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Annotation of Net2/vm/kern_lock.c, revision 1.1

1.1     ! root        1: /* 
        !             2:  * Copyright (c) 1991 Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * This code is derived from software contributed to Berkeley by
        !             6:  * The Mach Operating System project at Carnegie-Mellon University.
        !             7:  *
        !             8:  * Redistribution and use in source and binary forms, with or without
        !             9:  * modification, are permitted provided that the following conditions
        !            10:  * are met:
        !            11:  * 1. Redistributions of source code must retain the above copyright
        !            12:  *    notice, this list of conditions and the following disclaimer.
        !            13:  * 2. Redistributions in binary form must reproduce the above copyright
        !            14:  *    notice, this list of conditions and the following disclaimer in the
        !            15:  *    documentation and/or other materials provided with the distribution.
        !            16:  * 3. All advertising materials mentioning features or use of this software
        !            17:  *    must display the following acknowledgement:
        !            18:  *     This product includes software developed by the University of
        !            19:  *     California, Berkeley and its contributors.
        !            20:  * 4. Neither the name of the University nor the names of its contributors
        !            21:  *    may be used to endorse or promote products derived from this software
        !            22:  *    without specific prior written permission.
        !            23:  *
        !            24:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            25:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            26:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            27:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            28:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            29:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            30:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            31:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            32:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            33:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            34:  * SUCH DAMAGE.
        !            35:  *
        !            36:  *     @(#)kern_lock.c 7.4 (Berkeley) 4/21/91
        !            37:  *
        !            38:  *
        !            39:  * Copyright (c) 1987, 1990 Carnegie-Mellon University.
        !            40:  * All rights reserved.
        !            41:  *
        !            42:  * Authors: Avadis Tevanian, Jr., Michael Wayne Young
        !            43:  * 
        !            44:  * Permission to use, copy, modify and distribute this software and
        !            45:  * its documentation is hereby granted, provided that both the copyright
        !            46:  * notice and this permission notice appear in all copies of the
        !            47:  * software, derivative works or modified versions, and any portions
        !            48:  * thereof, and that both notices appear in supporting documentation.
        !            49:  * 
        !            50:  * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS" 
        !            51:  * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND 
        !            52:  * FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
        !            53:  * 
        !            54:  * Carnegie Mellon requests users of this software to return to
        !            55:  *
        !            56:  *  Software Distribution Coordinator  or  [email protected]
        !            57:  *  School of Computer Science
        !            58:  *  Carnegie Mellon University
        !            59:  *  Pittsburgh PA 15213-3890
        !            60:  *
        !            61:  * any improvements or extensions that they make and grant Carnegie the
        !            62:  * rights to redistribute these changes.
        !            63:  */
        !            64: 
        !            65: /*
        !            66:  *     Locking primitives implementation
        !            67:  */
        !            68: 
        !            69: #include "param.h"
        !            70: #include "vm_param.h"
        !            71: #include "lock.h"
        !            72: 
        !            73: /* XXX */
        !            74: #include "proc.h"
        !            75: typedef        int *thread_t;
        !            76: #define        current_thread()        ((thread_t)&curproc->p_thread)
        !            77: /* XXX */
        !            78: 
        !            79: #if    NCPUS > 1
        !            80: 
        !            81: /*
        !            82:  *     Module:         lock
        !            83:  *     Function:
        !            84:  *             Provide reader/writer sychronization.
        !            85:  *     Implementation:
        !            86:  *             Simple interlock on a bit.  Readers first interlock
        !            87:  *             increment the reader count, then let go.  Writers hold
        !            88:  *             the interlock (thus preventing further readers), and
        !            89:  *             wait for already-accepted readers to go away.
        !            90:  */
        !            91: 
        !            92: /*
        !            93:  *     The simple-lock routines are the primitives out of which
        !            94:  *     the lock package is built.  The implementation is left
        !            95:  *     to the machine-dependent code.
        !            96:  */
        !            97: 
        !            98: #ifdef notdef
        !            99: /*
        !           100:  *     A sample implementation of simple locks.
