sys/kern/kern_rwlock.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (c) 2006 John Baldwin <jhb@FreeBSD.org>
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  16  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  17  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  18  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  19  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  20  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  21  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  22  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  23  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  24  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  25  * SUCH DAMAGE.
  26  */
  27
  28 /*
  29  * Machine independent bits of reader/writer lock implementation.
  30  */
  31
  32 #include <sys/cdefs.h>
  33 __FBSDID("$FreeBSD$");
  34
  35 #include "opt_ddb.h"
  36 #include "opt_hwpmc_hooks.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/smp.h>
  49 #include <sys/sysctl.h>
  50 #include <sys/systm.h>
  51 #include <sys/turnstile.h>
  52
  53 #include <machine/cpu.h>
  54
  55 #if defined(SMP) && !defined(NO_ADAPTIVE_RWLOCKS)
  56 #define ADAPTIVE_RWLOCKS
  57 #endif
  58
  59 #ifdef HWPMC_HOOKS
  60 #include <sys/pmckern.h>
  61 PMC_SOFT_DECLARE( , , lock, failed);
  62 #endif
  63
  64 /*
  65  * Return the rwlock address when the lock cookie address is provided.
  66  * This functionality assumes that struct rwlock* have a member named rw_lock.
  67  */
  68 #define rwlock2rw(c)    (__containerof(c, struct rwlock, rw_lock))
  69
  70 #ifdef DDB
  71 #include <ddb/ddb.h>
  72
  73 static void     db_show_rwlock(const struct lock_object *lock);
  74 #endif
  75 static void     assert_rw(const struct lock_object *lock, int what);
  76 static void     lock_rw(struct lock_object *lock, uintptr_t how);
  77 #ifdef KDTRACE_HOOKS
  78 static int      owner_rw(const struct lock_object *lock, struct thread **owner);
  79 #endif
  80 static uintptr_t unlock_rw(struct lock_object *lock);
  81
  82 struct lock_class lock_class_rw = {
  83         .lc_name = "rw",
  84         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE | LC_UPGRADABLE,
  85         .lc_assert = assert_rw,
  86 #ifdef DDB
  87         .lc_ddb_show = db_show_rwlock,
  88 #endif
  89         .lc_lock = lock_rw,
  90         .lc_unlock = unlock_rw,
  91 #ifdef KDTRACE_HOOKS
  92         .lc_owner = owner_rw,
  93 #endif
  94 };
  95
  96 #ifdef ADAPTIVE_RWLOCKS
  97 #ifdef RWLOCK_CUSTOM_BACKOFF
  98 static u_short __read_frequently rowner_retries;
  99 static u_short __read_frequently rowner_loops;
 100 static SYSCTL_NODE(_debug, OID_AUTO, rwlock,
 101     CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
 102     "rwlock debugging");
 103 SYSCTL_U16(_debug_rwlock, OID_AUTO, retry, CTLFLAG_RW, &rowner_retries, 0, "");
 104 SYSCTL_U16(_debug_rwlock, OID_AUTO, loops, CTLFLAG_RW, &rowner_loops, 0, "");
 105
 106 static struct lock_delay_config __read_frequently rw_delay;
 107
 108 SYSCTL_U16(_debug_rwlock, OID_AUTO, delay_base, CTLFLAG_RW, &rw_delay.base,
 109     0, "");
 110 SYSCTL_U16(_debug_rwlock, OID_AUTO, delay_max, CTLFLAG_RW, &rw_delay.max,
 111     0, "");
 112
 113 static void
 114 rw_lock_delay_init(void *arg __unused)
 115 {
 116
 117         lock_delay_default_init(&rw_delay);
 118         rowner_retries = 10;
 119         rowner_loops = max(10000, rw_delay.max);
 120 }
 121 LOCK_DELAY_SYSINIT(rw_lock_delay_init);
 122 #else
 123 #define rw_delay        locks_delay
 124 #define rowner_retries  locks_delay_retries
 125 #define rowner_loops    locks_delay_loops
 126 #endif
 127 #endif
 128
 129 /*
 130  * Return a pointer to the owning thread if the lock is write-locked or
 131  * NULL if the lock is unlocked or read-locked.
 132  */
 133
 134 #define lv_rw_wowner(v)                                                 \
 135         ((v) & RW_LOCK_READ ? NULL :                                    \
 136          (struct thread *)RW_OWNER((v)))
 137
 138 #define rw_wowner(rw)   lv_rw_wowner(RW_READ_VALUE(rw))
 139
 140 /*
 141  * Returns if a write owner is recursed.  Write ownership is not assured
 142  * here and should be previously checked.
 143  */
 144 #define rw_recursed(rw)         ((rw)->rw_recurse != 0)
 145
 146 /*
 147  * Return true if curthread helds the lock.
 148  */
 149 #define rw_wlocked(rw)          (rw_wowner((rw)) == curthread)
 150
 151 /*
 152  * Return a pointer to the owning thread for this lock who should receive
 153  * any priority lent by threads that block on this lock.  Currently this
 154  * is identical to rw_wowner().
 155  */
 156 #define rw_owner(rw)            rw_wowner(rw)
 157
 158 #ifndef INVARIANTS
 159 #define __rw_assert(c, what, file, line)
 160 #endif
 161
 162 void
 163 assert_rw(const struct lock_object *lock, int what)
 164 {
 165
 166         rw_assert((const struct rwlock *)lock, what);
 167 }
 168
 169 void
 170 lock_rw(struct lock_object *lock, uintptr_t how)
 171 {
 172         struct rwlock *rw;
 173
 174         rw = (struct rwlock *)lock;
 175         if (how)
 176                 rw_rlock(rw);
 177         else
 178                 rw_wlock(rw);
 179 }
 180
 181 uintptr_t
 182 unlock_rw(struct lock_object *lock)
 183 {
 184         struct rwlock *rw;
 185
 186         rw = (struct rwlock *)lock;
 187         rw_assert(rw, RA_LOCKED | LA_NOTRECURSED);
 188         if (rw->rw_lock & RW_LOCK_READ) {
 189                 rw_runlock(rw);
 190                 return (1);
 191         } else {
 192                 rw_wunlock(rw);
 193                 return (0);
 194         }
 195 }
 196
 197 #ifdef KDTRACE_HOOKS
 198 int
 199 owner_rw(const struct lock_object *lock, struct thread **owner)
 200 {
 201         const struct rwlock *rw = (const struct rwlock *)lock;
 202         uintptr_t x = rw->rw_lock;
 203
 204         *owner = rw_wowner(rw);
 205         return ((x & RW_LOCK_READ) != 0 ?  (RW_READERS(x) != 0) :
 206             (*owner != NULL));
 207 }
 208 #endif
 209
 210 void
 211 _rw_init_flags(volatile uintptr_t *c, const char *name, int opts)
 212 {
 213         struct rwlock *rw;
 214         int flags;
 215
 216         rw = rwlock2rw(c);
 217
 218         MPASS((opts & ~(RW_DUPOK | RW_NOPROFILE | RW_NOWITNESS | RW_QUIET |
 219             RW_RECURSE | RW_NEW)) == 0);
 220         ASSERT_ATOMIC_LOAD_PTR(rw->rw_lock,
 221             ("%s: rw_lock not aligned for %s: %p", __func__, name,
 222             &rw->rw_lock));
 223
 224         flags = LO_UPGRADABLE;
 225         if (opts & RW_DUPOK)
 226                 flags |= LO_DUPOK;
 227         if (opts & RW_NOPROFILE)
 228                 flags |= LO_NOPROFILE;
