sys/kern/kern_sx.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause
   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 #include <sys/param.h>
  47 #include <sys/systm.h>
  48 #include <sys/kdb.h>
  49 #include <sys/kernel.h>
  50 #include <sys/ktr.h>
  51 #include <sys/lock.h>
  52 #include <sys/mutex.h>
  53 #include <sys/proc.h>
  54 #include <sys/sched.h>
  55 #include <sys/sleepqueue.h>
  56 #include <sys/sx.h>
  57 #include <sys/smp.h>
  58 #include <sys/sysctl.h>
  59
  60 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  61 #include <machine/cpu.h>
  62 #endif
  63
  64 #ifdef DDB
  65 #include <ddb/ddb.h>
  66 #endif
  67
  68 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  69 #define ADAPTIVE_SX
  70 #endif
  71
  72 #ifdef HWPMC_HOOKS
  73 #include <sys/pmckern.h>
  74 PMC_SOFT_DECLARE( , , lock, failed);
  75 #endif
  76
  77 /* Handy macros for sleep queues. */
  78 #define SQ_EXCLUSIVE_QUEUE      0
  79 #define SQ_SHARED_QUEUE         1
  80
  81 /*
  82  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  83  * drop Giant anytime we have to sleep or if we adaptively spin.
  84  */
  85 #define GIANT_DECLARE                                                   \
  86         int _giantcnt = 0;                                              \
  87         WITNESS_SAVE_DECL(Giant)                                        \
  88
  89 #define GIANT_SAVE(work) do {                                           \
  90         if (__predict_false(mtx_owned(&Giant))) {                       \
  91                 work++;                                                 \
  92                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
  93                 while (mtx_owned(&Giant)) {                             \
  94                         _giantcnt++;                                    \
  95                         mtx_unlock(&Giant);                             \
  96                 }                                                       \
  97         }                                                               \
  98 } while (0)
  99
 100 #define GIANT_RESTORE() do {                                            \
 101         if (_giantcnt > 0) {                                            \
 102                 mtx_assert(&Giant, MA_NOTOWNED);                        \
 103                 while (_giantcnt--)                                     \
 104                         mtx_lock(&Giant);                               \
 105                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
 106         }                                                               \
 107 } while (0)
 108
 109 /*
 110  * Returns true if an exclusive lock is recursed.  It assumes
 111  * curthread currently has an exclusive lock.
 112  */
 113 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
 114
 115 static void     assert_sx(const struct lock_object *lock, int what);
 116 #ifdef DDB
 117 static void     db_show_sx(const struct lock_object *lock);
 118 #endif
 119 static void     lock_sx(struct lock_object *lock, uintptr_t how);
 120 #ifdef KDTRACE_HOOKS
 121 static int      owner_sx(const struct lock_object *lock, struct thread **owner);
 122 #endif
 123 static uintptr_t unlock_sx(struct lock_object *lock);
 124
 125 struct lock_class lock_class_sx = {
 126         .lc_name = "sx",
 127         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
 128         .lc_assert = assert_sx,
 129 #ifdef DDB
 130         .lc_ddb_show = db_show_sx,
 131 #endif
 132         .lc_lock = lock_sx,
 133         .lc_unlock = unlock_sx,
 134 #ifdef KDTRACE_HOOKS
 135         .lc_owner = owner_sx,
 136 #endif
 137 };
 138
 139 #ifndef INVARIANTS
 140 #define _sx_assert(sx, what, file, line)
 141 #endif
 142
 143 #ifdef ADAPTIVE_SX
 144 #ifdef SX_CUSTOM_BACKOFF
 145 static u_short __read_frequently asx_retries;
 146 static u_short __read_frequently asx_loops;
 147 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
 148     "sxlock debugging");
 149 SYSCTL_U16(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
 150 SYSCTL_U16(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
 151
 152 static struct lock_delay_config __read_frequently sx_delay;
 153
 154 SYSCTL_U16(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base,
 155     0, "");
 156 SYSCTL_U16(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
 157     0, "");
 158
 159 static void
 160 sx_lock_delay_init(void *arg __unused)
 161 {
 162
 163         lock_delay_default_init(&sx_delay);
 164         asx_retries = 10;
 165         asx_loops = max(10000, sx_delay.max);
 166 }
 167 LOCK_DELAY_SYSINIT(sx_lock_delay_init);
 168 #else
 169 #define sx_delay        locks_delay
 170 #define asx_retries     locks_delay_retries
 171 #define asx_loops       locks_delay_loops
 172 #endif
 173 #endif
 174
 175 void
 176 assert_sx(const struct lock_object *lock, int what)
 177 {
 178
 179         sx_assert((const struct sx *)lock, what);
 180 }
 181
 182 void
 183 lock_sx(struct lock_object *lock, uintptr_t how)
 184 {
 185         struct sx *sx;
 186
 187         sx = (struct sx *)lock;
 188         if (how)
 189                 sx_slock(sx);
 190         else
 191                 sx_xlock(sx);
 192 }
 193
 194 uintptr_t
 195 unlock_sx(struct lock_object *lock)
 196 {
 197         struct sx *sx;
 198
 199         sx = (struct sx *)lock;
 200         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
 201         if (sx_xlocked(sx)) {
 202                 sx_xunlock(sx);
 203                 return (0);
 204         } else {
 205                 sx_sunlock(sx);
 206                 return (1);
 207         }
 208 }
 209
 210 #ifdef KDTRACE_HOOKS
 211 int
 212 owner_sx(const struct lock_object *lock, struct thread **owner)
 213 {
 214         const struct sx *sx;
 215         uintptr_t x;
 216
 217         sx = (const struct sx *)lock;
 218         x = sx->sx_lock;
 219         *owner = NULL;
 220         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
 221             ((*owner = (struct thread *)SX_OWNER(x)) != NULL));
 222 }
 223 #endif
 224
 225 void
 226 sx_sysinit(void *arg)
 227 {
 228         struct sx_args *sargs = arg;
 229
 230         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
 231 }
 232
 233 void
 234 sx_init_flags(struct sx *sx, const char *description, int opts)
 235 {
 236         int flags;
 237
 238         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 239             SX_NOPROFILE | SX_NEW)) == 0);
 240         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
 241             ("%s: sx_lock not aligned for %s: %p", __func__, description,
 242             &sx->sx_lock));
 243
 244         flags = LO_SLEEPABLE | LO_UPGRADABLE;
 245         if (opts & SX_DUPOK)
 246                 flags |= LO_DUPOK;
 247         if (opts & SX_NOPROFILE)
 248                 flags |= LO_NOPROFILE;
 249         if (!(opts & SX_NOWITNESS))
 250                 flags |= LO_WITNESS;
 251         if (opts & SX_RECURSE)
 252                 flags |= LO_RECURSABLE;
 253         if (opts & SX_QUIET)
 254                 flags |= LO_QUIET;
 255         if (opts & SX_NEW)
 256                 flags |= LO_NEW;
 257
 258         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
 259         sx->sx_lock = SX_LOCK_UNLOCKED;
 260         sx->sx_recurse = 0;
 261 }
 262
 263 void
 264 sx_destroy(struct sx *sx)
 265 {
 266
 267         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
 268         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
