xnu-1228.tar.gz

[apple/xnu.git] / osfmk / i386 / locks_i386.c

/*
 * Copyright (c) 2000-2007 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */
/* 
 * Mach Operating System
 * Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
 * All Rights Reserved.
 * 
 * Permission to use, copy, modify and distribute this software and its
 * documentation is hereby granted, provided that both the copyright
 * notice and this permission notice appear in all copies of the
 * software, derivative works or modified versions, and any portions
 * thereof, and that both notices appear in supporting documentation.
 * 
 * CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
 * CONDITION.  CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
 * ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
 * 
 * Carnegie Mellon requests users of this software to return to
 * 
 *  Software Distribution Coordinator  or  Software.Distribution@CS.CMU.EDU
 *  School of Computer Science
 *  Carnegie Mellon University
 *  Pittsburgh PA 15213-3890
 * 
 * any improvements or extensions that they make and grant Carnegie Mellon
 * the rights to redistribute these changes.
 */
/*
 *      File:   kern/lock.c
 *      Author: Avadis Tevanian, Jr., Michael Wayne Young
 *      Date:   1985
 *
 *      Locking primitives implementation
 */

#include <mach_kdb.h>
#include <mach_ldebug.h>

#include <kern/lock.h>
#include <kern/locks.h>
#include <kern/kalloc.h>
#include <kern/misc_protos.h>
#include <kern/thread.h>
#include <kern/processor.h>
#include <kern/cpu_data.h>
#include <kern/cpu_number.h>
#include <kern/sched_prim.h>
#include <kern/xpr.h>
#include <kern/debug.h>
#include <string.h>

#if     MACH_KDB
#include <ddb/db_command.h>
#include <ddb/db_output.h>
#include <ddb/db_sym.h>
#include <ddb/db_print.h>
#endif  /* MACH_KDB */

#include <i386/machine_cpu.h>

#include <sys/kdebug.h>

/*
 * We need only enough declarations from the BSD-side to be able to
 * test if our probe is active, and to call __dtrace_probe().  Setting
 * NEED_DTRACE_DEFS gets a local copy of those definitions pulled in.
 */
#if     CONFIG_DTRACE
#define NEED_DTRACE_DEFS
#include <../bsd/sys/lockstat.h>
#endif

#define LCK_RW_LCK_EXCLUSIVE_CODE       0x100
#define LCK_RW_LCK_EXCLUSIVE1_CODE      0x101
#define LCK_RW_LCK_SHARED_CODE          0x102
#define LCK_RW_LCK_SH_TO_EX_CODE        0x103
#define LCK_RW_LCK_SH_TO_EX1_CODE       0x104
#define LCK_RW_LCK_EX_TO_SH_CODE        0x105

#define LCK_MTX_LCK_SPIN                0x200

#define ANY_LOCK_DEBUG  (USLOCK_DEBUG || LOCK_DEBUG || MUTEX_DEBUG)

unsigned int LcksOpts=0;
unsigned int lock_wait_time[2] = { (unsigned int)-1, 0 } ;

/* Forwards */

#if     MACH_KDB
void    db_print_simple_lock(
                        simple_lock_t   addr);

void    db_print_mutex(
                        mutex_t         * addr);
#endif  /* MACH_KDB */


#if     USLOCK_DEBUG
/*
 *      Perform simple lock checks.
 */
int     uslock_check = 1;
int     max_lock_loops  = 100000000;
decl_simple_lock_data(extern , printf_lock)
decl_simple_lock_data(extern , panic_lock)
#if     MACH_KDB
decl_simple_lock_data(extern , kdb_lock)
#endif  /* MACH_KDB */
#endif  /* USLOCK_DEBUG */


/*
 *      We often want to know the addresses of the callers
 *      of the various lock routines.  However, this information
 *      is only used for debugging and statistics.
 */
typedef void    *pc_t;
#define INVALID_PC      ((void *) VM_MAX_KERNEL_ADDRESS)
#define INVALID_THREAD  ((void *) VM_MAX_KERNEL_ADDRESS)
#if     ANY_LOCK_DEBUG
#define OBTAIN_PC(pc,l) ((pc) = (void *) GET_RETURN_PC(&(l)))
#define DECL_PC(pc)     pc_t pc;
#else   /* ANY_LOCK_DEBUG */
#define DECL_PC(pc)
#ifdef  lint
/*
 *      Eliminate lint complaints about unused local pc variables.
 */
#define OBTAIN_PC(pc,l) ++pc
#else   /* lint */
#define OBTAIN_PC(pc,l)
#endif  /* lint */
#endif  /* USLOCK_DEBUG */


/*
 *      Portable lock package implementation of usimple_locks.
 */

#if     USLOCK_DEBUG
#define USLDBG(stmt)    stmt
void            usld_lock_init(usimple_lock_t, unsigned short);
void            usld_lock_pre(usimple_lock_t, pc_t);
void            usld_lock_post(usimple_lock_t, pc_t);
void            usld_unlock(usimple_lock_t, pc_t);
void            usld_lock_try_pre(usimple_lock_t, pc_t);
void            usld_lock_try_post(usimple_lock_t, pc_t);
int             usld_lock_common_checks(usimple_lock_t, char *);
#else   /* USLOCK_DEBUG */
#define USLDBG(stmt)
#endif  /* USLOCK_DEBUG */

/*
 * Forward definitions
 */

void lck_rw_lock_shared_gen(
        lck_rw_t        *lck);

lck_rw_type_t lck_rw_done_gen(
        lck_rw_t        *lck);

