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Annotation of src/sys/kern/kern_mutex.c, Revision 1.51

1.51    ! rmind       1: /*     $NetBSD: kern_mutex.c,v 1.50 2011/03/20 23:19:16 rmind 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>
1.51    ! rmind      43: __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.50 2011/03/20 23:19:16 rmind 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>
1.50      rmind      56: #include <sys/types.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:  */
                    120:
                    121: #define        MUTEX_SPIN_SPLRAISE(mtx)                                        \
                    122: do {                                                                   \
1.36      ad        123:        struct cpu_info *x__ci;                                         \
1.2       ad        124:        int x__cnt, s;                                                  \
1.36      ad        125:        s = splraiseipl(mtx->mtx_ipl);                                  \
                    126:        x__ci = curcpu();                                               \
1.2       ad        127:        x__cnt = x__ci->ci_mtx_count--;                                 \
1.37      ad        128:        __insn_barrier();                                               \
1.51    ! rmind     129:        if (x__cnt == 0)                                                \
1.2       ad        130:                x__ci->ci_mtx_oldspl = (s);                             \
                    131: } while (/* CONSTCOND */ 0)
                    132:
                    133: #define        MUTEX_SPIN_SPLRESTORE(mtx)                                      \
                    134: do {                                                                   \
                    135:        struct cpu_info *x__ci = curcpu();                              \
                    136:        int s = x__ci->ci_mtx_oldspl;                                   \
                    137:        __insn_barrier();                                               \
1.51    ! rmind     138:        if (++(x__ci->ci_mtx_count) == 0)                       \
1.2       ad        139:                splx(s);                                                \
                    140: } while (/* CONSTCOND */ 0)
                    141:
                    142: /*
                    143:  * For architectures that provide 'simple' mutexes: they provide a
                    144:  * CAS function that is either MP-safe, or does not need to be MP
                    145:  * safe.  Adaptive mutexes on these architectures do not require an
                    146:  * additional interlock.
                    147:  */
                    148:
                    149: #ifdef __HAVE_SIMPLE_MUTEXES
                    150:
                    151: #define        MUTEX_OWNER(owner)                                              \
                    152:        (owner & MUTEX_THREAD)
                    153: #define        MUTEX_HAS_WAITERS(mtx)                                          \
                    154:        (((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
                    155:
1.23      yamt      156: #define        MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug)                         \
1.49      skrll     157:        if (!dodebug)                                                   \
                    158:                (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG;                  \
1.2       ad        159: do {                                                                   \
                    160: } while (/* CONSTCOND */ 0);
                    161:
1.23      yamt      162: #define        MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl)                        \
1.2       ad        163: do {                                                                   \
                    164:        (mtx)->mtx_owner = MUTEX_BIT_SPIN;                              \
1.49      skrll     165:        if (!dodebug)                                                   \
                    166:                (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG;                  \
1.2       ad        167:        (mtx)->mtx_ipl = makeiplcookie((ipl));                          \
                    168:        __cpu_simple_lock_init(&(mtx)->mtx_lock);                       \
                    169: } while (/* CONSTCOND */ 0)
                    170:
                    171: #define        MUTEX_DESTROY(mtx)                                              \
                    172: do {                                                                   \
                    173:        (mtx)->mtx_owner = MUTEX_THREAD;                                \
                    174: } while (/* CONSTCOND */ 0);
                    175:
                    176: #define        MUTEX_SPIN_P(mtx)               \
                    177:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0)
                    178: #define        MUTEX_ADAPTIVE_P(mtx)           \
                    179:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0)
                    180:
1.49      skrll     181: #define        MUTEX_DEBUG_P(mtx)      (((mtx)->mtx_owner & MUTEX_BIT_NODEBUG) == 0)
1.23      yamt      182: #if defined(LOCKDEBUG)
1.49      skrll     183: #define        MUTEX_OWNED(owner)              (((owner) & ~MUTEX_BIT_NODEBUG) != 0)
