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 1.27 2008/01/09 10:59:12 corecode 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 * Locking primitives implementation. 59 * Locks provide shared/exclusive sychronization. 60 */ 61 62 #ifdef SIMPLELOCK_DEBUG 63 #define COUNT(td, x) (td)->td_locks += (x) 64 #else 65 #define COUNT(td, x) 66 #endif 67 68 #define LOCK_WAIT_TIME 100 69 #define LOCK_SAMPLE_WAIT 7 70 71 #if defined(DIAGNOSTIC) 72 #define LOCK_INLINE 73 #else 74 #define LOCK_INLINE __inline 75 #endif 76 77 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \ 78 LK_SHARE_NONZERO | LK_WAIT_NONZERO) 79 80 static int acquire(struct lock *lkp, int extflags, int wanted); 81 82 static LOCK_INLINE void 83 sharelock(struct lock *lkp, int incr) { 84 lkp->lk_flags |= LK_SHARE_NONZERO; 85 lkp->lk_sharecount += incr; 86 } 87 88 static LOCK_INLINE int 89 shareunlock(struct lock *lkp, int decr) 90 { 91 int dowakeup = 0; 92 93 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr")); 94 95 if (lkp->lk_sharecount == decr) { 96 lkp->lk_flags &= ~LK_SHARE_NONZERO; 97 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) { 98 dowakeup = 1; 99 } 100 lkp->lk_sharecount = 0; 101 } else { 102 lkp->lk_sharecount -= decr; 103 } 104 return(dowakeup); 105 } 106 107 /* 108 * lock acquisition helper routine. Called with the lock's spinlock held. 109 */ 110 static int 111 acquire(struct lock *lkp, int extflags, int wanted) 112 { 113 int error; 114 115 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) { 116 return EBUSY; 117 } 118 119 while ((lkp->lk_flags & wanted) != 0) { 120 lkp->lk_flags |= LK_WAIT_NONZERO; 121 lkp->lk_waitcount++; 122 123 /* 124 * Atomic spinlock release/sleep/reacquire. 125 */ 126 error = ssleep(lkp, &lkp->lk_spinlock, 127 ((extflags & LK_PCATCH) ? PCATCH : 0), 128 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 return error; 138 if (extflags & LK_SLEEPFAIL) 139 return ENOLCK; 140 } 141 return 0; 142 } 143 144 /* 145 * Set, change, or release a lock. 146 * 147 * Shared requests increment the shared count. Exclusive requests set the 148 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already 149 * accepted shared locks and shared-to-exclusive upgrades to go away. 150 * 151 * A spinlock is held for most of the procedure. We must not do anything 152 * fancy while holding the spinlock. 153 */ 154 int 155 #ifndef DEBUG_LOCKS 156 lockmgr(struct lock *lkp, u_int flags) 157 #else 158 debuglockmgr(struct lock *lkp, u_int flags, 159 const char *name, const char *file, int line) 160 #endif 161 { 162 thread_t td; 163 int error; 164 int extflags; 165 int dowakeup; 166 167 error = 0; 168 dowakeup = 0; 169 170 if (mycpu->gd_intr_nesting_level && 171 (flags & LK_NOWAIT) == 0 && 172 (flags & LK_TYPE_MASK) != LK_RELEASE && 173 panic_cpu_gd != mycpu 174 ) { 175 176 #ifndef DEBUG_LOCKS 177 panic("lockmgr %s from %p: called from interrupt, ipi, " 178 "or hard code section", 179 lkp->lk_wmesg, ((int **)&lkp)[-1]); 180 #else 181 panic("lockmgr %s from %s:%d: called from interrupt, ipi, " 182 "or hard code section", 183 lkp->lk_wmesg, file, line); 184 #endif 185 } 186 187 /* 188 * So sue me, I'm too tired. 