kern_rwlock.c revision 174629
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 174629 2007-12-15 23:13:31Z jeff $"); 36154941Sjhb 37154941Sjhb#include "opt_ddb.h" 38167801Sjhb#include "opt_no_adaptive_rwlocks.h" 39154941Sjhb 40154941Sjhb#include <sys/param.h> 41154941Sjhb#include <sys/ktr.h> 42154941Sjhb#include <sys/lock.h> 43154941Sjhb#include <sys/mutex.h> 44154941Sjhb#include <sys/proc.h> 45154941Sjhb#include <sys/rwlock.h> 46154941Sjhb#include <sys/systm.h> 47154941Sjhb#include <sys/turnstile.h> 48171516Sattilio 49154941Sjhb#include <machine/cpu.h> 50154941Sjhb 51171052SattilioCTASSERT((RW_RECURSE & LO_CLASSFLAGS) == RW_RECURSE); 52171052Sattilio 53167801Sjhb#if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS) 54167801Sjhb#define ADAPTIVE_RWLOCKS 55167801Sjhb#endif 56167801Sjhb 57154941Sjhb#ifdef DDB 58154941Sjhb#include <ddb/ddb.h> 59154941Sjhb 60154941Sjhbstatic void db_show_rwlock(struct lock_object *lock); 61154941Sjhb#endif 62173733Sattiliostatic void assert_rw(struct lock_object *lock, int what); 63167368Sjhbstatic void lock_rw(struct lock_object *lock, int how); 64167368Sjhbstatic int unlock_rw(struct lock_object *lock); 65154941Sjhb 66154941Sjhbstruct lock_class lock_class_rw = { 67167365Sjhb .lc_name = "rw", 68167365Sjhb .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE, 69173733Sattilio .lc_assert = assert_rw, 70154941Sjhb#ifdef DDB 71167365Sjhb .lc_ddb_show = db_show_rwlock, 72154941Sjhb#endif 73167368Sjhb .lc_lock = lock_rw, 74167368Sjhb .lc_unlock = unlock_rw, 75154941Sjhb}; 76154941Sjhb 77157826Sjhb/* 78157826Sjhb * Return a pointer to the owning thread if the lock is write-locked or 79157826Sjhb * NULL if the lock is unlocked or read-locked. 80157826Sjhb */ 81157826Sjhb#define rw_wowner(rw) \ 82154941Sjhb ((rw)->rw_lock & RW_LOCK_READ ? NULL : \ 83154941Sjhb (struct thread *)RW_OWNER((rw)->rw_lock)) 84154941Sjhb 85157826Sjhb/* 86171052Sattilio * Returns if a write owner is recursed. Write ownership is not assured 87171052Sattilio * here and should be previously checked. 88171052Sattilio */ 89171052Sattilio#define rw_recursed(rw) ((rw)->rw_recurse != 0) 90171052Sattilio 91171052Sattilio/* 92171052Sattilio * Return true if curthread helds the lock. 93171052Sattilio */ 94171052Sattilio#define rw_wlocked(rw) (rw_wowner((rw)) == curthread) 95171052Sattilio 96171052Sattilio/* 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 99157826Sjhb * is identical to rw_wowner(). 100157826Sjhb */ 101157826Sjhb#define rw_owner(rw) rw_wowner(rw) 102157826Sjhb 103154941Sjhb#ifndef INVARIANTS 104154941Sjhb#define _rw_assert(rw, what, file, line) 105154941Sjhb#endif 106154941Sjhb 107154941Sjhbvoid 108173733Sattilioassert_rw(struct lock_object *lock, int what) 109173733Sattilio{ 110173733Sattilio 111173733Sattilio rw_assert((struct rwlock *)lock, what); 112173733Sattilio} 113173733Sattilio 114173733Sattiliovoid 115167368Sjhblock_rw(struct lock_object *lock, int how) 116167368Sjhb{ 117167368Sjhb struct rwlock *rw; 118167368Sjhb 119167368Sjhb rw = (struct rwlock *)lock; 120167368Sjhb if (how) 121167368Sjhb rw_wlock(rw); 122167368Sjhb else 123167368Sjhb rw_rlock(rw); 124167368Sjhb} 125167368Sjhb 126167368Sjhbint 127167368Sjhbunlock_rw(struct lock_object *lock) 128167368Sjhb{ 129167368Sjhb struct rwlock *rw; 130167368Sjhb 131167368Sjhb 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 143171052Sattiliorw_init_flags(struct rwlock *rw, const char *name, int opts) 144154941Sjhb{ 145171052Sattilio int flags; 146154941Sjhb 147171052Sattilio MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET | 148171052Sattilio RW_RECURSE)) == 0); 149171052Sattilio 150171052Sattilio flags = LO_UPGRADABLE | LO_RECURSABLE; 151171052Sattilio if (opts & RW_DUPOK) 152171052Sattilio flags |= LO_DUPOK; 153171052Sattilio if (opts & RW_NOPROFILE) 154171052Sattilio flags |= LO_NOPROFILE; 155171052Sattilio if (!