sys/kern/kern_sx.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   3  *
   4  * Copyright (c) 2007 Attilio Rao <attilio@freebsd.org>
   5  * Copyright (c) 2001 Jason Evans <jasone@freebsd.org>
   6  * All rights reserved.
   7  *
   8  * Redistribution and use in source and binary forms, with or without
   9  * modification, are permitted provided that the following conditions
  10  * are met:
  11  * 1. Redistributions of source code must retain the above copyright
  12  *    notice(s), this list of conditions and the following disclaimer as
  13  *    the first lines of this file unmodified other than the possible
  14  *    addition of one or more copyright notices.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice(s), this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
  20  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
  21  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
  22  * DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
  23  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  24  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
  25  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  26  * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
  29  * DAMAGE.
  30  */
  31
  32 /*
  33  * Shared/exclusive locks.  This implementation attempts to ensure
  34  * deterministic lock granting behavior, so that slocks and xlocks are
  35  * interleaved.
  36  *
  37  * Priority propagation will not generally raise the priority of lock holders,
  38  * so should not be relied upon in combination with sx locks.
  39  */
  40
  41 #include "opt_ddb.h"
  42 #include "opt_hwpmc_hooks.h"
  43 #include "opt_no_adaptive_sx.h"
  44
  45 #include <sys/cdefs.h>
  46 __FBSDID("$FreeBSD$");
  47
  48 #include <sys/param.h>
  49 #include <sys/systm.h>
  50 #include <sys/kdb.h>
  51 #include <sys/kernel.h>
  52 #include <sys/ktr.h>
  53 #include <sys/lock.h>
  54 #include <sys/mutex.h>
  55 #include <sys/proc.h>
  56 #include <sys/sched.h>
  57 #include <sys/sleepqueue.h>
  58 #include <sys/sx.h>
  59 #include <sys/smp.h>
  60 #include <sys/sysctl.h>
  61
  62 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  63 #include <machine/cpu.h>
  64 #endif
  65
  66 #ifdef DDB
  67 #include <ddb/ddb.h>
  68 #endif
  69
  70 #if defined(SMP) && !defined(NO_ADAPTIVE_SX)
  71 #define ADAPTIVE_SX
  72 #endif
  73
  74 #ifdef HWPMC_HOOKS
  75 #include <sys/pmckern.h>
  76 PMC_SOFT_DECLARE( , , lock, failed);
  77 #endif
  78
  79 /* Handy macros for sleep queues. */
  80 #define SQ_EXCLUSIVE_QUEUE      0
  81 #define SQ_SHARED_QUEUE         1
  82
  83 /*
  84  * Variations on DROP_GIANT()/PICKUP_GIANT() for use in this file.  We
  85  * drop Giant anytime we have to sleep or if we adaptively spin.
  86  */
  87 #define GIANT_DECLARE                                                   \
  88         int _giantcnt = 0;                                              \
  89         WITNESS_SAVE_DECL(Giant)                                        \
  90
  91 #define GIANT_SAVE(work) do {                                           \
  92         if (__predict_false(mtx_owned(&Giant))) {                       \
  93                 work++;                                                 \
  94                 WITNESS_SAVE(&Giant.lock_object, Giant);                \
  95                 while (mtx_owned(&Giant)) {                             \
  96                         _giantcnt++;                                    \
  97                         mtx_unlock(&Giant);                             \
  98                 }                                                       \
  99         }                                                               \
 100 } while (0)
 101
 102 #define GIANT_RESTORE() do {                                            \
 103         if (_giantcnt > 0) {                                            \
 104                 mtx_assert(&Giant, MA_NOTOWNED);                        \
 105                 while (_giantcnt--)                                     \
 106                         mtx_lock(&Giant);                               \
 107                 WITNESS_RESTORE(&Giant.lock_object, Giant);             \
 108         }                                                               \
 109 } while (0)
 110
 111 /*
 112  * Returns true if an exclusive lock is recursed.  It assumes
 113  * curthread currently has an exclusive lock.
 114  */
 115 #define sx_recursed(sx)         ((sx)->sx_recurse != 0)
 116
 117 static void     assert_sx(const struct lock_object *lock, int what);
 118 #ifdef DDB
 119 static void     db_show_sx(const struct lock_object *lock);
 120 #endif
 121 static void     lock_sx(struct lock_object *lock, uintptr_t how);
 122 #ifdef KDTRACE_HOOKS
 123 static int      owner_sx(const struct lock_object *lock, struct thread **owner);
 124 #endif
 125 static uintptr_t unlock_sx(struct lock_object *lock);
 126
 127 struct lock_class lock_class_sx = {
 128         .lc_name = "sx",
 129         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE | LC_UPGRADABLE,
 130         .lc_assert = assert_sx,
 131 #ifdef DDB
 132         .lc_ddb_show = db_show_sx,
 133 #endif
 134         .lc_lock = lock_sx,
 135         .lc_unlock = unlock_sx,
 136 #ifdef KDTRACE_HOOKS
 137         .lc_owner = owner_sx,
 138 #endif
 139 };
 140
 141 #ifndef INVARIANTS
 142 #define _sx_assert(sx, what, file, line)
 143 #endif
 144
 145 #ifdef ADAPTIVE_SX
 146 static __read_frequently u_int asx_retries;
 147 static __read_frequently u_int asx_loops;
 148 static SYSCTL_NODE(_debug, OID_AUTO, sx, CTLFLAG_RD, NULL, "sxlock debugging");
 149 SYSCTL_UINT(_debug_sx, OID_AUTO, retries, CTLFLAG_RW, &asx_retries, 0, "");
 150 SYSCTL_UINT(_debug_sx, OID_AUTO, loops, CTLFLAG_RW, &asx_loops, 0, "");
 151
 152 static struct lock_delay_config __read_frequently sx_delay;
 153
 154 SYSCTL_INT(_debug_sx, OID_AUTO, delay_base, CTLFLAG_RW, &sx_delay.base,
 155     0, "");
 156 SYSCTL_INT(_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 #endif
 169
 170 void
 171 assert_sx(const struct lock_object *lock, int what)
 172 {
 173
 174         sx_assert((const struct sx *)lock, what);
 175 }
 176
 177 void
 178 lock_sx(struct lock_object *lock, uintptr_t how)
 179 {
 180         struct sx *sx;
 181
 182         sx = (struct sx *)lock;
 183         if (how)
 184                 sx_slock(sx);
 185         else
 186                 sx_xlock(sx);
 187 }
 188
 189 uintptr_t
 190 unlock_sx(struct lock_object *lock)
 191 {
 192         struct sx *sx;
 193
 194         sx = (struct sx *)lock;
 195         sx_assert(sx, SA_LOCKED | SA_NOTRECURSED);
 196         if (sx_xlocked(sx)) {
 197                 sx_xunlock(sx);
 198                 return (0);
 199         } else {
 200                 sx_sunlock(sx);
 201                 return (1);
 202         }
 203 }
 204
 205 #ifdef KDTRACE_HOOKS
 206 int
 207 owner_sx(const struct lock_object *lock, struct thread **owner)
 208 {
 209         const struct sx *sx;
 210         uintptr_t x;
 211
 212         sx = (const struct sx *)lock;
 213         x = sx->sx_lock;
 214         *owner = NULL;
 215         return ((x & SX_LOCK_SHARED) != 0 ? (SX_SHARERS(x) != 0) :
 216             ((*owner = (struct thread *)SX_OWNER(x)) != NULL));
 217 }
 218 #endif
 219
 220 void
 221 sx_sysinit(void *arg)
