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 #include <vm/uma.h>
  57
  58 #ifdef DDB
  59 #include <ddb/ddb.h>
  60 #endif
  61
  62 /*
  63  * A cookie to mark destroyed rmlocks.  This is stored in the head of
  64  * rm_activeReaders.
  65  */
  66 #define RM_DESTROYED    ((void *)0xdead)
  67
  68 #define rm_destroyed(rm)                                                \
  69         (LIST_FIRST(&(rm)->rm_activeReaders) == RM_DESTROYED)
  70
  71 #define RMPF_ONQUEUE    1
  72 #define RMPF_SIGNAL     2
  73
  74 #ifndef INVARIANTS
  75 #define _rm_assert(c, what, file, line)
  76 #endif
  77
  78 static void     assert_rm(const struct lock_object *lock, int what);
  79 #ifdef DDB
  80 static void     db_show_rm(const struct lock_object *lock);
  81 #endif
  82 static void     lock_rm(struct lock_object *lock, uintptr_t how);
  83 #ifdef KDTRACE_HOOKS
  84 static int      owner_rm(const struct lock_object *lock, struct thread **owner);
  85 #endif
  86 static uintptr_t unlock_rm(struct lock_object *lock);
  87
  88 struct lock_class lock_class_rm = {
  89         .lc_name = "rm",
  90         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
  91         .lc_assert = assert_rm,
  92 #ifdef DDB
  93         .lc_ddb_show = db_show_rm,
  94 #endif
  95         .lc_lock = lock_rm,
  96         .lc_unlock = unlock_rm,
  97 #ifdef KDTRACE_HOOKS
  98         .lc_owner = owner_rm,
  99 #endif
 100 };
 101
 102 struct lock_class lock_class_rm_sleepable = {
 103         .lc_name = "sleepable rm",
 104         .lc_flags = LC_SLEEPLOCK | LC_SLEEPABLE | LC_RECURSABLE,
 105         .lc_assert = assert_rm,
 106 #ifdef DDB
 107         .lc_ddb_show = db_show_rm,
 108 #endif
 109         .lc_lock = lock_rm,
 110         .lc_unlock = unlock_rm,
 111 #ifdef KDTRACE_HOOKS
 112         .lc_owner = owner_rm,
 113 #endif
 114 };
 115
 116 static void
 117 assert_rm(const struct lock_object *lock, int what)
 118 {
 119
 120         rm_assert((const struct rmlock *)lock, what);
 121 }
 122
 123 static void
 124 lock_rm(struct lock_object *lock, uintptr_t how)
 125 {
 126         struct rmlock *rm;
 127         struct rm_priotracker *tracker;
 128
 129         rm = (struct rmlock *)lock;
 130         if (how == 0)
 131                 rm_wlock(rm);
 132         else {
 133                 tracker = (struct rm_priotracker *)how;
 134                 rm_rlock(rm, tracker);
 135         }
 136 }
 137
 138 static uintptr_t
 139 unlock_rm(struct lock_object *lock)
 140 {
 141         struct thread *td;
 142         struct pcpu *pc;
 143         struct rmlock *rm;
 144         struct rm_queue *queue;
 145         struct rm_priotracker *tracker;
 146         uintptr_t how;
 147
 148         rm = (struct rmlock *)lock;
 149         tracker = NULL;
 150         how = 0;
 151         rm_assert(rm, RA_LOCKED | RA_NOTRECURSED);
 152         if (rm_wowned(rm))
 153                 rm_wunlock(rm);
 154         else {
 155                 /*
 156                  * Find the right rm_priotracker structure for curthread.
 157                  * The guarantee about its uniqueness is given by the fact
 158                  * we already asserted the lock wasn't recursively acquired.
 159                  */
 160                 critical_enter();
 161                 td = curthread;
 162                 pc = get_pcpu();
 163                 for (queue = pc->pc_rm_queue.rmq_next;
 164                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 165                         tracker = (struct rm_priotracker *)queue;
 166                                 if ((tracker->rmp_rmlock == rm) &&
 167                                     (tracker->rmp_thread == td)) {
 168                                         how = (uintptr_t)tracker;
 169                                         break;
 170                                 }
 171                 }
 172                 KASSERT(tracker != NULL,
 173                     ("rm_priotracker is non-NULL when lock held in read mode"));
 174                 critical_exit();
 175                 rm_runlock(rm, tracker);
 176         }
 177         return (how);
 178 }
 179
 180 #ifdef KDTRACE_HOOKS
 181 static int
 182 owner_rm(const struct lock_object *lock, struct thread **owner)
 183 {
 184         const struct rmlock *rm;
 185         struct lock_class *lc;
 186
 187         rm = (const struct rmlock *)lock;
 188         lc = LOCK_CLASS(&rm->rm_wlock_object);
 189         return (lc->lc_owner(&rm->rm_wlock_object, owner));
 190 }
 191 #endif
 192
 193 static struct mtx rm_spinlock;
 194
 195 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
 196
 197 /*
 198  * Add or remove tracker from per-cpu list.
