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Annotation of src/sys/kern/kern_mutex.c, Revision 1.43

1.43    ! ad          1: /*     $NetBSD: kern_mutex.c,v 1.42 2008/05/31 13:15:21 ad Exp $       */
1.2       ad          2:
                      3: /*-
1.30      ad          4:  * Copyright (c) 2002, 2006, 2007, 2008 The NetBSD Foundation, Inc.
1.2       ad          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:  *
                     19:  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
                     20:  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
                     21:  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
                     22:  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
                     23:  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
                     24:  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
                     25:  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
                     26:  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
                     27:  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
                     28:  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
                     29:  * POSSIBILITY OF SUCH DAMAGE.
                     30:  */
                     31:
                     32: /*
                     33:  * Kernel mutex implementation, modeled after those found in Solaris,
                     34:  * a description of which can be found in:
                     35:  *
                     36:  *     Solaris Internals: Core Kernel Architecture, Jim Mauro and
                     37:  *         Richard McDougall.
                     38:  */
                     39:
                     40: #define        __MUTEX_PRIVATE
                     41:
                     42: #include <sys/cdefs.h>
1.43    ! ad         43: __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.42 2008/05/31 13:15:21 ad Exp $");
1.2       ad         44:
                     45: #include <sys/param.h>
                     46: #include <sys/proc.h>
                     47: #include <sys/mutex.h>
                     48: #include <sys/sched.h>
                     49: #include <sys/sleepq.h>
                     50: #include <sys/systm.h>
                     51: #include <sys/lockdebug.h>
                     52: #include <sys/kernel.h>
1.24      ad         53: #include <sys/atomic.h>
                     54: #include <sys/intr.h>
1.29      xtraeme    55: #include <sys/lock.h>
1.31      ad         56: #include <sys/pool.h>
1.2       ad         57:
                     58: #include <dev/lockstat.h>
                     59:
1.28      ad         60: #include <machine/lock.h>
                     61:
1.2       ad         62: /*
                     63:  * When not running a debug kernel, spin mutexes are not much
                     64:  * more than an splraiseipl() and splx() pair.
                     65:  */
                     66:
                     67: #if defined(DIAGNOSTIC) || defined(MULTIPROCESSOR) || defined(LOCKDEBUG)
                     68: #define        FULL
                     69: #endif
                     70:
                     71: /*
                     72:  * Debugging support.
                     73:  */
                     74:
                     75: #define        MUTEX_WANTLOCK(mtx)                                     \
1.23      yamt       76:     LOCKDEBUG_WANTLOCK(MUTEX_DEBUG_P(mtx), (mtx),              \
1.40      ad         77:         (uintptr_t)__builtin_return_address(0), false, false)
1.2       ad         78: #define        MUTEX_LOCKED(mtx)                                       \
1.42      ad         79:     LOCKDEBUG_LOCKED(MUTEX_DEBUG_P(mtx), (mtx), NULL,          \
1.2       ad         80:         (uintptr_t)__builtin_return_address(0), 0)
                     81: #define        MUTEX_UNLOCKED(mtx)                                     \
1.23      yamt       82:     LOCKDEBUG_UNLOCKED(MUTEX_DEBUG_P(mtx), (mtx),              \
1.2       ad         83:         (uintptr_t)__builtin_return_address(0), 0)
                     84: #define        MUTEX_ABORT(mtx, msg)                                   \
1.17      ad         85:     mutex_abort(mtx, __func__, msg)
1.2       ad         86:
                     87: #if defined(LOCKDEBUG)
                     88:
                     89: #define        MUTEX_DASSERT(mtx, cond)                                \
                     90: do {                                                           \
                     91:        if (!(cond))                                            \
                     92:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                     93: } while (/* CONSTCOND */ 0);
                     94:
                     95: #else  /* LOCKDEBUG */
                     96:
                     97: #define        MUTEX_DASSERT(mtx, cond)        /* nothing */
                     98:
                     99: #endif /* LOCKDEBUG */
                    100:
                    101: #if defined(DIAGNOSTIC)
                    102:
                    103: #define        MUTEX_ASSERT(mtx, cond)                                 \
                    104: do {                                                           \
                    105:        if (!(cond))                                            \
                    106:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                    107: } while (/* CONSTCOND */ 0)
                    108:
                    109: #else  /* DIAGNOSTIC */
                    110:
                    111: #define        MUTEX_ASSERT(mtx, cond) /* nothing */
                    112:
                    113: #endif /* DIAGNOSTIC */
                    114:
                    115: /*
                    116:  * Spin mutex SPL save / restore.
