sys/kern/kern_lock.c

   1 /*
   2  * Copyright (c) 1995
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * Copyright (C) 1997
   6  *      John S. Dyson.  All rights reserved.
   7  *
   8  * This code contains ideas from software contributed to Berkeley by
   9  * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
  10  * System project at Carnegie-Mellon University.
  11  *
  12  * Redistribution and use in source and binary forms, with or without
  13  * modification, are permitted provided that the following conditions
  14  * are met:
  15  * 1. Redistributions of source code must retain the above copyright
  16  *    notice, this list of conditions and the following disclaimer.
  17  * 2. Redistributions in binary form must reproduce the above copyright
  18  *    notice, this list of conditions and the following disclaimer in the
  19  *    documentation and/or other materials provided with the distribution.
  20  * 3. All advertising materials mentioning features or use of this software
  21  *    must display the following acknowledgement:
  22  *      This product includes software developed by the University of
  23  *      California, Berkeley and its contributors.
  24  * 4. 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  *      @(#)kern_lock.c 8.18 (Berkeley) 5/21/95
  41  * $FreeBSD: src/sys/kern/kern_lock.c,v 1.31.2.3 2001/12/25 01:44:44 dillon Exp $
  42  * $DragonFly: src/sys/kern/kern_lock.c,v 1.27 2008/01/09 10:59:12 corecode Exp $
  43  */
  44
  45 #include "opt_lint.h"
  46
  47 #include <sys/param.h>
  48 #include <sys/systm.h>
  49 #include <sys/kernel.h>
  50 #include <sys/proc.h>
  51 #include <sys/lock.h>
  52 #include <sys/sysctl.h>
  53 #include <sys/spinlock.h>
  54 #include <sys/thread2.h>
  55 #include <sys/spinlock2.h>
  56
  57 /*
  58  * Locking primitives implementation.
  59  * Locks provide shared/exclusive sychronization.
  60  */
  61
  62 #ifdef DEBUG_LOCKS
  63 #define COUNT(td, x) (td)->td_locks += (x)
  64 #else
  65 #define COUNT(td, x)
  66 #endif
  67
  68 #define LOCK_WAIT_TIME 100
  69 #define LOCK_SAMPLE_WAIT 7
  70
  71 #if defined(DIAGNOSTIC)
  72 #define LOCK_INLINE
  73 #else
  74 #define LOCK_INLINE __inline
  75 #endif
  76
  77 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
  78         LK_SHARE_NONZERO | LK_WAIT_NONZERO)
  79
  80 static int acquire(struct lock *lkp, int extflags, int wanted);
  81
  82 static LOCK_INLINE void
  83 sharelock(struct lock *lkp, int incr) {
  84         lkp->lk_flags |= LK_SHARE_NONZERO;
  85         lkp->lk_sharecount += incr;
  86 }
  87
  88 static LOCK_INLINE int
  89 shareunlock(struct lock *lkp, int decr)
  90 {
  91         int dowakeup = 0;
  92
  93         KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
  94
  95         if (lkp->lk_sharecount == decr) {
  96                 lkp->lk_flags &= ~LK_SHARE_NONZERO;
  97                 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
  98                         dowakeup = 1;
  99                 }
 100                 lkp->lk_sharecount = 0;
 101         } else {
 102                 lkp->lk_sharecount -= decr;
 103         }
 104         return(dowakeup);
 105 }
 106
 107 /*
 108  * lock acquisition helper routine.  Called with the lock's spinlock held.
 109  */
 110 static int
 111 acquire(struct lock *lkp, int extflags, int wanted)
 112 {
 113         int error;
 114
 115         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
 116                 return EBUSY;
 117         }
 118
 119         while ((lkp->lk_flags & wanted) != 0) {
 120                 lkp->lk_flags |= LK_WAIT_NONZERO;
 121                 lkp->lk_waitcount++;
 122
 123                 /*
 124                  * Atomic spinlock release/sleep/reacquire.
