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Annotation of src/sys/kern/kern_mutex.c, Revision 1.18

1.18    ! dsl         1: /*     $NetBSD: kern_mutex.c,v 1.17 2007/09/17 21:33:34 ad Exp $       */
1.2       ad          2:
                      3: /*-
                      4:  * Copyright (c) 2002, 2006, 2007 The NetBSD Foundation, Inc.
                      5:  * All rights reserved.
                      6:  *
                      7:  * This code is derived from software contributed to The NetBSD Foundation
                      8:  * by Jason R. Thorpe and Andrew Doran.
                      9:  *
                     10:  * Redistribution and use in source and binary forms, with or without
                     11:  * modification, are permitted provided that the following conditions
                     12:  * are met:
                     13:  * 1. Redistributions of source code must retain the above copyright
                     14:  *    notice, this list of conditions and the following disclaimer.
                     15:  * 2. Redistributions in binary form must reproduce the above copyright
                     16:  *    notice, this list of conditions and the following disclaimer in the
                     17:  *    documentation and/or other materials provided with the distribution.
                     18:  * 3. All advertising materials mentioning features or use of this software
                     19:  *    must display the following acknowledgement:
                     20:  *     This product includes software developed by the NetBSD
                     21:  *     Foundation, Inc. and its contributors.
                     22:  * 4. Neither the name of The NetBSD Foundation nor the names of its
                     23:  *    contributors may be used to endorse or promote products derived
                     24:  *    from this software without specific prior written permission.
                     25:  *
                     26:  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
                     27:  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
                     28:  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
                     29:  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
                     30:  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
                     31:  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
                     32:  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
                     33:  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
                     34:  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
                     35:  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
                     36:  * POSSIBILITY OF SUCH DAMAGE.
                     37:  */
                     38:
                     39: /*
                     40:  * Kernel mutex implementation, modeled after those found in Solaris,
                     41:  * a description of which can be found in:
                     42:  *
                     43:  *     Solaris Internals: Core Kernel Architecture, Jim Mauro and
                     44:  *         Richard McDougall.
                     45:  */
                     46:
                     47: #define        __MUTEX_PRIVATE
                     48:
                     49: #include <sys/cdefs.h>
1.18    ! dsl        50: __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.17 2007/09/17 21:33:34 ad Exp $");
        !            51:
        !            52: #include "opt_multiprocessor.h"
1.2       ad         53:
                     54: #include <sys/param.h>
                     55: #include <sys/proc.h>
                     56: #include <sys/mutex.h>
                     57: #include <sys/sched.h>
                     58: #include <sys/sleepq.h>
                     59: #include <sys/systm.h>
                     60: #include <sys/lockdebug.h>
                     61: #include <sys/kernel.h>
                     62:
                     63: #include <dev/lockstat.h>
                     64:
                     65: #include <machine/intr.h>
                     66:
                     67: /*
                     68:  * When not running a debug kernel, spin mutexes are not much
                     69:  * more than an splraiseipl() and splx() pair.
                     70:  */
                     71:
                     72: #if defined(DIAGNOSTIC) || defined(MULTIPROCESSOR) || defined(LOCKDEBUG)
                     73: #define        FULL
                     74: #endif
                     75:
                     76: /*
                     77:  * Debugging support.
                     78:  */
                     79:
                     80: #define        MUTEX_WANTLOCK(mtx)                                     \
                     81:     LOCKDEBUG_WANTLOCK(MUTEX_GETID(mtx),                       \
                     82:         (uintptr_t)__builtin_return_address(0), 0)
                     83: #define        MUTEX_LOCKED(mtx)                                       \
                     84:     LOCKDEBUG_LOCKED(MUTEX_GETID(mtx),                         \
                     85:         (uintptr_t)__builtin_return_address(0), 0)
                     86: #define        MUTEX_UNLOCKED(mtx)                                     \
                     87:     LOCKDEBUG_UNLOCKED(MUTEX_GETID(mtx),                       \
                     88:         (uintptr_t)__builtin_return_address(0), 0)
                     89: #define        MUTEX_ABORT(mtx, msg)                                   \
1.17      ad         90:     mutex_abort(mtx, __func__, msg)
1.2       ad         91:
                     92: #if defined(LOCKDEBUG)
                     93:
                     94: #define        MUTEX_DASSERT(mtx, cond)                                \
                     95: do {                                                           \
                     96:        if (!(cond))                                            \
                     97:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                     98: } while (/* CONSTCOND */ 0);
                     99:
                    100: #else  /* LOCKDEBUG */
                    101:
                    102: #define        MUTEX_DASSERT(mtx, cond)        /* nothing */
                    103:
                    104: #endif /* LOCKDEBUG */
                    105:
                    106: #if defined(DIAGNOSTIC)
                    107:
                    108: #define        MUTEX_ASSERT(mtx, cond)                                 \
                    109: do {                                                           \
                    110:        if (!(cond))                                            \
                    111:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                    112: } while (/* CONSTCOND */ 0)
                    113:
                    114: #else  /* DIAGNOSTIC */
                    115:
                    116: #define        MUTEX_ASSERT(mtx, cond) /* nothing */
                    117:
                    118: #endif /* DIAGNOSTIC */
                    119:
                    120: /*
                    121:  * Spin mutex SPL save / restore.
