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                 if (!rw_recursed(rw))
 303                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_WLOCK_ACQUIRE,
 304                             rw, 0, 0, file, line);
 305                 curthread->td_locks++;
 306         }
 307         return (rval);
 308 }
 309
 310 void
 311 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
 312 {
 313         struct rwlock *rw;
 314
 315         if (SCHEDULER_STOPPED())
 316                 return;
 317
 318         rw = rwlock2rw(c);
 319
 320         KASSERT(rw->rw_lock != RW_DESTROYED,
 321             ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
 322         __rw_assert(c, RA_WLOCKED, file, line);
 323         WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
 324         LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
 325             line);
 326         if (!rw_recursed(rw))
 327                 LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_WUNLOCK_RELEASE, rw);
 328         __rw_wunlock(rw, curthread, file, line);
 329         curthread->td_locks--;
 330 }
 331 /*
 332  * Determines whether a new reader can acquire a lock.  Succeeds if the
 333  * reader already owns a read lock and the lock is locked for read to
 334  * prevent deadlock from reader recursion.  Also succeeds if the lock
 335  * is unlocked and has no writer waiters or spinners.  Failing otherwise
 336  * prioritizes writers before readers.
 337  */
 338 #define RW_CAN_READ(_rw)                                                \
 339     ((curthread->td_rw_rlocks && (_rw) & RW_LOCK_READ) || ((_rw) &      \
 340     (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER)) ==  \
 341     RW_LOCK_READ)
 342
 343 void
 344 __rw_rlock(volatile uintptr_t *c, const char *file, int line)
 345 {
 346         struct rwlock *rw;
 347         struct turnstile *ts;
 348 #ifdef ADAPTIVE_RWLOCKS
 349         volatile struct thread *owner;
 350         int spintries = 0;
 351         int i;
 352 #endif
 353 #ifdef LOCK_PROFILING
 354         uint64_t waittime = 0;
 355         int contested = 0;
 356 #endif
 357         uintptr_t v;
 358 #ifdef KDTRACE_HOOKS
 359         uintptr_t state;
 360         uint64_t spin_cnt = 0;
 361         uint64_t sleep_cnt = 0;
 362         int64_t sleep_time = 0;
 363         int64_t all_time = 0;
 364 #endif
 365
 366         if (SCHEDULER_STOPPED())
 367                 return;
 368
 369         rw = rwlock2rw(c);
 370
 371         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 372             ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d",
 373             curthread, rw->lock_object.lo_name, file, line));
 374         KASSERT(rw->rw_lock != RW_DESTROYED,
 375             ("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
 376         KASSERT(rw_wowner(rw) != curthread,
 377             ("rw_rlock: wlock already held for %s @ %s:%d",
 378             rw->lock_object.lo_name, file, line));
 379         WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
 380
 381 #ifdef KDTRACE_HOOKS
 382         all_time -= lockstat_nsecs(&rw->lock_object);
 383         state = rw->rw_lock;
 384 #endif
 385         for (;;) {
 386 #ifdef KDTRACE_HOOKS
 387                 spin_cnt++;
 388 #endif
 389                 /*
 390                  * Handle the easy case.  If no other thread has a write
 391                  * lock, then try to bump up the count of read locks.  Note
 392                  * that we have to preserve the current state of the
 393                  * RW_LOCK_WRITE_WAITERS flag.  If we fail to acquire a
 394                  * read lock, then rw_lock must have changed, so restart
 395                  * the loop.  Note that this handles the case of a
 396                  * completely unlocked rwlock since such a lock is encoded
 397                  * as a read lock with no waiters.
 398                  */
 399                 v = rw->rw_lock;
 400                 if (RW_CAN_READ(v)) {
 401                         /*
 402                          * The RW_LOCK_READ_WAITERS flag should only be set
 403                          * if the lock has been unlocked and write waiters
 404                          * were present.
 405                          */
 406                         if (atomic_cmpset_acq_ptr(&rw->rw_lock, v,
 407                             v + RW_ONE_READER)) {
 408                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 409                                         CTR4(KTR_LOCK,
 410                                             "%s: %p succeed %p -> %p", __func__,
 411                                             rw, (void *)v,
 412                                             (void *)(v + RW_ONE_READER));
 413                                 break;
 414                         }
 415                         continue;
 416                 }
 417 #ifdef HWPMC_HOOKS
 418                 PMC_SOFT_CALL( , , lock, failed);
 419 #endif
 420                 lock_profile_obtain_lock_failed(&rw->lock_object,
 421                     &contested, &waittime);
 422
 423 #ifdef ADAPTIVE_RWLOCKS
 424                 /*
 425                  * If the owner is running on another CPU, spin until
 426                  * the owner stops running or the state of the lock
 427                  * changes.
