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/param.h>
  46 #include <sys/systm.h>
  47 #include <sys/kdb.h>
  48 #include <sys/kernel.h>
  49 #include <sys/ktr.h>
  50 #include <sys/lock.h>
  51 #include <sys/mutex.h>
  52 #include <sys/proc.h>
  53 #include <sys/sched.h>
  54 #include <sys/sleepqueue.h>
  55 #include <sys/sx.h>
  56 #include <sys/smp.h>
  57 #include <sys/sysctl.h>
  58
  59 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  60 #include <machine/cpu.h>
  61 #endif
  62
  63 #ifdef DDB
  64 #include <ddb/ddb.h>
  65 #endif
  66
  67 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  68 #define ADAPTIVE_SX
  69 #endif
  70
  71 #ifdef HWPMC_HOOKS
  72 #include <sys/pmckern.h>
  73 PMC_SOFT_DECLARE( , , lock, failed);
  74 #endif
  75
  76 /* Handy macros for sleep queues. */
  77 #define SQ_EXCLUSIVE_QUEUE      0
  78 #define SQ_SHARED_QUEUE         1
  79
  80 /*
  81  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  82  * drop Giant anytime we have to sleep or if we adaptively spin.
  83  */
  84 #define GIANT_DECLARE                                                   \
  85         int _giantcnt = 0;                                              \
  86         WITNESS_SAVE_DECL(Giant)                                        \
  87
  88 #define GIANT_SAVE(work) do {                                           \
  89         if (__predict_false(mtx_owned(&Giant))) {                       \
  90                 work++;                                                 \
  91                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
  92                 while (mtx_owned(&Giant)) {                             \
  93                         _giantcnt++;                                    \
  94                         mtx_unlock(&Giant);                             \
  95                 }                                                       \
  96         }                                                               \
  97 } while (0)
  98
  99 #define GIANT_RESTORE() do {                                            \
 100         if (_giantcnt > 0) {                                            \
 101                 mtx_assert(&Giant, MA_NOTOWNED);                        \
 102                 while (_giantcnt--)                                     \
 103                         mtx_lock(&Giant);                               \
 104                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
 105         }                                                               \
 106 } while (0)
 107
 108 /*
 109  * Returns true if an exclusive lock is recursed.  It assumes
 110  * curthread currently has an exclusive lock.
 111  */
 112 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
 113
 114 static void     assert_sx(const struct lock_object *lock, int what);
 115 #ifdef DDB
 116 static void     db_show_sx(const struct lock_object *lock);
 117 #endif
 118 static void     lock_sx(struct lock_object *lock, uintptr_t how);
 119 #ifdef KDTRACE_HOOKS
 120 static int      owner_sx(const struct lock_object *lock, struct thread **owner);
 121 #endif
 122 static uintptr_t unlock_sx(struct lock_object *lock);
 123
 124 struct lock_class lock_class_sx = {
 125         .lc_name = "sx",
 126         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
 127         .lc_assert = assert_sx,
 128 #ifdef DDB
 129         .lc_ddb_show = db_show_sx,
 130 #endif
 131         .lc_lock = lock_sx,
 132         .lc_unlock = unlock_sx,
 133 #ifdef KDTRACE_HOOKS
 134         .lc_owner = owner_sx,
 135 #endif
 136 };
 137
 138 #ifndef INVARIANTS
 139 #define _sx_assert(sx, what, file, line)
 140 #endif
 141
 142 #ifdef ADAPTIVE_SX
 143 #ifdef SX_CUSTOM_BACKOFF
 144 static u_short __read_frequently asx_retries;
 145 static u_short __read_frequently asx_loops;
 146 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD | CTLFLAG_MPSAFE, NULL,
 147     "sxlock debugging");
 148 SYSCTL_U16(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
 149 SYSCTL_U16(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
 150
 151 static struct lock_delay_config __read_frequently sx_delay;
 152
 153 SYSCTL_U16(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base,
 154     0, "");
 155 SYSCTL_U16(_debug_sx, OID_AUTO, delay_max, CTLFLAG_RW, &sx_delay.max,
 156     0, "");
 157
 158 static void
 159 sx_lock_delay_init(void *arg __unused)
 160 {
 161
 162         lock_delay_default_init(&sx_delay);
 163         asx_retries = 10;
 164         asx_loops = max(10000, sx_delay.max);
 165 }
 166 LOCK_DELAY_SYSINIT(sx_lock_delay_init);
 167 #else
 168 #define sx_delay        locks_delay
 169 #define asx_retries     locks_delay_retries
 170 #define asx_loops       locks_delay_loops
 171 #endif
 172 #endif
 173
 174 void
 175 assert_sx(const struct lock_object *lock, int what)
 176 {
 177
 178         sx_assert((const struct sx *)lock, what);
 179 }
 180
 181 void
 182 lock_sx(struct lock_object *lock, uintptr_t how)
 183 {
 184         struct sx *sx;
 185
 186         sx = (struct sx *)lock;
 187         if (how)
 188                 sx_slock(sx);
 189         else
 190                 sx_xlock(sx);
 191 }
 192
 193 uintptr_t
 194 unlock_sx(struct lock_object *lock)
 195 {
 196         struct sx *sx;
 197
 198         sx = (struct sx *)lock;
 199         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
 200         if (sx_xlocked(sx)) {
 201                 sx_xunlock(sx);
 202                 return (0);
 203         } else {
 204                 sx_sunlock(sx);
 205                 return (1);
 206         }
 207 }
 208
 209 #ifdef KDTRACE_HOOKS
 210 int
 211 owner_sx(const struct lock_object *lock, struct thread **owner)
 212 {
 213         const struct sx *sx;
 214         uintptr_t x;
 215
 216         sx = (const struct sx *)lock;
 217         x = sx->sx_lock;
 218         *owner = NULL;
 219         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
 220             ((*owner = (struct thread *)SX_OWNER(x)) != NULL));
 221 }
 222 #endif
 223
 224 void
 225 sx_sysinit(void *arg)
 226 {
 227         struct sx_args *sargs = arg;
 228
 229         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
 230 }
 231
 232 void
 233 sx_init_flags(struct sx *sx, const char *description, int opts)
 234 {
 235         int flags;
 236
 237         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 238             SX_NOPROFILE | SX_NEW)) == 0);
 239         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
 240             ("%s: sx_lock not aligned for %s: %p", __func__, description,
 241             &sx->sx_lock));
 242
 243         flags = LO_SLEEPABLE | LO_UPGRADABLE;
 244         if (opts & SX_DUPOK)
 245                 flags |= LO_DUPOK;
 246         if (opts & SX_NOPROFILE)
 247                 flags |= LO_NOPROFILE;
 248         if (!(opts & SX_NOWITNESS))
 249                 flags |= LO_WITNESS;
 250         if (opts & SX_RECURSE)
 251                 flags |= LO_RECURSABLE;
 252         if (opts & SX_QUIET)
 253                 flags |= LO_QUIET;
 254         if (opts & SX_NEW)
 255                 flags |= LO_NEW;
 256
 257         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
 258         sx->sx_lock = SX_LOCK_UNLOCKED;
 259         sx->sx_recurse = 0;
 260 }
 261
 262 void
 263 sx_destroy(struct sx *sx)
 264 {
 265
 266         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
 267         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
