1 /*- 2 * SPDX-License-Identifier: BSD-3-Clause 3 * 4 * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved. 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 3. Berkeley Software Design Inc's name may not be used to endorse or 15 * promote products derived from this software without specific prior 16 * written permission. 17 * 18 * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND 19 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21 * ARE DISCLAIMED. IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE 22 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28 * SUCH DAMAGE. 29 * 30 * from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $ 31 * and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $ 32 */ 33 34 /* 35 * Implementation of turnstiles used to hold queue of threads blocked on 36 * non-sleepable locks. Sleepable locks use condition variables to 37 * implement their queues. Turnstiles differ from a sleep queue in that 38 * turnstile queue's are assigned to a lock held by an owning thread. Thus, 39 * when one thread is enqueued onto a turnstile, it can lend its priority 40 * to the owning thread. 41 * 42 * We wish to avoid bloating locks with an embedded turnstile and we do not 43 * want to use back-pointers in the locks for the same reason. Thus, we 44 * use a similar approach to that of Solaris 7 as described in Solaris 45 * Internals by Jim Mauro and Richard McDougall. Turnstiles are looked up 46 * in a hash table based on the address of the lock. Each entry in the 47 * hash table is a linked-lists of turnstiles and is called a turnstile 48 * chain. Each chain contains a spin mutex that protects all of the 49 * turnstiles in the chain. 50 * 51 * Each time a thread is created, a turnstile is allocated from a UMA zone 52 * and attached to that thread. When a thread blocks on a lock, if it is the 53 * first thread to block, it lends its turnstile to the lock. If the lock 54 * already has a turnstile, then it gives its turnstile to the lock's 55 * turnstile's free list. When a thread is woken up, it takes a turnstile from 56 * the free list if there are any other waiters. If it is the only thread 57 * blocked on the lock, then it reclaims the turnstile associated with the lock 58 * and removes it from the hash table. 59 */ 60 61 #include <sys/cdefs.h> 62 __FBSDID("$FreeBSD$"); 63 64 #include "opt_ddb.h" 65 #include "opt_turnstile_profiling.h" 66 #include "opt_sched.h" 67 68 #include <sys/param.h> 69 #include <sys/systm.h> 70 #include <sys/kdb.h> 71 #include <sys/kernel.h> 72 #include <sys/ktr.h> 73 #include <sys/lock.h> 74 #include <sys/mutex.h> 75 #include <sys/proc.h> 76 #include <sys/queue.h> 77 #include <sys/sched.h> 78 #include <sys/sdt.h> 79 #include <sys/sysctl.h> 80 #include <sys/turnstile.h> 81 82 #include <vm/uma.h> 83 84 #ifdef DDB 85 #include <ddb/ddb.h> 86 #include <sys/lockmgr.h> 87 #include <sys/sx.h> 88 #endif 89 90 /* 91 * Constants for the hash table of turnstile chains. TC_SHIFT is a magic 92 * number chosen because the sleep queue's use the same value for the 93 * shift. Basically, we ignore the lower 8 bits of the address. 94 * TC_TABLESIZE must be a power of two for TC_MASK to work properly. 95 */ 96 #define TC_TABLESIZE 128 /* Must be power of 2. */ 97 #define TC_MASK (TC_TABLESIZE - 1) 98 #define TC_SHIFT 8 99 #define TC_HASH(lock) (((uintptr_t)(lock) >> TC_SHIFT) & TC_MASK) 100 #define TC_LOOKUP(lock) &turnstile_chains[TC_HASH(lock)] 101 102 /* 103 * There are three different lists of turnstiles as follows. The list 104 * connected by ts_link entries is a per-thread list of all the turnstiles 105 * attached to locks that we own. This is used to fixup our priority when 106 * a lock is released. The other two lists use the ts_hash entries. The 107 * first of these two is the turnstile chain list that a turnstile is on 108 * when it is attached to a lock. The second list to use ts_hash is the 109 * free list hung off of a turnstile that is attached to a lock. 110 * 111 * Each turnstile contains three lists of threads. The two ts_blocked lists 112 * are linked list of threads blocked on the turnstile's lock. One list is 113 * for exclusive waiters, and the other is for shared waiters. The 114 * ts_pending list is a linked list of threads previously awakened by 115 * turnstile_signal() or turnstile_wait() that are waiting to be put on 116 * the run queue. 