 199  *
 200  * The per-cpu list can be traversed at any time in forward direction from an
 201  * interrupt on the *local* cpu.
 202  */
 203 static void inline
 204 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
 205 {
 206         struct rm_queue *next;
 207
 208         /* Initialize all tracker pointers */
 209         tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
 210         next = pc->pc_rm_queue.rmq_next;
 211         tracker->rmp_cpuQueue.rmq_next = next;
 212
 213         /* rmq_prev is not used during froward traversal. */
 214         next->rmq_prev = &tracker->rmp_cpuQueue;
 215
 216         /* Update pointer to first element. */
 217         pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
 218 }
 219
 220 /*
 221  * Return a count of the number of trackers the thread 'td' already
 222  * has on this CPU for the lock 'rm'.
 223  */
 224 static int
 225 rm_trackers_present(const struct pcpu *pc, const struct rmlock *rm,
 226     const struct thread *td)
 227 {
 228         struct rm_queue *queue;
 229         struct rm_priotracker *tracker;
 230         int count;
 231
 232         count = 0;
 233         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
 234             queue = queue->rmq_next) {
 235                 tracker = (struct rm_priotracker *)queue;
 236                 if ((tracker->rmp_rmlock == rm) && (tracker->rmp_thread == td))
 237                         count++;
 238         }
 239         return (count);
 240 }
 241
 242 static void inline
 243 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
 244 {
 245         struct rm_queue *next, *prev;
 246
 247         next = tracker->rmp_cpuQueue.rmq_next;
 248         prev = tracker->rmp_cpuQueue.rmq_prev;
 249
 250         /* Not used during forward traversal. */
 251         next->rmq_prev = prev;
 252
 253         /* Remove from list. */
 254         prev->rmq_next = next;
 255 }
 256
 257 static void
 258 rm_cleanIPI(void *arg)
 259 {
 260         struct pcpu *pc;
 261         struct rmlock *rm = arg;
 262         struct rm_priotracker *tracker;
 263         struct rm_queue *queue;
 264         pc = get_pcpu();
 265
 266         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
 267             queue = queue->rmq_next) {
 268                 tracker = (struct rm_priotracker *)queue;
 269                 if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
 270                         tracker->rmp_flags = RMPF_ONQUEUE;
 271                         mtx_lock_spin(&rm_spinlock);
 272                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 273                             rmp_qentry);
 274                         mtx_unlock_spin(&rm_spinlock);
 275                 }
 276         }
 277 }
 278
 279 void
 280 rm_init_flags(struct rmlock *rm, const char *name, int opts)
 281 {
 282         struct lock_class *lc;
 283         int liflags, xflags;
 284
 285         liflags = 0;
 286         if (!(opts & RM_NOWITNESS))
 287                 liflags |= LO_WITNESS;
 288         if (opts & RM_RECURSE)
 289                 liflags |= LO_RECURSABLE;
 290         if (opts & RM_NEW)
 291                 liflags |= LO_NEW;
 292         rm->rm_writecpus = all_cpus;
 293         LIST_INIT(&rm->rm_activeReaders);
 294         if (opts & RM_SLEEPABLE) {
 295                 liflags |= LO_SLEEPABLE;
 296                 lc = &lock_class_rm_sleepable;
 297                 xflags = (opts & RM_NEW ? SX_NEW : 0);
 298                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx",
 299                     xflags | SX_NOWITNESS);
 300         } else {
 301                 lc = &lock_class_rm;
 302                 xflags = (opts & RM_NEW ? MTX_NEW : 0);
 303                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx",
 304                     xflags | MTX_NOWITNESS);
 305         }
 306         lock_init(&rm->lock_object, lc, name, NULL, liflags);
 307 }
 308
 309 void
 310 rm_init(struct rmlock *rm, const char *name)
 311 {
 312
 313         rm_init_flags(rm, name, 0);
 314 }
 315
 316 void
 317 rm_destroy(struct rmlock *rm)
 318 {
 319
 320         rm_assert(rm, RA_UNLOCKED);
 321         LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
 322         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 323                 sx_destroy(&rm->rm_lock_sx);
 324         else
 325                 mtx_destroy(&rm->rm_lock_mtx);
 326         lock_destroy(&rm->lock_object);
 327 }
 328
 329 int
 330 rm_wowned(const struct rmlock *rm)
 331 {
 332
 333         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 334                 return (sx_xlocked(&rm->rm_lock_sx));
 335         else
 336                 return (mtx_owned(&rm->rm_lock_mtx));
 337 }
 338
 339 void
 340 rm_sysinit(void *arg)
 341 {
 342         struct rm_args *args;
 343
 344         args = arg;
 345         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_flags);
 346 }
 347
 348 static __noinline int
 349 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 350 {
 351         struct pcpu *pc;
 352
 353         critical_enter();
 354         pc = get_pcpu();
 355
 356         /* Check if we just need to do a proper critical_exit. */
 357         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
 358                 critical_exit();
 359                 return (1);
 360         }
 361
 362         /* Remove our tracker from the per-cpu list. */
 363         rm_tracker_remove(pc, tracker);
 364
 365         /*
 366          * Check to see if the IPI granted us the lock after all.  The load of
 367          * rmp_flags must happen after the tracker is removed from the list.