 428                  */
 429                 if ((v & RW_LOCK_READ) == 0) {
 430                         owner = (struct thread *)RW_OWNER(v);
 431                         if (TD_IS_RUNNING(owner)) {
 432                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 433                                         CTR3(KTR_LOCK,
 434                                             "%s: spinning on %p held by %p",
 435                                             __func__, rw, owner);
 436                                 KTR_STATE1(KTR_SCHED, "thread",
 437                                     sched_tdname(curthread), "spinning",
 438                                     "lockname:\"%s\"", rw->lock_object.lo_name);
 439                                 while ((struct thread*)RW_OWNER(rw->rw_lock) ==
 440                                     owner && TD_IS_RUNNING(owner)) {
 441                                         cpu_spinwait();
 442 #ifdef KDTRACE_HOOKS
 443                                         spin_cnt++;
 444 #endif
 445                                 }
 446                                 KTR_STATE0(KTR_SCHED, "thread",
 447                                     sched_tdname(curthread), "running");
 448                                 continue;
 449                         }
 450                 } else if (spintries < rowner_retries) {
 451                         spintries++;
 452                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 453                             "spinning", "lockname:\"%s\"",
 454                             rw->lock_object.lo_name);
 455                         for (i = 0; i < rowner_loops; i++) {
 456                                 v = rw->rw_lock;
 457                                 if ((v & RW_LOCK_READ) == 0 || RW_CAN_READ(v))
 458                                         break;
 459                                 cpu_spinwait();
 460                         }
 461                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 462                             "running");
 463                         if (i != rowner_loops)
 464                                 continue;
 465                 }
 466 #endif
 467
 468                 /*
 469                  * Okay, now it's the hard case.  Some other thread already
 470                  * has a write lock or there are write waiters present,
 471                  * acquire the turnstile lock so we can begin the process
 472                  * of blocking.
 473                  */
 474                 ts = turnstile_trywait(&rw->lock_object);
 475
 476                 /*
 477                  * The lock might have been released while we spun, so
 478                  * recheck its state and restart the loop if needed.
 479                  */
 480                 v = rw->rw_lock;
 481                 if (RW_CAN_READ(v)) {
 482                         turnstile_cancel(ts);
 483                         continue;
 484                 }
 485
 486 #ifdef ADAPTIVE_RWLOCKS
 487                 /*
 488                  * The current lock owner might have started executing
 489                  * on another CPU (or the lock could have changed
 490                  * owners) while we were waiting on the turnstile
 491                  * chain lock.  If so, drop the turnstile lock and try
 492                  * again.
 493                  */
 494                 if ((v & RW_LOCK_READ) == 0) {
 495                         owner = (struct thread *)RW_OWNER(v);
 496                         if (TD_IS_RUNNING(owner)) {
 497                                 turnstile_cancel(ts);
 498                                 continue;
 499                         }
 500                 }
 501 #endif
 502
 503                 /*
 504                  * The lock is held in write mode or it already has waiters.
 505                  */
 506                 MPASS(!RW_CAN_READ(v));
 507
 508                 /*
 509                  * If the RW_LOCK_READ_WAITERS flag is already set, then
 510                  * we can go ahead and block.  If it is not set then try
 511                  * to set it.  If we fail to set it drop the turnstile
 512                  * lock and restart the loop.
 513                  */
 514                 if (!(v & RW_LOCK_READ_WAITERS)) {
 515                         if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 516                             v | RW_LOCK_READ_WAITERS)) {
 517                                 turnstile_cancel(ts);
 518                                 continue;
 519                         }
 520                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 521                                 CTR2(KTR_LOCK, "%s: %p set read waiters flag",
 522                                     __func__, rw);
 523                 }
 524
 525                 /*
 526                  * We were unable to acquire the lock and the read waiters
 527                  * flag is set, so we must block on the turnstile.