117 * 118 * Locking key: 119 * c - turnstile chain lock 120 * q - td_contested lock 121 */ 122 struct turnstile { 123 struct mtx ts_lock; /* Spin lock for self. */ 124 struct threadqueue ts_blocked[2]; /* (c + q) Blocked threads. */ 125 struct threadqueue ts_pending; /* (c) Pending threads. */ 126 LIST_ENTRY(turnstile) ts_hash; /* (c) Chain and free list. */ 127 LIST_ENTRY(turnstile) ts_link; /* (q) Contested locks. */ 128 LIST_HEAD(, turnstile) ts_free; /* (c) Free turnstiles. */ 129 struct lock_object *ts_lockobj; /* (c) Lock we reference. */ 130 struct thread *ts_owner; /* (c + q) Who owns the lock. */ 131 }; 132 133 struct turnstile_chain { 134 LIST_HEAD(, turnstile) tc_turnstiles; /* List of turnstiles. */ 135 struct mtx tc_lock; /* Spin lock for this chain. */ 136 #ifdef TURNSTILE_PROFILING 137 u_int tc_depth; /* Length of tc_queues. */ 138 u_int tc_max_depth; /* Max length of tc_queues. */ 139 #endif 140 }; 141 142 #ifdef TURNSTILE_PROFILING 143 u_int turnstile_max_depth; 144 static SYSCTL_NODE(_debug, OID_AUTO, turnstile, CTLFLAG_RD, 0, 145 "turnstile profiling"); 146 static SYSCTL_NODE(_debug_turnstile, OID_AUTO, chains, CTLFLAG_RD, 0, 147 "turnstile chain stats"); 148 SYSCTL_UINT(_debug_turnstile, OID_AUTO, max_depth, CTLFLAG_RD, 149 &turnstile_max_depth, 0, "maximum depth achieved of a single chain"); 150 #endif 151 static struct mtx td_contested_lock; 152 static struct turnstile_chain turnstile_chains[TC_TABLESIZE]; 153 static uma_zone_t turnstile_zone; 154 155 /* 156 * Prototypes for non-exported routines. 157 */ 158 static void init_turnstile0(void *dummy); 159 #ifdef TURNSTILE_PROFILING 160 static void init_turnstile_profiling(void *arg); 161 #endif 162 static void propagate_priority(struct thread *td); 163 static int turnstile_adjust_thread(struct turnstile *ts, 164 struct thread *td); 165 static struct thread *turnstile_first_waiter(struct turnstile *ts); 166 static void turnstile_setowner(struct turnstile *ts, struct thread *owner); 167 #ifdef INVARIANTS 168 static void turnstile_dtor(void *mem, int size, void *arg); 169 #endif 170 static int turnstile_init(void *mem, int size, int flags); 171 static void turnstile_fini(void *mem, int size); 172 173 SDT_PROVIDER_DECLARE(sched); 174 SDT_PROBE_DEFINE(sched, , , sleep); 175 SDT_PROBE_DEFINE2(sched, , , wakeup, "struct thread *", 176 "struct proc *"); 177 178 /* 179 * Walks the chain of turnstiles and their owners to propagate the priority 180 * of the thread being blocked to all the threads holding locks that have to 181 * release their locks before this thread can run again. 182 */ 183 static void 184 propagate_priority(struct thread *td) 185 { 186 struct turnstile *ts; 187 int pri; 188 189 THREAD_LOCK_ASSERT(td, MA_OWNED); 190 pri = td->td_priority; 191 ts = td->td_blocked; 192 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); 193 /* 194 * Grab a recursive lock on this turnstile chain so it stays locked 195 * for the whole operation. The caller expects us to return with 196 * the original lock held. We only ever lock down the chain so 197 * the lock order is constant. 198 */ 199 mtx_lock_spin(&ts->ts_lock); 200 for (;;) { 201 td = ts->ts_owner; 202 203 if (td == NULL) { 204 /* 205 * This might be a read lock with no owner. There's 206 * not much we can do, so just bail. 207 */ 208 mtx_unlock_spin(&ts->ts_lock); 209 return; 210 } 211 212 thread_lock_flags(td, MTX_DUPOK); 213 mtx_unlock_spin(&ts->ts_lock); 214 MPASS(td->td_proc != NULL); 215 MPASS(td->td_proc->p_magic == P_MAGIC); 216 217 /* 218 * If the thread is asleep, then we are probably about 219 * to deadlock. To make debugging this easier, show 220 * backtrace of misbehaving thread and panic to not 221 * leave the kernel deadlocked. 222 */ 223 if (TD_IS_SLEEPING(td)) { 224 printf( 225 "Sleeping thread (tid %d, pid %d) owns a non-sleepable lock\n", 226 td->td_tid, td->td_proc->p_pid); 227 kdb_backtrace_thread(td); 228 panic("sleeping thread"); 229 } 230 231 /* 232 * If this thread already has higher priority than the 233 * thread that is being blocked, we are finished. 234 */ 235 if (td->td_priority <= pri) { 236 thread_unlock(td); 237 return; 238 } 239 240 /* 241 * Bump this thread's priority. 242 */ 243 sched_lend_prio(td, pri); 244 245 /* 246 * If lock holder is actually running or on the run queue 247 * then we are done. 248 */ 249 if (TD_IS_RUNNING(td) || TD_ON_RUNQ(td)) { 250 MPASS(td->td_blocked == NULL); 251 thread_unlock(td); 252 return; 253 } 254 255 #ifndef SMP 256 /* 257 * For UP, we check to see if td is curthread (this shouldn't 258 * ever happen however as it would mean we are in a deadlock.) 