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Annotation of src/sys/kern/kern_mutex.c, Revision 1.45

1.45    ! rmind       1: /*     $NetBSD: kern_mutex.c,v 1.44 2008/10/15 06:51:20 wrstuden 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>
1.45    ! rmind      43: __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.44 2008/10/15 06:51:20 wrstuden 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:
1.44      wrstuden   62: #include "opt_sa.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),              \
1.40      ad         79:         (uintptr_t)__builtin_return_address(0), false, false)
1.2       ad         80: #define        MUTEX_LOCKED(mtx)                                       \
1.42      ad         81:     LOCKDEBUG_LOCKED(MUTEX_DEBUG_P(mtx), (mtx), NULL,          \
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",
1.42      ad        259:        LOCKOPS_SPIN,
1.2       ad        260:        mutex_dump
                    261: };
                    262:
                    263: lockops_t mutex_adaptive_lockops = {
                    264:        "Mutex",
1.42      ad        265:        LOCKOPS_SLEEP,
1.2       ad        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:  */
1.43      ad        311: void __noinline
1.2       ad        312: mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
                    313: {
                    314:
1.23      yamt      315:        LOCKDEBUG_ABORT(mtx, (MUTEX_SPIN_P(mtx) ?
1.3       ad        316:            &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
1.2       ad        317: }
                    318:
                    319: /*
                    320:  * mutex_init:
                    321:  *
                    322:  *     Initialize a mutex for use.  Note that adaptive mutexes are in
                    323:  *     essence spin mutexes that can sleep to avoid deadlock and wasting
                    324:  *     CPU time.  We can't easily provide a type of mutex that always
                    325:  *     sleeps - see comments in mutex_vector_enter() about releasing
                    326:  *     mutexes unlocked.
                    327:  */
                    328: void
                    329: mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
                    330: {
1.23      yamt      331:        bool dodebug;
1.2       ad        332:
                    333:        memset(mtx, 0, sizeof(*mtx));
                    334:
1.15      ad        335:        switch (type) {
                    336:        case MUTEX_ADAPTIVE:
                    337:                KASSERT(ipl == IPL_NONE);
                    338:                break;
1.22      ad        339:        case MUTEX_DEFAULT:
1.15      ad        340:        case MUTEX_DRIVER:
1.26      ad        341:                if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK ||
                    342:                    ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET ||
                    343:                    ipl == IPL_SOFTSERIAL) {
1.22      ad        344:                        type = MUTEX_ADAPTIVE;
1.26      ad        345:                } else {
1.22      ad        346:                        type = MUTEX_SPIN;
                    347:                }
1.15      ad        348:                break;
                    349:        default:
                    350:                break;
                    351:        }
1.2       ad        352:
                    353:        switch (type) {
1.11      ad        354:        case MUTEX_NODEBUG:
1.23      yamt      355:                dodebug = LOCKDEBUG_ALLOC(mtx, NULL,
1.19      ad        356:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      357:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.11      ad        358:                break;
1.2       ad        359:        case MUTEX_ADAPTIVE:
1.23      yamt      360:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops,
1.19      ad        361:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      362:                MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug);
1.2       ad        363:                break;
                    364:        case MUTEX_SPIN:
1.23      yamt      365:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops,
1.19      ad        366:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      367:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.2       ad        368:                break;
                    369:        default:
                    370:                panic("mutex_init: impossible type");
                    371:                break;
                    372:        }
                    373: }
                    374:
                    375: /*
                    376:  * mutex_destroy:
                    377:  *
                    378:  *     Tear down a mutex.
                    379:  */
                    380: void
                    381: mutex_destroy(kmutex_t *mtx)
                    382: {
                    383:
                    384:        if (MUTEX_ADAPTIVE_P(mtx)) {
                    385:                MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
                    386:                    !MUTEX_HAS_WAITERS(mtx));
                    387:        } else {
1.16      skrll     388:                MUTEX_ASSERT(mtx, !__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock));
1.2       ad        389:        }
                    390:
1.23      yamt      391:        LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), mtx);
1.2       ad        392:        MUTEX_DESTROY(mtx);
                    393: }
                    394:
                    395: /*
                    396:  * mutex_onproc:
                    397:  *
                    398:  *     Return true if an adaptive mutex owner is running on a CPU in the
                    399:  *     system.  If the target is waiting on the kernel big lock, then we
1.15      ad        400:  *     must release it.  This is necessary to avoid deadlock.