 229         if (!(opts & RW_NOWITNESS))
 230                 flags |= LO_WITNESS;
 231         if (opts & RW_RECURSE)
 232                 flags |= LO_RECURSABLE;
 233         if (opts & RW_QUIET)
 234                 flags |= LO_QUIET;
 235         if (opts & RW_NEW)
 236                 flags |= LO_NEW;
 237
 238         lock_init(&rw->lock_object, &lock_class_rw, name, NULL, flags);
 239         rw->rw_lock = RW_UNLOCKED;
 240         rw->rw_recurse = 0;
 241 }
 242
 243 void
 244 _rw_destroy(volatile uintptr_t *c)
 245 {
 246         struct rwlock *rw;
 247
 248         rw = rwlock2rw(c);
 249
 250         KASSERT(rw->rw_lock == RW_UNLOCKED, ("rw lock %p not unlocked", rw));
 251         KASSERT(rw->rw_recurse == 0, ("rw lock %p still recursed", rw));
 252         rw->rw_lock = RW_DESTROYED;
 253         lock_destroy(&rw->lock_object);
 254 }
 255
 256 void
 257 rw_sysinit(void *arg)
 258 {
 259         struct rw_args *args;
 260
 261         args = arg;
 262         rw_init_flags((struct rwlock *)args->ra_rw, args->ra_desc,
 263             args->ra_flags);
 264 }
 265
 266 int
 267 _rw_wowned(const volatile uintptr_t *c)
 268 {
 269
 270         return (rw_wowner(rwlock2rw(c)) == curthread);
 271 }
 272
 273 void
 274 _rw_wlock_cookie(volatile uintptr_t *c, const char *file, int line)
 275 {
 276         struct rwlock *rw;
 277         uintptr_t tid, v;
 278
 279         rw = rwlock2rw(c);
 280
 281         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
 282             !TD_IS_IDLETHREAD(curthread),
 283             ("rw_wlock() by idle thread %p on rwlock %s @ %s:%d",
 284             curthread, rw->lock_object.lo_name, file, line));
 285         KASSERT(rw->rw_lock != RW_DESTROYED,
 286             ("rw_wlock() of destroyed rwlock @ %s:%d", file, line));
 287         WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 288             line, NULL);
 289         tid = (uintptr_t)curthread;
 290         v = RW_UNLOCKED;
 291         if (!_rw_write_lock_fetch(rw, &v, tid))
 292                 _rw_wlock_hard(rw, v, file, line);
 293         else
 294                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw,
 295                     0, 0, file, line, LOCKSTAT_WRITER);
 296
 297         LOCK_LOG_LOCK("WLOCK", &rw->lock_object, 0, rw->rw_recurse, file, line);
 298         WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
 299         TD_LOCKS_INC(curthread);
 300 }
 301
 302 int
 303 __rw_try_wlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
 304 {
 305         struct thread *td;
 306         uintptr_t tid, v;
 307         int rval;
 308         bool recursed;
 309
 310         td = curthread;
 311         tid = (uintptr_t)td;
 312         if (SCHEDULER_STOPPED_TD(td))
 313                 return (1);
 314
 315         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
 316             ("rw_try_wlock() by idle thread %p on rwlock %s @ %s:%d",
 317             curthread, rw->lock_object.lo_name, file, line));
 318         KASSERT(rw->rw_lock != RW_DESTROYED,
 319             ("rw_try_wlock() of destroyed rwlock @ %s:%d", file, line));
 320
 321         rval = 1;
 322         recursed = false;
 323         v = RW_UNLOCKED;
 324         for (;;) {
 325                 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
 326                         break;
 327                 if (v == RW_UNLOCKED)
 328                         continue;
 329                 if (v == tid && (rw->lock_object.lo_flags & LO_RECURSABLE)) {
 330                         rw->rw_recurse++;
 331                         atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
 332                         break;
 333                 }
 334                 rval = 0;
 335                 break;
 336         }
 337
 338         LOCK_LOG_TRY("WLOCK", &rw->lock_object, 0, rval, file, line);
 339         if (rval) {
 340                 WITNESS_LOCK(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 341                     file, line);
 342                 if (!recursed)
 343                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
 344                             rw, 0, 0, file, line, LOCKSTAT_WRITER);
 345                 TD_LOCKS_INC(curthread);
 346         }
 347         return (rval);
 348 }
 349
 350 int
 351 __rw_try_wlock(volatile uintptr_t *c, const char *file, int line)
 352 {
 353         struct rwlock *rw;
 354
 355         rw = rwlock2rw(c);
 356         return (__rw_try_wlock_int(rw LOCK_FILE_LINE_ARG));
 357 }
 358
 359 void
 360 _rw_wunlock_cookie(volatile uintptr_t *c, const char *file, int line)
 361 {
 362         struct rwlock *rw;
 363
 364         rw = rwlock2rw(c);
 365
 366         KASSERT(rw->rw_lock != RW_DESTROYED,
 367             ("rw_wunlock() of destroyed rwlock @ %s:%d", file, line));
 368         __rw_assert(c, RA_WLOCKED, file, line);
 369         WITNESS_UNLOCK(&rw->lock_object, LOP_EXCLUSIVE, file, line);
 370         LOCK_LOG_LOCK("WUNLOCK", &rw->lock_object, 0, rw->rw_recurse, file,
 371             line);
 372
 373 #ifdef LOCK_PROFILING
 374         _rw_wunlock_hard(rw, (uintptr_t)curthread, file, line);
 375 #else
 376         __rw_wunlock(rw, curthread, file, line);
 377 #endif
 378
 379         TD_LOCKS_DEC(curthread);
 380 }
 381
 382 /*
 383  * Determines whether a new reader can acquire a lock.  Succeeds if the
 384  * reader already owns a read lock and the lock is locked for read to
 385  * prevent deadlock from reader recursion.  Also succeeds if the lock
 386  * is unlocked and has no writer waiters or spinners.  Failing otherwise
 387  * prioritizes writers before readers.
 388  */
 389 static bool __always_inline
 390 __rw_can_read(struct thread *td, uintptr_t v, bool fp)
 391 {
 392
 393         if ((v & (RW_LOCK_READ | RW_LOCK_WRITE_WAITERS | RW_LOCK_WRITE_SPINNER))
 394             == RW_LOCK_READ)
 395                 return (true);
 396         if (!fp && td->td_rw_rlocks && (v & RW_LOCK_READ))
 397                 return (true);
 398         return (false);
 399 }
 400
 401 static bool __always_inline
 402 __rw_rlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp, bool fp
 403     LOCK_FILE_LINE_ARG_DEF)
 404 {
 405
 406         /*
 407          * Handle the easy case.  If no other thread has a write
 408          * lock, then try to bump up the count of read locks.  Note
 409          * that we have to preserve the current state of the
 410          * RW_LOCK_WRITE_WAITERS flag.  If we fail to acquire a
 411          * read lock, then rw_lock must have changed, so restart
 412          * the loop.  Note that this handles the case of a
 413          * completely unlocked rwlock since such a lock is encoded
 414          * as a read lock with no waiters.
