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Annotation of src/sys/kern/kern_mutex.c, Revision 1.49

1.49    ! skrll       1: /*     $NetBSD: kern_mutex.c,v 1.48 2010/02/06 04:50:19 cube 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>
1.49    ! skrll      43: __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.48 2010/02/06 04:50:19 cube Exp $");
1.2       ad         44:
                     45: #include <sys/param.h>
1.46      pooka      46: #include <sys/atomic.h>
1.2       ad         47: #include <sys/proc.h>
                     48: #include <sys/mutex.h>
                     49: #include <sys/sched.h>
                     50: #include <sys/sleepq.h>
                     51: #include <sys/systm.h>
                     52: #include <sys/lockdebug.h>
                     53: #include <sys/kernel.h>
1.24      ad         54: #include <sys/intr.h>
1.29      xtraeme    55: #include <sys/lock.h>
1.2       ad         56:
                     57: #include <dev/lockstat.h>
                     58:
1.28      ad         59: #include <machine/lock.h>
                     60:
1.44      wrstuden   61: #include "opt_sa.h"
                     62:
1.2       ad         63: /*
                     64:  * When not running a debug kernel, spin mutexes are not much
                     65:  * more than an splraiseipl() and splx() pair.
                     66:  */
                     67:
                     68: #if defined(DIAGNOSTIC) || defined(MULTIPROCESSOR) || defined(LOCKDEBUG)
                     69: #define        FULL
                     70: #endif
                     71:
                     72: /*
                     73:  * Debugging support.
                     74:  */
                     75:
                     76: #define        MUTEX_WANTLOCK(mtx)                                     \
1.23      yamt       77:     LOCKDEBUG_WANTLOCK(MUTEX_DEBUG_P(mtx), (mtx),              \
1.40      ad         78:         (uintptr_t)__builtin_return_address(0), false, false)
1.2       ad         79: #define        MUTEX_LOCKED(mtx)                                       \
1.42      ad         80:     LOCKDEBUG_LOCKED(MUTEX_DEBUG_P(mtx), (mtx), NULL,          \
1.2       ad         81:         (uintptr_t)__builtin_return_address(0), 0)
                     82: #define        MUTEX_UNLOCKED(mtx)                                     \
1.23      yamt       83:     LOCKDEBUG_UNLOCKED(MUTEX_DEBUG_P(mtx), (mtx),              \
1.2       ad         84:         (uintptr_t)__builtin_return_address(0), 0)
                     85: #define        MUTEX_ABORT(mtx, msg)                                   \
1.17      ad         86:     mutex_abort(mtx, __func__, msg)
1.2       ad         87:
                     88: #if defined(LOCKDEBUG)
                     89:
                     90: #define        MUTEX_DASSERT(mtx, cond)                                \
                     91: do {                                                           \
                     92:        if (!(cond))                                            \
                     93:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                     94: } while (/* CONSTCOND */ 0);
                     95:
                     96: #else  /* LOCKDEBUG */
                     97:
                     98: #define        MUTEX_DASSERT(mtx, cond)        /* nothing */
                     99:
                    100: #endif /* LOCKDEBUG */
                    101:
                    102: #if defined(DIAGNOSTIC)
                    103:
                    104: #define        MUTEX_ASSERT(mtx, cond)                                 \
                    105: do {                                                           \
                    106:        if (!(cond))                                            \
                    107:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                    108: } while (/* CONSTCOND */ 0)
                    109:
                    110: #else  /* DIAGNOSTIC */
                    111:
                    112: #define        MUTEX_ASSERT(mtx, cond) /* nothing */
                    113:
                    114: #endif /* DIAGNOSTIC */
                    115:
                    116: /*
                    117:  * Spin mutex SPL save / restore.
                    118:  */
1.12      matt      119: #ifndef MUTEX_COUNT_BIAS
                    120: #define        MUTEX_COUNT_BIAS        0
                    121: #endif
1.2       ad        122:
                    123: #define        MUTEX_SPIN_SPLRAISE(mtx)                                        \
                    124: do {                                                                   \
1.36      ad        125:        struct cpu_info *x__ci;                                         \
1.2       ad        126:        int x__cnt, s;                                                  \
1.36      ad        127:        s = splraiseipl(mtx->mtx_ipl);                                  \
                    128:        x__ci = curcpu();                                               \
1.2       ad        129:        x__cnt = x__ci->ci_mtx_count--;                                 \
1.37      ad        130:        __insn_barrier();                                               \
1.12      matt      131:        if (x__cnt == MUTEX_COUNT_BIAS)                                 \
1.2       ad        132:                x__ci->ci_mtx_oldspl = (s);                             \
                    133: } while (/* CONSTCOND */ 0)
                    134:
                    135: #define        MUTEX_SPIN_SPLRESTORE(mtx)                                      \
                    136: do {                                                                   \
                    137:        struct cpu_info *x__ci = curcpu();                              \
                    138:        int s = x__ci->ci_mtx_oldspl;                                   \
                    139:        __insn_barrier();                                               \
1.12      matt      140:        if (++(x__ci->ci_mtx_count) == MUTEX_COUNT_BIAS)                \
1.2       ad        141:                splx(s);                                                \
                    142: } while (/* CONSTCOND */ 0)
                    143:
                    144: /*
                    145:  * For architectures that provide 'simple' mutexes: they provide a
                    146:  * CAS function that is either MP-safe, or does not need to be MP
                    147:  * safe.  Adaptive mutexes on these architectures do not require an
                    148:  * additional interlock.