                    117:  */
1.12      matt      118: #ifndef MUTEX_COUNT_BIAS
                    119: #define        MUTEX_COUNT_BIAS        0
                    120: #endif
1.2       ad        121:
                    122: #define        MUTEX_SPIN_SPLRAISE(mtx)                                        \
                    123: do {                                                                   \
1.36      ad        124:        struct cpu_info *x__ci;                                         \
1.2       ad        125:        int x__cnt, s;                                                  \
1.36      ad        126:        s = splraiseipl(mtx->mtx_ipl);                                  \
                    127:        x__ci = curcpu();                                               \
1.2       ad        128:        x__cnt = x__ci->ci_mtx_count--;                                 \
1.37      ad        129:        __insn_barrier();                                               \
1.12      matt      130:        if (x__cnt == MUTEX_COUNT_BIAS)                                 \
1.2       ad        131:                x__ci->ci_mtx_oldspl = (s);                             \
                    132: } while (/* CONSTCOND */ 0)
                    133:
                    134: #define        MUTEX_SPIN_SPLRESTORE(mtx)                                      \
                    135: do {                                                                   \
                    136:        struct cpu_info *x__ci = curcpu();                              \
                    137:        int s = x__ci->ci_mtx_oldspl;                                   \
                    138:        __insn_barrier();                                               \
1.12      matt      139:        if (++(x__ci->ci_mtx_count) == MUTEX_COUNT_BIAS)                \
1.2       ad        140:                splx(s);                                                \
                    141: } while (/* CONSTCOND */ 0)
                    142:
                    143: /*
                    144:  * For architectures that provide 'simple' mutexes: they provide a
                    145:  * CAS function that is either MP-safe, or does not need to be MP
                    146:  * safe.  Adaptive mutexes on these architectures do not require an
                    147:  * additional interlock.
                    148:  */
                    149:
                    150: #ifdef __HAVE_SIMPLE_MUTEXES
                    151:
                    152: #define        MUTEX_OWNER(owner)                                              \
                    153:        (owner & MUTEX_THREAD)
                    154: #define        MUTEX_HAS_WAITERS(mtx)                                          \
                    155:        (((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
                    156:
1.23      yamt      157: #define        MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug)                         \
1.2       ad        158: do {                                                                   \
1.23      yamt      159:        if (dodebug)                                                    \
                    160:                (mtx)->mtx_owner |= MUTEX_BIT_DEBUG;                    \
1.2       ad        161: } while (/* CONSTCOND */ 0);
                    162:
1.23      yamt      163: #define        MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl)                        \
1.2       ad        164: do {                                                                   \
                    165:        (mtx)->mtx_owner = MUTEX_BIT_SPIN;                              \
1.23      yamt      166:        if (dodebug)                                                    \
                    167:                (mtx)->mtx_owner |= MUTEX_BIT_DEBUG;                    \
1.2       ad        168:        (mtx)->mtx_ipl = makeiplcookie((ipl));                          \
                    169:        __cpu_simple_lock_init(&(mtx)->mtx_lock);                       \
                    170: } while (/* CONSTCOND */ 0)
                    171:
                    172: #define        MUTEX_DESTROY(mtx)                                              \
                    173: do {                                                                   \
                    174:        (mtx)->mtx_owner = MUTEX_THREAD;                                \
                    175: } while (/* CONSTCOND */ 0);
                    176:
                    177: #define        MUTEX_SPIN_P(mtx)               \
                    178:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0)
                    179: #define        MUTEX_ADAPTIVE_P(mtx)           \
                    180:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0)
                    181:
1.23      yamt      182: #define        MUTEX_DEBUG_P(mtx)      (((mtx)->mtx_owner & MUTEX_BIT_DEBUG) != 0)
                    183: #if defined(LOCKDEBUG)
                    184: #define        MUTEX_OWNED(owner)              (((owner) & ~MUTEX_BIT_DEBUG) != 0)
                    185: #define        MUTEX_INHERITDEBUG(new, old)    (new) |= (old) & MUTEX_BIT_DEBUG
                    186: #else /* defined(LOCKDEBUG) */
                    187: #define        MUTEX_OWNED(owner)              ((owner) != 0)
                    188: #define        MUTEX_INHERITDEBUG(new, old)    /* nothing */
                    189: #endif /* defined(LOCKDEBUG) */
1.2       ad        190:
                    191: static inline int
                    192: MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
                    193: {
                    194:        int rv;
1.23      yamt      195:        uintptr_t old = 0;
                    196:        uintptr_t new = curthread;
                    197:
                    198:        MUTEX_INHERITDEBUG(old, mtx->mtx_owner);
                    199:        MUTEX_INHERITDEBUG(new, old);
                    200:        rv = MUTEX_CAS(&mtx->mtx_owner, old, new);
1.7       itohy     201:        MUTEX_RECEIVE(mtx);
1.2       ad        202:        return rv;
                    203: }
                    204:
                    205: static inline int
                    206: MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
                    207: {
                    208:        int rv;
                    209:        rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS);
1.7       itohy     210:        MUTEX_RECEIVE(mtx);
1.2       ad        211:        return rv;
                    212: }
                    213:
                    214: static inline void
                    215: MUTEX_RELEASE(kmutex_t *mtx)
                    216: {
1.23      yamt      217:        uintptr_t new;
                    218:
1.7       itohy     219:        MUTEX_GIVE(mtx);
1.23      yamt      220:        new = 0;
                    221:        MUTEX_INHERITDEBUG(new, mtx->mtx_owner);
                    222:        mtx->mtx_owner = new;
1.2       ad        223: }
1.4       ad        224:
                    225: static inline void
                    226: MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
                    227: {
                    228:        /* nothing */
                    229: }
1.2       ad        230: #endif /* __HAVE_SIMPLE_MUTEXES */
                    231:
                    232: /*
                    233:  * Patch in stubs via strong alias where they are not available.
