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 1.16 2006/03/02 19:07:59 dillon 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 static int acquiredrain(struct lock *lkp, int extflags) ;
  88
  89 static LOCK_INLINE void
  90 sharelock(struct lock *lkp, int incr) {
  91         lkp->lk_flags |= LK_SHARE_NONZERO;
  92         lkp->lk_sharecount += incr;
  93 }
  94
  95 static LOCK_INLINE void
  96 shareunlock(struct lock *lkp, int decr) {
  97
  98         KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
  99
 100         if (lkp->lk_sharecount == decr) {
 101                 lkp->lk_flags &= ~LK_SHARE_NONZERO;
 102                 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
 103                         wakeup(lkp);
 104                 }
 105                 lkp->lk_sharecount = 0;
 106         } else {
 107                 lkp->lk_sharecount -= decr;
 108         }
 109 }
 110
 111 /*
 112  * lock acquisition helper routine.  Called with the lock's spinlock held.
 113  */
 114 static int
 115 acquire(struct lock *lkp, int extflags, int wanted)
 116 {
 117         int error;
 118
 119         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
 120                 return EBUSY;
 121         }
 122
 123         if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
 124                 if ((lkp->lk_flags & wanted) == 0)
 125                         return 0;
 126         }
 127
 128         while ((lkp->lk_flags & wanted) != 0) {
 129                 lkp->lk_flags |= LK_WAIT_NONZERO;
 130                 lkp->lk_waitcount++;
 131
 132                 /*
 133                  * Use the _quick version so the critical section is left
 134                  * intact, protecting the tsleep interlock.  See
 135                  * tsleep_interlock() for a description of what is
 136                  * happening here.
 137                  */
 138                 tsleep_interlock(lkp);
 139                 spin_unlock_quick(&lkp->lk_spinlock);
 140                 error = tsleep(lkp,
 141                                ((extflags & LK_PCATCH) ? PCATCH : 0),
 142                                lkp->lk_wmesg,
 143                                ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
 144                 spin_lock_quick(&lkp->lk_spinlock);
 145                 if (lkp->lk_waitcount == 1) {
 146                         lkp->lk_flags &= ~LK_WAIT_NONZERO;
 147                         lkp->lk_waitcount = 0;
 148                 } else {
 149                         lkp->lk_waitcount--;
 150                 }
 151                 if (error)
 152                         return error;
 153                 if (extflags & LK_SLEEPFAIL)
 154                         return ENOLCK;
 155         }
 156         return 0;
 157 }
 158
 159 /*
 160  * Set, change, or release a lock.
 161  *
 162  * Shared requests increment the shared count. Exclusive requests set the
 163  * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
 164  * accepted shared locks and shared-to-exclusive upgrades to go away.
 165  *
 166  * A spinlock is held for most of the procedure.  We must not do anything
 167  * fancy while holding the spinlock.