 222 {
 223         struct sx_args *sargs = arg;
 224
 225         sx_init_flags(sargs->sa_sx, sargs->sa_desc, sargs->sa_flags);
 226 }
 227
 228 void
 229 sx_init_flags(struct sx *sx, const char *description, int opts)
 230 {
 231         int flags;
 232
 233         MPASS((opts & ~(SX_QUIET | SX_RECURSE | SX_NOWITNESS | SX_DUPOK |
 234             SX_NOPROFILE | SX_NEW)) == 0);
 235         ASSERT_ATOMIC_LOAD_PTR(sx->sx_lock,
 236             ("%s: sx_lock not aligned for %s: %p", __func__, description,
 237             &sx->sx_lock));
 238
 239         flags = LO_SLEEPABLE | LO_UPGRADABLE;
 240         if (opts & SX_DUPOK)
 241                 flags |= LO_DUPOK;
 242         if (opts & SX_NOPROFILE)
 243                 flags |= LO_NOPROFILE;
 244         if (!(opts & SX_NOWITNESS))
 245                 flags |= LO_WITNESS;
 246         if (opts & SX_RECURSE)
 247                 flags |= LO_RECURSABLE;
 248         if (opts & SX_QUIET)
 249                 flags |= LO_QUIET;
 250         if (opts & SX_NEW)
 251                 flags |= LO_NEW;
 252
 253         lock_init(&sx->lock_object, &lock_class_sx, description, NULL, flags);
 254         sx->sx_lock = SX_LOCK_UNLOCKED;
 255         sx->sx_recurse = 0;
 256 }
 257
 258 void
 259 sx_destroy(struct sx *sx)
 260 {
 261
 262         KASSERT(sx->sx_lock == SX_LOCK_UNLOCKED, ("sx lock still held"));
 263         KASSERT(sx->sx_recurse == 0, ("sx lock still recursed"));
 264         sx->sx_lock = SX_LOCK_DESTROYED;
 265         lock_destroy(&sx->lock_object);
 266 }
 267
 268 int
 269 sx_try_slock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 270 {
 271         uintptr_t x;
 272
 273         if (SCHEDULER_STOPPED())
 274                 return (1);
 275
 276         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 277             ("sx_try_slock() by idle thread %p on sx %s @ %s:%d",
 278             curthread, sx->lock_object.lo_name, file, line));
 279
 280         x = sx->sx_lock;
 281         for (;;) {
 282                 KASSERT(x != SX_LOCK_DESTROYED,
 283                     ("sx_try_slock() of destroyed sx @ %s:%d", file, line));
 284                 if (!(x & SX_LOCK_SHARED))
 285                         break;
 286                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, x + SX_ONE_SHARER)) {
 287                         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 1, file, line);
 288                         WITNESS_LOCK(&sx->lock_object, LOP_TRYLOCK, file, line);
 289                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 290                             sx, 0, 0, file, line, LOCKSTAT_READER);
 291                         TD_LOCKS_INC(curthread);
 292                         curthread->td_sx_slocks++;
 293                         return (1);
 294                 }
 295         }
 296
 297         LOCK_LOG_TRY("SLOCK", &sx->lock_object, 0, 0, file, line);
 298         return (0);
 299 }
 300
 301 int
 302 sx_try_slock_(struct sx *sx, const char *file, int line)
 303 {
 304
 305         return (sx_try_slock_int(sx LOCK_FILE_LINE_ARG));
 306 }
 307
 308 int
 309 _sx_xlock(struct sx *sx, int opts, const char *file, int line)
 310 {
 311         uintptr_t tid, x;
 312         int error = 0;
 313
 314         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
 315             !TD_IS_IDLETHREAD(curthread),
 316             ("sx_xlock() by idle thread %p on sx %s @ %s:%d",
 317             curthread, sx->lock_object.lo_name, file, line));
 318         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 319             ("sx_xlock() of destroyed sx @ %s:%d", file, line));
 320         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE, file,
 321             line, NULL);
 322         tid = (uintptr_t)curthread;
 323         x = SX_LOCK_UNLOCKED;
 324         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 325                 error = _sx_xlock_hard(sx, x, opts LOCK_FILE_LINE_ARG);
 326         else
 327                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 328                     0, 0, file, line, LOCKSTAT_WRITER);
 329         if (!error) {
 330                 LOCK_LOG_LOCK("XLOCK", &sx->lock_object, 0, sx->sx_recurse,
 331                     file, line);
 332                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 333                 TD_LOCKS_INC(curthread);
 334         }
 335
 336         return (error);
 337 }
 338
 339 int
 340 sx_try_xlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 341 {
 342         struct thread *td;
 343         uintptr_t tid, x;
 344         int rval;
 345         bool recursed;
 346
 347         td = curthread;
 348         tid = (uintptr_t)td;
 349         if (SCHEDULER_STOPPED_TD(td))
 350                 return (1);
 351
 352         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(td),
 353             ("sx_try_xlock() by idle thread %p on sx %s @ %s:%d",
 354             curthread, sx->lock_object.lo_name, file, line));
 355         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 356             ("sx_try_xlock() of destroyed sx @ %s:%d", file, line));
 357
 358         rval = 1;
 359         recursed = false;
 360         x = SX_LOCK_UNLOCKED;
 361         for (;;) {
 362                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 363                         break;
 364                 if (x == SX_LOCK_UNLOCKED)
 365                         continue;
 366                 if (x == tid && (sx->lock_object.lo_flags & LO_RECURSABLE)) {
 367                         sx->sx_recurse++;
 368                         atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 369                         break;
 370                 }
 371                 rval = 0;
 372                 break;
 373         }
 374
 375         LOCK_LOG_TRY("XLOCK", &sx->lock_object, 0, rval, file, line);
 376         if (rval) {
 377                 WITNESS_LOCK(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 378                     file, line);
 379                 if (!recursed)
 380                         LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire,
 381                             sx, 0, 0, file, line, LOCKSTAT_WRITER);
 382                 TD_LOCKS_INC(curthread);
 383         }
 384
 385         return (rval);
 386 }
 387
 388 int
 389 sx_try_xlock_(struct sx *sx, const char *file, int line)
 390 {
 391
 392         return (sx_try_xlock_int(sx LOCK_FILE_LINE_ARG));
 393 }
 394
 395 void
 396 _sx_xunlock(struct sx *sx, const char *file, int line)
 397 {
 398
 399         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 400             ("sx_xunlock() of destroyed sx @ %s:%d", file, line));
 401         _sx_assert(sx, SA_XLOCKED, file, line);
 402         WITNESS_UNLOCK(&sx->lock_object, LOP_EXCLUSIVE, file, line);
 403         LOCK_LOG_LOCK("XUNLOCK", &sx->lock_object, 0, sx->sx_recurse, file,
 404             line);
 405 #if LOCK_DEBUG > 0
 406         _sx_xunlock_hard(sx, (uintptr_t)curthread, file, line);
 407 #else
 408         __sx_xunlock(sx, curthread, file, line);
 409 #endif
 410         TD_LOCKS_DEC(curthread);
 411 }
 412
 413 /*
 414  * Try to do a non-blocking upgrade from a shared lock to an exclusive lock.
 415  * This will only succeed if this thread holds a single shared lock.
 416  * Return 1 if if the upgrade succeed, 0 otherwise.
