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 * $Id: kern_lock.c,v 1.24 1999/03/12 03:09:29 julian Exp $ 42 */ 43 44 #include "opt_lint.h" 45 46 #include <sys/param.h> 47 #include <sys/proc.h> 48 #include <sys/lock.h> 49 #include <sys/systm.h> 50 51 /* 52 * Locking primitives implementation. 53 * Locks provide shared/exclusive sychronization. 54 */ 55 56 #ifdef SIMPLELOCK_DEBUG 57 #define COUNT(p, x) if (p) (p)->p_locks += (x) 58 #else 59 #define COUNT(p, x) 60 #endif 61 62 #define LOCK_WAIT_TIME 100 63 #define LOCK_SAMPLE_WAIT 7 64 65 #if defined(DIAGNOSTIC) 66 #define LOCK_INLINE 67 #else 68 #define LOCK_INLINE __inline 69 #endif 70 71 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 72 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 73 74 static int acquire(struct lock *lkp, int extflags, int wanted); 75 static int apause(struct lock *lkp, int flags); 76 static int acquiredrain(struct lock *lkp, int extflags) ; 77 78 static LOCK_INLINE void 79 sharelock(struct lock *lkp, int incr) { 80 lkp->lk_flags |= LK_SHARE_NONZERO; 81 lkp->lk_sharecount += incr; 82 } 83 84 static LOCK_INLINE void 85 shareunlock(struct lock *lkp, int decr) { 86 87 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 88 89 if (lkp->lk_sharecount == decr) { 90 lkp->lk_flags &= ~LK_SHARE_NONZERO; 91 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 92 wakeup(lkp); 93 } 94 lkp->lk_sharecount = 0; 95 } else { 96 lkp->lk_sharecount -= decr; 97 } 98 } 99 100 /* 101 * This is the waitloop optimization, and note for this to work 102 * simple_lock and simple_unlock should be subroutines to avoid 103 * optimization troubles. 104 */ 105 static int 106 apause(struct lock *lkp, int flags) { 107 int lock_wait; 108 lock_wait = LOCK_WAIT_TIME; 109 for (; lock_wait > 0; lock_wait--) { 110 int i; 111 if ((lkp->lk_flags & flags) == 0) 112 return 0; 113 simple_unlock(&lkp->lk_interlock); 114 for (i = LOCK_SAMPLE_WAIT; i > 0; i--) { 115 if ((lkp->lk_flags & flags) == 0) { 116 simple_lock(&lkp->lk_interlock); 117 if ((lkp->lk_flags & flags) == 0) 118 return 0; 119 break; 120 } 121 } 122 } 123 return 1; 124 } 125 126 static int 127 acquire(struct lock *lkp, int extflags, int wanted) { 128 int s, error; 129 130 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 131 return EBUSY; 132 } 133 134 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 135 error = apause(lkp, wanted); 136 if (error == 0) 137 return 0; 138 } 139 140 s = splhigh(); 141 while ((lkp->lk_flags & wanted) != 0) { 142 lkp->lk_flags |= LK_WAIT_NONZERO; 143 lkp->lk_waitcount++; 144 simple_unlock(&lkp->lk_interlock); 145 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo); 146 simple_lock(&lkp->lk_interlock); 147 if (lkp->lk_waitcount == 1) { 148 lkp->lk_flags &= ~LK_WAIT_NONZERO; 149 lkp->lk_waitcount = 0; 150 } else { 151 lkp->lk_waitcount--; 152 } 153 if (error) { 154 splx(s); 155 return error; 156 } 157 if (extflags & LK_SLEEPFAIL) { 158 splx(s); 159 return ENOLCK; 160 } 161 } 162 splx(s); 163 return 0; 164 } 165 166 /* 167 * Set, change, or release a lock. 168 * 169 * Shared requests increment the shared count. Exclusive requests set the 170 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 171 * accepted shared locks and shared-to-exclusive upgrades to go away. 172 */ 173 int 174 #ifndef DEBUG_LOCKS 175 lockmgr(lkp, flags, interlkp, p) 176 #else 177 debuglockmgr(lkp, flags, interlkp, p, name, file, line) 178 #endif 179 struct lock *lkp; 180 u_int flags; 181 struct simplelock *interlkp; 182 struct proc *p; 183 #ifdef DEBUG_LOCKS 184 const char *name; /* Name of lock function */ 185 const char *file; /* Name of file call is from */ 186 int line; /* Line number in file */ 187 #endif 188 { 189 int error; 190 pid_t pid; 191 int extflags; 192 193 error = 0; 194 if (p == NULL) 195 pid = LK_KERNPROC; 196 else 197 pid = p->p_pid; 198 199 simple_lock(&lkp->lk_interlock); 200 if (flags & LK_INTERLOCK) 201 simple_unlock(interlkp); 202 203 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 204 205 switch (flags & LK_TYPE_MASK) { 206 207 case LK_SHARED: 208 /* 209 * If we are not the exclusive lock holder, we have to block 210 * while there is an exclusive lock holder or while an 211 * exclusive lock request or upgrade request is in progress. 