 415          */
 416         while (__rw_can_read(td, *vp, fp)) {
 417                 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, vp,
 418                         *vp + RW_ONE_READER)) {
 419                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 420                                 CTR4(KTR_LOCK,
 421                                     "%s: %p succeed %p -> %p", __func__,
 422                                     rw, (void *)*vp,
 423                                     (void *)(*vp + RW_ONE_READER));
 424                         td->td_rw_rlocks++;
 425                         return (true);
 426                 }
 427         }
 428         return (false);
 429 }
 430
 431 static void __noinline
 432 __rw_rlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
 433     LOCK_FILE_LINE_ARG_DEF)
 434 {
 435         struct turnstile *ts;
 436         struct thread *owner;
 437 #ifdef ADAPTIVE_RWLOCKS
 438         int spintries = 0;
 439         int i, n;
 440 #endif
 441 #ifdef LOCK_PROFILING
 442         uint64_t waittime = 0;
 443         int contested = 0;
 444 #endif
 445 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
 446         struct lock_delay_arg lda;
 447 #endif
 448 #ifdef KDTRACE_HOOKS
 449         u_int sleep_cnt = 0;
 450         int64_t sleep_time = 0;
 451         int64_t all_time = 0;
 452 #endif
 453 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 454         uintptr_t state = 0;
 455         int doing_lockprof = 0;
 456 #endif
 457
 458 #ifdef KDTRACE_HOOKS
 459         if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
 460                 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
 461                         goto out_lockstat;
 462                 doing_lockprof = 1;
 463                 all_time -= lockstat_nsecs(&rw->lock_object);
 464                 state = v;
 465         }
 466 #endif
 467 #ifdef LOCK_PROFILING
 468         doing_lockprof = 1;
 469         state = v;
 470 #endif
 471
 472         if (SCHEDULER_STOPPED())
 473                 return;
 474
 475 #if defined(ADAPTIVE_RWLOCKS)
 476         lock_delay_arg_init(&lda, &rw_delay);
 477 #elif defined(KDTRACE_HOOKS)
 478         lock_delay_arg_init_noadapt(&lda);
 479 #endif
 480
 481 #ifdef HWPMC_HOOKS
 482         PMC_SOFT_CALL( , , lock, failed);
 483 #endif
 484         lock_profile_obtain_lock_failed(&rw->lock_object,
 485             &contested, &waittime);
 486
 487         for (;;) {
 488                 if (__rw_rlock_try(rw, td, &v, false LOCK_FILE_LINE_ARG))
 489                         break;
 490 #ifdef KDTRACE_HOOKS
 491                 lda.spin_cnt++;
 492 #endif
 493
 494 #ifdef ADAPTIVE_RWLOCKS
 495                 /*
 496                  * If the owner is running on another CPU, spin until
 497                  * the owner stops running or the state of the lock
 498                  * changes.
 499                  */
 500                 if ((v & RW_LOCK_READ) == 0) {
 501                         owner = (struct thread *)RW_OWNER(v);
 502                         if (TD_IS_RUNNING(owner)) {
 503                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 504                                         CTR3(KTR_LOCK,
 505                                             "%s: spinning on %p held by %p",
 506                                             __func__, rw, owner);
 507                                 KTR_STATE1(KTR_SCHED, "thread",
 508                                     sched_tdname(curthread), "spinning",
 509                                     "lockname:\"%s\"", rw->lock_object.lo_name);
 510                                 do {
 511                                         lock_delay(&lda);
 512                                         v = RW_READ_VALUE(rw);
 513                                         owner = lv_rw_wowner(v);
 514                                 } while (owner != NULL && TD_IS_RUNNING(owner));
 515                                 KTR_STATE0(KTR_SCHED, "thread",
 516                                     sched_tdname(curthread), "running");
 517                                 continue;
 518                         }
 519                 } else {
 520                         if ((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) {
 521                                 MPASS(!__rw_can_read(td, v, false));
 522                                 lock_delay_spin(2);
 523                                 v = RW_READ_VALUE(rw);
 524                                 continue;
 525                         }
 526                         if (spintries < rowner_retries) {
 527                                 spintries++;
 528                                 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 529                                     "spinning", "lockname:\"%s\"",
 530                                     rw->lock_object.lo_name);
 531                                 n = RW_READERS(v);
 532                                 for (i = 0; i < rowner_loops; i += n) {
 533                                         lock_delay_spin(n);
 534                                         v = RW_READ_VALUE(rw);
 535                                         if (!(v & RW_LOCK_READ))
 536                                                 break;
 537                                         n = RW_READERS(v);
 538                                         if (n == 0)
 539                                                 break;
 540                                         if (__rw_can_read(td, v, false))
 541                                                 break;
 542                                 }
 543 #ifdef KDTRACE_HOOKS
 544                                 lda.spin_cnt += rowner_loops - i;
 545 #endif
 546                                 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 547                                     "running");
 548                                 if (i < rowner_loops)
 549                                         continue;
 550                         }
 551                 }
 552 #endif
 553
 554                 /*
 555                  * Okay, now it's the hard case.  Some other thread already
 556                  * has a write lock or there are write waiters present,
 557                  * acquire the turnstile lock so we can begin the process
 558                  * of blocking.
 559                  */
 560                 ts = turnstile_trywait(&rw->lock_object);
 561
 562                 /*
 563                  * The lock might have been released while we spun, so
 564                  * recheck its state and restart the loop if needed.
 565                  */
 566                 v = RW_READ_VALUE(rw);
 567 retry_ts:
 568                 if (((v & RW_LOCK_WRITE_SPINNER) && RW_READERS(v) == 0) ||
 569                     __rw_can_read(td, v, false)) {
 570                         turnstile_cancel(ts);
 571                         continue;
 572                 }
 573
 574                 owner = lv_rw_wowner(v);
 575
 576 #ifdef ADAPTIVE_RWLOCKS
 577                 /*
 578                  * The current lock owner might have started executing
 579                  * on another CPU (or the lock could have changed
 580                  * owners) while we were waiting on the turnstile
 581                  * chain lock.  If so, drop the turnstile lock and try
 582                  * again.
 583                  */
 584                 if (owner != NULL) {
 585                         if (TD_IS_RUNNING(owner)) {
 586                                 turnstile_cancel(ts);
 587                                 continue;
 588                         }
 589                 }
 590 #endif
 591
 592                 /*
 593                  * The lock is held in write mode or it already has waiters.
 594                  */
 595                 MPASS(!__rw_can_read(td, v, false));
 596
 597                 /*
 598                  * If the RW_LOCK_READ_WAITERS flag is already set, then
 599                  * we can go ahead and block.  If it is not set then try
 600                  * to set it.  If we fail to set it drop the turnstile
 601                  * lock and restart the loop.
 602                  */
 603                 if (!(v & RW_LOCK_READ_WAITERS)) {
 604                         if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
 605                             v | RW_LOCK_READ_WAITERS))
 606                                 goto retry_ts;
 607                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 608                                 CTR2(KTR_LOCK, "%s: %p set read waiters flag",
 609                                     __func__, rw);
 610                 }
 611
 612                 /*
 613                  * We were unable to acquire the lock and the read waiters
 614                  * flag is set, so we must block on the turnstile.
