subr_turnstile.c revision 126884
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 <sys/cdefs.h> 60__FBSDID("$FreeBSD: head/sys/kern/subr_turnstile.c 126884 2004-03-12 19:05:46Z jhb $"); 61 62#include <sys/param.h> 63#include <sys/systm.h> 64#include <sys/kernel.h> 65#include <sys/ktr.h> 66#include <sys/lock.h> 67#include <sys/malloc.h> 68#include <sys/mutex.h> 69#include <sys/proc.h> 70#include <sys/queue.h> 71#include <sys/resourcevar.h> 72#include <sys/turnstile.h> 73#include <sys/sched.h> 74 75/* 76 * Constants for the hash table of turnstile chains. TC_SHIFT is a magic 77 * number chosen because the sleep queue's use the same value for the 78 * shift. Basically, we ignore the lower 8 bits of the address. 79 * TC_TABLESIZE must be a power of two for TC_MASK to work properly. 80 */ 81#define TC_TABLESIZE 128 /* Must be power of 2. */ 82#define TC_MASK (TC_TABLESIZE - 1) 83#define TC_SHIFT 8 84#define TC_HASH(lock) (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK) 85#define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)] 86 87/* 88 * There are three different lists of turnstiles as follows. The list 89 * connected by ts_link entries is a per-thread list of all the turnstiles 90 * attached to locks that we own. This is used to fixup our priority when 91 * a lock is released. The other two lists use the ts_hash entries. The 92 * first of these two is the turnstile chain list that a turnstile is on 93 * when it is attached to a lock. The second list to use ts_hash is the 94 * free list hung off of a turnstile that is attached to a lock. 95 * 96 * Each turnstile contains two lists of threads. The ts_blocked list is 97 * a linked list of threads blocked on the turnstile's lock. The 98 * ts_pending list is a linked list of threads previously awakened by 99 * turnstile_signal() or turnstile_wait() that are waiting to be put on 100 * the run queue. 101 * 102 * Locking key: 103 * c - turnstile chain lock 104 * q - td_contested lock 105 */ 106struct turnstile { 107 TAILQ_HEAD(, thread) ts_blocked; /* (c + q) Blocked threads. */ 108 TAILQ_HEAD(, thread) ts_pending; /* (c) Pending threads. */ 109 LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */ 110 LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */ 111 LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */ 112 struct lock_object *ts_lockobj; /* (c) Lock we reference. */ 113 struct thread *ts_owner; /* (c + q) Who owns the lock. */ 114}; 115 116struct turnstile_chain { 117 LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */ 118 struct mtx tc_lock; /* Spin lock for this chain. */ 119}; 120 121static struct mtx td_contested_lock; 122static struct turnstile_chain turnstile_chains[TC_TABLESIZE]; 123 124MALLOC_DEFINE(M_TURNSTILE, "turnstiles", "turnstiles"); 125 126/* 127 * Prototypes for non-exported routines. 128 */ 129static void init_turnstile0(void *dummy); 130static void propagate_priority(struct thread *); 131static void turnstile_setowner(struct turnstile *ts, struct thread *owner); 132 133/* 134 * Walks the chain of turnstiles and their owners to propagate the priority 135 * of the thread being blocked to all the threads holding locks that have to 136 * release their locks before this thread can run again. 