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 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 if (lkp->lk_lockholder != pid) { 209 if ((lkp->lk_flags & LK_SHARE_NONZERO) != 0 && 210 (flags & LK_CANRECURSE) != 0) { 211 sharelock(lkp, 1); 212 COUNT(p, 1); 213 break; 214 } 215 error = acquire(lkp, extflags, 216 LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE); 217 if (error) 218 break; 219 sharelock(lkp, 1); 220 COUNT(p, 1); 221 break; 222 } 223 /* 224 * We hold an exclusive lock, so downgrade it to shared. 225 * An alternative would be to fail with EDEADLK. 226 */ 227 sharelock(lkp, 1); 228 COUNT(p, 1); 229 /* fall into downgrade */ 230 231 case LK_DOWNGRADE: 232 #if !defined(MAX_PERF) 233 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 234 panic("lockmgr: not holding exclusive lock"); 235 #endif 236 sharelock(lkp, lkp->lk_exclusivecount); 237 lkp->lk_exclusivecount = 0; 238 lkp->lk_flags &= ~LK_HAVE_EXCL; 239 lkp->lk_lockholder = LK_NOPROC; 240 if (lkp->lk_waitcount) 241 wakeup((void *)lkp); 242 break; 243 244 case LK_EXCLUPGRADE: 245 /* 246 * If another process is ahead of us to get an upgrade, 247 * then we want to fail rather than have an intervening 248 * exclusive access. 249 */ 250 if (lkp->lk_flags & LK_WANT_UPGRADE) { 251 shareunlock(lkp, 1); 252 COUNT(p, -1); 253 error = EBUSY; 254 break; 255 } 256 /* fall into normal upgrade */ 257 258 case LK_UPGRADE: 259 /* 260 * Upgrade a shared lock to an exclusive one. If another 261 * shared lock has already requested an upgrade to an 262 * exclusive lock, our shared lock is released and an 263 * exclusive lock is requested (which will be granted 264 * after the upgrade). If we return an error, the file 265 * will always be unlocked. 266 */ 267 #if !defined(MAX_PERF) 268 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0)) 269 panic("lockmgr: upgrade exclusive lock"); 270 #endif 271 shareunlock(lkp, 1); 272 COUNT(p, -1); 273 /* 274 * If we are just polling, check to see if we will block. 275 */ 276 if ((extflags & LK_NOWAIT) && 277 ((lkp->lk_flags & LK_WANT_UPGRADE) || 278 lkp->lk_sharecount > 1)) { 279 error = EBUSY; 280 break; 281 } 282 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 283 /* 284 * We are first shared lock to request an upgrade, so 285 * request upgrade and wait for the shared count to 286 * drop to zero, then take exclusive lock. 287 */ 288 lkp->lk_flags |= LK_WANT_UPGRADE; 289 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 290 lkp->lk_flags &= ~LK_WANT_UPGRADE; 291 292 if (error) 293 break; 294 lkp->lk_flags |= LK_HAVE_EXCL; 295 lkp->lk_lockholder = pid; 296 #if !defined(MAX_PERF) 297 if (lkp->lk_exclusivecount != 0) 298 panic("lockmgr: non-zero exclusive count"); 299 #endif 300 lkp->lk_exclusivecount = 1; 301 #if defined(DEBUG_LOCKS) 302 lkp->lk_filename = file; 303 lkp->lk_lineno = line; 304 lkp->lk_lockername = name; 305 #endif 306 COUNT(p, 1); 307 break; 308 } 309 /* 310 * Someone else has requested upgrade. Release our shared 311 * lock, awaken upgrade requestor if we are the last shared 312 * lock, then request an exclusive lock. 313 */ 314 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 315 LK_WAIT_NONZERO) 316 wakeup((void *)lkp); 317 /* fall into exclusive request */ 318 319 case LK_EXCLUSIVE: 320 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 321 /* 322 * Recursive lock. 323 */ 324 #if !defined(MAX_PERF) 325 if ((extflags & LK_CANRECURSE) == 0) 326 panic("lockmgr: locking against myself"); 327 #endif 328 lkp->lk_exclusivecount++; 329 COUNT(p, 1); 330 break; 331 } 332 /* 333 * If we are just polling, check to see if we will sleep. 