sys/kern/kern_rmlock.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-3-Clause
   3  *
   4  * Copyright (c) 2007 Stephan Uphoff <ups@FreeBSD.org>
   5  * All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  * 3. Neither the name of the author nor the names of any co-contributors
  16  *    may be used to endorse or promote products derived from this software
  17  *    without specific prior written permission.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER 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
  29  * SUCH DAMAGE.
  30  */
  31
  32 /*
  33  * Machine independent bits of reader/writer lock implementation.
  34  */
  35
  36 #include <sys/cdefs.h>
  37 __FBSDID("$FreeBSD$");
  38
  39 #include "opt_ddb.h"
  40
  41 #include <sys/param.h>
  42 #include <sys/systm.h>
  43
  44 #include <sys/kernel.h>
  45 #include <sys/kdb.h>
  46 #include <sys/ktr.h>
  47 #include <sys/lock.h>
  48 #include <sys/mutex.h>
  49 #include <sys/proc.h>
  50 #include <sys/rmlock.h>
  51 #include <sys/sched.h>
  52 #include <sys/smp.h>
  53 #include <sys/turnstile.h>
  54 #include <sys/lock_profile.h>
  55 #include <machine/cpu.h>
  56
  57 #ifdef DDB
  58 #include <ddb/ddb.h>
  59 #endif
  60
  61 /*
  62  * A cookie to mark destroyed rmlocks.  This is stored in the head of
  63  * rm_activeReaders.
  64  */
  65 #define RM_DESTROYED    ((void *)0xdead)
  66
  67 #define rm_destroyed(rm)                                                \
  68         (LIST_FIRST(&(rm)->rm_activeReaders) == RM_DESTROYED)
  69
  70 #define RMPF_ONQUEUE    1
  71 #define RMPF_SIGNAL     2
  72
  73 #ifndef INVARIANTS
  74 #define _rm_assert(c, what, file, line)
  75 #endif
  76
  77 static void     assert_rm(const struct lock_object *lock, int what);
  78 #ifdef DDB
  79 static void     db_show_rm(const struct lock_object *lock);
  80 #endif
  81 static void     lock_rm(struct lock_object *lock, uintptr_t how);
  82 #ifdef KDTRACE_HOOKS
  83 static int      owner_rm(const struct lock_object *lock, struct thread **owner);
  84 #endif
  85 static uintptr_t unlock_rm(struct lock_object *lock);
  86
  87 struct lock_class lock_class_rm = {
  88         .lc_name = "rm",
  89         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
  90         .lc_assert = assert_rm,
  91 #ifdef DDB
  92         .lc_ddb_show = db_show_rm,
  93 #endif
  94         .lc_lock = lock_rm,
  95         .lc_unlock = unlock_rm,
  96 #ifdef KDTRACE_HOOKS
  97         .lc_owner = owner_rm,
  98 #endif
  99 };
 100
 101 struct lock_class lock_class_rm_sleepable = {
 102         .lc_name = "sleepable rm",
 103         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE,
 104         .lc_assert = assert_rm,
 105 #ifdef DDB
 106         .lc_ddb_show = db_show_rm,
 107 #endif
 108         .lc_lock = lock_rm,
 109         .lc_unlock = unlock_rm,
 110 #ifdef KDTRACE_HOOKS
 111         .lc_owner = owner_rm,
 112 #endif
 113 };
 114
 115 static void
 116 assert_rm(const struct lock_object *lock, int what)
 117 {
 118
 119         rm_assert((const struct rmlock *)lock, what);
 120 }
 121
 122 static void
 123 lock_rm(struct lock_object *lock, uintptr_t how)
 124 {
 125         struct rmlock *rm;
 126         struct rm_priotracker *tracker;
 127
 128         rm = (struct rmlock *)lock;
 129         if (how == 0)
 130                 rm_wlock(rm);
 131         else {
 132                 tracker = (struct rm_priotracker *)how;
 133                 rm_rlock(rm, tracker);
 134         }
 135 }
 136
 137 static uintptr_t
 138 unlock_rm(struct lock_object *lock)
 139 {
 140         struct thread *td;
 141         struct pcpu *pc;
 142         struct rmlock *rm;
 143         struct rm_queue *queue;
 144         struct rm_priotracker *tracker;
 145         uintptr_t how;
 146
 147         rm = (struct rmlock *)lock;
 148         tracker = NULL;
 149         how = 0;
 150         rm_assert(rm, RA_LOCKED | RA_NOTRECURSED);
 151         if (rm_wowned(rm))
 152                 rm_wunlock(rm);
 153         else {
 154                 /*
 155                  * Find the right rm_priotracker structure for curthread.
 156                  * The guarantee about its uniqueness is given by the fact
 157                  * we already asserted the lock wasn't recursively acquired.
