sys/kern/kern_rwlock.c

   1 /*-
   2  * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  24  * SUCH DAMAGE.
  25  */
  26
  27 /*
  28  * Machine independent bits of reader/writer lock implementation.
  29  */
  30
  31 #include <sys/cdefs.h>
  32 __FBSDID("$FreeBSD$");
  33
  34 #include "opt_ddb.h"
  35 #include "opt_hwpmc_hooks.h"
  36 #include "opt_kdtrace.h"
  37 #include "opt_no_adaptive_rwlocks.h"
  38
  39 #include <sys/param.h>
  40 #include <sys/kdb.h>
  41 #include <sys/ktr.h>
  42 #include <sys/kernel.h>
  43 #include <sys/lock.h>
  44 #include <sys/mutex.h>
  45 #include <sys/proc.h>
  46 #include <sys/rwlock.h>
  47 #include <sys/sched.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/systm.h>
  50 #include <sys/turnstile.h>
  51
  52 #include <machine/cpu.h>
  53
  54 #if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS)
  55 #define ADAPTIVE_RWLOCKS
  56 #endif
  57
  58 #ifdef HWPMC_HOOKS
  59 #include <sys/pmckern.h>
  60 PMC_SOFT_DECLARE( , , lock, failed);
  61 #endif
  62
  63 /*
  64  * Return the rwlock address when the lock cookie address is provided.
  65  * This functionality assumes that struct rwlock* have a member named rw_lock.
  66  */
  67 #define rwlock2rw(c)    (__containerof(c, struct rwlock, rw_lock))
  68
  69 #ifdef ADAPTIVE_RWLOCKS
  70 static int rowner_retries = 10;
  71 static int rowner_loops = 10000;
  72 static SYSCTL_NODE(_debug, OID_AUTO, rwlock, CTLFLAG_RD, NULL,
  73     "rwlock debugging");
  74 SYSCTL_INT(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
  75 SYSCTL_INT(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
  76 #endif
  77
  78 #ifdef DDB
  79 #include <ddb/ddb.h>
  80
  81 static void     db_show_rwlock(const struct lock_object *lock);
  82 #endif
  83 static void     assert_rw(const struct lock_object *lock, int what);
  84 static void     lock_rw(struct lock_object *lock, uintptr_t how);
  85 #ifdef KDTRACE_HOOKS
  86 static int      owner_rw(const struct lock_object *lock, struct thread **owner);
  87 #endif
  88 static uintptr_t unlock_rw(struct lock_object *lock);
  89
  90 struct lock_class lock_class_rw = {
  91         .lc_name = "rw",
  92         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE,
  93         .lc_assert = assert_rw,
  94 #ifdef DDB
  95         .lc_ddb_show = db_show_rwlock,
  96 #endif
  97         .lc_lock = lock_rw,
  98         .lc_unlock = unlock_rw,
  99 #ifdef KDTRACE_HOOKS
 100         .lc_owner = owner_rw,
 101 #endif
 102 };
 103
 104 /*
 105  * Return a pointer to the owning thread if the lock is write-locked or
 106  * NULL if the lock is unlocked or read-locked.
 107  */
 108 #define rw_wowner(rw)                                                   \
 109         ((rw)->rw_lock & RW_LOCK_READ ? NULL :                          \
 110             (struct thread *)RW_OWNER((rw)->rw_lock))
 111
 112 /*
 113  * Returns if a write owner is recursed.  Write ownership is not assured
 114  * here and should be previously checked.
 115  */
 116 #define rw_recursed(rw)         ((rw)->rw_recurse != 0)
 117
 118 /*
 119  * Return true if curthread helds the lock.
 120  */
 121 #define rw_wlocked(rw)          (rw_wowner((rw)) == curthread)
 122
 123 /*
 124  * Return a pointer to the owning thread for this lock who should receive
 125  * any priority lent by threads that block on this lock.  Currently this
 126  * is identical to rw_wowner().
