kern_rwlock.c revision 173960
1154941Sjhb/*- 2154941Sjhb * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org> 3154941Sjhb * All rights reserved. 4154941Sjhb * 5154941Sjhb * Redistribution and use in source and binary forms, with or without 6154941Sjhb * modification, are permitted provided that the following conditions 7154941Sjhb * are met: 8154941Sjhb * 1. Redistributions of source code must retain the above copyright 9154941Sjhb * notice, this list of conditions and the following disclaimer. 10154941Sjhb * 2. Redistributions in binary form must reproduce the above copyright 11154941Sjhb * notice, this list of conditions and the following disclaimer in the 12154941Sjhb * documentation and/or other materials provided with the distribution. 13154941Sjhb * 3. Neither the name of the author nor the names of any co-contributors 14154941Sjhb * may be used to endorse or promote products derived from this software 15154941Sjhb * without specific prior written permission. 16154941Sjhb * 17154941Sjhb * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18154941Sjhb * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19154941Sjhb * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20154941Sjhb * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21154941Sjhb * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22154941Sjhb * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23154941Sjhb * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24154941Sjhb * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25154941Sjhb * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26154941Sjhb * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27154941Sjhb * SUCH DAMAGE. 28154941Sjhb */ 29154941Sjhb 30154941Sjhb/* 31154941Sjhb * Machine independent bits of reader/writer lock implementation. 32154941Sjhb */ 33154941Sjhb 34154941Sjhb#include <sys/cdefs.h> 35154941Sjhb__FBSDID("$FreeBSD: head/sys/kern/kern_rwlock.c 173960 2007-11-26 22:37:35Z attilio $"); 36154941Sjhb 37154941Sjhb#include "opt_ddb.h" 38192853Ssson#include "opt_no_adaptive_rwlocks.h" 39167801Sjhb 40154941Sjhb#include <sys/param.h> 41154941Sjhb#include <sys/ktr.h> 42154941Sjhb#include <sys/lock.h> 43177912Sjeff#include <sys/mutex.h> 44154941Sjhb#include <sys/proc.h> 45154941Sjhb#include <sys/rwlock.h> 46154941Sjhb#include <sys/systm.h> 47154941Sjhb#include <sys/turnstile.h> 48177912Sjeff 49154941Sjhb#include <machine/cpu.h> 50154941Sjhb 51171516SattilioCTASSERT((RW_RECURSE & LO_CLASSFLAGS) == RW_RECURSE); 52154941Sjhb 53154941Sjhb#if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS) 54171052Sattilio#define ADAPTIVE_RWLOCKS 55171052Sattilio#endif 56167801Sjhb 57167801Sjhb#ifdef DDB 58167801Sjhb#include <ddb/ddb.h> 59167801Sjhb 60177912Sjeffstatic void db_show_rwlock(struct lock_object *lock); 61177912Sjeff#endif 62177912Sjeffstatic void assert_rw(struct lock_object *lock, int what); 63177912Sjeffstatic void lock_rw(struct lock_object *lock, int how); 64177912Sjeffstatic int unlock_rw(struct lock_object *lock); 65177912Sjeff 66177912Sjeffstruct lock_class lock_class_rw = { 67177912Sjeff .lc_name = "rw", 68154941Sjhb .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE, 69154941Sjhb .lc_assert = assert_rw, 70154941Sjhb#ifdef DDB 71154941Sjhb .lc_ddb_show = db_show_rwlock, 72154941Sjhb#endif 73173733Sattilio .lc_lock = lock_rw, 74167368Sjhb .lc_unlock = unlock_rw, 75192853Ssson}; 76192853Ssson 77192853Ssson/* 78167368Sjhb * Return a pointer to the owning thread if the lock is write-locked or 79154941Sjhb * NULL if the lock is unlocked or read-locked. 80154941Sjhb */ 81167365Sjhb#define rw_wowner(rw) \ 82167365Sjhb ((rw)->rw_lock & RW_LOCK_READ ? NULL : \ 83173733Sattilio (struct thread *)RW_OWNER((rw)->rw_lock)) 84154941Sjhb 85167365Sjhb/* 86154941Sjhb * Returns if a write owner is recursed. Write ownership is not assured 87167368Sjhb * here and should be previously checked. 88167368Sjhb */ 89192853Ssson#define rw_recursed(rw) ((rw)->rw_recurse != 0) 90192853Ssson 91192853Ssson/* 92154941Sjhb * Return true if curthread helds the lock. 93154941Sjhb */ 94157826Sjhb#define rw_wlocked(rw) (rw_wowner((rw)) == curthread) 95157826Sjhb 96157826Sjhb/* 97157826Sjhb * Return a pointer to the owning thread for this lock who should receive 98157826Sjhb * any priority lent by threads that block on this lock. Currently this 99154941Sjhb * is identical to rw_wowner(). 