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         /* Check to see if the IPI granted us the lock after all. */
 366         if (tracker->rmp_flags) {
 367                 /* Just add back tracker - we hold the lock. */
 368                 rm_tracker_add(pc, tracker);
 369                 critical_exit();
 370                 return (1);
 371         }
 372
 373         /*
 374          * We allow readers to acquire a lock even if a writer is blocked if
 375          * the lock is recursive and the reader already holds the lock.
 376          */
 377         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 378                 /*
 379                  * Just grant the lock if this thread already has a tracker
 380                  * for this lock on the per-cpu queue.
 381                  */
 382                 if (rm_trackers_present(pc, rm, curthread) != 0) {
 383                         mtx_lock_spin(&rm_spinlock);
 384                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 385                             rmp_qentry);
 386                         tracker->rmp_flags = RMPF_ONQUEUE;
 387                         mtx_unlock_spin(&rm_spinlock);
 388                         rm_tracker_add(pc, tracker);
 389                         critical_exit();
 390                         return (1);
 391                 }
 392         }
 393
 394         sched_unpin();
 395         critical_exit();
 396
 397         if (trylock) {
 398                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 399                         if (!sx_try_xlock(&rm->rm_lock_sx))
 400                                 return (0);
 401                 } else {
 402                         if (!mtx_trylock(&rm->rm_lock_mtx))
 403                                 return (0);
 404                 }
 405         } else {
 406                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 407                         THREAD_SLEEPING_OK();
 408                         sx_xlock(&rm->rm_lock_sx);
 409                         THREAD_NO_SLEEPING();
 410                 } else
 411                         mtx_lock(&rm->rm_lock_mtx);
 412         }
 413
 414         critical_enter();
 415         pc = get_pcpu();
 416         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
 417         rm_tracker_add(pc, tracker);
 418         sched_pin();
 419         critical_exit();
 420
 421         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 422                 sx_xunlock(&rm->rm_lock_sx);
 423         else
 424                 mtx_unlock(&rm->rm_lock_mtx);
 425
 426         return (1);
 427 }
 428
 429 int
 430 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 431 {
 432         struct thread *td = curthread;
 433         struct pcpu *pc;
 434
 435         if (SCHEDULER_STOPPED())
 436                 return (1);
 437
 438         tracker->rmp_flags  = 0;
 439         tracker->rmp_thread = td;
 440         tracker->rmp_rmlock = rm;
 441
 442         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 443                 THREAD_NO_SLEEPING();
 444
 445         td->td_critnest++;      /* critical_enter(); */
 446
 447         __compiler_membar();
 448
 449         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 450
 451         rm_tracker_add(pc, tracker);
 452
 453         sched_pin();
 454
 455         __compiler_membar();
 456
 457         td->td_critnest--;
 458
 459         /*
 460          * Fast path to combine two common conditions into a single
 461          * conditional jump.
 462          */
 463         if (__predict_true(0 == (td->td_owepreempt |
 464             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus))))
 465                 return (1);
 466
 467         /* We do not have a read token and need to acquire one. */
 468         return _rm_rlock_hard(rm, tracker, trylock);
 469 }
 470
 471 static __noinline void
 472 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
 473 {
 474
 475         if (td->td_owepreempt) {
 476                 td->td_critnest++;
 477                 critical_exit();
 478         }
 479
 480         if (!tracker->rmp_flags)
 481                 return;
 482
 483         mtx_lock_spin(&rm_spinlock);
 484         LIST_REMOVE(tracker, rmp_qentry);
 485
 486         if (tracker->rmp_flags & RMPF_SIGNAL) {
 487                 struct rmlock *rm;
 488                 struct turnstile *ts;
 489
 490                 rm = tracker->rmp_rmlock;
 491
 492                 turnstile_chain_lock(&rm->lock_object);
 493                 mtx_unlock_spin(&rm_spinlock);
 494
 495                 ts = turnstile_lookup(&rm->lock_object);
 496
 497                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
 498                 turnstile_unpend(ts);
 499                 turnstile_chain_unlock(&rm->lock_object);
 500         } else
 501                 mtx_unlock_spin(&rm_spinlock);
 502 }
 503
 504 void
 505 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
 506 {
 507         struct pcpu *pc;
 508         struct thread *td = tracker->rmp_thread;
 509
 510         if (SCHEDULER_STOPPED())
 511                 return;
 512
 513         td->td_critnest++;      /* critical_enter(); */
 514         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 515         rm_tracker_remove(pc, tracker);
 516         td->td_critnest--;
 517         sched_unpin();
 518
 519         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 520                 THREAD_SLEEPING_OK();
 521
 522         if (__predict_true(0 == (td->td_owepreempt | tracker->rmp_flags)))
 523                 return;
 524
 525         _rm_unlock_hard(td, tracker);
 526 }
 527
 528 void
 529 _rm_wlock(struct rmlock *rm)
 530 {
 531         struct rm_priotracker *prio;
 532         struct turnstile *ts;
 533         cpuset_t readcpus;
 534
 535         if (SCHEDULER_STOPPED())
 536                 return;
 537
 538         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 539                 sx_xlock(&rm->rm_lock_sx);
 540         else
 541                 mtx_lock(&rm->rm_lock_mtx);
 542
 543         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
 544                 /* Get all read tokens back */
 545                 readcpus = all_cpus;
 546                 CPU_ANDNOT(&readcpus, &rm->rm_writecpus);
 547                 rm->rm_writecpus = all_cpus;
 548
 549                 /*
 550                  * Assumes rm->rm_writecpus update is visible on other CPUs
 551                  * before rm_cleanIPI is called.
