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  * 0: no warnings, 1: warnings, 2: panic
  59  */
  60 static int lockmgr_from_int = 1;
  61 SYSCTL_INT(_debug, OID_AUTO, lockmgr_from_int, CTLFLAG_RW, &lockmgr_from_int, 0, "");
  62
  63 /*
  64  * Locking primitives implementation.
  65  * Locks provide shared/exclusive sychronization.
  66  */
  67
  68 #ifdef SIMPLELOCK_DEBUG
  69 #define COUNT(td, x) (td)->td_locks += (x)
  70 #else
  71 #define COUNT(td, x)
  72 #endif
  73
  74 #define LOCK_WAIT_TIME 100
  75 #define LOCK_SAMPLE_WAIT 7
  76
  77 #if defined(DIAGNOSTIC)
  78 #define LOCK_INLINE
  79 #else
  80 #define LOCK_INLINE __inline
  81 #endif
  82
  83 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
  84         LK_SHARE_NONZERO | LK_WAIT_NONZERO)
  85
  86 static int acquire(struct lock *lkp, int extflags, int wanted);
  87
  88 static LOCK_INLINE void
  89 sharelock(struct lock *lkp, int incr) {
  90         lkp->lk_flags |= LK_SHARE_NONZERO;
  91         lkp->lk_sharecount += incr;
  92 }
  93
  94 static LOCK_INLINE int
  95 shareunlock(struct lock *lkp, int decr)
  96 {
  97         int dowakeup = 0;
  98
  99         KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
 100
 101         if (lkp->lk_sharecount == decr) {
 102                 lkp->lk_flags &= ~LK_SHARE_NONZERO;
 103                 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
 104                         dowakeup = 1;
 105                 }
 106                 lkp->lk_sharecount = 0;
 107         } else {
 108                 lkp->lk_sharecount -= decr;
 109         }
 110         return(dowakeup);
 111 }
 112
 113 /*
 114  * lock acquisition helper routine.  Called with the lock's spinlock held.
 115  */
 116 static int
 117 acquire(struct lock *lkp, int extflags, int wanted)
 118 {
 119         int error;
 120
 121         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
 122                 return EBUSY;
 123         }
 124
 125         while ((lkp->lk_flags & wanted) != 0) {
 126                 lkp->lk_flags |= LK_WAIT_NONZERO;
 127                 lkp->lk_waitcount++;
 128
 129                 /*
 130                  * Atomic spinlock release/sleep/reacquire.
 131                  */
 132                 error = msleep(lkp, &lkp->lk_spinlock,
 133                                ((extflags & LK_PCATCH) ? PCATCH : 0),
 134                                lkp->lk_wmesg,
 135                                ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
 136                 if (lkp->lk_waitcount == 1) {
 137                         lkp->lk_flags &= ~LK_WAIT_NONZERO;
 138                         lkp->lk_waitcount = 0;
 139                 } else {
 140                         lkp->lk_waitcount--;
 141                 }
 142                 if (error)
 143                         return error;
 144                 if (extflags & LK_SLEEPFAIL)
 145                         return ENOLCK;
 146         }
 147         return 0;
 148 }
 149
 150 /*
 151  * Set, change, or release a lock.
 152  *
 153  * Shared requests increment the shared count. Exclusive requests set the
 154  * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
 155  * accepted shared locks and shared-to-exclusive upgrades to go away.
 156  *
 157  * A spinlock is held for most of the procedure.  We must not do anything
 158  * fancy while holding the spinlock.