259 */ 260 KASSERT(td != curthread, ("Deadlock detected")); 261 #endif 262 263 /* 264 * If we aren't blocked on a lock, we should be. 265 */ 266 KASSERT(TD_ON_LOCK(td), ( 267 "thread %d(%s):%d holds %s but isn't blocked on a lock\n", 268 td->td_tid, td->td_name, td->td_state, 269 ts->ts_lockobj->lo_name)); 270 271 /* 272 * Pick up the lock that td is blocked on. 273 */ 274 ts = td->td_blocked; 275 MPASS(ts != NULL); 276 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); 277 /* Resort td on the list if needed. */ 278 if (!turnstile_adjust_thread(ts, td)) { 279 mtx_unlock_spin(&ts->ts_lock); 280 return; 281 } 282 /* The thread lock is released as ts lock above. */ 283 } 284 } 285 286 /* 287 * Adjust the thread's position on a turnstile after its priority has been 288 * changed. 289 */ 290 static int 291 turnstile_adjust_thread(struct turnstile *ts, struct thread *td) 292 { 293 struct thread *td1, *td2; 294 int queue; 295 296 THREAD_LOCK_ASSERT(td, MA_OWNED); 297 MPASS(TD_ON_LOCK(td)); 298 299 /* 300 * This thread may not be blocked on this turnstile anymore 301 * but instead might already be woken up on another CPU 302 * that is waiting on the thread lock in turnstile_unpend() to 303 * finish waking this thread up. We can detect this case 304 * by checking to see if this thread has been given a 305 * turnstile by either turnstile_signal() or 306 * turnstile_broadcast(). In this case, treat the thread as 307 * if it was already running. 308 */ 309 if (td->td_turnstile != NULL) 310 return (0); 311 312 /* 313 * Check if the thread needs to be moved on the blocked chain. 314 * It needs to be moved if either its priority is lower than 315 * the previous thread or higher than the next thread. 316 */ 317 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); 318 td1 = TAILQ_PREV(td, threadqueue, td_lockq); 319 td2 = TAILQ_NEXT(td, td_lockq); 320 if ((td1 != NULL && td->td_priority < td1->td_priority) || 321 (td2 != NULL && td->td_priority > td2->td_priority)) { 322 323 /* 324 * Remove thread from blocked chain and determine where 325 * it should be moved to. 326 */ 327 queue = td->td_tsqueue; 328 MPASS(queue == TS_EXCLUSIVE_QUEUE || queue == TS_SHARED_QUEUE); 329 mtx_lock_spin(&td_contested_lock); 330 TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq); 331 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) { 332 MPASS(td1->td_proc->p_magic == P_MAGIC); 333 if (td1->td_priority > td->td_priority) 334 break; 335 } 336 337 if (td1 == NULL) 338 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); 339 else 340 TAILQ_INSERT_BEFORE(td1, td, td_lockq); 341 mtx_unlock_spin(&td_contested_lock); 342 if (td1 == NULL) 343 CTR3(KTR_LOCK, 344 "turnstile_adjust_thread: td %d put at tail on [%p] %s", 345 td->td_tid, ts->ts_lockobj, ts->ts_lockobj->lo_name); 346 else 347 CTR4(KTR_LOCK, 348 "turnstile_adjust_thread: td %d moved before %d on [%p] %s", 349 td->td_tid, td1->td_tid, ts->ts_lockobj, 350 ts->ts_lockobj->lo_name); 351 } 352 return (1); 353 } 354 355 /* 356 * Early initialization of turnstiles. This is not done via a SYSINIT() 357 * since this needs to be initialized very early when mutexes are first 358 * initialized. 359 */ 360 void 361 init_turnstiles(void) 362 { 363 int i; 364 365 for (i = 0; i < TC_TABLESIZE; i++) { 366 LIST_INIT(&turnstile_chains[i].tc_turnstiles); 367 mtx_init(&turnstile_chains[i].tc_lock, "turnstile chain", 368 NULL, MTX_SPIN); 369 } 370 mtx_init(&td_contested_lock, "td_contested", NULL, MTX_SPIN); 371 LIST_INIT(&thread0.td_contested); 372 thread0.td_turnstile = NULL; 373 } 374 375 #ifdef TURNSTILE_PROFILING 376 static void 377 init_turnstile_profiling(void *arg) 378 { 379 struct sysctl_oid *chain_oid; 380 char chain_name[10]; 381 int i; 382 383 for (i = 0; i < TC_TABLESIZE; i++) { 384 snprintf(chain_name, sizeof(chain_name), "%d", i); 385 chain_oid = SYSCTL_ADD_NODE(NULL, 386 SYSCTL_STATIC_CHILDREN(_debug_turnstile_chains), OID_AUTO, 387 chain_name, CTLFLAG_RD, NULL, "turnstile chain stats"); 388 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO, 389 "depth", CTLFLAG_RD, &turnstile_chains[i].tc_depth, 0, 390 NULL); 391 SYSCTL_ADD_UINT(NULL, SYSCTL_CHILDREN(chain_oid), OID_AUTO, 392 "max_depth", CTLFLAG_RD, &turnstile_chains[i].tc_max_depth, 393 0, NULL); 394 } 395 } 396 SYSINIT(turnstile_profiling, SI_SUB_LOCK, SI_ORDER_ANY, 397 init_turnstile_profiling, NULL); 398 #endif 399 400 static void 401 init_turnstile0(void *dummy) 402 { 403 404 turnstile_zone = uma_zcreate("TURNSTILE", sizeof(struct turnstile), 405 NULL, 406 #ifdef INVARIANTS 407 turnstile_dtor, 408 #else 409 NULL, 410 #endif 411 turnstile_init, turnstile_fini, UMA_ALIGN_CACHE, UMA_ZONE_NOFREE); 412 thread0.td_turnstile = turnstile_alloc(); 413 } 414 SYSINIT(turnstile0, SI_SUB_LOCK, SI_ORDER_ANY, init_turnstile0, NULL); 415 416 /* 417 * Update a thread on the turnstile list after it's priority has been changed. 418 * The old priority is passed in as an argument. 