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) 2013-2017
   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  * This code is derived from software contributed to The DragonFly Project
  14  * by Matthew Dillon <dillon@backplane.com>.  Extensively rewritten.
  15  *
  16  * Redistribution and use in source and binary forms, with or without
  17  * modification, are permitted provided that the following conditions
  18  * are met:
  19  * 1. Redistributions of source code must retain the above copyright
  20  *    notice, this list of conditions and the following disclaimer.
  21  * 2. Redistributions in binary form must reproduce the above copyright
  22  *    notice, this list of conditions and the following disclaimer in the
  23  *    documentation and/or other materials provided with the distribution.
  24  * 3. Neither the name of the University nor the names of its contributors
  25  *    may be used to endorse or promote products derived from this software
  26  *    without specific prior written permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  29  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  30  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  31  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  32  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  33  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  34  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  35  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  36  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  37  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  38  * SUCH DAMAGE.
  39  */
  40
  41 #include "opt_lint.h"
  42
  43 #include <sys/param.h>
  44 #include <sys/systm.h>
  45 #include <sys/kernel.h>
  46 #include <sys/proc.h>
  47 #include <sys/lock.h>
  48 #include <sys/sysctl.h>
  49 #include <sys/spinlock.h>
  50 #include <sys/thread2.h>
  51 #include <sys/spinlock2.h>
  52 #include <sys/indefinite2.h>
  53
  54 static void undo_shreq(struct lock *lkp);
  55 static int undo_upreq(struct lock *lkp);
  56 static int undo_exreq(struct lock *lkp);
  57
  58 #ifdef DEBUG_CANCEL_LOCKS
  59
  60 static int sysctl_cancel_lock(SYSCTL_HANDLER_ARGS);
  61 static int sysctl_cancel_test(SYSCTL_HANDLER_ARGS);
  62
  63 static struct lock cancel_lk;
  64 LOCK_SYSINIT(cancellk, &cancel_lk, "cancel", 0);
  65 SYSCTL_PROC(_kern, OID_AUTO, cancel_lock, CTLTYPE_INT|CTLFLAG_RW, 0, 0,
  66             sysctl_cancel_lock, "I", "test cancelable locks");
  67 SYSCTL_PROC(_kern, OID_AUTO, cancel_test, CTLTYPE_INT|CTLFLAG_RW, 0, 0,
  68             sysctl_cancel_test, "I", "test cancelable locks");
  69
  70 #endif
  71
  72 int lock_test_mode;
  73 SYSCTL_INT(_debug, OID_AUTO, lock_test_mode, CTLFLAG_RW,
  74            &lock_test_mode, 0, "");
  75
  76 /*
  77  * Locking primitives implementation.
  78  * Locks provide shared/exclusive sychronization.
  79  */
  80
  81 #ifdef DEBUG_LOCKS
  82 #define COUNT(td, x) (td)->td_locks += (x)
  83 #else
  84 #define COUNT(td, x) do { } while (0)
  85 #endif
  86
  87 /*
  88  * Helper, assert basic conditions
  89  */
  90 static __inline void
  91 _lockmgr_assert(struct lock *lkp, u_int flags)
  92 {
  93         if (mycpu->gd_intr_nesting_level &&
  94             (flags & LK_NOWAIT) == 0 &&
  95             (flags & LK_TYPE_MASK) != LK_RELEASE &&
  96             panic_cpu_gd != mycpu
  97         ) {
  98                 panic("lockmgr %s from %p: called from interrupt, ipi, "
  99                       "or hard code section",
 100                       lkp->lk_wmesg, ((int **)&lkp)[-1]);
 101         }
 102 }
 103
 104 /*
 105  * Acquire a shared lock
 106  */
 107 int
 108 lockmgr_shared(struct lock *lkp, u_int flags)
 109 {
 110         uint32_t extflags;
 111         thread_t td;
 112         uint64_t count;
 113         int error;
 114         int pflags;
 115         int timo;
 116         int didloop;
 117
 118         _lockmgr_assert(lkp, flags);
 119         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 120         td = curthread;
 121
 122         count = lkp->lk_count;
 123         cpu_ccfence();
 124
 125         /*
 126          * If the caller already holds the lock exclusively then
 127          * we silently obtain another count on the exclusive lock.
 128          * Avoid accessing lk_lockholder until testing exclusivity.
 129          *
 130          * WARNING!  The old FreeBSD behavior was to downgrade,
 131          *           but this creates a problem when recursions
 132          *           return to the caller and the caller expects
 133          *           its original exclusive lock to remain exclusively
 134          *           locked.
 135          */
 136         if ((count & LKC_XMASK) && lkp->lk_lockholder == td) {
 137                 KKASSERT(lkp->lk_count & LKC_XMASK);
 138                 if ((extflags & LK_CANRECURSE) == 0) {
 139                         if (extflags & LK_NOWAIT)
 140                                 return EBUSY;
 141                         panic("lockmgr: locking against myself");
 142                 }
 143                 atomic_add_64(&lkp->lk_count, 1);
 144                 COUNT(td, 1);
 145                 return 0;
 146         }
 147
 148         /*
 149          * Unless TDF_DEADLKTREAT is set, we cannot add LKC_SCOUNT while
 150          * SHARED is set and either EXREQ or UPREQ are set.
 151          *
 152          * NOTE: In the race-to-0 case (see undo_shreq()), we could
 153          *       theoretically work the SMASK == 0 case here.
 154          */
 155         if ((td->td_flags & TDF_DEADLKTREAT) == 0) {
 156                 while ((count & LKC_SHARED) &&
 157                        (count & (LKC_EXREQ | LKC_UPREQ))) {
 158                         /*
 159                          * Immediate failure conditions
 160                          */
 161                         if (extflags & LK_CANCELABLE) {
 162                                 if (count & LKC_CANCEL)
 163                                         return ENOLCK;
 164                         }
 165                         if (extflags & LK_NOWAIT)
 166                                 return EBUSY;
 167
 168                         /*
 169                          * Interlocked tsleep
 170                          */
 171                         pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 172                         timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 173
 174                         tsleep_interlock(lkp, pflags);
 175                         count = atomic_fetchadd_long(&lkp->lk_count, 0);
 176
 177                         if ((count & LKC_SHARED) &&
 178                             (count & (LKC_EXREQ | LKC_UPREQ))) {
 179                                 error = tsleep(lkp, pflags | PINTERLOCKED,
 180                                                lkp->lk_wmesg, timo);
 181                                 if (error)
 182                                         return error;
 183                                 count = lkp->lk_count;
 184                                 cpu_ccfence();
 185                                 continue;
 186                         }
 187                         break;
 188                 }
 189         }
 190
 191         /*
 192          * Bump the SCOUNT field.  The shared lock is granted only once
 193          * the SHARED flag gets set.  If it is already set, we are done.
