sys/kern/kern_lock.c

   1 /*
   2  * Copyright (c) 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  * Copyright (C) 1997
   5  *      John S. Dyson.  All rights reserved.
   6  * Copyright (C) 2013-2014
   7  *      Matthew Dillon, All rights reserved.
   8  *
   9  * This code contains ideas from software contributed to Berkeley by
  10  * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
  11  * System project at Carnegie-Mellon University.
  12  *
  13  * Redistribution and use in source and binary forms, with or without
  14  * modification, are permitted provided that the following conditions
  15  * are met:
  16  * 1. Redistributions of source code must retain the above copyright
  17  *    notice, this list of conditions and the following disclaimer.
  18  * 2. Redistributions in binary form must reproduce the above copyright
  19  *    notice, this list of conditions and the following disclaimer in the
  20  *    documentation and/or other materials provided with the distribution.
  21  * 3. Neither the name of the University nor the names of its contributors
  22  *    may be used to endorse or promote products derived from this software
  23  *    without specific prior written permission.
  24  *
  25  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  31  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  */
  37
  38 #include "opt_lint.h"
  39
  40 #include <sys/param.h>
  41 #include <sys/systm.h>
  42 #include <sys/kernel.h>
  43 #include <sys/proc.h>
  44 #include <sys/lock.h>
  45 #include <sys/sysctl.h>
  46 #include <sys/spinlock.h>
  47 #include <sys/thread2.h>
  48 #include <sys/spinlock2.h>
  49
  50 static void undo_upreq(struct lock *lkp);
  51
  52 #ifdef DEBUG_CANCEL_LOCKS
  53
  54 static int sysctl_cancel_lock(SYSCTL_HANDLER_ARGS);
  55 static int sysctl_cancel_test(SYSCTL_HANDLER_ARGS);
  56
  57 static struct lock cancel_lk;
  58 LOCK_SYSINIT(cancellk, &cancel_lk, "cancel", 0);
  59 SYSCTL_PROC(_kern, OID_AUTO, cancel_lock, CTLTYPE_INT|CTLFLAG_RW, 0, 0,
  60             sysctl_cancel_lock, "I", "test cancelable locks");
  61 SYSCTL_PROC(_kern, OID_AUTO, cancel_test, CTLTYPE_INT|CTLFLAG_RW, 0, 0,
  62             sysctl_cancel_test, "I", "test cancelable locks");
  63
  64 #endif
  65
  66 /*
  67  * Locking primitives implementation.
  68  * Locks provide shared/exclusive sychronization.
  69  */
  70
  71 #ifdef DEBUG_LOCKS
  72 #define COUNT(td, x) (td)->td_locks += (x)
  73 #else
  74 #define COUNT(td, x)
  75 #endif
  76
  77 #define LOCK_WAIT_TIME 100
  78 #define LOCK_SAMPLE_WAIT 7
  79
  80 /*
  81  * Set, change, or release a lock.
  82  */
  83 int
  84 #ifndef DEBUG_LOCKS
  85 lockmgr(struct lock *lkp, u_int flags)
  86 #else
  87 debuglockmgr(struct lock *lkp, u_int flags,
  88              const char *name, const char *file, int line)
  89 #endif
  90 {
  91         thread_t td;
  92         thread_t otd;
  93         int error;
  94         int extflags;
  95         int count;
  96         int pflags;
  97         int wflags;
  98         int timo;
  99 #ifdef DEBUG_LOCKS
 100         int i;
 101 #endif
 102
 103         error = 0;
 104
 105         if (mycpu->gd_intr_nesting_level &&
 106             (flags & LK_NOWAIT) == 0 &&
 107             (flags & LK_TYPE_MASK) != LK_RELEASE &&
 108             panic_cpu_gd != mycpu
 109         ) {
 110
 111 #ifndef DEBUG_LOCKS
 112                 panic("lockmgr %s from %p: called from interrupt, ipi, "
 113                       "or hard code section",
 114                       lkp->lk_wmesg, ((int **)&lkp)[-1]);
 115 #else
 116                 panic("lockmgr %s from %s:%d: called from interrupt, ipi, "
 117                       "or hard code section",
 118                       lkp->lk_wmesg, file, line);
 119 #endif
 120         }
 121
 122 #ifdef DEBUG_LOCKS
 123         if (mycpu->gd_spinlocks && ((flags & LK_NOWAIT) == 0)) {
 124                 panic("lockmgr %s from %s:%d: called with %d spinlocks held",
 125                       lkp->lk_wmesg, file, line, mycpu->gd_spinlocks);
 126         }
 127 #endif
 128
 129         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 130         td = curthread;
 131
 132 again:
 133         count = lkp->lk_count;
 134         cpu_ccfence();
 135
 136         switch (flags & LK_TYPE_MASK) {
 137         case LK_SHARED:
 138                 /*
 139                  * Shared lock critical path case
 140                  */
 141                 if ((count & (LKC_EXREQ|LKC_UPREQ|LKC_EXCL)) == 0) {
 142                         if (atomic_cmpset_int(&lkp->lk_count,
 143                                               count, count + 1)) {
 144                                 COUNT(td, 1);
 145                                 break;
 146                         }
 147                         goto again;
 148                 }
 149
 150                 /*
 151                  * If the caller already holds the lock exclusively then
 152                  * we silently obtain another count on the exclusive lock.
