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         rm->rm_writecpus = all_cpus;
 292         LIST_INIT(&rm->rm_activeReaders);
 293         if (opts & RM_SLEEPABLE) {
 294                 liflags |= LO_SLEEPABLE;
 295                 lc = &lock_class_rm_sleepable;
 296                 xflags = (opts & RM_NEW ? SX_NEW : 0);
 297                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx",
 298                     xflags | SX_NOWITNESS);
 299         } else {
 300                 lc = &lock_class_rm;
 301                 xflags = (opts & RM_NEW ? MTX_NEW : 0);
 302                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx",
 303                     xflags | MTX_NOWITNESS);
 304         }
 305         lock_init(&rm->lock_object, lc, name, NULL, liflags);
 306 }
 307
 308 void
 309 rm_init(struct rmlock *rm, const char *name)
 310 {
 311
 312         rm_init_flags(rm, name, 0);
 313 }
 314
 315 void
 316 rm_destroy(struct rmlock *rm)
 317 {
 318
 319         rm_assert(rm, RA_UNLOCKED);
 320         LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
 321         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 322                 sx_destroy(&rm->rm_lock_sx);
 323         else
 324                 mtx_destroy(&rm->rm_lock_mtx);
 325         lock_destroy(&rm->lock_object);
 326 }
 327
 328 int
 329 rm_wowned(const struct rmlock *rm)
 330 {
 331
 332         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 333                 return (sx_xlocked(&rm->rm_lock_sx));
 334         else
 335                 return (mtx_owned(&rm->rm_lock_mtx));
 336 }
 337
 338 void
 339 rm_sysinit(void *arg)
 340 {
 341         struct rm_args *args;
 342
 343         args = arg;
 344         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_flags);
 345 }
 346
 347 static __noinline int
 348 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 349 {
 350         struct pcpu *pc;
 351
 352         critical_enter();
 353         pc = get_pcpu();
 354
 355         /* Check if we just need to do a proper critical_exit. */
 356         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
 357                 critical_exit();
 358                 return (1);
 359         }
 360
 361         /* Remove our tracker from the per-cpu list. */
 362         rm_tracker_remove(pc, tracker);
 363
 364         /* Check to see if the IPI granted us the lock after all. */
 365         if (tracker->rmp_flags) {
 366                 /* Just add back tracker - we hold the lock. */
 367                 rm_tracker_add(pc, tracker);
 368                 critical_exit();
 369                 return (1);
 370         }
 371
 372         /*
 373          * We allow readers to acquire a lock even if a writer is blocked if
 374          * the lock is recursive and the reader already holds the lock.
 375          */
 376         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 377                 /*
 378                  * Just grant the lock if this thread already has a tracker
 379                  * for this lock on the per-cpu queue.
 380                  */
 381                 if (rm_trackers_present(pc, rm, curthread) != 0) {
 382                         mtx_lock_spin(&rm_spinlock);
 383                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 384                             rmp_qentry);
 385                         tracker->rmp_flags = RMPF_ONQUEUE;
 386                         mtx_unlock_spin(&rm_spinlock);
 387                         rm_tracker_add(pc, tracker);
 388                         critical_exit();
 389                         return (1);
 390                 }
 391         }
 392
 393         sched_unpin();
 394         critical_exit();
 395
 396         if (trylock) {
 397                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 398                         if (!sx_try_xlock(&rm->rm_lock_sx))
 399                                 return (0);
 400                 } else {
 401                         if (!mtx_trylock(&rm->rm_lock_mtx))
 402                                 return (0);
 403                 }
 404         } else {
 405                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 406                         THREAD_SLEEPING_OK();
 407                         sx_xlock(&rm->rm_lock_sx);
 408                         THREAD_NO_SLEEPING();
 409                 } else
 410                         mtx_lock(&rm->rm_lock_mtx);
 411         }
 412
 413         critical_enter();
 414         pc = get_pcpu();
 415         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
 416         rm_tracker_add(pc, tracker);
 417         sched_pin();
 418         critical_exit();
 419
 420         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 421                 sx_xunlock(&rm->rm_lock_sx);
 422         else
 423                 mtx_unlock(&rm->rm_lock_mtx);
 424
 425         return (1);
 426 }
 427
 428 int
 429 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 430 {
 431         struct thread *td = curthread;
 432         struct pcpu *pc;
 433
 434         if (SCHEDULER_STOPPED())
 435                 return (1);
 436
 437         tracker->rmp_flags  = 0;
 438         tracker->rmp_thread = td;
 439         tracker->rmp_rmlock = rm;
 440
 441         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 442                 THREAD_NO_SLEEPING();
 443
 444         td->td_critnest++;      /* critical_enter(); */
 445
 446         __compiler_membar();
 447
 448         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 449
 450         rm_tracker_add(pc, tracker);
 451
 452         sched_pin();
 453
 454         __compiler_membar();
 455
 456         td->td_critnest--;
 457
 458         /*
 459          * Fast path to combine two common conditions into a single
 460          * conditional jump.
