kern_lock.c revision 50477
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 50477 1999-08-28 01:08:13Z peter $ 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 74static int acquire(struct lock *lkp, int extflags, int wanted); 75static int apause(struct lock *lkp, int flags); 76static int acquiredrain(struct lock *lkp, int extflags) ; 77 78static LOCK_INLINE void 79sharelock(struct lock *lkp, int incr) { 80 lkp->lk_flags |= LK_SHARE_NONZERO; 81 lkp->lk_sharecount += incr; 82} 83 84static LOCK_INLINE void 85shareunlock(struct lock *lkp, int decr) { 86 87 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 88 89 if (lkp->lk_sharecount == decr) { 90 lkp->lk_flags &= ~LK_SHARE_NONZERO; 91 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 92 wakeup(lkp); 93 } 94 lkp->lk_sharecount = 0; 95 } else { 96 lkp->lk_sharecount -= decr; 97 } 98} 99 100/* 101 * This is the waitloop optimization, and note for this to work 102 * simple_lock and simple_unlock should be subroutines to avoid 103 * optimization troubles. 104 */ 105static int 106apause(struct lock *lkp, int flags) { 107 int lock_wait; 108 lock_wait = LOCK_WAIT_TIME; 109 for (; lock_wait > 0; lock_wait--) { 110 int i; 111 if ((lkp->lk_flags & flags) == 0) 112 return 0; 113 simple_unlock(&lkp->lk_interlock); 114 for (i = LOCK_SAMPLE_WAIT; i > 0; i--) { 115 if ((lkp->lk_flags & flags) == 0) { 116 simple_lock(&lkp->lk_interlock); 117 if ((lkp->lk_flags & flags) == 0) 118 return 0; 119 break; 120 } 121 } 122 } 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 !defined(MAX_PERF) 248 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0) 249 panic("lockmgr: not holding exclusive lock"); 250#endif 251 sharelock(lkp, lkp->lk_exclusivecount); 252 lkp->lk_exclusivecount = 0; 253 lkp->lk_flags &= ~LK_HAVE_EXCL; 254 lkp->lk_lockholder = LK_NOPROC; 255 if (lkp->lk_waitcount) 256 wakeup((void *)lkp); 257 break; 258 259 case LK_EXCLUPGRADE: 260 /* 261 * If another process is ahead of us to get an upgrade, 262 * then we want to fail rather than have an intervening 263 * exclusive access. 264 */ 265 if (lkp->lk_flags & LK_WANT_UPGRADE) { 266 shareunlock(lkp, 1); 267 COUNT(p, -1); 268 error = EBUSY; 269 break; 270 } 271 /* fall into normal upgrade */ 272 273 case LK_UPGRADE: 274 /* 275 * Upgrade a shared lock to an exclusive one. If another 276 * shared lock has already requested an upgrade to an 277 * exclusive lock, our shared lock is released and an 278 * exclusive lock is requested (which will be granted 279 * after the upgrade). If we return an error, the file 280 * will always be unlocked. 281 */ 282#if !defined(MAX_PERF) 283 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0)) 284 panic("lockmgr: upgrade exclusive lock"); 285#endif 286 shareunlock(lkp, 1); 287 COUNT(p, -1); 288 /* 289 * If we are just polling, check to see if we will block. 290 */ 291 if ((extflags & LK_NOWAIT) && 292 ((lkp->lk_flags & LK_WANT_UPGRADE) || 293 lkp->lk_sharecount > 1)) { 294 error = EBUSY; 295 break; 296 } 297 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 298 /* 299 * We are first shared lock to request an upgrade, so 300 * request upgrade and wait for the shared count to 301 * drop to zero, then take exclusive lock. 302 */ 303 lkp->lk_flags |= LK_WANT_UPGRADE; 304 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 305 lkp->lk_flags &= ~LK_WANT_UPGRADE; 306 307 if (error) 308 break; 309 lkp->lk_flags |= LK_HAVE_EXCL; 310 lkp->lk_lockholder = pid; 311#if !defined(MAX_PERF) 312 if (lkp->lk_exclusivecount != 0) 313 panic("lockmgr: non-zero exclusive count"); 314#endif 315 lkp->lk_exclusivecount = 1; 316#if defined(DEBUG_LOCKS) 317 lkp->lk_filename = file; 318 lkp->lk_lineno = line; 319 lkp->lk_lockername = name; 320#endif 321 COUNT(p, 1); 322 break; 323 } 324 /* 325 * Someone else has requested upgrade. Release our shared 326 * lock, awaken upgrade requestor if we are the last shared 327 * lock, then request an exclusive lock. 328 */ 329 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 330 LK_WAIT_NONZERO) 331 wakeup((void *)lkp); 332 /* fall into exclusive request */ 333 334 case LK_EXCLUSIVE: 335 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) { 336 /* 337 * Recursive lock. 338 */ 339#if !defined(MAX_PERF) 340 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 341 panic("lockmgr: locking against myself"); 342#endif 343 if ((extflags & LK_CANRECURSE) != 0) { 344 lkp->lk_exclusivecount++; 345 COUNT(p, 1); 346 break; 347 } 348 } 349 /* 350 * If we are just polling, check to see if we will sleep. 