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Annotation of src/sys/kern/kern_mutex.c, Revision 1.39

1.39    ! yamt        1: /*     $NetBSD: kern_mutex.c,v 1.38 2008/04/28 20:24:03 martin 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>
1.39    ! yamt       43: __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.38 2008/04/28 20:24:03 martin Exp $");
1.18      dsl        44:
                     45: #include "opt_multiprocessor.h"
1.2       ad         46:
                     47: #include <sys/param.h>
                     48: #include <sys/proc.h>
                     49: #include <sys/mutex.h>
                     50: #include <sys/sched.h>
                     51: #include <sys/sleepq.h>
                     52: #include <sys/systm.h>
                     53: #include <sys/lockdebug.h>
                     54: #include <sys/kernel.h>
1.24      ad         55: #include <sys/atomic.h>
                     56: #include <sys/intr.h>
1.29      xtraeme    57: #include <sys/lock.h>
1.31      ad         58: #include <sys/pool.h>
1.2       ad         59:
                     60: #include <dev/lockstat.h>
                     61:
1.28      ad         62: #include <machine/lock.h>
                     63:
1.2       ad         64: /*
                     65:  * When not running a debug kernel, spin mutexes are not much
                     66:  * more than an splraiseipl() and splx() pair.
                     67:  */
                     68:
                     69: #if defined(DIAGNOSTIC) || defined(MULTIPROCESSOR) || defined(LOCKDEBUG)
                     70: #define        FULL
                     71: #endif
                     72:
                     73: /*
                     74:  * Debugging support.
                     75:  */
                     76:
                     77: #define        MUTEX_WANTLOCK(mtx)                                     \
1.23      yamt       78:     LOCKDEBUG_WANTLOCK(MUTEX_DEBUG_P(mtx), (mtx),              \
1.2       ad         79:         (uintptr_t)__builtin_return_address(0), 0)
                     80: #define        MUTEX_LOCKED(mtx)                                       \
1.23      yamt       81:     LOCKDEBUG_LOCKED(MUTEX_DEBUG_P(mtx), (mtx),                        \
1.2       ad         82:         (uintptr_t)__builtin_return_address(0), 0)
                     83: #define        MUTEX_UNLOCKED(mtx)                                     \
1.23      yamt       84:     LOCKDEBUG_UNLOCKED(MUTEX_DEBUG_P(mtx), (mtx),              \
1.2       ad         85:         (uintptr_t)__builtin_return_address(0), 0)
                     86: #define        MUTEX_ABORT(mtx, msg)                                   \
1.17      ad         87:     mutex_abort(mtx, __func__, msg)
1.2       ad         88:
                     89: #if defined(LOCKDEBUG)
                     90:
                     91: #define        MUTEX_DASSERT(mtx, cond)                                \
                     92: do {                                                           \
                     93:        if (!(cond))                                            \
                     94:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                     95: } while (/* CONSTCOND */ 0);
                     96:
                     97: #else  /* LOCKDEBUG */
                     98:
                     99: #define        MUTEX_DASSERT(mtx, cond)        /* nothing */
                    100:
                    101: #endif /* LOCKDEBUG */
                    102:
                    103: #if defined(DIAGNOSTIC)
                    104:
                    105: #define        MUTEX_ASSERT(mtx, cond)                                 \
                    106: do {                                                           \
                    107:        if (!(cond))                                            \
                    108:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                    109: } while (/* CONSTCOND */ 0)
                    110:
                    111: #else  /* DIAGNOSTIC */
                    112:
                    113: #define        MUTEX_ASSERT(mtx, cond) /* nothing */
                    114:
                    115: #endif /* DIAGNOSTIC */
                    116:
                    117: /*
                    118:  * Spin mutex SPL save / restore.
                    119:  */
1.12      matt      120: #ifndef MUTEX_COUNT_BIAS
                    121: #define        MUTEX_COUNT_BIAS        0
                    122: #endif
1.2       ad        123:
                    124: #define        MUTEX_SPIN_SPLRAISE(mtx)                                        \
                    125: do {                                                                   \
1.36      ad        126:        struct cpu_info *x__ci;                                         \
1.2       ad        127:        int x__cnt, s;                                                  \
1.36      ad        128:        s = splraiseipl(mtx->mtx_ipl);                                  \
                    129:        x__ci = curcpu();                                               \
1.2       ad        130:        x__cnt = x__ci->ci_mtx_count--;                                 \
1.37      ad        131:        __insn_barrier();                                               \
1.12      matt      132:        if (x__cnt == MUTEX_COUNT_BIAS)                                 \
1.2       ad        133:                x__ci->ci_mtx_oldspl = (s);                             \
                    134: } while (/* CONSTCOND */ 0)
                    135:
                    136: #define        MUTEX_SPIN_SPLRESTORE(mtx)                                      \
                    137: do {                                                                   \
                    138:        struct cpu_info *x__ci = curcpu();                              \
                    139:        int s = x__ci->ci_mtx_oldspl;                                   \
                    140:        __insn_barrier();                                               \
1.12      matt      141:        if (++(x__ci->ci_mtx_count) == MUTEX_COUNT_BIAS)                \
1.2       ad        142:                splx(s);                                                \
                    143: } while (/* CONSTCOND */ 0)
                    144:
                    145: /*
                    146:  * For architectures that provide 'simple' mutexes: they provide a
                    147:  * CAS function that is either MP-safe, or does not need to be MP
                    148:  * safe.  Adaptive mutexes on these architectures do not require an
                    149:  * additional interlock.
