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         if (opts & RM_DUPOK)
 293                 liflags |= LO_DUPOK;
 294         rm->rm_writecpus = all_cpus;
 295         LIST_INIT(&rm->rm_activeReaders);
 296         if (opts & RM_SLEEPABLE) {
 297                 liflags |= LO_SLEEPABLE;
 298                 lc = &lock_class_rm_sleepable;
 299                 xflags = (opts & RM_NEW ? SX_NEW : 0);
 300                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx",
 301                     xflags | SX_NOWITNESS);
 302         } else {
 303                 lc = &lock_class_rm;
 304                 xflags = (opts & RM_NEW ? MTX_NEW : 0);
 305                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx",
 306                     xflags | MTX_NOWITNESS);
 307         }
 308         lock_init(&rm->lock_object, lc, name, NULL, liflags);
 309 }
 310
 311 void
 312 rm_init(struct rmlock *rm, const char *name)
 313 {
 314
 315         rm_init_flags(rm, name, 0);
 316 }
 317
 318 void
 319 rm_destroy(struct rmlock *rm)
 320 {
 321
 322         rm_assert(rm, RA_UNLOCKED);
 323         LIST_FIRST(&rm->rm_activeReaders) = RM_DESTROYED;
 324         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 325                 sx_destroy(&rm->rm_lock_sx);
 326         else
 327                 mtx_destroy(&rm->rm_lock_mtx);
 328         lock_destroy(&rm->lock_object);
 329 }
 330
 331 int
 332 rm_wowned(const struct rmlock *rm)
 333 {
 334
 335         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 336                 return (sx_xlocked(&rm->rm_lock_sx));
 337         else
 338                 return (mtx_owned(&rm->rm_lock_mtx));
 339 }
 340
 341 void
 342 rm_sysinit(void *arg)
 343 {
 344         struct rm_args *args;
 345
 346         args = arg;
 347         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_flags);
 348 }
 349
 350 static __noinline int
 351 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 352 {
 353         struct pcpu *pc;
 354
 355         critical_enter();
 356         pc = get_pcpu();
 357
 358         /* Check if we just need to do a proper critical_exit. */
 359         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
 360                 critical_exit();
 361                 return (1);
 362         }
 363
 364         /* Remove our tracker from the per-cpu list. */
 365         rm_tracker_remove(pc, tracker);
 366
 367         /*
 368          * Check to see if the IPI granted us the lock after all.  The load of
 369          * rmp_flags must happen after the tracker is removed from the list.
 370          */
 371         atomic_interrupt_fence();
 372         if (tracker->rmp_flags) {
 373                 /* Just add back tracker - we hold the lock. */
 374                 rm_tracker_add(pc, tracker);
 375                 critical_exit();
 376                 return (1);
 377         }
 378
 379         /*
 380          * We allow readers to acquire a lock even if a writer is blocked if
 381          * the lock is recursive and the reader already holds the lock.
 382          */
 383         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 384                 /*
 385                  * Just grant the lock if this thread already has a tracker
 386                  * for this lock on the per-cpu queue.
