Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_lock.c
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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 * $FreeBSD$ 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 { 108 #ifdef SMP 109 int i, lock_wait; 110 #endif 111 112 if ((lkp->lk_flags & flags) == 0) 113 return 0; 114 #ifdef SMP 115 for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) { 116 simple_unlock(&lkp->lk_interlock); 117 for (i = LOCK_SAMPLE_WAIT; i > 0; i--) 118 if ((lkp->lk_flags & flags) == 0) 119 break; 120 simple_lock(&lkp->lk_interlock); 121 if ((lkp->lk_flags & flags) == 0) 122 return 0; 123 } 124 #endif 125 return 1; 126 } 127 128 static int 129 acquire(struct lock *lkp, int extflags, int wanted) { 130 int s, error; 131 132 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 133 return EBUSY; 134 } 135 136 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 137 error = apause(lkp, wanted); 138 if (error == 0) 139 return 0; 140 } 141 142 s = splhigh(); 143 while ((lkp->lk_flags & wanted) != 0) { 144 lkp->lk_flags |= LK_WAIT_NONZERO; 145 lkp->lk_waitcount++; 146 simple_unlock(&lkp->lk_interlock); 147 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, 148 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 149 simple_lock(&lkp->lk_interlock); 150 if (lkp->lk_waitcount == 1) { 151 lkp->lk_flags &= ~LK_WAIT_NONZERO; 152 lkp->lk_waitcount = 0; 153 } else { 154 lkp->lk_waitcount--; 155 } 156 if (error) { 157 splx(s); 158 return error; 159 } 160 if (extflags & LK_SLEEPFAIL) { 161 splx(s); 162 return ENOLCK; 163 } 164 } 165 splx(s); 166 return 0; 167 } 168 169 /* 170 * Set, change, or release a lock. 171 * 172 * Shared requests increment the shared count. Exclusive requests set the 173 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 174 * accepted shared locks and shared-to-exclusive upgrades to go away. 175 */ 176 int 177 #ifndef DEBUG_LOCKS 178 lockmgr(lkp, flags, interlkp, p) 179 #else 180 debuglockmgr(lkp, flags, interlkp, p, name, file, line) 181 #endif 182 struct lock *lkp; 183 u_int flags; 184 struct simplelock *interlkp; 185 struct proc *p; 186 #ifdef DEBUG_LOCKS 187 const char *name; /* Name of lock function */ 188 const char *file; /* Name of file call is from */ 189 int line; /* Line number in file */ 190 #endif 191 { 192 int error; 193 pid_t pid; 194 int extflags; 195 196 error = 0; 197 if (p == NULL) 198 pid = LK_KERNPROC; 199 else 200 pid = p->p_pid; 201 202 simple_lock(&lkp->lk_interlock); 203 if (flags & LK_INTERLOCK) 204 simple_unlock(interlkp); 205 206 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 207 208 switch (flags & LK_TYPE_MASK) { 209 210 case LK_SHARED: 211 /* 212 * If we are not the exclusive lock holder, we have to block 213 * while there is an exclusive lock holder or while an 214 * exclusive lock request or upgrade request is in progress. 215 * 216 * However, if P_DEADLKTREAT is set, we override exclusive 217 * lock requests or upgrade requests ( but not the exclusive 218 * lock itself ). 219 */ 220 if (lkp->lk_lockholder != pid) { 221 if (p && (p->p_flag & P_DEADLKTREAT)) { 222 error = acquire( 223 lkp, 224 extflags, 225 LK_HAVE_EXCL 226 ); 227 } else { 228 error = acquire( 229 lkp, 230 extflags, 231 LK_HAVE_EXCL | LK_WANT_EXCL | 232 LK_WANT_UPGRADE 233 ); 234 } 235 if (error) 236 break; 237 sharelock(lkp, 1); 238 COUNT(p, 1); 239 break; 240 } 241 /* 242 * We hold an exclusive lock, so downgrade it to shared. 243 * An alternative would be to fail with EDEADLK. 