 268         sx->sx_lock = SX_LOCK_DESTROYED;
 269         lock_destroy(&sx->lock_object);
 270 }
 271
 272 int
 273 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 274 {
 275         uintptr_t x;
 276
 277         if (SCHEDULER_STOPPED())
 278                 return (1);
 279
 280         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 281             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
 282             curthread, sx->lock_object.lo_name, file, line));
 283
 284         x = sx->sx_lock;
 285         for (;;) {
 286                 KASSERT(x != SX_LOCK_DESTROYED,
 287                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
 288                 if (!(x & SX_LOCK_SHARED))
 289                         break;
 290                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) {
 291                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
 292                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
 293                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 294                             sx, 0, 0, file, line, LOCKSTAT_READER);
 295                         TD_LOCKS_INC(curthread);
 296                         curthread->td_sx_slocks++;
 297                         return (1);
 298                 }
 299         }
 300
 301         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
 302         return (0);
 303 }
 304
 305 int
 306 sx_try_slock_(struct sx *sx, const char *file, int line)
 307 {
 308
 309         return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG));
 310 }
 311
 312 int
 313 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
 314 {
 315         uintptr_t tid, x;
 316         int error = 0;
 317
 318         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
 319             !TD_IS_IDLETHREAD(curthread),
 320             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
 321             curthread, sx->lock_object.lo_name, file, line));
 322         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 323             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
 324         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 325             line, NULL);
 326         tid = (uintptr_t)curthread;
 327         x = SX_LOCK_UNLOCKED;
 328         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 329                 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG);
 330         else
 331                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 332                     0, 0, file, line, LOCKSTAT_WRITER);
 333         if (!error) {
 334                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
 335                     file, line);
 336                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 337                 TD_LOCKS_INC(curthread);
 338         }
 339
 340         return (error);
 341 }
 342
 343 int
 344 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 345 {
 346         struct thread *td;
 347         uintptr_t tid, x;
 348         int rval;
 349         bool recursed;
 350
 351         td = curthread;
 352         tid = (uintptr_t)td;
 353         if (SCHEDULER_STOPPED())
 354                 return (1);
 355
 356         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
 357             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
 358             curthread, sx->lock_object.lo_name, file, line));
 359         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 360             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
 361
 362         rval = 1;
 363         recursed = false;
 364         x = SX_LOCK_UNLOCKED;
 365         for (;;) {
 366                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 367                         break;
 368                 if (x == SX_LOCK_UNLOCKED)
 369                         continue;
 370                 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
 371                         sx->sx_recurse++;
 372                         atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 373                         break;
 374                 }
 375                 rval = 0;
 376                 break;
 377         }
 378
 379         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
 380         if (rval) {
 381                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 382                     file, line);
 383                 if (!recursed)
 384                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 385                             sx, 0, 0, file, line, LOCKSTAT_WRITER);
 386                 TD_LOCKS_INC(curthread);
 387         }
 388
 389         return (rval);
 390 }
 391
 392 int
 393 sx_try_xlock_(struct sx *sx, const char *file, int line)
 394 {
 395
 396         return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG));
 397 }
 398
 399 void
 400 _sx_xunlock(struct sx *sx, const char *file, int line)
 401 {
 402
 403         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 404             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
 405         _sx_assert(sx, SA_XLOCKED, file, line);
 406         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 407         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
 408             line);
 409 #if LOCK_DEBUG > 0
 410         _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line);
 411 #else
 412         __sx_xunlock(sx, curthread, file, line);
 413 #endif
 414         TD_LOCKS_DEC(curthread);
 415 }
 416
 417 /*
 418  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
 419  * This will only succeed if this thread holds a single shared lock.
 420  * Return 1 if if the upgrade succeed, 0 otherwise.
 421  */
 422 int
 423 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 424 {
 425         uintptr_t x;
 426         uintptr_t waiters;
 427         int success;
 428
 429         if (SCHEDULER_STOPPED())
 430                 return (1);
 431
 432         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 433             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
 434         _sx_assert(sx, SA_SLOCKED, file, line);
 435
 436         /*
 437          * Try to switch from one shared lock to an exclusive lock.  We need
 438          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
 439          * we will wake up the exclusive waiters when we drop the lock.
 440          */
 441         success = 0;
 442         x = SX_READ_VALUE(sx);
 443         for (;;) {
 444                 if (SX_SHARERS(x) > 1)
 445                         break;
 446                 waiters = (x & SX_LOCK_WAITERS);
 447                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
 448                     (uintptr_t)curthread | waiters)) {
 449                         success = 1;
 450                         break;
 451                 }
 452         }
 453         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
 454         if (success) {
 455                 curthread->td_sx_slocks--;
 456                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 457                     file, line);
 458                 LOCKSTAT_RECORD0(sx__upgrade, sx);
 459         }
 460         return (success);
 461 }
 462
 463 int
 464 sx_try_upgrade_(struct sx *sx, const char *file, int line)
 465 {
 466
 467         return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG));
 468 }
 469
 470 /*
 471  * Downgrade an unrecursed exclusive lock into a single shared lock.