419 */ 420 void 421 turnstile_adjust(struct thread *td, u_char oldpri) 422 { 423 struct turnstile *ts; 424 425 MPASS(TD_ON_LOCK(td)); 426 427 /* 428 * Pick up the lock that td is blocked on. 429 */ 430 ts = td->td_blocked; 431 MPASS(ts != NULL); 432 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); 433 mtx_assert(&ts->ts_lock, MA_OWNED); 434 435 /* Resort the turnstile on the list. */ 436 if (!turnstile_adjust_thread(ts, td)) 437 return; 438 /* 439 * If our priority was lowered and we are at the head of the 440 * turnstile, then propagate our new priority up the chain. 441 * Note that we currently don't try to revoke lent priorities 442 * when our priority goes up. 443 */ 444 MPASS(td->td_tsqueue == TS_EXCLUSIVE_QUEUE || 445 td->td_tsqueue == TS_SHARED_QUEUE); 446 if (td == TAILQ_FIRST(&ts->ts_blocked[td->td_tsqueue]) && 447 td->td_priority < oldpri) { 448 propagate_priority(td); 449 } 450 } 451 452 /* 453 * Set the owner of the lock this turnstile is attached to. 454 */ 455 static void 456 turnstile_setowner(struct turnstile *ts, struct thread *owner) 457 { 458 459 mtx_assert(&td_contested_lock, MA_OWNED); 460 MPASS(ts->ts_owner == NULL); 461 462 /* A shared lock might not have an owner. */ 463 if (owner == NULL) 464 return; 465 466 MPASS(owner->td_proc->p_magic == P_MAGIC); 467 ts->ts_owner = owner; 468 LIST_INSERT_HEAD(&owner->td_contested, ts, ts_link); 469 } 470 471 #ifdef INVARIANTS 472 /* 473 * UMA zone item deallocator. 474 */ 475 static void 476 turnstile_dtor(void *mem, int size, void *arg) 477 { 478 struct turnstile *ts; 479 480 ts = mem; 481 MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE])); 482 MPASS(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])); 483 MPASS(TAILQ_EMPTY(&ts->ts_pending)); 484 } 485 #endif 486 487 /* 488 * UMA zone item initializer. 489 */ 490 static int 491 turnstile_init(void *mem, int size, int flags) 492 { 493 struct turnstile *ts; 494 495 bzero(mem, size); 496 ts = mem; 497 TAILQ_INIT(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]); 498 TAILQ_INIT(&ts->ts_blocked[TS_SHARED_QUEUE]); 499 TAILQ_INIT(&ts->ts_pending); 500 LIST_INIT(&ts->ts_free); 501 mtx_init(&ts->ts_lock, "turnstile lock", NULL, MTX_SPIN | MTX_RECURSE); 502 return (0); 503 } 504 505 static void 506 turnstile_fini(void *mem, int size) 507 { 508 struct turnstile *ts; 509 510 ts = mem; 511 mtx_destroy(&ts->ts_lock); 512 } 513 514 /* 515 * Get a turnstile for a new thread. 516 */ 517 struct turnstile * 518 turnstile_alloc(void) 519 { 520 521 return (uma_zalloc(turnstile_zone, M_WAITOK)); 522 } 523 524 /* 525 * Free a turnstile when a thread is destroyed. 526 */ 527 void 528 turnstile_free(struct turnstile *ts) 529 { 530 531 uma_zfree(turnstile_zone, ts); 532 } 533 534 /* 535 * Lock the turnstile chain associated with the specified lock. 536 */ 537 void 538 turnstile_chain_lock(struct lock_object *lock) 539 { 540 struct turnstile_chain *tc; 541 542 tc = TC_LOOKUP(lock); 543 mtx_lock_spin(&tc->tc_lock); 544 } 545 546 struct turnstile * 547 turnstile_trywait(struct lock_object *lock) 548 { 549 struct turnstile_chain *tc; 550 struct turnstile *ts; 551 552 tc = TC_LOOKUP(lock); 553 mtx_lock_spin(&tc->tc_lock); 554 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 555 if (ts->ts_lockobj == lock) { 556 mtx_lock_spin(&ts->ts_lock); 557 return (ts); 558 } 559 560 ts = curthread->td_turnstile; 561 MPASS(ts != NULL); 562 mtx_lock_spin(&ts->ts_lock); 563 KASSERT(ts->ts_lockobj == NULL, ("stale ts_lockobj pointer")); 564 ts->ts_lockobj = lock; 565 566 return (ts); 567 } 568 569 void 570 turnstile_cancel(struct turnstile *ts) 571 { 572 struct turnstile_chain *tc; 573 struct lock_object *lock; 574 575 mtx_assert(&ts->ts_lock, MA_OWNED); 576 577 mtx_unlock_spin(&ts->ts_lock); 578 lock = ts->ts_lockobj; 579 if (ts == curthread->td_turnstile) 580 ts->ts_lockobj = NULL; 581 tc = TC_LOOKUP(lock); 582 mtx_unlock_spin(&tc->tc_lock); 583 } 584 585 /* 586 * Look up the turnstile for a lock in the hash table locking the associated 587 * turnstile chain along the way. If no turnstile is found in the hash 588 * table, NULL is returned. 589 */ 590 struct turnstile * 591 turnstile_lookup(struct lock_object *lock) 592 { 593 struct turnstile_chain *tc; 594 struct turnstile *ts; 595 596 tc = TC_LOOKUP(lock); 597 mtx_assert(&tc->tc_lock, MA_OWNED); 598 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 599 if (ts->ts_lockobj == lock) { 600 mtx_lock_spin(&ts->ts_lock); 601 return (ts); 602 } 603 return (NULL); 604 } 605 606 /* 607 * Unlock the turnstile chain associated with a given lock. 608 */ 609 void 610 turnstile_chain_unlock(struct lock_object *lock) 611 { 612 struct turnstile_chain *tc; 613 614 tc = TC_LOOKUP(lock); 615 mtx_unlock_spin(&tc->tc_lock); 616 } 617 618 /* 619 * Return a pointer to the thread waiting on this turnstile with the 620 * most important priority or NULL if the turnstile has no waiters. 