sys/kern/kern_rmlock.c

   1 /*-
   2  * Copyright (c) 2007 Stephan Uphoff <ups@FreeBSD.org>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the author nor the names of any co-contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  29
  30 /*
  31  * Machine independent bits of reader/writer lock implementation.
  32  */
  33
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "opt_ddb.h"
  38 #include "opt_kdtrace.h"
  39
  40 #include <sys/param.h>
  41 #include <sys/systm.h>
  42
  43 #include <sys/kernel.h>
  44 #include <sys/kdb.h>
  45 #include <sys/ktr.h>
  46 #include <sys/lock.h>
  47 #include <sys/mutex.h>
  48 #include <sys/proc.h>
  49 #include <sys/rmlock.h>
  50 #include <sys/sched.h>
  51 #include <sys/smp.h>
  52 #include <sys/turnstile.h>
  53 #include <sys/lock_profile.h>
  54 #include <machine/cpu.h>
  55
  56 #ifdef DDB
  57 #include <ddb/ddb.h>
  58 #endif
  59
  60 /*
  61  * A cookie to mark destroyed rmlocks.  This is stored in the head of
  62  * rm_activeReaders.
  63  */
  64 #define RM_DESTROYED    ((void *)0xdead)
  65
  66 #define rm_destroyed(rm)                                                \
  67         (LIST_FIRST(&(rm)->rm_activeReaders) == RM_DESTROYED)
  68
  69 #define RMPF_ONQUEUE    1
  70 #define RMPF_SIGNAL     2
  71
  72 #ifndef INVARIANTS
  73 #define _rm_assert(c, what, file, line)
  74 #endif
  75
  76 static void     assert_rm(const struct lock_object *lock, int what);
  77 #ifdef DDB
  78 static void     db_show_rm(const struct lock_object *lock);
  79 #endif
  80 static void     lock_rm(struct lock_object *lock, uintptr_t how);
  81 #ifdef KDTRACE_HOOKS
  82 static int      owner_rm(const struct lock_object *lock, struct thread **owner);
  83 #endif
  84 static uintptr_t unlock_rm(struct lock_object *lock);
  85
  86 struct lock_class lock_class_rm = {
  87         .lc_name = "rm",
  88         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
  89         .lc_assert = assert_rm,
  90 #ifdef DDB
  91         .lc_ddb_show = db_show_rm,
  92 #endif
  93         .lc_lock = lock_rm,
  94         .lc_unlock = unlock_rm,
  95 #ifdef KDTRACE_HOOKS
  96         .lc_owner = owner_rm,
  97 #endif
  98 };
  99
 100 struct lock_class lock_class_rm_sleepable = {
 101         .lc_name = "sleepable rm",
 102         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE,
 103         .lc_assert = assert_rm,
 104 #ifdef DDB
 105         .lc_ddb_show = db_show_rm,
 106 #endif
 107         .lc_lock = lock_rm,
 108         .lc_unlock = unlock_rm,
 109 #ifdef KDTRACE_HOOKS
 110         .lc_owner = owner_rm,
 111 #endif
 112 };
 113
 114 static void
 115 assert_rm(const struct lock_object *lock, int what)
 116 {
 117
 118         rm_assert((const struct rmlock *)lock, what);
 119 }
 120
 121 static void
 122 lock_rm(struct lock_object *lock, uintptr_t how)
 123 {
 124         struct rmlock *rm;
 125         struct rm_priotracker *tracker;
 126
 127         rm = (struct rmlock *)lock;
 128         if (how == 0)
 129                 rm_wlock(rm);
 130         else {
 131                 tracker = (struct rm_priotracker *)how;
 132                 rm_rlock(rm, tracker);
 133         }
 134 }
 135
 136 static uintptr_t
 137 unlock_rm(struct lock_object *lock)
 138 {
 139         struct thread *td;
 140         struct pcpu *pc;
 141         struct rmlock *rm;
 142         struct rm_queue *queue;
 143         struct rm_priotracker *tracker;
 144         uintptr_t how;
 145
 146         rm = (struct rmlock *)lock;
 147         tracker = NULL;
 148         how = 0;
 149         rm_assert(rm, RA_LOCKED | RA_NOTRECURSED);
 150         if (rm_wowned(rm))
 151                 rm_wunlock(rm);
 152         else {
 153                 /*
 154                  * Find the right rm_priotracker structure for curthread.