                    150:  */
                    151:
                    152: #ifdef __HAVE_SIMPLE_MUTEXES
                    153:
                    154: #define        MUTEX_OWNER(owner)                                              \
                    155:        (owner & MUTEX_THREAD)
                    156: #define        MUTEX_HAS_WAITERS(mtx)                                          \
                    157:        (((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
                    158:
1.23      yamt      159: #define        MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug)                         \
1.2       ad        160: do {                                                                   \
1.23      yamt      161:        if (dodebug)                                                    \
                    162:                (mtx)->mtx_owner |= MUTEX_BIT_DEBUG;                    \
1.2       ad        163: } while (/* CONSTCOND */ 0);
                    164:
1.23      yamt      165: #define        MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl)                        \
1.2       ad        166: do {                                                                   \
                    167:        (mtx)->mtx_owner = MUTEX_BIT_SPIN;                              \
1.23      yamt      168:        if (dodebug)                                                    \
                    169:                (mtx)->mtx_owner |= MUTEX_BIT_DEBUG;                    \
1.2       ad        170:        (mtx)->mtx_ipl = makeiplcookie((ipl));                          \
                    171:        __cpu_simple_lock_init(&(mtx)->mtx_lock);                       \
                    172: } while (/* CONSTCOND */ 0)
                    173:
                    174: #define        MUTEX_DESTROY(mtx)                                              \
                    175: do {                                                                   \
                    176:        (mtx)->mtx_owner = MUTEX_THREAD;                                \
                    177: } while (/* CONSTCOND */ 0);
                    178:
                    179: #define        MUTEX_SPIN_P(mtx)               \
                    180:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0)
                    181: #define        MUTEX_ADAPTIVE_P(mtx)           \
                    182:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0)
                    183:
1.23      yamt      184: #define        MUTEX_DEBUG_P(mtx)      (((mtx)->mtx_owner & MUTEX_BIT_DEBUG) != 0)
                    185: #if defined(LOCKDEBUG)
                    186: #define        MUTEX_OWNED(owner)              (((owner) & ~MUTEX_BIT_DEBUG) != 0)
                    187: #define        MUTEX_INHERITDEBUG(new, old)    (new) |= (old) & MUTEX_BIT_DEBUG
                    188: #else /* defined(LOCKDEBUG) */
                    189: #define        MUTEX_OWNED(owner)              ((owner) != 0)
                    190: #define        MUTEX_INHERITDEBUG(new, old)    /* nothing */
                    191: #endif /* defined(LOCKDEBUG) */
1.2       ad        192:
                    193: static inline int
                    194: MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
                    195: {
                    196:        int rv;
1.23      yamt      197:        uintptr_t old = 0;
                    198:        uintptr_t new = curthread;
                    199:
                    200:        MUTEX_INHERITDEBUG(old, mtx->mtx_owner);
                    201:        MUTEX_INHERITDEBUG(new, old);
                    202:        rv = MUTEX_CAS(&mtx->mtx_owner, old, new);
1.7       itohy     203:        MUTEX_RECEIVE(mtx);
1.2       ad        204:        return rv;
                    205: }
                    206:
                    207: static inline int
                    208: MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
                    209: {
                    210:        int rv;
                    211:        rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS);
1.7       itohy     212:        MUTEX_RECEIVE(mtx);
1.2       ad        213:        return rv;
                    214: }
                    215:
                    216: static inline void
                    217: MUTEX_RELEASE(kmutex_t *mtx)
                    218: {
1.23      yamt      219:        uintptr_t new;
                    220:
1.7       itohy     221:        MUTEX_GIVE(mtx);
1.23      yamt      222:        new = 0;
                    223:        MUTEX_INHERITDEBUG(new, mtx->mtx_owner);
                    224:        mtx->mtx_owner = new;
1.2       ad        225: }
1.4       ad        226:
                    227: static inline void
                    228: MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
                    229: {
                    230:        /* nothing */
                    231: }
1.2       ad        232: #endif /* __HAVE_SIMPLE_MUTEXES */
                    233:
                    234: /*
                    235:  * Patch in stubs via strong alias where they are not available.