(opts & RW_NOWITNESS)) 156171052Sattilio flags |= LO_WITNESS; 157171052Sattilio if (opts & RW_QUIET) 158171052Sattilio flags |= LO_QUIET; 159171052Sattilio flags |= opts & RW_RECURSE; 160171052Sattilio 161154941Sjhb rw->rw_lock = RW_UNLOCKED; 162171052Sattilio rw->rw_recurse = 0; 163171052Sattilio lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags); 164154941Sjhb} 165154941Sjhb 166154941Sjhbvoid 167154941Sjhbrw_destroy(struct rwlock *rw) 168154941Sjhb{ 169154941Sjhb 170154941Sjhb KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock not unlocked")); 171171052Sattilio KASSERT(rw->rw_recurse == 0, ("rw lock still recursed")); 172169394Sjhb rw->rw_lock = RW_DESTROYED; 173167787Sjhb lock_destroy(&rw->lock_object); 174154941Sjhb} 175154941Sjhb 176154941Sjhbvoid 177154941Sjhbrw_sysinit(void *arg) 178154941Sjhb{ 179154941Sjhb struct rw_args *args = arg; 180154941Sjhb 181154941Sjhb rw_init(args->ra_rw, args->ra_desc); 182154941Sjhb} 183154941Sjhb 184167024Srwatsonint 185167024Srwatsonrw_wowned(struct rwlock *rw) 186167024Srwatson{ 187167024Srwatson 188167024Srwatson return (rw_wowner(rw) == curthread); 189167024Srwatson} 190167024Srwatson 191154941Sjhbvoid 192154941Sjhb_rw_wlock(struct rwlock *rw, const char *file, int line) 193154941Sjhb{ 194154941Sjhb 195154941Sjhb MPASS(curthread != NULL); 196169394Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 197169394Sjhb ("rw_wlock() of destroyed rwlock @ %s:%d", file, line)); 198167787Sjhb 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); 202167787Sjhb WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 203160771Sjhb curthread->td_locks++; 204154941Sjhb} 205154941Sjhb 206154941Sjhbvoid 207154941Sjhb_rw_wunlock(struct rwlock *rw, const char *file, int line) 208154941Sjhb{ 209154941Sjhb 210154941Sjhb MPASS(curthread != NULL); 211169394Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 212169394Sjhb ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line)); 213154941Sjhb _rw_assert(rw, RA_WLOCKED, file, line); 214160771Sjhb curthread->td_locks--; 215167787Sjhb WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line); 216171052Sattilio LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file, 217171052Sattilio line); 218171052Sattilio if (!rw_recursed(rw)) 219171052Sattilio lock_profile_release_lock(&rw->lock_object); 220154941Sjhb __rw_wunlock(rw, curthread, file, line); 221154941Sjhb} 222154941Sjhb 223154941Sjhbvoid 224154941Sjhb_rw_rlock(struct rwlock *rw, const char *file, int line) 225154941Sjhb{ 226170295Sjeff struct turnstile *ts; 227167801Sjhb#ifdef ADAPTIVE_RWLOCKS 228157846Sjhb volatile struct thread *owner; 229157851Swkoszek#endif 230167307Sjhb uint64_t waittime = 0; 231167054Skmacy int contested = 0; 232154941Sjhb uintptr_t x; 233154941Sjhb 234169394Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 235169394Sjhb ("rw_rlock() of destroyed rwlock @ %s:%d", file, line)); 236157826Sjhb KASSERT(rw_wowner(rw) != curthread, 237154941Sjhb ("%s (%s): wlock already held @ %s:%d", __func__, 238167787Sjhb rw->lock_object.lo_name, file, line)); 239167787Sjhb WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line); 240154941Sjhb 241154941Sjhb /* 242154941Sjhb * Note that we don't make any attempt to try to block read 243154941Sjhb * locks once a writer has blocked on the lock. The reason is 244154941Sjhb * that we currently allow for read locks to recurse and we 245154941Sjhb * don't keep track of all the holders of read locks. Thus, if 246154941Sjhb * we were to block readers once a writer blocked and a reader 247154941Sjhb * tried to recurse on their reader lock after a writer had 248154941Sjhb * blocked we would end up in a deadlock since the reader would 249154941Sjhb * be blocked on the writer, and the writer would be blocked 250154941Sjhb * waiting for the reader to release its original read lock. 251154941Sjhb */ 252154941Sjhb for (;;) { 253154941Sjhb /* 254154941Sjhb * Handle the easy case. If no other thread has a write 255154941Sjhb * lock, then try to bump up the count of read locks. Note 256154941Sjhb * that we have to preserve the current state of the 257154941Sjhb * RW_LOCK_WRITE_WAITERS flag. If we fail to acquire a 258154941Sjhb * read lock, then rw_lock must have changed, so restart 259154941Sjhb * the loop. Note that this handles the case of a 260154941Sjhb * completely unlocked rwlock since such a lock is encoded 261154941Sjhb * as a read lock with no waiters. 262154941Sjhb */ 263154941Sjhb x = rw->rw_lock; 264154941Sjhb if (x & RW_LOCK_READ) { 265154941Sjhb 266154941Sjhb /* 267154941Sjhb * The RW_LOCK_READ_WAITERS flag should only be set 268154941Sjhb * if another thread currently holds a write lock, 269154941Sjhb * and in that case RW_LOCK_READ should be clear. 270154941Sjhb */ 271154941Sjhb MPASS((x & RW_LOCK_READ_WAITERS) == 0); 272154941Sjhb if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, 273154941Sjhb x + RW_ONE_READER)) { 274167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 275154941Sjhb CTR4(KTR_LOCK, 276154941Sjhb "%s: %p succeed %p -> %p", __func__, 277154941Sjhb rw, (void *)x, 278154941Sjhb (void *)(x + RW_ONE_READER)); 279154941Sjhb break; 280154941Sjhb } 281157846Sjhb cpu_spinwait(); 282154941Sjhb continue; 283154941Sjhb } 284174629Sjeff lock_profile_obtain_lock_failed(&rw->lock_object, 285174629Sjeff &contested, &waittime); 286154941Sjhb 287173960Sattilio#ifdef ADAPTIVE_RWLOCKS 288154941Sjhb /* 289173960Sattilio * If the owner is running on another CPU, spin until 290173960Sattilio * the owner stops running or the state of the lock 291173960Sattilio * changes. 