                    234:  */
                    235:
                    236: #if defined(LOCKDEBUG)
                    237: #undef __HAVE_MUTEX_STUBS
                    238: #undef __HAVE_SPIN_MUTEX_STUBS
                    239: #endif
                    240:
                    241: #ifndef __HAVE_MUTEX_STUBS
1.8       itohy     242: __strong_alias(mutex_enter,mutex_vector_enter);
                    243: __strong_alias(mutex_exit,mutex_vector_exit);
1.2       ad        244: #endif
                    245:
                    246: #ifndef __HAVE_SPIN_MUTEX_STUBS
1.8       itohy     247: __strong_alias(mutex_spin_enter,mutex_vector_enter);
                    248: __strong_alias(mutex_spin_exit,mutex_vector_exit);
1.2       ad        249: #endif
                    250:
                    251: void   mutex_abort(kmutex_t *, const char *, const char *);
                    252: void   mutex_dump(volatile void *);
                    253: int    mutex_onproc(uintptr_t, struct cpu_info **);
                    254:
                    255: lockops_t mutex_spin_lockops = {
                    256:        "Mutex",
1.42      ad        257:        LOCKOPS_SPIN,
1.2       ad        258:        mutex_dump
                    259: };
                    260:
                    261: lockops_t mutex_adaptive_lockops = {
                    262:        "Mutex",
1.42      ad        263:        LOCKOPS_SLEEP,
1.2       ad        264:        mutex_dump
                    265: };
                    266:
1.5       yamt      267: syncobj_t mutex_syncobj = {
                    268:        SOBJ_SLEEPQ_SORTED,
                    269:        turnstile_unsleep,
                    270:        turnstile_changepri,
                    271:        sleepq_lendpri,
1.27      ad        272:        (void *)mutex_owner,
1.5       yamt      273: };
                    274:
1.31      ad        275: /* Mutex cache */
                    276: #define        MUTEX_OBJ_MAGIC 0x5aa3c85d
                    277: struct kmutexobj {
                    278:        kmutex_t        mo_lock;
                    279:        u_int           mo_magic;
                    280:        u_int           mo_refcnt;
                    281: };
                    282:
                    283: static int     mutex_obj_ctor(void *, void *, int);
                    284:
                    285: static pool_cache_t    mutex_obj_cache;
                    286:
1.2       ad        287: /*
                    288:  * mutex_dump:
                    289:  *
                    290:  *     Dump the contents of a mutex structure.
                    291:  */
                    292: void
                    293: mutex_dump(volatile void *cookie)
                    294: {
                    295:        volatile kmutex_t *mtx = cookie;
                    296:
                    297:        printf_nolog("owner field  : %#018lx wait/spin: %16d/%d\n",
                    298:            (long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx),
                    299:            MUTEX_SPIN_P(mtx));
                    300: }
                    301:
                    302: /*
                    303:  * mutex_abort:
                    304:  *
1.3       ad        305:  *     Dump information about an error and panic the system.  This
                    306:  *     generates a lot of machine code in the DIAGNOSTIC case, so
                    307:  *     we ask the compiler to not inline it.
1.2       ad        308:  */
1.43    ! ad        309: void __noinline
1.2       ad        310: mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
                    311: {
                    312:
1.23      yamt      313:        LOCKDEBUG_ABORT(mtx, (MUTEX_SPIN_P(mtx) ?
1.3       ad        314:            &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
1.2       ad        315: }
                    316:
                    317: /*
                    318:  * mutex_init:
                    319:  *
                    320:  *     Initialize a mutex for use.  Note that adaptive mutexes are in
                    321:  *     essence spin mutexes that can sleep to avoid deadlock and wasting
                    322:  *     CPU time.  We can't easily provide a type of mutex that always
                    323:  *     sleeps - see comments in mutex_vector_enter() about releasing
                    324:  *     mutexes unlocked.
                    325:  */
                    326: void
                    327: mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
                    328: {
1.23      yamt      329:        bool dodebug;
1.2       ad        330:
                    331:        memset(mtx, 0, sizeof(*mtx));
                    332:
1.15      ad        333:        switch (type) {
                    334:        case MUTEX_ADAPTIVE:
                    335:                KASSERT(ipl == IPL_NONE);
                    336:                break;
1.22      ad        337:        case MUTEX_DEFAULT:
1.15      ad        338:        case MUTEX_DRIVER:
1.26      ad        339:                if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK ||
                    340:                    ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET ||
                    341:                    ipl == IPL_SOFTSERIAL) {
1.22      ad        342:                        type = MUTEX_ADAPTIVE;
1.26      ad        343:                } else {
1.22      ad        344:                        type = MUTEX_SPIN;
                    345:                }
1.15      ad        346:                break;
                    347:        default:
                    348:                break;
                    349:        }
1.2       ad        350:
                    351:        switch (type) {
1.11      ad        352:        case MUTEX_NODEBUG:
1.23      yamt      353:                dodebug = LOCKDEBUG_ALLOC(mtx, NULL,
1.19      ad        354:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      355:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.11      ad        356:                break;
1.2       ad        357:        case MUTEX_ADAPTIVE:
1.23      yamt      358:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops,
1.19      ad        359:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      360:                MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug);
1.2       ad        361:                break;
                    362:        case MUTEX_SPIN:
1.23      yamt      363:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops,
1.19      ad        364:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      365:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.2       ad        366:                break;
                    367:        default:
                    368:                panic("mutex_init: impossible type");
                    369:                break;
                    370:        }
                    371: }
                    372:
                    373: /*
                    374:  * mutex_destroy:
                    375:  *
                    376:  *     Tear down a mutex.