 528                  */
 529                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 530                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
 531                             rw);
 532 #ifdef KDTRACE_HOOKS
 533                 sleep_time -= lockstat_nsecs(&rw->lock_object);
 534 #endif
 535                 turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE);
 536 #ifdef KDTRACE_HOOKS
 537                 sleep_time += lockstat_nsecs(&rw->lock_object);
 538                 sleep_cnt++;
 539 #endif
 540                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 541                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
 542                             __func__, rw);
 543         }
 544 #ifdef KDTRACE_HOOKS
 545         all_time += lockstat_nsecs(&rw->lock_object);
 546         if (sleep_time)
 547                 LOCKSTAT_RECORD4(LS_RW_RLOCK_BLOCK, rw, sleep_time,
 548                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 549                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 550
 551         /* Record only the loops spinning and not sleeping. */
 552         if (spin_cnt > sleep_cnt)
 553                 LOCKSTAT_RECORD4(LS_RW_RLOCK_SPIN, rw, all_time - sleep_time,
 554                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 555                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 556 #endif
 557         /*
 558          * TODO: acquire "owner of record" here.  Here be turnstile dragons
 559          * however.  turnstiles don't like owners changing between calls to
 560          * turnstile_wait() currently.
 561          */
 562         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_RLOCK_ACQUIRE, rw, contested,
 563             waittime, file, line);
 564         LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
 565         WITNESS_LOCK(&rw->lock_object, 0, file, line);
 566         curthread->td_locks++;
 567         curthread->td_rw_rlocks++;
 568 }
 569
 570 int
 571 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
 572 {
 573         struct rwlock *rw;
 574         uintptr_t x;
 575
 576         if (SCHEDULER_STOPPED())
 577                 return (1);
 578
 579         rw = rwlock2rw(c);
 580
 581         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 582             ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
 583             curthread, rw->lock_object.lo_name, file, line));
 584
 585         for (;;) {
 586                 x = rw->rw_lock;
 587                 KASSERT(rw->rw_lock != RW_DESTROYED,
 588                     ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
 589                 if (!(x & RW_LOCK_READ))
 590                         break;
 591                 if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, x + RW_ONE_READER)) {
 592                         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
 593                             line);
 594                         WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
 595                         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_RLOCK_ACQUIRE,
 596                             rw, 0, 0, file, line);
 597                         curthread->td_locks++;
 598                         curthread->td_rw_rlocks++;
 599                         return (1);
 600                 }
 601         }
 602
 603         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
 604         return (0);
 605 }
 606
 607 void
 608 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
 609 {
 610         struct rwlock *rw;
 611         struct turnstile *ts;
 612         uintptr_t x, v, queue;
 613
 614         if (SCHEDULER_STOPPED())
 615                 return;
 616
 617         rw = rwlock2rw(c);
 618
 619         KASSERT(rw->rw_lock != RW_DESTROYED,
 620             ("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
 621         __rw_assert(c, RA_RLOCKED, file, line);
 622         WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
 623         LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
 624
 625         /* TODO: drop "owner of record" here. */
 626
 627         for (;;) {
 628                 /*
 629                  * See if there is more than one read lock held.  If so,
 630                  * just drop one and return.
 631                  */
 632                 x = rw->rw_lock;
 633                 if (RW_READERS(x) > 1) {
 634                         if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
 635                             x - RW_ONE_READER)) {
 636                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 637                                         CTR4(KTR_LOCK,
 638                                             "%s: %p succeeded %p -> %p",
 639                                             __func__, rw, (void *)x,
 640                                             (void *)(x - RW_ONE_READER));
 641                                 break;
 642                         }
 643                         continue;
 644                 }
 645                 /*
 646                  * If there aren't any waiters for a write lock, then try
 647                  * to drop it quickly.
 648                  */
 649                 if (!(x & RW_LOCK_WAITERS)) {
 650                         MPASS((x & ~RW_LOCK_WRITE_SPINNER) ==
 651                             RW_READERS_LOCK(1));
 652                         if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
 653                             RW_UNLOCKED)) {
 654                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 655                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
 656                                             __func__, rw);
 657                                 break;
 658                         }
 659                         continue;
 660                 }
 661                 /*
 662                  * Ok, we know we have waiters and we think we are the
 663                  * last reader, so grab the turnstile lock.
 664                  */
 665                 turnstile_chain_lock(&rw->lock_object);
 666                 v = rw->rw_lock & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
 667                 MPASS(v & RW_LOCK_WAITERS);
 668
 669                 /*
 670                  * Try to drop our lock leaving the lock in a unlocked
 671                  * state.