                    122:  */
1.12      matt      123: #ifndef MUTEX_COUNT_BIAS
                    124: #define        MUTEX_COUNT_BIAS        0
                    125: #endif
1.2       ad        126:
                    127: #define        MUTEX_SPIN_SPLRAISE(mtx)                                        \
                    128: do {                                                                   \
                    129:        struct cpu_info *x__ci = curcpu();                              \
                    130:        int x__cnt, s;                                                  \
                    131:        x__cnt = x__ci->ci_mtx_count--;                                 \
                    132:        s = splraiseipl(mtx->mtx_ipl);                                  \
1.12      matt      133:        if (x__cnt == MUTEX_COUNT_BIAS)                                 \
1.2       ad        134:                x__ci->ci_mtx_oldspl = (s);                             \
                    135: } while (/* CONSTCOND */ 0)
                    136:
                    137: #define        MUTEX_SPIN_SPLRESTORE(mtx)                                      \
                    138: do {                                                                   \
                    139:        struct cpu_info *x__ci = curcpu();                              \
                    140:        int s = x__ci->ci_mtx_oldspl;                                   \
                    141:        __insn_barrier();                                               \
1.12      matt      142:        if (++(x__ci->ci_mtx_count) == MUTEX_COUNT_BIAS)                \
1.2       ad        143:                splx(s);                                                \
                    144: } while (/* CONSTCOND */ 0)
                    145:
                    146: /*
                    147:  * For architectures that provide 'simple' mutexes: they provide a
                    148:  * CAS function that is either MP-safe, or does not need to be MP
                    149:  * safe.  Adaptive mutexes on these architectures do not require an
                    150:  * additional interlock.
                    151:  */
                    152:
                    153: #ifdef __HAVE_SIMPLE_MUTEXES
                    154:
                    155: #define        MUTEX_OWNER(owner)                                              \
                    156:        (owner & MUTEX_THREAD)
                    157: #define        MUTEX_OWNED(owner)                                              \
                    158:        (owner != 0)
                    159: #define        MUTEX_HAS_WAITERS(mtx)                                          \
                    160:        (((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
                    161:
                    162: #define        MUTEX_INITIALIZE_ADAPTIVE(mtx, id)                              \
                    163: do {                                                                   \
                    164:        (mtx)->mtx_id = (id);                                           \
                    165: } while (/* CONSTCOND */ 0);
                    166:
                    167: #define        MUTEX_INITIALIZE_SPIN(mtx, id, ipl)                             \
                    168: do {                                                                   \
                    169:        (mtx)->mtx_owner = MUTEX_BIT_SPIN;                              \
                    170:        (mtx)->mtx_ipl = makeiplcookie((ipl));                          \
                    171:        (mtx)->mtx_id = (id);                                           \
                    172:        __cpu_simple_lock_init(&(mtx)->mtx_lock);                       \
                    173: } while (/* CONSTCOND */ 0)
                    174:
                    175: #define        MUTEX_DESTROY(mtx)                                              \
                    176: do {                                                                   \
                    177:        (mtx)->mtx_owner = MUTEX_THREAD;                                \
                    178:        (mtx)->mtx_id = -1;                                             \
                    179: } while (/* CONSTCOND */ 0);
                    180:
                    181: #define        MUTEX_SPIN_P(mtx)               \
                    182:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0)
                    183: #define        MUTEX_ADAPTIVE_P(mtx)           \
                    184:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0)
                    185:
                    186: #define        MUTEX_GETID(mtx)                ((mtx)->mtx_id)
                    187:
                    188: static inline int
                    189: MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
                    190: {
                    191:        int rv;
                    192:        rv = MUTEX_CAS(&mtx->mtx_owner, 0UL, curthread);
1.7       itohy     193:        MUTEX_RECEIVE(mtx);
1.2       ad        194:        return rv;
                    195: }
                    196:
                    197: static inline int
                    198: MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
                    199: {
                    200:        int rv;
                    201:        rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS);
1.7       itohy     202:        MUTEX_RECEIVE(mtx);
1.2       ad        203:        return rv;
                    204: }
                    205:
                    206: static inline void
                    207: MUTEX_RELEASE(kmutex_t *mtx)
                    208: {
1.7       itohy     209:        MUTEX_GIVE(mtx);
1.2       ad        210:        mtx->mtx_owner = 0;
                    211: }
1.4       ad        212:
                    213: static inline void
                    214: MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
                    215: {
                    216:        /* nothing */
                    217: }
1.2       ad        218: #endif /* __HAVE_SIMPLE_MUTEXES */
                    219:
                    220: /*
                    221:  * Patch in stubs via strong alias where they are not available.
