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/5.3/sys/kern/kern_lock.c 136588 2004-10-16 08:43:07Z cvs2svn $");
45
46 #include <sys/param.h>
47 #include <sys/kernel.h>
48 #include <sys/ktr.h>
49 #include <sys/lock.h>
50 #include <sys/lockmgr.h>
51 #include <sys/mutex.h>
52 #include <sys/proc.h>
53 #include <sys/systm.h>
54
55 /*
56 * Locking primitives implementation.
57 * Locks provide shared/exclusive sychronization.
58 */
59
60 #define LOCK_WAIT_TIME 100
61 #define LOCK_SAMPLE_WAIT 7
62
63 #if defined(DIAGNOSTIC)
64 #define LOCK_INLINE
65 #else
66 #define LOCK_INLINE __inline
67 #endif
68
69 #define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
70 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
71
72 /*
73 * Mutex array variables. Rather than each lockmgr lock having its own mutex,
74 * share a fixed (at boot time) number of mutexes across all lockmgr locks in
75 * order to keep sizeof(struct lock) down.
76 */
77 static struct mtx lock_mtx;
78
79 static int acquire(struct lock **lkpp, int extflags, int wanted);
80 static int apause(struct lock *lkp, int flags);
81 static int acquiredrain(struct lock *lkp, int extflags) ;
82
83 static void
84 lockmgr_init(void *dummy __unused)
85 {
86 mtx_init(&lock_mtx, "lockmgr", NULL, MTX_DEF);
87 }
88 SYSINIT(lmgrinit, SI_SUB_LOCKMGR, SI_ORDER_FIRST, lockmgr_init, NULL)
89
90 static LOCK_INLINE void
91 sharelock(struct lock *lkp, int incr) {
92 lkp->lk_flags |= LK_SHARE_NONZERO;
93 lkp->lk_sharecount += incr;
94 }
95
96 static LOCK_INLINE void
97 shareunlock(struct lock *lkp, int decr) {
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 wakeup(lkp);
105 }
106 lkp->lk_sharecount = 0;
107 } else {
108 lkp->lk_sharecount -= decr;
109 }
110 }
111
112 /*
113 * This is the waitloop optimization.
114 */
115 static int
116 apause(struct lock *lkp, int flags)
117 {
118 #ifdef SMP
119 int i, lock_wait;
120 #endif
121
122 if ((lkp->lk_flags & flags) == 0)
123 return 0;
124 #ifdef SMP
125 for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) {
126 mtx_unlock(lkp->lk_interlock);
127 for (i = LOCK_SAMPLE_WAIT; i > 0; i--)
128 if ((lkp->lk_flags & flags) == 0)
129 break;
130 mtx_lock(lkp->lk_interlock);
131 if ((lkp->lk_flags & flags) == 0)
132 return 0;
133 }
134 #endif
135 return 1;
136 }
137
138 static int
139 acquire(struct lock **lkpp, int extflags, int wanted) {
140 struct lock *lkp = *lkpp;
141 int s, error;
142
143 CTR3(KTR_LOCK,
144 "acquire(): lkp == %p, extflags == 0x%x, wanted == 0x%x",
145 lkp, extflags, wanted);
146
147 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
148 return EBUSY;
149 }
150
151 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
152 error = apause(lkp, wanted);
153 if (error == 0)
154 return 0;
155 }
156
157 s = splhigh();
158 while ((lkp->lk_flags & wanted) != 0) {
159 lkp->lk_flags |= LK_WAIT_NONZERO;
160 lkp->lk_waitcount++;
161 error = msleep(lkp, lkp->lk_interlock, lkp->lk_prio,
162 lkp->lk_wmesg,
163 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
164 if (lkp->lk_waitcount == 1) {
165 lkp->lk_flags &= ~LK_WAIT_NONZERO;
166 lkp->lk_waitcount = 0;
167 } else {
168 lkp->lk_waitcount--;
169 }
170 if (error) {
171 splx(s);
172 return error;
173 }
174 if (extflags & LK_SLEEPFAIL) {
175 splx(s);
176 return ENOLCK;
177 }
178 if (lkp->lk_newlock != NULL) {
179 mtx_lock(lkp->lk_newlock->lk_interlock);
180 mtx_unlock(lkp->lk_interlock);
181 if (lkp->lk_waitcount == 0)
182 wakeup((void *)(&lkp->lk_newlock));
183 *lkpp = lkp = lkp->lk_newlock;
184 }
185 }
186 splx(s);
187 return 0;
188 }
189
190 /*
191 * Set, change, or release a lock.