                    236:  */
                    237:
                    238: #if defined(LOCKDEBUG)
                    239: #undef __HAVE_MUTEX_STUBS
                    240: #undef __HAVE_SPIN_MUTEX_STUBS
                    241: #endif
                    242:
                    243: #ifndef __HAVE_MUTEX_STUBS
1.8       itohy     244: __strong_alias(mutex_enter,mutex_vector_enter);
                    245: __strong_alias(mutex_exit,mutex_vector_exit);
1.2       ad        246: #endif
                    247:
                    248: #ifndef __HAVE_SPIN_MUTEX_STUBS
1.8       itohy     249: __strong_alias(mutex_spin_enter,mutex_vector_enter);
                    250: __strong_alias(mutex_spin_exit,mutex_vector_exit);
1.2       ad        251: #endif
                    252:
                    253: void   mutex_abort(kmutex_t *, const char *, const char *);
                    254: void   mutex_dump(volatile void *);
                    255: int    mutex_onproc(uintptr_t, struct cpu_info **);
                    256:
                    257: lockops_t mutex_spin_lockops = {
                    258:        "Mutex",
                    259:        0,
                    260:        mutex_dump
                    261: };
                    262:
                    263: lockops_t mutex_adaptive_lockops = {
                    264:        "Mutex",
                    265:        1,
                    266:        mutex_dump
                    267: };
                    268:
1.5       yamt      269: syncobj_t mutex_syncobj = {
                    270:        SOBJ_SLEEPQ_SORTED,
                    271:        turnstile_unsleep,
                    272:        turnstile_changepri,
                    273:        sleepq_lendpri,
1.27      ad        274:        (void *)mutex_owner,
1.5       yamt      275: };
                    276:
1.31      ad        277: /* Mutex cache */
                    278: #define        MUTEX_OBJ_MAGIC 0x5aa3c85d
                    279: struct kmutexobj {
                    280:        kmutex_t        mo_lock;
                    281:        u_int           mo_magic;
                    282:        u_int           mo_refcnt;
                    283: };
                    284:
                    285: static int     mutex_obj_ctor(void *, void *, int);
                    286:
                    287: static pool_cache_t    mutex_obj_cache;
                    288:
1.2       ad        289: /*
                    290:  * mutex_dump:
                    291:  *
                    292:  *     Dump the contents of a mutex structure.
                    293:  */
                    294: void
                    295: mutex_dump(volatile void *cookie)
                    296: {
                    297:        volatile kmutex_t *mtx = cookie;
                    298:
                    299:        printf_nolog("owner field  : %#018lx wait/spin: %16d/%d\n",
                    300:            (long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx),
                    301:            MUTEX_SPIN_P(mtx));
                    302: }
                    303:
                    304: /*
                    305:  * mutex_abort:
                    306:  *
1.3       ad        307:  *     Dump information about an error and panic the system.  This
                    308:  *     generates a lot of machine code in the DIAGNOSTIC case, so
                    309:  *     we ask the compiler to not inline it.
1.2       ad        310:  */
1.8       itohy     311:
                    312: #if __GNUC_PREREQ__(3, 0)
                    313: __attribute ((noinline)) __attribute ((noreturn))
                    314: #endif
                    315: void
1.2       ad        316: mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
                    317: {
                    318:
1.23      yamt      319:        LOCKDEBUG_ABORT(mtx, (MUTEX_SPIN_P(mtx) ?
1.3       ad        320:            &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
1.2       ad        321:        /* NOTREACHED */
                    322: }
                    323:
                    324: /*
                    325:  * mutex_init:
                    326:  *
                    327:  *     Initialize a mutex for use.  Note that adaptive mutexes are in
                    328:  *     essence spin mutexes that can sleep to avoid deadlock and wasting
                    329:  *     CPU time.  We can't easily provide a type of mutex that always
                    330:  *     sleeps - see comments in mutex_vector_enter() about releasing
                    331:  *     mutexes unlocked.
                    332:  */
                    333: void
                    334: mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
                    335: {
1.23      yamt      336:        bool dodebug;
1.2       ad        337:
                    338:        memset(mtx, 0, sizeof(*mtx));
                    339:
1.15      ad        340:        switch (type) {
                    341:        case MUTEX_ADAPTIVE:
                    342:                KASSERT(ipl == IPL_NONE);
                    343:                break;
1.22      ad        344:        case MUTEX_DEFAULT:
1.15      ad        345:        case MUTEX_DRIVER:
1.26      ad        346:                if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK ||
                    347:                    ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET ||
                    348:                    ipl == IPL_SOFTSERIAL) {
1.22      ad        349:                        type = MUTEX_ADAPTIVE;
1.26      ad        350:                } else {
1.22      ad        351:                        type = MUTEX_SPIN;
                    352:                }
1.15      ad        353:                break;
                    354:        default:
                    355:                break;
                    356:        }
1.2       ad        357:
                    358:        switch (type) {
1.11      ad        359:        case MUTEX_NODEBUG:
1.23      yamt      360:                dodebug = LOCKDEBUG_ALLOC(mtx, NULL,
1.19      ad        361:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      362:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.11      ad        363:                break;
1.2       ad        364:        case MUTEX_ADAPTIVE:
1.23      yamt      365:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops,
1.19      ad        366:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      367:                MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug);
1.2       ad        368:                break;
                    369:        case MUTEX_SPIN:
1.23      yamt      370:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops,
1.19      ad        371:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      372:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.2       ad        373:                break;
                    374:        default:
                    375:                panic("mutex_init: impossible type");
                    376:                break;
                    377:        }
                    378: }
                    379:
                    380: /*
                    381:  * mutex_destroy:
                    382:  *
                    383:  *     Tear down a mutex.