                    377:  */
                    378: void
                    379: mutex_destroy(kmutex_t *mtx)
                    380: {
                    381:
                    382:        if (MUTEX_ADAPTIVE_P(mtx)) {
                    383:                MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
                    384:                    !MUTEX_HAS_WAITERS(mtx));
                    385:        } else {
1.16      skrll     386:                MUTEX_ASSERT(mtx, !__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock));
1.2       ad        387:        }
                    388:
1.23      yamt      389:        LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), mtx);
1.2       ad        390:        MUTEX_DESTROY(mtx);
                    391: }
                    392:
                    393: /*
                    394:  * mutex_onproc:
                    395:  *
                    396:  *     Return true if an adaptive mutex owner is running on a CPU in the
                    397:  *     system.  If the target is waiting on the kernel big lock, then we
1.15      ad        398:  *     must release it.  This is necessary to avoid deadlock.
1.2       ad        399:  *
                    400:  *     Note that we can't use the mutex owner field as an LWP pointer.  We
                    401:  *     don't have full control over the timing of our execution, and so the
                    402:  *     pointer could be completely invalid by the time we dereference it.
                    403:  */
                    404: #ifdef MULTIPROCESSOR
                    405: int
                    406: mutex_onproc(uintptr_t owner, struct cpu_info **cip)
                    407: {
                    408:        CPU_INFO_ITERATOR cii;
                    409:        struct cpu_info *ci;
                    410:        struct lwp *l;
                    411:
                    412:        if (!MUTEX_OWNED(owner))
                    413:                return 0;
                    414:        l = (struct lwp *)MUTEX_OWNER(owner);
                    415:
1.15      ad        416:        /* See if the target is running on a CPU somewhere. */
1.10      ad        417:        if ((ci = *cip) != NULL && ci->ci_curlwp == l)
1.15      ad        418:                goto run;
                    419:        for (CPU_INFO_FOREACH(cii, ci))
                    420:                if (ci->ci_curlwp == l)
                    421:                        goto run;
1.2       ad        422:
1.15      ad        423:        /* No: it may be safe to block now. */
1.2       ad        424:        *cip = NULL;
                    425:        return 0;
1.15      ad        426:
                    427:  run:
                    428:        /* Target is running; do we need to block? */
                    429:        *cip = ci;
                    430:        return ci->ci_biglock_wanted != l;
1.2       ad        431: }
1.15      ad        432: #endif /* MULTIPROCESSOR */
1.2       ad        433:
                    434: /*
                    435:  * mutex_vector_enter:
                    436:  *
                    437:  *     Support routine for mutex_enter() that must handles all cases.  In
                    438:  *     the LOCKDEBUG case, mutex_enter() is always aliased here, even if
                    439:  *     fast-path stubs are available.  If an mutex_spin_enter() stub is
                    440:  *     not available, then it is also aliased directly here.
                    441:  */
                    442: void
                    443: mutex_vector_enter(kmutex_t *mtx)
                    444: {
                    445:        uintptr_t owner, curthread;
                    446:        turnstile_t *ts;
                    447: #ifdef MULTIPROCESSOR
                    448:        struct cpu_info *ci = NULL;
                    449:        u_int count;
                    450: #endif
                    451:        LOCKSTAT_COUNTER(spincnt);
                    452:        LOCKSTAT_COUNTER(slpcnt);
                    453:        LOCKSTAT_TIMER(spintime);
                    454:        LOCKSTAT_TIMER(slptime);
                    455:        LOCKSTAT_FLAG(lsflag);
                    456:
                    457:        /*
                    458:         * Handle spin mutexes.
                    459:         */
                    460:        if (MUTEX_SPIN_P(mtx)) {
                    461: #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
                    462:                u_int spins = 0;
                    463: #endif
                    464:                MUTEX_SPIN_SPLRAISE(mtx);
                    465:                MUTEX_WANTLOCK(mtx);
                    466: #ifdef FULL
                    467:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
                    468:                        MUTEX_LOCKED(mtx);
                    469:                        return;
                    470:                }
                    471: #if !defined(MULTIPROCESSOR)
                    472:                MUTEX_ABORT(mtx, "locking against myself");
                    473: #else /* !MULTIPROCESSOR */
                    474:
                    475:                LOCKSTAT_ENTER(lsflag);
                    476:                LOCKSTAT_START_TIMER(lsflag, spintime);
                    477:                count = SPINLOCK_BACKOFF_MIN;
                    478:
                    479:                /*
                    480:                 * Spin testing the lock word and do exponential backoff
                    481:                 * to reduce cache line ping-ponging between CPUs.
