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.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * 3. Berkeley Software Design Inc's name may not be used to endorse or
13 * promote products derived from this software without specific prior
14 * written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19 * ARE DISCLAIMED. IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23 * HOWEVER 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
26 * SUCH DAMAGE.
27 *
28 * from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
29 * and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
30 */
31
32 /*
33 * Implementation of turnstiles used to hold queue of threads blocked on
34 * non-sleepable locks. Sleepable locks use condition variables to
35 * implement their queues. Turnstiles differ from a sleep queue in that
36 * turnstile queue's are assigned to a lock held by an owning thread. Thus,
37 * when one thread is enqueued onto a turnstile, it can lend its priority
38 * to the owning thread.
39 *
40 * We wish to avoid bloating locks with an embedded turnstile and we do not
41 * want to use back-pointers in the locks for the same reason. Thus, we
42 * use a similar approach to that of Solaris 7 as described in Solaris
43 * Internals by Jim Mauro and Richard McDougall. Turnstiles are looked up
44 * in a hash table based on the address of the lock. Each entry in the
45 * hash table is a linked-lists of turnstiles and is called a turnstile
46 * chain. Each chain contains a spin mutex that protects all of the
47 * turnstiles in the chain.
48 *
49 * Each time a thread is created, a turnstile is malloc'd and attached to
50 * that thread. When a thread blocks on a lock, if it is the first thread
51 * to block, it lends its turnstile to the lock. If the lock already has
52 * a turnstile, then it gives its turnstile to the lock's turnstile's free
53 * list. When a thread is woken up, it takes a turnstile from the free list
54 * if there are any other waiters. If it is the only thread blocked on the
55 * lock, then it reclaims the turnstile associated with the lock and removes
56 * it from the hash table.
57 *
58 * XXX: We should probably implement some sort of sleep queue that condition
59 * variables and sleepqueue's share. On Solaris condition variables are
60 * implemented using a hash table of sleep queues similar to our current
61 * sleep queues. We might want to investigate doing that ourselves.
62 */
63
64 #include <sys/cdefs.h>
65 __FBSDID("$FreeBSD: releng/5.2/sys/kern/subr_turnstile.c 123462 2003-12-11 20:01:52Z jhb $");
66
67 #include <sys/param.h>
68 #include <sys/systm.h>
69 #include <sys/kernel.h>
70 #include <sys/ktr.h>
71 #include <sys/lock.h>
72 #include <sys/malloc.h>
73 #include <sys/mutex.h>
74 #include <sys/proc.h>
75 #include <sys/queue.h>
76 #include <sys/resourcevar.h>
77 #include <sys/turnstile.h>
78 #include <sys/sched.h>
79
80 /*
81 * Constants for the hash table of turnstile chains. TC_SHIFT is a magic
82 * number chosen because the sleep queue's use the same value for the
83 * shift. Basically, we ignore the lower 8 bits of the address.
84 * TC_TABLESIZE must be a power of two for TC_MASK to work properly.
85 */
86 #define TC_TABLESIZE 128 /* Must be power of 2. */
87 #define TC_MASK (TC_TABLESIZE - 1)
88 #define TC_SHIFT 8
89 #define TC_HASH(lock) (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK)
90 #define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)]
91
92 /*
93 * There are three different lists of turnstiles as follows. The list
94 * connected by ts_link entries is a per-thread list of all the turnstiles
95 * attached to locks that we own. This is used to fixup our priority when
96 * a lock is released. The other two lists use the ts_hash entries. The
97 * first of these two is turnstile chain list that a turnstile is on when
98 * it is attached to a lock. The second list to use ts_hash is the free
99 * list hung off a turnstile that is attached to a lock.
100 *
101 * Each turnstile contains two lists of threads. The ts_blocked list is
102 * a linked list of threads blocked on the turnstile's lock. The
103 * ts_pending list is a linked list of threads previously awoken by
104 * turnstile_signal() or turnstile_wait() that are waiting to be put on
105 * the run queue.