 461          */
 462         if (__predict_true(0 == (td->td_owepreempt |
 463             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus))))
 464                 return (1);
 465
 466         /* We do not have a read token and need to acquire one. */
 467         return _rm_rlock_hard(rm, tracker, trylock);
 468 }
 469
 470 static __noinline void
 471 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
 472 {
 473
 474         if (td->td_owepreempt) {
 475                 td->td_critnest++;
 476                 critical_exit();
 477         }
 478
 479         if (!tracker->rmp_flags)
 480                 return;
 481
 482         mtx_lock_spin(&rm_spinlock);
 483         LIST_REMOVE(tracker, rmp_qentry);
 484
 485         if (tracker->rmp_flags & RMPF_SIGNAL) {
 486                 struct rmlock *rm;
 487                 struct turnstile *ts;
 488
 489                 rm = tracker->rmp_rmlock;
 490
 491                 turnstile_chain_lock(&rm->lock_object);
 492                 mtx_unlock_spin(&rm_spinlock);
 493
 494                 ts = turnstile_lookup(&rm->lock_object);
 495
 496                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
 497                 turnstile_unpend(ts);
 498                 turnstile_chain_unlock(&rm->lock_object);
 499         } else
 500                 mtx_unlock_spin(&rm_spinlock);
 501 }
 502
 503 void
 504 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
 505 {
 506         struct pcpu *pc;
 507         struct thread *td = tracker->rmp_thread;
 508
 509         if (SCHEDULER_STOPPED())
 510                 return;
 511
 512         td->td_critnest++;      /* critical_enter(); */
 513         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 514         rm_tracker_remove(pc, tracker);
 515         td->td_critnest--;
 516         sched_unpin();
 517
 518         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 519                 THREAD_SLEEPING_OK();
 520
 521         if (__predict_true(0 == (td->td_owepreempt | tracker->rmp_flags)))
 522                 return;
 523
 524         _rm_unlock_hard(td, tracker);
 525 }
 526
 527 void
 528 _rm_wlock(struct rmlock *rm)
 529 {
 530         struct rm_priotracker *prio;
 531         struct turnstile *ts;
 532         cpuset_t readcpus;
 533
 534         if (SCHEDULER_STOPPED())
 535                 return;
 536
 537         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 538                 sx_xlock(&rm->rm_lock_sx);
 539         else
 540                 mtx_lock(&rm->rm_lock_mtx);
 541
 542         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
 543                 /* Get all read tokens back */
 544                 readcpus = all_cpus;
 545                 CPU_NAND(&readcpus, &rm->rm_writecpus);
 546                 rm->rm_writecpus = all_cpus;
 547
 548                 /*
 549                  * Assumes rm->rm_writecpus update is visible on other CPUs
 550                  * before rm_cleanIPI is called.
