subr_turnstile.c revision 122590
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: head/sys/kern/subr_turnstile.c 122590 2003-11-12 23:48:42Z 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 */ 111struct 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 121struct turnstile_chain { 122 LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */ 123 struct mtx tc_lock; /* Spin lock for this chain. */ 124}; 125 126static struct mtx td_contested_lock; 127static struct turnstile_chain turnstile_chains[TC_TABLESIZE]; 128 129MALLOC_DEFINE(M_TURNSTILE, "turnstiles", "turnstiles"); 130 131/* 132 * Prototypes for non-exported routines. 133 */ 134static void init_turnstile0(void *dummy); 135static void propagate_priority(struct thread *); 136static 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 */ 143static void 144propagate_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 * If this turnstile has no threads on its blocked queue 237 * then it's possible that it was just woken up on another 238 * CPU. If so, we are done. 239 */ 240 if (TAILQ_EMPTY(&ts->ts_blocked)) { 241 mtx_unlock_spin(&tc->tc_lock); 242 return; 243 } 244 245 /* 246 * Check if the thread needs to be moved up on 247 * the blocked chain. It doesn't need to be moved 248 * if it is already at the head of the list or if 249 * the item in front of it still has a higher priority. 250 */ 251 if (td == TAILQ_FIRST(&ts->ts_blocked)) { 252 mtx_unlock_spin(&tc->tc_lock); 253 continue; 254 } 255 256 td1 = TAILQ_PREV(td, threadqueue, td_lockq); 257 if (td1->td_priority <= pri) { 258 mtx_unlock_spin(&tc->tc_lock); 259 continue; 260 } 261 262 /* 263 * Remove thread from blocked chain and determine where 264 * it should be moved up to. Since we know that td1 has 265 * a lower priority than td, we know that at least one 266 * thread in the chain has a lower priority and that 267 * td1 will thus not be NULL after the loop. 268 */ 269 mtx_lock_spin(&td_contested_lock); 270 TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq); 271 TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq) { 272 MPASS(td1->td_proc->p_magic == P_MAGIC); 273 if (td1->td_priority > pri) 274 break; 275 } 276 277 MPASS(td1 != NULL); 278 TAILQ_INSERT_BEFORE(td1, td, td_lockq); 279 mtx_unlock_spin(&td_contested_lock); 280 CTR4(KTR_LOCK, 281 "propagate_priority: td %p moved before %p on [%p] %s", 282 td, td1, ts->ts_lockobj, ts->ts_lockobj->lo_name); 283 mtx_unlock_spin(&tc->tc_lock); 284 } 285} 286 287/* 288 * Early initialization of turnstiles. This is not done via a SYSINIT() 289 * since this needs to be initialized very early when mutexes are first 290 * initialized. 291 */ 292void 293init_turnstiles(void) 294{ 295 int i; 296 297 for (i = 0; i < TC_TABLESIZE; i++) { 298 LIST_INIT(&turnstile_chains[i].tc_turnstiles); 299 mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain", 300 NULL, MTX_SPIN); 301 } 302 mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN); 303#ifdef INVARIANTS 304 thread0.td_turnstile = NULL; 305#endif 306} 307 308static void 309init_turnstile0(void *dummy) 310{ 311 312 thread0.td_turnstile = turnstile_alloc(); 313} 314SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL); 315 316/* 317 * Set the owner of the lock this turnstile is attached to. 318 */ 319static void 320turnstile_setowner(struct turnstile *ts, struct thread *owner) 321{ 322 323 mtx_assert(&td_contested_lock, MA_OWNED); 324 MPASS(owner->td_proc->p_magic == P_MAGIC); 325 MPASS(ts->ts_owner == NULL); 326 ts->ts_owner = owner; 327 LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link); 328} 329 330/* 331 * Malloc a turnstile for a new thread, initialize it and return it. 332 */ 333struct turnstile * 334turnstile_alloc(void) 335{ 336 struct turnstile *ts; 337 338 ts = malloc(sizeof(struct turnstile), M_TURNSTILE, M_WAITOK | M_ZERO); 339 TAILQ_INIT(&ts->ts_blocked); 340 TAILQ_INIT(&ts->ts_pending); 341 LIST_INIT(&ts->ts_free); 342 return (ts); 343} 344 345/* 346 * Free a turnstile when a thread is destroyed. 