                    222:  */
                    223:
                    224: #if defined(LOCKDEBUG)
                    225: #undef __HAVE_MUTEX_STUBS
                    226: #undef __HAVE_SPIN_MUTEX_STUBS
                    227: #endif
                    228:
                    229: #ifndef __HAVE_MUTEX_STUBS
1.8       itohy     230: __strong_alias(mutex_enter,mutex_vector_enter);
                    231: __strong_alias(mutex_exit,mutex_vector_exit);
1.2       ad        232: #endif
                    233:
                    234: #ifndef __HAVE_SPIN_MUTEX_STUBS
1.8       itohy     235: __strong_alias(mutex_spin_enter,mutex_vector_enter);
                    236: __strong_alias(mutex_spin_exit,mutex_vector_exit);
1.2       ad        237: #endif
                    238:
                    239: void   mutex_abort(kmutex_t *, const char *, const char *);
                    240: void   mutex_dump(volatile void *);
                    241: int    mutex_onproc(uintptr_t, struct cpu_info **);
1.6       ad        242: static struct lwp *mutex_owner(wchan_t);
1.2       ad        243:
                    244: lockops_t mutex_spin_lockops = {
                    245:        "Mutex",
                    246:        0,
                    247:        mutex_dump
                    248: };
                    249:
                    250: lockops_t mutex_adaptive_lockops = {
                    251:        "Mutex",
                    252:        1,
                    253:        mutex_dump
                    254: };
                    255:
1.5       yamt      256: syncobj_t mutex_syncobj = {
                    257:        SOBJ_SLEEPQ_SORTED,
                    258:        turnstile_unsleep,
                    259:        turnstile_changepri,
                    260:        sleepq_lendpri,
1.6       ad        261:        mutex_owner,
1.5       yamt      262: };
                    263:
1.2       ad        264: /*
                    265:  * mutex_dump:
                    266:  *
                    267:  *     Dump the contents of a mutex structure.
                    268:  */
                    269: void
                    270: mutex_dump(volatile void *cookie)
                    271: {
                    272:        volatile kmutex_t *mtx = cookie;
                    273:
                    274:        printf_nolog("owner field  : %#018lx wait/spin: %16d/%d\n",
                    275:            (long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx),
                    276:            MUTEX_SPIN_P(mtx));
                    277: }
                    278:
                    279: /*
                    280:  * mutex_abort:
                    281:  *
1.3       ad        282:  *     Dump information about an error and panic the system.  This
                    283:  *     generates a lot of machine code in the DIAGNOSTIC case, so
                    284:  *     we ask the compiler to not inline it.
1.2       ad        285:  */
1.8       itohy     286:
                    287: #if __GNUC_PREREQ__(3, 0)
                    288: __attribute ((noinline)) __attribute ((noreturn))
                    289: #endif
                    290: void
1.2       ad        291: mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
                    292: {
                    293:
                    294:        LOCKDEBUG_ABORT(MUTEX_GETID(mtx), mtx, (MUTEX_SPIN_P(mtx) ?
1.3       ad        295:            &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
1.2       ad        296:        /* NOTREACHED */
                    297: }
                    298:
                    299: /*
                    300:  * mutex_init:
                    301:  *
                    302:  *     Initialize a mutex for use.  Note that adaptive mutexes are in
                    303:  *     essence spin mutexes that can sleep to avoid deadlock and wasting
                    304:  *     CPU time.  We can't easily provide a type of mutex that always
                    305:  *     sleeps - see comments in mutex_vector_enter() about releasing
                    306:  *     mutexes unlocked.