                    482:                 */
                    483:                do {
                    484:                        if (panicstr != NULL)
                    485:                                break;
1.16      skrll     486:                        while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        487:                                SPINLOCK_BACKOFF(count);
                    488: #ifdef LOCKDEBUG
                    489:                                if (SPINLOCK_SPINOUT(spins))
                    490:                                        MUTEX_ABORT(mtx, "spinout");
                    491: #endif /* LOCKDEBUG */
                    492:                        }
                    493:                } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    494:
                    495:                if (count != SPINLOCK_BACKOFF_MIN) {
                    496:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    497:                        LOCKSTAT_EVENT(lsflag, mtx,
                    498:                            LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    499:                }
                    500:                LOCKSTAT_EXIT(lsflag);
                    501: #endif /* !MULTIPROCESSOR */
                    502: #endif /* FULL */
                    503:                MUTEX_LOCKED(mtx);
                    504:                return;
                    505:        }
                    506:
                    507:        curthread = (uintptr_t)curlwp;
                    508:
                    509:        MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    510:        MUTEX_ASSERT(mtx, curthread != 0);
                    511:        MUTEX_WANTLOCK(mtx);
                    512:
                    513:        if (panicstr == NULL) {
                    514:                LOCKDEBUG_BARRIER(&kernel_lock, 1);
                    515:        }
                    516:
                    517:        LOCKSTAT_ENTER(lsflag);
                    518:
                    519:        /*
                    520:         * Adaptive mutex; spin trying to acquire the mutex.  If we
                    521:         * determine that the owner is not running on a processor,
                    522:         * then we stop spinning, and sleep instead.
                    523:         */
1.34      ad        524:        for (owner = mtx->mtx_owner;;) {
1.2       ad        525:                if (!MUTEX_OWNED(owner)) {
                    526:                        /*
                    527:                         * Mutex owner clear could mean two things:
                    528:                         *
                    529:                         *      * The mutex has been released.
                    530:                         *      * The owner field hasn't been set yet.
                    531:                         *
                    532:                         * Try to acquire it again.  If that fails,
                    533:                         * we'll just loop again.
                    534:                         */
                    535:                        if (MUTEX_ACQUIRE(mtx, curthread))
                    536:                                break;
1.34      ad        537:                        owner = mtx->mtx_owner;
1.2       ad        538:                        continue;
                    539:                }
                    540:
                    541:                if (panicstr != NULL)
                    542:                        return;
                    543:                if (MUTEX_OWNER(owner) == curthread)
                    544:                        MUTEX_ABORT(mtx, "locking against myself");
                    545:
                    546: #ifdef MULTIPROCESSOR
                    547:                /*
                    548:                 * Check to see if the owner is running on a processor.
                    549:                 * If so, then we should just spin, as the owner will
                    550:                 * likely release the lock very soon.
                    551:                 */
                    552:                if (mutex_onproc(owner, &ci)) {
                    553:                        LOCKSTAT_START_TIMER(lsflag, spintime);
                    554:                        count = SPINLOCK_BACKOFF_MIN;
                    555:                        for (;;) {
1.34      ad        556:                                SPINLOCK_BACKOFF(count);
1.2       ad        557:                                owner = mtx->mtx_owner;
                    558:                                if (!mutex_onproc(owner, &ci))
                    559:                                        break;
                    560:                        }
                    561:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    562:                        LOCKSTAT_COUNT(spincnt, 1);
                    563:                        if (!MUTEX_OWNED(owner))
                    564:                                continue;
                    565:                }
                    566: #endif
                    567:
                    568:                ts = turnstile_lookup(mtx);
                    569:
                    570:                /*
                    571:                 * Once we have the turnstile chain interlock, mark the
                    572:                 * mutex has having waiters.  If that fails, spin again:
                    573:                 * chances are that the mutex has been released.
                    574:                 */
                    575:                if (!MUTEX_SET_WAITERS(mtx, owner)) {
                    576:                        turnstile_exit(mtx);
1.34      ad        577:                        owner = mtx->mtx_owner;
1.2       ad        578:                        continue;
                    579:                }
                    580:
                    581: #ifdef MULTIPROCESSOR
                    582:                /*
                    583:                 * mutex_exit() is permitted to release the mutex without
                    584:                 * any interlocking instructions, and the following can
                    585:                 * occur as a result:
                    586:                 *
                    587:                 *  CPU 1: MUTEX_SET_WAITERS()      CPU2: mutex_exit()
                    588:                 * ---------------------------- ----------------------------
                    589:                 *              ..                  acquire cache line
                    590:                 *              ..                   test for waiters
                    591:                 *      acquire cache line    <-      lose cache line
                    592:                 *       lock cache line                   ..
                    593:                 *     verify mutex is held                ..
                    594:                 *          set waiters                    ..
                    595:                 *       unlock cache line                 ..
                    596:                 *        lose cache line     ->    acquire cache line
                    597:                 *              ..                clear lock word, waiters
                    598:                 *        return success
                    599:                 *
                    600:                 * There is a another race that can occur: a third CPU could
                    601:                 * acquire the mutex as soon as it is released.  Since
                    602:                 * adaptive mutexes are primarily spin mutexes, this is not
                    603:                 * something that we need to worry about too much.  What we
                    604:                 * do need to ensure is that the waiters bit gets set.
                    605:                 *
                    606:                 * To allow the unlocked release, we need to make some
                    607:                 * assumptions here:
                    608:                 *
                    609:                 * o Release is the only non-atomic/unlocked operation
                    610:                 *   that can be performed on the mutex.  (It must still
                    611:                 *   be atomic on the local CPU, e.g. in case interrupted
                    612:                 *   or preempted).