 368          */
 369         atomic_interrupt_fence();
 370         if (tracker->rmp_flags) {
 371                 /* Just add back tracker - we hold the lock. */
 372                 rm_tracker_add(pc, tracker);
 373                 critical_exit();
 374                 return (1);
 375         }
 376
 377         /*
 378          * We allow readers to acquire a lock even if a writer is blocked if
 379          * the lock is recursive and the reader already holds the lock.
 380          */
 381         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 382                 /*
 383                  * Just grant the lock if this thread already has a tracker
 384                  * for this lock on the per-cpu queue.
 385                  */
 386                 if (rm_trackers_present(pc, rm, curthread) != 0) {
 387                         mtx_lock_spin(&rm_spinlock);
 388                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 389                             rmp_qentry);
 390                         tracker->rmp_flags = RMPF_ONQUEUE;
 391                         mtx_unlock_spin(&rm_spinlock);
 392                         rm_tracker_add(pc, tracker);
 393                         critical_exit();
 394                         return (1);
 395                 }
 396         }
 397
 398         sched_unpin();
 399         critical_exit();
 400
 401         if (trylock) {
 402                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 403                         if (!sx_try_xlock(&rm->rm_lock_sx))
 404                                 return (0);
 405                 } else {
 406                         if (!mtx_trylock(&rm->rm_lock_mtx))
 407                                 return (0);
 408                 }
 409         } else {
 410                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 411                         THREAD_SLEEPING_OK();
 412                         sx_xlock(&rm->rm_lock_sx);
 413                         THREAD_NO_SLEEPING();
 414                 } else
 415                         mtx_lock(&rm->rm_lock_mtx);
 416         }
 417
 418         critical_enter();
 419         pc = get_pcpu();
 420         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
 421         rm_tracker_add(pc, tracker);
 422         sched_pin();
 423         critical_exit();
 424
 425         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 426                 sx_xunlock(&rm->rm_lock_sx);
 427         else
 428                 mtx_unlock(&rm->rm_lock_mtx);
 429
 430         return (1);
 431 }
 432
 433 int
 434 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 435 {
 436         struct thread *td = curthread;
 437         struct pcpu *pc;
 438
 439         if (SCHEDULER_STOPPED())
 440                 return (1);
 441
 442         tracker->rmp_flags  = 0;
 443         tracker->rmp_thread = td;
 444         tracker->rmp_rmlock = rm;
 445
 446         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 447                 THREAD_NO_SLEEPING();
 448
 449         td->td_critnest++;      /* critical_enter(); */
 450
 451         atomic_interrupt_fence();
 452
 453         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 454
 455         rm_tracker_add(pc, tracker);
 456
 457         sched_pin();
 458
 459         atomic_interrupt_fence();
 460
 461         td->td_critnest--;
 462
 463         /*
 464          * Fast path to combine two common conditions into a single
 465          * conditional jump.
