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