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 * 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 = ssleep(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 /* 208 * So sue me, I'm too tired. 209 */ 210 if (spin_trylock_wr(&lkp->lk_spinlock) == FALSE) { 211 if (flags & LK_NOSPINWAIT) 212 return(EBUSY); 213 spin_lock_wr(&lkp->lk_spinlock); 214 } 215 216 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK; 217 td = curthread; 218 219 switch (flags & LK_TYPE_MASK) { 220 case LK_SHARED: 221 /* 222 * If we are not the exclusive lock holder, we have to block 223 * while there is an exclusive lock holder or while an 224 * exclusive lock request or upgrade request is in progress. 225 * 226 * However, if P_DEADLKTREAT is set, we override exclusive 227 * lock requests or upgrade requests ( but not the exclusive 228 * lock itself ). 229 */ 230 if (lkp->lk_lockholder != td) { 231 if (td->td_flags & TDF_DEADLKTREAT) { 232 error = acquire( 233 lkp, 234 extflags, 235 LK_HAVE_EXCL 236 ); 237 } else { 238 error = acquire( 239 lkp, 240 extflags, 241 LK_HAVE_EXCL | LK_WANT_EXCL | 242 LK_WANT_UPGRADE 243 ); 244 } 245 if (error) 246 break; 247 sharelock(lkp, 1); 248 COUNT(td, 1); 249 break; 250 } 251 /* 252 * We hold an exclusive lock, so downgrade it to shared. 253 * An alternative would be to fail with EDEADLK. 254 */ 255 sharelock(lkp, 1); 256 COUNT(td, 1); 257 /* fall into downgrade */ 258 259 case LK_DOWNGRADE: 260 if (lkp->lk_lockholder != td || lkp->lk_exclusivecount == 0) { 261 spin_unlock_wr(&lkp->lk_spinlock); 262 panic("lockmgr: not holding exclusive lock"); 263 } 264 sharelock(lkp, lkp->lk_exclusivecount); 265 lkp->lk_exclusivecount = 0; 266 lkp->lk_flags &= ~LK_HAVE_EXCL; 267 lkp->lk_lockholder = LK_NOTHREAD; 268 if (lkp->lk_waitcount) 269 dowakeup = 1; 270 break; 271 272 case LK_EXCLUPGRADE: 273 /* 274 * If another process is ahead of us to get an upgrade, 275 * then we want to fail rather than have an intervening 276 * exclusive access. 277 */ 278 if (lkp->lk_flags & LK_WANT_UPGRADE) { 279 dowakeup = shareunlock(lkp, 1); 280 COUNT(td, -1); 281 error = EBUSY; 282 break; 283 } 284 /* fall into normal upgrade */ 285 286 case LK_UPGRADE: 287 /* 288 * Upgrade a shared lock to an exclusive one. If another 289 * shared lock has already requested an upgrade to an 290 * exclusive lock, our shared lock is released and an 291 * exclusive lock is requested (which will be granted 292 * after the upgrade). If we return an error, the file 293 * will always be unlocked. 294 */ 295 if ((lkp->lk_lockholder == td) || (lkp->lk_sharecount <= 0)) { 296 spin_unlock_wr(&lkp->lk_spinlock); 297 panic("lockmgr: upgrade exclusive lock"); 298 } 299 dowakeup += shareunlock(lkp, 1); 300 COUNT(td, -1); 301 /* 302 * If we are just polling, check to see if we will block. 303 */ 304 if ((extflags & LK_NOWAIT) && 305 ((lkp->lk_flags & LK_WANT_UPGRADE) || 306 lkp->lk_sharecount > 1)) { 307 error = EBUSY; 308 break; 309 } 310 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) { 311 /* 312 * We are first shared lock to request an upgrade, so 313 * request upgrade and wait for the shared count to 314 * drop to zero, then take exclusive lock. 315 */ 316 lkp->lk_flags |= LK_WANT_UPGRADE; 317 error = acquire(lkp, extflags, LK_SHARE_NONZERO); 318 lkp->lk_flags &= ~LK_WANT_UPGRADE; 319 320 if (error) 321 break; 322 lkp->lk_flags |= LK_HAVE_EXCL; 323 lkp->lk_lockholder = td; 324 if (lkp->lk_exclusivecount != 0) { 325 spin_unlock_wr(&lkp->lk_spinlock); 326 panic("lockmgr: non-zero exclusive count"); 327 } 328 lkp->lk_exclusivecount = 1; 329 #if defined(DEBUG_LOCKS) 330 lkp->lk_filename = file; 331 lkp->lk_lineno = line; 332 lkp->lk_lockername = name; 333 #endif 334 COUNT(td, 1); 335 break; 336 } 337 /* 338 * Someone else has requested upgrade. Release our