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1.1 root 1: /*
2: * Copyright (c) 1999 Apple Computer, Inc. All rights reserved.
3: *
4: * @APPLE_LICENSE_HEADER_START@
5: *
6: * Portions Copyright (c) 1999 Apple Computer, Inc. All Rights
7: * Reserved. This file contains Original Code and/or Modifications of
8: * Original Code as defined in and that are subject to the Apple Public
9: * Source License Version 1.1 (the "License"). You may not use this file
10: * except in compliance with the License. Please obtain a copy of the
11: * License at http://www.apple.com/publicsource and read it before using
12: * this file.
13: *
14: * The Original Code and all software distributed under the License are
15: * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
16: * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
17: * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
18: * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT. Please see the
19: * License for the specific language governing rights and limitations
20: * under the License.
21: *
22: * @APPLE_LICENSE_HEADER_END@
23: */
24:
25: /* Copyright (c) 1995, 1997 Apple Computer, Inc. All Rights Reserved */
26: /*
27: * Copyright (c) 1995
28: * The Regents of the University of California. All rights reserved.
29: *
30: * This code contains ideas from software contributed to Berkeley by
31: * Avadis Tevanian, Jr., Michael Wayne Young, and the Mach Operating
32: * System project at Carnegie-Mellon University.
33: *
34: * Redistribution and use in source and binary forms, with or without
35: * modification, are permitted provided that the following conditions
36: * are met:
37: * 1. Redistributions of source code must retain the above copyright
38: * notice, this list of conditions and the following disclaimer.
39: * 2. Redistributions in binary form must reproduce the above copyright
40: * notice, this list of conditions and the following disclaimer in the
41: * documentation and/or other materials provided with the distribution.
42: * 3. All advertising materials mentioning features or use of this software
43: * must display the following acknowledgement:
44: * This product includes software developed by the University of
45: * California, Berkeley and its contributors.
46: * 4. Neither the name of the University nor the names of its contributors
47: * may be used to endorse or promote products derived from this software
48: * without specific prior written permission.
49: *
50: * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
51: * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
52: * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
53: * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
54: * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
55: * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
56: * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
57: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
58: * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
59: * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
60: * SUCH DAMAGE.
61: *
62: * @(#)kern_lock.c 8.18 (Berkeley) 5/21/95
63: */
64:
65: #include <sys/param.h>
66: #include <sys/proc.h>
67: #include <sys/lock.h>
68: #include <machine/cpu.h>
69:
70: #include <mach/mach_types.h>
71:
72: /*
73: * Locking primitives implementation.
74: * Locks provide shared/exclusive sychronization.
75: */
76:
77: #if 0
78: #define COUNT(p, x) if (p) (p)->p_locks += (x)
79: #else
80: #define COUNT(p, x)
81: #endif
82:
83: #if NCPUS > 1
84:
85: /*
86: * For multiprocessor system, try spin lock first.
87: *
88: * This should be inline expanded below, but we cannot have #if
89: * inside a multiline define.
90: */
91: int lock_wait_time = 100;
92: #define PAUSE(lkp, wanted) \
93: if (lock_wait_time > 0) { \
94: int i; \
95: \
96: simple_unlock(&lkp->lk_interlock); \
97: for (i = lock_wait_time; i > 0; i--) \
98: if (!(wanted)) \
99: break; \
100: simple_lock(&lkp->lk_interlock); \
101: } \
102: if (!(wanted)) \
103: break;
104:
105: #else /* NCPUS == 1 */
106:
107: /*
108: * It is an error to spin on a uniprocessor as nothing will ever cause
109: * the simple lock to clear while we are executing.
110: */
111: #define PAUSE(lkp, wanted)
112:
113: #endif /* NCPUS == 1 */
114:
115: /*
116: * Acquire a resource.
117: */
118: #define ACQUIRE(lkp, error, extflags, wanted) \
119: PAUSE(lkp, wanted); \
120: for (error = 0; wanted; ) { \
121: (lkp)->lk_waitcount++; \
122: simple_unlock(&(lkp)->lk_interlock); \
123: error = tsleep((void *)lkp, (lkp)->lk_prio, \
124: (lkp)->lk_wmesg, (lkp)->lk_timo); \
125: simple_lock(&(lkp)->lk_interlock); \
126: (lkp)->lk_waitcount--; \
127: if (error) \
128: break; \
129: if ((extflags) & LK_SLEEPFAIL) { \
130: error = ENOLCK; \
131: break; \
132: } \
133: }
134:
135: /*
136: * Initialize a lock; required before use.
