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 1.25 2006/12/23 00:35:04 swildner 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 88 static LOCK_INLINE void 89 sharelock(struct lock *lkp, int incr) { 90 lkp->lk_flags |= LK_SHARE_NONZERO; 91 lkp->lk_sharecount += incr; 92 } 93 94 static LOCK_INLINE int 95 shareunlock(struct lock *lkp, int decr) 96 { 97 int dowakeup = 0; 98 99 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 100 101 if (lkp->lk_sharecount == decr) { 102 lkp->lk_flags &= ~LK_SHARE_NONZERO; 103 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 104 dowakeup = 1; 105 } 106 lkp->lk_sharecount = 0; 107 } else { 108 lkp->lk_sharecount -= decr; 109 } 110 return(dowakeup); 111 } 112 113 /* 114 * lock acquisition helper routine. Called with the lock's spinlock held. 115 */ 116 static int 117 acquire(struct lock *lkp, int extflags, int wanted) 118 { 119 int error; 120 121 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 122 return EBUSY; 123 } 124 125 while ((lkp->lk_flags & wanted) != 0) { 126 lkp->lk_flags |= LK_WAIT_NONZERO; 127 lkp->lk_waitcount++; 128 129 /* 130 * Atomic spinlock release/sleep/reacquire. 131 */ 132 error = msleep(lkp, &lkp->lk_spinlock, 133 ((extflags & LK_PCATCH) ? PCATCH : 0), 134 lkp->lk_wmesg, 135 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0)); 136 if (lkp->lk_waitcount == 1) { 137 lkp->lk_flags &= ~LK_WAIT_NONZERO; 138 lkp->lk_waitcount = 0; 139 } else { 140 lkp->lk_waitcount--; 141 } 142 if (error) 143 return error; 144 if (extflags & LK_SLEEPFAIL) 145 return ENOLCK; 146 } 147 return 0; 148 } 149 150 /* 151 * Set, change, or release a lock. 152 * 153 * Shared requests increment the shared count. Exclusive requests set the 154 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 155 * accepted shared locks and shared-to-exclusive upgrades to go away. 156 * 157 * A spinlock is held for most of the procedure. We must not do anything 158 * fancy while holding the spinlock. 159 */ 160 int 161 #ifndef DEBUG_LOCKS 162 lockmgr(struct lock *lkp, u_int flags) 163 #else 164 debuglockmgr(struct lock *lkp, u_int flags, 165 const char *name, const char *file, int line) 166 #endif 167 { 168 thread_t td; 169 int error; 170 int extflags; 171 int dowakeup; 172 static int didpanic; 173 174 error = 0; 175 dowakeup = 0; 176 177 if (lockmgr_from_int && mycpu->gd_intr_nesting_level && 178 (flags & LK_NOWAIT) == 0 && 179 (flags & LK_TYPE_MASK) != LK_RELEASE && didpanic == 0) { 180 #ifndef DEBUG_LOCKS 181 if (lockmgr_from_int == 2) { 182 didpanic = 1; 183 panic( 184 "lockmgr %s from %p: called from interrupt", 185 lkp->lk_wmesg, ((int **)&lkp)[-1]); 186 didpanic = 0; 187 } else { 188 kprintf( 189 "lockmgr %s from %p: called from interrupt\n", 190 lkp->lk_wmesg, ((int **)&lkp)[-1]); 191 } 192 #else 193 if (lockmgr_from_int == 2) { 194 didpanic = 1; 195 panic( 196 "lockmgr %s from %s:%d: called from interrupt", 197 lkp->lk_wmesg, file, line); 198 didpanic = 0; 199 } else { 200 kprintf( 201 "lockmgr %s from %s:%d: called from interrupt\n", 202 lkp->lk_wmesg, file, line); 203 } 204 #endif 205 } 206 207 spin_lock_wr(&lkp->lk_spinlock); 208 209 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 210 td = curthread; 211 212 switch (flags & LK_TYPE_MASK) { 213 case LK_SHARED: 214 /* 215 * If we are not the exclusive lock holder, we have to block 216 * while there is an exclusive lock holder or while an 217 * exclusive lock request or upgrade request is in progress. 