                    384:  */
                    385: void
                    386: mutex_destroy(kmutex_t *mtx)
                    387: {
                    388:
                    389:        if (MUTEX_ADAPTIVE_P(mtx)) {
                    390:                MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
                    391:                    !MUTEX_HAS_WAITERS(mtx));
                    392:        } else {
1.16      skrll     393:                MUTEX_ASSERT(mtx, !__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock));
1.2       ad        394:        }
                    395:
1.23      yamt      396:        LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), mtx);
1.2       ad        397:        MUTEX_DESTROY(mtx);
                    398: }
                    399:
                    400: /*
                    401:  * mutex_onproc:
                    402:  *
                    403:  *     Return true if an adaptive mutex owner is running on a CPU in the
                    404:  *     system.  If the target is waiting on the kernel big lock, then we
1.15      ad        405:  *     must release it.  This is necessary to avoid deadlock.
1.2       ad        406:  *
                    407:  *     Note that we can't use the mutex owner field as an LWP pointer.  We
                    408:  *     don't have full control over the timing of our execution, and so the
                    409:  *     pointer could be completely invalid by the time we dereference it.
                    410:  */
                    411: #ifdef MULTIPROCESSOR
                    412: int
                    413: mutex_onproc(uintptr_t owner, struct cpu_info **cip)
                    414: {
                    415:        CPU_INFO_ITERATOR cii;
                    416:        struct cpu_info *ci;
                    417:        struct lwp *l;
                    418:
                    419:        if (!MUTEX_OWNED(owner))
                    420:                return 0;
                    421:        l = (struct lwp *)MUTEX_OWNER(owner);
                    422:
1.15      ad        423:        /* See if the target is running on a CPU somewhere. */
1.10      ad        424:        if ((ci = *cip) != NULL && ci->ci_curlwp == l)
1.15      ad        425:                goto run;
                    426:        for (CPU_INFO_FOREACH(cii, ci))
                    427:                if (ci->ci_curlwp == l)
                    428:                        goto run;
1.2       ad        429:
1.15      ad        430:        /* No: it may be safe to block now. */
1.2       ad        431:        *cip = NULL;
                    432:        return 0;
1.15      ad        433:
                    434:  run:
                    435:        /* Target is running; do we need to block? */
                    436:        *cip = ci;
                    437:        return ci->ci_biglock_wanted != l;
1.2       ad        438: }
1.15      ad        439: #endif /* MULTIPROCESSOR */
1.2       ad        440:
                    441: /*
                    442:  * mutex_vector_enter:
                    443:  *
                    444:  *     Support routine for mutex_enter() that must handles all cases.  In
                    445:  *     the LOCKDEBUG case, mutex_enter() is always aliased here, even if
                    446:  *     fast-path stubs are available.  If an mutex_spin_enter() stub is
                    447:  *     not available, then it is also aliased directly here.
                    448:  */
                    449: void
                    450: mutex_vector_enter(kmutex_t *mtx)
                    451: {
                    452:        uintptr_t owner, curthread;
                    453:        turnstile_t *ts;
                    454: #ifdef MULTIPROCESSOR
                    455:        struct cpu_info *ci = NULL;
                    456:        u_int count;
                    457: #endif
                    458:        LOCKSTAT_COUNTER(spincnt);
                    459:        LOCKSTAT_COUNTER(slpcnt);
                    460:        LOCKSTAT_TIMER(spintime);
                    461:        LOCKSTAT_TIMER(slptime);
                    462:        LOCKSTAT_FLAG(lsflag);
                    463:
                    464:        /*
                    465:         * Handle spin mutexes.
                    466:         */
                    467:        if (MUTEX_SPIN_P(mtx)) {
                    468: #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
                    469:                u_int spins = 0;
                    470: #endif
                    471:                MUTEX_SPIN_SPLRAISE(mtx);
                    472:                MUTEX_WANTLOCK(mtx);
                    473: #ifdef FULL
                    474:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
                    475:                        MUTEX_LOCKED(mtx);
                    476:                        return;
                    477:                }
                    478: #if !defined(MULTIPROCESSOR)
                    479:                MUTEX_ABORT(mtx, "locking against myself");
                    480: #else /* !MULTIPROCESSOR */
                    481:
                    482:                LOCKSTAT_ENTER(lsflag);
                    483:                LOCKSTAT_START_TIMER(lsflag, spintime);
                    484:                count = SPINLOCK_BACKOFF_MIN;
                    485:
                    486:                /*
                    487:                 * Spin testing the lock word and do exponential backoff
                    488:                 * to reduce cache line ping-ponging between CPUs.
