1 /* 2 * Copyright (c) 1995 3 * The Regents of the University of California. All rights reserved. 4 * 5 * This code contains ideas from software contributed to Berkeley by 6 * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating 7 * System project at Carnegie-Mellon University. 8 * 9 * Redistribution and use in source and binary forms, with or without 10 * modification, are permitted provided that the following conditions 11 * are met: 12 * 1. Redistributions of source code must retain the above copyright 13 * notice, this list of conditions and the following disclaimer. 14 * 2. Redistributions in binary form must reproduce the above copyright 15 * notice, this list of conditions and the following disclaimer in the 16 * documentation and/or other materials provided with the distribution. 17 * 3. All advertising materials mentioning features or use of this software 18 * must display the following acknowledgement: 19 * This product includes software developed by the University of 20 * California, Berkeley and its contributors. 21 * 4. Neither the name of the University nor the names of its contributors 22 * may be used to endorse or promote products derived from this software 23 * without specific prior written permission. 24 * 25 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 26 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 27 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 28 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 29 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 30 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 31 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 32 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 33 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 34 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 35 * SUCH DAMAGE. 36 * 37 * @(#)kern_lock.c 8.18 (Berkeley) 5/21/95 38 * $Id: kern_lock.c,v 1.5 1997/03/25 17:11:30 peter Exp $ 39 */ 40 41 #include <sys/param.h> 42 #include <sys/proc.h> 43 #include <sys/lock.h> 44 #include <sys/systm.h> 45 46 /* 47 * Locking primitives implementation. 48 * Locks provide shared/exclusive sychronization. 49 */ 50 51 #ifdef SIMPLELOCK_DEBUG 52 #define COUNT(p, x) if (p) (p)->p_locks += (x) 53 #else 54 #define COUNT(p, x) 55 #endif 56 57 #if NCPUS > 1 58 59 /* 60 * For multiprocessor system, try spin lock first. 61 * 62 * This should be inline expanded below, but we cannot have #if 63 * inside a multiline define. 64 */ 65 int lock_wait_time = 100; 66 #define PAUSE(lkp, wanted) \ 67 if (lock_wait_time > 0) { \ 68 int i; \ 69 \ 70 simple_unlock(&lkp->lk_interlock); \ 71 for (i = lock_wait_time; i > 0; i--) \ 72 if (!(wanted)) \ 73 break; \ 74 simple_lock(&lkp->lk_interlock); \ 75 } \ 76 if (!(wanted)) \ 77 break; 78 79 #else /* NCPUS == 1 */ 80 81 /* 82 * It is an error to spin on a uniprocessor as nothing will ever cause 83 * the simple lock to clear while we are executing. 84 */ 85 #define PAUSE(lkp, wanted) 86 87 #endif /* NCPUS == 1 */ 88 89 /* 90 * Acquire a resource. 91 */ 92 #define ACQUIRE(lkp, error, extflags, wanted) \ 93 PAUSE(lkp, wanted); \ 94 for (error = 0; wanted; ) { \ 95 (lkp)->lk_waitcount++; \ 96 simple_unlock(&(lkp)->lk_interlock); \ 97 error = tsleep((void *)lkp, (lkp)->lk_prio, \ 98 (lkp)->lk_wmesg, (lkp)->lk_timo); \ 99 simple_lock(&(lkp)->lk_interlock); \ 100 (lkp)->lk_waitcount--; \ 101 if (error) \ 102 break; \ 103 if ((extflags) & LK_SLEEPFAIL) { \ 104 error = ENOLCK; \ 105 break; \ 106 } \ 107 } 108 109 /* 110 * Initialize a lock; required before use. 111 */ 112 void 113 lockinit(lkp, prio, wmesg, timo, flags) 114 struct lock *lkp; 115 int prio; 116 char *wmesg; 117 int timo; 118 int flags; 119 { 120 121 simple_lock_init(&lkp->lk_interlock); 122 lkp->lk_flags = flags & LK_EXTFLG_MASK; 123 lkp->lk_sharecount = 0; 124 lkp->lk_waitcount = 0; 125 lkp->lk_exclusivecount = 0; 126 lkp->lk_prio = prio; 127 lkp->lk_wmesg = wmesg; 128 lkp->lk_timo = timo; 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, p) 159 __volatile struct lock *lkp; 160 u_int flags; 161 struct simplelock *interlkp; 162 struct proc *p; 163 { 164 int error; 165 pid_t pid; 166 int extflags; 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, lkp->lk_prio, 399 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(SIMPLELOCK_DEBUG) && NCPUS == 1 447 #include <sys/kernel.h> 448 #include <sys/sysctl.h> 449 450 static int lockpausetime = 0; 451 SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 452 453 int simplelockrecurse; 454 455 /* 456 * Simple lock functions so that the debugger can see from whence 457 * they are being called. 458 */ 459 void 460 simple_lock_init(alp) 461 struct simplelock *alp; 462 { 463 464 alp->lock_data = 0; 465 } 466 467 void 468 _simple_lock(alp, id, l) 469 __volatile struct simplelock *alp; 470 const char *id; 471 int l; 472 { 473 474 if (simplelockrecurse) 475 return; 476 if (alp->lock_data == 1) { 477 if (lockpausetime == -1) 478 panic("%s:%d: simple_lock: lock held", id, l); 479 printf("%s:%d: simple_lock: lock held\n", id, l); 480 if (lockpausetime == 1) { 481 Debugger("simple_lock"); 482 /*BACKTRACE(curproc); */ 483 } else if (lockpausetime > 1) { 484 printf("%s:%d: simple_lock: lock held...", id, l); 485 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 486 lockpausetime * hz); 487 printf(" continuing\n"); 488 } 489 } 490 alp->lock_data = 1; 491 if (curproc) 492 curproc->p_simple_locks++; 493 } 494 495 int 496 _simple_lock_try(alp, id, l) 497 __volatile struct simplelock *alp; 498 const char *id; 499 int l; 500 { 501 502 if (alp->lock_data) 503 return (0); 504 if (simplelockrecurse) 505 return (1); 506 alp->lock_data = 1; 507 if (curproc) 508 curproc->p_simple_locks++; 509 return (1); 510 } 511 512 void 513 _simple_unlock(alp, id, l) 514 __volatile struct simplelock *alp; 515 const char *id; 516 int l; 517 { 518 519 if (simplelockrecurse) 520 return; 521 if (alp->lock_data == 0) { 522 if (lockpausetime == -1) 523 panic("%s:%d: simple_unlock: lock not held", id, l); 524 printf("%s:%d: simple_unlock: lock not held\n", id, l); 525 if (lockpausetime == 1) { 526 Debugger("simple_unlock"); 527 /* BACKTRACE(curproc); */ 528 } else if (lockpausetime > 1) { 529 printf("%s:%d: simple_unlock: lock not held...", id, l); 530 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 531 lockpausetime * hz); 532 printf(" continuing\n"); 533 } 534 } 535 alp->lock_data = 0; 536 if (curproc) 537 curproc->p_simple_locks--; 538 } 539 #endif /* SIMPLELOCK_DEBUG && NCPUS == 1 */ 540