292173960Sattilio */ 293173960Sattilio owner = (struct thread *)RW_OWNER(x); 294173960Sattilio if (TD_IS_RUNNING(owner)) { 295173960Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 296173960Sattilio CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 297173960Sattilio __func__, rw, owner); 298173960Sattilio while ((struct thread*)RW_OWNER(rw->rw_lock) == owner && 299173960Sattilio TD_IS_RUNNING(owner)) 300173960Sattilio cpu_spinwait(); 301173960Sattilio continue; 302173960Sattilio } 303173960Sattilio#endif 304173960Sattilio 305173960Sattilio /* 306154941Sjhb * Okay, now it's the hard case. Some other thread already 307154941Sjhb * has a write lock, so acquire the turnstile lock so we can 308154941Sjhb * begin the process of blocking. 309154941Sjhb */ 310170295Sjeff ts = turnstile_trywait(&rw->lock_object); 311154941Sjhb 312154941Sjhb /* 313154941Sjhb * The lock might have been released while we spun, so 314154941Sjhb * recheck its state and restart the loop if there is no 315154941Sjhb * longer a write lock. 316154941Sjhb */ 317154941Sjhb x = rw->rw_lock; 318154941Sjhb if (x & RW_LOCK_READ) { 319170295Sjeff turnstile_cancel(ts); 320157846Sjhb cpu_spinwait(); 321154941Sjhb continue; 322154941Sjhb } 323154941Sjhb 324173960Sattilio#ifdef ADAPTIVE_RWLOCKS 325154941Sjhb /* 326173960Sattilio * If the current owner of the lock is executing on another 327173960Sattilio * CPU quit the hard path and try to spin. 328173960Sattilio */ 329173960Sattilio owner = (struct thread *)RW_OWNER(x); 330173960Sattilio if (TD_IS_RUNNING(owner)) { 331173960Sattilio turnstile_cancel(ts); 332173960Sattilio cpu_spinwait(); 333173960Sattilio continue; 334173960Sattilio } 335173960Sattilio#endif 336173960Sattilio 337173960Sattilio /* 338154941Sjhb * Ok, it's still a write lock. If the RW_LOCK_READ_WAITERS 339154941Sjhb * flag is already set, then we can go ahead and block. If 340154941Sjhb * it is not set then try to set it. If we fail to set it 341154941Sjhb * drop the turnstile lock and restart the loop. 342154941Sjhb */ 343157826Sjhb if (!(x & RW_LOCK_READ_WAITERS)) { 344157826Sjhb if (!atomic_cmpset_ptr(&rw->rw_lock, x, 345157826Sjhb x | RW_LOCK_READ_WAITERS)) { 346170295Sjeff turnstile_cancel(ts); 347157826Sjhb cpu_spinwait(); 348157826Sjhb continue; 349157826Sjhb } 350167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 351157826Sjhb CTR2(KTR_LOCK, "%s: %p set read waiters flag", 352157826Sjhb __func__, rw); 353154941Sjhb } 354154941Sjhb 355154941Sjhb /* 356154941Sjhb * We were unable to acquire the lock and the read waiters 357154941Sjhb * flag is set, so we must block on the turnstile. 358154941Sjhb */ 359167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 360154941Sjhb CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 361154941Sjhb rw); 362170295Sjeff turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE); 363167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 364154941Sjhb CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 365154941Sjhb __func__, rw); 366154941Sjhb } 367154941Sjhb 368154941Sjhb /* 369154941Sjhb * TODO: acquire "owner of record" here. Here be turnstile dragons 370154941Sjhb * however. turnstiles don't like owners changing between calls to 371154941Sjhb * turnstile_wait() currently. 372154941Sjhb */ 373174629Sjeff lock_profile_obtain_lock_success( &rw->lock_object, contested, 374174629Sjeff waittime, file, line); 375167787Sjhb LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line); 376167787Sjhb WITNESS_LOCK(&rw->lock_object, 0, file, line); 377160771Sjhb curthread->td_locks++; 378154941Sjhb} 379154941Sjhb 380154941Sjhbvoid 381154941Sjhb_rw_runlock(struct rwlock *rw, const char *file, int line) 382154941Sjhb{ 383154941Sjhb struct turnstile *ts; 384154941Sjhb uintptr_t x; 385154941Sjhb 386169394Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 387169394Sjhb ("rw_runlock() of destroyed rwlock @ %s:%d", file, line)); 388154941Sjhb _rw_assert(rw, RA_RLOCKED, file, line); 389160771Sjhb curthread->td_locks--; 390167787Sjhb WITNESS_UNLOCK(&rw->lock_object, 0, file, line); 391167787Sjhb LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line); 392154941Sjhb 393154941Sjhb /* TODO: drop "owner of record" here. */ 394154941Sjhb 395154941Sjhb for (;;) { 396154941Sjhb /* 397154941Sjhb * See if there is more than one read lock held. If so, 398154941Sjhb * just drop one and return. 