                    613:                 *
                    614:                 * o At any given time, MUTEX_SET_WAITERS() can only ever
1.21      pooka     615:                 *   be in progress on one CPU in the system - guaranteed
1.2       ad        616:                 *   by the turnstile chain lock.
                    617:                 *
                    618:                 * o No other operations other than MUTEX_SET_WAITERS()
                    619:                 *   and release can modify a mutex with a non-zero
                    620:                 *   owner field.
                    621:                 *
                    622:                 * o The result of a successful MUTEX_SET_WAITERS() call
                    623:                 *   is an unbuffered write that is immediately visible
                    624:                 *   to all other processors in the system.
                    625:                 *
                    626:                 * o If the holding LWP switches away, it posts a store
                    627:                 *   fence before changing curlwp, ensuring that any
                    628:                 *   overwrite of the mutex waiters flag by mutex_exit()
                    629:                 *   completes before the modification of curlwp becomes
                    630:                 *   visible to this CPU.
                    631:                 *
1.14      yamt      632:                 * o mi_switch() posts a store fence before setting curlwp
1.2       ad        633:                 *   and before resuming execution of an LWP.
                    634:                 *
                    635:                 * o _kernel_lock() posts a store fence before setting
                    636:                 *   curcpu()->ci_biglock_wanted, and after clearing it.
                    637:                 *   This ensures that any overwrite of the mutex waiters
                    638:                 *   flag by mutex_exit() completes before the modification
                    639:                 *   of ci_biglock_wanted becomes visible.
                    640:                 *
                    641:                 * We now post a read memory barrier (after setting the
                    642:                 * waiters field) and check the lock holder's status again.
                    643:                 * Some of the possible outcomes (not an exhaustive list):
                    644:                 *
                    645:                 * 1. The onproc check returns true: the holding LWP is
                    646:                 *    running again.  The lock may be released soon and
                    647:                 *    we should spin.  Importantly, we can't trust the
                    648:                 *    value of the waiters flag.
                    649:                 *
                    650:                 * 2. The onproc check returns false: the holding LWP is
1.39      yamt      651:                 *    not running.  We now have the opportunity to check
1.2       ad        652:                 *    if mutex_exit() has blatted the modifications made
                    653:                 *    by MUTEX_SET_WAITERS().
                    654:                 *
                    655:                 * 3. The onproc check returns false: the holding LWP may
                    656:                 *    or may not be running.  It has context switched at
                    657:                 *    some point during our check.  Again, we have the
                    658:                 *    chance to see if the waiters bit is still set or
                    659:                 *    has been overwritten.
                    660:                 *
                    661:                 * 4. The onproc check returns false: the holding LWP is
                    662:                 *    running on a CPU, but wants the big lock.  It's OK
                    663:                 *    to check the waiters field in this case.
                    664:                 *
                    665:                 * 5. The has-waiters check fails: the mutex has been
                    666:                 *    released, the waiters flag cleared and another LWP
                    667:                 *    now owns the mutex.
                    668:                 *
                    669:                 * 6. The has-waiters check fails: the mutex has been
                    670:                 *    released.
                    671:                 *
                    672:                 * If the waiters bit is not set it's unsafe to go asleep,
                    673:                 * as we might never be awoken.
                    674:                 */
1.24      ad        675:                if ((membar_consumer(), mutex_onproc(owner, &ci)) ||
                    676:                    (membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) {
1.2       ad        677:                        turnstile_exit(mtx);
1.34      ad        678:                        owner = mtx->mtx_owner;
1.2       ad        679:                        continue;
                    680:                }
                    681: #endif /* MULTIPROCESSOR */
                    682:
                    683:                LOCKSTAT_START_TIMER(lsflag, slptime);
                    684:
1.5       yamt      685:                turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
1.2       ad        686:
                    687:                LOCKSTAT_STOP_TIMER(lsflag, slptime);
                    688:                LOCKSTAT_COUNT(slpcnt, 1);
1.34      ad        689:
                    690:                owner = mtx->mtx_owner;
1.2       ad        691:        }
                    692:
                    693:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
                    694:            slpcnt, slptime);
                    695:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
                    696:            spincnt, spintime);
                    697:        LOCKSTAT_EXIT(lsflag);
                    698:
                    699:        MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    700:        MUTEX_LOCKED(mtx);
                    701: }
                    702:
                    703: /*
                    704:  * mutex_vector_exit:
                    705:  *
                    706:  *     Support routine for mutex_exit() that handles all cases.