100154941Sjhb */ 101154941Sjhb#define rw_owner(rw) rw_wowner(rw) 102157826Sjhb 103171052Sattilio#ifndef INVARIANTS 104171052Sattilio#define _rw_assert(rw, what, file, line) 105171052Sattilio#endif 106171052Sattilio 107171052Sattiliovoid 108171052Sattilioassert_rw(struct lock_object *lock, int what) 109171052Sattilio{ 110171052Sattilio 111171052Sattilio rw_assert((struct rwlock *)lock, what); 112171052Sattilio} 113171052Sattilio 114157826Sjhbvoid 115157826Sjhblock_rw(struct lock_object *lock, int how) 116157826Sjhb{ 117157826Sjhb struct rwlock *rw; 118157826Sjhb 119157826Sjhb rw = (struct rwlock *)lock; 120154941Sjhb if (how) 121154941Sjhb rw_wlock(rw); 122154941Sjhb else 123154941Sjhb rw_rlock(rw); 124154941Sjhb} 125173733Sattilio 126173733Sattilioint 127173733Sattiliounlock_rw(struct lock_object *lock) 128173733Sattilio{ 129173733Sattilio struct rwlock *rw; 130173733Sattilio 131173733Sattilio rw = (struct rwlock *)lock; 132167368Sjhb rw_assert(rw, RA_LOCKED | LA_NOTRECURSED); 133167368Sjhb if (rw->rw_lock & RW_LOCK_READ) { 134167368Sjhb rw_runlock(rw); 135167368Sjhb return (0); 136167368Sjhb } else { 137167368Sjhb rw_wunlock(rw); 138167368Sjhb return (1); 139167368Sjhb } 140167368Sjhb} 141167368Sjhb 142167368Sjhbvoid 143167368Sjhbrw_init_flags(struct rwlock *rw, const char *name, int opts) 144167368Sjhb{ 145167368Sjhb int flags; 146167368Sjhb 147167368Sjhb MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET | 148167368Sjhb RW_RECURSE)) == 0); 149167368Sjhb 150167368Sjhb flags = LO_UPGRADABLE | LO_RECURSABLE; 151167368Sjhb if (opts & RW_DUPOK) 152167368Sjhb flags |= LO_DUPOK; 153167368Sjhb if (opts & RW_NOPROFILE) 154167368Sjhb flags |= LO_NOPROFILE; 155167368Sjhb if (!(opts & RW_NOWITNESS)) 156167368Sjhb flags |= LO_WITNESS; 157167368Sjhb if (opts & RW_QUIET) 158167368Sjhb flags |= LO_QUIET; 159192853Ssson flags |= opts & RW_RECURSE; 160192853Ssson 161192853Ssson rw->rw_lock = RW_UNLOCKED; 162192853Ssson rw->rw_recurse = 0; 163192853Ssson lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags); 164192853Ssson} 165192853Ssson 166192853Sssonvoid 167192853Sssonrw_destroy(struct rwlock *rw) 168192853Ssson{ 169192853Ssson 170192853Ssson KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock not unlocked")); 171192853Ssson KASSERT(rw->rw_recurse == 0, ("rw lock still recursed")); 172167368Sjhb rw->rw_lock = RW_DESTROYED; 173171052Sattilio lock_destroy(&rw->lock_object); 174154941Sjhb} 175171052Sattilio 176154941Sjhbvoid 177171052Sattiliorw_sysinit(void *arg) 178171052Sattilio{ 179171052Sattilio struct rw_args *args = arg; 180171052Sattilio 181171052Sattilio rw_init(args->ra_rw, args->ra_desc); 182171052Sattilio} 183171052Sattilio 184171052Sattilioint 185171052Sattiliorw_wowned(struct rwlock *rw) 186171052Sattilio{ 187171052Sattilio 188171052Sattilio return (rw_wowner(rw) == curthread); 189171052Sattilio} 190171052Sattilio 191154941Sjhbvoid 192171052Sattilio_rw_wlock(struct rwlock *rw, const char *file, int line) 193171052Sattilio{ 194154941Sjhb 195154941Sjhb MPASS(curthread != NULL); 196154941Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 197154941Sjhb ("rw_wlock() of destroyed rwlock @ %s:%d", file, line)); 198154941Sjhb WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file, 199154941Sjhb line); 200154941Sjhb __rw_wlock(rw, curthread, file, line); 201171052Sattilio LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line); 202169394Sjhb WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 203167787Sjhb curthread->td_locks++; 204154941Sjhb} 205154941Sjhb 206154941Sjhbvoid 207154941Sjhb_rw_wunlock(struct rwlock *rw, const char *file, int line) 208154941Sjhb{ 209154941Sjhb 210154941Sjhb MPASS(curthread != NULL); 211154941Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 212154941Sjhb ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line)); 213154941Sjhb _rw_assert(rw, RA_WLOCKED, file, line); 214185778Skmacy curthread->td_locks--; 215185778Skmacy WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 216185778Skmacy LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file, 217185778Skmacy line); 218185778Skmacy if (!rw_recursed(rw)) 219185778Skmacy lock_profile_release_lock(&rw->lock_object); 220185778Skmacy __rw_wunlock(rw, curthread, file, line); 221185778Skmacy} 222167024Srwatson 223167024Srwatsonvoid 224167024Srwatson_rw_rlock(struct rwlock *rw, const char *file, int line) 225167024Srwatson{ 226167024Srwatson struct turnstile *ts; 227167024Srwatson#ifdef ADAPTIVE_RWLOCKS 228167024Srwatson volatile struct thread *owner; 229154941Sjhb#endif 230154941Sjhb#ifdef LOCK_PROFILING_SHARED 231154941Sjhb uint64_t waittime = 0; 232154941Sjhb int contested = 0; 233154941Sjhb#endif 234169394Sjhb uintptr_t x; 235169394Sjhb 236167787Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 237182914Sjhb ("rw_rlock() of destroyed rwlock @ %s:%d", file, line)); 238154941Sjhb KASSERT(rw_wowner(rw) != curthread, 239171052Sattilio ("%s (%s): wlock already held @ %s:%d", __func__, 240167787Sjhb rw->lock_object.lo_name, file, line)); 241160771Sjhb WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line); 242154941Sjhb 243154941Sjhb /* 244177843Sattilio * Note that we don't make any attempt to try to block read 245177843Sattilio * locks once a writer has blocked on the lock. The reason is 246177843Sattilio * that we currently allow for read locks to recurse and we 247177843Sattilio * don't keep track of all the holders of read locks. Thus, if 248177843Sattilio * we were to block readers once a writer blocked