 194          *
 195          * (Racing an EXREQ or UPREQ operation is ok here, we already did
 196          * our duty above).
 197          */
 198         count = atomic_fetchadd_64(&lkp->lk_count, LKC_SCOUNT) + LKC_SCOUNT;
 199         error = 0;
 200         didloop = 0;
 201
 202         for (;;) {
 203                 /*
 204                  * We may be able to grant ourselves the bit trivially.
 205                  * We're done once the SHARED bit is granted.
 206                  */
 207                 if ((count & (LKC_XMASK | LKC_EXREQ |
 208                               LKC_UPREQ | LKC_SHARED)) == 0) {
 209                         if (atomic_fcmpset_64(&lkp->lk_count,
 210                                               &count, count | LKC_SHARED)) {
 211                                 /* count |= LKC_SHARED; NOT USED */
 212                                 break;
 213                         }
 214                         continue;
 215                 }
 216                 if ((td->td_flags & TDF_DEADLKTREAT) &&
 217                     (count & (LKC_XMASK | LKC_SHARED)) == 0) {
 218                         if (atomic_fcmpset_64(&lkp->lk_count,
 219                                               &count, count | LKC_SHARED)) {
 220                                 /* count |= LKC_SHARED; NOT USED */
 221                                 break;
 222                         }
 223                         continue;
 224                 }
 225                 if (count & LKC_SHARED)
 226                         break;
 227
 228                 /*
 229                  * Slow path
 230                  */
 231                 pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 232                 timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 233
 234                 if (extflags & LK_CANCELABLE) {
 235                         if (count & LKC_CANCEL) {
 236                                 undo_shreq(lkp);
 237                                 error = ENOLCK;
 238                                 break;
 239                         }
 240                 }
 241                 if (extflags & LK_NOWAIT) {
 242                         undo_shreq(lkp);
 243                         error = EBUSY;
 244                         break;
 245                 }
 246
 247                 /*
 248                  * Interlocked after the first loop.
 249                  */
 250                 if (didloop) {
 251                         error = tsleep(lkp, pflags | PINTERLOCKED,
 252                                        lkp->lk_wmesg, timo);
 253                         if (extflags & LK_SLEEPFAIL) {
 254                                 undo_shreq(lkp);
 255                                 error = ENOLCK;
 256                                 break;
 257                         }
 258                         if (error) {
 259                                 undo_shreq(lkp);
 260                                 break;
 261                         }
 262                 }
 263                 didloop = 1;
 264
 265                 /*
 266                  * Reload, shortcut grant case, then loop interlock
 267                  * and loop.
 268                  */
 269                 count = lkp->lk_count;
 270                 if (count & LKC_SHARED)
 271                         break;
 272                 tsleep_interlock(lkp, pflags);
 273                 count = atomic_fetchadd_64(&lkp->lk_count, 0);
 274         }
 275         if (error == 0)
 276                 COUNT(td, 1);
 277
 278         return error;
 279 }
 280
 281 /*
 282  * Acquire an exclusive lock
 283  */
 284 int
 285 lockmgr_exclusive(struct lock *lkp, u_int flags)
 286 {
 287         uint64_t count;
 288         uint64_t ncount;
 289         uint32_t extflags;
 290         thread_t td;
 291         int error;
 292         int pflags;
 293         int timo;
 294
 295         _lockmgr_assert(lkp, flags);
 296         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 297         td = curthread;
 298
 299         error = 0;
 300         count = lkp->lk_count;
 301         cpu_ccfence();
 302
 303         /*
 304          * Recursive lock if we already hold it exclusively.  Avoid testing
 305          * lk_lockholder until after testing lk_count.
 306          */
 307         if ((count & LKC_XMASK) && lkp->lk_lockholder == td) {
 308                 if ((extflags & LK_CANRECURSE) == 0) {
 309                         if (extflags & LK_NOWAIT)
 310                                 return EBUSY;
 311                         panic("lockmgr: locking against myself");
 312                 }
 313                 count = atomic_fetchadd_64(&lkp->lk_count, 1) + 1;
 314                 KKASSERT((count & LKC_XMASK) > 1);
 315                 COUNT(td, 1);
 316                 return 0;
 317         }
 318
 319         /*
 320          * Trivially acquire the lock, or block until we can set EXREQ.
 321          * Set EXREQ2 if EXREQ is already set or the lock is already
 322          * held exclusively.  EXREQ2 is an aggregation bit to request
 323          * a wakeup.
 324          *
 325          * WARNING! We cannot set EXREQ if the lock is already held
 326          *          exclusively because it may race another EXREQ
 327          *          being cleared and granted.  We use the exclusivity
 328          *          to prevent both EXREQ and UPREQ from being set.
 329          *
 330          *          This means that both shared and exclusive requests
 331          *          have equal priority against a current exclusive holder's
 332          *          release.  Exclusive requests still have priority over
 333          *          new shared requests when the lock is already held shared.
 334          */
 335         for (;;) {
 336                 /*
 337                  * Normal trivial case
 338                  */
 339                 if ((count & (LKC_UPREQ | LKC_EXREQ |
 340                               LKC_XMASK)) == 0 &&
 341                     ((count & LKC_SHARED) == 0 ||
 342                      (count & LKC_SMASK) == 0)) {
 343                         ncount = (count + 1) & ~LKC_SHARED;
 344                         if (atomic_fcmpset_64(&lkp->lk_count,
 345                                               &count, ncount)) {
 346                                 lkp->lk_lockholder = td;
 347                                 COUNT(td, 1);
 348                                 return 0;
 349                         }
 350                         continue;
 351                 }
 352
 353                 if (extflags & LK_CANCELABLE) {
 354                         if (count & LKC_CANCEL)
 355                                 return ENOLCK;
 356                 }
 357                 if (extflags & LK_NOWAIT)
 358                         return EBUSY;
 359
 360                 /*
 361                  * Interlock to set EXREQ or EXREQ2
 362                  */
 363                 pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 364                 timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 365
 366                 if (count & (LKC_EXREQ | LKC_XMASK))
 367                         ncount = count | LKC_EXREQ2;
 368                 else
 369                         ncount = count | LKC_EXREQ;
 370                 tsleep_interlock(lkp, pflags);
 371                 if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
 372                         /*
 373                          * If we successfully transitioned to EXREQ we
 374                          * can break out, otherwise we had set EXREQ2 and
 375                          * we block.