621 */ 622 static struct thread * 623 turnstile_first_waiter(struct turnstile *ts) 624 { 625 struct thread *std, *xtd; 626 627 std = TAILQ_FIRST(&ts->ts_blocked[TS_SHARED_QUEUE]); 628 xtd = TAILQ_FIRST(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]); 629 if (xtd == NULL || (std != NULL && std->td_priority < xtd->td_priority)) 630 return (std); 631 return (xtd); 632 } 633 634 /* 635 * Take ownership of a turnstile and adjust the priority of the new 636 * owner appropriately. 637 */ 638 void 639 turnstile_claim(struct turnstile *ts) 640 { 641 struct thread *td, *owner; 642 struct turnstile_chain *tc; 643 644 mtx_assert(&ts->ts_lock, MA_OWNED); 645 MPASS(ts != curthread->td_turnstile); 646 647 owner = curthread; 648 mtx_lock_spin(&td_contested_lock); 649 turnstile_setowner(ts, owner); 650 mtx_unlock_spin(&td_contested_lock); 651 652 td = turnstile_first_waiter(ts); 653 MPASS(td != NULL); 654 MPASS(td->td_proc->p_magic == P_MAGIC); 655 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); 656 657 /* 658 * Update the priority of the new owner if needed. 659 */ 660 thread_lock(owner); 661 if (td->td_priority < owner->td_priority) 662 sched_lend_prio(owner, td->td_priority); 663 thread_unlock(owner); 664 tc = TC_LOOKUP(ts->ts_lockobj); 665 mtx_unlock_spin(&ts->ts_lock); 666 mtx_unlock_spin(&tc->tc_lock); 667 } 668 669 /* 670 * Block the current thread on the turnstile assicated with 'lock'. This 671 * function will context switch and not return until this thread has been 672 * woken back up. This function must be called with the appropriate 673 * turnstile chain locked and will return with it unlocked. 674 */ 675 void 676 turnstile_wait(struct turnstile *ts, struct thread *owner, int queue) 677 { 678 struct turnstile_chain *tc; 679 struct thread *td, *td1; 680 struct lock_object *lock; 681 682 td = curthread; 683 mtx_assert(&ts->ts_lock, MA_OWNED); 684 if (owner) 685 MPASS(owner->td_proc->p_magic == P_MAGIC); 686 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 687 688 /* 689 * If the lock does not already have a turnstile, use this thread's 690 * turnstile. Otherwise insert the current thread into the 691 * turnstile already in use by this lock. 692 */ 693 tc = TC_LOOKUP(ts->ts_lockobj); 694 mtx_assert(&tc->tc_lock, MA_OWNED); 695 if (ts == td->td_turnstile) { 696 #ifdef TURNSTILE_PROFILING 697 tc->tc_depth++; 698 if (tc->tc_depth > tc->tc_max_depth) { 699 tc->tc_max_depth = tc->tc_depth; 700 if (tc->tc_max_depth > turnstile_max_depth) 701 turnstile_max_depth = tc->tc_max_depth; 702 } 703 #endif 704 LIST_INSERT_HEAD(&tc->tc_turnstiles, ts, ts_hash); 705 KASSERT(TAILQ_EMPTY(&ts->ts_pending), 706 ("thread's turnstile has pending threads")); 707 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]), 708 ("thread's turnstile has exclusive waiters")); 709 KASSERT(TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]), 710 ("thread's turnstile has shared waiters")); 711 KASSERT(LIST_EMPTY(&ts->ts_free), 712 ("thread's turnstile has a non-empty free list")); 713 MPASS(ts->ts_lockobj != NULL); 714 mtx_lock_spin(&td_contested_lock); 715 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); 716 turnstile_setowner(ts, owner); 717 mtx_unlock_spin(&td_contested_lock); 718 } else { 719 TAILQ_FOREACH(td1, &ts->ts_blocked[queue], td_lockq) 720 if (td1->td_priority > td->td_priority) 721 break; 722 mtx_lock_spin(&td_contested_lock); 723 if (td1 != NULL) 724 TAILQ_INSERT_BEFORE(td1, td, td_lockq); 725 else 726 TAILQ_INSERT_TAIL(&ts->ts_blocked[queue], td, td_lockq); 727 MPASS(owner == ts->ts_owner); 728 mtx_unlock_spin(&td_contested_lock); 729 MPASS(td->td_turnstile != NULL); 730 LIST_INSERT_HEAD(&ts->ts_free, td->td_turnstile, ts_hash); 731 } 732 thread_lock(td); 733 thread_lock_set(td, &ts->ts_lock); 734 td->td_turnstile = NULL; 735 736 /* Save who we are blocked on and switch. */ 737 lock = ts->ts_lockobj; 738 td->td_tsqueue = queue; 739 td->td_blocked = ts; 740 td->td_lockname = lock->lo_name; 741 td->td_blktick = ticks; 742 TD_SET_LOCK(td); 743 mtx_unlock_spin(&tc->tc_lock); 744 propagate_priority(td); 745 746 if (LOCK_LOG_TEST(lock, 0)) 747 CTR4(KTR_LOCK, "%s: td %d blocked on [%p] %s", __func__, 748 td->td_tid, lock, lock->lo_name); 749 750 SDT_PROBE0(sched, , , sleep); 751 752 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); 753 mi_switch(SW_VOL | SWT_TURNSTILE, NULL); 754 755 if (LOCK_LOG_TEST(lock, 0)) 756 CTR4(KTR_LOCK, "%s: td %d free from blocked on [%p] %s", 757 __func__, td->td_tid, lock, lock->lo_name); 758 thread_unlock(td); 759 } 760 761 /* 762 * Pick the highest priority thread on this turnstile and put it on the 763 * pending list. This must be called with the turnstile chain locked. 