kern_lock.c revision 1.6
1 /* $NetBSD: kern_lock.c,v 1.6 1998/03/01 02:22:29 fvdl Exp $ */ 2 3 /* 4 * Copyright (c) 1995 5 * The Regents of the University of California. All rights reserved. 6 * 7 * This code contains ideas from software contributed to Berkeley by 8 * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating 9 * System project at Carnegie-Mellon University. 10 * 11 * Redistribution and use in source and binary forms, with or without 12 * modification, are permitted provided that the following conditions 13 * are met: 14 * 1. Redistributions of source code must retain the above copyright 15 * notice, this list of conditions and the following disclaimer. 16 * 2. Redistributions in binary form must reproduce the above copyright 17 * notice, this list of conditions and the following disclaimer in the 18 * documentation and/or other materials provided with the distribution. 19 * 3. All advertising materials mentioning features or use of this software 20 * must display the following acknowledgement: 21 * This product includes software developed by the University of 22 * California, Berkeley and its contributors. 23 * 4. Neither the name of the University nor the names of its contributors 24 * may be used to endorse or promote products derived from this software 25 * without specific prior written permission. 26 * 27 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 28 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 29 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 30 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 31 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 32 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 33 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 34 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 35 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 36 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 37 * SUCH DAMAGE. 38 * 39 * @(#)kern_lock.c 8.18 (Berkeley) 5/21/95 40 */ 41 42 #include <sys/param.h> 43 #include <sys/proc.h> 44 #include <sys/lock.h> 45 #include <sys/systm.h> 46 #include <machine/cpu.h> 47 48 /* 49 * Locking primitives implementation. 50 * Locks provide shared/exclusive sychronization. 51 */ 52 53 #ifdef LOCKDEBUG 54 #define COUNT(p, x) if (p) (p)->p_locks += (x) 55 #else 56 #define COUNT(p, x) 57 #endif 58 59 #if NCPUS > 1 60 61 /* 62 * For multiprocessor system, try spin lock first. 63 * 64 * This should be inline expanded below, but we cannot have #if 65 * inside a multiline define. 66 */ 67 int lock_wait_time = 100; 68 #define PAUSE(lkp, wanted) \ 69 if (lock_wait_time > 0) { \ 70 int i; \ 71 \ 72 simple_unlock(&lkp->lk_interlock); \ 73 for (i = lock_wait_time; i > 0; i--) \ 74 if (!(wanted)) \ 75 break; \ 76 simple_lock(&lkp->lk_interlock); \ 77 } \ 78 if (!(wanted)) \ 79 break; 80 81 #else /* NCPUS == 1 */ 82 83 /* 84 * It is an error to spin on a uniprocessor as nothing will ever cause 85 * the simple lock to clear while we are executing. 86 */ 87 #define PAUSE(lkp, wanted) 88 89 #endif /* NCPUS == 1 */ 90 91 /* 92 * Acquire a resource. 93 */ 94 #define ACQUIRE(lkp, error, extflags, wanted) \ 95 PAUSE(lkp, wanted); \ 96 for (error = 0; wanted; ) { \ 97 (lkp)->lk_waitcount++; \ 98 simple_unlock(&(lkp)->lk_interlock); \ 99 error = tsleep((void *)lkp, (lkp)->lk_prio, \ 100 (lkp)->lk_wmesg, (lkp)->lk_timo); \ 101 simple_lock(&(lkp)->lk_interlock); \ 102 (lkp)->lk_waitcount--; \ 103 if (error) \ 104 break; \ 105 if ((extflags) & LK_SLEEPFAIL) { \ 106 error = ENOLCK; \ 107 break; \ 108 } \ 109 } 110 111 /* 112 * Initialize a lock; required before use. 113 */ 114 void 115 lockinit(lkp, prio, wmesg, timo, flags) 116 struct lock *lkp; 117 int prio; 118 const char *wmesg; 119 int timo; 120 int flags; 121 { 122 123 bzero(lkp, sizeof(struct lock)); 124 simple_lock_init(&lkp->lk_interlock); 125 lkp->lk_flags = flags & LK_EXTFLG_MASK; 126 lkp->lk_prio = prio; 127 lkp->lk_timo = timo; 128 lkp->lk_wmesg = wmesg; 129 lkp->lk_lockholder = LK_NOPROC; 130 } 131 132 /* 133 * Determine the status of a lock. 134 */ 135 int 136 lockstatus(lkp) 137 struct lock *lkp; 138 { 139 int lock_type = 0; 140 141 simple_lock(&lkp->lk_interlock); 142 if (lkp->lk_exclusivecount != 0) 143 lock_type = LK_EXCLUSIVE; 144 else if (lkp->lk_sharecount != 0) 145 lock_type = LK_SHARED; 146 simple_unlock(&lkp->lk_interlock); 147 return (lock_type); 148 } 149 150 /* 151 * Set, change, or release a lock. 152 * 153 * Shared requests increment the shared count. Exclusive requests set the 154 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 155 * accepted shared locks and shared-to-exclusive upgrades to go away. 156 */ 157 int 158 lockmgr(lkp, flags, interlkp) 159 __volatile struct lock *lkp; 160 u_int flags; 161 struct simplelock *interlkp; 162 { 163 int error; 164 pid_t pid; 165 int extflags; 166 struct proc *p = curproc; 167 168 error = 0; 169 if (p) 170 pid = p->p_pid; 171 else 172 pid = LK_KERNPROC; 173 simple_lock(&lkp->lk_interlock); 174 if (flags & LK_INTERLOCK) 175 simple_unlock(interlkp); 176 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 177 #ifdef DIAGNOSTIC 178 /* 179 * Once a lock has drained, the LK_DRAINING flag is set and an 180 * exclusive lock is returned. The only valid operation thereafter 181 * is a single release of that exclusive lock. This final release 182 * clears the LK_DRAINING flag and sets the LK_DRAINED flag. Any 183 * further requests of any sort will result in a panic. The bits 184 * selected for these two flags are chosen so that they will be set 185 * in memory that is freed (freed memory is filled with 0xdeadbeef). 186 * The final release is permitted to give a new lease on life to 187 * the lock by specifying LK_REENABLE. 188 */ 189 if (lkp->lk_flags & (LK_DRAINING|LK_DRAINED)) { 190 if (lkp->lk_flags & LK_DRAINED) 191 panic("lockmgr: using decommissioned lock"); 192 if ((flags & LK_TYPE_MASK) != LK_RELEASE || 193 lkp->lk_lockholder != pid) 194 panic("lockmgr: non-release on draining lock: %d\n", 195 flags & LK_TYPE_MASK); 196 lkp->lk_flags &= ~LK_DRAINING; 197 if ((flags & LK_REENABLE) == 0) 198 lkp->lk_flags |= LK_DRAINED; 199 } 200 #endif DIAGNOSTIC 201 202 switch (flags & LK_TYPE_MASK) { 203 204 case LK_SHARED: 205 if (lkp->lk_lockholder != pid) { 206 /* 207 * If just polling, check to see if we will block. 208 */ 209 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & 210 (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE))) { 211 error = EBUSY; 212 break; 213 } 214 /* 215 * Wait for exclusive locks and upgrades to clear. 216 */ 217 ACQUIRE(lkp, error, extflags, lkp->lk_flags & 218 (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)); 219 if (error) 220 break; 221 lkp->lk_sharecount++; 222 COUNT(p, 1); 223 break; 224 } 225 /* 226 * We hold an exclusive lock, so downgrade it to shared. 227 * An alternative would be to fail with EDEADLK. 228 */ 229 lkp->lk_sharecount++; 230 COUNT(p, 1); 231 /* fall into downgrade */ 232 233 case LK_DOWNGRADE: 234 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 235 panic("lockmgr: not holding exclusive lock"); 236 lkp->lk_sharecount += 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 lkp->lk_sharecount--; 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 (lkp->lk_lockholder == pid || lkp->lk_sharecount <= 0) 268 panic("lockmgr: upgrade exclusive lock"); 269 lkp->lk_sharecount--; 270 COUNT(p, -1); 271 /* 272 * If we are just polling, check to see if we will block. 