        !           101:  *     assumes:
        !           102:  *             boolean_t test_and_set(boolean_t *)
        !           103:  *                     indivisibly sets the boolean to TRUE
        !           104:  *                     and returns its old value
        !           105:  *             and that setting a boolean to FALSE is indivisible.
        !           106:  */
        !           107: /*
        !           108:  *     simple_lock_init initializes a simple lock.  A simple lock
        !           109:  *     may only be used for exclusive locks.
        !           110:  */
        !           111: 
        !           112: void simple_lock_init(l)
        !           113:        simple_lock_t   l;
        !           114: {
        !           115:        *(boolean_t *)l = FALSE;
        !           116: }
        !           117: 
        !           118: void simple_lock(l)
        !           119:        simple_lock_t   l;
        !           120: {
        !           121:        while (test_and_set((boolean_t *)l))
        !           122:                continue;
        !           123: }
        !           124: 
        !           125: void simple_unlock(l)
        !           126:        simple_lock_t   l;
        !           127: {
        !           128:        *(boolean_t *)l = FALSE;
        !           129: }
        !           130: 
        !           131: boolean_t simple_lock_try(l)
        !           132:        simple_lock_t   l;
        !           133: {
        !           134:        return (!test_and_set((boolean_t *)l));
        !           135: }
        !           136: #endif notdef
        !           137: #endif NCPUS > 1
        !           138: 
        !           139: #if    NCPUS > 1
        !           140: int lock_wait_time = 100;
        !           141: #else  NCPUS > 1
        !           142: 
        !           143:        /*
        !           144:         *      It is silly to spin on a uni-processor as if we
        !           145:         *      thought something magical would happen to the
        !           146:         *      want_write bit while we are executing.
        !           147:         */
        !           148: int lock_wait_time = 0;
        !           149: #endif NCPUS > 1
        !           150: 
        !           151: 
        !           152: /*
        !           153:  *     Routine:        lock_init
        !           154:  *     Function:
        !           155:  *             Initialize a lock; required before use.
        !           156:  *             Note that clients declare the "struct lock"
        !           157:  *             variables and then initialize them, rather
        !           158:  *             than getting a new one from this module.
        !           159:  */
        !           160: void lock_init(l, can_sleep)
        !           161:        lock_t          l;
        !           162:        boolean_t       can_sleep;
        !           163: {
        !           164:        bzero(l, sizeof(lock_data_t));
        !           165:        simple_lock_init(&l->interlock);
        !           166:        l->want_write = FALSE;
        !           167:        l->want_upgrade = FALSE;
        !           168:        l->read_count = 0;
        !           169:        l->can_sleep = can_sleep;
        !           170:        l->thread = (char *)-1;         /* XXX */
        !           171:        l->recursion_depth = 0;
        !           172: }
        !           173: 
        !           174: void lock_sleepable(l, can_sleep)
        !           175:        lock_t          l;
        !           176:        boolean_t       can_sleep;
        !           177: {
        !           178:        simple_lock(&l->interlock);
        !           179:        l->can_sleep = can_sleep;
        !           180:        simple_unlock(&l->interlock);
        !           181: }
        !           182: 
        !           183: 
        !           184: /*
        !           185:  *     Sleep locks.  These use the same data structure and algorithm
        !           186:  *     as the spin locks, but the process sleeps while it is waiting
        !           187:  *     for the lock.  These work on uniprocessor systems.
        !           188:  */
        !           189: 
        !           190: void lock_write(l)
        !           191:        register lock_t l;
        !           192: {
        !           193:        register int    i;
        !           194: 
        !           195:        simple_lock(&l->interlock);
        !           196: 
        !           197:        if (((thread_t)l->thread) == current_thread()) {
        !           198:                /*
        !           199:                 *      Recursive lock.
        !           200:                 */
        !           201:                l->recursion_depth++;
        !           202:                simple_unlock(&l->interlock);
        !           203:                return;
        !           204:        }
        !           205: 
        !           206:        /*
        !           207:         *      Try to acquire the want_write bit.
