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: src/sys/kern/kern_lock.c,v 1.31.2.3 2001/12/25 01:44:44 dillon Exp $ 42 * $DragonFly: src/sys/kern/kern_lock.c,v 1.16 2006/03/02 19:07:59 dillon Exp $ 43 */ 44 45 #include "opt_lint.h" 46 47 #include <sys/param.h> 48 #include <sys/systm.h> 49 #include <sys/kernel.h> 50 #include <sys/proc.h> 51 #include <sys/lock.h> 52 #include <sys/sysctl.h> 53 #include <sys/spinlock.h> 54 #include <sys/thread2.h> 55 #include <sys/spinlock2.h> 56 57 /* 58 * 0: no warnings, 1: warnings, 2: panic 59 */ 60 static int lockmgr_from_int = 1; 61 SYSCTL_INT(_debug, OID_AUTO, lockmgr_from_int, CTLFLAG_RW, &lockmgr_from_int, 0, ""); 62 63 /* 64 * Locking primitives implementation. 65 * Locks provide shared/exclusive sychronization. 66 */ 67 68 #ifdef SIMPLELOCK_DEBUG 69 #define COUNT(td, x) (td)->td_locks += (x) 70 #else 71 #define COUNT(td, x) 72 #endif 73 74 #define LOCK_WAIT_TIME 100 75 #define LOCK_SAMPLE_WAIT 7 76 77 #if defined(DIAGNOSTIC) 78 #define LOCK_INLINE 79 #else 80 #define LOCK_INLINE __inline 81 #endif 82 83 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 84 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 85 86 static int acquire(struct lock *lkp, int extflags, int wanted); 87 static int acquiredrain(struct lock *lkp, int extflags) ; 88 89 static LOCK_INLINE void 90 sharelock(struct lock *lkp, int incr) { 91 lkp->lk_flags |= LK_SHARE_NONZERO; 92 lkp->lk_sharecount += incr; 93 } 94 95 static LOCK_INLINE void 96 shareunlock(struct lock *lkp, int decr) { 97 98 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 99 100 if (lkp->lk_sharecount == decr) { 101 lkp->lk_flags &= ~LK_SHARE_NONZERO; 102 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 103 wakeup(lkp); 104 } 105 lkp->lk_sharecount = 0; 106 } else { 107 lkp->lk_sharecount -= decr; 108 } 109 } 110 111 /* 112 * lock acquisition helper routine. Called with the lock's spinlock held. 113 */ 114 static int 115 acquire(struct lock *lkp, int extflags, int wanted) 116 { 117 int error; 118 119 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 120 return EBUSY; 121 } 122 123 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 124 if ((lkp->lk_flags & wanted) == 0) 125 return 0; 126 } 127 128 while ((lkp->lk_flags & wanted) != 0) { 129 lkp->lk_flags |= LK_WAIT_NONZERO; 130 lkp->lk_waitcount++; 131 132 /* 133 * Use the _quick version so the critical section is left 134 * intact, protecting the tsleep interlock. See 135 * tsleep_interlock() for a description of what is 136 * happening here. 137 */ 138 tsleep_interlock(lkp); 139 spin_unlock_quick(&lkp->lk_spinlock); 140 error = tsleep(lkp, 141 ((extflags & LK_PCATCH) ? PCATCH : 0), 142 lkp->lk_wmesg, 143 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 144 spin_lock_quick(&lkp->lk_spinlock); 145 if (lkp->lk_waitcount == 1) { 146 lkp->lk_flags &= ~LK_WAIT_NONZERO; 147 lkp->lk_waitcount = 0; 148 } else { 149 lkp->lk_waitcount--; 150 } 151 if (error) 152 return error; 153 if (extflags & LK_SLEEPFAIL) 154 return ENOLCK; 155 } 156 return 0; 157 } 158 159 /* 160 * Set, change, or release a lock. 161 * 162 * Shared requests increment the shared count. Exclusive requests set the 163 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 164 * accepted shared locks and shared-to-exclusive upgrades to go away. 165 * 166 * A spinlock is held for most of the procedure. We must not do anything 167 * fancy while holding the spinlock. 