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[dragonfly.git] / sys / kern / kern_lock.c
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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 */
43
44#include "opt_lint.h"
45
46#include <sys/param.h>
47#include <sys/proc.h>
48#include <sys/lock.h>
49#include <sys/systm.h>
50
51/*
52 * Locking primitives implementation.
53 * Locks provide shared/exclusive sychronization.
54 */
55
56#ifdef SIMPLELOCK_DEBUG
57#define COUNT(p, x) if (p) (p)->p_locks += (x)
58#else
59#define COUNT(p, x)
60#endif
61
62#define LOCK_WAIT_TIME 100
63#define LOCK_SAMPLE_WAIT 7
64
65#if defined(DIAGNOSTIC)
66#define LOCK_INLINE
67#else
68#define LOCK_INLINE __inline
69#endif
70
71#define LK_ALL (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | \
72 LK_SHARE_NONZERO | LK_WAIT_NONZERO)
73
74static int acquire(struct lock *lkp, int extflags, int wanted);
75static int apause(struct lock *lkp, int flags);
76static int acquiredrain(struct lock *lkp, int extflags) ;
77
78static LOCK_INLINE void
79sharelock(struct lock *lkp, int incr) {
80 lkp->lk_flags |= LK_SHARE_NONZERO;
81 lkp->lk_sharecount += incr;
82}
83
84static LOCK_INLINE void
85shareunlock(struct lock *lkp, int decr) {
86
87 KASSERT(lkp->lk_sharecount >= decr, ("shareunlock: count < decr"));
88
89 if (lkp->lk_sharecount == decr) {
90 lkp->lk_flags &= ~LK_SHARE_NONZERO;
91 if (lkp->lk_flags & (LK_WANT_UPGRADE | LK_WANT_EXCL)) {
92 wakeup(lkp);
93 }
94 lkp->lk_sharecount = 0;
95 } else {
96 lkp->lk_sharecount -= decr;
97 }
98}
99
100/*
101 * This is the waitloop optimization, and note for this to work
102 * simple_lock and simple_unlock should be subroutines to avoid
103 * optimization troubles.
104 */
105static int
106apause(struct lock *lkp, int flags)
107{
108#ifdef SMP
109 int i, lock_wait;
110#endif
111
112 if ((lkp->lk_flags & flags) == 0)
113 return 0;
114#ifdef SMP
115 for (lock_wait = LOCK_WAIT_TIME; lock_wait > 0; lock_wait--) {
116 simple_unlock(&lkp->lk_interlock);
117 for (i = LOCK_SAMPLE_WAIT; i > 0; i--)
118 if ((lkp->lk_flags & flags) == 0)
119 break;
120 simple_lock(&lkp->lk_interlock);
121 if ((lkp->lk_flags & flags) == 0)
122 return 0;
123 }
124#endif
125 return 1;
126}
127
128static int
129acquire(struct lock *lkp, int extflags, int wanted) {
130 int s, error;
131
132 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & wanted)) {
133 return EBUSY;
134 }
135
136 if (((lkp->lk_flags | extflags) & LK_NOPAUSE) == 0) {
137 error = apause(lkp, wanted);
138 if (error == 0)
139 return 0;
140 }
141
142 s = splhigh();
143 while ((lkp->lk_flags & wanted) != 0) {
144 lkp->lk_flags |= LK_WAIT_NONZERO;
145 lkp->lk_waitcount++;
146 simple_unlock(&lkp->lk_interlock);
147 error = tsleep(lkp, lkp->lk_prio, lkp->lk_wmesg,
148 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
149 simple_lock(&lkp->lk_interlock);
150 if (lkp->lk_waitcount == 1) {
151 lkp->lk_flags &= ~LK_WAIT_NONZERO;
152 lkp->lk_waitcount = 0;
153 } else {
154 lkp->lk_waitcount--;
155 }
156 if (error) {
157 splx(s);
158 return error;
159 }
160 if (extflags & LK_SLEEPFAIL) {
161 splx(s);
162 return ENOLCK;
163 }
164 }
165 splx(s);
166 return 0;
167}
168
169/*
170 * Set, change, or release a lock.
