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Annotation of src/sys/kern/kern_mutex.c, Revision 1.63

1.63    ! msaitoh     1: /*     $NetBSD: kern_mutex.c,v 1.62 2015/05/25 21:02:37 prlw1 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>
1.63    ! msaitoh    43: __KERNEL_RCSID(0, "$NetBSD: kern_mutex.c,v 1.62 2015/05/25 21:02:37 prlw1 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:
1.2       ad         62: /*
                     63:  * When not running a debug kernel, spin mutexes are not much
                     64:  * more than an splraiseipl() and splx() pair.
                     65:  */
                     66:
                     67: #if defined(DIAGNOSTIC) || defined(MULTIPROCESSOR) || defined(LOCKDEBUG)
                     68: #define        FULL
                     69: #endif
                     70:
                     71: /*
                     72:  * Debugging support.
                     73:  */
                     74:
                     75: #define        MUTEX_WANTLOCK(mtx)                                     \
1.23      yamt       76:     LOCKDEBUG_WANTLOCK(MUTEX_DEBUG_P(mtx), (mtx),              \
1.54      mlelstv    77:         (uintptr_t)__builtin_return_address(0), 0)
1.2       ad         78: #define        MUTEX_LOCKED(mtx)                                       \
1.42      ad         79:     LOCKDEBUG_LOCKED(MUTEX_DEBUG_P(mtx), (mtx), NULL,          \
1.2       ad         80:         (uintptr_t)__builtin_return_address(0), 0)
                     81: #define        MUTEX_UNLOCKED(mtx)                                     \
1.23      yamt       82:     LOCKDEBUG_UNLOCKED(MUTEX_DEBUG_P(mtx), (mtx),              \
1.2       ad         83:         (uintptr_t)__builtin_return_address(0), 0)
                     84: #define        MUTEX_ABORT(mtx, msg)                                   \
1.17      ad         85:     mutex_abort(mtx, __func__, msg)
1.2       ad         86:
                     87: #if defined(LOCKDEBUG)
                     88:
                     89: #define        MUTEX_DASSERT(mtx, cond)                                \
                     90: do {                                                           \
                     91:        if (!(cond))                                            \
                     92:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                     93: } while (/* CONSTCOND */ 0);
                     94:
                     95: #else  /* LOCKDEBUG */
                     96:
                     97: #define        MUTEX_DASSERT(mtx, cond)        /* nothing */
                     98:
                     99: #endif /* LOCKDEBUG */
                    100:
                    101: #if defined(DIAGNOSTIC)
                    102:
                    103: #define        MUTEX_ASSERT(mtx, cond)                                 \
                    104: do {                                                           \
                    105:        if (!(cond))                                            \
                    106:                MUTEX_ABORT(mtx, "assertion failed: " #cond);   \
                    107: } while (/* CONSTCOND */ 0)
                    108:
                    109: #else  /* DIAGNOSTIC */
                    110:
                    111: #define        MUTEX_ASSERT(mtx, cond) /* nothing */
                    112:
                    113: #endif /* DIAGNOSTIC */
                    114:
                    115: /*
1.60      matt      116:  * Some architectures can't use __cpu_simple_lock as is so allow a way
                    117:  * for them to use an alternate definition.
                    118:  */
                    119: #ifndef MUTEX_SPINBIT_LOCK_INIT
                    120: #define MUTEX_SPINBIT_LOCK_INIT(mtx)   __cpu_simple_lock_init(&(mtx)->mtx_lock)
                    121: #endif
                    122: #ifndef MUTEX_SPINBIT_LOCKED_P
                    123: #define MUTEX_SPINBIT_LOCKED_P(mtx)    __SIMPLELOCK_LOCKED_P(&(mtx)->mtx_lock)
                    124: #endif
                    125: #ifndef MUTEX_SPINBIT_LOCK_TRY
                    126: #define MUTEX_SPINBIT_LOCK_TRY(mtx)    __cpu_simple_lock_try(&(mtx)->mtx_lock)
                    127: #endif
                    128: #ifndef MUTEX_SPINBIT_LOCK_UNLOCK
                    129: #define MUTEX_SPINBIT_LOCK_UNLOCK(mtx) __cpu_simple_unlock(&(mtx)->mtx_lock)
                    130: #endif
                    131:
                    132: #ifndef MUTEX_INITIALIZE_SPIN_IPL
                    133: #define MUTEX_INITIALIZE_SPIN_IPL(mtx, ipl) \
                    134:                                        ((mtx)->mtx_ipl = makeiplcookie((ipl)))
                    135: #endif
                    136:
                    137: /*
1.2       ad        138:  * Spin mutex SPL save / restore.