                    149:  */
                    150:
                    151: #ifdef __HAVE_SIMPLE_MUTEXES
                    152:
                    153: #define        MUTEX_OWNER(owner)                                              \
                    154:        (owner & MUTEX_THREAD)
                    155: #define        MUTEX_HAS_WAITERS(mtx)                                          \
                    156:        (((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
                    157:
1.23      yamt      158: #define        MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug)                         \
1.49    ! skrll     159:        if (!dodebug)                                                   \
        !           160:                (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG;                  \
1.2       ad        161: do {                                                                   \
                    162: } while (/* CONSTCOND */ 0);
                    163:
1.23      yamt      164: #define        MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl)                        \
1.2       ad        165: do {                                                                   \
                    166:        (mtx)->mtx_owner = MUTEX_BIT_SPIN;                              \
1.49    ! skrll     167:        if (!dodebug)                                                   \
        !           168:                (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG;                  \
1.2       ad        169:        (mtx)->mtx_ipl = makeiplcookie((ipl));                          \
                    170:        __cpu_simple_lock_init(&(mtx)->mtx_lock);                       \
                    171: } while (/* CONSTCOND */ 0)
                    172:
                    173: #define        MUTEX_DESTROY(mtx)                                              \
                    174: do {                                                                   \
                    175:        (mtx)->mtx_owner = MUTEX_THREAD;                                \
                    176: } while (/* CONSTCOND */ 0);
                    177:
                    178: #define        MUTEX_SPIN_P(mtx)               \
                    179:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0)
                    180: #define        MUTEX_ADAPTIVE_P(mtx)           \
                    181:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0)
                    182:
1.49    ! skrll     183: #define        MUTEX_DEBUG_P(mtx)      (((mtx)->mtx_owner & MUTEX_BIT_NODEBUG) == 0)
1.23      yamt      184: #if defined(LOCKDEBUG)
1.49    ! skrll     185: #define        MUTEX_OWNED(owner)              (((owner) & ~MUTEX_BIT_NODEBUG) != 0)
        !           186: #define        MUTEX_INHERITDEBUG(new, old)    (new) |= (old) & MUTEX_BIT_NODEBUG
1.23      yamt      187: #else /* defined(LOCKDEBUG) */
                    188: #define        MUTEX_OWNED(owner)              ((owner) != 0)
                    189: #define        MUTEX_INHERITDEBUG(new, old)    /* nothing */
                    190: #endif /* defined(LOCKDEBUG) */
1.2       ad        191:
                    192: static inline int
                    193: MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
                    194: {
                    195:        int rv;
1.23      yamt      196:        uintptr_t old = 0;
                    197:        uintptr_t new = curthread;
                    198:
                    199:        MUTEX_INHERITDEBUG(old, mtx->mtx_owner);
                    200:        MUTEX_INHERITDEBUG(new, old);
                    201:        rv = MUTEX_CAS(&mtx->mtx_owner, old, new);
1.7       itohy     202:        MUTEX_RECEIVE(mtx);
1.2       ad        203:        return rv;
                    204: }
                    205:
                    206: static inline int
                    207: MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
                    208: {
                    209:        int rv;
                    210:        rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS);
1.7       itohy     211:        MUTEX_RECEIVE(mtx);
1.2       ad        212:        return rv;
                    213: }
                    214:
                    215: static inline void
                    216: MUTEX_RELEASE(kmutex_t *mtx)
                    217: {
1.23      yamt      218:        uintptr_t new;
                    219:
1.7       itohy     220:        MUTEX_GIVE(mtx);
1.23      yamt      221:        new = 0;
                    222:        MUTEX_INHERITDEBUG(new, mtx->mtx_owner);
                    223:        mtx->mtx_owner = new;
1.2       ad        224: }
1.4       ad        225:
                    226: static inline void
                    227: MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
                    228: {
                    229:        /* nothing */
                    230: }
1.2       ad        231: #endif /* __HAVE_SIMPLE_MUTEXES */
                    232:
                    233: /*
                    234:  * Patch in stubs via strong alias where they are not available.