 269         sx->sx_lock = SX_LOCK_DESTROYED;
 270         lock_destroy(&sx->lock_object);
 271 }
 272
 273 int
 274 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 275 {
 276         uintptr_t x;
 277
 278         if (SCHEDULER_STOPPED())
 279                 return (1);
 280
 281         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 282             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
 283             curthread, sx->lock_object.lo_name, file, line));
 284
 285         x = sx->sx_lock;
 286         for (;;) {
 287                 KASSERT(x != SX_LOCK_DESTROYED,
 288                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
 289                 if (!(x & SX_LOCK_SHARED))
 290                         break;
 291                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) {
 292                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
 293                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
 294                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 295                             sx, 0, 0, file, line, LOCKSTAT_READER);
 296                         TD_LOCKS_INC(curthread);
 297                         curthread->td_sx_slocks++;
 298                         return (1);
 299                 }
 300         }
 301
 302         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
 303         return (0);
 304 }
 305
 306 int
 307 sx_try_slock_(struct sx *sx, const char *file, int line)
 308 {
 309
 310         return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG));
 311 }
 312
 313 int
 314 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
 315 {
 316         uintptr_t tid, x;
 317         int error = 0;
 318
 319         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
 320             !TD_IS_IDLETHREAD(curthread),
 321             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
 322             curthread, sx->lock_object.lo_name, file, line));
 323         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 324             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
 325         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 326             line, NULL);
 327         tid = (uintptr_t)curthread;
 328         x = SX_LOCK_UNLOCKED;
 329         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 330                 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG);
 331         else
 332                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 333                     0, 0, file, line, LOCKSTAT_WRITER);
 334         if (!error) {
 335                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
 336                     file, line);
 337                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 338                 TD_LOCKS_INC(curthread);
 339         }
 340
 341         return (error);
 342 }
 343
 344 int
 345 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 346 {
 347         struct thread *td;
 348         uintptr_t tid, x;
 349         int rval;
 350         bool recursed;
 351
 352         td = curthread;
 353         tid = (uintptr_t)td;
 354         if (SCHEDULER_STOPPED_TD(td))
 355                 return (1);
 356
 357         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
 358             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
 359             curthread, sx->lock_object.lo_name, file, line));
 360         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 361             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
 362
 363         rval = 1;
 364         recursed = false;
 365         x = SX_LOCK_UNLOCKED;
 366         for (;;) {
 367                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 368                         break;
 369                 if (x == SX_LOCK_UNLOCKED)
 370                         continue;
 371                 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
 372                         sx->sx_recurse++;
 373                         atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 374                         break;
 375                 }
 376                 rval = 0;
 377                 break;
 378         }
 379
 380         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
 381         if (rval) {
 382                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 383                     file, line);
 384                 if (!recursed)
 385                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 386                             sx, 0, 0, file, line, LOCKSTAT_WRITER);
 387                 TD_LOCKS_INC(curthread);
 388         }
 389
 390         return (rval);
 391 }
 392
 393 int
 394 sx_try_xlock_(struct sx *sx, const char *file, int line)
 395 {
 396
 397         return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG));
 398 }
 399
 400 void
 401 _sx_xunlock(struct sx *sx, const char *file, int line)
 402 {
 403
 404         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 405             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
 406         _sx_assert(sx, SA_XLOCKED, file, line);
 407         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 408         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
 409             line);
 410 #if LOCK_DEBUG > 0
 411         _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line);
 412 #else
 413         __sx_xunlock(sx, curthread, file, line);
 414 #endif
 415         TD_LOCKS_DEC(curthread);
 416 }
 417
 418 /*
 419  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
 420  * This will only succeed if this thread holds a single shared lock.
 421  * Return 1 if if the upgrade succeed, 0 otherwise.
 422  */
 423 int
 424 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 425 {
 426         uintptr_t x;
 427         uintptr_t waiters;
 428         int success;
 429
 430         if (SCHEDULER_STOPPED())
 431                 return (1);
 432
 433         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 434             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
 435         _sx_assert(sx, SA_SLOCKED, file, line);
 436
 437         /*
 438          * Try to switch from one shared lock to an exclusive lock.  We need
 439          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
 440          * we will wake up the exclusive waiters when we drop the lock.
 441          */
 442         success = 0;
 443         x = SX_READ_VALUE(sx);
 444         for (;;) {
 445                 if (SX_SHARERS(x) > 1)
 446                         break;
 447                 waiters = (x & SX_LOCK_WAITERS);
 448                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
 449                     (uintptr_t)curthread | waiters)) {
 450                         success = 1;
 451                         break;
 452                 }
 453         }
 454         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
 455         if (success) {
 456                 curthread->td_sx_slocks--;
 457                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 458                     file, line);
 459                 LOCKSTAT_RECORD0(sx__upgrade, sx);
 460         }
 461         return (success);
 462 }
 463
 464 int
 465 sx_try_upgrade_(struct sx *sx, const char *file, int line)
 466 {
 467
 468         return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG));
 469 }
 470
 471 /*
 472  * Downgrade an unrecursed exclusive lock into a single shared lock.