 155                  * The guarantee about its uniqueness is given by the fact
 156                  * we already asserted the lock wasn't recursively acquired.
 157                  */
 158                 critical_enter();
 159                 td = curthread;
 160                 pc = pcpu_find(curcpu);
 161                 for (queue = pc->pc_rm_queue.rmq_next;
 162                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 163                         tracker = (struct rm_priotracker *)queue;
 164                                 if ((tracker->rmp_rmlock == rm) &&
 165                                     (tracker->rmp_thread == td)) {
 166                                         how = (uintptr_t)tracker;
 167                                         break;
 168                                 }
 169                 }
 170                 KASSERT(tracker != NULL,
 171                     ("rm_priotracker is non-NULL when lock held in read mode"));
 172                 critical_exit();
 173                 rm_runlock(rm, tracker);
 174         }
 175         return (how);
 176 }
 177
 178 #ifdef KDTRACE_HOOKS
 179 static int
 180 owner_rm(const struct lock_object *lock, struct thread **owner)
 181 {
 182         const struct rmlock *rm;
 183         struct lock_class *lc;
 184
 185         rm = (const struct rmlock *)lock;
 186         lc = LOCK_CLASS(&rm->rm_wlock_object);
 187         return (lc->lc_owner(&rm->rm_wlock_object, owner));
 188 }
 189 #endif
 190
 191 static struct mtx rm_spinlock;
 192
 193 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
 194
 195 /*
 196  * Add or remove tracker from per-cpu list.
 197  *
 198  * The per-cpu list can be traversed at any time in forward direction from an
 199  * interrupt on the *local* cpu.
 200  */
 201 static void inline
 202 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
 203 {
 204         struct rm_queue *next;
 205
 206         /* Initialize all tracker pointers */
 207         tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
 208         next = pc->pc_rm_queue.rmq_next;
 209         tracker->rmp_cpuQueue.rmq_next = next;
 210
 211         /* rmq_prev is not used during froward traversal. */
 212         next->rmq_prev = &tracker->rmp_cpuQueue;
 213
 214         /* Update pointer to first element. */
 215         pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
 216 }
 217
 218 /*
 219  * Return a count of the number of trackers the thread 'td' already
 220  * has on this CPU for the lock 'rm'.
 221  */
 222 static int
 223 rm_trackers_present(const struct pcpu *pc, const struct rmlock *rm,
 224     const struct thread *td)
 225 {
 226         struct rm_queue *queue;
 227         struct rm_priotracker *tracker;
 228         int count;
 229
 230         count = 0;
 231         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
 232             queue = queue->rmq_next) {
 233                 tracker = (struct rm_priotracker *)queue;
 234                 if ((tracker->rmp_rmlock == rm) && (tracker->rmp_thread == td))
 235                         count++;
 236         }
 237         return (count);
 238 }
 239
 240 static void inline
 241 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
 242 {
 243         struct rm_queue *next, *prev;
 244
 245         next = tracker->rmp_cpuQueue.rmq_next;
 246         prev = tracker->rmp_cpuQueue.rmq_prev;
 247
 248         /* Not used during forward traversal. */
 249         next->rmq_prev = prev;
 250
 251         /* Remove from list. */
 252         prev->rmq_next = next;
 253 }
 254
 255 static void
 256 rm_cleanIPI(void *arg)
 257 {
 258         struct pcpu *pc;
 259         struct rmlock *rm = arg;
 260         struct rm_priotracker *tracker;
 261         struct rm_queue *queue;
 262         pc = pcpu_find(curcpu);
 263
 264         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
 265             queue = queue->rmq_next) {
 266                 tracker = (struct rm_priotracker *)queue;
 267                 if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
 268                         tracker->rmp_flags = RMPF_ONQUEUE;
 269                         mtx_lock_spin(&rm_spinlock);
 270                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 271                             rmp_qentry);
 272                         mtx_unlock_spin(&rm_spinlock);
 273                 }
 274         }
 275 }
 276
 277 void
 278 rm_init_flags(struct rmlock *rm, const char *name, int opts)
 279 {
 280         struct lock_class *lc;
 281         int liflags, xflags;
 282
 283         liflags = 0;
 284         if (!(opts & RM_NOWITNESS))
 285                 liflags |= LO_WITNESS;
 286         if (opts & RM_RECURSE)
 287                 liflags |= LO_RECURSABLE;
 288         if (opts & RM_NEW)
 289                 liflags |= LO_NEW;
 290         rm->rm_writecpus = all_cpus;
 291         LIST_INIT(&rm->rm_activeReaders);
 292         if (opts & RM_SLEEPABLE) {
 293                 liflags |= LO_SLEEPABLE;
 294                 lc = &lock_class_rm_sleepable;
 295                 xflags = (opts & RM_NEW ? SX_NEW : 0);
 296                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx",
 297                     xflags | SX_NOWITNESS);
 298         } else {
 299                 lc = &lock_class_rm;
 300                 xflags = (opts & RM_NEW ? MTX_NEW : 0);
