FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_lock.c
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 */
42
43 #include <sys/cdefs.h>
44 __FBSDID("$FreeBSD: releng/6.1/sys/kern/kern_lock.c 158179 2006-04-30 16:44:43Z cvs2svn $");
45
46 #include <sys/param.h>
47 #include <sys/kdb.h>
48 #include <sys/kernel.h>
49 #include <sys/ktr.h>
50 #include <sys/lock.h>
51 #include <sys/lockmgr.h>
52 #include <sys/mutex.h>
53 #include <sys/proc.h>
54 #include <sys/systm.h>
55 #ifdef DEBUG_LOCKS
56 #include <sys/stack.h>
57 #endif
58
59 /*
60 * Locking primitives implementation.
61 * Locks provide shared/exclusive sychronization.
62 */
63
64 #define COUNT(td, x) if ((td)) (td)->td_locks += (x)
65 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
66 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
67
68 static int acquire(struct lock **lkpp, int extflags, int wanted);
69 static int acquiredrain(struct lock *lkp, int extflags) ;
70
71 static __inline void
72 sharelock(struct thread *td, struct lock *lkp, int incr) {
73 lkp->lk_flags |= LK_SHARE_NONZERO;
74 lkp->lk_sharecount += incr;
75 COUNT(td, incr);
76 }
77
78 static __inline void
79 shareunlock(struct thread *td, struct lock *lkp, int decr) {
80
81 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
82
83 COUNT(td, -decr);
84 if (lkp->lk_sharecount == decr) {
85 lkp->lk_flags &= ~LK_SHARE_NONZERO;
86 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
87 wakeup(lkp);
88 }
89 lkp->lk_sharecount = 0;
90 } else {
91 lkp->lk_sharecount -= decr;
92 }
93 }
94
95 static int
96 acquire(struct lock **lkpp, int extflags, int wanted)
97 {
98 struct lock *lkp = *lkpp;
99 int error;
100 CTR3(KTR_LOCK,
101 "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x",
102 lkp, extflags, wanted);
103
104 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted))
105 return EBUSY;
106 error = 0;
107 while ((lkp->lk_flags & wanted) != 0) {
108 CTR2(KTR_LOCK,
109 "acquire(): lkp == %p, lk_flags == 0x%x sleeping",
110 lkp, lkp->lk_flags);
111 lkp->lk_flags |= LK_WAIT_NONZERO;
112 lkp->lk_waitcount++;
113 error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio,
114 lkp->lk_wmesg,
115 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
116 lkp->lk_waitcount--;
117 if (lkp->lk_waitcount == 0)
118 lkp->lk_flags &= ~LK_WAIT_NONZERO;
119 if (error)
120 break;
121 if (extflags & LK_SLEEPFAIL) {
122 error = ENOLCK;
123 break;
124 }
125 if (lkp->lk_newlock != NULL) {
126 mtx_lock(lkp->lk_newlock->lk_interlock);
127 mtx_unlock(lkp->lk_interlock);
128 if (lkp->lk_waitcount == 0)
129 wakeup((void *)(&lkp->lk_newlock));
130 *lkpp = lkp = lkp->lk_newlock;
131 }
132 }
133 mtx_assert(lkp->lk_interlock, MA_OWNED);
134 return (error);
135 }
136
137 /*
138 * Set, change, or release a lock.
139 *
140 * Shared requests increment the shared count. Exclusive requests set the
141 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
142 * accepted shared locks and shared-to-exclusive upgrades to go away.
