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 1.18 1998/03/07 19:25:34 dyson 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 #if defined(DIAGNOSTIC) 87 if (lkp->lk_sharecount < decr) 88 #if defined(DDB) 89 Debugger("shareunlock: count < decr"); 90 #else 91 panic("shareunlock: count < decr"); 92 #endif 93 #endif 94 95 if (lkp->lk_sharecount == decr) { 96 lkp->lk_flags &= ~LK_SHARE_NONZERO; 97 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 98 wakeup(lkp); 99 } 100 lkp->lk_sharecount = 0; 101 } else { 102 lkp->lk_sharecount -= decr; 103 } 104 } 105 106 /* 107 * This is the waitloop optimization, and note for this to work 108 * simple_lock and simple_unlock should be subroutines to avoid 109 * optimization troubles. 110 */ 111 static int 112 apause(struct lock *lkp, int flags) { 113 int lock_wait; 114 lock_wait = LOCK_WAIT_TIME; 115 for (; lock_wait > 0; lock_wait--) { 116 int i; 117 if ((lkp->lk_flags & flags) == 0) 118 return 0; 119 simple_unlock(&lkp->lk_interlock); 120 for (i = LOCK_SAMPLE_WAIT; i > 0; i--) { 121 if ((lkp->lk_flags & flags) == 0) { 122 simple_lock(&lkp->lk_interlock); 123 if ((lkp->lk_flags & flags) == 0) 124 return 0; 125 break; 126 } 127 } 128 } 129 return 1; 130 } 131 132 static int 133 acquire(struct lock *lkp, int extflags, int wanted) { 134 int s, error; 135 136 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 137 return EBUSY; 138 } 139 140 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 141 error = apause(lkp, wanted); 142 if (error == 0) 143 return 0; 144 } 145 146 s = splhigh(); 147 while ((lkp->lk_flags & wanted) != 0) { 148 lkp->lk_flags |= LK_WAIT_NONZERO; 149 lkp->lk_waitcount++; 150 simple_unlock(&lkp->lk_interlock); 151 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo); 152 simple_lock(&lkp->lk_interlock); 153 if (lkp->lk_waitcount == 1) { 154 lkp->lk_flags &= ~LK_WAIT_NONZERO; 155 lkp->lk_waitcount = 0; 156 } else { 157 lkp->lk_waitcount--; 158 } 159 if (error) { 160 splx(s); 161 return error; 162 } 163 if (extflags & LK_SLEEPFAIL) { 164 splx(s); 165 return ENOLCK; 166 } 167 } 168 splx(s); 169 return 0; 170 } 171 172 /* 173 * Set, change, or release a lock. 174 * 175 * Shared requests increment the shared count. Exclusive requests set the 176 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 177 * accepted shared locks and shared-to-exclusive upgrades to go away. 178 */ 179 int 180 lockmgr(lkp, flags, interlkp, p) 181 struct lock *lkp; 182 u_int flags; 183 struct simplelock *interlkp; 184 struct proc *p; 185 { 186 int error; 187 pid_t pid; 188 int extflags; 189 190 error = 0; 191 if (p == NULL) 192 pid = LK_KERNPROC; 193 else 194 pid = p->p_pid; 195 196 simple_lock(&lkp->lk_interlock); 197 if (flags & LK_INTERLOCK) 198 simple_unlock(interlkp); 199 200 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 201 202 switch (flags & LK_TYPE_MASK) { 203 204 case LK_SHARED: 205 if (lkp->lk_lockholder != pid) { 206 error = acquire(lkp, extflags, 207 LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE); 208 if (error) 209 break; 210 sharelock(lkp, 1); 211 COUNT(p, 1); 212 break; 213 } 214 /* 215 * We hold an exclusive lock, so downgrade it to shared. 216 * An alternative would be to fail with EDEADLK. 