 472  */
 473 void
 474 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 475 {
 476         uintptr_t x;
 477         int wakeup_swapper;
 478
 479         if (SCHEDULER_STOPPED())
 480                 return;
 481
 482         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 483             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
 484         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
 485 #ifndef INVARIANTS
 486         if (sx_recursed(sx))
 487                 panic("downgrade of a recursed lock");
 488 #endif
 489
 490         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
 491
 492         /*
 493          * Try to switch from an exclusive lock with no shared waiters
 494          * to one sharer with no shared waiters.  If there are
 495          * exclusive waiters, we don't need to lock the sleep queue so
 496          * long as we preserve the flag.  We do one quick try and if
 497          * that fails we grab the sleepq lock to keep the flags from
 498          * changing and do it the slow way.
 499          *
 500          * We have to lock the sleep queue if there are shared waiters
 501          * so we can wake them up.
 502          */
 503         x = sx->sx_lock;
 504         if (!(x & SX_LOCK_SHARED_WAITERS) &&
 505             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
 506             (x & SX_LOCK_EXCLUSIVE_WAITERS)))
 507                 goto out;
 508
 509         /*
 510          * Lock the sleep queue so we can read the waiters bits
 511          * without any races and wakeup any shared waiters.
 512          */
 513         sleepq_lock(&sx->lock_object);
 514
 515         /*
 516          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
 517          * shared lock.  If there are any shared waiters, wake them up.
 518          */
 519         wakeup_swapper = 0;
 520         x = sx->sx_lock;
 521         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
 522             (x & SX_LOCK_EXCLUSIVE_WAITERS));
 523         if (x & SX_LOCK_SHARED_WAITERS)
 524                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 525                     0, SQ_SHARED_QUEUE);
 526         sleepq_release(&sx->lock_object);
 527
 528         if (wakeup_swapper)
 529                 kick_proc0();
 530
 531 out:
 532         curthread->td_sx_slocks++;
 533         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 534         LOCKSTAT_RECORD0(sx__downgrade, sx);
 535 }
 536
 537 void
 538 sx_downgrade_(struct sx *sx, const char *file, int line)
 539 {
 540
 541         sx_downgrade_int(sx LOCK_FILE_LINE_ARG);
 542 }
 543
 544 #ifdef  ADAPTIVE_SX
 545 static inline void
 546 sx_drop_critical(uintptr_t x, bool *in_critical, int *extra_work)
 547 {
 548
 549         if (x & SX_LOCK_WRITE_SPINNER)
 550                 return;
 551         if (*in_critical) {
 552                 critical_exit();
 553                 *in_critical = false;
 554                 (*extra_work)--;
 555         }
 556 }
 557 #else
 558 #define sx_drop_critical(x, in_critical, extra_work) do { } while (0)
 559 #endif
 560
 561 /*
 562  * This function represents the so-called 'hard case' for sx_xlock
 563  * operation.  All 'easy case' failures are redirected to this.  Note
 564  * that ideally this would be a static function, but it needs to be
 565  * accessible from at least sx.h.
 566  */
 567 int
 568 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
 569 {
 570         GIANT_DECLARE;
 571         uintptr_t tid, setx;
 572 #ifdef ADAPTIVE_SX
 573         struct thread *owner;
 574         u_int i, n, spintries = 0;
 575         enum { READERS, WRITER } sleep_reason = READERS;
 576         bool in_critical = false;
 577 #endif
 578 #ifdef LOCK_PROFILING
 579         uint64_t waittime = 0;
 580         int contested = 0;
 581 #endif
 582         int error = 0;
 583 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
 584         struct lock_delay_arg lda;
 585 #endif
 586 #ifdef  KDTRACE_HOOKS
 587         u_int sleep_cnt = 0;
 588         int64_t sleep_time = 0;
 589         int64_t all_time = 0;
 590 #endif
 591 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 592         uintptr_t state = 0;
 593         int doing_lockprof = 0;
 594 #endif
 595         int extra_work = 0;
 596
 597         tid = (uintptr_t)curthread;
 598
 599 #ifdef KDTRACE_HOOKS
 600         if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
 601                 while (x == SX_LOCK_UNLOCKED) {
 602                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 603                                 goto out_lockstat;
 604                 }
 605                 extra_work = 1;
 606                 doing_lockprof = 1;
 607                 all_time -= lockstat_nsecs(&sx->lock_object);
 608                 state = x;
 609         }
 610 #endif
 611 #ifdef LOCK_PROFILING
 612         extra_work = 1;
 613         doing_lockprof = 1;
 614         state = x;
 615 #endif
 616
 617         if (SCHEDULER_STOPPED())
 618                 return (0);
 619
 620         if (__predict_false(x == SX_LOCK_UNLOCKED))
 621                 x = SX_READ_VALUE(sx);
 622
 623         /* If we already hold an exclusive lock, then recurse. */
 624         if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) {
 625                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
 626             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
 627                     sx->lock_object.lo_name, file, line));
 628                 sx->sx_recurse++;
 629                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 630                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 631                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
 632                 return (0);
 633         }
 634
 635         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 636                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 637                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
 638
 639 #if defined(ADAPTIVE_SX)
 640         lock_delay_arg_init(&lda, &sx_delay);
 641 #elif defined(KDTRACE_HOOKS)
 642         lock_delay_arg_init_noadapt(&lda);
 643 #endif
 644
 645 #ifdef HWPMC_HOOKS
 646         PMC_SOFT_CALL( , , lock, failed);
 647 #endif
 648         lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested,
 649             &waittime);
 650
 651 #ifndef INVARIANTS
 652         GIANT_SAVE(extra_work);
 653 #endif
 654
 655         THREAD_CONTENDS_ON_LOCK(&sx->lock_object);
 656
 657         for (;;) {
 658                 if (x == SX_LOCK_UNLOCKED) {
 659                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 660                                 break;
 661                         continue;
 662                 }
 663 #ifdef INVARIANTS
 664                 GIANT_SAVE(extra_work);
 665 #endif
 666 #ifdef KDTRACE_HOOKS
 667                 lda.spin_cnt++;
 668 #endif
 669 #ifdef ADAPTIVE_SX
 670                 if (x == (SX_LOCK_SHARED | SX_LOCK_WRITE_SPINNER)) {
 671                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 672                                 break;
 673                         continue;
 674                 }
 675
 676                 /*
 677                  * If the lock is write locked and the owner is
 678                  * running on another CPU, spin until the owner stops
 679                  * running or the state of the lock changes.