                    139:  */
                    140:
                    141: #define        MUTEX_SPIN_SPLRAISE(mtx)                                        \
                    142: do {                                                                   \
1.36      ad        143:        struct cpu_info *x__ci;                                         \
1.2       ad        144:        int x__cnt, s;                                                  \
1.60      matt      145:        s = splraiseipl(MUTEX_SPIN_IPL(mtx));                           \
1.36      ad        146:        x__ci = curcpu();                                               \
1.2       ad        147:        x__cnt = x__ci->ci_mtx_count--;                                 \
1.37      ad        148:        __insn_barrier();                                               \
1.51      rmind     149:        if (x__cnt == 0)                                                \
1.2       ad        150:                x__ci->ci_mtx_oldspl = (s);                             \
                    151: } while (/* CONSTCOND */ 0)
                    152:
                    153: #define        MUTEX_SPIN_SPLRESTORE(mtx)                                      \
                    154: do {                                                                   \
                    155:        struct cpu_info *x__ci = curcpu();                              \
                    156:        int s = x__ci->ci_mtx_oldspl;                                   \
                    157:        __insn_barrier();                                               \
1.51      rmind     158:        if (++(x__ci->ci_mtx_count) == 0)                       \
1.2       ad        159:                splx(s);                                                \
                    160: } while (/* CONSTCOND */ 0)
                    161:
                    162: /*
                    163:  * For architectures that provide 'simple' mutexes: they provide a
                    164:  * CAS function that is either MP-safe, or does not need to be MP
                    165:  * safe.  Adaptive mutexes on these architectures do not require an
                    166:  * additional interlock.
                    167:  */
                    168:
                    169: #ifdef __HAVE_SIMPLE_MUTEXES
                    170:
                    171: #define        MUTEX_OWNER(owner)                                              \
                    172:        (owner & MUTEX_THREAD)
                    173: #define        MUTEX_HAS_WAITERS(mtx)                                          \
                    174:        (((int)(mtx)->mtx_owner & MUTEX_BIT_WAITERS) != 0)
                    175:
1.23      yamt      176: #define        MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug)                         \
1.49      skrll     177:        if (!dodebug)                                                   \
                    178:                (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG;                  \
1.2       ad        179: do {                                                                   \
                    180: } while (/* CONSTCOND */ 0);
                    181:
1.23      yamt      182: #define        MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl)                        \
1.2       ad        183: do {                                                                   \
                    184:        (mtx)->mtx_owner = MUTEX_BIT_SPIN;                              \
1.49      skrll     185:        if (!dodebug)                                                   \
                    186:                (mtx)->mtx_owner |= MUTEX_BIT_NODEBUG;                  \
1.60      matt      187:        MUTEX_INITIALIZE_SPIN_IPL((mtx), (ipl));                        \
                    188:        MUTEX_SPINBIT_LOCK_INIT((mtx));                                 \
1.2       ad        189: } while (/* CONSTCOND */ 0)
                    190:
                    191: #define        MUTEX_DESTROY(mtx)                                              \
                    192: do {                                                                   \
                    193:        (mtx)->mtx_owner = MUTEX_THREAD;                                \
                    194: } while (/* CONSTCOND */ 0);
                    195:
                    196: #define        MUTEX_SPIN_P(mtx)               \
                    197:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) != 0)
                    198: #define        MUTEX_ADAPTIVE_P(mtx)           \
                    199:     (((mtx)->mtx_owner & MUTEX_BIT_SPIN) == 0)
                    200:
1.49      skrll     201: #define        MUTEX_DEBUG_P(mtx)      (((mtx)->mtx_owner & MUTEX_BIT_NODEBUG) == 0)
1.23      yamt      202: #if defined(LOCKDEBUG)
1.49      skrll     203: #define        MUTEX_OWNED(owner)              (((owner) & ~MUTEX_BIT_NODEBUG) != 0)
