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 1.13 2005/01/19 18:00:39 drhodus 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 54 /* 55 * 0: no warnings, 1: warnings, 2: panic 56 */ 57 static int lockmgr_from_int = 1; 58 SYSCTL_INT(_debug, OID_AUTO, lockmgr_from_int, CTLFLAG_RW, &lockmgr_from_int, 0, ""); 59 60 /* 61 * Locking primitives implementation. 62 * Locks provide shared/exclusive sychronization. 63 */ 64 65 #ifdef SIMPLELOCK_DEBUG 66 #define COUNT(td, x) (td)->td_locks += (x) 67 #else 68 #define COUNT(td, x) 69 #endif 70 71 #define LOCK_WAIT_TIME 100 72 #define LOCK_SAMPLE_WAIT 7 73 74 #if defined(DIAGNOSTIC) 75 #define LOCK_INLINE 76 #else 77 #define LOCK_INLINE __inline 78 #endif 79 80 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 81 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 82 83 static int acquire(struct lock *lkp, int extflags, int wanted); 84 static int acquiredrain(struct lock *lkp, int extflags) ; 85 86 static LOCK_INLINE void 87 sharelock(struct lock *lkp, int incr) { 88 lkp->lk_flags |= LK_SHARE_NONZERO; 89 lkp->lk_sharecount += incr; 90 } 91 92 static LOCK_INLINE void 93 shareunlock(struct lock *lkp, int decr) { 94 95 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 96 97 if (lkp->lk_sharecount == decr) { 98 lkp->lk_flags &= ~LK_SHARE_NONZERO; 99 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 100 wakeup(lkp); 101 } 102 lkp->lk_sharecount = 0; 103 } else { 104 lkp->lk_sharecount -= decr; 105 } 106 } 107 108 static int 109 acquire(struct lock *lkp, int extflags, int wanted) 110 { 111 int s, error; 112 113 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 114 return EBUSY; 115 } 116 117 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 118 if ((lkp->lk_flags & wanted) == 0) 119 return 0; 120 } 121 122 s = splhigh(); 123 while ((lkp->lk_flags & wanted) != 0) { 124 lkp->lk_flags |= LK_WAIT_NONZERO; 125 lkp->lk_waitcount++; 126 /* note: serialization lock is held through tsleep */ 127 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, 128 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 129 if (lkp->lk_waitcount == 1) { 130 lkp->lk_flags &= ~LK_WAIT_NONZERO; 131 lkp->lk_waitcount = 0; 132 } else { 133 lkp->lk_waitcount--; 134 } 135 if (error) { 136 splx(s); 137 return error; 138 } 139 if (extflags & LK_SLEEPFAIL) { 140 splx(s); 141 return ENOLCK; 142 } 143 } 144 splx(s); 145 return 0; 146 } 147 148 /* 149 * Set, change, or release a lock. 150 * 151 * Shared requests increment the shared count. Exclusive requests set the 152 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 153 * accepted shared locks and shared-to-exclusive upgrades to go away. 154 */ 155 int 156 #ifndef DEBUG_LOCKS 157 lockmgr(struct lock *lkp, u_int flags, lwkt_tokref_t interlkp, 158 struct thread *td) 159 #else 160 debuglockmgr(struct lock *lkp, u_int flags, lwkt_tokref_t interlkp, 161 struct thread *td, const char *name, const char *file, int line) 162 #endif 163 { 164 int error; 165 int extflags; 166 lwkt_tokref ilock; 167 static int didpanic; 168 169 error = 0; 170 171 if (lockmgr_from_int && mycpu->gd_intr_nesting_level && 172 (flags & LK_NOWAIT) == 0 && 173 (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) { 174 #ifndef DEBUG_LOCKS 175 if (lockmgr_from_int == 2) { 176 didpanic = 1; 177 panic( 