347 */ 348void 349turnstile_free(struct turnstile *ts) 350{ 351 352 MPASS(ts != NULL); 353 MPASS(TAILQ_EMPTY(&ts->ts_blocked)); 354 MPASS(TAILQ_EMPTY(&ts->ts_pending)); 355 free(ts, M_TURNSTILE); 356} 357 358/* 359 * Look up the turnstile for a lock in the hash table locking the associated 360 * turnstile chain along the way. Return with the turnstile chain locked. 361 * If no turnstile is found in the hash table, NULL is returned. 362 */ 363struct turnstile * 364turnstile_lookup(struct lock_object *lock) 365{ 366 struct turnstile_chain *tc; 367 struct turnstile *ts; 368 369 tc = TC_LOOKUP(lock); 370 mtx_lock_spin(&tc->tc_lock); 371 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 372 if (ts->ts_lockobj == lock) 373 return (ts); 374 return (NULL); 375} 376 377/* 378 * Unlock the turnstile chain associated with a given lock. 379 */ 380void 381turnstile_release(struct lock_object *lock) 382{ 383 struct turnstile_chain *tc; 384 385 tc = TC_LOOKUP(lock); 386 mtx_unlock_spin(&tc->tc_lock); 387} 388 389/* 390 * Take ownership of a turnstile and adjust the priority of the new 391 * owner appropriately. 392 */ 393void 394turnstile_claim(struct turnstile *ts) 395{ 396 struct turnstile_chain *tc; 397 struct thread *td, *owner; 398 399 tc = TC_LOOKUP(ts->ts_lockobj); 400 mtx_assert(&tc->tc_lock, MA_OWNED); 401 402 owner = curthread; 403 mtx_lock_spin(&td_contested_lock); 404 turnstile_setowner(ts, owner); 405 mtx_unlock_spin(&td_contested_lock); 406 407 td = TAILQ_FIRST(&ts->ts_blocked); 408 MPASS(td != NULL); 409 MPASS(td->td_proc->p_magic == P_MAGIC); 410 mtx_unlock_spin(&tc->tc_lock); 411 412 /* 413 * Update the priority of the new owner if needed. 414 */ 415 mtx_lock_spin(&sched_lock); 416 if (td->td_priority < owner->td_priority) 417 owner->td_priority = td->td_priority; 418 mtx_unlock_spin(&sched_lock); 419} 420 421/* 422 * Block the current thread on the turnstile ts. This function will context 423 * switch and not return until this thread has been woken back up. This 424 * function must be called with the appropriate turnstile chain locked and 425 * will return with it unlocked. 426 */ 427void 428turnstile_wait(struct turnstile *ts, struct lock_object *lock, 429 struct thread *owner) 430{ 431 struct turnstile_chain *tc; 432 struct thread *td, *td1; 433 434 td = curthread; 435 tc = TC_LOOKUP(lock); 436 mtx_assert(&tc->tc_lock, MA_OWNED); 437 MPASS(td->td_turnstile != NULL); 438 MPASS(owner != NULL); 439 MPASS(owner->td_proc->p_magic == P_MAGIC); 440 441 /* If the passed in turnstile is NULL, use this thread's turnstile. */ 442 if (ts == NULL) { 443 ts = td->td_turnstile; 444 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash); 445 KASSERT(TAILQ_EMPTY(&ts->ts_pending), 446 ("thread's turnstile has pending threads")); 447 KASSERT(TAILQ_EMPTY(&ts->ts_blocked), 448 ("thread's turnstile has a non-empty queue")); 449 KASSERT(LIST_EMPTY(&ts->ts_free), 450 ("thread's turnstile has a non-empty free list")); 451 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer")); 452 ts->ts_lockobj = lock; 453 mtx_lock_spin(&td_contested_lock); 454 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq); 455 turnstile_setowner(ts, owner); 456 mtx_unlock_spin(&td_contested_lock); 457 } else { 458 TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq) 459 if (td1->td_priority > td->td_priority) 460 break; 461 mtx_lock_spin(&td_contested_lock); 462 if (td1 != NULL) 463 TAILQ_INSERT_BEFORE(td1, td, td_lockq); 464 else 465 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq); 466 mtx_unlock_spin(&td_contested_lock); 467 MPASS(td->td_turnstile != NULL); 468 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash); 469 MPASS(owner == ts->ts_owner); 470 } 471#ifdef INVARIANTS 472 td->td_turnstile = NULL; 473#endif 474 mtx_unlock_spin(&tc->tc_lock); 475 476 mtx_lock_spin(&sched_lock); 477 /* 478 * Handle race condition where a thread on another CPU that owns 479 * lock 'lock' could have woken us in between us dropping the 480 * turnstile chain lock and acquiring the sched_lock. 481 */ 482 if (td->td_flags & TDF_TSNOBLOCK) { 483 td->td_flags &= ~TDF_TSNOBLOCK; 484 mtx_unlock_spin(&sched_lock); 485 return; 486 } 487 488#ifdef notyet 489 /* 490 * If we're borrowing an interrupted thread's VM context, we 491 * must clean up before going to sleep. 492 */ 493 if (td->td_ithd != NULL) { 494 struct ithd *it = td->td_ithd; 495 496 if (it->it_interrupted) { 497 if (LOCK_LOG_TEST(lock, 0)) 498 CTR3(KTR_LOCK, "%s: %p interrupted %p", 499 __func__, it, it->it_interrupted); 500 intr_thd_fixup(it); 501 } 502 } 503#endif 504 505 /* Save who we are blocked on and switch. */ 506 td->td_blocked = ts; 507 td->td_lockname = lock->lo_name; 508 TD_SET_LOCK(td); 509 propagate_priority(td); 510 511 if (LOCK_LOG_TEST(lock, 0)) 512 CTR4(KTR_LOCK, "%s: td %p blocked on [%p] %s", __func__, td, 513 lock, lock->lo_name); 514 515 td->td_proc->p_stats->p_ru.ru_nvcsw++; 516 mi_switch(); 517 518 if (LOCK_LOG_TEST(lock, 0)) 519 CTR4(KTR_LOCK, "%s: td %p free from blocked on [%p] %s", 520 __func__, td, lock, lock->lo_name); 521 522 mtx_unlock_spin(&sched_lock); 523} 524 525/* 526 * Pick the highest priority thread on this turnstile and put it on the 527 * pending list. This must be called with the turnstile chain locked. 528 */ 529int 530turnstile_signal(struct turnstile *ts) 531{ 532 struct turnstile_chain *tc; 533 struct thread *td; 534 int empty; 535 536 MPASS(ts != NULL); 537 MPASS(curthread->td_proc->p_magic == P_MAGIC); 538 MPASS(ts->ts_owner == curthread); 539 tc = TC_LOOKUP(ts->ts_lockobj); 540 mtx_assert(&tc->tc_lock, MA_OWNED); 541 542 /* 543 * Pick the highest priority thread blocked on this lock and 544 * move it to the pending list. 545 */ 546 td = TAILQ_FIRST(&ts->ts_blocked); 547 MPASS(td->td_proc->p_magic == P_MAGIC); 548 mtx_lock_spin(&td_contested_lock); 549 TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq); 550 mtx_unlock_spin(&td_contested_lock); 551 TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq); 552 553 /* 554 * If the turnstile is now empty, remove it from its chain and 555 * give it to the about-to-be-woken thread. Otherwise take a 556 * turnstile from the free list and give it to the thread. 557 */ 558 empty = TAILQ_EMPTY(&ts->ts_blocked); 559 if (empty) 560 MPASS(LIST_EMPTY(&ts->ts_free)); 561 else 562 ts = LIST_FIRST(&ts->ts_free); 563 LIST_REMOVE(ts, ts_hash); 564 td->td_turnstile = ts; 565 566 return (empty); 567} 568 569/* 570 * Put all blocked threads on the pending list. This must be called with 571 * the turnstile chain locked. 572 */ 573void 574turnstile_wakeup(struct turnstile *ts) 575{ 576 struct turnstile_chain *tc; 577 struct turnstile *ts1; 578 struct thread *td; 579 580 MPASS(ts != NULL); 581 MPASS(curthread->td_proc->p_magic == P_MAGIC); 582 MPASS(ts->ts_owner == curthread); 583 tc = TC_LOOKUP(ts->ts_lockobj); 584 mtx_assert(&tc->tc_lock, MA_OWNED); 585 586 /* 587 * Transfer the blocked list to the pending list. 588 */ 589 mtx_lock_spin(&td_contested_lock); 590 TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked, td_lockq); 591 mtx_unlock_spin(&td_contested_lock); 592 593 /* 594 * Give a turnstile to each thread. The last thread gets 595 * this turnstile. 