 680                  */
 681                 if ((x & SX_LOCK_SHARED) == 0) {
 682                         sx_drop_critical(x, &in_critical, &extra_work);
 683                         sleep_reason = WRITER;
 684                         owner = lv_sx_owner(x);
 685                         if (!TD_IS_RUNNING(owner))
 686                                 goto sleepq;
 687                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 688                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
 689                                     __func__, sx, owner);
 690                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 691                             "spinning", "lockname:\"%s\"",
 692                             sx->lock_object.lo_name);
 693                         do {
 694                                 lock_delay(&lda);
 695                                 x = SX_READ_VALUE(sx);
 696                                 owner = lv_sx_owner(x);
 697                         } while (owner != NULL && TD_IS_RUNNING(owner));
 698                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 699                             "running");
 700                         continue;
 701                 } else if (SX_SHARERS(x) > 0) {
 702                         sleep_reason = READERS;
 703                         if (spintries == asx_retries)
 704                                 goto sleepq;
 705                         if (!(x & SX_LOCK_WRITE_SPINNER)) {
 706                                 if (!in_critical) {
 707                                         critical_enter();
 708                                         in_critical = true;
 709                                         extra_work++;
 710                                 }
 711                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 712                                     x | SX_LOCK_WRITE_SPINNER)) {
 713                                         critical_exit();
 714                                         in_critical = false;
 715                                         extra_work--;
 716                                         continue;
 717                                 }
 718                         }
 719                         spintries++;
 720                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 721                             "spinning", "lockname:\"%s\"",
 722                             sx->lock_object.lo_name);
 723                         n = SX_SHARERS(x);
 724                         for (i = 0; i < asx_loops; i += n) {
 725                                 lock_delay_spin(n);
 726                                 x = SX_READ_VALUE(sx);
 727                                 if (!(x & SX_LOCK_WRITE_SPINNER))
 728                                         break;
 729                                 if (!(x & SX_LOCK_SHARED))
 730                                         break;
 731                                 n = SX_SHARERS(x);
 732                                 if (n == 0)
 733                                         break;
 734                         }
 735 #ifdef KDTRACE_HOOKS
 736                         lda.spin_cnt += i;
 737 #endif
 738                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 739                             "running");
 740                         if (i < asx_loops)
 741                                 continue;
 742                 }
 743 sleepq:
 744 #endif
 745                 sleepq_lock(&sx->lock_object);
 746                 x = SX_READ_VALUE(sx);
 747 retry_sleepq:
 748
 749                 /*
 750                  * If the lock was released while spinning on the
 751                  * sleep queue chain lock, try again.
 752                  */
 753                 if (x == SX_LOCK_UNLOCKED) {
 754                         sleepq_release(&sx->lock_object);
 755                         sx_drop_critical(x, &in_critical, &extra_work);
 756                         continue;
 757                 }
 758
 759 #ifdef ADAPTIVE_SX
 760                 /*
 761                  * The current lock owner might have started executing
 762                  * on another CPU (or the lock could have changed
 763                  * owners) while we were waiting on the sleep queue
 764                  * chain lock.  If so, drop the sleep queue lock and try
 765                  * again.
 766                  */
 767                 if (!(x & SX_LOCK_SHARED)) {
 768                         owner = (struct thread *)SX_OWNER(x);
 769                         if (TD_IS_RUNNING(owner)) {
 770                                 sleepq_release(&sx->lock_object);
 771                                 sx_drop_critical(x, &in_critical,
 772                                     &extra_work);
 773                                 continue;
 774                         }
 775                 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) {
 776                         sleepq_release(&sx->lock_object);
 777                         sx_drop_critical(x, &in_critical, &extra_work);
 778                         continue;
 779                 }
 780 #endif
 781
 782                 /*
 783                  * If an exclusive lock was released with both shared
 784                  * and exclusive waiters and a shared waiter hasn't
 785                  * woken up and acquired the lock yet, sx_lock will be
 786                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 787                  * If we see that value, try to acquire it once.  Note
 788                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 789                  * as there are other exclusive waiters still.  If we
 790                  * fail, restart the loop.
 791                  */
 792                 setx = x & (SX_LOCK_WAITERS | SX_LOCK_WRITE_SPINNER);
 793                 if ((x & ~setx) == SX_LOCK_SHARED) {
 794                         setx &= ~SX_LOCK_WRITE_SPINNER;
 795                         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid | setx))
 796                                 goto retry_sleepq;
 797                         sleepq_release(&sx->lock_object);
 798                         CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 799                             __func__, sx);
 800                         break;
 801                 }
 802
 803 #ifdef ADAPTIVE_SX
 804                 /*
 805                  * It is possible we set the SX_LOCK_WRITE_SPINNER bit.
 806                  * It is an invariant that when the bit is set, there is
 807                  * a writer ready to grab the lock. Thus clear the bit since
 808                  * we are going to sleep.
 809                  */
 810                 if (in_critical) {
 811                         if ((x & SX_LOCK_WRITE_SPINNER) ||
 812                             !((x & SX_LOCK_EXCLUSIVE_WAITERS))) {
 813                                 setx = x & ~SX_LOCK_WRITE_SPINNER;
 814                                 setx |= SX_LOCK_EXCLUSIVE_WAITERS;
 815                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 816                                     setx)) {
 817                                         goto retry_sleepq;
 818                                 }
 819                         }
 820                         critical_exit();
 821                         in_critical = false;
 822                 } else {
 823 #endif
 824                         /*
 825                          * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 826                          * than loop back and retry.
 827                          */
 828                         if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 829                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 830                                     x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 831                                         goto retry_sleepq;
 832                                 }
 833                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 834                                         CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 835                                             __func__, sx);
 836                         }
 837 #ifdef ADAPTIVE_SX
 838                 }
 839 #endif
 840
 841                 /*
 842                  * Since we have been unable to acquire the exclusive
 843                  * lock and the exclusive waiters flag is set, we have
 844                  * to sleep.