106 *
107 * Locking key:
108 * c - turnstile chain lock
109 * q - td_contested lock
110 */
111 struct turnstile {
112 TAILQ_HEAD(, thread) ts_blocked; /* (c + q) Blocked threads. */
113 TAILQ_HEAD(, thread) ts_pending; /* (c) Pending threads. */
114 LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */
115 LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */
116 LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */
117 struct lock_object *ts_lockobj; /* (c) Lock we reference. */
118 struct thread *ts_owner; /* (c + q) Who owns the lock. */
119 };
120
121 struct turnstile_chain {
122 LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */
123 struct mtx tc_lock; /* Spin lock for this chain. */
124 };
125
126 static struct mtx td_contested_lock;
127 static struct turnstile_chain turnstile_chains[TC_TABLESIZE];
128
129 MALLOC_DEFINE(M_TURNSTILE, "turnstiles", "turnstiles");
130
131 /*
132 * Prototypes for non-exported routines.
133 */
134 static void init_turnstile0(void *dummy);
135 static void propagate_priority(struct thread *);
136 static void turnstile_setowner(struct turnstile *ts, struct thread *owner);
137
138 /*
139 * Walks the chain of turnstiles and their owners to propagate the priority
140 * of the thread being blocked to all the threads holding locks that have to
141 * release their locks before this thread can run again.
142 */
143 static void
144 propagate_priority(struct thread *td)
145 {
146 struct turnstile_chain *tc;
147 struct turnstile *ts;
148 struct thread *td1;
149 int pri;
150
151 mtx_assert(&sched_lock, MA_OWNED);
152 pri = td->td_priority;
153 ts = td->td_blocked;
154 for (;;) {
155 td = ts->ts_owner;
156
157 if (td == NULL) {
158 /*
159 * This really isn't quite right. Really
160 * ought to bump priority of thread that
161 * next acquires the lock.
162 */
163 return;
164 }
165
166 MPASS(td->td_proc != NULL);
167 MPASS(td->td_proc->p_magic == P_MAGIC);
168
169 /*
170 * XXX: The owner of a turnstile can be stale if it is the
171 * first thread to grab a slock of a sx lock. In that case
172 * it is possible for us to be at SSLEEP or some other
173 * weird state. We should probably just return if the state
174 * isn't SRUN or SLOCK.
175 */
176 KASSERT(!TD_IS_SLEEPING(td),
177 ("sleeping thread (pid %d) owns a non-sleepable lock",
178 td->td_proc->p_pid));
179
180 /*
181 * If this thread already has higher priority than the
182 * thread that is being blocked, we are finished.
183 */
184 if (td->td_priority <= pri)
185 return;
186
187 /*
188 * If lock holder is actually running, just bump priority.
189 */
190 if (TD_IS_RUNNING(td)) {
191 td->td_priority = pri;
192 return;
193 }
194
195 #ifndef SMP
196 /*
197 * For UP, we check to see if td is curthread (this shouldn't
198 * ever happen however as it would mean we are in a deadlock.)
199 */
200 KASSERT(td != curthread, ("Deadlock detected"));
201 #endif
202
203 /*
204 * If on run queue move to new run queue, and quit.
205 * XXXKSE this gets a lot more complicated under threads
206 * but try anyhow.
207 */
208 if (TD_ON_RUNQ(td)) {
209 MPASS(td->td_blocked == NULL);
210 sched_prio(td, pri);
211 return;
212 }
213
214 /*
215 * Bump this thread's priority.
216 */
217 td->td_priority = pri;
218
219 /*
220 * If we aren't blocked on a lock, we should be.
221 */
222 KASSERT(TD_ON_LOCK(td), (
223 "process %d(%s):%d holds %s but isn't blocked on a lock\n",
224 td->td_proc->p_pid, td->td_proc->p_comm, td->td_state,
225 ts->ts_lockobj->lo_name));
226
227 /*
228 * Pick up the lock that td is blocked on.
229 */
230 ts = td->td_blocked;
231 MPASS(ts != NULL);
232 tc = TC_LOOKUP(ts->ts_lockobj);
233 mtx_lock_spin(&tc->tc_lock);
234
235 /*
236 * This thread may not be blocked on this turnstile anymore
237 * but instead might already be woken up on another CPU
238 * that is waiting on sched_lock in turnstile_unpend() to
239 * finish waking this thread up. We can detect this case
240 * by checking to see if this thread has been given a
241 * turnstile by either turnstile_signal() or
242 * turnstile_wakeup(). In this case, treat the thread as
243 * if it was already running.
