kern_lock.c revision 28345
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 1.7 1997/08/04 19:11:12 fsmp Exp $ 42 */ 43 44#include <sys/param.h> 45#include <sys/proc.h> 46#include <sys/lock.h> 47#include <sys/systm.h> 48 49/* 50 * Locking primitives implementation. 51 * Locks provide shared/exclusive sychronization. 52 */ 53 54#ifdef SIMPLELOCK_DEBUG 55#define COUNT(p, x) if (p) (p)->p_locks += (x) 56#else 57#define COUNT(p, x) 58#endif 59 60#define LOCK_WAIT_TIME 100 61#define LOCK_SAMPLE_WAIT 7 62 63#if defined(DIAGNOSTIC) 64#define LOCK_INLINE 65#else 66#define LOCK_INLINE inline 67#endif 68 69static int acquire(struct lock *lkp, int extflags, int wanted); 70 71static LOCK_INLINE void 72sharelock(struct lock *lkp, int incr) { 73 lkp->lk_flags |= LK_SHARE_NONZERO; 74 lkp->lk_sharecount += incr; 75} 76 77static LOCK_INLINE void 78shareunlock(struct lock *lkp, int decr) { 79#if defined(DIAGNOSTIC) 80 if (lkp->lk_sharecount < decr) 81#if defined(DDB) 82 Debugger("shareunlock: count < decr"); 83#else 84 panic("shareunlock: count < decr"); 85#endif 86#endif 87 88 lkp->lk_sharecount -= decr; 89 if (lkp->lk_sharecount == 0) 90 lkp->lk_flags &= ~LK_SHARE_NONZERO; 91} 92 93static int 94apause(struct lock *lkp, int flags) { 95 int lock_wait; 96 lock_wait = LOCK_WAIT_TIME; 97 for (; lock_wait > 0; lock_wait--) { 98 int i; 99 if ((lkp->lk_flags & flags) == 0) 100 return 0; 101 simple_unlock(&lkp->lk_interlock); 102 for (i = LOCK_SAMPLE_WAIT; i > 0; i--) { 103 if ((lkp->lk_flags & flags) == 0) { 104 simple_lock(&lkp->lk_interlock); 105 if ((lkp->lk_flags & flags) == 0) 106 return 0; 107 break; 108 } 109 } 110 } 111 return 1; 112} 113 114 115static int 116acquire(struct lock *lkp, int extflags, int wanted) { 117 int error; 118 int lock_wait; 119 120 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 121 return EBUSY; 122 } 123 124 error = apause(lkp, wanted); 125 if (error == 0) 126 return 0; 127 128 while ((lkp->lk_flags & wanted) != 0) { 129 lkp->lk_flags |= LK_WAIT_NONZERO; 130 lkp->lk_waitcount++; 131 simple_unlock(&lkp->lk_interlock); 132 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, lkp->lk_timo); 133 simple_lock(&lkp->lk_interlock); 134 lkp->lk_waitcount--; 135 if (lkp->lk_waitcount == 0) 136 lkp->lk_flags &= ~LK_WAIT_NONZERO; 137 if (error) 138 return error; 139 if (extflags & LK_SLEEPFAIL) { 140 return ENOLCK; 141 } 142 } 143 return 0; 144} 145 146#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 147 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 148 149static int 150acquiredrain(struct lock *lkp, int extflags) { 151 int error; 152 int lock_wait; 153 154 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 155 return EBUSY; 156 } 157 158 error = apause(lkp, LK_ALL); 159 if (error == 0) 160 return 0; 161 162 while (lkp->lk_flags & LK_ALL) { 163 lkp->lk_flags |= LK_WAITDRAIN; 164 simple_unlock(&lkp->lk_interlock); 165 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 166 lkp->lk_wmesg, lkp->lk_timo); 167 simple_lock(&lkp->lk_interlock); 168 if (error) 169 return error; 170 if (extflags & LK_SLEEPFAIL) { 171 return ENOLCK; 172 } 173 } 174 return 0; 175} 176 177/* 178 * Initialize a lock; required before use. 179 */ 180void 181lockinit(lkp, prio, wmesg, timo, flags) 