 845                  */
 846                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 847                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 848                             __func__, sx);
 849
 850 #ifdef KDTRACE_HOOKS
 851                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 852 #endif
 853                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 854                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 855                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 856                 /*
 857                  * Hack: this can land in thread_suspend_check which will
 858                  * conditionally take a mutex, tripping over an assert if a
 859                  * lock we are waiting for is set.
 860                  */
 861                 THREAD_CONTENTION_DONE(&sx->lock_object);
 862                 if (!(opts & SX_INTERRUPTIBLE))
 863                         sleepq_wait(&sx->lock_object, 0);
 864                 else
 865                         error = sleepq_wait_sig(&sx->lock_object, 0);
 866                 THREAD_CONTENDS_ON_LOCK(&sx->lock_object);
 867 #ifdef KDTRACE_HOOKS
 868                 sleep_time += lockstat_nsecs(&sx->lock_object);
 869                 sleep_cnt++;
 870 #endif
 871                 if (error) {
 872                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 873                                 CTR2(KTR_LOCK,
 874                         "%s: interruptible sleep by %p suspended by signal",
 875                                     __func__, sx);
 876                         break;
 877                 }
 878                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 879                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 880                             __func__, sx);
 881                 x = SX_READ_VALUE(sx);
 882         }
 883         THREAD_CONTENTION_DONE(&sx->lock_object);
 884         if (__predict_true(!extra_work))
 885                 return (error);
 886 #ifdef ADAPTIVE_SX
 887         if (in_critical)
 888                 critical_exit();
 889 #endif
 890         GIANT_RESTORE();
 891 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 892         if (__predict_true(!doing_lockprof))
 893                 return (error);
 894 #endif
 895 #ifdef KDTRACE_HOOKS
 896         all_time += lockstat_nsecs(&sx->lock_object);
 897         if (sleep_time)
 898                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
 899                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 900                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 901         if (lda.spin_cnt > sleep_cnt)
 902                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
 903                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 904                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 905 out_lockstat:
 906 #endif
 907         if (!error)
 908                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 909                     contested, waittime, file, line, LOCKSTAT_WRITER);
 910         return (error);
 911 }
 912
 913 /*
 914  * This function represents the so-called 'hard case' for sx_xunlock
 915  * operation.  All 'easy case' failures are redirected to this.  Note
 916  * that ideally this would be a static function, but it needs to be
 917  * accessible from at least sx.h.
 918  */
 919 void
 920 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
 921 {
 922         uintptr_t tid, setx;
 923         int queue, wakeup_swapper;
 924
 925         if (SCHEDULER_STOPPED())
 926                 return;
 927
 928         tid = (uintptr_t)curthread;
 929
 930         if (__predict_false(x == tid))
 931                 x = SX_READ_VALUE(sx);
 932
 933         MPASS(!(x & SX_LOCK_SHARED));
 934
 935         if (__predict_false(x & SX_LOCK_RECURSED)) {
 936                 /* The lock is recursed, unrecurse one level. */
 937                 if ((--sx->sx_recurse) == 0)
 938                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 939                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 940                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 941                 return;
 942         }
 943
 944         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
 945         if (x == tid &&
 946             atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
 947                 return;
 948
 949         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 950                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 951
 952         sleepq_lock(&sx->lock_object);
 953         x = SX_READ_VALUE(sx);
 954         MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS));
 955
 956         /*
 957          * The wake up algorithm here is quite simple and probably not
 958          * ideal.  It gives precedence to shared waiters if they are
 959          * present.  For this condition, we have to preserve the
 960          * state of the exclusive waiters flag.
 961          * If interruptible sleeps left the shared queue empty avoid a
 962          * starvation for the threads sleeping on the exclusive queue by giving
 963          * them precedence and cleaning up the shared waiters bit anyway.
 964          */
 965         setx = SX_LOCK_UNLOCKED;
 966         queue = SQ_SHARED_QUEUE;
 967         if ((x & SX_LOCK_EXCLUSIVE_WAITERS) != 0 &&
 968             sleepq_sleepcnt(&sx->lock_object, SQ_EXCLUSIVE_QUEUE) != 0) {
 969                 queue = SQ_EXCLUSIVE_QUEUE;
 970                 setx |= (x & SX_LOCK_SHARED_WAITERS);
 971         }
 972         atomic_store_rel_ptr(&sx->sx_lock, setx);
 973
 974         /* Wake up all the waiters for the specific queue. */
 975         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 976                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 977                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 978                     "exclusive");
 979
 980         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 981             queue);
 982         sleepq_release(&sx->lock_object);
 983         if (wakeup_swapper)
 984                 kick_proc0();
 985 }
 986
 987 static bool __always_inline
 988 __sx_can_read(struct thread *td, uintptr_t x, bool fp)
 989 {
 990
 991         if ((x & (SX_LOCK_SHARED | SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_WRITE_SPINNER))
 992                         == SX_LOCK_SHARED)
 993                 return (true);
 994         if (!fp && td->td_sx_slocks && (x & SX_LOCK_SHARED))
 995                 return (true);
 996         return (false);
 997 }
 998
 999 static bool __always_inline
1000 __sx_slock_try(struct sx *sx, struct thread *td, uintptr_t *xp, bool fp
1001     LOCK_FILE_LINE_ARG_DEF)
1002 {
1003
1004         /*
1005          * If no other thread has an exclusive lock then try to bump up
1006          * the count of sharers.  Since we have to preserve the state
1007          * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
1008          * shared lock loop back and retry.