 125                  */
 126                 error = ssleep(lkp, &lkp->lk_spinlock,
 127                                ((extflags & LK_PCATCH) ? PCATCH : 0),
 128                                lkp->lk_wmesg,
 129                                ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
 130                 if (lkp->lk_waitcount == 1) {
 131                         lkp->lk_flags &= ~LK_WAIT_NONZERO;
 132                         lkp->lk_waitcount = 0;
 133                 } else {
 134                         lkp->lk_waitcount--;
 135                 }
 136                 if (error)
 137                         return error;
 138                 if (extflags & LK_SLEEPFAIL)
 139                         return ENOLCK;
 140         }
 141         return 0;
 142 }
 143
 144 /*
 145  * Set, change, or release a lock.
 146  *
 147  * Shared requests increment the shared count. Exclusive requests set the
 148  * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
 149  * accepted shared locks and shared-to-exclusive upgrades to go away.
 150  *
 151  * A spinlock is held for most of the procedure.  We must not do anything
 152  * fancy while holding the spinlock.
 153  */
 154 int
 155 #ifndef DEBUG_LOCKS
 156 lockmgr(struct lock *lkp, u_int flags)
 157 #else
 158 debuglockmgr(struct lock *lkp, u_int flags,
 159              const char *name, const char *file, int line)
 160 #endif
 161 {
 162         thread_t td;
 163         int error;
 164         int extflags;
 165         int dowakeup;
 166 #ifdef DEBUG_LOCKS
 167         int i;
 168 #endif
 169
 170         error = 0;
 171         dowakeup = 0;
 172
 173         if (mycpu->gd_intr_nesting_level &&
 174             (flags & LK_NOWAIT) == 0 &&
 175             (flags & LK_TYPE_MASK) != LK_RELEASE &&
 176             panic_cpu_gd != mycpu
 177         ) {
 178
 179 #ifndef DEBUG_LOCKS
 180                 panic("lockmgr %s from %p: called from interrupt, ipi, "
 181                       "or hard code section",
 182                       lkp->lk_wmesg, ((int **)&lkp)[-1]);
 183 #else
 184                 panic("lockmgr %s from %s:%d: called from interrupt, ipi, "
 185                       "or hard code section",
 186                       lkp->lk_wmesg, file, line);
 187 #endif
 188         }
 189
 190 #ifdef DEBUG_LOCKS
 191         if (mycpu->gd_spinlocks_wr &&
 192             ((flags & LK_NOWAIT) == 0)
 193         ) {
 194                 panic("lockmgr %s from %s:%d: called with %d spinlocks held",
 195                       lkp->lk_wmesg, file, line, mycpu->gd_spinlocks_wr);
 196         }
 197 #endif
 198
 199         /*
 200          * So sue me, I'm too tired.
 201          */
 202         if (spin_trylock(&lkp->lk_spinlock) == FALSE) {
 203                 if (flags & LK_NOSPINWAIT)
 204                         return(EBUSY);
 205                 spin_lock(&lkp->lk_spinlock);
 206         }
 207
 208         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 209         td = curthread;
 210
 211         switch (flags & LK_TYPE_MASK) {
 212         case LK_SHARED:
 213                 /*
 214                  * If we are not the exclusive lock holder, we have to block
 215                  * while there is an exclusive lock holder or while an
 216                  * exclusive lock request or upgrade request is in progress.
 217                  *
 218                  * However, if TDF_DEADLKTREAT is set, we override exclusive
 219                  * lock requests or upgrade requests ( but not the exclusive
 220                  * lock itself ).
 221                  */
 222                 if (lkp->lk_lockholder != td) {
 223                         if (td->td_flags & TDF_DEADLKTREAT) {
 224                                 error = acquire(
 225                                             lkp,
 226                                             extflags,
 227                                             LK_HAVE_EXCL
 228                                         );
 229                         } else {
 230                                 error = acquire(
 231                                             lkp,
 232                                             extflags,
 233                                             LK_HAVE_EXCL | LK_WANT_EXCL |
 234                                              LK_WANT_UPGRADE
 235                                         );
 236                         }
 237                         if (error)
 238                                 break;
 239                         sharelock(lkp, 1);
 240                         COUNT(td, 1);
 241                         break;
 242                 }
 243                 /*
 244                  * We hold an exclusive lock, so downgrade it to shared.
 245                  * An alternative would be to fail with EDEADLK.