 387                  */
 388                 if (rm_trackers_present(pc, rm, curthread) != 0) {
 389                         mtx_lock_spin(&rm_spinlock);
 390                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 391                             rmp_qentry);
 392                         tracker->rmp_flags = RMPF_ONQUEUE;
 393                         mtx_unlock_spin(&rm_spinlock);
 394                         rm_tracker_add(pc, tracker);
 395                         critical_exit();
 396                         return (1);
 397                 }
 398         }
 399
 400         sched_unpin();
 401         critical_exit();
 402
 403         if (trylock) {
 404                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 405                         if (!sx_try_xlock(&rm->rm_lock_sx))
 406                                 return (0);
 407                 } else {
 408                         if (!mtx_trylock(&rm->rm_lock_mtx))
 409                                 return (0);
 410                 }
 411         } else {
 412                 if (rm->lock_object.lo_flags & LO_SLEEPABLE) {
 413                         THREAD_SLEEPING_OK();
 414                         sx_xlock(&rm->rm_lock_sx);
 415                         THREAD_NO_SLEEPING();
 416                 } else
 417                         mtx_lock(&rm->rm_lock_mtx);
 418         }
 419
 420         critical_enter();
 421         pc = get_pcpu();
 422         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
 423         rm_tracker_add(pc, tracker);
 424         sched_pin();
 425         critical_exit();
 426
 427         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 428                 sx_xunlock(&rm->rm_lock_sx);
 429         else
 430                 mtx_unlock(&rm->rm_lock_mtx);
 431
 432         return (1);
 433 }
 434
 435 int
 436 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 437 {
 438         struct thread *td = curthread;
 439         struct pcpu *pc;
 440
 441         if (SCHEDULER_STOPPED())
 442                 return (1);
 443
 444         tracker->rmp_flags  = 0;
 445         tracker->rmp_thread = td;
 446         tracker->rmp_rmlock = rm;
 447
 448         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 449                 THREAD_NO_SLEEPING();
 450
 451         td->td_critnest++;      /* critical_enter(); */
 452         atomic_interrupt_fence();
 453
 454         pc = cpuid_to_pcpu[td->td_oncpu];
 455         rm_tracker_add(pc, tracker);
 456         sched_pin();
 457
 458         atomic_interrupt_fence();
 459         td->td_critnest--;
 460
 461         /*
 462          * Fast path to combine two common conditions into a single
 463          * conditional jump.
 464          */
 465         if (__predict_true(0 == (td->td_owepreempt |
 466             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus))))
 467                 return (1);
 468
 469         /* We do not have a read token and need to acquire one. */
 470         return _rm_rlock_hard(rm, tracker, trylock);
 471 }
 472
 473 static __noinline void
 474 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
 475 {
 476
 477         if (td->td_owepreempt) {
 478                 td->td_critnest++;
 479                 critical_exit();
 480         }
 481
 482         if (!tracker->rmp_flags)
 483                 return;
 484
 485         mtx_lock_spin(&rm_spinlock);
 486         LIST_REMOVE(tracker, rmp_qentry);
 487
 488         if (tracker->rmp_flags & RMPF_SIGNAL) {
 489                 struct rmlock *rm;
 490                 struct turnstile *ts;
 491
 492                 rm = tracker->rmp_rmlock;
 493
 494                 turnstile_chain_lock(&rm->lock_object);
 495                 mtx_unlock_spin(&rm_spinlock);
 496
 497                 ts = turnstile_lookup(&rm->lock_object);
 498
 499                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
 500                 turnstile_unpend(ts);
 501                 turnstile_chain_unlock(&rm->lock_object);
 502         } else
 503                 mtx_unlock_spin(&rm_spinlock);
 504 }
 505
 506 void
 507 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
 508 {
 509         struct pcpu *pc;
 510         struct thread *td = tracker->rmp_thread;
 511
 512         if (SCHEDULER_STOPPED())
 513                 return;
 514
 515         td->td_critnest++;      /* critical_enter(); */
 516         atomic_interrupt_fence();
 517
 518         pc = cpuid_to_pcpu[td->td_oncpu];
 519         rm_tracker_remove(pc, tracker);
 520
 521         atomic_interrupt_fence();
 522         td->td_critnest--;
 523         sched_unpin();
 524
 525         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 526                 THREAD_SLEEPING_OK();
 527
 528         if (__predict_true(0 == (td->td_owepreempt | tracker->rmp_flags)))
 529                 return;
 530
 531         _rm_unlock_hard(td, tracker);
 532 }
 533
 534 void
 535 _rm_wlock(struct rmlock *rm)
 536 {
 537         struct rm_priotracker *prio;
 538         struct turnstile *ts;
 539         cpuset_t readcpus;
 540
 541         if (SCHEDULER_STOPPED())
 542                 return;
 543
 544         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 545                 sx_xlock(&rm->rm_lock_sx);
 546         else
 547                 mtx_lock(&rm->rm_lock_mtx);
 548
 549         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
 550                 /* Get all read tokens back */
 551                 readcpus = all_cpus;
 552                 CPU_ANDNOT(&readcpus, &readcpus, &rm->rm_writecpus);
 553                 rm->rm_writecpus = all_cpus;
 554
 555                 /*
 556                  * Assumes rm->rm_writecpus update is visible on other CPUs
 557                  * before rm_cleanIPI is called.
