kern_lock.c revision 144372
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 */ 42 43#include <sys/cdefs.h> 44__FBSDID("$FreeBSD: head/sys/kern/kern_lock.c 144372 2005-03-31 05:18:19Z jeff $"); 45 46#include <sys/param.h> 47#include <sys/kernel.h> 48#include <sys/ktr.h> 49#include <sys/lock.h> 50#include <sys/lockmgr.h> 51#include <sys/mutex.h> 52#include <sys/proc.h> 53#include <sys/systm.h> 54 55/* 56 * Locking primitives implementation. 57 * Locks provide shared/exclusive sychronization. 58 */ 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 COUNT(td, x) if ((td)) (td)->td_locks += (x) 70 71#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 72 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 73 74/* 75 * Mutex array variables. Rather than each lockmgr lock having its own mutex, 76 * share a fixed (at boot time) number of mutexes across all lockmgr locks in 77 * order to keep sizeof(struct lock) down. 78 */ 79static struct mtx lock_mtx; 80 81static int acquire(struct lock **lkpp, int extflags, int wanted); 82static int acquiredrain(struct lock *lkp, int extflags) ; 83 84static void 85lockmgr_init(void *dummy __unused) 86{ 87 mtx_init(&lock_mtx, "lockmgr", NULL, MTX_DEF); 88} 89SYSINIT(lmgrinit, SI_SUB_LOCKMGR, SI_ORDER_FIRST, lockmgr_init, NULL) 90 91static LOCK_INLINE void 92sharelock(struct thread *td, struct lock *lkp, int incr) { 93 lkp->lk_flags |= LK_SHARE_NONZERO; 94 lkp->lk_sharecount += incr; 95 COUNT(td, incr); 96} 97 98static LOCK_INLINE void 99shareunlock(struct thread *td, struct lock *lkp, int decr) { 100 101 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 102 103 COUNT(td, -decr); 104 if (lkp->lk_sharecount == decr) { 105 lkp->lk_flags &= ~LK_SHARE_NONZERO; 106 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 107 wakeup(lkp); 108 } 109 lkp->lk_sharecount = 0; 110 } else { 111 lkp->lk_sharecount -= decr; 112 } 113} 114 115static int 116acquire(struct lock **lkpp, int extflags, int wanted) 117{ 118 struct lock *lkp = *lkpp; 119 int s, error; 120 CTR3(KTR_LOCK, 121 "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x", 122 lkp, extflags, wanted); 123 124 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 125 return EBUSY; 126 } 127 128 s = splhigh(); 129 while ((lkp->lk_flags & wanted) != 0) { 130 lkp->lk_flags |= LK_WAIT_NONZERO; 131 lkp->lk_waitcount++; 132 error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio, 133 lkp->lk_wmesg, 134 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 135 if (lkp->lk_waitcount == 1) { 136 lkp->lk_flags &= ~LK_WAIT_NONZERO; 137 lkp->lk_waitcount = 0; 138 } else { 139 lkp->lk_waitcount--; 140 } 141 if (error) { 142 splx(s); 143 return error; 144 } 145 if (extflags & LK_SLEEPFAIL) { 146 splx(s); 147 return ENOLCK; 148 } 149 if (lkp->lk_newlock != NULL) { 150 mtx_lock(lkp->lk_newlock->lk_interlock); 151 mtx_unlock(lkp->lk_interlock); 152 if (lkp->lk_waitcount == 0) 153 wakeup((void *)(&lkp->lk_newlock)); 154 *lkpp = lkp = lkp->lk_newlock; 155 } 156 } 157 splx(s); 158 return 0; 159} 160 161/* 162 * Set, change, or release a lock. 163 * 164 * Shared requests increment the shared count. Exclusive requests set the 165 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 166 * accepted shared locks and shared-to-exclusive upgrades to go away. 167 */ 168int 169#ifndef DEBUG_LOCKS 170lockmgr(lkp, flags, interlkp, td) 171#else 172debuglockmgr(lkp, flags, interlkp, td, name, file, line) 173#endif 174 struct lock *lkp; 175 u_int flags; 176 struct mtx *interlkp; 177 struct thread *td; 178#ifdef DEBUG_LOCKS 179 const char *name; /* Name of lock function */ 180 const char *file; /* Name of file call is from */ 181 int line; /* Line number in file */ 182#endif 183{ 184 int error; 185 struct thread *thr; 186 int extflags, lockflags; 187 188 error = 0; 189 if (td == NULL) 190 thr = LK_KERNPROC; 191 else 192 thr = td; 193 194 if ((flags & LK_INTERNAL) == 0) 195 mtx_lock(lkp->lk_interlock); 