 417  */
 418 int
 419 sx_try_upgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 420 {
 421         uintptr_t x;
 422         uintptr_t waiters;
 423         int success;
 424
 425         if (SCHEDULER_STOPPED())
 426                 return (1);
 427
 428         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 429             ("sx_try_upgrade() of destroyed sx @ %s:%d", file, line));
 430         _sx_assert(sx, SA_SLOCKED, file, line);
 431
 432         /*
 433          * Try to switch from one shared lock to an exclusive lock.  We need
 434          * to maintain the SX_LOCK_EXCLUSIVE_WAITERS flag if set so that
 435          * we will wake up the exclusive waiters when we drop the lock.
 436          */
 437         success = 0;
 438         x = SX_READ_VALUE(sx);
 439         for (;;) {
 440                 if (SX_SHARERS(x) > 1)
 441                         break;
 442                 waiters = (x & SX_LOCK_WAITERS);
 443                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x,
 444                     (uintptr_t)curthread | waiters)) {
 445                         success = 1;
 446                         break;
 447                 }
 448         }
 449         LOCK_LOG_TRY("XUPGRADE", &sx->lock_object, 0, success, file, line);
 450         if (success) {
 451                 curthread->td_sx_slocks--;
 452                 WITNESS_UPGRADE(&sx->lock_object, LOP_EXCLUSIVE | LOP_TRYLOCK,
 453                     file, line);
 454                 LOCKSTAT_RECORD0(sx__upgrade, sx);
 455         }
 456         return (success);
 457 }
 458
 459 int
 460 sx_try_upgrade_(struct sx *sx, const char *file, int line)
 461 {
 462
 463         return (sx_try_upgrade_int(sx LOCK_FILE_LINE_ARG));
 464 }
 465
 466 /*
 467  * Downgrade an unrecursed exclusive lock into a single shared lock.
 468  */
 469 void
 470 sx_downgrade_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
 471 {
 472         uintptr_t x;
 473         int wakeup_swapper;
 474
 475         if (SCHEDULER_STOPPED())
 476                 return;
 477
 478         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
 479             ("sx_downgrade() of destroyed sx @ %s:%d", file, line));
 480         _sx_assert(sx, SA_XLOCKED | SA_NOTRECURSED, file, line);
 481 #ifndef INVARIANTS
 482         if (sx_recursed(sx))
 483                 panic("downgrade of a recursed lock");
 484 #endif
 485
 486         WITNESS_DOWNGRADE(&sx->lock_object, 0, file, line);
 487
 488         /*
 489          * Try to switch from an exclusive lock with no shared waiters
 490          * to one sharer with no shared waiters.  If there are
 491          * exclusive waiters, we don't need to lock the sleep queue so
 492          * long as we preserve the flag.  We do one quick try and if
 493          * that fails we grab the sleepq lock to keep the flags from
 494          * changing and do it the slow way.
 495          *
 496          * We have to lock the sleep queue if there are shared waiters
 497          * so we can wake them up.
 498          */
 499         x = sx->sx_lock;
 500         if (!(x & SX_LOCK_SHARED_WAITERS) &&
 501             atomic_cmpset_rel_ptr(&sx->sx_lock, x, SX_SHARERS_LOCK(1) |
 502             (x & SX_LOCK_EXCLUSIVE_WAITERS)))
 503                 goto out;
 504
 505         /*
 506          * Lock the sleep queue so we can read the waiters bits
 507          * without any races and wakeup any shared waiters.
 508          */
 509         sleepq_lock(&sx->lock_object);
 510
 511         /*
 512          * Preserve SX_LOCK_EXCLUSIVE_WAITERS while downgraded to a single
 513          * shared lock.  If there are any shared waiters, wake them up.
 514          */
 515         wakeup_swapper = 0;
 516         x = sx->sx_lock;
 517         atomic_store_rel_ptr(&sx->sx_lock, SX_SHARERS_LOCK(1) |
 518             (x & SX_LOCK_EXCLUSIVE_WAITERS));
 519         if (x & SX_LOCK_SHARED_WAITERS)
 520                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
 521                     0, SQ_SHARED_QUEUE);
 522         sleepq_release(&sx->lock_object);
 523
 524         if (wakeup_swapper)
 525                 kick_proc0();
 526
 527 out:
 528         curthread->td_sx_slocks++;
 529         LOCK_LOG_LOCK("XDOWNGRADE", &sx->lock_object, 0, 0, file, line);
 530         LOCKSTAT_RECORD0(sx__downgrade, sx);
 531 }
 532
 533 void
 534 sx_downgrade_(struct sx *sx, const char *file, int line)
 535 {
 536
 537         sx_downgrade_int(sx LOCK_FILE_LINE_ARG);
 538 }
 539
 540 #ifdef  ADAPTIVE_SX
 541 static inline void
 542 sx_drop_critical(uintptr_t x, bool *in_critical, int *extra_work)
 543 {
 544
 545         if (x & SX_LOCK_WRITE_SPINNER)
 546                 return;
 547         if (*in_critical) {
 548                 critical_exit();
 549                 *in_critical = false;
 550                 (*extra_work)--;
 551         }
 552 }
 553 #else
 554 #define sx_drop_critical(x, in_critical, extra_work) do { } while(0)
 555 #endif
 556
 557 /*
 558  * This function represents the so-called 'hard case' for sx_xlock
 559  * operation.  All 'easy case' failures are redirected to this.  Note
 560  * that ideally this would be a static function, but it needs to be
 561  * accessible from at least sx.h.
 562  */
 563 int
 564 _sx_xlock_hard(struct sx *sx, uintptr_t x, int opts LOCK_FILE_LINE_ARG_DEF)
 565 {
 566         GIANT_DECLARE;
 567         uintptr_t tid, setx;
 568 #ifdef ADAPTIVE_SX
 569         volatile struct thread *owner;
 570         u_int i, n, spintries = 0;
 571         enum { READERS, WRITER } sleep_reason = READERS;
 572         bool in_critical = false;
 573 #endif
 574 #ifdef LOCK_PROFILING
 575         uint64_t waittime = 0;
 576         int contested = 0;
 577 #endif
 578         int error = 0;
 579 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
 580         struct lock_delay_arg lda;
 581 #endif
 582 #ifdef  KDTRACE_HOOKS
 583         u_int sleep_cnt = 0;
 584         int64_t sleep_time = 0;
 585         int64_t all_time = 0;
 586 #endif
 587 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 588         uintptr_t state = 0;
 589         int doing_lockprof = 0;
 590 #endif
 591         int extra_work = 0;
 592
 593         tid = (uintptr_t)curthread;
 594
 595 #ifdef KDTRACE_HOOKS
 596         if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
 597                 while (x == SX_LOCK_UNLOCKED) {
 598                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 599                                 goto out_lockstat;
 600                 }
 601                 extra_work = 1;
 602                 doing_lockprof = 1;
 603                 all_time -= lockstat_nsecs(&sx->lock_object);
 604                 state = x;
 605         }
 606 #endif
 607 #ifdef LOCK_PROFILING
 608         extra_work = 1;
 609         doing_lockprof = 1;
 610         state = x;
 611 #endif
 612
 613         if (SCHEDULER_STOPPED())
 614                 return (0);
 615
 616 #if defined(ADAPTIVE_SX)
 617         lock_delay_arg_init(&lda, &sx_delay);
 618 #elif defined(KDTRACE_HOOKS)
 619         lock_delay_arg_init(&lda, NULL);
 620 #endif
 621
 622         if (__predict_false(x == SX_LOCK_UNLOCKED))
 623                 x = SX_READ_VALUE(sx);
 624
 625         /* If we already hold an exclusive lock, then recurse. */
 626         if (__predict_false(lv_sx_owner(x) == (struct thread *)tid)) {
 627                 KASSERT((sx->lock_object.lo_flags & LO_RECURSABLE) != 0,
 628             ("_sx_xlock_hard: recursed on non-recursive sx %s @ %s:%d\n",
 629                     sx->lock_object.lo_name, file, line));
 630                 sx->sx_recurse++;
 631                 atomic_set_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 632                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 633                         CTR2(KTR_LOCK, "%s: %p recursing", __func__, sx);
 634                 return (0);
 635         }
 636
 637         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 638                 CTR5(KTR_LOCK, "%s: %s contested (lock=%p) at %s:%d", __func__,
 639                     sx->lock_object.lo_name, (void *)sx->sx_lock, file, line);
 640
 641 #ifdef HWPMC_HOOKS
 642         PMC_SOFT_CALL( , , lock, failed);
 643 #endif
 644         lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
 645             &waittime);
 646
 647 #ifndef INVARIANTS
 648         GIANT_SAVE(extra_work);
 649 #endif
 650
 651         for (;;) {
 652                 if (x == SX_LOCK_UNLOCKED) {
 653                         if (atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid))
 654                                 break;
 655                         continue;
 656                 }
 657 #ifdef INVARIANTS
 658                 GIANT_SAVE(extra_work);
 659 #endif
 660 #ifdef KDTRACE_HOOKS
 661                 lda.spin_cnt++;
 662 #endif
 663 #ifdef ADAPTIVE_SX
 664                 /*
 665                  * If the lock is write locked and the owner is
 666                  * running on another CPU, spin until the owner stops
 667                  * running or the state of the lock changes.