                    184: #define        MUTEX_INHERITDEBUG(new, old)    (new) |= (old) & MUTEX_BIT_NODEBUG
1.23      yamt      185: #else /* defined(LOCKDEBUG) */
                    186: #define        MUTEX_OWNED(owner)              ((owner) != 0)
                    187: #define        MUTEX_INHERITDEBUG(new, old)    /* nothing */
                    188: #endif /* defined(LOCKDEBUG) */
1.2       ad        189:
                    190: static inline int
                    191: MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
                    192: {
                    193:        int rv;
1.23      yamt      194:        uintptr_t old = 0;
                    195:        uintptr_t new = curthread;
                    196:
                    197:        MUTEX_INHERITDEBUG(old, mtx->mtx_owner);
                    198:        MUTEX_INHERITDEBUG(new, old);
                    199:        rv = MUTEX_CAS(&mtx->mtx_owner, old, new);
1.7       itohy     200:        MUTEX_RECEIVE(mtx);
1.2       ad        201:        return rv;
                    202: }
                    203:
                    204: static inline int
                    205: MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
                    206: {
                    207:        int rv;
                    208:        rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS);
1.7       itohy     209:        MUTEX_RECEIVE(mtx);
1.2       ad        210:        return rv;
                    211: }
                    212:
                    213: static inline void
                    214: MUTEX_RELEASE(kmutex_t *mtx)
                    215: {
1.23      yamt      216:        uintptr_t new;
                    217:
1.7       itohy     218:        MUTEX_GIVE(mtx);
1.23      yamt      219:        new = 0;
                    220:        MUTEX_INHERITDEBUG(new, mtx->mtx_owner);
                    221:        mtx->mtx_owner = new;
1.2       ad        222: }
1.4       ad        223:
                    224: static inline void
                    225: MUTEX_CLEAR_WAITERS(kmutex_t *mtx)
                    226: {
                    227:        /* nothing */
                    228: }
1.2       ad        229: #endif /* __HAVE_SIMPLE_MUTEXES */
                    230:
                    231: /*
                    232:  * Patch in stubs via strong alias where they are not available.
                    233:  */
                    234:
                    235: #if defined(LOCKDEBUG)
                    236: #undef __HAVE_MUTEX_STUBS
                    237: #undef __HAVE_SPIN_MUTEX_STUBS
                    238: #endif
                    239:
                    240: #ifndef __HAVE_MUTEX_STUBS
1.8       itohy     241: __strong_alias(mutex_enter,mutex_vector_enter);
                    242: __strong_alias(mutex_exit,mutex_vector_exit);
1.2       ad        243: #endif
                    244:
                    245: #ifndef __HAVE_SPIN_MUTEX_STUBS
1.8       itohy     246: __strong_alias(mutex_spin_enter,mutex_vector_enter);
                    247: __strong_alias(mutex_spin_exit,mutex_vector_exit);
1.2       ad        248: #endif
                    249:
1.50      rmind     250: static void            mutex_abort(kmutex_t *, const char *, const char *);
                    251: static void            mutex_dump(volatile void *);
1.2       ad        252:
                    253: lockops_t mutex_spin_lockops = {
                    254:        "Mutex",
1.42      ad        255:        LOCKOPS_SPIN,
1.2       ad        256:        mutex_dump
                    257: };
                    258:
                    259: lockops_t mutex_adaptive_lockops = {
                    260:        "Mutex",
1.42      ad        261:        LOCKOPS_SLEEP,
1.2       ad        262:        mutex_dump
                    263: };
                    264:
1.5       yamt      265: syncobj_t mutex_syncobj = {
                    266:        SOBJ_SLEEPQ_SORTED,
                    267:        turnstile_unsleep,
                    268:        turnstile_changepri,
                    269:        sleepq_lendpri,
1.27      ad        270:        (void *)mutex_owner,
1.5       yamt      271: };
                    272:
1.2       ad        273: /*
                    274:  * mutex_dump:
                    275:  *
                    276:  *     Dump the contents of a mutex structure.
                    277:  */
                    278: void
                    279: mutex_dump(volatile void *cookie)
                    280: {
                    281:        volatile kmutex_t *mtx = cookie;
                    282:
                    283:        printf_nolog("owner field  : %#018lx wait/spin: %16d/%d\n",
                    284:            (long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx),
                    285:            MUTEX_SPIN_P(mtx));
                    286: }
                    287:
                    288: /*
                    289:  * mutex_abort:
                    290:  *
1.3       ad        291:  *     Dump information about an error and panic the system.  This
                    292:  *     generates a lot of machine code in the DIAGNOSTIC case, so
                    293:  *     we ask the compiler to not inline it.
1.2       ad        294:  */
1.43      ad        295: void __noinline
1.2       ad        296: mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
                    297: {
                    298:
1.23      yamt      299:        LOCKDEBUG_ABORT(mtx, (MUTEX_SPIN_P(mtx) ?