1.2       ad        401:  *
                    402:  *     Note that we can't use the mutex owner field as an LWP pointer.  We
                    403:  *     don't have full control over the timing of our execution, and so the
                    404:  *     pointer could be completely invalid by the time we dereference it.
                    405:  */
                    406: #ifdef MULTIPROCESSOR
                    407: int
                    408: mutex_onproc(uintptr_t owner, struct cpu_info **cip)
                    409: {
                    410:        CPU_INFO_ITERATOR cii;
                    411:        struct cpu_info *ci;
                    412:        struct lwp *l;
                    413:
                    414:        if (!MUTEX_OWNED(owner))
                    415:                return 0;
                    416:        l = (struct lwp *)MUTEX_OWNER(owner);
                    417:
1.15      ad        418:        /* See if the target is running on a CPU somewhere. */
1.10      ad        419:        if ((ci = *cip) != NULL && ci->ci_curlwp == l)
1.15      ad        420:                goto run;
                    421:        for (CPU_INFO_FOREACH(cii, ci))
                    422:                if (ci->ci_curlwp == l)
                    423:                        goto run;
1.2       ad        424:
1.15      ad        425:        /* No: it may be safe to block now. */
1.2       ad        426:        *cip = NULL;
                    427:        return 0;
1.15      ad        428:
                    429:  run:
                    430:        /* Target is running; do we need to block? */
                    431:        *cip = ci;
                    432:        return ci->ci_biglock_wanted != l;
1.2       ad        433: }
1.15      ad        434: #endif /* MULTIPROCESSOR */
1.2       ad        435:
                    436: /*
                    437:  * mutex_vector_enter:
                    438:  *
1.45    ! rmind     439:  *     Support routine for mutex_enter() that must handle all cases.  In
1.2       ad        440:  *     the LOCKDEBUG case, mutex_enter() is always aliased here, even if
                    441:  *     fast-path stubs are available.  If an mutex_spin_enter() stub is
                    442:  *     not available, then it is also aliased directly here.
                    443:  */
                    444: void
                    445: mutex_vector_enter(kmutex_t *mtx)
                    446: {
                    447:        uintptr_t owner, curthread;
                    448:        turnstile_t *ts;
                    449: #ifdef MULTIPROCESSOR
                    450:        struct cpu_info *ci = NULL;
                    451:        u_int count;
                    452: #endif
1.44      wrstuden  453: #ifdef KERN_SA
                    454:        int f;
                    455: #endif
1.2       ad        456:        LOCKSTAT_COUNTER(spincnt);
                    457:        LOCKSTAT_COUNTER(slpcnt);
                    458:        LOCKSTAT_TIMER(spintime);
                    459:        LOCKSTAT_TIMER(slptime);
                    460:        LOCKSTAT_FLAG(lsflag);
                    461:
                    462:        /*
                    463:         * Handle spin mutexes.
                    464:         */
                    465:        if (MUTEX_SPIN_P(mtx)) {
                    466: #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
                    467:                u_int spins = 0;
                    468: #endif
                    469:                MUTEX_SPIN_SPLRAISE(mtx);
                    470:                MUTEX_WANTLOCK(mtx);
                    471: #ifdef FULL
                    472:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
                    473:                        MUTEX_LOCKED(mtx);
                    474:                        return;
                    475:                }
                    476: #if !defined(MULTIPROCESSOR)
                    477:                MUTEX_ABORT(mtx, "locking against myself");
                    478: #else /* !MULTIPROCESSOR */
                    479:
                    480:                LOCKSTAT_ENTER(lsflag);
                    481:                LOCKSTAT_START_TIMER(lsflag, spintime);
                    482:                count = SPINLOCK_BACKOFF_MIN;
                    483:
                    484:                /*
                    485:                 * Spin testing the lock word and do exponential backoff
                    486:                 * to reduce cache line ping-ponging between CPUs.
