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_no_adaptive_rwlocks.h"
  37
  38 #include <sys/param.h>
  39 #include <sys/kdb.h>
  40 #include <sys/ktr.h>
  41 #include <sys/kernel.h>
  42 #include <sys/lock.h>
  43 #include <sys/mutex.h>
  44 #include <sys/proc.h>
  45 #include <sys/rwlock.h>
  46 #include <sys/sched.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 | RW_NEW)) == 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         if (opts & RW_NEW)
 207                 flags |= LO_NEW;
 208
 209         lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
 210         rw->rw_lock = RW_UNLOCKED;
 211         rw->rw_recurse = 0;
 212 }
 213
 214 void
 215 _rw_destroy(volatile uintptr_t *c)
 216 {
 217         struct rwlock *rw;
 218
 219         rw = rwlock2rw(c);
 220
 221         KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw));
 222         KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw));
 223         rw->rw_lock = RW_DESTROYED;
 224         lock_destroy(&rw->lock_object);
 225 }
 226
 227 void
 228 rw_sysinit(void *arg)
 229 {
 230         struct rw_args *args = arg;
 231
 232         rw_init((struct rwlock *)args->ra_rw, args->ra_desc);
 233 }
 234
 235 void
 236 rw_sysinit_flags(void *arg)
 237 {
 238         struct rw_args_flags *args = arg;
 239
 240         rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc,
 241             args->ra_flags);
 242 }
 243
 244 int
 245 _rw_wowned(const volatile uintptr_t *c)
 246 {
 247
 248         return (rw_wowner(rwlock2rw(c)) == curthread);
 249 }
 250
 251 void
 252 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line)
 253 {
 254         struct rwlock *rw;
 255
 256         if (SCHEDULER_STOPPED())
 257                 return;
 258
 259         rw = rwlock2rw(c);
 260
 261         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 262             ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d",
 263             curthread, rw->lock_object.lo_name, file, line));
 264         KASSERT(rw->rw_lock != RW_DESTROYED,
 265             ("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
 266         WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 267             line, NULL);
 268         __rw_wlock(rw, curthread, file, line);
 269         LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
 270         WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
 271         TD_LOCKS_INC(curthread);
 272 }
 273
 274 int
 275 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
 276 {
 277         struct rwlock *rw;
 278         int rval;
 279
 280         if (SCHEDULER_STOPPED())
 281                 return (1);
 282
 283         rw = rwlock2rw(c);
 284
 285         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 286             ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d",
 287             curthread, rw->lock_object.lo_name, file, line));
 288         KASSERT(rw->rw_lock != RW_DESTROYED,
 289             ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
 290
 291         if (rw_wlocked(rw) &&
 292             (rw->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 293                 rw->rw_recurse++;
 294                 rval = 1;
 295         } else
 296                 rval = atomic_cmpset_acq_ptr(&rw->rw_lock, RW_UNLOCKED,
 297                     (uintptr_t)curthread);
 298
 299         LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
 300         if (rval) {
 301                 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 302                     file, line);
 303                 if (!rw_recursed(rw))
 304                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
 305                             rw, 0, 0, file, line, LOCKSTAT_WRITER);
 306                 TD_LOCKS_INC(curthread);
 307         }
 308         return (rval);
 309 }
 310
 311 void
 312 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
 313 {
 314         struct rwlock *rw;
 315
 316         if (SCHEDULER_STOPPED())
 317                 return;
 318
 319         rw = rwlock2rw(c);
 320
 321         KASSERT(rw->rw_lock != RW_DESTROYED,
 322             ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
 323         __rw_assert(c, RA_WLOCKED, file, line);
 324         WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
 325         LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
 326             line);
 327         __rw_wunlock(rw, curthread, file, line);
 328         TD_LOCKS_DEC(curthread);
 329 }
 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                 /*
 387                  * Handle the easy case.  If no other thread has a write
 388                  * lock, then try to bump up the count of read locks.  Note
 389                  * that we have to preserve the current state of the
 390                  * RW_LOCK_WRITE_WAITERS flag.  If we fail to acquire a
 391                  * read lock, then rw_lock must have changed, so restart
 392                  * the loop.  Note that this handles the case of a
 393                  * completely unlocked rwlock since such a lock is encoded
 394                  * as a read lock with no waiters.