143 */
144 int
145 lockmgr(lkp, flags, interlkp, td)
146 struct lock *lkp;
147 u_int flags;
148 struct mtx *interlkp;
149 struct thread *td;
150 {
151 int error;
152 struct thread *thr;
153 int extflags, lockflags;
154
155 error = 0;
156 if (td == NULL)
157 thr = LK_KERNPROC;
158 else
159 thr = td;
160
161 if ((flags & LK_INTERNAL) == 0)
162 mtx_lock(lkp->lk_interlock);
163 CTR6(KTR_LOCK,
164 "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), owner == %p, exclusivecount == %d, flags == 0x%x, "
165 "td == %p", lkp, lkp->lk_wmesg, lkp->lk_lockholder,
166 lkp->lk_exclusivecount, flags, td);
167 #ifdef DEBUG_LOCKS
168 {
169 struct stack stack; /* XXX */
170 stack_save(&stack);
171 CTRSTACK(KTR_LOCK, &stack, 0, 1);
172 }
173 #endif
174
175 if (flags & LK_INTERLOCK) {
176 mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED);
177 mtx_unlock(interlkp);
178 }
179
180 if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0)
181 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
182 &lkp->lk_interlock->mtx_object,
183 "Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg);
184
185 if (panicstr != NULL) {
186 mtx_unlock(lkp->lk_interlock);
187 return (0);
188 }
189 if ((lkp->lk_flags & LK_NOSHARE) &&
190 (flags & LK_TYPE_MASK) == LK_SHARED) {
191 flags &= ~LK_TYPE_MASK;
192 flags |= LK_EXCLUSIVE;
193 }
194 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
195
196 switch (flags & LK_TYPE_MASK) {
197
198 case LK_SHARED:
199 /*
200 * If we are not the exclusive lock holder, we have to block
201 * while there is an exclusive lock holder or while an
202 * exclusive lock request or upgrade request is in progress.
203 *
204 * However, if TDP_DEADLKTREAT is set, we override exclusive
205 * lock requests or upgrade requests ( but not the exclusive
206 * lock itself ).
207 */
208 if (lkp->lk_lockholder != thr) {
209 lockflags = LK_HAVE_EXCL;
210 if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT))
211 lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE;
212 error = acquire(&lkp, extflags, lockflags);
213 if (error)
214 break;
215 sharelock(td, lkp, 1);
216 #if defined(DEBUG_LOCKS)
217 stack_save(&lkp->lk_stack);
218 #endif
219 break;
220 }
221 /*
222 * We hold an exclusive lock, so downgrade it to shared.
223 * An alternative would be to fail with EDEADLK.
224 */
225 sharelock(td, lkp, 1);
226 /* FALLTHROUGH downgrade */
227
228 case LK_DOWNGRADE:
229 KASSERT(lkp->lk_lockholder == thr && lkp->lk_exclusivecount != 0,
230 ("lockmgr: not holding exclusive lock "
231 "(owner thread (%p) != thread (%p), exlcnt (%d) != 0",
232 lkp->lk_lockholder, thr, lkp->lk_exclusivecount));
233 sharelock(td, lkp, lkp->lk_exclusivecount);
234 COUNT(td, -lkp->lk_exclusivecount);
235 lkp->lk_exclusivecount = 0;
236 lkp->lk_flags &= ~LK_HAVE_EXCL;
237 lkp->lk_lockholder = LK_NOPROC;
238 if (lkp->lk_waitcount)
239 wakeup((void *)lkp);
240 break;
241
242 case LK_EXCLUPGRADE:
243 /*
244 * If another process is ahead of us to get an upgrade,
245 * then we want to fail rather than have an intervening
246 * exclusive access.
247 */
248 if (lkp->lk_flags & LK_WANT_UPGRADE) {
249 shareunlock(td, lkp, 1);
250 error = EBUSY;
251 break;
252 }
253 /* FALLTHROUGH normal upgrade */
254
255 case LK_UPGRADE:
256 /*
257 * Upgrade a shared lock to an exclusive one. If another
258 * shared lock has already requested an upgrade to an
259 * exclusive lock, our shared lock is released and an
260 * exclusive lock is requested (which will be granted
261 * after the upgrade). If we return an error, the file
262 * will always be unlocked.
263 */
264 if (lkp->lk_lockholder == thr)
265 panic("lockmgr: upgrade exclusive lock");
266 if (lkp->lk_sharecount <= 0)
267 panic("lockmgr: upgrade without shared");
268 shareunlock(td, lkp, 1);
269 /*
270 * If we are just polling, check to see if we will block.
271 */
272 if ((extflags & LK_NOWAIT) &&
273 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
274 lkp->lk_sharecount > 1)) {
275 error = EBUSY;
276 break;
277 }
278 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
279 /*
280 * We are first shared lock to request an upgrade, so
281 * request upgrade and wait for the shared count to
282 * drop to zero, then take exclusive lock.