 668                  */
 669                 if ((x & SX_LOCK_SHARED) == 0) {
 670                         sx_drop_critical(x, &in_critical, &extra_work);
 671                         sleep_reason = WRITER;
 672                         owner = lv_sx_owner(x);
 673                         if (!TD_IS_RUNNING(owner))
 674                                 goto sleepq;
 675                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 676                                 CTR3(KTR_LOCK, "%s: spinning on %p held by %p",
 677                                     __func__, sx, owner);
 678                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 679                             "spinning", "lockname:\"%s\"",
 680                             sx->lock_object.lo_name);
 681                         do {
 682                                 lock_delay(&lda);
 683                                 x = SX_READ_VALUE(sx);
 684                                 owner = lv_sx_owner(x);
 685                         } while (owner != NULL && TD_IS_RUNNING(owner));
 686                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 687                             "running");
 688                         continue;
 689                 } else if (SX_SHARERS(x) > 0) {
 690                         sleep_reason = READERS;
 691                         if (spintries == asx_retries)
 692                                 goto sleepq;
 693                         if (!(x & SX_LOCK_WRITE_SPINNER)) {
 694                                 if (!in_critical) {
 695                                         critical_enter();
 696                                         in_critical = true;
 697                                         extra_work++;
 698                                 }
 699                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 700                                     x | SX_LOCK_WRITE_SPINNER)) {
 701                                         critical_exit();
 702                                         in_critical = false;
 703                                         extra_work--;
 704                                         continue;
 705                                 }
 706                         }
 707                         spintries++;
 708                         KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
 709                             "spinning", "lockname:\"%s\"",
 710                             sx->lock_object.lo_name);
 711                         n = SX_SHARERS(x);
 712                         for (i = 0; i < asx_loops; i += n) {
 713                                 lock_delay_spin(n);
 714                                 x = SX_READ_VALUE(sx);
 715                                 if (!(x & SX_LOCK_WRITE_SPINNER))
 716                                         break;
 717                                 if (!(x & SX_LOCK_SHARED))
 718                                         break;
 719                                 n = SX_SHARERS(x);
 720                                 if (n == 0)
 721                                         break;
 722                         }
 723 #ifdef KDTRACE_HOOKS
 724                         lda.spin_cnt += i;
 725 #endif
 726                         KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
 727                             "running");
 728                         if (i < asx_loops)
 729                                 continue;
 730                 }
 731 sleepq:
 732 #endif
 733                 sleepq_lock(&sx->lock_object);
 734                 x = SX_READ_VALUE(sx);
 735 retry_sleepq:
 736
 737                 /*
 738                  * If the lock was released while spinning on the
 739                  * sleep queue chain lock, try again.
 740                  */
 741                 if (x == SX_LOCK_UNLOCKED) {
 742                         sleepq_release(&sx->lock_object);
 743                         sx_drop_critical(x, &in_critical, &extra_work);
 744                         continue;
 745                 }
 746
 747 #ifdef ADAPTIVE_SX
 748                 /*
 749                  * The current lock owner might have started executing
 750                  * on another CPU (or the lock could have changed
 751                  * owners) while we were waiting on the sleep queue
 752                  * chain lock.  If so, drop the sleep queue lock and try
 753                  * again.
 754                  */
 755                 if (!(x & SX_LOCK_SHARED)) {
 756                         owner = (struct thread *)SX_OWNER(x);
 757                         if (TD_IS_RUNNING(owner)) {
 758                                 sleepq_release(&sx->lock_object);
 759                                 sx_drop_critical(x, &in_critical,
 760                                     &extra_work);
 761                                 continue;
 762                         }
 763                 } else if (SX_SHARERS(x) > 0 && sleep_reason == WRITER) {
 764                         sleepq_release(&sx->lock_object);
 765                         sx_drop_critical(x, &in_critical, &extra_work);
 766                         continue;
 767                 }
 768 #endif
 769
 770                 /*
 771                  * If an exclusive lock was released with both shared
 772                  * and exclusive waiters and a shared waiter hasn't
 773                  * woken up and acquired the lock yet, sx_lock will be
 774                  * set to SX_LOCK_UNLOCKED | SX_LOCK_EXCLUSIVE_WAITERS.
 775                  * If we see that value, try to acquire it once.  Note
 776                  * that we have to preserve SX_LOCK_EXCLUSIVE_WAITERS
 777                  * as there are other exclusive waiters still.  If we
 778                  * fail, restart the loop.
 779                  */
 780                 setx = x & (SX_LOCK_WAITERS | SX_LOCK_WRITE_SPINNER);
 781                 if ((x & ~setx) == SX_LOCK_SHARED) {
 782                         setx &= ~SX_LOCK_WRITE_SPINNER;
 783                         if (!atomic_fcmpset_acq_ptr(&sx->sx_lock, &x, tid | setx))
 784                                 goto retry_sleepq;
 785                         sleepq_release(&sx->lock_object);
 786                         CTR2(KTR_LOCK, "%s: %p claimed by new writer",
 787                             __func__, sx);
 788                         break;
 789                 }
 790
 791 #ifdef ADAPTIVE_SX
 792                 /*
 793                  * It is possible we set the SX_LOCK_WRITE_SPINNER bit.
 794                  * It is an invariant that when the bit is set, there is
 795                  * a writer ready to grab the lock. Thus clear the bit since
 796                  * we are going to sleep.