 395                  */
 396                 v = rw->rw_lock;
 397                 if (RW_CAN_READ(v)) {
 398                         /*
 399                          * The RW_LOCK_READ_WAITERS flag should only be set
 400                          * if the lock has been unlocked and write waiters
 401                          * were present.
 402                          */
 403                         if (atomic_cmpset_acq_ptr(&rw->rw_lock, v,
 404                             v + RW_ONE_READER)) {
 405                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 406                                         CTR4(KTR_LOCK,
 407                                             "%s: %p succeed %p -> %p", __func__,
 408                                             rw, (void *)v,
 409                                             (void *)(v + RW_ONE_READER));
 410                                 break;
 411                         }
 412                         continue;
 413                 }
 414 #ifdef KDTRACE_HOOKS
 415                 spin_cnt++;
 416 #endif
 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 #ifdef KDTRACE_HOOKS
 462                         spin_cnt += rowner_loops - i;
 463 #endif
 464                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 465                             "running");
 466                         if (i != rowner_loops)
 467                                 continue;
 468                 }
 469 #endif
 470
 471                 /*
 472                  * Okay, now it's the hard case.  Some other thread already
 473                  * has a write lock or there are write waiters present,
 474                  * acquire the turnstile lock so we can begin the process
 475                  * of blocking.
 476                  */
 477                 ts = turnstile_trywait(&rw->lock_object);
 478
 479                 /*
 480                  * The lock might have been released while we spun, so
 481                  * recheck its state and restart the loop if needed.
 482                  */
 483                 v = rw->rw_lock;
 484                 if (RW_CAN_READ(v)) {
 485                         turnstile_cancel(ts);
 486                         continue;
 487                 }
 488
 489 #ifdef ADAPTIVE_RWLOCKS
 490                 /*
 491                  * The current lock owner might have started executing
 492                  * on another CPU (or the lock could have changed
 493                  * owners) while we were waiting on the turnstile
 494                  * chain lock.  If so, drop the turnstile lock and try
 495                  * again.
 496                  */
 497                 if ((v & RW_LOCK_READ) == 0) {
 498                         owner = (struct thread *)RW_OWNER(v);
 499                         if (TD_IS_RUNNING(owner)) {
 500                                 turnstile_cancel(ts);
 501                                 continue;
 502                         }
 503                 }
 504 #endif
 505
 506                 /*
 507                  * The lock is held in write mode or it already has waiters.
 508                  */
 509                 MPASS(!RW_CAN_READ(v));
 510
 511                 /*
 512                  * If the RW_LOCK_READ_WAITERS flag is already set, then
 513                  * we can go ahead and block.  If it is not set then try
 514                  * to set it.  If we fail to set it drop the turnstile
 515                  * lock and restart the loop.
 516                  */
 517                 if (!(v & RW_LOCK_READ_WAITERS)) {
 518                         if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 519                             v | RW_LOCK_READ_WAITERS)) {
 520                                 turnstile_cancel(ts);
 521                                 continue;
 522                         }
 523                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 524                                 CTR2(KTR_LOCK, "%s: %p set read waiters flag",
 525                                     __func__, rw);
 526                 }
 527
 528                 /*
 529                  * We were unable to acquire the lock and the read waiters
 530                  * flag is set, so we must block on the turnstile.
 531                  */
 532                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 533                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
 534                             rw);
 535 #ifdef KDTRACE_HOOKS
 536                 sleep_time -= lockstat_nsecs(&rw->lock_object);
 537 #endif
 538                 turnstile_wait(ts, rw_owner(rw), TS_SHARED_QUEUE);
 539 #ifdef KDTRACE_HOOKS
 540                 sleep_time += lockstat_nsecs(&rw->lock_object);
 541                 sleep_cnt++;
 542 #endif
 543                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 544                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
 545                             __func__, rw);
 546         }
 547 #ifdef KDTRACE_HOOKS
 548         all_time += lockstat_nsecs(&rw->lock_object);
 549         if (sleep_time)
 550                 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
 551                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 552                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 553
 554         /* Record only the loops spinning and not sleeping. */
 555         if (spin_cnt > sleep_cnt)
 556                 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
 557                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 558                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 559 #endif
 560         /*
 561          * TODO: acquire "owner of record" here.  Here be turnstile dragons
 562          * however.  turnstiles don't like owners changing between calls to
 563          * turnstile_wait() currently.