 672                  *
 673                  * If you wanted to do explicit lock handoff you'd have to
 674                  * do it here.  You'd also want to use turnstile_signal()
 675                  * and you'd have to handle the race where a higher
 676                  * priority thread blocks on the write lock before the
 677                  * thread you wakeup actually runs and have the new thread
 678                  * "steal" the lock.  For now it's a lot simpler to just
 679                  * wakeup all of the waiters.
 680                  *
 681                  * As above, if we fail, then another thread might have
 682                  * acquired a read lock, so drop the turnstile lock and
 683                  * restart.
 684                  */
 685                 x = RW_UNLOCKED;
 686                 if (v & RW_LOCK_WRITE_WAITERS) {
 687                         queue = TS_EXCLUSIVE_QUEUE;
 688                         x |= (v & RW_LOCK_READ_WAITERS);
 689                 } else
 690                         queue = TS_SHARED_QUEUE;
 691                 if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v,
 692                     x)) {
 693                         turnstile_chain_unlock(&rw->lock_object);
 694                         continue;
 695                 }
 696                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 697                         CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
 698                             __func__, rw);
 699
 700                 /*
 701                  * Ok.  The lock is released and all that's left is to
 702                  * wake up the waiters.  Note that the lock might not be
 703                  * free anymore, but in that case the writers will just
 704                  * block again if they run before the new lock holder(s)
 705                  * release the lock.
 706                  */
 707                 ts = turnstile_lookup(&rw->lock_object);
 708                 MPASS(ts != NULL);
 709                 turnstile_broadcast(ts, queue);
 710                 turnstile_unpend(ts, TS_SHARED_LOCK);
 711                 turnstile_chain_unlock(&rw->lock_object);
 712                 break;
 713         }
 714         LOCKSTAT_PROFILE_RELEASE_LOCK(LS_RW_RUNLOCK_RELEASE, rw);
 715         curthread->td_locks--;
 716         curthread->td_rw_rlocks--;
 717 }
 718
 719 /*
 720  * This function is called when we are unable to obtain a write lock on the
 721  * first try.  This means that at least one other thread holds either a
 722  * read or write lock.
 723  */
 724 void
 725 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
 726     int line)
 727 {
 728         struct rwlock *rw;
 729         struct turnstile *ts;
 730 #ifdef ADAPTIVE_RWLOCKS
 731         volatile struct thread *owner;
 732         int spintries = 0;
 733         int i;
 734 #endif
 735         uintptr_t v, x;
 736 #ifdef LOCK_PROFILING
 737         uint64_t waittime = 0;
 738         int contested = 0;
 739 #endif
 740 #ifdef KDTRACE_HOOKS
 741         uintptr_t state;
 742         uint64_t spin_cnt = 0;
 743         uint64_t sleep_cnt = 0;
 744         int64_t sleep_time = 0;
 745         int64_t all_time = 0;
 746 #endif
 747
 748         if (SCHEDULER_STOPPED())
 749                 return;
 750
 751         rw = rwlock2rw(c);
 752
 753         if (rw_wlocked(rw)) {
 754                 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
 755                     ("%s: recursing but non-recursive rw %s @ %s:%d\n",
 756                     __func__, rw->lock_object.lo_name, file, line));
 757                 rw->rw_recurse++;
 758                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 759                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
 760                 return;
 761         }
 762
 763         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 764                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 765                     rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
 766
 767 #ifdef KDTRACE_HOOKS
 768         all_time -= lockstat_nsecs(&rw->lock_object);
 769         state = rw->rw_lock;
 770 #endif
 771         while (!_rw_write_lock(rw, tid)) {
 772 #ifdef KDTRACE_HOOKS
 773                 spin_cnt++;
 774 #endif
 775 #ifdef HWPMC_HOOKS
 776                 PMC_SOFT_CALL( , , lock, failed);
 777 #endif
 778                 lock_profile_obtain_lock_failed(&rw->lock_object,
 779                     &contested, &waittime);
 780 #ifdef ADAPTIVE_RWLOCKS
 781                 /*
 782                  * If the lock is write locked and the owner is
 783                  * running on another CPU, spin until the owner stops
 784                  * running or the state of the lock changes.