212 * 213 * However, if P_DEADLKTREAT is set, we override exclusive 214 * lock requests or upgrade requests ( but not the exclusive 215 * lock itself ). 216 */ 217 if (lkp->lk_lockholder != pid) { 218 if (p && (p->p_flag & P_DEADLKTREAT)) { 219 error = acquire( 220 lkp, 221 extflags, 222 LK_HAVE_EXCL 223 ); 224 } else { 225 error = acquire( 226 lkp, 227 extflags, 228 LK_HAVE_EXCL | LK_WANT_EXCL | 229 LK_WANT_UPGRADE 230 ); 231 } 232 if (error) 233 break; 234 sharelock(lkp, 1); 235 COUNT(p, 1); 236 break; 237 } 238 /* 239 * We hold an exclusive lock, so downgrade it to shared. 240 * An alternative would be to fail with EDEADLK. 241 */ 242 sharelock(lkp, 1); 243 COUNT(p, 1); 244 /* fall into downgrade */ 245 246 case LK_DOWNGRADE: 247 #if !defined(MAX_PERF) 248 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 249 panic("lockmgr: not holding exclusive lock"); 250 #endif 251 sharelock(lkp, lkp->lk_exclusivecount); 252 lkp->lk_exclusivecount = 0; 253 lkp->lk_flags &= ~LK_HAVE_EXCL; 254 lkp->lk_lockholder = LK_NOPROC; 255 if (lkp->lk_waitcount) 256 wakeup((void *)lkp); 257 break; 258 259 case LK_EXCLUPGRADE: 260 /* 261 * If another process is ahead of us to get an upgrade, 262 * then we want to fail rather than have an intervening 263 * exclusive access. 264 */ 265 if (lkp->lk_flags & LK_WANT_UPGRADE) { 266 shareunlock(lkp, 1); 267 COUNT(p, -1); 268 error = EBUSY; 269 break; 270 } 271 /* fall into normal upgrade */ 272 273 case LK_UPGRADE: 274 /* 275 * Upgrade a shared lock to an exclusive one. If another 276 * shared lock has already requested an upgrade to an 277 * exclusive lock, our shared lock is released and an 278 * exclusive lock is requested (which will be granted 279 * after the upgrade). If we return an error, the file 280 * will always be unlocked. 281 */ 282 #if !defined(MAX_PERF) 283 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0)) 284 panic("lockmgr: upgrade exclusive lock"); 285 #endif 286 shareunlock(lkp, 1); 287 COUNT(p, -1); 288 /* 289 * If we are just polling, check to see if we will block. 290 */ 291 if ((extflags & LK_NOWAIT) && 292 ((lkp->lk_flags & LK_WANT_UPGRADE) || 293 lkp->lk_sharecount > 1)) { 294 error = EBUSY; 295 break; 296 } 297 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 298 /* 299 * We are first shared lock to request an upgrade, so 300 * request upgrade and wait for the shared count to 301 * drop to zero, then take exclusive lock. 302 */ 303 lkp->lk_flags |= LK_WANT_UPGRADE; 304 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 305 lkp->lk_flags &= ~LK_WANT_UPGRADE; 306 307 if (error) 308 break; 309 lkp->lk_flags |= LK_HAVE_EXCL; 310 lkp->lk_lockholder = pid; 311 #if !defined(MAX_PERF) 312 if (lkp->lk_exclusivecount != 0) 313 panic("lockmgr: non-zero exclusive count"); 314 #endif 315 lkp->lk_exclusivecount = 1; 316 #if defined(DEBUG_LOCKS) 317 lkp->lk_filename = file; 318 lkp->lk_lineno = line; 319 lkp->lk_lockername = name; 320 #endif 321 COUNT(p, 1); 322 break; 323 } 324 /* 325 * Someone else has requested upgrade. Release our shared 326 * lock, awaken upgrade requestor if we are the last shared 327 * lock, then request an exclusive lock. 328 */ 329 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 330 LK_WAIT_NONZERO) 331 wakeup((void *)lkp); 332 /* fall into exclusive request */ 333 334 case LK_EXCLUSIVE: 335 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 336 /* 337 * Recursive lock. 338 */ 339 #if !defined(MAX_PERF) 340 if ((extflags & LK_CANRECURSE) == 0) 341 panic("lockmgr: locking against myself"); 342 #endif 343 lkp->lk_exclusivecount++; 344 COUNT(p, 1); 345 break; 346 } 347 /* 348 * If we are just polling, check to see if we will sleep. 