 159  */
 160 int
 161 #ifndef DEBUG_LOCKS
 162 lockmgr(struct lock *lkp, u_int flags)
 163 #else
 164 debuglockmgr(struct lock *lkp, u_int flags,
 165              const char *name, const char *file, int line)
 166 #endif
 167 {
 168         thread_t td;
 169         int error;
 170         int extflags;
 171         int dowakeup;
 172         static int didpanic;
 173
 174         error = 0;
 175         dowakeup = 0;
 176
 177         if (lockmgr_from_int && mycpu->gd_intr_nesting_level &&
 178             (flags & LK_NOWAIT) == 0 &&
 179             (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) {
 180 #ifndef DEBUG_LOCKS
 181                     if (lockmgr_from_int == 2) {
 182                             didpanic = 1;
 183                             panic(
 184                                 "lockmgr %s from %p: called from interrupt",
 185                                 lkp->lk_wmesg, ((int **)&lkp)[-1]);
 186                             didpanic = 0;
 187                     } else {
 188                             kprintf(
 189                                 "lockmgr %s from %p: called from interrupt\n",
 190                                 lkp->lk_wmesg, ((int **)&lkp)[-1]);
 191                     }
 192 #else
 193                     if (lockmgr_from_int == 2) {
 194                             didpanic = 1;
 195                             panic(
 196                                 "lockmgr %s from %s:%d: called from interrupt",
 197                                 lkp->lk_wmesg, file, line);
 198                             didpanic = 0;
 199                     } else {
 200                             kprintf(
 201                                 "lockmgr %s from %s:%d: called from interrupt\n",
 202                                 lkp->lk_wmesg, file, line);
 203                     }
 204 #endif
 205         }
 206
 207         spin_lock_wr(&lkp->lk_spinlock);
 208
 209         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 210         td = curthread;
 211
 212         switch (flags & LK_TYPE_MASK) {
 213         case LK_SHARED:
 214                 /*
 215                  * If we are not the exclusive lock holder, we have to block
 216                  * while there is an exclusive lock holder or while an
 217                  * exclusive lock request or upgrade request is in progress.
 218                  *
 219                  * However, if P_DEADLKTREAT is set, we override exclusive
 220                  * lock requests or upgrade requests ( but not the exclusive
 221                  * lock itself ).
 222                  */
 223                 if (lkp->lk_lockholder != td) {
 224                         if (td->td_flags & TDF_DEADLKTREAT) {
 225                                 error = acquire(
 226                                             lkp,
 227                                             extflags,
 228                                             LK_HAVE_EXCL
 229                                         );
 230                         } else {
 231                                 error = acquire(
 232                                             lkp,
 233                                             extflags,
 234                                             LK_HAVE_EXCL | LK_WANT_EXCL |
 235                                              LK_WANT_UPGRADE
 236                                         );
 237                         }
 238                         if (error)
 239                                 break;
 240                         sharelock(lkp, 1);
 241                         COUNT(td, 1);
 242                         break;
 243                 }
 244                 /*
 245                  * We hold an exclusive lock, so downgrade it to shared.
 246                  * An alternative would be to fail with EDEADLK.
 247                  */
 248                 sharelock(lkp, 1);
 249                 COUNT(td, 1);
 250                 /* fall into downgrade */
 251
 252         case LK_DOWNGRADE:
 253                 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) {
 254                         spin_unlock_wr(&lkp->lk_spinlock);
 255                         panic("lockmgr: not holding exclusive lock");
 256                 }
 257                 sharelock(lkp, lkp->lk_exclusivecount);
 258                 lkp->lk_exclusivecount = 0;
 259                 lkp->lk_flags &= ~LK_HAVE_EXCL;
 260                 lkp->lk_lockholder = LK_NOTHREAD;
 261                 if (lkp->lk_waitcount)
 262                         dowakeup = 1;
 263                 break;
 264
 265         case LK_EXCLUPGRADE:
 266                 /*
 267                  * If another process is ahead of us to get an upgrade,
 268                  * then we want to fail rather than have an intervening
 269                  * exclusive access.
 270                  */
 271                 if (lkp->lk_flags & LK_WANT_UPGRADE) {
 272                         dowakeup = shareunlock(lkp, 1);
 273                         COUNT(td, -1);
 274                         error = EBUSY;
 275                         break;
 276                 }
 277                 /* fall into normal upgrade */
 278
 279         case LK_UPGRADE:
 280                 /*
 281                  * Upgrade a shared lock to an exclusive one. If another
 282                  * shared lock has already requested an upgrade to an
 283                  * exclusive lock, our shared lock is released and an
 284                  * exclusive lock is requested (which will be granted
 285                  * after the upgrade). If we return an error, the file
 286                  * will always be unlocked.