 552                  */
 553 #ifdef SMP
 554                 smp_rendezvous_cpus(readcpus,
 555                     smp_no_rendezvous_barrier,
 556                     rm_cleanIPI,
 557                     smp_no_rendezvous_barrier,
 558                     rm);
 559
 560 #else
 561                 rm_cleanIPI(rm);
 562 #endif
 563
 564                 mtx_lock_spin(&rm_spinlock);
 565                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
 566                         ts = turnstile_trywait(&rm->lock_object);
 567                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
 568                         mtx_unlock_spin(&rm_spinlock);
 569                         turnstile_wait(ts, prio->rmp_thread,
 570                             TS_EXCLUSIVE_QUEUE);
 571                         mtx_lock_spin(&rm_spinlock);
 572                 }
 573                 mtx_unlock_spin(&rm_spinlock);
 574         }
 575 }
 576
 577 void
 578 _rm_wunlock(struct rmlock *rm)
 579 {
 580
 581         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 582                 sx_xunlock(&rm->rm_lock_sx);
 583         else
 584                 mtx_unlock(&rm->rm_lock_mtx);
 585 }
 586
 587 #if LOCK_DEBUG > 0
 588
 589 void
 590 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 591 {
 592
 593         if (SCHEDULER_STOPPED())
 594                 return;
 595
 596         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 597             ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
 598             curthread, rm->lock_object.lo_name, file, line));
 599         KASSERT(!rm_destroyed(rm),
 600             ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
 601         _rm_assert(rm, RA_UNLOCKED, file, line);
 602
 603         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
 604             file, line, NULL);
 605
 606         _rm_wlock(rm);
 607
 608         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
 609         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 610         TD_LOCKS_INC(curthread);
 611 }
 612
 613 void
 614 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 615 {
 616
 617         if (SCHEDULER_STOPPED())
 618                 return;
 619
 620         KASSERT(!rm_destroyed(rm),
 621             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
 622         _rm_assert(rm, RA_WLOCKED, file, line);
 623         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 624         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
 625         _rm_wunlock(rm);
 626         TD_LOCKS_DEC(curthread);
 627 }
 628
 629 int
 630 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 631     int trylock, const char *file, int line)
 632 {
 633
 634         if (SCHEDULER_STOPPED())
 635                 return (1);
 636
 637 #ifdef INVARIANTS
 638         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
 639                 critical_enter();
 640                 KASSERT(rm_trackers_present(get_pcpu(), rm,
 641                     curthread) == 0,
 642                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
 643                     rm->lock_object.lo_name, file, line));
 644                 critical_exit();
 645         }
 646 #endif
 647         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 648             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
 649             curthread, rm->lock_object.lo_name, file, line));
 650         KASSERT(!rm_destroyed(rm),
 651             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
 652         if (!trylock) {
 653                 KASSERT(!rm_wowned(rm),
 654                     ("rm_rlock: wlock already held for %s @ %s:%d",
 655                     rm->lock_object.lo_name, file, line));
 656                 WITNESS_CHECKORDER(&rm->lock_object,
 657                     LOP_NEWORDER | LOP_NOSLEEP, file, line, NULL);
 658         }
 659
 660         if (_rm_rlock(rm, tracker, trylock)) {
 661                 if (trylock)
 662                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
 663                             line);
 664                 else
 665                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
 666                             line);
 667                 WITNESS_LOCK(&rm->lock_object, LOP_NOSLEEP, file, line);
 668                 TD_LOCKS_INC(curthread);
 669                 return (1);
 670         } else if (trylock)
 671                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 672
 673         return (0);
 674 }
 675
 676 void
 677 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 678     const char *file, int line)
 679 {
 680
 681         if (SCHEDULER_STOPPED())
 682                 return;
 683
 684         KASSERT(!rm_destroyed(rm),
 685             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
 686         _rm_assert(rm, RA_RLOCKED, file, line);
 687         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
 688         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
 689         _rm_runlock(rm, tracker);
 690         TD_LOCKS_DEC(curthread);
 691 }
 692
 693 #else
 694
 695 /*
 696  * Just strip out file and line arguments if no lock debugging is enabled in
 697  * the kernel - we are called from a kernel module.