137: */
138: void
139: lockinit(lkp, prio, wmesg, timo, flags)
140: struct lock__bsd__ *lkp;
141: int prio;
142: char *wmesg;
143: int timo;
144: int flags;
145: {
146:
147: bzero(lkp, sizeof(struct lock__bsd__));
148: simple_lock_init(&lkp->lk_interlock);
149: lkp->lk_flags = flags & LK_EXTFLG_MASK;
150: lkp->lk_prio = prio;
151: lkp->lk_timo = timo;
152: lkp->lk_wmesg = wmesg;
153: lkp->lk_lockholder = LK_NOPROC;
154: lkp->lk_lockthread = 0;
155: }
156:
157: /*
158: * Determine the status of a lock.
159: */
160: int
161: lockstatus(lkp)
162: struct lock__bsd__ *lkp;
163: {
164: int lock_type = 0;
165:
166: simple_lock(&lkp->lk_interlock);
167: if (lkp->lk_exclusivecount != 0)
168: lock_type = LK_EXCLUSIVE;
169: else if (lkp->lk_sharecount != 0)
170: lock_type = LK_SHARED;
171: simple_unlock(&lkp->lk_interlock);
172: return (lock_type);
173: }
174:
175: /*
176: * Set, change, or release a lock.
177: *
178: * Shared requests increment the shared count. Exclusive requests set the
179: * LK_WANT_EXCL flag (preventing further shared locks), and wait for already
180: * accepted shared locks and shared-to-exclusive upgrades to go away.
181: */
182: int
183: lockmgr(lkp, flags, interlkp, p)
184: struct lock__bsd__ *lkp;
185: u_int flags;
186: simple_lock_t interlkp;
187: struct proc *p;
188: {
189: int error;
190: pid_t pid;
191: int extflags;
192: void *self;
193:
194: error = 0; self = current_thread();
195: if (p)
196: pid = p->p_pid;
197: else
198: pid = LK_KERNPROC;
199: simple_lock(&lkp->lk_interlock);
200: if (flags & LK_INTERLOCK)
201: simple_unlock(interlkp);
202: extflags = (flags | lkp->lk_flags) & LK_EXTFLG_MASK;
203: #if 0
204: /*
205: * Once a lock has drained, the LK_DRAINING flag is set and an
206: * exclusive lock is returned. The only valid operation thereafter
207: * is a single release of that exclusive lock. This final release
208: * clears the LK_DRAINING flag and sets the LK_DRAINED flag. Any
209: * further requests of any sort will result in a panic. The bits
210: * selected for these two flags are chosen so that they will be set
211: * in memory that is freed (freed memory is filled with 0xdeadbeef).
212: * The final release is permitted to give a new lease on life to
213: * the lock by specifying LK_REENABLE.
214: */
215: if (lkp->lk_flags & (LK_DRAINING|LK_DRAINED)) {
216: if (lkp->lk_flags & LK_DRAINED)
217: panic("lockmgr: using decommissioned lock");
218: if ((flags & LK_TYPE_MASK) != LK_RELEASE ||
219: (lkp->lk_lockholder != pid && lkp->lk_lockthread != self)
220: panic("lockmgr: non-release on draining lock: %d\n",
221: flags & LK_TYPE_MASK);
222: lkp->lk_flags &= ~LK_DRAINING;
223: if ((flags & LK_REENABLE) == 0)
224: lkp->lk_flags |= LK_DRAINED;
225: }
226: #endif
227:
228: switch (flags & LK_TYPE_MASK) {
229:
230: case LK_SHARED:
231: if (lkp->lk_lockholder != pid || lkp->lk_lockthread != self) {
232: /*
233: * If just polling, check to see if we will block.
234: */
235: if ((extflags & LK_NOWAIT) && (lkp->lk_flags &
236: (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE))) {
237: error = EBUSY;
238: break;
239: }
240: /*
241: * Wait for exclusive locks and upgrades to clear.