192 *
193 * Shared requests increment the shared count. Exclusive requests set the
194 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
195 * accepted shared locks and shared-to-exclusive upgrades to go away.
196 */
197 int
198 #ifndef DEBUG_LOCKS
199 lockmgr(lkp, flags, interlkp, td)
200 #else
201 debuglockmgr(lkp, flags, interlkp, td, name, file, line)
202 #endif
203 struct lock *lkp;
204 u_int flags;
205 struct mtx *interlkp;
206 struct thread *td;
207 #ifdef DEBUG_LOCKS
208 const char *name; /* Name of lock function */
209 const char *file; /* Name of file call is from */
210 int line; /* Line number in file */
211 #endif
212 {
213 int error;
214 struct thread *thr;
215 int extflags, lockflags;
216
217 CTR5(KTR_LOCK,
218 "lockmgr(): lkp == %p (lk_wmesg == \"%s\"), flags == 0x%x, "
219 "interlkp == %p, td == %p", lkp, lkp->lk_wmesg, flags, interlkp, td);
220
221 error = 0;
222 if (td == NULL)
223 thr = LK_KERNPROC;
224 else
225 thr = td;
226
227 if ((flags & LK_INTERNAL) == 0)
228 mtx_lock(lkp->lk_interlock);
229 if (flags & LK_INTERLOCK) {
230 mtx_assert(interlkp, MA_OWNED | MA_NOTRECURSED);
231 mtx_unlock(interlkp);
232 }
233
234 if ((flags & (LK_NOWAIT|LK_RELEASE)) == 0)
235 WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK,
236 &lkp->lk_interlock->mtx_object,
237 "Acquiring lockmgr lock \"%s\"", lkp->lk_wmesg);
238
239 if (panicstr != NULL) {
240 mtx_unlock(lkp->lk_interlock);
241 return (0);
242 }
243
244 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
245
246 switch (flags & LK_TYPE_MASK) {
247
248 case LK_SHARED:
249 /*
250 * If we are not the exclusive lock holder, we have to block
251 * while there is an exclusive lock holder or while an
252 * exclusive lock request or upgrade request is in progress.
253 *
254 * However, if TDP_DEADLKTREAT is set, we override exclusive
255 * lock requests or upgrade requests ( but not the exclusive
256 * lock itself ).
257 */
258 if (lkp->lk_lockholder != thr) {
259 lockflags = LK_HAVE_EXCL;
260 if (td != NULL && !(td->td_pflags & TDP_DEADLKTREAT))
261 lockflags |= LK_WANT_EXCL | LK_WANT_UPGRADE;
262 error = acquire(&lkp, extflags, lockflags);
263 if (error)
264 break;
265 sharelock(lkp, 1);
266 #if defined(DEBUG_LOCKS)
267 lkp->lk_slockholder = thr;
268 lkp->lk_sfilename = file;
269 lkp->lk_slineno = line;
270 lkp->lk_slockername = name;
271 #endif
272 break;
273 }
274 /*
275 * We hold an exclusive lock, so downgrade it to shared.
276 * An alternative would be to fail with EDEADLK.