                    487:                 */
                    488:                do {
                    489:                        if (panicstr != NULL)
                    490:                                break;
1.16      skrll     491:                        while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        492:                                SPINLOCK_BACKOFF(count);
                    493: #ifdef LOCKDEBUG
                    494:                                if (SPINLOCK_SPINOUT(spins))
                    495:                                        MUTEX_ABORT(mtx, "spinout");
                    496: #endif /* LOCKDEBUG */
                    497:                        }
                    498:                } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    499:
                    500:                if (count != SPINLOCK_BACKOFF_MIN) {
                    501:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    502:                        LOCKSTAT_EVENT(lsflag, mtx,
                    503:                            LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    504:                }
                    505:                LOCKSTAT_EXIT(lsflag);
                    506: #endif /* !MULTIPROCESSOR */
                    507: #endif /* FULL */
                    508:                MUTEX_LOCKED(mtx);
                    509:                return;
                    510:        }
                    511:
                    512:        curthread = (uintptr_t)curlwp;
                    513:
                    514:        MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    515:        MUTEX_ASSERT(mtx, curthread != 0);
                    516:        MUTEX_WANTLOCK(mtx);
                    517:
                    518:        if (panicstr == NULL) {
                    519:                LOCKDEBUG_BARRIER(&kernel_lock, 1);
                    520:        }
                    521:
                    522:        LOCKSTAT_ENTER(lsflag);
                    523:
                    524:        /*
                    525:         * Adaptive mutex; spin trying to acquire the mutex.  If we
                    526:         * determine that the owner is not running on a processor,
                    527:         * then we stop spinning, and sleep instead.
                    528:         */
1.34      ad        529:        for (owner = mtx->mtx_owner;;) {
1.2       ad        530:                if (!MUTEX_OWNED(owner)) {
                    531:                        /*
                    532:                         * Mutex owner clear could mean two things:
                    533:                         *
                    534:                         *      * The mutex has been released.
                    535:                         *      * The owner field hasn't been set yet.
                    536:                         *
                    537:                         * Try to acquire it again.  If that fails,
                    538:                         * we'll just loop again.
                    539:                         */
                    540:                        if (MUTEX_ACQUIRE(mtx, curthread))
                    541:                                break;
1.34      ad        542:                        owner = mtx->mtx_owner;
1.2       ad        543:                        continue;
                    544:                }
                    545:
1.45    ! rmind     546:                if (__predict_false(panicstr != NULL))
1.2       ad        547:                        return;
1.45    ! rmind     548:                if (__predict_false(MUTEX_OWNER(owner) == curthread))
1.2       ad        549:                        MUTEX_ABORT(mtx, "locking against myself");
                    550:
                    551: #ifdef MULTIPROCESSOR
                    552:                /*
                    553:                 * Check to see if the owner is running on a processor.
                    554:                 * If so, then we should just spin, as the owner will
                    555:                 * likely release the lock very soon.
                    556:                 */
                    557:                if (mutex_onproc(owner, &ci)) {
                    558:                        LOCKSTAT_START_TIMER(lsflag, spintime);
                    559:                        count = SPINLOCK_BACKOFF_MIN;
                    560:                        for (;;) {
1.34      ad        561:                                SPINLOCK_BACKOFF(count);
1.2       ad        562:                                owner = mtx->mtx_owner;
                    563:                                if (!mutex_onproc(owner, &ci))
                    564:                                        break;
                    565:                        }
                    566:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    567:                        LOCKSTAT_COUNT(spincnt, 1);
                    568:                        if (!MUTEX_OWNED(owner))
                    569:                                continue;
                    570:                }
                    571: #endif
                    572:
                    573:                ts = turnstile_lookup(mtx);
                    574:
                    575:                /*
                    576:                 * Once we have the turnstile chain interlock, mark the
                    577:                 * mutex has having waiters.  If that fails, spin again:
                    578:                 * chances are that the mutex has been released.
                    579:                 */
                    580:                if (!MUTEX_SET_WAITERS(mtx, owner)) {
                    581:                        turnstile_exit(mtx);
1.34      ad        582:                        owner = mtx->mtx_owner;
1.2       ad        583:                        continue;
                    584:                }
                    585:
                    586: #ifdef MULTIPROCESSOR
                    587:                /*
                    588:                 * mutex_exit() is permitted to release the mutex without
                    589:                 * any interlocking instructions, and the following can
                    590:                 * occur as a result:
                    591:                 *
                    592:                 *  CPU 1: MUTEX_SET_WAITERS()      CPU2: mutex_exit()
                    593:                 * ---------------------------- ----------------------------
                    594:                 *              ..                  acquire cache line
                    595:                 *              ..                   test for waiters
                    596:                 *      acquire cache line    <-      lose cache line
                    597:                 *       lock cache line                   ..
                    598:                 *     verify mutex is held                ..
                    599:                 *          set waiters                    ..
