sys/kern/kern_sx.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
   5  * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
   6  * All rights reserved.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice(s), this list of conditions and the following disclaimer as
  13  *    the first lines of this file unmodified other than the possible
  14  *    addition of one or more copyright notices.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice(s), this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
  20  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  21  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  22  * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
  23  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  24  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  25  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  26  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
  29  * DAMAGE.
  30  */
  31
  32 /*
  33  * Shared/exclusive locks.  This implementation attempts to ensure
  34  * deterministic lock granting behavior, so that slocks and xlocks are
  35  * interleaved.
  36  *
  37  * Priority propagation will not generally raise the priority of lock holders,
  38  * so should not be relied upon in combination with sx locks.
  39  */
  40
  41 #include "opt_ddb.h"
  42 #include "opt_hwpmc_hooks.h"
  43 #include "opt_no_adaptive_sx.h"
  44
  45 #include <sys/cdefs.h>
  46 __FBSDID("$FreeBSD$");
  47
  48 #include <sys/param.h>
  49 #include <sys/systm.h>
  50 #include <sys/kdb.h>
  51 #include <sys/kernel.h>
  52 #include <sys/ktr.h>
  53 #include <sys/lock.h>
  54 #include <sys/mutex.h>
  55 #include <sys/proc.h>
  56 #include <sys/sched.h>
  57 #include <sys/sleepqueue.h>
  58 #include <sys/sx.h>
  59 #include <sys/smp.h>
  60 #include <sys/sysctl.h>
  61
  62 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  63 #include <machine/cpu.h>
  64 #endif
  65
  66 #ifdef DDB
  67 #include <ddb/ddb.h>
  68 #endif
  69
  70 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  71 #define ADAPTIVE_SX
  72 #endif
  73
  74 CTASSERT((SX_NOADAPTIVE & LO_CLASSFLAGS) == SX_NOADAPTIVE);
  75
  76 #ifdef HWPMC_HOOKS
  77 #include <sys/pmckern.h>
  78 PMC_SOFT_DECLARE( , , lock, failed);
  79 #endif
  80
  81 /* Handy macros for sleep queues. */
  82 #define SQ_EXCLUSIVE_QUEUE      0
  83 #define SQ_SHARED_QUEUE         1
  84
  85 /*
  86  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  87  * drop Giant anytime we have to sleep or if we adaptively spin.
  88  */
  89 #define GIANT_DECLARE                                                   \
  90         int _giantcnt = 0;                                              \
  91         WITNESS_SAVE_DECL(Giant)                                        \
  92
  93 #define GIANT_SAVE(work) do {                                           \
  94         if (__predict_false(mtx_owned(&Giant))) {                       \
  95                 work++;                                                 \
  96                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
  97                 while (mtx_owned(&Giant)) {                             \
  98                         _giantcnt++;                                    \
  99                         mtx_unlock(&Giant);                             \
 100                 }                                                       \
 101         }                                                               \
 102 } while (0)
 103
 104 #define GIANT_RESTORE() do {                                            \
 105         if (_giantcnt > 0) {                                            \
 106                 mtx_assert(&Giant, MA_NOTOWNED);                        \
 107                 while (_giantcnt--)                                     \
 108                         mtx_lock(&Giant);                               \
 109                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
 110         }                                                               \
 111 } while (0)
 112
 113 /*
 114  * Returns true if an exclusive lock is recursed.  It assumes
 115  * curthread currently has an exclusive lock.
 116  */
 117 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
 118
 119 static void     assert_sx(const struct lock_object *lock, int what);
 120 #ifdef DDB
 121 static void     db_show_sx(const struct lock_object *lock);
 122 #endif
 123 static void     lock_sx(struct lock_object *lock, uintptr_t how);
 124 #ifdef KDTRACE_HOOKS
 125 static int      owner_sx(const struct lock_object *lock, struct thread **owner);
 126 #endif
 127 static uintptr_t unlock_sx(struct lock_object *lock);
 128
 129 struct lock_class lock_class_sx = {
 130         .lc_name = "sx",
 131         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
 132         .lc_assert = assert_sx,
 133 #ifdef DDB
 134         .lc_ddb_show = db_show_sx,
 135 #endif
 136         .lc_lock = lock_sx,
 137         .lc_unlock = unlock_sx,
 138 #ifdef KDTRACE_HOOKS
 139         .lc_owner = owner_sx,
 140 #endif
 141 };
 142
 143 #ifndef INVARIANTS
 144 #define _sx_assert(sx, what, file, line)
 145 #endif
 146
 147 #ifdef ADAPTIVE_SX
 148 static __read_frequently u_int asx_retries = 10;
 149 static __read_frequently u_int asx_loops = 10000;
 150 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
 151 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
 152 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
 153
 154 static struct lock_delay_config __read_frequently sx_delay;
 155
 156 SYSCTL_INT(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base,
 157     0, "");
 158 SYSCTL_INT(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
 159     0, "");
 160
 161 LOCK_DELAY_SYSINIT_DEFAULT(sx_delay);
 162 #endif
 163
 164 void
 165 assert_sx(const struct lock_object *lock, int what)
 166 {
 167
 168         sx_assert((const struct sx *)lock, what);
 169 }
 170
 171 void
 172 lock_sx(struct lock_object *lock, uintptr_t how)
 173 {
 174         struct sx *sx;
 175
 176         sx = (struct sx *)lock;
 177         if (how)
 178                 sx_slock(sx);
 179         else
 180                 sx_xlock(sx);
 181 }
 182
 183 uintptr_t
 184 unlock_sx(struct lock_object *lock)
 185 {
 186         struct sx *sx;
 187
 188         sx = (struct sx *)lock;
 189         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
 190         if (sx_xlocked(sx)) {
 191                 sx_xunlock(sx);
 192                 return (0);
 193         } else {
 194                 sx_sunlock(sx);
 195                 return (1);
 196         }
 197 }
 198
 199 #ifdef KDTRACE_HOOKS
 200 int
 201 owner_sx(const struct lock_object *lock, struct thread **owner)
 202 {
 203         const struct sx *sx;
 204         uintptr_t x;
 205
 206         sx = (const struct sx *)lock;
 207         x = sx->sx_lock;
 208         *owner = NULL;
 209         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
 210             ((*owner = (struct thread *)SX_OWNER(x)) != NULL));
 211 }
 212 #endif
 213
 214 void
