UP, we check to see if td is curthread (this shouldn't
251 * ever happen however as it would mean we are in a deadlock.)
252 */
--- 8 unchanged lines hidden (view full) ---
261 td->td_tid, td->td_proc->p_comm, td->td_state,
262 ts->ts_lockobj->lo_name));
263
264 /*
265 * Pick up the lock that td is blocked on.
266 */
267 ts = td->td_blocked;
268 MPASS(ts != NULL);
269 MPASS(td->td_lock == &ts->ts_lock);
270 /* Resort td on the list if needed. */
271 if (!turnstile_adjust_thread(ts, td)) {
272 mtx_unlock_spin(&ts->ts_lock);
273 return;
274 }
275 /* The thread lock is released as ts lock above. */
276 }
277}
278
279/*
280 * Adjust the thread's position on a turnstile after its priority has been
281 * changed.
282 */
283static int
284turnstile_adjust_thread(struct turnstile *ts, struct thread *td)
285{
286 struct thread *td1, *td2;
287 int queue;
288
289 THREAD_LOCK_ASSERT(td, MA_OWNED);
290 MPASS(TD_ON_LOCK(td));
291
292 /*
293 * This thread may not be blocked on this turnstile anymore
294 * but instead might already be woken up on another CPU
295 * that is waiting on the thread lock in turnstile_unpend() to
296 * finish waking this thread up. We can detect this case
297 * by checking to see if this thread has been given a
298 * turnstile by either turnstile_signal() or
299 * turnstile_broadcast(). In this case, treat the thread as
300 * if it was already running.
301 */
302 if (td->td_turnstile != NULL)
303 return (0);
304
305 /*
306 * Check if the thread needs to be moved on the blocked chain.
307 * It needs to be moved if either its priority is lower than
308 * the previous thread or higher than the next thread.
309 */
310 MPASS(td->td_lock == &ts->ts_lock);
311 td1 = TAILQ_PREV(td, threadqueue, td_lockq);
312 td2 = TAILQ_NEXT(td, td_lockq);
313 if ((td1 != NULL && td->td_priority < td1->td_priority) ||
314 (td2 != NULL && td->td_priority > td2->td_priority)) {
315
316 /*
317 * Remove thread from blocked chain and determine where
318 * it should be moved to.
--- 72 unchanged lines hidden (view full) ---
391#endif
392
393static void
394init_turnstile0(void *dummy)
395{
396
397 turnstile_zone = uma_zcreate("TURNSTILE", sizeof(struct turnstile),
398#ifdef INVARIANTS
399 NULL, turnstile_dtor, turnstile_init, turnstile_fini,
400 UMA_ALIGN_CACHE, 0);
401#else
402 NULL, NULL, turnstile_init, turnstile_fini, UMA_ALIGN_CACHE, 0);
403#endif
404 thread0.td_turnstile = turnstile_alloc();
405}
406SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
407
408/*
409 * Update a thread on the turnstile list after it's priority has been changed.
410 * The old priority is passed in as an argument.
411 */
412void
413turnstile_adjust(struct thread *td, u_char oldpri)
414{
415 struct turnstile *ts;
416
417 MPASS(TD_ON_LOCK(td));
418
419 /*
420 * Pick up the lock that td is blocked on.
421 */
422 ts = td->td_blocked;
423 MPASS(ts != NULL);
424 MPASS(td->td_lock == &ts->ts_lock);
425 mtx_assert(&ts->ts_lock, MA_OWNED);
426
427 /* Resort the turnstile on the list. */
428 if (!turnstile_adjust_thread(ts, td))
429 return;
430 /*
431 * If our priority was lowered and we are at the head of the
432 * turnstile, then propagate our new priority up the chain.
433 * Note that we currently don't try to revoke lent priorities
434 * when our priority goes up.
435 */
436 MPASS(td->td_tsqueue == TS_EXCLUSIVE_QUEUE ||
437 td->td_tsqueue == TS_SHARED_QUEUE);
438 if (td == TAILQ_FIRST(&ts->ts_blocked[td->td_tsqueue]) &&
439 td->td_priority < oldpri) {
440 propagate_priority(td);
441 }
442}
443
444/*
445 * Set the owner of the lock this turnstile is attached to.
