kern_mutex.c

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/*-
 * Copyright (c) 1998 Berkeley Software Design, Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Berkeley Software Design Inc's name may not be used to endorse or
 *    promote products derived from this software without specific prior
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY BERKELEY SOFTWARE DESIGN INC ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL BERKELEY SOFTWARE DESIGN INC BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      from BSDI $Id: mutex_witness.c,v 1.1.2.20 2000/04/27 03:10:27 cp Exp $
 *      and BSDI $Id: synch_machdep.c,v 2.3.2.39 2000/04/27 03:10:25 cp Exp $
 */

/*
 * Machine independent bits of mutex implementation.
 */

#include <sys/cdefs.h>
__FBSDID("$BSDSUniX$");

#include "opt_adaptive_mutexes.h"
#include "opt_ddb.h"
#include "opt_global.h"
#include "opt_hwpmc_hooks.h"
#include "opt_kdtrace.h"
#include "opt_sched.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/bus.h>
#include <sys/conf.h>
#include <sys/kdb.h>
#include <sys/kernel.h>
#include <sys/ktr.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/sbuf.h>
#include <sys/sysctl.h>
#include <sys/turnstile.h>
#include <sys/vmmeter.h>
#include <sys/lock_profile.h>

#include <machine/atomic.h>
#include <machine/bus.h>
#include <machine/cpu.h>

#include <ddb/ddb.h>

#include <fs/devfs/devfs_int.h>

#include <vm/vm.h>
#include <vm/vm_extern.h>

#if defined(SMP) && !defined(NO_ADAPTIVE_MUTEXES)
#define ADAPTIVE_MUTEXES
#endif

#ifdef HWPMC_HOOKS
#include <sys/pmckern.h>
PMC_SOFT_DEFINE( , , lock, failed);
#endif

/*
 * Internal utility macros.
 */
#define mtx_unowned(m)  ((m)->mtx_lock == MTX_UNOWNED)

#define mtx_destroyed(m) ((m)->mtx_lock == MTX_DESTROYED)

#define mtx_owner(m)    ((struct thread *)((m)->mtx_lock & ~MTX_FLAGMASK))

static void     assert_mtx(struct lock_object *lock, int what);
#ifdef DDB
static void     db_show_mtx(struct lock_object *lock);
#endif
static void     lock_mtx(struct lock_object *lock, int how);
static void     lock_spin(struct lock_object *lock, int how);
#ifdef KDTRACE_HOOKS
static int      owner_mtx(struct lock_object *lock, struct thread **owner);
#endif
static int      unlock_mtx(struct lock_object *lock);
static int      unlock_spin(struct lock_object *lock);

/*
 * Lock classes for sleep and spin mutexes.
 */
struct lock_class lock_class_mtx_sleep = {
        .lc_name = "sleep mutex",
        .lc_flags = LC_SLEEPLOCK | LC_RECURSABLE,
        .lc_assert = assert_mtx,
#ifdef DDB
        .lc_ddb_show = db_show_mtx,
#endif
        .lc_lock = lock_mtx,
        .lc_unlock = unlock_mtx,
#ifdef KDTRACE_HOOKS
        .lc_owner = owner_mtx,
#endif
};
struct lock_class lock_class_mtx_spin = {
        .lc_name = "spin mutex",
        .lc_flags = LC_SPINLOCK | LC_RECURSABLE,
        .lc_assert = assert_mtx,
#ifdef DDB
        .lc_ddb_show = db_show_mtx,
#endif
        .lc_lock = lock_spin,
        .lc_unlock = unlock_spin,
#ifdef KDTRACE_HOOKS
        .lc_owner = owner_mtx,
#endif
};