334 */ 335 if ((extflags & LK_NOWAIT) && 336 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 337 error = EBUSY; 338 break; 339 } 340 /* 341 * Try to acquire the want_exclusive flag. 342 */ 343 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 344 if (error) 345 break; 346 lkp->lk_flags |= LK_WANT_EXCL; 347 /* 348 * Wait for shared locks and upgrades to finish. 349 */ 350 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 351 lkp->lk_flags &= ~LK_WANT_EXCL; 352 if (error) 353 break; 354 lkp->lk_flags |= LK_HAVE_EXCL; 355 lkp->lk_lockholder = pid; 356 #if !defined(MAX_PERF) 357 if (lkp->lk_exclusivecount != 0) 358 panic("lockmgr: non-zero exclusive count"); 359 #endif 360 lkp->lk_exclusivecount = 1; 361 #if defined(DEBUG_LOCKS) 362 lkp->lk_filename = file; 363 lkp->lk_lineno = line; 364 lkp->lk_lockername = name; 365 #endif 366 COUNT(p, 1); 367 break; 368 369 case LK_RELEASE: 370 if (lkp->lk_exclusivecount != 0) { 371 #if !defined(MAX_PERF) 372 if (pid != lkp->lk_lockholder) 373 panic("lockmgr: pid %d, not %s %d unlocking", 374 pid, "exclusive lock holder", 375 lkp->lk_lockholder); 376 #endif 377 COUNT(p, -1); 378 if (lkp->lk_exclusivecount == 1) { 379 lkp->lk_flags &= ~LK_HAVE_EXCL; 380 lkp->lk_lockholder = LK_NOPROC; 381 lkp->lk_exclusivecount = 0; 382 } else { 383 lkp->lk_exclusivecount--; 384 } 385 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 386 shareunlock(lkp, 1); 387 COUNT(p, -1); 388 } 389 if (lkp->lk_flags & LK_WAIT_NONZERO) 390 wakeup((void *)lkp); 391 break; 392 393 case LK_DRAIN: 394 /* 395 * Check that we do not already hold the lock, as it can 396 * never drain if we do. Unfortunately, we have no way to 397 * check for holding a shared lock, but at least we can 398 * check for an exclusive one. 399 */ 400 #if !defined(MAX_PERF) 401 if (lkp->lk_lockholder == pid) 402 panic("lockmgr: draining against myself"); 403 #endif 404 405 error = acquiredrain(lkp, extflags); 406 if (error) 407 break; 408 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 409 lkp->lk_lockholder = pid; 410 lkp->lk_exclusivecount = 1; 411 #if defined(DEBUG_LOCKS) 412 lkp->lk_filename = file; 413 lkp->lk_lineno = line; 414 lkp->lk_lockername = name; 415 #endif 416 COUNT(p, 1); 417 break; 418 419 default: 420 #if !defined(MAX_PERF) 421 simple_unlock(&lkp->lk_interlock); 422 panic("lockmgr: unknown locktype request %d", 423 flags & LK_TYPE_MASK); 424 #endif 425 /* NOTREACHED */ 426 } 427 if ((lkp->lk_flags & LK_WAITDRAIN) && 428 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 429 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 430 lkp->lk_flags &= ~LK_WAITDRAIN; 431 wakeup((void *)&lkp->lk_flags); 432 } 433 simple_unlock(&lkp->lk_interlock); 434 return (error); 435 } 436 437 static int 438 acquiredrain(struct lock *lkp, int extflags) { 439 int error; 440 441 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 442 return EBUSY; 443 } 444 445 error = apause(lkp, LK_ALL); 446 if (error == 0) 447 return 0; 448 449 while (lkp->lk_flags & LK_ALL) { 450 lkp->lk_flags |= LK_WAITDRAIN; 451 simple_unlock(&lkp->lk_interlock); 452 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 453 lkp->lk_wmesg, lkp->lk_timo); 454 simple_lock(&lkp->lk_interlock); 455 if (error) 456 return error; 457 if (extflags & LK_SLEEPFAIL) { 458 return ENOLCK; 459 } 460 } 461 return 0; 462 } 463 464 /* 465 * Initialize a lock; required before use. 466 */ 467 void 468 lockinit(lkp, prio, wmesg, timo, flags) 469 struct lock *lkp; 470 int prio; 471 char *wmesg; 472 int timo; 473 int flags; 474 { 475 476 simple_lock_init(&lkp->lk_interlock); 