446 */
447static void
448turnstile_setowner(struct turnstile *ts, struct thread *owner)
449{
--- 35 unchanged lines hidden (view full) ---
485 struct turnstile *ts;
486
487 bzero(mem, size);
488 ts = mem;
489 TAILQ_INIT(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]);
490 TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]);
491 TAILQ_INIT(&ts->ts_pending);
492 LIST_INIT(&ts->ts_free);
493 mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN | MTX_RECURSE);
494 return (0);
495}
496
497static void
498turnstile_fini(void *mem, int size)
499{
500 struct turnstile *ts;
501
502 ts = mem;
503 mtx_destroy(&ts->ts_lock);
504}
505
506/*
507 * Get a turnstile for a new thread.
508 */
509struct turnstile *
510turnstile_alloc(void)
511{
512
513 return (uma_zalloc(turnstile_zone, M_WAITOK));
--- 8 unchanged lines hidden (view full) ---
522
523 uma_zfree(turnstile_zone, ts);
524}
525
526/*
527 * Lock the turnstile chain associated with the specified lock.
528 */
529void
530turnstile_chain_lock(struct lock_object *lock)
531{
532 struct turnstile_chain *tc;
533
534 tc = TC_LOOKUP(lock);
535 mtx_lock_spin(&tc->tc_lock);
536}
537
538struct turnstile *
539turnstile_trywait(struct lock_object *lock)
540{
541 struct turnstile_chain *tc;
542 struct turnstile *ts;
543
544 tc = TC_LOOKUP(lock);
545 mtx_lock_spin(&tc->tc_lock);
546 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
547 if (ts->ts_lockobj == lock) {
548 mtx_lock_spin(&ts->ts_lock);
549 return (ts);
550 }
551
552 ts = curthread->td_turnstile;
553 MPASS(ts != NULL);
554 mtx_lock_spin(&ts->ts_lock);
555 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
556 ts->ts_lockobj = lock;
557
558 return (ts);
559}
560
561void
562turnstile_cancel(struct turnstile *ts)
563{
564 struct turnstile_chain *tc;
565 struct lock_object *lock;
566
567 mtx_assert(&ts->ts_lock, MA_OWNED);
568
569 mtx_unlock_spin(&ts->ts_lock);
570 lock = ts->ts_lockobj;
571 if (ts == curthread->td_turnstile)
572 ts->ts_lockobj = NULL;
573 tc = TC_LOOKUP(lock);
574 mtx_unlock_spin(&tc->tc_lock);
575}
576
577/*
578 * Look up the turnstile for a lock in the hash table locking the associated
579 * turnstile chain along the way. If no turnstile is found in the hash
580 * table, NULL is returned.
581 */
582struct turnstile *
583turnstile_lookup(struct lock_object *lock)
584{
585 struct turnstile_chain *tc;
586 struct turnstile *ts;
587
588 tc = TC_LOOKUP(lock);
589 mtx_assert(&tc->tc_lock, MA_OWNED);
590 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
591 if (ts->ts_lockobj == lock) {
592 mtx_lock_spin(&ts->ts_lock);
593 return (ts);
594 }
595 return (NULL);
596}
597
598/*
599 * Unlock the turnstile chain associated with a given lock.
600 */
601void
602turnstile_chain_unlock(struct lock_object *lock)
603{
604 struct turnstile_chain *tc;
605
606 tc = TC_LOOKUP(lock);
607 mtx_unlock_spin(&tc->tc_lock);
608}
609
610/*
--- 12 unchanged lines hidden (view full) ---
623 return (xtd);
624}
625
626/*
627 * Take ownership of a turnstile and adjust the priority of the new
628 * owner appropriately.
629 */
630void
631turnstile_claim(struct turnstile *ts)
632{
633 struct thread *td, *owner;
634 struct turnstile_chain *tc;
635
636 mtx_assert(&ts->ts_lock, MA_OWNED);
637 MPASS(ts != curthread->td_turnstile);
638
639 owner = curthread;
640 mtx_lock_spin(&td_contested_lock);
641 turnstile_setowner(ts, owner);
642 mtx_unlock_spin(&td_contested_lock);
643
644 td = turnstile_first_waiter(ts);
645 MPASS(td != NULL);
646 MPASS(td->td_proc->p_magic == P_MAGIC);
647 MPASS(td->td_lock == &ts->ts_lock);
648
649 /*
650 * Update the priority of the new owner if needed.