 168  */
 169 int
 170 #ifndef DEBUG_LOCKS
 171 lockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp,
 172         struct thread *td)
 173 #else
 174 debuglockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp,
 175         struct thread *td, const char *name, const char *file, int line)
 176 #endif
 177 {
 178         int error;
 179         int extflags;
 180         static int didpanic;
 181
 182         error = 0;
 183
 184         if (lockmgr_from_int && mycpu->gd_intr_nesting_level &&
 185             (flags & LK_NOWAIT) == 0 &&
 186             (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) {
 187 #ifndef DEBUG_LOCKS
 188                     if (lockmgr_from_int == 2) {
 189                             didpanic = 1;
 190                             if (flags & LK_INTERLOCK)
 191                                     spin_unlock(interlkp);
 192                             panic(
 193                                 "lockmgr %s from %p: called from interrupt",
 194                                 lkp->lk_wmesg, ((int **)&lkp)[-1]);
 195                             didpanic = 0;
 196                     } else {
 197                             printf(
 198                                 "lockmgr %s from %p: called from interrupt\n",
 199                                 lkp->lk_wmesg, ((int **)&lkp)[-1]);
 200                     }
 201 #else
 202                     if (lockmgr_from_int == 2) {
 203                             didpanic = 1;
 204                             if (flags & LK_INTERLOCK)
 205                                     spin_unlock(interlkp);
 206                             panic(
 207                                 "lockmgr %s from %s:%d: called from interrupt",
 208                                 lkp->lk_wmesg, file, line);
 209                             didpanic = 0;
 210                     } else {
 211                             printf(
 212                                 "lockmgr %s from %s:%d: called from interrupt\n",
 213                                 lkp->lk_wmesg, file, line);
 214                     }
 215 #endif
 216         }
 217
 218         spin_lock(&lkp->lk_spinlock);
 219         if (flags & LK_INTERLOCK)
 220                 spin_unlock(interlkp);
 221
 222         extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
 223
 224         switch (flags & LK_TYPE_MASK) {
 225         case LK_SHARED:
 226                 /*
 227                  * If we are not the exclusive lock holder, we have to block
 228                  * while there is an exclusive lock holder or while an
 229                  * exclusive lock request or upgrade request is in progress.
 230                  *
 231                  * However, if P_DEADLKTREAT is set, we override exclusive
 232                  * lock requests or upgrade requests ( but not the exclusive
 233                  * lock itself ).
 234                  */
 235                 if (lkp->lk_lockholder != td) {
 236                         if (td->td_flags & TDF_DEADLKTREAT) {
 237                                 error = acquire(
 238                                             lkp,
 239                                             extflags,
 240                                             LK_HAVE_EXCL
 241                                         );
 242                         } else {
 243                                 error = acquire(
 244                                             lkp,
 245                                             extflags,
 246                                             LK_HAVE_EXCL | LK_WANT_EXCL |
 247                                              LK_WANT_UPGRADE
 248                                         );
 249                         }
 250                         if (error)
 251                                 break;
 252                         sharelock(lkp, 1);
 253                         COUNT(td, 1);
 254                         break;
 255                 }
 256                 /*
 257                  * We hold an exclusive lock, so downgrade it to shared.
 258                  * An alternative would be to fail with EDEADLK.
 259                  */
 260                 sharelock(lkp, 1);
 261                 COUNT(td, 1);
 262                 /* fall into downgrade */
 263
 264         case LK_DOWNGRADE:
 265                 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) {
 266                         spin_unlock(&lkp->lk_spinlock);
 267                         panic("lockmgr: not holding exclusive lock");
 268                 }
 269                 sharelock(lkp, lkp->lk_exclusivecount);
 270                 lkp->lk_exclusivecount = 0;
 271                 lkp->lk_flags &= ~LK_HAVE_EXCL;
 272                 lkp->lk_lockholder = LK_NOTHREAD;
 273                 if (lkp->lk_waitcount)
 274                         wakeup((void *)lkp);
 275                 break;
 276
 277         case LK_EXCLUPGRADE:
 278                 /*
 279                  * If another process is ahead of us to get an upgrade,
 280                  * then we want to fail rather than have an intervening
 281                  * exclusive access.
 282                  */
 283                 if (lkp->lk_flags & LK_WANT_UPGRADE) {
 284                         shareunlock(lkp, 1);
 285                         COUNT(td, -1);
 286                         error = EBUSY;
 287                         break;
 288                 }
 289                 /* fall into normal upgrade */
 290
 291         case LK_UPGRADE:
 292                 /*
 293                  * Upgrade a shared lock to an exclusive one. If another
 294                  * shared lock has already requested an upgrade to an
 295                  * exclusive lock, our shared lock is released and an
 296                  * exclusive lock is requested (which will be granted
 297                  * after the upgrade). If we return an error, the file
 298                  * will always be unlocked.