                    600:                 *       unlock cache line                 ..
                    601:                 *        lose cache line     ->    acquire cache line
                    602:                 *              ..                clear lock word, waiters
                    603:                 *        return success
                    604:                 *
                    605:                 * There is a another race that can occur: a third CPU could
                    606:                 * acquire the mutex as soon as it is released.  Since
                    607:                 * adaptive mutexes are primarily spin mutexes, this is not
                    608:                 * something that we need to worry about too much.  What we
                    609:                 * do need to ensure is that the waiters bit gets set.
                    610:                 *
                    611:                 * To allow the unlocked release, we need to make some
                    612:                 * assumptions here:
                    613:                 *
                    614:                 * o Release is the only non-atomic/unlocked operation
                    615:                 *   that can be performed on the mutex.  (It must still
                    616:                 *   be atomic on the local CPU, e.g. in case interrupted
                    617:                 *   or preempted).
                    618:                 *
                    619:                 * o At any given time, MUTEX_SET_WAITERS() can only ever
1.21      pooka     620:                 *   be in progress on one CPU in the system - guaranteed
1.2       ad        621:                 *   by the turnstile chain lock.
                    622:                 *
                    623:                 * o No other operations other than MUTEX_SET_WAITERS()
                    624:                 *   and release can modify a mutex with a non-zero
                    625:                 *   owner field.
                    626:                 *
                    627:                 * o The result of a successful MUTEX_SET_WAITERS() call
                    628:                 *   is an unbuffered write that is immediately visible
                    629:                 *   to all other processors in the system.
                    630:                 *
                    631:                 * o If the holding LWP switches away, it posts a store
                    632:                 *   fence before changing curlwp, ensuring that any
                    633:                 *   overwrite of the mutex waiters flag by mutex_exit()
                    634:                 *   completes before the modification of curlwp becomes
                    635:                 *   visible to this CPU.
                    636:                 *
1.14      yamt      637:                 * o mi_switch() posts a store fence before setting curlwp
1.2       ad        638:                 *   and before resuming execution of an LWP.
                    639:                 *
                    640:                 * o _kernel_lock() posts a store fence before setting
                    641:                 *   curcpu()->ci_biglock_wanted, and after clearing it.
                    642:                 *   This ensures that any overwrite of the mutex waiters
                    643:                 *   flag by mutex_exit() completes before the modification
                    644:                 *   of ci_biglock_wanted becomes visible.
                    645:                 *
                    646:                 * We now post a read memory barrier (after setting the
                    647:                 * waiters field) and check the lock holder's status again.
                    648:                 * Some of the possible outcomes (not an exhaustive list):
                    649:                 *
                    650:                 * 1. The onproc check returns true: the holding LWP is
                    651:                 *    running again.  The lock may be released soon and
                    652:                 *    we should spin.  Importantly, we can't trust the
                    653:                 *    value of the waiters flag.
                    654:                 *
                    655:                 * 2. The onproc check returns false: the holding LWP is
1.39      yamt      656:                 *    not running.  We now have the opportunity to check
1.2       ad        657:                 *    if mutex_exit() has blatted the modifications made
                    658:                 *    by MUTEX_SET_WAITERS().
                    659:                 *
                    660:                 * 3. The onproc check returns false: the holding LWP may
                    661:                 *    or may not be running.  It has context switched at
                    662:                 *    some point during our check.  Again, we have the
                    663:                 *    chance to see if the waiters bit is still set or
                    664:                 *    has been overwritten.
                    665:                 *
                    666:                 * 4. The onproc check returns false: the holding LWP is
                    667:                 *    running on a CPU, but wants the big lock.  It's OK
                    668:                 *    to check the waiters field in this case.
                    669:                 *
                    670:                 * 5. The has-waiters check fails: the mutex has been
                    671:                 *    released, the waiters flag cleared and another LWP
                    672:                 *    now owns the mutex.
                    673:                 *
                    674:                 * 6. The has-waiters check fails: the mutex has been
                    675:                 *    released.
                    676:                 *
                    677:                 * If the waiters bit is not set it's unsafe to go asleep,
                    678:                 * as we might never be awoken.
                    679:                 */
1.24      ad        680:                if ((membar_consumer(), mutex_onproc(owner, &ci)) ||
                    681:                    (membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) {
1.2       ad        682:                        turnstile_exit(mtx);
1.34      ad        683:                        owner = mtx->mtx_owner;
1.2       ad        684:                        continue;
                    685:                }
                    686: #endif /* MULTIPROCESSOR */
                    687:
1.44      wrstuden  688: #ifdef KERN_SA
                    689:                /*
                    690:                 * Sleeping for a mutex should not generate an upcall.