                    235:  */
                    236:
                    237: #if defined(LOCKDEBUG)
                    238: #undef __HAVE_MUTEX_STUBS
                    239: #undef __HAVE_SPIN_MUTEX_STUBS
                    240: #endif
                    241:
                    242: #ifndef __HAVE_MUTEX_STUBS
1.8       itohy     243: __strong_alias(mutex_enter,mutex_vector_enter);
                    244: __strong_alias(mutex_exit,mutex_vector_exit);
1.2       ad        245: #endif
                    246:
                    247: #ifndef __HAVE_SPIN_MUTEX_STUBS
1.8       itohy     248: __strong_alias(mutex_spin_enter,mutex_vector_enter);
                    249: __strong_alias(mutex_spin_exit,mutex_vector_exit);
1.2       ad        250: #endif
                    251:
                    252: void   mutex_abort(kmutex_t *, const char *, const char *);
                    253: void   mutex_dump(volatile void *);
                    254: int    mutex_onproc(uintptr_t, struct cpu_info **);
                    255:
                    256: lockops_t mutex_spin_lockops = {
                    257:        "Mutex",
1.42      ad        258:        LOCKOPS_SPIN,
1.2       ad        259:        mutex_dump
                    260: };
                    261:
                    262: lockops_t mutex_adaptive_lockops = {
                    263:        "Mutex",
1.42      ad        264:        LOCKOPS_SLEEP,
1.2       ad        265:        mutex_dump
                    266: };
                    267:
1.5       yamt      268: syncobj_t mutex_syncobj = {
                    269:        SOBJ_SLEEPQ_SORTED,
                    270:        turnstile_unsleep,
                    271:        turnstile_changepri,
                    272:        sleepq_lendpri,
1.27      ad        273:        (void *)mutex_owner,
1.5       yamt      274: };
                    275:
1.2       ad        276: /*
                    277:  * mutex_dump:
                    278:  *
                    279:  *     Dump the contents of a mutex structure.
                    280:  */
                    281: void
                    282: mutex_dump(volatile void *cookie)
                    283: {
                    284:        volatile kmutex_t *mtx = cookie;
                    285:
                    286:        printf_nolog("owner field  : %#018lx wait/spin: %16d/%d\n",
                    287:            (long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx),
                    288:            MUTEX_SPIN_P(mtx));
                    289: }
                    290:
                    291: /*
                    292:  * mutex_abort:
                    293:  *
1.3       ad        294:  *     Dump information about an error and panic the system.  This
                    295:  *     generates a lot of machine code in the DIAGNOSTIC case, so
                    296:  *     we ask the compiler to not inline it.
1.2       ad        297:  */
1.43      ad        298: void __noinline
1.2       ad        299: mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
                    300: {
                    301:
1.23      yamt      302:        LOCKDEBUG_ABORT(mtx, (MUTEX_SPIN_P(mtx) ?
1.3       ad        303:            &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
1.2       ad        304: }
                    305:
                    306: /*
                    307:  * mutex_init:
                    308:  *
                    309:  *     Initialize a mutex for use.  Note that adaptive mutexes are in
                    310:  *     essence spin mutexes that can sleep to avoid deadlock and wasting
                    311:  *     CPU time.  We can't easily provide a type of mutex that always
                    312:  *     sleeps - see comments in mutex_vector_enter() about releasing
                    313:  *     mutexes unlocked.
                    314:  */
                    315: void
                    316: mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
                    317: {
1.23      yamt      318:        bool dodebug;
1.2       ad        319:
                    320:        memset(mtx, 0, sizeof(*mtx));
                    321:
1.15      ad        322:        switch (type) {
                    323:        case MUTEX_ADAPTIVE:
                    324:                KASSERT(ipl == IPL_NONE);
                    325:                break;
1.22      ad        326:        case MUTEX_DEFAULT:
1.15      ad        327:        case MUTEX_DRIVER:
1.26      ad        328:                if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK ||
                    329:                    ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET ||
                    330:                    ipl == IPL_SOFTSERIAL) {
1.22      ad        331:                        type = MUTEX_ADAPTIVE;
1.26      ad        332:                } else {
1.22      ad        333:                        type = MUTEX_SPIN;
                    334:                }
1.15      ad        335:                break;
                    336:        default:
                    337:                break;
                    338:        }
1.2       ad        339:
                    340:        switch (type) {
1.11      ad        341:        case MUTEX_NODEBUG:
1.23      yamt      342:                dodebug = LOCKDEBUG_ALLOC(mtx, NULL,
1.19      ad        343:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      344:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.11      ad        345:                break;
1.2       ad        346:        case MUTEX_ADAPTIVE:
1.23      yamt      347:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops,
1.19      ad        348:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      349:                MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug);
1.2       ad        350:                break;
                    351:        case MUTEX_SPIN:
1.23      yamt      352:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops,
1.19      ad        353:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      354:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.2       ad        355:                break;
                    356:        default:
                    357:                panic("mutex_init: impossible type");
                    358:                break;
                    359:        }
                    360: }
                    361:
                    362: /*
                    363:  * mutex_destroy:
                    364:  *
                    365:  *     Tear down a mutex.