 158                  */
 159                 critical_enter();
 160                 td = curthread;
 161                 pc = get_pcpu();
 162                 for (queue = pc->pc_rm_queue.rmq_next;
 163                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 164                         tracker = (struct rm_priotracker *)queue;
 165                                 if ((tracker->rmp_rmlock == rm) &&
 166                                     (tracker->rmp_thread == td)) {
 167                                         how = (uintptr_t)tracker;
 168                                         break;
 169                                 }
 170                 }
 171                 KASSERT(tracker != NULL,
 172                     ("rm_priotracker is non-NULL when lock held in read mode"));
 173                 critical_exit();
 174                 rm_runlock(rm, tracker);
 175         }
 176         return (how);
 177 }
 178
 179 #ifdef KDTRACE_HOOKS
 180 static int
 181 owner_rm(const struct lock_object *lock, struct thread **owner)
 182 {
 183         const struct rmlock *rm;
 184         struct lock_class *lc;
 185
 186         rm = (const struct rmlock *)lock;
 187         lc = LOCK_CLASS(&rm->rm_wlock_object);
 188         return (lc->lc_owner(&rm->rm_wlock_object, owner));
 189 }
 190 #endif
 191
 192 static struct mtx rm_spinlock;
 193
 194 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
 195
 196 /*
 197  * Add or remove tracker from per-cpu list.
 198  *
 199  * The per-cpu list can be traversed at any time in forward direction from an
 200  * interrupt on the *local* cpu.
 201  */
 202 static void inline
 203 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
 204 {
 205         struct rm_queue *next;
 206
 207         /* Initialize all tracker pointers */
 208         tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
 209         next = pc->pc_rm_queue.rmq_next;
 210         tracker->rmp_cpuQueue.rmq_next = next;
 211
 212         /* rmq_prev is not used during froward traversal. */
 213         next->rmq_prev = &tracker->rmp_cpuQueue;
 214
 215         /* Update pointer to first element. */
 216         pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
 217 }
 218
 219 /*
 220  * Return a count of the number of trackers the thread 'td' already
 221  * has on this CPU for the lock 'rm'.
 222  */
 223 static int
 224 rm_trackers_present(const struct pcpu *pc, const struct rmlock *rm,
 225     const struct thread *td)
 226 {
 227         struct rm_queue *queue;
 228         struct rm_priotracker *tracker;
 229         int count;
 230
 231         count = 0;
 232         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
 233             queue = queue->rmq_next) {
 234                 tracker = (struct rm_priotracker *)queue;
 235                 if ((tracker->rmp_rmlock == rm) && (tracker->rmp_thread == td))
 236                         count++;
 237         }
 238         return (count);
 239 }
 240
 241 static void inline
 242 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
 243 {
 244         struct rm_queue *next, *prev;
 245
 246         next = tracker->rmp_cpuQueue.rmq_next;
 247         prev = tracker->rmp_cpuQueue.rmq_prev;
 248
 249         /* Not used during forward traversal. */
 250         next->rmq_prev = prev;
 251
 252         /* Remove from list. */
 253         prev->rmq_next = next;
 254 }
 255
 256 static void
 257 rm_cleanIPI(void *arg)
 258 {
 259         struct pcpu *pc;
 260         struct rmlock *rm = arg;
 261         struct rm_priotracker *tracker;
 262         struct rm_queue *queue;
 263         pc = get_pcpu();
 264
 265         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
 266             queue = queue->rmq_next) {
 267                 tracker = (struct rm_priotracker *)queue;
 268                 if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
 269                         tracker->rmp_flags = RMPF_ONQUEUE;
 270                         mtx_lock_spin(&rm_spinlock);
 271                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 272                             rmp_qentry);
 273                         mtx_unlock_spin(&rm_spinlock);
 274                 }
 275         }
 276 }
 277
 278 void
 279 rm_init_flags(struct rmlock *rm, const char *name, int opts)
 280 {
 281         struct lock_class *lc;
 282         int liflags, xflags;
 283
 284         liflags = 0;
 285         if (!(opts & RM_NOWITNESS))
 286                 liflags |= LO_WITNESS;
 287         if (opts & RM_RECURSE)
 288                 liflags |= LO_RECURSABLE;
 289         if (opts & RM_NEW)
 290                 liflags |= LO_NEW;
 291         if (opts & RM_DUPOK)
 292                 liflags |= LO_DUPOK;
 293         rm->rm_writecpus = all_cpus;
 294         LIST_INIT(&rm->rm_activeReaders);
 295         if (opts & RM_SLEEPABLE) {
 296                 liflags |= LO_SLEEPABLE;
 297                 lc = &lock_class_rm_sleepable;
 298                 xflags = (opts & RM_NEW ? SX_NEW : 0);
 299                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx",
 300                     xflags | SX_NOWITNESS);
 301         } else {
 302                 lc = &lock_class_rm;
 303                 xflags = (opts & RM_NEW ? MTX_NEW : 0);
 304                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx",
 305                     xflags | MTX_NOWITNESS);
 306         }
 307         lock_init(&rm->lock_object, lc, name, NULL, liflags);
 308 }
 309
 310 void
 311 rm_init(struct rmlock *rm, const char *name)