171 *
172 * Shared requests increment the shared count. Exclusive requests set the
173 * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
174 * accepted shared locks and shared-to-exclusive upgrades to go away.
175 */
176int
177#ifndef DEBUG_LOCKS
178lockmgr(lkp, flags, interlkp, p)
179#else
180debuglockmgr(lkp, flags, interlkp, p, name, file, line)
181#endif
182 struct lock *lkp;
183 u_int flags;
184 struct simplelock *interlkp;
185 struct proc *p;
186#ifdef DEBUG_LOCKS
187 const char *name; /* Name of lock function */
188 const char *file; /* Name of file call is from */
189 int line; /* Line number in file */
190#endif
191{
192 int error;
193 pid_t pid;
194 int extflags;
195
196 error = 0;
197 if (p == NULL)
198 pid = LK_KERNPROC;
199 else
200 pid = p->p_pid;
201
202 simple_lock(&lkp->lk_interlock);
203 if (flags & LK_INTERLOCK)
204 simple_unlock(interlkp);
205
206 extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
207
208 switch (flags & LK_TYPE_MASK) {
209
210 case LK_SHARED:
211 /*
212 * If we are not the exclusive lock holder, we have to block
213 * while there is an exclusive lock holder or while an
214 * exclusive lock request or upgrade request is in progress.
215 *
216 * However, if P_DEADLKTREAT is set, we override exclusive
217 * lock requests or upgrade requests ( but not the exclusive
218 * lock itself ).
219 */
220 if (lkp->lk_lockholder != pid) {
221 if (p && (p->p_flag & P_DEADLKTREAT)) {
222 error = acquire(
223 lkp,
224 extflags,
225 LK_HAVE_EXCL
226 );
227 } else {
228 error = acquire(
229 lkp,
230 extflags,
231 LK_HAVE_EXCL | LK_WANT_EXCL |
232 LK_WANT_UPGRADE
233 );
234 }
235 if (error)
236 break;
237 sharelock(lkp, 1);
238 COUNT(p, 1);
239 break;
240 }
241 /*
242 * We hold an exclusive lock, so downgrade it to shared.
243 * An alternative would be to fail with EDEADLK.
244 */
245 sharelock(lkp, 1);
246 COUNT(p, 1);
247 /* fall into downgrade */
248
249 case LK_DOWNGRADE:
250 if (lkp->lk_lockholder != pid || lkp->lk_exclusivecount == 0)
251 panic("lockmgr: not holding exclusive lock");
252 sharelock(lkp, lkp->lk_exclusivecount);
253 lkp->lk_exclusivecount = 0;
254 lkp->lk_flags &= ~LK_HAVE_EXCL;
255 lkp->lk_lockholder = LK_NOPROC;
256 if (lkp->lk_waitcount)
257 wakeup((void *)lkp);
258 break;
259
260 case LK_EXCLUPGRADE:
261 /*
262 * If another process is ahead of us to get an upgrade,
263 * then we want to fail rather than have an intervening
264 * exclusive access.
265 */
266 if (lkp->lk_flags & LK_WANT_UPGRADE) {
267 shareunlock(lkp, 1);
268 COUNT(p, -1);
269 error = EBUSY;
270 break;
271 }
272 /* fall into normal upgrade */
273
274 case LK_UPGRADE:
275 /*
276 * Upgrade a shared lock to an exclusive one. If another
277 * shared lock has already requested an upgrade to an
278 * exclusive lock, our shared lock is released and an
279 * exclusive lock is requested (which will be granted
280 * after the upgrade). If we return an error, the file
281 * will always be unlocked.
282 */
283 if ((lkp->lk_lockholder == pid) || (lkp->lk_sharecount <= 0))
284 panic("lockmgr: upgrade exclusive lock");
285 shareunlock(lkp, 1);
286 COUNT(p, -1);
287 /*
288 * If we are just polling, check to see if we will block.