 127  */
 128 #define rw_owner(rw)            rw_wowner(rw)
 129
 130 #ifndef INVARIANTS
 131 #define __rw_assert(c, what, file, line)
 132 #endif
 133
 134 void
 135 assert_rw(const struct lock_object *lock, int what)
 136 {
 137
 138         rw_assert((const struct rwlock *)lock, what);
 139 }
 140
 141 void
 142 lock_rw(struct lock_object *lock, uintptr_t how)
 143 {
 144         struct rwlock *rw;
 145
 146         rw = (struct rwlock *)lock;
 147         if (how)
 148                 rw_rlock(rw);
 149         else
 150                 rw_wlock(rw);
 151 }
 152
 153 uintptr_t
 154 unlock_rw(struct lock_object *lock)
 155 {
 156         struct rwlock *rw;
 157
 158         rw = (struct rwlock *)lock;
 159         rw_assert(rw, RA_LOCKED | LA_NOTRECURSED);
 160         if (rw->rw_lock & RW_LOCK_READ) {
 161                 rw_runlock(rw);
 162                 return (1);
 163         } else {
 164                 rw_wunlock(rw);
 165                 return (0);
 166         }
 167 }
 168
 169 #ifdef KDTRACE_HOOKS
 170 int
 171 owner_rw(const struct lock_object *lock, struct thread **owner)
 172 {
 173         const struct rwlock *rw = (const struct rwlock *)lock;
 174         uintptr_t x = rw->rw_lock;
 175
 176         *owner = rw_wowner(rw);
 177         return ((x & RW_LOCK_READ) != 0 ?  (RW_READERS(x) != 0) :
 178             (*owner != NULL));
 179 }
 180 #endif
 181
 182 void
 183 _rw_init_flags(volatile uintptr_t *c, const char *name, int opts)
 184 {
 185         struct rwlock *rw;
 186         int flags;
 187
 188         rw = rwlock2rw(c);
 189
 190         MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
 191             RW_RECURSE)) == 0);
 192         ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
 193             ("%s: rw_lock not aligned for %s: %p", __func__, name,
 194             &rw->rw_lock));
 195
 196         flags = LO_UPGRADABLE;
 197         if (opts & RW_DUPOK)
 198                 flags |= LO_DUPOK;
 199         if (opts & RW_NOPROFILE)
 200                 flags |= LO_NOPROFILE;
 201         if (!(opts & RW_NOWITNESS))
 202                 flags |= LO_WITNESS;
 203         if (opts & RW_RECURSE)
 204                 flags |= LO_RECURSABLE;
 205         if (opts & RW_QUIET)
 206                 flags |= LO_QUIET;
 207
 208         lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
 209         rw->rw_lock = RW_UNLOCKED;
 210         rw->rw_recurse = 0;
 211 }
 212
 213 void
 214 _rw_destroy(volatile uintptr_t *c)
 215 {
 216         struct rwlock *rw;
 217
 218         rw = rwlock2rw(c);
 219
 220         KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw));
 221         KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw));
 222         rw->rw_lock = RW_DESTROYED;
 223         lock_destroy(&rw->lock_object);
 224 }
 225
 226 void
 227 rw_sysinit(void *arg)
 228 {
 229         struct rw_args *args = arg;
 230
 231         rw_init((struct rwlock *)args->ra_rw, args->ra_desc);
 232 }
 233
 234 void
 235 rw_sysinit_flags(void *arg)
 236 {
 237         struct rw_args_flags *args = arg;
 238
 239         rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc,
 240             args->ra_flags);
 241 }
 242
 243 int
 244 _rw_wowned(const volatile uintptr_t *c)
 245 {
 246
 247         return (rw_wowner(rwlock2rw(c)) == curthread);
 248 }
 249
 250 void
 251 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line)
 252 {
 253         struct rwlock *rw;
 254
 255         if (SCHEDULER_STOPPED())
 256                 return;
 257
 258         rw = rwlock2rw(c);
 259
 260         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 261             ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d",
 262             curthread, rw->lock_object.lo_name, file, line));
 263         KASSERT(rw->rw_lock != RW_DESTROYED,
 264             ("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
 265         WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 266             line, NULL);
 267         __rw_wlock(rw, curthread, file, line);
 268         LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
 269         WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
 270         curthread->td_locks++;
 271 }
 272
 273 int
 274 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
 275 {
 276         struct rwlock *rw;
 277         int rval;
 278
 279         if (SCHEDULER_STOPPED())
 280                 return (1);
 281
 282         rw = rwlock2rw(c);
 283
 284         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 285             ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d",
 286             curthread, rw->lock_object.lo_name, file, line));
 287         KASSERT(rw->rw_lock != RW_DESTROYED,
 288             ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
 289
 290         if (rw_wlocked(rw) &&
 291             (rw->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 292                 rw->rw_recurse++;
 293                 rval = 1;
 294         } else
 295                 rval = atomic_cmpset_acq_ptr(&rw->rw_lock, RW_UNLOCKED,
 296                     (uintptr_t)curthread);
 297
 298         LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
 299         if (rval) {
 300                 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 301                     file, line);
 302                 curthread->td_locks++;
 303         }
 304         return (rval);
 305 }
 306
 307 void
 308 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
 309 {
 310         struct rwlock *rw;
 311
 312         if (SCHEDULER_STOPPED())
 313                 return;
 314
 315         rw = rwlock2rw(c);
 316
 317         KASSERT(rw->rw_lock != RW_DESTROYED,
 318             ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
 319         __rw_assert(c, RA_WLOCKED, file, line);
 320         WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
 321         LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
 322             line);
 323         if (!rw_recursed(rw))
 324                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_WUNLOCK_RELEASE, rw);
 325         __rw_wunlock(rw, curthread, file, line);
 326         curthread->td_locks--;
 327 }
 328 /*
 329  * Determines whether a new reader can acquire a lock.  Succeeds if the
 330  * reader already owns a read lock and the lock is locked for read to
 331  * prevent deadlock from reader recursion.  Also succeeds if the lock
 332  * is unlocked and has no writer waiters or spinners.  Failing otherwise
 333  * prioritizes writers before readers.
