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 1.14 2005/06/06 15:02:27 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/thread2.h> 54 55 /* 56 * 0: no warnings, 1: warnings, 2: panic 57 */ 58 static int lockmgr_from_int = 1; 59 SYSCTL_INT(_debug, OID_AUTO, lockmgr_from_int, CTLFLAG_RW, &lockmgr_from_int, 0, ""); 60 61 /* 62 * Locking primitives implementation. 63 * Locks provide shared/exclusive sychronization. 64 */ 65 66 #ifdef SIMPLELOCK_DEBUG 67 #define COUNT(td, x) (td)->td_locks += (x) 68 #else 69 #define COUNT(td, x) 70 #endif 71 72 #define LOCK_WAIT_TIME 100 73 #define LOCK_SAMPLE_WAIT 7 74 75 #if defined(DIAGNOSTIC) 76 #define LOCK_INLINE 77 #else 78 #define LOCK_INLINE __inline 79 #endif 80 81 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 82 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 83 84 static int acquire(struct lock *lkp, int extflags, int wanted); 85 static int acquiredrain(struct lock *lkp, int extflags) ; 86 87 static LOCK_INLINE void 88 sharelock(struct lock *lkp, int incr) { 89 lkp->lk_flags |= LK_SHARE_NONZERO; 90 lkp->lk_sharecount += incr; 91 } 92 93 static LOCK_INLINE void 94 shareunlock(struct lock *lkp, int decr) { 95 96 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 97 98 if (lkp->lk_sharecount == decr) { 99 lkp->lk_flags &= ~LK_SHARE_NONZERO; 100 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 101 wakeup(lkp); 102 } 103 lkp->lk_sharecount = 0; 104 } else { 105 lkp->lk_sharecount -= decr; 106 } 107 } 108 109 static int 110 acquire(struct lock *lkp, int extflags, int wanted) 111 { 112 int error; 113 114 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 115 return EBUSY; 116 } 117 118 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 119 if ((lkp->lk_flags & wanted) == 0) 120 return 0; 121 } 122 123 crit_enter(); 124 while ((lkp->lk_flags & wanted) != 0) { 125 lkp->lk_flags |= LK_WAIT_NONZERO; 126 lkp->lk_waitcount++; 127 /* note: serialization lock is held through tsleep */ 128 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, 129 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 130 if (lkp->lk_waitcount == 1) { 131 lkp->lk_flags &= ~LK_WAIT_NONZERO; 132 lkp->lk_waitcount = 0; 133 } else { 134 lkp->lk_waitcount--; 135 } 136 if (error) { 137 crit_exit(); 138 return error; 139 } 140 if (extflags & LK_SLEEPFAIL) { 141 crit_exit(); 142 return ENOLCK; 143 } 144 } 145 crit_exit(); 146 return 0; 147 } 148 149 /* 150 * Set, change, or release a lock. 151 * 152 * Shared requests increment the shared count. Exclusive requests set the 153 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 154 * accepted shared locks and shared-to-exclusive upgrades to go away. 155 */ 156 int 157 #ifndef DEBUG_LOCKS 158 lockmgr(struct lock *lkp, u_int flags, lwkt_tokref_t interlkp, 159 struct thread *td) 160 #else 161 debuglockmgr(struct lock *lkp, u_int flags, lwkt_tokref_t interlkp, 162 struct thread *td, const char *name, const char *file, int line) 163 #endif 164 { 165 int error; 166 int extflags; 167 lwkt_tokref ilock; 168 static int didpanic; 169 170 error = 0; 171 172 if (lockmgr_from_int && mycpu->gd_intr_nesting_level && 173 (flags & LK_NOWAIT) == 0 && 174 (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) { 175 #ifndef DEBUG_LOCKS 176 if (lockmgr_from_int == 2) { 177 didpanic = 1; 178 panic( 179 "lockmgr %s from %p: called from interrupt", 180 lkp->lk_wmesg, ((int **)&lkp)[-1]); 181 didpanic = 0; 182 } else { 183 printf( 184 "lockmgr %s from %p: called from interrupt\n", 185 lkp->lk_wmesg, ((int **)&lkp)[-1]); 186 } 187 #else 188 if (lockmgr_from_int == 2) { 189 didpanic = 1; 190 panic( 191 "lockmgr %s from %s:%d: called from interrupt", 192 lkp->lk_wmesg, file, line); 193 didpanic = 0; 194 } else { 195 printf( 196 "lockmgr %s from %s:%d: called from interrupt\n", 197 lkp->lk_wmesg, file, line); 198 } 199 #endif 200 } 201 202 lwkt_gettoken(&ilock, &lkp->lk_interlock); 203 if (flags & LK_INTERLOCK) 204 lwkt_reltoken(interlkp); 205 206 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 207 208 switch (flags & LK_TYPE_MASK) { 209 210 case LK_SHARED: 211 /* 212 * If we are not the exclusive lock holder, we have to block 213 * while there is an exclusive lock holder or while an 214 * exclusive lock request or upgrade request is in progress. 215 * 216 * However, if P_DEADLKTREAT is set, we override exclusive 217 * lock requests or upgrade requests ( but not the exclusive 218 * lock itself ). 219 */ 220 if (lkp->lk_lockholder != td) { 221 if (td->td_flags & TDF_DEADLKTREAT) { 222 error = acquire( 223 lkp, 224 extflags, 225 LK_HAVE_EXCL 226 ); 227 } else { 228 error = acquire( 229 lkp, 230 extflags, 231 LK_HAVE_EXCL | LK_WANT_EXCL | 232 LK_WANT_UPGRADE 233 ); 234 } 235 if (error) 236 break; 237 sharelock(lkp, 1); 238 COUNT(td, 1); 239 break; 240 } 241 /* 242 * We hold an exclusive lock, so downgrade it to shared. 243 * An alternative would be to fail with EDEADLK. 244 */ 245 sharelock(lkp, 1); 246 COUNT(td, 1); 247 /* fall into downgrade */ 248 249 case LK_DOWNGRADE: 250 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) 251 panic("lockmgr: not holding exclusive lock"); 252 sharelock(lkp, lkp->lk_exclusivecount); 253 lkp->lk_exclusivecount = 0; 254 lkp->lk_flags &= ~LK_HAVE_EXCL; 255 lkp->lk_lockholder = LK_NOTHREAD; 256 if (lkp->lk_waitcount) 257 wakeup((void *)lkp); 258 break; 259 260 case LK_EXCLUPGRADE: 261 /* 262 * If another process is ahead of us to get an upgrade, 263 * then we want to fail rather than have an intervening 264 * exclusive access. 265 */ 266 if (lkp->lk_flags & LK_WANT_UPGRADE) { 267 shareunlock(lkp, 1); 268 COUNT(td, -1); 269 error = EBUSY; 270 break; 271 } 272 /* fall into normal upgrade */ 273 274 case LK_UPGRADE: 275 /* 276 * Upgrade a shared lock to an exclusive one. If another 277 * shared lock has already requested an upgrade to an 278 * exclusive lock, our shared lock is released and an 279 * exclusive lock is requested (which will be granted 280 * after the upgrade). If we return an error, the file 281 * will always be unlocked. 282 */ 283 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) 284 panic("lockmgr: upgrade exclusive lock"); 285 shareunlock(lkp, 1); 286 COUNT(td, -1); 287 /* 288 * If we are just polling, check to see if we will block. 289 */ 290 if ((extflags & LK_NOWAIT) && 291 ((lkp->lk_flags & LK_WANT_UPGRADE) || 292 lkp->lk_sharecount > 1)) { 293 error = EBUSY; 294 break; 295 } 296 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 297 /* 298 * We are first shared lock to request an upgrade, so 299 * request upgrade and wait for the shared count to 300 * drop to zero, then take exclusive lock. 301 */ 302 lkp->lk_flags |= LK_WANT_UPGRADE; 303 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 304 lkp->lk_flags &= ~LK_WANT_UPGRADE; 305 306 if (error) 307 break; 308 lkp->lk_flags |= LK_HAVE_EXCL; 309 lkp->lk_lockholder = td; 310 if (lkp->lk_exclusivecount != 0) 311 panic("lockmgr: non-zero exclusive