196#ifdef DEBUG_LOCKS 197 CTR6(KTR_LOCK, 198 "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), flags == 0x%x, " 199 "td == %p %s:%d", lkp, lkp->lk_wmesg, flags, td, file, line); 200#else 201 CTR6(KTR_LOCK, 202 "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), owner == %p, exclusivecount == %d, flags == 0x%x, " 203 "td == %p", lkp, lkp->lk_wmesg, lkp->lk_lockholder, 204 lkp->lk_exclusivecount, flags, td); 205#endif 206 207 if (flags & LK_INTERLOCK) { 208 mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED); 209 mtx_unlock(interlkp); 210 } 211 212 if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0) 213 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, 214 &lkp->lk_interlock->mtx_object, 215 "Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg); 216 217 if (panicstr != NULL) { 218 mtx_unlock(lkp->lk_interlock); 219 return (0); 220 } 221 if ((lkp->lk_flags & LK_NOSHARE) && 222 (flags & LK_TYPE_MASK) == LK_SHARED) { 223 flags &= ~LK_TYPE_MASK; 224 flags |= LK_EXCLUSIVE; 225 } 226 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 227 228 switch (flags & LK_TYPE_MASK) { 229 230 case LK_SHARED: 231 /* 232 * If we are not the exclusive lock holder, we have to block 233 * while there is an exclusive lock holder or while an 234 * exclusive lock request or upgrade request is in progress. 235 * 236 * However, if TDP_DEADLKTREAT is set, we override exclusive 237 * lock requests or upgrade requests ( but not the exclusive 238 * lock itself ). 239 */ 240 if (lkp->lk_lockholder != thr) { 241 lockflags = LK_HAVE_EXCL; 242 if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT)) 243 lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE; 244 error = acquire(&lkp, extflags, lockflags); 245 if (error) 246 break; 247 sharelock(td, lkp, 1); 248#if defined(DEBUG_LOCKS) 249 lkp->lk_slockholder = thr; 250 lkp->lk_sfilename = file; 251 lkp->lk_slineno = line; 252 lkp->lk_slockername = name; 253#endif 254 break; 255 } 256 /* 257 * We hold an exclusive lock, so downgrade it to shared. 258 * An alternative would be to fail with EDEADLK. 259 */ 260 sharelock(td, lkp, 1); 261 /* FALLTHROUGH downgrade */ 262 263 case LK_DOWNGRADE: 264 KASSERT(lkp->lk_lockholder == thr && lkp->lk_exclusivecount != 0, 265 ("lockmgr: not holding exclusive lock " 266 "(owner thread (%p) != thread (%p), exlcnt (%d) != 0", 267 lkp->lk_lockholder, thr, lkp->lk_exclusivecount)); 268 sharelock(td, lkp, lkp->lk_exclusivecount); 269 COUNT(td, -lkp->lk_exclusivecount); 270 lkp->lk_exclusivecount = 0; 271 lkp->lk_flags &= ~LK_HAVE_EXCL; 272 lkp->lk_lockholder = LK_NOPROC; 273 if (lkp->lk_waitcount) 274 wakeup((void *)lkp); 275 break; 276 277 case LK_EXCLUPGRADE: 278 /* 279 * If another process is ahead of us to get an upgrade, 280 * then we want to fail rather than have an intervening 281 * exclusive access. 282 */ 283 if (lkp->lk_flags & LK_WANT_UPGRADE) { 284 shareunlock(td, lkp, 1); 285 error = EBUSY; 286 break; 287 } 288 /* FALLTHROUGH normal upgrade */ 289 290 case LK_UPGRADE: 291 /* 292 * Upgrade a shared lock to an exclusive one. If another 293 * shared lock has already requested an upgrade to an 294 * exclusive lock, our shared lock is released and an 295 * exclusive lock is requested (which will be granted 296 * after the upgrade). If we return an error, the file 297 * will always be unlocked. 298 */ 299 if ((lkp->lk_lockholder == thr) || (lkp->lk_sharecount <= 0)) 300 panic("lockmgr: upgrade exclusive lock"); 301 shareunlock(td, lkp, 1); 302 /* 303 * If we are just polling, check to see if we will block. 