subr_turnstile.c revision 161337
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 161337 2006-08-15 18:29:01Z jhb $"); 61 62#include "opt_ddb.h" 63#include "opt_turnstile_profiling.h" 64 65#include <sys/param.h> 66#include <sys/systm.h> 67#include <sys/kernel.h> 68#include <sys/ktr.h> 69#include <sys/lock.h> 70#include <sys/malloc.h> 71#include <sys/mutex.h> 72#include <sys/proc.h> 73#include <sys/queue.h> 74#include <sys/sched.h> 75#include <sys/sysctl.h> 76#include <sys/turnstile.h> 77 78#ifdef DDB 79#include <sys/kdb.h> 80#include <ddb/ddb.h> 81#include <sys/lockmgr.h> 82#include <sys/sx.h> 83#endif 84 85/* 86 * Constants for the hash table of turnstile chains. TC_SHIFT is a magic 87 * number chosen because the sleep queue's use the same value for the 88 * shift. Basically, we ignore the lower 8 bits of the address. 89 * TC_TABLESIZE must be a power of two for TC_MASK to work properly. 90 */ 91#define TC_TABLESIZE 128 /* Must be power of 2. */ 92#define TC_MASK (TC_TABLESIZE - 1) 93#define TC_SHIFT 8 94#define TC_HASH(lock) (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK) 95#define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)] 96 97/* 98 * There are three different lists of turnstiles as follows. The list 99 * connected by ts_link entries is a per-thread list of all the turnstiles 100 * attached to locks that we own. This is used to fixup our priority when 101 * a lock is released. The other two lists use the ts_hash entries. The 102 * first of these two is the turnstile chain list that a turnstile is on 103 * when it is attached to a lock. The second list to use ts_hash is the 104 * free list hung off of a turnstile that is attached to a lock. 105 * 106 * Each turnstile contains three lists of threads. The two ts_blocked lists 107 * are linked list of threads blocked on the turnstile's lock. One list is 108 * for exclusive waiters, and the other is for shared waiters. The 109 * ts_pending list is a linked list of threads previously awakened by 110 * turnstile_signal() or turnstile_wait() that are waiting to be put on 111 * the run queue. 112 * 113 * Locking key: 114 * c - turnstile chain lock 115 * q - td_contested lock 116 */ 117struct turnstile { 118 struct threadqueue ts_blocked[2]; /* (c + q) Blocked threads. */ 119 struct threadqueue ts_pending; /* (c) Pending threads. */ 120 LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */ 121 LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */ 122 LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */ 123 struct lock_object *ts_lockobj; /* (c) Lock we reference. */ 124 struct thread *ts_owner; /* (c + q) Who owns the lock. */ 125}; 126 127struct turnstile_chain { 128 LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */ 129 struct mtx tc_lock; /* Spin lock for this chain. */ 130#ifdef TURNSTILE_PROFILING 131 u_int tc_depth; /* Length of tc_queues. */ 132 u_int tc_max_depth; /* Max length of tc_queues. */ 133#endif 134}; 135 136#ifdef TURNSTILE_PROFILING 137u_int turnstile_max_depth; 138SYSCTL_NODE(_debug, OID_AUTO, turnstile, CTLFLAG_RD, 0, "turnstile profiling"); 139SYSCTL_NODE(_debug_turnstile, OID_AUTO, chains, CTLFLAG_RD, 0, 140 "turnstile chain stats"); 141SYSCTL_UINT(_debug_turnstile, OID_AUTO, max_depth, CTLFLAG_RD, 142 &turnstile_max_depth, 0, "maxmimum depth achieved of a single chain"); 143#endif 144static struct mtx td_contested_lock; 145static struct turnstile_chain turnstile_chains[TC_TABLESIZE]; 146 147static MALLOC_DEFINE(M_TURNSTILE, "turnstiles", "turnstiles"); 148 149/* 150 * Prototypes for non-exported routines. 151 */ 152static void init_turnstile0(void *dummy); 153#ifdef TURNSTILE_PROFILING 154static void init_turnstile_profiling(void *arg); 155#endif 156static void propagate_priority(struct thread *td); 157static int turnstile_adjust_thread(struct turnstile *ts, 158 struct thread *td); 159static struct thread *turnstile_first_waiter(struct turnstile *ts); 160static void turnstile_setowner(struct turnstile *ts, struct thread *owner); 161 162/* 163 * Walks the chain of turnstiles and their owners to propagate the priority 164 * of the thread being blocked to all the threads holding locks that have to 165 * release their locks before this thread can run again. 