 153                  *
 154                  * WARNING!  The old FreeBSD behavior was to downgrade,
 155                  *           but this creates a problem when recursions
 156                  *           return to the caller and the caller expects
 157                  *           its original exclusive lock to remain exclusively
 158                  *           locked.
 159                  */
 160                 if (lkp->lk_lockholder == td) {
 161                         KKASSERT(count & LKC_EXCL);
 162                         if ((extflags & LK_CANRECURSE) == 0) {
 163                                 if (extflags & LK_NOWAIT) {
 164                                         error = EBUSY;
 165                                         break;
 166                                 }
 167                                 panic("lockmgr: locking against myself");
 168                         }
 169                         atomic_add_int(&lkp->lk_count, 1);
 170                         COUNT(td, 1);
 171                         break;
 172                 }
 173
 174                 /*
 175                  * Slow path
 176                  */
 177                 pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 178                 timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 179                 wflags = (td->td_flags & TDF_DEADLKTREAT) ?
 180                                 LKC_EXCL : (LKC_EXCL|LKC_EXREQ|LKC_UPREQ);
 181
 182                 /*
 183                  * Block while the lock is held exclusively or, conditionally,
 184                  * if other threads are tring to obtain an exclusive lock or
 185                  * upgrade to one.
 186                  */
 187                 if (count & wflags) {
 188                         if (extflags & LK_CANCELABLE) {
 189                                 if (count & LKC_CANCEL) {
 190                                         error = ENOLCK;
 191                                         break;
 192                                 }
 193                         }
 194                         if (extflags & LK_NOWAIT) {
 195                                 error = EBUSY;
 196                                 break;
 197                         }
 198                         tsleep_interlock(lkp, pflags);
 199                         if (!atomic_cmpset_int(&lkp->lk_count, count,
 200                                               count | LKC_SHREQ)) {
 201                                 goto again;
 202                         }
 203
 204                         mycpu->gd_cnt.v_lock_name[0] = 'S';
 205                         strncpy(mycpu->gd_cnt.v_lock_name + 1,
 206                                 lkp->lk_wmesg,
 207                                 sizeof(mycpu->gd_cnt.v_lock_name) - 2);
 208                         ++mycpu->gd_cnt.v_lock_colls;
 209
 210                         error = tsleep(lkp, pflags | PINTERLOCKED,
 211                                        lkp->lk_wmesg, timo);
 212                         if (error)
 213                                 break;
 214                         if (extflags & LK_SLEEPFAIL) {
 215                                 error = ENOLCK;
 216                                 break;
 217                         }
 218                         goto again;
 219                 }
 220
 221                 /*
 222                  * Otherwise we can bump the count
 223                  */
 224                 if (atomic_cmpset_int(&lkp->lk_count, count, count + 1)) {
 225                         COUNT(td, 1);
 226                         break;
 227                 }
 228                 goto again;
 229
 230         case LK_EXCLUSIVE:
 231                 /*
 232                  * Exclusive lock critical path.