349 */ 350 if ((extflags & LK_NOWAIT) && 351 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 352 error = EBUSY; 353 break; 354 } 355 /* 356 * Try to acquire the want_exclusive flag. 357 */ 358 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 359 if (error) 360 break; 361 lkp->lk_flags |= LK_WANT_EXCL; 362 /* 363 * Wait for shared locks and upgrades to finish. 364 */ 365 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 366 lkp->lk_flags &= ~LK_WANT_EXCL; 367 if (error) 368 break; 369 lkp->lk_flags |= LK_HAVE_EXCL; 370 lkp->lk_lockholder = pid; 371 #if !defined(MAX_PERF) 372 if (lkp->lk_exclusivecount != 0) 373 panic("lockmgr: non-zero exclusive count"); 374 #endif 375 lkp->lk_exclusivecount = 1; 376 #if defined(DEBUG_LOCKS) 377 lkp->lk_filename = file; 378 lkp->lk_lineno = line; 379 lkp->lk_lockername = name; 380 #endif 381 COUNT(p, 1); 382 break; 383 384 case LK_RELEASE: 385 if (lkp->lk_exclusivecount != 0) { 386 #if !defined(MAX_PERF) 387 if (pid != lkp->lk_lockholder) 388 panic("lockmgr: pid %d, not %s %d unlocking", 389 pid, "exclusive lock holder", 390 lkp->lk_lockholder); 391 #endif 392 COUNT(p, -1); 393 if (lkp->lk_exclusivecount == 1) { 394 lkp->lk_flags &= ~LK_HAVE_EXCL; 395 lkp->lk_lockholder = LK_NOPROC; 396 lkp->lk_exclusivecount = 0; 397 } else { 398 lkp->lk_exclusivecount--; 399 } 400 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 401 shareunlock(lkp, 1); 402 COUNT(p, -1); 403 } 404 if (lkp->lk_flags & LK_WAIT_NONZERO) 405 wakeup((void *)lkp); 406 break; 407 408 case LK_DRAIN: 409 /* 410 * Check that we do not already hold the lock, as it can 411 * never drain if we do. Unfortunately, we have no way to 412 * check for holding a shared lock, but at least we can 413 * check for an exclusive one. 414 */ 415 #if !defined(MAX_PERF) 416 if (lkp->lk_lockholder == pid) 417 panic("lockmgr: draining against myself"); 418 #endif 419 420 error = acquiredrain(lkp, extflags); 421 if (error) 422 break; 423 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 424 lkp->lk_lockholder = pid; 425 lkp->lk_exclusivecount = 1; 426 #if defined(DEBUG_LOCKS) 427 lkp->lk_filename = file; 428 lkp->lk_lineno = line; 429 lkp->lk_lockername = name; 430 #endif 431 COUNT(p, 1); 432 break; 433 434 default: 435 #if !defined(MAX_PERF) 436 simple_unlock(&lkp->lk_interlock); 437 panic("lockmgr: unknown locktype request %d", 438 flags & LK_TYPE_MASK); 439 #endif 440 /* NOTREACHED */ 441 } 442 if ((lkp->lk_flags & LK_WAITDRAIN) && 443 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 444 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 445 lkp->lk_flags &= ~LK_WAITDRAIN; 446 wakeup((void *)&lkp->lk_flags); 447 } 448 simple_unlock(&lkp->lk_interlock); 449 return (error); 450 } 451 452 static int 453 acquiredrain(struct lock *lkp, int extflags) { 454 int error; 455 456 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 457 return EBUSY; 458 } 459 460 error = apause(lkp, LK_ALL); 461 if (error == 0) 462 return 0; 463 464 while (lkp->lk_flags & LK_ALL) { 465 lkp->lk_flags |= LK_WAITDRAIN; 466 simple_unlock(&lkp->lk_interlock); 467 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 468 lkp->lk_wmesg, lkp->lk_timo); 469 simple_lock(&lkp->lk_interlock); 470 if (error) 471 return error; 472 if (extflags & LK_SLEEPFAIL) { 473 return ENOLCK; 474 } 475 } 476 return 0; 477 } 478 479 /* 480 * Initialize a