 334  */
 335 #define RW_CAN_READ(_rw)                                                \
 336     ((curthread->td_rw_rlocks && (_rw) & RW_LOCK_READ) || ((_rw) &      \
 337     (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) ==  \
 338     RW_LOCK_READ)
 339
 340 void
 341 __rw_rlock(volatile uintptr_t *c, const char *file, int line)
 342 {
 343         struct rwlock *rw;
 344         struct turnstile *ts;
 345 #ifdef ADAPTIVE_RWLOCKS
 346         volatile struct thread *owner;
 347         int spintries = 0;
 348         int i;
 349 #endif
 350 #ifdef LOCK_PROFILING
 351         uint64_t waittime = 0;
 352         int contested = 0;
 353 #endif
 354         uintptr_t v;
 355 #ifdef KDTRACE_HOOKS
 356         uint64_t spin_cnt = 0;
 357         uint64_t sleep_cnt = 0;
 358         int64_t sleep_time = 0;
 359 #endif
 360
 361         if (SCHEDULER_STOPPED())
 362                 return;
 363
 364         rw = rwlock2rw(c);
 365
 366         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 367             ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d",
 368             curthread, rw->lock_object.lo_name, file, line));
 369         KASSERT(rw->rw_lock != RW_DESTROYED,
 370             ("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
 371         KASSERT(rw_wowner(rw) != curthread,
 372             ("rw_rlock: wlock already held for %s @ %s:%d",
 373             rw->lock_object.lo_name, file, line));
 374         WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
 375
 376         for (;;) {
 377 #ifdef KDTRACE_HOOKS
 378                 spin_cnt++;
 379 #endif
 380                 /*
 381                  * Handle the easy case.  If no other thread has a write
 382                  * lock, then try to bump up the count of read locks.  Note
 383                  * that we have to preserve the current state of the
 384                  * RW_LOCK_WRITE_WAITERS flag.  If we fail to acquire a
 385                  * read lock, then rw_lock must have changed, so restart
 386                  * the loop.  Note that this handles the case of a
 387                  * completely unlocked rwlock since such a lock is encoded
 388                  * as a read lock with no waiters.
 389                  */
 390                 v = rw->rw_lock;
 391                 if (RW_CAN_READ(v)) {
 392                         /*
 393                          * The RW_LOCK_READ_WAITERS flag should only be set
 394                          * if the lock has been unlocked and write waiters
 395                          * were present.
 396                          */
 397                         if (atomic_cmpset_acq_ptr(&rw->rw_lock, v,
 398                             v + RW_ONE_READER)) {
 399                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 400                                         CTR4(KTR_LOCK,
 401                                             "%s: %p succeed %p -> %p", __func__,
 402                                             rw, (void *)v,
 403                                             (void *)(v + RW_ONE_READER));
 404                                 break;
 405                         }
 406                         continue;
 407                 }
 408 #ifdef HWPMC_HOOKS
 409                 PMC_SOFT_CALL( , , lock, failed);
 410 #endif
 411                 lock_profile_obtain_lock_failed(&rw->lock_object,
 412                     &contested, &waittime);
 413
 414 #ifdef ADAPTIVE_RWLOCKS
 415                 /*
 416                  * If the owner is running on another CPU, spin until
 417                  * the owner stops running or the state of the lock
 418                  * changes.
 419                  */
 420                 if ((v & RW_LOCK_READ) == 0) {
 421                         owner = (struct thread *)RW_OWNER(v);
 422                         if (TD_IS_RUNNING(owner)) {
 423                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 424                                         CTR3(KTR_LOCK,
 425                                             "%s: spinning on %p held by %p",
 426                                             __func__, rw, owner);
 427                                 KTR_STATE1(KTR_SCHED, "thread",
 428                                     sched_tdname(curthread), "spinning",
 429                                     "lockname:\"%s\"", rw->lock_object.lo_name);
 430                                 while ((struct thread*)RW_OWNER(rw->rw_lock) ==
 431                                     owner && TD_IS_RUNNING(owner)) {
 432                                         cpu_spinwait();
 433 #ifdef KDTRACE_HOOKS
 434                                         spin_cnt++;
 435 #endif
 436                                 }
 437                                 KTR_STATE0(KTR_SCHED, "thread",
 438                                     sched_tdname(curthread), "running");
 439                                 continue;
 440                         }
 441                 } else if (spintries < rowner_retries) {
 442                         spintries++;
 443                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 444                             "spinning", "lockname:\"%s\"",
 445                             rw->lock_object.lo_name);
 446                         for (i = 0; i < rowner_loops; i++) {
 447                                 v = rw->rw_lock;
 448                                 if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(v))
 449                                         break;
 450                                 cpu_spinwait();
 451                         }
 452                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 453                             "running");
 454                         if (i != rowner_loops)
 455                                 continue;
 456                 }
 457 #endif
 458
 459                 /*
 460                  * Okay, now it's the hard case.  Some other thread already
 461                  * has a write lock or there are write waiters present,
 462                  * acquire the turnstile lock so we can begin the process
 463                  * of blocking.
 464                  */
 465                 ts = turnstile_trywait(&rw->lock_object);
 466
 467                 /*
 468                  * The lock might have been released while we spun, so
 469                  * recheck its state and restart the loop if needed.
 470                  */
 471                 v = rw->rw_lock;
 472                 if (RW_CAN_READ(v)) {
 473                         turnstile_cancel(ts);
 474                         continue;
 475                 }
 476
 477 #ifdef ADAPTIVE_RWLOCKS
 478                 /*
 479                  * The current lock owner might have started executing
 480                  * on another CPU (or the lock could have changed
 481                  * owners) while we were waiting on the turnstile
 482                  * chain lock.  If so, drop the turnstile lock and try
 483                  * again.
 484                  */
 485                 if ((v & RW_LOCK_READ) == 0) {
 486                         owner = (struct thread *)RW_OWNER(v);
 487                         if (TD_IS_RUNNING(owner)) {
 488                                 turnstile_cancel(ts);
 489                                 continue;
 490                         }
 491                 }
 492 #endif
 493
 494                 /*
 495                  * The lock is held in write mode or it already has waiters.