 233                  */
 234                 if (count == 0) {
 235                         if (atomic_cmpset_int(&lkp->lk_count, count,
 236                                               LKC_EXCL | (count + 1))) {
 237                                 lkp->lk_lockholder = td;
 238                                 COUNT(td, 1);
 239                                 break;
 240                         }
 241                         goto again;
 242                 }
 243
 244                 /*
 245                  * Recursive lock if we already hold it exclusively.
 246                  */
 247                 if (lkp->lk_lockholder == td) {
 248                         KKASSERT(count & LKC_EXCL);
 249                         if ((extflags & LK_CANRECURSE) == 0) {
 250                                 if (extflags & LK_NOWAIT) {
 251                                         error = EBUSY;
 252                                         break;
 253                                 }
 254                                 panic("lockmgr: locking against myself");
 255                         }
 256                         atomic_add_int(&lkp->lk_count, 1);
 257                         COUNT(td, 1);
 258                         break;
 259                 }
 260
 261                 /*
 262                  * We will block, handle LK_NOWAIT
 263                  */
 264                 if (extflags & LK_NOWAIT) {
 265                         error = EBUSY;
 266                         break;
 267                 }
 268                 if (extflags & LK_CANCELABLE) {
 269                         if (count & LKC_CANCEL) {
 270                                 error = ENOLCK;
 271                                 break;
 272                         }
 273                 }
 274
 275                 /*
 276                  * Wait until we can obtain the exclusive lock.  EXREQ is
 277                  * automatically cleared when all current holders release
 278                  * so if we abort the operation we can safely leave it set.
 279                  * There might be other exclusive requesters.
 280                  */
 281                 pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 282                 timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 283
 284                 tsleep_interlock(lkp, pflags);
 285                 if (!atomic_cmpset_int(&lkp->lk_count, count,
 286                                        count | LKC_EXREQ)) {
 287                         goto again;
 288                 }
 289
 290                 mycpu->gd_cnt.v_lock_name[0] = 'X';
 291                 strncpy(mycpu->gd_cnt.v_lock_name + 1,
 292                         lkp->lk_wmesg,
 293                         sizeof(mycpu->gd_cnt.v_lock_name) - 2);
 294                 ++mycpu->gd_cnt.v_lock_colls;
 295
 296                 error = tsleep(lkp, pflags | PINTERLOCKED,
 297                                lkp->lk_wmesg, timo);
 298                 if (error)
 299                         break;
 300                 if (extflags & LK_SLEEPFAIL) {
 301                         error = ENOLCK;
 302                         break;
 303                 }
 304                 goto again;
 305
 306         case LK_DOWNGRADE:
 307                 /*
 308                  * Downgrade an exclusive lock into a shared lock.  All
 309                  * counts on a recursive exclusive lock become shared.
 310                  *
 311                  * This function always succeeds.
 312                  */
 313                 if (lkp->lk_lockholder != td ||
 314                     (count & (LKC_EXCL|LKC_MASK)) != (LKC_EXCL|1)) {
 315                         panic("lockmgr: not holding exclusive lock");
 316                 }
 317
 318 #ifdef DEBUG_LOCKS
 319                 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
 320                         if (td->td_lockmgr_stack[i] == lkp &&
 321                             td->td_lockmgr_stack_id[i] > 0
 322                         ) {
 323                                 td->td_lockmgr_stack_id[i]--;
 324                                 break;
 325                         }
 326                 }
 327 #endif
 328                 /*
 329                  * NOTE! Must NULL-out lockholder before releasing LKC_EXCL.
 330                  */
 331                 otd = lkp->lk_lockholder;
 332                 lkp->lk_lockholder = NULL;
 333                 if (atomic_cmpset_int(&lkp->lk_count, count,
 334                                       count & ~(LKC_EXCL|LKC_SHREQ))) {
 335                         if (count & LKC_SHREQ)
 336                                 wakeup(lkp);
 337                         break;
 338                 }
 339                 lkp->lk_lockholder = otd;
 340                 goto again;
 341
 342         case LK_EXCLUPGRADE:
 343                 /*
 344                  * Upgrade from a single shared lock to an exclusive lock.
 345                  *
 346                  * If another process is ahead of us to get an upgrade,
 347                  * then we want to fail rather than have an intervening
 348                  * exclusive access.  The shared lock is released on
 349                  * failure.