651 */
652 thread_lock(owner);
653 if (td->td_priority < owner->td_priority)
654 sched_lend_prio(owner, td->td_priority);
655 thread_unlock(owner);
656 tc = TC_LOOKUP(ts->ts_lockobj);
657 mtx_unlock_spin(&ts->ts_lock);
658 mtx_unlock_spin(&tc->tc_lock);
659}
660
661/*
662 * Block the current thread on the turnstile assicated with 'lock'. This
663 * function will context switch and not return until this thread has been
664 * woken back up. This function must be called with the appropriate
665 * turnstile chain locked and will return with it unlocked.
666 */
667void
668turnstile_wait(struct turnstile *ts, struct thread *owner, int queue)
669{
670 struct turnstile_chain *tc;
671 struct thread *td, *td1;
672 struct lock_object *lock;
673
674 td = curthread;
675 mtx_assert(&ts->ts_lock, MA_OWNED);
676 if (queue == TS_SHARED_QUEUE)
677 MPASS(owner != NULL);
678 if (owner)
679 MPASS(owner->td_proc->p_magic == P_MAGIC);
680 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
681
682 /*
683 * If the lock does not already have a turnstile, use this thread's
684 * turnstile. Otherwise insert the current thread into the
685 * turnstile already in use by this lock.
686 */
687 tc = TC_LOOKUP(ts->ts_lockobj);
688 if (ts == td->td_turnstile) {
689 mtx_assert(&tc->tc_lock, MA_OWNED);
690#ifdef TURNSTILE_PROFILING
691 tc->tc_depth++;
692 if (tc->tc_depth > tc->tc_max_depth) {
693 tc->tc_max_depth = tc->tc_depth;
694 if (tc->tc_max_depth > turnstile_max_depth)
695 turnstile_max_depth = tc->tc_max_depth;
696 }
697#endif
698 tc = TC_LOOKUP(ts->ts_lockobj);
699 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash);
700 KASSERT(TAILQ_EMPTY(&ts->ts_pending),
701 ("thread's turnstile has pending threads"));
702 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]),
703 ("thread's turnstile has exclusive waiters"));
704 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]),
705 ("thread's turnstile has shared waiters"));
706 KASSERT(LIST_EMPTY(&ts->ts_free),
707 ("thread's turnstile has a non-empty free list"));
708 MPASS(ts->ts_lockobj != NULL);
709 mtx_lock_spin(&td_contested_lock);
710 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
711 turnstile_setowner(ts, owner);
712 mtx_unlock_spin(&td_contested_lock);
713 } else {
714 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq)
715 if (td1->td_priority > td->td_priority)
716 break;
717 mtx_lock_spin(&td_contested_lock);
718 if (td1 != NULL)
719 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
720 else
721 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq);
722 MPASS(owner == ts->ts_owner);
723 mtx_unlock_spin(&td_contested_lock);
724 MPASS(td->td_turnstile != NULL);
725 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
726 }
727 thread_lock(td);
728 thread_lock_set(td, &ts->ts_lock);
729 td->td_turnstile = NULL;
730
731 /* Save who we are blocked on and switch. */
732 lock = ts->ts_lockobj;
733 td->td_tsqueue = queue;
734 td->td_blocked = ts;
735 td->td_lockname = lock->lo_name;
736 TD_SET_LOCK(td);
737 mtx_unlock_spin(&tc->tc_lock);
738 propagate_priority(td);
739
740 if (LOCK_LOG_TEST(lock, 0))
741 CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__,
742 td->td_tid, lock, lock->lo_name);
743
744 MPASS(td->td_lock == &ts->ts_lock);
745 SCHED_STAT_INC(switch_turnstile);
746 mi_switch(SW_VOL, NULL);
747
748 if (LOCK_LOG_TEST(lock, 0))
749 CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s",
750 __func__, td->td_tid, lock, lock->lo_name);
751 thread_unlock(td);
752}
753
754/*
755 * Pick the highest priority thread on this turnstile and put it on the
756 * pending list. This must be called with the turnstile chain locked.