and a reader 249177843Sattilio * tried to recurse on their reader lock after a writer had 250177843Sattilio * blocked we would end up in a deadlock since the reader would 251177843Sattilio * be blocked on the writer, and the writer would be blocked 252177843Sattilio * waiting for the reader to release its original read lock. 253177843Sattilio */ 254177843Sattilio for (;;) { 255177843Sattilio /* 256177843Sattilio * Handle the easy case. If no other thread has a write 257177843Sattilio * lock, then try to bump up the count of read locks. Note 258177843Sattilio * that we have to preserve the current state of the 259177843Sattilio * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a 260177843Sattilio * read lock, then rw_lock must have changed, so restart 261177843Sattilio * the loop. Note that this handles the case of a 262177843Sattilio * completely unlocked rwlock since such a lock is encoded 263177843Sattilio * as a read lock with no waiters. 264177843Sattilio */ 265177843Sattilio x = rw->rw_lock; 266177843Sattilio if (x & RW_LOCK_READ) { 267177843Sattilio 268154941Sjhb /* 269154941Sjhb * The RW_LOCK_READ_WAITERS flag should only be set 270154941Sjhb * if another thread currently holds a write lock, 271154941Sjhb * and in that case RW_LOCK_READ should be clear. 272154941Sjhb */ 273169394Sjhb MPASS((x & RW_LOCK_READ_WAITERS) == 0); 274169394Sjhb if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, 275154941Sjhb x + RW_ONE_READER)) { 276160771Sjhb#ifdef LOCK_PROFILING_SHARED 277167787Sjhb if (RW_READERS(x) == 0) 278171052Sattilio lock_profile_obtain_lock_success( 279171052Sattilio &rw->lock_object, contested, 280171052Sattilio waittime, file, line); 281192853Ssson#endif 282154941Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 283154941Sjhb CTR4(KTR_LOCK, 284176017Sjeff "%s: %p succeed %p -> %p", __func__, 285176017Sjeff rw, (void *)x, 286176017Sjeff (void *)(x + RW_ONE_READER)); 287176017Sjeff break; 288176017Sjeff } 289176017Sjeff cpu_spinwait(); 290176017Sjeff continue; 291176017Sjeff } 292176017Sjeff 293176017Sjeff#ifdef ADAPTIVE_RWLOCKS 294176017Sjeff /* 295154941Sjhb * If the owner is running on another CPU, spin until 296154941Sjhb * the owner stops running or the state of the lock 297154941Sjhb * changes. 298154941Sjhb */ 299170295Sjeff owner = (struct thread *)RW_OWNER(x); 300167801Sjhb if (TD_IS_RUNNING(owner)) { 301157846Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 302177912Sjeff CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 303177912Sjeff __func__, rw, owner); 304157851Swkoszek#ifdef LOCK_PROFILING_SHARED 305189846Sjeff lock_profile_obtain_lock_failed(&rw->lock_object, 306167307Sjhb &contested, &waittime); 307167054Skmacy#endif 308189846Sjeff while ((struct thread*)RW_OWNER(rw->rw_lock) == owner && 309176017Sjeff TD_IS_RUNNING(owner)) 310192853Ssson cpu_spinwait(); 311192853Ssson continue; 312192853Ssson } 313192853Ssson#endif 314192853Ssson 315154941Sjhb /* 316169394Sjhb * Okay, now it's the hard case. Some other thread already 317169394Sjhb * has a write lock, so acquire the turnstile lock so we can 318157826Sjhb * begin the process of blocking. 319154941Sjhb */ 320167787Sjhb ts = turnstile_trywait(&rw->lock_object); 321182914Sjhb 322154941Sjhb /* 323154941Sjhb * The lock might have been released while we spun, so 324192853Ssson * recheck its state and restart the loop if there is no 325192853Ssson * longer a write lock. 326192853Ssson */ 327154941Sjhb x = rw->rw_lock; 328154941Sjhb if (x & RW_LOCK_READ) { 329154941Sjhb turnstile_cancel(ts); 330154941Sjhb cpu_spinwait(); 331154941Sjhb continue; 332154941Sjhb } 333154941Sjhb 334154941Sjhb#ifdef ADAPTIVE_RWLOCKS 335154941Sjhb /* 336154941Sjhb * If the current owner of the lock is executing on another 337176017Sjeff * CPU quit the hard path and try to spin. 338176017Sjeff */ 339154941Sjhb owner = (struct thread *)RW_OWNER(x); 340154941Sjhb if (TD_IS_RUNNING(owner)) { 341176017Sjeff turnstile_cancel(ts); 342176017Sjeff cpu_spinwait(); 343154941Sjhb continue; 344176017Sjeff } 345176017Sjeff#endif 346167787Sjhb 347154941Sjhb /* 348154941Sjhb * Ok, it's still a write lock. If the RW_LOCK_READ_WAITERS 349176017Sjeff * flag is already set, then we can go ahead and block. If 350176017Sjeff * it is not set then try to set it. If we fail to set it 351154941Sjhb * drop the turnstile lock and restart the loop. 352154941Sjhb */ 353157846Sjhb if (!(x & RW_LOCK_READ_WAITERS)) { 354154941Sjhb if (!atomic_cmpset_ptr(&rw->rw_lock, x, 355154941Sjhb x | RW_LOCK_READ_WAITERS)) { 356174629Sjeff turnstile_cancel(ts); 357174629Sjeff cpu_spinwait(); 358154941Sjhb continue; 359173960Sattilio } 360154941Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 361173960Sattilio CTR2(KTR_LOCK, "%s: %p set read waiters flag", 362173960Sattilio __func__, rw); 363173960Sattilio } 364173960Sattilio 365176017Sjeff /* 366176017Sjeff * We were unable to acquire the lock and the read waiters 367176017Sjeff * flag is set, so we must block on the turnstile. 