        !           208:         */
        !           209:        while (l->want_write) {
        !           210:                if ((i = lock_wait_time) > 0) {
        !           211:                        simple_unlock(&l->interlock);
        !           212:                        while (--i > 0 && l->want_write)
        !           213:                                continue;
        !           214:                        simple_lock(&l->interlock);
        !           215:                }
        !           216: 
        !           217:                if (l->can_sleep && l->want_write) {
        !           218:                        l->waiting = TRUE;
        !           219:                        thread_sleep((int) l, &l->interlock, FALSE);
        !           220:                        simple_lock(&l->interlock);
        !           221:                }
        !           222:        }
        !           223:        l->want_write = TRUE;
        !           224: 
        !           225:        /* Wait for readers (and upgrades) to finish */
        !           226: 
        !           227:        while ((l->read_count != 0) || l->want_upgrade) {
        !           228:                if ((i = lock_wait_time) > 0) {
        !           229:                        simple_unlock(&l->interlock);
        !           230:                        while (--i > 0 && (l->read_count != 0 ||
        !           231:                                        l->want_upgrade))
        !           232:                                continue;
        !           233:                        simple_lock(&l->interlock);
        !           234:                }
        !           235: 
        !           236:                if (l->can_sleep && (l->read_count != 0 || l->want_upgrade)) {
        !           237:                        l->waiting = TRUE;
        !           238:                        thread_sleep((int) l, &l->interlock, FALSE);
        !           239:                        simple_lock(&l->interlock);
        !           240:                }
        !           241:        }
        !           242:        simple_unlock(&l->interlock);
        !           243: }
        !           244: 
        !           245: void lock_done(l)
        !           246:        register lock_t l;
        !           247: {
        !           248:        simple_lock(&l->interlock);
        !           249: 
        !           250:        if (l->read_count != 0)
        !           251:                l->read_count--;
        !           252:        else
        !           253:        if (l->recursion_depth != 0)
        !           254:                l->recursion_depth--;
        !           255:        else
        !           256:        if (l->want_upgrade)
        !           257:                l->want_upgrade = FALSE;
        !           258:        else
        !           259:                l->want_write = FALSE;
        !           260: 
        !           261:        if (l->waiting) {
        !           262:                l->waiting = FALSE;
        !           263:                thread_wakeup((int) l);
        !           264:        }
        !           265:        simple_unlock(&l->interlock);
        !           266: }
        !           267: 
        !           268: void lock_read(l)
        !           269:        register lock_t l;
        !           270: {
        !           271:        register int    i;
        !           272: 
        !           273:        simple_lock(&l->interlock);
        !           274: 
        !           275:        if (((thread_t)l->thread) == current_thread()) {
        !           276:                /*
        !           277:                 *      Recursive lock.
        !           278:                 */
        !           279:                l->read_count++;
        !           280:                simple_unlock(&l->interlock);
        !           281:                return;
        !           282:        }
        !           283: 
        !           284:        while (l->want_write || l->want_upgrade) {
        !           285:                if ((i = lock_wait_time) > 0) {
        !           286:                        simple_unlock(&l->interlock);
        !           287:                        while (--i > 0 && (l->want_write || l->want_upgrade))
        !           288:                                continue;
        !           289:                        simple_lock(&l->interlock);
        !           290:                }
        !           291: 
        !           292:                if (l->can_sleep && (l->want_write || l->want_upgrade)) {
        !           293:                        l->waiting = TRUE;
        !           294:                        thread_sleep((int) l, &l->interlock, FALSE);
        !           295:                        simple_lock(&l->interlock);
        !           296:                }
        !           297:        }
        !           298: 
        !           299:        l->read_count++;
        !           300:        simple_unlock(&l->interlock);
        !           301: }
        !           302: 
        !           303: /*
        !           304:  *     Routine:        lock_read_to_write
        !           305:  *     Function:
        !           306:  *             Improves a read-only lock to one with
        !           307:  *             write permission.  If another reader has
        !           308:  *             already requested an upgrade to a write lock,
        !           309:  *             no lock is held upon return.