                    691:                 * So set LP_SA_NOBLOCK to indicate this.
                    692:                 * f indicates if we should clear LP_SA_NOBLOCK when done.
                    693:                 */
                    694:                f = ~curlwp->l_pflag & LP_SA_NOBLOCK;
                    695:                curlwp->l_pflag |= LP_SA_NOBLOCK;
                    696: #endif /* KERN_SA */
                    697:
1.2       ad        698:                LOCKSTAT_START_TIMER(lsflag, slptime);
                    699:
1.5       yamt      700:                turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
1.2       ad        701:
                    702:                LOCKSTAT_STOP_TIMER(lsflag, slptime);
                    703:                LOCKSTAT_COUNT(slpcnt, 1);
1.34      ad        704:
1.44      wrstuden  705: #ifdef KERN_SA
                    706:                curlwp->l_pflag ^= f;
                    707: #endif /* KERN_SA */
                    708:
1.34      ad        709:                owner = mtx->mtx_owner;
1.2       ad        710:        }
                    711:
                    712:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
                    713:            slpcnt, slptime);
                    714:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
                    715:            spincnt, spintime);
                    716:        LOCKSTAT_EXIT(lsflag);
                    717:
                    718:        MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    719:        MUTEX_LOCKED(mtx);
                    720: }
                    721:
                    722: /*
                    723:  * mutex_vector_exit:
                    724:  *
                    725:  *     Support routine for mutex_exit() that handles all cases.
                    726:  */
                    727: void
                    728: mutex_vector_exit(kmutex_t *mtx)
                    729: {
                    730:        turnstile_t *ts;
                    731:        uintptr_t curthread;
                    732:
                    733:        if (MUTEX_SPIN_P(mtx)) {
                    734: #ifdef FULL
1.33      ad        735:                if (__predict_false(!__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock))) {
                    736:                        if (panicstr != NULL)
                    737:                                return;
1.2       ad        738:                        MUTEX_ABORT(mtx, "exiting unheld spin mutex");
1.33      ad        739:                }
1.2       ad        740:                MUTEX_UNLOCKED(mtx);
                    741:                __cpu_simple_unlock(&mtx->mtx_lock);
                    742: #endif
                    743:                MUTEX_SPIN_SPLRESTORE(mtx);
                    744:                return;
                    745:        }
                    746:
1.11      ad        747:        if (__predict_false((uintptr_t)panicstr | cold)) {
1.2       ad        748:                MUTEX_UNLOCKED(mtx);
                    749:                MUTEX_RELEASE(mtx);
                    750:                return;
                    751:        }
                    752:
                    753:        curthread = (uintptr_t)curlwp;
                    754:        MUTEX_DASSERT(mtx, curthread != 0);
                    755:        MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    756:        MUTEX_UNLOCKED(mtx);
                    757:
1.15      ad        758: #ifdef LOCKDEBUG
                    759:        /*
                    760:         * Avoid having to take the turnstile chain lock every time
                    761:         * around.  Raise the priority level to splhigh() in order
                    762:         * to disable preemption and so make the following atomic.
                    763:         */
                    764:        {
                    765:                int s = splhigh();
                    766:                if (!MUTEX_HAS_WAITERS(mtx)) {
                    767:                        MUTEX_RELEASE(mtx);
                    768:                        splx(s);
                    769:                        return;
                    770:                }
                    771:                splx(s);
                    772:        }
                    773: #endif
                    774:
1.2       ad        775:        /*
                    776:         * Get this lock's turnstile.  This gets the interlock on
                    777:         * the sleep queue.  Once we have that, we can clear the
                    778:         * lock.  If there was no turnstile for the lock, there
                    779:         * were no waiters remaining.
                    780:         */
                    781:        ts = turnstile_lookup(mtx);
                    782:
                    783:        if (ts == NULL) {
                    784:                MUTEX_RELEASE(mtx);
                    785:                turnstile_exit(mtx);
                    786:        } else {
                    787:                MUTEX_RELEASE(mtx);
                    788:                turnstile_wakeup(ts, TS_WRITER_Q,
                    789:                    TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    790:        }
                    791: }
                    792:
1.4       ad        793: #ifndef __HAVE_SIMPLE_MUTEXES
                    794: /*
                    795:  * mutex_wakeup:
                    796:  *
                    797:  *     Support routine for mutex_exit() that wakes up all waiters.
