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 1.5 2003/07/21 07:57:47 dillon Exp $ 43 */ 44 45 #include "opt_lint.h" 46 47 #include <sys/param.h> 48 #include <sys/proc.h> 49 #include <sys/lock.h> 50 #include <sys/systm.h> 51 52 /* 53 * Locking primitives implementation. 54 * Locks provide shared/exclusive sychronization. 55 */ 56 57 #ifdef SIMPLELOCK_DEBUG 58 #define COUNT(td, x) (td)->td_locks += (x) 59 #else 60 #define COUNT(td, x) 61 #endif 62 63 #define LOCK_WAIT_TIME 100 64 #define LOCK_SAMPLE_WAIT 7 65 66 #if defined(DIAGNOSTIC) 67 #define LOCK_INLINE 68 #else 69 #define LOCK_INLINE __inline 70 #endif 71 72 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 73 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 74 75 static int acquire(struct lock *lkp, int extflags, int wanted); 76 static int acquiredrain(struct lock *lkp, int extflags) ; 77 78 static LOCK_INLINE void 79 sharelock(struct lock *lkp, int incr) { 80 lkp->lk_flags |= LK_SHARE_NONZERO; 81 lkp->lk_sharecount += incr; 82 } 83 84 static LOCK_INLINE void 85 shareunlock(struct lock *lkp, int decr) { 86 87 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 88 89 if (lkp->lk_sharecount == decr) { 90 lkp->lk_flags &= ~LK_SHARE_NONZERO; 91 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 92 wakeup(lkp); 93 } 94 lkp->lk_sharecount = 0; 95 } else { 96 lkp->lk_sharecount -= decr; 97 } 98 } 99 100 static int 101 acquire(struct lock *lkp, int extflags, int wanted) 102 { 103 int s, error; 104 105 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 106 return EBUSY; 107 } 108 109 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) { 110 if ((lkp->lk_flags & wanted) == 0) 111 return 0; 112 } 113 114 s = splhigh(); 115 while ((lkp->lk_flags & wanted) != 0) { 116 lkp->lk_flags |= LK_WAIT_NONZERO; 117 lkp->lk_waitcount++; 118 lwkt_reltoken(&lkp->lk_interlock); 119 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg, 120 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 121 lwkt_gettoken(&lkp->lk_interlock); 122 if (lkp->lk_waitcount == 1) { 123 lkp->lk_flags &= ~LK_WAIT_NONZERO; 124 lkp->lk_waitcount = 0; 125 } else { 126 lkp->lk_waitcount--; 127 } 128 if (error) { 129 splx(s); 130 return error; 131 } 132 if (extflags & LK_SLEEPFAIL) { 133 splx(s); 134 return ENOLCK; 135 } 136 } 137 splx(s); 138 return 0; 139 } 140 141 /* 142 * Set, change, or release a lock. 143 * 144 * Shared requests increment the shared count. Exclusive requests set the 145 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 146 * accepted shared locks and shared-to-exclusive upgrades to go away. 147 */ 148 int 149 #ifndef DEBUG_LOCKS 150 lockmgr(struct lock *lkp, u_int flags, struct lwkt_token *interlkp, 151 struct thread *td) 152 #else 153 debuglockmgr(struct lock *lkp, u_int flags, struct lwkt_token *interlkp, 154 struct thread *td, const char *name, const char *file, int line) 155 #endif 156 { 157 int error; 158 int extflags; 159 160 error = 0; 161 162 lwkt_gettoken(&lkp->lk_interlock); 163 if (flags & LK_INTERLOCK) 164 lwkt_reltoken(interlkp); 165 166 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 167 168 switch (flags & LK_TYPE_MASK) { 169 170 case LK_SHARED: 171 /* 172 * If we are not the exclusive lock holder, we have to block 173 * while there is an exclusive lock holder or while an 174 * exclusive lock request or upgrade request is in progress. 175 * 176 * However, if P_DEADLKTREAT is set, we override exclusive 177 * lock requests or upgrade requests ( but not the exclusive 178 * lock itself ). 179 */ 180 if (lkp->lk_lockholder != td) { 181 if (td->td_flags & TDF_DEADLKTREAT) { 182 error = acquire( 183 lkp, 184 extflags, 185 LK_HAVE_EXCL 186 ); 187 } else { 188 error = acquire( 189 lkp, 190 extflags, 191 LK_HAVE_EXCL | LK_WANT_EXCL | 192 LK_WANT_UPGRADE 193 ); 194 } 195 if (error) 196 break; 197 sharelock(lkp, 1); 198 COUNT(td, 1); 199 break; 200 } 201 /* 202 * We hold an exclusive lock, so downgrade it to shared. 203 * An alternative would be to fail with EDEADLK. 