217 */ 218 sharelock(lkp, 1); 219 COUNT(p, 1); 220 /* fall into downgrade */ 221 222 case LK_DOWNGRADE: 223 #if !defined(MAX_PERF) 224 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 225 panic("lockmgr: not holding exclusive lock"); 226 #endif 227 sharelock(lkp, lkp->lk_exclusivecount); 228 lkp->lk_exclusivecount = 0; 229 lkp->lk_flags &= ~LK_HAVE_EXCL; 230 lkp->lk_lockholder = LK_NOPROC; 231 if (lkp->lk_waitcount) 232 wakeup((void *)lkp); 233 break; 234 235 case LK_EXCLUPGRADE: 236 /* 237 * If another process is ahead of us to get an upgrade, 238 * then we want to fail rather than have an intervening 239 * exclusive access. 240 */ 241 if (lkp->lk_flags & LK_WANT_UPGRADE) { 242 shareunlock(lkp, 1); 243 COUNT(p, -1); 244 error = EBUSY; 245 break; 246 } 247 /* fall into normal upgrade */ 248 249 case LK_UPGRADE: 250 /* 251 * Upgrade a shared lock to an exclusive one. If another 252 * shared lock has already requested an upgrade to an 253 * exclusive lock, our shared lock is released and an 254 * exclusive lock is requested (which will be granted 255 * after the upgrade). If we return an error, the file 256 * will always be unlocked. 257 */ 258 #if !defined(MAX_PERF) 259 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0)) 260 panic("lockmgr: upgrade exclusive lock"); 261 #endif 262 shareunlock(lkp, 1); 263 COUNT(p, -1); 264 /* 265 * If we are just polling, check to see if we will block. 266 */ 267 if ((extflags & LK_NOWAIT) && 268 ((lkp->lk_flags & LK_WANT_UPGRADE) || 269 lkp->lk_sharecount > 1)) { 270 error = EBUSY; 271 break; 272 } 273 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 274 /* 275 * We are first shared lock to request an upgrade, so 276 * request upgrade and wait for the shared count to 277 * drop to zero, then take exclusive lock. 278 */ 279 lkp->lk_flags |= LK_WANT_UPGRADE; 280 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 281 lkp->lk_flags &= ~LK_WANT_UPGRADE; 282 283 if (error) 284 break; 285 lkp->lk_flags |= LK_HAVE_EXCL; 286 lkp->lk_lockholder = pid; 287 #if !defined(MAX_PERF) 288 if (lkp->lk_exclusivecount != 0) 289 panic("lockmgr: non-zero exclusive count"); 290 #endif 291 lkp->lk_exclusivecount = 1; 292 COUNT(p, 1); 293 break; 294 } 295 /* 296 * Someone else has requested upgrade. Release our shared 297 * lock, awaken upgrade requestor if we are the last shared 298 * lock, then request an exclusive lock. 299 */ 300 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 301 LK_WAIT_NONZERO) 302 wakeup((void *)lkp); 303 /* fall into exclusive request */ 304 305 case LK_EXCLUSIVE: 306 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 307 /* 308 * Recursive lock. 309 */ 310 #if !defined(MAX_PERF) 311 if ((extflags & LK_CANRECURSE) == 0) 312 panic("lockmgr: locking against myself"); 313 #endif 314 lkp->lk_exclusivecount++; 315 COUNT(p, 1); 316 break; 317 } 318 /* 319 * If we are just polling, check to see if we will sleep. 320 */ 321 if ((extflags & LK_NOWAIT) && 322 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 323 error = EBUSY; 324 break; 325 } 326 /* 327 * Try to acquire the want_exclusive flag. 328 */ 329 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 330 if (error) 331 break; 332 lkp->lk_flags |= LK_WANT_EXCL; 333 /* 334 * Wait for shared locks and upgrades to finish. 