 215 sx_sysinit(void *arg)
 216 {
 217         struct sx_args *sargs = arg;
 218
 219         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
 220 }
 221
 222 void
 223 sx_init_flags(struct sx *sx, const char *description, int opts)
 224 {
 225         int flags;
 226
 227         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 228             SX_NOPROFILE | SX_NOADAPTIVE | SX_NEW)) == 0);
 229         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
 230             ("%s: sx_lock not aligned for %s: %p", __func__, description,
 231             &sx->sx_lock));
 232
 233         flags = LO_SLEEPABLE | LO_UPGRADABLE;
 234         if (opts & SX_DUPOK)
 235                 flags |= LO_DUPOK;
 236         if (opts & SX_NOPROFILE)
 237                 flags |= LO_NOPROFILE;
 238         if (!(opts & SX_NOWITNESS))
 239                 flags |= LO_WITNESS;
 240         if (opts & SX_RECURSE)
 241                 flags |= LO_RECURSABLE;
 242         if (opts & SX_QUIET)
 243                 flags |= LO_QUIET;
 244         if (opts & SX_NEW)
 245                 flags |= LO_NEW;
 246
 247         flags |= opts & SX_NOADAPTIVE;
 248         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
 249         sx->sx_lock = SX_LOCK_UNLOCKED;
 250         sx->sx_recurse = 0;
 251 }
 252
 253 void
 254 sx_destroy(struct sx *sx)
 255 {
 256
 257         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
 258         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
 259         sx->sx_lock = SX_LOCK_DESTROYED;
 260         lock_destroy(&sx->lock_object);
 261 }
 262
 263 int
 264 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 265 {
 266         uintptr_t x;
 267
 268         if (SCHEDULER_STOPPED())
 269                 return (1);
 270
 271         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 272             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
 273             curthread, sx->lock_object.lo_name, file, line));
 274
 275         x = sx->sx_lock;
 276         for (;;) {
 277                 KASSERT(x != SX_LOCK_DESTROYED,
 278                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
 279                 if (!(x & SX_LOCK_SHARED))
 280                         break;
 281                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) {
 282                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
 283                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
 284                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 285                             sx, 0, 0, file, line, LOCKSTAT_READER);
 286                         TD_LOCKS_INC(curthread);
 287                         return (1);
 288                 }
 289         }
 290
 291         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
 292         return (0);
 293 }
 294
 295 int
 296 sx_try_slock_(struct sx *sx, const char *file, int line)
 297 {
 298
 299         return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG));
 300 }
 301
 302 int
 303 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
 304 {
 305         uintptr_t tid, x;
 306         int error = 0;
 307
 308         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
 309             !TD_IS_IDLETHREAD(curthread),
 310             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
 311             curthread, sx->lock_object.lo_name, file, line));
 312         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 313             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
 314         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 315             line, NULL);
 316         tid = (uintptr_t)curthread;
 317         x = SX_LOCK_UNLOCKED;
 318         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 319                 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG);
 320         else
 321                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 322                     0, 0, file, line, LOCKSTAT_WRITER);
 323         if (!error) {
 324                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
 325                     file, line);
 326                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 327                 TD_LOCKS_INC(curthread);
 328         }
 329
 330         return (error);
 331 }
 332
 333 int
 334 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 335 {
 336         struct thread *td;
 337         uintptr_t tid, x;
 338         int rval;
 339         bool recursed;
 340
 341         td = curthread;
 342         tid = (uintptr_t)td;
 343         if (SCHEDULER_STOPPED_TD(td))
 344                 return (1);
 345
 346         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
 347             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
 348             curthread, sx->lock_object.lo_name, file, line));
 349         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 350             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
 351
 352         rval = 1;
 353         recursed = false;
 354         x = SX_LOCK_UNLOCKED;
 355         for (;;) {
 356                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 357                         break;
 358                 if (x == SX_LOCK_UNLOCKED)
 359                         continue;
 360                 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
 361                         sx->sx_recurse++;
 362                         atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 363                         break;
 364                 }
 365                 rval = 0;
 366                 break;
 367         }
 368
 369         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
 370         if (rval) {
 371                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 372                     file, line);
 373                 if (!recursed)
 374                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 375                             sx, 0, 0, file, line, LOCKSTAT_WRITER);
 376                 TD_LOCKS_INC(curthread);
 377         }
 378
 379         return (rval);
 380 }
 381
 382 int
 383 sx_try_xlock_(struct sx *sx, const char *file, int line)
 384 {
 385
 386         return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG));
 387 }
 388
 389 void
 390 _sx_xunlock(struct sx *sx, const char *file, int line)
 391 {
 392
 393         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 394             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
 395         _sx_assert(sx, SA_XLOCKED, file, line);
 396         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 397         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
 398             line);
 399 #if LOCK_DEBUG > 0
 400         _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line);
 401 #else
 402         __sx_xunlock(sx, curthread, file, line);
 403 #endif
 404         TD_LOCKS_DEC(curthread);
 405 }
 406
 407 /*
 408  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
 409  * This will only succeed if this thread holds a single shared lock.