166 */ 167static void 168propagate_priority(struct thread *td) 169{ 170 struct turnstile_chain *tc; 171 struct turnstile *ts; 172 int pri; 173 174 mtx_assert(&sched_lock, MA_OWNED); 175 pri = td->td_priority; 176 ts = td->td_blocked; 177 for (;;) { 178 td = ts->ts_owner; 179 180 if (td == NULL) { 181 /* 182 * This might be a read lock with no owner. There's 183 * not much we can do, so just bail. 184 */ 185 return; 186 } 187 188 MPASS(td->td_proc != NULL); 189 MPASS(td->td_proc->p_magic == P_MAGIC); 190 191 /* 192 * If the thread is asleep, then we are probably about 193 * to deadlock. To make debugging this easier, just 194 * panic and tell the user which thread misbehaved so 195 * they can hopefully get a stack trace from the truly 196 * misbehaving thread. 197 */ 198 if (TD_IS_SLEEPING(td)) { 199 printf( 200 "Sleeping thread (tid %d, pid %d) owns a non-sleepable lock\n", 201 td->td_tid, td->td_proc->p_pid); 202#ifdef DDB 203 db_trace_thread(td, -1); 204#endif 205 panic("sleeping thread"); 206 } 207 208 /* 209 * If this thread already has higher priority than the 210 * thread that is being blocked, we are finished. 211 */ 212 if (td->td_priority <= pri) 213 return; 214 215 /* 216 * Bump this thread's priority. 217 */ 218 sched_lend_prio(td, pri); 219 220 /* 221 * If lock holder is actually running or on the run queue 222 * then we are done. 223 */ 224 if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) { 225 MPASS(td->td_blocked == NULL); 226 return; 227 } 228 229#ifndef SMP 230 /* 231 * For UP, we check to see if td is curthread (this shouldn't 232 * ever happen however as it would mean we are in a deadlock.) 233 */ 234 KASSERT(td != curthread, ("Deadlock detected")); 235#endif 236 237 /* 238 * If we aren't blocked on a lock, we should be. 239 */ 240 KASSERT(TD_ON_LOCK(td), ( 241 "thread %d(%s):%d holds %s but isn't blocked on a lock\n", 242 td->td_tid, td->td_proc->p_comm, td->td_state, 243 ts->ts_lockobj->lo_name)); 244 245 /* 246 * Pick up the lock that td is blocked on. 247 */ 248 ts = td->td_blocked; 249 MPASS(ts != NULL); 250 tc = TC_LOOKUP(ts->ts_lockobj); 251 mtx_lock_spin(&tc->tc_lock); 252 253 /* Resort td on the list if needed. */ 254 if (!turnstile_adjust_thread(ts, td)) { 255 mtx_unlock_spin(&tc->tc_lock); 256 return; 257 } 258 mtx_unlock_spin(&tc->tc_lock); 259 } 260} 261 262/* 263 * Adjust the thread's position on a turnstile after its priority has been 264 * changed. 265 */ 266static int 267turnstile_adjust_thread(struct turnstile *ts, struct thread *td) 268{ 269 struct turnstile_chain *tc; 270 struct thread *td1, *td2; 271 int queue; 272 273 mtx_assert(&sched_lock, MA_OWNED); 274 MPASS(TD_ON_LOCK(td)); 275 276 /* 277 * This thread may not be blocked on this turnstile anymore 278 * but instead might already be woken up on another CPU 279 * that is waiting on sched_lock in turnstile_unpend() to 280 * finish waking this thread up. We can detect this case 281 * by checking to see if this thread has been given a 282 * turnstile by either turnstile_signal() or 283 * turnstile_broadcast(). In this case, treat the thread as 284 * if it was already running. 285 */ 286 if (td->td_turnstile != NULL) 287 return (0); 288 289 /* 290 * Check if the thread needs to be moved on the blocked chain. 291 * It needs to be moved if either its priority is lower than 292 * the previous thread or higher than the next thread. 293 */ 294 tc = TC_LOOKUP(ts->ts_lockobj); 295 mtx_assert(&tc->tc_lock, MA_OWNED); 296 td1 = TAILQ_PREV(td, threadqueue, td_lockq); 297 td2 = TAILQ_NEXT(td, td_lockq); 298 if ((td1 != NULL && td->td_priority < td1->td_priority) || 299 (td2 != NULL && td->td_priority > td2->td_priority)) { 300 301 /* 302 * Remove thread from blocked chain and determine where 303 * it should be moved to. 304 */ 305 queue = td->td_tsqueue; 306 MPASS(queue == TS_EXCLUSIVE_QUEUE || queue == TS_SHARED_QUEUE); 307 mtx_lock_spin(&td_contested_lock); 308 TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq); 309 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) { 310 MPASS(td1->td_proc->p_magic == P_MAGIC); 311 if (td1->td_priority > td->td_priority) 312 break; 313 } 314 315 if (td1 == NULL) 316 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); 317 else 318 TAILQ_INSERT_BEFORE(td1, td, td_lockq); 319 mtx_unlock_spin(&td_contested_lock); 320 if (td1 == NULL) 321 CTR3(KTR_LOCK, 322 "turnstile_adjust_thread: td %d put at tail on [%p] %s", 323 td->td_tid, ts->ts_lockobj, ts->ts_lockobj->lo_name); 324 else 325 CTR4(KTR_LOCK, 326 "turnstile_adjust_thread: td %d moved before %d on [%p] %s", 327 td->td_tid, td1->td_tid, ts->ts_lockobj, 328 ts->ts_lockobj->lo_name); 329 } 330 return (1); 331} 332 333/* 334 * Early initialization of turnstiles. This is not done via a SYSINIT() 335 * since this needs to be initialized very early when mutexes are first 336 * initialized. 