757 */
758int
759turnstile_signal(struct turnstile *ts, int queue)
760{
761 struct turnstile_chain *tc;
762 struct thread *td;
763 int empty;
764
765 MPASS(ts != NULL);
766 mtx_assert(&ts->ts_lock, MA_OWNED);
767 MPASS(curthread->td_proc->p_magic == P_MAGIC);
768 MPASS(ts->ts_owner == curthread ||
769 (queue == TS_EXCLUSIVE_QUEUE && ts->ts_owner == NULL));
770 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
771
772 /*
773 * Pick the highest priority thread blocked on this lock and
774 * move it to the pending list.
775 */
776 td = TAILQ_FIRST(&ts->ts_blocked[queue]);
777 MPASS(td->td_proc->p_magic == P_MAGIC);
--- 5 unchanged lines hidden (view full) ---
783 /*
784 * If the turnstile is now empty, remove it from its chain and
785 * give it to the about-to-be-woken thread. Otherwise take a
786 * turnstile from the free list and give it to the thread.
787 */
788 empty = TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) &&
789 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]);
790 if (empty) {
791 tc = TC_LOOKUP(ts->ts_lockobj);
792 mtx_assert(&tc->tc_lock, MA_OWNED);
793 MPASS(LIST_EMPTY(&ts->ts_free));
794#ifdef TURNSTILE_PROFILING
795 tc->tc_depth--;
796#endif
797 } else
798 ts = LIST_FIRST(&ts->ts_free);
799 MPASS(ts != NULL);
800 LIST_REMOVE(ts, ts_hash);
--- 9 unchanged lines hidden (view full) ---
810void
811turnstile_broadcast(struct turnstile *ts, int queue)
812{
813 struct turnstile_chain *tc;
814 struct turnstile *ts1;
815 struct thread *td;
816
817 MPASS(ts != NULL);
818 mtx_assert(&ts->ts_lock, MA_OWNED);
819 MPASS(curthread->td_proc->p_magic == P_MAGIC);
820 MPASS(ts->ts_owner == curthread ||
821 (queue == TS_EXCLUSIVE_QUEUE && ts->ts_owner == NULL));
822 /*
823 * We must have the chain locked so that we can remove the empty
824 * turnstile from the hash queue.
825 */
826 tc = TC_LOOKUP(ts->ts_lockobj);
827 mtx_assert(&tc->tc_lock, MA_OWNED);
828 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
829
830 /*
831 * Transfer the blocked list to the pending list.
832 */
833 mtx_lock_spin(&td_contested_lock);
--- 23 unchanged lines hidden (view full) ---
857 * Wakeup all threads on the pending list and adjust the priority of the
858 * current thread appropriately. This must be called with the turnstile
859 * chain locked.
860 */
861void
862turnstile_unpend(struct turnstile *ts, int owner_type)
863{
864 TAILQ_HEAD( ,thread) pending_threads;
865 struct turnstile *nts;
866 struct thread *td;
867 u_char cp, pri;
868
869 MPASS(ts != NULL);
870 mtx_assert(&ts->ts_lock, MA_OWNED);
871 MPASS(ts->ts_owner == curthread ||
872 (owner_type == TS_SHARED_LOCK && ts->ts_owner == NULL));
873 MPASS(!TAILQ_EMPTY(&ts->ts_pending));
874
875 /*
876 * Move the list of pending threads out of the turnstile and
877 * into a local variable.
878 */
879 TAILQ_INIT(&pending_threads);
880 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq);
881#ifdef INVARIANTS
882 if (TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) &&
883 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]))
884 ts->ts_lockobj = NULL;
885#endif
886 /*
887 * Adjust the priority of curthread based on other contested
888 * locks it owns. Don't lower the priority below the base
889 * priority however.
890 */
891 td = curthread;
892 pri = PRI_MAX;
893 thread_lock(td);
894 mtx_lock_spin(&td_contested_lock);
895 /*
896 * Remove the turnstile from this thread's list of contested locks
897 * since this thread doesn't own it anymore. New threads will
898 * not be blocking on the turnstile until it is claimed by a new
899 * owner. There might not be a current owner if this is a shared
900 * lock.