764 */ 765 int 766 turnstile_signal(struct turnstile *ts, int queue) 767 { 768 struct turnstile_chain *tc; 769 struct thread *td; 770 int empty; 771 772 MPASS(ts != NULL); 773 mtx_assert(&ts->ts_lock, MA_OWNED); 774 MPASS(curthread->td_proc->p_magic == P_MAGIC); 775 MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL); 776 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 777 778 /* 779 * Pick the highest priority thread blocked on this lock and 780 * move it to the pending list. 781 */ 782 td = TAILQ_FIRST(&ts->ts_blocked[queue]); 783 MPASS(td->td_proc->p_magic == P_MAGIC); 784 mtx_lock_spin(&td_contested_lock); 785 TAILQ_REMOVE(&ts->ts_blocked[queue], td, td_lockq); 786 mtx_unlock_spin(&td_contested_lock); 787 TAILQ_INSERT_TAIL(&ts->ts_pending, td, td_lockq); 788 789 /* 790 * If the turnstile is now empty, remove it from its chain and 791 * give it to the about-to-be-woken thread. Otherwise take a 792 * turnstile from the free list and give it to the thread. 793 */ 794 empty = TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) && 795 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE]); 796 if (empty) { 797 tc = TC_LOOKUP(ts->ts_lockobj); 798 mtx_assert(&tc->tc_lock, MA_OWNED); 799 MPASS(LIST_EMPTY(&ts->ts_free)); 800 #ifdef TURNSTILE_PROFILING 801 tc->tc_depth--; 802 #endif 803 } else 804 ts = LIST_FIRST(&ts->ts_free); 805 MPASS(ts != NULL); 806 LIST_REMOVE(ts, ts_hash); 807 td->td_turnstile = ts; 808 809 return (empty); 810 } 811 812 /* 813 * Put all blocked threads on the pending list. This must be called with 814 * the turnstile chain locked. 815 */ 816 void 817 turnstile_broadcast(struct turnstile *ts, int queue) 818 { 819 struct turnstile_chain *tc; 820 struct turnstile *ts1; 821 struct thread *td; 822 823 MPASS(ts != NULL); 824 mtx_assert(&ts->ts_lock, MA_OWNED); 825 MPASS(curthread->td_proc->p_magic == P_MAGIC); 826 MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL); 827 /* 828 * We must have the chain locked so that we can remove the empty 829 * turnstile from the hash queue. 830 */ 831 tc = TC_LOOKUP(ts->ts_lockobj); 832 mtx_assert(&tc->tc_lock, MA_OWNED); 833 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 834 835 /* 836 * Transfer the blocked list to the pending list. 837 */ 838 mtx_lock_spin(&td_contested_lock); 839 TAILQ_CONCAT(&ts->ts_pending, &ts->ts_blocked[queue], td_lockq); 840 mtx_unlock_spin(&td_contested_lock); 841 842 /* 843 * Give a turnstile to each thread. The last thread gets 844 * this turnstile if the turnstile is empty. 845 */ 846 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) { 847 if (LIST_EMPTY(&ts->ts_free)) { 848 MPASS(TAILQ_NEXT(td, td_lockq) == NULL); 849 ts1 = ts; 850 #ifdef TURNSTILE_PROFILING 851 tc->tc_depth--; 852 #endif 853 } else 854 ts1 = LIST_FIRST(&ts->ts_free); 855 MPASS(ts1 != NULL); 856 LIST_REMOVE(ts1, ts_hash); 857 td->td_turnstile = ts1; 858 } 859 } 860 861 /* 862 * Wakeup all threads on the pending list and adjust the priority of the 863 * current thread appropriately. This must be called with the turnstile 864 * chain locked. 865 */ 866 void 867 turnstile_unpend(struct turnstile *ts, int owner_type) 868 { 869 TAILQ_HEAD( ,thread) pending_threads; 870 struct turnstile *nts; 871 struct thread *td; 872 u_char cp, pri; 873 874 MPASS(ts != NULL); 875 mtx_assert(&ts->ts_lock, MA_OWNED); 876 MPASS(ts->ts_owner == curthread || ts->ts_owner == NULL); 877 MPASS(!TAILQ_EMPTY(&ts->ts_pending)); 878 879 /* 880 * Move the list of pending threads out of the turnstile and 881 * into a local variable. 882 */ 883 TAILQ_INIT(&pending_threads); 884 TAILQ_CONCAT(&pending_threads, &ts->ts_pending, td_lockq); 885 #ifdef INVARIANTS 886 if (TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) && 887 TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])) 888 ts->ts_lockobj = NULL; 889 #endif 890 /* 891 * Adjust the priority of curthread based on other contested 892 * locks it owns. Don't lower the priority below the base 893 * priority however. 894 */ 895 td = curthread; 896 pri = PRI_MAX; 897 thread_lock(td); 898 mtx_lock_spin(&td_contested_lock); 899 /* 900 * Remove the turnstile from this thread's list of contested locks 901 * since this thread doesn't own it anymore. New threads will 902 * not be blocking on the turnstile until it is claimed by a new 903 * owner. There might not be a current owner if this is a shared 904 * lock. 905 */ 906 if (ts->ts_owner != NULL) { 907 ts->ts_owner = NULL; 908 LIST_REMOVE(ts, ts_link); 909 } 910 LIST_FOREACH(nts, &td->td_contested, ts_link) { 911 cp = turnstile_first_waiter(nts)->td_priority; 912 if (cp < pri) 913 pri = cp; 914 } 915 mtx_unlock_spin(&td_contested_lock); 916 sched_unlend_prio(td, pri); 917 thread_unlock(td); 918 /* 919 * Wake up all the pending threads. If a thread is not blocked 920 * on a lock, then it is currently executing on another CPU in 921 * turnstile_wait() or sitting on a run queue waiting to resume 922 * in turnstile_wait(). Set a flag to force it to try to acquire 923 * the lock again instead of blocking. 