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
59 #include "opt_turnstile_profiling.h"
60
61 #include <sys/cdefs.h>
62 __FBSDID("$FreeBSD: releng/6.0/sys/kern/subr_turnstile.c 151124 2005-10-09 03:25:37Z delphij $");
63
64 #include <sys/param.h>
65 #include <sys/systm.h>
66 #include <sys/kernel.h>
67 #include <sys/ktr.h>
68 #include <sys/lock.h>
69 #include <sys/malloc.h>
70 #include <sys/mutex.h>
71 #include <sys/proc.h>
72 #include <sys/queue.h>
73 #include <sys/sched.h>
74 #include <sys/sysctl.h>
75 #include <sys/turnstile.h>
76
77 /*
78 * Constants for the hash table of turnstile chains. TC_SHIFT is a magic
79 * number chosen because the sleep queue's use the same value for the
80 * shift. Basically, we ignore the lower 8 bits of the address.
81 * TC_TABLESIZE must be a power of two for TC_MASK to work properly.
82 */
83 #define TC_TABLESIZE 128 /* Must be power of 2. */
84 #define TC_MASK (TC_TABLESIZE - 1)
85 #define TC_SHIFT 8
86 #define TC_HASH(lock) (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK)
87 #define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)]
88
89 /*
90 * There are three different lists of turnstiles as follows. The list
91 * connected by ts_link entries is a per-thread list of all the turnstiles
92 * attached to locks that we own. This is used to fixup our priority when
93 * a lock is released. The other two lists use the ts_hash entries. The
94 * first of these two is the turnstile chain list that a turnstile is on
95 * when it is attached to a lock. The second list to use ts_hash is the
96 * free list hung off of a turnstile that is attached to a lock.
97 *
98 * Each turnstile contains two lists of threads. The ts_blocked list is
99 * a linked list of threads blocked on the turnstile's lock. The
100 * ts_pending list is a linked list of threads previously awakened by
101 * turnstile_signal() or turnstile_wait() that are waiting to be put on
102 * the run queue.
103 *
104 * Locking key:
105 * c - turnstile chain lock
106 * q - td_contested lock
107 */
108 struct turnstile {
109 TAILQ_HEAD(, thread) ts_blocked; /* (c + q) Blocked threads. */
110 TAILQ_HEAD(, thread) ts_pending; /* (c) Pending threads. */
111 LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */
112 LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */
113 LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */
114 struct lock_object *ts_lockobj; /* (c) Lock we reference. */
115 struct thread *ts_owner; /* (c + q) Who owns the lock. */
116 };
117
118 struct turnstile_chain {
119 LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */
120 struct mtx tc_lock; /* Spin lock for this chain. */
121 #ifdef TURNSTILE_PROFILING
122 u_int tc_depth; /* Length of tc_queues. */
123 u_int tc_max_depth; /* Max length of tc_queues. */
124 #endif
125 };
126
127 #ifdef TURNSTILE_PROFILING
128 u_int turnstile_max_depth;
129 SYSCTL_NODE(_debug, OID_AUTO, turnstile, CTLFLAG_RD, 0, "turnstile profiling");
130 SYSCTL_NODE(_debug_turnstile, OID_AUTO, chains, CTLFLAG_RD, 0,
131 "turnstile chain stats");
132 SYSCTL_UINT(_debug_turnstile, OID_AUTO, max_depth, CTLFLAG_RD,
133 &turnstile_max_depth, 0, "maxmimum depth achieved of a single chain");
134 #endif
135 static struct mtx td_contested_lock;
136 static struct turnstile_chain turnstile_chains[TC_TABLESIZE];
137
138 static MALLOC_DEFINE(M_TURNSTILE, "turnstiles", "turnstiles");
139
140 /*
141 * Prototypes for non-exported routines.