1.3       ad        300:            &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
1.2       ad        301: }
                    302:
                    303: /*
                    304:  * mutex_init:
                    305:  *
                    306:  *     Initialize a mutex for use.  Note that adaptive mutexes are in
                    307:  *     essence spin mutexes that can sleep to avoid deadlock and wasting
                    308:  *     CPU time.  We can't easily provide a type of mutex that always
                    309:  *     sleeps - see comments in mutex_vector_enter() about releasing
                    310:  *     mutexes unlocked.
                    311:  */
                    312: void
                    313: mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
                    314: {
1.23      yamt      315:        bool dodebug;
1.2       ad        316:
                    317:        memset(mtx, 0, sizeof(*mtx));
                    318:
1.15      ad        319:        switch (type) {
                    320:        case MUTEX_ADAPTIVE:
                    321:                KASSERT(ipl == IPL_NONE);
                    322:                break;
1.22      ad        323:        case MUTEX_DEFAULT:
1.15      ad        324:        case MUTEX_DRIVER:
1.26      ad        325:                if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK ||
                    326:                    ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET ||
                    327:                    ipl == IPL_SOFTSERIAL) {
1.22      ad        328:                        type = MUTEX_ADAPTIVE;
1.26      ad        329:                } else {
1.22      ad        330:                        type = MUTEX_SPIN;
                    331:                }
1.15      ad        332:                break;
                    333:        default:
                    334:                break;
                    335:        }
1.2       ad        336:
                    337:        switch (type) {
1.11      ad        338:        case MUTEX_NODEBUG:
1.23      yamt      339:                dodebug = LOCKDEBUG_ALLOC(mtx, NULL,
1.19      ad        340:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      341:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.11      ad        342:                break;
1.2       ad        343:        case MUTEX_ADAPTIVE:
1.23      yamt      344:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops,
1.19      ad        345:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      346:                MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug);
1.2       ad        347:                break;
                    348:        case MUTEX_SPIN:
1.23      yamt      349:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops,
1.19      ad        350:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      351:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.2       ad        352:                break;
                    353:        default:
                    354:                panic("mutex_init: impossible type");
                    355:                break;
                    356:        }
                    357: }
                    358:
                    359: /*
                    360:  * mutex_destroy:
                    361:  *
                    362:  *     Tear down a mutex.
                    363:  */
                    364: void
                    365: mutex_destroy(kmutex_t *mtx)
                    366: {
                    367:
                    368:        if (MUTEX_ADAPTIVE_P(mtx)) {
                    369:                MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
                    370:                    !MUTEX_HAS_WAITERS(mtx));
                    371:        } else {
1.16      skrll     372:                MUTEX_ASSERT(mtx, !__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock));
1.2       ad        373:        }
                    374:
1.23      yamt      375:        LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), mtx);
1.2       ad        376:        MUTEX_DESTROY(mtx);
                    377: }
                    378:
1.50      rmind     379: #ifdef MULTIPROCESSOR
1.2       ad        380: /*
1.50      rmind     381:  * mutex_oncpu:
1.2       ad        382:  *
                    383:  *     Return true if an adaptive mutex owner is running on a CPU in the
                    384:  *     system.  If the target is waiting on the kernel big lock, then we
1.15      ad        385:  *     must release it.  This is necessary to avoid deadlock.
1.2       ad        386:  */
1.50      rmind     387: static bool
                    388: mutex_oncpu(uintptr_t owner)
1.2       ad        389: {
                    390:        struct cpu_info *ci;
1.50      rmind     391:        lwp_t *l;
1.2       ad        392:
1.50      rmind     393:        KASSERT(kpreempt_disabled());
                    394:
                    395:        if (!MUTEX_OWNED(owner)) {
                    396:                return false;
                    397:        }
1.2       ad        398:
1.50      rmind     399:        /*
                    400:         * See lwp_dtor() why dereference of the LWP pointer is safe.
                    401:         * We must have kernel preemption disabled for that.
                    402:         */
                    403:        l = (lwp_t *)MUTEX_OWNER(owner);
                    404:        ci = l->l_cpu;
1.2       ad        405:
1.50      rmind     406:        if (ci && ci->ci_curlwp == l) {
                    407:                /* Target is running; do we need to block? */
                    408:                return (ci->ci_biglock_wanted != l);
                    409:        }
1.15      ad        410:
1.50      rmind     411:        /* Not running.  It may be safe to block now. */
                    412:        return false;
1.2       ad        413: }
1.15      ad        414: #endif /* MULTIPROCESSOR */
1.2       ad        415:
                    416: /*
                    417:  * mutex_vector_enter:
                    418:  *
1.45      rmind     419:  *     Support routine for mutex_enter() that must handle all cases.  In
1.2       ad        420:  *     the LOCKDEBUG case, mutex_enter() is always aliased here, even if
                    421:  *     fast-path stubs are available.  If an mutex_spin_enter() stub is
                    422:  *     not available, then it is also aliased directly here.