                    307:  */
                    308: void
                    309: mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
                    310: {
                    311:        u_int id;
                    312:
                    313:        memset(mtx, 0, sizeof(*mtx));
                    314:
1.15      ad        315:        switch (type) {
                    316:        case MUTEX_ADAPTIVE:
                    317:        case MUTEX_DEFAULT:
                    318:                KASSERT(ipl == IPL_NONE);
                    319:                break;
                    320:        case MUTEX_DRIVER:
1.2       ad        321:                type = (ipl == IPL_NONE ? MUTEX_ADAPTIVE : MUTEX_SPIN);
1.15      ad        322:                break;
                    323:        default:
                    324:                break;
                    325:        }
1.2       ad        326:
                    327:        switch (type) {
1.11      ad        328:        case MUTEX_NODEBUG:
                    329:                id = LOCKDEBUG_ALLOC(mtx, NULL);
1.15      ad        330:                MUTEX_INITIALIZE_SPIN(mtx, id, ipl);
1.11      ad        331:                break;
1.2       ad        332:        case MUTEX_ADAPTIVE:
                    333:        case MUTEX_DEFAULT:
                    334:                id = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops);
                    335:                MUTEX_INITIALIZE_ADAPTIVE(mtx, id);
                    336:                break;
                    337:        case MUTEX_SPIN:
                    338:                id = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops);
                    339:                MUTEX_INITIALIZE_SPIN(mtx, id, ipl);
                    340:                break;
                    341:        default:
                    342:                panic("mutex_init: impossible type");
                    343:                break;
                    344:        }
                    345: }
                    346:
                    347: /*
                    348:  * mutex_destroy:
                    349:  *
                    350:  *     Tear down a mutex.
                    351:  */
                    352: void
                    353: mutex_destroy(kmutex_t *mtx)
                    354: {
                    355:
                    356:        if (MUTEX_ADAPTIVE_P(mtx)) {
                    357:                MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
                    358:                    !MUTEX_HAS_WAITERS(mtx));
                    359:        } else {
1.16      skrll     360:                MUTEX_ASSERT(mtx, !__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock));
1.2       ad        361:        }
                    362:
                    363:        LOCKDEBUG_FREE(mtx, MUTEX_GETID(mtx));
                    364:        MUTEX_DESTROY(mtx);
                    365: }
                    366:
                    367: /*
                    368:  * mutex_onproc:
                    369:  *
                    370:  *     Return true if an adaptive mutex owner is running on a CPU in the
                    371:  *     system.  If the target is waiting on the kernel big lock, then we
1.15      ad        372:  *     must release it.  This is necessary to avoid deadlock.
1.2       ad        373:  *
                    374:  *     Note that we can't use the mutex owner field as an LWP pointer.  We
                    375:  *     don't have full control over the timing of our execution, and so the
                    376:  *     pointer could be completely invalid by the time we dereference it.
                    377:  */
                    378: #ifdef MULTIPROCESSOR
                    379: int
                    380: mutex_onproc(uintptr_t owner, struct cpu_info **cip)
                    381: {
                    382:        CPU_INFO_ITERATOR cii;
                    383:        struct cpu_info *ci;
                    384:        struct lwp *l;
                    385:
                    386:        if (!MUTEX_OWNED(owner))
                    387:                return 0;
                    388:        l = (struct lwp *)MUTEX_OWNER(owner);
                    389:
1.15      ad        390:        /* See if the target is running on a CPU somewhere. */
1.10      ad        391:        if ((ci = *cip) != NULL && ci->ci_curlwp == l)
1.15      ad        392:                goto run;
                    393:        for (CPU_INFO_FOREACH(cii, ci))
                    394:                if (ci->ci_curlwp == l)
                    395:                        goto run;
1.2       ad        396:
1.15      ad        397:        /* No: it may be safe to block now. */
1.2       ad        398:        *cip = NULL;
                    399:        return 0;
1.15      ad        400:
                    401:  run:
                    402:        /* Target is running; do we need to block? */
                    403:        *cip = ci;
                    404:        return ci->ci_biglock_wanted != l;
1.2       ad        405: }
1.15      ad        406: #endif /* MULTIPROCESSOR */
1.2       ad        407:
                    408: /*
                    409:  * mutex_vector_enter:
                    410:  *
                    411:  *     Support routine for mutex_enter() that must handles all cases.  In
                    412:  *     the LOCKDEBUG case, mutex_enter() is always aliased here, even if
                    413:  *     fast-path stubs are available.  If an mutex_spin_enter() stub is
                    414:  *     not available, then it is also aliased directly here.
                    415:  */
                    416: void
                    417: mutex_vector_enter(kmutex_t *mtx)
                    418: {
                    419:        uintptr_t owner, curthread;
                    420:        turnstile_t *ts;
                    421: #ifdef MULTIPROCESSOR
                    422:        struct cpu_info *ci = NULL;
                    423:        u_int count;
                    424: #endif
                    425:        LOCKSTAT_COUNTER(spincnt);
                    426:        LOCKSTAT_COUNTER(slpcnt);
                    427:        LOCKSTAT_TIMER(spintime);
                    428:        LOCKSTAT_TIMER(slptime);
                    429:        LOCKSTAT_FLAG(lsflag);
                    430:
                    431:        /*
                    432:         * Handle spin mutexes.