289 */
290 if ((extflags & LK_NOWAIT) &&
291 ((lkp->lk_flags & LK_WANT_UPGRADE) ||
292 lkp->lk_sharecount > 1)) {
293 error = EBUSY;
294 break;
295 }
296 if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
297 /*
298 * We are first shared lock to request an upgrade, so
299 * request upgrade and wait for the shared count to
300 * drop to zero, then take exclusive lock.
301 */
302 lkp->lk_flags |= LK_WANT_UPGRADE;
303 error = acquire(lkp, extflags, LK_SHARE_NONZERO);
304 lkp->lk_flags &= ~LK_WANT_UPGRADE;
305
306 if (error)
307 break;
308 lkp->lk_flags |= LK_HAVE_EXCL;
309 lkp->lk_lockholder = pid;
310 if (lkp->lk_exclusivecount != 0)
311 panic("lockmgr: non-zero exclusive count");
312 lkp->lk_exclusivecount = 1;
313#if defined(DEBUG_LOCKS)
314 lkp->lk_filename = file;
315 lkp->lk_lineno = line;
316 lkp->lk_lockername = name;
317#endif
318 COUNT(p, 1);
319 break;
320 }
321 /*
322 * Someone else has requested upgrade. Release our shared
323 * lock, awaken upgrade requestor if we are the last shared
324 * lock, then request an exclusive lock.
325 */
326 if ( (lkp->lk_flags & (LK_SHARE_NONZERO|LK_WAIT_NONZERO)) ==
327 LK_WAIT_NONZERO)
328 wakeup((void *)lkp);
329 /* fall into exclusive request */
330
331 case LK_EXCLUSIVE:
332 if (lkp->lk_lockholder == pid && pid != LK_KERNPROC) {
333 /*
334 * Recursive lock.
335 */
336 if ((extflags & (LK_NOWAIT | LK_CANRECURSE)) == 0)
337 panic("lockmgr: locking against myself");
338 if ((extflags & LK_CANRECURSE) != 0) {
339 lkp->lk_exclusivecount++;
340 COUNT(p, 1);
341 break;
342 }
343 }
344 /*
345 * If we are just polling, check to see if we will sleep.
346 */
347 if ((extflags & LK_NOWAIT) &&
348 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE | LK_SHARE_NONZERO))) {
349 error = EBUSY;
350 break;
351 }
352 /*
353 * Try to acquire the want_exclusive flag.
354 */
355 error = acquire(lkp, extflags, (LK_HAVE_EXCL | LK_WANT_EXCL));
356 if (error)
357 break;
358 lkp->lk_flags |= LK_WANT_EXCL;
359 /*
360 * Wait for shared locks and upgrades to finish.
361 */
362 error = acquire(lkp, extflags, LK_WANT_UPGRADE | LK_SHARE_NONZERO);
363 lkp->lk_flags &= ~LK_WANT_EXCL;
364 if (error)
365 break;
366 lkp->lk_flags |= LK_HAVE_EXCL;
367 lkp->lk_lockholder = pid;
368 if (lkp->lk_exclusivecount != 0)
369 panic("lockmgr: non-zero exclusive count");
370 lkp->lk_exclusivecount = 1;
371#if defined(DEBUG_LOCKS)
372 lkp->lk_filename = file;
373 lkp->lk_lineno = line;
374 lkp->lk_lockername = name;
375#endif
376 COUNT(p, 1);
377 break;
378
379 case LK_RELEASE:
380 if (lkp->lk_exclusivecount != 0) {
381 if (lkp->lk_lockholder != pid &&
382 lkp->lk_lockholder != LK_KERNPROC) {
383 panic("lockmgr: pid %d, not %s %d unlocking",
384 pid, "exclusive lock holder",
385 lkp->lk_lockholder);
386 }
387 if (lkp->lk_lockholder != LK_KERNPROC) {
388 COUNT(p, -1);
389 }
390 if (lkp->lk_exclusivecount == 1) {
391 lkp->lk_flags &= ~LK_HAVE_EXCL;
392 lkp->lk_lockholder = LK_NOPROC;
393 lkp->lk_exclusivecount = 0;
394 } else {
395 lkp->lk_exclusivecount--;
396 }
397 } else if (lkp->lk_flags & LK_SHARE_NONZERO) {
398 shareunlock(lkp, 1);
399 COUNT(p, -1);
400 }
401 if (lkp->lk_flags & LK_WAIT_NONZERO)
402 wakeup((void *)lkp);
403 break;
404
405 case LK_DRAIN:
406 /*
407 * Check that we do not already hold the lock, as it can
408 * never drain if we do. Unfortunately, we have no way to
409 * check for holding a shared lock, but at least we can
410 * check for an exclusive one.