 564          */
 565         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
 566             waittime, file, line, LOCKSTAT_READER);
 567         LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
 568         WITNESS_LOCK(&rw->lock_object, 0, file, line);
 569         TD_LOCKS_INC(curthread);
 570         curthread->td_rw_rlocks++;
 571 }
 572
 573 int
 574 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
 575 {
 576         struct rwlock *rw;
 577         uintptr_t x;
 578
 579         if (SCHEDULER_STOPPED())
 580                 return (1);
 581
 582         rw = rwlock2rw(c);
 583
 584         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 585             ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
 586             curthread, rw->lock_object.lo_name, file, line));
 587
 588         for (;;) {
 589                 x = rw->rw_lock;
 590                 KASSERT(rw->rw_lock != RW_DESTROYED,
 591                     ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
 592                 if (!(x & RW_LOCK_READ))
 593                         break;
 594                 if (atomic_cmpset_acq_ptr(&rw->rw_lock, x, x + RW_ONE_READER)) {
 595                         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
 596                             line);
 597                         WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
 598                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
 599                             rw, 0, 0, file, line, LOCKSTAT_READER);
 600                         TD_LOCKS_INC(curthread);
 601                         curthread->td_rw_rlocks++;
 602                         return (1);
 603                 }
 604         }
 605
 606         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
 607         return (0);
 608 }
 609
 610 void
 611 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
 612 {
 613         struct rwlock *rw;
 614         struct turnstile *ts;
 615         uintptr_t x, v, queue;
 616
 617         if (SCHEDULER_STOPPED())
 618                 return;
 619
 620         rw = rwlock2rw(c);
 621
 622         KASSERT(rw->rw_lock != RW_DESTROYED,
 623             ("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
 624         __rw_assert(c, RA_RLOCKED, file, line);
 625         WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
 626         LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
 627
 628         /* TODO: drop "owner of record" here. */
 629
 630         for (;;) {
 631                 /*
 632                  * See if there is more than one read lock held.  If so,
 633                  * just drop one and return.
 634                  */
 635                 x = rw->rw_lock;
 636                 if (RW_READERS(x) > 1) {
 637                         if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
 638                             x - RW_ONE_READER)) {
 639                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 640                                         CTR4(KTR_LOCK,
 641                                             "%s: %p succeeded %p -> %p",
 642                                             __func__, rw, (void *)x,
 643                                             (void *)(x - RW_ONE_READER));
 644                                 break;
 645                         }
 646                         continue;
 647                 }
 648                 /*
 649                  * If there aren't any waiters for a write lock, then try
 650                  * to drop it quickly.
 651                  */
 652                 if (!(x & RW_LOCK_WAITERS)) {
 653                         MPASS((x & ~RW_LOCK_WRITE_SPINNER) ==
 654                             RW_READERS_LOCK(1));
 655                         if (atomic_cmpset_rel_ptr(&rw->rw_lock, x,
 656                             RW_UNLOCKED)) {
 657                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 658                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
 659                                             __func__, rw);
 660                                 break;
 661                         }
 662                         continue;
 663                 }
 664                 /*
 665                  * Ok, we know we have waiters and we think we are the
 666                  * last reader, so grab the turnstile lock.
 667                  */
 668                 turnstile_chain_lock(&rw->lock_object);
 669                 v = rw->rw_lock & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
 670                 MPASS(v & RW_LOCK_WAITERS);
 671
 672                 /*
 673                  * Try to drop our lock leaving the lock in a unlocked
 674                  * state.
 675                  *
 676                  * If you wanted to do explicit lock handoff you'd have to
 677                  * do it here.  You'd also want to use turnstile_signal()
 678                  * and you'd have to handle the race where a higher
 679                  * priority thread blocks on the write lock before the
 680                  * thread you wakeup actually runs and have the new thread
 681                  * "steal" the lock.  For now it's a lot simpler to just
 682                  * wakeup all of the waiters.
 683                  *
 684                  * As above, if we fail, then another thread might have
 685                  * acquired a read lock, so drop the turnstile lock and
 686                  * restart.