 376                          */
 377                         if ((count & (LKC_EXREQ | LKC_XMASK)) == 0) {
 378                                 count = ncount;
 379                                 break;
 380                         }
 381
 382                         error = tsleep(lkp, pflags | PINTERLOCKED,
 383                                        lkp->lk_wmesg, timo);
 384                         count = lkp->lk_count;  /* relod */
 385                         cpu_ccfence();
 386                 }
 387 #ifdef INVARIANTS
 388                 if (lock_test_mode > 0) {
 389                         --lock_test_mode;
 390                         print_backtrace(8);
 391                 }
 392 #endif
 393                 if (error)
 394                         return error;
 395                 if (extflags & LK_SLEEPFAIL)
 396                         return ENOLCK;
 397         }
 398
 399         /*
 400          * Once EXREQ has been set, wait for it to be granted
 401          * We enter the loop with tsleep_interlock() already called.
 402          */
 403         for (;;) {
 404                 /*
 405                  * Waiting for EXREQ to be granted to us.
 406                  *
 407                  * NOTE! If we try to trivially get the exclusive lock
 408                  *       (basically by racing undo_shreq()) and succeed,
 409                  *       we must still wakeup(lkp) for another exclusive
 410                  *       lock trying to acquire EXREQ.  Easier to simply
 411                  *       wait for our own wakeup.
 412                  */
 413                 if ((count & LKC_EXREQ) == 0) {
 414                         KKASSERT(count & LKC_XMASK);
 415                         lkp->lk_lockholder = td;
 416                         COUNT(td, 1);
 417                         break;
 418                 }
 419
 420                 /*
 421                  * Block waiting for our exreq to be granted.
 422                  * Check cancelation.  NOWAIT was already dealt with.
 423                  */
 424                 if (extflags & LK_CANCELABLE) {
 425                         if (count & LKC_CANCEL) {
 426                                 if (undo_exreq(lkp) == 0) {
 427                                         lkp->lk_lockholder = LK_KERNTHREAD;
 428                                         lockmgr_release(lkp, 0);
 429                                 }
 430                                 error = ENOLCK;
 431                                 break;
 432                         }
 433                 }
 434
 435                 pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 436                 timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 437
 438                 error = tsleep(lkp, pflags | PINTERLOCKED, lkp->lk_wmesg, timo);
 439 #ifdef INVARIANTS
 440                 if (lock_test_mode > 0) {
 441                         --lock_test_mode;
 442                         print_backtrace(8);
 443                 }
 444 #endif
 445                 /*
 446                  * A tsleep error is uncommon.  If it occurs we have to
 447                  * undo our EXREQ.  If we are granted the exclusive lock
 448                  * as we try to undo we have to deal with it.
 449                  */
 450                 if (extflags & LK_SLEEPFAIL) {
 451                         if (undo_exreq(lkp) == 0) {
 452                                 lkp->lk_lockholder = LK_KERNTHREAD;
 453                                 lockmgr_release(lkp, 0);
 454                         }
 455                         if (error == 0)
 456                                 error = ENOLCK;
 457                         break;
 458                 }
 459                 if (error) {
 460                         if (undo_exreq(lkp))
 461                                 break;
 462                         lkp->lk_lockholder = td;
 463                         COUNT(td, 1);
 464                         error = 0;
 465                         break;
 466                 }
 467
 468                 /*
 469                  * Reload after sleep, shortcut grant case.
 470                  * Then set the interlock and loop.
 471                  */
 472                 count = lkp->lk_count;
 473                 cpu_ccfence();
 474                 if ((count & LKC_EXREQ) == 0) {
 475                         KKASSERT(count & LKC_XMASK);
 476                         lkp->lk_lockholder = td;
 477                         COUNT(td, 1);
 478                         break;
 479                 }
 480                 tsleep_interlock(lkp, pflags);
 481                 count = atomic_fetchadd_64(&lkp->lk_count, 0);
 482         }
 483         return error;
 484 }
 485
 486 /*
 487  * Downgrade an exclusive lock to shared.
 488  *
 489  * This function always succeeds as long as the caller owns a legal
 490  * exclusive lock with one reference.  UPREQ and EXREQ is ignored.
 491  */
 492 int
 493 lockmgr_downgrade(struct lock *lkp, u_int flags)
 494 {
 495         uint64_t count;
 496         uint64_t ncount;
 497         uint32_t extflags;
 498         thread_t otd;
 499         thread_t td;
 500
 501         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 502         td = curthread;
 503         count = lkp->lk_count;
 504
 505         for (;;) {
 506                 cpu_ccfence();
 507
 508                 /*
 509                  * Downgrade an exclusive lock into a shared lock.  All
 510                  * counts on a recursive exclusive lock become shared.
 511                  *
 512                  * NOTE: Currently to reduce confusion we only allow
 513                  *       there to be one exclusive lock count, and panic
 514                  *       if there are more.
 515                  */
 516                 if (lkp->lk_lockholder != td || (count & LKC_XMASK) != 1) {
 517                         panic("lockmgr: not holding exclusive lock: "
 518                               "%p/%p %016jx", lkp->lk_lockholder, td, count);
 519                 }
 520
 521                 /*
 522                  * NOTE! Must NULL-out lockholder before releasing the
 523                  *       exclusive lock.
 524                  *
 525                  * NOTE! There might be pending shared requests, check
 526                  *       and wake them up.
 527                  */
 528                 otd = lkp->lk_lockholder;
 529                 lkp->lk_lockholder = NULL;
 530                 ncount = (count & ~(LKC_XMASK | LKC_EXREQ2)) +
 531                          ((count & LKC_XMASK) << LKC_SSHIFT);
 532                 ncount |= LKC_SHARED;
 533
 534                 if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
 535                         /*
 536                          * Wakeup any shared waiters (prior SMASK), or
 537                          * any exclusive requests that couldn't set EXREQ
 538                          * because the lock had been held exclusively.
 539                          */
 540                         if (count & (LKC_SMASK | LKC_EXREQ2))
 541                                 wakeup(lkp);
 542                         /* count = ncount; NOT USED */
 543                         break;
 544                 }
 545                 lkp->lk_lockholder = otd;
 546                 /* retry */
 547         }
 548         return 0;
 549 }
 550
 551 /*
 552  * Upgrade a shared lock to exclusive.  If LK_EXCLUPGRADE then guarantee
 553  * that no other exclusive requester can get in front of us and fail
 554  * immediately if another upgrade is pending.  If we fail, the shared
 555  * lock is released.