182 struct lock *lkp; 183 int prio; 184 char *wmesg; 185 int timo; 186 int flags; 187{ 188 189 simple_lock_init(&lkp->lk_interlock); 190 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 191 lkp->lk_sharecount = 0; 192 lkp->lk_waitcount = 0; 193 lkp->lk_exclusivecount = 0; 194 lkp->lk_prio = prio; 195 lkp->lk_wmesg = wmesg; 196 lkp->lk_timo = timo; 197 lkp->lk_lockholder = LK_NOPROC; 198} 199 200/* 201 * Determine the status of a lock. 202 */ 203int 204lockstatus(lkp) 205 struct lock *lkp; 206{ 207 int lock_type = 0; 208 209 simple_lock(&lkp->lk_interlock); 210 if (lkp->lk_exclusivecount != 0) 211 lock_type = LK_EXCLUSIVE; 212 else if (lkp->lk_sharecount != 0) 213 lock_type = LK_SHARED; 214 simple_unlock(&lkp->lk_interlock); 215 return (lock_type); 216} 217 218/* 219 * Set, change, or release a lock. 220 * 221 * Shared requests increment the shared count. Exclusive requests set the 222 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 223 * accepted shared locks and shared-to-exclusive upgrades to go away. 224 */ 225int 226lockmgr(lkp, flags, interlkp, p) 227 struct lock *lkp; 228 u_int flags; 229 struct simplelock *interlkp; 230 struct proc *p; 231{ 232 int error; 233 pid_t pid; 234 int extflags; 235 236 error = 0; 237 if (p == NULL) 238 panic("lockmgr: called with null process"); 239 pid = p->p_pid; 240 241 simple_lock(&lkp->lk_interlock); 242 if (flags & LK_INTERLOCK) 243 simple_unlock(interlkp); 244 245 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 246 247 switch (flags & LK_TYPE_MASK) { 248 249 case LK_SHARED: 250 if (lkp->lk_lockholder != pid) { 251 error = acquire(lkp, extflags, 252 LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE); 253 if (error) 254 break; 255 sharelock(lkp, 1); 256 COUNT(p, 1); 257 break; 258 } 259 /* 260 * We hold an exclusive lock, so downgrade it to shared. 261 * An alternative would be to fail with EDEADLK. 262 */ 263 sharelock(lkp, 1); 264 COUNT(p, 1); 265 /* fall into downgrade */ 266 267 case LK_DOWNGRADE: 268 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 269 panic("lockmgr: not holding exclusive lock"); 270 sharelock(lkp, lkp->lk_exclusivecount); 271 lkp->lk_exclusivecount = 0; 272 lkp->lk_flags &= ~LK_HAVE_EXCL; 273 lkp->lk_lockholder = LK_NOPROC; 274 if (lkp->lk_waitcount) 275 wakeup((void *)lkp); 276 break; 277 278 case LK_EXCLUPGRADE: 279 /* 280 * If another process is ahead of us to get an upgrade, 281 * then we want to fail rather than have an intervening 282 * exclusive access. 283 */ 284 if (lkp->lk_flags & LK_WANT_UPGRADE) { 285 shareunlock(lkp, 1); 286 COUNT(p, -1); 287 error = EBUSY; 288 break; 289 } 290 /* fall into normal upgrade */ 291 292 case LK_UPGRADE: 293 /* 294 * Upgrade a shared lock to an exclusive one. If another 295 * shared lock has already requested an upgrade to an 296 * exclusive lock, our shared lock is released and an 297 * exclusive lock is requested (which will be granted 298 * after the upgrade). If we return an error, the file 299 * will always be unlocked. 300 */ 301 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0)) 302 panic("lockmgr: upgrade exclusive lock"); 303 shareunlock(lkp, 1); 304 COUNT(p, -1); 305 /* 306 * If we are just polling, check to see if we will block. 