 797                  */
 798                 if (in_critical) {
 799                         if ((x & SX_LOCK_WRITE_SPINNER) ||
 800                             !((x & SX_LOCK_EXCLUSIVE_WAITERS))) {
 801                                 setx = x & ~SX_LOCK_WRITE_SPINNER;
 802                                 setx |= SX_LOCK_EXCLUSIVE_WAITERS;
 803                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 804                                     setx)) {
 805                                         goto retry_sleepq;
 806                                 }
 807                         }
 808                         critical_exit();
 809                         in_critical = false;
 810                 } else {
 811 #endif
 812                         /*
 813                          * Try to set the SX_LOCK_EXCLUSIVE_WAITERS.  If we fail,
 814                          * than loop back and retry.
 815                          */
 816                         if (!(x & SX_LOCK_EXCLUSIVE_WAITERS)) {
 817                                 if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
 818                                     x | SX_LOCK_EXCLUSIVE_WAITERS)) {
 819                                         goto retry_sleepq;
 820                                 }
 821                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 822                                         CTR2(KTR_LOCK, "%s: %p set excl waiters flag",
 823                                             __func__, sx);
 824                         }
 825 #ifdef ADAPTIVE_SX
 826                 }
 827 #endif
 828
 829                 /*
 830                  * Since we have been unable to acquire the exclusive
 831                  * lock and the exclusive waiters flag is set, we have
 832                  * to sleep.
 833                  */
 834                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 835                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
 836                             __func__, sx);
 837
 838 #ifdef KDTRACE_HOOKS
 839                 sleep_time -= lockstat_nsecs(&sx->lock_object);
 840 #endif
 841                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
 842                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
 843                     SLEEPQ_INTERRUPTIBLE : 0), SQ_EXCLUSIVE_QUEUE);
 844                 if (!(opts & SX_INTERRUPTIBLE))
 845                         sleepq_wait(&sx->lock_object, 0);
 846                 else
 847                         error = sleepq_wait_sig(&sx->lock_object, 0);
 848 #ifdef KDTRACE_HOOKS
 849                 sleep_time += lockstat_nsecs(&sx->lock_object);
 850                 sleep_cnt++;
 851 #endif
 852                 if (error) {
 853                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 854                                 CTR2(KTR_LOCK,
 855                         "%s: interruptible sleep by %p suspended by signal",
 856                                     __func__, sx);
 857                         break;
 858                 }
 859                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 860                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
 861                             __func__, sx);
 862                 x = SX_READ_VALUE(sx);
 863         }
 864         if (__predict_true(!extra_work))
 865                 return (error);
 866 #ifdef ADAPTIVE_SX
 867         if (in_critical)
 868                 critical_exit();
 869 #endif
 870         GIANT_RESTORE();
 871 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
 872         if (__predict_true(!doing_lockprof))
 873                 return (error);
 874 #endif
 875 #ifdef KDTRACE_HOOKS
 876         all_time += lockstat_nsecs(&sx->lock_object);
 877         if (sleep_time)
 878                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
 879                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 880                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 881         if (lda.spin_cnt > sleep_cnt)
 882                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
 883                     LOCKSTAT_WRITER, (state & SX_LOCK_SHARED) == 0,
 884                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
 885 out_lockstat:
 886 #endif
 887         if (!error)
 888                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
 889                     contested, waittime, file, line, LOCKSTAT_WRITER);
 890         return (error);
 891 }
 892
 893 /*
 894  * This function represents the so-called 'hard case' for sx_xunlock
 895  * operation.  All 'easy case' failures are redirected to this.  Note
 896  * that ideally this would be a static function, but it needs to be
 897  * accessible from at least sx.h.
 898  */
 899 void
 900 _sx_xunlock_hard(struct sx *sx, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
 901 {
 902         uintptr_t tid, setx;
 903         int queue, wakeup_swapper;
 904
 905         if (SCHEDULER_STOPPED())
 906                 return;
 907
 908         tid = (uintptr_t)curthread;
 909
 910         if (__predict_false(x == tid))
 911                 x = SX_READ_VALUE(sx);
 912
 913         MPASS(!(x & SX_LOCK_SHARED));
 914
 915         if (__predict_false(x & SX_LOCK_RECURSED)) {
 916                 /* The lock is recursed, unrecurse one level. */
 917                 if ((--sx->sx_recurse) == 0)
 918                         atomic_clear_ptr(&sx->sx_lock, SX_LOCK_RECURSED);
 919                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
 920                         CTR2(KTR_LOCK, "%s: %p unrecursing", __func__, sx);
 921                 return;
 922         }
 923
 924         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_WRITER);
 925         if (x == tid &&
 926             atomic_cmpset_rel_ptr(&sx->sx_lock, tid, SX_LOCK_UNLOCKED))
 927                 return;
 928
 929         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 930                 CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
 931
 932         sleepq_lock(&sx->lock_object);
 933         x = SX_READ_VALUE(sx);
 934         MPASS(x & (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS));
 935
 936         /*
 937          * The wake up algorithm here is quite simple and probably not
 938          * ideal.  It gives precedence to shared waiters if they are
 939          * present.  For this condition, we have to preserve the
 940          * state of the exclusive waiters flag.
 941          * If interruptible sleeps left the shared queue empty avoid a
 942          * starvation for the threads sleeping on the exclusive queue by giving
 943          * them precedence and cleaning up the shared waiters bit anyway.
 944          */
 945         setx = SX_LOCK_UNLOCKED;
 946         queue = SQ_SHARED_QUEUE;
 947         if ((x & SX_LOCK_EXCLUSIVE_WAITERS) != 0 &&
 948             sleepq_sleepcnt(&sx->lock_object, SQ_EXCLUSIVE_QUEUE) != 0) {
 949                 queue = SQ_EXCLUSIVE_QUEUE;
 950                 setx |= (x & SX_LOCK_SHARED_WAITERS);
 951         }
 952         atomic_store_rel_ptr(&sx->sx_lock, setx);
 953
 954         /* Wake up all the waiters for the specific queue. */
 955         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 956                 CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
 957                     __func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
 958                     "exclusive");
 959
 960         wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
 961             queue);
 962         sleepq_release(&sx->lock_object);
 963         if (wakeup_swapper)
 964                 kick_proc0();
 965 }
 966
 967 static bool __always_inline
 968 __sx_can_read(struct thread *td, uintptr_t x, bool fp)
 969 {
 970
 971         if ((x & (SX_LOCK_SHARED | SX_LOCK_EXCLUSIVE_WAITERS | SX_LOCK_WRITE_SPINNER))
 972                         == SX_LOCK_SHARED)
 973                 return (true);
 974         if (!fp && td->td_sx_slocks && (x & SX_LOCK_SHARED))
 975                 return (true);
 976         return (false);
 977 }
 978
 979 static bool __always_inline
 980 __sx_slock_try(struct sx *sx, struct thread *td, uintptr_t *xp, bool fp
 981     LOCK_FILE_LINE_ARG_DEF)
 982 {
 983
 984         /*
 985          * If no other thread has an exclusive lock then try to bump up
 986          * the count of sharers.  Since we have to preserve the state
 987          * of SX_LOCK_EXCLUSIVE_WAITERS, if we fail to acquire the
 988          * shared lock loop back and retry.