273 */ 274 if ((extflags & LK_NOWAIT) && 275 ((lkp->lk_flags & LK_WANT_UPGRADE) || 276 lkp->lk_sharecount > 1)) { 277 error = EBUSY; 278 break; 279 } 280 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 281 /* 282 * We are first shared lock to request an upgrade, so 283 * request upgrade and wait for the shared count to 284 * drop to zero, then take exclusive lock. 285 */ 286 lkp->lk_flags |= LK_WANT_UPGRADE; 287 ACQUIRE(lkp, error, extflags, lkp->lk_sharecount); 288 lkp->lk_flags &= ~LK_WANT_UPGRADE; 289 if (error) 290 break; 291 lkp->lk_flags |= LK_HAVE_EXCL; 292 lkp->lk_lockholder = pid; 293 if (lkp->lk_exclusivecount != 0) 294 panic("lockmgr: non-zero exclusive count"); 295 lkp->lk_exclusivecount = 1; 296 COUNT(p, 1); 297 break; 298 } 299 /* 300 * Someone else has requested upgrade. Release our shared 301 * lock, awaken upgrade requestor if we are the last shared 302 * lock, then request an exclusive lock. 303 */ 304 if (lkp->lk_sharecount == 0 && lkp->lk_waitcount) 305 wakeup((void *)lkp); 306 /* fall into exclusive request */ 307 308 case LK_EXCLUSIVE: 309 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 310 /* 311 * Recursive lock. 312 */ 313 if ((extflags & LK_CANRECURSE) == 0) 314 panic("lockmgr: locking against myself"); 315 lkp->lk_exclusivecount++; 316 COUNT(p, 1); 317 break; 318 } 319 /* 320 * If we are just polling, check to see if we will sleep. 321 */ 322 if ((extflags & LK_NOWAIT) && ((lkp->lk_flags & 323 (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) || 324 lkp->lk_sharecount != 0)) { 325 error = EBUSY; 326 break; 327 } 328 /* 329 * Try to acquire the want_exclusive flag. 330 */ 331 ACQUIRE(lkp, error, extflags, lkp->lk_flags & 332 (LK_HAVE_EXCL | LK_WANT_EXCL)); 333 if (error) 334 break; 335 lkp->lk_flags |= LK_WANT_EXCL; 336 /* 337 * Wait for shared locks and upgrades to finish. 338 */ 339 ACQUIRE(lkp, error, extflags, lkp->lk_sharecount != 0 || 340 (lkp->lk_flags & LK_WANT_UPGRADE)); 341 lkp->lk_flags &= ~LK_WANT_EXCL; 342 if (error) 343 break; 344 lkp->lk_flags |= LK_HAVE_EXCL; 345 lkp->lk_lockholder = pid; 346 if (lkp->lk_exclusivecount != 0) 347 panic("lockmgr: non-zero exclusive count"); 348 lkp->lk_exclusivecount = 1; 349 COUNT(p, 1); 350 break; 351 352 case LK_RELEASE: 353 if (lkp->lk_exclusivecount != 0) { 354 if (pid != lkp->lk_lockholder) 355 panic("lockmgr: pid %d, not %s %d unlocking", 356 pid, "exclusive lock holder", 357 lkp->lk_lockholder); 358 lkp->lk_exclusivecount--; 359 COUNT(p, -1); 360 if (lkp->lk_exclusivecount == 0) { 361 lkp->lk_flags &= ~LK_HAVE_EXCL; 362 lkp->lk_lockholder = LK_NOPROC; 363 } 364 } else if (lkp->lk_sharecount != 0) { 365 lkp->lk_sharecount--; 366 COUNT(p, -1); 367 } 368 if (lkp->lk_waitcount) 369 wakeup((void *)lkp); 370 break; 371 372 case LK_DRAIN: 373 /* 374 * Check that we do not already hold the lock, as it can 375 * never drain if we do. Unfortunately, we have no way to 376 * check for holding a shared lock, but at least we can 377 * check for an exclusive one. 378 */ 379 if (lkp->lk_lockholder == pid) 380 panic("lockmgr: draining against myself"); 381 /* 382 * If we are just polling, check to see if we will sleep. 383 */ 384 if ((extflags & LK_NOWAIT) && ((lkp->lk_flags & 385 (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) || 386 lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0)) { 387 error = EBUSY; 388 break; 389 } 390 PAUSE(lkp, ((lkp->lk_flags & 391 (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) || 392 lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0)); 393 for (error = 0; ((lkp->lk_flags & 394 (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) || 395 lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0); ) { 396 lkp->lk_flags |= LK_WAITDRAIN; 397 simple_unlock(&lkp->lk_interlock); 398 if ((error = tsleep((void *)&lkp->lk_flags, 399 lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo))) 400 return (error); 401 if ((extflags) & LK_SLEEPFAIL) 402 return (ENOLCK); 403 simple_lock(&lkp->lk_interlock); 404 } 405 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 406 lkp->lk_lockholder = pid; 407 lkp->lk_exclusivecount = 1; 408 COUNT(p, 1); 409 break; 410 411 default: 412 