 556  *
 557  * If LK_EXCLUPGRADE is not set and we cannot upgrade because someone
 558  * else is in front of us, we release the shared lock and acquire the
 559  * exclusive lock normally.  If a failure occurs, the shared lock is
 560  * released.
 561  */
 562 int
 563 lockmgr_upgrade(struct lock *lkp, u_int flags)
 564 {
 565         uint64_t count;
 566         uint64_t ncount;
 567         uint32_t extflags;
 568         thread_t td;
 569         int error;
 570         int pflags;
 571         int timo;
 572
 573         _lockmgr_assert(lkp, flags);
 574         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 575         td = curthread;
 576         error = 0;
 577         count = lkp->lk_count;
 578         cpu_ccfence();
 579
 580         /*
 581          * If we already hold the lock exclusively this operation
 582          * succeeds and is a NOP.
 583          */
 584         if (count & LKC_XMASK) {
 585                 if (lkp->lk_lockholder == td)
 586                         return 0;
 587                 panic("lockmgr: upgrade unowned lock");
 588         }
 589         if ((count & LKC_SMASK) == 0)
 590                 panic("lockmgr: upgrade unowned lock");
 591
 592         /*
 593          * Loop to acquire LKC_UPREQ
 594          */
 595         for (;;) {
 596                 /*
 597                  * If UPREQ is already pending, release the shared lock
 598                  * and acquire an exclusive lock normally.
 599                  *
 600                  * If NOWAIT or EXCLUPGRADE the operation must be atomic,
 601                  * and this isn't, so we fail.
 602                  */
 603                 if (count & LKC_UPREQ) {
 604                         lockmgr_release(lkp, 0);
 605                         if ((flags & LK_TYPE_MASK) == LK_EXCLUPGRADE)
 606                                 error = EBUSY;
 607                         else if (extflags & LK_NOWAIT)
 608                                 error = EBUSY;
 609                         else
 610                                 error = lockmgr_exclusive(lkp, flags);
 611                         return error;
 612                 }
 613
 614                 /*
 615                  * Try to immediately grant the upgrade, handle NOWAIT,
 616                  * or release the shared lock and simultaneously set UPREQ.
 617                  */
 618                 if ((count & LKC_SMASK) == LKC_SCOUNT) {
 619                         /*
 620                          * Immediate grant
 621                          */
 622                         ncount = (count - LKC_SCOUNT + 1) & ~LKC_SHARED;
 623                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
 624                                 lkp->lk_lockholder = td;
 625                                 return 0;
 626                         }
 627                 } else if (extflags & LK_NOWAIT) {
 628                         /*
 629                          * Early EBUSY if an immediate grant is impossible
 630                          */
 631                         lockmgr_release(lkp, 0);
 632                         return EBUSY;
 633                 } else {
 634                         /*
 635                          * Multiple shared locks present, request the
 636                          * upgrade and break to the next loop.
 637                          */
 638                         pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 639                         tsleep_interlock(lkp, pflags);
 640                         ncount = (count - LKC_SCOUNT) | LKC_UPREQ;
 641                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
 642                                 count = ncount;
 643                                 break;
 644                         }
 645                 }
 646                 /* retry */
 647         }
 648
 649         /*
 650          * We have acquired LKC_UPREQ, wait until the upgrade is granted
 651          * or the tsleep fails.
 652          *
 653          * NOWAIT and EXCLUPGRADE have already been handled.  The first
 654          * tsleep_interlock() has already been associated.
 655          */
 656         for (;;) {
 657                 cpu_ccfence();
 658
 659                 /*
 660                  * We were granted our upgrade.  No other UPREQ can be
 661                  * made pending because we are now exclusive.
 662                  */
 663                 if ((count & LKC_UPREQ) == 0) {
 664                         KKASSERT((count & LKC_XMASK) == 1);
 665                         lkp->lk_lockholder = td;
 666                         break;
 667                 }
 668
 669                 if (extflags & LK_CANCELABLE) {
 670                         if (count & LKC_CANCEL) {
 671                                 if (undo_upreq(lkp) == 0) {
 672                                         lkp->lk_lockholder = LK_KERNTHREAD;
 673                                         lockmgr_release(lkp, 0);
 674                                 }
 675                                 error = ENOLCK;
 676                                 break;
 677                         }
 678                 }
 679
 680                 pflags = (extflags & LK_PCATCH) ? PCATCH : 0;
 681                 timo = (extflags & LK_TIMELOCK) ? lkp->lk_timo : 0;
 682
 683                 error = tsleep(lkp, pflags | PINTERLOCKED, lkp->lk_wmesg, timo);
 684                 if (extflags & LK_SLEEPFAIL) {
 685                         if (undo_upreq(lkp) == 0) {
 686                                 lkp->lk_lockholder = LK_KERNTHREAD;
 687                                 lockmgr_release(lkp, 0);
 688                         }
 689                         if (error == 0)
 690                                 error = ENOLCK;
 691                         break;
 692                 }
 693                 if (error) {
 694                         if (undo_upreq(lkp))
 695                                 break;
 696                         error = 0;
 697                 }
 698
 699                 /*
 700                  * Reload the lock, short-cut the UPGRANT code before
 701                  * taking the time to interlock and loop.
 702                  */
 703                 count = lkp->lk_count;
 704                 if ((count & LKC_UPREQ) == 0) {
 705                         KKASSERT((count & LKC_XMASK) == 1);
 706                         lkp->lk_lockholder = td;
 707                         break;
 708                 }
 709                 tsleep_interlock(lkp, pflags);
 710                 count = atomic_fetchadd_64(&lkp->lk_count, 0);
 711                 /* retry */
 712         }
 713         return error;
 714 }
 715
 716 /*
 717  * Release a held lock
 718  *
 719  * NOTE: When releasing to an unlocked state, we set the SHARED bit
 720  *       to optimize shared lock requests.
 721  */
 722 int
 723 lockmgr_release(struct lock *lkp, u_int flags)
 724 {
 725         uint64_t count;
 726         uint64_t ncount;
 727         uint32_t extflags;
 728         thread_t otd;
 729         thread_t td;
 730
 731         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 732         td = curthread;
 733
 734         count = lkp->lk_count;
 735         cpu_ccfence();
 736
 737         for (;;) {
 738                 /*
 739                  * Release the currently held lock, grant all requests
 740                  * possible.
 741                  *
 742                  * WARNING! lksleep() assumes that LK_RELEASE does not
 743                  *          block.