count"); 312 lkp->lk_exclusivecount = 1; 313 #if defined(DEBUG_LOCKS) 314 lkp->lk_filename = file; 315 lkp->lk_lineno = line; 316 lkp->lk_lockername = name; 317 #endif 318 COUNT(td, 1); 319 break; 320 } 321 /* 322 * Someone else has requested upgrade. Release our shared 323 * lock, awaken upgrade requestor if we are the last shared 324 * lock, then request an exclusive lock. 325 */ 326 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 327 LK_WAIT_NONZERO) 328 wakeup((void *)lkp); 329 /* fall into exclusive request */ 330 331 case LK_EXCLUSIVE: 332 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) { 333 /* 334 * Recursive lock. 335 */ 336 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 337 panic("lockmgr: locking against myself"); 338 if ((extflags & LK_CANRECURSE) != 0) { 339 lkp->lk_exclusivecount++; 340 COUNT(td, 1); 341 break; 342 } 343 } 344 /* 345 * If we are just polling, check to see if we will sleep. 346 */ 347 if ((extflags & LK_NOWAIT) && 348 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 349 error = EBUSY; 350 break; 351 } 352 /* 353 * Try to acquire the want_exclusive flag. 354 */ 355 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 356 if (error) 357 break; 358 lkp->lk_flags |= LK_WANT_EXCL; 359 /* 360 * Wait for shared locks and upgrades to finish. 361 */ 362 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 363 lkp->lk_flags &= ~LK_WANT_EXCL; 364 if (error) 365 break; 366 lkp->lk_flags |= LK_HAVE_EXCL; 367 lkp->lk_lockholder = td; 368 if (lkp->lk_exclusivecount != 0) 369 panic("lockmgr: non-zero exclusive count"); 370 lkp->lk_exclusivecount = 1; 371 #if defined(DEBUG_LOCKS) 372 lkp->lk_filename = file; 373 lkp->lk_lineno = line; 374 lkp->lk_lockername = name; 375 #endif 376 COUNT(td, 1); 377 break; 378 379 case LK_RELEASE: 380 if (lkp->lk_exclusivecount != 0) { 381 if (lkp->lk_lockholder != td && 382 lkp->lk_lockholder != LK_KERNTHREAD) { 383 panic("lockmgr: pid %d, not %s thr %p unlocking", 384 (td->td_proc ? td->td_proc->p_pid : -99), 385 "exclusive lock holder", 386 lkp->lk_lockholder); 387 } 388 if (lkp->lk_lockholder != LK_KERNTHREAD) { 389 COUNT(td, -1); 390 } 391 if (lkp->lk_exclusivecount == 1) { 392 lkp->lk_flags &= ~LK_HAVE_EXCL; 393 lkp->lk_lockholder = LK_NOTHREAD; 394 lkp->lk_exclusivecount = 0; 395 } else { 396 lkp->lk_exclusivecount--; 397 } 398 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 399 shareunlock(lkp, 1); 400 COUNT(td, -1); 401 } 402 if (lkp->lk_flags & LK_WAIT_NONZERO) 403 wakeup((void *)lkp); 404 break; 405 406 case LK_DRAIN: 407 /* 408 * Check that we do not already hold the lock, as it can 409 * never drain if we do. Unfortunately, we have no way to 410 * check for holding a shared lock, but at least we can 411 * check for an exclusive one. 412 */ 413 if (lkp->lk_lockholder == td) 414 panic("lockmgr: draining against myself"); 415 416 error = acquiredrain(lkp, extflags); 417 if (error) 418 break; 419 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 420 lkp->lk_lockholder = td; 421 lkp->lk_exclusivecount = 1; 422 #if defined(DEBUG_LOCKS) 423 lkp->lk_filename = file; 424 lkp->lk_lineno = line; 425 lkp->lk_lockername = name; 426 #endif 427 COUNT(td, 1); 428 break; 429 430 default: 431 lwkt_reltoken(&ilock); 432 panic("lockmgr: unknown locktype request %d", 433 flags & LK_TYPE_MASK); 434 /* NOTREACHED */ 435 } 436 if ((lkp->lk_flags & LK_WAITDRAIN) && 437 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 438 