351 */ 352 if ((extflags & LK_NOWAIT) && 353 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 354 error = EBUSY; 355 break; 356 } 357 /* 358 * Try to acquire the want_exclusive flag. 359 */ 360 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 361 if (error) 362 break; 363 lkp->lk_flags |= LK_WANT_EXCL; 364 /* 365 * Wait for shared locks and upgrades to finish. 366 */ 367 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 368 lkp->lk_flags &= ~LK_WANT_EXCL; 369 if (error) 370 break; 371 lkp->lk_flags |= LK_HAVE_EXCL; 372 lkp->lk_lockholder = pid; 373#if !defined(MAX_PERF) 374 if (lkp->lk_exclusivecount != 0) 375 panic("lockmgr: non-zero exclusive count"); 376#endif 377 lkp->lk_exclusivecount = 1; 378#if defined(DEBUG_LOCKS) 379 lkp->lk_filename = file; 380 lkp->lk_lineno = line; 381 lkp->lk_lockername = name; 382#endif 383 COUNT(p, 1); 384 break; 385 386 case LK_RELEASE: 387 if (lkp->lk_exclusivecount != 0) { 388#if !defined(MAX_PERF) 389 if (lkp->lk_lockholder != pid && 390 lkp->lk_lockholder != LK_KERNPROC) 391 panic("lockmgr: pid %d, not %s %d unlocking", 392 pid, "exclusive lock holder", 393 lkp->lk_lockholder); 394#endif 395 COUNT(p, -1); 396 if (lkp->lk_exclusivecount == 1) { 397 lkp->lk_flags &= ~LK_HAVE_EXCL; 398 lkp->lk_lockholder = LK_NOPROC; 399 lkp->lk_exclusivecount = 0; 400 } else { 401 lkp->lk_exclusivecount--; 402 } 403 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 404 shareunlock(lkp, 1); 405 COUNT(p, -1); 406 } 407 if (lkp->lk_flags & LK_WAIT_NONZERO) 408 wakeup((void *)lkp); 409 break; 410 411 case LK_DRAIN: 412 /* 413 * Check that we do not already hold the lock, as it can 414 * never drain if we do. Unfortunately, we have no way to 415 * check for holding a shared lock, but at least we can 416 * check for an exclusive one. 417 */ 418#if !defined(MAX_PERF) 419 if (lkp->lk_lockholder == pid) 420 panic("lockmgr: draining against myself"); 421#endif 422 423 error = acquiredrain(lkp, extflags); 424 if (error) 425 break; 426 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 427 lkp->lk_lockholder = pid; 428 lkp->lk_exclusivecount = 1; 429#if defined(DEBUG_LOCKS) 430 lkp->lk_filename = file; 431 lkp->lk_lineno = line; 432 lkp->lk_lockername = name; 433#endif 434 COUNT(p, 1); 435 break; 436 437 default: 438#if !defined(MAX_PERF) 439 simple_unlock(&lkp->lk_interlock); 440 panic("lockmgr: unknown locktype request %d", 441 flags & LK_TYPE_MASK); 442#endif 443 /* NOTREACHED */ 444 } 445 if ((lkp->lk_flags & LK_WAITDRAIN) && 446 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 447 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 448 lkp->lk_flags &= ~LK_WAITDRAIN; 449 wakeup((void *)&lkp->lk_flags); 450 } 451 simple_unlock(&lkp->lk_interlock); 452 return (error); 453} 454 455static int 456acquiredrain(struct lock *lkp, int extflags) { 457 int error; 458 459 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 460 return EBUSY; 461 } 462 463 error = apause(lkp, LK_ALL); 464 if (error == 0) 465 return 0; 466 467 while (lkp->lk_flags & LK_ALL) { 468 lkp->lk_flags |= LK_WAITDRAIN; 469 simple_unlock(&lkp->lk_interlock); 470 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 471 lkp->lk_wmesg, lkp->lk_timo); 472 simple_lock(&lkp->lk_interlock); 473 if (error) 474 return error; 475 if (extflags & LK_SLEEPFAIL) { 476 return ENOLCK; 477 } 478 } 479 return 0; 480} 481 482/* 483 * Initialize a lock; required before use. 484 */ 485void 