/*
 *      Routine:        lck_spin_alloc_init
 */
lck_spin_t *
lck_spin_alloc_init(
        lck_grp_t       *grp,
        lck_attr_t      *attr)
{
        lck_spin_t      *lck;

        if ((lck = (lck_spin_t *)kalloc(sizeof(lck_spin_t))) != 0)
                lck_spin_init(lck, grp, attr);

        return(lck);
}

/*
 *      Routine:        lck_spin_free
 */
void
lck_spin_free(
        lck_spin_t      *lck,
        lck_grp_t       *grp)
{
        lck_spin_destroy(lck, grp);
        kfree(lck, sizeof(lck_spin_t));
}

/*
 *      Routine:        lck_spin_init
 */
void
lck_spin_init(
        lck_spin_t      *lck,
        lck_grp_t       *grp,
        __unused lck_attr_t     *attr)
{
        usimple_lock_init((usimple_lock_t) lck, 0);
        lck_grp_reference(grp);
        lck_grp_lckcnt_incr(grp, LCK_TYPE_SPIN);
}

/*
 *      Routine:        lck_spin_destroy
 */
void
lck_spin_destroy(
        lck_spin_t      *lck,
        lck_grp_t       *grp)
{
        if (lck->lck_spin_data[0] == LCK_SPIN_TAG_DESTROYED)
                return;
        lck->lck_spin_data[0] = LCK_SPIN_TAG_DESTROYED;
        lck_grp_lckcnt_decr(grp, LCK_TYPE_SPIN);
        lck_grp_deallocate(grp);
        return;
}

/*
 *      Routine:        lck_spin_lock
 */
void
lck_spin_lock(
        lck_spin_t      *lck)
{
        usimple_lock((usimple_lock_t) lck);
}

/*
 *      Routine:        lck_spin_unlock
 */
void
lck_spin_unlock(
        lck_spin_t      *lck)
{
        usimple_unlock((usimple_lock_t) lck);
}


/*
 *      Routine:        lck_spin_try_lock
 */
boolean_t
lck_spin_try_lock(
        lck_spin_t      *lck)
{
        return((boolean_t)usimple_lock_try((usimple_lock_t) lck));
}

/*
 *      Initialize a usimple_lock.
 *
 *      No change in preemption state.
 */
void
usimple_lock_init(
        usimple_lock_t  l,
        __unused unsigned short tag)
{
#ifndef MACHINE_SIMPLE_LOCK
        USLDBG(usld_lock_init(l, tag));
        hw_lock_init(&l->interlock);
#else
        simple_lock_init((simple_lock_t)l,tag);
#endif
}


/*
 *      Acquire a usimple_lock.
 *
 *      Returns with preemption disabled.  Note
 *      that the hw_lock routines are responsible for
 *      maintaining preemption state.
 */
void
usimple_lock(
        usimple_lock_t  l)
{
#ifndef MACHINE_SIMPLE_LOCK
        DECL_PC(pc);

        OBTAIN_PC(pc, l);
        USLDBG(usld_lock_pre(l, pc));

        if(!hw_lock_to(&l->interlock, LockTimeOutTSC))  /* Try to get the lock with a timeout */ 
                panic("simple lock deadlock detection: lock=%p, cpu=%d, owning thread=0x%x", l, cpu_number(), l->interlock.lock_data);

        USLDBG(usld_lock_post(l, pc));
#else
        simple_lock((simple_lock_t)l);
#endif
}


/*
 *      Release a usimple_lock.
 *
 *      Returns with preemption enabled.  Note
 *      that the hw_lock routines are responsible for
 *      maintaining preemption state.
 */
void
usimple_unlock(
        usimple_lock_t  l)
{
#ifndef MACHINE_SIMPLE_LOCK
        DECL_PC(pc);

        OBTAIN_PC(pc, l);
        USLDBG(usld_unlock(l, pc));
        hw_lock_unlock(&l->interlock);
#else
        simple_unlock_rwmb((simple_lock_t)l);
#endif
}


/*
 *      Conditionally acquire a usimple_lock.
 *
 *      On success, returns with preemption disabled.
 *      On failure, returns with preemption in the same state
 *      as when first invoked.  Note that the hw_lock routines
 *      are responsible for maintaining preemption state.
 *
 *      XXX No stats are gathered on a miss; I preserved this
 *      behavior from the original assembly-language code, but
 *      doesn't it make sense to log misses?  XXX
 */
unsigned int
usimple_lock_try(
        usimple_lock_t  l)
{
#ifndef MACHINE_SIMPLE_LOCK
        unsigned int    success;
        DECL_PC(pc);

        OBTAIN_PC(pc, l);
        USLDBG(usld_lock_try_pre(l, pc));
        if ((success = hw_lock_try(&l->interlock))) {
                USLDBG(usld_lock_try_post(l, pc));
        }
        return success;
#else
        return(simple_lock_try((simple_lock_t)l));
#endif
}

#if     USLOCK_DEBUG
/*
 *      States of a usimple_lock.  The default when initializing
 *      a usimple_lock is setting it up for debug checking.
 */
#define USLOCK_CHECKED          0x0001          /* lock is being checked */
#define USLOCK_TAKEN            0x0002          /* lock has been taken */
#define USLOCK_INIT             0xBAA0          /* lock has been initialized */
#define USLOCK_INITIALIZED      (USLOCK_INIT|USLOCK_CHECKED)
#define USLOCK_CHECKING(l)      (uslock_check &&                        \
                                 ((l)->debug.state & USLOCK_CHECKED))

/*
 *      Trace activities of a particularly interesting lock.
 */
void    usl_trace(usimple_lock_t, int, pc_t, const char *);