 466          */
 467         if (__predict_true(0 == (td->td_owepreempt |
 468             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus))))
 469                 return (1);
 470
 471         /* We do not have a read token and need to acquire one. */
 472         return _rm_rlock_hard(rm, tracker, trylock);
 473 }
 474
 475 static __noinline void
 476 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
 477 {
 478
 479         if (td->td_owepreempt) {
 480                 td->td_critnest++;
 481                 critical_exit();
 482         }
 483
 484         if (!tracker->rmp_flags)
 485                 return;
 486
 487         mtx_lock_spin(&rm_spinlock);
 488         LIST_REMOVE(tracker, rmp_qentry);
 489
 490         if (tracker->rmp_flags & RMPF_SIGNAL) {
 491                 struct rmlock *rm;
 492                 struct turnstile *ts;
 493
 494                 rm = tracker->rmp_rmlock;
 495
 496                 turnstile_chain_lock(&rm->lock_object);
 497                 mtx_unlock_spin(&rm_spinlock);
 498
 499                 ts = turnstile_lookup(&rm->lock_object);
 500
 501                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
 502                 turnstile_unpend(ts);
 503                 turnstile_chain_unlock(&rm->lock_object);
 504         } else
 505                 mtx_unlock_spin(&rm_spinlock);
 506 }
 507
 508 void
 509 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
 510 {
 511         struct pcpu *pc;
 512         struct thread *td = tracker->rmp_thread;
 513
 514         if (SCHEDULER_STOPPED())
 515                 return;
 516
 517         td->td_critnest++;      /* critical_enter(); */
 518         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 519         rm_tracker_remove(pc, tracker);
 520         td->td_critnest--;
 521         sched_unpin();
 522
 523         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 524                 THREAD_SLEEPING_OK();
 525
 526         if (__predict_true(0 == (td->td_owepreempt | tracker->rmp_flags)))
 527                 return;
 528
 529         _rm_unlock_hard(td, tracker);
 530 }
 531
 532 void
 533 _rm_wlock(struct rmlock *rm)
 534 {
 535         struct rm_priotracker *prio;
 536         struct turnstile *ts;
 537         cpuset_t readcpus;
 538
 539         if (SCHEDULER_STOPPED())
 540                 return;
 541
 542         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 543                 sx_xlock(&rm->rm_lock_sx);
 544         else
 545                 mtx_lock(&rm->rm_lock_mtx);
 546
 547         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
 548                 /* Get all read tokens back */
 549                 readcpus = all_cpus;
 550                 CPU_ANDNOT(&readcpus, &rm->rm_writecpus);
 551                 rm->rm_writecpus = all_cpus;
 552
 553                 /*
 554                  * Assumes rm->rm_writecpus update is visible on other CPUs
 555                  * before rm_cleanIPI is called.
 556                  */
 557 #ifdef SMP
 558                 smp_rendezvous_cpus(readcpus,
 559                     smp_no_rendezvous_barrier,
 560                     rm_cleanIPI,
 561                     smp_no_rendezvous_barrier,
 562                     rm);
 563
 564 #else
 565                 rm_cleanIPI(rm);
 566 #endif
 567
 568                 mtx_lock_spin(&rm_spinlock);
 569                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
 570                         ts = turnstile_trywait(&rm->lock_object);
 571                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
 572                         mtx_unlock_spin(&rm_spinlock);
 573                         turnstile_wait(ts, prio->rmp_thread,
 574                             TS_EXCLUSIVE_QUEUE);
 575                         mtx_lock_spin(&rm_spinlock);
 576                 }
 577                 mtx_unlock_spin(&rm_spinlock);
 578         }
 579 }
 580
 581 void
 582 _rm_wunlock(struct rmlock *rm)
 583 {
 584
 585         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 586                 sx_xunlock(&rm->rm_lock_sx);
 587         else
 588                 mtx_unlock(&rm->rm_lock_mtx);
 589 }
 590
 591 #if LOCK_DEBUG > 0
 592
 593 void
 594 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 595 {
 596
 597         if (SCHEDULER_STOPPED())
 598                 return;
 599
 600         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 601             ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
 602             curthread, rm->lock_object.lo_name, file, line));
 603         KASSERT(!rm_destroyed(rm),
 604             ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
 605         _rm_assert(rm, RA_UNLOCKED, file, line);
 606
 607         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
 608             file, line, NULL);
 609
 610         _rm_wlock(rm);
 611
 612         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
 613         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 614         TD_LOCKS_INC(curthread);
 615 }
 616
 617 void
 618 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 619 {
 620
 621         if (SCHEDULER_STOPPED())
 622                 return;
 623
 624         KASSERT(!rm_destroyed(rm),
 625             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
 626         _rm_assert(rm, RA_WLOCKED, file, line);
 627         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 628         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
 629         _rm_wunlock(rm);
 630         TD_LOCKS_DEC(curthread);
 631 }
 632
 633 int
 634 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 635     int trylock, const char *file, int line)
 636 {
 637
 638         if (SCHEDULER_STOPPED())
 639                 return (1);
 640
 641 #ifdef INVARIANTS
 642         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
 643                 critical_enter();
 644                 KASSERT(rm_trackers_present(get_pcpu(), rm,
 645                     curthread) == 0,
 646                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
 647                     rm->lock_object.lo_name, file, line));
 648                 critical_exit();
 649         }
 650 #endif
 651         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 652             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
 653             curthread, rm->lock_object.lo_name, file, line));
 654         KASSERT(!rm_destroyed(rm),
 655             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
 656         if (!trylock) {
 657                 KASSERT(!rm_wowned(rm),
 658                     ("rm_rlock: wlock already held for %s @ %s:%d",
 659                     rm->lock_object.lo_name, file, line));
 660                 WITNESS_CHECKORDER(&rm->lock_object,
 661                     LOP_NEWORDER | LOP_NOSLEEP, file, line, NULL);
 662         }
 663
 664         if (_rm_rlock(rm, tracker, trylock)) {
 665                 if (trylock)
 666                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
 667                             line);
 668                 else
 669                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
 670                             line);
 671                 WITNESS_LOCK(&rm->lock_object, LOP_NOSLEEP, file, line);
 672                 TD_LOCKS_INC(curthread);
 673                 return (1);
 674         } else if (trylock)
 675                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 676
 677         return (0);
 678 }
 679
 680 void
 681 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 682     const char *file, int line)
 683 {
 684
 685         if (SCHEDULER_STOPPED())
 686                 return;
 687
 688         KASSERT(!rm_destroyed(rm),
 689             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
 690         _rm_assert(rm, RA_RLOCKED, file, line);
 691         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
 692         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
 693         _rm_runlock(rm, tracker);
 694         TD_LOCKS_DEC(curthread);
 695 }
 696
 697 #else
 698
 699 /*
 700  * Just strip out file and line arguments if no lock debugging is enabled in
 701  * the kernel - we are called from a kernel module.