/*
 * System-wide mutexes
 */
struct mtx blocked_lock;
struct mtx Giant;

void
assert_mtx(struct lock_object *lock, int what)
{

        mtx_assert((struct mtx *)lock, what);
}

void
lock_mtx(struct lock_object *lock, int how)
{

        mtx_lock((struct mtx *)lock);
}

void
lock_spin(struct lock_object *lock, int how)
{

        panic("spin locks can only use msleep_spin");
}

int
unlock_mtx(struct lock_object *lock)
{
        struct mtx *m;

        m = (struct mtx *)lock;
        mtx_assert(m, MA_OWNED | MA_NOTRECURSED);
        mtx_unlock(m);
        return (0);
}

int
unlock_spin(struct lock_object *lock)
{

        panic("spin locks can only use msleep_spin");
}

#ifdef KDTRACE_HOOKS
int
owner_mtx(struct lock_object *lock, struct thread **owner)
{
        struct mtx *m = (struct mtx *)lock;

        *owner = mtx_owner(m);
        return (mtx_unowned(m) == 0);
}
#endif

/*
 * Function versions of the inlined __mtx_* macros.  These are used by
 * modules and can also be called from assembly language if needed.
 */
void
_mtx_lock_flags(struct mtx *m, int opts, const char *file, int line)
{

        if (SCHEDULER_STOPPED())
                return;
        KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
            ("mtx_lock() by idle thread %p on sleep mutex %s @ %s:%d",
            curthread, m->lock_object.lo_name, file, line));
        KASSERT(m->mtx_lock != MTX_DESTROYED,
            ("mtx_lock() of destroyed mutex @ %s:%d", file, line));
        KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
            ("mtx_lock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
            file, line));
        WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE,
            file, line, NULL);

        __mtx_lock(m, curthread, opts, file, line);
        LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
            line);
        WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
        curthread->td_locks++;
}

void
_mtx_unlock_flags(struct mtx *m, int opts, const char *file, int line)
{

        if (SCHEDULER_STOPPED())
                return;
        KASSERT(m->mtx_lock != MTX_DESTROYED,
            ("mtx_unlock() of destroyed mutex @ %s:%d", file, line));
        KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
            ("mtx_unlock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
            file, line));
        curthread->td_locks--;
        WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
        LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file,
            line);
        mtx_assert(m, MA_OWNED);

        if (m->mtx_recurse == 0)
                LOCKSTAT_PROFILE_RELEASE_LOCK(LS_MTX_UNLOCK_RELEASE, m);
        __mtx_unlock(m, curthread, opts, file, line);
}

void
_mtx_lock_spin_flags(struct mtx *m, int opts, const char *file, int line)
{

        if (SCHEDULER_STOPPED())
                return;
        KASSERT(m->mtx_lock != MTX_DESTROYED,
            ("mtx_lock_spin() of destroyed mutex @ %s:%d", file, line));
        KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
            ("mtx_lock_spin() of sleep mutex %s @ %s:%d",
            m->lock_object.lo_name, file, line));
        if (mtx_owned(m))
                KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0,
            ("mtx_lock_spin: recursed on non-recursive mutex %s @ %s:%d\n",
                    m->lock_object.lo_name, file, line));
        WITNESS_CHECKORDER(&m->lock_object, opts | LOP_NEWORDER | LOP_EXCLUSIVE,
            file, line, NULL);
        __mtx_lock_spin(m, curthread, opts, file, line);
        LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
            line);
        WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
}

void
_mtx_unlock_spin_flags(struct mtx *m, int opts, const char *file, int line)
{

        if (SCHEDULER_STOPPED())
                return;
        KASSERT(m->mtx_lock != MTX_DESTROYED,
            ("mtx_unlock_spin() of destroyed mutex @ %s:%d", file, line));
        KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
            ("mtx_unlock_spin() of sleep mutex %s @ %s:%d",
            m->lock_object.lo_name, file, line));
        WITNESS_UNLOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
        LOCK_LOG_LOCK("UNLOCK", &m->lock_object, opts, m->mtx_recurse, file,
            line);
        mtx_assert(m, MA_OWNED);