 744                  *
 745                  * Always succeeds.
 746                  * Never blocks.
 747                  */
 748                 if ((count & (LKC_SMASK | LKC_XMASK)) == 0)
 749                         panic("lockmgr: LK_RELEASE: no lock held");
 750
 751                 if (count & LKC_XMASK) {
 752                         /*
 753                          * Release exclusively held lock
 754                          */
 755                         if (lkp->lk_lockholder != LK_KERNTHREAD &&
 756                             lkp->lk_lockholder != td) {
 757                                 panic("lockmgr: pid %d, not exclusive "
 758                                       "lock holder thr %p/%p unlocking",
 759                                     (td->td_proc ? td->td_proc->p_pid : -1),
 760                                     td, lkp->lk_lockholder);
 761                         }
 762                         if ((count & (LKC_UPREQ | LKC_EXREQ |
 763                                       LKC_XMASK)) == 1) {
 764                                 /*
 765                                  * Last exclusive count is being released
 766                                  * with no UPREQ or EXREQ.  The SHARED
 767                                  * bit can be set or not without messing
 768                                  * anything up, so precondition it to
 769                                  * SHARED (which is the most cpu-optimal).
 770                                  *
 771                                  * Wakeup any EXREQ2.  EXREQ cannot be
 772                                  * set while an exclusive count is present
 773                                  * so we have to wakeup any EXREQ2 we find.
 774                                  *
 775                                  * We could hint the EXREQ2 by leaving
 776                                  * SHARED unset, but atm I don't see any
 777                                  * usefulness.
 778                                  */
 779                                 otd = lkp->lk_lockholder;
 780                                 lkp->lk_lockholder = NULL;
 781                                 ncount = (count - 1);
 782                                 ncount &= ~(LKC_CANCEL | LKC_EXREQ2);
 783                                 ncount |= LKC_SHARED;
 784                                 if (atomic_fcmpset_64(&lkp->lk_count,
 785                                                       &count, ncount)) {
 786                                         if (count & (LKC_SMASK | LKC_EXREQ2))
 787                                                 wakeup(lkp);
 788                                         if (otd != LK_KERNTHREAD)
 789                                                 COUNT(td, -1);
 790                                         /* count = ncount; NOT USED */
 791                                         break;
 792                                 }
 793                                 lkp->lk_lockholder = otd;
 794                                 /* retry */
 795                         } else if ((count & (LKC_UPREQ | LKC_XMASK)) ==
 796                                    (LKC_UPREQ | 1)) {
 797                                 /*
 798                                  * Last exclusive count is being released but
 799                                  * an upgrade request is present, automatically
 800                                  * grant an exclusive state to the owner of
 801                                  * the upgrade request.  Transfer count to
 802                                  * grant.
 803                                  *
 804                                  * EXREQ cannot be set while an exclusive
 805                                  * holder exists, so do not clear EXREQ2.
 806                                  */
 807                                 otd = lkp->lk_lockholder;
 808                                 lkp->lk_lockholder = NULL;
 809                                 ncount = count & ~LKC_UPREQ;
 810                                 if (atomic_fcmpset_64(&lkp->lk_count,
 811                                                       &count, ncount)) {
 812                                         wakeup(lkp);
 813                                         if (otd != LK_KERNTHREAD)
 814                                                 COUNT(td, -1);
 815                                         /* count = ncount; NOT USED */
 816                                         break;
 817                                 }
 818                                 lkp->lk_lockholder = otd;
 819                                 /* retry */
 820                         } else if ((count & (LKC_EXREQ | LKC_XMASK)) ==
 821                                    (LKC_EXREQ | 1)) {
 822                                 /*
 823                                  * Last exclusive count is being released but
 824                                  * an exclusive request is present.  We
 825                                  * automatically grant an exclusive state to
 826                                  * the owner of the exclusive request,
 827                                  * transfering our count.
 828                                  *
 829                                  * This case virtually never occurs because
 830                                  * EXREQ is not set while exclusive holders
 831                                  * exist.  However, it might be set if a
 832                                  * an exclusive request is pending and a
 833                                  * shared holder upgrades.
 834                                  *
 835                                  * Don't bother clearing EXREQ2.  A thread
 836                                  * waiting to set EXREQ can't do it while
 837                                  * an exclusive lock is present.
 838                                  */
 839                                 otd = lkp->lk_lockholder;
 840                                 lkp->lk_lockholder = NULL;
 841                                 ncount = count & ~LKC_EXREQ;
 842                                 if (atomic_fcmpset_64(&lkp->lk_count,
 843                                                       &count, ncount)) {
 844                                         wakeup(lkp);
 845                                         if (otd != LK_KERNTHREAD)
 846                                                 COUNT(td, -1);
 847                                         /* count = ncount; NOT USED */
 848                                         break;
 849                                 }
 850                                 lkp->lk_lockholder = otd;
 851                                 /* retry */
 852                         } else {
 853                                 /*
 854                                  * Multiple exclusive counts, drop by 1.
 855                                  * Since we are the holder and there is more
 856                                  * than one count, we can just decrement it.
 857                                  */
 858                                 count =
 859                                     atomic_fetchadd_long(&lkp->lk_count, -1);
 860                                 /* count = count - 1  NOT NEEDED */
 861                                 if (lkp->lk_lockholder != LK_KERNTHREAD)
 862                                         COUNT(td, -1);
 863                                 break;
 864                         }
 865                         /* retry */
 866                 } else {
 867                         /*
 868                          * Release shared lock
 869                          */
 870                         KKASSERT((count & LKC_SHARED) && (count & LKC_SMASK));
 871                         if ((count & (LKC_EXREQ | LKC_UPREQ | LKC_SMASK)) ==
 872                             LKC_SCOUNT) {
 873                                 /*
 874                                  * Last shared count is being released,
 875                                  * no exclusive or upgrade request present.
 876                                  * Generally leave the shared bit set.
 877                                  * Clear the CANCEL bit.
 878                                  */
 879                                 ncount = (count - LKC_SCOUNT) & ~LKC_CANCEL;
 880                                 if (atomic_fcmpset_64(&lkp->lk_count,
 881                                                       &count, ncount)) {
 882                                         COUNT(td, -1);
 883                                         /* count = ncount; NOT USED */
 884                                         break;
 885                                 }
 886                                 /* retry */
 887                         } else if ((count & (LKC_UPREQ | LKC_SMASK)) ==
 888                                    (LKC_UPREQ | LKC_SCOUNT)) {
 889                                 /*
 890                                  * Last shared count is being released but
 891                                  * an upgrade request is present, automatically
 892                                  * grant an exclusive state to the owner of
 893                                  * the upgrade request and transfer the count.
