sys/kern/kern_rmlock.c

   1 /*-
   2  * Copyright (c) 2007 Stephan Uphoff <ups@FreeBSD.org>
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the author nor the names of any co-contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  29
  30 /*
  31  * Machine independent bits of reader/writer lock implementation.
  32  */
  33
  34 #include <sys/cdefs.h>
  35 __FBSDID("$FreeBSD$");
  36
  37 #include "opt_ddb.h"
  38 #include "opt_kdtrace.h"
  39
  40 #include <sys/param.h>
  41 #include <sys/systm.h>
  42
  43 #include <sys/kernel.h>
  44 #include <sys/ktr.h>
  45 #include <sys/lock.h>
  46 #include <sys/mutex.h>
  47 #include <sys/proc.h>
  48 #include <sys/rmlock.h>
  49 #include <sys/sched.h>
  50 #include <sys/smp.h>
  51 #include <sys/turnstile.h>
  52 #include <sys/lock_profile.h>
  53 #include <machine/cpu.h>
  54
  55 #ifdef DDB
  56 #include <ddb/ddb.h>
  57 #endif
  58
  59 #define RMPF_ONQUEUE    1
  60 #define RMPF_SIGNAL     2
  61
  62 /*
  63  * To support usage of rmlock in CVs and msleep yet another list for the
  64  * priority tracker would be needed.  Using this lock for cv and msleep also
  65  * does not seem very useful
  66  */
  67
  68 static __inline void compiler_memory_barrier(void) {
  69         __asm __volatile("":::"memory");
  70 }
  71
  72 static void     assert_rm(struct lock_object *lock, int what);
  73 static void     lock_rm(struct lock_object *lock, int how);
  74 #ifdef KDTRACE_HOOKS
  75 static int      owner_rm(struct lock_object *lock, struct thread **owner);
  76 #endif
  77 static int      unlock_rm(struct lock_object *lock);
  78
  79 struct lock_class lock_class_rm = {
  80         .lc_name = "rm",
  81         .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
  82         .lc_assert = assert_rm,
  83 #if 0
  84 #ifdef DDB
  85         .lc_ddb_show = db_show_rwlock,
  86 #endif
  87 #endif
  88         .lc_lock = lock_rm,
  89         .lc_unlock = unlock_rm,
  90 #ifdef KDTRACE_HOOKS
  91         .lc_owner = owner_rm,
  92 #endif
  93 };
  94
  95 static void
  96 assert_rm(struct lock_object *lock, int what)
  97 {
  98
  99         panic("assert_rm called");
 100 }
 101
 102 static void
 103 lock_rm(struct lock_object *lock, int how)
 104 {
 105
 106         panic("lock_rm called");
 107 }
 108
 109 static int
 110 unlock_rm(struct lock_object *lock)
 111 {
 112
 113         panic("unlock_rm called");
 114 }
 115
 116 #ifdef KDTRACE_HOOKS
 117 static int
 118 owner_rm(struct lock_object *lock, struct thread **owner)
 119 {
 120
 121         panic("owner_rm called");
 122 }
 123 #endif
 124
 125 static struct mtx rm_spinlock;
 126
 127 MTX_SYSINIT(rm_spinlock, &rm_spinlock, "rm_spinlock", MTX_SPIN);
 128
 129 /*
 130  * Add or remove tracker from per-cpu list.
 131  *
 132  * The per-cpu list can be traversed at any time in forward direction from an
 133  * interrupt on the *local* cpu.