168 */ 169 int 170 #ifndef DEBUG_LOCKS 171 lockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp, 172 struct thread *td) 173 #else 174 debuglockmgr(struct lock *lkp, u_int flags, struct spinlock *interlkp, 175 struct thread *td, const char *name, const char *file, int line) 176 #endif 177 { 178 int error; 179 int extflags; 180 static int didpanic; 181 182 error = 0; 183 184 if (lockmgr_from_int && mycpu->gd_intr_nesting_level && 185 (flags & LK_NOWAIT) == 0 && 186 (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) { 187 #ifndef DEBUG_LOCKS 188 if (lockmgr_from_int == 2) { 189 didpanic = 1; 190 if (flags & LK_INTERLOCK) 191 spin_unlock(interlkp); 192 panic( 193 "lockmgr %s from %p: called from interrupt", 194 lkp->lk_wmesg, ((int **)&lkp)[-1]); 195 didpanic = 0; 196 } else { 197 printf( 198 "lockmgr %s from %p: called from interrupt\n", 199 lkp->lk_wmesg, ((int **)&lkp)[-1]); 200 } 201 #else 202 if (lockmgr_from_int == 2) { 203 didpanic = 1; 204 if (flags & LK_INTERLOCK) 205 spin_unlock(interlkp); 206 panic( 207 "lockmgr %s from %s:%d: called from interrupt", 208 lkp->lk_wmesg, file, line); 209 didpanic = 0; 210 } else { 211 printf( 212 "lockmgr %s from %s:%d: called from interrupt\n", 213 lkp->lk_wmesg, file, line); 214 } 215 #endif 216 } 217 218 spin_lock(&lkp->lk_spinlock); 219 if (flags & LK_INTERLOCK) 220 spin_unlock(interlkp); 221 222 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 223 224 switch (flags & LK_TYPE_MASK) { 225 case LK_SHARED: 226 /* 227 * If we are not the exclusive lock holder, we have to block 228 * while there is an exclusive lock holder or while an 229 * exclusive lock request or upgrade request is in progress. 230 * 231 * However, if P_DEADLKTREAT is set, we override exclusive 232 * lock requests or upgrade requests ( but not the exclusive 233 * lock itself ). 234 */ 235 if (lkp->lk_lockholder != td) { 236 if (td->td_flags & TDF_DEADLKTREAT) { 237 error = acquire( 238 lkp, 239 extflags, 240 LK_HAVE_EXCL 241 ); 242 } else { 243 error = acquire( 244 lkp, 245 extflags, 246 LK_HAVE_EXCL | LK_WANT_EXCL | 247 LK_WANT_UPGRADE 248 ); 249 } 250 if (error) 251 break; 252 sharelock(lkp, 1); 253 COUNT(td, 1); 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(lkp, 1); 261 COUNT(td, 1); 262 /* fall into downgrade */ 263 264 case LK_DOWNGRADE: 265 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) { 266 spin_unlock(&lkp->lk_spinlock); 267 panic("lockmgr: not holding exclusive lock"); 268 } 269 sharelock(lkp, lkp->lk_exclusivecount); 270 lkp->lk_exclusivecount = 0; 271 lkp->lk_flags &= ~LK_HAVE_EXCL; 272 lkp->lk_lockholder = LK_NOTHREAD; 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(lkp, 1); 285 COUNT(td, -1); 286 error = EBUSY; 287 break; 288 } 289 /* fall into normal upgrade */ 290 291 case LK_UPGRADE: 292 /* 293 * Upgrade a shared lock to an exclusive one. If another 294 * shared lock has already requested an upgrade to an 295 * exclusive lock, our shared lock is released and an 296 * exclusive lock is requested (which will be granted 297 * after the upgrade). If we return an error, the file 298 * will always be unlocked. 299 */ 300 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) { 301 spin_unlock(&lkp->lk_spinlock); 302 panic("lockmgr: upgrade exclusive lock"); 303 } 304 shareunlock(lkp, 1); 305 COUNT(td, -1); 306 /* 307 * If we are just polling, check to see if we will block. 308 */ 309 if ((extflags & LK_NOWAIT) && 310 ((lkp->lk_flags & LK_WANT_UPGRADE) || 311 lkp->lk_sharecount > 1)) { 312 error = EBUSY; 313 break; 314 } 315 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 316 /* 317 * We are first shared lock to request an upgrade, so 318 * request upgrade and wait for the shared count to 319 * drop to zero, then take exclusive lock. 320 */ 321 lkp->lk_flags |= LK_WANT_UPGRADE; 322 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 323 lkp->lk_flags &= ~LK_WANT_UPGRADE; 324 325 if (error) 326 break; 327 lkp->lk_flags |= LK_HAVE_EXCL; 328 lkp->lk_lockholder = td; 329 if (lkp->lk_exclusivecount != 0) { 