 687                  */
 688                 x = RW_UNLOCKED;
 689                 if (v & RW_LOCK_WRITE_WAITERS) {
 690                         queue = TS_EXCLUSIVE_QUEUE;
 691                         x |= (v & RW_LOCK_READ_WAITERS);
 692                 } else
 693                         queue = TS_SHARED_QUEUE;
 694                 if (!atomic_cmpset_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v,
 695                     x)) {
 696                         turnstile_chain_unlock(&rw->lock_object);
 697                         continue;
 698                 }
 699                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 700                         CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
 701                             __func__, rw);
 702
 703                 /*
 704                  * Ok.  The lock is released and all that's left is to
 705                  * wake up the waiters.  Note that the lock might not be
 706                  * free anymore, but in that case the writers will just
 707                  * block again if they run before the new lock holder(s)
 708                  * release the lock.
 709                  */
 710                 ts = turnstile_lookup(&rw->lock_object);
 711                 MPASS(ts != NULL);
 712                 turnstile_broadcast(ts, queue);
 713                 turnstile_unpend(ts, TS_SHARED_LOCK);
 714                 turnstile_chain_unlock(&rw->lock_object);
 715                 break;
 716         }
 717         LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER);
 718         TD_LOCKS_DEC(curthread);
 719         curthread->td_rw_rlocks--;
 720 }
 721
 722 /*
 723  * This function is called when we are unable to obtain a write lock on the
 724  * first try.  This means that at least one other thread holds either a
 725  * read or write lock.
 726  */
 727 void
 728 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
 729     int line)
 730 {
 731         struct rwlock *rw;
 732         struct turnstile *ts;
 733 #ifdef ADAPTIVE_RWLOCKS
 734         volatile struct thread *owner;
 735         int spintries = 0;
 736         int i;
 737 #endif
 738         uintptr_t v, x;
 739 #ifdef LOCK_PROFILING
 740         uint64_t waittime = 0;
 741         int contested = 0;
 742 #endif
 743 #ifdef KDTRACE_HOOKS
 744         uintptr_t state;
 745         uint64_t spin_cnt = 0;
 746         uint64_t sleep_cnt = 0;
 747         int64_t sleep_time = 0;
 748         int64_t all_time = 0;
 749 #endif
 750
 751         if (SCHEDULER_STOPPED())
 752                 return;
 753
 754         rw = rwlock2rw(c);
 755
 756         if (rw_wlocked(rw)) {
 757                 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
 758                     ("%s: recursing but non-recursive rw %s @ %s:%d\n",
 759                     __func__, rw->lock_object.lo_name, file, line));
 760                 rw->rw_recurse++;
 761                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 762                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
 763                 return;
 764         }
 765
 766         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 767                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 768                     rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
 769
 770 #ifdef KDTRACE_HOOKS
 771         all_time -= lockstat_nsecs(&rw->lock_object);
 772         state = rw->rw_lock;
 773 #endif
 774         while (!_rw_write_lock(rw, tid)) {
 775 #ifdef KDTRACE_HOOKS
 776                 spin_cnt++;
 777 #endif
 778 #ifdef HWPMC_HOOKS
 779                 PMC_SOFT_CALL( , , lock, failed);
 780 #endif
 781                 lock_profile_obtain_lock_failed(&rw->lock_object,
 782                     &contested, &waittime);
 783 #ifdef ADAPTIVE_RWLOCKS
 784                 /*
 785                  * If the lock is write locked and the owner is
 786                  * running on another CPU, spin until the owner stops
 787                  * running or the state of the lock changes.