 558                  */
 559 #ifdef SMP
 560                 smp_rendezvous_cpus(readcpus,
 561                     smp_no_rendezvous_barrier,
 562                     rm_cleanIPI,
 563                     smp_no_rendezvous_barrier,
 564                     rm);
 565
 566 #else
 567                 rm_cleanIPI(rm);
 568 #endif
 569
 570                 mtx_lock_spin(&rm_spinlock);
 571                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
 572                         ts = turnstile_trywait(&rm->lock_object);
 573                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
 574                         mtx_unlock_spin(&rm_spinlock);
 575                         turnstile_wait(ts, prio->rmp_thread,
 576                             TS_EXCLUSIVE_QUEUE);
 577                         mtx_lock_spin(&rm_spinlock);
 578                 }
 579                 mtx_unlock_spin(&rm_spinlock);
 580         }
 581 }
 582
 583 void
 584 _rm_wunlock(struct rmlock *rm)
 585 {
 586
 587         if (rm->lock_object.lo_flags & LO_SLEEPABLE)
 588                 sx_xunlock(&rm->rm_lock_sx);
 589         else
 590                 mtx_unlock(&rm->rm_lock_mtx);
 591 }
 592
 593 #if LOCK_DEBUG > 0
 594
 595 void
 596 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 597 {
 598
 599         if (SCHEDULER_STOPPED())
 600                 return;
 601
 602         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 603             ("rm_wlock() by idle thread %p on rmlock %s @ %s:%d",
 604             curthread, rm->lock_object.lo_name, file, line));
 605         KASSERT(!rm_destroyed(rm),
 606             ("rm_wlock() of destroyed rmlock @ %s:%d", file, line));
 607         _rm_assert(rm, RA_UNLOCKED, file, line);
 608
 609         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
 610             file, line, NULL);
 611
 612         _rm_wlock(rm);
 613
 614         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
 615         WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 616         TD_LOCKS_INC(curthread);
 617 }
 618
 619 void
 620 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 621 {
 622
 623         if (SCHEDULER_STOPPED())
 624                 return;
 625
 626         KASSERT(!rm_destroyed(rm),
 627             ("rm_wunlock() of destroyed rmlock @ %s:%d", file, line));
 628         _rm_assert(rm, RA_WLOCKED, file, line);
 629         WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 630         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
 631         _rm_wunlock(rm);
 632         TD_LOCKS_DEC(curthread);
 633 }
 634
 635 int
 636 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 637     int trylock, const char *file, int line)
 638 {
 639
 640         if (SCHEDULER_STOPPED())
 641                 return (1);
 642
 643 #ifdef INVARIANTS
 644         if (!(rm->lock_object.lo_flags & LO_RECURSABLE) && !trylock) {
 645                 critical_enter();
 646                 KASSERT(rm_trackers_present(get_pcpu(), rm,
 647                     curthread) == 0,
 648                     ("rm_rlock: recursed on non-recursive rmlock %s @ %s:%d\n",
 649                     rm->lock_object.lo_name, file, line));
 650                 critical_exit();
 651         }
 652 #endif
 653         KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
 654             ("rm_rlock() by idle thread %p on rmlock %s @ %s:%d",
 655             curthread, rm->lock_object.lo_name, file, line));
 656         KASSERT(!rm_destroyed(rm),
 657             ("rm_rlock() of destroyed rmlock @ %s:%d", file, line));
 658         if (!trylock) {
 659                 KASSERT(!rm_wowned(rm),
 660                     ("rm_rlock: wlock already held for %s @ %s:%d",
 661                     rm->lock_object.lo_name, file, line));
 662                 WITNESS_CHECKORDER(&rm->lock_object,
 663                     LOP_NEWORDER | LOP_NOSLEEP, file, line, NULL);
 664         }
 665
 666         if (_rm_rlock(rm, tracker, trylock)) {
 667                 if (trylock)
 668                         LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 1, file,
 669                             line);
 670                 else
 671                         LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file,
 672                             line);
 673                 WITNESS_LOCK(&rm->lock_object, LOP_NOSLEEP, file, line);
 674                 TD_LOCKS_INC(curthread);
 675                 return (1);
 676         } else if (trylock)
 677                 LOCK_LOG_TRY("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 678
 679         return (0);
 680 }
 681
 682 void
 683 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 684     const char *file, int line)
 685 {
 686
 687         if (SCHEDULER_STOPPED())
 688                 return;
 689
 690         KASSERT(!rm_destroyed(rm),
 691             ("rm_runlock() of destroyed rmlock @ %s:%d", file, line));
 692         _rm_assert(rm, RA_RLOCKED, file, line);
 693         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
 694         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
 695         _rm_runlock(rm, tracker);
 696         TD_LOCKS_DEC(curthread);
 697 }
 698
 699 #else
 700
 701 /*
 702  * Just strip out file and line arguments if no lock debugging is enabled in
 703  * the kernel - we are called from a kernel module.