 301                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx",
 302                     xflags | MTX_NOWITNESS);
 303         }
 304         lock_init(&rm->lock_object, lc, name, NULL, liflags);
 305 }
 306
 307 void
 308 rm_init(struct rmlock *rm, const char *name)
 309 {
 310
 311         rm_init_flags(rm, name, 0);
 312 }
 313
 314 void
 315 rm_destroy(struct rmlock *rm)
 316 {
 317
 318         rm_assert(rm, RA_UNLOCKED);
 319         LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
 320         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 321                 sx_destroy(&rm->rm_lock_sx);
 322         else
 323                 mtx_destroy(&rm->rm_lock_mtx);
 324         lock_destroy(&rm->lock_object);
 325 }
 326
 327 int
 328 rm_wowned(const struct rmlock *rm)
 329 {
 330
 331         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 332                 return (sx_xlocked(&rm->rm_lock_sx));
 333         else
 334                 return (mtx_owned(&rm->rm_lock_mtx));
 335 }
 336
 337 void
 338 rm_sysinit(void *arg)
 339 {
 340         struct rm_args *args = arg;
 341
 342         rm_init(args->ra_rm, args->ra_desc);
 343 }
 344
 345 void
 346 rm_sysinit_flags(void *arg)
 347 {
 348         struct rm_args_flags *args = arg;
 349
 350         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_opts);
 351 }
 352
 353 static int
 354 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 355 {
 356         struct pcpu *pc;
 357
 358         critical_enter();
 359         pc = pcpu_find(curcpu);
 360
 361         /* Check if we just need to do a proper critical_exit. */
 362         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
 363                 critical_exit();
 364                 return (1);
 365         }
 366
 367         /* Remove our tracker from the per-cpu list. */
 368         rm_tracker_remove(pc, tracker);
 369
 370         /* Check to see if the IPI granted us the lock after all. */
 371         if (tracker->rmp_flags) {
 372                 /* Just add back tracker - we hold the lock. */
 373                 rm_tracker_add(pc, tracker);
 374                 critical_exit();
 375                 return (1);
 376         }
 377
 378         /*
 379          * We allow readers to acquire a lock even if a writer is blocked if
 380          * the lock is recursive and the reader already holds the lock.
 381          */
 382         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 383                 /*
 384                  * Just grant the lock if this thread already has a tracker
 385                  * for this lock on the per-cpu queue.
 386                  */
 387                 if (rm_trackers_present(pc, rm, curthread) != 0) {
 388                         mtx_lock_spin(&rm_spinlock);
 389                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 390                             rmp_qentry);
 391                         tracker->rmp_flags = RMPF_ONQUEUE;
 392                         mtx_unlock_spin(&rm_spinlock);
 393                         rm_tracker_add(pc, tracker);
 394                         critical_exit();
 395                         return (1);
 396                 }
 397         }
 398
 399         sched_unpin();
 400         critical_exit();
 401
 402         if (trylock) {
 403                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 404                         if (!sx_try_xlock(&rm->rm_lock_sx))
 405                                 return (0);
 406                 } else {
 407                         if (!mtx_trylock(&rm->rm_lock_mtx))
 408                                 return (0);
 409                 }
 410         } else {
 411                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 412                         THREAD_SLEEPING_OK();
 413                         sx_xlock(&rm->rm_lock_sx);
 414                         THREAD_NO_SLEEPING();
 415                 } else
 416                         mtx_lock(&rm->rm_lock_mtx);
 417         }
 418
 419         critical_enter();
 420         pc = pcpu_find(curcpu);
 421         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
 422         rm_tracker_add(pc, tracker);
 423         sched_pin();
 424         critical_exit();
 425
 426         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 427                 sx_xunlock(&rm->rm_lock_sx);
 428         else
 429                 mtx_unlock(&rm->rm_lock_mtx);
 430
 431         return (1);
 432 }
 433
 434 int
 435 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 436 {
 437         struct thread *td = curthread;
 438         struct pcpu *pc;
 439
 440         if (SCHEDULER_STOPPED())
 441                 return (1);
 442
 443         tracker->rmp_flags  = 0;
 444         tracker->rmp_thread = td;
 445         tracker->rmp_rmlock = rm;
 446
 447         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 448                 THREAD_NO_SLEEPING();
 449
 450         td->td_critnest++;      /* critical_enter(); */
 451
 452         __compiler_membar();
 453
 454         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 455
 456         rm_tracker_add(pc, tracker);
 457
 458         sched_pin();
 459
 460         __compiler_membar();
 461
 462         td->td_critnest--;
 463
 464         /*
 465          * Fast path to combine two common conditions into a single
 466          * conditional jump.