                    366:  */
                    367: void
                    368: mutex_destroy(kmutex_t *mtx)
                    369: {
                    370:
                    371:        if (MUTEX_ADAPTIVE_P(mtx)) {
                    372:                MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
                    373:                    !MUTEX_HAS_WAITERS(mtx));
                    374:        } else {
1.16      skrll     375:                MUTEX_ASSERT(mtx, !__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock));
1.2       ad        376:        }
                    377:
1.23      yamt      378:        LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), mtx);
1.2       ad        379:        MUTEX_DESTROY(mtx);
                    380: }
                    381:
                    382: /*
                    383:  * mutex_onproc:
                    384:  *
                    385:  *     Return true if an adaptive mutex owner is running on a CPU in the
                    386:  *     system.  If the target is waiting on the kernel big lock, then we
1.15      ad        387:  *     must release it.  This is necessary to avoid deadlock.
1.2       ad        388:  *
                    389:  *     Note that we can't use the mutex owner field as an LWP pointer.  We
                    390:  *     don't have full control over the timing of our execution, and so the
                    391:  *     pointer could be completely invalid by the time we dereference it.
                    392:  */
                    393: #ifdef MULTIPROCESSOR
                    394: int
                    395: mutex_onproc(uintptr_t owner, struct cpu_info **cip)
                    396: {
                    397:        CPU_INFO_ITERATOR cii;
                    398:        struct cpu_info *ci;
                    399:        struct lwp *l;
                    400:
                    401:        if (!MUTEX_OWNED(owner))
                    402:                return 0;
                    403:        l = (struct lwp *)MUTEX_OWNER(owner);
                    404:
1.15      ad        405:        /* See if the target is running on a CPU somewhere. */
1.10      ad        406:        if ((ci = *cip) != NULL && ci->ci_curlwp == l)
1.15      ad        407:                goto run;
                    408:        for (CPU_INFO_FOREACH(cii, ci))
                    409:                if (ci->ci_curlwp == l)
                    410:                        goto run;
1.2       ad        411:
1.15      ad        412:        /* No: it may be safe to block now. */
1.2       ad        413:        *cip = NULL;
                    414:        return 0;
1.15      ad        415:
                    416:  run:
                    417:        /* Target is running; do we need to block? */
                    418:        *cip = ci;
                    419:        return ci->ci_biglock_wanted != l;
1.2       ad        420: }
1.15      ad        421: #endif /* MULTIPROCESSOR */
1.2       ad        422:
                    423: /*
                    424:  * mutex_vector_enter:
                    425:  *
1.45      rmind     426:  *     Support routine for mutex_enter() that must handle all cases.  In
1.2       ad        427:  *     the LOCKDEBUG case, mutex_enter() is always aliased here, even if
                    428:  *     fast-path stubs are available.  If an mutex_spin_enter() stub is
                    429:  *     not available, then it is also aliased directly here.
                    430:  */
                    431: void
                    432: mutex_vector_enter(kmutex_t *mtx)
                    433: {
                    434:        uintptr_t owner, curthread;
                    435:        turnstile_t *ts;
                    436: #ifdef MULTIPROCESSOR
                    437:        struct cpu_info *ci = NULL;
                    438:        u_int count;
                    439: #endif
1.44      wrstuden  440: #ifdef KERN_SA
                    441:        int f;
                    442: #endif
1.2       ad        443:        LOCKSTAT_COUNTER(spincnt);
                    444:        LOCKSTAT_COUNTER(slpcnt);
                    445:        LOCKSTAT_TIMER(spintime);
                    446:        LOCKSTAT_TIMER(slptime);
                    447:        LOCKSTAT_FLAG(lsflag);
                    448:
                    449:        /*
                    450:         * Handle spin mutexes.
                    451:         */
                    452:        if (MUTEX_SPIN_P(mtx)) {
                    453: #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
                    454:                u_int spins = 0;
                    455: #endif
                    456:                MUTEX_SPIN_SPLRAISE(mtx);
                    457:                MUTEX_WANTLOCK(mtx);
                    458: #ifdef FULL
                    459:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
                    460:                        MUTEX_LOCKED(mtx);
                    461:                        return;
                    462:                }
                    463: #if !defined(MULTIPROCESSOR)
                    464:                MUTEX_ABORT(mtx, "locking against myself");
                    465: #else /* !MULTIPROCESSOR */
                    466:
                    467:                LOCKSTAT_ENTER(lsflag);
                    468:                LOCKSTAT_START_TIMER(lsflag, spintime);
                    469:                count = SPINLOCK_BACKOFF_MIN;
                    470:
                    471:                /*
                    472:                 * Spin testing the lock word and do exponential backoff
                    473:                 * to reduce cache line ping-ponging between CPUs.