 894                                  */
 895                                 ncount = (count - LKC_SCOUNT + 1) &
 896                                          ~(LKC_UPREQ | LKC_CANCEL | LKC_SHARED);
 897                                 if (atomic_fcmpset_64(&lkp->lk_count,
 898                                                       &count, ncount)) {
 899                                         wakeup(lkp);
 900                                         COUNT(td, -1);
 901                                         /* count = ncount; NOT USED */
 902                                         break;
 903                                 }
 904                                 /* retry */
 905                         } else if ((count & (LKC_EXREQ | LKC_SMASK)) ==
 906                                    (LKC_EXREQ | LKC_SCOUNT)) {
 907                                 /*
 908                                  * Last shared count is being released but
 909                                  * an exclusive request is present, we
 910                                  * automatically grant an exclusive state to
 911                                  * the owner of the request and transfer
 912                                  * the count.
 913                                  */
 914                                 ncount = (count - LKC_SCOUNT + 1) &
 915                                          ~(LKC_EXREQ | LKC_EXREQ2 |
 916                                            LKC_CANCEL | LKC_SHARED);
 917                                 if (atomic_fcmpset_64(&lkp->lk_count,
 918                                                       &count, ncount)) {
 919                                         wakeup(lkp);
 920                                         COUNT(td, -1);
 921                                         /* count = ncount; NOT USED */
 922                                         break;
 923                                 }
 924                                 /* retry */
 925                         } else {
 926                                 /*
 927                                  * Shared count is greater than 1.  We can
 928                                  * just use undo_shreq() to clean things up.
 929                                  * undo_shreq() will also handle races to 0
 930                                  * after the fact.
 931                                  */
 932                                 undo_shreq(lkp);
 933                                 COUNT(td, -1);
 934                                 break;
 935                         }
 936                         /* retry */
 937                 }
 938                 /* retry */
 939         }
 940         return 0;
 941 }
 942
 943 /*
 944  * Start canceling blocked requesters or later requestors.
 945  * Only blocked requesters using CANCELABLE can be canceled.
 946  *
 947  * This is intended to then allow other requesters (usually the
 948  * caller) to obtain a non-cancelable lock.
 949  *
 950  * Don't waste time issuing a wakeup if nobody is pending.
 951  */
 952 int
 953 lockmgr_cancel_beg(struct lock *lkp, u_int flags)
 954 {
 955         uint64_t count;
 956
 957         count = lkp->lk_count;
 958         for (;;) {
 959                 cpu_ccfence();
 960
 961                 KKASSERT((count & LKC_CANCEL) == 0);    /* disallowed case */
 962
 963                 /* issue w/lock held */
 964                 KKASSERT((count & (LKC_XMASK | LKC_SMASK)) != 0);
 965
 966                 if (!atomic_fcmpset_64(&lkp->lk_count,
 967                                        &count, count | LKC_CANCEL)) {
 968                         continue;
 969                 }
 970                 /* count |= LKC_CANCEL; NOT USED */
 971
 972                 /*
 973                  * Wakeup any waiters.
 974                  *
 975                  * NOTE: EXREQ2 only matters when EXREQ is set, so don't
 976                  *       bother checking EXREQ2.
 977                  */
 978                 if (count & (LKC_EXREQ | LKC_SMASK | LKC_UPREQ)) {
 979                         wakeup(lkp);
 980                 }
 981                 break;
 982         }
 983         return 0;
 984 }
 985
 986 /*
 987  * End our cancel request (typically after we have acquired
 988  * the lock ourselves).
 989  */
 990 int
 991 lockmgr_cancel_end(struct lock *lkp, u_int flags)
 992 {
 993         atomic_clear_long(&lkp->lk_count, LKC_CANCEL);
 994
 995         return 0;
 996 }
 997
 998 /*
 999  * Backout SCOUNT from a failed shared lock attempt and handle any race
1000  * to 0.  This function is also used by the release code for the less
1001  * optimal race to 0 case.
1002  *
1003  * WARNING! Since we are unconditionally decrementing LKC_SCOUNT, it is
1004  *          possible for the lock to get into a LKC_SHARED + ZERO SCOUNT
1005  *          situation.  A shared request can block with a ZERO SCOUNT if
1006  *          EXREQ or UPREQ is pending in this situation.  Be sure to always
1007  *          issue a wakeup() in this situation if we are unable to
1008  *          transition to an exclusive lock, to handle the race.
1009  *
1010  * Always succeeds
1011  * Must not block
1012  */
1013 static void
1014 undo_shreq(struct lock *lkp)
1015 {
1016         uint64_t count;
1017         uint64_t ncount;
1018
1019         count = atomic_fetchadd_64(&lkp->lk_count, -LKC_SCOUNT) - LKC_SCOUNT;
1020         while ((count & (LKC_EXREQ | LKC_UPREQ | LKC_CANCEL)) &&
1021                (count & (LKC_SMASK | LKC_XMASK)) == 0) {
1022                 /*
1023                  * Note that UPREQ must have priority over EXREQ, and EXREQ
1024                  * over CANCEL, so if the atomic op fails we have to loop up.
1025                  */
1026                 if (count & LKC_UPREQ) {
1027                         ncount = (count + 1) & ~(LKC_UPREQ | LKC_CANCEL |
1028                                                  LKC_SHARED);
1029                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1030                                 wakeup(lkp);
1031                                 /* count = ncount; NOT USED */
1032                                 break;
1033                         }
1034                         wakeup(lkp);
1035                         continue;
1036                 }
1037                 if (count & LKC_EXREQ) {
1038                         ncount = (count + 1) & ~(LKC_EXREQ | LKC_EXREQ2 |
1039                                                  LKC_CANCEL | LKC_SHARED);
1040                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1041                                 wakeup(lkp);
1042                                 /* count = ncount; NOT USED */
1043                                 break;
1044                         }
1045                         wakeup(lkp);
1046                         continue;
1047                 }
1048                 if (count & LKC_CANCEL) {
1049                         ncount = count & ~LKC_CANCEL;
1050                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1051                                 wakeup(lkp);
1052                                 /* count = ncount; NOT USED */
1053                                 break;
1054                         }
1055                 }
1056                 /* retry */
1057         }
1058 }
1059
1060 /*
1061  * Undo an exclusive request.  Returns EBUSY if we were able to undo the
1062  * request, and 0 if the request was granted before we could undo it.