137 */ 138static void 139propagate_priority(struct thread *td) 140{ 141 struct turnstile_chain *tc; 142 struct turnstile *ts; 143 struct thread *td1; 144 int pri; 145 146 mtx_assert(&sched_lock, MA_OWNED); 147 pri = td->td_priority; 148 ts = td->td_blocked; 149 for (;;) { 150 td = ts->ts_owner; 151 152 if (td == NULL) { 153 /* 154 * This really isn't quite right. Really 155 * ought to bump priority of thread that 156 * next acquires the lock. 157 */ 158 return; 159 } 160 161 MPASS(td->td_proc != NULL); 162 MPASS(td->td_proc->p_magic == P_MAGIC); 163 164 /* 165 * XXX: The owner of a turnstile can be stale if it is the 166 * first thread to grab a slock of a sx lock. In that case 167 * it is possible for us to be at SSLEEP or some other 168 * weird state. We should probably just return if the state 169 * isn't SRUN or SLOCK. 170 */ 171 KASSERT(!TD_IS_SLEEPING(td), 172 ("sleeping thread (pid %d) owns a non-sleepable lock", 173 td->td_proc->p_pid)); 174 175 /* 176 * If this thread already has higher priority than the 177 * thread that is being blocked, we are finished. 178 */ 179 if (td->td_priority <= pri) 180 return; 181 182 /* 183 * If lock holder is actually running, just bump priority. 184 */ 185 if (TD_IS_RUNNING(td)) { 186 td->td_priority = pri; 187 return; 188 } 189 190#ifndef SMP 191 /* 192 * For UP, we check to see if td is curthread (this shouldn't 193 * ever happen however as it would mean we are in a deadlock.) 194 */ 195 KASSERT(td != curthread, ("Deadlock detected")); 196#endif 197 198 /* 199 * If on run queue move to new run queue, and quit. 200 * XXXKSE this gets a lot more complicated under threads 201 * but try anyhow. 202 */ 203 if (TD_ON_RUNQ(td)) { 204 MPASS(td->td_blocked == NULL); 205 sched_prio(td, pri); 206 return; 207 } 208 209 /* 210 * Bump this thread's priority. 211 */ 212 td->td_priority = pri; 213 214 /* 215 * If we aren't blocked on a lock, we should be. 216 */ 217 KASSERT(TD_ON_LOCK(td), ( 218 "process %d(%s):%d holds %s but isn't blocked on a lock\n", 219 td->td_proc->p_pid, td->td_proc->p_comm, td->td_state, 220 ts->ts_lockobj->lo_name)); 221 222 /* 223 * Pick up the lock that td is blocked on. 224 */ 225 ts = td->td_blocked; 226 MPASS(ts != NULL); 227 tc = TC_LOOKUP(ts->ts_lockobj); 228 mtx_lock_spin(&tc->tc_lock); 229 230 /* 231 * This thread may not be blocked on this turnstile anymore 232 * but instead might already be woken up on another CPU 233 * that is waiting on sched_lock in turnstile_unpend() to 234 * finish waking this thread up. We can detect this case 235 * by checking to see if this thread has been given a 236 * turnstile by either turnstile_signal() or 237 * turnstile_wakeup(). In this case, treat the thread as 238 * if it was already running. 239 */ 240 if (td->td_turnstile != NULL) { 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 thread0.td_turnstile = NULL; 304} 305 306static void 307init_turnstile0(void *dummy) 308{ 309 310 thread0.td_turnstile = turnstile_alloc(); 311} 312SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL); 313 314/* 315 * Set the owner of the lock this turnstile is attached to. 316 */ 317static void 318turnstile_setowner(struct turnstile *ts, struct thread *owner) 319{ 320 321 mtx_assert(&td_contested_lock, MA_OWNED); 322 MPASS(owner->td_proc->p_magic == P_MAGIC); 323 MPASS(ts->ts_owner == NULL); 324 ts->ts_owner = owner; 325 LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link); 326} 327 328/* 329 * Malloc a turnstile for a new thread, initialize it and return it. 330 */ 331struct turnstile * 332turnstile_alloc(void) 333{ 334 struct turnstile *ts; 335 336 ts = malloc(sizeof(struct turnstile), M_TURNSTILE, M_WAITOK | M_ZERO); 337 TAILQ_INIT(&ts->ts_blocked); 338 TAILQ_INIT(&ts->ts_pending); 339 LIST_INIT(&ts->ts_free); 340 return (ts); 341} 342 343/* 344 * Free a turnstile when a thread is destroyed. 