                    423:  */
                    424: void
                    425: mutex_vector_enter(kmutex_t *mtx)
                    426: {
                    427:        uintptr_t owner, curthread;
                    428:        turnstile_t *ts;
                    429: #ifdef MULTIPROCESSOR
                    430:        u_int count;
                    431: #endif
1.44      wrstuden  432: #ifdef KERN_SA
                    433:        int f;
                    434: #endif
1.2       ad        435:        LOCKSTAT_COUNTER(spincnt);
                    436:        LOCKSTAT_COUNTER(slpcnt);
                    437:        LOCKSTAT_TIMER(spintime);
                    438:        LOCKSTAT_TIMER(slptime);
                    439:        LOCKSTAT_FLAG(lsflag);
                    440:
                    441:        /*
                    442:         * Handle spin mutexes.
                    443:         */
                    444:        if (MUTEX_SPIN_P(mtx)) {
                    445: #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
                    446:                u_int spins = 0;
                    447: #endif
                    448:                MUTEX_SPIN_SPLRAISE(mtx);
                    449:                MUTEX_WANTLOCK(mtx);
                    450: #ifdef FULL
                    451:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
                    452:                        MUTEX_LOCKED(mtx);
                    453:                        return;
                    454:                }
                    455: #if !defined(MULTIPROCESSOR)
                    456:                MUTEX_ABORT(mtx, "locking against myself");
                    457: #else /* !MULTIPROCESSOR */
                    458:
                    459:                LOCKSTAT_ENTER(lsflag);
                    460:                LOCKSTAT_START_TIMER(lsflag, spintime);
                    461:                count = SPINLOCK_BACKOFF_MIN;
                    462:
                    463:                /*
                    464:                 * Spin testing the lock word and do exponential backoff
                    465:                 * to reduce cache line ping-ponging between CPUs.
                    466:                 */
                    467:                do {
                    468:                        if (panicstr != NULL)
                    469:                                break;
1.16      skrll     470:                        while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        471:                                SPINLOCK_BACKOFF(count);
                    472: #ifdef LOCKDEBUG
                    473:                                if (SPINLOCK_SPINOUT(spins))
                    474:                                        MUTEX_ABORT(mtx, "spinout");
                    475: #endif /* LOCKDEBUG */
                    476:                        }
                    477:                } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    478:
                    479:                if (count != SPINLOCK_BACKOFF_MIN) {
                    480:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    481:                        LOCKSTAT_EVENT(lsflag, mtx,
                    482:                            LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    483:                }
                    484:                LOCKSTAT_EXIT(lsflag);
                    485: #endif /* !MULTIPROCESSOR */
                    486: #endif /* FULL */
                    487:                MUTEX_LOCKED(mtx);
                    488:                return;
                    489:        }
                    490:
                    491:        curthread = (uintptr_t)curlwp;
                    492:
                    493:        MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    494:        MUTEX_ASSERT(mtx, curthread != 0);
                    495:        MUTEX_WANTLOCK(mtx);
                    496:
                    497:        if (panicstr == NULL) {
                    498:                LOCKDEBUG_BARRIER(&kernel_lock, 1);
                    499:        }
                    500:
                    501:        LOCKSTAT_ENTER(lsflag);
                    502:
                    503:        /*
                    504:         * Adaptive mutex; spin trying to acquire the mutex.  If we
                    505:         * determine that the owner is not running on a processor,
                    506:         * then we stop spinning, and sleep instead.
                    507:         */
1.50      rmind     508:        KPREEMPT_DISABLE(curlwp);
1.34      ad        509:        for (owner = mtx->mtx_owner;;) {
1.2       ad        510:                if (!MUTEX_OWNED(owner)) {
                    511:                        /*
                    512:                         * Mutex owner clear could mean two things:
                    513:                         *
                    514:                         *      * The mutex has been released.
                    515:                         *      * The owner field hasn't been set yet.
                    516:                         *
                    517:                         * Try to acquire it again.  If that fails,
                    518:                         * we'll just loop again.