142 */
143 static void init_turnstile0(void *dummy);
144 #ifdef TURNSTILE_PROFILING
145 static void init_turnstile_profiling(void *arg);
146 #endif
147 static void propagate_priority(struct thread *td);
148 static int turnstile_adjust_thread(struct turnstile *ts,
149 struct thread *td);
150 static void turnstile_setowner(struct turnstile *ts, struct thread *owner);
151
152 /*
153 * Walks the chain of turnstiles and their owners to propagate the priority
154 * of the thread being blocked to all the threads holding locks that have to
155 * release their locks before this thread can run again.
156 */
157 static void
158 propagate_priority(struct thread *td)
159 {
160 struct turnstile_chain *tc;
161 struct turnstile *ts;
162 int pri;
163
164 mtx_assert(&sched_lock, MA_OWNED);
165 pri = td->td_priority;
166 ts = td->td_blocked;
167 for (;;) {
168 td = ts->ts_owner;
169
170 if (td == NULL) {
171 /*
172 * This really isn't quite right. Really
173 * ought to bump priority of thread that
174 * next acquires the lock.
175 */
176 return;
177 }
178
179 MPASS(td->td_proc != NULL);
180 MPASS(td->td_proc->p_magic == P_MAGIC);
181
182 /*
183 * XXX: The owner of a turnstile can be stale if it is the
184 * first thread to grab a slock of a sx lock. In that case
185 * it is possible for us to be at SSLEEP or some other
186 * weird state. We should probably just return if the state
187 * isn't SRUN or SLOCK.
188 */
189 KASSERT(!TD_IS_SLEEPING(td),
190 ("sleeping thread (tid %d) owns a non-sleepable lock",
191 td->td_tid));
192
193 /*
194 * If this thread already has higher priority than the
195 * thread that is being blocked, we are finished.
196 */
197 if (td->td_priority <= pri)
198 return;
199
200 /*
201 * Bump this thread's priority.
202 */
203 sched_lend_prio(td, pri);
204
205 /*
206 * If lock holder is actually running or on the run queue
207 * then we are done.
208 */
209 if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) {
210 MPASS(td->td_blocked == NULL);
211 return;
212 }
213
214 #ifndef SMP
215 /*
216 * For UP, we check to see if td is curthread (this shouldn't
217 * ever happen however as it would mean we are in a deadlock.)
218 */
219 KASSERT(td != curthread, ("Deadlock detected"));
220 #endif
221
222 /*
223 * If we aren't blocked on a lock, we should be.
224 */
225 KASSERT(TD_ON_LOCK(td), (
226 "thread %d(%s):%d holds %s but isn't blocked on a lock\n",
227 td->td_tid, td->td_proc->p_comm, td->td_state,
228 ts->ts_lockobj->lo_name));
229
230 /*
231 * Pick up the lock that td is blocked on.
232 */
233 ts = td->td_blocked;
234 MPASS(ts != NULL);
235 tc = TC_LOOKUP(ts->ts_lockobj);
236 mtx_lock_spin(&tc->tc_lock);
237
238 /* Resort td on the list if needed. */
239 if (!turnstile_adjust_thread(ts, td)) {
240 mtx_unlock_spin(&tc->tc_lock);
241 return;
242 }
243 mtx_unlock_spin(&tc->tc_lock);
244 }
245 }
246
247 /*
248 * Adjust the thread's position on a turnstile after its priority has been
249 * changed.
250 */
251 static int
252 turnstile_adjust_thread(struct turnstile *ts, struct thread *td)
253 {
254 struct turnstile_chain *tc;
255 struct thread *td1, *td2;
256
257 mtx_assert(&sched_lock, MA_OWNED);
258 MPASS(TD_ON_LOCK(td));
259
260 /*
261 * This thread may not be blocked on this turnstile anymore
262 * but instead might already be woken up on another CPU
263 * that is waiting on sched_lock in turnstile_unpend() to
264 * finish waking this thread up. We can detect this case
265 * by checking to see if this thread has been given a
266 * turnstile by either turnstile_signal() or
267 * turnstile_broadcast(). In this case, treat the thread as
268 * if it was already running.
269 */
270 if (td->td_turnstile != NULL)
271 return (0);
272
273 /*
274 * Check if the thread needs to be moved on the blocked chain.
275 * It needs to be moved if either its priority is lower than
276 * the previous thread or higher than the next thread.