 246                  */
 247                 sharelock(lkp, 1);
 248                 COUNT(td, 1);
 249                 /* fall into downgrade */
 250
 251         case LK_DOWNGRADE:
 252                 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) {
 253                         spin_unlock(&lkp->lk_spinlock);
 254                         panic("lockmgr: not holding exclusive lock");
 255                 }
 256
 257 #ifdef DEBUG_LOCKS
 258                 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
 259                         if (td->td_lockmgr_stack[i] == lkp &&
 260                             td->td_lockmgr_stack_id[i] > 0
 261                         ) {
 262                                 td->td_lockmgr_stack_id[i]--;
 263                                 break;
 264                         }
 265                 }
 266 #endif
 267
 268                 sharelock(lkp, lkp->lk_exclusivecount);
 269                 lkp->lk_exclusivecount = 0;
 270                 lkp->lk_flags &= ~LK_HAVE_EXCL;
 271                 lkp->lk_lockholder = LK_NOTHREAD;
 272                 if (lkp->lk_waitcount)
 273                         dowakeup = 1;
 274                 break;
 275
 276         case LK_EXCLUPGRADE:
 277                 /*
 278                  * If another process is ahead of us to get an upgrade,
 279                  * then we want to fail rather than have an intervening
 280                  * exclusive access.
 281                  */
 282                 if (lkp->lk_flags & LK_WANT_UPGRADE) {
 283                         dowakeup = shareunlock(lkp, 1);
 284                         COUNT(td, -1);
 285                         error = EBUSY;
 286                         break;
 287                 }
 288                 /* fall into normal upgrade */
 289
 290         case LK_UPGRADE:
 291                 /*
 292                  * Upgrade a shared lock to an exclusive one. If another
 293                  * shared lock has already requested an upgrade to an
 294                  * exclusive lock, our shared lock is released and an
 295                  * exclusive lock is requested (which will be granted
 296                  * after the upgrade). If we return an error, the file
 297                  * will always be unlocked.
 298                  */
 299                 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) {
 300                         spin_unlock(&lkp->lk_spinlock);
 301                         panic("lockmgr: upgrade exclusive lock");
 302                 }
 303                 dowakeup += shareunlock(lkp, 1);
 304                 COUNT(td, -1);
 305                 /*
 306                  * If we are just polling, check to see if we will block.
 307                  */
 308                 if ((extflags & LK_NOWAIT) &&
 309                     ((lkp->lk_flags & LK_WANT_UPGRADE) ||
 310                      lkp->lk_sharecount > 1)) {
 311                         error = EBUSY;
 312                         break;
 313                 }
 314                 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
 315                         /*
 316                          * We are first shared lock to request an upgrade, so
 317                          * request upgrade and wait for the shared count to
 318                          * drop to zero, then take exclusive lock.
 319                          *
 320                          * Although I don't think this can occur for
 321                          * robustness we also wait for any exclusive locks
 322                          * to be released.  LK_WANT_UPGRADE is supposed to
 323                          * prevent new exclusive locks but might not in the
 324                          * future.
 325                          */
 326                         lkp->lk_flags |= LK_WANT_UPGRADE;
 327                         error = acquire(lkp, extflags,
 328                                         LK_HAVE_EXCL | LK_SHARE_NONZERO);
 329                         lkp->lk_flags &= ~LK_WANT_UPGRADE;
 330
 331                         if (error)
 332                                 break;
 333                         lkp->lk_flags |= LK_HAVE_EXCL;
 334                         lkp->lk_lockholder = td;
 335                         if (lkp->lk_exclusivecount != 0) {
 336                                 spin_unlock(&lkp->lk_spinlock);
 337                                 panic("lockmgr(1): non-zero exclusive count");
 338                         }
 339                         lkp->lk_exclusivecount = 1;
 340 #if defined(DEBUG_LOCKS)
 341                         lkp->lk_filename = file;
 342                         lkp->lk_lineno = line;
 343                         lkp->lk_lockername = name;
 344
 345                         for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
 346                                 /*
 347                                  * Recursive lockmgr path
 348                                  */
 349                                 if (td->td_lockmgr_stack[i] == lkp &&
 350                                     td->td_lockmgr_stack_id[i] != 0
 351                                 ) {
 352                                         td->td_lockmgr_stack_id[i]++;
 353                                         goto lkmatch2;
 354                                 }
 355                        }
 356
 357                         for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
 358                                 /*
 359                                  * Use new lockmgr tracking slot
 360                                  */
 361                                 if (td->td_lockmgr_stack_id[i] == 0) {
 362                                         td->td_lockmgr_stack_id[i]++;
 363                                         td->td_lockmgr_stack[i] = lkp;
 364                                         break;
 365                                 }
 366                         }
 367 lkmatch2:
 368                         ;
 369 #endif
 370                         COUNT(td, 1);
 371                         break;
 372                 }
 373                 /*
 374                  * Someone else has requested upgrade. Release our shared
 375                  * lock, awaken upgrade requestor if we are the last shared
 376                  * lock, then request an exclusive lock.