924 */ 925 while (!TAILQ_EMPTY(&pending_threads)) { 926 td = TAILQ_FIRST(&pending_threads); 927 TAILQ_REMOVE(&pending_threads, td, td_lockq); 928 SDT_PROBE2(sched, , , wakeup, td, td->td_proc); 929 thread_lock(td); 930 THREAD_LOCKPTR_ASSERT(td, &ts->ts_lock); 931 MPASS(td->td_proc->p_magic == P_MAGIC); 932 MPASS(TD_ON_LOCK(td)); 933 TD_CLR_LOCK(td); 934 MPASS(TD_CAN_RUN(td)); 935 td->td_blocked = NULL; 936 td->td_lockname = NULL; 937 td->td_blktick = 0; 938 #ifdef INVARIANTS 939 td->td_tsqueue = 0xff; 940 #endif 941 sched_add(td, SRQ_BORING); 942 thread_unlock(td); 943 } 944 mtx_unlock_spin(&ts->ts_lock); 945 } 946 947 /* 948 * Give up ownership of a turnstile. This must be called with the 949 * turnstile chain locked. 950 */ 951 void 952 turnstile_disown(struct turnstile *ts) 953 { 954 struct thread *td; 955 u_char cp, pri; 956 957 MPASS(ts != NULL); 958 mtx_assert(&ts->ts_lock, MA_OWNED); 959 MPASS(ts->ts_owner == curthread); 960 MPASS(TAILQ_EMPTY(&ts->ts_pending)); 961 MPASS(!TAILQ_EMPTY(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE]) || 962 !TAILQ_EMPTY(&ts->ts_blocked[TS_SHARED_QUEUE])); 963 964 /* 965 * Remove the turnstile from this thread's list of contested locks 966 * since this thread doesn't own it anymore. New threads will 967 * not be blocking on the turnstile until it is claimed by a new 968 * owner. 969 */ 970 mtx_lock_spin(&td_contested_lock); 971 ts->ts_owner = NULL; 972 LIST_REMOVE(ts, ts_link); 973 mtx_unlock_spin(&td_contested_lock); 974 975 /* 976 * Adjust the priority of curthread based on other contested 977 * locks it owns. Don't lower the priority below the base 978 * priority however. 979 */ 980 td = curthread; 981 pri = PRI_MAX; 982 thread_lock(td); 983 mtx_unlock_spin(&ts->ts_lock); 984 mtx_lock_spin(&td_contested_lock); 985 LIST_FOREACH(ts, &td->td_contested, ts_link) { 986 cp = turnstile_first_waiter(ts)->td_priority; 987 if (cp < pri) 988 pri = cp; 989 } 990 mtx_unlock_spin(&td_contested_lock); 991 sched_unlend_prio(td, pri); 992 thread_unlock(td); 993 } 994 995 /* 996 * Return the first thread in a turnstile. 997 */ 998 struct thread * 999 turnstile_head(struct turnstile *ts, int queue) 1000 { 1001 #ifdef INVARIANTS 1002 1003 MPASS(ts != NULL); 1004 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 1005 mtx_assert(&ts->ts_lock, MA_OWNED); 1006 #endif 1007 return (TAILQ_FIRST(&ts->ts_blocked[queue])); 1008 } 1009 1010 /* 1011 * Returns true if a sub-queue of a turnstile is empty. 1012 */ 1013 int 1014 turnstile_empty(struct turnstile *ts, int queue) 1015 { 1016 #ifdef INVARIANTS 1017 1018 MPASS(ts != NULL); 1019 MPASS(queue == TS_SHARED_QUEUE || queue == TS_EXCLUSIVE_QUEUE); 1020 mtx_assert(&ts->ts_lock, MA_OWNED); 1021 #endif 1022 return (TAILQ_EMPTY(&ts->ts_blocked[queue])); 1023 } 1024 1025 #ifdef DDB 1026 static void 1027 print_thread(struct thread *td, const char *prefix) 1028 { 1029 1030 db_printf("%s%p (tid %d, pid %d, \"%s\")\n", prefix, td, td->td_tid, 1031 td->td_proc->p_pid, td->td_name); 1032 } 1033 1034 static void 1035 print_queue(struct threadqueue *queue, const char *header, const char *prefix) 1036 { 1037 struct thread *td; 1038 1039 db_printf("%s:\n", header); 1040 if (TAILQ_EMPTY(queue)) { 1041 db_printf("%sempty\n", prefix); 1042 return; 1043 } 1044 TAILQ_FOREACH(td, queue, td_lockq) { 1045 print_thread(td, prefix); 1046 } 1047 } 1048 1049 DB_SHOW_COMMAND(turnstile, db_show_turnstile) 1050 { 1051 struct turnstile_chain *tc; 1052 struct turnstile *ts; 1053 struct lock_object *lock; 1054 int i; 1055 1056 if (!have_addr) 1057 return; 1058 1059 /* 1060 * First, see if there is an active turnstile for the lock indicated 1061 * by the address. 1062 */ 1063 lock = (struct lock_object *)addr; 1064 tc = TC_LOOKUP(lock); 1065 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 1066 if (ts->ts_lockobj == lock) 1067 goto found; 1068 1069 /* 1070 * Second, see if there is an active turnstile at the address 1071 * indicated. 