 287                  */
 288                 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) {
 289                         spin_unlock_wr(&lkp->lk_spinlock);
 290                         panic("lockmgr: upgrade exclusive lock");
 291                 }
 292                 dowakeup += shareunlock(lkp, 1);
 293                 COUNT(td, -1);
 294                 /*
 295                  * If we are just polling, check to see if we will block.
 296                  */
 297                 if ((extflags & LK_NOWAIT) &&
 298                     ((lkp->lk_flags & LK_WANT_UPGRADE) ||
 299                      lkp->lk_sharecount > 1)) {
 300                         error = EBUSY;
 301                         break;
 302                 }
 303                 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
 304                         /*
 305                          * We are first shared lock to request an upgrade, so
 306                          * request upgrade and wait for the shared count to
 307                          * drop to zero, then take exclusive lock.
 308                          */
 309                         lkp->lk_flags |= LK_WANT_UPGRADE;
 310                         error = acquire(lkp, extflags, LK_SHARE_NONZERO);
 311                         lkp->lk_flags &= ~LK_WANT_UPGRADE;
 312
 313                         if (error)
 314                                 break;
 315                         lkp->lk_flags |= LK_HAVE_EXCL;
 316                         lkp->lk_lockholder = td;
 317                         if (lkp->lk_exclusivecount != 0) {
 318                                 spin_unlock_wr(&lkp->lk_spinlock);
 319                                 panic("lockmgr: non-zero exclusive count");
 320                         }
 321                         lkp->lk_exclusivecount = 1;
 322 #if defined(DEBUG_LOCKS)
 323                         lkp->lk_filename = file;
 324                         lkp->lk_lineno = line;
 325                         lkp->lk_lockername = name;
 326 #endif
 327                         COUNT(td, 1);
 328                         break;
 329                 }
 330                 /*
 331                  * Someone else has requested upgrade. Release our shared
 332                  * lock, awaken upgrade requestor if we are the last shared
 333                  * lock, then request an exclusive lock.
 334                  */
 335                 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
 336                         LK_WAIT_NONZERO) {
 337                         ++dowakeup;
 338                 }
 339                 /* fall into exclusive request */
 340
 341         case LK_EXCLUSIVE:
 342                 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
 343                         /*
 344                          *      Recursive lock.
 345                          */
 346                         if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) {
 347                                 spin_unlock_wr(&lkp->lk_spinlock);
 348                                 panic("lockmgr: locking against myself");
 349                         }
 350                         if ((extflags & LK_CANRECURSE) != 0) {
 351                                 lkp->lk_exclusivecount++;
 352                                 COUNT(td, 1);
 353                                 break;
 354                         }
 355                 }
 356                 /*
 357                  * If we are just polling, check to see if we will sleep.
 358                  */
 359                 if ((extflags & LK_NOWAIT) &&
 360                     (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
 361                         error = EBUSY;
 362                         break;
 363                 }
 364                 /*
 365                  * Try to acquire the want_exclusive flag.
 366                  */
 367                 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
 368                 if (error)
 369                         break;
 370                 lkp->lk_flags |= LK_WANT_EXCL;
 371                 /*
 372                  * Wait for shared locks and upgrades to finish.