                    433:         */
                    434:        if (MUTEX_SPIN_P(mtx)) {
                    435: #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
                    436:                u_int spins = 0;
                    437: #endif
                    438:                MUTEX_SPIN_SPLRAISE(mtx);
                    439:                MUTEX_WANTLOCK(mtx);
                    440: #ifdef FULL
                    441:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
                    442:                        MUTEX_LOCKED(mtx);
                    443:                        return;
                    444:                }
                    445: #if !defined(MULTIPROCESSOR)
                    446:                MUTEX_ABORT(mtx, "locking against myself");
                    447: #else /* !MULTIPROCESSOR */
                    448:
                    449:                LOCKSTAT_ENTER(lsflag);
                    450:                LOCKSTAT_START_TIMER(lsflag, spintime);
                    451:                count = SPINLOCK_BACKOFF_MIN;
                    452:
                    453:                /*
                    454:                 * Spin testing the lock word and do exponential backoff
                    455:                 * to reduce cache line ping-ponging between CPUs.
                    456:                 */
                    457:                do {
                    458:                        if (panicstr != NULL)
                    459:                                break;
1.16      skrll     460:                        while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        461:                                SPINLOCK_BACKOFF(count);
                    462: #ifdef LOCKDEBUG
                    463:                                if (SPINLOCK_SPINOUT(spins))
                    464:                                        MUTEX_ABORT(mtx, "spinout");
                    465: #endif /* LOCKDEBUG */
                    466:                        }
                    467:                } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    468:
                    469:                if (count != SPINLOCK_BACKOFF_MIN) {
                    470:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    471:                        LOCKSTAT_EVENT(lsflag, mtx,
                    472:                            LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    473:                }
                    474:                LOCKSTAT_EXIT(lsflag);
                    475: #endif /* !MULTIPROCESSOR */
                    476: #endif /* FULL */
                    477:                MUTEX_LOCKED(mtx);
                    478:                return;
                    479:        }
                    480:
                    481:        curthread = (uintptr_t)curlwp;
                    482:
                    483:        MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    484:        MUTEX_ASSERT(mtx, curthread != 0);
                    485:        MUTEX_WANTLOCK(mtx);
                    486:
                    487: #ifdef LOCKDEBUG
                    488:        if (panicstr == NULL) {
                    489:                simple_lock_only_held(NULL, "mutex_enter");
                    490: #ifdef MULTIPROCESSOR
                    491:                LOCKDEBUG_BARRIER(&kernel_lock, 1);
                    492: #else
                    493:                LOCKDEBUG_BARRIER(NULL, 1);
                    494: #endif
                    495:        }
                    496: #endif
                    497:
                    498:        LOCKSTAT_ENTER(lsflag);
                    499:
                    500:        /*
                    501:         * Adaptive mutex; spin trying to acquire the mutex.  If we
                    502:         * determine that the owner is not running on a processor,
                    503:         * then we stop spinning, and sleep instead.
                    504:         */
                    505:        for (;;) {
                    506:                owner = mtx->mtx_owner;
                    507:                if (!MUTEX_OWNED(owner)) {
                    508:                        /*
                    509:                         * Mutex owner clear could mean two things:
                    510:                         *
                    511:                         *      * The mutex has been released.
                    512:                         *      * The owner field hasn't been set yet.
                    513:                         *
                    514:                         * Try to acquire it again.  If that fails,
                    515:                         * we'll just loop again.
                    516:                         */
                    517:                        if (MUTEX_ACQUIRE(mtx, curthread))
                    518:                                break;
                    519:                        continue;
                    520:                }
                    521:
                    522:                if (panicstr != NULL)
                    523:                        return;
                    524:                if (MUTEX_OWNER(owner) == curthread)
                    525:                        MUTEX_ABORT(mtx, "locking against myself");
                    526:
                    527: #ifdef MULTIPROCESSOR
                    528:                /*
                    529:                 * Check to see if the owner is running on a processor.
                    530:                 * If so, then we should just spin, as the owner will
                    531:                 * likely release the lock very soon.
                    532:                 */
                    533:                if (mutex_onproc(owner, &ci)) {
                    534:                        LOCKSTAT_START_TIMER(lsflag, spintime);
                    535:                        count = SPINLOCK_BACKOFF_MIN;
                    536:                        for (;;) {
                    537:                                owner = mtx->mtx_owner;
                    538:                                if (!mutex_onproc(owner, &ci))
                    539:                                        break;
                    540:                                SPINLOCK_BACKOFF(count);
                    541:                        }
                    542:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    543:                        LOCKSTAT_COUNT(spincnt, 1);
                    544:                        if (!MUTEX_OWNED(owner))
                    545:                                continue;
                    546:                }
                    547: #endif
                    548:
                    549:                ts = turnstile_lookup(mtx);
                    550:
                    551:                /*
                    552:                 * Once we have the turnstile chain interlock, mark the
                    553:                 * mutex has having waiters.  If that fails, spin again:
                    554:                 * chances are that the mutex has been released.