 377                  */
 378                 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
 379                         LK_WAIT_NONZERO) {
 380                         ++dowakeup;
 381                 }
 382                 /* fall into exclusive request */
 383
 384         case LK_EXCLUSIVE:
 385                 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
 386                         /*
 387                          *      Recursive lock.
 388                          */
 389                         if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) {
 390                                 spin_unlock(&lkp->lk_spinlock);
 391                                 panic("lockmgr: locking against myself");
 392                         }
 393                         if ((extflags & LK_CANRECURSE) != 0) {
 394                                 lkp->lk_exclusivecount++;
 395                                 COUNT(td, 1);
 396                                 break;
 397                         }
 398                 }
 399                 /*
 400                  * If we are just polling, check to see if we will sleep.
 401                  */
 402                 if ((extflags & LK_NOWAIT) &&
 403                     (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL |
 404                                       LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
 405                         error = EBUSY;
 406                         break;
 407                 }
 408                 /*
 409                  * Wait for exclusive lock holders to release and try to
 410                  * acquire the want_exclusive flag.
 411                  */
 412                 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
 413                 if (error)
 414                         break;
 415                 lkp->lk_flags |= LK_WANT_EXCL;
 416
 417                 /*
 418                  * Wait for shared locks and upgrades to finish.  We can lose
 419                  * the race against a successful shared lock upgrade in which
 420                  * case LK_HAVE_EXCL will get set regardless of our
 421                  * acquisition of LK_WANT_EXCL, so we have to acquire
 422                  * LK_HAVE_EXCL here as well.
 423                  */
 424                 error = acquire(lkp, extflags, LK_HAVE_EXCL |
 425                                                LK_WANT_UPGRADE |
 426                                                LK_SHARE_NONZERO);
 427                 lkp->lk_flags &= ~LK_WANT_EXCL;
 428                 if (error)
 429                         break;
 430                 lkp->lk_flags |= LK_HAVE_EXCL;
 431                 lkp->lk_lockholder = td;
 432                 if (lkp->lk_exclusivecount != 0) {
 433                         spin_unlock(&lkp->lk_spinlock);
 434                         panic("lockmgr(2): non-zero exclusive count");
 435                 }
 436                 lkp->lk_exclusivecount = 1;
 437 #if defined(DEBUG_LOCKS)
 438                 lkp->lk_filename = file;
 439                 lkp->lk_lineno = line;
 440                 lkp->lk_lockername = name;
 441
 442                 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
 443                         /*
 444                          * Recursive lockmgr path
 445                          */
 446                         if (td->td_lockmgr_stack[i] == lkp &&
 447                             td->td_lockmgr_stack_id[i] != 0
 448                         ) {
 449                                 td->td_lockmgr_stack_id[i]++;
 450                                 goto lkmatch1;
 451                         }
 452                 }
 453
 454                 for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
 455                         /*
 456                          * Use new lockmgr tracking slot
 457                          */
 458                         if (td->td_lockmgr_stack_id[i] == 0) {
 459                                 td->td_lockmgr_stack_id[i]++;
 460                                 td->td_lockmgr_stack[i] = lkp;
 461                                 break;
 462                         }
 463                 }
 464 lkmatch1:
 465                 ;
 466 #endif
 467                 COUNT(td, 1);
 468                 break;
 469
 470         case LK_RELEASE:
 471                 if (lkp->lk_exclusivecount != 0) {
 472                         if (lkp->lk_lockholder != td &&
 473                             lkp->lk_lockholder != LK_KERNTHREAD) {
 474                                 spin_unlock(&lkp->lk_spinlock);
 475                                 panic("lockmgr: pid %d, not %s thr %p/%p unlocking",
 476                                     (td->td_proc ? td->td_proc->p_pid : -1),
 477                                     "exclusive lock holder",
 478                                     td, lkp->lk_lockholder);
 479                         }
 480                         if (lkp->lk_lockholder != LK_KERNTHREAD) {
 481                                 COUNT(td, -1);
 482                         }
 483                         if (lkp->lk_exclusivecount == 1) {
 484                                 lkp->lk_flags &= ~LK_HAVE_EXCL;
 485                                 lkp->lk_lockholder = LK_NOTHREAD;
 486                                 lkp->lk_exclusivecount = 0;
 487                         } else {
 488                                 lkp->lk_exclusivecount--;
 489                         }
 490 #ifdef DEBUG_LOCKS
 491                         for (i = 0; i < LOCKMGR_DEBUG_ARRAY_SIZE; i++) {
 492                                 if (td->td_lockmgr_stack[i] == lkp &&
 493                                     td->td_lockmgr_stack_id[i] > 0
 494                                 ) {
 495                                         td->td_lockmgr_stack_id[i]--;
 496                                         break;
 497                                 }
 498                         }
 499 #endif
 500                 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
 501                         dowakeup += shareunlock(lkp, 1);
 502                         COUNT(td, -1);
 503                 }
 504                 if (lkp->lk_flags & LK_WAIT_NONZERO)
 505                         ++dowakeup;
 506                 break;
 507
 508         default:
 509                 spin_unlock(&lkp->lk_spinlock);
 510                 panic("lockmgr: unknown locktype request %d",
 511                     flags & LK_TYPE_MASK);
 512                 /* NOTREACHED */
 513         }
 514         spin_unlock(&lkp->lk_spinlock);
 515         if (dowakeup)
 516                 wakeup(lkp);
 517         return (error);
 518 }
 519
 520 void
 521 lockmgr_kernproc(struct lock *lp)
 522 {
 523         struct thread *td __debugvar = curthread;
 524
 525         if (lp->lk_lockholder != LK_KERNTHREAD) {
 526                 KASSERT(lp->lk_lockholder == td,
 527                     ("lockmgr_kernproc: lock not owned by curthread %p", td));
 528                 COUNT(td, -1);
 529                 lp->lk_lockholder = LK_KERNTHREAD;
 530         }
 531 }
 532
 533 #if 0
 534 /*
 535  * Set the lock to be exclusively held.  The caller is holding the lock's
 536  * spinlock and the spinlock remains held on return.  A panic will occur
 537  * if the lock cannot be set to exclusive.
 538  */
 539 void
 540 lockmgr_setexclusive_interlocked(struct lock *lkp)
 541 {
 542         thread_t td = curthread;
 543
 544         KKASSERT((lkp->lk_flags & (LK_HAVE_EXCL|LK_SHARE_NONZERO)) == 0);
 545         KKASSERT(lkp->lk_exclusivecount == 0);
 546         lkp->lk_flags |= LK_HAVE_EXCL;
 547         lkp->lk_lockholder = td;
 548         lkp->lk_exclusivecount = 1;
 549         COUNT(td, 1);
 550 }
 551
 552 /*
 553  * Clear the caller's exclusive lock.  The caller is holding the lock's
 554  * spinlock.  THIS FUNCTION WILL UNLOCK THE SPINLOCK.
 555  *
 556  * A panic will occur if the caller does not hold the lock.
 557  */
 558 void
 559 lockmgr_clrexclusive_interlocked(struct lock *lkp)
 560 {
 561         thread_t td __debugvar = curthread;
 562         int dowakeup = 0;
 563
 564         KKASSERT((lkp->lk_flags & LK_HAVE_EXCL) && lkp->lk_exclusivecount == 1
 565                  && lkp->lk_lockholder == td);
 566         lkp->lk_lockholder = LK_NOTHREAD;
 567         lkp->lk_flags &= ~LK_HAVE_EXCL;
 568         lkp->lk_exclusivecount = 0;
 569         if (lkp->lk_flags & LK_WAIT_NONZERO)
 570                 dowakeup = 1;
 571         COUNT(td, -1);
 572         spin_unlock(&lkp->lk_spinlock);
 573         if (dowakeup)
 574                 wakeup((void *)lkp);
 575 }
 576
 577 #endif
 578
 579 /*
 580  * Initialize a lock; required before use.