                    707:  */
                    708: void
                    709: mutex_vector_exit(kmutex_t *mtx)
                    710: {
                    711:        turnstile_t *ts;
                    712:        uintptr_t curthread;
                    713:
                    714:        if (MUTEX_SPIN_P(mtx)) {
                    715: #ifdef FULL
1.33      ad        716:                if (__predict_false(!__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock))) {
                    717:                        if (panicstr != NULL)
                    718:                                return;
1.2       ad        719:                        MUTEX_ABORT(mtx, "exiting unheld spin mutex");
1.33      ad        720:                }
1.2       ad        721:                MUTEX_UNLOCKED(mtx);
                    722:                __cpu_simple_unlock(&mtx->mtx_lock);
                    723: #endif
                    724:                MUTEX_SPIN_SPLRESTORE(mtx);
                    725:                return;
                    726:        }
                    727:
1.11      ad        728:        if (__predict_false((uintptr_t)panicstr | cold)) {
1.2       ad        729:                MUTEX_UNLOCKED(mtx);
                    730:                MUTEX_RELEASE(mtx);
                    731:                return;
                    732:        }
                    733:
                    734:        curthread = (uintptr_t)curlwp;
                    735:        MUTEX_DASSERT(mtx, curthread != 0);
                    736:        MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    737:        MUTEX_UNLOCKED(mtx);
                    738:
1.15      ad        739: #ifdef LOCKDEBUG
                    740:        /*
                    741:         * Avoid having to take the turnstile chain lock every time
                    742:         * around.  Raise the priority level to splhigh() in order
                    743:         * to disable preemption and so make the following atomic.
                    744:         */
                    745:        {
                    746:                int s = splhigh();
                    747:                if (!MUTEX_HAS_WAITERS(mtx)) {
                    748:                        MUTEX_RELEASE(mtx);
                    749:                        splx(s);
                    750:                        return;
                    751:                }
                    752:                splx(s);
                    753:        }
                    754: #endif
                    755:
1.2       ad        756:        /*
                    757:         * Get this lock's turnstile.  This gets the interlock on
                    758:         * the sleep queue.  Once we have that, we can clear the
                    759:         * lock.  If there was no turnstile for the lock, there
                    760:         * were no waiters remaining.
                    761:         */
                    762:        ts = turnstile_lookup(mtx);
                    763:
                    764:        if (ts == NULL) {
                    765:                MUTEX_RELEASE(mtx);
                    766:                turnstile_exit(mtx);
                    767:        } else {
                    768:                MUTEX_RELEASE(mtx);
                    769:                turnstile_wakeup(ts, TS_WRITER_Q,
                    770:                    TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    771:        }
                    772: }
                    773:
1.4       ad        774: #ifndef __HAVE_SIMPLE_MUTEXES
                    775: /*
                    776:  * mutex_wakeup:
                    777:  *
                    778:  *     Support routine for mutex_exit() that wakes up all waiters.
                    779:  *     We assume that the mutex has been released, but it need not
                    780:  *     be.
                    781:  */
                    782: void
                    783: mutex_wakeup(kmutex_t *mtx)
                    784: {
                    785:        turnstile_t *ts;
                    786:
                    787:        ts = turnstile_lookup(mtx);
                    788:        if (ts == NULL) {
                    789:                turnstile_exit(mtx);
                    790:                return;
                    791:        }
                    792:        MUTEX_CLEAR_WAITERS(mtx);
                    793:        turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    794: }
                    795: #endif /* !__HAVE_SIMPLE_MUTEXES */
                    796:
1.2       ad        797: /*
                    798:  * mutex_owned:
                    799:  *
1.3       ad        800:  *     Return true if the current LWP (adaptive) or CPU (spin)
                    801:  *     holds the mutex.
1.2       ad        802:  */
                    803: int
                    804: mutex_owned(kmutex_t *mtx)
                    805: {
                    806:
1.35      ad        807:        if (mtx == NULL)
                    808:                return 0;
1.2       ad        809:        if (MUTEX_ADAPTIVE_P(mtx))
                    810:                return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
                    811: #ifdef FULL
1.16      skrll     812:        return __SIMPLELOCK_LOCKED_P(&mtx->mtx_lock);
1.2       ad        813: #else
                    814:        return 1;
                    815: #endif
                    816: }
                    817:
                    818: /*
                    819:  * mutex_owner:
                    820:  *
1.6       ad        821:  *     Return the current owner of an adaptive mutex.  Used for
                    822:  *     priority inheritance.
1.2       ad        823:  */
1.27      ad        824: lwp_t *
                    825: mutex_owner(kmutex_t *mtx)
1.2       ad        826: {
                    827:
                    828:        MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    829:        return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner);
                    830: }
                    831:
                    832: /*
                    833:  * mutex_tryenter:
                    834:  *
                    835:  *     Try to acquire the mutex; return non-zero if we did.
                    836:  */
                    837: int
                    838: mutex_tryenter(kmutex_t *mtx)
                    839: {
                    840:        uintptr_t curthread;
                    841:
                    842:        /*
                    843:         * Handle spin mutexes.
                    844:         */
                    845:        if (MUTEX_SPIN_P(mtx)) {
                    846:                MUTEX_SPIN_SPLRAISE(mtx);
                    847: #ifdef FULL
                    848:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
1.4       ad        849:                        MUTEX_WANTLOCK(mtx);
1.2       ad        850:                        MUTEX_LOCKED(mtx);
                    851:                        return 1;
                    852:                }
                    853:                MUTEX_SPIN_SPLRESTORE(mtx);
                    854: #else
1.4       ad        855:                MUTEX_WANTLOCK(mtx);
1.2       ad        856:                MUTEX_LOCKED(mtx);
                    857:                return 1;
                    858: #endif
                    859:        } else {
                    860:                curthread = (uintptr_t)curlwp;
                    861:                MUTEX_ASSERT(mtx, curthread != 0);
                    862:                if (MUTEX_ACQUIRE(mtx, curthread)) {
1.4       ad        863:                        MUTEX_WANTLOCK(mtx);
1.2       ad        864:                        MUTEX_LOCKED(mtx);
                    865:                        MUTEX_DASSERT(mtx,
                    866:                            MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    867:                        return 1;
                    868:                }
                    869:        }
                    870:
                    871:        return 0;
                    872: }
                    873:
                    874: #if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL)
                    875: /*
                    876:  * mutex_spin_retry:
                    877:  *
                    878:  *     Support routine for mutex_spin_enter().  Assumes that the caller
                    879:  *     has already raised the SPL, and adjusted counters.