 496                  */
 497                 MPASS(!RW_CAN_READ(v));
 498
 499                 /*
 500                  * If the RW_LOCK_READ_WAITERS flag is already set, then
 501                  * we can go ahead and block.  If it is not set then try
 502                  * to set it.  If we fail to set it drop the turnstile
 503                  * lock and restart the loop.
 504                  */
 505                 if (!(v & RW_LOCK_READ_WAITERS)) {
 506                         if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 507                             v | RW_LOCK_READ_WAITERS)) {
 508                                 turnstile_cancel(ts);
 509                                 continue;
 510                         }
 511                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 512                                 CTR2(KTR_LOCK, "%s: %p set read waiters flag",
 513                                     __func__, rw);
 514                 }
 515
 516                 /*
 517                  * We were unable to acquire the lock and the read waiters
 518                  * flag is set, so we must block on the turnstile.
 519                  */
 520                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 521                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
 522                             rw);
 523 #ifdef KDTRACE_HOOKS
 524                 sleep_time -= lockstat_nsecs();
 525 #endif
 526                 turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE);
 527 #ifdef KDTRACE_HOOKS
 528                 sleep_time += lockstat_nsecs();
 529                 sleep_cnt++;
 530 #endif
 531                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 532                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
 533                             __func__, rw);
 534         }
 535
 536         /*
 537          * TODO: acquire "owner of record" here.  Here be turnstile dragons
 538          * however.  turnstiles don't like owners changing between calls to
 539          * turnstile_wait() currently.
 540          */
 541         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_RLOCK_ACQUIRE, rw, contested,
 542             waittime, file, line);
 543         LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
 544         WITNESS_LOCK(&rw->lock_object, 0, file, line);
 545         curthread->td_locks++;
 546         curthread->td_rw_rlocks++;
 547 #ifdef KDTRACE_HOOKS
 548         if (sleep_time)
 549                 LOCKSTAT_RECORD1(LS_RW_RLOCK_BLOCK, rw, sleep_time);
 550
 551         /*
 552          * Record only the loops spinning and not sleeping.
 553          */
 554         if (spin_cnt > sleep_cnt)
 555                 LOCKSTAT_RECORD1(LS_RW_RLOCK_SPIN, rw, (spin_cnt - sleep_cnt));
 556 #endif
 557 }
 558
 559 int
 560 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
 561 {
 562         struct rwlock *rw;
 563         uintptr_t x;
 564
 565         if (SCHEDULER_STOPPED())
 566                 return (1);
 567
 568         rw = rwlock2rw(c);
 569
 570         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 571             ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
 572             curthread, rw->lock_object.lo_name, file, line));
 573
 574         for (;;) {
 575                 x = rw->rw_lock;
 576                 KASSERT(rw->rw_lock != RW_DESTROYED,
 577                     ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
 578                 if (!(x & RW_LOCK_READ))
 579                         break;
 580                 if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, x + RW_ONE_READER)) {
 581                         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
 582                             line);
 583                         WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
 584                         curthread->td_locks++;
 585                         curthread->td_rw_rlocks++;
 586                         return (1);
 587                 }
 588         }
 589
 590         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
 591         return (0);
 592 }
 593
 594 void
 595 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
 596 {
 597         struct rwlock *rw;
 598         struct turnstile *ts;
 599         uintptr_t x, v, queue;
 600
 601         if (SCHEDULER_STOPPED())
 602                 return;
 603
 604         rw = rwlock2rw(c);
 605
 606         KASSERT(rw->rw_lock != RW_DESTROYED,
 607             ("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
 608         __rw_assert(c, RA_RLOCKED, file, line);
 609         WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
 610         LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
 611
 612         /* TODO: drop "owner of record" here. */
 613
 614         for (;;) {
 615                 /*
 616                  * See if there is more than one read lock held.  If so,
 617                  * just drop one and return.
 618                  */
 619                 x = rw->rw_lock;
 620                 if (RW_READERS(x) > 1) {
 621                         if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
 622                             x - RW_ONE_READER)) {
 623                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 624                                         CTR4(KTR_LOCK,
 625                                             "%s: %p succeeded %p -> %p",
 626                                             __func__, rw, (void *)x,
 627                                             (void *)(x - RW_ONE_READER));
 628                                 break;
 629                         }
 630                         continue;
 631                 }
 632                 /*
 633                  * If there aren't any waiters for a write lock, then try
 634                  * to drop it quickly.
 635                  */
 636                 if (!(x & RW_LOCK_WAITERS)) {
 637                         MPASS((x & ~RW_LOCK_WRITE_SPINNER) ==
 638                             RW_READERS_LOCK(1));
 639                         if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
 640                             RW_UNLOCKED)) {
 641                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 642                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
 643                                             __func__, rw);
 644                                 break;
 645                         }
 646                         continue;
 647                 }
 648                 /*
 649                  * Ok, we know we have waiters and we think we are the
 650                  * last reader, so grab the turnstile lock.
 651                  */
 652                 turnstile_chain_lock(&rw->lock_object);
 653                 v = rw->rw_lock & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
 654                 MPASS(v & RW_LOCK_WAITERS);
 655
 656                 /*
 657                  * Try to drop our lock leaving the lock in a unlocked
 658                  * state.