189 */ 190 if (spin_trylock(&lkp->lk_spinlock) == FALSE) { 191 if (flags & LK_NOSPINWAIT) 192 return(EBUSY); 193 spin_lock(&lkp->lk_spinlock); 194 } 195 196 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 197 td = curthread; 198 199 switch (flags & LK_TYPE_MASK) { 200 case LK_SHARED: 201 /* 202 * If we are not the exclusive lock holder, we have to block 203 * while there is an exclusive lock holder or while an 204 * exclusive lock request or upgrade request is in progress. 205 * 206 * However, if P_DEADLKTREAT is set, we override exclusive 207 * lock requests or upgrade requests ( but not the exclusive 208 * lock itself ). 209 */ 210 if (lkp->lk_lockholder != td) { 211 if (td->td_flags & TDF_DEADLKTREAT) { 212 error = acquire( 213 lkp, 214 extflags, 215 LK_HAVE_EXCL 216 ); 217 } else { 218 error = acquire( 219 lkp, 220 extflags, 221 LK_HAVE_EXCL | LK_WANT_EXCL | 222 LK_WANT_UPGRADE 223 ); 224 } 225 if (error) 226 break; 227 sharelock(lkp, 1); 228 COUNT(td, 1); 229 break; 230 } 231 /* 232 * We hold an exclusive lock, so downgrade it to shared. 233 * An alternative would be to fail with EDEADLK. 234 */ 235 sharelock(lkp, 1); 236 COUNT(td, 1); 237 /* fall into downgrade */ 238 239 case LK_DOWNGRADE: 240 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) { 241 spin_unlock(&lkp->lk_spinlock); 242 panic("lockmgr: not holding exclusive lock"); 243 } 244 sharelock(lkp, lkp->lk_exclusivecount); 245 lkp->lk_exclusivecount = 0; 246 lkp->lk_flags &= ~LK_HAVE_EXCL; 247 lkp->lk_lockholder = LK_NOTHREAD; 248 if (lkp->lk_waitcount) 249 dowakeup = 1; 250 break; 251 252 case LK_EXCLUPGRADE: 253 /* 254 * If another process is ahead of us to get an upgrade, 255 * then we want to fail rather than have an intervening 256 * exclusive access. 257 */ 258 if (lkp->lk_flags & LK_WANT_UPGRADE) { 259 dowakeup = shareunlock(lkp, 1); 260 COUNT(td, -1); 261 error = EBUSY; 262 break; 263 } 264 /* fall into normal upgrade */ 265 266 case LK_UPGRADE: 267 /* 268 * Upgrade a shared lock to an exclusive one. If another 269 * shared lock has already requested an upgrade to an 270 * exclusive lock, our shared lock is released and an 271 * exclusive lock is requested (which will be granted 272 * after the upgrade). If we return an error, the file 273 * will always be unlocked. 274 */ 275 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) { 276 spin_unlock(&lkp->lk_spinlock); 277 panic("lockmgr: upgrade exclusive lock"); 278 } 279 dowakeup += shareunlock(lkp, 1); 280 COUNT(td, -1); 281 /* 282 * If we are just polling, check to see if we will block. 283 */ 284 if ((extflags & LK_NOWAIT) && 285 ((lkp->lk_flags & LK_WANT_UPGRADE) || 286 lkp->lk_sharecount > 1)) { 287 error = EBUSY; 288 break; 289 } 290 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 291 /* 292 * We are first shared lock to request an upgrade, so 293 * request upgrade and wait for the shared count to 294 * drop to zero, then take exclusive lock. 295 */ 296 lkp->lk_flags |= LK_WANT_UPGRADE; 297 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 298 lkp->lk_flags &= ~LK_WANT_UPGRADE; 299 300 if (error) 301 break; 302 lkp->lk_flags |= LK_HAVE_EXCL; 303 lkp->lk_lockholder = td; 304 if (lkp->lk_exclusivecount != 0) { 305 spin_unlock(&lkp->lk_spinlock); 306 panic("lockmgr: non-zero exclusive count"); 307 } 308 lkp->lk_exclusivecount = 1; 309 #if defined(DEBUG_LOCKS) 310 lkp->lk_filename = file; 311 lkp->lk_lineno = line; 312 lkp->lk_lockername = name; 313 #endif 314 COUNT(td, 1); 315 break; 316 } 317 /* 318 * Someone else has requested upgrade. Release our shared 319 * lock, awaken upgrade requestor if we are