                    474:                 */
                    475:                do {
                    476:                        if (panicstr != NULL)
                    477:                                break;
1.16      skrll     478:                        while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        479:                                SPINLOCK_BACKOFF(count);
                    480: #ifdef LOCKDEBUG
                    481:                                if (SPINLOCK_SPINOUT(spins))
                    482:                                        MUTEX_ABORT(mtx, "spinout");
                    483: #endif /* LOCKDEBUG */
                    484:                        }
                    485:                } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    486:
                    487:                if (count != SPINLOCK_BACKOFF_MIN) {
                    488:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    489:                        LOCKSTAT_EVENT(lsflag, mtx,
                    490:                            LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    491:                }
                    492:                LOCKSTAT_EXIT(lsflag);
                    493: #endif /* !MULTIPROCESSOR */
                    494: #endif /* FULL */
                    495:                MUTEX_LOCKED(mtx);
                    496:                return;
                    497:        }
                    498:
                    499:        curthread = (uintptr_t)curlwp;
                    500:
                    501:        MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    502:        MUTEX_ASSERT(mtx, curthread != 0);
                    503:        MUTEX_WANTLOCK(mtx);
                    504:
                    505:        if (panicstr == NULL) {
                    506:                LOCKDEBUG_BARRIER(&kernel_lock, 1);
                    507:        }
                    508:
                    509:        LOCKSTAT_ENTER(lsflag);
                    510:
                    511:        /*
                    512:         * Adaptive mutex; spin trying to acquire the mutex.  If we
                    513:         * determine that the owner is not running on a processor,
                    514:         * then we stop spinning, and sleep instead.
                    515:         */
1.34      ad        516:        for (owner = mtx->mtx_owner;;) {
1.2       ad        517:                if (!MUTEX_OWNED(owner)) {
                    518:                        /*
                    519:                         * Mutex owner clear could mean two things:
                    520:                         *
                    521:                         *      * The mutex has been released.
                    522:                         *      * The owner field hasn't been set yet.
                    523:                         *
                    524:                         * Try to acquire it again.  If that fails,
                    525:                         * we'll just loop again.
                    526:                         */
                    527:                        if (MUTEX_ACQUIRE(mtx, curthread))
                    528:                                break;
1.34      ad        529:                        owner = mtx->mtx_owner;
1.2       ad        530:                        continue;
                    531:                }
                    532:
1.45      rmind     533:                if (__predict_false(panicstr != NULL))
1.2       ad        534:                        return;
1.45      rmind     535:                if (__predict_false(MUTEX_OWNER(owner) == curthread))
1.2       ad        536:                        MUTEX_ABORT(mtx, "locking against myself");
                    537:
                    538: #ifdef MULTIPROCESSOR
                    539:                /*
                    540:                 * Check to see if the owner is running on a processor.
                    541:                 * If so, then we should just spin, as the owner will
                    542:                 * likely release the lock very soon.
                    543:                 */
                    544:                if (mutex_onproc(owner, &ci)) {
                    545:                        LOCKSTAT_START_TIMER(lsflag, spintime);
                    546:                        count = SPINLOCK_BACKOFF_MIN;
                    547:                        for (;;) {
1.34      ad        548:                                SPINLOCK_BACKOFF(count);
1.2       ad        549:                                owner = mtx->mtx_owner;
                    550:                                if (!mutex_onproc(owner, &ci))
                    551:                                        break;
                    552:                        }
                    553:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    554:                        LOCKSTAT_COUNT(spincnt, 1);
                    555:                        if (!MUTEX_OWNED(owner))
                    556:                                continue;
                    557:                }
                    558: #endif
                    559:
                    560:                ts = turnstile_lookup(mtx);
                    561:
                    562:                /*
                    563:                 * Once we have the turnstile chain interlock, mark the
                    564:                 * mutex has having waiters.  If that fails, spin again:
                    565:                 * chances are that the mutex has been released.
                    566:                 */
                    567:                if (!MUTEX_SET_WAITERS(mtx, owner)) {
                    568:                        turnstile_exit(mtx);
1.34      ad        569:                        owner = mtx->mtx_owner;
1.2       ad        570:                        continue;
                    571:                }
                    572:
                    573: #ifdef MULTIPROCESSOR
                    574:                /*
                    575:                 * mutex_exit() is permitted to release the mutex without
                    576:                 * any interlocking instructions, and the following can
                    577:                 * occur as a result:
                    578:                 *
                    579:                 *  CPU 1: MUTEX_SET_WAITERS()      CPU2: mutex_exit()
                    580:                 * ---------------------------- ----------------------------
                    581:                 *              ..                  acquire cache line
                    582:                 *              ..                   test for waiters
                    583:                 *      acquire cache line    <-      lose cache line
                    584:                 *       lock cache line                   ..