399154941Sjhb */ 400154941Sjhb x = rw->rw_lock; 401154941Sjhb if (RW_READERS(x) > 1) { 402154941Sjhb if (atomic_cmpset_ptr(&rw->rw_lock, x, 403154941Sjhb x - RW_ONE_READER)) { 404167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 405154941Sjhb CTR4(KTR_LOCK, 406154941Sjhb "%s: %p succeeded %p -> %p", 407154941Sjhb __func__, rw, (void *)x, 408154941Sjhb (void *)(x - RW_ONE_READER)); 409154941Sjhb break; 410154941Sjhb } 411154941Sjhb continue; 412167307Sjhb } 413154941Sjhb 414164159Skmacy 415154941Sjhb /* 416154941Sjhb * We should never have read waiters while at least one 417154941Sjhb * thread holds a read lock. (See note above) 418154941Sjhb */ 419154941Sjhb KASSERT(!(x & RW_LOCK_READ_WAITERS), 420154941Sjhb ("%s: waiting readers", __func__)); 421154941Sjhb 422154941Sjhb /* 423154941Sjhb * If there aren't any waiters for a write lock, then try 424154941Sjhb * to drop it quickly. 425154941Sjhb */ 426154941Sjhb if (!(x & RW_LOCK_WRITE_WAITERS)) { 427154941Sjhb 428154941Sjhb /* 429154941Sjhb * There shouldn't be any flags set and we should 430154941Sjhb * be the only read lock. If we fail to release 431154941Sjhb * the single read lock, then another thread might 432154941Sjhb * have just acquired a read lock, so go back up 433154941Sjhb * to the multiple read locks case. 434154941Sjhb */ 435154941Sjhb MPASS(x == RW_READERS_LOCK(1)); 436154941Sjhb if (atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1), 437154941Sjhb RW_UNLOCKED)) { 438167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 439154941Sjhb CTR2(KTR_LOCK, "%s: %p last succeeded", 440154941Sjhb __func__, rw); 441154941Sjhb break; 442154941Sjhb } 443154941Sjhb continue; 444154941Sjhb } 445154941Sjhb 446154941Sjhb /* 447154941Sjhb * There should just be one reader with one or more 448154941Sjhb * writers waiting. 449154941Sjhb */ 450154941Sjhb MPASS(x == (RW_READERS_LOCK(1) | RW_LOCK_WRITE_WAITERS)); 451154941Sjhb 452154941Sjhb /* 453154941Sjhb * Ok, we know we have a waiting writer and we think we 454154941Sjhb * are the last reader, so grab the turnstile lock. 455154941Sjhb */ 456170295Sjeff turnstile_chain_lock(&rw->lock_object); 457154941Sjhb 458154941Sjhb /* 459154941Sjhb * Try to drop our lock leaving the lock in a unlocked 460154941Sjhb * state. 461154941Sjhb * 462154941Sjhb * If you wanted to do explicit lock handoff you'd have to 463154941Sjhb * do it here. You'd also want to use turnstile_signal() 464154941Sjhb * and you'd have to handle the race where a higher 465154941Sjhb * priority thread blocks on the write lock before the 466154941Sjhb * thread you wakeup actually runs and have the new thread 467154941Sjhb * "steal" the lock. For now it's a lot simpler to just 468154941Sjhb * wakeup all of the waiters. 469154941Sjhb * 470154941Sjhb * As above, if we fail, then another thread might have 471154941Sjhb * acquired a read lock, so drop the turnstile lock and 472154941Sjhb * restart. 473154941Sjhb */ 474154941Sjhb if (!atomic_cmpset_ptr(&rw->rw_lock, 475154941Sjhb RW_READERS_LOCK(1) | RW_LOCK_WRITE_WAITERS, RW_UNLOCKED)) { 476170295Sjeff turnstile_chain_unlock(&rw->lock_object); 477154941Sjhb continue; 478154941Sjhb } 479167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 480154941Sjhb CTR2(KTR_LOCK, "%s: %p last succeeded with waiters", 481154941Sjhb __func__, rw); 482154941Sjhb 483154941Sjhb /* 484154941Sjhb * Ok. The lock is released and all that's left is to 485154941Sjhb * wake up the waiters. Note that the lock might not be 486154941Sjhb * free anymore, but in that case the writers will just 487154941Sjhb * block again if they run before the new lock holder(s) 488154941Sjhb * release the lock. 489154941Sjhb */ 490167787Sjhb ts = turnstile_lookup(&rw->lock_object); 491157846Sjhb MPASS(ts != NULL); 492154941Sjhb turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE); 493154941Sjhb turnstile_unpend(ts, TS_SHARED_LOCK); 494170295Sjeff turnstile_chain_unlock(&rw->lock_object); 495154941Sjhb break; 496154941Sjhb } 497174629Sjeff lock_profile_release_lock(&rw->lock_object); 498154941Sjhb} 499154941Sjhb 500154941Sjhb/* 501154941Sjhb * This function is called when we are unable to obtain a write lock on the 502154941Sjhb * first try. This means that at least one other thread holds either a 503154941Sjhb * read or write lock. 504154941Sjhb */ 505154941Sjhbvoid 