 299                  */
 300                 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) {
 301                         spin_unlock(&lkp->lk_spinlock);
 302                         panic("lockmgr: upgrade exclusive lock");
 303                 }
 304                 shareunlock(lkp, 1);
 305                 COUNT(td, -1);
 306                 /*
 307                  * If we are just polling, check to see if we will block.
 308                  */
 309                 if ((extflags & LK_NOWAIT) &&
 310                     ((lkp->lk_flags & LK_WANT_UPGRADE) ||
 311                      lkp->lk_sharecount > 1)) {
 312                         error = EBUSY;
 313                         break;
 314                 }
 315                 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
 316                         /*
 317                          * We are first shared lock to request an upgrade, so
 318                          * request upgrade and wait for the shared count to
 319                          * drop to zero, then take exclusive lock.
 320                          */
 321                         lkp->lk_flags |= LK_WANT_UPGRADE;
 322                         error = acquire(lkp, extflags, LK_SHARE_NONZERO);
 323                         lkp->lk_flags &= ~LK_WANT_UPGRADE;
 324
 325                         if (error)
 326                                 break;
 327                         lkp->lk_flags |= LK_HAVE_EXCL;
 328                         lkp->lk_lockholder = td;
 329                         if (lkp->lk_exclusivecount != 0) {
 330                                 spin_unlock(&lkp->lk_spinlock);
 331                                 panic("lockmgr: non-zero exclusive count");
 332                         }
 333                         lkp->lk_exclusivecount = 1;
 334 #if defined(DEBUG_LOCKS)
 335                         lkp->lk_filename = file;
 336                         lkp->lk_lineno = line;
 337                         lkp->lk_lockername = name;
 338 #endif
 339                         COUNT(td, 1);
 340                         break;
 341                 }
 342                 /*
 343                  * Someone else has requested upgrade. Release our shared
 344                  * lock, awaken upgrade requestor if we are the last shared
 345                  * lock, then request an exclusive lock.
 346                  */
 347                 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
 348                         LK_WAIT_NONZERO)
 349                         wakeup((void *)lkp);
 350                 /* fall into exclusive request */
 351
 352         case LK_EXCLUSIVE:
 353                 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) {
 354                         /*
 355                          *      Recursive lock.
 356                          */
 357                         if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) {
 358                                 spin_unlock(&lkp->lk_spinlock);
 359                                 panic("lockmgr: locking against myself");
 360                         }
 361                         if ((extflags & LK_CANRECURSE) != 0) {
 362                                 lkp->lk_exclusivecount++;
 363                                 COUNT(td, 1);
 364                                 break;
 365                         }
 366                 }
 367                 /*
 368                  * If we are just polling, check to see if we will sleep.
 369                  */
 370                 if ((extflags & LK_NOWAIT) &&
 371                     (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
 372                         error = EBUSY;
 373                         break;
 374                 }
 375                 /*
 376                  * Try to acquire the want_exclusive flag.
 377                  */
 378                 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
 379                 if (error)
 380                         break;
 381                 lkp->lk_flags |= LK_WANT_EXCL;
 382                 /*
 383                  * Wait for shared locks and upgrades to finish.