 350                  */
 351                 if (count & LKC_UPREQ) {
 352                         flags = LK_RELEASE;
 353                         error = EBUSY;
 354                         goto again;
 355                 }
 356                 /* fall through into normal upgrade */
 357
 358         case LK_UPGRADE:
 359                 /*
 360                  * Upgrade a shared lock to an exclusive one.  This can cause
 361                  * the lock to be temporarily released and stolen by other
 362                  * threads.  LK_SLEEPFAIL or LK_NOWAIT may be used to detect
 363                  * this case, or use LK_EXCLUPGRADE.
 364                  *
 365                  * If the lock is already exclusively owned by us, this
 366                  * operation is a NOP.
 367                  *
 368                  * If we return an error (even NOWAIT), the current lock will
 369                  * be released.
 370                  *
 371                  * Start with the critical path.
 372                  */
 373                 if ((count & (LKC_UPREQ|LKC_EXCL|LKC_MASK)) == 1) {
 374                         if (atomic_cmpset_int(&lkp->lk_count, count,
 375                                               count | LKC_EXCL)) {
 376                                 lkp->lk_lockholder = td;
 377                                 break;
 378                         }
 379                         goto again;
 380                 }
 381
 382                 /*
 383                  * If we already hold the lock exclusively this operation
 384                  * succeeds and is a NOP.
 385                  */
 386                 if (count & LKC_EXCL) {
 387                         if (lkp->lk_lockholder == td)
 388                                 break;
 389                         panic("lockmgr: upgrade unowned lock");
 390                 }
 391                 if ((count & LKC_MASK) == 0)
 392                         panic("lockmgr: upgrade unowned lock");
 393
 394                 /*
 395                  * We cannot upgrade without blocking at this point.
 396                  */
 397                 if (extflags & LK_NOWAIT) {
 398                         flags = LK_RELEASE;
 399                         error = EBUSY;
 400                         goto again;
 401                 }
 402                 if (extflags & LK_CANCELABLE) {
 403                         if (count & LKC_CANCEL) {
 404                                 error = ENOLCK;
 405                                 break;
 406                         }
 407                 }
 408
 409                 /*
 410                  * Release the shared lock and request the upgrade.
 411                  */
 412                 pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 413                 timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 414                 tsleep_interlock(lkp, pflags);
 415                 wflags = (count & LKC_UPREQ) ? LKC_EXREQ : LKC_UPREQ;
 416
 417                 /*
 418                  * If someone else owns UPREQ and this transition would
 419                  * allow it to be granted, we have to grant it.  Otherwise
 420                  * we release the shared lock.
 421                  */
 422                 if ((count & (LKC_UPREQ|LKC_MASK)) == (LKC_UPREQ | 1)) {
 423                         wflags |= LKC_EXCL | LKC_UPGRANT;
 424                         wflags |= count;
 425                         wflags &= ~LKC_UPREQ;
 426                 } else {
 427                         wflags |= (count - 1);
 428                 }
 429
 430                 if (atomic_cmpset_int(&lkp->lk_count, count, wflags)) {
 431                         COUNT(td, -1);
 432
 433                         /*
 434                          * Must wakeup the thread granted the upgrade.
 435                          */
 436                         if ((count & (LKC_UPREQ|LKC_MASK)) == (LKC_UPREQ | 1))
 437                                 wakeup(lkp);
 438
 439                         mycpu->gd_cnt.v_lock_name[0] = 'U';
 440                         strncpy(mycpu->gd_cnt.v_lock_name + 1,
 441                                 lkp->lk_wmesg,
 442                                 sizeof(mycpu->gd_cnt.v_lock_name) - 2);
 443                         ++mycpu->gd_cnt.v_lock_colls;
 444
 445                         error = tsleep(lkp, pflags | PINTERLOCKED,
 446                                        lkp->lk_wmesg, timo);
 447                         if (error)
 448                                 break;
 449                         if (extflags & LK_SLEEPFAIL) {
 450                                 error = ENOLCK;
 451                                 break;
 452                         }
 453
 454                         /*
 455                          * Refactor to either LK_EXCLUSIVE or LK_WAITUPGRADE,
 456                          * depending on whether we were able to acquire the
 457                          * LKC_UPREQ bit.
