Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)
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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_lock.c
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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("$FreeBSD$"); 45 46 #include <sys/param.h> 47 #include <sys/kernel.h> 48 #include <sys/kdb.h> 49 #include <sys/ktr.h> 50 #include <sys/lock.h> 51 #include <sys/lockmgr.h> 52 #include <sys/mutex.h> 53 #include <sys/proc.h> 54 #include <sys/systm.h> 55 56 /* 57 * Locking primitives implementation. 58 * Locks provide shared/exclusive sychronization. 59 */ 60 61 #define LOCK_WAIT_TIME 100 62 #define LOCK_SAMPLE_WAIT 7 63 64 #if defined(DIAGNOSTIC) 65 #define LOCK_INLINE 66 #else 67 #define LOCK_INLINE __inline 68 #endif 69 70 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 71 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 72 73 /* 74 * Mutex array variables. Rather than each lockmgr lock having its own mutex, 75 * share a fixed (at boot time) number of mutexes across all lockmgr locks in 76 * order to keep sizeof(struct lock) down. 77 */ 78 static struct mtx lock_mtx; 79 80 static int acquire(struct lock **lkpp, int extflags, int wanted); 81 static int apause(struct lock *lkp, int flags); 82 static int acquiredrain(struct lock *lkp, int extflags) ; 83 84 static void 85 lockmgr_init(void *dummy __unused) 86 { 87 mtx_init(&lock_mtx, "lockmgr", NULL, MTX_DEF); 88 } 89 SYSINIT(lmgrinit, SI_SUB_LOCKMGR, SI_ORDER_FIRST, lockmgr_init, NULL) 90 91 static LOCK_INLINE void 92 sharelock(struct lock *lkp, int incr) { 93 lkp->lk_flags |= LK_SHARE_NONZERO; 94 lkp->lk_sharecount += incr; 95 } 96 97 static LOCK_INLINE void 98 shareunlock(struct lock *lkp, int decr) { 99 100 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 101 102 if (lkp->lk_sharecount == decr) { 103 lkp->lk_flags &= ~LK_SHARE_NONZERO; 104 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 105 wakeup(lkp); 106 } 107 lkp->lk_sharecount = 0; 108 } else { 109 lkp->lk_sharecount -= decr; 110 } 111 } 112 113 /* 114 * This is the waitloop optimization. 115 */ 116 static int 117 apause(struct lock *lkp, int flags) 118 { 119 #ifdef SMP 120 int i, lock_wait; 121 #endif 122 123 if ((lkp->lk_flags & flags) == 0) 124 return 0; 125 #ifdef SMP 126 for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) { 127 mtx_unlock(lkp->lk_interlock); 128 for (i = LOCK_SAMPLE_WAIT; i > 0; i--) 129 if ((lkp->lk_flags & flags) == 0) 130 break; 131 mtx_lock(lkp->lk_interlock); 132 if ((lkp->lk_flags & flags) == 0) 133 return 0; 134 } 135 #endif 136 return 1; 137 } 138 139 static int 140 acquire(struct lock **lkpp, int extflags, int wanted) { 141 struct lock *lkp = *lkpp; 142 int s, error; 143 144 CTR3(KTR_LOCK, 145 "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x", 146 lkp, extflags, wanted); 147 148 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 149 return EBUSY; 150 } 151 152 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 153 error = apause(lkp, wanted); 154 if (error == 0) 155 return 0; 156 } 157 158 s = splhigh(); 159 while ((lkp->lk_flags & wanted) != 0) { 160 lkp->lk_flags |= LK_WAIT_NONZERO; 161 lkp->lk_waitcount++; 162 error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio, 163 lkp->lk_wmesg, 164 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 165 if (lkp->lk_waitcount == 1) { 166 lkp->lk_flags &= ~LK_WAIT_NONZERO; 167 lkp->lk_waitcount = 0; 168 } else { 169 lkp->lk_waitcount--; 170 } 171 if (error) { 172 splx(s); 173 return error; 174 } 175 if (extflags & LK_SLEEPFAIL) { 176 splx(s); 177 return ENOLCK; 178 } 179 if (lkp->lk_newlock != NULL) { 180 mtx_lock(lkp->lk_newlock->lk_interlock); 181 mtx_unlock(lkp->lk_interlock); 182 if (lkp->lk_waitcount == 0) 183 wakeup((void *)(&lkp->lk_newlock)); 184 *lkpp = lkp = lkp->lk_newlock; 185 } 186 } 187 splx(s); 188 return 0; 189 } 190 191 /* 192 * Set, change, or release a lock. 193 * 194 * Shared requests increment the shared count. Exclusive requests set the 195 