337 */ 338void 339init_turnstiles(void) 340{ 341 int i; 342 343 for (i = 0; i < TC_TABLESIZE; i++) { 344 LIST_INIT(&turnstile_chains[i].tc_turnstiles); 345 mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain", 346 NULL, MTX_SPIN); 347 } 348 mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN); 349 LIST_INIT(&thread0.td_contested); 350 thread0.td_turnstile = NULL; 351} 352 353#ifdef TURNSTILE_PROFILING 354static void 355init_turnstile_profiling(void *arg) 356{ 357 struct sysctl_oid *chain_oid; 358 char chain_name[10]; 359 int i; 360 361 for (i = 0; i < TC_TABLESIZE; i++) { 362 snprintf(chain_name, sizeof(chain_name), "%d", i); 363 chain_oid = SYSCTL_ADD_NODE(NULL, 364 SYSCTL_STATIC_CHILDREN(_debug_turnstile_chains), OID_AUTO, 365 chain_name, CTLFLAG_RD, NULL, "turnstile chain stats"); 366 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO, 367 "depth", CTLFLAG_RD, &turnstile_chains[i].tc_depth, 0, 368 NULL); 369 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO, 370 "max_depth", CTLFLAG_RD, &turnstile_chains[i].tc_max_depth, 371 0, NULL); 372 } 373} 374SYSINIT(turnstile_profiling, SI_SUB_LOCK, SI_ORDER_ANY, 375 init_turnstile_profiling, NULL); 376#endif 377 378static void 379init_turnstile0(void *dummy) 380{ 381 382 thread0.td_turnstile = turnstile_alloc(); 383} 384SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL); 385 386/* 387 * Update a thread on the turnstile list after it's priority has been changed. 388 * The old priority is passed in as an argument. 389 */ 390void 391turnstile_adjust(struct thread *td, u_char oldpri) 392{ 393 struct turnstile_chain *tc; 394 struct turnstile *ts; 395 396 mtx_assert(&sched_lock, MA_OWNED); 397 MPASS(TD_ON_LOCK(td)); 398 399 /* 400 * Pick up the lock that td is blocked on. 401 */ 402 ts = td->td_blocked; 403 MPASS(ts != NULL); 404 tc = TC_LOOKUP(ts->ts_lockobj); 405 mtx_lock_spin(&tc->tc_lock); 406 407 /* Resort the turnstile on the list. */ 408 if (!turnstile_adjust_thread(ts, td)) { 409 mtx_unlock_spin(&tc->tc_lock); 410 return; 411 } 412 413 /* 414 * If our priority was lowered and we are at the head of the 415 * turnstile, then propagate our new priority up the chain. 416 * Note that we currently don't try to revoke lent priorities 417 * when our priority goes up. 418 */ 419 MPASS(td->td_tsqueue == TS_EXCLUSIVE_QUEUE || 420 td->td_tsqueue == TS_SHARED_QUEUE); 421 if (td == TAILQ_FIRST(&ts->ts_blocked[td->td_tsqueue]) && 422 td->td_priority < oldpri) { 423 mtx_unlock_spin(&tc->tc_lock); 424 propagate_priority(td); 425 } else 426 mtx_unlock_spin(&tc->tc_lock); 427} 428 429/* 430 * Set the owner of the lock this turnstile is attached to. 431 */ 432static void 433turnstile_setowner(struct turnstile *ts, struct thread *owner) 434{ 435 436 mtx_assert(&td_contested_lock, MA_OWNED); 437 MPASS(ts->ts_owner == NULL); 438 439 /* A shared lock might not have an owner. */ 440 if (owner == NULL) 441 return; 442 443 MPASS(owner->td_proc->p_magic == P_MAGIC); 444 ts->ts_owner = owner; 445 LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link); 446} 447 448/* 449 * Malloc a turnstile for a new thread, initialize it and return it. 450 */ 451struct turnstile * 452turnstile_alloc(void) 453{ 454 struct turnstile *ts; 455 456 ts = malloc(sizeof(struct turnstile), M_TURNSTILE, M_WAITOK | M_ZERO); 457 TAILQ_INIT(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]); 458 TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]); 459 TAILQ_INIT(&ts->ts_pending); 460 LIST_INIT(&ts->ts_free); 461 return (ts); 462} 463 464/* 465 * Free a turnstile when a thread is destroyed. 466 */ 467void 468turnstile_free(struct turnstile *ts) 469{ 470 471 MPASS(ts != NULL); 472 MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE])); 473 MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])); 474 MPASS(TAILQ_EMPTY(&ts->ts_pending)); 475 free(ts, M_TURNSTILE); 476} 477 478/* 479 * Lock the turnstile chain associated with the specified lock. 480 */ 481void 482turnstile_lock(struct lock_object *lock) 483{ 484 struct turnstile_chain *tc; 485 486 tc = TC_LOOKUP(lock); 487 mtx_lock_spin(&tc->tc_lock); 488} 489 490/* 491 * Look up the turnstile for a lock in the hash table locking the associated 492 * turnstile chain along the way. If no turnstile is found in the hash 493 * table, NULL is returned. 