 467          */
 468         if (0 == (td->td_owepreempt |
 469             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)))
 470                 return (1);
 471
 472         /* We do not have a read token and need to acquire one. */
 473         return _rm_rlock_hard(rm, tracker, trylock);
 474 }
 475
 476 static void
 477 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
 478 {
 479
 480         if (td->td_owepreempt) {
 481                 td->td_critnest++;
 482                 critical_exit();
 483         }
 484
 485         if (!tracker->rmp_flags)
 486                 return;
 487
 488         mtx_lock_spin(&rm_spinlock);
 489         LIST_REMOVE(tracker, rmp_qentry);
 490
 491         if (tracker->rmp_flags & RMPF_SIGNAL) {
 492                 struct rmlock *rm;
 493                 struct turnstile *ts;
 494
 495                 rm = tracker->rmp_rmlock;
 496
 497                 turnstile_chain_lock(&rm->lock_object);
 498                 mtx_unlock_spin(&rm_spinlock);
 499
 500                 ts = turnstile_lookup(&rm->lock_object);
 501
 502                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
 503                 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
 504                 turnstile_chain_unlock(&rm->lock_object);
 505         } else
 506                 mtx_unlock_spin(&rm_spinlock);
 507 }
 508
 509 void
 510 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
 511 {
 512         struct pcpu *pc;
 513         struct thread *td = tracker->rmp_thread;
 514
 515         if (SCHEDULER_STOPPED())
 516                 return;
 517
 518         td->td_critnest++;      /* critical_enter(); */
 519         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 520         rm_tracker_remove(pc, tracker);
 521         td->td_critnest--;
 522         sched_unpin();
 523
 524         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 525                 THREAD_SLEEPING_OK();
 526
 527         if (0 == (td->td_owepreempt | tracker->rmp_flags))
 528                 return;
 529
 530         _rm_unlock_hard(td, tracker);
 531 }
 532
 533 void
 534 _rm_wlock(struct rmlock *rm)
 535 {
 536         struct rm_priotracker *prio;
 537         struct turnstile *ts;
 538         cpuset_t readcpus;
 539
 540         if (SCHEDULER_STOPPED())
 541                 return;
 542
 543         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 544                 sx_xlock(&rm->rm_lock_sx);
 545         else
 546                 mtx_lock(&rm->rm_lock_mtx);
 547
 548         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
 549                 /* Get all read tokens back */
 550                 readcpus = all_cpus;
 551                 CPU_NAND(&readcpus, &rm->rm_writecpus);
 552                 rm->rm_writecpus = all_cpus;
 553
 554                 /*
 555                  * Assumes rm->rm_writecpus update is visible on other CPUs
 556                  * before rm_cleanIPI is called.