277 */
278 tc = TC_LOOKUP(ts->ts_lockobj);
279 mtx_assert(&tc->tc_lock, MA_OWNED);
280 td1 = TAILQ_PREV(td, threadqueue, td_lockq);
281 td2 = TAILQ_NEXT(td, td_lockq);
282 if ((td1 != NULL && td->td_priority < td1->td_priority) ||
283 (td2 != NULL && td->td_priority > td2->td_priority)) {
284
285 /*
286 * Remove thread from blocked chain and determine where
287 * it should be moved to.
288 */
289 mtx_lock_spin(&td_contested_lock);
290 TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
291 TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq) {
292 MPASS(td1->td_proc->p_magic == P_MAGIC);
293 if (td1->td_priority > td->td_priority)
294 break;
295 }
296
297 if (td1 == NULL)
298 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
299 else
300 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
301 mtx_unlock_spin(&td_contested_lock);
302 if (td1 == NULL)
303 CTR3(KTR_LOCK,
304 "turnstile_adjust_thread: td %d put at tail on [%p] %s",
305 td->td_tid, ts->ts_lockobj, ts->ts_lockobj->lo_name);
306 else
307 CTR4(KTR_LOCK,
308 "turnstile_adjust_thread: td %d moved before %d on [%p] %s",
309 td->td_tid, td1->td_tid, ts->ts_lockobj,
310 ts->ts_lockobj->lo_name);
311 }
312 return (1);
313 }
314
315 /*
316 * Early initialization of turnstiles. This is not done via a SYSINIT()
317 * since this needs to be initialized very early when mutexes are first
318 * initialized.
319 */
320 void
321 init_turnstiles(void)
322 {
323 int i;
324
325 for (i = 0; i < TC_TABLESIZE; i++) {
326 LIST_INIT(&turnstile_chains[i].tc_turnstiles);
327 mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain",
328 NULL, MTX_SPIN);
329 }
330 mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN);
331 thread0.td_turnstile = NULL;
332 }
333
334 #ifdef TURNSTILE_PROFILING
335 static void
336 init_turnstile_profiling(void *arg)
337 {
338 struct sysctl_oid *chain_oid;
339 char chain_name[10];
340 int i;
341
342 for (i = 0; i < TC_TABLESIZE; i++) {
343 snprintf(chain_name, sizeof(chain_name), "%d", i);
344 chain_oid = SYSCTL_ADD_NODE(NULL,
345 SYSCTL_STATIC_CHILDREN(_debug_turnstile_chains), OID_AUTO,
346 chain_name, CTLFLAG_RD, NULL, "turnstile chain stats");
347 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
348 "depth", CTLFLAG_RD, &turnstile_chains[i].tc_depth, 0,
349 NULL);
350 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO,
351 "max_depth", CTLFLAG_RD, &turnstile_chains[i].tc_max_depth,
352 0, NULL);
353 }
354 }
355 SYSINIT(turnstile_profiling, SI_SUB_LOCK, SI_ORDER_ANY,
356 init_turnstile_profiling, NULL);
357 #endif
358
359 static void
360 init_turnstile0(void *dummy)
361 {
362
363 thread0.td_turnstile = turnstile_alloc();
364 }
365 SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL);
366
367 /*
368 * Update a thread on the turnstile list after it's priority has been changed.
369 * The old priority is passed in as an argument.
370 */
371 void
372 turnstile_adjust(struct thread *td, u_char oldpri)
373 {
374 struct turnstile_chain *tc;
375 struct turnstile *ts;
376
377 mtx_assert(&sched_lock, MA_OWNED);
378 MPASS(TD_ON_LOCK(td));
379
380 /*
381 * Pick up the lock that td is blocked on.
382 */
383 ts = td->td_blocked;
384 MPASS(ts != NULL);
385 tc = TC_LOOKUP(ts->ts_lockobj);
386 mtx_lock_spin(&tc->tc_lock);
387
388 /* Resort the turnstile on the list. */
389 if (!turnstile_adjust_thread(ts, td)) {
390 mtx_unlock_spin(&tc->tc_lock);
391 return;
392 }
393
394 /*
395 * If our priority was lowered and we are at the head of the
396 * turnstile, then propagate our new priority up the chain.