506154941Sjhb_rw_wlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) 507154941Sjhb{ 508170295Sjeff struct turnstile *ts; 509167801Sjhb#ifdef ADAPTIVE_RWLOCKS 510157846Sjhb volatile struct thread *owner; 511157851Swkoszek#endif 512171516Sattilio uint64_t waittime = 0; 513154941Sjhb uintptr_t v; 514171516Sattilio int contested = 0; 515154941Sjhb 516171052Sattilio if (rw_wlocked(rw)) { 517171052Sattilio KASSERT(rw->lock_object.lo_flags & RW_RECURSE, 518171052Sattilio ("%s: recursing but non-recursive rw %s @ %s:%d\n", 519171052Sattilio __func__, rw->lock_object.lo_name, file, line)); 520171052Sattilio rw->rw_recurse++; 521171052Sattilio atomic_set_ptr(&rw->rw_lock, RW_LOCK_RECURSED); 522171052Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 523171052Sattilio CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw); 524171052Sattilio return; 525171052Sattilio } 526171052Sattilio 527167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 528154941Sjhb CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__, 529167787Sjhb rw->lock_object.lo_name, (void *)rw->rw_lock, file, line); 530154941Sjhb 531154941Sjhb while (!_rw_write_lock(rw, tid)) { 532174629Sjeff lock_profile_obtain_lock_failed(&rw->lock_object, 533174629Sjeff &contested, &waittime); 534173960Sattilio#ifdef ADAPTIVE_RWLOCKS 535173960Sattilio /* 536173960Sattilio * If the lock is write locked and the owner is 537173960Sattilio * running on another CPU, spin until the owner stops 538173960Sattilio * running or the state of the lock changes. 539173960Sattilio */ 540173960Sattilio v = rw->rw_lock; 541173960Sattilio owner = (struct thread *)RW_OWNER(v); 542173960Sattilio if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) { 543173960Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 544173960Sattilio CTR3(KTR_LOCK, "%s: spinning on %p held by %p", 545173960Sattilio __func__, rw, owner); 546173960Sattilio while ((struct thread*)RW_OWNER(rw->rw_lock) == owner && 547173960Sattilio TD_IS_RUNNING(owner)) 548173960Sattilio cpu_spinwait(); 549173960Sattilio continue; 550173960Sattilio } 551173960Sattilio#endif 552173960Sattilio 553170295Sjeff ts = turnstile_trywait(&rw->lock_object); 554154941Sjhb v = rw->rw_lock; 555154941Sjhb 556154941Sjhb /* 557154941Sjhb * If the lock was released while spinning on the 558154941Sjhb * turnstile chain lock, try again. 559154941Sjhb */ 560154941Sjhb if (v == RW_UNLOCKED) { 561170295Sjeff turnstile_cancel(ts); 562154941Sjhb cpu_spinwait(); 563154941Sjhb continue; 564154941Sjhb } 565154941Sjhb 566173960Sattilio#ifdef ADAPTIVE_RWLOCKS 567154941Sjhb /* 568173960Sattilio * If the current owner of the lock is executing on another 569173960Sattilio * CPU quit the hard path and try to spin. 570173960Sattilio */ 571173960Sattilio if (!(v & RW_LOCK_READ)) { 572173960Sattilio owner = (struct thread *)RW_OWNER(v); 573173960Sattilio if (TD_IS_RUNNING(owner)) { 574173960Sattilio turnstile_cancel(ts); 575173960Sattilio cpu_spinwait(); 576173960Sattilio continue; 577173960Sattilio } 578173960Sattilio } 579173960Sattilio#endif 580173960Sattilio 581173960Sattilio /* 582154941Sjhb * If the lock was released by a writer with both readers 583154941Sjhb * and writers waiting and a reader hasn't woken up and 584154941Sjhb * acquired the lock yet, rw_lock will be set to the 585154941Sjhb * value RW_UNLOCKED | RW_LOCK_WRITE_WAITERS. If we see 586154941Sjhb * that value, try to acquire it once. Note that we have 587154941Sjhb * to preserve the RW_LOCK_WRITE_WAITERS flag as there are 588168073Sjhb * other writers waiting still. If we fail, restart the 589154941Sjhb * loop. 590154941Sjhb */ 591154941Sjhb if (v == (RW_UNLOCKED | RW_LOCK_WRITE_WAITERS)) { 592154941Sjhb if (atomic_cmpset_acq_ptr(&rw->rw_lock, 593154941Sjhb RW_UNLOCKED | RW_LOCK_WRITE_WAITERS, 594154941Sjhb tid | RW_LOCK_WRITE_WAITERS)) { 595170295Sjeff turnstile_claim(ts); 596154941Sjhb CTR2(KTR_LOCK, "%s: %p claimed by new writer", 597154941Sjhb __func__, rw); 598154941Sjhb break; 599154941Sjhb } 600170295Sjeff turnstile_cancel(ts); 601154941Sjhb cpu_spinwait(); 602154941Sjhb continue; 603154941Sjhb } 604154941Sjhb 605154941Sjhb /* 606154941Sjhb * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to 607154941Sjhb * set it. If we fail to set it, then loop back and try 608154941Sjhb * again. 609154941Sjhb */ 610157826Sjhb if (!