368176017Sjeff */ 369176017Sjeff if (LOCK_LOG_TEST(&rw->lock_object, 0)) 370176017Sjeff CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 371176017Sjeff rw); 372176017Sjeff#ifdef LOCK_PROFILING_SHARED 373192853Ssson lock_profile_obtain_lock_failed(&rw->lock_object, &contested, 374176017Sjeff &waittime); 375192853Ssson#endif 376192853Ssson turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE); 377192853Ssson if (LOCK_LOG_TEST(&rw->lock_object, 0)) 378192853Ssson CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 379176017Sjeff __func__, rw); 380176017Sjeff } 381177912Sjeff 382177912Sjeff /* 383177912Sjeff * TODO: acquire "owner of record" here. Here be turnstile dragons 384177912Sjeff * however. turnstiles don't like owners changing between calls to 385177912Sjeff * turnstile_wait() currently. 386177912Sjeff */ 387177912Sjeff 388177912Sjeff LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line); 389177912Sjeff WITNESS_LOCK(&rw->lock_object, 0, file, line); 390177912Sjeff curthread->td_locks++; 391173960Sattilio} 392173960Sattilio 393173960Sattiliovoid 394173960Sattilio_rw_runlock(struct rwlock *rw, const char *file, int line) 395154941Sjhb{ 396176017Sjeff struct turnstile *ts; 397176017Sjeff uintptr_t x; 398176017Sjeff 399154941Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 400170295Sjeff ("rw_runlock() of destroyed rwlock @ %s:%d", file, line)); 401154941Sjhb _rw_assert(rw, RA_RLOCKED, file, line); 402154941Sjhb curthread->td_locks--; 403154941Sjhb WITNESS_UNLOCK(&rw->lock_object, 0, file, line); 404176017Sjeff LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line); 405154941Sjhb 406176017Sjeff /* TODO: drop "owner of record" here. */ 407176017Sjeff 408170295Sjeff for (;;) { 409157846Sjhb /* 410154941Sjhb * See if there is more than one read lock held. If so, 411154941Sjhb * just drop one and return. 412154941Sjhb */ 413173960Sattilio x = rw->rw_lock; 414154941Sjhb if (RW_READERS(x) > 1) { 415173960Sattilio if (atomic_cmpset_ptr(&rw->rw_lock, x, 416173960Sattilio x - RW_ONE_READER)) { 417173960Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 418176017Sjeff CTR4(KTR_LOCK, 419176017Sjeff "%s: %p succeeded %p -> %p", 420176017Sjeff __func__, rw, (void *)x, 421176017Sjeff (void *)(x - RW_ONE_READER)); 422176017Sjeff break; 423176017Sjeff } 424176017Sjeff continue; 425173960Sattilio } 426173960Sattilio 427173960Sattilio 428173960Sattilio /* 429176017Sjeff * We should never have read waiters while at least one 430154941Sjhb * thread holds a read lock. (See note above) 431176017Sjeff */ 432176017Sjeff KASSERT(!(x & RW_LOCK_READ_WAITERS), 433176017Sjeff ("%s: waiting readers", __func__)); 434176017Sjeff#ifdef LOCK_PROFILING_SHARED 435176017Sjeff lock_profile_release_lock(&rw->lock_object); 436176017Sjeff#endif 437176017Sjeff 438176017Sjeff /* 439176017Sjeff * If there aren't any waiters for a write lock, then try 440176017Sjeff * to drop it quickly. 441176017Sjeff */ 442170295Sjeff if (!(x & RW_LOCK_WRITE_WAITERS)) { 443157826Sjhb 444157826Sjhb /* 445157826Sjhb * There shouldn't be any flags set and we should 446167787Sjhb * be the only read lock. If we fail to release 447157826Sjhb * the single read lock, then another thread might 448157826Sjhb * have just acquired a read lock, so go back up 449154941Sjhb * to the multiple read locks case. 450154941Sjhb */ 451154941Sjhb MPASS(x == RW_READERS_LOCK(1)); 452154941Sjhb if (atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1), 453154941Sjhb RW_UNLOCKED)) { 454154941Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 455167787Sjhb CTR2(KTR_LOCK, "%s: %p last succeeded", 456154941Sjhb __func__, rw); 457154941Sjhb break; 458192853Ssson } 459192853Ssson continue; 460192853Ssson } 461170295Sjeff 462192853Ssson /* 463192853Ssson * There should just be one reader with one or more 464192853Ssson * writers waiting. 465192853Ssson */ 466167787Sjhb MPASS(x == (RW_READERS_LOCK(1) | RW_LOCK_WRITE_WAITERS)); 467154941Sjhb 468154941Sjhb /* 469154941Sjhb * Ok, we know we have a waiting writer and we think we 470154941Sjhb * are the last reader, so grab the turnstile lock. 471154941Sjhb */ 472154941Sjhb turnstile_chain_lock(&rw->lock_object); 473154941Sjhb 474154941Sjhb /* 475154941Sjhb * Try to drop our lock leaving the lock in a unlocked 476192853Ssson * state. 477174629Sjeff * 478167787Sjhb * If you wanted to do explicit lock handoff you'd have to 479167787Sjhb * do it here. You'd also want to use turnstile_signal() 480160771Sjhb * and you'd have to handle the race where a higher 481176017Sjeff * priority thread blocks on the write lock before the 482192853Ssson * thread you wakeup actually runs and have the new thread 483192853Ssson * "steal" the lock. For now it's a lot simpler to just 484192853Ssson * wakeup all of the waiters. 485192853Ssson * 486192853Ssson * As above, if we fail, then another thread might have 487192853Ssson * acquired a read lock, so drop the turnstile lock and 488192853Ssson * restart. 