304 */ 305 if ((extflags & LK_NOWAIT) && 306 ((lkp->lk_flags & LK_WANT_UPGRADE) || 307 lkp->lk_sharecount > 1)) { 308 error = EBUSY; 309 break; 310 } 311 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 312 /* 313 * We are first shared lock to request an upgrade, so 314 * request upgrade and wait for the shared count to 315 * drop to zero, then take exclusive lock. 316 */ 317 lkp->lk_flags |= LK_WANT_UPGRADE; 318 error = acquire(&lkp, extflags, LK_SHARE_NONZERO); 319 lkp->lk_flags &= ~LK_WANT_UPGRADE; 320 321 if (error) { 322 if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO)) 323 wakeup((void *)lkp); 324 break; 325 } 326 if (lkp->lk_exclusivecount != 0) 327 panic("lockmgr: non-zero exclusive count"); 328 lkp->lk_flags |= LK_HAVE_EXCL; 329 lkp->lk_lockholder = thr; 330 lkp->lk_exclusivecount = 1; 331 COUNT(td, 1); 332#if defined(DEBUG_LOCKS) 333 lkp->lk_filename = file; 334 lkp->lk_lineno = line; 335 lkp->lk_lockername = name; 336#endif 337 break; 338 } 339 /* 340 * Someone else has requested upgrade. Release our shared 341 * lock, awaken upgrade requestor if we are the last shared 342 * lock, then request an exclusive lock. 343 */ 344 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 345 LK_WAIT_NONZERO) 346 wakeup((void *)lkp); 347 /* FALLTHROUGH exclusive request */ 348 349 case LK_EXCLUSIVE: 350 if (lkp->lk_lockholder == thr && thr != LK_KERNPROC) { 351 /* 352 * Recursive lock. 353 */ 354 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 355 panic("lockmgr: locking against myself"); 356 if ((extflags & LK_CANRECURSE) != 0) { 357 lkp->lk_exclusivecount++; 358 COUNT(td, 1); 359 break; 360 } 361 } 362 /* 363 * If we are just polling, check to see if we will sleep. 364 */ 365 if ((extflags & LK_NOWAIT) && 366 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 367 error = EBUSY; 368 break; 369 } 370 /* 371 * Try to acquire the want_exclusive flag. 372 */ 373 error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 374 if (error) 375 break; 376 lkp->lk_flags |= LK_WANT_EXCL; 377 /* 378 * Wait for shared locks and upgrades to finish. 379 */ 380 error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO); 381 lkp->lk_flags &= ~LK_WANT_EXCL; 382 if (error) { 383 if (lkp->lk_flags & LK_WAIT_NONZERO) 384 wakeup((void *)lkp); 385 break; 386 } 387 lkp->lk_flags |= LK_HAVE_EXCL; 388 lkp->lk_lockholder = thr; 389 if (lkp->lk_exclusivecount != 0) 390 panic("lockmgr: non-zero exclusive count"); 391 lkp->lk_exclusivecount = 1; 392 COUNT(td, 1); 393#if defined(DEBUG_LOCKS) 394 lkp->lk_filename = file; 395 lkp->lk_lineno = line; 396 lkp->lk_lockername = name; 397#endif 398 break; 399 400 case LK_RELEASE: 401 if (lkp->lk_exclusivecount != 0) { 402 if (lkp->lk_lockholder != thr && 403 lkp->lk_lockholder != LK_KERNPROC) { 404 panic("lockmgr: thread %p, not %s %p unlocking", 405 thr, "exclusive lock holder", 406 lkp->lk_lockholder); 407 } 408 if (lkp->lk_lockholder != LK_KERNPROC) 409 COUNT(td, -1); 410 if (lkp->lk_exclusivecount == 1) { 411 lkp->lk_flags &= ~LK_HAVE_EXCL; 412 lkp->lk_lockholder = LK_NOPROC; 413 lkp->lk_exclusivecount = 0; 414 } else { 415 lkp->lk_exclusivecount--; 416 } 417 } else if (lkp->lk_flags & LK_SHARE_NONZERO) 418 shareunlock(td, lkp, 1); 419 if (lkp->lk_flags & LK_WAIT_NONZERO) 420 wakeup((void *)lkp); 421 break; 422 423 case LK_DRAIN: 424 /* 425 * Check that we do not already hold the lock, as it can 426 * never drain if we do. Unfortunately, we have no way to 427 * check for holding a shared lock, but at least we can 428 * check for an exclusive one. 429 */ 430 if (lkp->lk_lockholder == thr) 431 panic("lockmgr: draining against myself"); 432 433 error = acquiredrain(lkp, extflags); 434 if (error) 435 break; 436 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 437 lkp->lk_lockholder = thr; 438 lkp->lk_exclusivecount = 1; 439 COUNT(td, 1); 440#if defined(DEBUG_LOCKS) 441 lkp->lk_filename = file; 442 lkp->lk_lineno = line; 443 lkp->lk_lockername = name; 444#endif 445 break; 446 447 default: 448 mtx_unlock(lkp->lk_interlock); 449 panic("lockmgr: unknown locktype request %d", 450 flags & LK_TYPE_MASK); 451 /* NOTREACHED */ 452 } 453 if ((lkp->lk_flags & LK_WAITDRAIN) && 454 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 455 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 456 