 134  */
 135 static void inline
 136 rm_tracker_add(struct pcpu *pc, struct rm_priotracker *tracker)
 137 {
 138         struct rm_queue *next;
 139
 140         /* Initialize all tracker pointers */
 141         tracker->rmp_cpuQueue.rmq_prev = &pc->pc_rm_queue;
 142         next = pc->pc_rm_queue.rmq_next;
 143         tracker->rmp_cpuQueue.rmq_next = next;
 144
 145         /* rmq_prev is not used during froward traversal. */
 146         next->rmq_prev = &tracker->rmp_cpuQueue;
 147
 148         /* Update pointer to first element. */
 149         pc->pc_rm_queue.rmq_next = &tracker->rmp_cpuQueue;
 150 }
 151
 152 static void inline
 153 rm_tracker_remove(struct pcpu *pc, struct rm_priotracker *tracker)
 154 {
 155         struct rm_queue *next, *prev;
 156
 157         next = tracker->rmp_cpuQueue.rmq_next;
 158         prev = tracker->rmp_cpuQueue.rmq_prev;
 159
 160         /* Not used during forward traversal. */
 161         next->rmq_prev = prev;
 162
 163         /* Remove from list. */
 164         prev->rmq_next = next;
 165 }
 166
 167 static void
 168 rm_cleanIPI(void *arg)
 169 {
 170         struct pcpu *pc;
 171         struct rmlock *rm = arg;
 172         struct rm_priotracker *tracker;
 173         struct rm_queue *queue;
 174         pc = pcpu_find(curcpu);
 175
 176         for (queue = pc->pc_rm_queue.rmq_next; queue != &pc->pc_rm_queue;
 177             queue = queue->rmq_next) {
 178                 tracker = (struct rm_priotracker *)queue;
 179                 if (tracker->rmp_rmlock == rm && tracker->rmp_flags == 0) {
 180                         tracker->rmp_flags = RMPF_ONQUEUE;
 181                         mtx_lock_spin(&rm_spinlock);
 182                         LIST_INSERT_HEAD(&rm->rm_activeReaders, tracker,
 183                             rmp_qentry);
 184                         mtx_unlock_spin(&rm_spinlock);
 185                 }
 186         }
 187 }
 188
 189 CTASSERT((RM_SLEEPABLE & LO_CLASSFLAGS) == RM_SLEEPABLE);
 190
 191 void
 192 rm_init_flags(struct rmlock *rm, const char *name, int opts)
 193 {
 194         int liflags;
 195
 196         liflags = 0;
 197         if (!(opts & RM_NOWITNESS))
 198                 liflags |= LO_WITNESS;
 199         if (opts & RM_RECURSE)
 200                 liflags |= LO_RECURSABLE;
 201         rm->rm_writecpus = all_cpus;
 202         LIST_INIT(&rm->rm_activeReaders);
 203         if (opts & RM_SLEEPABLE) {
 204                 liflags |= RM_SLEEPABLE;
 205                 sx_init_flags(&rm->rm_lock_sx, "rmlock_sx", SX_RECURSE);
 206         } else
 207                 mtx_init(&rm->rm_lock_mtx, name, "rmlock_mtx", MTX_NOWITNESS);
 208         lock_init(&rm->lock_object, &lock_class_rm, name, NULL, liflags);
 209 }
 210
 211 void
 212 rm_init(struct rmlock *rm, const char *name)
 213 {
 214
 215         rm_init_flags(rm, name, 0);
 216 }
 217
 218 void
 219 rm_destroy(struct rmlock *rm)
 220 {
 221
 222         if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 223                 sx_destroy(&rm->rm_lock_sx);
 224         else
 225                 mtx_destroy(&rm->rm_lock_mtx);
 226         lock_destroy(&rm->lock_object);
 227 }
 228
 229 int
 230 rm_wowned(struct rmlock *rm)
 231 {
 232
 233         if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 234                 return (sx_xlocked(&rm->rm_lock_sx));
 235         else
 236                 return (mtx_owned(&rm->rm_lock_mtx));
 237 }
 238
 239 void
 240 rm_sysinit(void *arg)
 241 {
 242         struct rm_args *args = arg;
 243
 244         rm_init(args->ra_rm, args->ra_desc);
 245 }
 246
 247 void
 248 rm_sysinit_flags(void *arg)
 249 {
 250         struct rm_args_flags *args = arg;
 251
 252         rm_init_flags(args->ra_rm, args->ra_desc, args->ra_opts);
 253 }
 254
 255 static int
 256 _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 257 {
 258         struct pcpu *pc;
 259         struct rm_queue *queue;
 260         struct rm_priotracker *atracker;
 261
 262         critical_enter();
 263         pc = pcpu_find(curcpu);
 264
 265         /* Check if we just need to do a proper critical_exit. */
 266         if (!CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)) {
 267                 critical_exit();
 268                 return (1);
 269         }
 270
 271         /* Remove our tracker from the per-cpu list. */
 272         rm_tracker_remove(pc, tracker);
 273
 274         /* Check to see if the IPI granted us the lock after all. */
 275         if (tracker->rmp_flags) {
 276                 /* Just add back tracker - we hold the lock. */
 277                 rm_tracker_add(pc, tracker);
 278                 critical_exit();
 279                 return (1);
 280         }
 281
 282         /*
 283          * We allow readers to aquire a lock even if a writer is blocked if
 284          * the lock is recursive and the reader already holds the lock.