 473  */
 474 void
 475 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 476 {
 477         uintptr_t x;
 478         int wakeup_swapper;
 479
 480         if (SCHEDULER_STOPPED())
 481                 return;
 482
 483         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 484             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
 485         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
 486 #ifndef INVARIANTS
 487         if (sx_recursed(sx))
 488                 panic("downgrade of a recursed lock");
 489 #endif
 490
 491         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
 492
 493         /*
 494          * Try to switch from an exclusive lock with no shared waiters
 495          * to one sharer with no shared waiters.  If there are
 496          * exclusive waiters, we don't need to lock the sleep queue so
 497          * long as we preserve the flag.  We do one quick try and if
 498          * that fails we grab the sleepq lock to keep the flags from
 499          * changing and do it the slow way.
 500          *
 501          * We have to lock the sleep queue if there are shared waiters
 502          * so we can wake them up.
 503          */
 504         x = sx->sx_lock;
 505         if (!(x & SX_LOCK_SHARED_WAITERS) &&
 506             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
 507             (x & SX_LOCK_EXCLUSIVE_WAITERS)))
 508                 goto out;
 509
 510         /*
 511          * Lock the sleep queue so we can read the waiters bits
 512          * without any races and wakeup any shared waiters.
 513          */
 514         sleepq_lock(&sx->lock_object);
 515
 516         /*
 517          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
 518          * shared lock.  If there are any shared waiters, wake them up.
 519          */
 520         wakeup_swapper = 0;
 521         x = sx->sx_lock;
 522         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
 523             (x & SX_LOCK_EXCLUSIVE_WAITERS));
 524         if (x & SX_LOCK_SHARED_WAITERS)
 525                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 526                     0, SQ_SHARED_QUEUE);
 527         sleepq_release(&sx->lock_object);
 528
 529         if (wakeup_swapper)
 530                 kick_proc0();
 531
 532 out:
 533         curthread->td_sx_slocks++;
 534         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 535         LOCKSTAT_RECORD0(sx__downgrade, sx);
 536 }
 537
 538 void
 539 sx_downgrade_(struct sx *sx, const char *file, int line)
 540 {
 541
 542         sx_downgrade_int(sx LOCK_FILE_LINE_ARG);
 543 }
 544
 545 #ifdef  ADAPTIVE_SX
 546 static inline void
 547 sx_drop_critical(uintptr_t x, bool *in_critical, int *extra_work)
 548 {
 549
 550         if (x & SX_LOCK_WRITE_SPINNER)
 551                 return;
 552         if (*in_critical) {
 553                 critical_exit();
 554                 *in_critical = false;
 555                 (*extra_work)--;
 556         }
 557 }
 558 #else
 559 #define sx_drop_critical(x, in_critical, extra_work) do { } while(0)
 560 #endif
 561
 562 /*
 563  * This function represents the so-called 'hard case' for sx_xlock
 564  * operation.  All 'easy case' failures are redirected to this.  Note
 565  * that ideally this would be a static function, but it needs to be
 566  * accessible from at least sx.h.
 567  */
 568 int
 569 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
 570 {
 571         GIANT_DECLARE;
 572         uintptr_t tid, setx;
 573 #ifdef ADAPTIVE_SX
 574         struct thread *owner;
 575         u_int i, n, spintries = 0;
 576         enum { READERS, WRITER } sleep_reason = READERS;
 577         bool in_critical = false;
 578 #endif
 579 #ifdef LOCK_PROFILING
 580         uint64_t waittime = 0;
 581         int contested = 0;
 582 #endif
 583         int error = 0;
 584 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
 585         struct lock_delay_arg lda;
 586 #endif
 587 #ifdef  KDTRACE_HOOKS
 588         u_int sleep_cnt = 0;
 589         int64_t sleep_time = 0;
 590         int64_t all_time = 0;
 591 #endif
 592 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 593         uintptr_t state = 0;
 594         int doing_lockprof = 0;
 595 #endif
 596         int extra_work = 0;
 597
 598         tid = (uintptr_t)curthread;
 599
 600 #ifdef KDTRACE_HOOKS
 601         if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
 602                 while (x == SX_LOCK_UNLOCKED) {
 603                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 604                                 goto out_lockstat;
 605                 }
 606                 extra_work = 1;
 607                 doing_lockprof = 1;
 608                 all_time -= lockstat_nsecs(&sx->lock_object);
 609                 state = x;
 610         }
 611 #endif
 612 #ifdef LOCK_PROFILING
 613         extra_work = 1;
 614         doing_lockprof = 1;
 615         state = x;
 616 #endif
 617
 618         if (SCHEDULER_STOPPED())
 619                 return (0);
 620
 621         if (__predict_false(x == SX_LOCK_UNLOCKED))
 622                 x = SX_READ_VALUE(sx);
 623
 624         /* If we already hold an exclusive lock, then recurse. */
 625         if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) {
 626                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
 627             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
 628                     sx->lock_object.lo_name, file, line));
 629                 sx->sx_recurse++;
 630                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 631                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 632                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
 633                 return (0);
 634         }
 635
 636         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 637                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 638                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
 639
 640 #if defined(ADAPTIVE_SX)
 641         lock_delay_arg_init(&lda, &sx_delay);
 642 #elif defined(KDTRACE_HOOKS)
 643         lock_delay_arg_init_noadapt(&lda);
 644 #endif
 645
 646 #ifdef HWPMC_HOOKS
 647         PMC_SOFT_CALL( , , lock, failed);
 648 #endif
 649         lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested,
 650             &waittime);
 651
 652 #ifndef INVARIANTS
 653         GIANT_SAVE(extra_work);
 654 #endif
 655
 656         for (;;) {
 657                 if (x == SX_LOCK_UNLOCKED) {
 658                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 659                                 break;
 660                         continue;
 661                 }
 662 #ifdef INVARIANTS
 663                 GIANT_SAVE(extra_work);
 664 #endif
 665 #ifdef KDTRACE_HOOKS
 666                 lda.spin_cnt++;
 667 #endif
 668 #ifdef ADAPTIVE_SX
 669                 if (x == (SX_LOCK_SHARED | SX_LOCK_WRITE_SPINNER)) {
 670                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 671                                 break;
 672                         continue;
 673                 }
 674
 675                 /*
 676                  * If the lock is write locked and the owner is
 677                  * running on another CPU, spin until the owner stops
 678                  * running or the state of the lock changes.