 551                  */
 552 #ifdef SMP
 553                 smp_rendezvous_cpus(readcpus,
 554                     smp_no_rendezvous_barrier,
 555                     rm_cleanIPI,
 556                     smp_no_rendezvous_barrier,
 557                     rm);
 558
 559 #else
 560                 rm_cleanIPI(rm);
 561 #endif
 562
 563                 mtx_lock_spin(&rm_spinlock);
 564                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
 565                         ts = turnstile_trywait(&rm->lock_object);
 566                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
 567                         mtx_unlock_spin(&rm_spinlock);
 568                         turnstile_wait(ts, prio->rmp_thread,
 569                             TS_EXCLUSIVE_QUEUE);
 570                         mtx_lock_spin(&rm_spinlock);
 571                 }
 572                 mtx_unlock_spin(&rm_spinlock);
 573         }
 574 }
 575
 576 void
 577 _rm_wunlock(struct rmlock *rm)
 578 {
 579
 580         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 581                 sx_xunlock(&rm->rm_lock_sx);
 582         else
 583                 mtx_unlock(&rm->rm_lock_mtx);
 584 }
 585
 586 #if LOCK_DEBUG > 0
 587
 588 void
 589 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 590 {
 591
 592         if (SCHEDULER_STOPPED())
 593                 return;
 594
 595         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 596             ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
 597             curthread, rm->lock_object.lo_name, file, line));
 598         KASSERT(!rm_destroyed(rm),
 599             ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
 600         _rm_assert(rm, RA_UNLOCKED, file, line);
 601
 602         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
 603             file, line, NULL);
 604
 605         _rm_wlock(rm);
 606
 607         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
 608         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 609         TD_LOCKS_INC(curthread);
 610 }
 611
 612 void
 613 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 614 {
 615
 616         if (SCHEDULER_STOPPED())
 617                 return;
 618
 619         KASSERT(!rm_destroyed(rm),
 620             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
 621         _rm_assert(rm, RA_WLOCKED, file, line);
 622         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 623         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
 624         _rm_wunlock(rm);
 625         TD_LOCKS_DEC(curthread);
 626 }
 627
 628 int
 629 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 630     int trylock, const char *file, int line)
 631 {
 632
 633         if (SCHEDULER_STOPPED())
 634                 return (1);
 635
 636 #ifdef INVARIANTS
 637         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
 638                 critical_enter();
 639                 KASSERT(rm_trackers_present(get_pcpu(), rm,
 640                     curthread) == 0,
 641                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
 642                     rm->lock_object.lo_name, file, line));
 643                 critical_exit();
 644         }
 645 #endif
 646         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 647             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
 648             curthread, rm->lock_object.lo_name, file, line));
 649         KASSERT(!rm_destroyed(rm),
 650             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
 651         if (!trylock) {
 652                 KASSERT(!rm_wowned(rm),
 653                     ("rm_rlock: wlock already held for %s @ %s:%d",
 654                     rm->lock_object.lo_name, file, line));
 655                 WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER, file, line,
 656                     NULL);
 657         }
 658
 659         if (_rm_rlock(rm, tracker, trylock)) {
 660                 if (trylock)
 661                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
 662                             line);
 663                 else
 664                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
 665                             line);
 666                 WITNESS_LOCK(&rm->lock_object, 0, file, line);
 667                 TD_LOCKS_INC(curthread);
 668                 return (1);
 669         } else if (trylock)
 670                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 671
 672         return (0);
 673 }
 674
 675 void
 676 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 677     const char *file, int line)
 678 {
 679
 680         if (SCHEDULER_STOPPED())
 681                 return;
 682
 683         KASSERT(!rm_destroyed(rm),
 684             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
 685         _rm_assert(rm, RA_RLOCKED, file, line);
 686         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
 687         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
 688         _rm_runlock(rm, tracker);
 689         TD_LOCKS_DEC(curthread);
 690 }
 691
 692 #else
 693
 694 /*
 695  * Just strip out file and line arguments if no lock debugging is enabled in
 696  * the kernel - we are called from a kernel module.
 697  */
 698 void
 699 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 700 {
 701
 702         _rm_wlock(rm);
 703 }
 704
 705 void
 706 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 707 {
 708
 709         _rm_wunlock(rm);
 710 }
 711
 712 int
 713 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 714     int trylock, const char *file, int line)
 715 {
 716
 717         return _rm_rlock(rm, tracker, trylock);
 718 }
 719
 720 void
 721 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 722     const char *file, int line)
 723 {
 724
 725         _rm_runlock(rm, tracker);
 726 }
 727
 728 #endif
 729
 730 #ifdef INVARIANT_SUPPORT
 731 #ifndef INVARIANTS
 732 #undef _rm_assert
 733 #endif
 734
 735 /*
 736  * Note that this does not need to use witness_assert() for read lock
 737  * assertions since an exact count of read locks held by this thread
 738  * is computable.