        __mtx_unlock_spin(m);
}

/*
 * The important part of mtx_trylock{,_flags}()
 * Tries to acquire lock `m.'  If this function is called on a mutex that
 * is already owned, it will recursively acquire the lock.
 */
int
_mtx_trylock(struct mtx *m, int opts, const char *file, int line)
{
#ifdef LOCK_PROFILING
        uint64_t waittime = 0;
        int contested = 0;
#endif
        int rval;

        if (SCHEDULER_STOPPED())
                return (1);

        KASSERT(kdb_active != 0 || !TD_IS_IDLETHREAD(curthread),
            ("mtx_trylock() by idle thread %p on sleep mutex %s @ %s:%d",
            curthread, m->lock_object.lo_name, file, line));
        KASSERT(m->mtx_lock != MTX_DESTROYED,
            ("mtx_trylock() of destroyed mutex @ %s:%d", file, line));
        KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_sleep,
            ("mtx_trylock() of spin mutex %s @ %s:%d", m->lock_object.lo_name,
            file, line));

        if (mtx_owned(m) && (m->lock_object.lo_flags & LO_RECURSABLE) != 0) {
                m->mtx_recurse++;
                atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
                rval = 1;
        } else
                rval = _mtx_obtain_lock(m, (uintptr_t)curthread);

        LOCK_LOG_TRY("LOCK", &m->lock_object, opts, rval, file, line);
        if (rval) {
                WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE | LOP_TRYLOCK,
                    file, line);
                curthread->td_locks++;
                if (m->mtx_recurse == 0)
                        LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE,
                            m, contested, waittime, file, line);

        }

        return (rval);
}

/*
 * _mtx_lock_sleep: the tougher part of acquiring an MTX_DEF lock.
 *
 * We call this if the lock is either contested (i.e. we need to go to
 * sleep waiting for it), or if we need to recurse on it.
 */
void
_mtx_lock_sleep(struct mtx *m, uintptr_t tid, int opts, const char *file,
    int line)
{
        struct turnstile *ts;
        uintptr_t v;
#ifdef ADAPTIVE_MUTEXES
        volatile struct thread *owner;
#endif
#ifdef KTR
        int cont_logged = 0;
#endif
#ifdef LOCK_PROFILING
        int contested = 0;
        uint64_t waittime = 0;
#endif
#ifdef KDTRACE_HOOKS
        uint64_t spin_cnt = 0;
        uint64_t sleep_cnt = 0;
        int64_t sleep_time = 0;
        int64_t all_time = 0;
#endif

        if (SCHEDULER_STOPPED())
                return;

        if (mtx_owned(m)) {
                KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0,
            ("_mtx_lock_sleep: recursed on non-recursive mutex %s @ %s:%d\n",
                    m->lock_object.lo_name, file, line));
                m->mtx_recurse++;
                atomic_set_ptr(&m->mtx_lock, MTX_RECURSED);
                if (LOCK_LOG_TEST(&m->lock_object, opts))
                        CTR1(KTR_LOCK, "_mtx_lock_sleep: %p recursing", m);
                return;
        }

#ifdef HWPMC_HOOKS
        PMC_SOFT_CALL( , , lock, failed);
#endif
        lock_profile_obtain_lock_failed(&m->lock_object,
                    &contested, &waittime);
        if (LOCK_LOG_TEST(&m->lock_object, opts))
                CTR4(KTR_LOCK,
                    "_mtx_lock_sleep: %s contested (lock=%p) at %s:%d",
                    m->lock_object.lo_name, (void *)m->mtx_lock, file, line);
#ifdef KDTRACE_HOOKS
        all_time -= lockstat_nsecs(&m->lock_object);
#endif