1063  * When 0 is returned, the lock state has not been modified.  The caller
1064  * is responsible for setting the lockholder to curthread.
1065  */
1066 static
1067 int
1068 undo_exreq(struct lock *lkp)
1069 {
1070         uint64_t count;
1071         uint64_t ncount;
1072         int error;
1073
1074         count = lkp->lk_count;
1075         error = 0;
1076
1077         for (;;) {
1078                 cpu_ccfence();
1079
1080                 if ((count & LKC_EXREQ) == 0) {
1081                         /*
1082                          * EXREQ was granted.  We own the exclusive lock.
1083                          */
1084                         break;
1085                 }
1086                 if (count & LKC_XMASK) {
1087                         /*
1088                          * Clear the EXREQ we still own.  Only wakeup on
1089                          * EXREQ2 if no UPREQ.  There are still exclusive
1090                          * holders so do not wake up any shared locks or
1091                          * any UPREQ.
1092                          *
1093                          * If there is an UPREQ it will issue a wakeup()
1094                          * for any EXREQ wait looops, so we can clear EXREQ2
1095                          * now.
1096                          */
1097                         ncount = count & ~(LKC_EXREQ | LKC_EXREQ2);
1098                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1099                                 if ((count & (LKC_EXREQ2 | LKC_UPREQ)) ==
1100                                     LKC_EXREQ2) {
1101                                         wakeup(lkp);
1102                                 }
1103                                 error = EBUSY;
1104                                 /* count = ncount; NOT USED */
1105                                 break;
1106                         }
1107                         /* retry */
1108                 } else if (count & LKC_UPREQ) {
1109                         /*
1110                          * Clear the EXREQ we still own.  We cannot wakeup any
1111                          * shared or exclusive waiters because there is an
1112                          * uprequest pending (that we do not handle here).
1113                          *
1114                          * If there is an UPREQ it will issue a wakeup()
1115                          * for any EXREQ wait looops, so we can clear EXREQ2
1116                          * now.
1117                          */
1118                         ncount = count & ~(LKC_EXREQ | LKC_EXREQ2);
1119                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1120                                 error = EBUSY;
1121                                 break;
1122                         }
1123                         /* retry */
1124                 } else if ((count & LKC_SHARED) && (count & LKC_SMASK)) {
1125                         /*
1126                          * No UPREQ, lock not held exclusively, but the lock
1127                          * is held shared.  Clear EXREQ, wakeup anyone trying
1128                          * to get the EXREQ bit (they have to set it
1129                          * themselves, EXREQ2 is an aggregation).
1130                          */
1131                         ncount = count & ~(LKC_EXREQ | LKC_EXREQ2);
1132                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1133                                 if (count & LKC_EXREQ2)
1134                                         wakeup(lkp);
1135                                 error = EBUSY;
1136                                 /* count = ncount; NOT USED */
1137                                 break;
1138                         }
1139                         /* retry */
1140                 } else {
1141                         /*
1142                          * No UPREQ, lock not held exclusively or shared.
1143                          * Grant the EXREQ and wakeup anyone waiting on
1144                          * EXREQ2.
1145                          */
1146                         ncount = (count + 1) & ~(LKC_EXREQ | LKC_EXREQ2);
1147                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1148                                 if (count & LKC_EXREQ2)
1149                                         wakeup(lkp);
1150                                 /* count = ncount; NOT USED */
1151                                 /* we are granting, error == 0 */
1152                                 break;
1153                         }
1154                         /* retry */
1155                 }
1156                 /* retry */
1157         }
1158         return error;
1159 }
1160
1161 /*
1162  * Undo an upgrade request.  Returns EBUSY if we were able to undo the
1163  * request, and 0 if the request was granted before we could undo it.
1164  * When 0 is returned, the lock state has not been modified.  The caller
1165  * is responsible for setting the lockholder to curthread.
1166  */
1167 static
1168 int
1169 undo_upreq(struct lock *lkp)
1170 {
1171         uint64_t count;
1172         uint64_t ncount;
1173         int error;
1174
1175         count = lkp->lk_count;
1176         error = 0;
1177
1178         for (;;) {
1179                 cpu_ccfence();
1180
1181                 if ((count & LKC_UPREQ) == 0) {
1182                         /*
1183                          * UPREQ was granted
1184                          */
1185                         break;
1186                 }
1187                 if (count & LKC_XMASK) {
1188                         /*
1189                          * Clear the UPREQ we still own.  Nobody to wakeup
1190                          * here because there is an existing exclusive
1191                          * holder.
1192                          */
1193                         if (atomic_fcmpset_64(&lkp->lk_count, &count,
1194                                               count & ~LKC_UPREQ)) {
1195                                 error = EBUSY;
1196                                 /* count &= ~LKC_UPREQ; NOT USED */
1197                                 break;
1198                         }
1199                 } else if (count & LKC_EXREQ) {
1200                         /*
1201                          * Clear the UPREQ we still own.  Grant the exclusive
1202                          * request and wake it up.
1203                          */
1204                         ncount = (count + 1);
1205                         ncount &= ~(LKC_EXREQ | LKC_EXREQ2 | LKC_UPREQ);
1206
1207                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1208                                 wakeup(lkp);
1209                                 error = EBUSY;
1210                                 /* count = ncount; NOT USED */
1211                                 break;
1212                         }
1213                 } else {
1214                         /*
1215                          * Clear the UPREQ we still own.  Wakeup any shared
1216                          * waiters.
1217                          */
1218                         ncount = count & ~LKC_UPREQ;
1219                         if (count & LKC_SMASK)
1220                                 ncount |= LKC_SHARED;
1221
1222                         if (atomic_fcmpset_64(&lkp->lk_count, &count, ncount)) {
1223                                 if ((count & LKC_SHARED) == 0 &&
1224                                     (ncount & LKC_SHARED)) {
1225                                         wakeup(lkp);
1226                                 }
1227                                 error = EBUSY;
1228                                 /* count = ncount; NOT USED */
1229                                 break;
1230                         }
1231                 }
1232                 /* retry */
1233         }
1234         return error;
1235 }
1236
1237 void
1238 lockmgr_kernproc(struct lock *lp)
1239 {
1240         struct thread *td __debugvar = curthread;
1241
1242         if (lp->lk_lockholder != LK_KERNTHREAD) {
1243                 KASSERT(lp->lk_lockholder == td,
1244                     ("lockmgr_kernproc: lock not owned by curthread %p: %p",
1245                     td, lp->lk_lockholder));
1246                 lp->lk_lockholder = LK_KERNTHREAD;
1247                 COUNT(td, -1);
1248         }
1249 }
1250
1251 /*
1252  * Initialize a lock; required before use.