 739  */
 740 void
 741 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
 742 {
 743         int count;
 744
 745         if (SCHEDULER_STOPPED())
 746                 return;
 747         switch (what) {
 748         case RA_LOCKED:
 749         case RA_LOCKED | RA_RECURSED:
 750         case RA_LOCKED | RA_NOTRECURSED:
 751         case RA_RLOCKED:
 752         case RA_RLOCKED | RA_RECURSED:
 753         case RA_RLOCKED | RA_NOTRECURSED:
 754                 /*
 755                  * Handle the write-locked case.  Unlike other
 756                  * primitives, writers can never recurse.
 757                  */
 758                 if (rm_wowned(rm)) {
 759                         if (what & RA_RLOCKED)
 760                                 panic("Lock %s exclusively locked @ %s:%d\n",
 761                                     rm->lock_object.lo_name, file, line);
 762                         if (what & RA_RECURSED)
 763                                 panic("Lock %s not recursed @ %s:%d\n",
 764                                     rm->lock_object.lo_name, file, line);
 765                         break;
 766                 }
 767
 768                 critical_enter();
 769                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 770                 critical_exit();
 771
 772                 if (count == 0)
 773                         panic("Lock %s not %slocked @ %s:%d\n",
 774                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
 775                             "read " : "", file, line);
 776                 if (count > 1) {
 777                         if (what & RA_NOTRECURSED)
 778                                 panic("Lock %s recursed @ %s:%d\n",
 779                                     rm->lock_object.lo_name, file, line);
 780                 } else if (what & RA_RECURSED)
 781                         panic("Lock %s not recursed @ %s:%d\n",
 782                             rm->lock_object.lo_name, file, line);
 783                 break;
 784         case RA_WLOCKED:
 785                 if (!rm_wowned(rm))
 786                         panic("Lock %s not exclusively locked @ %s:%d\n",
 787                             rm->lock_object.lo_name, file, line);
 788                 break;
 789         case RA_UNLOCKED:
 790                 if (rm_wowned(rm))
 791                         panic("Lock %s exclusively locked @ %s:%d\n",
 792                             rm->lock_object.lo_name, file, line);
 793
 794                 critical_enter();
 795                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 796                 critical_exit();
 797
 798                 if (count != 0)
 799                         panic("Lock %s read locked @ %s:%d\n",
 800                             rm->lock_object.lo_name, file, line);
 801                 break;
 802         default:
 803                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
 804                     line);
 805         }
 806 }
 807 #endif /* INVARIANT_SUPPORT */
 808
 809 #ifdef DDB
 810 static void
 811 print_tracker(struct rm_priotracker *tr)
 812 {
 813         struct thread *td;
 814
 815         td = tr->rmp_thread;
 816         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
 817             td->td_proc->p_pid, td->td_name);
 818         if (tr->rmp_flags & RMPF_ONQUEUE) {
 819                 db_printf("ONQUEUE");
 820                 if (tr->rmp_flags & RMPF_SIGNAL)
 821                         db_printf(",SIGNAL");
 822         } else
 823                 db_printf("0");
 824         db_printf("}\n");
 825 }
 826
 827 static void
 828 db_show_rm(const struct lock_object *lock)
 829 {
 830         struct rm_priotracker *tr;
 831         struct rm_queue *queue;
 832         const struct rmlock *rm;
 833         struct lock_class *lc;
 834         struct pcpu *pc;
 835
 836         rm = (const struct rmlock *)lock;
 837         db_printf(" writecpus: ");
 838         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
 839         db_printf("\n");
 840         db_printf(" per-CPU readers:\n");
 841         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
 842                 for (queue = pc->pc_rm_queue.rmq_next;
 843                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 844                         tr = (struct rm_priotracker *)queue;
 845                         if (tr->rmp_rmlock == rm)
 846                                 print_tracker(tr);
 847                 }
 848         db_printf(" active readers:\n");
 849         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
 850                 print_tracker(tr);
 851         lc = LOCK_CLASS(&rm->rm_wlock_object);
 852         db_printf("Backing write-lock (%s):\n", lc->lc_name);
 853         lc->lc_ddb_show(&rm->rm_wlock_object);
 854 }
 855 #endif