 373                  */
 374                 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
 375                 lkp->lk_flags &= ~LK_WANT_EXCL;
 376                 if (error)
 377                         break;
 378                 lkp->lk_flags |= LK_HAVE_EXCL;
 379                 lkp->lk_lockholder = td;
 380                 if (lkp->lk_exclusivecount != 0) {
 381                         spin_unlock_wr(&lkp->lk_spinlock);
 382                         panic("lockmgr: non-zero exclusive count");
 383                 }
 384                 lkp->lk_exclusivecount = 1;
 385 #if defined(DEBUG_LOCKS)
 386                         lkp->lk_filename = file;
 387                         lkp->lk_lineno = line;
 388                         lkp->lk_lockername = name;
 389 #endif
 390                 COUNT(td, 1);
 391                 break;
 392
 393         case LK_RELEASE:
 394                 if (lkp->lk_exclusivecount != 0) {
 395                         if (lkp->lk_lockholder != td &&
 396                             lkp->lk_lockholder != LK_KERNTHREAD) {
 397                                 spin_unlock_wr(&lkp->lk_spinlock);
 398                                 panic("lockmgr: pid %d, not %s thr %p unlocking",
 399                                     (td->td_proc ? td->td_proc->p_pid : -99),
 400                                     "exclusive lock holder",
 401                                     lkp->lk_lockholder);
 402                         }
 403                         if (lkp->lk_lockholder != LK_KERNTHREAD) {
 404                                 COUNT(td, -1);
 405                         }
 406                         if (lkp->lk_exclusivecount == 1) {
 407                                 lkp->lk_flags &= ~LK_HAVE_EXCL;
 408                                 lkp->lk_lockholder = LK_NOTHREAD;
 409                                 lkp->lk_exclusivecount = 0;
 410                         } else {
 411                                 lkp->lk_exclusivecount--;
 412                         }
 413                 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
 414                         dowakeup += shareunlock(lkp, 1);
 415                         COUNT(td, -1);
 416                 }
 417                 if (lkp->lk_flags & LK_WAIT_NONZERO)
 418                         ++dowakeup;
 419                 break;
 420
 421         default:
 422                 spin_unlock_wr(&lkp->lk_spinlock);
 423                 panic("lockmgr: unknown locktype request %d",
 424                     flags & LK_TYPE_MASK);
 425                 /* NOTREACHED */
 426         }
 427         spin_unlock_wr(&lkp->lk_spinlock);
 428         if (dowakeup)
 429                 wakeup(lkp);
 430         return (error);
 431 }
 432
 433 void
 434 lockmgr_kernproc(struct lock *lp)
 435 {
 436         struct thread *td = curthread;
 437
 438         if (lp->lk_lockholder != LK_KERNTHREAD) {
 439                 KASSERT(lp->lk_lockholder == td,
 440                     ("lockmgr_kernproc: lock not owned by curthread %p", td));
 441                 COUNT(td, -1);
 442                 lp->lk_lockholder = LK_KERNTHREAD;
 443         }
 444 }
 445
 446 /*
 447  * Set the lock to be exclusively held.  The caller is holding the lock's
 448  * spinlock and the spinlock remains held on return.  A panic will occur
 449  * if the lock cannot be set to exclusive.
 450  */
 451 void
 452 lockmgr_setexclusive_interlocked(struct lock *lkp)
 453 {
 454         thread_t td = curthread;
 455
 456         KKASSERT((lkp->lk_flags & (LK_HAVE_EXCL|LK_SHARE_NONZERO)) == 0);
 457         KKASSERT(lkp->lk_exclusivecount == 0);
 458         lkp->lk_flags |= LK_HAVE_EXCL;
 459         lkp->lk_lockholder = td;
 460         lkp->lk_exclusivecount = 1;
 461         COUNT(td, 1);
 462 }
 463
 464 /*
 465  * Clear the caller's exclusive lock.  The caller is holding the lock's
 466  * spinlock.  THIS FUNCTION WILL UNLOCK THE SPINLOCK.
 467  *
 468  * A panic will occur if the caller does not hold the lock.
 469  */
 470 void
 471 lockmgr_clrexclusive_interlocked(struct lock *lkp)
 472 {
 473         thread_t td = curthread;
 474         int dowakeup = 0;
 475
 476         KKASSERT((lkp->lk_flags & LK_HAVE_EXCL) && lkp->lk_exclusivecount == 1
 477                  && lkp->lk_lockholder == td);
 478         lkp->lk_lockholder = LK_NOTHREAD;
 479         lkp->lk_flags &= ~LK_HAVE_EXCL;
 480         lkp->lk_exclusivecount = 0;
 481         if (lkp->lk_flags & LK_WAIT_NONZERO)
 482                 dowakeup = 1;
 483         COUNT(td, -1);
 484         spin_unlock_wr(&lkp->lk_spinlock);
 485         if (dowakeup)
 486                 wakeup((void *)lkp);
 487 }
 488
 489 /*
 490  * Initialize a lock; required before use.