307 */ 308 if ((extflags & LK_NOWAIT) && 309 ((lkp->lk_flags & LK_WANT_UPGRADE) || 310 lkp->lk_sharecount > 1)) { 311 error = EBUSY; 312 break; 313 } 314 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 315 /* 316 * We are first shared lock to request an upgrade, so 317 * request upgrade and wait for the shared count to 318 * drop to zero, then take exclusive lock. 319 */ 320 lkp->lk_flags |= LK_WANT_UPGRADE; 321 error = acquire(lkp, extflags , LK_SHARE_NONZERO); 322 lkp->lk_flags &= ~LK_WANT_UPGRADE; 323 if (error) 324 break; 325 lkp->lk_flags |= LK_HAVE_EXCL; 326 lkp->lk_lockholder = pid; 327 if (lkp->lk_exclusivecount != 0) 328 panic("lockmgr: non-zero exclusive count"); 329 lkp->lk_exclusivecount = 1; 330 COUNT(p, 1); 331 break; 332 } 333 /* 334 * Someone else has requested upgrade. Release our shared 335 * lock, awaken upgrade requestor if we are the last shared 336 * lock, then request an exclusive lock. 337 */ 338 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 339 LK_WAIT_NONZERO) 340 wakeup((void *)lkp); 341 /* fall into exclusive request */ 342 343 case LK_EXCLUSIVE: 344 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 345 /* 346 * Recursive lock. 347 */ 348 if ((extflags & LK_CANRECURSE) == 0) 349 panic("lockmgr: locking against myself"); 350 lkp->lk_exclusivecount++; 351 COUNT(p, 1); 352 break; 353 } 354 /* 355 * If we are just polling, check to see if we will sleep. 356 */ 357 if ((extflags & LK_NOWAIT) && 358 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 359 error = EBUSY; 360 break; 361 } 362 /* 363 * Try to acquire the want_exclusive flag. 364 */ 365 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 366 if (error) 367 break; 368 lkp->lk_flags |= LK_WANT_EXCL; 369 /* 370 * Wait for shared locks and upgrades to finish. 371 */ 372 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 373 lkp->lk_flags &= ~LK_WANT_EXCL; 374 if (error) 375 break; 376 lkp->lk_flags |= LK_HAVE_EXCL; 377 lkp->lk_lockholder = pid; 378 if (lkp->lk_exclusivecount != 0) 379 panic("lockmgr: non-zero exclusive count"); 380 lkp->lk_exclusivecount = 1; 381 COUNT(p, 1); 382 break; 383 384 case LK_RELEASE: 385 if (lkp->lk_exclusivecount != 0) { 386 if (pid != lkp->lk_lockholder) 387 panic("lockmgr: pid %d, not %s %d unlocking", 388 pid, "exclusive lock holder", 389 lkp->lk_lockholder); 390 lkp->lk_exclusivecount--; 391 COUNT(p, -1); 392 if (lkp->lk_exclusivecount == 0) { 393 lkp->lk_flags &= ~LK_HAVE_EXCL; 394 lkp->lk_lockholder = LK_NOPROC; 395 } 396 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 397 shareunlock(lkp, 1); 398 COUNT(p, -1); 399 } 400 if (lkp->lk_flags & LK_WAIT_NONZERO) 401 wakeup((void *)lkp); 402 break; 403 404 case LK_DRAIN: 405 /* 406 * Check that we do not already hold the lock, as it can 407 * never drain if we do. Unfortunately, we have no way to 408 * check for holding a shared lock, but at least we can 409 * check for an exclusive one. 410 */ 411 if (lkp->lk_lockholder == pid) 412 panic("lockmgr: draining against myself"); 413 414 error = acquiredrain(lkp, extflags); 415 if (error) 416 break; 417 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 418 lkp->lk_lockholder = pid; 419 lkp->lk_exclusivecount = 1; 420 