 458                          */
 459                         if (count & LKC_UPREQ)
 460                                 flags = LK_EXCLUSIVE;   /* someone else */
 461                         else
 462                                 flags = LK_WAITUPGRADE; /* we own the bit */
 463                 }
 464                 goto again;
 465
 466         case LK_WAITUPGRADE:
 467                 /*
 468                  * We own the LKC_UPREQ bit, wait until we are granted the
 469                  * exclusive lock (LKC_UPGRANT is set).
 470                  *
 471                  * IF THE OPERATION FAILS (tsleep error tsleep+LK_SLEEPFAIL),
 472                  * we have to undo the upgrade request and clean up any lock
 473                  * that might have been granted via a race.
 474                  */
 475                 if (count & LKC_UPGRANT) {
 476                         if (atomic_cmpset_int(&lkp->lk_count, count,
 477                                               count & ~LKC_UPGRANT)) {
 478                                 lkp->lk_lockholder = td;
 479                                 KKASSERT(count & LKC_EXCL);
 480                                 break;
 481                         }
 482                         /* retry */
 483                 } else if ((count & LKC_CANCEL) && (extflags & LK_CANCELABLE)) {
 484                         undo_upreq(lkp);
 485                         error = ENOLCK;
 486                         break;
 487                 } else {
 488                         pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 489                         timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 490                         tsleep_interlock(lkp, pflags);
 491                         if (atomic_cmpset_int(&lkp->lk_count, count, count)) {
 492
 493                                 mycpu->gd_cnt.v_lock_name[0] = 'U';
 494                                 strncpy(mycpu->gd_cnt.v_lock_name + 1,
 495                                         lkp->lk_wmesg,
 496                                         sizeof(mycpu->gd_cnt.v_lock_name) - 2);
 497                                 ++mycpu->gd_cnt.v_lock_colls;
 498
 499                                 error = tsleep(lkp, pflags | PINTERLOCKED,
 500                                                lkp->lk_wmesg, timo);
 501                                 if (error) {
 502                                         undo_upreq(lkp);
 503                                         break;
 504                                 }
 505                                 if (extflags & LK_SLEEPFAIL) {
 506                                         error = ENOLCK;
 507                                         undo_upreq(lkp);
 508                                         break;
 509                                 }
 510                         }
 511                         /* retry */
 512                 }
 513                 goto again;
 514
 515         case LK_RELEASE:
 516                 /*
 517                  * Release the currently held lock.  If releasing the current
 518                  * lock as part of an error return, error will ALREADY be
 519                  * non-zero.
 520                  *
 521                  * When releasing the last lock we automatically transition
 522                  * LKC_UPREQ to LKC_EXCL|1.
 523                  *
 524                  * WARNING! We cannot detect when there are multiple exclusive
 525                  *          requests pending.  We clear EXREQ unconditionally
 526                  *          on the 1->0 transition so it is possible for
 527                  *          shared requests to race the next exclusive
 528                  *          request.
 529                  *
 530                  * Always succeeds.
 531                  */
 532                 if ((count & LKC_MASK) == 0)
 533                         panic("lockmgr: LK_RELEASE: no lock held");
 534
 535                 if (count & LKC_EXCL) {
 536                         if (lkp->lk_lockholder != LK_KERNTHREAD &&
 537                             lkp->lk_lockholder != td) {
 538                                 panic("lockmgr: pid %d, not exlusive "
 539                                       "lock holder thr %p/%p unlocking",
 540                                     (td->td_proc ? td->td_proc->p_pid : -1),
 541                                     td, lkp->lk_lockholder);
 542                         }
 543                         if ((count & (LKC_UPREQ|LKC_MASK)) == 1) {
 544                                 /*
 545                                  * Last exclusive count is being released
 546                                  */
 547                                 otd = lkp->lk_lockholder;
 548                                 lkp->lk_lockholder = NULL;
 549                                 if (!atomic_cmpset_int(&lkp->lk_count, count,
 550                                               (count - 1) &
 551                                            ~(LKC_EXCL | LKC_EXREQ |
 552                                              LKC_SHREQ| LKC_CANCEL))) {
 553                                         lkp->lk_lockholder = otd;
 554                                         goto again;
 555                                 }
 556                                 if (count & (LKC_EXREQ|LKC_SHREQ))
 557                                         wakeup(lkp);
 558                                 /* success */
 559                         } else if ((count & (LKC_UPREQ|LKC_MASK)) ==
 560                                    (LKC_UPREQ | 1)) {
 561                                 /*
 562                                  * Last exclusive count is being released but
 563                                  * an upgrade request is present, automatically
 564                                  * grant an exclusive state to the owner of
 565                                  * the upgrade request.