                    798:  *     We assume that the mutex has been released, but it need not
                    799:  *     be.
                    800:  */
                    801: void
                    802: mutex_wakeup(kmutex_t *mtx)
                    803: {
                    804:        turnstile_t *ts;
                    805:
                    806:        ts = turnstile_lookup(mtx);
                    807:        if (ts == NULL) {
                    808:                turnstile_exit(mtx);
                    809:                return;
                    810:        }
                    811:        MUTEX_CLEAR_WAITERS(mtx);
                    812:        turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    813: }
                    814: #endif /* !__HAVE_SIMPLE_MUTEXES */
                    815:
1.2       ad        816: /*
                    817:  * mutex_owned:
                    818:  *
1.3       ad        819:  *     Return true if the current LWP (adaptive) or CPU (spin)
                    820:  *     holds the mutex.
1.2       ad        821:  */
                    822: int
                    823: mutex_owned(kmutex_t *mtx)
                    824: {
                    825:
1.35      ad        826:        if (mtx == NULL)
                    827:                return 0;
1.2       ad        828:        if (MUTEX_ADAPTIVE_P(mtx))
                    829:                return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
                    830: #ifdef FULL
1.16      skrll     831:        return __SIMPLELOCK_LOCKED_P(&mtx->mtx_lock);
1.2       ad        832: #else
                    833:        return 1;
                    834: #endif
                    835: }
                    836:
                    837: /*
                    838:  * mutex_owner:
                    839:  *
1.6       ad        840:  *     Return the current owner of an adaptive mutex.  Used for
                    841:  *     priority inheritance.
1.2       ad        842:  */
1.27      ad        843: lwp_t *
                    844: mutex_owner(kmutex_t *mtx)
1.2       ad        845: {
                    846:
                    847:        MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    848:        return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner);
                    849: }
                    850:
                    851: /*
                    852:  * mutex_tryenter:
                    853:  *
                    854:  *     Try to acquire the mutex; return non-zero if we did.
                    855:  */
                    856: int
                    857: mutex_tryenter(kmutex_t *mtx)
                    858: {
                    859:        uintptr_t curthread;
                    860:
                    861:        /*
                    862:         * Handle spin mutexes.
                    863:         */
                    864:        if (MUTEX_SPIN_P(mtx)) {
                    865:                MUTEX_SPIN_SPLRAISE(mtx);
                    866: #ifdef FULL
                    867:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
1.4       ad        868:                        MUTEX_WANTLOCK(mtx);
1.2       ad        869:                        MUTEX_LOCKED(mtx);
                    870:                        return 1;
                    871:                }
                    872:                MUTEX_SPIN_SPLRESTORE(mtx);
                    873: #else
1.4       ad        874:                MUTEX_WANTLOCK(mtx);
1.2       ad        875:                MUTEX_LOCKED(mtx);
                    876:                return 1;
                    877: #endif
                    878:        } else {
                    879:                curthread = (uintptr_t)curlwp;
                    880:                MUTEX_ASSERT(mtx, curthread != 0);
                    881:                if (MUTEX_ACQUIRE(mtx, curthread)) {
1.4       ad        882:                        MUTEX_WANTLOCK(mtx);
1.2       ad        883:                        MUTEX_LOCKED(mtx);
                    884:                        MUTEX_DASSERT(mtx,
                    885:                            MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    886:                        return 1;
                    887:                }
                    888:        }
                    889:
                    890:        return 0;
                    891: }
                    892:
                    893: #if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL)
                    894: /*
                    895:  * mutex_spin_retry:
                    896:  *
                    897:  *     Support routine for mutex_spin_enter().  Assumes that the caller
                    898:  *     has already raised the SPL, and adjusted counters.
                    899:  */
                    900: void
                    901: mutex_spin_retry(kmutex_t *mtx)
                    902: {
                    903: #ifdef MULTIPROCESSOR
                    904:        u_int count;
                    905:        LOCKSTAT_TIMER(spintime);
                    906:        LOCKSTAT_FLAG(lsflag);
                    907: #ifdef LOCKDEBUG
                    908:        u_int spins = 0;
                    909: #endif /* LOCKDEBUG */
                    910:
                    911:        MUTEX_WANTLOCK(mtx);
                    912:
                    913:        LOCKSTAT_ENTER(lsflag);
                    914:        LOCKSTAT_START_TIMER(lsflag, spintime);
                    915:        count = SPINLOCK_BACKOFF_MIN;
                    916:
                    917:        /*
                    918:         * Spin testing the lock word and do exponential backoff
                    919:         * to reduce cache line ping-ponging between CPUs.