397 * Note that we currently don't try to revoke lent priorities
398 * when our priority goes up.
399 */
400 if (td == TAILQ_FIRST(&ts->ts_blocked) && td->td_priority < oldpri) {
401 mtx_unlock_spin(&tc->tc_lock);
402 propagate_priority(td);
403 } else
404 mtx_unlock_spin(&tc->tc_lock);
405 }
406
407 /*
408 * Set the owner of the lock this turnstile is attached to.
409 */
410 static void
411 turnstile_setowner(struct turnstile *ts, struct thread *owner)
412 {
413
414 mtx_assert(&td_contested_lock, MA_OWNED);
415 MPASS(owner->td_proc->p_magic == P_MAGIC);
416 MPASS(ts->ts_owner == NULL);
417 ts->ts_owner = owner;
418 LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link);
419 }
420
421 /*
422 * Malloc a turnstile for a new thread, initialize it and return it.
423 */
424 struct turnstile *
425 turnstile_alloc(void)
426 {
427 struct turnstile *ts;
428
429 ts = malloc(sizeof(struct turnstile), M_TURNSTILE, M_WAITOK | M_ZERO);
430 TAILQ_INIT(&ts->ts_blocked);
431 TAILQ_INIT(&ts->ts_pending);
432 LIST_INIT(&ts->ts_free);
433 return (ts);
434 }
435
436 /*
437 * Free a turnstile when a thread is destroyed.
438 */
439 void
440 turnstile_free(struct turnstile *ts)
441 {
442
443 MPASS(ts != NULL);
444 MPASS(TAILQ_EMPTY(&ts->ts_blocked));
445 MPASS(TAILQ_EMPTY(&ts->ts_pending));
446 free(ts, M_TURNSTILE);
447 }
448
449 /*
450 * Lock the turnstile chain associated with the specified lock.
451 */
452 void
453 turnstile_lock(struct lock_object *lock)
454 {
455 struct turnstile_chain *tc;
456
457 tc = TC_LOOKUP(lock);
458 mtx_lock_spin(&tc->tc_lock);
459 }
460
461 /*
462 * Look up the turnstile for a lock in the hash table locking the associated
463 * turnstile chain along the way. If no turnstile is found in the hash
464 * table, NULL is returned.
465 */
466 struct turnstile *
467 turnstile_lookup(struct lock_object *lock)
468 {
469 struct turnstile_chain *tc;
470 struct turnstile *ts;
471
472 tc = TC_LOOKUP(lock);
473 mtx_assert(&tc->tc_lock, MA_OWNED);
474 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash)
475 if (ts->ts_lockobj == lock)
476 return (ts);
477 return (NULL);
478 }
479
480 /*
481 * Unlock the turnstile chain associated with a given lock.
482 */
483 void
484 turnstile_release(struct lock_object *lock)
485 {
486 struct turnstile_chain *tc;
487
488 tc = TC_LOOKUP(lock);
489 mtx_unlock_spin(&tc->tc_lock);
490 }
491
492 /*
493 * Take ownership of a turnstile and adjust the priority of the new
494 * owner appropriately.
495 */
496 void
497 turnstile_claim(struct lock_object *lock)
498 {
499 struct turnstile_chain *tc;
500 struct turnstile *ts;
501 struct thread *td, *owner;
502
503 tc = TC_LOOKUP(lock);
504 mtx_assert(&tc->tc_lock, MA_OWNED);
505 ts = turnstile_lookup(lock);
506 MPASS(ts != NULL);
507
508 owner = curthread;
509 mtx_lock_spin(&td_contested_lock);
510 turnstile_setowner(ts, owner);
511 mtx_unlock_spin(&td_contested_lock);
512
513 td = TAILQ_FIRST(&ts->ts_blocked);
514 MPASS(td != NULL);
515 MPASS(td->td_proc->p_magic == P_MAGIC);
516 mtx_unlock_spin(&tc->tc_lock);
517
518 /*
519 * Update the priority of the new owner if needed.