                    555:                 */
                    556:                if (!MUTEX_SET_WAITERS(mtx, owner)) {
                    557:                        turnstile_exit(mtx);
                    558:                        continue;
                    559:                }
                    560:
                    561: #ifdef MULTIPROCESSOR
                    562:                /*
                    563:                 * mutex_exit() is permitted to release the mutex without
                    564:                 * any interlocking instructions, and the following can
                    565:                 * occur as a result:
                    566:                 *
                    567:                 *  CPU 1: MUTEX_SET_WAITERS()      CPU2: mutex_exit()
                    568:                 * ---------------------------- ----------------------------
                    569:                 *              ..                  acquire cache line
                    570:                 *              ..                   test for waiters
                    571:                 *      acquire cache line    <-      lose cache line
                    572:                 *       lock cache line                   ..
                    573:                 *     verify mutex is held                ..
                    574:                 *          set waiters                    ..
                    575:                 *       unlock cache line                 ..
                    576:                 *        lose cache line     ->    acquire cache line
                    577:                 *              ..                clear lock word, waiters
                    578:                 *        return success
                    579:                 *
                    580:                 * There is a another race that can occur: a third CPU could
                    581:                 * acquire the mutex as soon as it is released.  Since
                    582:                 * adaptive mutexes are primarily spin mutexes, this is not
                    583:                 * something that we need to worry about too much.  What we
                    584:                 * do need to ensure is that the waiters bit gets set.
                    585:                 *
                    586:                 * To allow the unlocked release, we need to make some
                    587:                 * assumptions here:
                    588:                 *
                    589:                 * o Release is the only non-atomic/unlocked operation
                    590:                 *   that can be performed on the mutex.  (It must still
                    591:                 *   be atomic on the local CPU, e.g. in case interrupted
                    592:                 *   or preempted).
                    593:                 *
                    594:                 * o At any given time, MUTEX_SET_WAITERS() can only ever
                    595:                 *   be in progress on one CPU in the system - guarenteed
                    596:                 *   by the turnstile chain lock.
                    597:                 *
                    598:                 * o No other operations other than MUTEX_SET_WAITERS()
                    599:                 *   and release can modify a mutex with a non-zero
                    600:                 *   owner field.
                    601:                 *
                    602:                 * o The result of a successful MUTEX_SET_WAITERS() call
                    603:                 *   is an unbuffered write that is immediately visible
                    604:                 *   to all other processors in the system.
                    605:                 *
                    606:                 * o If the holding LWP switches away, it posts a store
                    607:                 *   fence before changing curlwp, ensuring that any
                    608:                 *   overwrite of the mutex waiters flag by mutex_exit()
                    609:                 *   completes before the modification of curlwp becomes
                    610:                 *   visible to this CPU.
                    611:                 *
1.14      yamt      612:                 * o mi_switch() posts a store fence before setting curlwp
1.2       ad        613:                 *   and before resuming execution of an LWP.
                    614:                 *
                    615:                 * o _kernel_lock() posts a store fence before setting
                    616:                 *   curcpu()->ci_biglock_wanted, and after clearing it.
                    617:                 *   This ensures that any overwrite of the mutex waiters
                    618:                 *   flag by mutex_exit() completes before the modification
                    619:                 *   of ci_biglock_wanted becomes visible.
                    620:                 *
                    621:                 * We now post a read memory barrier (after setting the
                    622:                 * waiters field) and check the lock holder's status again.
                    623:                 * Some of the possible outcomes (not an exhaustive list):
                    624:                 *
                    625:                 * 1. The onproc check returns true: the holding LWP is
                    626:                 *    running again.  The lock may be released soon and
                    627:                 *    we should spin.  Importantly, we can't trust the
                    628:                 *    value of the waiters flag.
                    629:                 *
                    630:                 * 2. The onproc check returns false: the holding LWP is
                    631:                 *    not running.  We now have the oppertunity to check
                    632:                 *    if mutex_exit() has blatted the modifications made
                    633:                 *    by MUTEX_SET_WAITERS().
                    634:                 *
                    635:                 * 3. The onproc check returns false: the holding LWP may
                    636:                 *    or may not be running.  It has context switched at
                    637:                 *    some point during our check.  Again, we have the
                    638:                 *    chance to see if the waiters bit is still set or
                    639:                 *    has been overwritten.
                    640:                 *
                    641:                 * 4. The onproc check returns false: the holding LWP is
                    642:                 *    running on a CPU, but wants the big lock.  It's OK
                    643:                 *    to check the waiters field in this case.
                    644:                 *
                    645:                 * 5. The has-waiters check fails: the mutex has been
                    646:                 *    released, the waiters flag cleared and another LWP
                    647:                 *    now owns the mutex.
                    648:                 *
                    649:                 * 6. The has-waiters check fails: the mutex has been
                    650:                 *    released.
