kern_lock.c revision 66296
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: head/sys/kern/kern_lock.c 66296 2000-09-23 12:18:06Z ps $ 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 69#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 70 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 71 72static int acquire(struct lock *lkp, int extflags, int wanted); 73static int apause(struct lock *lkp, int flags); 74static int acquiredrain(struct lock *lkp, int extflags) ; 75 76static LOCK_INLINE void 77sharelock(struct lock *lkp, int incr) { 78 lkp->lk_flags |= LK_SHARE_NONZERO; 79 lkp->lk_sharecount += incr; 80} 81 82static LOCK_INLINE void 83shareunlock(struct lock *lkp, int decr) { 84 85 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 86 87 if (lkp->lk_sharecount == decr) { 88 lkp->lk_flags &= ~LK_SHARE_NONZERO; 89 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 90 wakeup(lkp); 91 } 92 lkp->lk_sharecount = 0; 93 } else { 94 lkp->lk_sharecount -= decr; 95 } 96} 97 98/* 99 * This is the waitloop optimization, and note for this to work 100 * simple_lock and simple_unlock should be subroutines to avoid 101 * optimization troubles. 102 */ 103static int 104apause(struct lock *lkp, int flags) 105{ 106#ifdef SMP 107 int i, lock_wait; 108#endif 109 110 if ((lkp->lk_flags & flags) == 0) 111 return 0; 112#ifdef SMP 113 for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) { 114 simple_unlock(&lkp->lk_interlock); 115 for (i = LOCK_SAMPLE_WAIT; i > 0; i--) 116 if ((lkp->lk_flags & flags) == 0) 117 break; 118 simple_lock(&lkp->lk_interlock); 119 if ((lkp->lk_flags & flags) == 0) 120 return 0; 121 } 122#endif 123 return 1; 124} 125 126static int 127acquire(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 */ 173int 174#ifndef DEBUG_LOCKS 175lockmgr(lkp, flags, interlkp, p) 176#else 177debuglockmgr(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 /* 209 * If we are not the exclusive lock holder, we have to block 210 * while there is an exclusive lock holder or while an 211 * exclusive lock request or upgrade request is in progress. 212 * 213 * However, if P_DEADLKTREAT is set, we override exclusive 214 * lock requests or upgrade requests ( but not the exclusive 215 * lock itself ). 216 */ 217 if (lkp->lk_lockholder != pid) { 218 if (p && (p->p_flag & P_DEADLKTREAT)) { 219 error = acquire( 220 lkp, 221 extflags, 222 LK_HAVE_EXCL 223 ); 224 } else { 225 error = acquire( 226 lkp, 227 extflags, 228 LK_HAVE_EXCL | LK_WANT_EXCL | 229 LK_WANT_UPGRADE 230 ); 231 } 232 if (error) 233 break; 234 sharelock(lkp, 1); 235 COUNT(p, 1); 236 break; 237 } 238 /* 239 * We hold an exclusive lock, so downgrade it to shared. 240 * An alternative would be to fail with EDEADLK. 241 */ 242 sharelock(lkp, 1); 243 COUNT(p, 1); 244 /* fall into downgrade */ 245 246 case LK_DOWNGRADE: 247 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 248 panic("lockmgr: not holding exclusive lock"); 249 sharelock(lkp, lkp->lk_exclusivecount); 250 lkp->lk_exclusivecount = 0; 251 lkp->lk_flags &= ~LK_HAVE_EXCL; 252 lkp->lk_lockholder = LK_NOPROC; 253 if (lkp->lk_waitcount) 254 wakeup((void *)lkp); 255 break; 256 257 case LK_EXCLUPGRADE: 258 /* 259 * If another process is ahead of us to get an upgrade, 260 * then we want to fail rather than have an intervening 261 * exclusive access. 