        while (!_mtx_obtain_lock(m, tid)) {
#ifdef KDTRACE_HOOKS
                spin_cnt++;
#endif
#ifdef ADAPTIVE_MUTEXES
                /*
                 * If the owner is running on another CPU, spin until the
                 * owner stops running or the state of the lock changes.
                 */
                v = m->mtx_lock;
                if (v != MTX_UNOWNED) {
                        owner = (struct thread *)(v & ~MTX_FLAGMASK);
                        if (TD_IS_RUNNING(owner)) {
                                if (LOCK_LOG_TEST(&m->lock_object, 0))
                                        CTR3(KTR_LOCK,
                                            "%s: spinning on %p held by %p",
                                            __func__, m, owner);
                                while (mtx_owner(m) == owner &&
                                    TD_IS_RUNNING(owner)) {
                                        cpu_spinwait();
#ifdef KDTRACE_HOOKS
                                        spin_cnt++;
#endif
                                }
                                continue;
                        }
                }
#endif

                ts = turnstile_trywait(&m->lock_object);
                v = m->mtx_lock;

                /*
                 * Check if the lock has been released while spinning for
                 * the turnstile chain lock.
                 */
                if (v == MTX_UNOWNED) {
                        turnstile_cancel(ts);
                        continue;
                }

#ifdef ADAPTIVE_MUTEXES
                /*
                 * The current lock owner might have started executing
                 * on another CPU (or the lock could have changed
                 * owners) while we were waiting on the turnstile
                 * chain lock.  If so, drop the turnstile lock and try
                 * again.
                 */
                owner = (struct thread *)(v & ~MTX_FLAGMASK);
                if (TD_IS_RUNNING(owner)) {
                        turnstile_cancel(ts);
                        continue;
                }
#endif

                /*
                 * If the mutex isn't already contested and a failure occurs
                 * setting the contested bit, the mutex was either released
                 * or the state of the MTX_RECURSED bit changed.
                 */
                if ((v & MTX_CONTESTED) == 0 &&
                    !atomic_cmpset_ptr(&m->mtx_lock, v, v | MTX_CONTESTED)) {
                        turnstile_cancel(ts);
                        continue;
                }

                /*
                 * We definitely must sleep for this lock.
                 */
                mtx_assert(m, MA_NOTOWNED);

#ifdef KTR
                if (!cont_logged) {
                        CTR6(KTR_CONTENTION,
                            "contention: %p at %s:%d wants %s, taken by %s:%d",
                            (void *)tid, file, line, m->lock_object.lo_name,
                            WITNESS_FILE(&m->lock_object),
                            WITNESS_LINE(&m->lock_object));
                        cont_logged = 1;
                }
#endif

                /*
                 * Block on the turnstile.
                 */
#ifdef KDTRACE_HOOKS
                sleep_time -= lockstat_nsecs(&m->lock_object);
#endif
                turnstile_wait(ts, mtx_owner(m), TS_EXCLUSIVE_QUEUE);
#ifdef KDTRACE_HOOKS
                sleep_time += lockstat_nsecs(&m->lock_object);
                sleep_cnt++;
#endif
        }
#ifdef KDTRACE_HOOKS
        all_time += lockstat_nsecs(&m->lock_object);
#endif
#ifdef KTR
        if (cont_logged) {
                CTR4(KTR_CONTENTION,
                    "contention end: %s acquired by %p at %s:%d",
                    m->lock_object.lo_name, (void *)tid, file, line);
        }
#endif
        LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_LOCK_ACQUIRE, m, contested,
            waittime, file, line);
#ifdef KDTRACE_HOOKS
        if (sleep_time)
                LOCKSTAT_RECORD1(LS_MTX_LOCK_BLOCK, m, sleep_time);

        /*
         * Only record the loops spinning and not sleeping. 
         */
        if (spin_cnt > sleep_cnt)
                LOCKSTAT_RECORD1(LS_MTX_LOCK_SPIN, m, (all_time - sleep_time));
#endif
}

static void
_mtx_lock_spin_failed(struct mtx *m)
{
        struct thread *td;

        td = mtx_owner(m);