494 */ 495struct turnstile * 496turnstile_lookup(struct lock_object *lock) 497{ 498 struct turnstile_chain *tc; 499 struct turnstile *ts; 500 501 tc = TC_LOOKUP(lock); 502 mtx_assert(&tc->tc_lock, MA_OWNED); 503 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 504 if (ts->ts_lockobj == lock) 505 return (ts); 506 return (NULL); 507} 508 509/* 510 * Unlock the turnstile chain associated with a given lock. 511 */ 512void 513turnstile_release(struct lock_object *lock) 514{ 515 struct turnstile_chain *tc; 516 517 tc = TC_LOOKUP(lock); 518 mtx_unlock_spin(&tc->tc_lock); 519} 520 521/* 522 * Return a pointer to the thread waiting on this turnstile with the 523 * most important priority or NULL if the turnstile has no waiters. 524 */ 525static struct thread * 526turnstile_first_waiter(struct turnstile *ts) 527{ 528 struct thread *std, *xtd; 529 530 std = TAILQ_FIRST(&ts->ts_blocked[TS_SHARED_QUEUE]); 531 xtd = TAILQ_FIRST(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]); 532 if (xtd == NULL || (std != NULL && std->td_priority < xtd->td_priority)) 533 return (std); 534 return (xtd); 535} 536 537/* 538 * Take ownership of a turnstile and adjust the priority of the new 539 * owner appropriately. 540 */ 541void 542turnstile_claim(struct lock_object *lock) 543{ 544 struct turnstile_chain *tc; 545 struct turnstile *ts; 546 struct thread *td, *owner; 547 548 tc = TC_LOOKUP(lock); 549 mtx_assert(&tc->tc_lock, MA_OWNED); 550 ts = turnstile_lookup(lock); 551 MPASS(ts != NULL); 552 553 owner = curthread; 554 mtx_lock_spin(&td_contested_lock); 555 turnstile_setowner(ts, owner); 556 mtx_unlock_spin(&td_contested_lock); 557 558 td = turnstile_first_waiter(ts); 559 MPASS(td != NULL); 560 MPASS(td->td_proc->p_magic == P_MAGIC); 561 mtx_unlock_spin(&tc->tc_lock); 562 563 /* 564 * Update the priority of the new owner if needed. 565 */ 566 mtx_lock_spin(&sched_lock); 567 if (td->td_priority < owner->td_priority) 568 sched_lend_prio(owner, td->td_priority); 569 mtx_unlock_spin(&sched_lock); 570} 571 572/* 573 * Block the current thread on the turnstile assicated with 'lock'. This 574 * function will context switch and not return until this thread has been 575 * woken back up. This function must be called with the appropriate 576 * turnstile chain locked and will return with it unlocked. 577 */ 578void 579turnstile_wait(struct lock_object *lock, struct thread *owner, int queue) 580{ 581 struct turnstile_chain *tc; 582 struct turnstile *ts; 583 struct thread *td, *td1; 584 585 td = curthread; 586 tc = TC_LOOKUP(lock); 587 mtx_assert(&tc->tc_lock, MA_OWNED); 588 MPASS(td->td_turnstile != NULL); 589 if (queue == TS_SHARED_QUEUE) 590 MPASS(owner != NULL); 591 if (owner) 592 MPASS(owner->td_proc->p_magic == P_MAGIC); 593 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 594 595 /* Look up the turnstile associated with the lock 'lock'. */ 596 ts = turnstile_lookup(lock); 597 598 /* 599 * If the lock does not already have a turnstile, use this thread's 600 * turnstile. Otherwise insert the current thread into the 601 * turnstile already in use by this lock. 602 */ 603 if (ts == NULL) { 604#ifdef TURNSTILE_PROFILING 605 tc->tc_depth++; 606 if (tc->tc_depth > tc->tc_max_depth) { 607 tc->tc_max_depth = tc->tc_depth; 608 if (tc->tc_max_depth > turnstile_max_depth) 609 turnstile_max_depth = tc->tc_max_depth; 610 } 611#endif 612 ts = td->td_turnstile; 613 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash); 614 KASSERT(TAILQ_EMPTY(&ts->ts_pending), 615 ("thread's turnstile has pending threads")); 616 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]), 617 ("thread's turnstile has exclusive waiters")); 618 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]), 619 ("thread's turnstile has shared waiters")); 620 KASSERT(LIST_EMPTY(&ts->ts_free), 621 ("thread's turnstile has a non-empty free list")); 622 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer")); 623 ts->ts_lockobj = lock; 624 mtx_lock_spin(&td_contested_lock); 625 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); 626 