 788                  */
 789                 v = rw->rw_lock;
 790                 owner = (struct thread *)RW_OWNER(v);
 791                 if (!(v & RW_LOCK_READ) && TD_IS_RUNNING(owner)) {
 792                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 793                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
 794                                     __func__, rw, owner);
 795                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 796                             "spinning", "lockname:\"%s\"",
 797                             rw->lock_object.lo_name);
 798                         while ((struct thread*)RW_OWNER(rw->rw_lock) == owner &&
 799                             TD_IS_RUNNING(owner)) {
 800                                 cpu_spinwait();
 801 #ifdef KDTRACE_HOOKS
 802                                 spin_cnt++;
 803 #endif
 804                         }
 805                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 806                             "running");
 807                         continue;
 808                 }
 809                 if ((v & RW_LOCK_READ) && RW_READERS(v) &&
 810                     spintries < rowner_retries) {
 811                         if (!(v & RW_LOCK_WRITE_SPINNER)) {
 812                                 if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 813                                     v | RW_LOCK_WRITE_SPINNER)) {
 814                                         continue;
 815                                 }
 816                         }
 817                         spintries++;
 818                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 819                             "spinning", "lockname:\"%s\"",
 820                             rw->lock_object.lo_name);
 821                         for (i = 0; i < rowner_loops; i++) {
 822                                 if ((rw->rw_lock & RW_LOCK_WRITE_SPINNER) == 0)
 823                                         break;
 824                                 cpu_spinwait();
 825                         }
 826                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 827                             "running");
 828 #ifdef KDTRACE_HOOKS
 829                         spin_cnt += rowner_loops - i;
 830 #endif
 831                         if (i != rowner_loops)
 832                                 continue;
 833                 }
 834 #endif
 835                 ts = turnstile_trywait(&rw->lock_object);
 836                 v = rw->rw_lock;
 837
 838 #ifdef ADAPTIVE_RWLOCKS
 839                 /*
 840                  * The current lock owner might have started executing
 841                  * on another CPU (or the lock could have changed
 842                  * owners) while we were waiting on the turnstile
 843                  * chain lock.  If so, drop the turnstile lock and try
 844                  * again.
 845                  */
 846                 if (!(v & RW_LOCK_READ)) {
 847                         owner = (struct thread *)RW_OWNER(v);
 848                         if (TD_IS_RUNNING(owner)) {
 849                                 turnstile_cancel(ts);
 850                                 continue;
 851                         }
 852                 }
 853 #endif
 854                 /*
 855                  * Check for the waiters flags about this rwlock.
 856                  * If the lock was released, without maintain any pending
 857                  * waiters queue, simply try to acquire it.
 858                  * If a pending waiters queue is present, claim the lock
 859                  * ownership and maintain the pending queue.
 860                  */
 861                 x = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
 862                 if ((v & ~x) == RW_UNLOCKED) {
 863                         x &= ~RW_LOCK_WRITE_SPINNER;
 864                         if (atomic_cmpset_acq_ptr(&rw->rw_lock, v, tid | x)) {
 865                                 if (x)
 866                                         turnstile_claim(ts);
 867                                 else
 868                                         turnstile_cancel(ts);
 869                                 break;
 870                         }
 871                         turnstile_cancel(ts);
 872                         continue;
 873                 }
 874                 /*
 875                  * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
 876                  * set it.  If we fail to set it, then loop back and try
 877                  * again.
 878                  */
 879                 if (!(v & RW_LOCK_WRITE_WAITERS)) {
 880                         if (!atomic_cmpset_ptr(&rw->rw_lock, v,
 881                             v | RW_LOCK_WRITE_WAITERS)) {
 882                                 turnstile_cancel(ts);
 883                                 continue;
 884                         }
 885                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 886                                 CTR2(KTR_LOCK, "%s: %p set write waiters flag",
 887                                     __func__, rw);
 888                 }
 889                 /*
 890                  * We were unable to acquire the lock and the write waiters
 891                  * flag is set, so we must block on the turnstile.
 892                  */
 893                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 894                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
 895                             rw);
 896 #ifdef KDTRACE_HOOKS
 897                 sleep_time -= lockstat_nsecs(&rw->lock_object);
 898 #endif
 899                 turnstile_wait(ts, rw_owner(rw), TS_EXCLUSIVE_QUEUE);
 900 #ifdef KDTRACE_HOOKS
 901                 sleep_time += lockstat_nsecs(&rw->lock_object);
 902                 sleep_cnt++;
 903 #endif
 904                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 905                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
 906                             __func__, rw);
 907 #ifdef ADAPTIVE_RWLOCKS
 908                 spintries = 0;
 909 #endif
 910         }
 911 #ifdef KDTRACE_HOOKS
 912         all_time += lockstat_nsecs(&rw->lock_object);
 913         if (sleep_time)
 914                 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
 915                     LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
 916                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 917
 918         /* Record only the loops spinning and not sleeping. */
 919         if (spin_cnt > sleep_cnt)
 920                 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
 921                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 922                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 923 #endif
 924         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
 925             waittime, file, line, LOCKSTAT_WRITER);
 926 }
 927
 928 /*
 929  * This function is called if the first try at releasing a write lock failed.