 704  */
 705 void
 706 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 707 {
 708
 709         _rm_wlock(rm);
 710 }
 711
 712 void
 713 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 714 {
 715
 716         _rm_wunlock(rm);
 717 }
 718
 719 int
 720 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 721     int trylock, const char *file, int line)
 722 {
 723
 724         return _rm_rlock(rm, tracker, trylock);
 725 }
 726
 727 void
 728 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 729     const char *file, int line)
 730 {
 731
 732         _rm_runlock(rm, tracker);
 733 }
 734
 735 #endif
 736
 737 #ifdef INVARIANT_SUPPORT
 738 #ifndef INVARIANTS
 739 #undef _rm_assert
 740 #endif
 741
 742 /*
 743  * Note that this does not need to use witness_assert() for read lock
 744  * assertions since an exact count of read locks held by this thread
 745  * is computable.
 746  */
 747 void
 748 _rm_assert(const struct rmlock *rm, int what, const char *file, int line)
 749 {
 750         int count;
 751
 752         if (SCHEDULER_STOPPED())
 753                 return;
 754         switch (what) {
 755         case RA_LOCKED:
 756         case RA_LOCKED | RA_RECURSED:
 757         case RA_LOCKED | RA_NOTRECURSED:
 758         case RA_RLOCKED:
 759         case RA_RLOCKED | RA_RECURSED:
 760         case RA_RLOCKED | RA_NOTRECURSED:
 761                 /*
 762                  * Handle the write-locked case.  Unlike other
 763                  * primitives, writers can never recurse.
 764                  */
 765                 if (rm_wowned(rm)) {
 766                         if (what & RA_RLOCKED)
 767                                 panic("Lock %s exclusively locked @ %s:%d\n",
 768                                     rm->lock_object.lo_name, file, line);
 769                         if (what & RA_RECURSED)
 770                                 panic("Lock %s not recursed @ %s:%d\n",
 771                                     rm->lock_object.lo_name, file, line);
 772                         break;
 773                 }
 774
 775                 critical_enter();
 776                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 777                 critical_exit();
 778
 779                 if (count == 0)
 780                         panic("Lock %s not %slocked @ %s:%d\n",
 781                             rm->lock_object.lo_name, (what & RA_RLOCKED) ?