 566                                  */
 567                                 otd = lkp->lk_lockholder;
 568                                 lkp->lk_lockholder = NULL;
 569                                 if (!atomic_cmpset_int(&lkp->lk_count, count,
 570                                                 (count & ~LKC_UPREQ) |
 571                                                 LKC_UPGRANT)) {
 572                                         lkp->lk_lockholder = otd;
 573                                 }
 574                                 wakeup(lkp);
 575                                 /* success */
 576                         } else {
 577                                 otd = lkp->lk_lockholder;
 578                                 if (!atomic_cmpset_int(&lkp->lk_count, count,
 579                                                        count - 1)) {
 580                                         goto again;
 581                                 }
 582                                 /* success */
 583                         }
 584                         /* success */
 585                         if (otd != LK_KERNTHREAD)
 586                                 COUNT(td, -1);
 587                 } else {
 588                         if ((count & (LKC_UPREQ|LKC_MASK)) == 1) {
 589                                 /*
 590                                  * Last shared count is being released.
 591                                  */
 592                                 if (!atomic_cmpset_int(&lkp->lk_count, count,
 593                                               (count - 1) &
 594                                                ~(LKC_EXREQ | LKC_SHREQ |
 595                                                  LKC_CANCEL))) {
 596                                         goto again;
 597                                 }
 598                                 if (count & (LKC_EXREQ|LKC_SHREQ))
 599                                         wakeup(lkp);
 600                                 /* success */
 601                         } else if ((count & (LKC_UPREQ|LKC_MASK)) ==
 602                                    (LKC_UPREQ | 1)) {
 603                                 /*
 604                                  * Last shared count is being released but
 605                                  * an upgrade request is present, automatically
 606                                  * grant an exclusive state to the owner of
 607                                  * the upgrade request.  Masked count
 608                                  * remains 1.
 609                                  */
 610                                 if (!atomic_cmpset_int(&lkp->lk_count, count,
 611                                               (count & ~(LKC_UPREQ |
 612                                                          LKC_CANCEL)) |
 613                                               LKC_EXCL | LKC_UPGRANT)) {
 614                                         goto again;
 615                                 }
 616                                 wakeup(lkp);
 617                         } else {
 618                                 if (!atomic_cmpset_int(&lkp->lk_count, count,
 619                                                        count - 1)) {
 620                                         goto again;
 621                                 }
 622                         }
 623                         /* success */
 624                         COUNT(td, -1);
 625                 }
 626                 break;
 627
 628         case LK_CANCEL_BEG:
 629                 /*
 630                  * Start canceling blocked requestors or later requestors.
 631                  * requestors must use CANCELABLE.  Don't waste time issuing
 632                  * a wakeup if nobody is pending.
 633                  */
 634                 KKASSERT((count & LKC_CANCEL) == 0);    /* disallowed case */
 635                 KKASSERT((count & LKC_MASK) != 0);      /* issue w/lock held */
 636                 if (!atomic_cmpset_int(&lkp->lk_count,
 637                                        count, count | LKC_CANCEL)) {
 638                         goto again;
 639                 }
 640                 if (count & (LKC_EXREQ|LKC_SHREQ|LKC_UPREQ)) {
 641                         wakeup(lkp);
 642                 }
 643                 break;
 644
 645         case LK_CANCEL_END:
 646                 atomic_clear_int(&lkp->lk_count, LKC_CANCEL);
 647                 break;
 648
 649         default:
 650                 panic("lockmgr: unknown locktype request %d",
 651                     flags & LK_TYPE_MASK);
 652                 /* NOTREACHED */
 653         }
 654         return (error);
 655 }
 656
 657 /*
 658  * Undo an upgrade request
 659  */
 660 static
 661 void
 662 undo_upreq(struct lock *lkp)
 663 {
 664         int count;
 665
 666         for (;;) {
 667                 count = lkp->lk_count;
 668                 cpu_ccfence();
 669                 if (count & LKC_UPGRANT) {
 670                         /*
 671                          * UPREQ was shifted to UPGRANT.  We own UPGRANT now,
 672                          * another thread might own UPREQ.  Clear UPGRANT
 673                          * and release the granted lock.