520 */
521 mtx_lock_spin(&sched_lock);
522 if (td->td_priority < owner->td_priority)
523 sched_lend_prio(owner, td->td_priority);
524 mtx_unlock_spin(&sched_lock);
525 }
526
527 /*
528 * Block the current thread on the turnstile assicated with 'lock'. This
529 * function will context switch and not return until this thread has been
530 * woken back up. This function must be called with the appropriate
531 * turnstile chain locked and will return with it unlocked.
532 */
533 void
534 turnstile_wait(struct lock_object *lock, struct thread *owner)
535 {
536 struct turnstile_chain *tc;
537 struct turnstile *ts;
538 struct thread *td, *td1;
539
540 td = curthread;
541 tc = TC_LOOKUP(lock);
542 mtx_assert(&tc->tc_lock, MA_OWNED);
543 MPASS(td->td_turnstile != NULL);
544 MPASS(owner != NULL);
545 MPASS(owner->td_proc->p_magic == P_MAGIC);
546
547 /* Look up the turnstile associated with the lock 'lock'. */
548 ts = turnstile_lookup(lock);
549
550 /*
551 * If the lock does not already have a turnstile, use this thread's
552 * turnstile. Otherwise insert the current thread into the
553 * turnstile already in use by this lock.
554 */
555 if (ts == NULL) {
556 #ifdef TURNSTILE_PROFILING
557 tc->tc_depth++;
558 if (tc->tc_depth > tc->tc_max_depth) {
559 tc->tc_max_depth = tc->tc_depth;
560 if (tc->tc_max_depth > turnstile_max_depth)
561 turnstile_max_depth = tc->tc_max_depth;
562 }
563 #endif
564 ts = td->td_turnstile;
565 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash);
566 KASSERT(TAILQ_EMPTY(&ts->ts_pending),
567 ("thread's turnstile has pending threads"));
568 KASSERT(TAILQ_EMPTY(&ts->ts_blocked),
569 ("thread's turnstile has a non-empty queue"));
570 KASSERT(LIST_EMPTY(&ts->ts_free),
571 ("thread's turnstile has a non-empty free list"));
572 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer"));
573 ts->ts_lockobj = lock;
574 mtx_lock_spin(&td_contested_lock);
575 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
576 turnstile_setowner(ts, owner);
577 mtx_unlock_spin(&td_contested_lock);
578 } else {
579 TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq)
580 if (td1->td_priority > td->td_priority)
581 break;
582 mtx_lock_spin(&td_contested_lock);
583 if (td1 != NULL)
584 TAILQ_INSERT_BEFORE(td1, td, td_lockq);
585 else
586 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq);
587 mtx_unlock_spin(&td_contested_lock);
588 MPASS(td->td_turnstile != NULL);
589 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash);
590 MPASS(owner == ts->ts_owner);
591 }
592 td->td_turnstile = NULL;
593 mtx_unlock_spin(&tc->tc_lock);
594
595 mtx_lock_spin(&sched_lock);
596 /*
597 * Handle race condition where a thread on another CPU that owns
598 * lock 'lock' could have woken us in between us dropping the
599 * turnstile chain lock and acquiring the sched_lock.
600 */
601 if (td->td_flags & TDF_TSNOBLOCK) {
602 td->td_flags &= ~TDF_TSNOBLOCK;
603 mtx_unlock_spin(&sched_lock);
604 return;
605 }
606
607 #ifdef notyet
608 /*
609 * If we're borrowing an interrupted thread's VM context, we
610 * must clean up before going to sleep.