486lockinit(lkp, prio, wmesg, timo, flags) 487 struct lock *lkp; 488 int prio; 489 char *wmesg; 490 int timo; 491 int flags; 492{ 493 494 simple_lock_init(&lkp->lk_interlock); 495 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 496 lkp->lk_sharecount = 0; 497 lkp->lk_waitcount = 0; 498 lkp->lk_exclusivecount = 0; 499 lkp->lk_prio = prio; 500 lkp->lk_wmesg = wmesg; 501 lkp->lk_timo = timo; 502 lkp->lk_lockholder = LK_NOPROC; 503} 504 505/* 506 * Determine the status of a lock. 507 */ 508int 509lockstatus(lkp) 510 struct lock *lkp; 511{ 512 int lock_type = 0; 513 514 simple_lock(&lkp->lk_interlock); 515 if (lkp->lk_exclusivecount != 0) 516 lock_type = LK_EXCLUSIVE; 517 else if (lkp->lk_sharecount != 0) 518 lock_type = LK_SHARED; 519 simple_unlock(&lkp->lk_interlock); 520 return (lock_type); 521} 522 523/* 524 * Determine the number of holders of a lock. 525 */ 526int 527lockcount(lkp) 528 struct lock *lkp; 529{ 530 int count; 531 532 simple_lock(&lkp->lk_interlock); 533 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 534 simple_unlock(&lkp->lk_interlock); 535 return (count); 536} 537 538/* 539 * Print out information about state of a lock. Used by VOP_PRINT 540 * routines to display status about contained locks. 541 */ 542void 543lockmgr_printinfo(lkp) 544 struct lock *lkp; 545{ 546 547 if (lkp->lk_sharecount) 548 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 549 lkp->lk_sharecount); 550 else if (lkp->lk_flags & LK_HAVE_EXCL) 551 printf(" lock type %s: EXCL (count %d) by pid %d", 552 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder); 553 if (lkp->lk_waitcount > 0) 554 printf(" with %d pending", lkp->lk_waitcount); 555} 556 557#if defined(SIMPLELOCK_DEBUG) && (NCPUS == 1 || defined(COMPILING_LINT)) 558#include <sys/kernel.h> 559#include <sys/sysctl.h> 560 561static int lockpausetime = 0; 562SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, ""); 563 564static int simplelockrecurse; 565 566/* 567 * Simple lock functions so that the debugger can see from whence 568 * they are being called. 569 */ 570void 571simple_lock_init(alp) 572 struct simplelock *alp; 573{ 574 575 alp->lock_data = 0; 576} 577 578void 579_simple_lock(alp, id, l) 580 struct simplelock *alp; 581 const char *id; 582 int l; 583{ 584 585 if (simplelockrecurse) 586 return; 587 if (alp->lock_data == 1) { 588 if (lockpausetime == -1) 589 panic("%s:%d: simple_lock: lock held", id, l); 590 printf("%s:%d: simple_lock: lock held\n", id, l); 591 if (lockpausetime == 1) { 592 Debugger("simple_lock"); 593 /*BACKTRACE(curproc); */ 594 } else if (lockpausetime > 1) { 595 printf("%s:%d: simple_lock: lock held...", id, l); 596 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock", 597 lockpausetime * hz); 598 printf(" continuing\n"); 599 } 600 } 601 alp->lock_data = 1; 602 if (curproc) 603 curproc->p_simple_locks++; 604} 605 606int 607_simple_lock_try(alp, id, l) 608 struct simplelock *alp; 609 const char *id; 610 int l; 611{ 612 613 if (alp->lock_data) 614 return (0); 615 if (simplelockrecurse) 616 return (1); 617 alp->lock_data = 1; 618 if (curproc) 619 curproc->p_simple_locks++; 620 return (1); 621} 622 623void 624_simple_unlock(alp, id, l) 625 struct simplelock *alp; 626 const char *id; 627 int l; 628{ 629 630 if (simplelockrecurse) 631 return; 632 if (alp->lock_data == 0) { 633 if (lockpausetime == -1) 634 panic("%s:%d: simple_unlock: lock not held", id, l); 635 printf("%s:%d: simple_unlock: lock not held\n", id, l); 636 if (lockpausetime == 1) { 637 Debugger("simple_unlock"); 638 /* BACKTRACE(curproc); */ 639 } else if (lockpausetime > 1) { 640 printf("%s:%d: simple_unlock: lock not held...", id, l); 641 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock", 642 lockpausetime * hz); 643 printf(" continuing\n"); 644 } 645 } 646 alp->lock_data = 0; 647 if (curproc) 648 curproc->p_simple_locks--; 649} 650#elif defined(SIMPLELOCK_DEBUG) 651#error "SIMPLELOCK_DEBUG is not compatible with SMP!" 652#endif /* SIMPLELOCK_DEBUG && NCPUS == 1 */ 653