242: */
243: ACQUIRE(lkp, error, extflags, lkp->lk_flags &
244: (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE));
245: if (error)
246: break;
247: lkp->lk_sharecount++;
248: COUNT(p, 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: lkp->lk_sharecount++;
256: COUNT(p, 1);
257: /* fall into downgrade */
258:
259: case LK_DOWNGRADE:
260: if (lkp->lk_lockholder != pid ||
261: lkp->lk_lockthread != self ||
262: lkp->lk_exclusivecount == 0)
263: panic("lockmgr: not holding exclusive lock");
264: lkp->lk_sharecount += lkp->lk_exclusivecount;
265: lkp->lk_exclusivecount = 0;
266: lkp->lk_flags &= ~LK_HAVE_EXCL;
267: lkp->lk_lockholder = LK_NOPROC;
268: lkp->lk_lockthread = 0;
269: if (lkp->lk_waitcount)
270: wakeup((void *)lkp);
271: break;
272:
273: case LK_EXCLUPGRADE:
274: /*
275: * If another process is ahead of us to get an upgrade,
276: * then we want to fail rather than have an intervening
277: * exclusive access.
278: */
279: if (lkp->lk_flags & LK_WANT_UPGRADE) {
280: lkp->lk_sharecount--;
281: COUNT(p, -1);
282: error = EBUSY;
283: break;
284: }
285: /* fall into normal upgrade */
286:
287: case LK_UPGRADE:
288: /*
289: * Upgrade a shared lock to an exclusive one. If another
290: * shared lock has already requested an upgrade to an
291: * exclusive lock, our shared lock is released and an
292: * exclusive lock is requested (which will be granted
293: * after the upgrade). If we return an error, the file
294: * will always be unlocked.
295: */
296: if ((lkp->lk_lockholder == pid &&
297: lkp->lk_lockthread == self) ||
298: lkp->lk_sharecount <= 0)
299: panic("lockmgr: upgrade exclusive lock");
300: lkp->lk_sharecount--;
301: COUNT(p, -1);
302: /*
303: * If we are just polling, check to see if we will block.
304: */
305: if ((extflags & LK_NOWAIT) &&
306: ((lkp->lk_flags & LK_WANT_UPGRADE) ||
307: lkp->lk_sharecount > 1)) {
308: error = EBUSY;
309: break;
310: }
311: if ((lkp->lk_flags & LK_WANT_UPGRADE) == 0) {
312: /*
313: * We are first shared lock to request an upgrade, so
314: * request upgrade and wait for the shared count to
315: * drop to zero, then take exclusive lock.
316: */
317: lkp->lk_flags |= LK_WANT_UPGRADE;
318: ACQUIRE(lkp, error, extflags, lkp->lk_sharecount);
319: lkp->lk_flags &= ~LK_WANT_UPGRADE;
320: if (error)
321: break;
322: lkp->lk_flags |= LK_HAVE_EXCL;
323: lkp->lk_lockholder = pid;
324: lkp->lk_lockthread = self;
325: if (lkp->lk_exclusivecount != 0)
326: panic("lockmgr: non-zero exclusive count");
327: lkp->lk_exclusivecount = 1;
328: COUNT(p, 1);
329: break;
330: }
331: /*
332: * Someone else has requested upgrade. Release our shared
333: * lock, awaken upgrade requestor if we are the last shared
334: * lock, then request an exclusive lock.
335: */
336: if (lkp->lk_sharecount == 0 && lkp->lk_waitcount)
337: wakeup((void *)lkp);
338: /* fall into exclusive request */
339:
340: case LK_EXCLUSIVE:
341: if (lkp->lk_lockholder == pid && lkp->lk_lockthread == self) {
342: /*
343: * Recursive lock.
344: */
345: if ((extflags & LK_CANRECURSE) == 0)
346: panic("lockmgr: locking against myself");
347: lkp->lk_exclusivecount++;
348: COUNT(p, 1);
349: break;
350: }
351: /*
352: * If we are just polling, check to see if we will sleep.
353: */
354: if ((extflags & LK_NOWAIT) && ((lkp->lk_flags &
355: (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) ||
356: lkp->lk_sharecount != 0)) {
357: error = EBUSY;
358: break;
359: }
360: /*
361: * Try to acquire the want_exclusive flag.
362: */
363: ACQUIRE(lkp, error, extflags, lkp->lk_flags &
364: (LK_HAVE_EXCL | LK_WANT_EXCL));
365: if (error)
366: break;
367: lkp->lk_flags |= LK_WANT_EXCL;
368: /*
369: * Wait for shared locks and upgrades to finish.