 679                  */
 680                 if ((x & SX_LOCK_SHARED) == 0) {
 681                         sx_drop_critical(x, &in_critical, &extra_work);
 682                         sleep_reason = WRITER;
 683                         owner = lv_sx_owner(x);
 684                         if (!TD_IS_RUNNING(owner))
 685                                 goto sleepq;
 686                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 687                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
 688                                     __func__, sx, owner);
 689                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 690                             "spinning", "lockname:\"%s\"",
 691                             sx->lock_object.lo_name);
 692                         do {
 693                                 lock_delay(&lda);
 694                                 x = SX_READ_VALUE(sx);
 695                                 owner = lv_sx_owner(x);
 696                         } while (owner != NULL && TD_IS_RUNNING(owner));
 697                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 698                             "running");
 699                         continue;
 700                 } else if (SX_SHARERS(x) > 0) {
 701                         sleep_reason = READERS;
 702                         if (spintries == asx_retries)
 703                                 goto sleepq;
 704                         if (!(x & SX_LOCK_WRITE_SPINNER)) {
 705                                 if (!in_critical) {
 706                                         critical_enter();
 707                                         in_critical = true;
 708                                         extra_work++;
 709                                 }
 710                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 711                                     x | SX_LOCK_WRITE_SPINNER)) {
 712                                         critical_exit();
 713                                         in_critical = false;
 714                                         extra_work--;
 715                                         continue;
 716                                 }
 717                         }
 718                         spintries++;
 719                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 720                             "spinning", "lockname:\"%s\"",
 721                             sx->lock_object.lo_name);
 722                         n = SX_SHARERS(x);
 723                         for (i = 0; i < asx_loops; i += n) {
 724                                 lock_delay_spin(n);
 725                                 x = SX_READ_VALUE(sx);
 726                                 if (!(x & SX_LOCK_WRITE_SPINNER))
 727                                         break;
 728                                 if (!(x & SX_LOCK_SHARED))
 729                                         break;
 730                                 n = SX_SHARERS(x);
 731                                 if (n == 0)
 732                                         break;
 733                         }
 734 #ifdef KDTRACE_HOOKS
 735                         lda.spin_cnt += i;
 736 #endif
 737                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 738                             "running");
 739                         if (i < asx_loops)
 740                                 continue;
 741                 }
 742 sleepq:
 743 #endif
 744                 sleepq_lock(&sx->lock_object);
 745                 x = SX_READ_VALUE(sx);
 746 retry_sleepq:
 747
 748                 /*
 749                  * If the lock was released while spinning on the
 750                  * sleep queue chain lock, try again.
 751                  */
 752                 if (x == SX_LOCK_UNLOCKED) {
 753                         sleepq_release(&sx->lock_object);
 754                         sx_drop_critical(x, &in_critical, &extra_work);
 755                         continue;
 756                 }
 757
 758 #ifdef ADAPTIVE_SX
 759                 /*
 760                  * The current lock owner might have started executing
 761                  * on another CPU (or the lock could have changed
 762                  * owners) while we were waiting on the sleep queue
 763                  * chain lock.  If so, drop the sleep queue lock and try
 764                  * again.
 765                  */
 766                 if (!(x & SX_LOCK_SHARED)) {
 767                         owner = (struct thread *)SX_OWNER(x);
 768                         if (TD_IS_RUNNING(owner)) {
 769                                 sleepq_release(&sx->lock_object);
 770                                 sx_drop_critical(x, &in_critical,
 771                                     &extra_work);
 772                                 continue;
 773                         }
 774                 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) {
 775                         sleepq_release(&sx->lock_object);
 776                         sx_drop_critical(x, &in_critical, &extra_work);
 777                         continue;
 778                 }
 779 #endif
 780
 781                 /*
 782                  * If an exclusive lock was released with both shared
 783                  * and exclusive waiters and a shared waiter hasn't
 784                  * woken up and acquired the lock yet, sx_lock will be
 785                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 786                  * If we see that value, try to acquire it once.  Note
 787                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 788                  * as there are other exclusive waiters still.  If we
 789                  * fail, restart the loop.
 790                  */
 791                 setx = x & (SX_LOCK_WAITERS | SX_LOCK_WRITE_SPINNER);
 792                 if ((x & ~setx) == SX_LOCK_SHARED) {
 793                         setx &= ~SX_LOCK_WRITE_SPINNER;
 794                         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid | setx))
 795                                 goto retry_sleepq;
 796                         sleepq_release(&sx->lock_object);
 797                         CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 798                             __func__, sx);
 799                         break;
 800                 }
 801
 802 #ifdef ADAPTIVE_SX
 803                 /*
 804                  * It is possible we set the SX_LOCK_WRITE_SPINNER bit.
 805                  * It is an invariant that when the bit is set, there is
 806                  * a writer ready to grab the lock. Thus clear the bit since
 807                  * we are going to sleep.
 808                  */
 809                 if (in_critical) {
 810                         if ((x & SX_LOCK_WRITE_SPINNER) ||
 811                             !((x & SX_LOCK_EXCLUSIVE_WAITERS))) {
 812                                 setx = x & ~SX_LOCK_WRITE_SPINNER;
 813                                 setx |= SX_LOCK_EXCLUSIVE_WAITERS;
 814                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 815                                     setx)) {
 816                                         goto retry_sleepq;
 817                                 }
 818                         }
 819                         critical_exit();
 820                         in_critical = false;
 821                 } else {
 822 #endif
 823                         /*
 824                          * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 825                          * than loop back and retry.