                    489:                 */
                    490:                do {
                    491:                        if (panicstr != NULL)
                    492:                                break;
1.16      skrll     493:                        while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        494:                                SPINLOCK_BACKOFF(count);
                    495: #ifdef LOCKDEBUG
                    496:                                if (SPINLOCK_SPINOUT(spins))
                    497:                                        MUTEX_ABORT(mtx, "spinout");
                    498: #endif /* LOCKDEBUG */
                    499:                        }
                    500:                } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    501:
                    502:                if (count != SPINLOCK_BACKOFF_MIN) {
                    503:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    504:                        LOCKSTAT_EVENT(lsflag, mtx,
                    505:                            LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    506:                }
                    507:                LOCKSTAT_EXIT(lsflag);
                    508: #endif /* !MULTIPROCESSOR */
                    509: #endif /* FULL */
                    510:                MUTEX_LOCKED(mtx);
                    511:                return;
                    512:        }
                    513:
                    514:        curthread = (uintptr_t)curlwp;
                    515:
                    516:        MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    517:        MUTEX_ASSERT(mtx, curthread != 0);
                    518:        MUTEX_WANTLOCK(mtx);
                    519:
                    520:        if (panicstr == NULL) {
                    521:                LOCKDEBUG_BARRIER(&kernel_lock, 1);
                    522:        }
                    523:
                    524:        LOCKSTAT_ENTER(lsflag);
                    525:
                    526:        /*
                    527:         * Adaptive mutex; spin trying to acquire the mutex.  If we
                    528:         * determine that the owner is not running on a processor,
                    529:         * then we stop spinning, and sleep instead.
                    530:         */
1.34      ad        531:        for (owner = mtx->mtx_owner;;) {
1.2       ad        532:                if (!MUTEX_OWNED(owner)) {
                    533:                        /*
                    534:                         * Mutex owner clear could mean two things:
                    535:                         *
                    536:                         *      * The mutex has been released.
                    537:                         *      * The owner field hasn't been set yet.
                    538:                         *
                    539:                         * Try to acquire it again.  If that fails,
                    540:                         * we'll just loop again.
                    541:                         */
                    542:                        if (MUTEX_ACQUIRE(mtx, curthread))
                    543:                                break;
1.34      ad        544:                        owner = mtx->mtx_owner;
1.2       ad        545:                        continue;
                    546:                }
                    547:
                    548:                if (panicstr != NULL)
                    549:                        return;
                    550:                if (MUTEX_OWNER(owner) == curthread)
                    551:                        MUTEX_ABORT(mtx, "locking against myself");
                    552:
                    553: #ifdef MULTIPROCESSOR
                    554:                /*
                    555:                 * Check to see if the owner is running on a processor.
                    556:                 * If so, then we should just spin, as the owner will
                    557:                 * likely release the lock very soon.
                    558:                 */
                    559:                if (mutex_onproc(owner, &ci)) {
                    560:                        LOCKSTAT_START_TIMER(lsflag, spintime);
                    561:                        count = SPINLOCK_BACKOFF_MIN;
                    562:                        for (;;) {
1.34      ad        563:                                SPINLOCK_BACKOFF(count);
1.2       ad        564:                                owner = mtx->mtx_owner;
                    565:                                if (!mutex_onproc(owner, &ci))
                    566:                                        break;
                    567:                        }
                    568:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    569:                        LOCKSTAT_COUNT(spincnt, 1);
                    570:                        if (!MUTEX_OWNED(owner))
                    571:                                continue;
                    572:                }
                    573: #endif
                    574:
                    575:                ts = turnstile_lookup(mtx);
                    576:
                    577:                /*
                    578:                 * Once we have the turnstile chain interlock, mark the
                    579:                 * mutex has having waiters.  If that fails, spin again:
                    580:                 * chances are that the mutex has been released.
                    581:                 */
                    582:                if (!MUTEX_SET_WAITERS(mtx, owner)) {
                    583:                        turnstile_exit(mtx);
1.34      ad        584:                        owner = mtx->mtx_owner;
1.2       ad        585:                        continue;
                    586:                }
                    587:
                    588: #ifdef MULTIPROCESSOR
                    589:                /*
                    590:                 * mutex_exit() is permitted to release the mutex without
                    591:                 * any interlocking instructions, and the following can
                    592:                 * occur as a result:
                    593:                 *
                    594:                 *  CPU 1: MUTEX_SET_WAITERS()      CPU2: mutex_exit()
                    595:                 * ---------------------------- ----------------------------
                    596:                 *              ..                  acquire cache line
                    597:                 *              ..                   test for waiters
                    598:                 *      acquire cache line    <-      lose cache line
                    599:                 *       lock cache line                   ..
                    600:                 *     verify mutex is held                ..
                    601:                 *          set waiters                    ..
                    602:                 *       unlock cache line                 ..
                    603:                 *        lose cache line     ->    acquire cache line
                    604:                 *              ..                clear lock word, waiters
                    605:                 *        return success
                    606:                 *
                    607:                 * There is a another race that can occur: a third CPU could
                    608:                 * acquire the mutex as soon as it is released.  Since
                    609:                 * adaptive mutexes are primarily spin mutexes, this is not
                    610:                 * something that we need to worry about too much.  What we
                    611:                 * do need to ensure is that the waiters bit gets set.
                    612:                 *
                    613:                 * To allow the unlocked release, we need to make some
                    614:                 * assumptions here:
                    615:                 *
                    616:                 * o Release is the only non-atomic/unlocked operation
                    617:                 *   that can be performed on the mutex.  (It must still
                    618:                 *   be atomic on the local CPU, e.g. in case interrupted
                    619:                 *   or preempted).
                    620:                 *
                    621:                 * o At any given time, MUTEX_SET_WAITERS() can only ever
1.21      pooka     622:                 *   be in progress on one CPU in the system - guaranteed
1.2       ad        623:                 *   by the turnstile chain lock.