/*
 *      Initialize the debugging information contained
 *      in a usimple_lock.
 */
void
usld_lock_init(
        usimple_lock_t  l,
        __unused unsigned short tag)
{
        if (l == USIMPLE_LOCK_NULL)
                panic("lock initialization:  null lock pointer");
        l->lock_type = USLOCK_TAG;
        l->debug.state = uslock_check ? USLOCK_INITIALIZED : 0;
        l->debug.lock_cpu = l->debug.unlock_cpu = 0;
        l->debug.lock_pc = l->debug.unlock_pc = INVALID_PC;
        l->debug.lock_thread = l->debug.unlock_thread = INVALID_THREAD;
        l->debug.duration[0] = l->debug.duration[1] = 0;
        l->debug.unlock_cpu = l->debug.unlock_cpu = 0;
        l->debug.unlock_pc = l->debug.unlock_pc = INVALID_PC;
        l->debug.unlock_thread = l->debug.unlock_thread = INVALID_THREAD;
}


/*
 *      These checks apply to all usimple_locks, not just
 *      those with USLOCK_CHECKED turned on.
 */
int
usld_lock_common_checks(
        usimple_lock_t  l,
        char            *caller)
{
        if (l == USIMPLE_LOCK_NULL)
                panic("%s:  null lock pointer", caller);
        if (l->lock_type != USLOCK_TAG)
                panic("%s:  0x%x is not a usimple lock", caller, (integer_t) l);
        if (!(l->debug.state & USLOCK_INIT))
                panic("%s:  0x%x is not an initialized lock",
                      caller, (integer_t) l);
        return USLOCK_CHECKING(l);
}


/*
 *      Debug checks on a usimple_lock just before attempting
 *      to acquire it.
 */
/* ARGSUSED */
void
usld_lock_pre(
        usimple_lock_t  l,
        pc_t            pc)
{
        char    caller[] = "usimple_lock";


        if (!usld_lock_common_checks(l, caller))
                return;

/*
 *      Note that we have a weird case where we are getting a lock when we are]
 *      in the process of putting the system to sleep. We are running with no
 *      current threads, therefore we can't tell if we are trying to retake a lock
 *      we have or someone on the other processor has it.  Therefore we just
 *      ignore this test if the locking thread is 0.
 */

        if ((l->debug.state & USLOCK_TAKEN) && l->debug.lock_thread &&
            l->debug.lock_thread == (void *) current_thread()) {
                printf("%s:  lock %p already locked (at %p) by",
                      caller, l, l->debug.lock_pc);
                printf(" current thread %p (new attempt at pc %p)\n",
                       l->debug.lock_thread, pc);
                panic("%s", caller);
        }
        mp_disable_preemption();
        usl_trace(l, cpu_number(), pc, caller);
        mp_enable_preemption();
}


/*
 *      Debug checks on a usimple_lock just after acquiring it.
 *
 *      Pre-emption has been disabled at this point,
 *      so we are safe in using cpu_number.
 */
void
usld_lock_post(
        usimple_lock_t  l,
        pc_t            pc)
{
        register int    mycpu;
        char    caller[] = "successful usimple_lock";


        if (!usld_lock_common_checks(l, caller))
                return;

        if (!((l->debug.state & ~USLOCK_TAKEN) == USLOCK_INITIALIZED))
                panic("%s:  lock 0x%x became uninitialized",
                      caller, (integer_t) l);
        if ((l->debug.state & USLOCK_TAKEN))
                panic("%s:  lock 0x%x became TAKEN by someone else",
                      caller, (integer_t) l);

        mycpu = cpu_number();
        l->debug.lock_thread = (void *)current_thread();
        l->debug.state |= USLOCK_TAKEN;
        l->debug.lock_pc = pc;
        l->debug.lock_cpu = mycpu;

        usl_trace(l, mycpu, pc, caller);
}


/*
 *      Debug checks on a usimple_lock just before
 *      releasing it.  Note that the caller has not
 *      yet released the hardware lock.
 *
 *      Preemption is still disabled, so there's
 *      no problem using cpu_number.
 */
void
usld_unlock(
        usimple_lock_t  l,
        pc_t            pc)
{
        register int    mycpu;
        char    caller[] = "usimple_unlock";


        if (!usld_lock_common_checks(l, caller))
                return;

        mycpu = cpu_number();

        if (!(l->debug.state & USLOCK_TAKEN))
                panic("%s:  lock 0x%x hasn't been taken",
                      caller, (integer_t) l);
        if (l->debug.lock_thread != (void *) current_thread())
                panic("%s:  unlocking lock 0x%x, owned by thread %p",
                      caller, (integer_t) l, l->debug.lock_thread);
        if (l->debug.lock_cpu != mycpu) {
                printf("%s:  unlocking lock 0x%x on cpu 0x%x",
                       caller, (integer_t) l, mycpu);
                printf(" (acquired on cpu 0x%x)\n", l->debug.lock_cpu);
                panic("%s", caller);
        }
        usl_trace(l, mycpu, pc, caller);

        l->debug.unlock_thread = l->debug.lock_thread;
        l->debug.lock_thread = INVALID_PC;
        l->debug.state &= ~USLOCK_TAKEN;
        l->debug.unlock_pc = pc;
        l->debug.unlock_cpu = mycpu;
}


/*
 *      Debug checks on a usimple_lock just before
 *      attempting to acquire it.
 *
 *      Preemption isn't guaranteed to be disabled.
 */
void
usld_lock_try_pre(
        usimple_lock_t  l,
        pc_t            pc)
{
        char    caller[] = "usimple_lock_try";

        if (!usld_lock_common_checks(l, caller))
                return;
        mp_disable_preemption();
        usl_trace(l, cpu_number(), pc, caller);
        mp_enable_preemption();
}