370: */
371: ACQUIRE(lkp, error, extflags, lkp->lk_sharecount != 0 ||
372: (lkp->lk_flags & LK_WANT_UPGRADE));
373: lkp->lk_flags &= ~LK_WANT_EXCL;
374: if (error)
375: break;
376: lkp->lk_flags |= LK_HAVE_EXCL;
377: lkp->lk_lockholder = pid;
378: lkp->lk_lockthread = self;
379: if (lkp->lk_exclusivecount != 0)
380: panic("lockmgr: non-zero exclusive count");
381: lkp->lk_exclusivecount = 1;
382: COUNT(p, 1);
383: break;
384:
385: case LK_RELEASE:
386: if (lkp->lk_exclusivecount != 0) {
387: if (pid != lkp->lk_lockholder ||
388: lkp->lk_lockthread != self)
389: panic("lockmgr: pid %d, not %s %d unlocking",
390: pid, "exclusive lock holder",
391: lkp->lk_lockholder);
392: lkp->lk_exclusivecount--;
393: COUNT(p, -1);
394: if (lkp->lk_exclusivecount == 0) {
395: lkp->lk_flags &= ~LK_HAVE_EXCL;
396: lkp->lk_lockholder = LK_NOPROC;
397: lkp->lk_lockthread = 0;
398: }
399: } else if (lkp->lk_sharecount != 0) {
400: lkp->lk_sharecount--;
401: COUNT(p, -1);
402: }
403: if (lkp->lk_waitcount)
404: wakeup((void *)lkp);
405: break;
406:
407: case LK_DRAIN:
408: /*
409: * Check that we do not already hold the lock, as it can
410: * never drain if we do. Unfortunately, we have no way to
411: * check for holding a shared lock, but at least we can
412: * check for an exclusive one.
413: */
414: if (lkp->lk_lockholder == pid && lkp->lk_lockthread == self)
415: panic("lockmgr: draining against myself");
416: /*
417: * If we are just polling, check to see if we will sleep.
418: */
419: if ((extflags & LK_NOWAIT) && ((lkp->lk_flags &
420: (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) ||
421: lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0)) {
422: error = EBUSY;
423: break;
424: }
425: PAUSE(lkp, ((lkp->lk_flags &
426: (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) ||
427: lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0));
428: for (error = 0; ((lkp->lk_flags &
429: (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) ||
430: lkp->lk_sharecount != 0 || lkp->lk_waitcount != 0); ) {
431: lkp->lk_flags |= LK_WAITDRAIN;
432: simple_unlock(&lkp->lk_interlock);
433: if (error = tsleep((void *)&lkp->lk_flags, lkp->lk_prio,
434: lkp->lk_wmesg, lkp->lk_timo))
435: return (error);
436: if ((extflags) & LK_SLEEPFAIL)
437: return (ENOLCK);
438: simple_lock(&lkp->lk_interlock);
439: }
440: lkp->lk_flags |= LK_DRAINING | LK_HAVE_EXCL;
441: lkp->lk_lockholder = pid;
442: lkp->lk_lockthread = self;
443: lkp->lk_exclusivecount = 1;
444: COUNT(p, 1);
445: break;
446:
447: default:
448: simple_unlock(&lkp->lk_interlock);
449: panic("lockmgr: unknown locktype request %d",
450: flags & LK_TYPE_MASK);
451: /* NOTREACHED */
452: }
453: if ((lkp->lk_flags & LK_WAITDRAIN) && ((lkp->lk_flags &
454: (LK_HAVE_EXCL | LK_WANT_EXCL | LK_WANT_UPGRADE)) == 0 &&
455: lkp->lk_sharecount == 0 && lkp->lk_waitcount == 0)) {
456: lkp->lk_flags &= ~LK_WAITDRAIN;
457: wakeup((void *)&lkp->lk_flags);
458: }
459: simple_unlock(&lkp->lk_interlock);
460: return (error);
461: }
462:
463: /*
464: * Print out information about state of a lock. Used by VOP_PRINT
465: * routines to display ststus about contained locks.
466: */
467: lockmgr_printinfo(lkp)
468: struct lock__bsd__ *lkp;
469: {
470:
471: if (lkp->lk_sharecount)
472: printf(" lock type %s: SHARED (count %d)", lkp->lk_wmesg,
473: lkp->lk_sharecount);
474: else if (lkp->lk_flags & LK_HAVE_EXCL)
475: printf(" lock type %s: EXCL (count %d) by pid %d",
476: lkp->lk_wmesg, lkp->lk_exclusivecount, lkp->lk_lockholder);
477: if (lkp->lk_waitcount > 0)
478: printf(" with %d pending", lkp->lk_waitcount);
479: }
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