1.59      matt      204: #define        MUTEX_INHERITDEBUG(n, o)        (n) |= (o) & MUTEX_BIT_NODEBUG
1.23      yamt      205: #else /* defined(LOCKDEBUG) */
                    206: #define        MUTEX_OWNED(owner)              ((owner) != 0)
1.59      matt      207: #define        MUTEX_INHERITDEBUG(n, o)        /* nothing */
1.23      yamt      208: #endif /* defined(LOCKDEBUG) */
1.2       ad        209:
                    210: static inline int
                    211: MUTEX_ACQUIRE(kmutex_t *mtx, uintptr_t curthread)
                    212: {
                    213:        int rv;
1.59      matt      214:        uintptr_t oldown = 0;
                    215:        uintptr_t newown = curthread;
1.23      yamt      216:
1.59      matt      217:        MUTEX_INHERITDEBUG(oldown, mtx->mtx_owner);
                    218:        MUTEX_INHERITDEBUG(newown, oldown);
                    219:        rv = MUTEX_CAS(&mtx->mtx_owner, oldown, newown);
1.7       itohy     220:        MUTEX_RECEIVE(mtx);
1.2       ad        221:        return rv;
                    222: }
                    223:
                    224: static inline int
                    225: MUTEX_SET_WAITERS(kmutex_t *mtx, uintptr_t owner)
                    226: {
                    227:        int rv;
                    228:        rv = MUTEX_CAS(&mtx->mtx_owner, owner, owner | MUTEX_BIT_WAITERS);
1.7       itohy     229:        MUTEX_RECEIVE(mtx);
1.2       ad        230:        return rv;
                    231: }
                    232:
                    233: static inline void
                    234: MUTEX_RELEASE(kmutex_t *mtx)
                    235: {
1.59      matt      236:        uintptr_t newown;
1.23      yamt      237:
1.7       itohy     238:        MUTEX_GIVE(mtx);
1.59      matt      239:        newown = 0;
                    240:        MUTEX_INHERITDEBUG(newown, mtx->mtx_owner);
                    241:        mtx->mtx_owner = newown;
1.2       ad        242: }
                    243: #endif /* __HAVE_SIMPLE_MUTEXES */
                    244:
                    245: /*
                    246:  * Patch in stubs via strong alias where they are not available.
                    247:  */
                    248:
                    249: #if defined(LOCKDEBUG)
                    250: #undef __HAVE_MUTEX_STUBS
                    251: #undef __HAVE_SPIN_MUTEX_STUBS
                    252: #endif
                    253:
                    254: #ifndef __HAVE_MUTEX_STUBS
1.8       itohy     255: __strong_alias(mutex_enter,mutex_vector_enter);
                    256: __strong_alias(mutex_exit,mutex_vector_exit);
1.2       ad        257: #endif
                    258:
                    259: #ifndef __HAVE_SPIN_MUTEX_STUBS
1.8       itohy     260: __strong_alias(mutex_spin_enter,mutex_vector_enter);
                    261: __strong_alias(mutex_spin_exit,mutex_vector_exit);
1.2       ad        262: #endif
                    263:
1.50      rmind     264: static void            mutex_abort(kmutex_t *, const char *, const char *);
                    265: static void            mutex_dump(volatile void *);
1.2       ad        266:
                    267: lockops_t mutex_spin_lockops = {
                    268:        "Mutex",
1.42      ad        269:        LOCKOPS_SPIN,
1.2       ad        270:        mutex_dump
                    271: };
                    272:
                    273: lockops_t mutex_adaptive_lockops = {
                    274:        "Mutex",
1.42      ad        275:        LOCKOPS_SLEEP,
1.2       ad        276:        mutex_dump
                    277: };
                    278:
1.5       yamt      279: syncobj_t mutex_syncobj = {
                    280:        SOBJ_SLEEPQ_SORTED,
                    281:        turnstile_unsleep,
                    282:        turnstile_changepri,
                    283:        sleepq_lendpri,
1.27      ad        284:        (void *)mutex_owner,
1.5       yamt      285: };
                    286:
1.2       ad        287: /*
                    288:  * mutex_dump:
                    289:  *
                    290:  *     Dump the contents of a mutex structure.
                    291:  */
                    292: void
                    293: mutex_dump(volatile void *cookie)
                    294: {
                    295:        volatile kmutex_t *mtx = cookie;
                    296:
                    297:        printf_nolog("owner field  : %#018lx wait/spin: %16d/%d\n",
                    298:            (long)MUTEX_OWNER(mtx->mtx_owner), MUTEX_HAS_WAITERS(mtx),
                    299:            MUTEX_SPIN_P(mtx));
                    300: }
                    301:
                    302: /*
                    303:  * mutex_abort:
                    304:  *
1.3       ad        305:  *     Dump information about an error and panic the system.  This
                    306:  *     generates a lot of machine code in the DIAGNOSTIC case, so
                    307:  *     we ask the compiler to not inline it.