 659                  *
 660                  * If you wanted to do explicit lock handoff you'd have to
 661                  * do it here.  You'd also want to use turnstile_signal()
 662                  * and you'd have to handle the race where a higher
 663                  * priority thread blocks on the write lock before the
 664                  * thread you wakeup actually runs and have the new thread
 665                  * "steal" the lock.  For now it's a lot simpler to just
 666                  * wakeup all of the waiters.
 667                  *
 668                  * As above, if we fail, then another thread might have
 669                  * acquired a read lock, so drop the turnstile lock and
 670                  * restart.
 671                  */
 672                 x = RW_UNLOCKED;
 673                 if (v & RW_LOCK_WRITE_WAITERS) {
 674                         queue = TS_EXCLUSIVE_QUEUE;
 675                         x |= (v & RW_LOCK_READ_WAITERS);
 676                 } else
 677                         queue = TS_SHARED_QUEUE;
 678                 if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v,
 679                     x)) {
 680                         turnstile_chain_unlock(&rw->lock_object);
 681                         continue;
 682                 }
 683                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 684                         CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
 685                             __func__, rw);
 686
 687                 /*
 688                  * Ok.  The lock is released and all that's left is to
 689                  * wake up the waiters.  Note that the lock might not be
 690                  * free anymore, but in that case the writers will just
 691                  * block again if they run before the new lock holder(s)
 692                  * release the lock.
 693                  */
 694                 ts = turnstile_lookup(&rw->lock_object);
 695                 MPASS(ts != NULL);
 696                 turnstile_broadcast(ts, queue);
 697                 turnstile_unpend(ts, TS_SHARED_LOCK);
 698                 turnstile_chain_unlock(&rw->lock_object);
 699                 break;
 700         }
 701         LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_RUNLOCK_RELEASE, rw);
 702         curthread->td_locks--;
 703         curthread->td_rw_rlocks--;
 704 }
 705
 706 /*
 707  * This function is called when we are unable to obtain a write lock on the
 708  * first try.  This means that at least one other thread holds either a
 709  * read or write lock.
 710  */
 711 void
 712 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
 713     int line)
 714 {
 715         struct rwlock *rw;
 716         struct turnstile *ts;
 717 #ifdef ADAPTIVE_RWLOCKS
 718         volatile struct thread *owner;
 719         int spintries = 0;
 720         int i;
 721 #endif
 722         uintptr_t v, x;
 723 #ifdef LOCK_PROFILING
 724         uint64_t waittime = 0;
 725         int contested = 0;
 726 #endif
 727 #ifdef KDTRACE_HOOKS
 728         uint64_t spin_cnt = 0;
 729         uint64_t sleep_cnt = 0;
 730         int64_t sleep_time = 0;
 731 #endif
 732
 733         if (SCHEDULER_STOPPED())
 734                 return;
 735
 736         rw = rwlock2rw(c);
 737
 738         if (rw_wlocked(rw)) {
 739                 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
 740                     ("%s: recursing but non-recursive rw %s @ %s:%d\n",
 741                     __func__, rw->lock_object.lo_name, file, line));
 742                 rw->rw_recurse++;
 743                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 744                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
 745                 return;
 746         }
 747
 748         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 749                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 750                     rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
 751
 752         while (!_rw_write_lock(rw, tid)) {
 753 #ifdef KDTRACE_HOOKS
 754                 spin_cnt++;
 755 #endif
 756 #ifdef HWPMC_HOOKS
 757                 PMC_SOFT_CALL( , , lock, failed);
 758 #endif
 759                 lock_profile_obtain_lock_failed(&rw->lock_object,
 760                     &contested, &waittime);
 761 #ifdef ADAPTIVE_RWLOCKS
 762                 /*
 763                  * If the lock is write locked and the owner is
 764                  * running on another CPU, spin until the owner stops
 765                  * running or the state of the lock changes.
 766                  */
 767                 v = rw->rw_lock;
 768                 owner = (struct thread *)RW_OWNER(v);
 769                 if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) {
 770                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 771                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
 772                                     __func__, rw, owner);
 773                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 774                             "spinning", "lockname:\"%s\"",
 775                             rw->lock_object.lo_name);
 776                         while ((struct thread*)RW_OWNER(rw->rw_lock) == owner &&
 777                             TD_IS_RUNNING(owner)) {
 778                                 cpu_spinwait();
 779 #ifdef KDTRACE_HOOKS
 780                                 spin_cnt++;
 781 #endif
 782                         }
 783                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 784                             "running");
 785                         continue;
 786                 }
 787                 if ((v & RW_LOCK_READ) && RW_READERS(v) &&
 788                     spintries < rowner_retries) {
 789                         if (!(v & RW_LOCK_WRITE_SPINNER)) {
 790                                 if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 791                                     v | RW_LOCK_WRITE_SPINNER)) {
 792                                         continue;
 793                                 }
 794                         }
 795                         spintries++;
 796                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 797                             "spinning", "lockname:\"%s\"",
 798                             rw->lock_object.lo_name);
 799                         for (i = 0; i < rowner_loops; i++) {
 800                                 if ((rw->rw_lock & RW_LOCK_WRITE_SPINNER) == 0)
 801                                         break;
 802                                 cpu_spinwait();
 803                         }
 804                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 805                             "running");
 806 #ifdef KDTRACE_HOOKS
 807                         spin_cnt += rowner_loops - i;
 808 #endif
 809                         if (i != rowner_loops)
 810                                 continue;
 811                 }
 812 #endif
 813                 ts = turnstile_trywait(&rw->lock_object);
 814                 v = rw->rw_lock;
 815
 816 #ifdef ADAPTIVE_RWLOCKS
 817                 /*
 818                  * The current lock owner might have started executing
 819                  * on another CPU (or the lock could have changed
 820                  * owners) while we were waiting on the turnstile
 821                  * chain lock.  If so, drop the turnstile lock and try
 822                  * again.