330 spin_unlock(&lkp->lk_spinlock); 331 panic("lockmgr: non-zero exclusive count"); 332 } 333 lkp->lk_exclusivecount = 1; 334 #if defined(DEBUG_LOCKS) 335 lkp->lk_filename = file; 336 lkp->lk_lineno = line; 337 lkp->lk_lockername = name; 338 #endif 339 COUNT(td, 1); 340 break; 341 } 342 /* 343 * Someone else has requested upgrade. Release our shared 344 * lock, awaken upgrade requestor if we are the last shared 345 * lock, then request an exclusive lock. 346 */ 347 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 348 LK_WAIT_NONZERO) 349 wakeup((void *)lkp); 350 /* fall into exclusive request */ 351 352 case LK_EXCLUSIVE: 353 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) { 354 /* 355 * Recursive lock. 356 */ 357 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) { 358 spin_unlock(&lkp->lk_spinlock); 359 panic("lockmgr: locking against myself"); 360 } 361 if ((extflags & LK_CANRECURSE) != 0) { 362 lkp->lk_exclusivecount++; 363 COUNT(td, 1); 364 break; 365 } 366 } 367 /* 368 * If we are just polling, check to see if we will sleep. 369 */ 370 if ((extflags & LK_NOWAIT) && 371 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 372 error = EBUSY; 373 break; 374 } 375 /* 376 * Try to acquire the want_exclusive flag. 377 */ 378 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 379 if (error) 380 break; 381 lkp->lk_flags |= LK_WANT_EXCL; 382 /* 383 * Wait for shared locks and upgrades to finish. 384 */ 385 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 386 lkp->lk_flags &= ~LK_WANT_EXCL; 387 if (error) 388 break; 389 lkp->lk_flags |= LK_HAVE_EXCL; 390 lkp->lk_lockholder = td; 391 if (lkp->lk_exclusivecount != 0) { 392 spin_unlock(&lkp->lk_spinlock); 393 panic("lockmgr: non-zero exclusive count"); 394 } 395 lkp->lk_exclusivecount = 1; 396 #if defined(DEBUG_LOCKS) 397 lkp->lk_filename = file; 398 lkp->lk_lineno = line; 399 lkp->lk_lockername = name; 400 #endif 401 COUNT(td, 1); 402 break; 403 404 case LK_RELEASE: 405 if (lkp->lk_exclusivecount != 0) { 406 if (lkp->lk_lockholder != td && 407 lkp->lk_lockholder != LK_KERNTHREAD) { 408 spin_unlock(&lkp->lk_spinlock); 409 panic("lockmgr: pid %d, not %s thr %p unlocking", 410 (td->td_proc ? td->td_proc->p_pid : -99), 411 "exclusive lock holder", 412 lkp->lk_lockholder); 413 } 414 if (lkp->lk_lockholder != LK_KERNTHREAD) { 415 COUNT(td, -1); 416 } 417 if (lkp->lk_exclusivecount == 1) { 418 lkp->lk_flags &= ~LK_HAVE_EXCL; 419 lkp->lk_lockholder = LK_NOTHREAD; 420 lkp->lk_exclusivecount = 0; 421 } else { 422 lkp->lk_exclusivecount--; 423 } 424 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 425 shareunlock(lkp, 1); 426 COUNT(td, -1); 427 } 428 if (lkp->lk_flags & LK_WAIT_NONZERO) 429 wakeup((void *)lkp); 430 break; 431 432 case LK_DRAIN: 433 /* 434 * Check that we do not already hold the lock, as it can 435 * never drain if we do. Unfortunately, we have no way to 436 * check for holding a shared lock, but at least we can 437 * check for an exclusive one. 438 */ 439 if (lkp->lk_lockholder == td) { 440 spin_unlock(&lkp->lk_spinlock); 441 panic("lockmgr: draining against myself"); 442 } 443 444 error = acquiredrain(lkp, extflags); 445 if (error) 446 break; 447 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 448 lkp->lk_lockholder = td; 449 lkp->lk_exclusivecount = 1; 450 #if defined(DEBUG_LOCKS) 451 lkp->lk_filename = file; 452 lkp->lk_lineno = line; 453 lkp->lk_lockername = name; 454 #endif 455 COUNT(td, 1); 456 break; 457 458 default: 459 spin_unlock(&lkp->lk_spinlock); 460 panic("lockmgr: unknown locktype request %d", 461 flags & LK_TYPE_MASK); 462 /* NOTREACHED */ 463 } 464 if ((lkp->lk_flags & LK_WAITDRAIN) && 465 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 466 