                    519:                         */
                    520:                        if (MUTEX_ACQUIRE(mtx, curthread))
                    521:                                break;
1.34      ad        522:                        owner = mtx->mtx_owner;
1.2       ad        523:                        continue;
                    524:                }
1.50      rmind     525:                if (__predict_false(panicstr != NULL)) {
                    526:                        kpreempt_enable();
1.2       ad        527:                        return;
1.50      rmind     528:                }
                    529:                if (__predict_false(MUTEX_OWNER(owner) == curthread)) {
1.2       ad        530:                        MUTEX_ABORT(mtx, "locking against myself");
1.50      rmind     531:                }
1.2       ad        532: #ifdef MULTIPROCESSOR
                    533:                /*
                    534:                 * Check to see if the owner is running on a processor.
                    535:                 * If so, then we should just spin, as the owner will
                    536:                 * likely release the lock very soon.
                    537:                 */
1.50      rmind     538:                if (mutex_oncpu(owner)) {
1.2       ad        539:                        LOCKSTAT_START_TIMER(lsflag, spintime);
                    540:                        count = SPINLOCK_BACKOFF_MIN;
1.50      rmind     541:                        do {
                    542:                                kpreempt_enable();
1.34      ad        543:                                SPINLOCK_BACKOFF(count);
1.50      rmind     544:                                kpreempt_disable();
1.2       ad        545:                                owner = mtx->mtx_owner;
1.50      rmind     546:                        } while (mutex_oncpu(owner));
1.2       ad        547:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    548:                        LOCKSTAT_COUNT(spincnt, 1);
                    549:                        if (!MUTEX_OWNED(owner))
                    550:                                continue;
                    551:                }
                    552: #endif
                    553:
                    554:                ts = turnstile_lookup(mtx);
                    555:
                    556:                /*
                    557:                 * Once we have the turnstile chain interlock, mark the
                    558:                 * mutex has having waiters.  If that fails, spin again:
                    559:                 * chances are that the mutex has been released.
                    560:                 */
                    561:                if (!MUTEX_SET_WAITERS(mtx, owner)) {
                    562:                        turnstile_exit(mtx);
1.34      ad        563:                        owner = mtx->mtx_owner;
1.2       ad        564:                        continue;
                    565:                }
                    566:
                    567: #ifdef MULTIPROCESSOR
                    568:                /*
                    569:                 * mutex_exit() is permitted to release the mutex without
                    570:                 * any interlocking instructions, and the following can
                    571:                 * occur as a result:
                    572:                 *
                    573:                 *  CPU 1: MUTEX_SET_WAITERS()      CPU2: mutex_exit()
                    574:                 * ---------------------------- ----------------------------
                    575:                 *              ..                  acquire cache line
                    576:                 *              ..                   test for waiters
                    577:                 *      acquire cache line    <-      lose cache line
                    578:                 *       lock cache line                   ..
                    579:                 *     verify mutex is held                ..
                    580:                 *          set waiters                    ..
                    581:                 *       unlock cache line                 ..
                    582:                 *        lose cache line     ->    acquire cache line
                    583:                 *              ..                clear lock word, waiters
                    584:                 *        return success
                    585:                 *
1.50      rmind     586:                 * There is another race that can occur: a third CPU could
1.2       ad        587:                 * acquire the mutex as soon as it is released.  Since
                    588:                 * adaptive mutexes are primarily spin mutexes, this is not
                    589:                 * something that we need to worry about too much.  What we
                    590:                 * do need to ensure is that the waiters bit gets set.
                    591:                 *
                    592:                 * To allow the unlocked release, we need to make some
                    593:                 * assumptions here:
                    594:                 *
                    595:                 * o Release is the only non-atomic/unlocked operation
                    596:                 *   that can be performed on the mutex.  (It must still
                    597:                 *   be atomic on the local CPU, e.g. in case interrupted
                    598:                 *   or preempted).
                    599:                 *
                    600:                 * o At any given time, MUTEX_SET_WAITERS() can only ever
1.21      pooka     601:                 *   be in progress on one CPU in the system - guaranteed
1.2       ad        602:                 *   by the turnstile chain lock.
                    603:                 *
                    604:                 * o No other operations other than MUTEX_SET_WAITERS()
                    605:                 *   and release can modify a mutex with a non-zero
                    606:                 *   owner field.
                    607:                 *
                    608:                 * o The result of a successful MUTEX_SET_WAITERS() call
                    609:                 *   is an unbuffered write that is immediately visible
                    610:                 *   to all other processors in the system.
                    611:                 *
                    612:                 * o If the holding LWP switches away, it posts a store
                    613:                 *   fence before changing curlwp, ensuring that any
                    614:                 *   overwrite of the mutex waiters flag by mutex_exit()
                    615:                 *   completes before the modification of curlwp becomes
                    616:                 *   visible to this CPU.