1.2       ad        308:  */
1.43      ad        309: void __noinline
1.2       ad        310: mutex_abort(kmutex_t *mtx, const char *func, const char *msg)
                    311: {
                    312:
1.23      yamt      313:        LOCKDEBUG_ABORT(mtx, (MUTEX_SPIN_P(mtx) ?
1.3       ad        314:            &mutex_spin_lockops : &mutex_adaptive_lockops), func, msg);
1.2       ad        315: }
                    316:
                    317: /*
                    318:  * mutex_init:
                    319:  *
                    320:  *     Initialize a mutex for use.  Note that adaptive mutexes are in
                    321:  *     essence spin mutexes that can sleep to avoid deadlock and wasting
                    322:  *     CPU time.  We can't easily provide a type of mutex that always
                    323:  *     sleeps - see comments in mutex_vector_enter() about releasing
                    324:  *     mutexes unlocked.
                    325:  */
                    326: void
                    327: mutex_init(kmutex_t *mtx, kmutex_type_t type, int ipl)
                    328: {
1.23      yamt      329:        bool dodebug;
1.2       ad        330:
                    331:        memset(mtx, 0, sizeof(*mtx));
                    332:
1.15      ad        333:        switch (type) {
                    334:        case MUTEX_ADAPTIVE:
                    335:                KASSERT(ipl == IPL_NONE);
                    336:                break;
1.22      ad        337:        case MUTEX_DEFAULT:
1.15      ad        338:        case MUTEX_DRIVER:
1.26      ad        339:                if (ipl == IPL_NONE || ipl == IPL_SOFTCLOCK ||
                    340:                    ipl == IPL_SOFTBIO || ipl == IPL_SOFTNET ||
                    341:                    ipl == IPL_SOFTSERIAL) {
1.22      ad        342:                        type = MUTEX_ADAPTIVE;
1.26      ad        343:                } else {
1.22      ad        344:                        type = MUTEX_SPIN;
                    345:                }
1.15      ad        346:                break;
                    347:        default:
                    348:                break;
                    349:        }
1.2       ad        350:
                    351:        switch (type) {
1.11      ad        352:        case MUTEX_NODEBUG:
1.23      yamt      353:                dodebug = LOCKDEBUG_ALLOC(mtx, NULL,
1.19      ad        354:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      355:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.11      ad        356:                break;
1.2       ad        357:        case MUTEX_ADAPTIVE:
1.23      yamt      358:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_adaptive_lockops,
1.19      ad        359:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      360:                MUTEX_INITIALIZE_ADAPTIVE(mtx, dodebug);
1.2       ad        361:                break;
                    362:        case MUTEX_SPIN:
1.23      yamt      363:                dodebug = LOCKDEBUG_ALLOC(mtx, &mutex_spin_lockops,
1.19      ad        364:                    (uintptr_t)__builtin_return_address(0));
1.23      yamt      365:                MUTEX_INITIALIZE_SPIN(mtx, dodebug, ipl);
1.2       ad        366:                break;
                    367:        default:
                    368:                panic("mutex_init: impossible type");
                    369:                break;
                    370:        }
                    371: }
                    372:
                    373: /*
                    374:  * mutex_destroy:
                    375:  *
                    376:  *     Tear down a mutex.
                    377:  */
                    378: void
                    379: mutex_destroy(kmutex_t *mtx)
                    380: {
                    381:
                    382:        if (MUTEX_ADAPTIVE_P(mtx)) {
                    383:                MUTEX_ASSERT(mtx, !MUTEX_OWNED(mtx->mtx_owner) &&
                    384:                    !MUTEX_HAS_WAITERS(mtx));
                    385:        } else {
1.60      matt      386:                MUTEX_ASSERT(mtx, !MUTEX_SPINBIT_LOCKED_P(mtx));
1.2       ad        387:        }
                    388:
1.23      yamt      389:        LOCKDEBUG_FREE(MUTEX_DEBUG_P(mtx), mtx);
1.2       ad        390:        MUTEX_DESTROY(mtx);
                    391: }
                    392:
1.50      rmind     393: #ifdef MULTIPROCESSOR
1.2       ad        394: /*
1.50      rmind     395:  * mutex_oncpu:
1.2       ad        396:  *
                    397:  *     Return true if an adaptive mutex owner is running on a CPU in the
                    398:  *     system.  If the target is waiting on the kernel big lock, then we
1.15      ad        399:  *     must release it.  This is necessary to avoid deadlock.