218 * 219 * However, if P_DEADLKTREAT is set, we override exclusive 220 * lock requests or upgrade requests ( but not the exclusive 221 * lock itself ). 222 */ 223 if (lkp->lk_lockholder != td) { 224 if (td->td_flags & TDF_DEADLKTREAT) { 225 error = acquire( 226 lkp, 227 extflags, 228 LK_HAVE_EXCL 229 ); 230 } else { 231 error = acquire( 232 lkp, 233 extflags, 234 LK_HAVE_EXCL | LK_WANT_EXCL | 235 LK_WANT_UPGRADE 236 ); 237 } 238 if (error) 239 break; 240 sharelock(lkp, 1); 241 COUNT(td, 1); 242 break; 243 } 244 /* 245 * We hold an exclusive lock, so downgrade it to shared. 246 * An alternative would be to fail with EDEADLK. 247 */ 248 sharelock(lkp, 1); 249 COUNT(td, 1); 250 /* fall into downgrade */ 251 252 case LK_DOWNGRADE: 253 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) { 254 spin_unlock_wr(&lkp->lk_spinlock); 255 panic("lockmgr: not holding exclusive lock"); 256 } 257 sharelock(lkp, lkp->lk_exclusivecount); 258 lkp->lk_exclusivecount = 0; 259 lkp->lk_flags &= ~LK_HAVE_EXCL; 260 lkp->lk_lockholder = LK_NOTHREAD; 261 if (lkp->lk_waitcount) 262 dowakeup = 1; 263 break; 264 265 case LK_EXCLUPGRADE: 266 /* 267 * If another process is ahead of us to get an upgrade, 268 * then we want to fail rather than have an intervening 269 * exclusive access. 270 */ 271 if (lkp->lk_flags & LK_WANT_UPGRADE) { 272 dowakeup = shareunlock(lkp, 1); 273 COUNT(td, -1); 274 error = EBUSY; 275 break; 276 } 277 /* fall into normal upgrade */ 278 279 case LK_UPGRADE: 280 /* 281 * Upgrade a shared lock to an exclusive one. If another 282 * shared lock has already requested an upgrade to an 283 * exclusive lock, our shared lock is released and an 284 * exclusive lock is requested (which will be granted 285 * after the upgrade). If we return an error, the file 286 * will always be unlocked. 287 */ 288 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) { 289 spin_unlock_wr(&lkp->lk_spinlock); 290 panic("lockmgr: upgrade exclusive lock"); 291 } 292 dowakeup += shareunlock(lkp, 1); 293 COUNT(td, -1); 294 /* 295 * If we are just polling, check to see if we will block. 296 */ 297 if ((extflags & LK_NOWAIT) && 298 ((lkp->lk_flags & LK_WANT_UPGRADE) || 299 lkp->lk_sharecount > 1)) { 300 error = EBUSY; 301 break; 302 } 303 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 304 /* 305 * We are first shared lock to request an upgrade, so 306 * request upgrade and wait for the shared count to 307 * drop to zero, then take exclusive lock. 308 */ 309 lkp->lk_flags |= LK_WANT_UPGRADE; 310 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 311 lkp->lk_flags &= ~LK_WANT_UPGRADE; 312 313 if (error) 314 break; 315 lkp->lk_flags |= LK_HAVE_EXCL; 316 lkp->lk_lockholder = td; 317 if (lkp->lk_exclusivecount != 0) { 318 spin_unlock_wr(&lkp->lk_spinlock); 319 panic("lockmgr: non-zero exclusive count"); 320 } 321 lkp->lk_exclusivecount = 1; 322 #if defined(DEBUG_LOCKS) 323 lkp->lk_filename = file; 324 lkp->lk_lineno = line; 325 lkp->lk_lockername = name; 326 #endif 327 COUNT(td, 1); 328 break; 329 } 330 /* 331 * Someone else has requested upgrade. Release our shared 332 * lock, awaken upgrade requestor if we are the last shared 333 * lock, then request an exclusive lock. 334 */ 335 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 