901 */
902 if (ts->ts_owner != NULL) {
903 ts->ts_owner = NULL;
904 LIST_REMOVE(ts, ts_link);
905 }
906 LIST_FOREACH(nts, &td->td_contested, ts_link) {
907 cp = turnstile_first_waiter(nts)->td_priority;
908 if (cp < pri)
909 pri = cp;
910 }
911 mtx_unlock_spin(&td_contested_lock);
912 sched_unlend_prio(td, pri);
913 thread_unlock(td);
914 /*
915 * Wake up all the pending threads. If a thread is not blocked
916 * on a lock, then it is currently executing on another CPU in
917 * turnstile_wait() or sitting on a run queue waiting to resume
918 * in turnstile_wait(). Set a flag to force it to try to acquire
919 * the lock again instead of blocking.
920 */
921 while (!TAILQ_EMPTY(&pending_threads)) {
922 td = TAILQ_FIRST(&pending_threads);
923 TAILQ_REMOVE(&pending_threads, td, td_lockq);
924 thread_lock(td);
925 MPASS(td->td_lock == &ts->ts_lock);
926 MPASS(td->td_proc->p_magic == P_MAGIC);
927 MPASS(TD_ON_LOCK(td));
928 TD_CLR_LOCK(td);
929 MPASS(TD_CAN_RUN(td));
930 td->td_blocked = NULL;
931 td->td_lockname = NULL;
932#ifdef INVARIANTS
933 td->td_tsqueue = 0xff;
934#endif
935 sched_add(td, SRQ_BORING);
936 thread_unlock(td);
937 }
938 mtx_unlock_spin(&ts->ts_lock);
939}
940
941/*
942 * Give up ownership of a turnstile. This must be called with the
943 * turnstile chain locked.
944 */
945void
946turnstile_disown(struct turnstile *ts)
947{
948 struct thread *td;
949 u_char cp, pri;
950
951 MPASS(ts != NULL);
952 mtx_assert(&ts->ts_lock, MA_OWNED);
953 MPASS(ts->ts_owner == curthread);
954 MPASS(TAILQ_EMPTY(&ts->ts_pending));
955 MPASS(!TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) ||
956 !TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]));
957
958 /*
959 * Remove the turnstile from this thread's list of contested locks
960 * since this thread doesn't own it anymore. New threads will
961 * not be blocking on the turnstile until it is claimed by a new
962 * owner.
963 */
964 mtx_lock_spin(&td_contested_lock);
965 ts->ts_owner = NULL;
966 LIST_REMOVE(ts, ts_link);
967 mtx_unlock_spin(&td_contested_lock);
968
969 /*
970 * Adjust the priority of curthread based on other contested
971 * locks it owns. Don't lower the priority below the base
972 * priority however.
973 */
974 td = curthread;
975 pri = PRI_MAX;
976 thread_lock(td);
977 mtx_unlock_spin(&ts->ts_lock);
978 mtx_lock_spin(&td_contested_lock);
979 LIST_FOREACH(ts, &td->td_contested, ts_link) {
980 cp = turnstile_first_waiter(ts)->td_priority;
981 if (cp < pri)
982 pri = cp;
983 }
984 mtx_unlock_spin(&td_contested_lock);
985 sched_unlend_prio(td, pri);
986 thread_unlock(td);
987}
988
989/*
990 * Return the first thread in a turnstile.
991 */
992struct thread *
993turnstile_head(struct turnstile *ts, int queue)
994{
995#ifdef INVARIANTS
996
997 MPASS(ts != NULL);
998 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
999 mtx_assert(&ts->ts_lock, MA_OWNED);
1000#endif
1001 return (TAILQ_FIRST(&ts->ts_blocked[queue]));
1002}
1003
1004/*
1005 * Returns true if a sub-queue of a turnstile is empty.
1006 */
1007int
1008turnstile_empty(struct turnstile *ts, int queue)
1009{
1010#ifdef INVARIANTS
1011
1012 MPASS(ts != NULL);
1013 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE);
1014 mtx_assert(&ts->ts_lock, MA_OWNED);
1015#endif
1016 return (TAILQ_EMPTY(&ts->ts_blocked[queue]));
1017}
1018
1019#ifdef DDB
1020static void
1021print_thread(struct thread *td, const char *prefix)
1022{
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