611 */
612 if (td->td_ithd != NULL) {
613 struct ithd *it = td->td_ithd;
614
615 if (it->it_interrupted) {
616 if (LOCK_LOG_TEST(lock, 0))
617 CTR3(KTR_LOCK, "%s: %p interrupted %p",
618 __func__, it, it->it_interrupted);
619 intr_thd_fixup(it);
620 }
621 }
622 #endif
623
624 /* Save who we are blocked on and switch. */
625 td->td_blocked = ts;
626 td->td_lockname = lock->lo_name;
627 TD_SET_LOCK(td);
628 propagate_priority(td);
629
630 if (LOCK_LOG_TEST(lock, 0))
631 CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__,
632 td->td_tid, lock, lock->lo_name);
633
634 mi_switch(SW_VOL, NULL);
635
636 if (LOCK_LOG_TEST(lock, 0))
637 CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s",
638 __func__, td->td_tid, lock, lock->lo_name);
639
640 mtx_unlock_spin(&sched_lock);
641 }
642
643 /*
644 * Pick the highest priority thread on this turnstile and put it on the
645 * pending list. This must be called with the turnstile chain locked.
646 */
647 int
648 turnstile_signal(struct turnstile *ts)
649 {
650 struct turnstile_chain *tc;
651 struct thread *td;
652 int empty;
653
654 MPASS(ts != NULL);
655 MPASS(curthread->td_proc->p_magic == P_MAGIC);
656 MPASS(ts->ts_owner == curthread);
657 tc = TC_LOOKUP(ts->ts_lockobj);
658 mtx_assert(&tc->tc_lock, MA_OWNED);
659
660 /*
661 * Pick the highest priority thread blocked on this lock and
662 * move it to the pending list.
663 */
664 td = TAILQ_FIRST(&ts->ts_blocked);
665 MPASS(td->td_proc->p_magic == P_MAGIC);
666 mtx_lock_spin(&td_contested_lock);
667 TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq);
668 mtx_unlock_spin(&td_contested_lock);
669 TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq);
670
671 /*
672 * If the turnstile is now empty, remove it from its chain and
673 * give it to the about-to-be-woken thread. Otherwise take a
674 * turnstile from the free list and give it to the thread.
675 */
676 empty = TAILQ_EMPTY(&ts->ts_blocked);
677 if (empty) {
678 MPASS(LIST_EMPTY(&ts->ts_free));
679 #ifdef TURNSTILE_PROFILING
680 tc->tc_depth--;
681 #endif
682 } else
683 ts = LIST_FIRST(&ts->ts_free);
684 MPASS(ts != NULL);
685 LIST_REMOVE(ts, ts_hash);
686 td->td_turnstile = ts;
687
688 return (empty);
689 }
690
691 /*
692 * Put all blocked threads on the pending list. This must be called with
693 * the turnstile chain locked.
694 */
695 void
696 turnstile_broadcast(struct turnstile *ts)
697 {
698 struct turnstile_chain *tc;
699 struct turnstile *ts1;
700 struct thread *td;
701
702 MPASS(ts != NULL);
703 MPASS(curthread->td_proc->p_magic == P_MAGIC);
704 MPASS(ts->ts_owner == curthread);
705 tc = TC_LOOKUP(ts->ts_lockobj);
706 mtx_assert(&tc->tc_lock, MA_OWNED);
707
708 /*
709 * Transfer the blocked list to the pending list.
710 */
711 mtx_lock_spin(&td_contested_lock);
712 TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked, td_lockq);
713 mtx_unlock_spin(&td_contested_lock);
714
715 /*
716 * Give a turnstile to each thread. The last thread gets
717 * this turnstile.
718 */
719 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) {
720 if (LIST_EMPTY(&ts->ts_free)) {
721 MPASS(TAILQ_NEXT(td, td_lockq) == NULL);
722 ts1 = ts;
723 #ifdef TURNSTILE_PROFILING
724 tc->tc_depth--;
725 #endif
726 } else
727 ts1 = LIST_FIRST(&ts->ts_free);
728 MPASS(ts1 != NULL);
729 LIST_REMOVE(ts1, ts_hash);
730 td->td_turnstile = ts1;
731 }
732 }
733
734 /*
735 * Wakeup all threads on the pending list and adjust the priority of the
736 * current thread appropriately. This must be called with the turnstile
737 * chain locked.