 930  * This means that one of the 2 waiter bits must be set indicating that at
 931  * least one thread is waiting on this lock.
 932  */
 933 void
 934 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t tid, const char *file,
 935     int line)
 936 {
 937         struct rwlock *rw;
 938         struct turnstile *ts;
 939         uintptr_t v;
 940         int queue;
 941
 942         if (SCHEDULER_STOPPED())
 943                 return;
 944
 945         rw = rwlock2rw(c);
 946
 947         if (rw_wlocked(rw) && rw_recursed(rw)) {
 948                 rw->rw_recurse--;
 949                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 950                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
 951                 return;
 952         }
 953
 954         KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
 955             ("%s: neither of the waiter flags are set", __func__));
 956
 957         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 958                 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
 959
 960         turnstile_chain_lock(&rw->lock_object);
 961         ts = turnstile_lookup(&rw->lock_object);
 962         MPASS(ts != NULL);
 963
 964         /*
 965          * Use the same algo as sx locks for now.  Prefer waking up shared
 966          * waiters if we have any over writers.  This is probably not ideal.
 967          *
 968          * 'v' is the value we are going to write back to rw_lock.  If we
 969          * have waiters on both queues, we need to preserve the state of
 970          * the waiter flag for the queue we don't wake up.  For now this is
 971          * hardcoded for the algorithm mentioned above.
 972          *
 973          * In the case of both readers and writers waiting we wakeup the
 974          * readers but leave the RW_LOCK_WRITE_WAITERS flag set.  If a
 975          * new writer comes in before a reader it will claim the lock up
 976          * above.  There is probably a potential priority inversion in
 977          * there that could be worked around either by waking both queues
 978          * of waiters or doing some complicated lock handoff gymnastics.
 979          */
 980         v = RW_UNLOCKED;
 981         if (rw->rw_lock & RW_LOCK_WRITE_WAITERS) {
 982                 queue = TS_EXCLUSIVE_QUEUE;
 983                 v |= (rw->rw_lock & RW_LOCK_READ_WAITERS);
 984         } else
 985                 queue = TS_SHARED_QUEUE;
 986
 987         /* Wake up all waiters for the specific queue. */
 988         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 989                 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
 990                     queue == TS_SHARED_QUEUE ? "read" : "write");
 991         turnstile_broadcast(ts, queue);
 992         atomic_store_rel_ptr(&rw->rw_lock, v);
 993         turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
 994         turnstile_chain_unlock(&rw->lock_object);
 995 }
 996
 997 /*
 998  * Attempt to do a non-blocking upgrade from a read lock to a write
 999  * lock.  This will only succeed if this thread holds a single read
1000  * lock.  Returns true if the upgrade succeeded and false otherwise.
1001  */
1002 int
1003 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
1004 {
1005         struct rwlock *rw;
1006         uintptr_t v, x, tid;
1007         struct turnstile *ts;
1008         int success;
1009
1010         if (SCHEDULER_STOPPED())
1011                 return (1);
1012
1013         rw = rwlock2rw(c);
1014
1015         KASSERT(rw->rw_lock != RW_DESTROYED,
1016             ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
1017         __rw_assert(c, RA_RLOCKED, file, line);
1018
1019         /*
1020          * Attempt to switch from one reader to a writer.  If there
1021          * are any write waiters, then we will have to lock the
1022          * turnstile first to prevent races with another writer
1023          * calling turnstile_wait() before we have claimed this
1024          * turnstile.  So, do the simple case of no waiters first.
1025          */
1026         tid = (uintptr_t)curthread;
1027         success = 0;
1028         for (;;) {
1029                 v = rw->rw_lock;
1030                 if (RW_READERS(v) > 1)
1031                         break;
1032                 if (!(v & RW_LOCK_WAITERS)) {
1033                         success = atomic_cmpset_ptr(&rw->rw_lock, v, tid);
1034                         if (!success)
1035                                 continue;
1036                         break;
1037                 }
1038
1039                 /*
1040                  * Ok, we think we have waiters, so lock the turnstile.