 698  */
 699 void
 700 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 701 {
 702
 703         _rm_wlock(rm);
 704 }
 705
 706 void
 707 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 708 {
 709
 710         _rm_wunlock(rm);
 711 }
 712
 713 int
 714 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 715     int trylock, const char *file, int line)
 716 {
 717
 718         return _rm_rlock(rm, tracker, trylock);
 719 }
 720
 721 void
 722 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 723     const char *file, int line)
 724 {
 725
 726         _rm_runlock(rm, tracker);
 727 }
 728
 729 #endif
 730
 731 #ifdef INVARIANT_SUPPORT
 732 #ifndef INVARIANTS
 733 #undef _rm_assert
 734 #endif
 735
 736 /*
 737  * Note that this does not need to use witness_assert() for read lock
 738  * assertions since an exact count of read locks held by this thread
 739  * is computable.
 740  */
 741 void
 742 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
 743 {
 744         int count;
 745
 746         if (SCHEDULER_STOPPED())
 747                 return;
 748         switch (what) {
 749         case RA_LOCKED:
 750         case RA_LOCKED | RA_RECURSED:
 751         case RA_LOCKED | RA_NOTRECURSED:
 752         case RA_RLOCKED:
 753         case RA_RLOCKED | RA_RECURSED:
 754         case RA_RLOCKED | RA_NOTRECURSED:
 755                 /*
 756                  * Handle the write-locked case.  Unlike other
 757                  * primitives, writers can never recurse.
 758                  */
 759                 if (rm_wowned(rm)) {
 760                         if (what & RA_RLOCKED)
 761                                 panic("Lock %s exclusively locked @ %s:%d\n",
 762                                     rm->lock_object.lo_name, file, line);
 763                         if (what & RA_RECURSED)
 764                                 panic("Lock %s not recursed @ %s:%d\n",
 765                                     rm->lock_object.lo_name, file, line);
 766                         break;
 767                 }
 768
 769                 critical_enter();
 770                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 771                 critical_exit();
 772
 773                 if (count == 0)
 774                         panic("Lock %s not %slocked @ %s:%d\n",
 775                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
 776                             "read " : "", file, line);
 777                 if (count > 1) {
 778                         if (what & RA_NOTRECURSED)
 779                                 panic("Lock %s recursed @ %s:%d\n",
 780                                     rm->lock_object.lo_name, file, line);
 781                 } else if (what & RA_RECURSED)
 782                         panic("Lock %s not recursed @ %s:%d\n",
 783                             rm->lock_object.lo_name, file, line);
 784                 break;
 785         case RA_WLOCKED:
 786                 if (!rm_wowned(rm))
 787                         panic("Lock %s not exclusively locked @ %s:%d\n",
 788                             rm->lock_object.lo_name, file, line);
 789                 break;
 790         case RA_UNLOCKED:
 791                 if (rm_wowned(rm))
 792                         panic("Lock %s exclusively locked @ %s:%d\n",
 793                             rm->lock_object.lo_name, file, line);
 794
 795                 critical_enter();
 796                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 797                 critical_exit();
 798
 799                 if (count != 0)
 800                         panic("Lock %s read locked @ %s:%d\n",
 801                             rm->lock_object.lo_name, file, line);
 802                 break;
 803         default:
 804                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
 805                     line);
 806         }
 807 }
 808 #endif /* INVARIANT_SUPPORT */
 809
 810 #ifdef DDB
 811 static void
 812 print_tracker(struct rm_priotracker *tr)
 813 {
 814         struct thread *td;
 815
 816         td = tr->rmp_thread;
 817         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
 818             td->td_proc->p_pid, td->td_name);
 819         if (tr->rmp_flags & RMPF_ONQUEUE) {
 820                 db_printf("ONQUEUE");
 821                 if (tr->rmp_flags & RMPF_SIGNAL)
 822                         db_printf(",SIGNAL");
 823         } else
 824                 db_printf("0");
 825         db_printf("}\n");
 826 }
 827
 828 static void
 829 db_show_rm(const struct lock_object *lock)
 830 {
 831         struct rm_priotracker *tr;
 832         struct rm_queue *queue;
 833         const struct rmlock *rm;
 834         struct lock_class *lc;
 835         struct pcpu *pc;
 836
 837         rm = (const struct rmlock *)lock;
 838         db_printf(" writecpus: ");
 839         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
 840         db_printf("\n");
 841         db_printf(" per-CPU readers:\n");
 842         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
 843                 for (queue = pc->pc_rm_queue.rmq_next;
 844                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 845                         tr = (struct rm_priotracker *)queue;
 846                         if (tr->rmp_rmlock == rm)
 847                                 print_tracker(tr);
 848                 }
 849         db_printf(" active readers:\n");
 850         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
 851                 print_tracker(tr);
 852         lc = LOCK_CLASS(&rm->rm_wlock_object);
 853         db_printf("Backing write-lock (%s):\n", lc->lc_name);
 854         lc->lc_ddb_show(&rm->rm_wlock_object);
 855 }
 856 #endif
 857
 858 /*
 859  * Read-mostly sleepable locks.