 823                  */
 824                 if (!(v & RW_LOCK_READ)) {
 825                         owner = (struct thread *)RW_OWNER(v);
 826                         if (TD_IS_RUNNING(owner)) {
 827                                 turnstile_cancel(ts);
 828                                 continue;
 829                         }
 830                 }
 831 #endif
 832                 /*
 833                  * Check for the waiters flags about this rwlock.
 834                  * If the lock was released, without maintain any pending
 835                  * waiters queue, simply try to acquire it.
 836                  * If a pending waiters queue is present, claim the lock
 837                  * ownership and maintain the pending queue.
 838                  */
 839                 x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
 840                 if ((v & ~x) == RW_UNLOCKED) {
 841                         x &= ~RW_LOCK_WRITE_SPINNER;
 842                         if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid | x)) {
 843                                 if (x)
 844                                         turnstile_claim(ts);
 845                                 else
 846                                         turnstile_cancel(ts);
 847                                 break;
 848                         }
 849                         turnstile_cancel(ts);
 850                         continue;
 851                 }
 852                 /*
 853                  * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
 854                  * set it.  If we fail to set it, then loop back and try
 855                  * again.
 856                  */
 857                 if (!(v & RW_LOCK_WRITE_WAITERS)) {
 858                         if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 859                             v | RW_LOCK_WRITE_WAITERS)) {
 860                                 turnstile_cancel(ts);
 861                                 continue;
 862                         }
 863                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 864                                 CTR2(KTR_LOCK, "%s: %p set write waiters flag",
 865                                     __func__, rw);
 866                 }
 867                 /*
 868                  * We were unable to acquire the lock and the write waiters
 869                  * flag is set, so we must block on the turnstile.
 870                  */
 871                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 872                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
 873                             rw);
 874 #ifdef KDTRACE_HOOKS
 875                 sleep_time -= lockstat_nsecs();
 876 #endif
 877                 turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE);
 878 #ifdef KDTRACE_HOOKS
 879                 sleep_time += lockstat_nsecs();
 880                 sleep_cnt++;
 881 #endif
 882                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 883                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
 884                             __func__, rw);
 885 #ifdef ADAPTIVE_RWLOCKS
 886                 spintries = 0;
 887 #endif
 888         }
 889         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_WLOCK_ACQUIRE, rw, contested,
 890             waittime, file, line);
 891 #ifdef KDTRACE_HOOKS
 892         if (sleep_time)
 893                 LOCKSTAT_RECORD1(LS_RW_WLOCK_BLOCK, rw, sleep_time);
 894
 895         /*
 896          * Record only the loops spinning and not sleeping.
 897          */
 898         if (spin_cnt > sleep_cnt)
 899                 LOCKSTAT_RECORD1(LS_RW_WLOCK_SPIN, rw, (spin_cnt - sleep_cnt));
 900 #endif
 901 }
 902
 903 /*
 904  * This function is called if the first try at releasing a write lock failed.
 905  * This means that one of the 2 waiter bits must be set indicating that at
 906  * least one thread is waiting on this lock.
 907  */
 908 void
 909 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
 910     int line)
 911 {
 912         struct rwlock *rw;
 913         struct turnstile *ts;
 914         uintptr_t v;
 915         int queue;
 916
 917         if (SCHEDULER_STOPPED())
 918                 return;
 919
 920         rw = rwlock2rw(c);
 921
 922         if (rw_wlocked(rw) && rw_recursed(rw)) {
 923                 rw->rw_recurse--;
 924                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 925                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
 926                 return;
 927         }
 928
 929         KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
 930             ("%s: neither of the waiter flags are set", __func__));
 931
 932         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 933                 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
 934
 935         turnstile_chain_lock(&rw->lock_object);
 936         ts = turnstile_lookup(&rw->lock_object);
 937         MPASS(ts != NULL);
 938
 939         /*
 940          * Use the same algo as sx locks for now.  Prefer waking up shared
 941          * waiters if we have any over writers.  This is probably not ideal.
 942          *
 943          * 'v' is the value we are going to write back to rw_lock.  If we
 944          * have waiters on both queues, we need to preserve the state of
 945          * the waiter flag for the queue we don't wake up.  For now this is
 946          * hardcoded for the algorithm mentioned above.
 947          *
 948          * In the case of both readers and writers waiting we wakeup the
 949          * readers but leave the RW_LOCK_WRITE_WAITERS flag set.  If a
 950          * new writer comes in before a reader it will claim the lock up
 951          * above.  There is probably a potential priority inversion in
 952          * there that could be worked around either by waking both queues
 953          * of waiters or doing some complicated lock handoff gymnastics.