411 */
412 if (lkp->lk_lockholder == pid)
413 panic("lockmgr: draining against myself");
414
415 error = acquiredrain(lkp, extflags);
416 if (error)
417 break;
418 lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
419 lkp->lk_lockholder = pid;
420 lkp->lk_exclusivecount = 1;
421#if defined(DEBUG_LOCKS)
422 lkp->lk_filename = file;
423 lkp->lk_lineno = line;
424 lkp->lk_lockername = name;
425#endif
426 COUNT(p, 1);
427 break;
428
429 default:
430 simple_unlock(&lkp->lk_interlock);
431 panic("lockmgr: unknown locktype request %d",
432 flags & LK_TYPE_MASK);
433 /* NOTREACHED */
434 }
435 if ((lkp->lk_flags & LK_WAITDRAIN) &&
436 (lkp->lk_flags & (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE |
437 LK_SHARE_NONZERO | LK_WAIT_NONZERO)) == 0) {
438 lkp->lk_flags &= ~LK_WAITDRAIN;
439 wakeup((void *)&lkp->lk_flags);
440 }
441 simple_unlock(&lkp->lk_interlock);
442 return (error);
443}
444
445static int
446acquiredrain(struct lock *lkp, int extflags) {
447 int error;
448
449 if ((extflags & LK_NOWAIT) && (lkp->lk_flags & LK_ALL)) {
450 return EBUSY;
451 }
452
453 error = apause(lkp, LK_ALL);
454 if (error == 0)
455 return 0;
456
457 while (lkp->lk_flags & LK_ALL) {
458 lkp->lk_flags |= LK_WAITDRAIN;
459 simple_unlock(&lkp->lk_interlock);
460 error = tsleep(&lkp->lk_flags, lkp->lk_prio,
461 lkp->lk_wmesg,
462 ((extflags & LK_TIMELOCK) ? lkp->lk_timo : 0));
463 simple_lock(&lkp->lk_interlock);
464 if (error)
465 return error;
466 if (extflags & LK_SLEEPFAIL) {
467 return ENOLCK;
468 }
469 }
470 return 0;
471}
472
473/*
474 * Initialize a lock; required before use.
475 */
476void
477lockinit(lkp, prio, wmesg, timo, flags)
478 struct lock *lkp;
479 int prio;
480 char *wmesg;
481 int timo;
482 int flags;
483{
484
485 simple_lock_init(&lkp->lk_interlock);
486 lkp->lk_flags = (flags & LK_EXTFLG_MASK);
487 lkp->lk_sharecount = 0;
488 lkp->lk_waitcount = 0;
489 lkp->lk_exclusivecount = 0;
490 lkp->lk_prio = prio;
491 lkp->lk_wmesg = wmesg;
492 lkp->lk_timo = timo;
493 lkp->lk_lockholder = LK_NOPROC;
494}
495
496/*
497 * Determine the status of a lock.
498 */
499int
500lockstatus(lkp, p)
501 struct lock *lkp;
502 struct proc *p;
503{
504 int lock_type = 0;
505
506 simple_lock(&lkp->lk_interlock);
507 if (lkp->lk_exclusivecount != 0) {
508 if (p == NULL || lkp->lk_lockholder == p->p_pid)
509 lock_type = LK_EXCLUSIVE;
510 else
511 lock_type = LK_EXCLOTHER;
512 } else if (lkp->lk_sharecount != 0)
513 lock_type = LK_SHARED;
514 simple_unlock(&lkp->lk_interlock);
515 return (lock_type);
516}
517
518/*
519 * Determine the number of holders of a lock.