        /* If the mutex is unlocked, try again. */
        if (td == NULL)
                return;

        printf( "spin lock %p (%s) held by %p (tid %d) too long\n",
            m, m->lock_object.lo_name, td, td->td_tid);
#ifdef WITNESS
        witness_display_spinlock(&m->lock_object, td, printf);
#endif
        panic("spin lock held too long");
}

#ifdef SMP
/*
 * _mtx_lock_spin: the tougher part of acquiring an MTX_SPIN lock.
 *
 * This is only called if we need to actually spin for the lock. Recursion
 * is handled inline.
 */
void
_mtx_lock_spin(struct mtx *m, uintptr_t tid, int opts, const char *file,
    int line)
{
        int i = 0;
#ifdef LOCK_PROFILING
        int contested = 0;
        uint64_t waittime = 0;
#endif
#ifdef KDTRACE_HOOKS
        int64_t spin_time = 0;
#endif

        if (SCHEDULER_STOPPED())
                return;

        if (LOCK_LOG_TEST(&m->lock_object, opts))
                CTR1(KTR_LOCK, "_mtx_lock_spin: %p spinning", m);

#ifdef HWPMC_HOOKS
        PMC_SOFT_CALL( , , lock, failed);
#endif
        lock_profile_obtain_lock_failed(&m->lock_object, &contested, &waittime);
#ifdef KDTRACE_HOOKS
        spin_time -= lockstat_nsecs(&m->lock_object);
#endif
        while (!_mtx_obtain_lock(m, tid)) {

                /* Give interrupts a chance while we spin. */
                spinlock_exit();
                while (m->mtx_lock != MTX_UNOWNED) {
                        if (i++ < 10000000) {
                                cpu_spinwait();
                                continue;
                        }
                        if (i < 60000000 || kdb_active || panicstr != NULL)
                                DELAY(1);
                        else
                                _mtx_lock_spin_failed(m);
                        cpu_spinwait();
                }
                spinlock_enter();
        }
#ifdef KDTRACE_HOOKS
        spin_time += lockstat_nsecs(&m->lock_object);
#endif

        if (LOCK_LOG_TEST(&m->lock_object, opts))
                CTR1(KTR_LOCK, "_mtx_lock_spin: %p spin done", m);

        LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE, m,
            contested, waittime, (file), (line));
#ifdef KDTRACE_HOOKS
        if (spin_time != 0)
                LOCKSTAT_RECORD1(LS_MTX_SPIN_LOCK_SPIN, m, spin_time);
#endif
}
#endif /* SMP */

void
_thread_lock_flags(struct thread *td, int opts, const char *file, int line)
{
        struct mtx *m;
        uintptr_t tid;
        int i;
#ifdef LOCK_PROFILING
        int contested = 0;
        uint64_t waittime = 0;
#endif
#ifdef KDTRACE_HOOKS
        int64_t spin_time = 0;
#endif

        i = 0;
        tid = (uintptr_t)curthread;

        if (SCHEDULER_STOPPED())
                return;