 674                          */
 675                         if (atomic_cmpset_int(&lkp->lk_count, count,
 676                                               count & ~LKC_UPGRANT)) {
 677                                 lockmgr(lkp, LK_RELEASE);
 678                                 break;
 679                         }
 680                 } else if (count & LKC_EXCL) {
 681                         /*
 682                          * Clear the UPREQ we still own.  Nobody to wakeup
 683                          * here because there is an existing exclusive
 684                          * holder.
 685                          */
 686                         KKASSERT(count & LKC_UPREQ);
 687                         KKASSERT((count & LKC_MASK) > 0);
 688                         if (atomic_cmpset_int(&lkp->lk_count, count,
 689                                               count & ~LKC_UPREQ)) {
 690                                 wakeup(lkp);
 691                                 break;
 692                         }
 693                 } else if (count & LKC_EXREQ) {
 694                         /*
 695                          * Clear the UPREQ we still own.  We cannot wakeup any
 696                          * shared waiters because there is an exclusive
 697                          * request pending.
 698                          */
 699                         KKASSERT(count & LKC_UPREQ);
 700                         KKASSERT((count & LKC_MASK) > 0);
 701                         if (atomic_cmpset_int(&lkp->lk_count, count,
 702                                               count & ~LKC_UPREQ)) {
 703                                 break;
 704                         }
 705                 } else {
 706                         /*
 707                          * Clear the UPREQ we still own.  Wakeup any shared
 708                          * waiters.
 709                          */
 710                         KKASSERT(count & LKC_UPREQ);
 711                         KKASSERT((count & LKC_MASK) > 0);
 712                         if (atomic_cmpset_int(&lkp->lk_count, count,
 713                                               count &
 714                                               ~(LKC_UPREQ | LKC_SHREQ))) {
 715                                 if (count & LKC_SHREQ)
 716                                         wakeup(lkp);
 717                                 break;
 718                         }
 719                 }
 720                 /* retry */
 721         }
 722 }
 723
 724 void
 725 lockmgr_kernproc(struct lock *lp)
 726 {
 727         struct thread *td __debugvar = curthread;
 728
 729         if (lp->lk_lockholder != LK_KERNTHREAD) {
 730                 KASSERT(lp->lk_lockholder == td,
 731                     ("lockmgr_kernproc: lock not owned by curthread %p", td));
 732                 lp->lk_lockholder = LK_KERNTHREAD;
 733                 COUNT(td, -1);
 734         }
 735 }
 736
 737 /*
 738  * Initialize a lock; required before use.
 739  */
 740 void
 741 lockinit(struct lock *lkp, const char *wmesg, int timo, int flags)
 742 {
 743         lkp->lk_flags = (flags & LK_EXTFLG_MASK);
 744         lkp->lk_count = 0;
 745         lkp->lk_wmesg = wmesg;
 746         lkp->lk_timo = timo;
 747         lkp->lk_lockholder = LK_NOTHREAD;
 748 }
 749
 750 /*
 751  * Reinitialize a lock that is being reused for a different purpose, but
 752  * which may have pending (blocked) threads sitting on it.  The caller
 753  * must already hold the interlock.
 754  */
 755 void
 756 lockreinit(struct lock *lkp, const char *wmesg, int timo, int flags)
 757 {
 758         lkp->lk_wmesg = wmesg;
 759         lkp->lk_timo = timo;
 760 }
 761
 762 /*
 763  * De-initialize a lock.  The structure must no longer be used by anyone.
 764  */
 765 void
 766 lockuninit(struct lock *lkp)
 767 {
 768         KKASSERT((lkp->lk_count & (LKC_EXREQ|LKC_SHREQ|LKC_UPREQ)) == 0);
 769 }
 770
 771 /*
 772  * Determine the status of a lock.