 785                  */
 786                 v = rw->rw_lock;
 787                 owner = (struct thread *)RW_OWNER(v);
 788                 if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) {
 789                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 790                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
 791                                     __func__, rw, owner);
 792                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 793                             "spinning", "lockname:\"%s\"",
 794                             rw->lock_object.lo_name);
 795                         while ((struct thread*)RW_OWNER(rw->rw_lock) == owner &&
 796                             TD_IS_RUNNING(owner)) {
 797                                 cpu_spinwait();
 798 #ifdef KDTRACE_HOOKS
 799                                 spin_cnt++;
 800 #endif
 801                         }
 802                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 803                             "running");
 804                         continue;
 805                 }
 806                 if ((v & RW_LOCK_READ) && RW_READERS(v) &&
 807                     spintries < rowner_retries) {
 808                         if (!(v & RW_LOCK_WRITE_SPINNER)) {
 809                                 if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 810                                     v | RW_LOCK_WRITE_SPINNER)) {
 811                                         continue;
 812                                 }
 813                         }
 814                         spintries++;
 815                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 816                             "spinning", "lockname:\"%s\"",
 817                             rw->lock_object.lo_name);
 818                         for (i = 0; i < rowner_loops; i++) {
 819                                 if ((rw->rw_lock & RW_LOCK_WRITE_SPINNER) == 0)
 820                                         break;
 821                                 cpu_spinwait();
 822                         }
 823                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 824                             "running");
 825 #ifdef KDTRACE_HOOKS
 826                         spin_cnt += rowner_loops - i;
 827 #endif
 828                         if (i != rowner_loops)
 829                                 continue;
 830                 }
 831 #endif
 832                 ts = turnstile_trywait(&rw->lock_object);
 833                 v = rw->rw_lock;
 834
 835 #ifdef ADAPTIVE_RWLOCKS
 836                 /*
 837                  * The current lock owner might have started executing
 838                  * on another CPU (or the lock could have changed
 839                  * owners) while we were waiting on the turnstile
 840                  * chain lock.  If so, drop the turnstile lock and try
 841                  * again.
 842                  */
 843                 if (!(v & RW_LOCK_READ)) {
 844                         owner = (struct thread *)RW_OWNER(v);
 845                         if (TD_IS_RUNNING(owner)) {
 846                                 turnstile_cancel(ts);
 847                                 continue;
 848                         }
 849                 }
 850 #endif
 851                 /*
 852                  * Check for the waiters flags about this rwlock.
 853                  * If the lock was released, without maintain any pending
 854                  * waiters queue, simply try to acquire it.
 855                  * If a pending waiters queue is present, claim the lock
 856                  * ownership and maintain the pending queue.
 857                  */
 858                 x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
 859                 if ((v & ~x) == RW_UNLOCKED) {
 860                         x &= ~RW_LOCK_WRITE_SPINNER;
 861                         if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid | x)) {
 862                                 if (x)
 863                                         turnstile_claim(ts);
 864                                 else
 865                                         turnstile_cancel(ts);
 866                                 break;
 867                         }
 868                         turnstile_cancel(ts);
 869                         continue;
 870                 }
 871                 /*
 872                  * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
 873                  * set it.  If we fail to set it, then loop back and try
 874                  * again.
 875                  */
 876                 if (!(v & RW_LOCK_WRITE_WAITERS)) {
 877                         if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 878                             v | RW_LOCK_WRITE_WAITERS)) {
 879                                 turnstile_cancel(ts);
 880                                 continue;
 881                         }
 882                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 883                                 CTR2(KTR_LOCK, "%s: %p set write waiters flag",
 884                                     __func__, rw);
 885                 }
 886                 /*
 887                  * We were unable to acquire the lock and the write waiters
 888                  * flag is set, so we must block on the turnstile.
 889                  */
 890                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 891                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
 892                             rw);
 893 #ifdef KDTRACE_HOOKS
 894                 sleep_time -= lockstat_nsecs(&rw->lock_object);
 895 #endif
 896                 turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE);
 897 #ifdef KDTRACE_HOOKS
 898                 sleep_time += lockstat_nsecs(&rw->lock_object);
 899                 sleep_cnt++;
 900 #endif
 901                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 902                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
 903                             __func__, rw);
 904 #ifdef ADAPTIVE_RWLOCKS
 905                 spintries = 0;
 906 #endif
 907         }
 908 #ifdef KDTRACE_HOOKS
 909         all_time += lockstat_nsecs(&rw->lock_object);
 910         if (sleep_time)
 911                 LOCKSTAT_RECORD4(LS_RW_WLOCK_BLOCK, rw, sleep_time,
 912                     LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
 913                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 914
 915         /* Record only the loops spinning and not sleeping. */
 916         if (spin_cnt > sleep_cnt)
 917                 LOCKSTAT_RECORD4(LS_RW_WLOCK_SPIN, rw, all_time - sleep_time,
 918                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 919                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 920 #endif
 921         LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_RW_WLOCK_ACQUIRE, rw, contested,
 922             waittime, file, line);
 923 }
 924
 925 /*
 926  * This function is called if the first try at releasing a write lock failed.