#ifdef KDTRACE_HOOKS
        spin_time -= lockstat_nsecs(&td->td_lock->lock_object);
#endif
        for (;;) {
retry:
                spinlock_enter();
                m = td->td_lock;
                KASSERT(m->mtx_lock != MTX_DESTROYED,
                    ("thread_lock() of destroyed mutex @ %s:%d", file, line));
                KASSERT(LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin,
                    ("thread_lock() of sleep mutex %s @ %s:%d",
                    m->lock_object.lo_name, file, line));
                if (mtx_owned(m))
                        KASSERT((m->lock_object.lo_flags & LO_RECURSABLE) != 0,
            ("thread_lock: recursed on non-recursive mutex %s @ %s:%d\n",
                            m->lock_object.lo_name, file, line));
                WITNESS_CHECKORDER(&m->lock_object,
                    opts | LOP_NEWORDER | LOP_EXCLUSIVE, file, line, NULL);
                while (!_mtx_obtain_lock(m, tid)) {
                        if (m->mtx_lock == tid) {
                                m->mtx_recurse++;
                                break;
                        }
#ifdef HWPMC_HOOKS
                        PMC_SOFT_CALL( , , lock, failed);
#endif
                        lock_profile_obtain_lock_failed(&m->lock_object,
                            &contested, &waittime);
                        /* Give interrupts a chance while we spin. */
                        spinlock_exit();
                        while (m->mtx_lock != MTX_UNOWNED) {
                                if (i++ < 10000000)
                                        cpu_spinwait();
                                else if (i < 60000000 ||
                                    kdb_active || panicstr != NULL)
                                        DELAY(1);
                                else
                                        _mtx_lock_spin_failed(m);
                                cpu_spinwait();
                                if (m != td->td_lock)
                                        goto retry;
                        }
                        spinlock_enter();
                }
                if (m == td->td_lock)
                        break;
                __mtx_unlock_spin(m);   /* does spinlock_exit() */
        }
#ifdef KDTRACE_HOOKS
        spin_time += lockstat_nsecs(&m->lock_object);
#endif
        if (m->mtx_recurse == 0)
                LOCKSTAT_PROFILE_OBTAIN_LOCK_SUCCESS(LS_MTX_SPIN_LOCK_ACQUIRE,
                    m, contested, waittime, (file), (line));
        LOCK_LOG_LOCK("LOCK", &m->lock_object, opts, m->mtx_recurse, file,
            line);
        WITNESS_LOCK(&m->lock_object, opts | LOP_EXCLUSIVE, file, line);
        LOCKSTAT_RECORD1(LS_THREAD_LOCK_SPIN, m, spin_time);
}

struct mtx *
thread_lock_block(struct thread *td)
{
        struct mtx *lock;

        THREAD_LOCK_ASSERT(td, MA_OWNED);
        lock = td->td_lock;
        td->td_lock = &blocked_lock;
        mtx_unlock_spin(lock);

        return (lock);
}

void
thread_lock_unblock(struct thread *td, struct mtx *new)
{
        mtx_assert(new, MA_OWNED);
        MPASS(td->td_lock == &blocked_lock);
        atomic_store_rel_ptr((volatile void *)&td->td_lock, (uintptr_t)new);
}

void
thread_lock_set(struct thread *td, struct mtx *new)
{
        struct mtx *lock;

        mtx_assert(new, MA_OWNED);
        THREAD_LOCK_ASSERT(td, MA_OWNED);
        lock = td->td_lock;
        td->td_lock = new;
        mtx_unlock_spin(lock);
}

/*
 * _mtx_unlock_sleep: the tougher part of releasing an MTX_DEF lock.
 *
 * We are only called here if the lock is recursed or contested (i.e. we
 * need to wake up a blocked thread).
 */
void
_mtx_unlock_sleep(struct mtx *m, int opts, const char *file, int line)
{
        struct turnstile *ts;

        if (SCHEDULER_STOPPED())
                return;

        if (mtx_recursed(m)) {
                if (--(m->mtx_recurse) == 0)
                        atomic_clear_ptr(&m->mtx_lock, MTX_RECURSED);
                if (LOCK_LOG_TEST(&m->lock_object, opts))
                        CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p unrecurse", m);
                return;
        }

        /*
         * We have to lock the chain before the turnstile so this turnstile
         * can be removed from the hash list if it is empty.
         */
        turnstile_chain_lock(&m->lock_object);
        ts = turnstile_lookup(&m->lock_object);
        if (LOCK_LOG_TEST(&m->lock_object, opts))
                CTR1(KTR_LOCK, "_mtx_unlock_sleep: %p contested", m);
        MPASS(ts != NULL);
        turnstile_broadcast(ts, TS_EXCLUSIVE_QUEUE);
        _mtx_release_lock_quick(m);