520 */
521int
522lockcount(lkp)
523 struct lock *lkp;
524{
525 int count;
526
527 simple_lock(&lkp->lk_interlock);
528 count = lkp->lk_exclusivecount + lkp->lk_sharecount;
529 simple_unlock(&lkp->lk_interlock);
530 return (count);
531}
532
533/*
534 * Print out information about state of a lock. Used by VOP_PRINT
535 * routines to display status about contained locks.
536 */
537void
538lockmgr_printinfo(lkp)
539 struct lock *lkp;
540{
541
542 if (lkp->lk_sharecount)
543 printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
544 lkp->lk_sharecount);
545 else if (lkp->lk_flags & LK_HAVE_EXCL)
546 printf(" lock type %s: EXCL (count %d) by pid %d",
547 lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder);
548 if (lkp->lk_waitcount > 0)
549 printf(" with %d pending", lkp->lk_waitcount);
550}
551
552#if defined(SIMPLELOCK_DEBUG) && (MAXCPU == 1 || defined(COMPILING_LINT))
553#include <sys/kernel.h>
554#include <sys/sysctl.h>
555
556static int lockpausetime = 0;
557SYSCTL_INT(_debug, OID_AUTO, lockpausetime, CTLFLAG_RW, &lockpausetime, 0, "");
558
559static int simplelockrecurse;
560
561/*
562 * Simple lock functions so that the debugger can see from whence
563 * they are being called.
564 */
565void
566simple_lock_init(alp)
567 struct simplelock *alp;
568{
569
570 alp->lock_data = 0;
571}
572
573void
574_simple_lock(alp, id, l)
575 struct simplelock *alp;
576 const char *id;
577 int l;
578{
579
580 if (simplelockrecurse)
581 return;
582 if (alp->lock_data == 1) {
583 if (lockpausetime == -1)
584 panic("%s:%d: simple_lock: lock held", id, l);
585 printf("%s:%d: simple_lock: lock held\n", id, l);
586 if (lockpausetime == 1) {
587 Debugger("simple_lock");
588 /*BACKTRACE(curproc); */
589 } else if (lockpausetime > 1) {
590 printf("%s:%d: simple_lock: lock held...", id, l);
591 tsleep(&lockpausetime, PCATCH | PPAUSE, "slock",
592 lockpausetime * hz);
593 printf(" continuing\n");
594 }
595 }
596 alp->lock_data = 1;
597 if (curproc)
598 curproc->p_simple_locks++;
599}
600
601int
602_simple_lock_try(alp, id, l)
603 struct simplelock *alp;
604 const char *id;
605 int l;
606{
607
608 if (alp->lock_data)
609 return (0);
610 if (simplelockrecurse)
611 return (1);
612 alp->lock_data = 1;
613 if (curproc)
614 curproc->p_simple_locks++;
615 return (1);
616}
617
618void
619_simple_unlock(alp, id, l)
620 struct simplelock *alp;
621 const char *id;
622 int l;
623{
624
625 if (simplelockrecurse)
626 return;
627 if (alp->lock_data == 0) {
628 if (lockpausetime == -1)
629 panic("%s:%d: simple_unlock: lock not held", id, l);
630 printf("%s:%d: simple_unlock: lock not held\n", id, l);
631 if (lockpausetime == 1) {
632 Debugger("simple_unlock");
633 /* BACKTRACE(curproc); */
634 } else if (lockpausetime > 1) {
635 printf("%s:%d: simple_unlock: lock not held...", id, l);
636 tsleep(&lockpausetime, PCATCH | PPAUSE, "sunlock",
637 lockpausetime * hz);
638 printf(" continuing\n");
639 }
640 }
641 alp->lock_data = 0;
642 if (curproc)
643 curproc->p_simple_locks--;
644}
645#elif defined(SIMPLELOCK_DEBUG)
646#error "SIMPLELOCK_DEBUG is not compatible with SMP!"
647#endif /* SIMPLELOCK_DEBUG && MAXCPU == 1 */