 702  */
 703 void
 704 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 705 {
 706
 707         _rm_wlock(rm);
 708 }
 709
 710 void
 711 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 712 {
 713
 714         _rm_wunlock(rm);
 715 }
 716
 717 int
 718 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 719     int trylock, const char *file, int line)
 720 {
 721
 722         return _rm_rlock(rm, tracker, trylock);
 723 }
 724
 725 void
 726 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 727     const char *file, int line)
 728 {
 729
 730         _rm_runlock(rm, tracker);
 731 }
 732
 733 #endif
 734
 735 #ifdef INVARIANT_SUPPORT
 736 #ifndef INVARIANTS
 737 #undef _rm_assert
 738 #endif
 739
 740 /*
 741  * Note that this does not need to use witness_assert() for read lock
 742  * assertions since an exact count of read locks held by this thread
 743  * is computable.
 744  */
 745 void
 746 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
 747 {
 748         int count;
 749
 750         if (SCHEDULER_STOPPED())
 751                 return;
 752         switch (what) {
 753         case RA_LOCKED:
 754         case RA_LOCKED | RA_RECURSED:
 755         case RA_LOCKED | RA_NOTRECURSED:
 756         case RA_RLOCKED:
 757         case RA_RLOCKED | RA_RECURSED:
 758         case RA_RLOCKED | RA_NOTRECURSED:
 759                 /*
 760                  * Handle the write-locked case.  Unlike other
 761                  * primitives, writers can never recurse.
 762                  */
 763                 if (rm_wowned(rm)) {
 764                         if (what & RA_RLOCKED)
 765                                 panic("Lock %s exclusively locked @ %s:%d\n",
 766                                     rm->lock_object.lo_name, file, line);
 767                         if (what & RA_RECURSED)
 768                                 panic("Lock %s not recursed @ %s:%d\n",
 769                                     rm->lock_object.lo_name, file, line);
 770                         break;
 771                 }
 772
 773                 critical_enter();
 774                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 775                 critical_exit();
 776
 777                 if (count == 0)
 778                         panic("Lock %s not %slocked @ %s:%d\n",
 779                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
 780                             "read " : "", file, line);
 781                 if (count > 1) {
 782                         if (what & RA_NOTRECURSED)
 783                                 panic("Lock %s recursed @ %s:%d\n",
 784                                     rm->lock_object.lo_name, file, line);
 785                 } else if (what & RA_RECURSED)
 786                         panic("Lock %s not recursed @ %s:%d\n",
 787                             rm->lock_object.lo_name, file, line);
 788                 break;
 789         case RA_WLOCKED:
 790                 if (!rm_wowned(rm))
 791                         panic("Lock %s not exclusively locked @ %s:%d\n",
 792                             rm->lock_object.lo_name, file, line);
 793                 break;
 794         case RA_UNLOCKED:
 795                 if (rm_wowned(rm))
 796                         panic("Lock %s exclusively locked @ %s:%d\n",
 797                             rm->lock_object.lo_name, file, line);
 798
 799                 critical_enter();
 800                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 801                 critical_exit();
 802
 803                 if (count != 0)
 804                         panic("Lock %s read locked @ %s:%d\n",
 805                             rm->lock_object.lo_name, file, line);
 806                 break;
 807         default:
 808                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
 809                     line);
 810         }
 811 }
 812 #endif /* INVARIANT_SUPPORT */
 813
 814 #ifdef DDB
 815 static void
 816 print_tracker(struct rm_priotracker *tr)
 817 {
 818         struct thread *td;
 819
 820         td = tr->rmp_thread;
 821         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
 822             td->td_proc->p_pid, td->td_name);
 823         if (tr->rmp_flags & RMPF_ONQUEUE) {
 824                 db_printf("ONQUEUE");
 825                 if (tr->rmp_flags & RMPF_SIGNAL)
 826                         db_printf(",SIGNAL");
 827         } else
 828                 db_printf("0");
 829         db_printf("}\n");
 830 }
 831
 832 static void
 833 db_show_rm(const struct lock_object *lock)
 834 {
 835         struct rm_priotracker *tr;
 836         struct rm_queue *queue;
 837         const struct rmlock *rm;
 838         struct lock_class *lc;
 839         struct pcpu *pc;
 840
 841         rm = (const struct rmlock *)lock;
 842         db_printf(" writecpus: ");
 843         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
 844         db_printf("\n");
 845         db_printf(" per-CPU readers:\n");
 846         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
 847                 for (queue = pc->pc_rm_queue.rmq_next;
 848                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 849                         tr = (struct rm_priotracker *)queue;
 850                         if (tr->rmp_rmlock == rm)
 851                                 print_tracker(tr);
 852                 }
 853         db_printf(" active readers:\n");
 854         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
 855                 print_tracker(tr);
 856         lc = LOCK_CLASS(&rm->rm_wlock_object);
 857         db_printf("Backing write-lock (%s):\n", lc->lc_name);
 858         lc->lc_ddb_show(&rm->rm_wlock_object);
 859 }
 860 #endif
 861
 862 /*
 863  * Read-mostly sleepable locks.