/*
 *      Debug checks on a usimple_lock just after
 *      successfully attempting to acquire it.
 *
 *      Preemption has been disabled by the
 *      lock acquisition attempt, so it's safe
 *      to use cpu_number.
 */
void
usld_lock_try_post(
        usimple_lock_t  l,
        pc_t            pc)
{
        register int    mycpu;
        char    caller[] = "successful usimple_lock_try";

        if (!usld_lock_common_checks(l, caller))
                return;

        if (!((l->debug.state & ~USLOCK_TAKEN) == USLOCK_INITIALIZED))
                panic("%s:  lock 0x%x became uninitialized",
                      caller, (integer_t) l);
        if ((l->debug.state & USLOCK_TAKEN))
                panic("%s:  lock 0x%x became TAKEN by someone else",
                      caller, (integer_t) l);

        mycpu = cpu_number();
        l->debug.lock_thread = (void *) current_thread();
        l->debug.state |= USLOCK_TAKEN;
        l->debug.lock_pc = pc;
        l->debug.lock_cpu = mycpu;

        usl_trace(l, mycpu, pc, caller);
}


/*
 *      For very special cases, set traced_lock to point to a
 *      specific lock of interest.  The result is a series of
 *      XPRs showing lock operations on that lock.  The lock_seq
 *      value is used to show the order of those operations.
 */
usimple_lock_t          traced_lock;
unsigned int            lock_seq;

void
usl_trace(
        usimple_lock_t  l,
        int             mycpu,
        pc_t            pc,
        const char *    op_name)
{
        if (traced_lock == l) {
                XPR(XPR_SLOCK,
                    "seq %d, cpu %d, %s @ %x\n",
                    (integer_t) lock_seq, (integer_t) mycpu,
                    (integer_t) op_name, (integer_t) pc, 0);
                lock_seq++;
        }
}


#endif  /* USLOCK_DEBUG */

/*
 *      Routine:        lock_alloc
 *      Function:
 *              Allocate a lock for external users who cannot
 *              hard-code the structure definition into their
 *              objects.
 *              For now just use kalloc, but a zone is probably
 *              warranted.
 */
lock_t *
lock_alloc(
        boolean_t       can_sleep,
        unsigned short  tag,
        unsigned short  tag1)
{
        lock_t          *l;

        if ((l = (lock_t *)kalloc(sizeof(lock_t))) != 0)
          lock_init(l, can_sleep, tag, tag1);
        return(l);
}

/*
 *      Routine:        lock_free
 *      Function:
 *              Free a lock allocated for external users.
 *              For now just use kfree, but a zone is probably
 *              warranted.
 */
void
lock_free(
        lock_t          *l)
{
        kfree(l, sizeof(lock_t));
}

          
/*
 *      Routine:        lock_init
 *      Function:
 *              Initialize a lock; required before use.
 *              Note that clients declare the "struct lock"
 *              variables and then initialize them, rather
 *              than getting a new one from this module.
 */
void
lock_init(
        lock_t          *l,
        boolean_t       can_sleep,
        __unused unsigned short tag,
        __unused unsigned short tag1)
{
        hw_lock_byte_init(&l->lck_rw_interlock);
        l->lck_rw_want_write = FALSE;
        l->lck_rw_want_upgrade = FALSE;
        l->lck_rw_shared_count = 0;
        l->lck_rw_can_sleep = can_sleep;
        l->lck_rw_tag = tag;
        l->lck_rw_priv_excl = 1;
}


/*
 *      Sleep locks.  These use the same data structure and algorithm
 *      as the spin locks, but the process sleeps while it is waiting
 *      for the lock.  These work on uniprocessor systems.
 */

#define DECREMENTER_TIMEOUT 1000000

void
lock_write(
        register lock_t * l)
{
        lck_rw_lock_exclusive(l);
}

void
lock_done(
        register lock_t * l)
{
        (void) lck_rw_done(l);
}

void
lock_read(
        register lock_t * l)
{
        lck_rw_lock_shared(l);
}


/*
 *      Routine:        lock_read_to_write
 *      Function:
 *              Improves a read-only lock to one with
 *              write permission.  If another reader has
 *              already requested an upgrade to a write lock,
 *              no lock is held upon return.
 *
 *              Returns FALSE if the upgrade *failed*.
 */

boolean_t
lock_read_to_write(
        register lock_t * l)
{
        return lck_rw_lock_shared_to_exclusive(l);
}

void
lock_write_to_read(
        register lock_t * l)
{
        lck_rw_lock_exclusive_to_shared(l);
}



/*
 *      Routine:        lck_rw_alloc_init
 */
lck_rw_t *
lck_rw_alloc_init(
        lck_grp_t       *grp,
        lck_attr_t      *attr) {
        lck_rw_t        *lck;

        if ((lck = (lck_rw_t *)kalloc(sizeof(lck_rw_t))) != 0)
                lck_rw_init(lck, grp, attr);
                
        return(lck);
}

/*
 *      Routine:        lck_rw_free
 */
void
lck_rw_free(
        lck_rw_t        *lck,
        lck_grp_t       *grp) {
        lck_rw_destroy(lck, grp);
        kfree(lck, sizeof(lck_rw_t));
}