 410  * Return 1 if if the upgrade succeed, 0 otherwise.
 411  */
 412 int
 413 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 414 {
 415         uintptr_t x;
 416         uintptr_t waiters;
 417         int success;
 418
 419         if (SCHEDULER_STOPPED())
 420                 return (1);
 421
 422         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 423             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
 424         _sx_assert(sx, SA_SLOCKED, file, line);
 425
 426         /*
 427          * Try to switch from one shared lock to an exclusive lock.  We need
 428          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
 429          * we will wake up the exclusive waiters when we drop the lock.
 430          */
 431         success = 0;
 432         x = SX_READ_VALUE(sx);
 433         for (;;) {
 434                 if (SX_SHARERS(x) > 1)
 435                         break;
 436                 waiters = (x & SX_LOCK_EXCLUSIVE_WAITERS);
 437                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
 438                     (uintptr_t)curthread | waiters)) {
 439                         success = 1;
 440                         break;
 441                 }
 442         }
 443         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
 444         if (success) {
 445                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 446                     file, line);
 447                 LOCKSTAT_RECORD0(sx__upgrade, sx);
 448         }
 449         return (success);
 450 }
 451
 452 int
 453 sx_try_upgrade_(struct sx *sx, const char *file, int line)
 454 {
 455
 456         return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG));
 457 }
 458
 459 /*
 460  * Downgrade an unrecursed exclusive lock into a single shared lock.
 461  */
 462 void
 463 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 464 {
 465         uintptr_t x;
 466         int wakeup_swapper;
 467
 468         if (SCHEDULER_STOPPED())
 469                 return;
 470
 471         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 472             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
 473         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
 474 #ifndef INVARIANTS
 475         if (sx_recursed(sx))
 476                 panic("downgrade of a recursed lock");
 477 #endif
 478
 479         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
 480
 481         /*
 482          * Try to switch from an exclusive lock with no shared waiters
 483          * to one sharer with no shared waiters.  If there are
 484          * exclusive waiters, we don't need to lock the sleep queue so
 485          * long as we preserve the flag.  We do one quick try and if
 486          * that fails we grab the sleepq lock to keep the flags from
 487          * changing and do it the slow way.
 488          *
 489          * We have to lock the sleep queue if there are shared waiters
 490          * so we can wake them up.
 491          */
 492         x = sx->sx_lock;
 493         if (!(x & SX_LOCK_SHARED_WAITERS) &&
 494             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
 495             (x & SX_LOCK_EXCLUSIVE_WAITERS)))
 496                 goto out;
 497
 498         /*
 499          * Lock the sleep queue so we can read the waiters bits
 500          * without any races and wakeup any shared waiters.
 501          */
 502         sleepq_lock(&sx->lock_object);
 503
 504         /*
 505          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
 506          * shared lock.  If there are any shared waiters, wake them up.
 507          */
 508         wakeup_swapper = 0;
 509         x = sx->sx_lock;
 510         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
 511             (x & SX_LOCK_EXCLUSIVE_WAITERS));
 512         if (x & SX_LOCK_SHARED_WAITERS)
 513                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 514                     0, SQ_SHARED_QUEUE);
 515         sleepq_release(&sx->lock_object);
 516
 517         if (wakeup_swapper)
 518                 kick_proc0();
 519
 520 out:
 521         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 522         LOCKSTAT_RECORD0(sx__downgrade, sx);
 523 }
 524
 525 void
 526 sx_downgrade_(struct sx *sx, const char *file, int line)
 527 {
 528
 529         sx_downgrade_int(sx LOCK_FILE_LINE_ARG);
 530 }
 531
 532 /*
 533  * This function represents the so-called 'hard case' for sx_xlock
 534  * operation.  All 'easy case' failures are redirected to this.  Note
 535  * that ideally this would be a static function, but it needs to be
 536  * accessible from at least sx.h.