(v & RW_LOCK_WRITE_WAITERS)) { 611157826Sjhb if (!atomic_cmpset_ptr(&rw->rw_lock, v, 612157826Sjhb v | RW_LOCK_WRITE_WAITERS)) { 613170295Sjeff turnstile_cancel(ts); 614157826Sjhb cpu_spinwait(); 615157826Sjhb continue; 616157826Sjhb } 617167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 618157826Sjhb CTR2(KTR_LOCK, "%s: %p set write waiters flag", 619157826Sjhb __func__, rw); 620154941Sjhb } 621154941Sjhb 622157846Sjhb /* 623154941Sjhb * We were unable to acquire the lock and the write waiters 624154941Sjhb * flag is set, so we must block on the turnstile. 625154941Sjhb */ 626167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 627154941Sjhb CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__, 628154941Sjhb rw); 629170295Sjeff turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE); 630167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 631154941Sjhb CTR2(KTR_LOCK, "%s: %p resuming from turnstile", 632154941Sjhb __func__, rw); 633154941Sjhb } 634171516Sattilio lock_profile_obtain_lock_success(&rw->lock_object, contested, waittime, 635171516Sattilio file, line); 636154941Sjhb} 637154941Sjhb 638154941Sjhb/* 639154941Sjhb * This function is called if the first try at releasing a write lock failed. 640154941Sjhb * This means that one of the 2 waiter bits must be set indicating that at 641154941Sjhb * least one thread is waiting on this lock. 642154941Sjhb */ 643154941Sjhbvoid 644154941Sjhb_rw_wunlock_hard(struct rwlock *rw, uintptr_t tid, const char *file, int line) 645154941Sjhb{ 646154941Sjhb struct turnstile *ts; 647154941Sjhb uintptr_t v; 648154941Sjhb int queue; 649154941Sjhb 650171052Sattilio if (rw_wlocked(rw) && rw_recursed(rw)) { 651171052Sattilio if ((--rw->rw_recurse) == 0) 652171052Sattilio atomic_clear_ptr(&rw->rw_lock, RW_LOCK_RECURSED); 653171052Sattilio if (LOCK_LOG_TEST(&rw->lock_object, 0)) 654171052Sattilio CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw); 655171052Sattilio return; 656171052Sattilio } 657171052Sattilio 658154941Sjhb KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS), 659154941Sjhb ("%s: neither of the waiter flags are set", __func__)); 660154941Sjhb 661167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 662154941Sjhb CTR2(KTR_LOCK, "%s: %p contested", __func__, rw); 663154941Sjhb 664170295Sjeff turnstile_chain_lock(&rw->lock_object); 665167787Sjhb ts = turnstile_lookup(&rw->lock_object); 666154941Sjhb 667154941Sjhb MPASS(ts != NULL); 668154941Sjhb 669154941Sjhb /* 670154941Sjhb * Use the same algo as sx locks for now. Prefer waking up shared 671154941Sjhb * waiters if we have any over writers. This is probably not ideal. 672154941Sjhb * 673154941Sjhb * 'v' is the value we are going to write back to rw_lock. If we 674154941Sjhb * have waiters on both queues, we need to preserve the state of 675154941Sjhb * the waiter flag for the queue we don't wake up. For now this is 676154941Sjhb * hardcoded for the algorithm mentioned above. 677154941Sjhb * 678154941Sjhb * In the case of both readers and writers waiting we wakeup the 679154941Sjhb * readers but leave the RW_LOCK_WRITE_WAITERS flag set. If a 680154941Sjhb * new writer comes in before a reader it will claim the lock up 681154941Sjhb * above. There is probably a potential priority inversion in 682154941Sjhb * there that could be worked around either by waking both queues 683154941Sjhb * of waiters or doing some complicated lock handoff gymnastics. 684154941Sjhb */ 685157846Sjhb v = RW_UNLOCKED; 686154941Sjhb if (rw->rw_lock & RW_LOCK_READ_WAITERS) { 687154941Sjhb queue = TS_SHARED_QUEUE; 688157846Sjhb v |= (rw->rw_lock & RW_LOCK_WRITE_WAITERS); 689157846Sjhb } else 690154941Sjhb queue = TS_EXCLUSIVE_QUEUE; 691157846Sjhb 692157846Sjhb /* Wake up all waiters for the specific queue. */ 693167787Sjhb if (LOCK_LOG_TEST(&rw->lock_object, 0)) 694154941Sjhb CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw, 695154941Sjhb queue == TS_SHARED_QUEUE ? "read" : "write"); 696154941Sjhb turnstile_broadcast(ts, queue); 697154941Sjhb atomic_store_rel_ptr(&rw->rw_lock, v); 698154941Sjhb turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 699170295Sjeff turnstile_chain_unlock(&rw->lock_object); 700154941Sjhb} 701154941Sjhb 702157882Sjhb/* 703157882Sjhb * Attempt to do a non-blocking upgrade from a read lock to a write 704157882Sjhb * lock. This will only succeed if this thread holds a single read 705157882Sjhb * lock. Returns true if the upgrade succeeded and false otherwise. 