/*
 *      Routine:        lck_rw_init
 */
void
lck_rw_init(
        lck_rw_t        *lck,
        lck_grp_t       *grp,
        lck_attr_t      *attr)
{
        lck_attr_t      *lck_attr = (attr != LCK_ATTR_NULL) ?
                                        attr : &LockDefaultLckAttr;

        hw_lock_byte_init(&lck->lck_rw_interlock);
        lck->lck_rw_want_write = FALSE;
        lck->lck_rw_want_upgrade = FALSE;
        lck->lck_rw_shared_count = 0;
        lck->lck_rw_can_sleep = TRUE;
        lck->lck_rw_tag = 0;
        lck->lck_rw_priv_excl = ((lck_attr->lck_attr_val &
                                LCK_ATTR_RW_SHARED_PRIORITY) == 0);

        lck_grp_reference(grp);
        lck_grp_lckcnt_incr(grp, LCK_TYPE_RW);
}

/*
 *      Routine:        lck_rw_destroy
 */
void
lck_rw_destroy(
        lck_rw_t        *lck,
        lck_grp_t       *grp) {
        if (lck->lck_rw_tag == LCK_RW_TAG_DESTROYED)
                return;
        lck->lck_rw_tag = LCK_RW_TAG_DESTROYED;
        lck_grp_lckcnt_decr(grp, LCK_TYPE_RW);
        lck_grp_deallocate(grp);
        return;
}

/*
 *      Sleep locks.  These use the same data structure and algorithm
 *      as the spin locks, but the process sleeps while it is waiting
 *      for the lock.  These work on uniprocessor systems.
 */

#define DECREMENTER_TIMEOUT 1000000

#define RW_LOCK_READER_EVENT(x)         \
                ((event_t) (((unsigned char*) (x)) + (offsetof(lck_rw_t, lck_rw_tag))))

#define RW_LOCK_WRITER_EVENT(x)         \
                ((event_t) (((unsigned char*) (x)) + (offsetof(lck_rw_t, lck_rw_pad8))))

/*
 * We need to disable interrupts while holding the mutex interlock
 * to prevent an IPI intervening.
 * Hence, local helper functions lck_interlock_lock()/lck_interlock_unlock().
 */
static boolean_t
lck_interlock_lock(lck_rw_t *lck)
{
        boolean_t       istate;

        istate = ml_set_interrupts_enabled(FALSE);      
        hw_lock_byte_lock(&lck->lck_rw_interlock);

        return istate;
}

static void
lck_interlock_unlock(lck_rw_t *lck, boolean_t istate)
{               
        hw_lock_byte_unlock(&lck->lck_rw_interlock);
        ml_set_interrupts_enabled(istate);
}

/*
 * This inline is used when busy-waiting for an rw lock.
 * If interrupts were disabled when the lock primitive was called,
 * we poll the IPI handler for pending tlb flushes.
 * XXX This is a hack to avoid deadlocking on the pmap_system_lock.
 */
static inline void
lck_rw_lock_pause(boolean_t interrupts_enabled)
{
        if (!interrupts_enabled)
                handle_pending_TLB_flushes();
        cpu_pause();
}

/*
 *      Routine:        lck_rw_lock_exclusive
 */
void
lck_rw_lock_exclusive(
        lck_rw_t        *lck)
{
        int        i;
        wait_result_t   res;
#if     MACH_LDEBUG
        int                             decrementer;
#endif  /* MACH_LDEBUG */
        boolean_t       istate;
#if     CONFIG_DTRACE
        uint64_t wait_interval = 0;
        int slept = 0;
        int readers_at_sleep;
#endif

        istate = lck_interlock_lock(lck);
#if     CONFIG_DTRACE
        readers_at_sleep = lck->lck_rw_shared_count;
#endif

#if     MACH_LDEBUG
        decrementer = DECREMENTER_TIMEOUT;
#endif  /* MACH_LDEBUG */

        /*
         *      Try to acquire the lck_rw_want_write bit.
         */
        while (lck->lck_rw_want_write) {

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE_CODE) | DBG_FUNC_START, (int)lck, 0, 0, 0, 0);
                /*
                 * Either sleeping or spinning is happening, start
                 * a timing of our delay interval now.
                 */
#if     CONFIG_DTRACE
                if ((lockstat_probemap[LS_LCK_RW_LOCK_EXCL_SPIN] || lockstat_probemap[LS_LCK_RW_LOCK_EXCL_BLOCK]) && wait_interval == 0) {
                        wait_interval = mach_absolute_time();
                } else {
                        wait_interval = -1;
                }
#endif


                i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];
                if (i != 0) {
                        lck_interlock_unlock(lck, istate);
#if     MACH_LDEBUG
                        if (!--decrementer)
                                Debugger("timeout - lck_rw_want_write");
#endif  /* MACH_LDEBUG */
                        while (--i != 0 && lck->lck_rw_want_write)
                                lck_rw_lock_pause(istate);
                        istate = lck_interlock_lock(lck);
                }

                if (lck->lck_rw_can_sleep && lck->lck_rw_want_write) {
                        lck->lck_w_waiting = TRUE;
                        res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
                        if (res == THREAD_WAITING) {
                                lck_interlock_unlock(lck, istate);
                                res = thread_block(THREAD_CONTINUE_NULL);
#if     CONFIG_DTRACE
                                slept = 1;
#endif
                                istate = lck_interlock_lock(lck);
                        }
                }
                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE_CODE) | DBG_FUNC_END, (int)lck, res, 0, 0, 0);
        }
        lck->lck_rw_want_write = TRUE;

        /* Wait for readers (and upgrades) to finish */

#if     MACH_LDEBUG
        decrementer = DECREMENTER_TIMEOUT;
#endif  /* MACH_LDEBUG */
        while ((lck->lck_rw_shared_count != 0) || lck->lck_rw_want_upgrade) {

                i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE1_CODE) | DBG_FUNC_START,
                             (int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, i, 0);