 285          */
 286         if ((rm->lock_object.lo_flags & LO_RECURSABLE) != 0) {
 287                 /*
 288                  * Just grant the lock if this thread already has a tracker
 289                  * for this lock on the per-cpu queue.
 290                  */
 291                 for (queue = pc->pc_rm_queue.rmq_next;
 292                     queue != &pc->pc_rm_queue; queue = queue->rmq_next) {
 293                         atracker = (struct rm_priotracker *)queue;
 294                         if ((atracker->rmp_rmlock == rm) &&
 295                             (atracker->rmp_thread == tracker->rmp_thread)) {
 296                                 mtx_lock_spin(&rm_spinlock);
 297                                 LIST_INSERT_HEAD(&rm->rm_activeReaders,
 298                                     tracker, rmp_qentry);
 299                                 tracker->rmp_flags = RMPF_ONQUEUE;
 300                                 mtx_unlock_spin(&rm_spinlock);
 301                                 rm_tracker_add(pc, tracker);
 302                                 critical_exit();
 303                                 return (1);
 304                         }
 305                 }
 306         }
 307
 308         sched_unpin();
 309         critical_exit();
 310
 311         if (trylock) {
 312                 if (rm->lock_object.lo_flags & RM_SLEEPABLE) {
 313                         if (!sx_try_xlock(&rm->rm_lock_sx))
 314                                 return (0);
 315                 } else {
 316                         if (!mtx_trylock(&rm->rm_lock_mtx))
 317                                 return (0);
 318                 }
 319         } else {
 320                 if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 321                         sx_xlock(&rm->rm_lock_sx);
 322                 else
 323                         mtx_lock(&rm->rm_lock_mtx);
 324         }
 325
 326         critical_enter();
 327         pc = pcpu_find(curcpu);
 328         CPU_CLR(pc->pc_cpuid, &rm->rm_writecpus);
 329         rm_tracker_add(pc, tracker);
 330         sched_pin();
 331         critical_exit();
 332
 333         if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 334                 sx_xunlock(&rm->rm_lock_sx);
 335         else
 336                 mtx_unlock(&rm->rm_lock_mtx);
 337
 338         return (1);
 339 }
 340
 341 int
 342 _rm_rlock(struct rmlock *rm, struct rm_priotracker *tracker, int trylock)
 343 {
 344         struct thread *td = curthread;
 345         struct pcpu *pc;
 346
 347         tracker->rmp_flags  = 0;
 348         tracker->rmp_thread = td;
 349         tracker->rmp_rmlock = rm;
 350
 351         td->td_critnest++;      /* critical_enter(); */
 352
 353         compiler_memory_barrier();
 354
 355         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 356
 357         rm_tracker_add(pc, tracker);
 358
 359         sched_pin();
 360
 361         compiler_memory_barrier();
 362
 363         td->td_critnest--;
 364
 365         /*
 366          * Fast path to combine two common conditions into a single
 367          * conditional jump.