1.2       ad        400:  */
1.50      rmind     401: static bool
                    402: mutex_oncpu(uintptr_t owner)
1.2       ad        403: {
                    404:        struct cpu_info *ci;
1.50      rmind     405:        lwp_t *l;
1.2       ad        406:
1.50      rmind     407:        KASSERT(kpreempt_disabled());
                    408:
                    409:        if (!MUTEX_OWNED(owner)) {
                    410:                return false;
                    411:        }
1.2       ad        412:
1.50      rmind     413:        /*
                    414:         * See lwp_dtor() why dereference of the LWP pointer is safe.
                    415:         * We must have kernel preemption disabled for that.
                    416:         */
                    417:        l = (lwp_t *)MUTEX_OWNER(owner);
                    418:        ci = l->l_cpu;
1.2       ad        419:
1.50      rmind     420:        if (ci && ci->ci_curlwp == l) {
                    421:                /* Target is running; do we need to block? */
                    422:                return (ci->ci_biglock_wanted != l);
                    423:        }
1.15      ad        424:
1.50      rmind     425:        /* Not running.  It may be safe to block now. */
                    426:        return false;
1.2       ad        427: }
1.15      ad        428: #endif /* MULTIPROCESSOR */
1.2       ad        429:
                    430: /*
                    431:  * mutex_vector_enter:
                    432:  *
1.45      rmind     433:  *     Support routine for mutex_enter() that must handle all cases.  In
1.2       ad        434:  *     the LOCKDEBUG case, mutex_enter() is always aliased here, even if
1.62      prlw1     435:  *     fast-path stubs are available.  If a mutex_spin_enter() stub is
1.2       ad        436:  *     not available, then it is also aliased directly here.
                    437:  */
                    438: void
                    439: mutex_vector_enter(kmutex_t *mtx)
                    440: {
                    441:        uintptr_t owner, curthread;
                    442:        turnstile_t *ts;
                    443: #ifdef MULTIPROCESSOR
                    444:        u_int count;
                    445: #endif
                    446:        LOCKSTAT_COUNTER(spincnt);
                    447:        LOCKSTAT_COUNTER(slpcnt);
                    448:        LOCKSTAT_TIMER(spintime);
                    449:        LOCKSTAT_TIMER(slptime);
                    450:        LOCKSTAT_FLAG(lsflag);
                    451:
                    452:        /*
                    453:         * Handle spin mutexes.
                    454:         */
                    455:        if (MUTEX_SPIN_P(mtx)) {
                    456: #if defined(LOCKDEBUG) && defined(MULTIPROCESSOR)
                    457:                u_int spins = 0;
                    458: #endif
                    459:                MUTEX_SPIN_SPLRAISE(mtx);
                    460:                MUTEX_WANTLOCK(mtx);
                    461: #ifdef FULL
1.60      matt      462:                if (MUTEX_SPINBIT_LOCK_TRY(mtx)) {
1.2       ad        463:                        MUTEX_LOCKED(mtx);
                    464:                        return;
                    465:                }
                    466: #if !defined(MULTIPROCESSOR)
                    467:                MUTEX_ABORT(mtx, "locking against myself");
                    468: #else /* !MULTIPROCESSOR */
                    469:
                    470:                LOCKSTAT_ENTER(lsflag);
                    471:                LOCKSTAT_START_TIMER(lsflag, spintime);
                    472:                count = SPINLOCK_BACKOFF_MIN;
                    473:
                    474:                /*
                    475:                 * Spin testing the lock word and do exponential backoff
                    476:                 * to reduce cache line ping-ponging between CPUs.