 615                  */
 616                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 617                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
 618                             rw);
 619 #ifdef KDTRACE_HOOKS
 620                 sleep_time -= lockstat_nsecs(&rw->lock_object);
 621 #endif
 622                 MPASS(owner == rw_owner(rw));
 623                 turnstile_wait(ts, owner, TS_SHARED_QUEUE);
 624 #ifdef KDTRACE_HOOKS
 625                 sleep_time += lockstat_nsecs(&rw->lock_object);
 626                 sleep_cnt++;
 627 #endif
 628                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 629                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
 630                             __func__, rw);
 631                 v = RW_READ_VALUE(rw);
 632         }
 633 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 634         if (__predict_true(!doing_lockprof))
 635                 return;
 636 #endif
 637 #ifdef KDTRACE_HOOKS
 638         all_time += lockstat_nsecs(&rw->lock_object);
 639         if (sleep_time)
 640                 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
 641                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 642                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 643
 644         /* Record only the loops spinning and not sleeping. */
 645         if (lda.spin_cnt > sleep_cnt)
 646                 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
 647                     LOCKSTAT_READER, (state & RW_LOCK_READ) == 0,
 648                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
 649 out_lockstat:
 650 #endif
 651         /*
 652          * TODO: acquire "owner of record" here.  Here be turnstile dragons
 653          * however.  turnstiles don't like owners changing between calls to
 654          * turnstile_wait() currently.
 655          */
 656         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
 657             waittime, file, line, LOCKSTAT_READER);
 658 }
 659
 660 void
 661 __rw_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
 662 {
 663         struct thread *td;
 664         uintptr_t v;
 665
 666         td = curthread;
 667
 668         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED_TD(td) ||
 669             !TD_IS_IDLETHREAD(td),
 670             ("rw_rlock() by idle thread %p on rwlock %s @ %s:%d",
 671             td, rw->lock_object.lo_name, file, line));
 672         KASSERT(rw->rw_lock != RW_DESTROYED,
 673             ("rw_rlock() of destroyed rwlock @ %s:%d", file, line));
 674         KASSERT(rw_wowner(rw) != td,
 675             ("rw_rlock: wlock already held for %s @ %s:%d",
 676             rw->lock_object.lo_name, file, line));
 677         WITNESS_CHECKORDER(&rw->lock_object, LOP_NEWORDER, file, line, NULL);
 678
 679         v = RW_READ_VALUE(rw);
 680         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__acquire) ||
 681             !__rw_rlock_try(rw, td, &v, true LOCK_FILE_LINE_ARG)))
 682                 __rw_rlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
 683         else
 684                 lock_profile_obtain_lock_success(&rw->lock_object, 0, 0,
 685                     file, line);
 686
 687         LOCK_LOG_LOCK("RLOCK", &rw->lock_object, 0, 0, file, line);
 688         WITNESS_LOCK(&rw->lock_object, 0, file, line);
 689         TD_LOCKS_INC(curthread);
 690 }
 691
 692 void
 693 __rw_rlock(volatile uintptr_t *c, const char *file, int line)
 694 {
 695         struct rwlock *rw;
 696
 697         rw = rwlock2rw(c);
 698         __rw_rlock_int(rw LOCK_FILE_LINE_ARG);
 699 }
 700
 701 int
 702 __rw_try_rlock_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
 703 {
 704         uintptr_t x;
 705
 706         if (SCHEDULER_STOPPED())
 707                 return (1);
 708
 709         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 710             ("rw_try_rlock() by idle thread %p on rwlock %s @ %s:%d",
 711             curthread, rw->lock_object.lo_name, file, line));
 712
 713         x = rw->rw_lock;
 714         for (;;) {
 715                 KASSERT(rw->rw_lock != RW_DESTROYED,
 716                     ("rw_try_rlock() of destroyed rwlock @ %s:%d", file, line));
 717                 if (!(x & RW_LOCK_READ))
 718                         break;
 719                 if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &x, x + RW_ONE_READER)) {
 720                         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 1, file,
 721                             line);
 722                         WITNESS_LOCK(&rw->lock_object, LOP_TRYLOCK, file, line);
 723                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire,
 724                             rw, 0, 0, file, line, LOCKSTAT_READER);
 725                         TD_LOCKS_INC(curthread);
 726                         curthread->td_rw_rlocks++;
 727                         return (1);
 728                 }
 729         }
 730
 731         LOCK_LOG_TRY("RLOCK", &rw->lock_object, 0, 0, file, line);
 732         return (0);
 733 }
 734
 735 int
 736 __rw_try_rlock(volatile uintptr_t *c, const char *file, int line)
 737 {
 738         struct rwlock *rw;
 739
 740         rw = rwlock2rw(c);
 741         return (__rw_try_rlock_int(rw LOCK_FILE_LINE_ARG));
 742 }
 743
 744 static bool __always_inline
 745 __rw_runlock_try(struct rwlock *rw, struct thread *td, uintptr_t *vp)
 746 {
 747
 748         for (;;) {
 749                 if (RW_READERS(*vp) > 1 || !(*vp & RW_LOCK_WAITERS)) {
 750                         if (atomic_fcmpset_rel_ptr(&rw->rw_lock, vp,
 751                             *vp - RW_ONE_READER)) {
 752                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 753                                         CTR4(KTR_LOCK,
 754                                             "%s: %p succeeded %p -> %p",
 755                                             __func__, rw, (void *)*vp,
 756                                             (void *)(*vp - RW_ONE_READER));
 757                                 td->td_rw_rlocks--;
 758                                 return (true);
 759                         }
 760                         continue;
 761                 }
 762                 break;
 763         }
 764         return (false);
 765 }
 766
 767 static void __noinline
 768 __rw_runlock_hard(struct rwlock *rw, struct thread *td, uintptr_t v
 769     LOCK_FILE_LINE_ARG_DEF)
 770 {
 771         struct turnstile *ts;
 772         uintptr_t setv, queue;
 773
 774         if (SCHEDULER_STOPPED())
 775                 return;
 776
 777         if (__rw_runlock_try(rw, td, &v))
 778                 goto out_lockstat;
 779
 780         /*
 781          * Ok, we know we have waiters and we think we are the
 782          * last reader, so grab the turnstile lock.
 783          */
 784         turnstile_chain_lock(&rw->lock_object);
 785         v = RW_READ_VALUE(rw);
 786         for (;;) {
 787                 if (__rw_runlock_try(rw, td, &v))
 788                         break;
 789
 790                 MPASS(v & RW_LOCK_WAITERS);
 791
 792                 /*
 793                  * Try to drop our lock leaving the lock in a unlocked
 794                  * state.
 795                  *
 796                  * If you wanted to do explicit lock handoff you'd have to
 797                  * do it here.  You'd also want to use turnstile_signal()
 798                  * and you'd have to handle the race where a higher
 799                  * priority thread blocks on the write lock before the
 800                  * thread you wakeup actually runs and have the new thread
 801                  * "steal" the lock.  For now it's a lot simpler to just
 802                  * wakeup all of the waiters.
 803                  *
 804                  * As above, if we fail, then another thread might have
 805                  * acquired a read lock, so drop the turnstile lock and
 806                  * restart.
 807                  */
 808                 setv = RW_UNLOCKED;
 809                 queue = TS_SHARED_QUEUE;
 810                 if (v & RW_LOCK_WRITE_WAITERS) {
 811                         queue = TS_EXCLUSIVE_QUEUE;
 812                         setv |= (v & RW_LOCK_READ_WAITERS);
 813                 }
 814                 setv |= (v & RW_LOCK_WRITE_SPINNER);
 815                 if (!atomic_fcmpset_rel_ptr(&rw->rw_lock, &v, setv))
 816                         continue;
 817                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 818                         CTR2(KTR_LOCK, "%s: %p last succeeded with waiters",
 819                             __func__, rw);
 820
 821                 /*
 822                  * Ok.  The lock is released and all that's left is to
 823                  * wake up the waiters.  Note that the lock might not be
 824                  * free anymore, but in that case the writers will just
 825                  * block again if they run before the new lock holder(s)
 826                  * release the lock.