738 */
739 void
740 turnstile_unpend(struct turnstile *ts)
741 {
742 TAILQ_HEAD( ,thread) pending_threads;
743 struct turnstile_chain *tc;
744 struct thread *td;
745 u_char cp, pri;
746
747 MPASS(ts != NULL);
748 MPASS(ts->ts_owner == curthread);
749 tc = TC_LOOKUP(ts->ts_lockobj);
750 mtx_assert(&tc->tc_lock, MA_OWNED);
751 MPASS(!TAILQ_EMPTY(&ts->ts_pending));
752
753 /*
754 * Move the list of pending threads out of the turnstile and
755 * into a local variable.
756 */
757 TAILQ_INIT(&pending_threads);
758 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq);
759 #ifdef INVARIANTS
760 if (TAILQ_EMPTY(&ts->ts_blocked))
761 ts->ts_lockobj = NULL;
762 #endif
763
764 /*
765 * Remove the turnstile from this thread's list of contested locks
766 * since this thread doesn't own it anymore. New threads will
767 * not be blocking on the turnstile until it is claimed by a new
768 * owner.
769 */
770 mtx_lock_spin(&td_contested_lock);
771 ts->ts_owner = NULL;
772 LIST_REMOVE(ts, ts_link);
773 mtx_unlock_spin(&td_contested_lock);
774 critical_enter();
775 mtx_unlock_spin(&tc->tc_lock);
776
777 /*
778 * Adjust the priority of curthread based on other contested
779 * locks it owns. Don't lower the priority below the base
780 * priority however.
781 */
782 td = curthread;
783 pri = PRI_MAX;
784 mtx_lock_spin(&sched_lock);
785 mtx_lock_spin(&td_contested_lock);
786 LIST_FOREACH(ts, &td->td_contested, ts_link) {
787 cp = TAILQ_FIRST(&ts->ts_blocked)->td_priority;
788 if (cp < pri)
789 pri = cp;
790 }
791 mtx_unlock_spin(&td_contested_lock);
792 sched_unlend_prio(td, pri);
793
794 /*
795 * Wake up all the pending threads. If a thread is not blocked
796 * on a lock, then it is currently executing on another CPU in
797 * turnstile_wait() or sitting on a run queue waiting to resume
798 * in turnstile_wait(). Set a flag to force it to try to acquire
799 * the lock again instead of blocking.
800 */
801 while (!TAILQ_EMPTY(&pending_threads)) {
802 td = TAILQ_FIRST(&pending_threads);
803 TAILQ_REMOVE(&pending_threads, td, td_lockq);
804 MPASS(td->td_proc->p_magic == P_MAGIC);
805 if (TD_ON_LOCK(td)) {
806 td->td_blocked = NULL;
807 td->td_lockname = NULL;
808 TD_CLR_LOCK(td);
809 MPASS(TD_CAN_RUN(td));
810 setrunqueue(td, SRQ_BORING);
811 } else {
812 td->td_flags |= TDF_TSNOBLOCK;
813 MPASS(TD_IS_RUNNING(td) || TD_ON_RUNQ(td));
814 }
815 }
816 critical_exit();
817 mtx_unlock_spin(&sched_lock);
818 }
819
820 /*
821 * Return the first thread in a turnstile.
822 */
823 struct thread *
824 turnstile_head(struct turnstile *ts)
825 {
826 #ifdef INVARIANTS
827 struct turnstile_chain *tc;
828
829 MPASS(ts != NULL);
830 tc = TC_LOOKUP(ts->ts_lockobj);
831 mtx_assert(&tc->tc_lock, MA_OWNED);
832 #endif
833 return (TAILQ_FIRST(&ts->ts_blocked));
834 }
835
836 /*
837 * Returns true if a turnstile is empty.
838 */
839 int
840 turnstile_empty(struct turnstile *ts)
841 {
842 #ifdef INVARIANTS
843 struct turnstile_chain *tc;
844
845 MPASS(ts != NULL);
846 tc = TC_LOOKUP(ts->ts_lockobj);
847 mtx_assert(&tc->tc_lock, MA_OWNED);
848 #endif
849 return (TAILQ_EMPTY(&ts->ts_blocked));
850 }
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