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 467 lkp->lk_flags &= ~LK_WAITDRAIN; 468 wakeup((void *)&lkp->lk_flags); 469 } 470 spin_unlock(&lkp->lk_spinlock); 471 return (error); 472 } 473 474 /* 475 * lock acquisition helper routine. Called with the lock's spinlock held. 476 */ 477 static int 478 acquiredrain(struct lock *lkp, int extflags) 479 { 480 int error; 481 482 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 483 return EBUSY; 484 } 485 486 if ((lkp->lk_flags & LK_ALL) == 0) 487 return 0; 488 489 while (lkp->lk_flags & LK_ALL) { 490 lkp->lk_flags |= LK_WAITDRAIN; 491 /* 492 * Use the _quick version so the critical section is left 493 * intact, protecting the tsleep interlock. See 494 * tsleep_interlock() for a description of what is 495 * happening here. 496 */ 497 tsleep_interlock(&lkp->lk_flags); 498 spin_unlock_quick(&lkp->lk_spinlock); 499 error = tsleep(&lkp->lk_flags, 500 ((extflags & LK_PCATCH) ? PCATCH : 0), 501 lkp->lk_wmesg, 502 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 503 spin_lock_quick(&lkp->lk_spinlock); 504 if (error) 505 return error; 506 if (extflags & LK_SLEEPFAIL) { 507 return ENOLCK; 508 } 509 } 510 return 0; 511 } 512 513 /* 514 * Initialize a lock; required before use. 515 */ 516 void 517 lockinit(struct lock *lkp, char *wmesg, int timo, int flags) 518 { 519 spin_init(&lkp->lk_spinlock); 520 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 521 lkp->lk_sharecount = 0; 522 lkp->lk_waitcount = 0; 523 lkp->lk_exclusivecount = 0; 524 lkp->lk_wmesg = wmesg; 525 lkp->lk_timo = timo; 526 lkp->lk_lockholder = LK_NOTHREAD; 527 } 528 529 /* 530 * Reinitialize a lock that is being reused for a different purpose, but 531 * which may have pending (blocked) threads sitting on it. The caller 532 * must already hold the interlock. 533 */ 534 void 535 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags) 536 { 537 lkp->lk_flags = (lkp->lk_flags & ~(LK_EXTFLG_MASK|LK_DRAINING)) | 538 (flags & LK_EXTFLG_MASK); 539 lkp->lk_wmesg = wmesg; 540 lkp->lk_timo = timo; 541 } 542 543 /* 544 * Determine the status of a lock. 545 */ 546 int 547 lockstatus(struct lock *lkp, struct thread *td) 548 { 549 int lock_type = 0; 550 551 spin_lock(&lkp->lk_spinlock); 552 if (lkp->lk_exclusivecount != 0) { 553 if (td == NULL || lkp->lk_lockholder == td) 554 lock_type = LK_EXCLUSIVE; 555 else 556 lock_type = LK_EXCLOTHER; 557 } else if (lkp->lk_sharecount != 0) { 558 lock_type = LK_SHARED; 559 } 560 spin_unlock(&lkp->lk_spinlock); 561 return (lock_type); 562 } 563 564 /* 565 * Determine the number of holders of a lock. 566 * 567 * The non-blocking version can usually be used for assertions. 568 */ 569 int 570 lockcount(struct lock *lkp) 571 { 572 int count; 573 574 spin_lock(&lkp->lk_spinlock); 575 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 576 spin_unlock(&lkp->lk_spinlock); 577 return (count); 578 } 579 580 int 581 lockcountnb(struct lock *lkp) 582 { 583 return (lkp->lk_exclusivecount + lkp->lk_sharecount); 584 } 585 586 /* 587 * Print out information about state of a lock. Used by VOP_PRINT 588 * routines to display status about contained locks. 589 */ 590 void 591 lockmgr_printinfo(struct lock *lkp) 592 { 593 struct thread *td = lkp->lk_lockholder; 594 struct proc *p; 595 596 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD) 597 p = td->td_proc; 598 else 599 p = NULL; 600 601 if (lkp->lk_sharecount) 602 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 603 lkp->lk_sharecount); 604 else if (lkp->lk_flags & LK_HAVE_EXCL) 605 printf(" lock type %s: EXCL (count %d) by td %p pid %d", 606 lkp->lk_wmesg, lkp->lk_exclusivecount, td, 607 p ? p->p_pid : -99); 608 if (lkp->lk_waitcount > 0) 609 printf(" with %d pending", lkp->lk_waitcount); 610 } 611 612