the last shared 320 * lock, then request an exclusive lock. 321 */ 322 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 323 LK_WAIT_NONZERO) { 324 ++dowakeup; 325 } 326 /* fall into exclusive request */ 327 328 case LK_EXCLUSIVE: 329 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) { 330 /* 331 * Recursive lock. 332 */ 333 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) { 334 spin_unlock(&lkp->lk_spinlock); 335 panic("lockmgr: locking against myself"); 336 } 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 spin_unlock(&lkp->lk_spinlock); 369 panic("lockmgr: non-zero exclusive count"); 370 } 371 lkp->lk_exclusivecount = 1; 372 #if defined(DEBUG_LOCKS) 373 lkp->lk_filename = file; 374 lkp->lk_lineno = line; 375 lkp->lk_lockername = name; 376 #endif 377 COUNT(td, 1); 378 break; 379 380 case LK_RELEASE: 381 if (lkp->lk_exclusivecount != 0) { 382 if (lkp->lk_lockholder != td && 383 lkp->lk_lockholder != LK_KERNTHREAD) { 384 spin_unlock(&lkp->lk_spinlock); 385 panic("lockmgr: pid %d, not %s thr %p/%p unlocking", 386 (td->td_proc ? td->td_proc->p_pid : -1), 387 "exclusive lock holder", 388 td, lkp->lk_lockholder); 389 } 390 if (lkp->lk_lockholder != LK_KERNTHREAD) { 391 COUNT(td, -1); 392 } 393 if (lkp->lk_exclusivecount == 1) { 394 lkp->lk_flags &= ~LK_HAVE_EXCL; 395 lkp->lk_lockholder = LK_NOTHREAD; 396 lkp->lk_exclusivecount = 0; 397 } else { 398 lkp->lk_exclusivecount--; 399 } 400 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 401 dowakeup += shareunlock(lkp, 1); 402 COUNT(td, -1); 403 } 404 if (lkp->lk_flags & LK_WAIT_NONZERO) 405 ++dowakeup; 406 break; 407 408 default: 409 spin_unlock(&lkp->lk_spinlock); 410 panic("lockmgr: unknown locktype request %d", 411 flags & LK_TYPE_MASK); 412 /* NOTREACHED */ 413 } 414 spin_unlock(&lkp->lk_spinlock); 415 if (dowakeup) 416 wakeup(lkp); 417 return (error); 418 } 419 420 void 421 lockmgr_kernproc(struct lock *lp) 422 { 423 struct thread *td __debugvar = curthread; 424 425 if (lp->lk_lockholder != LK_KERNTHREAD) { 426 KASSERT(lp->lk_lockholder == td, 427 ("lockmgr_kernproc: lock not owned by curthread %p", td)); 428 COUNT(td, -1); 429 lp->lk_lockholder = LK_KERNTHREAD; 430 } 431 } 432 433 /* 434 * Set the lock to be exclusively held. The caller is holding the lock's 435 * spinlock and the spinlock remains held on return. A panic will occur 436 * if the lock cannot be set to exclusive. 437 */ 438 void 439 lockmgr_setexclusive_interlocked(struct lock *lkp) 440 { 441 thread_t td = curthread; 442 443 KKASSERT((lkp->lk_flags & (LK_HAVE_EXCL|LK_SHARE_NONZERO)) == 0); 444 KKASSERT(lkp->lk_exclusivecount == 0); 445 lkp->lk_flags |= LK_HAVE_EXCL; 446 lkp->lk_lockholder = td; 447 lkp->lk_exclusivecount = 1; 448 COUNT(td, 1); 449 } 450 451 /* 452 * Clear the caller's exclusive lock. The caller is holding the lock's 453 * spinlock. THIS FUNCTION WILL UNLOCK THE SPINLOCK. 454 * 455 * A panic will occur if the caller does not hold the lock. 456 */ 457 void 458 lockmgr_clrexclusive_interlocked(struct lock *lkp) 459 { 460 thread_t td __debugvar = curthread; 461 int dowakeup = 0; 462 463 KKASSERT((lkp->lk_flags & LK_HAVE_EXCL) && lkp->lk_exclusivecount == 1 464 && lkp->lk_lockholder == td); 465 lkp->lk_lockholder = LK_NOTHREAD; 466 lkp->lk_flags &= ~LK_HAVE_EXCL; 467 lkp->lk_exclusivecount = 0; 468 if (lkp->lk_flags & LK_WAIT_NONZERO) 469 dowakeup = 1; 470 COUNT(td, -1); 471 