 826                          */
 827                         if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 828                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 829                                     x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 830                                         goto retry_sleepq;
 831                                 }
 832                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 833                                         CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 834                                             __func__, sx);
 835                         }
 836 #ifdef ADAPTIVE_SX
 837                 }
 838 #endif
 839
 840                 /*
 841                  * Since we have been unable to acquire the exclusive
 842                  * lock and the exclusive waiters flag is set, we have
 843                  * to sleep.
 844                  */
 845                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 846                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 847                             __func__, sx);
 848
 849 #ifdef KDTRACE_HOOKS
 850                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 851 #endif
 852                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 853                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 854                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 855                 if (!(opts & SX_INTERRUPTIBLE))
 856                         sleepq_wait(&sx->lock_object, 0);
 857                 else
 858                         error = sleepq_wait_sig(&sx->lock_object, 0);
 859 #ifdef KDTRACE_HOOKS
 860                 sleep_time += lockstat_nsecs(&sx->lock_object);
 861                 sleep_cnt++;
 862 #endif
 863                 if (error) {
 864                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 865                                 CTR2(KTR_LOCK,
 866                         "%s: interruptible sleep by %p suspended by signal",
 867                                     __func__, sx);
 868                         break;
 869                 }
 870                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 871                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 872                             __func__, sx);
 873                 x = SX_READ_VALUE(sx);
 874         }
 875         if (__predict_true(!extra_work))
 876                 return (error);
 877 #ifdef ADAPTIVE_SX
 878         if (in_critical)
 879                 critical_exit();
 880 #endif
 881         GIANT_RESTORE();
 882 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 883         if (__predict_true(!doing_lockprof))
 884                 return (error);
 885 #endif
 886 #ifdef KDTRACE_HOOKS
 887         all_time += lockstat_nsecs(&sx->lock_object);
 888         if (sleep_time)
 889                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
 890                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 891                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 892         if (lda.spin_cnt > sleep_cnt)
 893                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
 894                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 895                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 896 out_lockstat:
 897 #endif
 898         if (!error)
 899                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 900                     contested, waittime, file, line, LOCKSTAT_WRITER);
 901         return (error);
 902 }
 903
 904 /*
 905  * This function represents the so-called 'hard case' for sx_xunlock
 906  * operation.  All 'easy case' failures are redirected to this.  Note
 907  * that ideally this would be a static function, but it needs to be
 908  * accessible from at least sx.h.
 909  */
 910 void
 911 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
 912 {
 913         uintptr_t tid, setx;
 914         int queue, wakeup_swapper;
 915
 916         if (SCHEDULER_STOPPED())
 917                 return;
 918
 919         tid = (uintptr_t)curthread;
 920
 921         if (__predict_false(x == tid))
 922                 x = SX_READ_VALUE(sx);
 923
 924         MPASS(!(x & SX_LOCK_SHARED));
 925
 926         if (__predict_false(x & SX_LOCK_RECURSED)) {
 927                 /* The lock is recursed, unrecurse one level. */
 928                 if ((--sx->sx_recurse) == 0)
 929                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 930                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 931                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 932                 return;
 933         }
 934
 935         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
 936         if (x == tid &&
 937             atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
 938                 return;
 939
 940         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 941                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 942
 943         sleepq_lock(&sx->lock_object);
 944         x = SX_READ_VALUE(sx);
 945         MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS));
 946
 947         /*
 948          * The wake up algorithm here is quite simple and probably not
 949          * ideal.  It gives precedence to shared waiters if they are
 950          * present.  For this condition, we have to preserve the
 951          * state of the exclusive waiters flag.
 952          * If interruptible sleeps left the shared queue empty avoid a
 953          * starvation for the threads sleeping on the exclusive queue by giving
 954          * them precedence and cleaning up the shared waiters bit anyway.
 955          */
 956         setx = SX_LOCK_UNLOCKED;
 957         queue = SQ_SHARED_QUEUE;
 958         if ((x & SX_LOCK_EXCLUSIVE_WAITERS) != 0 &&
 959             sleepq_sleepcnt(&sx->lock_object, SQ_EXCLUSIVE_QUEUE) != 0) {
 960                 queue = SQ_EXCLUSIVE_QUEUE;
 961                 setx |= (x & SX_LOCK_SHARED_WAITERS);
 962         }
 963         atomic_store_rel_ptr(&sx->sx_lock, setx);
 964
 965         /* Wake up all the waiters for the specific queue. */
 966         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 967                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 968                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 969                     "exclusive");
 970
 971         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 972             queue);
 973         sleepq_release(&sx->lock_object);
 974         if (wakeup_swapper)
 975                 kick_proc0();
 976 }
 977
 978 static bool __always_inline
 979 __sx_can_read(struct thread *td, uintptr_t x, bool fp)
 980 {
 981
 982         if ((x & (SX_LOCK_SHARED | SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_WRITE_SPINNER))
 983                         == SX_LOCK_SHARED)
 984                 return (true);
 985         if (!fp && td->td_sx_slocks && (x & SX_LOCK_SHARED))
 986                 return (true);
 987         return (false);
 988 }
 989
 990 static bool __always_inline
 991 __sx_slock_try(struct sx *sx, struct thread *td, uintptr_t *xp, bool fp
 992     LOCK_FILE_LINE_ARG_DEF)
 993 {
 994
 995         /*
 996          * If no other thread has an exclusive lock then try to bump up
 997          * the count of sharers.  Since we have to preserve the state
 998          * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
 999          * shared lock loop back and retry.