283 */
284 lkp->lk_flags |= LK_WANT_UPGRADE;
285 error = acquire(&lkp, extflags, LK_SHARE_NONZERO);
286 lkp->lk_flags &= ~LK_WANT_UPGRADE;
287
288 if (error) {
289 if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO))
290 wakeup((void *)lkp);
291 break;
292 }
293 if (lkp->lk_exclusivecount != 0)
294 panic("lockmgr: non-zero exclusive count");
295 lkp->lk_flags |= LK_HAVE_EXCL;
296 lkp->lk_lockholder = thr;
297 lkp->lk_exclusivecount = 1;
298 COUNT(td, 1);
299 #if defined(DEBUG_LOCKS)
300 stack_save(&lkp->lk_stack);
301 #endif
302 break;
303 }
304 /*
305 * Someone else has requested upgrade. Release our shared
306 * lock, awaken upgrade requestor if we are the last shared
307 * lock, then request an exclusive lock.
308 */
309 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
310 LK_WAIT_NONZERO)
311 wakeup((void *)lkp);
312 /* FALLTHROUGH exclusive request */
313
314 case LK_EXCLUSIVE:
315 if (lkp->lk_lockholder == thr && thr != LK_KERNPROC) {
316 /*
317 * Recursive lock.
318 */
319 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
320 panic("lockmgr: locking against myself");
321 if ((extflags & LK_CANRECURSE) != 0) {
322 lkp->lk_exclusivecount++;
323 COUNT(td, 1);
324 break;
325 }
326 }
327 /*
328 * If we are just polling, check to see if we will sleep.
329 */
330 if ((extflags & LK_NOWAIT) &&
331 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
332 error = EBUSY;
333 break;
334 }
335 /*
336 * Try to acquire the want_exclusive flag.
337 */
338 error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
339 if (error)
340 break;
341 lkp->lk_flags |= LK_WANT_EXCL;
342 /*
343 * Wait for shared locks and upgrades to finish.
344 */
345 error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO);
346 lkp->lk_flags &= ~LK_WANT_EXCL;
347 if (error) {
348 if (lkp->lk_flags & LK_WAIT_NONZERO)
349 wakeup((void *)lkp);
350 break;
351 }
352 lkp->lk_flags |= LK_HAVE_EXCL;
353 lkp->lk_lockholder = thr;
354 if (lkp->lk_exclusivecount != 0)
355 panic("lockmgr: non-zero exclusive count");
356 lkp->lk_exclusivecount = 1;
357 COUNT(td, 1);
358 #if defined(DEBUG_LOCKS)
359 stack_save(&lkp->lk_stack);
360 #endif
361 break;
362
363 case LK_RELEASE:
364 if (lkp->lk_exclusivecount != 0) {
365 if (lkp->lk_lockholder != thr &&
366 lkp->lk_lockholder != LK_KERNPROC) {
367 panic("lockmgr: thread %p, not %s %p unlocking",
368 thr, "exclusive lock holder",
369 lkp->lk_lockholder);
370 }
371 if (lkp->lk_lockholder != LK_KERNPROC)
372 COUNT(td, -1);
373 if (lkp->lk_exclusivecount == 1) {
374 lkp->lk_flags &= ~LK_HAVE_EXCL;
375 lkp->lk_lockholder = LK_NOPROC;
376 lkp->lk_exclusivecount = 0;
377 } else {
378 lkp->lk_exclusivecount--;
379 }
380 } else if (lkp->lk_flags & LK_SHARE_NONZERO)
381 shareunlock(td, lkp, 1);
382 if (lkp->lk_flags & LK_WAIT_NONZERO)
383 wakeup((void *)lkp);
384 break;
385
386 case LK_DRAIN:
387 /*
388 * Check that we do not already hold the lock, as it can
389 * never drain if we do. Unfortunately, we have no way to
390 * check for holding a shared lock, but at least we can
391 * check for an exclusive one.
392 */
393 if (lkp->lk_lockholder == thr)
394 panic("lockmgr: draining against myself");
395
396 error = acquiredrain(lkp, extflags);
397 if (error)
398 break;
399 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
400 lkp->lk_lockholder = thr;
401 lkp->lk_exclusivecount = 1;
402 COUNT(td, 1);
403 #if defined(DEBUG_LOCKS)
404 stack_save(&lkp->lk_stack);
405 #endif
406 break;
407
408 default:
409 mtx_unlock(lkp->lk_interlock);
410 panic("lockmgr: unknown locktype request %d",
411 flags & LK_TYPE_MASK);
412 /* NOTREACHED */
413 }
414 if ((lkp->lk_flags & LK_WAITDRAIN) &&
415 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
416 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
417 lkp->lk_flags &= ~LK_WAITDRAIN;
418 wakeup((void *)&lkp->lk_flags);
419 }
420 mtx_unlock(lkp->lk_interlock);
421 return (error);
422 }
423
424 static int
425 acquiredrain(struct lock *lkp, int extflags) {
426 int error;
427
428 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
429 return EBUSY;
430 }
431 while (lkp->lk_flags & LK_ALL) {
432 lkp->lk_flags |= LK_WAITDRAIN;
433 error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio,
434 lkp->lk_wmesg,
435 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
436 if (error)
437 return error;
438 if (extflags & LK_SLEEPFAIL) {
439 return ENOLCK;
440 }
441 }
442 return 0;
443 }
444
445 /*
446 * Transfer any waiting processes from one lock to another.