244 */
245 if (td->td_turnstile != NULL) {
246 mtx_unlock_spin(&tc->tc_lock);
247 return;
248 }
249
250 /*
251 * Check if the thread needs to be moved up on
252 * the blocked chain. It doesn't need to be moved
253 * if it is already at the head of the list or if
254 * the item in front of it still has a higher priority.
255 */
256 if (td == TAILQ_FIRST(&ts->ts_blocked)) {
257 mtx_unlock_spin(&tc->tc_lock);
258 continue;
259 }
260
261 td1 = TAILQ_PREV(td, threadqueue, td_lockq);
262 if (td1->td_priority <= pri) {
263 mtx_unlock_spin(&tc->tc_lock);
264 continue;
265 }
266
267 /*
268 * Remove thread from blocked chain and determine where
269 * it should be moved up to. Since we know that td1 has
270 * a lower priority than td, we know that at least one
271 * thread in the chain has a lower priority and that
272 * td1 will thus not be NULL after the loop.
273 */
274 mtx_lock_spin(&td_contested_lock);
275 TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
276 TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq) {
277 MPASS(td1->td_proc->p_magic == P_MAGIC);
278 if (td1->td_priority > pri)
279 break;
280 }
281
282 MPASS(td1 != NULL);
283 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
284 mtx_unlock_spin(&td_contested_lock);
285 CTR4(KTR_LOCK,
286 "propagate_priority: td %p moved before %p on [%p] %s",
287 td, td1, ts->ts_lockobj, ts->ts_lockobj->lo_name);
288 mtx_unlock_spin(&tc->tc_lock);
289 }
290 }
291
292 /*
293 * Early initialization of turnstiles. This is not done via a SYSINIT()
294 * since this needs to be initialized very early when mutexes are first
295 * initialized.
296 */
297 void
298 init_turnstiles(void)
299 {
300 int i;
301
302 for (i = 0; i < TC_TABLESIZE; i++) {
303 LIST_INIT(&turnstile_chains[i].tc_turnstiles);
304 mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain",
305 NULL, MTX_SPIN);
306 }
307 mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN);
308 thread0.td_turnstile = NULL;
309 }
310
311 static void
312 init_turnstile0(void *dummy)
313 {
314
315 thread0.td_turnstile = turnstile_alloc();
316 }
317 SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
318
319 /*
320 * Set the owner of the lock this turnstile is attached to.
321 */
322 static void
323 turnstile_setowner(struct turnstile *ts, struct thread *owner)
324 {
325
326 mtx_assert(&td_contested_lock, MA_OWNED);
327 MPASS(owner->td_proc->p_magic == P_MAGIC);
328 MPASS(ts->ts_owner == NULL);
329 ts->ts_owner = owner;
330 LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link);
331 }
332
333 /*
334 * Malloc a turnstile for a new thread, initialize it and return it.
335 */
336 struct turnstile *
337 turnstile_alloc(void)
338 {
339 struct turnstile *ts;
340
341 ts = malloc(sizeof(struct turnstile), M_TURNSTILE, M_WAITOK | M_ZERO);
342 TAILQ_INIT(&ts->ts_blocked);
343 TAILQ_INIT(&ts->ts_pending);
344 LIST_INIT(&ts->ts_free);
345 return (ts);
346 }
347
348 /*
349 * Free a turnstile when a thread is destroyed.
350 */
351 void
352 turnstile_free(struct turnstile *ts)
353 {
354
355 MPASS(ts != NULL);
356 MPASS(TAILQ_EMPTY(&ts->ts_blocked));
357 MPASS(TAILQ_EMPTY(&ts->ts_pending));
358 free(ts, M_TURNSTILE);
359 }
360
361 /*
362 * Look up the turnstile for a lock in the hash table locking the associated
363 * turnstile chain along the way. Return with the turnstile chain locked.
364 * If no turnstile is found in the hash table, NULL is returned.