 782                             "read " : "", file, line);
 783                 if (count > 1) {
 784                         if (what & RA_NOTRECURSED)
 785                                 panic("Lock %s recursed @ %s:%d\n",
 786                                     rm->lock_object.lo_name, file, line);
 787                 } else if (what & RA_RECURSED)
 788                         panic("Lock %s not recursed @ %s:%d\n",
 789                             rm->lock_object.lo_name, file, line);
 790                 break;
 791         case RA_WLOCKED:
 792                 if (!rm_wowned(rm))
 793                         panic("Lock %s not exclusively locked @ %s:%d\n",
 794                             rm->lock_object.lo_name, file, line);
 795                 break;
 796         case RA_UNLOCKED:
 797                 if (rm_wowned(rm))
 798                         panic("Lock %s exclusively locked @ %s:%d\n",
 799                             rm->lock_object.lo_name, file, line);
 800
 801                 critical_enter();
 802                 count = rm_trackers_present(get_pcpu(), rm, curthread);
 803                 critical_exit();
 804
 805                 if (count != 0)
 806                         panic("Lock %s read locked @ %s:%d\n",
 807                             rm->lock_object.lo_name, file, line);
 808                 break;
 809         default:
 810                 panic("Unknown rm lock assertion: %d @ %s:%d", what, file,
 811                     line);
 812         }
 813 }
 814 #endif /* INVARIANT_SUPPORT */
 815
 816 #ifdef DDB
 817 static void
 818 print_tracker(struct rm_priotracker *tr)
 819 {
 820         struct thread *td;
 821
 822         td = tr->rmp_thread;
 823         db_printf("   thread %p (tid %d, pid %d, \"%s\") {", td, td->td_tid,
 824             td->td_proc->p_pid, td->td_name);
 825         if (tr->rmp_flags & RMPF_ONQUEUE) {
 826                 db_printf("ONQUEUE");
 827                 if (tr->rmp_flags & RMPF_SIGNAL)
 828                         db_printf(",SIGNAL");
 829         } else
 830                 db_printf("0");
 831         db_printf("}\n");
 832 }
 833
 834 static void
 835 db_show_rm(const struct lock_object *lock)
 836 {
 837         struct rm_priotracker *tr;
 838         struct rm_queue *queue;
 839         const struct rmlock *rm;
 840         struct lock_class *lc;
 841         struct pcpu *pc;
 842
 843         rm = (const struct rmlock *)lock;
 844         db_printf(" writecpus: ");
 845         ddb_display_cpuset(__DEQUALIFY(const cpuset_t *, &rm->rm_writecpus));
 846         db_printf("\n");
 847         db_printf(" per-CPU readers:\n");
 848         STAILQ_FOREACH(pc, &cpuhead, pc_allcpu)
 849                 for (queue = pc->pc_rm_queue.rmq_next;
 850                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 851                         tr = (struct rm_priotracker *)queue;
 852                         if (tr->rmp_rmlock == rm)
 853                                 print_tracker(tr);
 854                 }
 855         db_printf(" active readers:\n");
 856         LIST_FOREACH(tr, &rm->rm_activeReaders, rmp_qentry)
 857                 print_tracker(tr);
 858         lc = LOCK_CLASS(&rm->rm_wlock_object);
 859         db_printf("Backing write-lock (%s):\n", lc->lc_name);
 860         lc->lc_ddb_show(&rm->rm_wlock_object);
 861 }
 862 #endif
 863
 864 /*
 865  * Read-mostly sleepable locks.
 866  *
 867  * These primitives allow both readers and writers to sleep. However, neither
 868  * readers nor writers are tracked and subsequently there is no priority
 869  * propagation.
 870  *
 871  * They are intended to be only used when write-locking is almost never needed
 872  * (e.g., they can guard against unloading a kernel module) while read-locking
 873  * happens all the time.
 874  *
 875  * Concurrent writers take turns taking the lock while going off cpu. If this is
 876  * of concern for your usecase, this is not the right primitive.
 877  *
 878  * Neither rms_rlock nor rms_runlock use thread fences. Instead interrupt
 879  * fences are inserted to ensure ordering with the code executed in the IPI
 880  * handler.
 881  *
 882  * No attempt is made to track which CPUs read locked at least once,
 883  * consequently write locking sends IPIs to all of them. This will become a
 884  * problem at some point. The easiest way to lessen it is to provide a bitmap.