 581  */
 582 void
 583 lockinit(struct lock *lkp, char *wmesg, int timo, int flags)
 584 {
 585         spin_init(&lkp->lk_spinlock);
 586         lkp->lk_flags = (flags & LK_EXTFLG_MASK);
 587         lkp->lk_sharecount = 0;
 588         lkp->lk_waitcount = 0;
 589         lkp->lk_exclusivecount = 0;
 590         lkp->lk_wmesg = wmesg;
 591         lkp->lk_timo = timo;
 592         lkp->lk_lockholder = LK_NOTHREAD;
 593 }
 594
 595 /*
 596  * Reinitialize a lock that is being reused for a different purpose, but
 597  * which may have pending (blocked) threads sitting on it.  The caller
 598  * must already hold the interlock.
 599  */
 600 void
 601 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags)
 602 {
 603         spin_lock(&lkp->lk_spinlock);
 604         lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) |
 605                         (flags & LK_EXTFLG_MASK);
 606         lkp->lk_wmesg = wmesg;
 607         lkp->lk_timo = timo;
 608         spin_unlock(&lkp->lk_spinlock);
 609 }
 610
 611 /*
 612  * Requires that the caller is the exclusive owner of this lock.
 613  */
 614 void
 615 lockuninit(struct lock *l)
 616 {
 617         /*
 618          * At this point we should have removed all the references to this lock
 619          * so there can't be anyone waiting on it.
 620          */
 621         KKASSERT(l->lk_waitcount == 0);
 622
 623         spin_uninit(&l->lk_spinlock);
 624 }
 625
 626 /*
 627  * Determine the status of a lock.
 628  */
 629 int
 630 lockstatus(struct lock *lkp, struct thread *td)
 631 {
 632         int lock_type = 0;
 633
 634         spin_lock(&lkp->lk_spinlock);
 635         if (lkp->lk_exclusivecount != 0) {
 636                 if (td == NULL || lkp->lk_lockholder == td)
 637                         lock_type = LK_EXCLUSIVE;
 638                 else
 639                         lock_type = LK_EXCLOTHER;
 640         } else if (lkp->lk_sharecount != 0) {
 641                 lock_type = LK_SHARED;
 642         }
 643         spin_unlock(&lkp->lk_spinlock);
 644         return (lock_type);
 645 }
 646
 647 /*
 648  * Return non-zero if the caller owns the lock shared or exclusive.
 649  * We can only guess re: shared locks.
 650  */
 651 int
 652 lockowned(struct lock *lkp)
 653 {
 654         thread_t td = curthread;
 655
 656         if (lkp->lk_exclusivecount)
 657                 return(lkp->lk_lockholder == td);
 658         return(lkp->lk_sharecount != 0);
 659 }
 660
 661 /*
 662  * Determine the number of holders of a lock.
 663  *
 664  * The non-blocking version can usually be used for assertions.
 665  */
 666 int
 667 lockcount(struct lock *lkp)
 668 {
 669         int count;
 670
 671         spin_lock(&lkp->lk_spinlock);
 672         count = lkp->lk_exclusivecount + lkp->lk_sharecount;
 673         spin_unlock(&lkp->lk_spinlock);
 674         return (count);
 675 }
 676
 677 int
 678 lockcountnb(struct lock *lkp)
 679 {
 680         return (lkp->lk_exclusivecount + lkp->lk_sharecount);
 681 }
 682
 683 /*
 684  * Print out information about state of a lock. Used by VOP_PRINT
 685  * routines to display status about contained locks.
 686  */
 687 void
 688 lockmgr_printinfo(struct lock *lkp)
 689 {
 690         struct thread *td = lkp->lk_lockholder;
 691         struct proc *p;
 692
 693         if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
 694                 p = td->td_proc;
 695         else
 696                 p = NULL;
 697
 698         if (lkp->lk_sharecount)
 699                 kprintf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
 700                     lkp->lk_sharecount);
 701         else if (lkp->lk_flags & LK_HAVE_EXCL)
 702                 kprintf(" lock type %s: EXCL (count %d) by td %p pid %d",
 703                     lkp->lk_wmesg, lkp->lk_exclusivecount, td,
 704                     p ? p->p_pid : -99);
 705         if (lkp->lk_waitcount > 0)
 706                 kprintf(" with %d pending", lkp->lk_waitcount);
 707 }
 708