178 "lockmgr %s from %p: called from interrupt", 179 lkp->lk_wmesg, ((int **)&lkp)[-1]); 180 didpanic = 0; 181 } else { 182 printf( 183 "lockmgr %s from %p: called from interrupt\n", 184 lkp->lk_wmesg, ((int **)&lkp)[-1]); 185 } 186 #else 187 if (lockmgr_from_int == 2) { 188 didpanic = 1; 189 panic( 190 "lockmgr %s from %s:%d: called from interrupt", 191 lkp->lk_wmesg, file, line); 192 didpanic = 0; 193 } else { 194 printf( 195 "lockmgr %s from %s:%d: called from interrupt\n", 196 lkp->lk_wmesg, file, line); 197 } 198 #endif 199 } 200 201 lwkt_gettoken(&ilock, &lkp->lk_interlock); 202 if (flags & LK_INTERLOCK) 203 lwkt_reltoken(interlkp); 204 205 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 206 207 switch (flags & LK_TYPE_MASK) { 208 209 case LK_SHARED: 210 /* 211 * If we are not the exclusive lock holder, we have to block 212 * while there is an exclusive lock holder or while an 213 * exclusive lock request or upgrade request is in progress. 214 * 215 * However, if P_DEADLKTREAT is set, we override exclusive 216 * lock requests or upgrade requests ( but not the exclusive 217 * lock itself ). 218 */ 219 if (lkp->lk_lockholder != td) { 220 if (td->td_flags & TDF_DEADLKTREAT) { 221 error = acquire( 222 lkp, 223 extflags, 224 LK_HAVE_EXCL 225 ); 226 } else { 227 error = acquire( 228 lkp, 229 extflags, 230 LK_HAVE_EXCL | LK_WANT_EXCL | 231 LK_WANT_UPGRADE 232 ); 233 } 234 if (error) 235 break; 236 sharelock(lkp, 1); 237 COUNT(td, 1); 238 break; 239 } 240 /* 241 * We hold an exclusive lock, so downgrade it to shared. 242 * An alternative would be to fail with EDEADLK. 243 */ 244 sharelock(lkp, 1); 245 COUNT(td, 1); 246 /* fall into downgrade */ 247 248 case LK_DOWNGRADE: 249 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) 250 panic("lockmgr: not holding exclusive lock"); 251 sharelock(lkp, lkp->lk_exclusivecount); 252 lkp->lk_exclusivecount = 0; 253 lkp->lk_flags &= ~LK_HAVE_EXCL; 254 lkp->lk_lockholder = LK_NOTHREAD; 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(td, -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 ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) 283 panic("lockmgr: upgrade exclusive lock"); 284 shareunlock(lkp, 1); 285 COUNT(td, -1); 286 /* 287 * If we are just polling, check to see if we will block. 288 */ 289 if ((extflags & LK_NOWAIT) && 290 ((lkp->lk_flags & LK_WANT_UPGRADE) || 291 lkp->lk_sharecount > 1)) { 292 error = EBUSY; 293 break; 294 } 295 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 296 /* 297 * We are first shared lock to request an upgrade, so 298 * request upgrade and wait for the shared count to 299 * drop to zero, then take exclusive lock. 300 */ 301 lkp->lk_flags |= LK_WANT_UPGRADE; 302 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 303 lkp->lk_flags &= ~LK_WANT_UPGRADE; 304 305 if (error) 306 break; 307 lkp->lk_flags |= LK_HAVE_EXCL; 308 lkp->lk_lockholder = td; 309 if (lkp->lk_exclusivecount != 0) 310 panic("lockmgr: non-zero exclusive count"); 311 lkp->lk_exclusivecount = 1; 312 #if defined(DEBUG_LOCKS) 313 lkp->lk_filename = file; 314 lkp->lk_lineno = line; 315 lkp->lk_lockername = name; 316 #endif 317 COUNT(td, 1); 318 break; 319 } 320 /* 321 * Someone else has requested upgrade. Release our shared 322 * lock, awaken upgrade requestor if we are the last shared 