1000          */
1001         while (__sx_can_read(td, *xp, fp)) {
1002                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp,
1003                     *xp + SX_ONE_SHARER)) {
1004                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1005                                 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p",
1006                                     __func__, sx, (void *)*xp,
1007                                     (void *)(*xp + SX_ONE_SHARER));
1008                         td->td_sx_slocks++;
1009                         return (true);
1010                 }
1011         }
1012         return (false);
1013 }
1014
1015 static int __noinline
1016 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
1017 {
1018         GIANT_DECLARE;
1019         struct thread *td;
1020 #ifdef ADAPTIVE_SX
1021         struct thread *owner;
1022         u_int i, n, spintries = 0;
1023 #endif
1024 #ifdef LOCK_PROFILING
1025         uint64_t waittime = 0;
1026         int contested = 0;
1027 #endif
1028         int error = 0;
1029 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
1030         struct lock_delay_arg lda;
1031 #endif
1032 #ifdef KDTRACE_HOOKS
1033         u_int sleep_cnt = 0;
1034         int64_t sleep_time = 0;
1035         int64_t all_time = 0;
1036 #endif
1037 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1038         uintptr_t state = 0;
1039 #endif
1040         int extra_work = 0;
1041
1042         td = curthread;
1043
1044 #ifdef KDTRACE_HOOKS
1045         if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
1046                 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1047                         goto out_lockstat;
1048                 extra_work = 1;
1049                 all_time -= lockstat_nsecs(&sx->lock_object);
1050                 state = x;
1051         }
1052 #endif
1053 #ifdef LOCK_PROFILING
1054         extra_work = 1;
1055         state = x;
1056 #endif
1057
1058         if (SCHEDULER_STOPPED())
1059                 return (0);
1060
1061 #if defined(ADAPTIVE_SX)
1062         lock_delay_arg_init(&lda, &sx_delay);
1063 #elif defined(KDTRACE_HOOKS)
1064         lock_delay_arg_init_noadapt(&lda);
1065 #endif
1066
1067 #ifdef HWPMC_HOOKS
1068         PMC_SOFT_CALL( , , lock, failed);
1069 #endif
1070         lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested,
1071             &waittime);
1072
1073 #ifndef INVARIANTS
1074         GIANT_SAVE(extra_work);
1075 #endif
1076
1077         /*
1078          * As with rwlocks, we don't make any attempt to try to block
1079          * shared locks once there is an exclusive waiter.
1080          */
1081         for (;;) {
1082                 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1083                         break;
1084 #ifdef INVARIANTS
1085                 GIANT_SAVE(extra_work);
1086 #endif
1087 #ifdef KDTRACE_HOOKS
1088                 lda.spin_cnt++;
1089 #endif
1090
1091 #ifdef ADAPTIVE_SX
1092                 /*
1093                  * If the owner is running on another CPU, spin until
1094                  * the owner stops running or the state of the lock
1095                  * changes.
1096                  */
1097                 if ((x & SX_LOCK_SHARED) == 0) {
1098                         owner = lv_sx_owner(x);
1099                         if (TD_IS_RUNNING(owner)) {
1100                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1101                                         CTR3(KTR_LOCK,
1102                                             "%s: spinning on %p held by %p",
1103                                             __func__, sx, owner);
1104                                 KTR_STATE1(KTR_SCHED, "thread",
1105                                     sched_tdname(curthread), "spinning",
1106                                     "lockname:\"%s\"", sx->lock_object.lo_name);
1107                                 do {
1108                                         lock_delay(&lda);
1109                                         x = SX_READ_VALUE(sx);
1110                                         owner = lv_sx_owner(x);
1111                                 } while (owner != NULL && TD_IS_RUNNING(owner));
1112                                 KTR_STATE0(KTR_SCHED, "thread",
1113                                     sched_tdname(curthread), "running");
1114                                 continue;
1115                         }
1116                 } else {
1117                         if ((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) {
1118                                 MPASS(!__sx_can_read(td, x, false));
1119                                 lock_delay_spin(2);
1120                                 x = SX_READ_VALUE(sx);
1121                                 continue;
1122                         }
1123                         if (spintries < asx_retries) {
1124                                 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1125                                     "spinning", "lockname:\"%s\"",
1126                                     sx->lock_object.lo_name);
1127                                 n = SX_SHARERS(x);
1128                                 for (i = 0; i < asx_loops; i += n) {
1129                                         lock_delay_spin(n);
1130                                         x = SX_READ_VALUE(sx);
1131                                         if (!(x & SX_LOCK_SHARED))
1132                                                 break;
1133                                         n = SX_SHARERS(x);
1134                                         if (n == 0)
1135                                                 break;
1136                                         if (__sx_can_read(td, x, false))
1137                                                 break;
1138                                 }
1139 #ifdef KDTRACE_HOOKS
1140                                 lda.spin_cnt += i;
1141 #endif
1142                                 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1143                                     "running");
1144                                 if (i < asx_loops)
1145                                         continue;
1146                         }
1147                 }
1148 #endif
1149
1150                 /*
1151                  * Some other thread already has an exclusive lock, so
1152                  * start the process of blocking.
1153                  */
1154                 sleepq_lock(&sx->lock_object);
1155                 x = SX_READ_VALUE(sx);
1156 retry_sleepq:
1157                 if (((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) ||
1158                     __sx_can_read(td, x, false)) {
1159                         sleepq_release(&sx->lock_object);
1160                         continue;
1161                 }
1162
1163 #ifdef ADAPTIVE_SX
1164                 /*
1165                  * If the owner is running on another CPU, spin until
1166                  * the owner stops running or the state of the lock
1167                  * changes.
1168                  */
1169                 if (!(x & SX_LOCK_SHARED)) {
1170                         owner = (struct thread *)SX_OWNER(x);
1171                         if (TD_IS_RUNNING(owner)) {
1172                                 sleepq_release(&sx->lock_object);
1173                                 x = SX_READ_VALUE(sx);
1174                                 continue;
1175                         }
1176                 }
1177 #endif
1178
1179                 /*
1180                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
1181                  * fail to set it drop the sleep queue lock and loop
1182                  * back.
1183                  */
1184                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
1185                         if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
1186                             x | SX_LOCK_SHARED_WAITERS))
1187                                 goto retry_sleepq;
1188                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1189                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
1190                                     __func__, sx);
1191                 }
1192
1193                 /*
1194                  * Since we have been unable to acquire the shared lock,
1195                  * we have to sleep.