 927  * This means that one of the 2 waiter bits must be set indicating that at
 928  * least one thread is waiting on this lock.
 929  */
 930 void
 931 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
 932     int line)
 933 {
 934         struct rwlock *rw;
 935         struct turnstile *ts;
 936         uintptr_t v;
 937         int queue;
 938
 939         if (SCHEDULER_STOPPED())
 940                 return;
 941
 942         rw = rwlock2rw(c);
 943
 944         if (rw_wlocked(rw) && rw_recursed(rw)) {
 945                 rw->rw_recurse--;
 946                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 947                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
 948                 return;
 949         }
 950
 951         KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
 952             ("%s: neither of the waiter flags are set", __func__));
 953
 954         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 955                 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
 956
 957         turnstile_chain_lock(&rw->lock_object);
 958         ts = turnstile_lookup(&rw->lock_object);
 959         MPASS(ts != NULL);
 960
 961         /*
 962          * Use the same algo as sx locks for now.  Prefer waking up shared
 963          * waiters if we have any over writers.  This is probably not ideal.
 964          *
 965          * 'v' is the value we are going to write back to rw_lock.  If we
 966          * have waiters on both queues, we need to preserve the state of
 967          * the waiter flag for the queue we don't wake up.  For now this is
 968          * hardcoded for the algorithm mentioned above.
 969          *
 970          * In the case of both readers and writers waiting we wakeup the
 971          * readers but leave the RW_LOCK_WRITE_WAITERS flag set.  If a
 972          * new writer comes in before a reader it will claim the lock up
 973          * above.  There is probably a potential priority inversion in
 974          * there that could be worked around either by waking both queues
 975          * of waiters or doing some complicated lock handoff gymnastics.
 976          */
 977         v = RW_UNLOCKED;
 978         if (rw->rw_lock & RW_LOCK_WRITE_WAITERS) {
 979                 queue = TS_EXCLUSIVE_QUEUE;
 980                 v |= (rw->rw_lock & RW_LOCK_READ_WAITERS);
 981         } else
 982                 queue = TS_SHARED_QUEUE;
 983
 984         /* Wake up all waiters for the specific queue. */
 985         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 986                 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
 987                     queue == TS_SHARED_QUEUE ? "read" : "write");
 988         turnstile_broadcast(ts, queue);
 989         atomic_store_rel_ptr(&rw->rw_lock, v);
 990         turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
 991         turnstile_chain_unlock(&rw->lock_object);
 992 }
 993
 994 /*
 995  * Attempt to do a non-blocking upgrade from a read lock to a write
 996  * lock.  This will only succeed if this thread holds a single read
 997  * lock.  Returns true if the upgrade succeeded and false otherwise.
 998  */
 999 int
1000 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
1001 {
1002         struct rwlock *rw;
1003         uintptr_t v, x, tid;
1004         struct turnstile *ts;
1005         int success;
1006
1007         if (SCHEDULER_STOPPED())
1008                 return (1);
1009
1010         rw = rwlock2rw(c);
1011
1012         KASSERT(rw->rw_lock != RW_DESTROYED,
1013             ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
1014         __rw_assert(c, RA_RLOCKED, file, line);
1015
1016         /*
1017          * Attempt to switch from one reader to a writer.  If there
1018          * are any write waiters, then we will have to lock the
1019          * turnstile first to prevent races with another writer
1020          * calling turnstile_wait() before we have claimed this
1021          * turnstile.  So, do the simple case of no waiters first.
1022          */
1023         tid = (uintptr_t)curthread;
1024         success = 0;
1025         for (;;) {
1026                 v = rw->rw_lock;
1027                 if (RW_READERS(v) > 1)
1028                         break;
1029                 if (!(v & RW_LOCK_WAITERS)) {
1030                         success = atomic_cmpset_ptr(&rw->rw_lock, v, tid);
1031                         if (!success)
1032                                 continue;
1033                         break;
1034                 }
1035
1036                 /*
1037                  * Ok, we think we have waiters, so lock the turnstile.