336 LK_WAIT_NONZERO) { 337 ++dowakeup; 338 } 339 /* fall into exclusive request */ 340 341 case LK_EXCLUSIVE: 342 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) { 343 /* 344 * Recursive lock. 345 */ 346 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) { 347 spin_unlock_wr(&lkp->lk_spinlock); 348 panic("lockmgr: locking against myself"); 349 } 350 if ((extflags & LK_CANRECURSE) != 0) { 351 lkp->lk_exclusivecount++; 352 COUNT(td, 1); 353 break; 354 } 355 } 356 /* 357 * If we are just polling, check to see if we will sleep. 358 */ 359 if ((extflags & LK_NOWAIT) && 360 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 361 error = EBUSY; 362 break; 363 } 364 /* 365 * Try to acquire the want_exclusive flag. 366 */ 367 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 368 if (error) 369 break; 370 lkp->lk_flags |= LK_WANT_EXCL; 371 /* 372 * Wait for shared locks and upgrades to finish. 373 */ 374 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 375 lkp->lk_flags &= ~LK_WANT_EXCL; 376 if (error) 377 break; 378 lkp->lk_flags |= LK_HAVE_EXCL; 379 lkp->lk_lockholder = td; 380 if (lkp->lk_exclusivecount != 0) { 381 spin_unlock_wr(&lkp->lk_spinlock); 382 panic("lockmgr: non-zero exclusive count"); 383 } 384 lkp->lk_exclusivecount = 1; 385 #if defined(DEBUG_LOCKS) 386 lkp->lk_filename = file; 387 lkp->lk_lineno = line; 388 lkp->lk_lockername = name; 389 #endif 390 COUNT(td, 1); 391 break; 392 393 case LK_RELEASE: 394 if (lkp->lk_exclusivecount != 0) { 395 if (lkp->lk_lockholder != td && 396 lkp->lk_lockholder != LK_KERNTHREAD) { 397 spin_unlock_wr(&lkp->lk_spinlock); 398 panic("lockmgr: pid %d, not %s thr %p unlocking", 399 (td->td_proc ? td->td_proc->p_pid : -99), 400 "exclusive lock holder", 401 lkp->lk_lockholder); 402 } 403 if (lkp->lk_lockholder != LK_KERNTHREAD) { 404 COUNT(td, -1); 405 } 406 if (lkp->lk_exclusivecount == 1) { 407 lkp->lk_flags &= ~LK_HAVE_EXCL; 408 lkp->lk_lockholder = LK_NOTHREAD; 409 lkp->lk_exclusivecount = 0; 410 } else { 411 lkp->lk_exclusivecount--; 412 } 413 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 414 dowakeup += shareunlock(lkp, 1); 415 COUNT(td, -1); 416 } 417 if (lkp->lk_flags & LK_WAIT_NONZERO) 418 ++dowakeup; 419 break; 420 421 default: 422 spin_unlock_wr(&lkp->lk_spinlock); 423 panic("lockmgr: unknown locktype request %d", 424 flags & LK_TYPE_MASK); 425 /* NOTREACHED */ 426 } 427 spin_unlock_wr(&lkp->lk_spinlock); 428 if (dowakeup) 429 wakeup(lkp); 430 return (error); 431 } 432 433 void 434 lockmgr_kernproc(struct lock *lp) 435 { 436 struct thread *td = curthread; 437 438 if (lp->lk_lockholder != LK_KERNTHREAD) { 439 KASSERT(lp->lk_lockholder == td, 440 ("lockmgr_kernproc: lock not owned by curthread %p", td)); 441 COUNT(td, -1); 442 lp->lk_lockholder = LK_KERNTHREAD; 443 } 444 } 445 446 /* 447 * Set the lock to be exclusively held. The caller is holding the lock's 448 * spinlock and the spinlock remains held on return. A panic will occur 449 * if the lock cannot be set to exclusive. 450 */ 451 void 452 lockmgr_setexclusive_interlocked(struct lock *lkp) 453 { 454 thread_t td = curthread; 455 456 KKASSERT((lkp->lk_flags & (LK_HAVE_EXCL|LK_SHARE_NONZERO)) == 0); 457 KKASSERT(lkp->lk_exclusivecount == 0); 458 lkp->lk_flags |= LK_HAVE_EXCL; 459 lkp->lk_lockholder = td; 460 lkp->lk_exclusivecount = 1; 461 COUNT(td, 1); 462 } 463 464 /* 465 * Clear the caller's exclusive lock. The caller is holding the lock's 466 * spinlock. THIS FUNCTION WILL UNLOCK THE SPINLOCK. 