                    624:                 *
                    625:                 * o No other operations other than MUTEX_SET_WAITERS()
                    626:                 *   and release can modify a mutex with a non-zero
                    627:                 *   owner field.
                    628:                 *
                    629:                 * o The result of a successful MUTEX_SET_WAITERS() call
                    630:                 *   is an unbuffered write that is immediately visible
                    631:                 *   to all other processors in the system.
                    632:                 *
                    633:                 * o If the holding LWP switches away, it posts a store
                    634:                 *   fence before changing curlwp, ensuring that any
                    635:                 *   overwrite of the mutex waiters flag by mutex_exit()
                    636:                 *   completes before the modification of curlwp becomes
                    637:                 *   visible to this CPU.
                    638:                 *
1.14      yamt      639:                 * o mi_switch() posts a store fence before setting curlwp
1.2       ad        640:                 *   and before resuming execution of an LWP.
                    641:                 *
                    642:                 * o _kernel_lock() posts a store fence before setting
                    643:                 *   curcpu()->ci_biglock_wanted, and after clearing it.
                    644:                 *   This ensures that any overwrite of the mutex waiters
                    645:                 *   flag by mutex_exit() completes before the modification
                    646:                 *   of ci_biglock_wanted becomes visible.
                    647:                 *
                    648:                 * We now post a read memory barrier (after setting the
                    649:                 * waiters field) and check the lock holder's status again.
                    650:                 * Some of the possible outcomes (not an exhaustive list):
                    651:                 *
                    652:                 * 1. The onproc check returns true: the holding LWP is
                    653:                 *    running again.  The lock may be released soon and
                    654:                 *    we should spin.  Importantly, we can't trust the
                    655:                 *    value of the waiters flag.
                    656:                 *
                    657:                 * 2. The onproc check returns false: the holding LWP is
1.39    ! yamt      658:                 *    not running.  We now have the opportunity to check
1.2       ad        659:                 *    if mutex_exit() has blatted the modifications made
                    660:                 *    by MUTEX_SET_WAITERS().
                    661:                 *
                    662:                 * 3. The onproc check returns false: the holding LWP may
                    663:                 *    or may not be running.  It has context switched at
                    664:                 *    some point during our check.  Again, we have the
                    665:                 *    chance to see if the waiters bit is still set or
                    666:                 *    has been overwritten.
                    667:                 *
                    668:                 * 4. The onproc check returns false: the holding LWP is
                    669:                 *    running on a CPU, but wants the big lock.  It's OK
                    670:                 *    to check the waiters field in this case.
                    671:                 *
                    672:                 * 5. The has-waiters check fails: the mutex has been
                    673:                 *    released, the waiters flag cleared and another LWP
                    674:                 *    now owns the mutex.
                    675:                 *
                    676:                 * 6. The has-waiters check fails: the mutex has been
                    677:                 *    released.
                    678:                 *
                    679:                 * If the waiters bit is not set it's unsafe to go asleep,
                    680:                 * as we might never be awoken.
                    681:                 */
1.24      ad        682:                if ((membar_consumer(), mutex_onproc(owner, &ci)) ||
                    683:                    (membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) {
1.2       ad        684:                        turnstile_exit(mtx);
1.34      ad        685:                        owner = mtx->mtx_owner;
1.2       ad        686:                        continue;
                    687:                }
                    688: #endif /* MULTIPROCESSOR */
                    689:
                    690:                LOCKSTAT_START_TIMER(lsflag, slptime);
                    691:
1.5       yamt      692:                turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
1.2       ad        693:
                    694:                LOCKSTAT_STOP_TIMER(lsflag, slptime);
                    695:                LOCKSTAT_COUNT(slpcnt, 1);
1.34      ad        696:
                    697:                owner = mtx->mtx_owner;
1.2       ad        698:        }
                    699:
                    700:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
                    701:            slpcnt, slptime);
                    702:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
                    703:            spincnt, spintime);
                    704:        LOCKSTAT_EXIT(lsflag);
                    705:
                    706:        MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    707:        MUTEX_LOCKED(mtx);
                    708: }
                    709:
                    710: /*
                    711:  * mutex_vector_exit:
                    712:  *
                    713:  *     Support routine for mutex_exit() that handles all cases.
                    714:  */
                    715: void
                    716: mutex_vector_exit(kmutex_t *mtx)
                    717: {
                    718:        turnstile_t *ts;
                    719:        uintptr_t curthread;
                    720:
                    721:        if (MUTEX_SPIN_P(mtx)) {
                    722: #ifdef FULL
1.33      ad        723:                if (__predict_false(!__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock))) {
                    724:                        if (panicstr != NULL)
                    725:                                return;
1.2       ad        726:                        MUTEX_ABORT(mtx, "exiting unheld spin mutex");
1.33      ad        727:                }
1.2       ad        728:                MUTEX_UNLOCKED(mtx);
                    729:                __cpu_simple_unlock(&mtx->mtx_lock);
                    730: #endif
                    731:                MUTEX_SPIN_SPLRESTORE(mtx);
                    732:                return;
                    733:        }
                    734:
1.11      ad        735:        if (__predict_false((uintptr_t)panicstr | cold)) {
1.2       ad        736:                MUTEX_UNLOCKED(mtx);
                    737:                MUTEX_RELEASE(mtx);
                    738:                return;
                    739:        }
                    740:
                    741:        curthread = (uintptr_t)curlwp;
                    742:        MUTEX_DASSERT(mtx, curthread != 0);
                    743:        MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    744:        MUTEX_UNLOCKED(mtx);
                    745:
1.15      ad        746: #ifdef LOCKDEBUG
                    747:        /*
                    748:         * Avoid having to take the turnstile chain lock every time
                    749:         * around.  Raise the priority level to splhigh() in order
                    750:         * to disable preemption and so make the following atomic.