 537  */
 538 int
 539 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
 540 {
 541         GIANT_DECLARE;
 542         uintptr_t tid;
 543 #ifdef ADAPTIVE_SX
 544         volatile struct thread *owner;
 545         u_int i, n, spintries = 0;
 546         enum { READERS, WRITER } sleep_reason;
 547         bool adaptive;
 548 #endif
 549 #ifdef LOCK_PROFILING
 550         uint64_t waittime = 0;
 551         int contested = 0;
 552 #endif
 553         int error = 0;
 554 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
 555         struct lock_delay_arg lda;
 556 #endif
 557 #ifdef  KDTRACE_HOOKS
 558         u_int sleep_cnt = 0;
 559         int64_t sleep_time = 0;
 560         int64_t all_time = 0;
 561 #endif
 562 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 563         uintptr_t state;
 564 #endif
 565         int extra_work = 0;
 566
 567         tid = (uintptr_t)curthread;
 568         if (SCHEDULER_STOPPED())
 569                 return (0);
 570
 571 #if defined(ADAPTIVE_SX)
 572         lock_delay_arg_init(&lda, &sx_delay);
 573 #elif defined(KDTRACE_HOOKS)
 574         lock_delay_arg_init(&lda, NULL);
 575 #endif
 576
 577         if (__predict_false(x == SX_LOCK_UNLOCKED))
 578                 x = SX_READ_VALUE(sx);
 579
 580         /* If we already hold an exclusive lock, then recurse. */
 581         if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) {
 582                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
 583             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
 584                     sx->lock_object.lo_name, file, line));
 585                 sx->sx_recurse++;
 586                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 587                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 588                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
 589                 return (0);
 590         }
 591
 592         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 593                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 594                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
 595
 596 #ifdef ADAPTIVE_SX
 597         adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0);
 598 #endif
 599
 600 #ifdef HWPMC_HOOKS
 601         PMC_SOFT_CALL( , , lock, failed);
 602 #endif
 603         lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 604             &waittime);
 605
 606 #ifdef LOCK_PROFILING
 607         extra_work = 1;
 608         state = x;
 609 #elif defined(KDTRACE_HOOKS)
 610         extra_work = lockstat_enabled;
 611         if (__predict_false(extra_work)) {
 612                 all_time -= lockstat_nsecs(&sx->lock_object);
 613                 state = x;
 614         }
 615 #endif
 616 #ifndef INVARIANTS
 617         GIANT_SAVE(extra_work);
 618 #endif
 619
 620         for (;;) {
 621                 if (x == SX_LOCK_UNLOCKED) {
 622                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 623                                 break;
 624                         continue;
 625                 }
 626 #ifdef INVARIANTS
 627                 GIANT_SAVE(extra_work);
 628 #endif
 629 #ifdef KDTRACE_HOOKS
 630                 lda.spin_cnt++;
 631 #endif
 632 #ifdef ADAPTIVE_SX
 633                 if (__predict_false(!adaptive))
 634                         goto sleepq;
 635                 /*
 636                  * If the lock is write locked and the owner is
 637                  * running on another CPU, spin until the owner stops
 638                  * running or the state of the lock changes.
 639                  */
 640                 if ((x & SX_LOCK_SHARED) == 0) {
 641                         sleep_reason = WRITER;
 642                         owner = lv_sx_owner(x);
 643                         if (!TD_IS_RUNNING(owner))
 644                                 goto sleepq;
 645                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 646                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
 647                                     __func__, sx, owner);
 648                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 649                             "spinning", "lockname:\"%s\"",
 650                             sx->lock_object.lo_name);
 651                         do {
 652                                 lock_delay(&lda);
 653                                 x = SX_READ_VALUE(sx);
 654                                 owner = lv_sx_owner(x);
 655                         } while (owner != NULL && TD_IS_RUNNING(owner));
 656                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 657                             "running");
 658                         continue;
 659                 } else if (SX_SHARERS(x) > 0) {
 660                         sleep_reason = READERS;
 661                         if (spintries == asx_retries)
 662                                 goto sleepq;
 663                         spintries++;
 664                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 665                             "spinning", "lockname:\"%s\"",
 666                             sx->lock_object.lo_name);
 667                         for (i = 0; i < asx_loops; i += n) {
 668                                 n = SX_SHARERS(x);
 669                                 lock_delay_spin(n);
 670                                 x = SX_READ_VALUE(sx);
 671                                 if ((x & SX_LOCK_SHARED) == 0 ||
 672                                     SX_SHARERS(x) == 0)
 673                                         break;
 674                         }
 675 #ifdef KDTRACE_HOOKS
 676                         lda.spin_cnt += i;
 677 #endif
 678                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 679                             "running");
 680                         if (i < asx_loops)
 681                                 continue;
 682                 }
 683 sleepq:
 684 #endif
 685                 sleepq_lock(&sx->lock_object);
 686                 x = SX_READ_VALUE(sx);
 687 retry_sleepq:
 688
 689                 /*
 690                  * If the lock was released while spinning on the
 691                  * sleep queue chain lock, try again.
 692                  */
 693                 if (x == SX_LOCK_UNLOCKED) {
 694                         sleepq_release(&sx->lock_object);
 695                         continue;
 696                 }
 697
 698 #ifdef ADAPTIVE_SX
 699                 /*
 700                  * The current lock owner might have started executing
 701                  * on another CPU (or the lock could have changed
 702                  * owners) while we were waiting on the sleep queue
 703                  * chain lock.  If so, drop the sleep queue lock and try
 704                  * again.
 705                  */
 706                 if (adaptive) {
 707                         if (!(x & SX_LOCK_SHARED)) {
 708                                 owner = (struct thread *)SX_OWNER(x);
 709                                 if (TD_IS_RUNNING(owner)) {
 710                                         sleepq_release(&sx->lock_object);
 711                                         continue;
 712                                 }
 713                         } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) {
 714                                 sleepq_release(&sx->lock_object);
 715                                 continue;
 716                         }
 717                 }
 718 #endif
 719
 720                 /*
 721                  * If an exclusive lock was released with both shared
 722                  * and exclusive waiters and a shared waiter hasn't
 723                  * woken up and acquired the lock yet, sx_lock will be
 724                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 725                  * If we see that value, try to acquire it once.  Note
 726                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 727                  * as there are other exclusive waiters still.  If we
 728                  * fail, restart the loop.
 729                  */
 730                 if (x == (SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS)) {
 731                         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
 732                             tid | SX_LOCK_EXCLUSIVE_WAITERS))
 733                                 goto retry_sleepq;
 734                         sleepq_release(&sx->lock_object);
 735                         CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 736                             __func__, sx);
 737                         break;
 738                 }
 739
 740                 /*
 741                  * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 742                  * than loop back and retry.
 743                  */
 744                 if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 745                         if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 746                             x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 747                                 goto retry_sleepq;
 748                         }
 749                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 750                                 CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 751                                     __func__, sx);
 752                 }
 753
 754                 /*
 755                  * Since we have been unable to acquire the exclusive
 756                  * lock and the exclusive waiters flag is set, we have
 757                  * to sleep.