                    617:                 *
1.14      yamt      618:                 * o mi_switch() posts a store fence before setting curlwp
1.2       ad        619:                 *   and before resuming execution of an LWP.
                    620:                 *
                    621:                 * o _kernel_lock() posts a store fence before setting
                    622:                 *   curcpu()->ci_biglock_wanted, and after clearing it.
                    623:                 *   This ensures that any overwrite of the mutex waiters
                    624:                 *   flag by mutex_exit() completes before the modification
                    625:                 *   of ci_biglock_wanted becomes visible.
                    626:                 *
                    627:                 * We now post a read memory barrier (after setting the
                    628:                 * waiters field) and check the lock holder's status again.
                    629:                 * Some of the possible outcomes (not an exhaustive list):
                    630:                 *
1.50      rmind     631:                 * 1. The on-CPU check returns true: the holding LWP is
1.2       ad        632:                 *    running again.  The lock may be released soon and
                    633:                 *    we should spin.  Importantly, we can't trust the
                    634:                 *    value of the waiters flag.
                    635:                 *
1.50      rmind     636:                 * 2. The on-CPU check returns false: the holding LWP is
1.39      yamt      637:                 *    not running.  We now have the opportunity to check
1.2       ad        638:                 *    if mutex_exit() has blatted the modifications made
                    639:                 *    by MUTEX_SET_WAITERS().
                    640:                 *
1.50      rmind     641:                 * 3. The on-CPU check returns false: the holding LWP may
1.2       ad        642:                 *    or may not be running.  It has context switched at
                    643:                 *    some point during our check.  Again, we have the
                    644:                 *    chance to see if the waiters bit is still set or
                    645:                 *    has been overwritten.
                    646:                 *
1.50      rmind     647:                 * 4. The on-CPU check returns false: the holding LWP is
1.2       ad        648:                 *    running on a CPU, but wants the big lock.  It's OK
                    649:                 *    to check the waiters field in this case.
                    650:                 *
                    651:                 * 5. The has-waiters check fails: the mutex has been
                    652:                 *    released, the waiters flag cleared and another LWP
                    653:                 *    now owns the mutex.
                    654:                 *
                    655:                 * 6. The has-waiters check fails: the mutex has been
                    656:                 *    released.
                    657:                 *
                    658:                 * If the waiters bit is not set it's unsafe to go asleep,
                    659:                 * as we might never be awoken.
                    660:                 */
1.50      rmind     661:                if ((membar_consumer(), mutex_oncpu(owner)) ||
1.24      ad        662:                    (membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) {
1.2       ad        663:                        turnstile_exit(mtx);
1.34      ad        664:                        owner = mtx->mtx_owner;
1.2       ad        665:                        continue;
                    666:                }
                    667: #endif /* MULTIPROCESSOR */
                    668:
1.44      wrstuden  669: #ifdef KERN_SA
                    670:                /*
                    671:                 * Sleeping for a mutex should not generate an upcall.
                    672:                 * So set LP_SA_NOBLOCK to indicate this.
                    673:                 * f indicates if we should clear LP_SA_NOBLOCK when done.
                    674:                 */
                    675:                f = ~curlwp->l_pflag & LP_SA_NOBLOCK;
                    676:                curlwp->l_pflag |= LP_SA_NOBLOCK;
                    677: #endif /* KERN_SA */
                    678:
1.2       ad        679:                LOCKSTAT_START_TIMER(lsflag, slptime);
                    680:
1.5       yamt      681:                turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
1.2       ad        682:
                    683:                LOCKSTAT_STOP_TIMER(lsflag, slptime);
                    684:                LOCKSTAT_COUNT(slpcnt, 1);
1.34      ad        685:
1.44      wrstuden  686: #ifdef KERN_SA
                    687:                curlwp->l_pflag ^= f;
                    688: #endif /* KERN_SA */
                    689:
1.34      ad        690:                owner = mtx->mtx_owner;
1.2       ad        691:        }
1.50      rmind     692:        KPREEMPT_ENABLE(curlwp);
1.2       ad        693:
                    694:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
                    695:            slpcnt, slptime);
                    696:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
                    697:            spincnt, spintime);
                    698:        LOCKSTAT_EXIT(lsflag);
                    699:
                    700:        MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    701:        MUTEX_LOCKED(mtx);
                    702: }
                    703:
                    704: /*
                    705:  * mutex_vector_exit:
                    706:  *
                    707:  *     Support routine for mutex_exit() that handles all cases.