 954          */
 955         v = RW_UNLOCKED;
 956         if (rw->rw_lock & RW_LOCK_WRITE_WAITERS) {
 957                 queue = TS_EXCLUSIVE_QUEUE;
 958                 v |= (rw->rw_lock & RW_LOCK_READ_WAITERS);
 959         } else
 960                 queue = TS_SHARED_QUEUE;
 961
 962         /* Wake up all waiters for the specific queue. */
 963         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 964                 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
 965                     queue == TS_SHARED_QUEUE ? "read" : "write");
 966         turnstile_broadcast(ts, queue);
 967         atomic_store_rel_ptr(&rw->rw_lock, v);
 968         turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
 969         turnstile_chain_unlock(&rw->lock_object);
 970 }
 971
 972 /*
 973  * Attempt to do a non-blocking upgrade from a read lock to a write
 974  * lock.  This will only succeed if this thread holds a single read
 975  * lock.  Returns true if the upgrade succeeded and false otherwise.
 976  */
 977 int
 978 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
 979 {
 980         struct rwlock *rw;
 981         uintptr_t v, x, tid;
 982         struct turnstile *ts;
 983         int success;
 984
 985         if (SCHEDULER_STOPPED())
 986                 return (1);
 987
 988         rw = rwlock2rw(c);
 989
 990         KASSERT(rw->rw_lock != RW_DESTROYED,
 991             ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
 992         __rw_assert(c, RA_RLOCKED, file, line);
 993
 994         /*
 995          * Attempt to switch from one reader to a writer.  If there
 996          * are any write waiters, then we will have to lock the
 997          * turnstile first to prevent races with another writer
 998          * calling turnstile_wait() before we have claimed this
 999          * turnstile.  So, do the simple case of no waiters first.
1000          */
1001         tid = (uintptr_t)curthread;
1002         success = 0;
1003         for (;;) {
1004                 v = rw->rw_lock;
1005                 if (RW_READERS(v) > 1)
1006                         break;
1007                 if (!(v & RW_LOCK_WAITERS)) {
1008                         success = atomic_cmpset_ptr(&rw->rw_lock, v, tid);
1009                         if (!success)
1010                                 continue;
1011                         break;
1012                 }
1013
1014                 /*
1015                  * Ok, we think we have waiters, so lock the turnstile.
1016                  */
1017                 ts = turnstile_trywait(&rw->lock_object);
1018                 v = rw->rw_lock;
1019                 if (RW_READERS(v) > 1) {
1020                         turnstile_cancel(ts);
1021                         break;
1022                 }
1023                 /*
1024                  * Try to switch from one reader to a writer again.  This time
1025                  * we honor the current state of the waiters flags.
1026                  * If we obtain the lock with the flags set, then claim
1027                  * ownership of the turnstile.
1028                  */
1029                 x = rw->rw_lock & RW_LOCK_WAITERS;
1030                 success = atomic_cmpset_ptr(&rw->rw_lock, v, tid | x);
1031                 if (success) {
1032                         if (x)
1033                                 turnstile_claim(ts);
1034                         else
1035                                 turnstile_cancel(ts);
1036                         break;
1037                 }
1038                 turnstile_cancel(ts);
1039         }
1040         LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
1041         if (success) {
1042                 curthread->td_rw_rlocks--;
1043                 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
1044                     file, line);
1045                 LOCKSTAT_RECORD0(LS_RW_TRYUPGRADE_UPGRADE, rw);
1046         }
1047         return (success);
1048 }
1049
1050 /*
1051  * Downgrade a write lock into a single read lock.
1052  */
1053 void
1054 __rw_downgrade(volatile uintptr_t *c, const char *file, int line)
1055 {
1056         struct rwlock *rw;
1057         struct turnstile *ts;
1058         uintptr_t tid, v;
1059         int rwait, wwait;
1060
1061         if (SCHEDULER_STOPPED())
1062                 return;
1063
1064         rw = rwlock2rw(c);
1065
1066         KASSERT(rw->rw_lock != RW_DESTROYED,
1067             ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
1068         __rw_assert(c, RA_WLOCKED | RA_NOTRECURSED, file, line);
1069 #ifndef INVARIANTS
1070         if (rw_recursed(rw))
1071                 panic("downgrade of a recursed lock");
1072 #endif
1073
1074         WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
1075
1076         /*
1077          * Convert from a writer to a single reader.  First we handle
1078          * the easy case with no waiters.  If there are any waiters, we
1079          * lock the turnstile and "disown" the lock.
1080          */
1081         tid = (uintptr_t)curthread;
1082         if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
1083                 goto out;
1084
1085         /*
1086          * Ok, we think we have waiters, so lock the turnstile so we can
1087          * read the waiter flags without any races.
1088          */
1089         turnstile_chain_lock(&rw->lock_object);
1090         v = rw->rw_lock & RW_LOCK_WAITERS;
1091         rwait = v & RW_LOCK_READ_WAITERS;
1092         wwait = v & RW_LOCK_WRITE_WAITERS;
1093         MPASS(rwait | wwait);
1094
1095         /*
1096          * Downgrade from a write lock while preserving waiters flag
1097          * and give up ownership of the turnstile.
1098          */
1099         ts = turnstile_lookup(&rw->lock_object);
1100         MPASS(ts != NULL);
1101         if (!wwait)
1102                 v &= ~RW_LOCK_READ_WAITERS;
1103         atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
1104         /*
1105          * Wake other readers if there are no writers pending.  Otherwise they
1106          * won't be able to acquire the lock anyway.