 758                  */
 759                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 760                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 761                             __func__, sx);
 762
 763 #ifdef KDTRACE_HOOKS
 764                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 765 #endif
 766                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 767                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 768                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 769                 if (!(opts & SX_INTERRUPTIBLE))
 770                         sleepq_wait(&sx->lock_object, 0);
 771                 else
 772                         error = sleepq_wait_sig(&sx->lock_object, 0);
 773 #ifdef KDTRACE_HOOKS
 774                 sleep_time += lockstat_nsecs(&sx->lock_object);
 775                 sleep_cnt++;
 776 #endif
 777                 if (error) {
 778                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 779                                 CTR2(KTR_LOCK,
 780                         "%s: interruptible sleep by %p suspended by signal",
 781                                     __func__, sx);
 782                         break;
 783                 }
 784                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 785                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 786                             __func__, sx);
 787                 x = SX_READ_VALUE(sx);
 788         }
 789 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 790         if (__predict_true(!extra_work))
 791                 return (error);
 792 #endif
 793 #ifdef KDTRACE_HOOKS
 794         all_time += lockstat_nsecs(&sx->lock_object);
 795         if (sleep_time)
 796                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
 797                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 798                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 799         if (lda.spin_cnt > sleep_cnt)
 800                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
 801                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 802                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 803 #endif
 804         if (!error)
 805                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 806                     contested, waittime, file, line, LOCKSTAT_WRITER);
 807         GIANT_RESTORE();
 808         return (error);
 809 }
 810
 811 /*
 812  * This function represents the so-called 'hard case' for sx_xunlock
 813  * operation.  All 'easy case' failures are redirected to this.  Note
 814  * that ideally this would be a static function, but it needs to be
 815  * accessible from at least sx.h.
 816  */
 817 void
 818 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
 819 {
 820         uintptr_t tid, setx;
 821         int queue, wakeup_swapper;
 822
 823         if (SCHEDULER_STOPPED())
 824                 return;
 825
 826         tid = (uintptr_t)curthread;
 827
 828         if (__predict_false(x == tid))
 829                 x = SX_READ_VALUE(sx);
 830
 831         MPASS(!(x & SX_LOCK_SHARED));
 832
 833         if (__predict_false(x & SX_LOCK_RECURSED)) {
 834                 /* The lock is recursed, unrecurse one level. */
 835                 if ((--sx->sx_recurse) == 0)
 836                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 837                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 838                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 839                 return;
 840         }
 841
 842         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
 843         if (x == tid &&
 844             atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
 845                 return;
 846
 847         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 848                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 849
 850         sleepq_lock(&sx->lock_object);
 851         x = SX_READ_VALUE(sx);
 852         MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS));
 853
 854         /*
 855          * The wake up algorithm here is quite simple and probably not
 856          * ideal.  It gives precedence to shared waiters if they are
 857          * present.  For this condition, we have to preserve the
 858          * state of the exclusive waiters flag.
 859          * If interruptible sleeps left the shared queue empty avoid a
 860          * starvation for the threads sleeping on the exclusive queue by giving
 861          * them precedence and cleaning up the shared waiters bit anyway.
 862          */
 863         setx = SX_LOCK_UNLOCKED;
 864         queue = SQ_EXCLUSIVE_QUEUE;
 865         if ((x & SX_LOCK_SHARED_WAITERS) != 0 &&
 866             sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
 867                 queue = SQ_SHARED_QUEUE;
 868                 setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS);
 869         }
 870         atomic_store_rel_ptr(&sx->sx_lock, setx);
 871
 872         /* Wake up all the waiters for the specific queue. */
 873         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 874                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 875                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 876                     "exclusive");
 877
 878         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 879             queue);
 880         sleepq_release(&sx->lock_object);
 881         if (wakeup_swapper)
 882                 kick_proc0();
 883 }
 884
 885 static bool __always_inline
 886 __sx_slock_try(struct sx *sx, uintptr_t *xp LOCK_FILE_LINE_ARG_DEF)
 887 {
 888
 889         /*
 890          * If no other thread has an exclusive lock then try to bump up
 891          * the count of sharers.  Since we have to preserve the state
 892          * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
 893          * shared lock loop back and retry.
 894          */
 895         while (*xp & SX_LOCK_SHARED) {
 896                 MPASS(!(*xp & SX_LOCK_SHARED_WAITERS));
 897                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp,
 898                     *xp + SX_ONE_SHARER)) {
 899                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 900                                 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p",
 901                                     __func__, sx, (void *)*xp,
 902                                     (void *)(*xp + SX_ONE_SHARER));
 903                         return (true);
 904                 }
 905         }
 906         return (false);
 907 }
 908
 909 static int __noinline
 910 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
 911 {
 912         GIANT_DECLARE;
 913 #ifdef ADAPTIVE_SX
 914         volatile struct thread *owner;
 915         bool adaptive;
 916 #endif
 917 #ifdef LOCK_PROFILING
 918         uint64_t waittime = 0;
 919         int contested = 0;
 920 #endif
 921         int error = 0;
 922 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
 923         struct lock_delay_arg lda;
 924 #endif
 925 #ifdef KDTRACE_HOOKS
 926         u_int sleep_cnt = 0;
 927         int64_t sleep_time = 0;
 928         int64_t all_time = 0;
 929 #endif
 930 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 931         uintptr_t state;
 932 #endif
 933         int extra_work = 0;
 934
 935         if (SCHEDULER_STOPPED())
 936                 return (0);
 937
 938 #if defined(ADAPTIVE_SX)
 939         lock_delay_arg_init(&lda, &sx_delay);
 940 #elif defined(KDTRACE_HOOKS)
 941         lock_delay_arg_init(&lda, NULL);
 942 #endif
 943
 944 #ifdef ADAPTIVE_SX
 945         adaptive = ((sx->lock_object.lo_flags & SX_NOADAPTIVE) == 0);
 946 #endif
 947
 948 #ifdef HWPMC_HOOKS
 949         PMC_SOFT_CALL( , , lock, failed);
 950 #endif
 951         lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 952             &waittime);
 953
 954 #ifdef LOCK_PROFILING
 955         extra_work = 1;
 956         state = x;
 957 #elif defined(KDTRACE_HOOKS)
 958         extra_work = lockstat_enabled;
 959         if (__predict_false(extra_work)) {
 960                 all_time -= lockstat_nsecs(&sx->lock_object);
 961                 state = x;
 962         }
 963 #endif
 964 #ifndef INVARIANTS
 965         GIANT_SAVE(extra_work);
 966 #endif
 967
 968         /*
 969          * As with rwlocks, we don't make any attempt to try to block
 970          * shared locks once there is an exclusive waiter.