                    920:         */
                    921:        do {
                    922:                if (panicstr != NULL)
                    923:                        break;
1.16      skrll     924:                while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        925:                        SPINLOCK_BACKOFF(count);
                    926: #ifdef LOCKDEBUG
                    927:                        if (SPINLOCK_SPINOUT(spins))
                    928:                                MUTEX_ABORT(mtx, "spinout");
                    929: #endif /* LOCKDEBUG */
                    930:                }
                    931:        } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    932:
                    933:        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    934:        LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    935:        LOCKSTAT_EXIT(lsflag);
                    936:
                    937:        MUTEX_LOCKED(mtx);
                    938: #else  /* MULTIPROCESSOR */
                    939:        MUTEX_ABORT(mtx, "locking against myself");
                    940: #endif /* MULTIPROCESSOR */
                    941: }
                    942: #endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */
1.31      ad        943:
                    944: /*
                    945:  * mutex_obj_init:
                    946:  *
                    947:  *     Initialize the mutex object store.
                    948:  */
                    949: void
                    950: mutex_obj_init(void)
                    951: {
                    952:
                    953:        mutex_obj_cache = pool_cache_init(sizeof(struct kmutexobj),
                    954:            coherency_unit, 0, 0, "mutex", NULL, IPL_NONE, mutex_obj_ctor,
                    955:            NULL, NULL);
                    956: }
                    957:
                    958: /*
                    959:  * mutex_obj_ctor:
                    960:  *
                    961:  *     Initialize a new lock for the cache.
                    962:  */
                    963: static int
                    964: mutex_obj_ctor(void *arg, void *obj, int flags)
                    965: {
                    966:        struct kmutexobj * mo = obj;
                    967:
                    968:        mo->mo_magic = MUTEX_OBJ_MAGIC;
                    969:
                    970:        return 0;
                    971: }
                    972:
                    973: /*
                    974:  * mutex_obj_alloc:
                    975:  *
                    976:  *     Allocate a single lock object.
                    977:  */
                    978: kmutex_t *
                    979: mutex_obj_alloc(kmutex_type_t type, int ipl)
                    980: {
                    981:        struct kmutexobj *mo;
                    982:
                    983:        mo = pool_cache_get(mutex_obj_cache, PR_WAITOK);
                    984:        mutex_init(&mo->mo_lock, type, ipl);
                    985:        mo->mo_refcnt = 1;
                    986:
                    987:        return (kmutex_t *)mo;
                    988: }
                    989:
                    990: /*
                    991:  * mutex_obj_hold:
                    992:  *
                    993:  *     Add a single reference to a lock object.  A reference to the object
                    994:  *     must already be held, and must be held across this call.
                    995:  */
                    996: void
                    997: mutex_obj_hold(kmutex_t *lock)
                    998: {
                    999:        struct kmutexobj *mo = (struct kmutexobj *)lock;
                   1000:
                   1001:        KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
                   1002:        KASSERT(mo->mo_refcnt > 0);
                   1003:
                   1004:        atomic_inc_uint(&mo->mo_refcnt);
                   1005: }
                   1006:
                   1007: /*
                   1008:  * mutex_obj_free:
                   1009:  *
                   1010:  *     Drop a reference from a lock object.  If the last reference is being
                   1011:  *     dropped, free the object and return true.  Otherwise, return false.
                   1012:  */
                   1013: bool
                   1014: mutex_obj_free(kmutex_t *lock)
                   1015: {
                   1016:        struct kmutexobj *mo = (struct kmutexobj *)lock;
                   1017:
                   1018:        KASSERT(mo->mo_magic == MUTEX_OBJ_MAGIC);
                   1019:        KASSERT(mo->mo_refcnt > 0);
                   1020:
                   1021:        if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
                   1022:                return false;
                   1023:        }
                   1024:        mutex_destroy(&mo->mo_lock);
                   1025:        pool_cache_put(mutex_obj_cache, mo);
                   1026:        return true;
                   1027: }

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