1107          */
1108         if (rwait && !wwait) {
1109                 turnstile_broadcast(ts, TS_SHARED_QUEUE);
1110                 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
1111         } else
1112                 turnstile_disown(ts);
1113         turnstile_chain_unlock(&rw->lock_object);
1114 out:
1115         curthread->td_rw_rlocks++;
1116         LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
1117         LOCKSTAT_RECORD0(LS_RW_DOWNGRADE_DOWNGRADE, rw);
1118 }
1119
1120 #ifdef INVARIANT_SUPPORT
1121 #ifndef INVARIANTS
1122 #undef __rw_assert
1123 #endif
1124
1125 /*
1126  * In the non-WITNESS case, rw_assert() can only detect that at least
1127  * *some* thread owns an rlock, but it cannot guarantee that *this*
1128  * thread owns an rlock.
1129  */
1130 void
1131 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
1132 {
1133         const struct rwlock *rw;
1134
1135         if (panicstr != NULL)
1136                 return;
1137
1138         rw = rwlock2rw(c);
1139
1140         switch (what) {
1141         case RA_LOCKED:
1142         case RA_LOCKED | RA_RECURSED:
1143         case RA_LOCKED | RA_NOTRECURSED:
1144         case RA_RLOCKED:
1145         case RA_RLOCKED | RA_RECURSED:
1146         case RA_RLOCKED | RA_NOTRECURSED:
1147 #ifdef WITNESS
1148                 witness_assert(&rw->lock_object, what, file, line);
1149 #else
1150                 /*
1151                  * If some other thread has a write lock or we have one
1152                  * and are asserting a read lock, fail.  Also, if no one
1153                  * has a lock at all, fail.
1154                  */
1155                 if (rw->rw_lock == RW_UNLOCKED ||
1156                     (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
1157                     rw_wowner(rw) != curthread)))
1158                         panic("Lock %s not %slocked @ %s:%d\n",
1159                             rw->lock_object.lo_name, (what & RA_RLOCKED) ?
1160                             "read " : "", file, line);
1161
1162                 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
1163                         if (rw_recursed(rw)) {
1164                                 if (what & RA_NOTRECURSED)
1165                                         panic("Lock %s recursed @ %s:%d\n",
1166                                             rw->lock_object.lo_name, file,
1167                                             line);
1168                         } else if (what & RA_RECURSED)
1169                                 panic("Lock %s not recursed @ %s:%d\n",
1170                                     rw->lock_object.lo_name, file, line);
1171                 }
1172 #endif
1173                 break;
1174         case RA_WLOCKED:
1175         case RA_WLOCKED | RA_RECURSED:
1176         case RA_WLOCKED | RA_NOTRECURSED:
1177                 if (rw_wowner(rw) != curthread)
1178                         panic("Lock %s not exclusively locked @ %s:%d\n",
1179                             rw->lock_object.lo_name, file, line);
1180                 if (rw_recursed(rw)) {
1181                         if (what & RA_NOTRECURSED)
1182                                 panic("Lock %s recursed @ %s:%d\n",
1183                                     rw->lock_object.lo_name, file, line);
1184                 } else if (what & RA_RECURSED)
1185                         panic("Lock %s not recursed @ %s:%d\n",
1186                             rw->lock_object.lo_name, file, line);
1187                 break;
1188         case RA_UNLOCKED:
1189 #ifdef WITNESS
1190                 witness_assert(&rw->lock_object, what, file, line);
1191 #else
1192                 /*
1193                  * If we hold a write lock fail.  We can't reliably check
1194                  * to see if we hold a read lock or not.
1195                  */
1196                 if (rw_wowner(rw) == curthread)
1197                         panic("Lock %s exclusively locked @ %s:%d\n",
1198                             rw->lock_object.lo_name, file, line);
1199 #endif
1200                 break;
1201         default:
1202                 panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
1203                     line);
1204         }
1205 }
1206 #endif /* INVARIANT_SUPPORT */
1207
1208 #ifdef DDB
1209 void
1210 db_show_rwlock(const struct lock_object *lock)
1211 {
1212         const struct rwlock *rw;
1213         struct thread *td;
1214
1215         rw = (const struct rwlock *)lock;
1216
1217         db_printf(" state: ");
1218         if (rw->rw_lock == RW_UNLOCKED)
1219                 db_printf("UNLOCKED\n");
1220         else if (rw->rw_lock == RW_DESTROYED) {
1221                 db_printf("DESTROYED\n");
1222                 return;
1223         } else if (rw->rw_lock & RW_LOCK_READ)
1224                 db_printf("RLOCK: %ju locks\n",
1225                     (uintmax_t)(RW_READERS(rw->rw_lock)));
1226         else {
1227                 td = rw_wowner(rw);
1228                 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1229                     td->td_tid, td->td_proc->p_pid, td->td_name);
1230                 if (rw_recursed(rw))
1231                         db_printf(" recursed: %u\n", rw->rw_recurse);
1232         }
1233         db_printf(" waiters: ");
1234         switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
1235         case RW_LOCK_READ_WAITERS:
1236                 db_printf("readers\n");
1237                 break;
1238         case RW_LOCK_WRITE_WAITERS:
1239                 db_printf("writers\n");
1240                 break;
1241         case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
1242                 db_printf("readers and writers\n");
1243                 break;
1244         default:
1245                 db_printf("none\n");
1246                 break;
1247         }
1248 }
1249
1250 #endif