489192853Ssson */ 490192853Ssson if (!atomic_cmpset_ptr(&rw->rw_lock, 491192853Ssson RW_READERS_LOCK(1) | RW_LOCK_WRITE_WAITERS, RW_UNLOCKED)) { 492154941Sjhb turnstile_chain_unlock(&rw->lock_object); 493154941Sjhb continue; 494177843Sattilio } 495177843Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 496177843Sattilio CTR2(KTR_LOCK, "%s: %p last succeeded with waiters", 497177843Sattilio __func__, rw); 498177843Sattilio 499177843Sattilio /* 500177843Sattilio * Ok. The lock is released and all that's left is to 501177843Sattilio * wake up the waiters. Note that the lock might not be 502177843Sattilio * free anymore, but in that case the writers will just 503177843Sattilio * block again if they run before the new lock holder(s) 504177843Sattilio * release the lock. 505177843Sattilio */ 506177843Sattilio ts = turnstile_lookup(&rw->lock_object); 507177843Sattilio MPASS(ts != NULL); 508177843Sattilio turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE); 509177843Sattilio turnstile_unpend(ts, TS_SHARED_LOCK); 510177843Sattilio turnstile_chain_unlock(&rw->lock_object); 511177843Sattilio break; 512177843Sattilio } 513177843Sattilio} 514177843Sattilio 515177843Sattilio/* 516177843Sattilio * This function is called when we are unable to obtain a write lock on the 517177843Sattilio * first try. This means that at least one other thread holds either a 518177843Sattilio * read or write lock. 519154941Sjhb */ 520154941Sjhbvoid 521154941Sjhb_rw_wlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) 522154941Sjhb{ 523176017Sjeff struct turnstile *ts; 524154941Sjhb#ifdef ADAPTIVE_RWLOCKS 525169394Sjhb volatile struct thread *owner; 526169394Sjhb#endif 527154941Sjhb uint64_t waittime = 0; 528160771Sjhb uintptr_t v; 529176017Sjeff int contested = 0; 530167787Sjhb 531167787Sjhb if (rw_wlocked(rw)) { 532154941Sjhb KASSERT(rw->lock_object.lo_flags & RW_RECURSE, 533154941Sjhb ("%s: recursing but non-recursive rw %s @ %s:%d\n", 534154941Sjhb __func__, rw->lock_object.lo_name, file, line)); 535154941Sjhb rw->rw_recurse++; 536154941Sjhb atomic_set_ptr(&rw->rw_lock, RW_LOCK_RECURSED); 537154941Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 538154941Sjhb CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw); 539154941Sjhb return; 540154941Sjhb } 541154941Sjhb 542154941Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 543154941Sjhb CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 544167787Sjhb rw->lock_object.lo_name, (void *)rw->rw_lock, file, line); 545154941Sjhb 546154941Sjhb while (!_rw_write_lock(rw, tid)) { 547154941Sjhb#ifdef ADAPTIVE_RWLOCKS 548154941Sjhb /* 549154941Sjhb * If the lock is write locked and the owner is 550154941Sjhb * running on another CPU, spin until the owner stops 551154941Sjhb * running or the state of the lock changes. 552167307Sjhb */ 553154941Sjhb v = rw->rw_lock; 554154941Sjhb owner = (struct thread *)RW_OWNER(v); 555154941Sjhb if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) { 556154941Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 557176017Sjeff CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 558176017Sjeff __func__, rw, owner); 559176017Sjeff lock_profile_obtain_lock_failed(&rw->lock_object, 560176017Sjeff &contested, &waittime); 561167787Sjhb while ((struct thread*)RW_OWNER(rw->rw_lock) == owner && 562154941Sjhb TD_IS_RUNNING(owner)) 563154941Sjhb cpu_spinwait(); 564154941Sjhb continue; 565154941Sjhb } 566154941Sjhb#endif 567154941Sjhb 568154941Sjhb ts = turnstile_trywait(&rw->lock_object); 569176017Sjeff v = rw->rw_lock; 570176017Sjeff 571154941Sjhb /* 572170295Sjeff * If the lock was released while spinning on the 573176017Sjeff * turnstile chain lock, try again. 574176017Sjeff */ 575154941Sjhb if (v == RW_UNLOCKED) { 576154941Sjhb turnstile_cancel(ts); 577154941Sjhb cpu_spinwait(); 578154941Sjhb continue; 579154941Sjhb } 580154941Sjhb 581154941Sjhb#ifdef ADAPTIVE_RWLOCKS 582154941Sjhb /* 583154941Sjhb * If the current owner of the lock is executing on another 584154941Sjhb * CPU quit the hard path and try to spin. 585154941Sjhb */ 586154941Sjhb if (!(v & RW_LOCK_READ)) { 587154941Sjhb owner = (struct thread *)RW_OWNER(v); 588154941Sjhb if (TD_IS_RUNNING(owner)) { 589154941Sjhb turnstile_cancel(ts); 590154941Sjhb cpu_spinwait(); 591154941Sjhb continue; 592176017Sjeff } 593176017Sjeff } 594176017Sjeff#endif 595176017Sjeff 596176017Sjeff /* 597176017Sjeff * If the lock was released by a writer with both readers 598176017Sjeff * and writers waiting and a reader hasn't woken up and 599176017Sjeff * acquired the lock yet, rw_lock will be set to the 600170295Sjeff * value RW_UNLOCKED | RW_LOCK_WRITE_WAITERS. If we see 601154941Sjhb * that value, try to acquire it once. Note that we have 602154941Sjhb * to preserve the RW_LOCK_WRITE_WAITERS flag as there are 603167787Sjhb * other writers waiting still. If we fail, restart the 604154941Sjhb * loop. 605154941Sjhb */ 606154941Sjhb if (v == (RW_UNLOCKED | RW_LOCK_WRITE_WAITERS)) { 607154941Sjhb if (atomic_cmpset_acq_ptr(&rw->rw_lock, 608154941Sjhb RW_UNLOCKED | RW_LOCK_WRITE_WAITERS, 609154941Sjhb tid | RW_LOCK_WRITE_WAITERS)) { 610154941Sjhb turnstile_claim(ts); 611154941Sjhb CTR2(KTR_LOCK, "%s: %p claimed by new writer", 612154941Sjhb __func__, rw); 613154941Sjhb break; 614167787Sjhb } 615157846Sjhb turnstile_cancel(ts); 616176017Sjeff cpu_spinwait(); 617154941Sjhb continue; 618170295Sjeff } 619154941Sjhb 620154941Sjhb /* 621192853Ssson * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to 622154941Sjhb * set it. If we fail to set it, then loop back and try 623154941Sjhb * again. 