                    477:                 */
                    478:                do {
                    479:                        if (panicstr != NULL)
                    480:                                break;
1.60      matt      481:                        while (MUTEX_SPINBIT_LOCKED_P(mtx)) {
1.63    ! msaitoh   482:                                SPINLOCK_BACKOFF(count);
1.2       ad        483: #ifdef LOCKDEBUG
                    484:                                if (SPINLOCK_SPINOUT(spins))
                    485:                                        MUTEX_ABORT(mtx, "spinout");
                    486: #endif /* LOCKDEBUG */
                    487:                        }
1.60      matt      488:                } while (!MUTEX_SPINBIT_LOCK_TRY(mtx));
1.2       ad        489:
                    490:                if (count != SPINLOCK_BACKOFF_MIN) {
                    491:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    492:                        LOCKSTAT_EVENT(lsflag, mtx,
                    493:                            LB_SPIN_MUTEX | LB_SPIN, 1, spintime);
                    494:                }
                    495:                LOCKSTAT_EXIT(lsflag);
                    496: #endif /* !MULTIPROCESSOR */
                    497: #endif /* FULL */
                    498:                MUTEX_LOCKED(mtx);
                    499:                return;
                    500:        }
                    501:
                    502:        curthread = (uintptr_t)curlwp;
                    503:
                    504:        MUTEX_DASSERT(mtx, MUTEX_ADAPTIVE_P(mtx));
                    505:        MUTEX_ASSERT(mtx, curthread != 0);
                    506:        MUTEX_WANTLOCK(mtx);
                    507:
                    508:        if (panicstr == NULL) {
                    509:                LOCKDEBUG_BARRIER(&kernel_lock, 1);
                    510:        }
                    511:
                    512:        LOCKSTAT_ENTER(lsflag);
                    513:
                    514:        /*
                    515:         * Adaptive mutex; spin trying to acquire the mutex.  If we
                    516:         * determine that the owner is not running on a processor,
                    517:         * then we stop spinning, and sleep instead.
                    518:         */
1.50      rmind     519:        KPREEMPT_DISABLE(curlwp);
1.34      ad        520:        for (owner = mtx->mtx_owner;;) {
1.2       ad        521:                if (!MUTEX_OWNED(owner)) {
                    522:                        /*
                    523:                         * Mutex owner clear could mean two things:
                    524:                         *
                    525:                         *      * The mutex has been released.
                    526:                         *      * The owner field hasn't been set yet.
                    527:                         *
                    528:                         * Try to acquire it again.  If that fails,
                    529:                         * we'll just loop again.
                    530:                         */
                    531:                        if (MUTEX_ACQUIRE(mtx, curthread))
                    532:                                break;
1.34      ad        533:                        owner = mtx->mtx_owner;
1.2       ad        534:                        continue;
                    535:                }
1.50      rmind     536:                if (__predict_false(panicstr != NULL)) {
1.61      uebayasi  537:                        KPREEMPT_ENABLE(curlwp);
1.2       ad        538:                        return;
1.50      rmind     539:                }
                    540:                if (__predict_false(MUTEX_OWNER(owner) == curthread)) {
1.2       ad        541:                        MUTEX_ABORT(mtx, "locking against myself");
1.50      rmind     542:                }
1.2       ad        543: #ifdef MULTIPROCESSOR
                    544:                /*
                    545:                 * Check to see if the owner is running on a processor.
                    546:                 * If so, then we should just spin, as the owner will
                    547:                 * likely release the lock very soon.
                    548:                 */
1.50      rmind     549:                if (mutex_oncpu(owner)) {
1.2       ad        550:                        LOCKSTAT_START_TIMER(lsflag, spintime);
                    551:                        count = SPINLOCK_BACKOFF_MIN;
1.50      rmind     552:                        do {
1.53      rmind     553:                                KPREEMPT_ENABLE(curlwp);
1.34      ad        554:                                SPINLOCK_BACKOFF(count);
1.53      rmind     555:                                KPREEMPT_DISABLE(curlwp);
1.2       ad        556:                                owner = mtx->mtx_owner;
1.50      rmind     557:                        } while (mutex_oncpu(owner));
1.2       ad        558:                        LOCKSTAT_STOP_TIMER(lsflag, spintime);
                    559:                        LOCKSTAT_COUNT(spincnt, 1);
                    560:                        if (!MUTEX_OWNED(owner))
                    561:                                continue;
                    562:                }
                    563: #endif
                    564:
                    565:                ts = turnstile_lookup(mtx);
                    566:
                    567:                /*
                    568:                 * Once we have the turnstile chain interlock, mark the
                    569:                 * mutex has having waiters.  If that fails, spin again:
                    570:                 * chances are that the mutex has been released.
                    571:                 */
                    572:                if (!MUTEX_SET_WAITERS(mtx, owner)) {
                    573:                        turnstile_exit(mtx);
1.34      ad        574:                        owner = mtx->mtx_owner;
1.2       ad        575:                        continue;
                    576:                }
                    577:
                    578: #ifdef MULTIPROCESSOR
                    579:                /*
                    580:                 * mutex_exit() is permitted to release the mutex without
                    581:                 * any interlocking instructions, and the following can
                    582:                 * occur as a result:
                    583:                 *
                    584:                 *  CPU 1: MUTEX_SET_WAITERS()      CPU2: mutex_exit()
                    585:                 * ---------------------------- ----------------------------
                    586:                 *              ..                  acquire cache line
                    587:                 *              ..                   test for waiters
                    588:                 *      acquire cache line    <-      lose cache line
                    589:                 *       lock cache line                   ..