365 */
366 struct turnstile *
367 turnstile_lookup(struct lock_object *lock)
368 {
369 struct turnstile_chain *tc;
370 struct turnstile *ts;
371
372 tc = TC_LOOKUP(lock);
373 mtx_lock_spin(&tc->tc_lock);
374 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
375 if (ts->ts_lockobj == lock)
376 return (ts);
377 return (NULL);
378 }
379
380 /*
381 * Unlock the turnstile chain associated with a given lock.
382 */
383 void
384 turnstile_release(struct lock_object *lock)
385 {
386 struct turnstile_chain *tc;
387
388 tc = TC_LOOKUP(lock);
389 mtx_unlock_spin(&tc->tc_lock);
390 }
391
392 /*
393 * Take ownership of a turnstile and adjust the priority of the new
394 * owner appropriately.
395 */
396 void
397 turnstile_claim(struct turnstile *ts)
398 {
399 struct turnstile_chain *tc;
400 struct thread *td, *owner;
401
402 tc = TC_LOOKUP(ts->ts_lockobj);
403 mtx_assert(&tc->tc_lock, MA_OWNED);
404
405 owner = curthread;
406 mtx_lock_spin(&td_contested_lock);
407 turnstile_setowner(ts, owner);
408 mtx_unlock_spin(&td_contested_lock);
409
410 td = TAILQ_FIRST(&ts->ts_blocked);
411 MPASS(td != NULL);
412 MPASS(td->td_proc->p_magic == P_MAGIC);
413 mtx_unlock_spin(&tc->tc_lock);
414
415 /*
416 * Update the priority of the new owner if needed.
417 */
418 mtx_lock_spin(&sched_lock);
419 if (td->td_priority < owner->td_priority)
420 owner->td_priority = td->td_priority;
421 mtx_unlock_spin(&sched_lock);
422 }
423
424 /*
425 * Block the current thread on the turnstile ts. This function will context
426 * switch and not return until this thread has been woken back up. This
427 * function must be called with the appropriate turnstile chain locked and
428 * will return with it unlocked.
429 */
430 void
431 turnstile_wait(struct turnstile *ts, struct lock_object *lock,
432 struct thread *owner)
433 {
434 struct turnstile_chain *tc;
435 struct thread *td, *td1;
436
437 td = curthread;
438 tc = TC_LOOKUP(lock);
439 mtx_assert(&tc->tc_lock, MA_OWNED);
440 MPASS(td->td_turnstile != NULL);
441 MPASS(owner != NULL);
442 MPASS(owner->td_proc->p_magic == P_MAGIC);
443
444 /* If the passed in turnstile is NULL, use this thread's turnstile. */
445 if (ts == NULL) {
446 ts = td->td_turnstile;
447 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash);
448 KASSERT(TAILQ_EMPTY(&ts->ts_pending),
449 ("thread's turnstile has pending threads"));
450 KASSERT(TAILQ_EMPTY(&ts->ts_blocked),
451 ("thread's turnstile has a non-empty queue"));
452 KASSERT(LIST_EMPTY(&ts->ts_free),
453 ("thread's turnstile has a non-empty free list"));
454 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
455 ts->ts_lockobj = lock;
456 mtx_lock_spin(&td_contested_lock);
457 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
458 turnstile_setowner(ts, owner);
459 mtx_unlock_spin(&td_contested_lock);
460 } else {
461 TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq)
462 if (td1->td_priority > td->td_priority)
463 break;
464 mtx_lock_spin(&td_contested_lock);
465 if (td1 != NULL)
466 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
467 else
468 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
469 mtx_unlock_spin(&td_contested_lock);
470 MPASS(td->td_turnstile != NULL);
471 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
472 MPASS(owner == ts->ts_owner);
473 }
474 td->td_turnstile = NULL;
475 mtx_unlock_spin(&tc->tc_lock);
476
477 mtx_lock_spin(&sched_lock);
478 /*
479 * Handle race condition where a thread on another CPU that owns
480 * lock 'lock' could have woken us in between us dropping the
481 * turnstile chain lock and acquiring the sched_lock.
482 */
483 if (td->td_flags & TDF_TSNOBLOCK) {
484 td->td_flags &= ~TDF_TSNOBLOCK;
485 mtx_unlock_spin(&sched_lock);
486 return;
487 }
488
489 #ifdef notyet
490 /*
491 * If we're borrowing an interrupted thread's VM context, we
492 * must clean up before going to sleep.