262 */ 263 if (lkp->lk_flags & LK_WANT_UPGRADE) { 264 shareunlock(lkp, 1); 265 COUNT(p, -1); 266 error = EBUSY; 267 break; 268 } 269 /* fall into normal upgrade */ 270 271 case LK_UPGRADE: 272 /* 273 * Upgrade a shared lock to an exclusive one. If another 274 * shared lock has already requested an upgrade to an 275 * exclusive lock, our shared lock is released and an 276 * exclusive lock is requested (which will be granted 277 * after the upgrade). If we return an error, the file 278 * will always be unlocked. 279 */ 280 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0)) 281 panic("lockmgr: upgrade exclusive lock"); 282 shareunlock(lkp, 1); 283 COUNT(p, -1); 284 /* 285 * If we are just polling, check to see if we will block. 286 */ 287 if ((extflags & LK_NOWAIT) && 288 ((lkp->lk_flags & LK_WANT_UPGRADE) || 289 lkp->lk_sharecount > 1)) { 290 error = EBUSY; 291 break; 292 } 293 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 294 /* 295 * We are first shared lock to request an upgrade, so 296 * request upgrade and wait for the shared count to 297 * drop to zero, then take exclusive lock. 298 */ 299 lkp->lk_flags |= LK_WANT_UPGRADE; 300 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 301 lkp->lk_flags &= ~LK_WANT_UPGRADE; 302 303 if (error) 304 break; 305 lkp->lk_flags |= LK_HAVE_EXCL; 306 lkp->lk_lockholder = pid; 307 if (lkp->lk_exclusivecount != 0) 308 panic("lockmgr: non-zero exclusive count"); 309 lkp->lk_exclusivecount = 1; 310#if defined(DEBUG_LOCKS) 311 lkp->lk_filename = file; 312 lkp->lk_lineno = line; 313 lkp->lk_lockername = name; 314#endif 315 COUNT(p, 1); 316 break; 317 } 318 /* 319 * Someone else has requested upgrade. Release our shared 320 * lock, awaken upgrade requestor if we are the last shared 321 * lock, then request an exclusive lock. 322 */ 323 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 324 LK_WAIT_NONZERO) 325 wakeup((void *)lkp); 326 /* fall into exclusive request */ 327 328 case LK_EXCLUSIVE: 329 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 330 /* 331 * Recursive lock. 332 */ 333 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 334 panic("lockmgr: locking against myself"); 335 if ((extflags & LK_CANRECURSE) != 0) { 336 lkp->lk_exclusivecount++; 337 COUNT(p, 1); 338 break; 339 } 340 } 341 /* 342 * If we are just polling, check to see if we will sleep. 343 */ 344 if ((extflags & LK_NOWAIT) && 345 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 346 error = EBUSY; 347 break; 348 } 349 /* 350 * Try to acquire the want_exclusive flag. 351 */ 352 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 353 if (error) 354 break; 355 lkp->lk_flags |= LK_WANT_EXCL; 356 /* 357 * Wait for shared locks and upgrades to finish. 358 */ 359 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 360 lkp->lk_flags &= ~LK_WANT_EXCL; 361 if (error) 362 break; 363 lkp->lk_flags |= LK_HAVE_EXCL; 364 lkp->lk_lockholder = pid; 365 if (lkp->lk_exclusivecount != 0) 366 panic("lockmgr: non-zero exclusive count"); 367 lkp->lk_exclusivecount = 1; 368#if defined(DEBUG_LOCKS) 369 lkp->lk_filename = file; 370 lkp->lk_lineno = line; 371 lkp->lk_lockername = name; 372#endif 373 COUNT(p, 1); 374 break; 375 376 case LK_RELEASE: 377 if (lkp->lk_exclusivecount != 0) { 378 if (lkp->lk_lockholder != pid && 379 lkp->lk_lockholder != LK_KERNPROC) { 380 panic("lockmgr: pid %d, not %s %d unlocking", 381 pid, "exclusive lock holder", 382 lkp->lk_lockholder); 383 } 384 if (lkp->lk_lockholder != LK_KERNPROC) { 385 COUNT(p, -1); 386 } 387 if (lkp->lk_exclusivecount == 1) { 388 lkp->lk_flags &= ~LK_HAVE_EXCL; 389 lkp->lk_lockholder = LK_NOPROC; 390 lkp->lk_exclusivecount = 0; 391 } else { 392 lkp->lk_exclusivecount--; 393 } 394 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 395 shareunlock(lkp, 1); 396 COUNT(p, -1); 397 } 398 if (lkp->lk_flags & LK_WAIT_NONZERO) 399 wakeup((void *)lkp); 400 break; 401 402 case LK_DRAIN: 403 /* 404 * Check that we do not already hold the lock, as it can 405 * never drain if we do. Unfortunately, we have no way to 406 * check for holding a shared lock, but at least we can 407 * check for an exclusive one. 408 */ 409 if (lkp->lk_lockholder == pid) 410 panic("lockmgr: draining against myself"); 411 412 error = acquiredrain(lkp, extflags); 413 if (error) 414 break; 415 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 416 lkp->lk_lockholder = pid; 417 lkp->lk_exclusivecount = 1; 418#if defined(DEBUG_LOCKS) 419 lkp->lk_filename = file; 420 lkp->lk_lineno = line; 421 lkp->lk_lockername = name; 422#endif 423 COUNT(p, 1); 424 break; 425 426 default: 427 simple_unlock(&lkp->lk_interlock); 428 panic("lockmgr: unknown locktype request %d", 429 flags & LK_TYPE_MASK); 430 /* NOTREACHED */ 431 } 432 if ((lkp->lk_flags & LK_WAITDRAIN) && 433 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 434 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 435 lkp->lk_flags &= ~LK_WAITDRAIN; 436 wakeup((void *)&lkp->lk_flags); 437 } 438 simple_unlock(&lkp->lk_interlock); 439 return (error); 440} 441 442static int 443acquiredrain(struct lock *lkp, int extflags) { 444 int error; 445 446 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 447 return EBUSY; 448 } 449 450 error = apause(lkp, LK_ALL); 451 if (error == 0) 452 return 0; 453 454 while (lkp->lk_flags & LK_ALL) { 455 lkp->lk_flags |= LK_WAITDRAIN; 456 simple_unlock(&lkp->lk_interlock); 457 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 458 lkp->lk_wmesg, lkp->lk_timo); 459 simple_lock(&lkp->lk_interlock); 460 if (error) 461 return error; 462 if (extflags & LK_SLEEPFAIL) { 463 return ENOLCK; 464 } 465 } 466 return 0; 467} 468 469/* 470 * Initialize a lock; required before use. 471 */ 472void 473lockinit(lkp, prio, wmesg, timo, flags) 474 struct lock *lkp; 475 int prio; 476 char *wmesg; 477 int timo; 478 int flags; 479{ 480 481 simple_lock_init(&lkp->lk_interlock); 482 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 483 lkp->lk_sharecount = 0; 484 lkp->lk_waitcount = 0; 485 lkp->lk_exclusivecount = 0; 486 lkp->lk_prio = prio; 487 lkp->lk_wmesg = wmesg; 488 lkp->lk_timo = timo; 489 lkp->lk_lockholder = LK_NOPROC; 490} 491 492/* 493 * Determine the status of a lock. 494 */ 495int 496lockstatus(lkp, p) 497 struct lock *lkp; 498 struct proc *p; 499{ 500 int lock_type = 0; 501 502 simple_lock(&lkp->lk_interlock); 503 if (lkp->lk_exclusivecount != 0) { 504 if (p == NULL || lkp->lk_lockholder == p->p_pid) 505 lock_type = LK_EXCLUSIVE; 506 else 507 lock_type = LK_EXCLOTHER; 508 } else if (lkp->lk_sharecount != 0) 509 lock_type = LK_SHARED; 510 simple_unlock(&lkp->lk_interlock); 511 return (lock_type); 512} 513 514/* 515 * Determine the number of holders of a lock. 516 */ 517int 518lockcount(lkp) 519 struct lock *lkp; 520{ 521 int count; 522 523 simple_lock(&lkp->lk_interlock); 524 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 525 simple_unlock(&lkp->lk_interlock); 526 return (count); 527} 528 529/* 530 * Print out information about state of a lock. Used by VOP_PRINT 531 * routines to display status about contained locks. 532 */ 533void 534lockmgr_printinfo(lkp) 535 struct lock *lkp; 536{ 537 538 if (lkp->lk_sharecount) 539 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 540 lkp->lk_sharecount); 541 else if (lkp->lk_flags & LK_HAVE_EXCL) 542 printf(" lock type %s: EXCL (count %d) by pid %d", 543 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 544 if (lkp->lk_waitcount > 0) 545 printf(" with %d pending", lkp->lk_waitcount); 546} 547 548#if defined(SIMPLELOCK_DEBUG) && (MAXCPU == 1 || defined(COMPILING_LINT)) 549#include <sys/kernel.h> 550#include <sys/sysctl.h> 551 552static int lockpausetime = 0; 553SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 554 555static int simplelockrecurse; 556 557/* 558 * Simple lock functions so that the debugger can see from whence 559 * they are being called. 560 */ 561void 562simple_lock_init(alp) 563 struct simplelock *alp; 564{ 565 566 alp->lock_data = 0; 567} 568 569void 570_simple_lock(alp, id, l) 571 struct simplelock *alp; 572 const char *id; 573 int l; 574{ 575 576 if (simplelockrecurse) 577 return; 578 if (alp->lock_data == 1) { 579 if (lockpausetime == -1) 580 panic("%s:%d: simple_lock: lock held", id, l); 581 printf("%s:%d: simple_lock: lock held\n", id, l); 582 if (lockpausetime == 1) { 583 Debugger("simple_lock"); 584 /*BACKTRACE(curproc); */ 585 } else if (lockpausetime > 1) { 586 printf("%s:%d: simple_lock: lock held...", id, l); 587 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 588 lockpausetime * hz); 589 printf(" continuing\n"); 590 } 591 } 592 alp->lock_data = 1; 593 if (curproc) 594 curproc->p_simple_locks++; 595} 596 597int 598_simple_lock_try(alp, id, l) 599 struct simplelock *alp; 600 const char *id; 601 int l; 602{ 603 604 if (alp->lock_data) 605 return (0); 606 if (simplelockrecurse) 607 return (1); 608 alp->lock_data = 1; 609 if (curproc) 610 curproc->p_simple_locks++; 611 return (1); 612} 613 614void 615_simple_unlock(alp, id, l) 616 struct simplelock *alp; 617 const char *id; 618 int l; 619{ 620 621 if (simplelockrecurse) 622 return; 623 if (alp->lock_data == 0) { 624 if (lockpausetime == -1) 625 panic("%s:%d: simple_unlock: lock not held", id, l); 626 printf("%s:%d: simple_unlock: lock not held\n", id, l); 627 if (lockpausetime == 1) { 628 Debugger("simple_unlock"); 629 /* BACKTRACE(curproc); */ 630 } else if (lockpausetime > 1) { 631 printf("%s:%d: simple_unlock: lock not held...", id, l); 632 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 633 lockpausetime * hz); 634 printf(" continuing\n"); 635 } 636 } 637 alp->lock_data = 0; 638 if (curproc) 639 curproc->p_simple_locks--; 640} 641#elif defined(SIMPLELOCK_DEBUG) 642#error "SIMPLELOCK_DEBUG is not compatible with SMP!" 643#endif /* SIMPLELOCK_DEBUG && MAXCPU == 1 */ 644