        !           310:  *
        !           311:  *             Returns TRUE if the upgrade *failed*.
        !           312:  */
        !           313: boolean_t lock_read_to_write(l)
        !           314:        register lock_t l;
        !           315: {
        !           316:        register int    i;
        !           317: 
        !           318:        simple_lock(&l->interlock);
        !           319: 
        !           320:        l->read_count--;
        !           321: 
        !           322:        if (((thread_t)l->thread) == current_thread()) {
        !           323:                /*
        !           324:                 *      Recursive lock.
        !           325:                 */
        !           326:                l->recursion_depth++;
        !           327:                simple_unlock(&l->interlock);
        !           328:                return(FALSE);
        !           329:        }
        !           330: 
        !           331:        if (l->want_upgrade) {
        !           332:                /*
        !           333:                 *      Someone else has requested upgrade.
        !           334:                 *      Since we've released a read lock, wake
        !           335:                 *      him up.
        !           336:                 */
        !           337:                if (l->waiting) {
        !           338:                        l->waiting = FALSE;
        !           339:                        thread_wakeup((int) l);
        !           340:                }
        !           341: 
        !           342:                simple_unlock(&l->interlock);
        !           343:                return (TRUE);
        !           344:        }
        !           345: 
        !           346:        l->want_upgrade = TRUE;
        !           347: 
        !           348:        while (l->read_count != 0) {
        !           349:                if ((i = lock_wait_time) > 0) {
        !           350:                        simple_unlock(&l->interlock);
        !           351:                        while (--i > 0 && l->read_count != 0)
        !           352:                                continue;
        !           353:                        simple_lock(&l->interlock);
        !           354:                }
        !           355: 
        !           356:                if (l->can_sleep && l->read_count != 0) {
        !           357:                        l->waiting = TRUE;
        !           358:                        thread_sleep((int) l, &l->interlock, FALSE);
        !           359:                        simple_lock(&l->interlock);
        !           360:                }
        !           361:        }
        !           362: 
        !           363:        simple_unlock(&l->interlock);
        !           364:        return (FALSE);
        !           365: }
        !           366: 
        !           367: void lock_write_to_read(l)
        !           368:        register lock_t l;
        !           369: {
        !           370:        simple_lock(&l->interlock);
        !           371: 
        !           372:        l->read_count++;
        !           373:        if (l->recursion_depth != 0)
        !           374:                l->recursion_depth--;
        !           375:        else
        !           376:        if (l->want_upgrade)
        !           377:                l->want_upgrade = FALSE;
        !           378:        else
        !           379:                l->want_write = FALSE;
        !           380: 
        !           381:        if (l->waiting) {
        !           382:                l->waiting = FALSE;
        !           383:                thread_wakeup((int) l);
        !           384:        }
        !           385: 
        !           386:        simple_unlock(&l->interlock);
        !           387: }
        !           388: 
        !           389: 
        !           390: /*
        !           391:  *     Routine:        lock_try_write
        !           392:  *     Function:
        !           393:  *             Tries to get a write lock.
        !           394:  *
        !           395:  *             Returns FALSE if the lock is not held on return.
        !           396:  */
        !           397: 
        !           398: boolean_t lock_try_write(l)
        !           399:        register lock_t l;
        !           400: {
        !           401: 
        !           402:        simple_lock(&l->interlock);
        !           403: 
        !           404:        if (((thread_t)l->thread) == current_thread()) {
        !           405:                /*
        !           406:                 *      Recursive lock
        !           407:                 */
        !           408:                l->recursion_depth++;
        !           409:                simple_unlock(&l->interlock);
        !           410:                return(TRUE);
        !           411:        }
        !           412: 
        !           413:        if (l->want_write || l->want_upgrade || l->read_count) {
        !           414:                /*
        !           415:                 *      Can't get lock.
        !           416:                 */
        !           417:                simple_unlock(&l->interlock);
        !           418:                return(FALSE);
        !           419:        }
        !           420: 
        !           421:        /*
        !           422:         *      Have lock.