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 196 * accepted shared locks and shared-to-exclusive upgrades to go away. 197 */ 198 int 199 #ifndef DEBUG_LOCKS 200 lockmgr(lkp, flags, interlkp, td) 201 #else 202 debuglockmgr(lkp, flags, interlkp, td, name, file, line) 203 #endif 204 struct lock *lkp; 205 u_int flags; 206 struct mtx *interlkp; 207 struct thread *td; 208 #ifdef DEBUG_LOCKS 209 const char *name; /* Name of lock function */ 210 const char *file; /* Name of file call is from */ 211 int line; /* Line number in file */ 212 #endif 213 { 214 int error; 215 struct thread *thr; 216 int extflags, lockflags; 217 218 CTR5(KTR_LOCK, 219 "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), flags == 0x%x, " 220 "interlkp == %p, td == %p", lkp, lkp->lk_wmesg, flags, interlkp, td); 221 222 error = 0; 223 if (td == NULL) 224 thr = LK_KERNPROC; 225 else 226 thr = td; 227 228 if ((flags & LK_INTERNAL) == 0) 229 mtx_lock(lkp->lk_interlock); 230 if (flags & LK_INTERLOCK) { 231 mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED); 232 mtx_unlock(interlkp); 233 } 234 235 if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0) 236 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, 237 &lkp->lk_interlock->mtx_object, 238 "Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg); 239 240 if (panicstr != NULL) { 241 mtx_unlock(lkp->lk_interlock); 242 return (0); 243 } 244 245 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 246 247 switch (flags & LK_TYPE_MASK) { 248 249 case LK_SHARED: 250 /* 251 * If we are not the exclusive lock holder, we have to block 252 * while there is an exclusive lock holder or while an 253 * exclusive lock request or upgrade request is in progress. 254 * 255 * However, if TDP_DEADLKTREAT is set, we override exclusive 256 * lock requests or upgrade requests ( but not the exclusive 257 * lock itself ). 258 */ 259 if (lkp->lk_lockholder != thr) { 260 lockflags = LK_HAVE_EXCL; 261 if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT)) 262 lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE; 263 error = acquire(&lkp, extflags, lockflags); 264 if (error) 265 break; 266 sharelock(lkp, 1); 267 #if defined(DEBUG_LOCKS) 268 lkp->lk_slockholder = thr; 269 lkp->lk_sfilename = file; 270 lkp->lk_slineno = line; 271 lkp->lk_slockername = name; 272 #endif 273 break; 274 } 275 /* 276 * We hold an exclusive lock, so downgrade it to shared. 277 * An alternative would be to fail with EDEADLK. 278 */ 279 sharelock(lkp, 1); 280 /* FALLTHROUGH downgrade */ 281 282 case LK_DOWNGRADE: 283 KASSERT(lkp->lk_lockholder == thr && lkp->lk_exclusivecount != 0, 284 ("lockmgr: not holding exclusive lock " 285 "(owner thread (%p) != thread (%p), exlcnt (%d) != 0", 286 lkp->lk_lockholder, thr, lkp->lk_exclusivecount)); 287 sharelock(lkp, lkp->lk_exclusivecount); 288 lkp->lk_exclusivecount = 0; 289 lkp->lk_flags &= ~LK_HAVE_EXCL; 290 lkp->lk_lockholder = LK_NOPROC; 291 if (lkp->lk_waitcount) 292 wakeup((void *)lkp); 293 break; 294 295 case LK_EXCLUPGRADE: 296 /* 297 * If another process is ahead of us to get an upgrade, 298 * then we want to fail rather than have an intervening 299 * exclusive access. 300 */ 301 if (lkp->lk_flags & LK_WANT_UPGRADE) { 302 shareunlock(lkp, 1); 303 error = EBUSY; 304 break; 305 } 306 /* FALLTHROUGH normal upgrade */ 307 308 case LK_UPGRADE: 309 /* 310 * Upgrade a shared lock to an exclusive one. If another 311 * shared lock has already requested an upgrade to an 312 * exclusive lock, our shared lock is released and an 313 * exclusive lock is requested (which will be granted 314 * after the upgrade). If we return an error, the file 315 * will always be unlocked. 316 */ 317 if ((lkp->lk_lockholder == thr) || (lkp->lk_sharecount <= 0)) 318 panic("lockmgr: upgrade exclusive lock"); 319 shareunlock(lkp, 1); 320 /* 321 * If we are just polling, check to see if we will block. 