        /*
         * This turnstile is now no longer associated with the mutex.  We can
         * unlock the chain lock so a new turnstile may take it's place.
         */
        turnstile_unpend(ts, TS_EXCLUSIVE_LOCK);
        turnstile_chain_unlock(&m->lock_object);
}

/*
 * All the unlocking of MTX_SPIN locks is done inline.
 * See the __mtx_unlock_spin() macro for the details.
 */

/*
 * The backing function for the INVARIANTS-enabled mtx_assert()
 */
#ifdef INVARIANT_SUPPORT
void
_mtx_assert(struct mtx *m, int what, const char *file, int line)
{

        if (panicstr != NULL || dumping)
                return;
        switch (what) {
        case MA_OWNED:
        case MA_OWNED | MA_RECURSED:
        case MA_OWNED | MA_NOTRECURSED:
                if (!mtx_owned(m))
                        panic("mutex %s not owned at %s:%d",
                            m->lock_object.lo_name, file, line);
                if (mtx_recursed(m)) {
                        if ((what & MA_NOTRECURSED) != 0)
                                panic("mutex %s recursed at %s:%d",
                                    m->lock_object.lo_name, file, line);
                } else if ((what & MA_RECURSED) != 0) {
                        panic("mutex %s unrecursed at %s:%d",
                            m->lock_object.lo_name, file, line);
                }
                break;
        case MA_NOTOWNED:
                if (mtx_owned(m))
                        panic("mutex %s owned at %s:%d",
                            m->lock_object.lo_name, file, line);
                break;
        default:
                panic("unknown mtx_assert at %s:%d", file, line);
        }
}
#endif

/*
 * The MUTEX_DEBUG-enabled mtx_validate()
 *
 * Most of these checks have been moved off into the LO_INITIALIZED flag
 * maintained by the witness code.
 */
#ifdef MUTEX_DEBUG

void    mtx_validate(struct mtx *);

void
mtx_validate(struct mtx *m)
{

/*
 * XXX: When kernacc() does not require Giant we can reenable this check
 */
#ifdef notyet
        /*
         * Can't call kernacc() from early init386(), especially when
         * initializing Giant mutex, because some stuff in kernacc()
         * requires Giant itself.
         */
        if (!cold)
                if (!kernacc((caddr_t)m, sizeof(m),
                    VM_PROT_READ | VM_PROT_WRITE))
                        panic("Can't read and write to mutex %p", m);
#endif
}
#endif

/*
 * General init routine used by the MTX_SYSINIT() macro.
 */
void
mtx_sysinit(void *arg)
{
        struct mtx_args *margs = arg;

        mtx_init(margs->ma_mtx, margs->ma_desc, NULL, margs->ma_opts);
}

/*
 * Mutex initialization routine; initialize lock `m' of type contained in
 * `opts' with options contained in `opts' and name `name.'  The optional
 * lock type `type' is used as a general lock category name for use with
 * witness.
 */
void
mtx_init(struct mtx *m, const char *name, const char *type, int opts)
{
        struct lock_class *class;
        int flags;

        MPASS((opts & ~(MTX_SPIN | MTX_QUIET | MTX_RECURSE |
                MTX_NOWITNESS | MTX_DUPOK | MTX_NOPROFILE)) == 0);
        ASSERT_ATOMIC_LOAD_PTR(m->mtx_lock,
            ("%s: mtx_lock not aligned for %s: %p", __func__, name,
            &m->mtx_lock));

#ifdef MUTEX_DEBUG
        /* Diagnostic and error correction */
        mtx_validate(m);
#endif

        /* Determine lock class and lock flags. */
        if (opts & MTX_SPIN)
                class = &lock_class_mtx_spin;
        else
                class = &lock_class_mtx_sleep;
        flags = 0;
        if (opts & MTX_QUIET)
                flags |= LO_QUIET;
        if (opts & MTX_RECURSE)
                flags |= LO_RECURSABLE;
        if ((opts & MTX_NOWITNESS) == 0)
                flags |= LO_WITNESS;
        if (opts & MTX_DUPOK)
                flags |= LO_DUPOK;
        if (opts & MTX_NOPROFILE)
                flags |= LO_NOPROFILE;