1009          */
1010         while (__sx_can_read(td, *xp, fp)) {
1011                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp,
1012                     *xp + SX_ONE_SHARER)) {
1013                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1014                                 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p",
1015                                     __func__, sx, (void *)*xp,
1016                                     (void *)(*xp + SX_ONE_SHARER));
1017                         td->td_sx_slocks++;
1018                         return (true);
1019                 }
1020         }
1021         return (false);
1022 }
1023
1024 static int __noinline
1025 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
1026 {
1027         GIANT_DECLARE;
1028         struct thread *td;
1029 #ifdef ADAPTIVE_SX
1030         struct thread *owner;
1031         u_int i, n, spintries = 0;
1032 #endif
1033 #ifdef LOCK_PROFILING
1034         uint64_t waittime = 0;
1035         int contested = 0;
1036 #endif
1037         int error = 0;
1038 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
1039         struct lock_delay_arg lda;
1040 #endif
1041 #ifdef KDTRACE_HOOKS
1042         u_int sleep_cnt = 0;
1043         int64_t sleep_time = 0;
1044         int64_t all_time = 0;
1045 #endif
1046 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1047         uintptr_t state = 0;
1048 #endif
1049         int extra_work __sdt_used = 0;
1050
1051         td = curthread;
1052
1053 #ifdef KDTRACE_HOOKS
1054         if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
1055                 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1056                         goto out_lockstat;
1057                 extra_work = 1;
1058                 all_time -= lockstat_nsecs(&sx->lock_object);
1059                 state = x;
1060         }
1061 #endif
1062 #ifdef LOCK_PROFILING
1063         extra_work = 1;
1064         state = x;
1065 #endif
1066
1067         if (SCHEDULER_STOPPED())
1068                 return (0);
1069
1070 #if defined(ADAPTIVE_SX)
1071         lock_delay_arg_init(&lda, &sx_delay);
1072 #elif defined(KDTRACE_HOOKS)
1073         lock_delay_arg_init_noadapt(&lda);
1074 #endif
1075
1076 #ifdef HWPMC_HOOKS
1077         PMC_SOFT_CALL( , , lock, failed);
1078 #endif
1079         lock_profile_obtain_lock_failed(&sx->lock_object, false, &contested,
1080             &waittime);
1081
1082 #ifndef INVARIANTS
1083         GIANT_SAVE(extra_work);
1084 #endif
1085
1086         THREAD_CONTENDS_ON_LOCK(&sx->lock_object);
1087
1088         /*
1089          * As with rwlocks, we don't make any attempt to try to block
1090          * shared locks once there is an exclusive waiter.
1091          */
1092         for (;;) {
1093                 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1094                         break;
1095 #ifdef INVARIANTS
1096                 GIANT_SAVE(extra_work);
1097 #endif
1098 #ifdef KDTRACE_HOOKS
1099                 lda.spin_cnt++;
1100 #endif
1101
1102 #ifdef ADAPTIVE_SX
1103                 /*
1104                  * If the owner is running on another CPU, spin until
1105                  * the owner stops running or the state of the lock
1106                  * changes.
1107                  */
1108                 if ((x & SX_LOCK_SHARED) == 0) {
1109                         owner = lv_sx_owner(x);
1110                         if (TD_IS_RUNNING(owner)) {
1111                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1112                                         CTR3(KTR_LOCK,
1113                                             "%s: spinning on %p held by %p",
1114                                             __func__, sx, owner);
1115                                 KTR_STATE1(KTR_SCHED, "thread",
1116                                     sched_tdname(curthread), "spinning",
1117                                     "lockname:\"%s\"", sx->lock_object.lo_name);
1118                                 do {
1119                                         lock_delay(&lda);
1120                                         x = SX_READ_VALUE(sx);
1121                                         owner = lv_sx_owner(x);
1122                                 } while (owner != NULL && TD_IS_RUNNING(owner));
1123                                 KTR_STATE0(KTR_SCHED, "thread",
1124                                     sched_tdname(curthread), "running");
1125                                 continue;
1126                         }
1127                 } else {
1128                         if ((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) {
1129                                 MPASS(!__sx_can_read(td, x, false));
1130                                 lock_delay_spin(2);
1131                                 x = SX_READ_VALUE(sx);
1132                                 continue;
1133                         }
1134                         if (spintries < asx_retries) {
1135                                 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1136                                     "spinning", "lockname:\"%s\"",
1137                                     sx->lock_object.lo_name);
1138                                 n = SX_SHARERS(x);
1139                                 for (i = 0; i < asx_loops; i += n) {
1140                                         lock_delay_spin(n);
1141                                         x = SX_READ_VALUE(sx);
1142                                         if (!(x & SX_LOCK_SHARED))
1143                                                 break;
1144                                         n = SX_SHARERS(x);
1145                                         if (n == 0)
1146                                                 break;
1147                                         if (__sx_can_read(td, x, false))
1148                                                 break;
1149                                 }
1150 #ifdef KDTRACE_HOOKS
1151                                 lda.spin_cnt += i;
1152 #endif
1153                                 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1154                                     "running");
1155                                 if (i < asx_loops)
1156                                         continue;
1157                         }
1158                 }
1159 #endif
1160
1161                 /*
1162                  * Some other thread already has an exclusive lock, so
1163                  * start the process of blocking.
1164                  */
1165                 sleepq_lock(&sx->lock_object);
1166                 x = SX_READ_VALUE(sx);
1167 retry_sleepq:
1168                 if (((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) ||
1169                     __sx_can_read(td, x, false)) {
1170                         sleepq_release(&sx->lock_object);
1171                         continue;
1172                 }
1173
1174 #ifdef ADAPTIVE_SX
1175                 /*
1176                  * If the owner is running on another CPU, spin until
1177                  * the owner stops running or the state of the lock
1178                  * changes.
1179                  */
1180                 if (!(x & SX_LOCK_SHARED)) {
1181                         owner = (struct thread *)SX_OWNER(x);
1182                         if (TD_IS_RUNNING(owner)) {
1183                                 sleepq_release(&sx->lock_object);
1184                                 x = SX_READ_VALUE(sx);
1185                                 continue;
1186                         }
1187                 }
1188 #endif
1189
1190                 /*
1191                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
1192                  * fail to set it drop the sleep queue lock and loop
1193                  * back.
1194                  */
1195                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
1196                         if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
1197                             x | SX_LOCK_SHARED_WAITERS))
1198                                 goto retry_sleepq;
1199                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1200                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
1201                                     __func__, sx);
1202                 }
1203
1204                 /*
1205                  * Since we have been unable to acquire the shared lock,
1206                  * we have to sleep.