#if     CONFIG_DTRACE
                /*
                 * Either sleeping or spinning is happening, start
                 * a timing of our delay interval now.  If we set it
                 * to -1 we don't have accurate data so we cannot later
                 * decide to record a dtrace spin or sleep event.
                 */
                if ((lockstat_probemap[LS_LCK_RW_LOCK_EXCL_SPIN] || lockstat_probemap[LS_LCK_RW_LOCK_EXCL_BLOCK]) && wait_interval == 0) {
                        wait_interval = mach_absolute_time();
                } else {
                        wait_interval = (unsigned) -1;
                }
#endif

                if (i != 0) {
                        lck_interlock_unlock(lck, istate);
#if     MACH_LDEBUG
                        if (!--decrementer)
                                Debugger("timeout - wait for readers");
#endif  /* MACH_LDEBUG */
                        while (--i != 0 && (lck->lck_rw_shared_count != 0 ||
                                            lck->lck_rw_want_upgrade))
                                lck_rw_lock_pause(istate);
                        istate = lck_interlock_lock(lck);
                }

                if (lck->lck_rw_can_sleep && (lck->lck_rw_shared_count != 0 || lck->lck_rw_want_upgrade)) {
                        lck->lck_w_waiting = TRUE;
                        res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
                        if (res == THREAD_WAITING) {
                                lck_interlock_unlock(lck, istate);
                                res = thread_block(THREAD_CONTINUE_NULL);
#if     CONFIG_DTRACE
                                slept = 1;
#endif
                                istate = lck_interlock_lock(lck);
                        }
                }
                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EXCLUSIVE1_CODE) | DBG_FUNC_END,
                             (int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, res, 0);
        }

        lck_interlock_unlock(lck, istate);
#if     CONFIG_DTRACE
        /*
         * Decide what latencies we suffered that are Dtrace events.
         * If we have set wait_interval, then we either spun or slept.
         * At least we get out from under the interlock before we record
         * which is the best we can do here to minimize the impact
         * of the tracing.
         * If we have set wait_interval to -1, then dtrace was not enabled when we
         * started sleeping/spinning so we don't record this event.
         */
        if (wait_interval != 0 && wait_interval != (unsigned) -1) {
                if (slept == 0) {
                        LOCKSTAT_RECORD2(LS_LCK_RW_LOCK_EXCL_SPIN, lck,
                            mach_absolute_time() - wait_interval, 1);
                } else {
                        /*
                         * For the blocking case, we also record if when we blocked
                         * it was held for read or write, and how many readers.
                         * Notice that above we recorded this before we dropped
                         * the interlock so the count is accurate.
                         */
                        LOCKSTAT_RECORD4(LS_LCK_RW_LOCK_EXCL_BLOCK, lck,
                            mach_absolute_time() - wait_interval, 1,
                            (readers_at_sleep == 0 ? 1 : 0), readers_at_sleep);
                }
        }
        LOCKSTAT_RECORD(LS_LCK_RW_LOCK_EXCL_ACQUIRE, lck, 1);
#endif
}


/*
 *      Routine:        lck_rw_done_gen
 */
lck_rw_type_t
lck_rw_done_gen(
        lck_rw_t        *lck)
{
        boolean_t       wakeup_readers = FALSE;
        boolean_t       wakeup_writers = FALSE;
        lck_rw_type_t   lck_rw_type;
        boolean_t       istate;

        istate = lck_interlock_lock(lck);

        if (lck->lck_rw_shared_count != 0) {
                lck_rw_type = LCK_RW_TYPE_SHARED;
                lck->lck_rw_shared_count--;
        }
        else {  
                lck_rw_type = LCK_RW_TYPE_EXCLUSIVE;
                if (lck->lck_rw_want_upgrade) 
                        lck->lck_rw_want_upgrade = FALSE;
                else 
                        lck->lck_rw_want_write = FALSE;
        }

        /*
         *      There is no reason to wakeup a waiting thread
         *      if the read-count is non-zero.  Consider:
         *              we must be dropping a read lock
         *              threads are waiting only if one wants a write lock
         *              if there are still readers, they can't proceed
         */

        if (lck->lck_rw_shared_count == 0) {
                if (lck->lck_w_waiting) {
                        lck->lck_w_waiting = FALSE;
                        wakeup_writers = TRUE;
                } 
                if (!(lck->lck_rw_priv_excl && wakeup_writers == TRUE) && 
                                lck->lck_r_waiting) {
                        lck->lck_r_waiting = FALSE;
                        wakeup_readers = TRUE;
                }
        }

        lck_interlock_unlock(lck, istate);

        if (wakeup_readers) 
                thread_wakeup(RW_LOCK_READER_EVENT(lck));
        if (wakeup_writers) 
                thread_wakeup(RW_LOCK_WRITER_EVENT(lck));

#if CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_DONE_RELEASE, lck, (lck_rw_type == LCK_RW_TYPE_EXCLUSIVE ? 1 : 0));
#endif

        return(lck_rw_type);
}




/*
 *      Routine:        lck_rw_unlock
 */
void
lck_rw_unlock(
        lck_rw_t        *lck,
        lck_rw_type_t   lck_rw_type)
{
        if (lck_rw_type == LCK_RW_TYPE_SHARED)
                lck_rw_unlock_shared(lck);
        else if (lck_rw_type == LCK_RW_TYPE_EXCLUSIVE)
                lck_rw_unlock_exclusive(lck);
        else
                panic("lck_rw_unlock(): Invalid RW lock type: %d\n", lck_rw_type);
}


/*
 *      Routine:        lck_rw_unlock_shared
 */
void
lck_rw_unlock_shared(
        lck_rw_t        *lck)
{
        lck_rw_type_t   ret;

        ret = lck_rw_done(lck);

        if (ret != LCK_RW_TYPE_SHARED)
                panic("lck_rw_unlock(): lock held in mode: %d\n", ret);
}