 885  */
 886
 887 #define RMS_NOOWNER     ((void *)0x1)
 888 #define RMS_TRANSIENT   ((void *)0x2)
 889 #define RMS_FLAGMASK    0xf
 890
 891 struct rmslock_pcpu {
 892         int influx;
 893         int readers;
 894 };
 895
 896 _Static_assert(sizeof(struct rmslock_pcpu) == 8, "bad size");
 897
 898 /*
 899  * Internal routines
 900  */
 901 static struct rmslock_pcpu *
 902 rms_int_pcpu(struct rmslock *rms)
 903 {
 904
 905         CRITICAL_ASSERT(curthread);
 906         return (zpcpu_get(rms->pcpu));
 907 }
 908
 909 static struct rmslock_pcpu *
 910 rms_int_remote_pcpu(struct rmslock *rms, int cpu)
 911 {
 912
 913         return (zpcpu_get_cpu(rms->pcpu, cpu));
 914 }
 915
 916 static void
 917 rms_int_influx_enter(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 918 {
 919
 920         CRITICAL_ASSERT(curthread);
 921         MPASS(pcpu->influx == 0);
 922         pcpu->influx = 1;
 923 }
 924
 925 static void
 926 rms_int_influx_exit(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 927 {
 928
 929         CRITICAL_ASSERT(curthread);
 930         MPASS(pcpu->influx == 1);
 931         pcpu->influx = 0;
 932 }
 933
 934 #ifdef INVARIANTS
 935 static void
 936 rms_int_debug_readers_inc(struct rmslock *rms)
 937 {
 938         int old;
 939         old = atomic_fetchadd_int(&rms->debug_readers, 1);
 940         KASSERT(old >= 0, ("%s: bad readers count %d\n", __func__, old));
 941 }
 942
 943 static void
 944 rms_int_debug_readers_dec(struct rmslock *rms)
 945 {
 946         int old;
 947
 948         old = atomic_fetchadd_int(&rms->debug_readers, -1);
 949         KASSERT(old > 0, ("%s: bad readers count %d\n", __func__, old));
 950 }
 951 #else
 952 static void
 953 rms_int_debug_readers_inc(struct rmslock *rms)
 954 {
 955 }
 956
 957 static void
 958 rms_int_debug_readers_dec(struct rmslock *rms)
 959 {
 960 }
 961 #endif
 962
 963 static void
 964 rms_int_readers_inc(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 965 {
 966
 967         CRITICAL_ASSERT(curthread);
 968         rms_int_debug_readers_inc(rms);
 969         pcpu->readers++;
 970 }
 971
 972 static void
 973 rms_int_readers_dec(struct rmslock *rms, struct rmslock_pcpu *pcpu)
 974 {
 975
 976         CRITICAL_ASSERT(curthread);
 977         rms_int_debug_readers_dec(rms);
 978         pcpu->readers--;
 979 }
 980
 981 /*
 982  * Public API
 983  */
 984 void
 985 rms_init(struct rmslock *rms, const char *name)
 986 {
 987
 988         rms->owner = RMS_NOOWNER;
 989         rms->writers = 0;
 990         rms->readers = 0;
 991         rms->debug_readers = 0;
 992         mtx_init(&rms->mtx, name, NULL, MTX_DEF | MTX_NEW);
 993         rms->pcpu = uma_zalloc_pcpu(pcpu_zone_8, M_WAITOK | M_ZERO);
 994 }
 995
 996 void
 997 rms_destroy(struct rmslock *rms)
 998 {
 999
1000         MPASS(rms->writers == 0);
1001         MPASS(rms->readers == 0);
1002         mtx_destroy(&rms->mtx);
1003         uma_zfree_pcpu(pcpu_zone_8, rms->pcpu);
1004 }
1005
1006 static void __noinline
1007 rms_rlock_fallback(struct rmslock *rms)
1008 {
1009
1010         rms_int_influx_exit(rms, rms_int_pcpu(rms));
1011         critical_exit();
1012
1013         mtx_lock(&rms->mtx);
1014         while (rms->writers > 0)
1015                 msleep(&rms->readers, &rms->mtx, PUSER - 1, mtx_name(&rms->mtx), 0);
1016         critical_enter();
1017         rms_int_readers_inc(rms, rms_int_pcpu(rms));
1018         mtx_unlock(&rms->mtx);
1019         critical_exit();
1020         TD_LOCKS_INC(curthread);
1021 }
1022
1023 void
1024 rms_rlock(struct rmslock *rms)