                    880:  */
                    881: void
                    882: mutex_spin_retry(kmutex_t *mtx)
                    883: {
                    884: #ifdef MULTIPROCESSOR
                    885:        u_int count;
                    886:        LOCKSTAT_TIMER(spintime);
                    887:        LOCKSTAT_FLAG(lsflag);
                    888: #ifdef LOCKDEBUG
                    889:        u_int spins = 0;
                    890: #endif /* LOCKDEBUG */
                    891:
                    892:        MUTEX_WANTLOCK(mtx);
                    893:
                    894:        LOCKSTAT_ENTER(lsflag);
                    895:        LOCKSTAT_START_TIMER(lsflag, spintime);
                    896:        count = SPINLOCK_BACKOFF_MIN;
                    897:
                    898:        /*
                    899:         * Spin testing the lock word and do exponential backoff
                    900:         * to reduce cache line ping-ponging between CPUs.
                    901:         */
                    902:        do {
                    903:                if (panicstr != NULL)
                    904:                        break;
1.16      skrll     905:                while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        906:                        SPINLOCK_BACKOFF(count);
                    907: #ifdef LOCKDEBUG
                    908:                        if (SPINLOCK_SPINOUT(spins))
                    909:                                MUTEX_ABORT(mtx, "spinout");
                    910: #endif /* LOCKDEBUG */
                    911:                }
                    912:        } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    913:
                    914:        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    915:        LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    916:        LOCKSTAT_EXIT(lsflag);
                    917:
                    918:        MUTEX_LOCKED(mtx);
                    919: #else  /* MULTIPROCESSOR */
                    920:        MUTEX_ABORT(mtx, "locking against myself");
                    921: #endif /* MULTIPROCESSOR */
                    922: }
                    923: #endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */
1.31      ad        924:
                    925: /*
                    926:  * mutex_obj_init:
                    927:  *
                    928:  *     Initialize the mutex object store.
                    929:  */
                    930: void
                    931: mutex_obj_init(void)
                    932: {
                    933:
                    934:        mutex_obj_cache = pool_cache_init(sizeof(struct kmutexobj),
                    935:            coherency_unit, 0, 0, "mutex", NULL, IPL_NONE, mutex_obj_ctor,
                    936:            NULL, NULL);
                    937: }
                    938:
                    939: /*
                    940:  * mutex_obj_ctor:
                    941:  *
                    942:  *     Initialize a new lock for the cache.
                    943:  */
                    944: static int
                    945: mutex_obj_ctor(void *arg, void *obj, int flags)
                    946: {
                    947:        struct kmutexobj * mo = obj;
                    948:
                    949:        mo->mo_magic = MUTEX_OBJ_MAGIC;
                    950:
                    951:        return 0;
                    952: }
                    953:
                    954: /*
                    955:  * mutex_obj_alloc:
                    956:  *
                    957:  *     Allocate a single lock object.
                    958:  */
                    959: kmutex_t *
                    960: mutex_obj_alloc(kmutex_type_t type, int ipl)
                    961: {
                    962:        struct kmutexobj *mo;
                    963:
                    964:        mo = pool_cache_get(mutex_obj_cache, PR_WAITOK);
                    965:        mutex_init(&mo->mo_lock, type, ipl);
                    966:        mo->mo_refcnt = 1;
                    967:
                    968:        return (kmutex_t *)mo;
                    969: }
                    970:
                    971: /*
                    972:  * mutex_obj_hold:
                    973:  *
                    974:  *     Add a single reference to a lock object.  A reference to the object
                    975:  *     must already be held, and must be held across this call.
                    976:  */
                    977: void
                    978: mutex_obj_hold(kmutex_t *lock)
                    979: {
                    980:        struct kmutexobj *mo = (struct kmutexobj *)lock;
                    981:
                    982:        KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
                    983:        KASSERT(mo->mo_refcnt > 0);
                    984:
                    985:        atomic_inc_uint(&mo->mo_refcnt);
                    986: }
                    987:
                    988: /*
                    989:  * mutex_obj_free:
                    990:  *
                    991:  *     Drop a reference from a lock object.  If the last reference is being
                    992:  *     dropped, free the object and return true.  Otherwise, return false.
                    993:  */
                    994: bool
                    995: mutex_obj_free(kmutex_t *lock)
                    996: {
                    997:        struct kmutexobj *mo = (struct kmutexobj *)lock;
                    998:
                    999:        KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
                   1000:        KASSERT(mo->mo_refcnt > 0);
                   1001:
                   1002:        if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
                   1003:                return false;
                   1004:        }
                   1005:        mutex_destroy(&mo->mo_lock);
                   1006:        pool_cache_put(mutex_obj_cache, mo);
                   1007:        return true;
                   1008: }

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