 312 {
 313
 314         rm_init_flags(rm, name, 0);
 315 }
 316
 317 void
 318 rm_destroy(struct rmlock *rm)
 319 {
 320
 321         rm_assert(rm, RA_UNLOCKED);
 322         LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
 323         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 324                 sx_destroy(&rm->rm_lock_sx);
 325         else
 326                 mtx_destroy(&rm->rm_lock_mtx);
 327         lock_destroy(&rm->lock_object);
 328 }
 329
 330 int
 331 rm_wowned(const struct rmlock *rm)
 332 {
 333
 334         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 335                 return (sx_xlocked(&rm->rm_lock_sx));
 336         else
 337                 return (mtx_owned(&rm->rm_lock_mtx));
 338 }
 339
 340 void
 341 rm_sysinit(void *arg)
 342 {
 343         struct rm_args *args;
 344
 345         args = arg;
 346         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_flags);
 347 }
 348
 349 static __noinline int
 350 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 351 {
 352         struct pcpu *pc;
 353
 354         critical_enter();
 355         pc = get_pcpu();
 356
 357         /* Check if we just need to do a proper critical_exit. */
 358         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
 359                 critical_exit();
 360                 return (1);
 361         }
 362
 363         /* Remove our tracker from the per-cpu list. */
 364         rm_tracker_remove(pc, tracker);
 365
 366         /*
 367          * Check to see if the IPI granted us the lock after all.  The load of
 368          * rmp_flags must happen after the tracker is removed from the list.
 369          */
 370         __compiler_membar();
 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 = get_pcpu();
 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 (__predict_true(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 __noinline 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);
 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 (__predict_true(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_rendezvous_barrier,
 561                     rm_cleanIPI,
 562                     smp_no_rendezvous_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         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 615         TD_LOCKS_INC(curthread);
 616 }
 617
 618 void
 619 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 620 {
 621
 622         if (SCHEDULER_STOPPED())
 623                 return;
 624
 625         KASSERT(!rm_destroyed(rm),
 626             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
 627         _rm_assert(rm, RA_WLOCKED, file, line);
 628         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 629         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
 630         _rm_wunlock(rm);
 631         TD_LOCKS_DEC(curthread);
 632 }
 633
 634 int
 635 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 636     int trylock, const char *file, int line)
 637 {
 638
 639         if (SCHEDULER_STOPPED())
 640                 return (1);
 641
 642 #ifdef INVARIANTS
 643         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
 644                 critical_enter();
 645                 KASSERT(rm_trackers_present(get_pcpu(), rm,
 646                     curthread) == 0,
 647                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
 648                     rm->lock_object.lo_name, file, line));
 649                 critical_exit();
 650         }
 651 #endif
 652         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 653             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
 654             curthread, rm->lock_object.lo_name, file, line));
 655         KASSERT(!rm_destroyed(rm),
 656             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
 657         if (!trylock) {
 658                 KASSERT(!rm_wowned(rm),
 659                     ("rm_rlock: wlock already held for %s @ %s:%d",
 660                     rm->lock_object.lo_name, file, line));
 661                 WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER, file, line,
 662                     NULL);
 663         }
 664
 665         if (_rm_rlock(rm, tracker, trylock)) {
 666                 if (trylock)
 667                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
 668                             line);
 669                 else
 670                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
 671                             line);
 672                 WITNESS_LOCK(&rm->lock_object, 0, file, line);
 673                 TD_LOCKS_INC(curthread);
 674                 return (1);
 675         } else if (trylock)
 676                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 677
 678         return (0);
 679 }
 680
 681 void
 682 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 683     const char *file, int line)
 684 {
 685
 686         if (SCHEDULER_STOPPED())
 687                 return;
 688
 689         KASSERT(!rm_destroyed(rm),
 690             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
 691         _rm_assert(rm, RA_RLOCKED, file, line);
 692         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
 693         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
 694         _rm_runlock(rm, tracker);
 695         TD_LOCKS_DEC(curthread);
 696 }
 697
 698 #else
 699
 700 /*
 701  * Just strip out file and line arguments if no lock debugging is enabled in
 702  * the kernel - we are called from a kernel module.