335 */ 336 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 337 lkp->lk_flags &= ~LK_WANT_EXCL; 338 if (error) 339 break; 340 lkp->lk_flags |= LK_HAVE_EXCL; 341 lkp->lk_lockholder = pid; 342 #if !defined(MAX_PERF) 343 if (lkp->lk_exclusivecount != 0) 344 panic("lockmgr: non-zero exclusive count"); 345 #endif 346 lkp->lk_exclusivecount = 1; 347 COUNT(p, 1); 348 break; 349 350 case LK_RELEASE: 351 if (lkp->lk_exclusivecount != 0) { 352 #if !defined(MAX_PERF) 353 if (pid != lkp->lk_lockholder) 354 panic("lockmgr: pid %d, not %s %d unlocking", 355 pid, "exclusive lock holder", 356 lkp->lk_lockholder); 357 #endif 358 COUNT(p, -1); 359 if (lkp->lk_exclusivecount == 1) { 360 lkp->lk_flags &= ~LK_HAVE_EXCL; 361 lkp->lk_lockholder = LK_NOPROC; 362 lkp->lk_exclusivecount = 0; 363 } else { 364 lkp->lk_exclusivecount--; 365 } 366 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 367 shareunlock(lkp, 1); 368 COUNT(p, -1); 369 } 370 if (lkp->lk_flags & LK_WAIT_NONZERO) 371 wakeup((void *)lkp); 372 break; 373 374 case LK_DRAIN: 375 /* 376 * Check that we do not already hold the lock, as it can 377 * never drain if we do. Unfortunately, we have no way to 378 * check for holding a shared lock, but at least we can 379 * check for an exclusive one. 380 */ 381 #if !defined(MAX_PERF) 382 if (lkp->lk_lockholder == pid) 383 panic("lockmgr: draining against myself"); 384 #endif 385 386 error = acquiredrain(lkp, extflags); 387 if (error) 388 break; 389 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 390 lkp->lk_lockholder = pid; 391 lkp->lk_exclusivecount = 1; 392 COUNT(p, 1); 393 break; 394 395 default: 396 #if !defined(MAX_PERF) 397 simple_unlock(&lkp->lk_interlock); 398 panic("lockmgr: unknown locktype request %d", 399 flags & LK_TYPE_MASK); 400 #endif 401 /* NOTREACHED */ 402 } 403 if ((lkp->lk_flags & LK_WAITDRAIN) && 404 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 405 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 406 lkp->lk_flags &= ~LK_WAITDRAIN; 407 wakeup((void *)&lkp->lk_flags); 408 } 409 simple_unlock(&lkp->lk_interlock); 410 return (error); 411 } 412 413 static int 414 acquiredrain(struct lock *lkp, int extflags) { 415 int error; 416 417 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 418 return EBUSY; 419 } 420 421 error = apause(lkp, LK_ALL); 422 if (error == 0) 423 return 0; 424 425 while (lkp->lk_flags & LK_ALL) { 426 lkp->lk_flags |= LK_WAITDRAIN; 427 simple_unlock(&lkp->lk_interlock); 428 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 429 lkp->lk_wmesg, lkp->lk_timo); 430 simple_lock(&lkp->lk_interlock); 431 if (error) 432 return error; 433 if (extflags & LK_SLEEPFAIL) { 434 return ENOLCK; 435 } 436 } 437 return 0; 438 } 439 440 /* 441 * Initialize a lock; required before use. 442 */ 443 void 444 lockinit(lkp, prio, wmesg, timo, flags) 445 struct lock *lkp; 446 int prio; 447 char *wmesg; 448 int timo; 449 int flags; 450 { 451 452 simple_lock_init(&lkp->lk_interlock); 453 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 454 lkp->lk_sharecount = 0; 455 lkp->lk_waitcount = 0; 456 lkp->lk_exclusivecount = 0; 457 lkp->lk_prio = prio; 458 lkp->lk_wmesg = wmesg; 459 lkp->lk_timo = timo; 460 lkp->lk_lockholder = LK_NOPROC; 461 } 462 463 /* 464 * Determine