467 * 468 * A panic will occur if the caller does not hold the lock. 469 */ 470 void 471 lockmgr_clrexclusive_interlocked(struct lock *lkp) 472 { 473 thread_t td = curthread; 474 int dowakeup = 0; 475 476 KKASSERT((lkp->lk_flags & LK_HAVE_EXCL) && lkp->lk_exclusivecount == 1 477 && lkp->lk_lockholder == td); 478 lkp->lk_lockholder = LK_NOTHREAD; 479 lkp->lk_flags &= ~LK_HAVE_EXCL; 480 lkp->lk_exclusivecount = 0; 481 if (lkp->lk_flags & LK_WAIT_NONZERO) 482 dowakeup = 1; 483 COUNT(td, -1); 484 spin_unlock_wr(&lkp->lk_spinlock); 485 if (dowakeup) 486 wakeup((void *)lkp); 487 } 488 489 /* 490 * Initialize a lock; required before use. 491 */ 492 void 493 lockinit(struct lock *lkp, char *wmesg, int timo, int flags) 494 { 495 spin_init(&lkp->lk_spinlock); 496 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 497 lkp->lk_sharecount = 0; 498 lkp->lk_waitcount = 0; 499 lkp->lk_exclusivecount = 0; 500 lkp->lk_wmesg = wmesg; 501 lkp->lk_timo = timo; 502 lkp->lk_lockholder = LK_NOTHREAD; 503 } 504 505 /* 506 * Reinitialize a lock that is being reused for a different purpose, but 507 * which may have pending (blocked) threads sitting on it. The caller 508 * must already hold the interlock. 509 */ 510 void 511 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags) 512 { 513 spin_lock_wr(&lkp->lk_spinlock); 514 lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) | 515 (flags & LK_EXTFLG_MASK); 516 lkp->lk_wmesg = wmesg; 517 lkp->lk_timo = timo; 518 spin_unlock_wr(&lkp->lk_spinlock); 519 } 520 521 /* 522 * Determine the status of a lock. 523 */ 524 int 525 lockstatus(struct lock *lkp, struct thread *td) 526 { 527 int lock_type = 0; 528 529 spin_lock_wr(&lkp->lk_spinlock); 530 if (lkp->lk_exclusivecount != 0) { 531 if (td == NULL || lkp->lk_lockholder == td) 532 lock_type = LK_EXCLUSIVE; 533 else 534 lock_type = LK_EXCLOTHER; 535 } else if (lkp->lk_sharecount != 0) { 536 lock_type = LK_SHARED; 537 } 538 spin_unlock_wr(&lkp->lk_spinlock); 539 return (lock_type); 540 } 541 542 /* 543 * Determine the number of holders of a lock. 544 * 545 * The non-blocking version can usually be used for assertions. 546 */ 547 int 548 lockcount(struct lock *lkp) 549 { 550 int count; 551 552 spin_lock_wr(&lkp->lk_spinlock); 553 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 554 spin_unlock_wr(&lkp->lk_spinlock); 555 return (count); 556 } 557 558 int 559 lockcountnb(struct lock *lkp) 560 { 561 return (lkp->lk_exclusivecount + lkp->lk_sharecount); 562 } 563 564 /* 565 * Print out information about state of a lock. Used by VOP_PRINT 566 * routines to display status about contained locks. 567 */ 568 void 569 lockmgr_printinfo(struct lock *lkp) 570 { 571 struct thread *td = lkp->lk_lockholder; 572 struct proc *p; 573 574 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD) 575 p = td->td_proc; 576 else 577 p = NULL; 578 579 if (lkp->lk_sharecount) 580 kprintf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 581 lkp->lk_sharecount); 582 else if (lkp->lk_flags & LK_HAVE_EXCL) 583 kprintf(" lock type %s: EXCL (count %d) by td %p pid %d", 584 lkp->lk_wmesg, lkp->lk_exclusivecount, td, 585 p ? p->p_pid : -99); 586 if (lkp->lk_waitcount > 0) 587 kprintf(" with %d pending", lkp->lk_waitcount); 588 } 589 590