1041                  */
1042                 ts = turnstile_trywait(&rw->lock_object);
1043                 v = rw->rw_lock;
1044                 if (RW_READERS(v) > 1) {
1045                         turnstile_cancel(ts);
1046                         break;
1047                 }
1048                 /*
1049                  * Try to switch from one reader to a writer again.  This time
1050                  * we honor the current state of the waiters flags.
1051                  * If we obtain the lock with the flags set, then claim
1052                  * ownership of the turnstile.
1053                  */
1054                 x = rw->rw_lock & RW_LOCK_WAITERS;
1055                 success = atomic_cmpset_ptr(&rw->rw_lock, v, tid | x);
1056                 if (success) {
1057                         if (x)
1058                                 turnstile_claim(ts);
1059                         else
1060                                 turnstile_cancel(ts);
1061                         break;
1062                 }
1063                 turnstile_cancel(ts);
1064         }
1065         LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
1066         if (success) {
1067                 curthread->td_rw_rlocks--;
1068                 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
1069                     file, line);
1070                 LOCKSTAT_RECORD0(rw__upgrade, rw);
1071         }
1072         return (success);
1073 }
1074
1075 /*
1076  * Downgrade a write lock into a single read lock.
1077  */
1078 void
1079 __rw_downgrade(volatile uintptr_t *c, const char *file, int line)
1080 {
1081         struct rwlock *rw;
1082         struct turnstile *ts;
1083         uintptr_t tid, v;
1084         int rwait, wwait;
1085
1086         if (SCHEDULER_STOPPED())
1087                 return;
1088
1089         rw = rwlock2rw(c);
1090
1091         KASSERT(rw->rw_lock != RW_DESTROYED,
1092             ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
1093         __rw_assert(c, RA_WLOCKED | RA_NOTRECURSED, file, line);
1094 #ifndef INVARIANTS
1095         if (rw_recursed(rw))
1096                 panic("downgrade of a recursed lock");
1097 #endif
1098
1099         WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
1100
1101         /*
1102          * Convert from a writer to a single reader.  First we handle
1103          * the easy case with no waiters.  If there are any waiters, we
1104          * lock the turnstile and "disown" the lock.
1105          */
1106         tid = (uintptr_t)curthread;
1107         if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
1108                 goto out;
1109
1110         /*
1111          * Ok, we think we have waiters, so lock the turnstile so we can
1112          * read the waiter flags without any races.
1113          */
1114         turnstile_chain_lock(&rw->lock_object);
1115         v = rw->rw_lock & RW_LOCK_WAITERS;
1116         rwait = v & RW_LOCK_READ_WAITERS;
1117         wwait = v & RW_LOCK_WRITE_WAITERS;
1118         MPASS(rwait | wwait);
1119
1120         /*
1121          * Downgrade from a write lock while preserving waiters flag
1122          * and give up ownership of the turnstile.
1123          */
1124         ts = turnstile_lookup(&rw->lock_object);
1125         MPASS(ts != NULL);
1126         if (!wwait)
1127                 v &= ~RW_LOCK_READ_WAITERS;
1128         atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
1129         /*
1130          * Wake other readers if there are no writers pending.  Otherwise they
1131          * won't be able to acquire the lock anyway.
1132          */
1133         if (rwait && !wwait) {
1134                 turnstile_broadcast(ts, TS_SHARED_QUEUE);
1135                 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
1136         } else
1137                 turnstile_disown(ts);
1138         turnstile_chain_unlock(&rw->lock_object);
1139 out:
1140         curthread->td_rw_rlocks++;
1141         LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
1142         LOCKSTAT_RECORD0(rw__downgrade, rw);
1143 }
1144
1145 #ifdef INVARIANT_SUPPORT
1146 #ifndef INVARIANTS
1147 #undef __rw_assert
1148 #endif
1149
1150 /*
1151  * In the non-WITNESS case, rw_assert() can only detect that at least
1152  * *some* thread owns an rlock, but it cannot guarantee that *this*
1153  * thread owns an rlock.