244 */ 245 sharelock(lkp, 1); 246 COUNT(p, 1); 247 /* fall into downgrade */ 248 249 case LK_DOWNGRADE: 250 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 251 panic("lockmgr: not holding exclusive lock"); 252 sharelock(lkp, lkp->lk_exclusivecount); 253 lkp->lk_exclusivecount = 0; 254 lkp->lk_flags &= ~LK_HAVE_EXCL; 255 lkp->lk_lockholder = LK_NOPROC; 256 if (lkp->lk_waitcount) 257 wakeup((void *)lkp); 258 break; 259 260 case LK_EXCLUPGRADE: 261 /* 262 * If another process is ahead of us to get an upgrade, 263 * then we want to fail rather than have an intervening 264 * exclusive access. 265 */ 266 if (lkp->lk_flags & LK_WANT_UPGRADE) { 267 shareunlock(lkp, 1); 268 COUNT(p, -1); 269 error = EBUSY; 270 break; 271 } 272 /* fall into normal upgrade */ 273 274 case LK_UPGRADE: 275 /* 276 * Upgrade a shared lock to an exclusive one. If another 277 * shared lock has already requested an upgrade to an 278 * exclusive lock, our shared lock is released and an 279 * exclusive lock is requested (which will be granted 280 * after the upgrade). If we return an error, the file 281 * will always be unlocked. 282 */ 283 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0)) 284 panic("lockmgr: upgrade exclusive lock"); 285 shareunlock(lkp, 1); 286 COUNT(p, -1); 287 /* 288 * If we are just polling, check to see if we will block. 289 */ 290 if ((extflags & LK_NOWAIT) && 291 ((lkp->lk_flags & LK_WANT_UPGRADE) || 292 lkp->lk_sharecount > 1)) { 293 error = EBUSY; 294 break; 295 } 296 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 297 /* 298 * We are first shared lock to request an upgrade, so 299 * request upgrade and wait for the shared count to 300 * drop to zero, then take exclusive lock. 301 */ 302 lkp->lk_flags |= LK_WANT_UPGRADE; 303 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 304 lkp->lk_flags &= ~LK_WANT_UPGRADE; 305 306 if (error) 307 break; 308 lkp->lk_flags |= LK_HAVE_EXCL; 309 lkp->lk_lockholder = pid; 310 if (lkp->lk_exclusivecount != 0) 311 panic("lockmgr: non-zero exclusive count"); 312 lkp->lk_exclusivecount = 1; 313 #if defined(DEBUG_LOCKS) 314 lkp->lk_filename = file; 315 lkp->lk_lineno = line; 316 lkp->lk_lockername = name; 317 #endif 318 COUNT(p, 1); 319 break; 320 } 321 /* 322 * Someone else has requested upgrade. Release our shared 323 * lock, awaken upgrade requestor if we are the last shared 324 * lock, then request an exclusive lock. 325 */ 326 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 327 LK_WAIT_NONZERO) 328 wakeup((void *)lkp); 329 /* fall into exclusive request */ 330 331 case LK_EXCLUSIVE: 332 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 333 /* 334 * Recursive lock. 335 */ 336 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 337 panic("lockmgr: locking against myself"); 338 if ((extflags & LK_CANRECURSE) != 0) { 339 lkp->lk_exclusivecount++; 340 COUNT(p, 1); 341 break; 342 } 343 } 344 /* 345 * If we are just polling, check to see if we will sleep. 346 */ 347 if ((extflags & LK_NOWAIT) && 348 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 349 error = EBUSY; 350 break; 351 } 352 /* 353 * Try to acquire the want_exclusive flag. 354 */ 355 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 356 if (error) 357 break; 358 lkp->lk_flags |= LK_WANT_EXCL; 359 /* 360 * Wait for shared locks and upgrades to finish. 