                    585:                 *     verify mutex is held                ..
                    586:                 *          set waiters                    ..
                    587:                 *       unlock cache line                 ..
                    588:                 *        lose cache line     ->    acquire cache line
                    589:                 *              ..                clear lock word, waiters
                    590:                 *        return success
                    591:                 *
                    592:                 * There is a another race that can occur: a third CPU could
                    593:                 * acquire the mutex as soon as it is released.  Since
                    594:                 * adaptive mutexes are primarily spin mutexes, this is not
                    595:                 * something that we need to worry about too much.  What we
                    596:                 * do need to ensure is that the waiters bit gets set.
                    597:                 *
                    598:                 * To allow the unlocked release, we need to make some
                    599:                 * assumptions here:
                    600:                 *
                    601:                 * o Release is the only non-atomic/unlocked operation
                    602:                 *   that can be performed on the mutex.  (It must still
                    603:                 *   be atomic on the local CPU, e.g. in case interrupted
                    604:                 *   or preempted).
                    605:                 *
                    606:                 * o At any given time, MUTEX_SET_WAITERS() can only ever
1.21      pooka     607:                 *   be in progress on one CPU in the system - guaranteed
1.2       ad        608:                 *   by the turnstile chain lock.
                    609:                 *
                    610:                 * o No other operations other than MUTEX_SET_WAITERS()
                    611:                 *   and release can modify a mutex with a non-zero
                    612:                 *   owner field.
                    613:                 *
                    614:                 * o The result of a successful MUTEX_SET_WAITERS() call
                    615:                 *   is an unbuffered write that is immediately visible
                    616:                 *   to all other processors in the system.
                    617:                 *
                    618:                 * o If the holding LWP switches away, it posts a store
                    619:                 *   fence before changing curlwp, ensuring that any
                    620:                 *   overwrite of the mutex waiters flag by mutex_exit()
                    621:                 *   completes before the modification of curlwp becomes
                    622:                 *   visible to this CPU.
                    623:                 *
1.14      yamt      624:                 * o mi_switch() posts a store fence before setting curlwp
1.2       ad        625:                 *   and before resuming execution of an LWP.
                    626:                 *
                    627:                 * o _kernel_lock() posts a store fence before setting
                    628:                 *   curcpu()->ci_biglock_wanted, and after clearing it.
                    629:                 *   This ensures that any overwrite of the mutex waiters
                    630:                 *   flag by mutex_exit() completes before the modification
                    631:                 *   of ci_biglock_wanted becomes visible.
                    632:                 *
                    633:                 * We now post a read memory barrier (after setting the
                    634:                 * waiters field) and check the lock holder's status again.
                    635:                 * Some of the possible outcomes (not an exhaustive list):
                    636:                 *
                    637:                 * 1. The onproc check returns true: the holding LWP is
                    638:                 *    running again.  The lock may be released soon and
                    639:                 *    we should spin.  Importantly, we can't trust the
                    640:                 *    value of the waiters flag.
                    641:                 *
                    642:                 * 2. The onproc check returns false: the holding LWP is
1.39      yamt      643:                 *    not running.  We now have the opportunity to check
1.2       ad        644:                 *    if mutex_exit() has blatted the modifications made
                    645:                 *    by MUTEX_SET_WAITERS().
                    646:                 *
                    647:                 * 3. The onproc check returns false: the holding LWP may
                    648:                 *    or may not be running.  It has context switched at
                    649:                 *    some point during our check.  Again, we have the
                    650:                 *    chance to see if the waiters bit is still set or
                    651:                 *    has been overwritten.
                    652:                 *
                    653:                 * 4. The onproc check returns false: the holding LWP is
                    654:                 *    running on a CPU, but wants the big lock.  It's OK
                    655:                 *    to check the waiters field in this case.
                    656:                 *
                    657:                 * 5. The has-waiters check fails: the mutex has been
                    658:                 *    released, the waiters flag cleared and another LWP
                    659:                 *    now owns the mutex.
                    660:                 *
                    661:                 * 6. The has-waiters check fails: the mutex has been
                    662:                 *    released.
                    663:                 *
                    664:                 * If the waiters bit is not set it's unsafe to go asleep,
                    665:                 * as we might never be awoken.
                    666:                 */
1.24      ad        667:                if ((membar_consumer(), mutex_onproc(owner, &ci)) ||
                    668:                    (membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) {
1.2       ad        669:                        turnstile_exit(mtx);
1.34      ad        670:                        owner = mtx->mtx_owner;
1.2       ad        671:                        continue;
                    672:                }
                    673: #endif /* MULTIPROCESSOR */
                    674:
1.44      wrstuden  675: #ifdef KERN_SA
                    676:                /*
                    677:                 * Sleeping for a mutex should not generate an upcall.
                    678:                 * So set LP_SA_NOBLOCK to indicate this.