                    651:                 *
                    652:                 * If the waiters bit is not set it's unsafe to go asleep,
                    653:                 * as we might never be awoken.
                    654:                 */
1.13      ad        655:                if ((mb_read(), mutex_onproc(owner, &ci)) ||
                    656:                    (mb_read(), !MUTEX_HAS_WAITERS(mtx))) {
1.2       ad        657:                        turnstile_exit(mtx);
                    658:                        continue;
                    659:                }
                    660: #endif /* MULTIPROCESSOR */
                    661:
                    662:                LOCKSTAT_START_TIMER(lsflag, slptime);
                    663:
1.5       yamt      664:                turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
1.2       ad        665:
                    666:                LOCKSTAT_STOP_TIMER(lsflag, slptime);
                    667:                LOCKSTAT_COUNT(slpcnt, 1);
                    668:        }
                    669:
                    670:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
                    671:            slpcnt, slptime);
                    672:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
                    673:            spincnt, spintime);
                    674:        LOCKSTAT_EXIT(lsflag);
                    675:
                    676:        MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    677:        MUTEX_LOCKED(mtx);
                    678: }
                    679:
                    680: /*
                    681:  * mutex_vector_exit:
                    682:  *
                    683:  *     Support routine for mutex_exit() that handles all cases.
                    684:  */
                    685: void
                    686: mutex_vector_exit(kmutex_t *mtx)
                    687: {
                    688:        turnstile_t *ts;
                    689:        uintptr_t curthread;
                    690:
                    691:        if (MUTEX_SPIN_P(mtx)) {
                    692: #ifdef FULL
1.16      skrll     693:                if (!__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock))
1.2       ad        694:                        MUTEX_ABORT(mtx, "exiting unheld spin mutex");
                    695:                MUTEX_UNLOCKED(mtx);
                    696:                __cpu_simple_unlock(&mtx->mtx_lock);
                    697: #endif
                    698:                MUTEX_SPIN_SPLRESTORE(mtx);
                    699:                return;
                    700:        }
                    701:
1.11      ad        702:        if (__predict_false((uintptr_t)panicstr | cold)) {
1.2       ad        703:                MUTEX_UNLOCKED(mtx);
                    704:                MUTEX_RELEASE(mtx);
                    705:                return;
                    706:        }
                    707:
                    708:        curthread = (uintptr_t)curlwp;
                    709:        MUTEX_DASSERT(mtx, curthread != 0);
                    710:        MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    711:        MUTEX_UNLOCKED(mtx);
                    712:
1.15      ad        713: #ifdef LOCKDEBUG
                    714:        /*
                    715:         * Avoid having to take the turnstile chain lock every time
                    716:         * around.  Raise the priority level to splhigh() in order
                    717:         * to disable preemption and so make the following atomic.
                    718:         */
                    719:        {
                    720:                int s = splhigh();
                    721:                if (!MUTEX_HAS_WAITERS(mtx)) {
                    722:                        MUTEX_RELEASE(mtx);
                    723:                        splx(s);
                    724:                        return;
                    725:                }
                    726:                splx(s);
                    727:        }
                    728: #endif
                    729:
1.2       ad        730:        /*
                    731:         * Get this lock's turnstile.  This gets the interlock on
                    732:         * the sleep queue.  Once we have that, we can clear the
                    733:         * lock.  If there was no turnstile for the lock, there
                    734:         * were no waiters remaining.
                    735:         */
                    736:        ts = turnstile_lookup(mtx);
                    737:
                    738:        if (ts == NULL) {
                    739:                MUTEX_RELEASE(mtx);
                    740:                turnstile_exit(mtx);
                    741:        } else {
                    742:                MUTEX_RELEASE(mtx);
                    743:                turnstile_wakeup(ts, TS_WRITER_Q,
                    744:                    TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    745:        }
                    746: }
                    747:
1.4       ad        748: #ifndef __HAVE_SIMPLE_MUTEXES
                    749: /*
                    750:  * mutex_wakeup:
                    751:  *
                    752:  *     Support routine for mutex_exit() that wakes up all waiters.
                    753:  *     We assume that the mutex has been released, but it need not
                    754:  *     be.
                    755:  */
                    756: void
                    757: mutex_wakeup(kmutex_t *mtx)
                    758: {
                    759:        turnstile_t *ts;
                    760:
                    761:        ts = turnstile_lookup(mtx);
                    762:        if (ts == NULL) {
                    763:                turnstile_exit(mtx);
                    764:                return;
                    765:        }
                    766:        MUTEX_CLEAR_WAITERS(mtx);
                    767:        turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    768: }
                    769: #endif /* !__HAVE_SIMPLE_MUTEXES */
                    770:
1.2       ad        771: /*
                    772:  * mutex_owned:
                    773:  *
1.3       ad        774:  *     Return true if the current LWP (adaptive) or CPU (spin)
                    775:  *     holds the mutex.