shared 339 * lock, awaken upgrade requestor if we are the last shared 340 * lock, then request an exclusive lock. 341 */ 342 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) == 343 LK_WAIT_NONZERO) { 344 ++dowakeup; 345 } 346 /* fall into exclusive request */ 347 348 case LK_EXCLUSIVE: 349 if (lkp->lk_lockholder == td && td != LK_KERNTHREAD) { 350 /* 351 * Recursive lock. 352 */ 353 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0) { 354 spin_unlock_wr(&lkp->lk_spinlock); 355 panic("lockmgr: locking against myself"); 356 } 357 if ((extflags & LK_CANRECURSE) != 0) { 358 lkp->lk_exclusivecount++; 359 COUNT(td, 1); 360 break; 361 } 362 } 363 /* 364 * If we are just polling, check to see if we will sleep. 365 */ 366 if ((extflags & LK_NOWAIT) && 367 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) { 368 error = EBUSY; 369 break; 370 } 371 /* 372 * Try to acquire the want_exclusive flag. 373 */ 374 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL)); 375 if (error) 376 break; 377 lkp->lk_flags |= LK_WANT_EXCL; 378 /* 379 * Wait for shared locks and upgrades to finish. 380 */ 381 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO); 382 lkp->lk_flags &= ~LK_WANT_EXCL; 383 if (error) 384 break; 385 lkp->lk_flags |= LK_HAVE_EXCL; 386 lkp->lk_lockholder = td; 387 if (lkp->lk_exclusivecount != 0) { 388 spin_unlock_wr(&lkp->lk_spinlock); 389 panic("lockmgr: non-zero exclusive count"); 390 } 391 lkp->lk_exclusivecount = 1; 392 #if defined(DEBUG_LOCKS) 393 lkp->lk_filename = file; 394 lkp->lk_lineno = line; 395 lkp->lk_lockername = name; 396 #endif 397 COUNT(td, 1); 398 break; 399 400 case LK_RELEASE: 401 if (lkp->lk_exclusivecount != 0) { 402 if (lkp->lk_lockholder != td && 403 lkp->lk_lockholder != LK_KERNTHREAD) { 404 spin_unlock_wr(&lkp->lk_spinlock); 405 panic("lockmgr: pid %d, not %s thr %p/%p unlocking", 406 (td->td_proc ? td->td_proc->p_pid : -1), 407 "exclusive lock holder", 408 td, lkp->lk_lockholder); 409 } 410 if (lkp->lk_lockholder != LK_KERNTHREAD) { 411 COUNT(td, -1); 412 } 413 if (lkp->lk_exclusivecount == 1) { 414 lkp->lk_flags &= ~LK_HAVE_EXCL; 415 lkp->lk_lockholder = LK_NOTHREAD; 416 lkp->lk_exclusivecount = 0; 417 } else { 418 lkp->lk_exclusivecount--; 419 } 420 } else if (lkp->lk_flags & LK_SHARE_NONZERO) { 421 dowakeup += shareunlock(lkp, 1); 422 COUNT(td, -1); 423 } 424 if (lkp->lk_flags & LK_WAIT_NONZERO) 425 ++dowakeup; 426 break; 427 428 default: 429 spin_unlock_wr(&lkp->lk_spinlock); 430 panic("lockmgr: unknown locktype request %d", 431 flags & LK_TYPE_MASK); 432 /* NOTREACHED */ 433 } 434 spin_unlock_wr(&lkp->lk_spinlock); 435 if (dowakeup) 436 wakeup(lkp); 437 return (error); 438 } 439 440 void 441 lockmgr_kernproc(struct lock *lp) 442 { 443 struct thread *td __debugvar = curthread; 444 445 if (lp->lk_lockholder != LK_KERNTHREAD) { 446 KASSERT(lp->lk_lockholder == td, 447 ("lockmgr_kernproc: lock not owned by curthread %p", td)); 448 COUNT(td, -1); 449 lp->lk_lockholder = LK_KERNTHREAD; 450 } 451 } 452 453 /* 454 * Set the lock to be exclusively held. The caller is holding the lock's 455 * spinlock and the spinlock remains held on return. A panic will occur 456 * if the lock cannot be set to exclusive. 457 */ 458 void 459 lockmgr_setexclusive_interlocked(struct lock *lkp) 460 { 461 thread_t td = curthread; 462 463 KKASSERT((lkp->lk_flags & (LK_HAVE_EXCL|LK_SHARE_NONZERO)) == 0); 464 KKASSERT(lkp->lk_exclusivecount == 0); 465 lkp->lk_flags |= LK_HAVE_EXCL; 466 lkp->lk_lockholder = td; 467 lkp->lk_exclusivecount = 1; 468 COUNT(td, 1); 469 } 470 471 /* 472 * Clear the caller's exclusive lock. The caller is holding the lock's 473 * spinlock. THIS FUNCTION WILL UNLOCK THE SPINLOCK. 