                    679:                 * f indicates if we should clear LP_SA_NOBLOCK when done.
                    680:                 */
                    681:                f = ~curlwp->l_pflag & LP_SA_NOBLOCK;
                    682:                curlwp->l_pflag |= LP_SA_NOBLOCK;
                    683: #endif /* KERN_SA */
                    684:
1.2       ad        685:                LOCKSTAT_START_TIMER(lsflag, slptime);
                    686:
1.5       yamt      687:                turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
1.2       ad        688:
                    689:                LOCKSTAT_STOP_TIMER(lsflag, slptime);
                    690:                LOCKSTAT_COUNT(slpcnt, 1);
1.34      ad        691:
1.44      wrstuden  692: #ifdef KERN_SA
                    693:                curlwp->l_pflag ^= f;
                    694: #endif /* KERN_SA */
                    695:
1.34      ad        696:                owner = mtx->mtx_owner;
1.2       ad        697:        }
                    698:
                    699:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
                    700:            slpcnt, slptime);
                    701:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
                    702:            spincnt, spintime);
                    703:        LOCKSTAT_EXIT(lsflag);
                    704:
                    705:        MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    706:        MUTEX_LOCKED(mtx);
                    707: }
                    708:
                    709: /*
                    710:  * mutex_vector_exit:
                    711:  *
                    712:  *     Support routine for mutex_exit() that handles all cases.
                    713:  */
                    714: void
                    715: mutex_vector_exit(kmutex_t *mtx)
                    716: {
                    717:        turnstile_t *ts;
                    718:        uintptr_t curthread;
                    719:
                    720:        if (MUTEX_SPIN_P(mtx)) {
                    721: #ifdef FULL
1.33      ad        722:                if (__predict_false(!__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock))) {
                    723:                        if (panicstr != NULL)
                    724:                                return;
1.2       ad        725:                        MUTEX_ABORT(mtx, "exiting unheld spin mutex");
1.33      ad        726:                }
1.2       ad        727:                MUTEX_UNLOCKED(mtx);
                    728:                __cpu_simple_unlock(&mtx->mtx_lock);
                    729: #endif
                    730:                MUTEX_SPIN_SPLRESTORE(mtx);
                    731:                return;
                    732:        }
                    733:
1.11      ad        734:        if (__predict_false((uintptr_t)panicstr | cold)) {
1.2       ad        735:                MUTEX_UNLOCKED(mtx);
                    736:                MUTEX_RELEASE(mtx);
                    737:                return;
                    738:        }
                    739:
                    740:        curthread = (uintptr_t)curlwp;
                    741:        MUTEX_DASSERT(mtx, curthread != 0);
                    742:        MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    743:        MUTEX_UNLOCKED(mtx);
                    744:
1.15      ad        745: #ifdef LOCKDEBUG
                    746:        /*
                    747:         * Avoid having to take the turnstile chain lock every time
                    748:         * around.  Raise the priority level to splhigh() in order
                    749:         * to disable preemption and so make the following atomic.
                    750:         */
                    751:        {
                    752:                int s = splhigh();
                    753:                if (!MUTEX_HAS_WAITERS(mtx)) {
                    754:                        MUTEX_RELEASE(mtx);
                    755:                        splx(s);
                    756:                        return;
                    757:                }
                    758:                splx(s);
                    759:        }
                    760: #endif
                    761:
1.2       ad        762:        /*
                    763:         * Get this lock's turnstile.  This gets the interlock on
                    764:         * the sleep queue.  Once we have that, we can clear the
                    765:         * lock.  If there was no turnstile for the lock, there
                    766:         * were no waiters remaining.
                    767:         */
                    768:        ts = turnstile_lookup(mtx);
                    769:
                    770:        if (ts == NULL) {
                    771:                MUTEX_RELEASE(mtx);
                    772:                turnstile_exit(mtx);
                    773:        } else {
                    774:                MUTEX_RELEASE(mtx);
                    775:                turnstile_wakeup(ts, TS_WRITER_Q,
                    776:                    TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    777:        }
                    778: }
                    779:
1.4       ad        780: #ifndef __HAVE_SIMPLE_MUTEXES
                    781: /*
                    782:  * mutex_wakeup:
                    783:  *
                    784:  *     Support routine for mutex_exit() that wakes up all waiters.
                    785:  *     We assume that the mutex has been released, but it need not
                    786:  *     be.
                    787:  */
                    788: void
                    789: mutex_wakeup(kmutex_t *mtx)
                    790: {
                    791:        turnstile_t *ts;
                    792:
                    793:        ts = turnstile_lookup(mtx);
                    794:        if (ts == NULL) {
                    795:                turnstile_exit(mtx);
                    796:                return;
                    797:        }
                    798:        MUTEX_CLEAR_WAITERS(mtx);
                    799:        turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    800: }
                    801: #endif /* !__HAVE_SIMPLE_MUTEXES */
                    802:
1.2       ad        803: /*
                    804:  * mutex_owned:
                    805:  *
1.3       ad        806:  *     Return true if the current LWP (adaptive) or CPU (spin)
                    807:  *     holds the mutex.