 384                  */
 385                 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
 386                 lkp->lk_flags &= ~LK_WANT_EXCL;
 387                 if (error)
 388                         break;
 389                 lkp->lk_flags |= LK_HAVE_EXCL;
 390                 lkp->lk_lockholder = td;
 391                 if (lkp->lk_exclusivecount != 0) {
 392                         spin_unlock(&lkp->lk_spinlock);
 393                         panic("lockmgr: non-zero exclusive count");
 394                 }
 395                 lkp->lk_exclusivecount = 1;
 396 #if defined(DEBUG_LOCKS)
 397                         lkp->lk_filename = file;
 398                         lkp->lk_lineno = line;
 399                         lkp->lk_lockername = name;
 400 #endif
 401                 COUNT(td, 1);
 402                 break;
 403
 404         case LK_RELEASE:
 405                 if (lkp->lk_exclusivecount != 0) {
 406                         if (lkp->lk_lockholder != td &&
 407                             lkp->lk_lockholder != LK_KERNTHREAD) {
 408                                 spin_unlock(&lkp->lk_spinlock);
 409                                 panic("lockmgr: pid %d, not %s thr %p unlocking",
 410                                     (td->td_proc ? td->td_proc->p_pid : -99),
 411                                     "exclusive lock holder",
 412                                     lkp->lk_lockholder);
 413                         }
 414                         if (lkp->lk_lockholder != LK_KERNTHREAD) {
 415                                 COUNT(td, -1);
 416                         }
 417                         if (lkp->lk_exclusivecount == 1) {
 418                                 lkp->lk_flags &= ~LK_HAVE_EXCL;
 419                                 lkp->lk_lockholder = LK_NOTHREAD;
 420                                 lkp->lk_exclusivecount = 0;
 421                         } else {
 422                                 lkp->lk_exclusivecount--;
 423                         }
 424                 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
 425                         shareunlock(lkp, 1);
 426                         COUNT(td, -1);
 427                 }
 428                 if (lkp->lk_flags & LK_WAIT_NONZERO)
 429                         wakeup((void *)lkp);
 430                 break;
 431
 432         case LK_DRAIN:
 433                 /*
 434                  * Check that we do not already hold the lock, as it can
 435                  * never drain if we do. Unfortunately, we have no way to
 436                  * check for holding a shared lock, but at least we can
 437                  * check for an exclusive one.
 438                  */
 439                 if (lkp->lk_lockholder == td) {
 440                         spin_unlock(&lkp->lk_spinlock);
 441                         panic("lockmgr: draining against myself");
 442                 }
 443
 444                 error = acquiredrain(lkp, extflags);
 445                 if (error)
 446                         break;
 447                 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
 448                 lkp->lk_lockholder = td;
 449                 lkp->lk_exclusivecount = 1;
 450 #if defined(DEBUG_LOCKS)
 451                         lkp->lk_filename = file;
 452                         lkp->lk_lineno = line;
 453                         lkp->lk_lockername = name;
 454 #endif
 455                 COUNT(td, 1);
 456                 break;
 457
 458         default:
 459                 spin_unlock(&lkp->lk_spinlock);
 460                 panic("lockmgr: unknown locktype request %d",
 461                     flags & LK_TYPE_MASK);
 462                 /* NOTREACHED */
 463         }
 464         if ((lkp->lk_flags & LK_WAITDRAIN) &&
 465             (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
 466                 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
 467                 lkp->lk_flags &= ~LK_WAITDRAIN;
 468                 wakeup((void *)&lkp->lk_flags);
 469         }
 470         spin_unlock(&lkp->lk_spinlock);
 471         return (error);
 472 }
 473
 474 /*
 475  * lock acquisition helper routine.  Called with the lock's spinlock held.
 476  */
 477 static int
 478 acquiredrain(struct lock *lkp, int extflags)
 479 {
 480         int error;
 481
 482         if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
 483                 return EBUSY;
 484         }
 485
 486         if ((lkp->lk_flags & LK_ALL) == 0)
 487                 return 0;
 488
 489         while (lkp->lk_flags & LK_ALL) {
 490                 lkp->lk_flags |= LK_WAITDRAIN;
 491                 /*
 492                  * Use the _quick version so the critical section is left
 493                  * intact, protecting the tsleep interlock.  See
 494                  * tsleep_interlock() for a description of what is
 495                  * happening here.