345 */ 346void 347turnstile_free(struct turnstile *ts) 348{ 349 350 MPASS(ts != NULL); 351 MPASS(TAILQ_EMPTY(&ts->ts_blocked)); 352 MPASS(TAILQ_EMPTY(&ts->ts_pending)); 353 free(ts, M_TURNSTILE); 354} 355 356/* 357 * Look up the turnstile for a lock in the hash table locking the associated 358 * turnstile chain along the way. Return with the turnstile chain locked. 359 * If no turnstile is found in the hash table, NULL is returned. 360 */ 361struct turnstile * 362turnstile_lookup(struct lock_object *lock) 363{ 364 struct turnstile_chain *tc; 365 struct turnstile *ts; 366 367 tc = TC_LOOKUP(lock); 368 mtx_lock_spin(&tc->tc_lock); 369 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 370 if (ts->ts_lockobj == lock) 371 return (ts); 372 return (NULL); 373} 374 375/* 376 * Unlock the turnstile chain associated with a given lock. 377 */ 378void 379turnstile_release(struct lock_object *lock) 380{ 381 struct turnstile_chain *tc; 382 383 tc = TC_LOOKUP(lock); 384 mtx_unlock_spin(&tc->tc_lock); 385} 386 387/* 388 * Take ownership of a turnstile and adjust the priority of the new 389 * owner appropriately. 390 */ 391void 392turnstile_claim(struct turnstile *ts) 393{ 394 struct turnstile_chain *tc; 395 struct thread *td, *owner; 396 397 tc = TC_LOOKUP(ts->ts_lockobj); 398 mtx_assert(&tc->tc_lock, MA_OWNED); 399 400 owner = curthread; 401 mtx_lock_spin(&td_contested_lock); 402 turnstile_setowner(ts, owner); 403 mtx_unlock_spin(&td_contested_lock); 404 405 td = TAILQ_FIRST(&ts->ts_blocked); 406 MPASS(td != NULL); 407 MPASS(td->td_proc->p_magic == P_MAGIC); 408 mtx_unlock_spin(&tc->tc_lock); 409 410 /* 411 * Update the priority of the new owner if needed. 412 */ 413 mtx_lock_spin(&sched_lock); 414 if (td->td_priority < owner->td_priority) 415 owner->td_priority = td->td_priority; 416 mtx_unlock_spin(&sched_lock); 417} 418 419/* 420 * Block the current thread on the turnstile ts. This function will context 421 * switch and not return until this thread has been woken back up. This 422 * function must be called with the appropriate turnstile chain locked and 423 * will return with it unlocked. 424 */ 425void 426turnstile_wait(struct turnstile *ts, struct lock_object *lock, 427 struct thread *owner) 428{ 429 struct turnstile_chain *tc; 430 struct thread *td, *td1; 431 432 td = curthread; 433 tc = TC_LOOKUP(lock); 434 mtx_assert(&tc->tc_lock, MA_OWNED); 435 MPASS(td->td_turnstile != NULL); 436 MPASS(owner != NULL); 437 MPASS(owner->td_proc->p_magic == P_MAGIC); 438 439 /* If the passed in turnstile is NULL, use this thread's turnstile. */ 440 if (ts == NULL) { 441 ts = td->td_turnstile; 442 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash); 443 KASSERT(TAILQ_EMPTY(&ts->ts_pending), 444 ("thread's turnstile has pending threads")); 445 KASSERT(TAILQ_EMPTY(&ts->ts_blocked), 446 ("thread's turnstile has a non-empty queue")); 447 KASSERT(LIST_EMPTY(&ts->ts_free), 448 ("thread's turnstile has a non-empty free list")); 449 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer")); 450 ts->ts_lockobj = lock; 451 mtx_lock_spin(&td_contested_lock); 452 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq); 453 turnstile_setowner(ts, owner); 454 mtx_unlock_spin(&td_contested_lock); 455 } else { 456 TAILQ_FOREACH(td1, &ts->ts_blocked, td_lockq) 457 if (td1->td_priority > td->td_priority) 458 break; 459 mtx_lock_spin(&td_contested_lock); 460 if (td1 != NULL) 461 TAILQ_INSERT_BEFORE(td1, td, td_lockq); 462 else 463 TAILQ_INSERT_TAIL(&ts->ts_blocked, td, td_lockq); 464 mtx_unlock_spin(&td_contested_lock); 465 MPASS(td->td_turnstile != NULL); 466 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash); 467 MPASS(owner == ts->ts_owner); 468 } 469 td->td_turnstile = NULL; 470 mtx_unlock_spin(&tc->tc_lock); 471 472 mtx_lock_spin(&sched_lock); 473 /* 474 * Handle race condition where a thread on another CPU that owns 475 * lock 'lock' could have woken us in between us dropping the 476 * turnstile chain lock and acquiring the sched_lock. 477 */ 478 if (td->td_flags & TDF_TSNOBLOCK) { 479 td->td_flags &= ~TDF_TSNOBLOCK; 480 mtx_unlock_spin(&sched_lock); 481 return; 482 } 483 484#ifdef notyet 485 /* 486 * If we're borrowing an interrupted thread's VM context, we 487 * must clean up before going to sleep. 488 */ 489 if (td->td_ithd != NULL) { 490 struct ithd *it = td->td_ithd; 491 492 if (it->it_interrupted) { 493 if (LOCK_LOG_TEST(lock, 0)) 494 CTR3(KTR_LOCK, "%s: %p interrupted %p", 495 __func__, it, it->it_interrupted); 496 intr_thd_fixup(it); 497 } 498 } 499#endif 500 501 /* Save who we are blocked on and switch. */ 502 td->td_blocked = ts; 503 td->td_lockname = lock->lo_name; 504 TD_SET_LOCK(td); 505 propagate_priority(td); 506 507 if (LOCK_LOG_TEST(lock, 0)) 508 CTR4(KTR_LOCK, "%s: td %p blocked on [%p] %s", __func__, td, 509 lock, lock->lo_name); 510 511 mi_switch(SW_VOL); 512 513 if (LOCK_LOG_TEST(lock, 0)) 514 CTR4(KTR_LOCK, "%s: td %p free from blocked on [%p] %s", 515 __func__, td, lock, lock->lo_name); 516 517 mtx_unlock_spin(&sched_lock); 518} 519 520/* 521 * Pick the highest priority thread on this turnstile and put it on the 522 * pending list. This must be called with the turnstile chain locked. 523 */ 524int 525turnstile_signal(struct turnstile *ts) 526{ 527 struct turnstile_chain *tc; 528 struct thread *td; 529 int empty; 530 531 MPASS(ts != NULL); 532 MPASS(curthread->td_proc->p_magic == P_MAGIC); 533 MPASS(ts->ts_owner == curthread); 534 tc = TC_LOOKUP(ts->ts_lockobj); 535 mtx_assert(&tc->tc_lock, MA_OWNED); 536 537 /* 538 * Pick the highest priority thread blocked on this lock and 539 * move it to the pending list. 540 */ 541 td = TAILQ_FIRST(&ts->ts_blocked); 542 MPASS(td->td_proc->p_magic == P_MAGIC); 543 mtx_lock_spin(&td_contested_lock); 544 TAILQ_REMOVE(&ts->ts_blocked, td, td_lockq); 545 mtx_unlock_spin(&td_contested_lock); 546 TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq); 547 548 /* 549 * If the turnstile is now empty, remove it from its chain and 550 * give it to the about-to-be-woken thread. Otherwise take a 551 * turnstile from the free list and give it to the thread. 552 */ 553 empty = TAILQ_EMPTY(&ts->ts_blocked); 554 if (empty) 555 MPASS(LIST_EMPTY(&ts->ts_free)); 556 else 557 ts = LIST_FIRST(&ts->ts_free); 558 MPASS(ts != NULL); 559 LIST_REMOVE(ts, ts_hash); 560 td->td_turnstile = ts; 561 562 return (empty); 563} 564 565/* 566 * Put all blocked threads on the pending list. This must be called with 567 * the turnstile chain locked. 568 */ 569void 570turnstile_wakeup(struct turnstile *ts) 571{ 572 struct turnstile_chain *tc; 573 struct turnstile *ts1; 574 struct thread *td; 575 576 MPASS(ts != NULL); 577 MPASS(curthread->td_proc->p_magic == P_MAGIC); 578 MPASS(ts->ts_owner == curthread); 579 tc = TC_LOOKUP(ts->ts_lockobj); 580 mtx_assert(&tc->tc_lock, MA_OWNED); 581 582 /* 583 * Transfer the blocked list to the pending list. 584 */ 585 mtx_lock_spin(&td_contested_lock); 586 TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked, td_lockq); 587 mtx_unlock_spin(&td_contested_lock); 588 589 /* 590 * Give a turnstile to each thread. The last thread gets 591 * this turnstile. 