turnstile_setowner(ts, owner); 627 mtx_unlock_spin(&td_contested_lock); 628 } else { 629 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) 630 if (td1->td_priority > td->td_priority) 631 break; 632 mtx_lock_spin(&td_contested_lock); 633 if (td1 != NULL) 634 TAILQ_INSERT_BEFORE(td1, td, td_lockq); 635 else 636 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); 637 MPASS(owner == ts->ts_owner); 638 mtx_unlock_spin(&td_contested_lock); 639 MPASS(td->td_turnstile != NULL); 640 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash); 641 } 642 td->td_turnstile = NULL; 643 mtx_unlock_spin(&tc->tc_lock); 644 645 mtx_lock_spin(&sched_lock); 646 /* 647 * Handle race condition where a thread on another CPU that owns 648 * lock 'lock' could have woken us in between us dropping the 649 * turnstile chain lock and acquiring the sched_lock. 650 */ 651 if (td->td_flags & TDF_TSNOBLOCK) { 652 td->td_flags &= ~TDF_TSNOBLOCK; 653 mtx_unlock_spin(&sched_lock); 654 return; 655 } 656 657#ifdef notyet 658 /* 659 * If we're borrowing an interrupted thread's VM context, we 660 * must clean up before going to sleep. 661 */ 662 if (td->td_ithd != NULL) { 663 struct ithd *it = td->td_ithd; 664 665 if (it->it_interrupted) { 666 if (LOCK_LOG_TEST(lock, 0)) 667 CTR3(KTR_LOCK, "%s: %p interrupted %p", 668 __func__, it, it->it_interrupted); 669 intr_thd_fixup(it); 670 } 671 } 672#endif 673 674 /* Save who we are blocked on and switch. */ 675 td->td_tsqueue = queue; 676 td->td_blocked = ts; 677 td->td_lockname = lock->lo_name; 678 TD_SET_LOCK(td); 679 propagate_priority(td); 680 681 if (LOCK_LOG_TEST(lock, 0)) 682 CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__, 683 td->td_tid, lock, lock->lo_name); 684 685 mi_switch(SW_VOL, NULL); 686 687 if (LOCK_LOG_TEST(lock, 0)) 688 CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s", 689 __func__, td->td_tid, lock, lock->lo_name); 690 691 mtx_unlock_spin(&sched_lock); 692} 693 694/* 695 * Pick the highest priority thread on this turnstile and put it on the 696 * pending list. This must be called with the turnstile chain locked. 697 */ 698int 699turnstile_signal(struct turnstile *ts, int queue) 700{ 701 struct turnstile_chain *tc; 702 struct thread *td; 703 int empty; 704 705 MPASS(ts != NULL); 706 MPASS(curthread->td_proc->p_magic == P_MAGIC); 707 MPASS(ts->ts_owner == curthread || 708 (queue == TS_EXCLUSIVE_QUEUE && ts->ts_owner == NULL)); 709 tc = TC_LOOKUP(ts->ts_lockobj); 710 mtx_assert(&tc->tc_lock, MA_OWNED); 711 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 712 713 /* 714 * Pick the highest priority thread blocked on this lock and 715 * move it to the pending list. 716 */ 717 td = TAILQ_FIRST(&ts->ts_blocked[queue]); 718 MPASS(td->td_proc->p_magic == P_MAGIC); 719 mtx_lock_spin(&td_contested_lock); 720 TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq); 721 mtx_unlock_spin(&td_contested_lock); 722 TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq); 723 724 /* 725 * If the turnstile is now empty, remove it from its chain and 726 * give it to the about-to-be-woken thread. Otherwise take a 727 * turnstile from the free list and give it to the thread. 728 */ 729 empty = TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) && 730 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]); 731 if (empty) { 732 MPASS(LIST_EMPTY(&ts->ts_free)); 733#ifdef TURNSTILE_PROFILING 734 tc->tc_depth--; 735#endif 736 } else 737 ts = LIST_FIRST(&ts->ts_free); 738 MPASS(ts != NULL); 739 LIST_REMOVE(ts, ts_hash); 740 td->td_turnstile = ts; 741 742 return (empty); 743} 744 745/* 746 * Put all blocked threads on the pending list. This must be called with 747 * the turnstile chain locked. 748 */ 749void 750turnstile_broadcast(struct turnstile *ts, int queue) 751{ 752 struct turnstile_chain *tc; 753 struct turnstile *ts1; 754 struct thread *td; 755 756 MPASS(ts != NULL); 757 MPASS(curthread->td_proc->p_magic == P_MAGIC); 758 MPASS(ts->ts_owner == curthread || 759 (queue == TS_EXCLUSIVE_QUEUE && ts->ts_owner == NULL)); 760 tc = TC_LOOKUP(ts->ts_lockobj); 761 mtx_assert(&tc->tc_lock, MA_OWNED); 762 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 763 764 /* 765 * Transfer the blocked list to the pending list. 766 */ 767 mtx_lock_spin(&td_contested_lock); 768 TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked[queue], td_lockq); 769 mtx_unlock_spin(&td_contested_lock); 770 771 /* 772 * Give a turnstile to each thread. The last thread gets 773 * this turnstile if the turnstile is empty. 