simple_unlock(&lkp->lk_interlock); 413 panic("lockmgr: unknown locktype request %d", 414 flags & LK_TYPE_MASK); 415 /* NOTREACHED */ 416 } 417 if ((lkp->lk_flags & LK_WAITDRAIN) && ((lkp->lk_flags & 418 (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) == 0 && 419 lkp->lk_sharecount == 0 && lkp->lk_waitcount == 0)) { 420 lkp->lk_flags &= ~LK_WAITDRAIN; 421 wakeup((void *)&lkp->lk_flags); 422 } 423 simple_unlock(&lkp->lk_interlock); 424 return (error); 425 } 426 427 /* 428 * Print out information about state of a lock. Used by VOP_PRINT 429 * routines to display ststus about contained locks. 430 */ 431 void 432 lockmgr_printinfo(lkp) 433 struct lock *lkp; 434 { 435 436 if (lkp->lk_sharecount) 437 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 438 lkp->lk_sharecount); 439 else if (lkp->lk_flags & LK_HAVE_EXCL) 440 printf(" lock type %s: EXCL (count %d) by pid %d", 441 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 442 if (lkp->lk_waitcount > 0) 443 printf(" with %d pending", lkp->lk_waitcount); 444 } 445 446 #if defined(LOCKDEBUG) && NCPUS == 1 447 #include <sys/kernel.h> 448 #include <vm/vm.h> 449 #include <sys/sysctl.h> 450 int lockpausetime = 0; 451 struct ctldebug debug2 = { "lockpausetime", &lockpausetime }; 452 int simplelockrecurse; 453 /* 454 * Simple lock functions so that the debugger can see from whence 455 * they are being called. 456 */ 457 void 458 simple_lock_init(alp) 459 struct simplelock *alp; 460 { 461 alp->lock_data = 0; 462 alp->lock_file = NULL; 463 alp->lock_line = 0; 464 alp->unlock_file = NULL; 465 alp->unlock_line = 0; 466 } 467 468 void 469 _simple_lock(alp, id, l) 470 __volatile struct simplelock *alp; 471 const char *id; 472 int l; 473 { 474 if (simplelockrecurse) 475 return; 476 if (alp->lock_data == 1) { 477 printf("simple_lock: lock held\n"); 478 printf("currently at: %s:%d\n", id, l); 479 printf("last locked: %s:%d\n", 480 alp->lock_file, alp->lock_line); 481 printf("last unlocked: %s:%d\n", 482 alp->unlock_file, alp->unlock_line); 483 if (lockpausetime == -1) 484 panic("simple_lock: lock held"); 485 if (lockpausetime == 1) { 486 #ifdef BACKTRACE 487 BACKTRACE(curproc); 488 #endif 489 } else if (lockpausetime > 1) { 490 printf("simple_lock: lock held, pausing..."); 491 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 492 lockpausetime * hz); 493 printf(" continuing\n"); 494 } 495 } 496 alp->lock_data = 1; 497 alp->lock_file = id; 498 alp->lock_line = l; 499 if (curproc) 500 curproc->p_simple_locks++; 501 } 502 503 int 504 _simple_lock_try(alp, id, l) 505 __volatile struct simplelock *alp; 506 const char *id; 507 int l; 508 { 509 510 if (alp->lock_data) 511 return (0); 512 if (simplelockrecurse) 513 return (1); 514 alp->lock_data = 1; 515 alp->lock_file = id; 516 alp->lock_line = l; 517 if (curproc) 518 curproc->p_simple_locks++; 519 return (1); 520 } 521 522 void 523 _simple_unlock(alp, id, l) 524 __volatile struct simplelock *alp; 525 const char *id; 526 int l; 527 { 528 529 if (simplelockrecurse) 530 return; 531 if (alp->lock_data == 0) { 532 printf("simple_unlock: lock not held\n"); 533 printf("currently at: %s:%d\n", id, l); 534 printf("last locked: %s:%d\n", 535 alp->lock_file, alp->lock_line); 536 printf("last unlocked: %s:%d\n", 537 alp->unlock_file, alp->unlock_line); 538 if (lockpausetime == -1) 539 panic("simple_unlock: lock not held"); 540 if (lockpausetime == 1) { 541 #ifdef BACKTRACE 542 BACKTRACE(curproc); 543 #endif 544 } else if (lockpausetime > 1) { 545 printf("simple_unlock: lock not held, pausing..."); 546 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 547 lockpausetime * hz); 548 printf(" continuing\n"); 549 } 550 } 551 alp->lock_data = 0; 552 alp->unlock_file = id; 553 alp->unlock_line = l; 554 if (curproc) 555 curproc->p_simple_locks--; 556 } 557 #endif /* LOCKDEBUG && NCPUS == 1 */ 558
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