1.2       ad        776:  */
                    777: int
                    778: mutex_owned(kmutex_t *mtx)
                    779: {
                    780:
                    781:        if (MUTEX_ADAPTIVE_P(mtx))
                    782:                return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
                    783: #ifdef FULL
1.16      skrll     784:        return __SIMPLELOCK_LOCKED_P(&mtx->mtx_lock);
1.2       ad        785: #else
                    786:        return 1;
                    787: #endif
                    788: }
                    789:
                    790: /*
                    791:  * mutex_owner:
                    792:  *
1.6       ad        793:  *     Return the current owner of an adaptive mutex.  Used for
                    794:  *     priority inheritance.
1.2       ad        795:  */
1.6       ad        796: static struct lwp *
                    797: mutex_owner(wchan_t obj)
1.2       ad        798: {
1.6       ad        799:        kmutex_t *mtx = (void *)(uintptr_t)obj; /* discard qualifiers */
1.2       ad        800:
                    801:        MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    802:        return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner);
                    803: }
                    804:
                    805: /*
                    806:  * mutex_tryenter:
                    807:  *
                    808:  *     Try to acquire the mutex; return non-zero if we did.
                    809:  */
                    810: int
                    811: mutex_tryenter(kmutex_t *mtx)
                    812: {
                    813:        uintptr_t curthread;
                    814:
                    815:        /*
                    816:         * Handle spin mutexes.
                    817:         */
                    818:        if (MUTEX_SPIN_P(mtx)) {
                    819:                MUTEX_SPIN_SPLRAISE(mtx);
                    820: #ifdef FULL
                    821:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
1.4       ad        822:                        MUTEX_WANTLOCK(mtx);
1.2       ad        823:                        MUTEX_LOCKED(mtx);
                    824:                        return 1;
                    825:                }
                    826:                MUTEX_SPIN_SPLRESTORE(mtx);
                    827: #else
1.4       ad        828:                MUTEX_WANTLOCK(mtx);
1.2       ad        829:                MUTEX_LOCKED(mtx);
                    830:                return 1;
                    831: #endif
                    832:        } else {
                    833:                curthread = (uintptr_t)curlwp;
                    834:                MUTEX_ASSERT(mtx, curthread != 0);
                    835:                if (MUTEX_ACQUIRE(mtx, curthread)) {
1.4       ad        836:                        MUTEX_WANTLOCK(mtx);
1.2       ad        837:                        MUTEX_LOCKED(mtx);
                    838:                        MUTEX_DASSERT(mtx,
                    839:                            MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    840:                        return 1;
                    841:                }
                    842:        }
                    843:
                    844:        return 0;
                    845: }
                    846:
                    847: #if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL)
                    848: /*
                    849:  * mutex_spin_retry:
                    850:  *
                    851:  *     Support routine for mutex_spin_enter().  Assumes that the caller
                    852:  *     has already raised the SPL, and adjusted counters.
                    853:  */
                    854: void
                    855: mutex_spin_retry(kmutex_t *mtx)
                    856: {
                    857: #ifdef MULTIPROCESSOR
                    858:        u_int count;
                    859:        LOCKSTAT_TIMER(spintime);
                    860:        LOCKSTAT_FLAG(lsflag);
                    861: #ifdef LOCKDEBUG
                    862:        u_int spins = 0;
                    863: #endif /* LOCKDEBUG */
                    864:
                    865:        MUTEX_WANTLOCK(mtx);
                    866:
                    867:        LOCKSTAT_ENTER(lsflag);
                    868:        LOCKSTAT_START_TIMER(lsflag, spintime);
                    869:        count = SPINLOCK_BACKOFF_MIN;
                    870:
                    871:        /*
                    872:         * Spin testing the lock word and do exponential backoff
                    873:         * to reduce cache line ping-ponging between CPUs.
                    874:         */
                    875:        do {
                    876:                if (panicstr != NULL)
                    877:                        break;
1.16      skrll     878:                while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        879:                        SPINLOCK_BACKOFF(count);
                    880: #ifdef LOCKDEBUG
                    881:                        if (SPINLOCK_SPINOUT(spins))
                    882:                                MUTEX_ABORT(mtx, "spinout");
                    883: #endif /* LOCKDEBUG */
                    884:                }
                    885:        } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    886:
                    887:        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    888:        LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    889:        LOCKSTAT_EXIT(lsflag);
                    890:
                    891:        MUTEX_LOCKED(mtx);
                    892: #else  /* MULTIPROCESSOR */
                    893:        MUTEX_ABORT(mtx, "locking against myself");
                    894: #endif /* MULTIPROCESSOR */
                    895: }
                    896: #endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */

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