277 */
278 sharelock(lkp, 1);
279 /* FALLTHROUGH downgrade */
280
281 case LK_DOWNGRADE:
282 KASSERT(lkp->lk_lockholder == thr && lkp->lk_exclusivecount != 0,
283 ("lockmgr: not holding exclusive lock "
284 "(owner thread (%p) != thread (%p), exlcnt (%d) != 0",
285 lkp->lk_lockholder, thr, lkp->lk_exclusivecount));
286 sharelock(lkp, lkp->lk_exclusivecount);
287 lkp->lk_exclusivecount = 0;
288 lkp->lk_flags &= ~LK_HAVE_EXCL;
289 lkp->lk_lockholder = LK_NOPROC;
290 if (lkp->lk_waitcount)
291 wakeup((void *)lkp);
292 break;
293
294 case LK_EXCLUPGRADE:
295 /*
296 * If another process is ahead of us to get an upgrade,
297 * then we want to fail rather than have an intervening
298 * exclusive access.
299 */
300 if (lkp->lk_flags & LK_WANT_UPGRADE) {
301 shareunlock(lkp, 1);
302 error = EBUSY;
303 break;
304 }
305 /* FALLTHROUGH normal upgrade */
306
307 case LK_UPGRADE:
308 /*
309 * Upgrade a shared lock to an exclusive one. If another
310 * shared lock has already requested an upgrade to an
311 * exclusive lock, our shared lock is released and an
312 * exclusive lock is requested (which will be granted
313 * after the upgrade). If we return an error, the file
314 * will always be unlocked.
315 */
316 if ((lkp->lk_lockholder == thr) || (lkp->lk_sharecount <= 0))
317 panic("lockmgr: upgrade exclusive lock");
318 shareunlock(lkp, 1);
319 /*
320 * If we are just polling, check to see if we will block.
321 */
322 if ((extflags & LK_NOWAIT) &&
323 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
324 lkp->lk_sharecount > 1)) {
325 error = EBUSY;
326 break;
327 }
328 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
329 /*
330 * We are first shared lock to request an upgrade, so
331 * request upgrade and wait for the shared count to
332 * drop to zero, then take exclusive lock.
333 */
334 lkp->lk_flags |= LK_WANT_UPGRADE;
335 error = acquire(&lkp, extflags, LK_SHARE_NONZERO);
336 lkp->lk_flags &= ~LK_WANT_UPGRADE;
337
338 if (error) {
339 if ((lkp->lk_flags & ( LK_WANT_EXCL | LK_WAIT_NONZERO)) == (LK_WANT_EXCL | LK_WAIT_NONZERO))
340 wakeup((void *)lkp);
341 break;
342 }
343
344 lkp->lk_flags |= LK_HAVE_EXCL;
345 lkp->lk_lockholder = thr;
346 if (lkp->lk_exclusivecount != 0)
347 panic("lockmgr: non-zero exclusive count");
348 lkp->lk_exclusivecount = 1;
349 #if defined(DEBUG_LOCKS)
350 lkp->lk_filename = file;
351 lkp->lk_lineno = line;
352 lkp->lk_lockername = name;
353 #endif
354 break;
355 }
356 /*
357 * Someone else has requested upgrade. Release our shared
358 * lock, awaken upgrade requestor if we are the last shared
359 * lock, then request an exclusive lock.
360 */
361 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
362 LK_WAIT_NONZERO)
363 wakeup((void *)lkp);
364 /* FALLTHROUGH exclusive request */
365
366 case LK_EXCLUSIVE:
367 if (lkp->lk_lockholder == thr && thr != LK_KERNPROC) {
368 /*
369 * Recursive lock.
370 */
371 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
372 panic("lockmgr: locking against myself");
373 if ((extflags & LK_CANRECURSE) != 0) {
374 lkp->lk_exclusivecount++;
375 break;
376 }
377 }
378 /*
379 * If we are just polling, check to see if we will sleep.
380 */
381 if ((extflags & LK_NOWAIT) &&
382 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
383 error = EBUSY;
384 break;
385 }
386 /*
387 * Try to acquire the want_exclusive flag.
388 */
389 error = acquire(&lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
390 if (error)
391 break;
392 lkp->lk_flags |= LK_WANT_EXCL;
393 /*
394 * Wait for shared locks and upgrades to finish.