spin_unlock(&lkp->lk_spinlock); 472 if (dowakeup) 473 wakeup((void *)lkp); 474 } 475 476 /* 477 * Initialize a lock; required before use. 478 */ 479 void 480 lockinit(struct lock *lkp, char *wmesg, int timo, int flags) 481 { 482 spin_init(&lkp->lk_spinlock); 483 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 484 lkp->lk_sharecount = 0; 485 lkp->lk_waitcount = 0; 486 lkp->lk_exclusivecount = 0; 487 lkp->lk_wmesg = wmesg; 488 lkp->lk_timo = timo; 489 lkp->lk_lockholder = LK_NOTHREAD; 490 } 491 492 /* 493 * Reinitialize a lock that is being reused for a different purpose, but 494 * which may have pending (blocked) threads sitting on it. The caller 495 * must already hold the interlock. 496 */ 497 void 498 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags) 499 { 500 spin_lock(&lkp->lk_spinlock); 501 lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) | 502 (flags & LK_EXTFLG_MASK); 503 lkp->lk_wmesg = wmesg; 504 lkp->lk_timo = timo; 505 spin_unlock(&lkp->lk_spinlock); 506 } 507 508 /* 509 * Requires that the caller is the exclusive owner of this lock. 510 */ 511 void 512 lockuninit(struct lock *l) 513 { 514 /* 515 * At this point we should have removed all the references to this lock 516 * so there can't be anyone waiting on it. 517 */ 518 KKASSERT(l->lk_waitcount == 0); 519 520 spin_uninit(&l->lk_spinlock); 521 } 522 523 /* 524 * Determine the status of a lock. 525 */ 526 int 527 lockstatus(struct lock *lkp, struct thread *td) 528 { 529 int lock_type = 0; 530 531 spin_lock(&lkp->lk_spinlock); 532 if (lkp->lk_exclusivecount != 0) { 533 if (td == NULL || lkp->lk_lockholder == td) 534 lock_type = LK_EXCLUSIVE; 535 else 536 lock_type = LK_EXCLOTHER; 537 } else if (lkp->lk_sharecount != 0) { 538 lock_type = LK_SHARED; 539 } 540 spin_unlock(&lkp->lk_spinlock); 541 return (lock_type); 542 } 543 544 /* 545 * Return non-zero if the caller owns the lock shared or exclusive. 546 * We can only guess re: shared locks. 547 */ 548 int 549 lockowned(struct lock *lkp) 550 { 551 thread_t td = curthread; 552 553 if (lkp->lk_exclusivecount) 554 return(lkp->lk_lockholder == td); 555 return(lkp->lk_sharecount != 0); 556 } 557 558 /* 559 * Determine the number of holders of a lock. 560 * 561 * The non-blocking version can usually be used for assertions. 562 */ 563 int 564 lockcount(struct lock *lkp) 565 { 566 int count; 567 568 spin_lock(&lkp->lk_spinlock); 569 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 570 spin_unlock(&lkp->lk_spinlock); 571 return (count); 572 } 573 574 int 575 lockcountnb(struct lock *lkp) 576 { 577 return (lkp->lk_exclusivecount + lkp->lk_sharecount); 578 } 579 580 /* 581 * Print out information about state of a lock. Used by VOP_PRINT 582 * routines to display status about contained locks. 583 */ 584 void 585 lockmgr_printinfo(struct lock *lkp) 586 { 587 struct thread *td = lkp->lk_lockholder; 588 struct proc *p; 589 590 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD) 591 p = td->td_proc; 592 else 593 p = NULL; 594 595 if (lkp->lk_sharecount) 596 kprintf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 597 lkp->lk_sharecount); 598 else if (lkp->lk_flags & LK_HAVE_EXCL) 599 kprintf(" lock type %s: EXCL (count %d) by td %p pid %d", 600 lkp->lk_wmesg, lkp->lk_exclusivecount, td, 601 p ? p->p_pid : -99); 602 if (lkp->lk_waitcount > 0) 603 kprintf(" with %d pending", lkp->lk_waitcount); 604 } 605 606