1025 {
1026         struct rmslock_pcpu *pcpu;
1027
1028         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
1029         MPASS(atomic_load_ptr(&rms->owner) != curthread);
1030
1031         critical_enter();
1032         pcpu = rms_int_pcpu(rms);
1033         rms_int_influx_enter(rms, pcpu);
1034         atomic_interrupt_fence();
1035         if (__predict_false(rms->writers > 0)) {
1036                 rms_rlock_fallback(rms);
1037                 return;
1038         }
1039         atomic_interrupt_fence();
1040         rms_int_readers_inc(rms, pcpu);
1041         atomic_interrupt_fence();
1042         rms_int_influx_exit(rms, pcpu);
1043         critical_exit();
1044         TD_LOCKS_INC(curthread);
1045 }
1046
1047 int
1048 rms_try_rlock(struct rmslock *rms)
1049 {
1050         struct rmslock_pcpu *pcpu;
1051
1052         MPASS(atomic_load_ptr(&rms->owner) != curthread);
1053
1054         critical_enter();
1055         pcpu = rms_int_pcpu(rms);
1056         rms_int_influx_enter(rms, pcpu);
1057         atomic_interrupt_fence();
1058         if (__predict_false(rms->writers > 0)) {
1059                 rms_int_influx_exit(rms, pcpu);
1060                 critical_exit();
1061                 return (0);
1062         }
1063         atomic_interrupt_fence();
1064         rms_int_readers_inc(rms, pcpu);
1065         atomic_interrupt_fence();
1066         rms_int_influx_exit(rms, pcpu);
1067         critical_exit();
1068         TD_LOCKS_INC(curthread);
1069         return (1);
1070 }
1071
1072 static void __noinline
1073 rms_runlock_fallback(struct rmslock *rms)
1074 {
1075
1076         rms_int_influx_exit(rms, rms_int_pcpu(rms));
1077         critical_exit();
1078
1079         mtx_lock(&rms->mtx);
1080         MPASS(rms->writers > 0);
1081         MPASS(rms->readers > 0);
1082         MPASS(rms->debug_readers == rms->readers);
1083         rms_int_debug_readers_dec(rms);
1084         rms->readers--;
1085         if (rms->readers == 0)
1086                 wakeup_one(&rms->writers);
1087         mtx_unlock(&rms->mtx);
1088         TD_LOCKS_DEC(curthread);
1089 }
1090
1091 void
1092 rms_runlock(struct rmslock *rms)
1093 {
1094         struct rmslock_pcpu *pcpu;
1095
1096         critical_enter();
1097         pcpu = rms_int_pcpu(rms);
1098         rms_int_influx_enter(rms, pcpu);
1099         atomic_interrupt_fence();
1100         if (__predict_false(rms->writers > 0)) {
1101                 rms_runlock_fallback(rms);
1102                 return;
1103         }
1104         atomic_interrupt_fence();
1105         rms_int_readers_dec(rms, pcpu);
1106         atomic_interrupt_fence();
1107         rms_int_influx_exit(rms, pcpu);
1108         critical_exit();
1109         TD_LOCKS_DEC(curthread);
1110 }
1111
1112 struct rmslock_ipi {
1113         struct rmslock *rms;
1114         struct smp_rendezvous_cpus_retry_arg srcra;
1115 };
1116
1117 static void
1118 rms_action_func(void *arg)
1119 {
1120         struct rmslock_ipi *rmsipi;
1121         struct rmslock_pcpu *pcpu;
1122         struct rmslock *rms;
1123
1124         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
1125         rms = rmsipi->rms;
1126         pcpu = rms_int_pcpu(rms);
1127
1128         if (pcpu->influx)
1129                 return;
1130         if (pcpu->readers != 0) {
1131                 atomic_add_int(&rms->readers, pcpu->readers);
1132                 pcpu->readers = 0;
1133         }
1134         smp_rendezvous_cpus_done(arg);
1135 }
1136
1137 static void
1138 rms_wait_func(void *arg, int cpu)
1139 {
1140         struct rmslock_ipi *rmsipi;
