Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_turnstile.c
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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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