1.2       ad        808:  */
                    809: int
                    810: mutex_owned(kmutex_t *mtx)
                    811: {
                    812:
1.35      ad        813:        if (mtx == NULL)
                    814:                return 0;
1.2       ad        815:        if (MUTEX_ADAPTIVE_P(mtx))
                    816:                return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
                    817: #ifdef FULL
1.16      skrll     818:        return __SIMPLELOCK_LOCKED_P(&mtx->mtx_lock);
1.2       ad        819: #else
                    820:        return 1;
                    821: #endif
                    822: }
                    823:
                    824: /*
                    825:  * mutex_owner:
                    826:  *
1.6       ad        827:  *     Return the current owner of an adaptive mutex.  Used for
                    828:  *     priority inheritance.
1.2       ad        829:  */
1.27      ad        830: lwp_t *
                    831: mutex_owner(kmutex_t *mtx)
1.2       ad        832: {
                    833:
                    834:        MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    835:        return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner);
                    836: }
                    837:
                    838: /*
                    839:  * mutex_tryenter:
                    840:  *
                    841:  *     Try to acquire the mutex; return non-zero if we did.
                    842:  */
                    843: int
                    844: mutex_tryenter(kmutex_t *mtx)
                    845: {
                    846:        uintptr_t curthread;
                    847:
                    848:        /*
                    849:         * Handle spin mutexes.
                    850:         */
                    851:        if (MUTEX_SPIN_P(mtx)) {
                    852:                MUTEX_SPIN_SPLRAISE(mtx);
                    853: #ifdef FULL
                    854:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
1.4       ad        855:                        MUTEX_WANTLOCK(mtx);
1.2       ad        856:                        MUTEX_LOCKED(mtx);
                    857:                        return 1;
                    858:                }
                    859:                MUTEX_SPIN_SPLRESTORE(mtx);
                    860: #else
1.4       ad        861:                MUTEX_WANTLOCK(mtx);
1.2       ad        862:                MUTEX_LOCKED(mtx);
                    863:                return 1;
                    864: #endif
                    865:        } else {
                    866:                curthread = (uintptr_t)curlwp;
                    867:                MUTEX_ASSERT(mtx, curthread != 0);
                    868:                if (MUTEX_ACQUIRE(mtx, curthread)) {
1.4       ad        869:                        MUTEX_WANTLOCK(mtx);
1.2       ad        870:                        MUTEX_LOCKED(mtx);
                    871:                        MUTEX_DASSERT(mtx,
                    872:                            MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    873:                        return 1;
                    874:                }
                    875:        }
                    876:
                    877:        return 0;
                    878: }
                    879:
                    880: #if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL)
                    881: /*
                    882:  * mutex_spin_retry:
                    883:  *
                    884:  *     Support routine for mutex_spin_enter().  Assumes that the caller
                    885:  *     has already raised the SPL, and adjusted counters.
                    886:  */
                    887: void
                    888: mutex_spin_retry(kmutex_t *mtx)
                    889: {
                    890: #ifdef MULTIPROCESSOR
                    891:        u_int count;
                    892:        LOCKSTAT_TIMER(spintime);
                    893:        LOCKSTAT_FLAG(lsflag);
                    894: #ifdef LOCKDEBUG
                    895:        u_int spins = 0;
                    896: #endif /* LOCKDEBUG */
                    897:
                    898:        MUTEX_WANTLOCK(mtx);
                    899:
                    900:        LOCKSTAT_ENTER(lsflag);
                    901:        LOCKSTAT_START_TIMER(lsflag, spintime);
                    902:        count = SPINLOCK_BACKOFF_MIN;
                    903:
                    904:        /*
                    905:         * Spin testing the lock word and do exponential backoff
                    906:         * to reduce cache line ping-ponging between CPUs.
                    907:         */
                    908:        do {
                    909:                if (panicstr != NULL)
                    910:                        break;
1.16      skrll     911:                while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        912:                        SPINLOCK_BACKOFF(count);
                    913: #ifdef LOCKDEBUG
                    914:                        if (SPINLOCK_SPINOUT(spins))
                    915:                                MUTEX_ABORT(mtx, "spinout");
                    916: #endif /* LOCKDEBUG */
                    917:                }
                    918:        } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    919:
                    920:        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    921:        LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    922:        LOCKSTAT_EXIT(lsflag);
                    923:
                    924:        MUTEX_LOCKED(mtx);
                    925: #else  /* MULTIPROCESSOR */
                    926:        MUTEX_ABORT(mtx, "locking against myself");
                    927: #endif /* MULTIPROCESSOR */
                    928: }
                    929: #endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */

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