395 */
396 error = acquire(&lkp, extflags, LK_HAVE_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO);
397 lkp->lk_flags &= ~LK_WANT_EXCL;
398 if (error) {
399 if (lkp->lk_flags & LK_WAIT_NONZERO)
400 wakeup((void *)lkp);
401 break;
402 }
403 lkp->lk_flags |= LK_HAVE_EXCL;
404 lkp->lk_lockholder = thr;
405 if (lkp->lk_exclusivecount != 0)
406 panic("lockmgr: non-zero exclusive count");
407 lkp->lk_exclusivecount = 1;
408 #if defined(DEBUG_LOCKS)
409 lkp->lk_filename = file;
410 lkp->lk_lineno = line;
411 lkp->lk_lockername = name;
412 #endif
413 break;
414
415 case LK_RELEASE:
416 if (lkp->lk_exclusivecount != 0) {
417 if (lkp->lk_lockholder != thr &&
418 lkp->lk_lockholder != LK_KERNPROC) {
419 panic("lockmgr: thread %p, not %s %p unlocking",
420 thr, "exclusive lock holder",
421 lkp->lk_lockholder);
422 }
423 if (lkp->lk_exclusivecount == 1) {
424 lkp->lk_flags &= ~LK_HAVE_EXCL;
425 lkp->lk_lockholder = LK_NOPROC;
426 lkp->lk_exclusivecount = 0;
427 } else {
428 lkp->lk_exclusivecount--;
429 }
430 } else if (lkp->lk_flags & LK_SHARE_NONZERO)
431 shareunlock(lkp, 1);
432 if (lkp->lk_flags & LK_WAIT_NONZERO)
433 wakeup((void *)lkp);
434 break;
435
436 case LK_DRAIN:
437 /*
438 * Check that we do not already hold the lock, as it can
439 * never drain if we do. Unfortunately, we have no way to
440 * check for holding a shared lock, but at least we can
441 * check for an exclusive one.
442 */
443 if (lkp->lk_lockholder == thr)
444 panic("lockmgr: draining against myself");
445
446 error = acquiredrain(lkp, extflags);
447 if (error)
448 break;
449 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
450 lkp->lk_lockholder = thr;
451 lkp->lk_exclusivecount = 1;
452 #if defined(DEBUG_LOCKS)
453 lkp->lk_filename = file;
454 lkp->lk_lineno = line;
455 lkp->lk_lockername = name;
456 #endif
457 break;
458
459 default:
460 mtx_unlock(lkp->lk_interlock);
461 panic("lockmgr: unknown locktype request %d",
462 flags & LK_TYPE_MASK);
463 /* NOTREACHED */
464 }
465 if ((lkp->lk_flags & LK_WAITDRAIN) &&
466 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
467 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
468 lkp->lk_flags &= ~LK_WAITDRAIN;
469 wakeup((void *)&lkp->lk_flags);
470 }
471 mtx_unlock(lkp->lk_interlock);
472 return (error);
473 }
474
475 static int
476 acquiredrain(struct lock *lkp, int extflags) {
477 int error;
478
479 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
480 return EBUSY;
481 }
482
483 error = apause(lkp, LK_ALL);
484 if (error == 0)
485 return 0;
486
487 while (lkp->lk_flags & LK_ALL) {
488 lkp->lk_flags |= LK_WAITDRAIN;
489 error = msleep(&lkp->lk_flags, lkp->lk_interlock, lkp->lk_prio,
490 lkp->lk_wmesg,
491 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
492 if (error)
493 return error;
494 if (extflags & LK_SLEEPFAIL) {
495 return ENOLCK;
496 }
497 }
498 return 0;
499 }
500
501 /*
502 * Transfer any waiting processes from one lock to another.