lock; required before use. 481 */ 482 void 483 lockinit(lkp, prio, wmesg, timo, flags) 484 struct lock *lkp; 485 int prio; 486 char *wmesg; 487 int timo; 488 int flags; 489 { 490 491 simple_lock_init(&lkp->lk_interlock); 492 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 493 lkp->lk_sharecount = 0; 494 lkp->lk_waitcount = 0; 495 lkp->lk_exclusivecount = 0; 496 lkp->lk_prio = prio; 497 lkp->lk_wmesg = wmesg; 498 lkp->lk_timo = timo; 499 lkp->lk_lockholder = LK_NOPROC; 500 } 501 502 /* 503 * Determine the status of a lock. 504 */ 505 int 506 lockstatus(lkp) 507 struct lock *lkp; 508 { 509 int lock_type = 0; 510 511 simple_lock(&lkp->lk_interlock); 512 if (lkp->lk_exclusivecount != 0) 513 lock_type = LK_EXCLUSIVE; 514 else if (lkp->lk_sharecount != 0) 515 lock_type = LK_SHARED; 516 simple_unlock(&lkp->lk_interlock); 517 return (lock_type); 518 } 519 520 /* 521 * Print out information about state of a lock. Used by VOP_PRINT 522 * routines to display status about contained locks. 523 */ 524 void 525 lockmgr_printinfo(lkp) 526 struct lock *lkp; 527 { 528 529 if (lkp->lk_sharecount) 530 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 531 lkp->lk_sharecount); 532 else if (lkp->lk_flags & LK_HAVE_EXCL) 533 printf(" lock type %s: EXCL (count %d) by pid %d", 534 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 535 if (lkp->lk_waitcount > 0) 536 printf(" with %d pending", lkp->lk_waitcount); 537 } 538 539 #if defined(SIMPLELOCK_DEBUG) && (NCPUS == 1 || defined(COMPILING_LINT)) 540 #include <sys/kernel.h> 541 #include <sys/sysctl.h> 542 543 static int lockpausetime = 0; 544 SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 545 546 static int simplelockrecurse; 547 548 /* 549 * Simple lock functions so that the debugger can see from whence 550 * they are being called. 551 */ 552 void 553 simple_lock_init(alp) 554 struct simplelock *alp; 555 { 556 557 alp->lock_data = 0; 558 } 559 560 void 561 _simple_lock(alp, id, l) 562 struct simplelock *alp; 563 const char *id; 564 int l; 565 { 566 567 if (simplelockrecurse) 568 return; 569 if (alp->lock_data == 1) { 570 if (lockpausetime == -1) 571 panic("%s:%d: simple_lock: lock held", id, l); 572 printf("%s:%d: simple_lock: lock held\n", id, l); 573 if (lockpausetime == 1) { 574 Debugger("simple_lock"); 575 /*BACKTRACE(curproc); */ 576 } else if (lockpausetime > 1) { 577 printf("%s:%d: simple_lock: lock held...", id, l); 578 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 579 lockpausetime * hz); 580 printf(" continuing\n"); 581 } 582 } 583 alp->lock_data = 1; 584 if (curproc) 585 curproc->p_simple_locks++; 586 } 587 588 int 589 _simple_lock_try(alp, id, l) 590 struct simplelock *alp; 591 const char *id; 592 int l; 593 { 594 595 if (alp->lock_data) 596 return (0); 597 if (simplelockrecurse) 598 return (1); 599 alp->lock_data = 1; 600 if (curproc) 601 curproc->p_simple_locks++; 602 return (1); 603 } 604 605 void 606 _simple_unlock(alp, id, l) 607 struct simplelock *alp; 608 const char *id; 609 int l; 610 { 611 612 if (simplelockrecurse) 613 return; 614 if (alp->lock_data == 0) { 615 if (lockpausetime == -1) 616 panic("%s:%d: simple_unlock: lock not held", id, l); 617 printf("%s:%d: simple_unlock: lock not held\n", id, l); 618 if (lockpausetime == 1) { 619 Debugger("simple_unlock"); 620 /* BACKTRACE(curproc); */ 621 } else if (lockpausetime > 1) { 622 printf("%s:%d: simple_unlock: lock not held...", id, l); 623 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 624 lockpausetime * hz); 625 printf(" continuing\n"); 626 } 627 } 628 alp->lock_data = 0; 629 if (curproc) 630 curproc->p_simple_locks--; 631 } 632 #elif defined(SIMPLELOCK_DEBUG) 633 #error "SIMPLELOCK_DEBUG is not compatible with SMP!" 634 #endif /* SIMPLELOCK_DEBUG && NCPUS == 1 */ 635