 827                  */
 828                 ts = turnstile_lookup(&rw->lock_object);
 829                 MPASS(ts != NULL);
 830                 turnstile_broadcast(ts, queue);
 831                 turnstile_unpend(ts);
 832                 td->td_rw_rlocks--;
 833                 break;
 834         }
 835         turnstile_chain_unlock(&rw->lock_object);
 836 out_lockstat:
 837         LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_READER);
 838 }
 839
 840 void
 841 _rw_runlock_cookie_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
 842 {
 843         struct thread *td;
 844         uintptr_t v;
 845
 846         KASSERT(rw->rw_lock != RW_DESTROYED,
 847             ("rw_runlock() of destroyed rwlock @ %s:%d", file, line));
 848         __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
 849         WITNESS_UNLOCK(&rw->lock_object, 0, file, line);
 850         LOCK_LOG_LOCK("RUNLOCK", &rw->lock_object, 0, 0, file, line);
 851
 852         td = curthread;
 853         v = RW_READ_VALUE(rw);
 854
 855         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(rw__release) ||
 856             !__rw_runlock_try(rw, td, &v)))
 857                 __rw_runlock_hard(rw, td, v LOCK_FILE_LINE_ARG);
 858         else
 859                 lock_profile_release_lock(&rw->lock_object);
 860
 861         TD_LOCKS_DEC(curthread);
 862 }
 863
 864 void
 865 _rw_runlock_cookie(volatile uintptr_t *c, const char *file, int line)
 866 {
 867         struct rwlock *rw;
 868
 869         rw = rwlock2rw(c);
 870         _rw_runlock_cookie_int(rw LOCK_FILE_LINE_ARG);
 871 }
 872
 873 #ifdef ADAPTIVE_RWLOCKS
 874 static inline void
 875 rw_drop_critical(uintptr_t v, bool *in_critical, int *extra_work)
 876 {
 877
 878         if (v & RW_LOCK_WRITE_SPINNER)
 879                 return;
 880         if (*in_critical) {
 881                 critical_exit();
 882                 *in_critical = false;
 883                 (*extra_work)--;
 884         }
 885 }
 886 #else
 887 #define rw_drop_critical(v, in_critical, extra_work) do { } while (0)
 888 #endif
 889
 890 /*
 891  * This function is called when we are unable to obtain a write lock on the
 892  * first try.  This means that at least one other thread holds either a
 893  * read or write lock.
 894  */
 895 void
 896 __rw_wlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
 897 {
 898         uintptr_t tid;
 899         struct rwlock *rw;
 900         struct turnstile *ts;
 901         struct thread *owner;
 902 #ifdef ADAPTIVE_RWLOCKS
 903         int spintries = 0;
 904         int i, n;
 905         enum { READERS, WRITER } sleep_reason = READERS;
 906         bool in_critical = false;
 907 #endif
 908         uintptr_t setv;
 909 #ifdef LOCK_PROFILING
 910         uint64_t waittime = 0;
 911         int contested = 0;
 912 #endif
 913 #if defined(ADAPTIVE_RWLOCKS) || defined(KDTRACE_HOOKS)
 914         struct lock_delay_arg lda;
 915 #endif
 916 #ifdef KDTRACE_HOOKS
 917         u_int sleep_cnt = 0;
 918         int64_t sleep_time = 0;
 919         int64_t all_time = 0;
 920 #endif
 921 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 922         uintptr_t state = 0;
 923         int doing_lockprof = 0;
 924 #endif
 925         int extra_work = 0;
 926
 927         tid = (uintptr_t)curthread;
 928         rw = rwlock2rw(c);
 929
 930 #ifdef KDTRACE_HOOKS
 931         if (LOCKSTAT_PROFILE_ENABLED(rw__acquire)) {
 932                 while (v == RW_UNLOCKED) {
 933                         if (_rw_write_lock_fetch(rw, &v, tid))
 934                                 goto out_lockstat;
 935                 }
 936                 extra_work = 1;
 937                 doing_lockprof = 1;
 938                 all_time -= lockstat_nsecs(&rw->lock_object);
 939                 state = v;
 940         }
 941 #endif
 942 #ifdef LOCK_PROFILING
 943         extra_work = 1;
 944         doing_lockprof = 1;
 945         state = v;
 946 #endif
 947
 948         if (SCHEDULER_STOPPED())
 949                 return;
 950
 951         if (__predict_false(v == RW_UNLOCKED))
 952                 v = RW_READ_VALUE(rw);
 953
 954         if (__predict_false(lv_rw_wowner(v) == (struct thread *)tid)) {
 955                 KASSERT(rw->lock_object.lo_flags & LO_RECURSABLE,
 956                     ("%s: recursing but non-recursive rw %s @ %s:%d\n",
 957                     __func__, rw->lock_object.lo_name, file, line));
 958                 rw->rw_recurse++;
 959                 atomic_set_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
 960                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
 961                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, rw);
 962                 return;
 963         }
 964
 965         if (LOCK_LOG_TEST(&rw->lock_object, 0))
 966                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 967                     rw->lock_object.lo_name, (void *)rw->rw_lock, file, line);
 968
 969 #if defined(ADAPTIVE_RWLOCKS)
 970         lock_delay_arg_init(&lda, &rw_delay);
 971 #elif defined(KDTRACE_HOOKS)
 972         lock_delay_arg_init_noadapt(&lda);
 973 #endif
 974
 975 #ifdef HWPMC_HOOKS
 976         PMC_SOFT_CALL( , , lock, failed);
 977 #endif
 978         lock_profile_obtain_lock_failed(&rw->lock_object,
 979             &contested, &waittime);
 980
 981         for (;;) {
 982                 if (v == RW_UNLOCKED) {
 983                         if (_rw_write_lock_fetch(rw, &v, tid))
 984                                 break;
 985                         continue;
 986                 }
 987 #ifdef KDTRACE_HOOKS
 988                 lda.spin_cnt++;
 989 #endif
 990
 991 #ifdef ADAPTIVE_RWLOCKS
 992                 if (v == (RW_LOCK_READ | RW_LOCK_WRITE_SPINNER)) {
 993                         if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid))
 994                                 break;
 995                         continue;
 996                 }
 997
 998                 /*
 999                  * If the lock is write locked and the owner is
1000                  * running on another CPU, spin until the owner stops
1001                  * running or the state of the lock changes.