                    751:         */
                    752:        {
                    753:                int s = splhigh();
                    754:                if (!MUTEX_HAS_WAITERS(mtx)) {
                    755:                        MUTEX_RELEASE(mtx);
                    756:                        splx(s);
                    757:                        return;
                    758:                }
                    759:                splx(s);
                    760:        }
                    761: #endif
                    762:
1.2       ad        763:        /*
                    764:         * Get this lock's turnstile.  This gets the interlock on
                    765:         * the sleep queue.  Once we have that, we can clear the
                    766:         * lock.  If there was no turnstile for the lock, there
                    767:         * were no waiters remaining.
                    768:         */
                    769:        ts = turnstile_lookup(mtx);
                    770:
                    771:        if (ts == NULL) {
                    772:                MUTEX_RELEASE(mtx);
                    773:                turnstile_exit(mtx);
                    774:        } else {
                    775:                MUTEX_RELEASE(mtx);
                    776:                turnstile_wakeup(ts, TS_WRITER_Q,
                    777:                    TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    778:        }
                    779: }
                    780:
1.4       ad        781: #ifndef __HAVE_SIMPLE_MUTEXES
                    782: /*
                    783:  * mutex_wakeup:
                    784:  *
                    785:  *     Support routine for mutex_exit() that wakes up all waiters.
                    786:  *     We assume that the mutex has been released, but it need not
                    787:  *     be.
                    788:  */
                    789: void
                    790: mutex_wakeup(kmutex_t *mtx)
                    791: {
                    792:        turnstile_t *ts;
                    793:
                    794:        ts = turnstile_lookup(mtx);
                    795:        if (ts == NULL) {
                    796:                turnstile_exit(mtx);
                    797:                return;
                    798:        }
                    799:        MUTEX_CLEAR_WAITERS(mtx);
                    800:        turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    801: }
                    802: #endif /* !__HAVE_SIMPLE_MUTEXES */
                    803:
1.2       ad        804: /*
                    805:  * mutex_owned:
                    806:  *
1.3       ad        807:  *     Return true if the current LWP (adaptive) or CPU (spin)
                    808:  *     holds the mutex.
1.2       ad        809:  */
                    810: int
                    811: mutex_owned(kmutex_t *mtx)
                    812: {
                    813:
1.35      ad        814:        if (mtx == NULL)
                    815:                return 0;
1.2       ad        816:        if (MUTEX_ADAPTIVE_P(mtx))
                    817:                return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
                    818: #ifdef FULL
1.16      skrll     819:        return __SIMPLELOCK_LOCKED_P(&mtx->mtx_lock);
1.2       ad        820: #else
                    821:        return 1;
                    822: #endif
                    823: }
                    824:
                    825: /*
                    826:  * mutex_owner:
                    827:  *
1.6       ad        828:  *     Return the current owner of an adaptive mutex.  Used for
                    829:  *     priority inheritance.
1.2       ad        830:  */
1.27      ad        831: lwp_t *
                    832: mutex_owner(kmutex_t *mtx)
1.2       ad        833: {
                    834:
                    835:        MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    836:        return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner);
                    837: }
                    838:
                    839: /*
                    840:  * mutex_tryenter:
                    841:  *
                    842:  *     Try to acquire the mutex; return non-zero if we did.
                    843:  */
                    844: int
                    845: mutex_tryenter(kmutex_t *mtx)
                    846: {
                    847:        uintptr_t curthread;
                    848:
                    849:        /*
                    850:         * Handle spin mutexes.
                    851:         */
                    852:        if (MUTEX_SPIN_P(mtx)) {
                    853:                MUTEX_SPIN_SPLRAISE(mtx);
                    854: #ifdef FULL
                    855:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
1.4       ad        856:                        MUTEX_WANTLOCK(mtx);
1.2       ad        857:                        MUTEX_LOCKED(mtx);
                    858:                        return 1;
                    859:                }
                    860:                MUTEX_SPIN_SPLRESTORE(mtx);
                    861: #else
1.4       ad        862:                MUTEX_WANTLOCK(mtx);
1.2       ad        863:                MUTEX_LOCKED(mtx);
                    864:                return 1;
                    865: #endif
                    866:        } else {
                    867:                curthread = (uintptr_t)curlwp;
                    868:                MUTEX_ASSERT(mtx, curthread != 0);
                    869:                if (MUTEX_ACQUIRE(mtx, curthread)) {
1.4       ad        870:                        MUTEX_WANTLOCK(mtx);
1.2       ad        871:                        MUTEX_LOCKED(mtx);
                    872:                        MUTEX_DASSERT(mtx,
                    873:                            MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    874:                        return 1;
                    875:                }
                    876:        }
                    877:
                    878:        return 0;
                    879: }
                    880:
                    881: #if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL)
                    882: /*
                    883:  * mutex_spin_retry:
                    884:  *
                    885:  *     Support routine for mutex_spin_enter().  Assumes that the caller
                    886:  *     has already raised the SPL, and adjusted counters.