                    590:                 *     verify mutex is held                ..
                    591:                 *          set waiters                    ..
                    592:                 *       unlock cache line                 ..
                    593:                 *        lose cache line     ->    acquire cache line
                    594:                 *              ..                clear lock word, waiters
                    595:                 *        return success
                    596:                 *
1.50      rmind     597:                 * There is another race that can occur: a third CPU could
1.2       ad        598:                 * acquire the mutex as soon as it is released.  Since
                    599:                 * adaptive mutexes are primarily spin mutexes, this is not
                    600:                 * something that we need to worry about too much.  What we
                    601:                 * do need to ensure is that the waiters bit gets set.
                    602:                 *
                    603:                 * To allow the unlocked release, we need to make some
                    604:                 * assumptions here:
                    605:                 *
                    606:                 * o Release is the only non-atomic/unlocked operation
                    607:                 *   that can be performed on the mutex.  (It must still
                    608:                 *   be atomic on the local CPU, e.g. in case interrupted
                    609:                 *   or preempted).
                    610:                 *
                    611:                 * o At any given time, MUTEX_SET_WAITERS() can only ever
1.21      pooka     612:                 *   be in progress on one CPU in the system - guaranteed
1.2       ad        613:                 *   by the turnstile chain lock.
                    614:                 *
                    615:                 * o No other operations other than MUTEX_SET_WAITERS()
                    616:                 *   and release can modify a mutex with a non-zero
                    617:                 *   owner field.
                    618:                 *
                    619:                 * o The result of a successful MUTEX_SET_WAITERS() call
                    620:                 *   is an unbuffered write that is immediately visible
                    621:                 *   to all other processors in the system.
                    622:                 *
                    623:                 * o If the holding LWP switches away, it posts a store
                    624:                 *   fence before changing curlwp, ensuring that any
                    625:                 *   overwrite of the mutex waiters flag by mutex_exit()
                    626:                 *   completes before the modification of curlwp becomes
                    627:                 *   visible to this CPU.
                    628:                 *
1.14      yamt      629:                 * o mi_switch() posts a store fence before setting curlwp
1.2       ad        630:                 *   and before resuming execution of an LWP.
                    631:                 *
                    632:                 * o _kernel_lock() posts a store fence before setting
                    633:                 *   curcpu()->ci_biglock_wanted, and after clearing it.
                    634:                 *   This ensures that any overwrite of the mutex waiters
                    635:                 *   flag by mutex_exit() completes before the modification
                    636:                 *   of ci_biglock_wanted becomes visible.
                    637:                 *
                    638:                 * We now post a read memory barrier (after setting the
                    639:                 * waiters field) and check the lock holder's status again.
                    640:                 * Some of the possible outcomes (not an exhaustive list):
                    641:                 *
1.50      rmind     642:                 * 1. The on-CPU check returns true: the holding LWP is
1.2       ad        643:                 *    running again.  The lock may be released soon and
                    644:                 *    we should spin.  Importantly, we can't trust the
                    645:                 *    value of the waiters flag.
                    646:                 *
1.50      rmind     647:                 * 2. The on-CPU check returns false: the holding LWP is
1.39      yamt      648:                 *    not running.  We now have the opportunity to check
1.2       ad        649:                 *    if mutex_exit() has blatted the modifications made
                    650:                 *    by MUTEX_SET_WAITERS().
                    651:                 *
1.50      rmind     652:                 * 3. The on-CPU check returns false: the holding LWP may
1.2       ad        653:                 *    or may not be running.  It has context switched at
                    654:                 *    some point during our check.  Again, we have the
                    655:                 *    chance to see if the waiters bit is still set or
                    656:                 *    has been overwritten.
                    657:                 *
1.50      rmind     658:                 * 4. The on-CPU check returns false: the holding LWP is
1.2       ad        659:                 *    running on a CPU, but wants the big lock.  It's OK
                    660:                 *    to check the waiters field in this case.
                    661:                 *
                    662:                 * 5. The has-waiters check fails: the mutex has been
                    663:                 *    released, the waiters flag cleared and another LWP
                    664:                 *    now owns the mutex.