1141         struct rmslock_pcpu *pcpu;
1142         struct rmslock *rms;
1143
1144         rmsipi = __containerof(arg, struct rmslock_ipi, srcra);
1145         rms = rmsipi->rms;
1146         pcpu = rms_int_remote_pcpu(rms, cpu);
1147
1148         while (atomic_load_int(&pcpu->influx))
1149                 cpu_spinwait();
1150 }
1151
1152 #ifdef INVARIANTS
1153 static void
1154 rms_assert_no_pcpu_readers(struct rmslock *rms)
1155 {
1156         struct rmslock_pcpu *pcpu;
1157         int cpu;
1158
1159         CPU_FOREACH(cpu) {
1160                 pcpu = rms_int_remote_pcpu(rms, cpu);
1161                 if (pcpu->readers != 0) {
1162                         panic("%s: got %d readers on cpu %d\n", __func__,
1163                             pcpu->readers, cpu);
1164                 }
1165         }
1166 }
1167 #else
1168 static void
1169 rms_assert_no_pcpu_readers(struct rmslock *rms)
1170 {
1171 }
1172 #endif
1173
1174 static void
1175 rms_wlock_switch(struct rmslock *rms)
1176 {
1177         struct rmslock_ipi rmsipi;
1178
1179         MPASS(rms->readers == 0);
1180         MPASS(rms->writers == 1);
1181
1182         rmsipi.rms = rms;
1183
1184         smp_rendezvous_cpus_retry(all_cpus,
1185             smp_no_rendezvous_barrier,
1186             rms_action_func,
1187             smp_no_rendezvous_barrier,
1188             rms_wait_func,
1189             &rmsipi.srcra);
1190 }
1191
1192 void
1193 rms_wlock(struct rmslock *rms)
1194 {
1195
1196         WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
1197         MPASS(atomic_load_ptr(&rms->owner) != curthread);
1198
1199         mtx_lock(&rms->mtx);
1200         rms->writers++;
1201         if (rms->writers > 1) {
1202                 msleep(&rms->owner, &rms->mtx, (PUSER - 1),
1203                     mtx_name(&rms->mtx), 0);
1204                 MPASS(rms->readers == 0);
1205                 KASSERT(rms->owner == RMS_TRANSIENT,
1206                     ("%s: unexpected owner value %p\n", __func__,
1207                     rms->owner));
1208                 goto out_grab;
1209         }
1210
1211         KASSERT(rms->owner == RMS_NOOWNER,
1212             ("%s: unexpected owner value %p\n", __func__, rms->owner));
1213
1214         rms_wlock_switch(rms);
1215         rms_assert_no_pcpu_readers(rms);
1216
1217         if (rms->readers > 0) {
1218                 msleep(&rms->writers, &rms->mtx, (PUSER - 1),
1219                     mtx_name(&rms->mtx), 0);
1220         }
1221
1222 out_grab:
1223         rms->owner = curthread;
1224         rms_assert_no_pcpu_readers(rms);
1225         mtx_unlock(&rms->mtx);
1226         MPASS(rms->readers == 0);
1227         TD_LOCKS_INC(curthread);
1228 }
1229
1230 void
1231 rms_wunlock(struct rmslock *rms)
1232 {
1233
1234         mtx_lock(&rms->mtx);
1235         KASSERT(rms->owner == curthread,
1236             ("%s: unexpected owner value %p\n", __func__, rms->owner));
1237         MPASS(rms->writers >= 1);
1238         MPASS(rms->readers == 0);
1239         rms->writers--;
1240         if (rms->writers > 0) {
1241                 wakeup_one(&rms->owner);
1242                 rms->owner = RMS_TRANSIENT;
1243         } else {
1244                 wakeup(&rms->readers);
1245                 rms->owner = RMS_NOOWNER;
1246         }
1247         mtx_unlock(&rms->mtx);
1248         TD_LOCKS_DEC(curthread);
1249 }
1250
1251 void
1252 rms_unlock(struct rmslock *rms)
1253 {
1254
1255         if (rms_wowned(rms))
1256                 rms_wunlock(rms);
1257         else
1258                 rms_runlock(rms);
1259 }