 971          */
 972         for (;;) {
 973                 if (__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG))
 974                         break;
 975 #ifdef INVARIANTS
 976                 GIANT_SAVE(extra_work);
 977 #endif
 978 #ifdef KDTRACE_HOOKS
 979                 lda.spin_cnt++;
 980 #endif
 981
 982 #ifdef ADAPTIVE_SX
 983                 if (__predict_false(!adaptive))
 984                         goto sleepq;
 985                 /*
 986                  * If the owner is running on another CPU, spin until
 987                  * the owner stops running or the state of the lock
 988                  * changes.
 989                  */
 990                 owner = lv_sx_owner(x);
 991                 if (TD_IS_RUNNING(owner)) {
 992                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 993                                 CTR3(KTR_LOCK,
 994                                     "%s: spinning on %p held by %p",
 995                                     __func__, sx, owner);
 996                         KTR_STATE1(KTR_SCHED, "thread",
 997                             sched_tdname(curthread), "spinning",
 998                             "lockname:\"%s\"", sx->lock_object.lo_name);
 999                         do {
1000                                 lock_delay(&lda);
1001                                 x = SX_READ_VALUE(sx);
1002                                 owner = lv_sx_owner(x);
1003                         } while (owner != NULL && TD_IS_RUNNING(owner));
1004                         KTR_STATE0(KTR_SCHED, "thread",
1005                             sched_tdname(curthread), "running");
1006                         continue;
1007                 }
1008 sleepq:
1009 #endif
1010
1011                 /*
1012                  * Some other thread already has an exclusive lock, so
1013                  * start the process of blocking.
1014                  */
1015                 sleepq_lock(&sx->lock_object);
1016                 x = SX_READ_VALUE(sx);
1017 retry_sleepq:
1018                 /*
1019                  * The lock could have been released while we spun.
1020                  * In this case loop back and retry.
1021                  */
1022                 if (x & SX_LOCK_SHARED) {
1023                         sleepq_release(&sx->lock_object);
1024                         continue;
1025                 }
1026
1027 #ifdef ADAPTIVE_SX
1028                 /*
1029                  * If the owner is running on another CPU, spin until
1030                  * the owner stops running or the state of the lock
1031                  * changes.
1032                  */
1033                 if (!(x & SX_LOCK_SHARED) && adaptive) {
1034                         owner = (struct thread *)SX_OWNER(x);
1035                         if (TD_IS_RUNNING(owner)) {
1036                                 sleepq_release(&sx->lock_object);
1037                                 x = SX_READ_VALUE(sx);
1038                                 continue;
1039                         }
1040                 }
1041 #endif
1042
1043                 /*
1044                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
1045                  * fail to set it drop the sleep queue lock and loop
1046                  * back.
1047                  */
1048                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
1049                         if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
1050                             x | SX_LOCK_SHARED_WAITERS))
1051                                 goto retry_sleepq;
1052                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1053                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
1054                                     __func__, sx);
1055                 }
1056
1057                 /*
1058                  * Since we have been unable to acquire the shared lock,
1059                  * we have to sleep.
1060                  */
1061                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1062                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
1063                             __func__, sx);
1064
1065 #ifdef KDTRACE_HOOKS
1066                 sleep_time -= lockstat_nsecs(&sx->lock_object);
1067 #endif
1068                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1069                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1070                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1071                 if (!(opts & SX_INTERRUPTIBLE))
1072                         sleepq_wait(&sx->lock_object, 0);
1073                 else
1074                         error = sleepq_wait_sig(&sx->lock_object, 0);
1075 #ifdef KDTRACE_HOOKS
1076                 sleep_time += lockstat_nsecs(&sx->lock_object);
1077                 sleep_cnt++;
1078 #endif
1079                 if (error) {
1080                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1081                                 CTR2(KTR_LOCK,
1082                         "%s: interruptible sleep by %p suspended by signal",
1083                                     __func__, sx);
1084                         break;
1085                 }
1086                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1087                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1088                             __func__, sx);
1089                 x = SX_READ_VALUE(sx);
1090         }
1091 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1092         if (__predict_true(!extra_work))
1093                 return (error);
1094 #endif
1095 #ifdef KDTRACE_HOOKS
1096         all_time += lockstat_nsecs(&sx->lock_object);
1097         if (sleep_time)
1098                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
1099                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1100                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1101         if (lda.spin_cnt > sleep_cnt)
1102                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
1103                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1104                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1105 #endif
1106         if (error == 0) {
1107                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
1108                     contested, waittime, file, line, LOCKSTAT_READER);
1109         }
1110         GIANT_RESTORE();
1111         return (error);
1112 }
1113
1114 int
1115 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF)
1116 {
1117         uintptr_t x;
1118         int error;
1119
1120         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
1121             !TD_IS_IDLETHREAD(curthread),
1122             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
1123             curthread, sx->lock_object.lo_name, file, line));
1124         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1125             ("sx_slock() of destroyed sx @ %s:%d", file, line));
1126         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
1127
1128         error = 0;
1129         x = SX_READ_VALUE(sx);
1130         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) ||
1131             !__sx_slock_try(sx, &x LOCK_FILE_LINE_ARG)))
1132                 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG);
1133         else
1134                 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0,
1135                     file, line);
1136         if (error == 0) {
1137                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
1138                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
1139                 TD_LOCKS_INC(curthread);
1140         }
1141         return (error);
1142 }
1143
1144 int
1145 _sx_slock(struct sx *sx, int opts, const char *file, int line)
1146 {
1147
1148         return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG));
1149 }
1150
1151 static bool __always_inline
1152 _sx_sunlock_try(struct sx *sx, uintptr_t *xp)
1153 {
1154
1155         for (;;) {
1156                 /*
1157                  * We should never have sharers while at least one thread
1158                  * holds a shared lock.