COUNT(p, 1); 421 break; 422 423 default: 424 simple_unlock(&lkp->lk_interlock); 425 panic("lockmgr: unknown locktype request %d", 426 flags & LK_TYPE_MASK); 427 /* NOTREACHED */ 428 } 429 if ((lkp->lk_flags & LK_WAITDRAIN) && 430 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 431 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 432 lkp->lk_flags &= ~LK_WAITDRAIN; 433 wakeup((void *)&lkp->lk_flags); 434 } 435 simple_unlock(&lkp->lk_interlock); 436 return (error); 437} 438 439/* 440 * Print out information about state of a lock. Used by VOP_PRINT 441 * routines to display ststus about contained locks. 442 */ 443void 444lockmgr_printinfo(lkp) 445 struct lock *lkp; 446{ 447 448 if (lkp->lk_sharecount) 449 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 450 lkp->lk_sharecount); 451 else if (lkp->lk_flags & LK_HAVE_EXCL) 452 printf(" lock type %s: EXCL (count %d) by pid %d", 453 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 454 if (lkp->lk_waitcount > 0) 455 printf(" with %d pending", lkp->lk_waitcount); 456} 457 458#if defined(SIMPLELOCK_DEBUG) && NCPUS == 1 459#include <sys/kernel.h> 460#include <sys/sysctl.h> 461 462static int lockpausetime = 0; 463SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 464 465int simplelockrecurse; 466 467/* 468 * Simple lock functions so that the debugger can see from whence 469 * they are being called. 470 */ 471void 472simple_lock_init(alp) 473 struct simplelock *alp; 474{ 475 476 alp->lock_data = 0; 477} 478 479void 480_simple_lock(alp, id, l) 481 struct simplelock *alp; 482 const char *id; 483 int l; 484{ 485 486 if (simplelockrecurse) 487 return; 488 if (alp->lock_data == 1) { 489 if (lockpausetime == -1) 490 panic("%s:%d: simple_lock: lock held", id, l); 491 printf("%s:%d: simple_lock: lock held\n", id, l); 492 if (lockpausetime == 1) { 493 Debugger("simple_lock"); 494 /*BACKTRACE(curproc); */ 495 } else if (lockpausetime > 1) { 496 printf("%s:%d: simple_lock: lock held...", id, l); 497 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 498 lockpausetime * hz); 499 printf(" continuing\n"); 500 } 501 } 502 alp->lock_data = 1; 503 if (curproc) 504 curproc->p_simple_locks++; 505} 506 507int 508_simple_lock_try(alp, id, l) 509 struct simplelock *alp; 510 const char *id; 511 int l; 512{ 513 514 if (alp->lock_data) 515 return (0); 516 if (simplelockrecurse) 517 return (1); 518 alp->lock_data = 1; 519 if (curproc) 520 curproc->p_simple_locks++; 521 return (1); 522} 523 524void 525_simple_unlock(alp, id, l) 526 struct simplelock *alp; 527 const char *id; 528 int l; 529{ 530 531 if (simplelockrecurse) 532 return; 533 if (alp->lock_data == 0) { 534 if (lockpausetime == -1) 535 panic("%s:%d: simple_unlock: lock not held", id, l); 536 printf("%s:%d: simple_unlock: lock not held\n", id, l); 537 if (lockpausetime == 1) { 538 Debugger("simple_unlock"); 539 /* BACKTRACE(curproc); */ 540 } else if (lockpausetime > 1) { 541 printf("%s:%d: simple_unlock: lock not held...", id, l); 542 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 543 lockpausetime * hz); 544 printf(" continuing\n"); 545 } 546 } 547 alp->lock_data = 0; 548 if (curproc) 549 curproc->p_simple_locks--; 550} 551#endif /* SIMPLELOCK_DEBUG && NCPUS == 1 */ 552