 864  *
 865  * These primitives allow both readers and writers to sleep. However, neither
 866  * readers nor writers are tracked and subsequently there is no priority
 867  * propagation.
 868  *
 869  * They are intended to be only used when write-locking is almost never needed
 870  * (e.g., they can guard against unloading a kernel module) while read-locking
 871  * happens all the time.
 872  *
 873  * Concurrent writers take turns taking the lock while going off cpu. If this is
 874  * of concern for your usecase, this is not the right primitive.
 875  *
 876  * Neither rms_rlock nor rms_runlock use thread fences. Instead interrupt
 877  * fences are inserted to ensure ordering with the code executed in the IPI
 878  * handler.
 879  *
 880  * No attempt is made to track which CPUs read locked at least once,
 881  * consequently write locking sends IPIs to all of them. This will become a
 882  * problem at some point. The easiest way to lessen it is to provide a bitmap.
 883  */
 884
 885 #define RMS_NOOWNER     ((void *)0x1)
 886 #define RMS_TRANSIENT   ((void *)0x2)
 887 #define RMS_FLAGMASK    0xf
 888
 889 struct rmslock_pcpu {
 890         int influx;
 891         int readers;
 892 };
 893
 894 _Static_assert(sizeof(struct rmslock_pcpu) == 8, "bad size");
 895
 896 /*
 897  * Internal routines
 898  */
 899 static struct rmslock_pcpu *
 900 rms_int_pcpu(struct rmslock *rms)
 901 {
 902
 903         CRITICAL_ASSERT(curthread);
 904         return (zpcpu_get(rms->pcpu));
 905 }
 906
 907 static struct rmslock_pcpu *
 908 rms_int_remote_pcpu(struct rmslock *rms, int cpu)
 909 {
 910
 911         return (zpcpu_get_cpu(rms->pcpu, cpu));
 912 }
 913
 914 static void
 915 rms_int_influx_enter(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 916 {
 917
 918         CRITICAL_ASSERT(curthread);
 919         MPASS(pcpu->influx == 0);
 920         pcpu->influx = 1;
 921 }
 922
 923 static void
 924 rms_int_influx_exit(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 925 {
 926
 927         CRITICAL_ASSERT(curthread);
 928         MPASS(pcpu->influx == 1);
 929         pcpu->influx = 0;
 930 }
 931
 932 #ifdef INVARIANTS
 933 static void
 934 rms_int_debug_readers_inc(struct rmslock *rms)
 935 {
 936         int old;
 937         old = atomic_fetchadd_int(&rms->debug_readers, 1);
 938         KASSERT(old >= 0, ("%s: bad readers count %d\n", __func__, old));
 939 }
 940
 941 static void
 942 rms_int_debug_readers_dec(struct rmslock *rms)
 943 {
 944         int old;
 945
 946         old = atomic_fetchadd_int(&rms->debug_readers, -1);
 947         KASSERT(old > 0, ("%s: bad readers count %d\n", __func__, old));
 948 }
 949 #else
 950 static void
 951 rms_int_debug_readers_inc(struct rmslock *rms)
 952 {
 953 }
 954
 955 static void
 956 rms_int_debug_readers_dec(struct rmslock *rms)
 957 {
 958 }
 959 #endif
 960
 961 static void
 962 rms_int_readers_inc(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 963 {
 964
 965         CRITICAL_ASSERT(curthread);
 966         rms_int_debug_readers_inc(rms);
 967         pcpu->readers++;
 968 }
 969
 970 static void
 971 rms_int_readers_dec(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 972 {
 973
 974         CRITICAL_ASSERT(curthread);
 975         rms_int_debug_readers_dec(rms);
 976         pcpu->readers--;
 977 }
 978
 979 /*
 980  * Public API
 981  */
 982 void
 983 rms_init(struct rmslock *rms, const char *name)
 984 {
 985
 986         rms->owner = RMS_NOOWNER;
 987         rms->writers = 0;
 988         rms->readers = 0;
 989         rms->debug_readers = 0;
 990         mtx_init(&rms->mtx, name, NULL, MTX_DEF | MTX_NEW);
 991         rms->pcpu = uma_zalloc_pcpu(pcpu_zone_8, M_WAITOK | M_ZERO);
 992 }
 993
 994 void
 995 rms_destroy(struct rmslock *rms)
 996 {
 997
 998         MPASS(rms->writers == 0);