1159                  */
1160                 KASSERT(!(*xp & SX_LOCK_SHARED_WAITERS),
1161                     ("%s: waiting sharers", __func__));
1162
1163                 /*
1164                  * See if there is more than one shared lock held.  If
1165                  * so, just drop one and return.
1166                  */
1167                 if (SX_SHARERS(*xp) > 1) {
1168                         if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp,
1169                             *xp - SX_ONE_SHARER)) {
1170                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1171                                         CTR4(KTR_LOCK,
1172                                             "%s: %p succeeded %p -> %p",
1173                                             __func__, sx, (void *)*xp,
1174                                             (void *)(*xp - SX_ONE_SHARER));
1175                                 return (true);
1176                         }
1177                         continue;
1178                 }
1179
1180                 /*
1181                  * If there aren't any waiters for an exclusive lock,
1182                  * then try to drop it quickly.
1183                  */
1184                 if (!(*xp & SX_LOCK_EXCLUSIVE_WAITERS)) {
1185                         MPASS(*xp == SX_SHARERS_LOCK(1));
1186                         *xp = SX_SHARERS_LOCK(1);
1187                         if (atomic_fcmpset_rel_ptr(&sx->sx_lock,
1188                             xp, SX_LOCK_UNLOCKED)) {
1189                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1190                                         CTR2(KTR_LOCK, "%s: %p last succeeded",
1191                                             __func__, sx);
1192                                 return (true);
1193                         }
1194                         continue;
1195                 }
1196                 break;
1197         }
1198         return (false);
1199 }
1200
1201 static void __noinline
1202 _sx_sunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
1203 {
1204         int wakeup_swapper = 0;
1205         uintptr_t setx;
1206
1207         if (SCHEDULER_STOPPED())
1208                 return;
1209
1210         if (_sx_sunlock_try(sx, &x))
1211                 goto out_lockstat;
1212
1213         /*
1214          * At this point, there should just be one sharer with
1215          * exclusive waiters.
1216          */
1217         MPASS(x == (SX_SHARERS_LOCK(1) | SX_LOCK_EXCLUSIVE_WAITERS));
1218
1219         sleepq_lock(&sx->lock_object);
1220         x = SX_READ_VALUE(sx);
1221         for (;;) {
1222                 MPASS(x & SX_LOCK_EXCLUSIVE_WAITERS);
1223                 MPASS(!(x & SX_LOCK_SHARED_WAITERS));
1224                 if (_sx_sunlock_try(sx, &x))
1225                         break;
1226
1227                 /*
1228                  * Wake up semantic here is quite simple:
1229                  * Just wake up all the exclusive waiters.
1230                  * Note that the state of the lock could have changed,
1231                  * so if it fails loop back and retry.
1232                  */
1233                 setx = x - SX_ONE_SHARER;
1234                 setx &= ~SX_LOCK_EXCLUSIVE_WAITERS;
1235                 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx))
1236                         continue;
1237                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1238                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1239                             "exclusive queue", __func__, sx);
1240                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1241                     0, SQ_EXCLUSIVE_QUEUE);
1242                 break;
1243         }
1244         sleepq_release(&sx->lock_object);
1245         if (wakeup_swapper)
1246                 kick_proc0();
1247 out_lockstat:
1248         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
1249 }
1250
1251 void
1252 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
1253 {
1254         uintptr_t x;
1255
1256         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1257             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
1258         _sx_assert(sx, SA_SLOCKED, file, line);
1259         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
1260         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
1261
1262         x = SX_READ_VALUE(sx);
1263         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) ||
1264             !_sx_sunlock_try(sx, &x)))
1265                 _sx_sunlock_hard(sx, x LOCK_FILE_LINE_ARG);
1266         else
1267                 lock_profile_release_lock(&sx->lock_object);
1268
1269         TD_LOCKS_DEC(curthread);
1270 }
1271
1272 void
1273 _sx_sunlock(struct sx *sx, const char *file, int line)
1274 {
1275
1276         _sx_sunlock_int(sx LOCK_FILE_LINE_ARG);
1277 }
1278
1279 #ifdef INVARIANT_SUPPORT
1280 #ifndef INVARIANTS
1281 #undef  _sx_assert
1282 #endif
1283
1284 /*
1285  * In the non-WITNESS case, sx_assert() can only detect that at least
1286  * *some* thread owns an slock, but it cannot guarantee that *this*
1287  * thread owns an slock.