 860  *
 861  * These primitives allow both readers and writers to sleep. However, neither
 862  * readers nor writers are tracked and subsequently there is no priority
 863  * propagation.
 864  *
 865  * They are intended to be only used when write-locking is almost never needed
 866  * (e.g., they can guard against unloading a kernel module) while read-locking
 867  * happens all the time.
 868  *
 869  * Concurrent writers take turns taking the lock while going off cpu. If this is
 870  * of concern for your usecase, this is not the right primitive.
 871  *
 872  * Neither rms_rlock nor rms_runlock use fences. Instead compiler barriers are
 873  * inserted to prevert reordering of generated code. Execution ordering is
 874  * provided with the use of an IPI handler.
 875  */
 876
 877 void
 878 rms_init(struct rmslock *rms, const char *name)
 879 {
 880
 881         rms->writers = 0;
 882         rms->readers = 0;
 883         mtx_init(&rms->mtx, name, NULL, MTX_DEF | MTX_NEW);
 884         rms->readers_pcpu = uma_zalloc_pcpu(pcpu_zone_int, M_WAITOK | M_ZERO);
 885         rms->readers_influx = uma_zalloc_pcpu(pcpu_zone_int, M_WAITOK | M_ZERO);
 886 }
 887
 888 void
 889 rms_destroy(struct rmslock *rms)
 890 {
 891
 892         MPASS(rms->writers == 0);
 893         MPASS(rms->readers == 0);
 894         mtx_destroy(&rms->mtx);
 895         uma_zfree_pcpu(pcpu_zone_int, rms->readers_pcpu);
 896         uma_zfree_pcpu(pcpu_zone_int, rms->readers_influx);
 897 }
 898
 899 static void __noinline
 900 rms_rlock_fallback(struct rmslock *rms)
 901 {
 902
 903         zpcpu_set_protected(rms->readers_influx, 0);
 904         critical_exit();
 905
 906         mtx_lock(&rms->mtx);
 907         MPASS(*zpcpu_get(rms->readers_pcpu) == 0);
 908         while (rms->writers > 0)
 909                 msleep(&rms->readers, &rms->mtx, PUSER - 1, mtx_name(&rms->mtx), 0);
 910         critical_enter();
 911         zpcpu_add_protected(rms->readers_pcpu, 1);
 912         mtx_unlock(&rms->mtx);
 913         critical_exit();
 914 }
 915
 916 void
 917 rms_rlock(struct rmslock *rms)
 918 {
 919
 920         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
 921
 922         critical_enter();
 923         zpcpu_set_protected(rms->readers_influx, 1);
 924         __compiler_membar();
 925         if (__predict_false(rms->writers > 0)) {
 926                 rms_rlock_fallback(rms);
 927                 return;
 928         }
 929         __compiler_membar();
 930         zpcpu_add_protected(rms->readers_pcpu, 1);
 931         __compiler_membar();
 932         zpcpu_set_protected(rms->readers_influx, 0);
 933         critical_exit();
 934 }
 935
 936 int
 937 rms_try_rlock(struct rmslock *rms)
 938 {
 939
 940         critical_enter();
 941         zpcpu_set_protected(rms->readers_influx, 1);
 942         __compiler_membar();
 943         if (__predict_false(rms->writers > 0)) {
 944                 __compiler_membar();
 945                 zpcpu_set_protected(rms->readers_influx, 0);
 946                 critical_exit();
 947                 return (0);
 948         }
 949         __compiler_membar();
 950         zpcpu_add_protected(rms->readers_pcpu, 1);
 951         __compiler_membar();
 952         zpcpu_set_protected(rms->readers_influx, 0);
 953         critical_exit();
 954         return (1);
 955 }
 956
 957 static void __noinline
 958 rms_runlock_fallback(struct rmslock *rms)
 959 {
 960
 961         zpcpu_set_protected(rms->readers_influx, 0);
 962         critical_exit();
 963
 964         mtx_lock(&rms->mtx);