 989          */
 990         while (__sx_can_read(td, *xp, fp)) {
 991                 if (atomic_fcmpset_acq_ptr(&sx->sx_lock, xp,
 992                     *xp + SX_ONE_SHARER)) {
 993                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
 994                                 CTR4(KTR_LOCK, "%s: %p succeed %p -> %p",
 995                                     __func__, sx, (void *)*xp,
 996                                     (void *)(*xp + SX_ONE_SHARER));
 997                         td->td_sx_slocks++;
 998                         return (true);
 999                 }
1000         }
1001         return (false);
1002 }
1003
1004 static int __noinline
1005 _sx_slock_hard(struct sx *sx, int opts, uintptr_t x LOCK_FILE_LINE_ARG_DEF)
1006 {
1007         GIANT_DECLARE;
1008         struct thread *td;
1009 #ifdef ADAPTIVE_SX
1010         volatile struct thread *owner;
1011         u_int i, n, spintries = 0;
1012 #endif
1013 #ifdef LOCK_PROFILING
1014         uint64_t waittime = 0;
1015         int contested = 0;
1016 #endif
1017         int error = 0;
1018 #if defined(ADAPTIVE_SX) || defined(KDTRACE_HOOKS)
1019         struct lock_delay_arg lda;
1020 #endif
1021 #ifdef KDTRACE_HOOKS
1022         u_int sleep_cnt = 0;
1023         int64_t sleep_time = 0;
1024         int64_t all_time = 0;
1025 #endif
1026 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1027         uintptr_t state = 0;
1028 #endif
1029         int extra_work = 0;
1030
1031         td = curthread;
1032
1033 #ifdef KDTRACE_HOOKS
1034         if (LOCKSTAT_PROFILE_ENABLED(sx__acquire)) {
1035                 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1036                         goto out_lockstat;
1037                 extra_work = 1;
1038                 all_time -= lockstat_nsecs(&sx->lock_object);
1039                 state = x;
1040         }
1041 #endif
1042 #ifdef LOCK_PROFILING
1043         extra_work = 1;
1044         state = x;
1045 #endif
1046
1047         if (SCHEDULER_STOPPED())
1048                 return (0);
1049
1050 #if defined(ADAPTIVE_SX)
1051         lock_delay_arg_init(&lda, &sx_delay);
1052 #elif defined(KDTRACE_HOOKS)
1053         lock_delay_arg_init(&lda, NULL);
1054 #endif
1055
1056 #ifdef HWPMC_HOOKS
1057         PMC_SOFT_CALL( , , lock, failed);
1058 #endif
1059         lock_profile_obtain_lock_failed(&sx->lock_object, &contested,
1060             &waittime);
1061
1062 #ifndef INVARIANTS
1063         GIANT_SAVE(extra_work);
1064 #endif
1065
1066         /*
1067          * As with rwlocks, we don't make any attempt to try to block
1068          * shared locks once there is an exclusive waiter.
1069          */
1070         for (;;) {
1071                 if (__sx_slock_try(sx, td, &x, false LOCK_FILE_LINE_ARG))
1072                         break;
1073 #ifdef INVARIANTS
1074                 GIANT_SAVE(extra_work);
1075 #endif
1076 #ifdef KDTRACE_HOOKS
1077                 lda.spin_cnt++;
1078 #endif
1079
1080 #ifdef ADAPTIVE_SX
1081                 /*
1082                  * If the owner is running on another CPU, spin until
1083                  * the owner stops running or the state of the lock
1084                  * changes.
1085                  */
1086                 if ((x & SX_LOCK_SHARED) == 0) {
1087                         owner = lv_sx_owner(x);
1088                         if (TD_IS_RUNNING(owner)) {
1089                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1090                                         CTR3(KTR_LOCK,
1091                                             "%s: spinning on %p held by %p",
1092                                             __func__, sx, owner);
1093                                 KTR_STATE1(KTR_SCHED, "thread",
1094                                     sched_tdname(curthread), "spinning",
1095                                     "lockname:\"%s\"", sx->lock_object.lo_name);
1096                                 do {
1097                                         lock_delay(&lda);
1098                                         x = SX_READ_VALUE(sx);
1099                                         owner = lv_sx_owner(x);
1100                                 } while (owner != NULL && TD_IS_RUNNING(owner));
1101                                 KTR_STATE0(KTR_SCHED, "thread",
1102                                     sched_tdname(curthread), "running");
1103                                 continue;
1104                         }
1105                 } else {
1106                         if ((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) {
1107                                 MPASS(!__sx_can_read(td, x, false));
1108                                 lock_delay_spin(2);
1109                                 x = SX_READ_VALUE(sx);
1110                                 continue;
1111                         }
1112                         if (spintries < asx_retries) {
1113                                 KTR_STATE1(KTR_SCHED, "thread", sched_tdname(curthread),
1114                                     "spinning", "lockname:\"%s\"",
1115                                     sx->lock_object.lo_name);
1116                                 n = SX_SHARERS(x);
1117                                 for (i = 0; i < asx_loops; i += n) {
1118                                         lock_delay_spin(n);
1119                                         x = SX_READ_VALUE(sx);
1120                                         if (!(x & SX_LOCK_SHARED))
1121                                                 break;
1122                                         n = SX_SHARERS(x);
1123                                         if (n == 0)
1124                                                 break;
1125                                         if (__sx_can_read(td, x, false))
1126                                                 break;
1127                                 }
1128 #ifdef KDTRACE_HOOKS
1129                                 lda.spin_cnt += i;
1130 #endif
1131                                 KTR_STATE0(KTR_SCHED, "thread", sched_tdname(curthread),
1132                                     "running");
1133                                 if (i < asx_loops)
1134                                         continue;
1135                         }
1136                 }
1137 #endif
1138
1139                 /*
1140                  * Some other thread already has an exclusive lock, so
1141                  * start the process of blocking.
1142                  */
1143                 sleepq_lock(&sx->lock_object);
1144                 x = SX_READ_VALUE(sx);
1145 retry_sleepq:
1146                 if (((x & SX_LOCK_WRITE_SPINNER) && SX_SHARERS(x) == 0) ||
1147                     __sx_can_read(td, x, false)) {
1148                         sleepq_release(&sx->lock_object);
1149                         continue;
1150                 }
1151
1152 #ifdef ADAPTIVE_SX
1153                 /*
1154                  * If the owner is running on another CPU, spin until
1155                  * the owner stops running or the state of the lock
1156                  * changes.
1157                  */
1158                 if (!(x & SX_LOCK_SHARED)) {
1159                         owner = (struct thread *)SX_OWNER(x);
1160                         if (TD_IS_RUNNING(owner)) {
1161                                 sleepq_release(&sx->lock_object);
1162                                 x = SX_READ_VALUE(sx);
1163                                 continue;
1164                         }
1165                 }
1166 #endif
1167
1168                 /*
1169                  * Try to set the SX_LOCK_SHARED_WAITERS flag.  If we
1170                  * fail to set it drop the sleep queue lock and loop
1171                  * back.
1172                  */
1173                 if (!(x & SX_LOCK_SHARED_WAITERS)) {
1174                         if (!atomic_fcmpset_ptr(&sx->sx_lock, &x,
1175                             x | SX_LOCK_SHARED_WAITERS))
1176                                 goto retry_sleepq;
1177                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1178                                 CTR2(KTR_LOCK, "%s: %p set shared waiters flag",
1179                                     __func__, sx);
1180                 }
1181
1182                 /*
1183                  * Since we have been unable to acquire the shared lock,
1184                  * we have to sleep.