1196                  */
1197                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1198                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
1199                             __func__, sx);
1200
1201 #ifdef KDTRACE_HOOKS
1202                 sleep_time -= lockstat_nsecs(&sx->lock_object);
1203 #endif
1204                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1205                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1206                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1207                 if (!(opts & SX_INTERRUPTIBLE))
1208                         sleepq_wait(&sx->lock_object, 0);
1209                 else
1210                         error = sleepq_wait_sig(&sx->lock_object, 0);
1211 #ifdef KDTRACE_HOOKS
1212                 sleep_time += lockstat_nsecs(&sx->lock_object);
1213                 sleep_cnt++;
1214 #endif
1215                 if (error) {
1216                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1217                                 CTR2(KTR_LOCK,
1218                         "%s: interruptible sleep by %p suspended by signal",
1219                                     __func__, sx);
1220                         break;
1221                 }
1222                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1223                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1224                             __func__, sx);
1225                 x = SX_READ_VALUE(sx);
1226         }
1227 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1228         if (__predict_true(!extra_work))
1229                 return (error);
1230 #endif
1231 #ifdef KDTRACE_HOOKS
1232         all_time += lockstat_nsecs(&sx->lock_object);
1233         if (sleep_time)
1234                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
1235                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1236                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1237         if (lda.spin_cnt > sleep_cnt)
1238                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
1239                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1240                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1241 out_lockstat:
1242 #endif
1243         if (error == 0) {
1244                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
1245                     contested, waittime, file, line, LOCKSTAT_READER);
1246         }
1247         GIANT_RESTORE();
1248         return (error);
1249 }
1250
1251 int
1252 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF)
1253 {
1254         struct thread *td;
1255         uintptr_t x;
1256         int error;
1257
1258         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
1259             !TD_IS_IDLETHREAD(curthread),
1260             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
1261             curthread, sx->lock_object.lo_name, file, line));
1262         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1263             ("sx_slock() of destroyed sx @ %s:%d", file, line));
1264         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
1265
1266         error = 0;
1267         td = curthread;
1268         x = SX_READ_VALUE(sx);
1269         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) ||
1270             !__sx_slock_try(sx, td, &x, true LOCK_FILE_LINE_ARG)))
1271                 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG);
1272         else
1273                 lock_profile_obtain_lock_success(&sx->lock_object, false, 0, 0,
1274                     file, line);
1275         if (error == 0) {
1276                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
1277                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
1278                 TD_LOCKS_INC(curthread);
1279         }
1280         return (error);
1281 }
1282
1283 int
1284 _sx_slock(struct sx *sx, int opts, const char *file, int line)
1285 {
1286
1287         return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG));
1288 }
1289
1290 static bool __always_inline
1291 _sx_sunlock_try(struct sx *sx, struct thread *td, uintptr_t *xp)
1292 {
1293
1294         for (;;) {
1295                 if (SX_SHARERS(*xp) > 1 || !(*xp & SX_LOCK_WAITERS)) {
1296                         if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp,
1297                             *xp - SX_ONE_SHARER)) {
1298                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1299                                         CTR4(KTR_LOCK,
1300                                             "%s: %p succeeded %p -> %p",
1301                                             __func__, sx, (void *)*xp,
1302                                             (void *)(*xp - SX_ONE_SHARER));
1303                                 td->td_sx_slocks--;
1304                                 return (true);
1305                         }
1306                         continue;
1307                 }
1308                 break;
1309         }
1310         return (false);
1311 }
1312
1313 static void __noinline
1314 _sx_sunlock_hard(struct sx *sx, struct thread *td, uintptr_t x
1315     LOCK_FILE_LINE_ARG_DEF)
1316 {
1317         int wakeup_swapper = 0;
1318         uintptr_t setx, queue;
1319
1320         if (SCHEDULER_STOPPED())
1321                 return;
1322
1323         if (_sx_sunlock_try(sx, td, &x))
1324                 goto out_lockstat;
1325
1326         sleepq_lock(&sx->lock_object);
1327         x = SX_READ_VALUE(sx);
1328         for (;;) {
1329                 if (_sx_sunlock_try(sx, td, &x))
1330                         break;
1331
1332                 /*
1333                  * Wake up semantic here is quite simple:
1334                  * Just wake up all the exclusive waiters.
1335                  * Note that the state of the lock could have changed,
1336                  * so if it fails loop back and retry.
1337                  */
1338                 setx = SX_LOCK_UNLOCKED;
1339                 queue = SQ_SHARED_QUEUE;
1340                 if (x & SX_LOCK_EXCLUSIVE_WAITERS) {
1341                         setx |= (x & SX_LOCK_SHARED_WAITERS);
1342                         queue = SQ_EXCLUSIVE_QUEUE;
1343                 }
1344                 setx |= (x & SX_LOCK_WRITE_SPINNER);
1345                 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx))
1346                         continue;
1347                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1348                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1349                             "exclusive queue", __func__, sx);
1350                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1351                     0, queue);
1352                 td->td_sx_slocks--;
1353                 break;
1354         }
1355         sleepq_release(&sx->lock_object);
1356         if (wakeup_swapper)
1357                 kick_proc0();
1358 out_lockstat:
1359         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
1360 }
1361
1362 void
1363 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
1364 {
1365         struct thread *td;
1366         uintptr_t x;
1367
1368         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1369             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
1370         _sx_assert(sx, SA_SLOCKED, file, line);
1371         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
1372         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
1373
1374         td = curthread;
1375         x = SX_READ_VALUE(sx);
1376         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) ||
1377             !_sx_sunlock_try(sx, td, &x)))
1378                 _sx_sunlock_hard(sx, td, x LOCK_FILE_LINE_ARG);
1379         else
1380                 lock_profile_release_lock(&sx->lock_object, false);
1381
1382         TD_LOCKS_DEC(curthread);
1383 }
1384
1385 void
1386 _sx_sunlock(struct sx *sx, const char *file, int line)
1387 {
1388
1389         _sx_sunlock_int(sx LOCK_FILE_LINE_ARG);
1390 }
1391
1392 #ifdef INVARIANT_SUPPORT
1393 #ifndef INVARIANTS
1394 #undef  _sx_assert
1395 #endif
1396
1397 /*
1398  * In the non-WITNESS case, sx_assert() can only detect that at least
1399  * *some* thread owns an slock, but it cannot guarantee that *this*
1400  * thread owns an slock.