                    887:  */
                    888: void
                    889: mutex_spin_retry(kmutex_t *mtx)
                    890: {
                    891: #ifdef MULTIPROCESSOR
                    892:        u_int count;
                    893:        LOCKSTAT_TIMER(spintime);
                    894:        LOCKSTAT_FLAG(lsflag);
                    895: #ifdef LOCKDEBUG
                    896:        u_int spins = 0;
                    897: #endif /* LOCKDEBUG */
                    898:
                    899:        MUTEX_WANTLOCK(mtx);
                    900:
                    901:        LOCKSTAT_ENTER(lsflag);
                    902:        LOCKSTAT_START_TIMER(lsflag, spintime);
                    903:        count = SPINLOCK_BACKOFF_MIN;
                    904:
                    905:        /*
                    906:         * Spin testing the lock word and do exponential backoff
                    907:         * to reduce cache line ping-ponging between CPUs.
                    908:         */
                    909:        do {
                    910:                if (panicstr != NULL)
                    911:                        break;
1.16      skrll     912:                while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        913:                        SPINLOCK_BACKOFF(count);
                    914: #ifdef LOCKDEBUG
                    915:                        if (SPINLOCK_SPINOUT(spins))
                    916:                                MUTEX_ABORT(mtx, "spinout");
                    917: #endif /* LOCKDEBUG */
                    918:                }
                    919:        } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    920:
                    921:        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    922:        LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    923:        LOCKSTAT_EXIT(lsflag);
                    924:
                    925:        MUTEX_LOCKED(mtx);
                    926: #else  /* MULTIPROCESSOR */
                    927:        MUTEX_ABORT(mtx, "locking against myself");
                    928: #endif /* MULTIPROCESSOR */
                    929: }
                    930: #endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */
1.31      ad        931:
                    932: /*
                    933:  * mutex_obj_init:
                    934:  *
                    935:  *     Initialize the mutex object store.
                    936:  */
                    937: void
                    938: mutex_obj_init(void)
                    939: {
                    940:
                    941:        mutex_obj_cache = pool_cache_init(sizeof(struct kmutexobj),
                    942:            coherency_unit, 0, 0, "mutex", NULL, IPL_NONE, mutex_obj_ctor,
                    943:            NULL, NULL);
                    944: }
                    945:
                    946: /*
                    947:  * mutex_obj_ctor:
                    948:  *
                    949:  *     Initialize a new lock for the cache.
                    950:  */
                    951: static int
                    952: mutex_obj_ctor(void *arg, void *obj, int flags)
                    953: {
                    954:        struct kmutexobj * mo = obj;
                    955:
                    956:        mo->mo_magic = MUTEX_OBJ_MAGIC;
                    957:
                    958:        return 0;
                    959: }
                    960:
                    961: /*
                    962:  * mutex_obj_alloc:
                    963:  *
                    964:  *     Allocate a single lock object.
                    965:  */
                    966: kmutex_t *
                    967: mutex_obj_alloc(kmutex_type_t type, int ipl)
                    968: {
                    969:        struct kmutexobj *mo;
                    970:
                    971:        mo = pool_cache_get(mutex_obj_cache, PR_WAITOK);
                    972:        mutex_init(&mo->mo_lock, type, ipl);
                    973:        mo->mo_refcnt = 1;
                    974:
                    975:        return (kmutex_t *)mo;
                    976: }
                    977:
                    978: /*
                    979:  * mutex_obj_hold:
                    980:  *
                    981:  *     Add a single reference to a lock object.  A reference to the object
                    982:  *     must already be held, and must be held across this call.
                    983:  */
                    984: void
                    985: mutex_obj_hold(kmutex_t *lock)
                    986: {
                    987:        struct kmutexobj *mo = (struct kmutexobj *)lock;
                    988:
                    989:        KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
                    990:        KASSERT(mo->mo_refcnt > 0);
                    991:
                    992:        atomic_inc_uint(&mo->mo_refcnt);
                    993: }
                    994:
                    995: /*
                    996:  * mutex_obj_free:
                    997:  *
                    998:  *     Drop a reference from a lock object.  If the last reference is being
                    999:  *     dropped, free the object and return true.  Otherwise, return false.
                   1000:  */
                   1001: bool
                   1002: mutex_obj_free(kmutex_t *lock)
                   1003: {
                   1004:        struct kmutexobj *mo = (struct kmutexobj *)lock;
                   1005:
                   1006:        KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
                   1007:        KASSERT(mo->mo_refcnt > 0);
                   1008:
                   1009:        if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
                   1010:                return false;
                   1011:        }
                   1012:        mutex_destroy(&mo->mo_lock);
                   1013:        pool_cache_put(mutex_obj_cache, mo);
                   1014:        return true;
                   1015: }

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