/*
 *      Routine:        lck_rw_unlock_exclusive
 */
void
lck_rw_unlock_exclusive(
        lck_rw_t        *lck)
{
        lck_rw_type_t   ret;

        ret = lck_rw_done(lck);

        if (ret != LCK_RW_TYPE_EXCLUSIVE)
                panic("lck_rw_unlock_exclusive(): lock held in mode: %d\n", ret);
}


/*
 *      Routine:        lck_rw_lock
 */
void
lck_rw_lock(
        lck_rw_t        *lck,
        lck_rw_type_t   lck_rw_type)
{
        if (lck_rw_type == LCK_RW_TYPE_SHARED)
                lck_rw_lock_shared(lck);
        else if (lck_rw_type == LCK_RW_TYPE_EXCLUSIVE)
                lck_rw_lock_exclusive(lck);
        else
                panic("lck_rw_lock(): Invalid RW lock type: %x\n", lck_rw_type);
}


/*
 *      Routine:        lck_rw_lock_shared_gen
 */
void
lck_rw_lock_shared_gen(
        lck_rw_t        *lck)
{
        int             i;
        wait_result_t      res;
#if     MACH_LDEBUG
        int             decrementer;
#endif  /* MACH_LDEBUG */
        boolean_t       istate;
#if     CONFIG_DTRACE
        uint64_t wait_interval = 0;
        int slept = 0;
        int readers_at_sleep;
#endif

        istate = lck_interlock_lock(lck);
#if     CONFIG_DTRACE
        readers_at_sleep = lck->lck_rw_shared_count;
#endif

#if     MACH_LDEBUG
        decrementer = DECREMENTER_TIMEOUT;
#endif  /* MACH_LDEBUG */
        while ((lck->lck_rw_want_write || lck->lck_rw_want_upgrade) &&
            ((lck->lck_rw_shared_count == 0) || lck->lck_rw_priv_excl)) {

                i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_CODE) | DBG_FUNC_START,
                             (int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, i, 0);
#if     CONFIG_DTRACE
                if ((lockstat_probemap[LS_LCK_RW_LOCK_SHARED_SPIN] || lockstat_probemap[LS_LCK_RW_LOCK_SHARED_BLOCK]) && wait_interval == 0) {
                        wait_interval = mach_absolute_time();
                } else {
                        wait_interval = -1;
                }
#endif

                if (i != 0) {
                        lck_interlock_unlock(lck, istate);
#if     MACH_LDEBUG
                        if (!--decrementer)
                                Debugger("timeout - wait no writers");
#endif  /* MACH_LDEBUG */
                        while (--i != 0 &&
                            (lck->lck_rw_want_write || lck->lck_rw_want_upgrade) &&
                               ((lck->lck_rw_shared_count == 0) || lck->lck_rw_priv_excl))
                                lck_rw_lock_pause(istate);
                        istate = lck_interlock_lock(lck);
                }

                if (lck->lck_rw_can_sleep &&
                    (lck->lck_rw_want_write || lck->lck_rw_want_upgrade) &&
                    ((lck->lck_rw_shared_count == 0) || lck->lck_rw_priv_excl)) {
                        lck->lck_r_waiting = TRUE;
                        res = assert_wait(RW_LOCK_READER_EVENT(lck), THREAD_UNINT);
                        if (res == THREAD_WAITING) {
                                lck_interlock_unlock(lck, istate);
                                res = thread_block(THREAD_CONTINUE_NULL);
#if     CONFIG_DTRACE
                                slept = 1;
#endif
                                istate = lck_interlock_lock(lck);
                        }
                }
                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_CODE) | DBG_FUNC_END,
                             (int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, res, 0);
        }

        lck->lck_rw_shared_count++;

        lck_interlock_unlock(lck, istate);
#if     CONFIG_DTRACE
        if (wait_interval != 0 && wait_interval != (unsigned) -1) {
                if (slept == 0) {
                        LOCKSTAT_RECORD2(LS_LCK_RW_LOCK_SHARED_SPIN, lck, mach_absolute_time() - wait_interval, 0);
                } else {
                        LOCKSTAT_RECORD4(LS_LCK_RW_LOCK_SHARED_BLOCK, lck,
                            mach_absolute_time() - wait_interval, 0,
                            (readers_at_sleep == 0 ? 1 : 0), readers_at_sleep);
                }
        }
        LOCKSTAT_RECORD(LS_LCK_RW_LOCK_SHARED_ACQUIRE, lck, 0);
#endif
}


/*
 *      Routine:        lck_rw_lock_shared_to_exclusive
 *      Function:
 *              Improves a read-only lock to one with
 *              write permission.  If another reader has
 *              already requested an upgrade to a write lock,
 *              no lock is held upon return.
 *
 *              Returns FALSE if the upgrade *failed*.
 */

boolean_t
lck_rw_lock_shared_to_exclusive(
        lck_rw_t        *lck)
{
        int         i;
        boolean_t           do_wakeup = FALSE;
        wait_result_t      res;
#if     MACH_LDEBUG
        int                decrementer;
#endif  /* MACH_LDEBUG */
        boolean_t       istate;
#if     CONFIG_DTRACE
        uint64_t wait_interval = 0;
        int slept = 0;
        int readers_at_sleep = 0;
#endif

        istate = lck_interlock_lock(lck);

        lck->lck_rw_shared_count--;     

        if (lck->lck_rw_want_upgrade) {
                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_CODE) | DBG_FUNC_START,
                             (int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, 0, 0);