 368          */
 369         if (0 == (td->td_owepreempt |
 370             CPU_ISSET(pc->pc_cpuid, &rm->rm_writecpus)))
 371                 return (1);
 372
 373         /* We do not have a read token and need to acquire one. */
 374         return _rm_rlock_hard(rm, tracker, trylock);
 375 }
 376
 377 static void
 378 _rm_unlock_hard(struct thread *td,struct rm_priotracker *tracker)
 379 {
 380
 381         if (td->td_owepreempt) {
 382                 td->td_critnest++;
 383                 critical_exit();
 384         }
 385
 386         if (!tracker->rmp_flags)
 387                 return;
 388
 389         mtx_lock_spin(&rm_spinlock);
 390         LIST_REMOVE(tracker, rmp_qentry);
 391
 392         if (tracker->rmp_flags & RMPF_SIGNAL) {
 393                 struct rmlock *rm;
 394                 struct turnstile *ts;
 395
 396                 rm = tracker->rmp_rmlock;
 397
 398                 turnstile_chain_lock(&rm->lock_object);
 399                 mtx_unlock_spin(&rm_spinlock);
 400
 401                 ts = turnstile_lookup(&rm->lock_object);
 402
 403                 turnstile_signal(ts, TS_EXCLUSIVE_QUEUE);
 404                 turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
 405                 turnstile_chain_unlock(&rm->lock_object);
 406         } else
 407                 mtx_unlock_spin(&rm_spinlock);
 408 }
 409
 410 void
 411 _rm_runlock(struct rmlock *rm, struct rm_priotracker *tracker)
 412 {
 413         struct pcpu *pc;
 414         struct thread *td = tracker->rmp_thread;
 415
 416         td->td_critnest++;      /* critical_enter(); */
 417         pc = cpuid_to_pcpu[td->td_oncpu]; /* pcpu_find(td->td_oncpu); */
 418         rm_tracker_remove(pc, tracker);
 419         td->td_critnest--;
 420         sched_unpin();
 421
 422         if (0 == (td->td_owepreempt | tracker->rmp_flags))
 423                 return;
 424
 425         _rm_unlock_hard(td, tracker);
 426 }
 427
 428 void
 429 _rm_wlock(struct rmlock *rm)
 430 {
 431         struct rm_priotracker *prio;
 432         struct turnstile *ts;
 433         cpuset_t readcpus;
 434
 435         if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 436                 sx_xlock(&rm->rm_lock_sx);
 437         else
 438                 mtx_lock(&rm->rm_lock_mtx);
 439
 440         if (CPU_CMP(&rm->rm_writecpus, &all_cpus)) {
 441                 /* Get all read tokens back */
 442                 readcpus = all_cpus;
 443                 CPU_NAND(&readcpus, &rm->rm_writecpus);
 444                 rm->rm_writecpus = all_cpus;
 445
 446                 /*
 447                  * Assumes rm->rm_writecpus update is visible on other CPUs
 448                  * before rm_cleanIPI is called.