1401  */
1402 void
1403 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1404 {
1405 #ifndef WITNESS
1406         int slocked = 0;
1407 #endif
1408
1409         if (SCHEDULER_STOPPED())
1410                 return;
1411         switch (what) {
1412         case SA_SLOCKED:
1413         case SA_SLOCKED | SA_NOTRECURSED:
1414         case SA_SLOCKED | SA_RECURSED:
1415 #ifndef WITNESS
1416                 slocked = 1;
1417                 /* FALLTHROUGH */
1418 #endif
1419         case SA_LOCKED:
1420         case SA_LOCKED | SA_NOTRECURSED:
1421         case SA_LOCKED | SA_RECURSED:
1422 #ifdef WITNESS
1423                 witness_assert(&sx->lock_object, what, file, line);
1424 #else
1425                 /*
1426                  * If some other thread has an exclusive lock or we
1427                  * have one and are asserting a shared lock, fail.
1428                  * Also, if no one has a lock at all, fail.
1429                  */
1430                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1431                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1432                     sx_xholder(sx) != curthread)))
1433                         panic("Lock %s not %slocked @ %s:%d\n",
1434                             sx->lock_object.lo_name, slocked ? "share " : "",
1435                             file, line);
1436
1437                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1438                         if (sx_recursed(sx)) {
1439                                 if (what & SA_NOTRECURSED)
1440                                         panic("Lock %s recursed @ %s:%d\n",
1441                                             sx->lock_object.lo_name, file,
1442                                             line);
1443                         } else if (what & SA_RECURSED)
1444                                 panic("Lock %s not recursed @ %s:%d\n",
1445                                     sx->lock_object.lo_name, file, line);
1446                 }
1447 #endif
1448                 break;
1449         case SA_XLOCKED:
1450         case SA_XLOCKED | SA_NOTRECURSED:
1451         case SA_XLOCKED | SA_RECURSED:
1452                 if (sx_xholder(sx) != curthread)
1453                         panic("Lock %s not exclusively locked @ %s:%d\n",
1454                             sx->lock_object.lo_name, file, line);
1455                 if (sx_recursed(sx)) {
1456                         if (what & SA_NOTRECURSED)
1457                                 panic("Lock %s recursed @ %s:%d\n",
1458                                     sx->lock_object.lo_name, file, line);
1459                 } else if (what & SA_RECURSED)
1460                         panic("Lock %s not recursed @ %s:%d\n",
1461                             sx->lock_object.lo_name, file, line);
1462                 break;
1463         case SA_UNLOCKED:
1464 #ifdef WITNESS
1465                 witness_assert(&sx->lock_object, what, file, line);
1466 #else
1467                 /*
1468                  * If we hold an exclusve lock fail.  We can't
1469                  * reliably check to see if we hold a shared lock or
1470                  * not.
1471                  */
1472                 if (sx_xholder(sx) == curthread)
1473                         panic("Lock %s exclusively locked @ %s:%d\n",
1474                             sx->lock_object.lo_name, file, line);
1475 #endif
1476                 break;
1477         default:
1478                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1479                     line);
1480         }
1481 }
1482 #endif  /* INVARIANT_SUPPORT */
1483
1484 #ifdef DDB
1485 static void
1486 db_show_sx(const struct lock_object *lock)
1487 {
1488         struct thread *td;
1489         const struct sx *sx;
1490
1491         sx = (const struct sx *)lock;
1492
1493         db_printf(" state: ");
1494         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1495                 db_printf("UNLOCKED\n");
1496         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1497                 db_printf("DESTROYED\n");
1498                 return;
1499         } else if (sx->sx_lock & SX_LOCK_SHARED)
1500                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1501         else {
1502                 td = sx_xholder(sx);
1503                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1504                     td->td_tid, td->td_proc->p_pid, td->td_name);
1505                 if (sx_recursed(sx))
1506                         db_printf(" recursed: %d\n", sx->sx_recurse);
1507         }
1508
1509         db_printf(" waiters: ");
1510         switch(sx->sx_lock &
1511             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1512         case SX_LOCK_SHARED_WAITERS:
1513                 db_printf("shared\n");
1514                 break;
1515         case SX_LOCK_EXCLUSIVE_WAITERS:
1516                 db_printf("exclusive\n");
1517                 break;
1518         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1519                 db_printf("exclusive and shared\n");
1520                 break;
1521         default:
1522                 db_printf("none\n");
1523         }
1524 }
1525
1526 /*
1527  * Check to see if a thread that is blocked on a sleep queue is actually
1528  * blocked on an sx lock.  If so, output some details and return true.
1529  * If the lock has an exclusive owner, return that in *ownerp.
1530  */
1531 int
1532 sx_chain(struct thread *td, struct thread **ownerp)
1533 {
1534         const struct sx *sx;
1535
1536         /*
1537          * Check to see if this thread is blocked on an sx lock.
1538          * First, we check the lock class.  If that is ok, then we
1539          * compare the lock name against the wait message.
1540          */
1541         sx = td->td_wchan;
1542         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1543             sx->lock_object.lo_name != td->td_wmesg)
1544                 return (0);
1545
1546         /* We think we have an sx lock, so output some details. */
1547         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1548         *ownerp = sx_xholder(sx);
1549         if (sx->sx_lock & SX_LOCK_SHARED)
1550                 db_printf("SLOCK (count %ju)\n",
1551                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1552         else
1553                 db_printf("XLOCK\n");
1554         return (1);
1555 }
1556 #endif