624154941Sjhb */ 625154941Sjhb if (!(v & RW_LOCK_WRITE_WAITERS)) { 626154941Sjhb if (!atomic_cmpset_ptr(&rw->rw_lock, v, 627154941Sjhb v | RW_LOCK_WRITE_WAITERS)) { 628154941Sjhb turnstile_cancel(ts); 629154941Sjhb cpu_spinwait(); 630154941Sjhb continue; 631154941Sjhb } 632170295Sjeff if (LOCK_LOG_TEST(&rw->lock_object, 0)) 633167801Sjhb CTR2(KTR_LOCK, "%s: %p set write waiters flag", 634157846Sjhb __func__, rw); 635176017Sjeff } 636176017Sjeff 637157851Swkoszek /* 638189846Sjeff * We were unable to acquire the lock and the write waiters 639189846Sjeff * flag is set, so we must block on the turnstile. 640171516Sattilio */ 641171516Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 642189846Sjeff CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 643192853Ssson rw); 644192853Ssson lock_profile_obtain_lock_failed(&rw->lock_object, &contested, 645192853Ssson &waittime); 646192853Ssson turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE); 647192853Ssson if (LOCK_LOG_TEST(&rw->lock_object, 0)) 648154941Sjhb CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 649171052Sattilio __func__, rw); 650171052Sattilio } 651171052Sattilio lock_profile_obtain_lock_success(&rw->lock_object, contested, waittime, 652171052Sattilio file, line); 653171052Sattilio} 654171052Sattilio 655171052Sattilio/* 656171052Sattilio * This function is called if the first try at releasing a write lock failed. 657171052Sattilio * This means that one of the 2 waiter bits must be set indicating that at 658171052Sattilio * least one thread is waiting on this lock. 659167787Sjhb */ 660154941Sjhbvoid 661167787Sjhb_rw_wunlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) 662154941Sjhb{ 663154941Sjhb struct turnstile *ts; 664192853Ssson uintptr_t v; 665192853Ssson int queue; 666192853Ssson 667174629Sjeff if (rw_wlocked(rw) && rw_recursed(rw)) { 668174629Sjeff if ((--rw->rw_recurse) == 0) 669173960Sattilio atomic_clear_ptr(&rw->rw_lock, RW_LOCK_RECURSED); 670173960Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 671173960Sattilio CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw); 672173960Sattilio return; 673173960Sattilio } 674173960Sattilio 675173960Sattilio KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS), 676173960Sattilio ("%s: neither of the waiter flags are set", __func__)); 677173960Sattilio 678173960Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 679173960Sattilio CTR2(KTR_LOCK, "%s: %p contested", __func__, rw); 680173960Sattilio 681173960Sattilio turnstile_chain_lock(&rw->lock_object); 682192853Ssson ts = turnstile_lookup(&rw->lock_object); 683173960Sattilio 684192853Ssson MPASS(ts != NULL); 685192853Ssson 686192853Ssson /* 687192853Ssson * Use the same algo as sx locks for now. Prefer waking up shared 688173960Sattilio * waiters if we have any over writers. This is probably not ideal. 689173960Sattilio * 690177912Sjeff * 'v' is the value we are going to write back to rw_lock. If we 691177912Sjeff * have waiters on both queues, we need to preserve the state of 692176017Sjeff * the waiter flag for the queue we don't wake up. For now this is 693176017Sjeff * hardcoded for the algorithm mentioned above. 694176017Sjeff * 695176017Sjeff * In the case of both readers and writers waiting we wakeup the 696176017Sjeff * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a 697176017Sjeff * new writer comes in before a reader it will claim the lock up 698176017Sjeff * above. There is probably a potential priority inversion in 699176017Sjeff * there that could be worked around either by waking both queues 700177912Sjeff * of waiters or doing some complicated lock handoff gymnastics. 701176017Sjeff */ 702176017Sjeff v = RW_UNLOCKED; 703176017Sjeff if (rw->rw_lock & RW_LOCK_READ_WAITERS) { 704176017Sjeff queue = TS_SHARED_QUEUE; 705192853Ssson v |= (rw->rw_lock & RW_LOCK_WRITE_WAITERS); 706192853Ssson } else 707192853Ssson queue = TS_EXCLUSIVE_QUEUE; 708177912Sjeff 709176017Sjeff /* Wake up all waiters for the specific queue. */ 710176017Sjeff if (LOCK_LOG_TEST(&rw->lock_object, 0)) 711173960Sattilio CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw, 712170295Sjeff queue == TS_SHARED_QUEUE ? "read" : "write"); 713154941Sjhb turnstile_broadcast(ts, queue); 714154941Sjhb atomic_store_rel_ptr(&rw->rw_lock, v); 715173960Sattilio turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 716154941Sjhb turnstile_chain_unlock(&rw->lock_object); 717173960Sattilio} 718173960Sattilio 719173960Sattilio/* 720173960Sattilio * Attempt to do a non-blocking upgrade from a read lock to a write 721173960Sattilio * lock. This will only succeed if this thread holds a single read 722173960Sattilio * lock. Returns true if the upgrade succeeded and false otherwise. 