447 */
448 void
449 transferlockers(from, to)
450 struct lock *from;
451 struct lock *to;
452 {
453
454 KASSERT(from != to, ("lock transfer to self"));
455 KASSERT((from->lk_flags&LK_WAITDRAIN) == 0, ("transfer draining lock"));
456
457 mtx_lock(from->lk_interlock);
458 if (from->lk_waitcount == 0) {
459 mtx_unlock(from->lk_interlock);
460 return;
461 }
462 from->lk_newlock = to;
463 wakeup((void *)from);
464 msleep(&from->lk_newlock, from->lk_interlock, from->lk_prio,
465 "lkxfer", 0);
466 from->lk_newlock = NULL;
467 from->lk_flags &= ~(LK_WANT_EXCL | LK_WANT_UPGRADE);
468 KASSERT(from->lk_waitcount == 0, ("active lock"));
469 mtx_unlock(from->lk_interlock);
470 }
471
472
473 /*
474 * Initialize a lock; required before use.
475 */
476 void
477 lockinit(lkp, prio, wmesg, timo, flags)
478 struct lock *lkp;
479 int prio;
480 const char *wmesg;
481 int timo;
482 int flags;
483 {
484 CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", "
485 "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags);
486
487 lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder);
488 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
489 lkp->lk_sharecount = 0;
490 lkp->lk_waitcount = 0;
491 lkp->lk_exclusivecount = 0;
492 lkp->lk_prio = prio;
493 lkp->lk_wmesg = wmesg;
494 lkp->lk_timo = timo;
495 lkp->lk_lockholder = LK_NOPROC;
496 lkp->lk_newlock = NULL;
497 #ifdef DEBUG_LOCKS
498 stack_zero(&lkp->lk_stack);
499 #endif
500 }
501
502 /*
503 * Destroy a lock.
504 */
505 void
506 lockdestroy(lkp)
507 struct lock *lkp;
508 {
509 CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
510 lkp, lkp->lk_wmesg);
511 }
512
513 /*
514 * Determine the status of a lock.
515 */
516 int
517 lockstatus(lkp, td)
518 struct lock *lkp;
519 struct thread *td;
520 {
521 int lock_type = 0;
522 int interlocked;
523
524 if (!kdb_active) {
525 interlocked = 1;
526 mtx_lock(lkp->lk_interlock);
527 } else
528 interlocked = 0;
529 if (lkp->lk_exclusivecount != 0) {
530 if (td == NULL || lkp->lk_lockholder == td)
531 lock_type = LK_EXCLUSIVE;
532 else
533 lock_type = LK_EXCLOTHER;
534 } else if (lkp->lk_sharecount != 0)
535 lock_type = LK_SHARED;
536 if (interlocked)
537 mtx_unlock(lkp->lk_interlock);
538 return (lock_type);
539 }
540
541 /*
542 * Determine the number of holders of a lock.
543 */
544 int
545 lockcount(lkp)
546 struct lock *lkp;
547 {
548 int count;
549
550 mtx_lock(lkp->lk_interlock);
551 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
552 mtx_unlock(lkp->lk_interlock);
553 return (count);
554 }
555
556 /*
557 * Print out information about state of a lock. Used by VOP_PRINT
558 * routines to display status about contained locks.
559 */
560 void
561 lockmgr_printinfo(lkp)
562 struct lock *lkp;
563 {
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 thread %p (pid %d)",
570 lkp->lk_wmesg, lkp->lk_exclusivecount,
571 lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid);
572 if (lkp->lk_waitcount > 0)
573 printf(" with %d pending", lkp->lk_waitcount);
574 #ifdef DEBUG_LOCKS
575 stack_print(&lkp->lk_stack);
576 #endif
577 }
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