204 */ 205 sharelock(lkp, 1); 206 COUNT(td, 1); 207 /* fall into downgrade */ 208 209 case LK_DOWNGRADE: 210 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) 211 panic("lockmgr: not holding exclusive lock"); 212 sharelock(lkp, lkp->lk_exclusivecount); 213 lkp->lk_exclusivecount = 0; 214 lkp->lk_flags &= ~LK_HAVE_EXCL; 215 lkp->lk_lockholder = LK_NOTHREAD; 216 if (lkp->lk_waitcount) 217 wakeup((void *)lkp); 218 break; 219 220 case LK_EXCLUPGRADE: 221 /* 222 * If another process is ahead of us to get an upgrade, 223 * then we want to fail rather than have an intervening 224 * exclusive access. 225 */ 226 if (lkp->lk_flags & LK_WANT_UPGRADE) { 227 shareunlock(lkp, 1); 228 COUNT(td, -1); 229 error = EBUSY; 230 break; 231 } 232 /* fall into normal upgrade */ 233 234 case LK_UPGRADE: 235 /* 236 * Upgrade a shared lock to an exclusive one. If another 237 * shared lock has already requested an upgrade to an 238 * exclusive lock, our shared lock is released and an 239 * exclusive lock is requested (which will be granted 240 * after the upgrade). If we return an error, the file 241 * will always be unlocked. 242 */ 243 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) 244 panic("lockmgr: upgrade exclusive lock"); 245 shareunlock(lkp, 1); 246 COUNT(td, -1); 247 /* 248 * If we are just polling, check to see if we will block. 249 */ 250 if ((extflags & LK_NOWAIT) && 251 ((lkp->lk_flags & LK_WANT_UPGRADE) || 252 lkp->lk_sharecount > 1)) { 253 error = EBUSY; 254 break; 255 } 256 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 257 /* 258 * We are first shared lock to request an upgrade, so 259 * request upgrade and wait for the shared count to 260 * drop to zero, then take exclusive lock. 261 */ 262 lkp->lk_flags |= LK_WANT_UPGRADE; 263 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 264 lkp->lk_flags &= ~LK_WANT_UPGRADE; 265 266 if (error) 267 break; 268 lkp->lk_flags |= LK_HAVE_EXCL; 269 lkp->lk_lockholder = td; 270 if (lkp->lk_exclusivecount != 0) 271 panic("lockmgr: non-zero exclusive count"); 272 lkp->lk_exclusivecount = 1; 273 #if defined(DEBUG_LOCKS) 274 lkp->lk_filename = file; 275 lkp->lk_lineno = line; 276 lkp->lk_lockername = name; 277 #endif 278 COUNT(td, 1); 279 break; 280 } 281 /* 282 * Someone else has requested upgrade. Release our shared 283 * lock, awaken upgrade requestor if we are the last shared 284 * lock, then request an exclusive lock. 285 */ 286 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 287 LK_WAIT_NONZERO) 288 wakeup((void *)lkp); 289 /* fall into exclusive request */ 290 291 case LK_EXCLUSIVE: 292 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) { 293 /* 294 * Recursive lock. 295 */ 296 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) 297 panic("lockmgr: locking against myself"); 298 if ((extflags & LK_CANRECURSE) != 0) { 299 lkp->lk_exclusivecount++; 300 COUNT(td, 1); 301 break; 302 } 303 } 304 /* 305 * If we are just polling, check to see if we will sleep. 306 */ 307 if ((extflags & LK_NOWAIT) && 308 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 309 error = EBUSY; 310 break; 311 } 312 /* 313 * Try to acquire the want_exclusive flag. 314 */ 315 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 316 if (error) 317 break; 318 lkp->lk_flags |= LK_WANT_EXCL; 319 /* 320 * Wait for shared locks and upgrades to finish. 321 */ 322 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 323 lkp->lk_flags &= ~LK_WANT_EXCL; 324 if (error) 325 break; 326 lkp->lk_flags |= LK_HAVE_EXCL; 327 lkp->lk_lockholder = td; 328 if (lkp->lk_exclusivecount != 0) 329 panic("lockmgr: non-zero exclusive count"); 330 lkp->lk_exclusivecount = 1; 331 #if defined(DEBUG_LOCKS) 332 lkp->lk_filename = file; 333 lkp->lk_lineno = line; 334 lkp->lk_lockername = name; 335 #endif 336 COUNT(td, 1); 337 break; 338 339 case LK_RELEASE: 340 if (lkp->lk_exclusivecount != 0) { 341 if (lkp->lk_lockholder != td && 342 lkp->lk_lockholder != LK_KERNTHREAD) { 343 panic("lockmgr: pid %d, not %s thr %p unlocking", 344 (td->td_proc ? td->td_proc->p_pid : -99), 345 "exclusive lock holder", 346 lkp->lk_lockholder); 347 } 348 if (lkp->lk_lockholder != LK_KERNTHREAD) { 349 COUNT(td, -1); 350 } 351 if (lkp->lk_exclusivecount == 1) { 352 lkp->lk_flags &= ~LK_HAVE_EXCL; 353 