723173960Sattilio */ 724173960Sattilioint 725173960Sattilio_rw_try_upgrade(struct rwlock *rw, const char *file, int line) 726173960Sattilio{ 727173960Sattilio uintptr_t v, tid; 728173960Sattilio struct turnstile *ts; 729173960Sattilio int success; 730179334Sattilio 731179334Sattilio KASSERT(rw->rw_lock != RW_DESTROYED, 732179334Sattilio ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line)); 733179334Sattilio _rw_assert(rw, RA_RLOCKED, file, line); 734179334Sattilio 735154941Sjhb /* 736176017Sjeff * Attempt to switch from one reader to a writer. If there 737176017Sjeff * are any write waiters, then we will have to lock the 738176017Sjeff * turnstile first to prevent races with another writer 739176017Sjeff * calling turnstile_wait() before we have claimed this 740176017Sjeff * turnstile. So, do the simple case of no waiters first. 741176017Sjeff */ 742176017Sjeff tid = (uintptr_t)curthread; 743176017Sjeff if (!(rw->rw_lock & RW_LOCK_WRITE_WAITERS)) { 744154941Sjhb success = atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1), 745154941Sjhb tid); 746170295Sjeff goto out; 747154941Sjhb } 748154941Sjhb 749154941Sjhb /* 750154941Sjhb * Ok, we think we have write waiters, so lock the 751154941Sjhb * turnstile. 752154941Sjhb */ 753154941Sjhb ts = turnstile_trywait(&rw->lock_object); 754154941Sjhb 755157826Sjhb /* 756157826Sjhb * Try to switch from one reader to a writer again. This time 757157826Sjhb * we honor the current state of the RW_LOCK_WRITE_WAITERS 758170295Sjeff * flag. If we obtain the lock with the flag set, then claim 759157826Sjhb * ownership of the turnstile. 760157826Sjhb */ 761157826Sjhb v = rw->rw_lock & RW_LOCK_WRITE_WAITERS; 762167787Sjhb success = atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v, 763157826Sjhb tid | v); 764157826Sjhb if (success && v) 765154941Sjhb turnstile_claim(ts); 766157846Sjhb else 767154941Sjhb turnstile_cancel(ts); 768154941Sjhbout: 769154941Sjhb LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line); 770167787Sjhb if (success) 771154941Sjhb WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 772154941Sjhb file, line); 773192853Ssson return (success); 774192853Ssson} 775192853Ssson 776170295Sjeff/* 777192853Ssson * Downgrade a write lock into a single read lock. 778192853Ssson */ 779192853Sssonvoid 780192853Ssson_rw_downgrade(struct rwlock *rw, const char *file, int line) 781167787Sjhb{ 782154941Sjhb struct turnstile *ts; 783154941Sjhb uintptr_t tid, v; 784176017Sjeff 785176017Sjeff KASSERT(rw->rw_lock != RW_DESTROYED, 786176017Sjeff ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line)); 787154941Sjhb _rw_assert(rw, RA_WLOCKED | RA_NOTRECURSED, file, line); 788192853Ssson#ifndef INVARIANTS 789192853Ssson if (rw_recursed(rw)) 790192853Ssson panic("downgrade of a recursed lock"); 791192853Ssson#endif 792192853Ssson 793192853Ssson WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line); 794192853Ssson 795192853Ssson /* 796192853Ssson * Convert from a writer to a single reader. First we handle 797192853Ssson * the easy case with no waiters. If there are any waiters, we 798192853Ssson * lock the turnstile, "disown" the lock, and awaken any read 799192853Ssson * waiters. 800154941Sjhb */ 801154941Sjhb tid = (uintptr_t)curthread; 802154941Sjhb if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1))) 803154941Sjhb goto out; 804154941Sjhb 805154941Sjhb /* 806154941Sjhb * Ok, we think we have waiters, so lock the turnstile so we can 807154941Sjhb * read the waiter flags without any races. 808154941Sjhb */ 809154941Sjhb turnstile_chain_lock(&rw->lock_object); 810154941Sjhb v = rw->rw_lock; 811154941Sjhb MPASS(v & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)); 812154941Sjhb 813154941Sjhb /* 814171052Sattilio * Downgrade from a write lock while preserving 815176017Sjeff * RW_LOCK_WRITE_WAITERS and give up ownership of the 816171052Sattilio * turnstile. If there are any read waiters, wake them up. 817171052Sattilio */ 818171052Sattilio ts = turnstile_lookup(&rw->lock_object); 819171052Sattilio MPASS(ts != NULL); 820171052Sattilio if (v & RW_LOCK_READ_WAITERS) 821154941Sjhb turnstile_broadcast(ts, TS_SHARED_QUEUE); 822154941Sjhb atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | 823154941Sjhb (v & RW_LOCK_WRITE_WAITERS)); 824167787Sjhb if (v & RW_LOCK_READ_WAITERS) 825154941Sjhb turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 826154941Sjhb else if (ts) 827170295Sjeff turnstile_disown(ts); 828167787Sjhb turnstile_chain_unlock(&rw->lock_object); 829154941Sjhbout: 830154941Sjhb LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line); 831154941Sjhb} 832154941Sjhb 833154941Sjhb#ifdef INVARIANT_SUPPORT 834154941Sjhb#ifndef INVARIANTS 835154941Sjhb#undef _rw_assert 836154941Sjhb#endif 837154941Sjhb 838154941Sjhb/* 839154941Sjhb * In the non-WITNESS case, rw_assert() can only detect that at least 840154941Sjhb * *some* thread owns an rlock, but it cannot guarantee that *this* 841154941Sjhb * thread owns an rlock. 