                    708:  */
                    709: void
                    710: mutex_vector_exit(kmutex_t *mtx)
                    711: {
                    712:        turnstile_t *ts;
                    713:        uintptr_t curthread;
                    714:
                    715:        if (MUTEX_SPIN_P(mtx)) {
                    716: #ifdef FULL
1.33      ad        717:                if (__predict_false(!__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock))) {
                    718:                        if (panicstr != NULL)
                    719:                                return;
1.2       ad        720:                        MUTEX_ABORT(mtx, "exiting unheld spin mutex");
1.33      ad        721:                }
1.2       ad        722:                MUTEX_UNLOCKED(mtx);
                    723:                __cpu_simple_unlock(&mtx->mtx_lock);
                    724: #endif
                    725:                MUTEX_SPIN_SPLRESTORE(mtx);
                    726:                return;
                    727:        }
                    728:
1.11      ad        729:        if (__predict_false((uintptr_t)panicstr | cold)) {
1.2       ad        730:                MUTEX_UNLOCKED(mtx);
                    731:                MUTEX_RELEASE(mtx);
                    732:                return;
                    733:        }
                    734:
                    735:        curthread = (uintptr_t)curlwp;
                    736:        MUTEX_DASSERT(mtx, curthread != 0);
                    737:        MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    738:        MUTEX_UNLOCKED(mtx);
                    739:
1.15      ad        740: #ifdef LOCKDEBUG
                    741:        /*
                    742:         * Avoid having to take the turnstile chain lock every time
                    743:         * around.  Raise the priority level to splhigh() in order
                    744:         * to disable preemption and so make the following atomic.
                    745:         */
                    746:        {
                    747:                int s = splhigh();
                    748:                if (!MUTEX_HAS_WAITERS(mtx)) {
                    749:                        MUTEX_RELEASE(mtx);
                    750:                        splx(s);
                    751:                        return;
                    752:                }
                    753:                splx(s);
                    754:        }
                    755: #endif
                    756:
1.2       ad        757:        /*
                    758:         * Get this lock's turnstile.  This gets the interlock on
                    759:         * the sleep queue.  Once we have that, we can clear the
                    760:         * lock.  If there was no turnstile for the lock, there
                    761:         * were no waiters remaining.
                    762:         */
                    763:        ts = turnstile_lookup(mtx);
                    764:
                    765:        if (ts == NULL) {
                    766:                MUTEX_RELEASE(mtx);
                    767:                turnstile_exit(mtx);
                    768:        } else {
                    769:                MUTEX_RELEASE(mtx);
                    770:                turnstile_wakeup(ts, TS_WRITER_Q,
                    771:                    TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    772:        }
                    773: }
                    774:
1.4       ad        775: #ifndef __HAVE_SIMPLE_MUTEXES
                    776: /*
                    777:  * mutex_wakeup:
                    778:  *
                    779:  *     Support routine for mutex_exit() that wakes up all waiters.
                    780:  *     We assume that the mutex has been released, but it need not
                    781:  *     be.
                    782:  */
                    783: void
                    784: mutex_wakeup(kmutex_t *mtx)
                    785: {
                    786:        turnstile_t *ts;
                    787:
                    788:        ts = turnstile_lookup(mtx);
                    789:        if (ts == NULL) {
                    790:                turnstile_exit(mtx);
                    791:                return;
                    792:        }
                    793:        MUTEX_CLEAR_WAITERS(mtx);
                    794:        turnstile_wakeup(ts, TS_WRITER_Q, TS_WAITERS(ts, TS_WRITER_Q), NULL);
                    795: }
                    796: #endif /* !__HAVE_SIMPLE_MUTEXES */
                    797:
1.2       ad        798: /*
                    799:  * mutex_owned:
                    800:  *
1.3       ad        801:  *     Return true if the current LWP (adaptive) or CPU (spin)
                    802:  *     holds the mutex.
1.2       ad        803:  */
                    804: int
                    805: mutex_owned(kmutex_t *mtx)
                    806: {
                    807:
1.35      ad        808:        if (mtx == NULL)
                    809:                return 0;
1.2       ad        810:        if (MUTEX_ADAPTIVE_P(mtx))
                    811:                return MUTEX_OWNER(mtx->mtx_owner) == (uintptr_t)curlwp;
                    812: #ifdef FULL
1.16      skrll     813:        return __SIMPLELOCK_LOCKED_P(&mtx->mtx_lock);
1.2       ad        814: #else
                    815:        return 1;
                    816: #endif
                    817: }
                    818:
                    819: /*
                    820:  * mutex_owner:
                    821:  *
1.6       ad        822:  *     Return the current owner of an adaptive mutex.  Used for
                    823:  *     priority inheritance.