the status of a lock. 465 */ 466 int 467 lockstatus(lkp) 468 struct lock *lkp; 469 { 470 int lock_type = 0; 471 472 simple_lock(&lkp->lk_interlock); 473 if (lkp->lk_exclusivecount != 0) 474 lock_type = LK_EXCLUSIVE; 475 else if (lkp->lk_sharecount != 0) 476 lock_type = LK_SHARED; 477 simple_unlock(&lkp->lk_interlock); 478 return (lock_type); 479 } 480 481 /* 482 * Print out information about state of a lock. Used by VOP_PRINT 483 * routines to display status about contained locks. 484 */ 485 void 486 lockmgr_printinfo(lkp) 487 struct lock *lkp; 488 { 489 490 if (lkp->lk_sharecount) 491 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 492 lkp->lk_sharecount); 493 else if (lkp->lk_flags & LK_HAVE_EXCL) 494 printf(" lock type %s: EXCL (count %d) by pid %d", 495 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 496 if (lkp->lk_waitcount > 0) 497 printf(" with %d pending", lkp->lk_waitcount); 498 } 499 500 #if defined(SIMPLELOCK_DEBUG) && (NCPUS == 1 || defined(COMPILING_LINT)) 501 #include <sys/kernel.h> 502 #include <sys/sysctl.h> 503 504 static int lockpausetime = 0; 505 SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 506 507 int simplelockrecurse; 508 509 /* 510 * Simple lock functions so that the debugger can see from whence 511 * they are being called. 512 */ 513 void 514 simple_lock_init(alp) 515 struct simplelock *alp; 516 { 517 518 alp->lock_data = 0; 519 } 520 521 void 522 _simple_lock(alp, id, l) 523 struct simplelock *alp; 524 const char *id; 525 int l; 526 { 527 528 if (simplelockrecurse) 529 return; 530 if (alp->lock_data == 1) { 531 if (lockpausetime == -1) 532 panic("%s:%d: simple_lock: lock held", id, l); 533 printf("%s:%d: simple_lock: lock held\n", id, l); 534 if (lockpausetime == 1) { 535 Debugger("simple_lock"); 536 /*BACKTRACE(curproc); */ 537 } else if (lockpausetime > 1) { 538 printf("%s:%d: simple_lock: lock held...", id, l); 539 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 540 lockpausetime * hz); 541 printf(" continuing\n"); 542 } 543 } 544 alp->lock_data = 1; 545 if (curproc) 546 curproc->p_simple_locks++; 547 } 548 549 int 550 _simple_lock_try(alp, id, l) 551 struct simplelock *alp; 552 const char *id; 553 int l; 554 { 555 556 if (alp->lock_data) 557 return (0); 558 if (simplelockrecurse) 559 return (1); 560 alp->lock_data = 1; 561 if (curproc) 562 curproc->p_simple_locks++; 563 return (1); 564 } 565 566 void 567 _simple_unlock(alp, id, l) 568 struct simplelock *alp; 569 const char *id; 570 int l; 571 { 572 573 if (simplelockrecurse) 574 return; 575 if (alp->lock_data == 0) { 576 if (lockpausetime == -1) 577 panic("%s:%d: simple_unlock: lock not held", id, l); 578 printf("%s:%d: simple_unlock: lock not held\n", id, l); 579 if (lockpausetime == 1) { 580 Debugger("simple_unlock"); 581 /* BACKTRACE(curproc); */ 582 } else if (lockpausetime > 1) { 583 printf("%s:%d: simple_unlock: lock not held...", id, l); 584 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 585 lockpausetime * hz); 586 printf(" continuing\n"); 587 } 588 } 589 alp->lock_data = 0; 590 if (curproc) 591 curproc->p_simple_locks--; 592 } 593 #elif defined(SIMPLELOCK_DEBUG) 594 #error "SIMPLELOCK_DEBUG is not compatible with SMP!" 595 #endif /* SIMPLELOCK_DEBUG && NCPUS == 1 */ 596