842154941Sjhb */ 843154941Sjhbvoid 844154941Sjhb_rw_assert(struct rwlock *rw, int what, const char *file, int line) 845154941Sjhb{ 846154941Sjhb 847157846Sjhb if (panicstr != NULL) 848176076Sjeff return; 849176076Sjeff switch (what) { 850176076Sjeff case RA_LOCKED: 851176076Sjeff case RA_LOCKED | RA_RECURSED: 852154941Sjhb case RA_LOCKED | RA_NOTRECURSED: 853157846Sjhb case RA_RLOCKED: 854157846Sjhb#ifdef WITNESS 855167787Sjhb witness_assert(&rw->lock_object, what, file, line); 856154941Sjhb#else 857154941Sjhb /* 858154941Sjhb * If some other thread has a write lock or we have one 859154941Sjhb * and are asserting a read lock, fail. Also, if no one 860154941Sjhb * has a lock at all, fail. 861170295Sjeff */ 862154941Sjhb if (rw->rw_lock == RW_UNLOCKED || 863154941Sjhb (!(rw->rw_lock & RW_LOCK_READ) && (what == RA_RLOCKED || 864157882Sjhb rw_wowner(rw) != curthread))) 865157882Sjhb panic("Lock %s not %slocked @ %s:%d\n", 866157882Sjhb rw->lock_object.lo_name, (what == RA_RLOCKED) ? 867157882Sjhb "read " : "", file, line); 868157882Sjhb 869157882Sjhb if (!(rw->rw_lock & RW_LOCK_READ)) { 870157882Sjhb if (rw_recursed(rw)) { 871157882Sjhb if (what & RA_NOTRECURSED) 872176017Sjeff panic("Lock %s recursed @ %s:%d\n", 873170295Sjeff rw->lock_object.lo_name, file, 874157882Sjhb line); 875157882Sjhb } else if (what & RA_RECURSED) 876169394Sjhb panic("Lock %s not recursed @ %s:%d\n", 877169394Sjhb rw->lock_object.lo_name, file, line); 878157882Sjhb } 879157882Sjhb#endif 880157882Sjhb break; 881157882Sjhb case RA_WLOCKED: 882157882Sjhb case RA_WLOCKED | RA_RECURSED: 883157882Sjhb case RA_WLOCKED | RA_NOTRECURSED: 884157882Sjhb if (rw_wowner(rw) != curthread) 885157882Sjhb panic("Lock %s not exclusively locked @ %s:%d\n", 886157882Sjhb rw->lock_object.lo_name, file, line); 887157882Sjhb if (rw_recursed(rw)) { 888176017Sjeff if (what & RA_NOTRECURSED) 889176017Sjeff panic("Lock %s recursed @ %s:%d\n", 890176017Sjeff rw->lock_object.lo_name, file, line); 891176017Sjeff } else if (what & RA_RECURSED) 892176017Sjeff panic("Lock %s not recursed @ %s:%d\n", 893176017Sjeff rw->lock_object.lo_name, file, line); 894176017Sjeff break; 895176017Sjeff case RA_UNLOCKED: 896176017Sjeff#ifdef WITNESS 897176017Sjeff witness_assert(&rw->lock_object, what, file, line); 898176017Sjeff#else 899157882Sjhb /* 900176017Sjeff * If we hold a write lock fail. We can't reliably check 901176017Sjeff * to see if we hold a read lock or not. 902176017Sjeff */ 903176017Sjeff if (rw_wowner(rw) == curthread) 904176017Sjeff panic("Lock %s exclusively locked @ %s:%d\n", 905176017Sjeff rw->lock_object.lo_name, file, line); 906176017Sjeff#endif 907176017Sjeff break; 908176017Sjeff default: 909176017Sjeff panic("Unknown rw lock assertion: %d @ %s:%d", what, file, 910176017Sjeff line); 911176017Sjeff } 912176017Sjeff} 913176017Sjeff#endif /* INVARIANT_SUPPORT */ 914176017Sjeff 915176017Sjeff#ifdef DDB 916176017Sjeffvoid 917176017Sjeffdb_show_rwlock(struct lock_object *lock) 918176017Sjeff{ 919176017Sjeff struct rwlock *rw; 920176017Sjeff struct thread *td; 921176017Sjeff 922176017Sjeff rw = (struct rwlock *)lock; 923176017Sjeff 924170295Sjeff db_printf(" state: "); 925176017Sjeff if (rw->rw_lock == RW_UNLOCKED) 926167787Sjhb db_printf("UNLOCKED\n"); 927176017Sjeff else if (rw->rw_lock == RW_DESTROYED) { 928176017Sjeff db_printf("DESTROYED\n"); 929167787Sjhb return; 930157882Sjhb } else if (rw->rw_lock & RW_LOCK_READ) 931192853Ssson db_printf("RLOCK: %ju locks\n", 932176017Sjeff (uintmax_t)(RW_READERS(rw->rw_lock))); 933157882Sjhb else { 934157882Sjhb td = rw_wowner(rw); 935157882Sjhb db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 936157882Sjhb td->td_tid, td->td_proc->p_pid, td->td_name); 937157882Sjhb if (rw_recursed(rw)) 938157882Sjhb db_printf(" recursed: %u\n", rw->rw_recurse); 939157882Sjhb } 940157882Sjhb db_printf(" waiters: "); 941157882Sjhb switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) { 942157882Sjhb case RW_LOCK_READ_WAITERS: 943157882Sjhb db_printf("readers\n"); 944176017Sjeff break; 945157882Sjhb case RW_LOCK_WRITE_WAITERS: 946169394Sjhb db_printf("writers\n"); 947169394Sjhb break; 948171052Sattilio case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS: 949171052Sattilio db_printf("readers and writers\n"); 950171052Sattilio break; 951171052Sattilio default: 952171052Sattilio db_printf("none\n"); 953157882Sjhb break; 954167787Sjhb } 955157882Sjhb} 956157882Sjhb 957157882Sjhb#endif 958157882Sjhb