1.2       ad        824:  */
1.27      ad        825: lwp_t *
                    826: mutex_owner(kmutex_t *mtx)
1.2       ad        827: {
                    828:
                    829:        MUTEX_ASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    830:        return (struct lwp *)MUTEX_OWNER(mtx->mtx_owner);
                    831: }
                    832:
                    833: /*
                    834:  * mutex_tryenter:
                    835:  *
                    836:  *     Try to acquire the mutex; return non-zero if we did.
                    837:  */
                    838: int
                    839: mutex_tryenter(kmutex_t *mtx)
                    840: {
                    841:        uintptr_t curthread;
                    842:
                    843:        /*
                    844:         * Handle spin mutexes.
                    845:         */
                    846:        if (MUTEX_SPIN_P(mtx)) {
                    847:                MUTEX_SPIN_SPLRAISE(mtx);
                    848: #ifdef FULL
                    849:                if (__cpu_simple_lock_try(&mtx->mtx_lock)) {
1.4       ad        850:                        MUTEX_WANTLOCK(mtx);
1.2       ad        851:                        MUTEX_LOCKED(mtx);
                    852:                        return 1;
                    853:                }
                    854:                MUTEX_SPIN_SPLRESTORE(mtx);
                    855: #else
1.4       ad        856:                MUTEX_WANTLOCK(mtx);
1.2       ad        857:                MUTEX_LOCKED(mtx);
                    858:                return 1;
                    859: #endif
                    860:        } else {
                    861:                curthread = (uintptr_t)curlwp;
                    862:                MUTEX_ASSERT(mtx, curthread != 0);
                    863:                if (MUTEX_ACQUIRE(mtx, curthread)) {
1.4       ad        864:                        MUTEX_WANTLOCK(mtx);
1.2       ad        865:                        MUTEX_LOCKED(mtx);
                    866:                        MUTEX_DASSERT(mtx,
                    867:                            MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    868:                        return 1;
                    869:                }
                    870:        }
                    871:
                    872:        return 0;
                    873: }
                    874:
                    875: #if defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL)
                    876: /*
                    877:  * mutex_spin_retry:
                    878:  *
                    879:  *     Support routine for mutex_spin_enter().  Assumes that the caller
                    880:  *     has already raised the SPL, and adjusted counters.
                    881:  */
                    882: void
                    883: mutex_spin_retry(kmutex_t *mtx)
                    884: {
                    885: #ifdef MULTIPROCESSOR
                    886:        u_int count;
                    887:        LOCKSTAT_TIMER(spintime);
                    888:        LOCKSTAT_FLAG(lsflag);
                    889: #ifdef LOCKDEBUG
                    890:        u_int spins = 0;
                    891: #endif /* LOCKDEBUG */
                    892:
                    893:        MUTEX_WANTLOCK(mtx);
                    894:
                    895:        LOCKSTAT_ENTER(lsflag);
                    896:        LOCKSTAT_START_TIMER(lsflag, spintime);
                    897:        count = SPINLOCK_BACKOFF_MIN;
                    898:
                    899:        /*
                    900:         * Spin testing the lock word and do exponential backoff
                    901:         * to reduce cache line ping-ponging between CPUs.
                    902:         */
                    903:        do {
                    904:                if (panicstr != NULL)
                    905:                        break;
1.16      skrll     906:                while (__SIMPLELOCK_LOCKED_P(&mtx->mtx_lock)) {
1.2       ad        907:                        SPINLOCK_BACKOFF(count);
                    908: #ifdef LOCKDEBUG
                    909:                        if (SPINLOCK_SPINOUT(spins))
                    910:                                MUTEX_ABORT(mtx, "spinout");
                    911: #endif /* LOCKDEBUG */
                    912:                }
                    913:        } while (!__cpu_simple_lock_try(&mtx->mtx_lock));
                    914:
                    915:        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    916:        LOCKSTAT_EVENT(lsflag, mtx, LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    917:        LOCKSTAT_EXIT(lsflag);
                    918:
                    919:        MUTEX_LOCKED(mtx);
                    920: #else  /* MULTIPROCESSOR */
                    921:        MUTEX_ABORT(mtx, "locking against myself");
                    922: #endif /* MULTIPROCESSOR */
                    923: }
                    924: #endif /* defined(__HAVE_SPIN_MUTEX_STUBS) || defined(FULL) */

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