706157882Sjhb */ 707157882Sjhbint 708157882Sjhb_rw_try_upgrade(struct rwlock *rw, const char *file, int line) 709157882Sjhb{ 710157882Sjhb uintptr_t v, tid; 711170295Sjeff struct turnstile *ts; 712157882Sjhb int success; 713157882Sjhb 714169394Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 715169394Sjhb ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line)); 716157882Sjhb _rw_assert(rw, RA_RLOCKED, file, line); 717157882Sjhb 718157882Sjhb /* 719157882Sjhb * Attempt to switch from one reader to a writer. If there 720157882Sjhb * are any write waiters, then we will have to lock the 721157882Sjhb * turnstile first to prevent races with another writer 722157882Sjhb * calling turnstile_wait() before we have claimed this 723157882Sjhb * turnstile. So, do the simple case of no waiters first. 724157882Sjhb */ 725157882Sjhb tid = (uintptr_t)curthread; 726157882Sjhb if (!(rw->rw_lock & RW_LOCK_WRITE_WAITERS)) { 727168073Sjhb success = atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1), 728168073Sjhb tid); 729157882Sjhb goto out; 730157882Sjhb } 731157882Sjhb 732157882Sjhb /* 733157882Sjhb * Ok, we think we have write waiters, so lock the 734157882Sjhb * turnstile. 735157882Sjhb */ 736170295Sjeff ts = turnstile_trywait(&rw->lock_object); 737157882Sjhb 738157882Sjhb /* 739157882Sjhb * Try to switch from one reader to a writer again. This time 740157882Sjhb * we honor the current state of the RW_LOCK_WRITE_WAITERS 741157882Sjhb * flag. If we obtain the lock with the flag set, then claim 742173960Sattilio * ownership of the turnstile. 743157882Sjhb */ 744157882Sjhb v = rw->rw_lock & RW_LOCK_WRITE_WAITERS; 745168073Sjhb success = atomic_cmpset_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v, 746157882Sjhb tid | v); 747157882Sjhb if (success && v) 748170295Sjeff turnstile_claim(ts); 749157882Sjhb else 750170295Sjeff turnstile_cancel(ts); 751157882Sjhbout: 752167787Sjhb LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line); 753157882Sjhb if (success) 754167787Sjhb WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK, 755157882Sjhb file, line); 756157882Sjhb return (success); 757157882Sjhb} 758157882Sjhb 759157882Sjhb/* 760157882Sjhb * Downgrade a write lock into a single read lock. 761157882Sjhb */ 762157882Sjhbvoid 763157882Sjhb_rw_downgrade(struct rwlock *rw, const char *file, int line) 764157882Sjhb{ 765157882Sjhb struct turnstile *ts; 766157882Sjhb uintptr_t tid, v; 767157882Sjhb 768169394Sjhb KASSERT(rw->rw_lock != RW_DESTROYED, 769169394Sjhb ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line)); 770171052Sattilio _rw_assert(rw, RA_WLOCKED | RA_NOTRECURSED, file, line); 771171052Sattilio#ifndef INVARIANTS 772171052Sattilio if (rw_recursed(rw)) 773171052Sattilio panic("downgrade of a recursed lock"); 774171052Sattilio#endif 775157882Sjhb 776167787Sjhb WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line); 777157882Sjhb 778157882Sjhb /* 779157882Sjhb * Convert from a writer to a single reader. First we handle 780157882Sjhb * the easy case with no waiters. If there are any waiters, we 781157882Sjhb * lock the turnstile, "disown" the lock, and awaken any read 782157882Sjhb * waiters. 783157882Sjhb */ 784157882Sjhb tid = (uintptr_t)curthread; 785157882Sjhb if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1))) 786157882Sjhb goto out; 787157882Sjhb 788157882Sjhb /* 789157882Sjhb * Ok, we think we have waiters, so lock the turnstile so we can 790157882Sjhb * read the waiter flags without any races. 791157882Sjhb */ 792170295Sjeff turnstile_chain_lock(&rw->lock_object); 793157882Sjhb v = rw->rw_lock; 794157882Sjhb MPASS(v & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)); 795157882Sjhb 796157882Sjhb /* 797157882Sjhb * Downgrade from a write lock while preserving 798157882Sjhb * RW_LOCK_WRITE_WAITERS and give up ownership of the 799157882Sjhb * turnstile. If there are any read waiters, wake them up. 800157882Sjhb */ 801167787Sjhb ts = turnstile_lookup(&rw->lock_object); 802157882Sjhb MPASS(ts != NULL); 803157882Sjhb if (v & RW_LOCK_READ_WAITERS) 804157882Sjhb turnstile_broadcast(ts, TS_SHARED_QUEUE); 805157882Sjhb atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | 806157882Sjhb (v & RW_LOCK_WRITE_WAITERS)); 807157882Sjhb if (v & RW_LOCK_READ_WAITERS) 808157882Sjhb turnstile_unpend(ts, TS_EXCLUSIVE_LOCK); 809170295Sjeff else if (ts) 810157882Sjhb turnstile_disown(ts); 811170295Sjeff turnstile_chain_unlock(&rw->lock_object); 812157882Sjhbout: 813167787Sjhb LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line); 814157882Sjhb} 815157882Sjhb 816154941Sjhb#ifdef INVARIANT_SUPPORT 817155162Sscottl#ifndef INVARIANTS 818154941Sjhb#undef _rw_assert 819154941Sjhb#endif 820154941Sjhb 821154941Sjhb/* 822154941Sjhb * In the non-WITNESS case, rw_assert() can only detect that at least 823154941Sjhb * *some* thread owns an rlock, but it cannot guarantee that *this* 824154941Sjhb * thread owns an rlock. 