lkp->lk_flags &= ~LK_WAITDRAIN; 457 wakeup((void *)&lkp->lk_flags); 458 } 459 mtx_unlock(lkp->lk_interlock); 460 return (error); 461} 462 463static int 464acquiredrain(struct lock *lkp, int extflags) { 465 int error; 466 467 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 468 return EBUSY; 469 } 470 while (lkp->lk_flags & LK_ALL) { 471 lkp->lk_flags |= LK_WAITDRAIN; 472 error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio, 473 lkp->lk_wmesg, 474 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 475 if (error) 476 return error; 477 if (extflags & LK_SLEEPFAIL) { 478 return ENOLCK; 479 } 480 } 481 return 0; 482} 483 484/* 485 * Transfer any waiting processes from one lock to another. 486 */ 487void 488transferlockers(from, to) 489 struct lock *from; 490 struct lock *to; 491{ 492 493 KASSERT(from != to, ("lock transfer to self")); 494 KASSERT((from->lk_flags&LK_WAITDRAIN) == 0, ("transfer draining lock")); 495 496 mtx_lock(from->lk_interlock); 497 if (from->lk_waitcount == 0) { 498 mtx_unlock(from->lk_interlock); 499 return; 500 } 501 from->lk_newlock = to; 502 wakeup((void *)from); 503 msleep(&from->lk_newlock, from->lk_interlock, from->lk_prio, 504 "lkxfer", 0); 505 from->lk_newlock = NULL; 506 from->lk_flags &= ~(LK_WANT_EXCL | LK_WANT_UPGRADE); 507 KASSERT(from->lk_waitcount == 0, ("active lock")); 508 mtx_unlock(from->lk_interlock); 509} 510 511 512/* 513 * Initialize a lock; required before use. 514 */ 515void 516lockinit(lkp, prio, wmesg, timo, flags) 517 struct lock *lkp; 518 int prio; 519 const char *wmesg; 520 int timo; 521 int flags; 522{ 523 CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", " 524 "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags); 525 526 lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder); 527 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 528 lkp->lk_sharecount = 0; 529 lkp->lk_waitcount = 0; 530 lkp->lk_exclusivecount = 0; 531 lkp->lk_prio = prio; 532 lkp->lk_wmesg = wmesg; 533 lkp->lk_timo = timo; 534 lkp->lk_lockholder = LK_NOPROC; 535 lkp->lk_newlock = NULL; 536#ifdef DEBUG_LOCKS 537 lkp->lk_filename = "none"; 538 lkp->lk_lockername = "never exclusive locked"; 539 lkp->lk_lineno = 0; 540 lkp->lk_slockholder = LK_NOPROC; 541 lkp->lk_sfilename = "none"; 542 lkp->lk_slockername = "never share locked"; 543 lkp->lk_slineno = 0; 544#endif 545} 546 547/* 548 * Destroy a lock. 549 */ 550void 551lockdestroy(lkp) 552 struct lock *lkp; 553{ 554 CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")", 555 lkp, lkp->lk_wmesg); 556} 557 558/* 559 * Determine the status of a lock. 560 */ 561int 562lockstatus(lkp, td) 563 struct lock *lkp; 564 struct thread *td; 565{ 566 int lock_type = 0; 567 568 mtx_lock(lkp->lk_interlock); 569 if (lkp->lk_exclusivecount != 0) { 570 if (td == NULL || lkp->lk_lockholder == td) 571 lock_type = LK_EXCLUSIVE; 572 else 573 lock_type = LK_EXCLOTHER; 574 } else if (lkp->lk_sharecount != 0) 575 lock_type = LK_SHARED; 576 mtx_unlock(lkp->lk_interlock); 577 return (lock_type); 578} 579 580/* 581 * Determine the number of holders of a lock. 582 */ 583int 584lockcount(lkp) 585 struct lock *lkp; 586{ 587 int count; 588 589 mtx_lock(lkp->lk_interlock); 590 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 591 mtx_unlock(lkp->lk_interlock); 592 return (count); 593} 594 595/* 596 * Print out information about state of a lock. Used by VOP_PRINT 597 * routines to display status about contained locks. 598 */ 599void 600lockmgr_printinfo(lkp) 601 struct lock *lkp; 602{ 603 604 if (lkp->lk_sharecount) 605 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 606 lkp->lk_sharecount); 607 else if (lkp->lk_flags & LK_HAVE_EXCL) 608 printf(" lock type %s: EXCL (count %d) by thread %p (pid %d)", 609 lkp->lk_wmesg, lkp->lk_exclusivecount, 610 lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid); 611 if (lkp->lk_waitcount > 0) 612 printf(" with %d pending", lkp->lk_waitcount); 613} 614