 491  */
 492 void
 493 lockinit(struct lock *lkp, char *wmesg, int timo, int flags)
 494 {
 495         spin_init(&lkp->lk_spinlock);
 496         lkp->lk_flags = (flags & LK_EXTFLG_MASK);
 497         lkp->lk_sharecount = 0;
 498         lkp->lk_waitcount = 0;
 499         lkp->lk_exclusivecount = 0;
 500         lkp->lk_wmesg = wmesg;
 501         lkp->lk_timo = timo;
 502         lkp->lk_lockholder = LK_NOTHREAD;
 503 }
 504
 505 /*
 506  * Reinitialize a lock that is being reused for a different purpose, but
 507  * which may have pending (blocked) threads sitting on it.  The caller
 508  * must already hold the interlock.
 509  */
 510 void
 511 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags)
 512 {
 513         spin_lock_wr(&lkp->lk_spinlock);
 514         lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) |
 515                         (flags & LK_EXTFLG_MASK);
 516         lkp->lk_wmesg = wmesg;
 517         lkp->lk_timo = timo;
 518         spin_unlock_wr(&lkp->lk_spinlock);
 519 }
 520
 521 /*
 522  * Requires that the caller is the exclusive owner of this lock.
 523  */
 524 void
 525 lockuninit(struct lock *l)
 526 {
 527         /*
 528          * At this point we should have removed all the references to this lock
 529          * so there can't be anyone waiting on it.
 530          */
 531         KKASSERT(l->lk_waitcount == 0);
 532
 533         spin_uninit(&l->lk_spinlock);
 534 }
 535
 536 /*
 537  * Determine the status of a lock.
 538  */
 539 int
 540 lockstatus(struct lock *lkp, struct thread *td)
 541 {
 542         int lock_type = 0;
 543
 544         spin_lock_wr(&lkp->lk_spinlock);
 545         if (lkp->lk_exclusivecount != 0) {
 546                 if (td == NULL || lkp->lk_lockholder == td)
 547                         lock_type = LK_EXCLUSIVE;
 548                 else
 549                         lock_type = LK_EXCLOTHER;
 550         } else if (lkp->lk_sharecount != 0) {
 551                 lock_type = LK_SHARED;
 552         }
 553         spin_unlock_wr(&lkp->lk_spinlock);
 554         return (lock_type);
 555 }
 556
 557 /*
 558  * Determine the number of holders of a lock.
 559  *
 560  * The non-blocking version can usually be used for assertions.
 561  */
 562 int
 563 lockcount(struct lock *lkp)
 564 {
 565         int count;
 566
 567         spin_lock_wr(&lkp->lk_spinlock);
 568         count = lkp->lk_exclusivecount + lkp->lk_sharecount;
 569         spin_unlock_wr(&lkp->lk_spinlock);
 570         return (count);
 571 }
 572
 573 int
 574 lockcountnb(struct lock *lkp)
 575 {
 576         return (lkp->lk_exclusivecount + lkp->lk_sharecount);
 577 }
 578
 579 /*
 580  * Print out information about state of a lock. Used by VOP_PRINT
 581  * routines to display status about contained locks.
 582  */
 583 void
 584 lockmgr_printinfo(struct lock *lkp)
 585 {
 586         struct thread *td = lkp->lk_lockholder;
 587         struct proc *p;
 588
 589         if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
 590                 p = td->td_proc;
 591         else
 592                 p = NULL;
 593
 594         if (lkp->lk_sharecount)
 595                 kprintf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
 596                     lkp->lk_sharecount);
 597         else if (lkp->lk_flags & LK_HAVE_EXCL)
 598                 kprintf(" lock type %s: EXCL (count %d) by td %p pid %d",
 599                     lkp->lk_wmesg, lkp->lk_exclusivecount, td,
 600                     p ? p->p_pid : -99);
 601         if (lkp->lk_waitcount > 0)
 602                 kprintf(" with %d pending", lkp->lk_waitcount);
 603 }
 604