493 */
494 if (td->td_ithd != NULL) {
495 struct ithd *it = td->td_ithd;
496
497 if (it->it_interrupted) {
498 if (LOCK_LOG_TEST(lock, 0))
499 CTR3(KTR_LOCK, "%s: %p interrupted %p",
500 __func__, it, it->it_interrupted);
501 intr_thd_fixup(it);
502 }
503 }
504 #endif
505
506 /* Save who we are blocked on and switch. */
507 td->td_blocked = ts;
508 td->td_lockname = lock->lo_name;
509 TD_SET_LOCK(td);
510 propagate_priority(td);
511
512 if (LOCK_LOG_TEST(lock, 0))
513 CTR4(KTR_LOCK, "%s: td %p blocked on [%p] %s", __func__, td,
514 lock, lock->lo_name);
515
516 td->td_proc->p_stats->p_ru.ru_nvcsw++;
517 mi_switch();
518
519 if (LOCK_LOG_TEST(lock, 0))
520 CTR4(KTR_LOCK, "%s: td %p free from blocked on [%p] %s",
521 __func__, td, lock, lock->lo_name);
522
523 mtx_unlock_spin(&sched_lock);
524 }
525
526 /*
527 * Pick the highest priority thread on this turnstile and put it on the
528 * pending list. This must be called with the turnstile chain locked.
529 */
530 int
531 turnstile_signal(struct turnstile *ts)
532 {
533 struct turnstile_chain *tc;
534 struct thread *td;
535 int empty;
536
537 MPASS(ts != NULL);
538 MPASS(curthread->td_proc->p_magic == P_MAGIC);
539 MPASS(ts->ts_owner == curthread);
540 tc = TC_LOOKUP(ts->ts_lockobj);
541 mtx_assert(&tc->tc_lock, MA_OWNED);
542
543 /*
544 * Pick the highest priority thread blocked on this lock and
545 * move it to the pending list.
546 */
547 td = TAILQ_FIRST(&ts->ts_blocked);
548 MPASS(td->td_proc->p_magic == P_MAGIC);
549 mtx_lock_spin(&td_contested_lock);
550 TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
551 mtx_unlock_spin(&td_contested_lock);
552 TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq);
553
554 /*
555 * If the turnstile is now empty, remove it from its chain and
556 * give it to the about-to-be-woken thread. Otherwise take a
557 * turnstile from the free list and give it to the thread.
558 */
559 empty = TAILQ_EMPTY(&ts->ts_blocked);
560 if (empty)
561 MPASS(LIST_EMPTY(&ts->ts_free));
562 else
563 ts = LIST_FIRST(&ts->ts_free);
564 LIST_REMOVE(ts, ts_hash);
565 td->td_turnstile = ts;
566
567 return (empty);
568 }
569
570 /*
571 * Put all blocked threads on the pending list. This must be called with
572 * the turnstile chain locked.
573 */
574 void
575 turnstile_wakeup(struct turnstile *ts)
576 {
577 struct turnstile_chain *tc;
578 struct turnstile *ts1;
579 struct thread *td;
580
581 MPASS(ts != NULL);
582 MPASS(curthread->td_proc->p_magic == P_MAGIC);
583 MPASS(ts->ts_owner == curthread);
584 tc = TC_LOOKUP(ts->ts_lockobj);
585 mtx_assert(&tc->tc_lock, MA_OWNED);
586
587 /*
588 * Transfer the blocked list to the pending list.
589 */
590 mtx_lock_spin(&td_contested_lock);
591 TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked, td_lockq);
592 mtx_unlock_spin(&td_contested_lock);
593
594 /*
595 * Give a turnstile to each thread. The last thread gets
596 * this turnstile.
597 */
598 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) {
599 if (LIST_EMPTY(&ts->ts_free)) {
600 MPASS(TAILQ_NEXT(td, td_lockq) == NULL);
601 ts1 = ts;
602 } else
603 ts1 = LIST_FIRST(&ts->ts_free);
604 LIST_REMOVE(ts1, ts_hash);
605 td->td_turnstile = ts1;
606 }
607 }
608
609 /*
610 * Wakeup all threads on the pending list and adjust the priority of the
611 * current thread appropriately. This must be called with the turnstile
612 * chain locked.