323 * lock, then request an exclusive lock. 324 */ 325 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 326 LK_WAIT_NONZERO) 327 wakeup((void *)lkp); 328 /* fall into exclusive request */ 329 330 case LK_EXCLUSIVE: 331 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) { 332 /* 333 * Recursive lock. 334 */ 335 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 336 panic("lockmgr: locking against myself"); 337 if ((extflags & LK_CANRECURSE) != 0) { 338 lkp->lk_exclusivecount++; 339 COUNT(td, 1); 340 break; 341 } 342 } 343 /* 344 * If we are just polling, check to see if we will sleep. 345 */ 346 if ((extflags & LK_NOWAIT) && 347 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 348 error = EBUSY; 349 break; 350 } 351 /* 352 * Try to acquire the want_exclusive flag. 353 */ 354 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 355 if (error) 356 break; 357 lkp->lk_flags |= LK_WANT_EXCL; 358 /* 359 * Wait for shared locks and upgrades to finish. 360 */ 361 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 362 lkp->lk_flags &= ~LK_WANT_EXCL; 363 if (error) 364 break; 365 lkp->lk_flags |= LK_HAVE_EXCL; 366 lkp->lk_lockholder = td; 367 if (lkp->lk_exclusivecount != 0) 368 panic("lockmgr: non-zero exclusive count"); 369 lkp->lk_exclusivecount = 1; 370 #if defined(DEBUG_LOCKS) 371 lkp->lk_filename = file; 372 lkp->lk_lineno = line; 373 lkp->lk_lockername = name; 374 #endif 375 COUNT(td, 1); 376 break; 377 378 case LK_RELEASE: 379 if (lkp->lk_exclusivecount != 0) { 380 if (lkp->lk_lockholder != td && 381 lkp->lk_lockholder != LK_KERNTHREAD) { 382 panic("lockmgr: pid %d, not %s thr %p unlocking", 383 (td->td_proc ? td->td_proc->p_pid : -99), 384 "exclusive lock holder", 385 lkp->lk_lockholder); 386 } 387 if (lkp->lk_lockholder != LK_KERNTHREAD) { 388 COUNT(td, -1); 389 } 390 if (lkp->lk_exclusivecount == 1) { 391 lkp->lk_flags &= ~LK_HAVE_EXCL; 392 lkp->lk_lockholder = LK_NOTHREAD; 393 lkp->lk_exclusivecount = 0; 394 } else { 395 lkp->lk_exclusivecount--; 396 } 397 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 398 shareunlock(lkp, 1); 399 COUNT(td, -1); 400 } 401 if (lkp->lk_flags & LK_WAIT_NONZERO) 402 wakeup((void *)lkp); 403 break; 404 405 case LK_DRAIN: 406 /* 407 * Check that we do not already hold the lock, as it can 408 * never drain if we do. Unfortunately, we have no way to 409 * check for holding a shared lock, but at least we can 410 * check for an exclusive one. 411 */ 412 if (lkp->lk_lockholder == td) 413 panic("lockmgr: draining against myself"); 414 415 error = acquiredrain(lkp, extflags); 416 if (error) 417 break; 418 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 419 lkp->lk_lockholder = td; 420 lkp->lk_exclusivecount = 1; 421 #if defined(DEBUG_LOCKS) 422 lkp->lk_filename = file; 423 lkp->lk_lineno = line; 424 lkp->lk_lockername = name; 425 #endif 426 COUNT(td, 1); 427 break; 428 429 default: 430 lwkt_reltoken(&ilock); 431 panic("lockmgr: unknown locktype request %d", 432 flags & LK_TYPE_MASK); 433 /* NOTREACHED */ 434 } 435 if ((lkp->lk_flags & LK_WAITDRAIN) && 436 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 437 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 438 lkp->lk_flags &= ~LK_WAITDRAIN; 439 wakeup((void *)&lkp->lk_flags); 440 } 441 lwkt_reltoken(&ilock); 442 return (error); 443 } 