1038                  */
1039                 ts = turnstile_trywait(&rw->lock_object);
1040                 v = rw->rw_lock;
1041                 if (RW_READERS(v) > 1) {
1042                         turnstile_cancel(ts);
1043                         break;
1044                 }
1045                 /*
1046                  * Try to switch from one reader to a writer again.  This time
1047                  * we honor the current state of the waiters flags.
1048                  * If we obtain the lock with the flags set, then claim
1049                  * ownership of the turnstile.
1050                  */
1051                 x = rw->rw_lock & RW_LOCK_WAITERS;
1052                 success = atomic_cmpset_ptr(&rw->rw_lock, v, tid | x);
1053                 if (success) {
1054                         if (x)
1055                                 turnstile_claim(ts);
1056                         else
1057                                 turnstile_cancel(ts);
1058                         break;
1059                 }
1060                 turnstile_cancel(ts);
1061         }
1062         LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
1063         if (success) {
1064                 curthread->td_rw_rlocks--;
1065                 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
1066                     file, line);
1067                 LOCKSTAT_RECORD0(LS_RW_TRYUPGRADE_UPGRADE, rw);
1068         }
1069         return (success);
1070 }
1071
1072 /*
1073  * Downgrade a write lock into a single read lock.
1074  */
1075 void
1076 __rw_downgrade(volatile uintptr_t *c, const char *file, int line)
1077 {
1078         struct rwlock *rw;
1079         struct turnstile *ts;
1080         uintptr_t tid, v;
1081         int rwait, wwait;
1082
1083         if (SCHEDULER_STOPPED())
1084                 return;
1085
1086         rw = rwlock2rw(c);
1087
1088         KASSERT(rw->rw_lock != RW_DESTROYED,
1089             ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
1090         __rw_assert(c, RA_WLOCKED | RA_NOTRECURSED, file, line);
1091 #ifndef INVARIANTS
1092         if (rw_recursed(rw))
1093                 panic("downgrade of a recursed lock");
1094 #endif
1095
1096         WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
1097
1098         /*
1099          * Convert from a writer to a single reader.  First we handle
1100          * the easy case with no waiters.  If there are any waiters, we
1101          * lock the turnstile and "disown" the lock.
1102          */
1103         tid = (uintptr_t)curthread;
1104         if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
1105                 goto out;
1106
1107         /*
1108          * Ok, we think we have waiters, so lock the turnstile so we can
1109          * read the waiter flags without any races.
1110          */
1111         turnstile_chain_lock(&rw->lock_object);
1112         v = rw->rw_lock & RW_LOCK_WAITERS;
1113         rwait = v & RW_LOCK_READ_WAITERS;
1114         wwait = v & RW_LOCK_WRITE_WAITERS;
1115         MPASS(rwait | wwait);
1116
1117         /*
1118          * Downgrade from a write lock while preserving waiters flag
1119          * and give up ownership of the turnstile.
1120          */
1121         ts = turnstile_lookup(&rw->lock_object);
1122         MPASS(ts != NULL);
1123         if (!wwait)
1124                 v &= ~RW_LOCK_READ_WAITERS;
1125         atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
1126         /*
1127          * Wake other readers if there are no writers pending.  Otherwise they
1128          * won't be able to acquire the lock anyway.
1129          */
1130         if (rwait && !wwait) {
1131                 turnstile_broadcast(ts, TS_SHARED_QUEUE);
1132                 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
1133         } else
1134                 turnstile_disown(ts);
1135         turnstile_chain_unlock(&rw->lock_object);
1136 out:
1137         curthread->td_rw_rlocks++;
1138         LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
1139         LOCKSTAT_RECORD0(LS_RW_DOWNGRADE_DOWNGRADE, rw);
1140 }
1141
1142 #ifdef INVARIANT_SUPPORT
1143 #ifndef INVARIANTS
1144 #undef __rw_assert
1145 #endif
1146
1147 /*
1148  * In the non-WITNESS case, rw_assert() can only detect that at least
1149  * *some* thread owns an rlock, but it cannot guarantee that *this*
1150  * thread owns an rlock.