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 439 lkp->lk_flags &= ~LK_WAITDRAIN; 440 wakeup((void *)&lkp->lk_flags); 441 } 442 lwkt_reltoken(&ilock); 443 return (error); 444 } 445 446 static int 447 acquiredrain(struct lock *lkp, int extflags) 448 { 449 int error; 450 451 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 452 return EBUSY; 453 } 454 455 if ((lkp->lk_flags & LK_ALL) == 0) 456 return 0; 457 458 while (lkp->lk_flags & LK_ALL) { 459 lkp->lk_flags |= LK_WAITDRAIN; 460 /* interlock serialization held through tsleep */ 461 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 462 lkp->lk_wmesg, 463 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 464 if (error) 465 return error; 466 if (extflags & LK_SLEEPFAIL) { 467 return ENOLCK; 468 } 469 } 470 return 0; 471 } 472 473 /* 474 * Initialize a lock; required before use. 475 */ 476 void 477 lockinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags) 478 { 479 lwkt_token_init(&lkp->lk_interlock); 480 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 481 lkp->lk_sharecount = 0; 482 lkp->lk_waitcount = 0; 483 lkp->lk_exclusivecount = 0; 484 lkp->lk_prio = prio; 485 lkp->lk_wmesg = wmesg; 486 lkp->lk_timo = timo; 487 lkp->lk_lockholder = LK_NOTHREAD; 488 } 489 490 /* 491 * Reinitialize a lock that is being reused for a different purpose, but 492 * which may have pending (blocked) threads sitting on it. The caller 493 * must already hold the interlock. 494 */ 495 void 496 lockreinit(struct lock *lkp, int prio, char *wmesg, int timo, int flags) 497 { 498 lkp->lk_flags = (lkp->lk_flags & ~(LK_EXTFLG_MASK|LK_DRAINING)) | 499 (flags & LK_EXTFLG_MASK); 500 lkp->lk_prio = prio; 501 lkp->lk_wmesg = wmesg; 502 lkp->lk_timo = timo; 503 } 504 505 /* 506 * Determine the status of a lock. 507 */ 508 int 509 lockstatus(struct lock *lkp, struct thread *td) 510 { 511 lwkt_tokref ilock; 512 int lock_type = 0; 513 514 lwkt_gettoken(&ilock, &lkp->lk_interlock); 515 if (lkp->lk_exclusivecount != 0) { 516 if (td == NULL || lkp->lk_lockholder == td) 517 lock_type = LK_EXCLUSIVE; 518 else 519 lock_type = LK_EXCLOTHER; 520 } else if (lkp->lk_sharecount != 0) { 521 lock_type = LK_SHARED; 522 } 523 lwkt_reltoken(&ilock); 524 return (lock_type); 525 } 526 527 /* 528 * Determine the number of holders of a lock. 529 * 530 * The non-blocking version can usually be used for assertions. 531 */ 532 int 533 lockcount(struct lock *lkp) 534 { 535 lwkt_tokref ilock; 536 int count; 537 538 lwkt_gettoken(&ilock, &lkp->lk_interlock); 539 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 540 lwkt_reltoken(&ilock); 541 return (count); 542 } 543 544 int 545 lockcountnb(struct lock *lkp) 546 { 547 return (lkp->lk_exclusivecount + lkp->lk_sharecount); 548 } 549 550 /* 551 * Print out information about state of a lock. Used by VOP_PRINT 552 * routines to display status about contained locks. 553 */ 554 void 555 lockmgr_printinfo(struct lock *lkp) 556 { 557 struct thread *td = lkp->lk_lockholder; 558 struct proc *p; 559 560 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD) 561 p = td->td_proc; 562 else 563 p = NULL; 564 565 if (lkp->lk_sharecount) 566 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 567 lkp->lk_sharecount); 568 else if (lkp->lk_flags & LK_HAVE_EXCL) 569 printf(" lock type %s: EXCL (count %d) by td %p pid %d", 570 lkp->lk_wmesg, lkp->lk_exclusivecount, td, 571 p ? p->p_pid : -99); 572 if (lkp->lk_waitcount > 0) 573 printf(" with %d pending", lkp->lk_waitcount); 574 } 575 576