                    665:                 *
                    666:                 * 6. The has-waiters check fails: the mutex has been
                    667:                 *    released.
                    668:                 *
                    669:                 * If the waiters bit is not set it's unsafe to go asleep,
                    670:                 * as we might never be awoken.
                    671:                 */
1.50      rmind     672:                if ((membar_consumer(), mutex_oncpu(owner)) ||
1.24      ad        673:                    (membar_consumer(), !MUTEX_HAS_WAITERS(mtx))) {
1.2       ad        674:                        turnstile_exit(mtx);
1.34      ad        675:                        owner = mtx->mtx_owner;
1.2       ad        676:                        continue;
                    677:                }
                    678: #endif /* MULTIPROCESSOR */
                    679:
                    680:                LOCKSTAT_START_TIMER(lsflag, slptime);
                    681:
1.5       yamt      682:                turnstile_block(ts, TS_WRITER_Q, mtx, &mutex_syncobj);
1.2       ad        683:
                    684:                LOCKSTAT_STOP_TIMER(lsflag, slptime);
                    685:                LOCKSTAT_COUNT(slpcnt, 1);
1.34      ad        686:
                    687:                owner = mtx->mtx_owner;
1.2       ad        688:        }
1.50      rmind     689:        KPREEMPT_ENABLE(curlwp);
1.2       ad        690:
                    691:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SLEEP1,
                    692:            slpcnt, slptime);
                    693:        LOCKSTAT_EVENT(lsflag, mtx, LB_ADAPTIVE_MUTEX | LB_SPIN,
                    694:            spincnt, spintime);
                    695:        LOCKSTAT_EXIT(lsflag);
                    696:
                    697:        MUTEX_DASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    698:        MUTEX_LOCKED(mtx);
                    699: }
                    700:
                    701: /*
                    702:  * mutex_vector_exit:
                    703:  *
                    704:  *     Support routine for mutex_exit() that handles all cases.
                    705:  */
                    706: void
                    707: mutex_vector_exit(kmutex_t *mtx)
                    708: {
                    709:        turnstile_t *ts;
                    710:        uintptr_t curthread;
                    711:
                    712:        if (MUTEX_SPIN_P(mtx)) {
                    713: #ifdef FULL
1.60      matt      714:                if (__predict_false(!MUTEX_SPINBIT_LOCKED_P(mtx))) {
1.33      ad        715:                        if (panicstr != NULL)
                    716:                                return;
1.2       ad        717:                        MUTEX_ABORT(mtx, "exiting unheld spin mutex");
1.33      ad        718:                }
1.2       ad        719:                MUTEX_UNLOCKED(mtx);
1.60      matt      720:                MUTEX_SPINBIT_LOCK_UNLOCK(mtx);
1.2       ad        721: #endif
                    722:                MUTEX_SPIN_SPLRESTORE(mtx);
                    723:                return;
                    724:        }
                    725:
1.11      ad        726:        if (__predict_false((uintptr_t)panicstr | cold)) {
1.2       ad        727:                MUTEX_UNLOCKED(mtx);
                    728:                MUTEX_RELEASE(mtx);
                    729:                return;
                    730:        }
                    731:
                    732:        curthread = (uintptr_t)curlwp;
                    733:        MUTEX_DASSERT(mtx, curthread != 0);
                    734:        MUTEX_ASSERT(mtx, MUTEX_OWNER(mtx->mtx_owner) == curthread);
                    735:        MUTEX_UNLOCKED(mtx);
1.58      mrg       736: #if !defined(LOCKDEBUG)
                    737:        __USE(curthread);
                    738: #endif
1.2       ad        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
1.60      matt      813:        return MUTEX_SPINBIT_LOCKED_P(mtx);
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
1.60      matt      849:                if (MUTEX_SPINBIT_LOCK_TRY(mtx)) {
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;
1.60      matt      906:                while (MUTEX_SPINBIT_LOCKED_P(mtx)) {
1.63    ! msaitoh   907:                        SPINLOCK_BACKOFF(count);
1.2       ad        908: #ifdef LOCKDEBUG
                    909:                        if (SPINLOCK_SPINOUT(spins))
                    910:                                MUTEX_ABORT(mtx, "spinout");
                    911: #endif /* LOCKDEBUG */
                    912:                }
1.60      matt      913:        } while (!MUTEX_SPINBIT_LOCK_TRY(mtx));
1.2       ad        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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