1207                  */
1208                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1209                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
1210                             __func__, sx);
1211
1212 #ifdef KDTRACE_HOOKS
1213                 sleep_time -= lockstat_nsecs(&sx->lock_object);
1214 #endif
1215                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1216                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1217                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1218                 /*
1219                  * Hack: this can land in thread_suspend_check which will
1220                  * conditionally take a mutex, tripping over an assert if a
1221                  * lock we are waiting for is set.
1222                  */
1223                 THREAD_CONTENTION_DONE(&sx->lock_object);
1224                 if (!(opts & SX_INTERRUPTIBLE))
1225                         sleepq_wait(&sx->lock_object, 0);
1226                 else
1227                         error = sleepq_wait_sig(&sx->lock_object, 0);
1228                 THREAD_CONTENDS_ON_LOCK(&sx->lock_object);
1229 #ifdef KDTRACE_HOOKS
1230                 sleep_time += lockstat_nsecs(&sx->lock_object);
1231                 sleep_cnt++;
1232 #endif
1233                 if (error) {
1234                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1235                                 CTR2(KTR_LOCK,
1236                         "%s: interruptible sleep by %p suspended by signal",
1237                                     __func__, sx);
1238                         break;
1239                 }
1240                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1241                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1242                             __func__, sx);
1243                 x = SX_READ_VALUE(sx);
1244         }
1245         THREAD_CONTENTION_DONE(&sx->lock_object);
1246 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1247         if (__predict_true(!extra_work))
1248                 return (error);
1249 #endif
1250 #ifdef KDTRACE_HOOKS
1251         all_time += lockstat_nsecs(&sx->lock_object);
1252         if (sleep_time)
1253                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
1254                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1255                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1256         if (lda.spin_cnt > sleep_cnt)
1257                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
1258                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1259                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1260 out_lockstat:
1261 #endif
1262         if (error == 0) {
1263                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
1264                     contested, waittime, file, line, LOCKSTAT_READER);
1265         }
1266         GIANT_RESTORE();
1267         return (error);
1268 }
1269
1270 int
1271 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF)
1272 {
1273         struct thread *td;
1274         uintptr_t x;
1275         int error;
1276
1277         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
1278             !TD_IS_IDLETHREAD(curthread),
1279             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
1280             curthread, sx->lock_object.lo_name, file, line));
1281         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1282             ("sx_slock() of destroyed sx @ %s:%d", file, line));
1283         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
1284
1285         error = 0;
1286         td = curthread;
1287         x = SX_READ_VALUE(sx);
1288         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) ||
1289             !__sx_slock_try(sx, td, &x, true LOCK_FILE_LINE_ARG)))
1290                 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG);
1291         else
1292                 lock_profile_obtain_lock_success(&sx->lock_object, false, 0, 0,
1293                     file, line);
1294         if (error == 0) {
1295                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
1296                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
1297                 TD_LOCKS_INC(curthread);
1298         }
1299         return (error);
1300 }
1301
1302 int
1303 _sx_slock(struct sx *sx, int opts, const char *file, int line)
1304 {
1305
1306         return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG));
1307 }
1308
1309 static bool __always_inline
1310 _sx_sunlock_try(struct sx *sx, struct thread *td, uintptr_t *xp)
1311 {
1312
1313         for (;;) {
1314                 if (SX_SHARERS(*xp) > 1 || !(*xp & SX_LOCK_WAITERS)) {
1315                         if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp,
1316                             *xp - SX_ONE_SHARER)) {
1317                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1318                                         CTR4(KTR_LOCK,
1319                                             "%s: %p succeeded %p -> %p",
1320                                             __func__, sx, (void *)*xp,
1321                                             (void *)(*xp - SX_ONE_SHARER));
1322                                 td->td_sx_slocks--;
1323                                 return (true);
1324                         }
1325                         continue;
1326                 }
1327                 break;
1328         }
1329         return (false);
1330 }
1331
1332 static void __noinline
1333 _sx_sunlock_hard(struct sx *sx, struct thread *td, uintptr_t x
1334     LOCK_FILE_LINE_ARG_DEF)
1335 {
1336         int wakeup_swapper = 0;
1337         uintptr_t setx, queue;
1338
1339         if (SCHEDULER_STOPPED())
1340                 return;
1341
1342         if (_sx_sunlock_try(sx, td, &x))
1343                 goto out_lockstat;
1344
1345         sleepq_lock(&sx->lock_object);
1346         x = SX_READ_VALUE(sx);
1347         for (;;) {
1348                 if (_sx_sunlock_try(sx, td, &x))
1349                         break;
1350
1351                 /*
1352                  * Wake up semantic here is quite simple:
1353                  * Just wake up all the exclusive waiters.
1354                  * Note that the state of the lock could have changed,
1355                  * so if it fails loop back and retry.
1356                  */
1357                 setx = SX_LOCK_UNLOCKED;
1358                 queue = SQ_SHARED_QUEUE;
1359                 if (x & SX_LOCK_EXCLUSIVE_WAITERS) {
1360                         setx |= (x & SX_LOCK_SHARED_WAITERS);
1361                         queue = SQ_EXCLUSIVE_QUEUE;
1362                 }
1363                 setx |= (x & SX_LOCK_WRITE_SPINNER);
1364                 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx))
1365                         continue;
1366                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1367                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1368                             "exclusive queue", __func__, sx);
1369                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1370                     0, queue);
1371                 td->td_sx_slocks--;
1372                 break;
1373         }
1374         sleepq_release(&sx->lock_object);
1375         if (wakeup_swapper)
1376                 kick_proc0();
1377 out_lockstat:
1378         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
1379 }
1380
1381 void
1382 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
1383 {
1384         struct thread *td;
1385         uintptr_t x;
1386
1387         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1388             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
1389         _sx_assert(sx, SA_SLOCKED, file, line);
1390         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
1391         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
1392
1393         td = curthread;
1394         x = SX_READ_VALUE(sx);
1395         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) ||
1396             !_sx_sunlock_try(sx, td, &x)))
1397                 _sx_sunlock_hard(sx, td, x LOCK_FILE_LINE_ARG);
1398         else
1399                 lock_profile_release_lock(&sx->lock_object, false);
1400
1401         TD_LOCKS_DEC(curthread);
1402 }
1403
1404 void
1405 _sx_sunlock(struct sx *sx, const char *file, int line)
1406 {
1407
1408         _sx_sunlock_int(sx LOCK_FILE_LINE_ARG);
1409 }
1410
1411 #ifdef INVARIANT_SUPPORT
1412 #ifndef INVARIANTS
1413 #undef  _sx_assert
1414 #endif
1415
1416 /*
1417  * In the non-WITNESS case, sx_assert() can only detect that at least
1418  * *some* thread owns an slock, but it cannot guarantee that *this*
1419  * thread owns an slock.