 965         MPASS(*zpcpu_get(rms->readers_pcpu) == 0);
 966         MPASS(rms->writers > 0);
 967         MPASS(rms->readers > 0);
 968         rms->readers--;
 969         if (rms->readers == 0)
 970                 wakeup_one(&rms->writers);
 971         mtx_unlock(&rms->mtx);
 972 }
 973
 974 void
 975 rms_runlock(struct rmslock *rms)
 976 {
 977
 978         critical_enter();
 979         zpcpu_set_protected(rms->readers_influx, 1);
 980         __compiler_membar();
 981         if (__predict_false(rms->writers > 0)) {
 982                 rms_runlock_fallback(rms);
 983                 return;
 984         }
 985         __compiler_membar();
 986         zpcpu_sub_protected(rms->readers_pcpu, 1);
 987         __compiler_membar();
 988         zpcpu_set_protected(rms->readers_influx, 0);
 989         critical_exit();
 990 }
 991
 992 struct rmslock_ipi {
 993         struct rmslock *rms;
 994         struct smp_rendezvous_cpus_retry_arg srcra;
 995 };
 996
 997 static void
 998 rms_action_func(void *arg)
 999 {
1000         struct rmslock_ipi *rmsipi;
1001         struct rmslock *rms;
1002         int readers;
1003
1004         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
1005         rms = rmsipi->rms;
1006
1007         if (*zpcpu_get(rms->readers_influx))
1008                 return;
1009         readers = zpcpu_replace(rms->readers_pcpu, 0);
1010         if (readers != 0)
1011                 atomic_add_int(&rms->readers, readers);
1012         smp_rendezvous_cpus_done(arg);
1013 }
1014
1015 static void
1016 rms_wait_func(void *arg, int cpu)
1017 {
1018         struct rmslock_ipi *rmsipi;
1019         struct rmslock *rms;
1020         int *in_op;
1021
1022         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
1023         rms = rmsipi->rms;
1024
1025         in_op = zpcpu_get_cpu(rms->readers_influx, cpu);
1026         while (atomic_load_int(in_op))
1027                 cpu_spinwait();
1028 }
1029
1030 static void
1031 rms_wlock_switch(struct rmslock *rms)
1032 {
1033         struct rmslock_ipi rmsipi;
1034
1035         MPASS(rms->readers == 0);
1036         MPASS(rms->writers == 1);
1037
1038         rmsipi.rms = rms;
1039
1040         smp_rendezvous_cpus_retry(all_cpus,
1041             smp_no_rendezvous_barrier,
1042             rms_action_func,
1043             smp_no_rendezvous_barrier,
1044             rms_wait_func,
1045             &rmsipi.srcra);
1046 }
1047
1048 void
1049 rms_wlock(struct rmslock *rms)
1050 {
1051
1052         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
1053
1054         mtx_lock(&rms->mtx);
1055         rms->writers++;
1056         if (rms->writers > 1) {
1057                 msleep(&rms->writers, &rms->mtx, (PUSER - 1) | PDROP,
1058                     mtx_name(&rms->mtx), 0);
1059                 MPASS(rms->readers == 0);
1060                 return;
1061         }
1062
1063         rms_wlock_switch(rms);
1064
1065         if (rms->readers > 0)
1066                 msleep(&rms->writers, &rms->mtx, (PUSER - 1) | PDROP,
1067                     mtx_name(&rms->mtx), 0);
1068         else
1069                 mtx_unlock(&rms->mtx);
1070         MPASS(rms->readers == 0);
1071 }
1072
1073 void
1074 rms_wunlock(struct rmslock *rms)
1075 {
1076
1077         mtx_lock(&rms->mtx);
1078         MPASS(rms->writers >= 1);
1079         MPASS(rms->readers == 0);
1080         rms->writers--;
1081         if (rms->writers > 0)
1082                 wakeup_one(&rms->writers);
1083         else
1084                 wakeup(&rms->readers);
1085         mtx_unlock(&rms->mtx);
1086 }