lkp->lk_lockholder = LK_NOTHREAD; 354 lkp->lk_exclusivecount = 0; 355 } else { 356 lkp->lk_exclusivecount--; 357 } 358 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 359 shareunlock(lkp, 1); 360 COUNT(td, -1); 361 } 362 if (lkp->lk_flags & LK_WAIT_NONZERO) 363 wakeup((void *)lkp); 364 break; 365 366 case LK_DRAIN: 367 /* 368 * Check that we do not already hold the lock, as it can 369 * never drain if we do. Unfortunately, we have no way to 370 * check for holding a shared lock, but at least we can 371 * check for an exclusive one. 372 */ 373 if (lkp->lk_lockholder == td) 374 panic("lockmgr: draining against myself"); 375 376 error = acquiredrain(lkp, extflags); 377 if (error) 378 break; 379 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL; 380 lkp->lk_lockholder = td; 381 lkp->lk_exclusivecount = 1; 382 #if defined(DEBUG_LOCKS) 383 lkp->lk_filename = file; 384 lkp->lk_lineno = line; 385 lkp->lk_lockername = name; 386 #endif 387 COUNT(td, 1); 388 break; 389 390 default: 391 lwkt_reltoken(&lkp->lk_interlock); 392 panic("lockmgr: unknown locktype request %d", 393 flags & LK_TYPE_MASK); 394 /* NOTREACHED */ 395 } 396 if ((lkp->lk_flags & LK_WAITDRAIN) && 397 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | 398 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) { 399 lkp->lk_flags &= ~LK_WAITDRAIN; 400 wakeup((void *)&lkp->lk_flags); 401 } 402 lwkt_reltoken(&lkp->lk_interlock); 403 return (error); 404 } 405 406 static int 407 acquiredrain(struct lock *lkp, int extflags) 408 { 409 int error; 410 411 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) { 412 return EBUSY; 413 } 414 415 if ((lkp->lk_flags & LK_ALL) == 0) 416 return 0; 417 418 while (lkp->lk_flags & LK_ALL) { 419 lkp->lk_flags |= LK_WAITDRAIN; 420 lwkt_reltoken(&lkp->lk_interlock); 421 error = tsleep(&lkp->lk_flags, lkp->lk_prio, 422 lkp->lk_wmesg, 423 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 424 lwkt_gettoken(&lkp->lk_interlock); 425 if (error) 426 return error; 427 if (extflags & LK_SLEEPFAIL) { 428 return ENOLCK; 429 } 430 } 431 return 0; 432 } 433 434 /* 435 * Initialize a lock; required before use. 436 */ 437 void 438 lockinit(lkp, prio, wmesg, timo, flags) 439 struct lock *lkp; 440 int prio; 441 char *wmesg; 442 int timo; 443 int flags; 444 { 445 lwkt_inittoken(&lkp->lk_interlock); 446 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 447 lkp->lk_sharecount = 0; 448 lkp->lk_waitcount = 0; 449 lkp->lk_exclusivecount = 0; 450 lkp->lk_prio = prio; 451 lkp->lk_wmesg = wmesg; 452 lkp->lk_timo = timo; 453 lkp->lk_lockholder = LK_NOTHREAD; 454 } 455 456 /* 457 * Determine the status of a lock. 458 */ 459 int 460 lockstatus(struct lock *lkp, struct thread *td) 461 { 462 int lock_type = 0; 463 464 lwkt_gettoken(&lkp->lk_interlock); 465 if (lkp->lk_exclusivecount != 0) { 466 if (td == NULL || lkp->lk_lockholder == td) 467 lock_type = LK_EXCLUSIVE; 468 else 469 lock_type = LK_EXCLOTHER; 470 } else if (lkp->lk_sharecount != 0) { 471 lock_type = LK_SHARED; 472 } 473 lwkt_reltoken(&lkp->lk_interlock); 474 return (lock_type); 475 } 476 477 /* 478 * Determine the number of holders of a lock. 479 */ 480 int 481 lockcount(lkp) 482 struct lock *lkp; 483 { 484 int count; 485 486 lwkt_gettoken(&lkp->lk_interlock); 487 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 488 lwkt_reltoken(&lkp->lk_interlock); 489 return (count); 490 } 491 492 /* 493 * Print out information about state of a lock. Used by VOP_PRINT 494 * routines to display status about contained locks. 495 */ 496 void 497 lockmgr_printinfo(lkp) 498 struct lock *lkp; 499 { 500 struct thread *td = lkp->lk_lockholder; 501 struct proc *p; 502 503 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD) 504 p = td->td_proc; 505 else 506 p = NULL; 507 508 if (lkp->lk_sharecount) 509 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 510 lkp->lk_sharecount); 511 else if (lkp->lk_flags & LK_HAVE_EXCL) 512 printf(" lock type %s: EXCL (count %d) by td %p pid %d", 513 lkp->lk_wmesg, lkp->lk_exclusivecount, td, 514 p ? p->p_pid : -99); 515 if (lkp->lk_waitcount > 0) 516 printf(" with %d pending", lkp->lk_waitcount); 517 } 518 519