 496                  */
 497                 tsleep_interlock(&lkp->lk_flags);
 498                 spin_unlock_quick(&lkp->lk_spinlock);
 499                 error = tsleep(&lkp->lk_flags,
 500                                ((extflags & LK_PCATCH) ? PCATCH : 0),
 501                                lkp->lk_wmesg,
 502                                ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
 503                 spin_lock_quick(&lkp->lk_spinlock);
 504                 if (error)
 505                         return error;
 506                 if (extflags & LK_SLEEPFAIL) {
 507                         return ENOLCK;
 508                 }
 509         }
 510         return 0;
 511 }
 512
 513 /*
 514  * Initialize a lock; required before use.
 515  */
 516 void
 517 lockinit(struct lock *lkp, char *wmesg, int timo, int flags)
 518 {
 519         spin_init(&lkp->lk_spinlock);
 520         lkp->lk_flags = (flags & LK_EXTFLG_MASK);
 521         lkp->lk_sharecount = 0;
 522         lkp->lk_waitcount = 0;
 523         lkp->lk_exclusivecount = 0;
 524         lkp->lk_wmesg = wmesg;
 525         lkp->lk_timo = timo;
 526         lkp->lk_lockholder = LK_NOTHREAD;
 527 }
 528
 529 /*
 530  * Reinitialize a lock that is being reused for a different purpose, but
 531  * which may have pending (blocked) threads sitting on it.  The caller
 532  * must already hold the interlock.
 533  */
 534 void
 535 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags)
 536 {
 537         lkp->lk_flags = (lkp->lk_flags & ~(LK_EXTFLG_MASK|LK_DRAINING)) |
 538                         (flags & LK_EXTFLG_MASK);
 539         lkp->lk_wmesg = wmesg;
 540         lkp->lk_timo = timo;
 541 }
 542
 543 /*
 544  * Determine the status of a lock.
 545  */
 546 int
 547 lockstatus(struct lock *lkp, struct thread *td)
 548 {
 549         int lock_type = 0;
 550
 551         spin_lock(&lkp->lk_spinlock);
 552         if (lkp->lk_exclusivecount != 0) {
 553                 if (td == NULL || lkp->lk_lockholder == td)
 554                         lock_type = LK_EXCLUSIVE;
 555                 else
 556                         lock_type = LK_EXCLOTHER;
 557         } else if (lkp->lk_sharecount != 0) {
 558                 lock_type = LK_SHARED;
 559         }
 560         spin_unlock(&lkp->lk_spinlock);
 561         return (lock_type);
 562 }
 563
 564 /*
 565  * Determine the number of holders of a lock.
 566  *
 567  * The non-blocking version can usually be used for assertions.
 568  */
 569 int
 570 lockcount(struct lock *lkp)
 571 {
 572         int count;
 573
 574         spin_lock(&lkp->lk_spinlock);
 575         count = lkp->lk_exclusivecount + lkp->lk_sharecount;
 576         spin_unlock(&lkp->lk_spinlock);
 577         return (count);
 578 }
 579
 580 int
 581 lockcountnb(struct lock *lkp)
 582 {
 583         return (lkp->lk_exclusivecount + lkp->lk_sharecount);
 584 }
 585
 586 /*
 587  * Print out information about state of a lock. Used by VOP_PRINT
 588  * routines to display status about contained locks.
 589  */
 590 void
 591 lockmgr_printinfo(struct lock *lkp)
 592 {
 593         struct thread *td = lkp->lk_lockholder;
 594         struct proc *p;
 595
 596         if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD)
 597                 p = td->td_proc;
 598         else
 599                 p = NULL;
 600
 601         if (lkp->lk_sharecount)
 602                 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
 603                     lkp->lk_sharecount);
 604         else if (lkp->lk_flags & LK_HAVE_EXCL)
 605                 printf(" lock type %s: EXCL (count %d) by td %p pid %d",
 606                     lkp->lk_wmesg, lkp->lk_exclusivecount, td,
 607                     p ? p->p_pid : -99);
 608         if (lkp->lk_waitcount > 0)
 609                 printf(" with %d pending", lkp->lk_waitcount);
 610 }
 611