503 */
504 void
505 transferlockers(from, to)
506 struct lock *from;
507 struct lock *to;
508 {
509
510 KASSERT(from != to, ("lock transfer to self"));
511 KASSERT((from->lk_flags&LK_WAITDRAIN) == 0, ("transfer draining lock"));
512 if (from->lk_waitcount == 0)
513 return;
514 from->lk_newlock = to;
515 wakeup((void *)from);
516 msleep(&from->lk_newlock, NULL, from->lk_prio, "lkxfer", 0);
517 from->lk_newlock = NULL;
518 from->lk_flags &= ~(LK_WANT_EXCL | LK_WANT_UPGRADE);
519 KASSERT(from->lk_waitcount == 0, ("active lock"));
520 }
521
522
523 /*
524 * Initialize a lock; required before use.
525 */
526 void
527 lockinit(lkp, prio, wmesg, timo, flags)
528 struct lock *lkp;
529 int prio;
530 const char *wmesg;
531 int timo;
532 int flags;
533 {
534 CTR5(KTR_LOCK, "lockinit(): lkp == %p, prio == %d, wmesg == \"%s\", "
535 "timo == %d, flags = 0x%x\n", lkp, prio, wmesg, timo, flags);
536
537 lkp->lk_interlock = mtx_pool_alloc(mtxpool_lockbuilder);
538 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
539 lkp->lk_sharecount = 0;
540 lkp->lk_waitcount = 0;
541 lkp->lk_exclusivecount = 0;
542 lkp->lk_prio = prio;
543 lkp->lk_wmesg = wmesg;
544 lkp->lk_timo = timo;
545 lkp->lk_lockholder = LK_NOPROC;
546 lkp->lk_newlock = NULL;
547 #ifdef DEBUG_LOCKS
548 lkp->lk_filename = "none";
549 lkp->lk_lockername = "never exclusive locked";
550 lkp->lk_lineno = 0;
551 lkp->lk_slockholder = LK_NOPROC;
552 lkp->lk_sfilename = "none";
553 lkp->lk_slockername = "never share locked";
554 lkp->lk_slineno = 0;
555 #endif
556 }
557
558 /*
559 * Destroy a lock.
560 */
561 void
562 lockdestroy(lkp)
563 struct lock *lkp;
564 {
565 CTR2(KTR_LOCK, "lockdestroy(): lkp == %p (lk_wmesg == \"%s\")",
566 lkp, lkp->lk_wmesg);
567 }
568
569 /*
570 * Determine the status of a lock.
571 */
572 int
573 lockstatus(lkp, td)
574 struct lock *lkp;
575 struct thread *td;
576 {
577 int lock_type = 0;
578
579 mtx_lock(lkp->lk_interlock);
580 if (lkp->lk_exclusivecount != 0) {
581 if (td == NULL || lkp->lk_lockholder == td)
582 lock_type = LK_EXCLUSIVE;
583 else
584 lock_type = LK_EXCLOTHER;
585 } else if (lkp->lk_sharecount != 0)
586 lock_type = LK_SHARED;
587 mtx_unlock(lkp->lk_interlock);
588 return (lock_type);
589 }
590
591 /*
592 * Determine the number of holders of a lock.
593 */
594 int
595 lockcount(lkp)
596 struct lock *lkp;
597 {
598 int count;
599
600 mtx_lock(lkp->lk_interlock);
601 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
602 mtx_unlock(lkp->lk_interlock);
603 return (count);
604 }
605
606 /*
607 * Print out information about state of a lock. Used by VOP_PRINT
608 * routines to display status about contained locks.
609 */
610 void
611 lockmgr_printinfo(lkp)
612 struct lock *lkp;
613 {
614
615 if (lkp->lk_sharecount)
616 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
617 lkp->lk_sharecount);
618 else if (lkp->lk_flags & LK_HAVE_EXCL)
619 printf(" lock type %s: EXCL (count %d) by thread %p (pid %d)",
620 lkp->lk_wmesg, lkp->lk_exclusivecount,
621 lkp->lk_lockholder, lkp->lk_lockholder->td_proc->p_pid);
622 if (lkp->lk_waitcount > 0)
623 printf(" with %d pending", lkp->lk_waitcount);
624 }
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