596 */ 597 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) { 598 if (LIST_EMPTY(&ts->ts_free)) { 599 MPASS(TAILQ_NEXT(td, td_lockq) == NULL); 600 ts1 = ts; 601 } else 602 ts1 = LIST_FIRST(&ts->ts_free); 603 LIST_REMOVE(ts1, ts_hash); 604 td->td_turnstile = ts1; 605 } 606} 607 608/* 609 * Wakeup all threads on the pending list and adjust the priority of the 610 * current thread appropriately. This must be called with the turnstile 611 * chain locked. 612 */ 613void 614turnstile_unpend(struct turnstile *ts) 615{ 616 TAILQ_HEAD( ,thread) pending_threads; 617 struct turnstile_chain *tc; 618 struct thread *td; 619 int cp, pri; 620 621 MPASS(ts != NULL); 622 MPASS(ts->ts_owner == curthread); 623 tc = TC_LOOKUP(ts->ts_lockobj); 624 mtx_assert(&tc->tc_lock, MA_OWNED); 625 MPASS(!TAILQ_EMPTY(&ts->ts_pending)); 626 627 /* 628 * Move the list of pending threads out of the turnstile and 629 * into a local variable. 630 */ 631 TAILQ_INIT(&pending_threads); 632 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq); 633#ifdef INVARIANTS 634 if (TAILQ_EMPTY(&ts->ts_blocked)) 635 ts->ts_lockobj = NULL; 636#endif 637 638 /* 639 * Remove the turnstile from this thread's list of contested locks 640 * since this thread doesn't own it anymore. New threads will 641 * not be blocking on the turnstile until it is claimed by a new 642 * owner. 643 */ 644 mtx_lock_spin(&td_contested_lock); 645 ts->ts_owner = NULL; 646 LIST_REMOVE(ts, ts_link); 647 mtx_unlock_spin(&td_contested_lock); 648 mtx_unlock_spin(&tc->tc_lock); 649 650 /* 651 * Adjust the priority of curthread based on other contested 652 * locks it owns. Don't lower the priority below the base 653 * priority however. 654 */ 655 td = curthread; 656 pri = PRI_MAX; 657 mtx_lock_spin(&sched_lock); 658 mtx_lock_spin(&td_contested_lock); 659 LIST_FOREACH(ts, &td->td_contested, ts_link) { 660 cp = TAILQ_FIRST(&ts->ts_blocked)->td_priority; 661 if (cp < pri) 662 pri = cp; 663 } 664 mtx_unlock_spin(&td_contested_lock); 665 if (pri > td->td_base_pri) 666 pri = td->td_base_pri; 667 td->td_priority = pri; 668 669 /* 670 * Wake up all the pending threads. If a thread is not blocked 671 * on a lock, then it is currently executing on another CPU in 672 * turnstile_wait(). Set a flag to force it to try to acquire 673 * the lock again instead of blocking. 674 */ 675 while (!TAILQ_EMPTY(&pending_threads)) { 676 td = TAILQ_FIRST(&pending_threads); 677 TAILQ_REMOVE(&pending_threads, td, td_lockq); 678 MPASS(td->td_proc->p_magic == P_MAGIC); 679 if (TD_ON_LOCK(td)) { 680 td->td_blocked = NULL; 681 td->td_lockname = NULL; 682 TD_CLR_LOCK(td); 683 MPASS(TD_CAN_RUN(td)); 684 setrunqueue(td); 685 } else { 686 td->td_flags |= TDF_TSNOBLOCK; 687 MPASS(TD_IS_RUNNING(td)); 688 } 689 } 690 mtx_unlock_spin(&sched_lock); 691} 692 693/* 694 * Return the first thread in a turnstile. 695 */ 696struct thread * 697turnstile_head(struct turnstile *ts) 698{ 699#ifdef INVARIANTS 700 struct turnstile_chain *tc; 701 702 MPASS(ts != NULL); 703 tc = TC_LOOKUP(ts->ts_lockobj); 704 mtx_assert(&tc->tc_lock, MA_OWNED); 705#endif 706 return (TAILQ_FIRST(&ts->ts_blocked)); 707} 708 709/* 710 * Returns true if a turnstile is empty. 711 */ 712int 713turnstile_empty(struct turnstile *ts) 714{ 715#ifdef INVARIANTS 716 struct turnstile_chain *tc; 717 718 MPASS(ts != NULL); 719 tc = TC_LOOKUP(ts->ts_lockobj); 720 mtx_assert(&tc->tc_lock, MA_OWNED); 721#endif 722 return (TAILQ_EMPTY(&ts->ts_blocked)); 723} 724