774 */ 775 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) { 776 if (LIST_EMPTY(&ts->ts_free)) { 777 MPASS(TAILQ_NEXT(td, td_lockq) == NULL); 778 ts1 = ts; 779#ifdef TURNSTILE_PROFILING 780 tc->tc_depth--; 781#endif 782 } else 783 ts1 = LIST_FIRST(&ts->ts_free); 784 MPASS(ts1 != NULL); 785 LIST_REMOVE(ts1, ts_hash); 786 td->td_turnstile = ts1; 787 } 788} 789 790/* 791 * Wakeup all threads on the pending list and adjust the priority of the 792 * current thread appropriately. This must be called with the turnstile 793 * chain locked. 794 */ 795void 796turnstile_unpend(struct turnstile *ts, int owner_type) 797{ 798 TAILQ_HEAD( ,thread) pending_threads; 799 struct turnstile_chain *tc; 800 struct thread *td; 801 u_char cp, pri; 802 803 MPASS(ts != NULL); 804 MPASS(ts->ts_owner == curthread || 805 (owner_type == TS_SHARED_LOCK && ts->ts_owner == NULL)); 806 tc = TC_LOOKUP(ts->ts_lockobj); 807 mtx_assert(&tc->tc_lock, MA_OWNED); 808 MPASS(!TAILQ_EMPTY(&ts->ts_pending)); 809 810 /* 811 * Move the list of pending threads out of the turnstile and 812 * into a local variable. 813 */ 814 TAILQ_INIT(&pending_threads); 815 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq); 816#ifdef INVARIANTS 817 if (TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) && 818 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])) 819 ts->ts_lockobj = NULL; 820#endif 821 822 /* 823 * Remove the turnstile from this thread's list of contested locks 824 * since this thread doesn't own it anymore. New threads will 825 * not be blocking on the turnstile until it is claimed by a new 826 * owner. There might not be a current owner if this is a shared 827 * lock. 828 */ 829 if (ts->ts_owner != NULL) { 830 mtx_lock_spin(&td_contested_lock); 831 ts->ts_owner = NULL; 832 LIST_REMOVE(ts, ts_link); 833 mtx_unlock_spin(&td_contested_lock); 834 } 835 critical_enter(); 836 mtx_unlock_spin(&tc->tc_lock); 837 838 /* 839 * Adjust the priority of curthread based on other contested 840 * locks it owns. Don't lower the priority below the base 841 * priority however. 842 */ 843 td = curthread; 844 pri = PRI_MAX; 845 mtx_lock_spin(&sched_lock); 846 mtx_lock_spin(&td_contested_lock); 847 LIST_FOREACH(ts, &td->td_contested, ts_link) { 848 cp = turnstile_first_waiter(ts)->td_priority; 849 if (cp < pri) 850 pri = cp; 851 } 852 mtx_unlock_spin(&td_contested_lock); 853 sched_unlend_prio(td, pri); 854 855 /* 856 * Wake up all the pending threads. If a thread is not blocked 857 * on a lock, then it is currently executing on another CPU in 858 * turnstile_wait() or sitting on a run queue waiting to resume 859 * in turnstile_wait(). Set a flag to force it to try to acquire 860 * the lock again instead of blocking. 861 */ 862 while (!TAILQ_EMPTY(&pending_threads)) { 863 td = TAILQ_FIRST(&pending_threads); 864 TAILQ_REMOVE(&pending_threads, td, td_lockq); 865 MPASS(td->td_proc->p_magic == P_MAGIC); 866 if (TD_ON_LOCK(td)) { 867 td->td_blocked = NULL; 868 td->td_lockname = NULL; 869#ifdef INVARIANTS 870 td->td_tsqueue = 0xff; 871#endif 872 TD_CLR_LOCK(td); 873 MPASS(TD_CAN_RUN(td)); 874 setrunqueue(td, SRQ_BORING); 875 } else { 876 td->td_flags |= TDF_TSNOBLOCK; 877 MPASS(TD_IS_RUNNING(td) || TD_ON_RUNQ(td)); 878 } 879 } 880 critical_exit(); 881 mtx_unlock_spin(&sched_lock); 882} 883 884/* 885 * Give up ownership of a turnstile. This must be called with the 886 * turnstile chain locked. 887 */ 888void 889turnstile_disown(struct turnstile *ts) 890{ 891 struct turnstile_chain *tc; 892 struct thread *td; 893 u_char cp, pri; 894 895 MPASS(ts != NULL); 896 MPASS(ts->ts_owner == curthread); 897 tc = TC_LOOKUP(ts->ts_lockobj); 898 mtx_assert(&tc->tc_lock, MA_OWNED); 899 MPASS(TAILQ_EMPTY(&ts->ts_pending)); 900 MPASS(!TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) || 901 !TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])); 902 903 /* 904 * Remove the turnstile from this thread's list of contested locks 905 * since this thread doesn't own it anymore. New threads will 906 * not be blocking on the turnstile until it is claimed by a new 907 * owner. 