 557                  */
 558 #ifdef SMP
 559                 smp_rendezvous_cpus(readcpus,
 560                     smp_no_rendevous_barrier,
 561                     rm_cleanIPI,
 562                     smp_no_rendevous_barrier,
 563                     rm);
 564
 565 #else
 566                 rm_cleanIPI(rm);
 567 #endif
 568
 569                 mtx_lock_spin(&rm_spinlock);
 570                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
 571                         ts = turnstile_trywait(&rm->lock_object);
 572                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
 573                         mtx_unlock_spin(&rm_spinlock);
 574                         turnstile_wait(ts, prio->rmp_thread,
 575                             TS_EXCLUSIVE_QUEUE);
 576                         mtx_lock_spin(&rm_spinlock);
 577                 }
 578                 mtx_unlock_spin(&rm_spinlock);
 579         }
 580 }
 581
 582 void
 583 _rm_wunlock(struct rmlock *rm)
 584 {
 585
 586         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 587                 sx_xunlock(&rm->rm_lock_sx);
 588         else
 589                 mtx_unlock(&rm->rm_lock_mtx);
 590 }
 591
 592 #if LOCK_DEBUG > 0
 593
 594 void
 595 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 596 {
 597
 598         if (SCHEDULER_STOPPED())
 599                 return;
 600
 601         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 602             ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
 603             curthread, rm->lock_object.lo_name, file, line));
 604         KASSERT(!rm_destroyed(rm),
 605             ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
 606         _rm_assert(rm, RA_UNLOCKED, file, line);
 607
 608         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
 609             file, line, NULL);
 610
 611         _rm_wlock(rm);
 612
 613         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
 614
 615         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 616
 617         curthread->td_locks++;
 618
 619 }
 620
 621 void
 622 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 623 {
 624
 625         if (SCHEDULER_STOPPED())
 626                 return;
 627
 628         KASSERT(!rm_destroyed(rm),
 629             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
 630         _rm_assert(rm, RA_WLOCKED, file, line);
 631         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 632         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
 633         _rm_wunlock(rm);
 634         curthread->td_locks--;
 635 }
 636
 637 int
 638 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 639     int trylock, const char *file, int line)
 640 {
 641
 642         if (SCHEDULER_STOPPED())
 643                 return (1);
 644
 645 #ifdef INVARIANTS
 646         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
 647                 critical_enter();
 648                 KASSERT(rm_trackers_present(pcpu_find(curcpu), rm,
 649                     curthread) == 0,
 650                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
 651                     rm->lock_object.lo_name, file, line));
 652                 critical_exit();
 653         }
 654 #endif
 655         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 656             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
 657             curthread, rm->lock_object.lo_name, file, line));
 658         KASSERT(!rm_destroyed(rm),
 659             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
 660         if (!trylock) {
 661                 KASSERT(!rm_wowned(rm),
 662                     ("rm_rlock: wlock already held for %s @ %s:%d",
 663                     rm->lock_object.lo_name, file, line));
 664                 WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER, file, line,
 665                     NULL);
 666         }
 667
 668         if (_rm_rlock(rm, tracker, trylock)) {
 669                 if (trylock)
 670                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
 671                             line);
 672                 else
 673                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
 674                             line);
 675                 WITNESS_LOCK(&rm->lock_object, 0, file, line);
 676
 677                 curthread->td_locks++;
 678
 679                 return (1);
 680         } else if (trylock)
 681                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 682
 683         return (0);
 684 }
 685
 686 void
 687 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 688     const char *file, int line)
 689 {
 690
 691         if (SCHEDULER_STOPPED())
 692                 return;
 693
 694         KASSERT(!rm_destroyed(rm),
 695             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
 696         _rm_assert(rm, RA_RLOCKED, file, line);
 697         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
 698         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
 699         _rm_runlock(rm, tracker);
 700         curthread->td_locks--;
 701 }
 702
 703 #else
 704
 705 /*
 706  * Just strip out file and line arguments if no lock debugging is enabled in
 707  * the kernel - we are called from a kernel module.
 708  */
 709 void
 710 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 711 {
 712
 713         _rm_wlock(rm);
 714 }
 715
 716 void
 717 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 718 {
 719
 720         _rm_wunlock(rm);
 721 }
 722
 723 int
 724 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 725     int trylock, const char *file, int line)
 726 {
 727
 728         return _rm_rlock(rm, tracker, trylock);
 729 }
 730
 731 void
 732 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 733     const char *file, int line)
 734 {
 735
 736         _rm_runlock(rm, tracker);
 737 }
 738
 739 #endif
 740
 741 #ifdef INVARIANT_SUPPORT
 742 #ifndef INVARIANTS
 743 #undef _rm_assert
 744 #endif
 745
 746 /*
 747  * Note that this does not need to use witness_assert() for read lock
 748  * assertions since an exact count of read locks held by this thread
 749  * is computable.