474 * 475 * A panic will occur if the caller does not hold the lock. 476 */ 477 void 478 lockmgr_clrexclusive_interlocked(struct lock *lkp) 479 { 480 thread_t td __debugvar = curthread; 481 int dowakeup = 0; 482 483 KKASSERT((lkp->lk_flags & LK_HAVE_EXCL) && lkp->lk_exclusivecount == 1 484 && lkp->lk_lockholder == td); 485 lkp->lk_lockholder = LK_NOTHREAD; 486 lkp->lk_flags &= ~LK_HAVE_EXCL; 487 lkp->lk_exclusivecount = 0; 488 if (lkp->lk_flags & LK_WAIT_NONZERO) 489 dowakeup = 1; 490 COUNT(td, -1); 491 spin_unlock_wr(&lkp->lk_spinlock); 492 if (dowakeup) 493 wakeup((void *)lkp); 494 } 495 496 /* 497 * Initialize a lock; required before use. 498 */ 499 void 500 lockinit(struct lock *lkp, char *wmesg, int timo, int flags) 501 { 502 spin_init(&lkp->lk_spinlock); 503 lkp->lk_flags = (flags & LK_EXTFLG_MASK); 504 lkp->lk_sharecount = 0; 505 lkp->lk_waitcount = 0; 506 lkp->lk_exclusivecount = 0; 507 lkp->lk_wmesg = wmesg; 508 lkp->lk_timo = timo; 509 lkp->lk_lockholder = LK_NOTHREAD; 510 } 511 512 /* 513 * Reinitialize a lock that is being reused for a different purpose, but 514 * which may have pending (blocked) threads sitting on it. The caller 515 * must already hold the interlock. 516 */ 517 void 518 lockreinit(struct lock *lkp, char *wmesg, int timo, int flags) 519 { 520 spin_lock_wr(&lkp->lk_spinlock); 521 lkp->lk_flags = (lkp->lk_flags & ~LK_EXTFLG_MASK) | 522 (flags & LK_EXTFLG_MASK); 523 lkp->lk_wmesg = wmesg; 524 lkp->lk_timo = timo; 525 spin_unlock_wr(&lkp->lk_spinlock); 526 } 527 528 /* 529 * Requires that the caller is the exclusive owner of this lock. 530 */ 531 void 532 lockuninit(struct lock *l) 533 { 534 /* 535 * At this point we should have removed all the references to this lock 536 * so there can't be anyone waiting on it. 537 */ 538 KKASSERT(l->lk_waitcount == 0); 539 540 spin_uninit(&l->lk_spinlock); 541 } 542 543 /* 544 * Determine the status of a lock. 545 */ 546 int 547 lockstatus(struct lock *lkp, struct thread *td) 548 { 549 int lock_type = 0; 550 551 spin_lock_wr(&lkp->lk_spinlock); 552 if (lkp->lk_exclusivecount != 0) { 553 if (td == NULL || lkp->lk_lockholder == td) 554 lock_type = LK_EXCLUSIVE; 555 else 556 lock_type = LK_EXCLOTHER; 557 } else if (lkp->lk_sharecount != 0) { 558 lock_type = LK_SHARED; 559 } 560 spin_unlock_wr(&lkp->lk_spinlock); 561 return (lock_type); 562 } 563 564 /* 565 * Return non-zero if the caller owns the lock shared or exclusive. 566 * We can only guess re: shared locks. 567 */ 568 int 569 lockowned(struct lock *lkp) 570 { 571 thread_t td = curthread; 572 573 if (lkp->lk_exclusivecount) 574 return(lkp->lk_lockholder == td); 575 return(lkp->lk_sharecount != 0); 576 } 577 578 /* 579 * Determine the number of holders of a lock. 580 * 581 * The non-blocking version can usually be used for assertions. 582 */ 583 int 584 lockcount(struct lock *lkp) 585 { 586 int count; 587 588 spin_lock_wr(&lkp->lk_spinlock); 589 count = lkp->lk_exclusivecount + lkp->lk_sharecount; 590 spin_unlock_wr(&lkp->lk_spinlock); 591 return (count); 592 } 593 594 int 595 lockcountnb(struct lock *lkp) 596 { 597 return (lkp->lk_exclusivecount + lkp->lk_sharecount); 598 } 599 600 /* 601 * Print out information about state of a lock. Used by VOP_PRINT 602 * routines to display status about contained locks. 603 */ 604 void 605 lockmgr_printinfo(struct lock *lkp) 606 { 607 struct thread *td = lkp->lk_lockholder; 608 struct proc *p; 609 610 if (td && td != LK_KERNTHREAD && td != LK_NOTHREAD) 611 p = td->td_proc; 612 else 613 p = NULL; 614 615 if (lkp->lk_sharecount) 616 kprintf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg, 617 lkp->lk_sharecount); 618 else if (lkp->lk_flags & LK_HAVE_EXCL) 619 kprintf(" lock type %s: EXCL (count %d) by td %p pid %d", 620 lkp->lk_wmesg, lkp->lk_exclusivecount, td, 621 p ? p->p_pid : -99); 622 if (lkp->lk_waitcount > 0) 623 kprintf(" with %d pending", lkp->lk_waitcount); 624 } 625 626