 449                  */
 450 #ifdef SMP
 451                 smp_rendezvous_cpus(readcpus,
 452                     smp_no_rendevous_barrier,
 453                     rm_cleanIPI,
 454                     smp_no_rendevous_barrier,
 455                     rm);
 456
 457 #else
 458                 rm_cleanIPI(rm);
 459 #endif
 460
 461                 mtx_lock_spin(&rm_spinlock);
 462                 while ((prio = LIST_FIRST(&rm->rm_activeReaders)) != NULL) {
 463                         ts = turnstile_trywait(&rm->lock_object);
 464                         prio->rmp_flags = RMPF_ONQUEUE | RMPF_SIGNAL;
 465                         mtx_unlock_spin(&rm_spinlock);
 466                         turnstile_wait(ts, prio->rmp_thread,
 467                             TS_EXCLUSIVE_QUEUE);
 468                         mtx_lock_spin(&rm_spinlock);
 469                 }
 470                 mtx_unlock_spin(&rm_spinlock);
 471         }
 472 }
 473
 474 void
 475 _rm_wunlock(struct rmlock *rm)
 476 {
 477
 478         if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 479                 sx_xunlock(&rm->rm_lock_sx);
 480         else
 481                 mtx_unlock(&rm->rm_lock_mtx);
 482 }
 483
 484 #ifdef LOCK_DEBUG
 485
 486 void _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 487 {
 488
 489         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER | LOP_EXCLUSIVE,
 490             file, line, NULL);
 491
 492         _rm_wlock(rm);
 493
 494         LOCK_LOG_LOCK("RMWLOCK", &rm->lock_object, 0, 0, file, line);
 495
 496         if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 497                 WITNESS_LOCK(&rm->rm_lock_sx.lock_object, LOP_EXCLUSIVE,
 498                     file, line);
 499         else
 500                 WITNESS_LOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 501
 502         curthread->td_locks++;
 503
 504 }
 505
 506 void
 507 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 508 {
 509
 510         curthread->td_locks--;
 511         if (rm->lock_object.lo_flags & RM_SLEEPABLE)
 512                 WITNESS_UNLOCK(&rm->rm_lock_sx.lock_object, LOP_EXCLUSIVE,
 513                     file, line);
 514         else
 515                 WITNESS_UNLOCK(&rm->lock_object, LOP_EXCLUSIVE, file, line);
 516         LOCK_LOG_LOCK("RMWUNLOCK", &rm->lock_object, 0, 0, file, line);
 517         _rm_wunlock(rm);
 518 }
 519
 520 int
 521 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 522     int trylock, const char *file, int line)
 523 {
 524         if (!trylock && (rm->lock_object.lo_flags & RM_SLEEPABLE))
 525                 WITNESS_CHECKORDER(&rm->rm_lock_sx.lock_object, LOP_NEWORDER,
 526                     file, line, NULL);
 527         WITNESS_CHECKORDER(&rm->lock_object, LOP_NEWORDER, file, line, NULL);
 528
 529         if (_rm_rlock(rm, tracker, trylock)) {
 530                 LOCK_LOG_LOCK("RMRLOCK", &rm->lock_object, 0, 0, file, line);
 531
 532                 WITNESS_LOCK(&rm->lock_object, 0, file, line);
 533
 534                 curthread->td_locks++;
 535
 536                 return (1);
 537         }
 538
 539         return (0);
 540 }
 541
 542 void
 543 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 544     const char *file, int line)
 545 {
 546
 547         curthread->td_locks--;
 548         WITNESS_UNLOCK(&rm->lock_object, 0, file, line);
 549         LOCK_LOG_LOCK("RMRUNLOCK", &rm->lock_object, 0, 0, file, line);
 550         _rm_runlock(rm, tracker);
 551 }
 552
 553 #else
 554
 555 /*
 556  * Just strip out file and line arguments if no lock debugging is enabled in
 557  * the kernel - we are called from a kernel module.
 558  */
 559 void
 560 _rm_wlock_debug(struct rmlock *rm, const char *file, int line)
 561 {
 562
 563         _rm_wlock(rm);
 564 }
 565
 566 void
 567 _rm_wunlock_debug(struct rmlock *rm, const char *file, int line)
 568 {
 569
 570         _rm_wunlock(rm);
 571 }
 572
 573 int
 574 _rm_rlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 575     int trylock, const char *file, int line)
 576 {
 577
 578         return _rm_rlock(rm, tracker, trylock);
 579 }
 580
 581 void
 582 _rm_runlock_debug(struct rmlock *rm, struct rm_priotracker *tracker,
 583     const char *file, int line)
 584 {
 585
 586         _rm_runlock(rm, tracker);
 587 }
 588
 589 #endif