1185                  */
1186                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1187                         CTR2(KTR_LOCK, "%s: %p blocking on sleep queue",
1188                             __func__, sx);
1189
1190 #ifdef KDTRACE_HOOKS
1191                 sleep_time -= lockstat_nsecs(&sx->lock_object);
1192 #endif
1193                 sleepq_add(&sx->lock_object, NULL, sx->lock_object.lo_name,
1194                     SLEEPQ_SX | ((opts & SX_INTERRUPTIBLE) ?
1195                     SLEEPQ_INTERRUPTIBLE : 0), SQ_SHARED_QUEUE);
1196                 if (!(opts & SX_INTERRUPTIBLE))
1197                         sleepq_wait(&sx->lock_object, 0);
1198                 else
1199                         error = sleepq_wait_sig(&sx->lock_object, 0);
1200 #ifdef KDTRACE_HOOKS
1201                 sleep_time += lockstat_nsecs(&sx->lock_object);
1202                 sleep_cnt++;
1203 #endif
1204                 if (error) {
1205                         if (LOCK_LOG_TEST(&sx->lock_object, 0))
1206                                 CTR2(KTR_LOCK,
1207                         "%s: interruptible sleep by %p suspended by signal",
1208                                     __func__, sx);
1209                         break;
1210                 }
1211                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1212                         CTR2(KTR_LOCK, "%s: %p resuming from sleep queue",
1213                             __func__, sx);
1214                 x = SX_READ_VALUE(sx);
1215         }
1216 #if defined(KDTRACE_HOOKS) || defined(LOCK_PROFILING)
1217         if (__predict_true(!extra_work))
1218                 return (error);
1219 #endif
1220 #ifdef KDTRACE_HOOKS
1221         all_time += lockstat_nsecs(&sx->lock_object);
1222         if (sleep_time)
1223                 LOCKSTAT_RECORD4(sx__block, sx, sleep_time,
1224                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1225                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1226         if (lda.spin_cnt > sleep_cnt)
1227                 LOCKSTAT_RECORD4(sx__spin, sx, all_time - sleep_time,
1228                     LOCKSTAT_READER, (state & SX_LOCK_SHARED) == 0,
1229                     (state & SX_LOCK_SHARED) == 0 ? 0 : SX_SHARERS(state));
1230 out_lockstat:
1231 #endif
1232         if (error == 0) {
1233                 LOCKSTAT_PROFILE_OBTAIN_RWLOCK_SUCCESS(sx__acquire, sx,
1234                     contested, waittime, file, line, LOCKSTAT_READER);
1235         }
1236         GIANT_RESTORE();
1237         return (error);
1238 }
1239
1240 int
1241 _sx_slock_int(struct sx *sx, int opts LOCK_FILE_LINE_ARG_DEF)
1242 {
1243         struct thread *td;
1244         uintptr_t x;
1245         int error;
1246
1247         KASSERT(kdb_active != 0 || SCHEDULER_STOPPED() ||
1248             !TD_IS_IDLETHREAD(curthread),
1249             ("sx_slock() by idle thread %p on sx %s @ %s:%d",
1250             curthread, sx->lock_object.lo_name, file, line));
1251         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1252             ("sx_slock() of destroyed sx @ %s:%d", file, line));
1253         WITNESS_CHECKORDER(&sx->lock_object, LOP_NEWORDER, file, line, NULL);
1254
1255         error = 0;
1256         td = curthread;
1257         x = SX_READ_VALUE(sx);
1258         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__acquire) ||
1259             !__sx_slock_try(sx, td, &x, true LOCK_FILE_LINE_ARG)))
1260                 error = _sx_slock_hard(sx, opts, x LOCK_FILE_LINE_ARG);
1261         else
1262                 lock_profile_obtain_lock_success(&sx->lock_object, 0, 0,
1263                     file, line);
1264         if (error == 0) {
1265                 LOCK_LOG_LOCK("SLOCK", &sx->lock_object, 0, 0, file, line);
1266                 WITNESS_LOCK(&sx->lock_object, 0, file, line);
1267                 TD_LOCKS_INC(curthread);
1268         }
1269         return (error);
1270 }
1271
1272 int
1273 _sx_slock(struct sx *sx, int opts, const char *file, int line)
1274 {
1275
1276         return (_sx_slock_int(sx, opts LOCK_FILE_LINE_ARG));
1277 }
1278
1279 static bool __always_inline
1280 _sx_sunlock_try(struct sx *sx, struct thread *td, uintptr_t *xp)
1281 {
1282
1283         for (;;) {
1284                 if (SX_SHARERS(*xp) > 1 || !(*xp & SX_LOCK_WAITERS)) {
1285                         if (atomic_fcmpset_rel_ptr(&sx->sx_lock, xp,
1286                             *xp - SX_ONE_SHARER)) {
1287                                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1288                                         CTR4(KTR_LOCK,
1289                                             "%s: %p succeeded %p -> %p",
1290                                             __func__, sx, (void *)*xp,
1291                                             (void *)(*xp - SX_ONE_SHARER));
1292                                 td->td_sx_slocks--;
1293                                 return (true);
1294                         }
1295                         continue;
1296                 }
1297                 break;
1298         }
1299         return (false);
1300 }
1301
1302 static void __noinline
1303 _sx_sunlock_hard(struct sx *sx, struct thread *td, uintptr_t x
1304     LOCK_FILE_LINE_ARG_DEF)
1305 {
1306         int wakeup_swapper = 0;
1307         uintptr_t setx, queue;
1308
1309         if (SCHEDULER_STOPPED())
1310                 return;
1311
1312         if (_sx_sunlock_try(sx, td, &x))
1313                 goto out_lockstat;
1314
1315         sleepq_lock(&sx->lock_object);
1316         x = SX_READ_VALUE(sx);
1317         for (;;) {
1318                 if (_sx_sunlock_try(sx, td, &x))
1319                         break;
1320
1321                 /*
1322                  * Wake up semantic here is quite simple:
1323                  * Just wake up all the exclusive waiters.
1324                  * Note that the state of the lock could have changed,
1325                  * so if it fails loop back and retry.
1326                  */
1327                 setx = SX_LOCK_UNLOCKED;
1328                 queue = SQ_SHARED_QUEUE;
1329                 if (x & SX_LOCK_EXCLUSIVE_WAITERS) {
1330                         setx |= (x & SX_LOCK_SHARED_WAITERS);
1331                         queue = SQ_EXCLUSIVE_QUEUE;
1332                 }
1333                 setx |= (x & SX_LOCK_WRITE_SPINNER);
1334                 if (!atomic_fcmpset_rel_ptr(&sx->sx_lock, &x, setx))
1335                         continue;
1336                 if (LOCK_LOG_TEST(&sx->lock_object, 0))
1337                         CTR2(KTR_LOCK, "%s: %p waking up all thread on"
1338                             "exclusive queue", __func__, sx);
1339                 wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX,
1340                     0, queue);
1341                 td->td_sx_slocks--;
1342                 break;
1343         }
1344         sleepq_release(&sx->lock_object);
1345         if (wakeup_swapper)
1346                 kick_proc0();
1347 out_lockstat:
1348         LOCKSTAT_PROFILE_RELEASE_RWLOCK(sx__release, sx, LOCKSTAT_READER);
1349 }
1350
1351 void
1352 _sx_sunlock_int(struct sx *sx LOCK_FILE_LINE_ARG_DEF)
1353 {
1354         struct thread *td;
1355         uintptr_t x;
1356
1357         KASSERT(sx->sx_lock != SX_LOCK_DESTROYED,
1358             ("sx_sunlock() of destroyed sx @ %s:%d", file, line));
1359         _sx_assert(sx, SA_SLOCKED, file, line);
1360         WITNESS_UNLOCK(&sx->lock_object, 0, file, line);
1361         LOCK_LOG_LOCK("SUNLOCK", &sx->lock_object, 0, 0, file, line);
1362
1363         td = curthread;
1364         x = SX_READ_VALUE(sx);
1365         if (__predict_false(LOCKSTAT_PROFILE_ENABLED(sx__release) ||
1366             !_sx_sunlock_try(sx, td, &x)))
1367                 _sx_sunlock_hard(sx, td, x LOCK_FILE_LINE_ARG);
1368         else
1369                 lock_profile_release_lock(&sx->lock_object);
1370
1371         TD_LOCKS_DEC(curthread);
1372 }
1373
1374 void
1375 _sx_sunlock(struct sx *sx, const char *file, int line)
1376 {
1377
1378         _sx_sunlock_int(sx LOCK_FILE_LINE_ARG);
1379 }
1380
1381 #ifdef INVARIANT_SUPPORT
1382 #ifndef INVARIANTS
1383 #undef  _sx_assert
1384 #endif
1385
1386 /*
1387  * In the non-WITNESS case, sx_assert() can only detect that at least
1388  * *some* thread owns an slock, but it cannot guarantee that *this*
1389  * thread owns an slock.