444 445 static int 446 acquiredrain(struct lock *lkp, int extflags) 447 { 448 int error; 449 450 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 451 return EBUSY; 452 } 453 454 if ((lkp->lk_flags & LK_ALL) == 0) 455 return 0; 456 457 while (lkp->lk_flags & LK_ALL) { 458 lkp->lk_flags |= LK_WAITDRAIN; 459 /* interlock serialization held through tsleep */ 460 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 461 lkp->lk_wmesg, 462 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 463 if (error) 464 return error; 465 if (extflags & LK_SLEEPFAIL) { 466 return ENOLCK; 467 } 468 } 469 return 0; 470 } 471 472 /* 473 * Initialize a lock; required before use. 474 */ 475 void 476 lockinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags) 477 { 478 lwkt_token_init(&lkp->lk_interlock); 479 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 480 lkp->lk_sharecount = 0; 481 lkp->lk_waitcount = 0; 482 lkp->lk_exclusivecount = 0; 483 lkp->lk_prio = prio; 484 lkp->lk_wmesg = wmesg; 485 lkp->lk_timo = timo; 486 lkp->lk_lockholder = LK_NOTHREAD; 487 } 488 489 /* 490 * Reinitialize a lock that is being reused for a different purpose, but 491 * which may have pending (blocked) threads sitting on it. The caller 492 * must already hold the interlock. 493 */ 494 void 495 lockreinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags) 496 { 497 lkp->lk_flags = (lkp->lk_flags & ~(LK_EXTFLG_MASK|LK_DRAINING)) | 498 (flags & LK_EXTFLG_MASK); 499 lkp->lk_prio = prio; 500 lkp->lk_wmesg = wmesg; 501 lkp->lk_timo = timo; 502 } 503 504 /* 505 * Determine the status of a lock. 506 */ 507 int 508 lockstatus(struct lock *lkp, struct thread *td) 509 { 510 lwkt_tokref ilock; 511 int lock_type = 0; 512 513 lwkt_gettoken(&ilock, &lkp->lk_interlock); 514 if (lkp->lk_exclusivecount != 0) { 515 if (td == NULL || lkp->lk_lockholder == td) 516 lock_type = LK_EXCLUSIVE; 517 else 518 lock_type = LK_EXCLOTHER; 519 } else if (lkp->lk_sharecount != 0) { 520 lock_type = LK_SHARED; 521 } 522 lwkt_reltoken(&ilock); 523 return (lock_type); 524 } 525 526 /* 527 * Determine the number of holders of a lock. 528 * 529 * The non-blocking version can usually be used for assertions. 530 */ 531 int 532 lockcount(struct lock *lkp) 533 { 534 lwkt_tokref ilock; 535 int count; 536 537 lwkt_gettoken(&ilock, &lkp->lk_interlock); 538 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 539 lwkt_reltoken(&ilock); 540 return (count); 541 } 542 543 int 544 lockcountnb(struct lock *lkp) 545 { 546 return (lkp->lk_exclusivecount + lkp->lk_sharecount); 547 } 548 549 /* 550 * Print out information about state of a lock. Used by VOP_PRINT 551 * routines to display status about contained locks. 552 */ 553 void 554 lockmgr_printinfo(struct lock *lkp) 555 { 556 struct thread *td = lkp->lk_lockholder; 557 struct proc *p; 558 559 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD) 560 p = td->td_proc; 561 else 562 p = NULL; 563 564 if (lkp->lk_sharecount) 565 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 566 lkp->lk_sharecount); 567 else if (lkp->lk_flags & LK_HAVE_EXCL) 568 printf(" lock type %s: EXCL (count %d) by td %p pid %d", 569 lkp->lk_wmesg, lkp->lk_exclusivecount, td, 570 p ? p->p_pid : -99); 571 if (lkp->lk_waitcount > 0) 572 printf(" with %d pending", lkp->lk_waitcount); 573 } 574 575