592 */ 593 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) { 594 if (LIST_EMPTY(&ts->ts_free)) { 595 MPASS(TAILQ_NEXT(td, td_lockq) == NULL); 596 ts1 = ts; 597 } else 598 ts1 = LIST_FIRST(&ts->ts_free); 599 MPASS(ts1 != NULL); 600 LIST_REMOVE(ts1, ts_hash); 601 td->td_turnstile = ts1; 602 } 603} 604 605/* 606 * Wakeup all threads on the pending list and adjust the priority of the 607 * current thread appropriately. This must be called with the turnstile 608 * chain locked. 609 */ 610void 611turnstile_unpend(struct turnstile *ts) 612{ 613 TAILQ_HEAD( ,thread) pending_threads; 614 struct turnstile_chain *tc; 615 struct thread *td; 616 int cp, pri; 617 618 MPASS(ts != NULL); 619 MPASS(ts->ts_owner == curthread); 620 tc = TC_LOOKUP(ts->ts_lockobj); 621 mtx_assert(&tc->tc_lock, MA_OWNED); 622 MPASS(!TAILQ_EMPTY(&ts->ts_pending)); 623 624 /* 625 * Move the list of pending threads out of the turnstile and 626 * into a local variable. 627 */ 628 TAILQ_INIT(&pending_threads); 629 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq); 630#ifdef INVARIANTS 631 if (TAILQ_EMPTY(&ts->ts_blocked)) 632 ts->ts_lockobj = NULL; 633#endif 634 635 /* 636 * Remove the turnstile from this thread's list of contested locks 637 * since this thread doesn't own it anymore. New threads will 638 * not be blocking on the turnstile until it is claimed by a new 639 * owner. 640 */ 641 mtx_lock_spin(&td_contested_lock); 642 ts->ts_owner = NULL; 643 LIST_REMOVE(ts, ts_link); 644 mtx_unlock_spin(&td_contested_lock); 645 mtx_unlock_spin(&tc->tc_lock); 646 647 /* 648 * Adjust the priority of curthread based on other contested 649 * locks it owns. Don't lower the priority below the base 650 * priority however. 651 */ 652 td = curthread; 653 pri = PRI_MAX; 654 mtx_lock_spin(&sched_lock); 655 mtx_lock_spin(&td_contested_lock); 656 LIST_FOREACH(ts, &td->td_contested, ts_link) { 657 cp = TAILQ_FIRST(&ts->ts_blocked)->td_priority; 658 if (cp < pri) 659 pri = cp; 660 } 661 mtx_unlock_spin(&td_contested_lock); 662 if (pri > td->td_base_pri) 663 pri = td->td_base_pri; 664 td->td_priority = pri; 665 666 /* 667 * Wake up all the pending threads. If a thread is not blocked 668 * on a lock, then it is currently executing on another CPU in 669 * turnstile_wait() or sitting on a run queue waiting to resume 670 * in turnstile_wait(). Set a flag to force it to try to acquire 671 * the lock again instead of blocking. 672 */ 673 while (!TAILQ_EMPTY(&pending_threads)) { 674 td = TAILQ_FIRST(&pending_threads); 675 TAILQ_REMOVE(&pending_threads, td, td_lockq); 676 MPASS(td->td_proc->p_magic == P_MAGIC); 677 if (TD_ON_LOCK(td)) { 678 td->td_blocked = NULL; 679 td->td_lockname = NULL; 680 TD_CLR_LOCK(td); 681 MPASS(TD_CAN_RUN(td)); 682 setrunqueue(td); 683 } else { 684 td->td_flags |= TDF_TSNOBLOCK; 685 MPASS(TD_IS_RUNNING(td) || TD_ON_RUNQ(td)); 686 } 687 } 688 mtx_unlock_spin(&sched_lock); 689} 690 691/* 692 * Return the first thread in a turnstile. 693 */ 694struct thread * 695turnstile_head(struct turnstile *ts) 696{ 697#ifdef INVARIANTS 698 struct turnstile_chain *tc; 699 700 MPASS(ts != NULL); 701 tc = TC_LOOKUP(ts->ts_lockobj); 702 mtx_assert(&tc->tc_lock, MA_OWNED); 703#endif 704 return (TAILQ_FIRST(&ts->ts_blocked)); 705} 706 707/* 708 * Returns true if a turnstile is empty. 709 */ 710int 711turnstile_empty(struct turnstile *ts) 712{ 713#ifdef INVARIANTS 714 struct turnstile_chain *tc; 715 716 MPASS(ts != NULL); 717 tc = TC_LOOKUP(ts->ts_lockobj); 718 mtx_assert(&tc->tc_lock, MA_OWNED); 719#endif 720 return (TAILQ_EMPTY(&ts->ts_blocked)); 721} 722