 999         MPASS(rms->readers == 0);
1000         mtx_destroy(&rms->mtx);
1001         uma_zfree_pcpu(pcpu_zone_8, rms->pcpu);
1002 }
1003
1004 static void __noinline
1005 rms_rlock_fallback(struct rmslock *rms)
1006 {
1007
1008         rms_int_influx_exit(rms, rms_int_pcpu(rms));
1009         critical_exit();
1010
1011         mtx_lock(&rms->mtx);
1012         while (rms->writers > 0)
1013                 msleep(&rms->readers, &rms->mtx, PUSER - 1, mtx_name(&rms->mtx), 0);
1014         critical_enter();
1015         rms_int_readers_inc(rms, rms_int_pcpu(rms));
1016         mtx_unlock(&rms->mtx);
1017         critical_exit();
1018 }
1019
1020 void
1021 rms_rlock(struct rmslock *rms)
1022 {
1023         struct rmslock_pcpu *pcpu;
1024
1025         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
1026         MPASS(atomic_load_ptr(&rms->owner) != curthread);
1027
1028         critical_enter();
1029         pcpu = rms_int_pcpu(rms);
1030         rms_int_influx_enter(rms, pcpu);
1031         atomic_interrupt_fence();
1032         if (__predict_false(rms->writers > 0)) {
1033                 rms_rlock_fallback(rms);
1034                 return;
1035         }
1036         atomic_interrupt_fence();
1037         rms_int_readers_inc(rms, pcpu);
1038         atomic_interrupt_fence();
1039         rms_int_influx_exit(rms, pcpu);
1040         critical_exit();
1041 }
1042
1043 int
1044 rms_try_rlock(struct rmslock *rms)
1045 {
1046         struct rmslock_pcpu *pcpu;
1047
1048         MPASS(atomic_load_ptr(&rms->owner) != curthread);
1049
1050         critical_enter();
1051         pcpu = rms_int_pcpu(rms);
1052         rms_int_influx_enter(rms, pcpu);
1053         atomic_interrupt_fence();
1054         if (__predict_false(rms->writers > 0)) {
1055                 rms_int_influx_exit(rms, pcpu);
1056                 critical_exit();
1057                 return (0);
1058         }
1059         atomic_interrupt_fence();
1060         rms_int_readers_inc(rms, pcpu);
1061         atomic_interrupt_fence();
1062         rms_int_influx_exit(rms, pcpu);
1063         critical_exit();
1064         return (1);
1065 }
1066
1067 static void __noinline
1068 rms_runlock_fallback(struct rmslock *rms)
1069 {
1070
1071         rms_int_influx_exit(rms, rms_int_pcpu(rms));
1072         critical_exit();
1073
1074         mtx_lock(&rms->mtx);
1075         MPASS(rms->writers > 0);
1076         MPASS(rms->readers > 0);
1077         MPASS(rms->debug_readers == rms->readers);
1078         rms_int_debug_readers_dec(rms);
1079         rms->readers--;
1080         if (rms->readers == 0)
1081                 wakeup_one(&rms->writers);
1082         mtx_unlock(&rms->mtx);
1083 }
1084
1085 void
1086 rms_runlock(struct rmslock *rms)
1087 {
1088         struct rmslock_pcpu *pcpu;
1089
1090         critical_enter();
1091         pcpu = rms_int_pcpu(rms);
1092         rms_int_influx_enter(rms, pcpu);
1093         atomic_interrupt_fence();
1094         if (__predict_false(rms->writers > 0)) {
1095                 rms_runlock_fallback(rms);
1096                 return;
1097         }
1098         atomic_interrupt_fence();
1099         rms_int_readers_dec(rms, pcpu);
1100         atomic_interrupt_fence();
1101         rms_int_influx_exit(rms, pcpu);
1102         critical_exit();
1103 }
1104
1105 struct rmslock_ipi {
1106         struct rmslock *rms;
1107         struct smp_rendezvous_cpus_retry_arg srcra;
1108 };
1109
1110 static void
1111 rms_action_func(void *arg)
1112 {
1113         struct rmslock_ipi *rmsipi;
1114         struct rmslock_pcpu *pcpu;
1115         struct rmslock *rms;
1116
1117         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
1118         rms = rmsipi->rms;
1119         pcpu = rms_int_pcpu(rms);
1120
1121         if (pcpu->influx)
1122                 return;