1002                  */
1003                 if (!(v & RW_LOCK_READ)) {
1004                         rw_drop_critical(v, &in_critical, &extra_work);
1005                         sleep_reason = WRITER;
1006                         owner = lv_rw_wowner(v);
1007                         if (!TD_IS_RUNNING(owner))
1008                                 goto ts;
1009                         if (LOCK_LOG_TEST(&rw->lock_object, 0))
1010                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
1011                                     __func__, rw, owner);
1012                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1013                             "spinning", "lockname:\"%s\"",
1014                             rw->lock_object.lo_name);
1015                         do {
1016                                 lock_delay(&lda);
1017                                 v = RW_READ_VALUE(rw);
1018                                 owner = lv_rw_wowner(v);
1019                         } while (owner != NULL && TD_IS_RUNNING(owner));
1020                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1021                             "running");
1022                         continue;
1023                 } else if (RW_READERS(v) > 0) {
1024                         sleep_reason = READERS;
1025                         if (spintries == rowner_retries)
1026                                 goto ts;
1027                         if (!(v & RW_LOCK_WRITE_SPINNER)) {
1028                                 if (!in_critical) {
1029                                         critical_enter();
1030                                         in_critical = true;
1031                                         extra_work++;
1032                                 }
1033                                 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
1034                                     v | RW_LOCK_WRITE_SPINNER)) {
1035                                         critical_exit();
1036                                         in_critical = false;
1037                                         extra_work--;
1038                                         continue;
1039                                 }
1040                         }
1041                         spintries++;
1042                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1043                             "spinning", "lockname:\"%s\"",
1044                             rw->lock_object.lo_name);
1045                         n = RW_READERS(v);
1046                         for (i = 0; i < rowner_loops; i += n) {
1047                                 lock_delay_spin(n);
1048                                 v = RW_READ_VALUE(rw);
1049                                 if (!(v & RW_LOCK_WRITE_SPINNER))
1050                                         break;
1051                                 if (!(v & RW_LOCK_READ))
1052                                         break;
1053                                 n = RW_READERS(v);
1054                                 if (n == 0)
1055                                         break;
1056                         }
1057 #ifdef KDTRACE_HOOKS
1058                         lda.spin_cnt += i;
1059 #endif
1060                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1061                             "running");
1062                         if (i < rowner_loops)
1063                                 continue;
1064                 }
1065 ts:
1066 #endif
1067                 ts = turnstile_trywait(&rw->lock_object);
1068                 v = RW_READ_VALUE(rw);
1069 retry_ts:
1070                 owner = lv_rw_wowner(v);
1071
1072 #ifdef ADAPTIVE_RWLOCKS
1073                 /*
1074                  * The current lock owner might have started executing
1075                  * on another CPU (or the lock could have changed
1076                  * owners) while we were waiting on the turnstile
1077                  * chain lock.  If so, drop the turnstile lock and try
1078                  * again.
1079                  */
1080                 if (owner != NULL) {
1081                         if (TD_IS_RUNNING(owner)) {
1082                                 turnstile_cancel(ts);
1083                                 rw_drop_critical(v, &in_critical, &extra_work);
1084                                 continue;
1085                         }
1086                 } else if (RW_READERS(v) > 0 && sleep_reason == WRITER) {
1087                         turnstile_cancel(ts);
1088                         rw_drop_critical(v, &in_critical, &extra_work);
1089                         continue;
1090                 }
1091 #endif
1092                 /*
1093                  * Check for the waiters flags about this rwlock.
1094                  * If the lock was released, without maintain any pending
1095                  * waiters queue, simply try to acquire it.
1096                  * If a pending waiters queue is present, claim the lock
1097                  * ownership and maintain the pending queue.
1098                  */
1099                 setv = v & (RW_LOCK_WAITERS | RW_LOCK_WRITE_SPINNER);
1100                 if ((v & ~setv) == RW_UNLOCKED) {
1101                         setv &= ~RW_LOCK_WRITE_SPINNER;
1102                         if (atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid | setv)) {
1103                                 if (setv)
1104                                         turnstile_claim(ts);
1105                                 else
1106                                         turnstile_cancel(ts);
1107                                 break;
1108                         }
1109                         goto retry_ts;
1110                 }
1111
1112 #ifdef ADAPTIVE_RWLOCKS
1113                 if (in_critical) {
1114                         if ((v & RW_LOCK_WRITE_SPINNER) ||
1115                             !((v & RW_LOCK_WRITE_WAITERS))) {
1116                                 setv = v & ~RW_LOCK_WRITE_SPINNER;
1117                                 setv |= RW_LOCK_WRITE_WAITERS;
1118                                 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v, setv))
1119                                         goto retry_ts;
1120                         }
1121                         critical_exit();
1122                         in_critical = false;
1123                         extra_work--;
1124                 } else {
1125 #endif
1126                         /*
1127                          * If the RW_LOCK_WRITE_WAITERS flag isn't set, then try to
1128                          * set it.  If we fail to set it, then loop back and try
1129                          * again.
1130                          */
1131                         if (!(v & RW_LOCK_WRITE_WAITERS)) {
1132                                 if (!atomic_fcmpset_ptr(&rw->rw_lock, &v,
1133                                     v | RW_LOCK_WRITE_WAITERS))
1134                                         goto retry_ts;
1135                                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1136                                         CTR2(KTR_LOCK, "%s: %p set write waiters flag",
1137                                             __func__, rw);
1138                         }
1139 #ifdef ADAPTIVE_RWLOCKS
1140                 }
1141 #endif
1142                 /*
1143                  * We were unable to acquire the lock and the write waiters
1144                  * flag is set, so we must block on the turnstile.
1145                  */
1146                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1147                         CTR2(KTR_LOCK, "%s: %p blocking on turnstile", __func__,
1148                             rw);
1149 #ifdef KDTRACE_HOOKS
1150                 sleep_time -= lockstat_nsecs(&rw->lock_object);
1151 #endif
1152                 MPASS(owner == rw_owner(rw));
1153                 turnstile_wait(ts, owner, TS_EXCLUSIVE_QUEUE);
1154 #ifdef KDTRACE_HOOKS
1155                 sleep_time += lockstat_nsecs(&rw->lock_object);
1156                 sleep_cnt++;
1157 #endif
1158                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1159                         CTR2(KTR_LOCK, "%s: %p resuming from turnstile",
1160                             __func__, rw);
1161 #ifdef ADAPTIVE_RWLOCKS
1162                 spintries = 0;
1163 #endif
1164                 v = RW_READ_VALUE(rw);
1165         }
1166         if (__predict_true(!extra_work))
1167                 return;
1168 #ifdef ADAPTIVE_RWLOCKS
1169         if (in_critical)
1170                 critical_exit();
1171 #endif
1172 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1173         if (__predict_true(!doing_lockprof))
1174                 return;
1175 #endif
1176 #ifdef KDTRACE_HOOKS
1177         all_time += lockstat_nsecs(&rw->lock_object);
1178         if (sleep_time)
1179                 LOCKSTAT_RECORD4(rw__block, rw, sleep_time,
1180                     LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1181                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1182
1183         /* Record only the loops spinning and not sleeping. */
1184         if (lda.spin_cnt > sleep_cnt)
1185                 LOCKSTAT_RECORD4(rw__spin, rw, all_time - sleep_time,
1186                     LOCKSTAT_WRITER, (state & RW_LOCK_READ) == 0,
1187                     (state & RW_LOCK_READ) == 0 ? 0 : RW_READERS(state));
1188 out_lockstat:
1189 #endif
1190         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(rw__acquire, rw, contested,
1191             waittime, file, line, LOCKSTAT_WRITER);
1192 }
1193
1194 /*
1195  * This function is called if lockstat is active or the first try at releasing
1196  * a write lock failed.  The latter means that the lock is recursed or one of
1197  * the 2 waiter bits must be set indicating that at least one thread is waiting
1198  * on this lock.