1420  */
1421 void
1422 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1423 {
1424 #ifndef WITNESS
1425         int slocked = 0;
1426 #endif
1427
1428         if (SCHEDULER_STOPPED())
1429                 return;
1430         switch (what) {
1431         case SA_SLOCKED:
1432         case SA_SLOCKED | SA_NOTRECURSED:
1433         case SA_SLOCKED | SA_RECURSED:
1434 #ifndef WITNESS
1435                 slocked = 1;
1436                 /* FALLTHROUGH */
1437 #endif
1438         case SA_LOCKED:
1439         case SA_LOCKED | SA_NOTRECURSED:
1440         case SA_LOCKED | SA_RECURSED:
1441 #ifdef WITNESS
1442                 witness_assert(&sx->lock_object, what, file, line);
1443 #else
1444                 /*
1445                  * If some other thread has an exclusive lock or we
1446                  * have one and are asserting a shared lock, fail.
1447                  * Also, if no one has a lock at all, fail.
1448                  */
1449                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1450                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1451                     sx_xholder(sx) != curthread)))
1452                         panic("Lock %s not %slocked @ %s:%d\n",
1453                             sx->lock_object.lo_name, slocked ? "share " : "",
1454                             file, line);
1455
1456                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1457                         if (sx_recursed(sx)) {
1458                                 if (what & SA_NOTRECURSED)
1459                                         panic("Lock %s recursed @ %s:%d\n",
1460                                             sx->lock_object.lo_name, file,
1461                                             line);
1462                         } else if (what & SA_RECURSED)
1463                                 panic("Lock %s not recursed @ %s:%d\n",
1464                                     sx->lock_object.lo_name, file, line);
1465                 }
1466 #endif
1467                 break;
1468         case SA_XLOCKED:
1469         case SA_XLOCKED | SA_NOTRECURSED:
1470         case SA_XLOCKED | SA_RECURSED:
1471                 if (sx_xholder(sx) != curthread)
1472                         panic("Lock %s not exclusively locked @ %s:%d\n",
1473                             sx->lock_object.lo_name, file, line);
1474                 if (sx_recursed(sx)) {
1475                         if (what & SA_NOTRECURSED)
1476                                 panic("Lock %s recursed @ %s:%d\n",
1477                                     sx->lock_object.lo_name, file, line);
1478                 } else if (what & SA_RECURSED)
1479                         panic("Lock %s not recursed @ %s:%d\n",
1480                             sx->lock_object.lo_name, file, line);
1481                 break;
1482         case SA_UNLOCKED:
1483 #ifdef WITNESS
1484                 witness_assert(&sx->lock_object, what, file, line);
1485 #else
1486                 /*
1487                  * If we hold an exclusve lock fail.  We can't
1488                  * reliably check to see if we hold a shared lock or
1489                  * not.
1490                  */
1491                 if (sx_xholder(sx) == curthread)
1492                         panic("Lock %s exclusively locked @ %s:%d\n",
1493                             sx->lock_object.lo_name, file, line);
1494 #endif
1495                 break;
1496         default:
1497                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1498                     line);
1499         }
1500 }
1501 #endif  /* INVARIANT_SUPPORT */
1502
1503 #ifdef DDB
1504 static void
1505 db_show_sx(const struct lock_object *lock)
1506 {
1507         struct thread *td;
1508         const struct sx *sx;
1509
1510         sx = (const struct sx *)lock;
1511
1512         db_printf(" state: ");
1513         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1514                 db_printf("UNLOCKED\n");
1515         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1516                 db_printf("DESTROYED\n");
1517                 return;
1518         } else if (sx->sx_lock & SX_LOCK_SHARED)
1519                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1520         else {
1521                 td = sx_xholder(sx);
1522                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1523                     td->td_tid, td->td_proc->p_pid, td->td_name);
1524                 if (sx_recursed(sx))
1525                         db_printf(" recursed: %d\n", sx->sx_recurse);
1526         }
1527
1528         db_printf(" waiters: ");
1529         switch(sx->sx_lock &
1530             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1531         case SX_LOCK_SHARED_WAITERS:
1532                 db_printf("shared\n");
1533                 break;
1534         case SX_LOCK_EXCLUSIVE_WAITERS:
1535                 db_printf("exclusive\n");
1536                 break;
1537         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1538                 db_printf("exclusive and shared\n");
1539                 break;
1540         default:
1541                 db_printf("none\n");
1542         }
1543 }
1544
1545 /*
1546  * Check to see if a thread that is blocked on a sleep queue is actually
1547  * blocked on an sx lock.  If so, output some details and return true.
1548  * If the lock has an exclusive owner, return that in *ownerp.
1549  */
1550 int
1551 sx_chain(struct thread *td, struct thread **ownerp)
1552 {
1553         const struct sx *sx;
1554
1555         /*
1556          * Check to see if this thread is blocked on an sx lock.
1557          * First, we check the lock class.  If that is ok, then we
1558          * compare the lock name against the wait message.
1559          */
1560         sx = td->td_wchan;
1561         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1562             sx->lock_object.lo_name != td->td_wmesg)
1563                 return (0);
1564
1565         /* We think we have an sx lock, so output some details. */
1566         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1567         *ownerp = sx_xholder(sx);
1568         if (sx->sx_lock & SX_LOCK_SHARED)
1569                 db_printf("SLOCK (count %ju)\n",
1570                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1571         else
1572                 db_printf("XLOCK\n");
1573         return (1);
1574 }
1575 #endif