1288  */
1289 void
1290 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1291 {
1292 #ifndef WITNESS
1293         int slocked = 0;
1294 #endif
1295
1296         if (panicstr != NULL)
1297                 return;
1298         switch (what) {
1299         case SA_SLOCKED:
1300         case SA_SLOCKED | SA_NOTRECURSED:
1301         case SA_SLOCKED | SA_RECURSED:
1302 #ifndef WITNESS
1303                 slocked = 1;
1304                 /* FALLTHROUGH */
1305 #endif
1306         case SA_LOCKED:
1307         case SA_LOCKED | SA_NOTRECURSED:
1308         case SA_LOCKED | SA_RECURSED:
1309 #ifdef WITNESS
1310                 witness_assert(&sx->lock_object, what, file, line);
1311 #else
1312                 /*
1313                  * If some other thread has an exclusive lock or we
1314                  * have one and are asserting a shared lock, fail.
1315                  * Also, if no one has a lock at all, fail.
1316                  */
1317                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1318                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1319                     sx_xholder(sx) != curthread)))
1320                         panic("Lock %s not %slocked @ %s:%d\n",
1321                             sx->lock_object.lo_name, slocked ? "share " : "",
1322                             file, line);
1323
1324                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1325                         if (sx_recursed(sx)) {
1326                                 if (what & SA_NOTRECURSED)
1327                                         panic("Lock %s recursed @ %s:%d\n",
1328                                             sx->lock_object.lo_name, file,
1329                                             line);
1330                         } else if (what & SA_RECURSED)
1331                                 panic("Lock %s not recursed @ %s:%d\n",
1332                                     sx->lock_object.lo_name, file, line);
1333                 }
1334 #endif
1335                 break;
1336         case SA_XLOCKED:
1337         case SA_XLOCKED | SA_NOTRECURSED:
1338         case SA_XLOCKED | SA_RECURSED:
1339                 if (sx_xholder(sx) != curthread)
1340                         panic("Lock %s not exclusively locked @ %s:%d\n",
1341                             sx->lock_object.lo_name, file, line);
1342                 if (sx_recursed(sx)) {
1343                         if (what & SA_NOTRECURSED)
1344                                 panic("Lock %s recursed @ %s:%d\n",
1345                                     sx->lock_object.lo_name, file, line);
1346                 } else if (what & SA_RECURSED)
1347                         panic("Lock %s not recursed @ %s:%d\n",
1348                             sx->lock_object.lo_name, file, line);
1349                 break;
1350         case SA_UNLOCKED:
1351 #ifdef WITNESS
1352                 witness_assert(&sx->lock_object, what, file, line);
1353 #else
1354                 /*
1355                  * If we hold an exclusve lock fail.  We can't
1356                  * reliably check to see if we hold a shared lock or
1357                  * not.
1358                  */
1359                 if (sx_xholder(sx) == curthread)
1360                         panic("Lock %s exclusively locked @ %s:%d\n",
1361                             sx->lock_object.lo_name, file, line);
1362 #endif
1363                 break;
1364         default:
1365                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1366                     line);
1367         }
1368 }
1369 #endif  /* INVARIANT_SUPPORT */
1370
1371 #ifdef DDB
1372 static void
1373 db_show_sx(const struct lock_object *lock)
1374 {
1375         struct thread *td;
1376         const struct sx *sx;
1377
1378         sx = (const struct sx *)lock;
1379
1380         db_printf(" state: ");
1381         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1382                 db_printf("UNLOCKED\n");
1383         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1384                 db_printf("DESTROYED\n");
1385                 return;
1386         } else if (sx->sx_lock & SX_LOCK_SHARED)
1387                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1388         else {
1389                 td = sx_xholder(sx);
1390                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1391                     td->td_tid, td->td_proc->p_pid, td->td_name);
1392                 if (sx_recursed(sx))
1393                         db_printf(" recursed: %d\n", sx->sx_recurse);
1394         }
1395
1396         db_printf(" waiters: ");
1397         switch(sx->sx_lock &
1398             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1399         case SX_LOCK_SHARED_WAITERS:
1400                 db_printf("shared\n");
1401                 break;
1402         case SX_LOCK_EXCLUSIVE_WAITERS:
1403                 db_printf("exclusive\n");
1404                 break;
1405         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1406                 db_printf("exclusive and shared\n");
1407                 break;
1408         default:
1409                 db_printf("none\n");
1410         }
1411 }
1412
1413 /*
1414  * Check to see if a thread that is blocked on a sleep queue is actually
1415  * blocked on an sx lock.  If so, output some details and return true.
1416  * If the lock has an exclusive owner, return that in *ownerp.
1417  */
1418 int
1419 sx_chain(struct thread *td, struct thread **ownerp)
1420 {
1421         struct sx *sx;
1422
1423         /*
1424          * Check to see if this thread is blocked on an sx lock.
1425          * First, we check the lock class.  If that is ok, then we
1426          * compare the lock name against the wait message.
1427          */
1428         sx = td->td_wchan;
1429         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1430             sx->lock_object.lo_name != td->td_wmesg)
1431                 return (0);
1432
1433         /* We think we have an sx lock, so output some details. */
1434         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1435         *ownerp = sx_xholder(sx);
1436         if (sx->sx_lock & SX_LOCK_SHARED)
1437                 db_printf("SLOCK (count %ju)\n",
1438                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1439         else
1440                 db_printf("XLOCK\n");
1441         return (1);
1442 }
1443 #endif