1072 */ 1073 for (i = 0; i < TC_TABLESIZE; i++) 1074 LIST_FOREACH(ts, &turnstile_chains[i].tc_turnstiles, ts_hash) { 1075 if (ts == (struct turnstile *)addr) 1076 goto found; 1077 } 1078 1079 db_printf("Unable to locate a turnstile via %p\n", (void *)addr); 1080 return; 1081 found: 1082 lock = ts->ts_lockobj; 1083 db_printf("Lock: %p - (%s) %s\n", lock, LOCK_CLASS(lock)->lc_name, 1084 lock->lo_name); 1085 if (ts->ts_owner) 1086 print_thread(ts->ts_owner, "Lock Owner: "); 1087 else 1088 db_printf("Lock Owner: none\n"); 1089 print_queue(&ts->ts_blocked[TS_SHARED_QUEUE], "Shared Waiters", "\t"); 1090 print_queue(&ts->ts_blocked[TS_EXCLUSIVE_QUEUE], "Exclusive Waiters", 1091 "\t"); 1092 print_queue(&ts->ts_pending, "Pending Threads", "\t"); 1093 1094 } 1095 1096 /* 1097 * Show all the threads a particular thread is waiting on based on 1098 * non-spin locks. 1099 */ 1100 static void 1101 print_lockchain(struct thread *td, const char *prefix) 1102 { 1103 struct lock_object *lock; 1104 struct lock_class *class; 1105 struct turnstile *ts; 1106 struct thread *owner; 1107 1108 /* 1109 * Follow the chain. We keep walking as long as the thread is 1110 * blocked on a lock that has an owner. 1111 */ 1112 while (!db_pager_quit) { 1113 db_printf("%sthread %d (pid %d, %s) ", prefix, td->td_tid, 1114 td->td_proc->p_pid, td->td_name); 1115 switch (td->td_state) { 1116 case TDS_INACTIVE: 1117 db_printf("is inactive\n"); 1118 return; 1119 case TDS_CAN_RUN: 1120 db_printf("can run\n"); 1121 return; 1122 case TDS_RUNQ: 1123 db_printf("is on a run queue\n"); 1124 return; 1125 case TDS_RUNNING: 1126 db_printf("running on CPU %d\n", td->td_oncpu); 1127 return; 1128 case TDS_INHIBITED: 1129 if (TD_ON_LOCK(td)) { 1130 ts = td->td_blocked; 1131 lock = ts->ts_lockobj; 1132 class = LOCK_CLASS(lock); 1133 db_printf("blocked on lock %p (%s) \"%s\"\n", 1134 lock, class->lc_name, lock->lo_name); 1135 if (ts->ts_owner == NULL) 1136 return; 1137 td = ts->ts_owner; 1138 break; 1139 } else if (TD_ON_SLEEPQ(td)) { 1140 if (!lockmgr_chain(td, &owner) && 1141 !sx_chain(td, &owner)) { 1142 db_printf("sleeping on %p \"%s\"\n", 1143 td->td_wchan, td->td_wmesg); 1144 return; 1145 } 1146 if (owner == NULL) 1147 return; 1148 td = owner; 1149 break; 1150 } 1151 db_printf("inhibited\n"); 1152 return; 1153 default: 1154 db_printf("??? (%#x)\n", td->td_state); 1155 return; 1156 } 1157 } 1158 } 1159 1160 DB_SHOW_COMMAND(lockchain, db_show_lockchain) 1161 { 1162 struct thread *td; 1163 1164 /* Figure out which thread to start with. */ 1165 if (have_addr) 1166 td = db_lookup_thread(addr, true); 1167 else 1168 td = kdb_thread; 1169 1170 print_lockchain(td, ""); 1171 } 1172 DB_SHOW_ALIAS(sleepchain, db_show_lockchain); 1173 1174 DB_SHOW_ALL_COMMAND(chains, db_show_allchains) 1175 { 1176 struct thread *td; 1177 struct proc *p; 1178 int i; 1179 1180 i = 1; 1181 FOREACH_PROC_IN_SYSTEM(p) { 1182 FOREACH_THREAD_IN_PROC(p, td) { 1183 if ((TD_ON_LOCK(td) && LIST_EMPTY(&td->td_contested)) 1184 || (TD_IS_INHIBITED(td) && TD_ON_SLEEPQ(td))) { 1185 db_printf("chain %d:\n", i++); 1186 print_lockchain(td, " "); 1187 } 1188 if (db_pager_quit) 1189 return; 1190 } 1191 } 1192 } 1193 DB_SHOW_ALIAS(allchains, db_show_allchains) 1194 1195 static void print_waiters(struct turnstile *ts, int indent); 1196 1197 static void 1198 print_waiter(struct thread *td, int indent) 1199 { 1200 struct turnstile *ts; 1201 int i; 1202 1203 if (db_pager_quit) 1204 return; 1205 for (i = 0; i < indent; i++) 1206 db_printf(" "); 1207 print_thread(td, "thread "); 1208 LIST_FOREACH(ts, &td->td_contested, ts_link) 1209 print_waiters(ts, indent + 1); 1210 } 1211 1212 static void 1213 print_waiters(struct turnstile *ts, int indent) 1214 { 1215 struct lock_object *lock; 1216 struct lock_class *class; 1217 struct thread *td; 1218 int i; 1219 1220 if (db_pager_quit) 1221 return; 1222 lock = ts->ts_lockobj; 1223 class = LOCK_CLASS(lock); 1224 for (i = 0; i < indent; i++) 1225 db_printf(" "); 1226 db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name, lock->lo_name); 1227 TAILQ_FOREACH(td, &ts->ts_blocked[TS_EXCLUSIVE_QUEUE], td_lockq) 1228 print_waiter(td, indent + 1); 1229 TAILQ_FOREACH(td, &ts->ts_blocked[TS_SHARED_QUEUE], td_lockq) 1230 print_waiter(td, indent + 1); 1231 TAILQ_FOREACH(td, &ts->ts_pending, td_lockq) 1232 print_waiter(td, indent + 1); 1233 } 1234 1235 DB_SHOW_COMMAND(locktree, db_show_locktree) 1236 { 1237 struct lock_object *lock; 1238 struct lock_class *class; 1239 struct turnstile_chain *tc; 1240 struct turnstile *ts; 1241 1242 if (!have_addr) 1243 return; 1244 lock = (struct lock_object *)addr; 1245 tc = TC_LOOKUP(lock); 1246 LIST_FOREACH(ts, &tc->tc_turnstiles, ts_hash) 1247 if (ts->ts_lockobj == lock) 1248 break; 1249 if (ts == NULL) { 1250 class = LOCK_CLASS(lock); 1251 db_printf("lock %p (%s) \"%s\"\n", lock, class->lc_name, 1252 lock->lo_name); 1253 } else 1254 print_waiters(ts, 0); 1255 } 1256 #endif 1257