908 */ 909 mtx_lock_spin(&td_contested_lock); 910 ts->ts_owner = NULL; 911 LIST_REMOVE(ts, ts_link); 912 mtx_unlock_spin(&td_contested_lock); 913 mtx_unlock_spin(&tc->tc_lock); 914 915 /* 916 * Adjust the priority of curthread based on other contested 917 * locks it owns. Don't lower the priority below the base 918 * priority however. 919 */ 920 td = curthread; 921 pri = PRI_MAX; 922 mtx_lock_spin(&sched_lock); 923 mtx_lock_spin(&td_contested_lock); 924 LIST_FOREACH(ts, &td->td_contested, ts_link) { 925 cp = turnstile_first_waiter(ts)->td_priority; 926 if (cp < pri) 927 pri = cp; 928 } 929 mtx_unlock_spin(&td_contested_lock); 930 sched_unlend_prio(td, pri); 931 mtx_unlock_spin(&sched_lock); 932} 933 934/* 935 * Return the first thread in a turnstile. 936 */ 937struct thread * 938turnstile_head(struct turnstile *ts, int queue) 939{ 940#ifdef INVARIANTS 941 struct turnstile_chain *tc; 942 943 MPASS(ts != NULL); 944 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 945 tc = TC_LOOKUP(ts->ts_lockobj); 946 mtx_assert(&tc->tc_lock, MA_OWNED); 947#endif 948 return (TAILQ_FIRST(&ts->ts_blocked[queue])); 949} 950 951/* 952 * Returns true if a sub-queue of a turnstile is empty. 953 */ 954int 955turnstile_empty(struct turnstile *ts, int queue) 956{ 957#ifdef INVARIANTS 958 struct turnstile_chain *tc; 959 960 MPASS(ts != NULL); 961 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 962 tc = TC_LOOKUP(ts->ts_lockobj); 963 mtx_assert(&tc->tc_lock, MA_OWNED); 964#endif 965 return (TAILQ_EMPTY(&ts->ts_blocked[queue])); 966} 967 968#ifdef DDB 969static void 970print_thread(struct thread *td, const char *prefix) 971{ 972 973 db_printf("%s%p (tid %d, pid %d, \"%s\")\n", prefix, td, td->td_tid, 974 td->td_proc->p_pid, td->td_name[0] != '\0' ? td->td_name : 975 td->td_proc->p_comm); 976} 977 978static void 979print_queue(struct threadqueue *queue, const char *header, const char *prefix) 980{ 981 struct thread *td; 982 983 db_printf("%s:\n", header); 984 if (TAILQ_EMPTY(queue)) { 985 db_printf("%sempty\n", prefix); 986 return; 987 } 988 TAILQ_FOREACH(td, queue, td_lockq) { 989 print_thread(td, prefix); 990 } 991} 992 993DB_SHOW_COMMAND(turnstile, db_show_turnstile) 994{ 995 struct turnstile_chain *tc; 996 struct turnstile *ts; 997 struct lock_object *lock; 998 int i; 999 1000 if (!have_addr) 1001 return; 1002 1003 /* 1004 * First, see if there is an active turnstile for the lock indicated 1005 * by the address. 1006 */ 1007 lock = (struct lock_object *)addr; 1008 tc = TC_LOOKUP(lock); 1009 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 1010 if (ts->ts_lockobj == lock) 1011 goto found; 1012 1013 /* 1014 * Second, see if there is an active turnstile at the address 1015 * indicated. 1016 */ 1017 for (i = 0; i < TC_TABLESIZE; i++) 1018 LIST_FOREACH(ts, &turnstile_chains[i].tc_turnstiles, ts_hash) { 1019 if (ts == (struct turnstile *)addr) 1020 goto found; 1021 } 1022 1023 db_printf("Unable to locate a turnstile via %p\n", (void *)addr); 1024 return; 1025found: 1026 lock = ts->ts_lockobj; 1027 db_printf("Lock: %p - (%s) %s\n", lock, LOCK_CLASS(lock)->lc_name, 1028 lock->lo_name); 1029 if (ts->ts_owner) 1030 print_thread(ts->ts_owner, "Lock Owner: "); 1031 else 1032 db_printf("Lock Owner: none\n"); 1033 print_queue(&ts->ts_blocked[TS_SHARED_QUEUE], "Shared Waiters", "\t"); 1034 print_queue(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE], "Exclusive Waiters", 1035 "\t"); 1036 print_queue(&ts->ts_pending, "Pending Threads", "\t"); 1037 1038} 1039 1040/* 1041 * Show all the threads a particular thread is waiting on based on 1042 * non-sleepable and non-spin locks. 1043 */ 1044static void 1045print_lockchain(struct thread *td, const char *prefix) 1046{ 1047 struct lock_object *lock; 1048 struct lock_class *class; 1049 struct turnstile *ts; 1050 1051 /* 1052 * Follow the chain. We keep walking as long as the thread is 1053 * blocked on a turnstile that has an owner. 