1123         if (pcpu->readers != 0) {
1124                 atomic_add_int(&rms->readers, pcpu->readers);
1125                 pcpu->readers = 0;
1126         }
1127         smp_rendezvous_cpus_done(arg);
1128 }
1129
1130 static void
1131 rms_wait_func(void *arg, int cpu)
1132 {
1133         struct rmslock_ipi *rmsipi;
1134         struct rmslock_pcpu *pcpu;
1135         struct rmslock *rms;
1136
1137         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
1138         rms = rmsipi->rms;
1139         pcpu = rms_int_remote_pcpu(rms, cpu);
1140
1141         while (atomic_load_int(&pcpu->influx))
1142                 cpu_spinwait();
1143 }
1144
1145 #ifdef INVARIANTS
1146 static void
1147 rms_assert_no_pcpu_readers(struct rmslock *rms)
1148 {
1149         struct rmslock_pcpu *pcpu;
1150         int cpu;
1151
1152         CPU_FOREACH(cpu) {
1153                 pcpu = rms_int_remote_pcpu(rms, cpu);
1154                 if (pcpu->readers != 0) {
1155                         panic("%s: got %d readers on cpu %d\n", __func__,
1156                             pcpu->readers, cpu);
1157                 }
1158         }
1159 }
1160 #else
1161 static void
1162 rms_assert_no_pcpu_readers(struct rmslock *rms)
1163 {
1164 }
1165 #endif
1166
1167 static void
1168 rms_wlock_switch(struct rmslock *rms)
1169 {
1170         struct rmslock_ipi rmsipi;
1171
1172         MPASS(rms->readers == 0);
1173         MPASS(rms->writers == 1);
1174
1175         rmsipi.rms = rms;
1176
1177         smp_rendezvous_cpus_retry(all_cpus,
1178             smp_no_rendezvous_barrier,
1179             rms_action_func,
1180             smp_no_rendezvous_barrier,
1181             rms_wait_func,
1182             &rmsipi.srcra);
1183 }
1184
1185 void
1186 rms_wlock(struct rmslock *rms)
1187 {
1188
1189         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
1190         MPASS(atomic_load_ptr(&rms->owner) != curthread);
1191
1192         mtx_lock(&rms->mtx);
1193         rms->writers++;
1194         if (rms->writers > 1) {
1195                 msleep(&rms->owner, &rms->mtx, (PUSER - 1),
1196                     mtx_name(&rms->mtx), 0);
1197                 MPASS(rms->readers == 0);
1198                 KASSERT(rms->owner == RMS_TRANSIENT,
1199                     ("%s: unexpected owner value %p\n", __func__,
1200                     rms->owner));
1201                 goto out_grab;
1202         }
1203
1204         KASSERT(rms->owner == RMS_NOOWNER,
1205             ("%s: unexpected owner value %p\n", __func__, rms->owner));
1206
1207         rms_wlock_switch(rms);
1208         rms_assert_no_pcpu_readers(rms);
1209
1210         if (rms->readers > 0) {
1211                 msleep(&rms->writers, &rms->mtx, (PUSER - 1),
1212                     mtx_name(&rms->mtx), 0);
1213         }
1214
1215 out_grab:
1216         rms->owner = curthread;
1217         rms_assert_no_pcpu_readers(rms);
1218         mtx_unlock(&rms->mtx);
1219         MPASS(rms->readers == 0);
1220 }
1221
1222 void
1223 rms_wunlock(struct rmslock *rms)
1224 {
1225
1226         mtx_lock(&rms->mtx);
1227         KASSERT(rms->owner == curthread,
1228             ("%s: unexpected owner value %p\n", __func__, rms->owner));
1229         MPASS(rms->writers >= 1);
1230         MPASS(rms->readers == 0);
1231         rms->writers--;
1232         if (rms->writers > 0) {
1233                 wakeup_one(&rms->owner);
1234                 rms->owner = RMS_TRANSIENT;
1235         } else {
1236                 wakeup(&rms->readers);
1237                 rms->owner = RMS_NOOWNER;
1238         }
1239         mtx_unlock(&rms->mtx);
1240 }
1241
1242 void
1243 rms_unlock(struct rmslock *rms)
1244 {
1245
1246         if (rms_wowned(rms))
1247                 rms_wunlock(rms);
1248         else
1249                 rms_runlock(rms);
1250 }