1199  */
1200 void
1201 __rw_wunlock_hard(volatile uintptr_t *c, uintptr_t v LOCK_FILE_LINE_ARG_DEF)
1202 {
1203         struct rwlock *rw;
1204         struct turnstile *ts;
1205         uintptr_t tid, setv;
1206         int queue;
1207
1208         tid = (uintptr_t)curthread;
1209         if (SCHEDULER_STOPPED())
1210                 return;
1211
1212         rw = rwlock2rw(c);
1213         if (__predict_false(v == tid))
1214                 v = RW_READ_VALUE(rw);
1215
1216         if (v & RW_LOCK_WRITER_RECURSED) {
1217                 if (--(rw->rw_recurse) == 0)
1218                         atomic_clear_ptr(&rw->rw_lock, RW_LOCK_WRITER_RECURSED);
1219                 if (LOCK_LOG_TEST(&rw->lock_object, 0))
1220                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, rw);
1221                 return;
1222         }
1223
1224         LOCKSTAT_PROFILE_RELEASE_RWLOCK(rw__release, rw, LOCKSTAT_WRITER);
1225         if (v == tid && _rw_write_unlock(rw, tid))
1226                 return;
1227
1228         KASSERT(rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS),
1229             ("%s: neither of the waiter flags are set", __func__));
1230
1231         if (LOCK_LOG_TEST(&rw->lock_object, 0))
1232                 CTR2(KTR_LOCK, "%s: %p contested", __func__, rw);
1233
1234         turnstile_chain_lock(&rw->lock_object);
1235
1236         /*
1237          * Use the same algo as sx locks for now.  Prefer waking up shared
1238          * waiters if we have any over writers.  This is probably not ideal.
1239          *
1240          * 'v' is the value we are going to write back to rw_lock.  If we
1241          * have waiters on both queues, we need to preserve the state of
1242          * the waiter flag for the queue we don't wake up.  For now this is
1243          * hardcoded for the algorithm mentioned above.
1244          *
1245          * In the case of both readers and writers waiting we wakeup the
1246          * readers but leave the RW_LOCK_WRITE_WAITERS flag set.  If a
1247          * new writer comes in before a reader it will claim the lock up
1248          * above.  There is probably a potential priority inversion in
1249          * there that could be worked around either by waking both queues
1250          * of waiters or doing some complicated lock handoff gymnastics.
1251          */
1252         setv = RW_UNLOCKED;
1253         v = RW_READ_VALUE(rw);
1254         queue = TS_SHARED_QUEUE;
1255         if (v & RW_LOCK_WRITE_WAITERS) {
1256                 queue = TS_EXCLUSIVE_QUEUE;
1257                 setv |= (v & RW_LOCK_READ_WAITERS);
1258         }
1259         atomic_store_rel_ptr(&rw->rw_lock, setv);
1260
1261         /* Wake up all waiters for the specific queue. */
1262         if (LOCK_LOG_TEST(&rw->lock_object, 0))
1263                 CTR3(KTR_LOCK, "%s: %p waking up %s waiters", __func__, rw,
1264                     queue == TS_SHARED_QUEUE ? "read" : "write");
1265
1266         ts = turnstile_lookup(&rw->lock_object);
1267         MPASS(ts != NULL);
1268         turnstile_broadcast(ts, queue);
1269         turnstile_unpend(ts);
1270         turnstile_chain_unlock(&rw->lock_object);
1271 }
1272
1273 /*
1274  * Attempt to do a non-blocking upgrade from a read lock to a write
1275  * lock.  This will only succeed if this thread holds a single read
1276  * lock.  Returns true if the upgrade succeeded and false otherwise.
1277  */
1278 int
1279 __rw_try_upgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
1280 {
1281         uintptr_t v, setv, tid;
1282         struct turnstile *ts;
1283         int success;
1284
1285         if (SCHEDULER_STOPPED())
1286                 return (1);
1287
1288         KASSERT(rw->rw_lock != RW_DESTROYED,
1289             ("rw_try_upgrade() of destroyed rwlock @ %s:%d", file, line));
1290         __rw_assert(&rw->rw_lock, RA_RLOCKED, file, line);
1291
1292         /*
1293          * Attempt to switch from one reader to a writer.  If there
1294          * are any write waiters, then we will have to lock the
1295          * turnstile first to prevent races with another writer
1296          * calling turnstile_wait() before we have claimed this
1297          * turnstile.  So, do the simple case of no waiters first.
1298          */
1299         tid = (uintptr_t)curthread;
1300         success = 0;
1301         v = RW_READ_VALUE(rw);
1302         for (;;) {
1303                 if (RW_READERS(v) > 1)
1304                         break;
1305                 if (!(v & RW_LOCK_WAITERS)) {
1306                         success = atomic_fcmpset_acq_ptr(&rw->rw_lock, &v, tid);
1307                         if (!success)
1308                                 continue;
1309                         break;
1310                 }
1311
1312                 /*
1313                  * Ok, we think we have waiters, so lock the turnstile.
1314                  */
1315                 ts = turnstile_trywait(&rw->lock_object);
1316                 v = RW_READ_VALUE(rw);
1317 retry_ts:
1318                 if (RW_READERS(v) > 1) {
1319                         turnstile_cancel(ts);
1320                         break;
1321                 }
1322                 /*
1323                  * Try to switch from one reader to a writer again.  This time
1324                  * we honor the current state of the waiters flags.
1325                  * If we obtain the lock with the flags set, then claim
1326                  * ownership of the turnstile.
1327                  */
1328                 setv = tid | (v & RW_LOCK_WAITERS);
1329                 success = atomic_fcmpset_ptr(&rw->rw_lock, &v, setv);
1330                 if (success) {
1331                         if (v & RW_LOCK_WAITERS)
1332                                 turnstile_claim(ts);
1333                         else
1334                                 turnstile_cancel(ts);
1335                         break;
1336                 }
1337                 goto retry_ts;
1338         }
1339         LOCK_LOG_TRY("WUPGRADE", &rw->lock_object, 0, success, file, line);
1340         if (success) {
1341                 curthread->td_rw_rlocks--;
1342                 WITNESS_UPGRADE(&rw->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
1343                     file, line);
1344                 LOCKSTAT_RECORD0(rw__upgrade, rw);
1345         }
1346         return (success);
1347 }
1348
1349 int
1350 __rw_try_upgrade(volatile uintptr_t *c, const char *file, int line)
1351 {
1352         struct rwlock *rw;
1353
1354         rw = rwlock2rw(c);
1355         return (__rw_try_upgrade_int(rw LOCK_FILE_LINE_ARG));
1356 }
1357
1358 /*
1359  * Downgrade a write lock into a single read lock.
1360  */
1361 void
1362 __rw_downgrade_int(struct rwlock *rw LOCK_FILE_LINE_ARG_DEF)
1363 {
1364         struct turnstile *ts;
1365         uintptr_t tid, v;
1366         int rwait, wwait;
1367
1368         if (SCHEDULER_STOPPED())
1369                 return;
1370
1371         KASSERT(rw->rw_lock != RW_DESTROYED,
1372             ("rw_downgrade() of destroyed rwlock @ %s:%d", file, line));
1373         __rw_assert(&rw->rw_lock, RA_WLOCKED | RA_NOTRECURSED, file, line);
1374 #ifndef INVARIANTS
1375         if (rw_recursed(rw))
1376                 panic("downgrade of a recursed lock");
1377 #endif
1378
1379         WITNESS_DOWNGRADE(&rw->lock_object, 0, file, line);
1380
1381         /*
1382          * Convert from a writer to a single reader.  First we handle
1383          * the easy case with no waiters.  If there are any waiters, we
1384          * lock the turnstile and "disown" the lock.