825154941Sjhb */ 826154941Sjhbvoid 827154941Sjhb_rw_assert(struct rwlock *rw, int what, const char *file, int line) 828154941Sjhb{ 829154941Sjhb 830154941Sjhb if (panicstr != NULL) 831154941Sjhb return; 832154941Sjhb switch (what) { 833154941Sjhb case RA_LOCKED: 834171052Sattilio case RA_LOCKED | RA_RECURSED: 835171052Sattilio case RA_LOCKED | RA_NOTRECURSED: 836154941Sjhb case RA_RLOCKED: 837154941Sjhb#ifdef WITNESS 838167787Sjhb witness_assert(&rw->lock_object, what, file, line); 839154941Sjhb#else 840154941Sjhb /* 841154941Sjhb * If some other thread has a write lock or we have one 842154941Sjhb * and are asserting a read lock, fail. Also, if no one 843154941Sjhb * has a lock at all, fail. 844154941Sjhb */ 845155061Sscottl if (rw->rw_lock == RW_UNLOCKED || 846155061Sscottl (!(rw->rw_lock & RW_LOCK_READ) && (what == RA_RLOCKED || 847157826Sjhb rw_wowner(rw) != curthread))) 848154941Sjhb panic("Lock %s not %slocked @ %s:%d\n", 849167787Sjhb rw->lock_object.lo_name, (what == RA_RLOCKED) ? 850154941Sjhb "read " : "", file, line); 851171052Sattilio 852171052Sattilio if (!(rw->rw_lock & RW_LOCK_READ)) { 853171052Sattilio if (rw_recursed(rw)) { 854171052Sattilio if (what & RA_NOTRECURSED) 855171052Sattilio panic("Lock %s recursed @ %s:%d\n", 856171052Sattilio rw->lock_object.lo_name, file, 857171052Sattilio line); 858171052Sattilio } else if (what & RA_RECURSED) 859171052Sattilio panic("Lock %s not recursed @ %s:%d\n", 860171052Sattilio rw->lock_object.lo_name, file, line); 861171052Sattilio } 862154941Sjhb#endif 863154941Sjhb break; 864154941Sjhb case RA_WLOCKED: 865171052Sattilio case RA_WLOCKED | RA_RECURSED: 866171052Sattilio case RA_WLOCKED | RA_NOTRECURSED: 867157826Sjhb if (rw_wowner(rw) != curthread) 868154941Sjhb panic("Lock %s not exclusively locked @ %s:%d\n", 869167787Sjhb rw->lock_object.lo_name, file, line); 870171052Sattilio if (rw_recursed(rw)) { 871171052Sattilio if (what & RA_NOTRECURSED) 872171052Sattilio panic("Lock %s recursed @ %s:%d\n", 873171052Sattilio rw->lock_object.lo_name, file, line); 874171052Sattilio } else if (what & RA_RECURSED) 875171052Sattilio panic("Lock %s not recursed @ %s:%d\n", 876171052Sattilio rw->lock_object.lo_name, file, line); 877154941Sjhb break; 878154941Sjhb case RA_UNLOCKED: 879154941Sjhb#ifdef WITNESS 880167787Sjhb witness_assert(&rw->lock_object, what, file, line); 881154941Sjhb#else 882154941Sjhb /* 883154941Sjhb * If we hold a write lock fail. We can't reliably check 884154941Sjhb * to see if we hold a read lock or not. 885154941Sjhb */ 886157826Sjhb if (rw_wowner(rw) == curthread) 887154941Sjhb panic("Lock %s exclusively locked @ %s:%d\n", 888167787Sjhb rw->lock_object.lo_name, file, line); 889154941Sjhb#endif 890154941Sjhb break; 891154941Sjhb default: 892154941Sjhb panic("Unknown rw lock assertion: %d @ %s:%d", what, file, 893154941Sjhb line); 894154941Sjhb } 895154941Sjhb} 896154941Sjhb#endif /* INVARIANT_SUPPORT */ 897154941Sjhb 898154941Sjhb#ifdef DDB 899154941Sjhbvoid 900154941Sjhbdb_show_rwlock(struct lock_object *lock) 901154941Sjhb{ 902154941Sjhb struct rwlock *rw; 903154941Sjhb struct thread *td; 904154941Sjhb 905154941Sjhb rw = (struct rwlock *)lock; 906154941Sjhb 907154941Sjhb db_printf(" state: "); 908154941Sjhb if (rw->rw_lock == RW_UNLOCKED) 909154941Sjhb db_printf("UNLOCKED\n"); 910169394Sjhb else if (rw->rw_lock == RW_DESTROYED) { 911169394Sjhb db_printf("DESTROYED\n"); 912169394Sjhb return; 913169394Sjhb } else if (rw->rw_lock & RW_LOCK_READ) 914167504Sjhb db_printf("RLOCK: %ju locks\n", 915167504Sjhb (uintmax_t)(RW_READERS(rw->rw_lock))); 916154941Sjhb else { 917157826Sjhb td = rw_wowner(rw); 918154941Sjhb db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td, 919173600Sjulian td->td_tid, td->td_proc->p_pid, td->td_name); 920171052Sattilio if (rw_recursed(rw)) 921171052Sattilio db_printf(" recursed: %u\n", rw->rw_recurse); 922154941Sjhb } 923154941Sjhb db_printf(" waiters: "); 924154941Sjhb switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) { 925154941Sjhb case RW_LOCK_READ_WAITERS: 926154941Sjhb db_printf("readers\n"); 927154941Sjhb break; 928154941Sjhb case RW_LOCK_WRITE_WAITERS: 929154941Sjhb db_printf("writers\n"); 930154941Sjhb break; 931154941Sjhb case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS: 932167492Sjhb db_printf("readers and writers\n"); 933154941Sjhb break; 934154941Sjhb default: 935154941Sjhb db_printf("none\n"); 936154941Sjhb break; 937154941Sjhb } 938154941Sjhb} 939154941Sjhb 940154941Sjhb#endif 941