322 */ 323 if ((extflags & LK_NOWAIT) && 324 ((lkp->lk_flags & LK_WANT_UPGRADE) || 325 lkp->lk_sharecount > 1)) { 326 error = EBUSY; 327 break; 328 } 329 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 330 /* 331 * We are first shared lock to request an upgrade, so 332 * request upgrade and wait for the shared count to 333 * drop to zero, then take exclusive lock. 334 */ 335 lkp->lk_flags |= LK_WANT_UPGRADE; 336 error = acquire(&lkp, extflags, LK_SHARE_NONZERO); 337 lkp->lk_flags &= ~LK_WANT_UPGRADE; 338 339 if (error) { 340 if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO)) 341 wakeup((void *)lkp); 342 break; 343 } 344 345 lkp->lk_flags |= LK_HAVE_EXCL; 346 lkp->lk_lockholder = thr; 347 if (lkp->lk_exclusivecount != 0) 348 panic("lockmgr: non-zero exclusive count"); 349 lkp->lk_exclusivecount = 1; 350 #if defined(DEBUG_LOCKS) 351 lkp->lk_filename = file; 352 lkp->lk_lineno = line; 353 lkp->lk_lockername = name; 354 #endif 355 break; 356 } 357 /* 358 * Someone else has requested upgrade. Release our shared 359 * lock, awaken upgrade requestor if we are the last shared 360 * lock, then request an exclusive lock. 361 */ 362 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 363 LK_WAIT_NONZERO) 364 wakeup((void *)lkp); 365 /* FALLTHROUGH exclusive request */ 366 367 case LK_EXCLUSIVE: 368 if (lkp->lk_lockholder == thr && thr != LK_KERNPROC) { 369 /* 370 * Recursive lock. 371 */ 372 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 373 panic("lockmgr: locking against myself"); 374 if ((extflags & LK_CANRECURSE) != 0) { 375 lkp->lk_exclusivecount++; 376 break; 377 } 378 } 379 /* 380 * If we are just polling, check to see if we will sleep. 381 */ 382 if ((extflags & LK_NOWAIT) && 383 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 384 error = EBUSY; 385 break; 386 } 387 /* 388 * Try to acquire the want_exclusive flag. 389 */ 390 error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 391 if (error) 392 break; 393 lkp->lk_flags |= LK_WANT_EXCL; 394 /* 395 * Wait for shared locks and upgrades to finish. 396 */ 397 error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO); 398 lkp->lk_flags &= ~LK_WANT_EXCL; 399 if (error) { 400 if (lkp->lk_flags & LK_WAIT_NONZERO) 401 wakeup((void *)lkp); 402 break; 403 } 404 lkp->lk_flags |= LK_HAVE_EXCL; 405 lkp->lk_lockholder = thr; 406 if (lkp->lk_exclusivecount != 0) 407 panic("lockmgr: non-zero exclusive count"); 408 lkp->lk_exclusivecount = 1; 409 #if defined(DEBUG_LOCKS) 410 lkp->lk_filename = file; 411 lkp->lk_lineno = line; 412 lkp->lk_lockername = name; 413 #endif 414 break; 415 416 case LK_RELEASE: 417 if (lkp->lk_exclusivecount != 0) { 418 if (lkp->lk_lockholder != thr && 419 lkp->lk_lockholder != LK_KERNPROC) { 420 panic("lockmgr: thread %p, not %s %p unlocking", 421 thr, "exclusive lock holder", 422 lkp->lk_lockholder); 423 } 424 if (lkp->lk_exclusivecount == 1) { 425 lkp->lk_flags &= ~LK_HAVE_EXCL; 426 lkp->lk_lockholder = LK_NOPROC; 427 lkp->lk_exclusivecount = 0; 428 } else { 429 lkp->lk_exclusivecount--; 430 } 431 } else if (lkp->lk_flags & LK_SHARE_NONZERO) 432 shareunlock(lkp, 1); 433 if (lkp->lk_flags & LK_WAIT_NONZERO) 434 wakeup((void *)lkp); 435 break; 436 437 case LK_DRAIN: 438 /* 439 * Check that we do not already hold the lock, as it can 440 * never drain if we do. Unfortunately, we have no way to 441 * check for holding a shared lock, but at least we can 442 * check for an exclusive one. 443 */ 444 if (lkp->lk_lockholder == thr) 445 panic("lockmgr: draining against myself"); 446 447 error = acquiredrain(lkp, extflags); 448 if (error) 449 break; 450 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 451 lkp->lk_lockholder = thr; 452 lkp->lk_exclusivecount = 1; 453 #if defined(DEBUG_LOCKS) 454 lkp->lk_filename = file; 455 lkp->lk_lineno = line; 456 lkp->lk_lockername = name; 457 #endif 458 break; 459 460 default: 461 mtx_unlock(lkp->lk_interlock); 462 panic("lockmgr: unknown locktype request %d", 463 flags & LK_TYPE_MASK); 464 /* NOTREACHED */ 465 } 466 if ((lkp->lk_flags & LK_WAITDRAIN) && 467 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 468 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 469 lkp->lk_flags &= ~LK_WAITDRAIN; 470 