1385          */
1386         tid = (uintptr_t)curthread;
1387         if (atomic_cmpset_rel_ptr(&rw->rw_lock, tid, RW_READERS_LOCK(1)))
1388                 goto out;
1389
1390         /*
1391          * Ok, we think we have waiters, so lock the turnstile so we can
1392          * read the waiter flags without any races.
1393          */
1394         turnstile_chain_lock(&rw->lock_object);
1395         v = rw->rw_lock & RW_LOCK_WAITERS;
1396         rwait = v & RW_LOCK_READ_WAITERS;
1397         wwait = v & RW_LOCK_WRITE_WAITERS;
1398         MPASS(rwait | wwait);
1399
1400         /*
1401          * Downgrade from a write lock while preserving waiters flag
1402          * and give up ownership of the turnstile.
1403          */
1404         ts = turnstile_lookup(&rw->lock_object);
1405         MPASS(ts != NULL);
1406         if (!wwait)
1407                 v &= ~RW_LOCK_READ_WAITERS;
1408         atomic_store_rel_ptr(&rw->rw_lock, RW_READERS_LOCK(1) | v);
1409         /*
1410          * Wake other readers if there are no writers pending.  Otherwise they
1411          * won't be able to acquire the lock anyway.
1412          */
1413         if (rwait && !wwait) {
1414                 turnstile_broadcast(ts, TS_SHARED_QUEUE);
1415                 turnstile_unpend(ts);
1416         } else
1417                 turnstile_disown(ts);
1418         turnstile_chain_unlock(&rw->lock_object);
1419 out:
1420         curthread->td_rw_rlocks++;
1421         LOCK_LOG_LOCK("WDOWNGRADE", &rw->lock_object, 0, 0, file, line);
1422         LOCKSTAT_RECORD0(rw__downgrade, rw);
1423 }
1424
1425 void
1426 __rw_downgrade(volatile uintptr_t *c, const char *file, int line)
1427 {
1428         struct rwlock *rw;
1429
1430         rw = rwlock2rw(c);
1431         __rw_downgrade_int(rw LOCK_FILE_LINE_ARG);
1432 }
1433
1434 #ifdef INVARIANT_SUPPORT
1435 #ifndef INVARIANTS
1436 #undef __rw_assert
1437 #endif
1438
1439 /*
1440  * In the non-WITNESS case, rw_assert() can only detect that at least
1441  * *some* thread owns an rlock, but it cannot guarantee that *this*
1442  * thread owns an rlock.
1443  */
1444 void
1445 __rw_assert(const volatile uintptr_t *c, int what, const char *file, int line)
1446 {
1447         const struct rwlock *rw;
1448
1449         if (SCHEDULER_STOPPED())
1450                 return;
1451
1452         rw = rwlock2rw(c);
1453
1454         switch (what) {
1455         case RA_LOCKED:
1456         case RA_LOCKED | RA_RECURSED:
1457         case RA_LOCKED | RA_NOTRECURSED:
1458         case RA_RLOCKED:
1459         case RA_RLOCKED | RA_RECURSED:
1460         case RA_RLOCKED | RA_NOTRECURSED:
1461 #ifdef WITNESS
1462                 witness_assert(&rw->lock_object, what, file, line);
1463 #else
1464                 /*
1465                  * If some other thread has a write lock or we have one
1466                  * and are asserting a read lock, fail.  Also, if no one
1467                  * has a lock at all, fail.
1468                  */
1469                 if (rw->rw_lock == RW_UNLOCKED ||
1470                     (!(rw->rw_lock & RW_LOCK_READ) && (what & RA_RLOCKED ||
1471                     rw_wowner(rw) != curthread)))
1472                         panic("Lock %s not %slocked @ %s:%d\n",
1473                             rw->lock_object.lo_name, (what & RA_RLOCKED) ?
1474                             "read " : "", file, line);
1475
1476                 if (!(rw->rw_lock & RW_LOCK_READ) && !(what & RA_RLOCKED)) {
1477                         if (rw_recursed(rw)) {
1478                                 if (what & RA_NOTRECURSED)
1479                                         panic("Lock %s recursed @ %s:%d\n",
1480                                             rw->lock_object.lo_name, file,
1481                                             line);
1482                         } else if (what & RA_RECURSED)
1483                                 panic("Lock %s not recursed @ %s:%d\n",
1484                                     rw->lock_object.lo_name, file, line);
1485                 }
1486 #endif
1487                 break;
1488         case RA_WLOCKED:
1489         case RA_WLOCKED | RA_RECURSED:
1490         case RA_WLOCKED | RA_NOTRECURSED:
1491                 if (rw_wowner(rw) != curthread)
1492                         panic("Lock %s not exclusively locked @ %s:%d\n",
1493                             rw->lock_object.lo_name, file, line);
1494                 if (rw_recursed(rw)) {
1495                         if (what & RA_NOTRECURSED)
1496                                 panic("Lock %s recursed @ %s:%d\n",
1497                                     rw->lock_object.lo_name, file, line);
1498                 } else if (what & RA_RECURSED)
1499                         panic("Lock %s not recursed @ %s:%d\n",
1500                             rw->lock_object.lo_name, file, line);
1501                 break;
1502         case RA_UNLOCKED:
1503 #ifdef WITNESS
1504                 witness_assert(&rw->lock_object, what, file, line);
1505 #else
1506                 /*
1507                  * If we hold a write lock fail.  We can't reliably check
1508                  * to see if we hold a read lock or not.
1509                  */
1510                 if (rw_wowner(rw) == curthread)
1511                         panic("Lock %s exclusively locked @ %s:%d\n",
1512                             rw->lock_object.lo_name, file, line);
1513 #endif
1514                 break;
1515         default:
1516                 panic("Unknown rw lock assertion: %d @ %s:%d", what, file,
1517                     line);
1518         }
1519 }
1520 #endif /* INVARIANT_SUPPORT */
1521
1522 #ifdef DDB
1523 void
1524 db_show_rwlock(const struct lock_object *lock)
1525 {
1526         const struct rwlock *rw;
1527         struct thread *td;
1528
1529         rw = (const struct rwlock *)lock;
1530
1531         db_printf(" state: ");
1532         if (rw->rw_lock == RW_UNLOCKED)
1533                 db_printf("UNLOCKED\n");
1534         else if (rw->rw_lock == RW_DESTROYED) {
1535                 db_printf("DESTROYED\n");
1536                 return;
1537         } else if (rw->rw_lock & RW_LOCK_READ)
1538                 db_printf("RLOCK: %ju locks\n",
1539                     (uintmax_t)(RW_READERS(rw->rw_lock)));
1540         else {
1541                 td = rw_wowner(rw);
1542                 db_printf("WLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1543                     td->td_tid, td->td_proc->p_pid, td->td_name);
1544                 if (rw_recursed(rw))
1545                         db_printf(" recursed: %u\n", rw->rw_recurse);
1546         }
1547         db_printf(" waiters: ");
1548         switch (rw->rw_lock & (RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS)) {
1549         case RW_LOCK_READ_WAITERS:
1550                 db_printf("readers\n");
1551                 break;
1552         case RW_LOCK_WRITE_WAITERS:
1553                 db_printf("writers\n");
1554                 break;
1555         case RW_LOCK_READ_WAITERS | RW_LOCK_WRITE_WAITERS:
1556                 db_printf("readers and writers\n");
1557                 break;
1558         default:
1559                 db_printf("none\n");
1560                 break;
1561         }
1562 }
1563
1564 #endif