1054 */ 1055 while (!db_pager_quit) { 1056 db_printf("%sthread %d (pid %d, %s) ", prefix, td->td_tid, 1057 td->td_proc->p_pid, td->td_name[0] != '\0' ? td->td_name : 1058 td->td_proc->p_comm); 1059 switch (td->td_state) { 1060 case TDS_INACTIVE: 1061 db_printf("is inactive\n"); 1062 return; 1063 case TDS_CAN_RUN: 1064 db_printf("can run\n"); 1065 return; 1066 case TDS_RUNQ: 1067 db_printf("is on a run queue\n"); 1068 return; 1069 case TDS_RUNNING: 1070 db_printf("running on CPU %d\n", td->td_oncpu); 1071 return; 1072 case TDS_INHIBITED: 1073 if (TD_ON_LOCK(td)) { 1074 ts = td->td_blocked; 1075 lock = ts->ts_lockobj; 1076 class = LOCK_CLASS(lock); 1077 db_printf("blocked on lock %p (%s) \"%s\"\n", 1078 lock, class->lc_name, lock->lo_name); 1079 if (ts->ts_owner == NULL) 1080 return; 1081 td = ts->ts_owner; 1082 break; 1083 } 1084 db_printf("inhibited\n"); 1085 return; 1086 default: 1087 db_printf("??? (%#x)\n", td->td_state); 1088 return; 1089 } 1090 } 1091} 1092 1093DB_SHOW_COMMAND(lockchain, db_show_lockchain) 1094{ 1095 struct thread *td; 1096 1097 /* Figure out which thread to start with. */ 1098 if (have_addr) 1099 td = db_lookup_thread(addr, TRUE); 1100 else 1101 td = kdb_thread; 1102 1103 print_lockchain(td, ""); 1104} 1105 1106DB_SHOW_COMMAND(allchains, db_show_allchains) 1107{ 1108 struct thread *td; 1109 struct proc *p; 1110 int i; 1111 1112 i = 1; 1113 LIST_FOREACH(p, &allproc, p_list) { 1114 FOREACH_THREAD_IN_PROC(p, td) { 1115 if (TD_ON_LOCK(td) && LIST_EMPTY(&td->td_contested)) { 1116 db_printf("chain %d:\n", i++); 1117 print_lockchain(td, " "); 1118 } 1119 if (db_pager_quit) 1120 return; 1121 } 1122 } 1123} 1124 1125/* 1126 * Show all the threads a particular thread is waiting on based on 1127 * sleepable locks. 1128 */ 1129static void 1130print_sleepchain(struct thread *td, const char *prefix) 1131{ 1132 struct thread *owner; 1133 1134 /* 1135 * Follow the chain. We keep walking as long as the thread is 1136 * blocked on a sleep lock that has an owner. 1137 */ 1138 while (!db_pager_quit) { 1139 db_printf("%sthread %d (pid %d, %s) ", prefix, td->td_tid, 1140 td->td_proc->p_pid, td->td_name[0] != '\0' ? td->td_name : 1141 td->td_proc->p_comm); 1142 switch (td->td_state) { 1143 case TDS_INACTIVE: 1144 db_printf("is inactive\n"); 1145 return; 1146 case TDS_CAN_RUN: 1147 db_printf("can run\n"); 1148 return; 1149 case TDS_RUNQ: 1150 db_printf("is on a run queue\n"); 1151 return; 1152 case TDS_RUNNING: 1153 db_printf("running on CPU %d\n", td->td_oncpu); 1154 return; 1155 case TDS_INHIBITED: 1156 if (TD_ON_SLEEPQ(td)) { 1157 if (lockmgr_chain(td, &owner) || 1158 sx_chain(td, &owner)) { 1159 if (owner == NULL) 1160 return; 1161 td = owner; 1162 break; 1163 } 1164 db_printf("sleeping on %p \"%s\"\n", 1165 td->td_wchan, td->td_wmesg); 1166 return; 1167 } 1168 db_printf("inhibited\n"); 1169 return; 1170 default: 1171 db_printf("??? (%#x)\n", td->td_state); 1172 return; 1173 } 1174 } 1175} 1176 1177DB_SHOW_COMMAND(sleepchain, db_show_sleepchain) 1178{ 1179 struct thread *td; 1180 1181 /* Figure out which thread to start with. */ 1182 if (have_addr) 1183 td = db_lookup_thread(addr, TRUE); 1184 else 1185 td = kdb_thread; 1186 1187 print_sleepchain(td, ""); 1188} 1189 1190static void print_waiters(struct turnstile *ts, int indent); 1191 1192static void 1193print_waiter(struct thread *td, int indent) 1194{ 1195 struct turnstile *ts; 1196 int i; 1197 1198 if (db_pager_quit) 1199 return; 1200 for (i = 0; i < indent; i++) 1201 db_printf(" "); 1202 print_thread(td, "thread "); 1203 LIST_FOREACH(ts, &td->td_contested, ts_link) 1204 print_waiters(ts, indent + 1); 1205} 1206 1207static void 1208print_waiters(struct turnstile *ts, int indent) 1209{ 1210 struct lock_object *lock; 1211 struct lock_class *class; 1212 struct thread *td; 1213 int i; 1214 1215 if (db_pager_quit) 1216 return; 1217 lock = ts->ts_lockobj; 1218 class = LOCK_CLASS(lock); 1219 for (i = 0; i < indent; i++) 1220 db_printf(" "); 1221 db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name, lock->lo_name); 1222 TAILQ_FOREACH(td, &ts->ts_blocked[TS_EXCLUSIVE_QUEUE], td_lockq) 1223 print_waiter(td, indent + 1); 1224 TAILQ_FOREACH(td, &ts->ts_blocked[TS_SHARED_QUEUE], td_lockq) 1225 print_waiter(td, indent + 1); 1226 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) 1227 print_waiter(td, indent + 1); 1228} 1229 1230DB_SHOW_COMMAND(locktree, db_show_locktree) 1231{ 1232 struct lock_object *lock; 1233 struct lock_class *class; 1234 struct turnstile_chain *tc; 1235 struct turnstile *ts; 1236 1237 if (!have_addr) 1238 return; 1239 lock = (struct lock_object *)addr; 1240 tc = TC_LOOKUP(lock); 1241 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 1242 if (ts->ts_lockobj == lock) 1243 break; 1244 if (ts == NULL) { 1245 class = LOCK_CLASS(lock); 1246 db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name, 1247 lock->lo_name); 1248 } else 1249 print_waiters(ts, 0); 1250} 1251#endif 1252