613 */
614 void
615 turnstile_unpend(struct turnstile *ts)
616 {
617 TAILQ_HEAD( ,thread) pending_threads;
618 struct turnstile_chain *tc;
619 struct thread *td;
620 int cp, pri;
621
622 MPASS(ts != NULL);
623 MPASS(ts->ts_owner == curthread);
624 tc = TC_LOOKUP(ts->ts_lockobj);
625 mtx_assert(&tc->tc_lock, MA_OWNED);
626 MPASS(!TAILQ_EMPTY(&ts->ts_pending));
627
628 /*
629 * Move the list of pending threads out of the turnstile and
630 * into a local variable.
631 */
632 TAILQ_INIT(&pending_threads);
633 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq);
634 #ifdef INVARIANTS
635 if (TAILQ_EMPTY(&ts->ts_blocked))
636 ts->ts_lockobj = NULL;
637 #endif
638
639 /*
640 * Remove the turnstile from this thread's list of contested locks
641 * since this thread doesn't own it anymore. New threads will
642 * not be blocking on the turnstile until it is claimed by a new
643 * owner.
644 */
645 mtx_lock_spin(&td_contested_lock);
646 ts->ts_owner = NULL;
647 LIST_REMOVE(ts, ts_link);
648 mtx_unlock_spin(&td_contested_lock);
649 mtx_unlock_spin(&tc->tc_lock);
650
651 /*
652 * Adjust the priority of curthread based on other contested
653 * locks it owns. Don't lower the priority below the base
654 * priority however.
655 */
656 td = curthread;
657 pri = PRI_MAX;
658 mtx_lock_spin(&sched_lock);
659 mtx_lock_spin(&td_contested_lock);
660 LIST_FOREACH(ts, &td->td_contested, ts_link) {
661 cp = TAILQ_FIRST(&ts->ts_blocked)->td_priority;
662 if (cp < pri)
663 pri = cp;
664 }
665 mtx_unlock_spin(&td_contested_lock);
666 if (pri > td->td_base_pri)
667 pri = td->td_base_pri;
668 td->td_priority = pri;
669
670 /*
671 * Wake up all the pending threads. If a thread is not blocked
672 * on a lock, then it is currently executing on another CPU in
673 * turnstile_wait() or sitting on a run queue waiting to resume
674 * in turnstile_wait(). Set a flag to force it to try to acquire
675 * the lock again instead of blocking.
676 */
677 while (!TAILQ_EMPTY(&pending_threads)) {
678 td = TAILQ_FIRST(&pending_threads);
679 TAILQ_REMOVE(&pending_threads, td, td_lockq);
680 MPASS(td->td_proc->p_magic == P_MAGIC);
681 if (TD_ON_LOCK(td)) {
682 td->td_blocked = NULL;
683 td->td_lockname = NULL;
684 TD_CLR_LOCK(td);
685 MPASS(TD_CAN_RUN(td));
686 setrunqueue(td);
687 } else {
688 td->td_flags |= TDF_TSNOBLOCK;
689 MPASS(TD_IS_RUNNING(td) || TD_ON_RUNQ(td));
690 }
691 }
692 mtx_unlock_spin(&sched_lock);
693 }
694
695 /*
696 * Return the first thread in a turnstile.
697 */
698 struct thread *
699 turnstile_head(struct turnstile *ts)
700 {
701 #ifdef INVARIANTS
702 struct turnstile_chain *tc;
703
704 MPASS(ts != NULL);
705 tc = TC_LOOKUP(ts->ts_lockobj);
706 mtx_assert(&tc->tc_lock, MA_OWNED);
707 #endif
708 return (TAILQ_FIRST(&ts->ts_blocked));
709 }
710
711 /*
712 * Returns true if a turnstile is empty.
713 */
714 int
715 turnstile_empty(struct turnstile *ts)
716 {
717 #ifdef INVARIANTS
718 struct turnstile_chain *tc;
719
720 MPASS(ts != NULL);
721 tc = TC_LOOKUP(ts->ts_lockobj);
722 mtx_assert(&tc->tc_lock, MA_OWNED);
723 #endif
724 return (TAILQ_EMPTY(&ts->ts_blocked));
725 }
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