 773  */
 774 int
 775 lockstatus(struct lock *lkp, struct thread *td)
 776 {
 777         int lock_type = 0;
 778         int count;
 779
 780         count = lkp->lk_count;
 781         cpu_ccfence();
 782
 783         if (count & LKC_EXCL) {
 784                 if (td == NULL || lkp->lk_lockholder == td)
 785                         lock_type = LK_EXCLUSIVE;
 786                 else
 787                         lock_type = LK_EXCLOTHER;
 788         } else if (count & LKC_MASK) {
 789                 lock_type = LK_SHARED;
 790         }
 791         return (lock_type);
 792 }
 793
 794 /*
 795  * Return non-zero if the caller owns the lock shared or exclusive.
 796  * We can only guess re: shared locks.
 797  */
 798 int
 799 lockowned(struct lock *lkp)
 800 {
 801         thread_t td = curthread;
 802         int count;
 803
 804         count = lkp->lk_count;
 805         cpu_ccfence();
 806
 807         if (count & LKC_EXCL)
 808                 return(lkp->lk_lockholder == td);
 809         else
 810                 return((count & LKC_MASK) != 0);
 811 }
 812
 813 /*
 814  * Determine the number of holders of a lock.
 815  *
 816  * The non-blocking version can usually be used for assertions.
 817  */
 818 int
 819 lockcount(struct lock *lkp)
 820 {
 821         return(lkp->lk_count & LKC_MASK);
 822 }
 823
 824 int
 825 lockcountnb(struct lock *lkp)
 826 {
 827         return(lkp->lk_count & LKC_MASK);
 828 }
 829
 830 /*
 831  * Print out information about state of a lock. Used by VOP_PRINT
 832  * routines to display status about contained locks.
 833  */
 834 void
 835 lockmgr_printinfo(struct lock *lkp)
 836 {
 837         struct thread *td = lkp->lk_lockholder;
 838         struct proc *p;
 839         int count;
 840
 841         count = lkp->lk_count;
 842         cpu_ccfence();
 843
 844         if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
 845                 p = td->td_proc;
 846         else
 847                 p = NULL;
 848
 849         if (count & LKC_EXCL) {
 850                 kprintf(" lock type %s: EXCLUS (count %08x) by td %p pid %d",
 851                     lkp->lk_wmesg, count, td,
 852                     p ? p->p_pid : -99);
 853         } else if (count & LKC_MASK) {
 854                 kprintf(" lock type %s: SHARED (count %08x)",
 855                     lkp->lk_wmesg, count);
 856         } else {
 857                 kprintf(" lock type %s: NOTHELD", lkp->lk_wmesg);
 858         }
 859         if (count & (LKC_EXREQ|LKC_SHREQ))
 860                 kprintf(" with waiters\n");
 861         else
 862                 kprintf("\n");
 863 }
 864
 865 void
 866 lock_sysinit(struct lock_args *arg)
 867 {
 868         lockinit(arg->la_lock, arg->la_desc, 0, arg->la_flags);
 869 }
 870
 871 #ifdef DEBUG_CANCEL_LOCKS
 872
 873 static
 874 int
 875 sysctl_cancel_lock(SYSCTL_HANDLER_ARGS)
 876 {
 877         int error;
 878
 879         if (req->newptr) {
 880                 SYSCTL_XUNLOCK();
 881                 lockmgr(&cancel_lk, LK_EXCLUSIVE);
 882                 kprintf("x");
 883                 error = tsleep(&error, PCATCH, "canmas", hz * 5);
 884                 lockmgr(&cancel_lk, LK_CANCEL_BEG);
 885                 kprintf("y");
 886                 error = tsleep(&error, PCATCH, "canmas", hz * 5);
 887                 kprintf("z");
 888                 lockmgr(&cancel_lk, LK_RELEASE);
 889                 SYSCTL_XLOCK();
 890                 SYSCTL_OUT(req, &error, sizeof(error));
 891         }
 892         error = 0;
 893
 894         return error;
 895 }
 896
 897 static
 898 int
 899 sysctl_cancel_test(SYSCTL_HANDLER_ARGS)
 900 {
 901         int error;
 902
 903         if (req->newptr) {
 904                 error = lockmgr(&cancel_lk, LK_EXCLUSIVE|LK_CANCELABLE);
 905                 if (error == 0)
 906                         lockmgr(&cancel_lk, LK_RELEASE);
 907                 SYSCTL_OUT(req, &error, sizeof(error));
 908                 kprintf("test %d\n", error);
 909         }
 910
 911         return 0;
 912 }
 913
 914 #endif