1154  */
1155 void
1156 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
1157 {
1158         const struct rwlock *rw;
1159
1160         if (panicstr != NULL)
1161                 return;
1162
1163         rw = rwlock2rw(c);
1164
1165         switch (what) {
1166         case RA_LOCKED:
1167         case RA_LOCKED | RA_RECURSED:
1168         case RA_LOCKED | RA_NOTRECURSED:
1169         case RA_RLOCKED:
1170         case RA_RLOCKED | RA_RECURSED:
1171         case RA_RLOCKED | RA_NOTRECURSED:
1172 #ifdef WITNESS
1173                 witness_assert(&rw->lock_object, what, file, line);
1174 #else
1175                 /*
1176                  * If some other thread has a write lock or we have one
1177                  * and are asserting a read lock, fail.  Also, if no one
1178                  * has a lock at all, fail.
1179                  */
1180                 if (rw->rw_lock == RW_UNLOCKED ||
1181                     (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
1182                     rw_wowner(rw) != curthread)))
1183                         panic("Lock %s not %slocked @ %s:%d\n",
1184                             rw->lock_object.lo_name, (what & RA_RLOCKED) ?
1185                             "read " : "", file, line);
1186
1187                 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
1188                         if (rw_recursed(rw)) {
1189                                 if (what & RA_NOTRECURSED)
1190                                         panic("Lock %s recursed @ %s:%d\n",
1191                                             rw->lock_object.lo_name, file,
1192                                             line);
1193                         } else if (what & RA_RECURSED)
1194                                 panic("Lock %s not recursed @ %s:%d\n",
1195                                     rw->lock_object.lo_name, file, line);
1196                 }
1197 #endif
1198                 break;
1199         case RA_WLOCKED:
1200         case RA_WLOCKED | RA_RECURSED:
1201         case RA_WLOCKED | RA_NOTRECURSED:
1202                 if (rw_wowner(rw) != curthread)
1203                         panic("Lock %s not exclusively locked @ %s:%d\n",
1204                             rw->lock_object.lo_name, file, line);
1205                 if (rw_recursed(rw)) {
1206                         if (what & RA_NOTRECURSED)
1207                                 panic("Lock %s recursed @ %s:%d\n",
1208                                     rw->lock_object.lo_name, file, line);
1209                 } else if (what & RA_RECURSED)
1210                         panic("Lock %s not recursed @ %s:%d\n",
1211                             rw->lock_object.lo_name, file, line);
1212                 break;
1213         case RA_UNLOCKED:
1214 #ifdef WITNESS
1215                 witness_assert(&rw->lock_object, what, file, line);
1216 #else
1217                 /*
1218                  * If we hold a write lock fail.  We can't reliably check
1219                  * to see if we hold a read lock or not.
1220                  */
1221                 if (rw_wowner(rw) == curthread)
1222                         panic("Lock %s exclusively locked @ %s:%d\n",
1223                             rw->lock_object.lo_name, file, line);
1224 #endif
1225                 break;
1226         default:
1227                 panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
1228                     line);
1229         }
1230 }
1231 #endif /* INVARIANT_SUPPORT */
1232
1233 #ifdef DDB
1234 void
1235 db_show_rwlock(const struct lock_object *lock)
1236 {
1237         const struct rwlock *rw;
1238         struct thread *td;
1239
1240         rw = (const struct rwlock *)lock;
1241
1242         db_printf(" state: ");
1243         if (rw->rw_lock == RW_UNLOCKED)
1244                 db_printf("UNLOCKED\n");
1245         else if (rw->rw_lock == RW_DESTROYED) {
1246                 db_printf("DESTROYED\n");
1247                 return;
1248         } else if (rw->rw_lock & RW_LOCK_READ)
1249                 db_printf("RLOCK: %ju locks\n",
1250                     (uintmax_t)(RW_READERS(rw->rw_lock)));
1251         else {
1252                 td = rw_wowner(rw);
1253                 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1254                     td->td_tid, td->td_proc->p_pid, td->td_name);
1255                 if (rw_recursed(rw))
1256                         db_printf(" recursed: %u\n", rw->rw_recurse);
1257         }
1258         db_printf(" waiters: ");
1259         switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
1260         case RW_LOCK_READ_WAITERS:
1261                 db_printf("readers\n");
1262                 break;
1263         case RW_LOCK_WRITE_WAITERS:
1264                 db_printf("writers\n");
1265                 break;
1266         case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
1267                 db_printf("readers and writers\n");
1268                 break;
1269         default:
1270                 db_printf("none\n");
1271                 break;
1272         }
1273 }
1274
1275 #endif