477 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 478 lkp->lk_sharecount = 0; 479 lkp->lk_waitcount = 0; 480 lkp->lk_exclusivecount = 0; 481 lkp->lk_prio = prio; 482 lkp->lk_wmesg = wmesg; 483 lkp->lk_timo = timo; 484 lkp->lk_lockholder = LK_NOPROC; 485 } 486 487 /* 488 * Determine the status of a lock. 489 */ 490 int 491 lockstatus(lkp) 492 struct lock *lkp; 493 { 494 int lock_type = 0; 495 496 simple_lock(&lkp->lk_interlock); 497 if (lkp->lk_exclusivecount != 0) 498 lock_type = LK_EXCLUSIVE; 499 else if (lkp->lk_sharecount != 0) 500 lock_type = LK_SHARED; 501 simple_unlock(&lkp->lk_interlock); 502 return (lock_type); 503 } 504 505 /* 506 * Print out information about state of a lock. Used by VOP_PRINT 507 * routines to display status about contained locks. 508 */ 509 void 510 lockmgr_printinfo(lkp) 511 struct lock *lkp; 512 { 513 514 if (lkp->lk_sharecount) 515 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 516 lkp->lk_sharecount); 517 else if (lkp->lk_flags & LK_HAVE_EXCL) 518 printf(" lock type %s: EXCL (count %d) by pid %d", 519 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 520 if (lkp->lk_waitcount > 0) 521 printf(" with %d pending", lkp->lk_waitcount); 522 } 523 524 #if defined(SIMPLELOCK_DEBUG) && (NCPUS == 1 || defined(COMPILING_LINT)) 525 #include <sys/kernel.h> 526 #include <sys/sysctl.h> 527 528 static int lockpausetime = 0; 529 SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 530 531 static int simplelockrecurse; 532 533 /* 534 * Simple lock functions so that the debugger can see from whence 535 * they are being called. 536 */ 537 void 538 simple_lock_init(alp) 539 struct simplelock *alp; 540 { 541 542 alp->lock_data = 0; 543 } 544 545 void 546 _simple_lock(alp, id, l) 547 struct simplelock *alp; 548 const char *id; 549 int l; 550 { 551 552 if (simplelockrecurse) 553 return; 554 if (alp->lock_data == 1) { 555 if (lockpausetime == -1) 556 panic("%s:%d: simple_lock: lock held", id, l); 557 printf("%s:%d: simple_lock: lock held\n", id, l); 558 if (lockpausetime == 1) { 559 Debugger("simple_lock"); 560 /*BACKTRACE(curproc); */ 561 } else if (lockpausetime > 1) { 562 printf("%s:%d: simple_lock: lock held...", id, l); 563 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 564 lockpausetime * hz); 565 printf(" continuing\n"); 566 } 567 } 568 alp->lock_data = 1; 569 if (curproc) 570 curproc->p_simple_locks++; 571 } 572 573 int 574 _simple_lock_try(alp, id, l) 575 struct simplelock *alp; 576 const char *id; 577 int l; 578 { 579 580 if (alp->lock_data) 581 return (0); 582 if (simplelockrecurse) 583 return (1); 584 alp->lock_data = 1; 585 if (curproc) 586 curproc->p_simple_locks++; 587 return (1); 588 } 589 590 void 591 _simple_unlock(alp, id, l) 592 struct simplelock *alp; 593 const char *id; 594 int l; 595 { 596 597 if (simplelockrecurse) 598 return; 599 if (alp->lock_data == 0) { 600 if (lockpausetime == -1) 601 panic("%s:%d: simple_unlock: lock not held", id, l); 602 printf("%s:%d: simple_unlock: lock not held\n", id, l); 603 if (lockpausetime == 1) { 604 Debugger("simple_unlock"); 605 /* BACKTRACE(curproc); */ 606 } else if (lockpausetime > 1) { 607 printf("%s:%d: simple_unlock: lock not held...", id, l); 608 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 609 lockpausetime * hz); 610 printf(" continuing\n"); 611 } 612 } 613 alp->lock_data = 0; 614 if (curproc) 615 curproc->p_simple_locks--; 616 } 617 #elif defined(SIMPLELOCK_DEBUG) 618 #error "SIMPLELOCK_DEBUG is not compatible with SMP!" 619 #endif /* SIMPLELOCK_DEBUG && NCPUS == 1 */
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