 703  */
 704 void
 705 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 706 {
 707
 708         _rm_wlock(rm);
 709 }
 710
 711 void
 712 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 713 {
 714
 715         _rm_wunlock(rm);
 716 }
 717
 718 int
 719 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 720     int trylock, const char *file, int line)
 721 {
 722
 723         return _rm_rlock(rm, tracker, trylock);
 724 }
 725
 726 void
 727 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 728     const char *file, int line)
 729 {
 730
 731         _rm_runlock(rm, tracker);
 732 }
 733
 734 #endif
 735
 736 #ifdef INVARIANT_SUPPORT
 737 #ifndef INVARIANTS
 738 #undef _rm_assert
 739 #endif
 740
 741 /*
 742  * Note that this does not need to use witness_assert() for read lock
 743  * assertions since an exact count of read locks held by this thread
 744  * is computable.
 745  */
 746 void
 747 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
 748 {
 749         int count;
 750
 751         if (SCHEDULER_STOPPED())
 752                 return;
 753         switch (what) {
 754         case RA_LOCKED:
 755         case RA_LOCKED | RA_RECURSED:
 756         case RA_LOCKED | RA_NOTRECURSED:
 757         case RA_RLOCKED:
 758         case RA_RLOCKED | RA_RECURSED:
 759         case RA_RLOCKED | RA_NOTRECURSED:
 760                 /*
 761                  * Handle the write-locked case.  Unlike other
 762                  * primitives, writers can never recurse.
 763                  */
 764                 if (rm_wowned(rm)) {
 765                         if (what & RA_RLOCKED)
 766                                 panic("Lock %s exclusively locked @ %s:%d\n",
 767                                     rm->lock_object.lo_name, file, line);
 768                         if (what & RA_RECURSED)
 769                                 panic("Lock %s not recursed @ %s:%d\n",
 770                                     rm->lock_object.lo_name, file, line);
 771                         break;
 772                 }
 773
 774                 critical_enter();
 775                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 776                 critical_exit();
 777
 778                 if (count == 0)
 779                         panic("Lock %s not %slocked @ %s:%d\n",
 780                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
 781                             "read " : "", file, line);
 782                 if (count > 1) {
 783                         if (what & RA_NOTRECURSED)
 784                                 panic("Lock %s recursed @ %s:%d\n",
 785                                     rm->lock_object.lo_name, file, line);
 786                 } else if (what & RA_RECURSED)
 787                         panic("Lock %s not recursed @ %s:%d\n",
 788                             rm->lock_object.lo_name, file, line);
 789                 break;
 790         case RA_WLOCKED:
 791                 if (!rm_wowned(rm))
 792                         panic("Lock %s not exclusively locked @ %s:%d\n",
 793                             rm->lock_object.lo_name, file, line);
 794                 break;
 795         case RA_UNLOCKED:
 796                 if (rm_wowned(rm))
 797                         panic("Lock %s exclusively locked @ %s:%d\n",
 798                             rm->lock_object.lo_name, file, line);
 799
 800                 critical_enter();
 801                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 802                 critical_exit();
 803
 804                 if (count != 0)
 805                         panic("Lock %s read locked @ %s:%d\n",
 806                             rm->lock_object.lo_name, file, line);
 807                 break;
 808         default:
 809                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
 810                     line);
 811         }
 812 }
 813 #endif /* INVARIANT_SUPPORT */
 814
 815 #ifdef DDB
 816 static void
 817 print_tracker(struct rm_priotracker *tr)
 818 {
 819         struct thread *td;
 820
 821         td = tr->rmp_thread;
 822         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
 823             td->td_proc->p_pid, td->td_name);
 824         if (tr->rmp_flags & RMPF_ONQUEUE) {
 825                 db_printf("ONQUEUE");
 826                 if (tr->rmp_flags & RMPF_SIGNAL)
 827                         db_printf(",SIGNAL");
 828         } else
 829                 db_printf("0");
 830         db_printf("}\n");
 831 }
 832
 833 static void
 834 db_show_rm(const struct lock_object *lock)
 835 {
 836         struct rm_priotracker *tr;
 837         struct rm_queue *queue;
 838         const struct rmlock *rm;
 839         struct lock_class *lc;
 840         struct pcpu *pc;
 841
 842         rm = (const struct rmlock *)lock;
 843         db_printf(" writecpus: ");
 844         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
 845         db_printf("\n");
 846         db_printf(" per-CPU readers:\n");
 847         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
 848                 for (queue = pc->pc_rm_queue.rmq_next;
 849                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 850                         tr = (struct rm_priotracker *)queue;
 851                         if (tr->rmp_rmlock == rm)
 852                                 print_tracker(tr);
 853                 }
 854         db_printf(" active readers:\n");
 855         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
 856                 print_tracker(tr);
 857         lc = LOCK_CLASS(&rm->rm_wlock_object);
 858         db_printf("Backing write-lock (%s):\n", lc->lc_name);
 859         lc->lc_ddb_show(&rm->rm_wlock_object);
 860 }
 861 #endif