1390  */
1391 void
1392 _sx_assert(const struct sx *sx, int what, const char *file, int line)
1393 {
1394 #ifndef WITNESS
1395         int slocked = 0;
1396 #endif
1397
1398         if (SCHEDULER_STOPPED())
1399                 return;
1400         switch (what) {
1401         case SA_SLOCKED:
1402         case SA_SLOCKED | SA_NOTRECURSED:
1403         case SA_SLOCKED | SA_RECURSED:
1404 #ifndef WITNESS
1405                 slocked = 1;
1406                 /* FALLTHROUGH */
1407 #endif
1408         case SA_LOCKED:
1409         case SA_LOCKED | SA_NOTRECURSED:
1410         case SA_LOCKED | SA_RECURSED:
1411 #ifdef WITNESS
1412                 witness_assert(&sx->lock_object, what, file, line);
1413 #else
1414                 /*
1415                  * If some other thread has an exclusive lock or we
1416                  * have one and are asserting a shared lock, fail.
1417                  * Also, if no one has a lock at all, fail.
1418                  */
1419                 if (sx->sx_lock == SX_LOCK_UNLOCKED ||
1420                     (!(sx->sx_lock & SX_LOCK_SHARED) && (slocked ||
1421                     sx_xholder(sx) != curthread)))
1422                         panic("Lock %s not %slocked @ %s:%d\n",
1423                             sx->lock_object.lo_name, slocked ? "share " : "",
1424                             file, line);
1425
1426                 if (!(sx->sx_lock & SX_LOCK_SHARED)) {
1427                         if (sx_recursed(sx)) {
1428                                 if (what & SA_NOTRECURSED)
1429                                         panic("Lock %s recursed @ %s:%d\n",
1430                                             sx->lock_object.lo_name, file,
1431                                             line);
1432                         } else if (what & SA_RECURSED)
1433                                 panic("Lock %s not recursed @ %s:%d\n",
1434                                     sx->lock_object.lo_name, file, line);
1435                 }
1436 #endif
1437                 break;
1438         case SA_XLOCKED:
1439         case SA_XLOCKED | SA_NOTRECURSED:
1440         case SA_XLOCKED | SA_RECURSED:
1441                 if (sx_xholder(sx) != curthread)
1442                         panic("Lock %s not exclusively locked @ %s:%d\n",
1443                             sx->lock_object.lo_name, file, line);
1444                 if (sx_recursed(sx)) {
1445                         if (what & SA_NOTRECURSED)
1446                                 panic("Lock %s recursed @ %s:%d\n",
1447                                     sx->lock_object.lo_name, file, line);
1448                 } else if (what & SA_RECURSED)
1449                         panic("Lock %s not recursed @ %s:%d\n",
1450                             sx->lock_object.lo_name, file, line);
1451                 break;
1452         case SA_UNLOCKED:
1453 #ifdef WITNESS
1454                 witness_assert(&sx->lock_object, what, file, line);
1455 #else
1456                 /*
1457                  * If we hold an exclusve lock fail.  We can't
1458                  * reliably check to see if we hold a shared lock or
1459                  * not.
1460                  */
1461                 if (sx_xholder(sx) == curthread)
1462                         panic("Lock %s exclusively locked @ %s:%d\n",
1463                             sx->lock_object.lo_name, file, line);
1464 #endif
1465                 break;
1466         default:
1467                 panic("Unknown sx lock assertion: %d @ %s:%d", what, file,
1468                     line);
1469         }
1470 }
1471 #endif  /* INVARIANT_SUPPORT */
1472
1473 #ifdef DDB
1474 static void
1475 db_show_sx(const struct lock_object *lock)
1476 {
1477         struct thread *td;
1478         const struct sx *sx;
1479
1480         sx = (const struct sx *)lock;
1481
1482         db_printf(" state: ");
1483         if (sx->sx_lock == SX_LOCK_UNLOCKED)
1484                 db_printf("UNLOCKED\n");
1485         else if (sx->sx_lock == SX_LOCK_DESTROYED) {
1486                 db_printf("DESTROYED\n");
1487                 return;
1488         } else if (sx->sx_lock & SX_LOCK_SHARED)
1489                 db_printf("SLOCK: %ju\n", (uintmax_t)SX_SHARERS(sx->sx_lock));
1490         else {
1491                 td = sx_xholder(sx);
1492                 db_printf("XLOCK: %p (tid %d, pid %d, \"%s\")\n", td,
1493                     td->td_tid, td->td_proc->p_pid, td->td_name);
1494                 if (sx_recursed(sx))
1495                         db_printf(" recursed: %d\n", sx->sx_recurse);
1496         }
1497
1498         db_printf(" waiters: ");
1499         switch(sx->sx_lock &
1500             (SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS)) {
1501         case SX_LOCK_SHARED_WAITERS:
1502                 db_printf("shared\n");
1503                 break;
1504         case SX_LOCK_EXCLUSIVE_WAITERS:
1505                 db_printf("exclusive\n");
1506                 break;
1507         case SX_LOCK_SHARED_WAITERS | SX_LOCK_EXCLUSIVE_WAITERS:
1508                 db_printf("exclusive and shared\n");
1509                 break;
1510         default:
1511                 db_printf("none\n");
1512         }
1513 }
1514
1515 /*
1516  * Check to see if a thread that is blocked on a sleep queue is actually
1517  * blocked on an sx lock.  If so, output some details and return true.
1518  * If the lock has an exclusive owner, return that in *ownerp.
1519  */
1520 int
1521 sx_chain(struct thread *td, struct thread **ownerp)
1522 {
1523         struct sx *sx;
1524
1525         /*
1526          * Check to see if this thread is blocked on an sx lock.
1527          * First, we check the lock class.  If that is ok, then we
1528          * compare the lock name against the wait message.
1529          */
1530         sx = td->td_wchan;
1531         if (LOCK_CLASS(&sx->lock_object) != &lock_class_sx ||
1532             sx->lock_object.lo_name != td->td_wmesg)
1533                 return (0);
1534
1535         /* We think we have an sx lock, so output some details. */
1536         db_printf("blocked on sx \"%s\" ", td->td_wmesg);
1537         *ownerp = sx_xholder(sx);
1538         if (sx->sx_lock & SX_LOCK_SHARED)
1539                 db_printf("SLOCK (count %ju)\n",
1540                     (uintmax_t)SX_SHARERS(sx->sx_lock));
1541         else
1542                 db_printf("XLOCK\n");
1543         return (1);
1544 }
1545 #endif