wakeup((void *)&lkp->lk_flags); 471 } 472 mtx_unlock(lkp->lk_interlock); 473 return (error); 474 } 475 476 static int 477 acquiredrain(struct lock *lkp, int extflags) { 478 int error; 479 480 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 481 return EBUSY; 482 } 483 484 error = apause(lkp, LK_ALL); 485 if (error == 0) 486 return 0; 487 488 while (lkp->lk_flags & LK_ALL) { 489 lkp->lk_flags |= LK_WAITDRAIN; 490 error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio, 491 lkp->lk_wmesg, 492 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 493 if (error) 494 return error; 495 if (extflags & LK_SLEEPFAIL) { 496 return ENOLCK; 497 } 498 } 499 return 0; 500 } 501 502 /* 503 * Transfer any waiting processes from one lock to another. 504 */ 505 void 506 transferlockers(from, to) 507 struct lock *from; 508 struct lock *to; 509 { 510 511 KASSERT(from != to, ("lock transfer to self")); 512 KASSERT((from->lk_flags&LK_WAITDRAIN) == 0, ("transfer draining lock")); 513 if (from->lk_waitcount == 0) 514 return; 515 from->lk_newlock = to; 516 wakeup((void *)from); 517 msleep(&from->lk_newlock, NULL, from->lk_prio, "lkxfer", 0); 518 from->lk_newlock = NULL; 519 from->lk_flags &= ~(LK_WANT_EXCL | LK_WANT_UPGRADE); 520 KASSERT(from->lk_waitcount == 0, ("active lock")); 521 } 522 523 524 /* 525 * Initialize a lock; required before use. 526 */ 527 void 528 lockinit(lkp, prio, wmesg, timo, flags) 529 struct lock *lkp; 530 int prio; 531 const char *wmesg; 532 int timo; 533 int flags; 534 { 535 CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", " 536 "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags); 537 538 lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder); 539 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 540 lkp->lk_sharecount = 0; 541 lkp->lk_waitcount = 0; 542 lkp->lk_exclusivecount = 0; 543 lkp->lk_prio = prio; 544 lkp->lk_wmesg = wmesg; 545 lkp->lk_timo = timo; 546 lkp->lk_lockholder = LK_NOPROC; 547 lkp->lk_newlock = NULL; 548 #ifdef DEBUG_LOCKS 549 lkp->lk_filename = "none"; 550 lkp->lk_lockername = "never exclusive locked"; 551 lkp->lk_lineno = 0; 552 lkp->lk_slockholder = LK_NOPROC; 553 lkp->lk_sfilename = "none"; 554 lkp->lk_slockername = "never share locked"; 555 lkp->lk_slineno = 0; 556 #endif 557 } 558 559 /* 560 * Destroy a lock. 561 */ 562 void 563 lockdestroy(lkp) 564 struct lock *lkp; 565 { 566 CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")", 567 lkp, lkp->lk_wmesg); 568 } 569 570 /* 571 * Determine the status of a lock. 572 */ 573 int 574 lockstatus(lkp, td) 575 struct lock *lkp; 576 struct thread *td; 577 { 578 int lock_type = 0; 579 int interlocked; 580 581 if (!kdb_active) { 582 interlocked = 1; 583 mtx_lock(lkp->lk_interlock); 584 } else 585 interlocked = 0; 586 if (lkp->lk_exclusivecount != 0) { 587 if (td == NULL || lkp->lk_lockholder == td) 588 lock_type = LK_EXCLUSIVE; 589 else 590 lock_type = LK_EXCLOTHER; 591 } else if (lkp->lk_sharecount != 0) 592 lock_type = LK_SHARED; 593 if (interlocked) 594 mtx_unlock(lkp->lk_interlock); 595 return (lock_type); 596 } 597 598 /* 599 * Determine the number of holders of a lock. 600 */ 601 int 602 lockcount(lkp) 603 struct lock *lkp; 604 { 605 int count; 606 607 mtx_lock(lkp->lk_interlock); 608 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 609 mtx_unlock(lkp->lk_interlock); 610 return (count); 611 } 612 613 /* 614 * Print out information about state of a lock. Used by VOP_PRINT 615 * routines to display status about contained locks. 616 */ 617 void 618 lockmgr_printinfo(lkp) 619 struct lock *lkp; 620 { 621 622 if (lkp->lk_sharecount) 623 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 624 lkp->lk_sharecount); 625 else if (lkp->lk_flags & LK_HAVE_EXCL) 626 printf(" lock type %s: EXCL (count %d) by thread %p (pid %d)", 627 lkp->lk_wmesg, lkp->lk_exclusivecount, 628 lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid); 629 if (lkp->lk_waitcount > 0) 630 printf(" with %d pending", lkp->lk_waitcount); 631 }
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