        !           423:         */
        !           424: 
        !           425:        l->want_write = TRUE;
        !           426:        simple_unlock(&l->interlock);
        !           427:        return(TRUE);
        !           428: }
        !           429: 
        !           430: /*
        !           431:  *     Routine:        lock_try_read
        !           432:  *     Function:
        !           433:  *             Tries to get a read lock.
        !           434:  *
        !           435:  *             Returns FALSE if the lock is not held on return.
        !           436:  */
        !           437: 
        !           438: boolean_t lock_try_read(l)
        !           439:        register lock_t l;
        !           440: {
        !           441:        simple_lock(&l->interlock);
        !           442: 
        !           443:        if (((thread_t)l->thread) == current_thread()) {
        !           444:                /*
        !           445:                 *      Recursive lock
        !           446:                 */
        !           447:                l->read_count++;
        !           448:                simple_unlock(&l->interlock);
        !           449:                return(TRUE);
        !           450:        }
        !           451: 
        !           452:        if (l->want_write || l->want_upgrade) {
        !           453:                simple_unlock(&l->interlock);
        !           454:                return(FALSE);
        !           455:        }
        !           456: 
        !           457:        l->read_count++;
        !           458:        simple_unlock(&l->interlock);
        !           459:        return(TRUE);
        !           460: }
        !           461: 
        !           462: /*
        !           463:  *     Routine:        lock_try_read_to_write
        !           464:  *     Function:
        !           465:  *             Improves a read-only lock to one with
        !           466:  *             write permission.  If another reader has
        !           467:  *             already requested an upgrade to a write lock,
        !           468:  *             the read lock is still held upon return.
        !           469:  *
        !           470:  *             Returns FALSE if the upgrade *failed*.
        !           471:  */
        !           472: boolean_t lock_try_read_to_write(l)
        !           473:        register lock_t l;
        !           474: {
        !           475: 
        !           476:        simple_lock(&l->interlock);
        !           477: 
        !           478:        if (((thread_t)l->thread) == current_thread()) {
        !           479:                /*
        !           480:                 *      Recursive lock
        !           481:                 */
        !           482:                l->read_count--;
        !           483:                l->recursion_depth++;
        !           484:                simple_unlock(&l->interlock);
        !           485:                return(TRUE);
        !           486:        }
        !           487: 
        !           488:        if (l->want_upgrade) {
        !           489:                simple_unlock(&l->interlock);
        !           490:                return(FALSE);
        !           491:        }
        !           492:        l->want_upgrade = TRUE;
        !           493:        l->read_count--;
        !           494: 
        !           495:        while (l->read_count != 0) {
        !           496:                l->waiting = TRUE;
        !           497:                thread_sleep((int) l, &l->interlock, FALSE);
        !           498:                simple_lock(&l->interlock);
        !           499:        }
        !           500: 
        !           501:        simple_unlock(&l->interlock);
        !           502:        return(TRUE);
        !           503: }
        !           504: 
        !           505: /*
        !           506:  *     Allow a process that has a lock for write to acquire it
        !           507:  *     recursively (for read, write, or update).
        !           508:  */
        !           509: void lock_set_recursive(l)
        !           510:        lock_t          l;
        !           511: {
        !           512:        simple_lock(&l->interlock);
        !           513:        if (!l->want_write) {
        !           514:                panic("lock_set_recursive: don't have write lock");
        !           515:        }
        !           516:        l->thread = (char *) current_thread();
        !           517:        simple_unlock(&l->interlock);
        !           518: }
        !           519: 
        !           520: /*
        !           521:  *     Prevent a lock from being re-acquired.
        !           522:  */
        !           523: void lock_clear_recursive(l)
        !           524:        lock_t          l;
        !           525: {
        !           526:        simple_lock(&l->interlock);
        !           527:        if (((thread_t) l->thread) != current_thread()) {
        !           528:                panic("lock_clear_recursive: wrong thread");
        !           529:        }
        !           530:        if (l->recursion_depth == 0)
        !           531:                l->thread = (char *)-1;         /* XXX */
        !           532:        simple_unlock(&l->interlock);
        !           533: }

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