1151  */
1152 void
1153 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
1154 {
1155         const struct rwlock *rw;
1156
1157         if (panicstr != NULL)
1158                 return;
1159
1160         rw = rwlock2rw(c);
1161
1162         switch (what) {
1163         case RA_LOCKED:
1164         case RA_LOCKED | RA_RECURSED:
1165         case RA_LOCKED | RA_NOTRECURSED:
1166         case RA_RLOCKED:
1167         case RA_RLOCKED | RA_RECURSED:
1168         case RA_RLOCKED | RA_NOTRECURSED:
1169 #ifdef WITNESS
1170                 witness_assert(&rw->lock_object, what, file, line);
1171 #else
1172                 /*
1173                  * If some other thread has a write lock or we have one
1174                  * and are asserting a read lock, fail.  Also, if no one
1175                  * has a lock at all, fail.
1176                  */
1177                 if (rw->rw_lock == RW_UNLOCKED ||
1178                     (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
1179                     rw_wowner(rw) != curthread)))
1180                         panic("Lock %s not %slocked @ %s:%d\n",
1181                             rw->lock_object.lo_name, (what & RA_RLOCKED) ?
1182                             "read " : "", file, line);
1183
1184                 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
1185                         if (rw_recursed(rw)) {
1186                                 if (what & RA_NOTRECURSED)
1187                                         panic("Lock %s recursed @ %s:%d\n",
1188                                             rw->lock_object.lo_name, file,
1189                                             line);
1190                         } else if (what & RA_RECURSED)
1191                                 panic("Lock %s not recursed @ %s:%d\n",
1192                                     rw->lock_object.lo_name, file, line);
1193                 }
1194 #endif
1195                 break;
1196         case RA_WLOCKED:
1197         case RA_WLOCKED | RA_RECURSED:
1198         case RA_WLOCKED | RA_NOTRECURSED:
1199                 if (rw_wowner(rw) != curthread)
1200                         panic("Lock %s not exclusively locked @ %s:%d\n",
1201                             rw->lock_object.lo_name, file, line);
1202                 if (rw_recursed(rw)) {
1203                         if (what & RA_NOTRECURSED)
1204                                 panic("Lock %s recursed @ %s:%d\n",
1205                                     rw->lock_object.lo_name, file, line);
1206                 } else if (what & RA_RECURSED)
1207                         panic("Lock %s not recursed @ %s:%d\n",
1208                             rw->lock_object.lo_name, file, line);
1209                 break;
1210         case RA_UNLOCKED:
1211 #ifdef WITNESS
1212                 witness_assert(&rw->lock_object, what, file, line);
1213 #else
1214                 /*
1215                  * If we hold a write lock fail.  We can't reliably check
1216                  * to see if we hold a read lock or not.
1217                  */
1218                 if (rw_wowner(rw) == curthread)
1219                         panic("Lock %s exclusively locked @ %s:%d\n",
1220                             rw->lock_object.lo_name, file, line);
1221 #endif
1222                 break;
1223         default:
1224                 panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
1225                     line);
1226         }
1227 }
1228 #endif /* INVARIANT_SUPPORT */
1229
1230 #ifdef DDB
1231 void
1232 db_show_rwlock(const struct lock_object *lock)
1233 {
1234         const struct rwlock *rw;
1235         struct thread *td;
1236
1237         rw = (const struct rwlock *)lock;
1238
1239         db_printf(" state: ");
1240         if (rw->rw_lock == RW_UNLOCKED)
1241                 db_printf("UNLOCKED\n");
1242         else if (rw->rw_lock == RW_DESTROYED) {
1243                 db_printf("DESTROYED\n");
1244                 return;
1245         } else if (rw->rw_lock & RW_LOCK_READ)
1246                 db_printf("RLOCK: %ju locks\n",
1247                     (uintmax_t)(RW_READERS(rw->rw_lock)));
1248         else {
1249                 td = rw_wowner(rw);
1250                 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1251                     td->td_tid, td->td_proc->p_pid, td->td_name);
1252                 if (rw_recursed(rw))
1253                         db_printf(" recursed: %u\n", rw->rw_recurse);
1254         }
1255         db_printf(" waiters: ");
1256         switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
1257         case RW_LOCK_READ_WAITERS:
1258                 db_printf("readers\n");
1259                 break;
1260         case RW_LOCK_WRITE_WAITERS:
1261                 db_printf("writers\n");
1262                 break;
1263         case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
1264                 db_printf("readers and writers\n");
1265                 break;
1266         default:
1267                 db_printf("none\n");
1268                 break;
1269         }
1270 }
1271
1272 #endif