 750  */
 751 void
 752 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
 753 {
 754         int count;
 755
 756         if (panicstr != NULL)
 757                 return;
 758         switch (what) {
 759         case RA_LOCKED:
 760         case RA_LOCKED | RA_RECURSED:
 761         case RA_LOCKED | RA_NOTRECURSED:
 762         case RA_RLOCKED:
 763         case RA_RLOCKED | RA_RECURSED:
 764         case RA_RLOCKED | RA_NOTRECURSED:
 765                 /*
 766                  * Handle the write-locked case.  Unlike other
 767                  * primitives, writers can never recurse.
 768                  */
 769                 if (rm_wowned(rm)) {
 770                         if (what & RA_RLOCKED)
 771                                 panic("Lock %s exclusively locked @ %s:%d\n",
 772                                     rm->lock_object.lo_name, file, line);
 773                         if (what & RA_RECURSED)
 774                                 panic("Lock %s not recursed @ %s:%d\n",
 775                                     rm->lock_object.lo_name, file, line);
 776                         break;
 777                 }
 778
 779                 critical_enter();
 780                 count = rm_trackers_present(pcpu_find(curcpu), rm, curthread);
 781                 critical_exit();
 782
 783                 if (count == 0)
 784                         panic("Lock %s not %slocked @ %s:%d\n",
 785                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
 786                             "read " : "", file, line);
 787                 if (count > 1) {
 788                         if (what & RA_NOTRECURSED)
 789                                 panic("Lock %s recursed @ %s:%d\n",
 790                                     rm->lock_object.lo_name, file, line);
 791                 } else if (what & RA_RECURSED)
 792                         panic("Lock %s not recursed @ %s:%d\n",
 793                             rm->lock_object.lo_name, file, line);
 794                 break;
 795         case RA_WLOCKED:
 796                 if (!rm_wowned(rm))
 797                         panic("Lock %s not exclusively locked @ %s:%d\n",
 798                             rm->lock_object.lo_name, file, line);
 799                 break;
 800         case RA_UNLOCKED:
 801                 if (rm_wowned(rm))
 802                         panic("Lock %s exclusively locked @ %s:%d\n",
 803                             rm->lock_object.lo_name, file, line);
 804
 805                 critical_enter();
 806                 count = rm_trackers_present(pcpu_find(curcpu), rm, curthread);
 807                 critical_exit();
 808
 809                 if (count != 0)
 810                         panic("Lock %s read locked @ %s:%d\n",
 811                             rm->lock_object.lo_name, file, line);
 812                 break;
 813         default:
 814                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
 815                     line);
 816         }
 817 }
 818 #endif /* INVARIANT_SUPPORT */
 819
 820 #ifdef DDB
 821 static void
 822 print_tracker(struct rm_priotracker *tr)
 823 {
 824         struct thread *td;
 825
 826         td = tr->rmp_thread;
 827         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
 828             td->td_proc->p_pid, td->td_name);
 829         if (tr->rmp_flags & RMPF_ONQUEUE) {
 830                 db_printf("ONQUEUE");
 831                 if (tr->rmp_flags & RMPF_SIGNAL)
 832                         db_printf(",SIGNAL");
 833         } else
 834                 db_printf("0");
 835         db_printf("}\n");
 836 }
 837
 838 static void
 839 db_show_rm(const struct lock_object *lock)
 840 {
 841         struct rm_priotracker *tr;
 842         struct rm_queue *queue;
 843         const struct rmlock *rm;
 844         struct lock_class *lc;
 845         struct pcpu *pc;
 846
 847         rm = (const struct rmlock *)lock;
 848         db_printf(" writecpus: ");
 849         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
 850         db_printf("\n");
 851         db_printf(" per-CPU readers:\n");
 852         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
 853                 for (queue = pc->pc_rm_queue.rmq_next;
 854                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 855                         tr = (struct rm_priotracker *)queue;
 856                         if (tr->rmp_rmlock == rm)
 857                                 print_tracker(tr);
 858                 }
 859         db_printf(" active readers:\n");
 860         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
 861                 print_tracker(tr);
 862         lc = LOCK_CLASS(&rm->rm_wlock_object);
 863         db_printf("Backing write-lock (%s):\n", lc->lc_name);
 864         lc->lc_ddb_show(&rm->rm_wlock_object);
 865 }
 866 #endif