        /* Initialize mutex. */
        m->mtx_lock = MTX_UNOWNED;
        m->mtx_recurse = 0;

        lock_init(&m->lock_object, class, name, type, flags);
}

/*
 * Remove lock `m' from all_mtx queue.  We don't allow MTX_QUIET to be
 * passed in as a flag here because if the corresponding mtx_init() was
 * called with MTX_QUIET set, then it will already be set in the mutex's
 * flags.
 */
void
mtx_destroy(struct mtx *m)
{

        if (!mtx_owned(m))
                MPASS(mtx_unowned(m));
        else {
                MPASS((m->mtx_lock & (MTX_RECURSED|MTX_CONTESTED)) == 0);

                /* Perform the non-mtx related part of mtx_unlock_spin(). */
                if (LOCK_CLASS(&m->lock_object) == &lock_class_mtx_spin)
                        spinlock_exit();
                else
                        curthread->td_locks--;

                lock_profile_release_lock(&m->lock_object);
                /* Tell witness this isn't locked to make it happy. */
                WITNESS_UNLOCK(&m->lock_object, LOP_EXCLUSIVE, __FILE__,
                    __LINE__);
        }

        m->mtx_lock = MTX_DESTROYED;
        lock_destroy(&m->lock_object);
}

/*
 * Intialize the mutex code and system mutexes.  This is called from the MD
 * startup code prior to mi_startup().  The per-CPU data space needs to be
 * setup before this is called.
 */
void
mutex_init(void)
{

        /* Setup turnstiles so that sleep mutexes work. */
        init_turnstiles();

        /*
         * Initialize mutexes.
         */
        mtx_init(&Giant, "Giant", NULL, MTX_DEF | MTX_RECURSE);
        mtx_init(&blocked_lock, "blocked lock", NULL, MTX_SPIN);
        blocked_lock.mtx_lock = 0xdeadc0de;     /* Always blocked. */
        mtx_init(&proc0.p_mtx, "process lock", NULL, MTX_DEF | MTX_DUPOK);
        mtx_init(&proc0.p_slock, "process slock", NULL, MTX_SPIN | MTX_RECURSE);
        mtx_init(&devmtx, "cdev", NULL, MTX_DEF);
        mtx_lock(&Giant);
}

#ifdef DDB
void
db_show_mtx(struct lock_object *lock)
{
        struct thread *td;
        struct mtx *m;

        m = (struct mtx *)lock;

        db_printf(" flags: {");
        if (LOCK_CLASS(lock) == &lock_class_mtx_spin)
                db_printf("SPIN");
        else
                db_printf("DEF");
        if (m->lock_object.lo_flags & LO_RECURSABLE)
                db_printf(", RECURSE");
        if (m->lock_object.lo_flags & LO_DUPOK)
                db_printf(", DUPOK");
        db_printf("}\n");
        db_printf(" state: {");
        if (mtx_unowned(m))
                db_printf("UNOWNED");
        else if (mtx_destroyed(m))
                db_printf("DESTROYED");
        else {
                db_printf("OWNED");
                if (m->mtx_lock & MTX_CONTESTED)
                        db_printf(", CONTESTED");
                if (m->mtx_lock & MTX_RECURSED)
                        db_printf(", RECURSED");
        }
        db_printf("}\n");
        if (!mtx_unowned(m) && !mtx_destroyed(m)) {
                td = mtx_owner(m);
                db_printf(" owner: %p (tid %d, pid %d, \"%s\")\n", td,
                    td->td_tid, td->td_proc->p_pid, td->td_name);
                if (mtx_recursed(m))
                        db_printf(" recursed: %d\n", m->mtx_recurse);
        }
}
#endif