1253  */
1254 void
1255 lockinit(struct lock *lkp, const char *wmesg, int timo, int flags)
1256 {
1257         lkp->lk_flags = (flags & LK_EXTFLG_MASK);
1258         lkp->lk_count = 0;
1259         lkp->lk_wmesg = wmesg;
1260         lkp->lk_timo = timo;
1261         lkp->lk_lockholder = NULL;
1262 }
1263
1264 /*
1265  * Reinitialize a lock that is being reused for a different purpose, but
1266  * which may have pending (blocked) threads sitting on it.  The caller
1267  * must already hold the interlock.
1268  */
1269 void
1270 lockreinit(struct lock *lkp, const char *wmesg, int timo, int flags)
1271 {
1272         lkp->lk_wmesg = wmesg;
1273         lkp->lk_timo = timo;
1274 }
1275
1276 /*
1277  * De-initialize a lock.  The structure must no longer be used by anyone.
1278  */
1279 void
1280 lockuninit(struct lock *lkp)
1281 {
1282         uint64_t count __unused;
1283
1284         count = lkp->lk_count;
1285         cpu_ccfence();
1286         KKASSERT((count & (LKC_EXREQ | LKC_UPREQ)) == 0 &&
1287                  ((count & LKC_SHARED) || (count & LKC_SMASK) == 0));
1288 }
1289
1290 /*
1291  * Determine the status of a lock.
1292  */
1293 int
1294 lockstatus(struct lock *lkp, struct thread *td)
1295 {
1296         int lock_type = 0;
1297         uint64_t count;
1298
1299         count = lkp->lk_count;
1300         cpu_ccfence();
1301
1302         if (count & (LKC_XMASK | LKC_SMASK | LKC_EXREQ | LKC_UPREQ)) {
1303                 if (count & LKC_XMASK) {
1304                         if (td == NULL || lkp->lk_lockholder == td)
1305                                 lock_type = LK_EXCLUSIVE;
1306                         else
1307                                 lock_type = LK_EXCLOTHER;
1308                 } else if ((count & LKC_SMASK) && (count & LKC_SHARED)) {
1309                         lock_type = LK_SHARED;
1310                 }
1311         }
1312         return (lock_type);
1313 }
1314
1315 /*
1316  * Return non-zero if the caller owns the lock shared or exclusive.
1317  * We can only guess re: shared locks.
1318  */
1319 int
1320 lockowned(struct lock *lkp)
1321 {
1322         thread_t td = curthread;
1323         uint64_t count;
1324
1325         count = lkp->lk_count;
1326         cpu_ccfence();
1327
1328         if (count & LKC_XMASK)
1329                 return(lkp->lk_lockholder == td);
1330         else
1331                 return((count & LKC_SMASK) != 0);
1332 }
1333
1334 #if 0
1335 /*
1336  * Determine the number of holders of a lock.
1337  *
1338  * REMOVED - Cannot be used due to our use of atomic_fetchadd_64()
1339  *           for shared locks.  Caller can only test if the lock has
1340  *           a count or not using lockinuse(lk) (sys/lock.h)
1341  */
1342 int
1343 lockcount(struct lock *lkp)
1344 {
1345         panic("lockcount cannot be used");
1346 }
1347
1348 int
1349 lockcountnb(struct lock *lkp)
1350 {
1351         panic("lockcount cannot be used");
1352 }
1353 #endif
1354
1355 /*
1356  * Print out information about state of a lock. Used by VOP_PRINT
1357  * routines to display status about contained locks.
1358  */
1359 void
1360 lockmgr_printinfo(struct lock *lkp)
1361 {
1362         struct thread *td = lkp->lk_lockholder;
1363         struct proc *p;
1364         uint64_t count;
1365
1366         count = lkp->lk_count;
1367         cpu_ccfence();
1368
1369         if (td && td != LK_KERNTHREAD)
1370                 p = td->td_proc;
1371         else
1372                 p = NULL;
1373
1374         if (count & LKC_XMASK) {
1375                 kprintf(" lock type %s: EXCLUS (count %016jx) by td %p pid %d",
1376                     lkp->lk_wmesg, (intmax_t)count, td,
1377                     p ? p->p_pid : -99);
1378         } else if ((count & LKC_SMASK) && (count & LKC_SHARED)) {
1379                 kprintf(" lock type %s: SHARED (count %016jx)",
1380                     lkp->lk_wmesg, (intmax_t)count);
1381         } else {
1382                 kprintf(" lock type %s: NOTHELD", lkp->lk_wmesg);
1383         }
1384         if ((count & (LKC_EXREQ | LKC_UPREQ)) ||
1385             ((count & LKC_XMASK) && (count & LKC_SMASK)))
1386                 kprintf(" with waiters\n");
1387         else
1388                 kprintf("\n");
1389 }
1390
1391 void
1392 lock_sysinit(struct lock_args *arg)
1393 {
1394         lockinit(arg->la_lock, arg->la_desc, 0, arg->la_flags);
1395 }
1396
1397 #ifdef DEBUG_CANCEL_LOCKS
1398
1399 static
1400 int
1401 sysctl_cancel_lock(SYSCTL_HANDLER_ARGS)
1402 {
1403         int error;
1404
1405         if (req->newptr) {
1406                 SYSCTL_XUNLOCK();
1407                 lockmgr(&cancel_lk, LK_EXCLUSIVE);
1408                 error = tsleep(&error, PCATCH, "canmas", hz * 5);
1409                 lockmgr(&cancel_lk, LK_CANCEL_BEG);
1410                 error = tsleep(&error, PCATCH, "canmas", hz * 5);
1411                 lockmgr(&cancel_lk, LK_RELEASE);
1412                 SYSCTL_XLOCK();
1413                 SYSCTL_OUT(req, &error, sizeof(error));
1414         }
1415         error = 0;
1416
1417         return error;
1418 }
1419
1420 static
1421 int
1422 sysctl_cancel_test(SYSCTL_HANDLER_ARGS)
1423 {
1424         int error;
1425
1426         if (req->newptr) {
1427                 error = lockmgr(&cancel_lk, LK_EXCLUSIVE|LK_CANCELABLE);
1428                 if (error == 0)
1429                         lockmgr(&cancel_lk, LK_RELEASE);
1430                 SYSCTL_OUT(req, &error, sizeof(error));
1431                 kprintf("test %d\n", error);
1432         }
1433
1434         return 0;
1435 }
1436
1437 #endif