361 */ 362 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 363 lkp->lk_flags &= ~LK_WANT_EXCL; 364 if (error) 365 break; 366 lkp->lk_flags |= LK_HAVE_EXCL; 367 lkp->lk_lockholder = pid; 368 if (lkp->lk_exclusivecount != 0) 369 panic("lockmgr: non-zero exclusive count"); 370 lkp->lk_exclusivecount = 1; 371 #if defined(DEBUG_LOCKS) 372 lkp->lk_filename = file; 373 lkp->lk_lineno = line; 374 lkp->lk_lockername = name; 375 #endif 376 COUNT(p, 1); 377 break; 378 379 case LK_RELEASE: 380 if (lkp->lk_exclusivecount != 0) { 381 if (lkp->lk_lockholder != pid && 382 lkp->lk_lockholder != LK_KERNPROC) { 383 panic("lockmgr: pid %d, not %s %d unlocking", 384 pid, "exclusive lock holder", 385 lkp->lk_lockholder); 386 } 387 if (lkp->lk_lockholder != LK_KERNPROC) { 388 COUNT(p, -1); 389 } 390 if (lkp->lk_exclusivecount == 1) { 391 lkp->lk_flags &= ~LK_HAVE_EXCL; 392 lkp->lk_lockholder = LK_NOPROC; 393 lkp->lk_exclusivecount = 0; 394 } else { 395 lkp->lk_exclusivecount--; 396 } 397 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 398 shareunlock(lkp, 1); 399 COUNT(p, -1); 400 } 401 if (lkp->lk_flags & LK_WAIT_NONZERO) 402 wakeup((void *)lkp); 403 break; 404 405 case LK_DRAIN: 406 /* 407 * Check that we do not already hold the lock, as it can 408 * never drain if we do. Unfortunately, we have no way to 409 * check for holding a shared lock, but at least we can 410 * check for an exclusive one. 411 */ 412 if (lkp->lk_lockholder == pid) 413 panic("lockmgr: draining against myself"); 414 415 error = acquiredrain(lkp, extflags); 416 if (error) 417 break; 418 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 419 lkp->lk_lockholder = pid; 420 lkp->lk_exclusivecount = 1; 421 #if defined(DEBUG_LOCKS) 422 lkp->lk_filename = file; 423 lkp->lk_lineno = line; 424 lkp->lk_lockername = name; 425 #endif 426 COUNT(p, 1); 427 break; 428 429 default: 430 simple_unlock(&lkp->lk_interlock); 431 panic("lockmgr: unknown locktype request %d", 432 flags & LK_TYPE_MASK); 433 /* NOTREACHED */ 434 } 435 if ((lkp->lk_flags & LK_WAITDRAIN) && 436 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 437 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 438 lkp->lk_flags &= ~LK_WAITDRAIN; 439 wakeup((void *)&lkp->lk_flags); 440 } 441 simple_unlock(&lkp->lk_interlock); 442 return (error); 443 } 444 445 static int 446 acquiredrain(struct lock *lkp, int extflags) { 447 int error; 448 449 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 450 return EBUSY; 451 } 452 453 error = apause(lkp, LK_ALL); 454 if (error == 0) 455 return 0; 456 457 while (lkp->lk_flags & LK_ALL) { 458 lkp->lk_flags |= LK_WAITDRAIN; 459 simple_unlock(&lkp->lk_interlock); 460 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 461 lkp->lk_wmesg, 462 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 463 simple_lock(&lkp->lk_interlock); 464 if (error) 465 return error; 466 if (extflags & LK_SLEEPFAIL) { 467 return ENOLCK; 468 } 469 } 470 return 0; 471 } 472 473 /* 474 * Initialize a lock; required before use. 475 */ 476 void 477 lockinit(lkp, prio, wmesg, timo, flags) 478 struct lock *lkp; 479 int prio; 480 char *wmesg; 481 int timo; 482 int flags; 483 { 484 485 simple_lock_init(&lkp->lk_interlock); 486 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 487 lkp->lk_sharecount = 0; 488 lkp->lk_waitcount = 0; 489 lkp->lk_exclusivecount = 0; 490 lkp->lk_prio = prio; 491 lkp->lk_wmesg = wmesg; 492 lkp->lk_timo = timo; 493 lkp->lk_lockholder = LK_NOPROC; 494 } 495 496 /* 497 * Determine the status of a lock. 498 */ 499 int 500 lockstatus(lkp, p) 501 struct lock *lkp; 502 struct proc *p; 503 { 504 int lock_type = 0; 505 506 simple_lock(&lkp->lk_interlock); 507 if (lkp->lk_exclusivecount != 0) { 508 if (p == NULL || lkp->lk_lockholder == p->p_pid) 509 lock_type = LK_EXCLUSIVE; 510 else 511 lock_type = LK_EXCLOTHER; 512 } else if (lkp->lk_sharecount != 0) 513 lock_type = LK_SHARED; 514 simple_unlock(&lkp->lk_interlock); 515 return (lock_type); 516 } 517 518 /* 519 * Determine the number of holders of a lock. 520 */ 521 int 522 lockcount(lkp) 523 struct lock *lkp; 524 { 525 int count; 526 527 simple_lock(&lkp->lk_interlock); 528 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 529 simple_unlock(&lkp->lk_interlock); 530 return (count); 531 } 532 533 /* 534 * Print out information about state of a lock. Used by VOP_PRINT 535 * routines to display status about contained locks. 536 */ 537 void 538 lockmgr_printinfo(lkp) 539 struct lock *lkp; 540 { 541 542 if (lkp->lk_sharecount) 543 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 544 lkp->lk_sharecount); 545 else if (lkp->lk_flags & LK_HAVE_EXCL) 546 printf(" lock type %s: EXCL (count %d) by pid %d", 547 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 548 if (lkp->lk_waitcount > 0) 549 printf(" with %d pending", lkp->lk_waitcount); 550 } 551 552 #if defined(SIMPLELOCK_DEBUG) && (MAXCPU == 1 || defined(COMPILING_LINT)) 553 #include <sys/kernel.h> 554 #include <sys/sysctl.h> 555 556 static int lockpausetime = 0; 557 SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 558 559 static int simplelockrecurse; 560 561 /* 562 * Simple lock functions so that the debugger can see from whence 563 * they are being called. 564 */ 565 void 566 simple_lock_init(alp) 567 struct simplelock *alp; 568 { 569 570 alp->lock_data = 0; 571 } 572 573 void 574 _simple_lock(alp, id, l) 575 struct simplelock *alp; 576 const char *id; 577 int l; 578 { 579 580 if (simplelockrecurse) 581 return; 582 if (alp->lock_data == 1) { 583 if (lockpausetime == -1) 584 panic("%s:%d: simple_lock: lock held", id, l); 585 printf("%s:%d: simple_lock: lock held\n", id, l); 586 if (lockpausetime == 1) { 587 Debugger("simple_lock"); 588 /*BACKTRACE(curproc); */ 589 } else if (lockpausetime > 1) { 590 printf("%s:%d: simple_lock: lock held...", id, l); 591 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 592 lockpausetime * hz); 593 printf(" continuing\n"); 594 } 595 } 596 alp->lock_data = 1; 597 if (curproc) 598 curproc->p_simple_locks++; 599 } 600 601 int 602 _simple_lock_try(alp, id, l) 603 struct simplelock *alp; 604 const char *id; 605 int l; 606 { 607 608 if (alp->lock_data) 609 return (0); 610 if (simplelockrecurse) 611 return (1); 612 alp->lock_data = 1; 613 if (curproc) 614 curproc->p_simple_locks++; 615 return (1); 616 } 617 618 void 619 _simple_unlock(alp, id, l) 620 struct simplelock *alp; 621 const char *id; 622 int l; 623 { 624 625 if (simplelockrecurse) 626 return; 627 if (alp->lock_data == 0) { 628 if (lockpausetime == -1) 629 panic("%s:%d: simple_unlock: lock not held", id, l); 630 printf("%s:%d: simple_unlock: lock not held\n", id, l); 631 if (lockpausetime == 1) { 632 Debugger("simple_unlock"); 633 /* BACKTRACE(curproc); */ 634 } else if (lockpausetime > 1) { 635 printf("%s:%d: simple_unlock: lock not held...", id, l); 636 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 637 lockpausetime * hz); 638 printf(" continuing\n"); 639 } 640 } 641 alp->lock_data = 0; 642 if (curproc) 643 curproc->p_simple_locks--; 644 } 645 #elif defined(SIMPLELOCK_DEBUG) 646 #error "SIMPLELOCK_DEBUG is not compatible with SMP!" 647 #endif /* SIMPLELOCK_DEBUG && MAXCPU == 1 */
Cache object: e207c6ed4ee27c87107d0f20e45c4f77
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