                /*
                 *      Someone else has requested upgrade.
                 *      Since we've released a read lock, wake
                 *      him up.
                 */
                if (lck->lck_w_waiting && (lck->lck_rw_shared_count == 0)) {
                        lck->lck_w_waiting = FALSE;
                        do_wakeup = TRUE;
                }

                lck_interlock_unlock(lck, istate);

                if (do_wakeup) 
                        thread_wakeup(RW_LOCK_WRITER_EVENT(lck));

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_CODE) | DBG_FUNC_END,
                             (int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, 0, 0);

                return (FALSE);
        }

        lck->lck_rw_want_upgrade = TRUE;

#if     MACH_LDEBUG
        decrementer = DECREMENTER_TIMEOUT;
#endif  /* MACH_LDEBUG */
        while (lck->lck_rw_shared_count != 0) {
#if     CONFIG_DTRACE
                if (lockstat_probemap[LS_LCK_RW_LOCK_SHARED_TO_EXCL_SPIN] && wait_interval == 0) {
                        wait_interval = mach_absolute_time();
                        readers_at_sleep = lck->lck_rw_shared_count;
                } else {
                        wait_interval = -1;
                }
#endif
                i = lock_wait_time[lck->lck_rw_can_sleep ? 1 : 0];

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX1_CODE) | DBG_FUNC_START,
                             (int)lck, lck->lck_rw_shared_count, i, 0, 0);

                if (i != 0) {
                        lck_interlock_unlock(lck, istate);
#if     MACH_LDEBUG
                        if (!--decrementer)
                                Debugger("timeout - lck_rw_shared_count");
#endif  /* MACH_LDEBUG */
                        while (--i != 0 && lck->lck_rw_shared_count != 0)
                                lck_rw_lock_pause(istate);
                        istate = lck_interlock_lock(lck);
                }

                if (lck->lck_rw_can_sleep && lck->lck_rw_shared_count != 0) {
                        lck->lck_w_waiting = TRUE;
                        res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
                        if (res == THREAD_WAITING) {
                                lck_interlock_unlock(lck, istate);
                                res = thread_block(THREAD_CONTINUE_NULL);
#if     CONFIG_DTRACE
                                slept = 1;
#endif
                                istate = lck_interlock_lock(lck);
                        }
                }
                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX1_CODE) | DBG_FUNC_END,
                             (int)lck, lck->lck_rw_shared_count, 0, 0, 0);
        }

        lck_interlock_unlock(lck, istate);
#if     CONFIG_DTRACE
        /*
         * We infer whether we took the sleep/spin path above by checking readers_at_sleep.
         */
        if (wait_interval != 0 && wait_interval != (unsigned) -1 && readers_at_sleep) {
                if (slept == 0) {
                        LOCKSTAT_RECORD2(LS_LCK_RW_LOCK_SHARED_TO_EXCL_SPIN, lck, mach_absolute_time() - wait_interval, 0);
                } else {
                        LOCKSTAT_RECORD4(LS_LCK_RW_LOCK_SHARED_TO_EXCL_BLOCK, lck,
                            mach_absolute_time() - wait_interval, 1,
                            (readers_at_sleep == 0 ? 1 : 0), readers_at_sleep);
                }
        }

        LOCKSTAT_RECORD(LS_LCK_RW_LOCK_SHARED_TO_EXCL_UPGRADE, lck, 1);
#endif
        return (TRUE);
}

/*
 *      Routine:        lck_rw_lock_exclusive_to_shared
 */
void
lck_rw_lock_exclusive_to_shared(
        lck_rw_t        *lck)
{
        boolean_t       wakeup_readers = FALSE;
        boolean_t       wakeup_writers = FALSE;
        boolean_t       istate;

        KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_TO_SH_CODE) | DBG_FUNC_START,
                             (int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, 0, 0);

        istate = lck_interlock_lock(lck);

        lck->lck_rw_shared_count++;
        if (lck->lck_rw_want_upgrade)
                lck->lck_rw_want_upgrade = FALSE;
        else
                lck->lck_rw_want_write = FALSE;

        if (lck->lck_w_waiting) {
                lck->lck_w_waiting = FALSE;
                wakeup_writers = TRUE;
        } 
        if (!(lck->lck_rw_priv_excl && wakeup_writers == TRUE) && 
                        lck->lck_r_waiting) {
                lck->lck_r_waiting = FALSE;
                wakeup_readers = TRUE;
        }

        lck_interlock_unlock(lck, istate);

        if (wakeup_readers)
                thread_wakeup(RW_LOCK_READER_EVENT(lck));
        if (wakeup_writers)
                thread_wakeup(RW_LOCK_WRITER_EVENT(lck));

        KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_TO_SH_CODE) | DBG_FUNC_END,
                             (int)lck, lck->lck_rw_want_write, lck->lck_rw_want_upgrade, lck->lck_rw_shared_count, 0);

#if CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_LOCK_EXCL_TO_SHARED_DOWNGRADE, lck, 0);
#endif
}


/*
 *      Routine:        lck_rw_try_lock
 */
boolean_t
lck_rw_try_lock(
        lck_rw_t        *lck,
        lck_rw_type_t   lck_rw_type)
{
        if (lck_rw_type == LCK_RW_TYPE_SHARED)
                return(lck_rw_try_lock_shared(lck));
        else if (lck_rw_type == LCK_RW_TYPE_EXCLUSIVE)
                return(lck_rw_try_lock_exclusive(lck));
        else
                panic("lck_rw_try_lock(): Invalid rw lock type: %x\n", lck_rw_type);
        return(FALSE);
}

/*
 *      Routine:        lck_rw_try_lock_exclusive
 *      Function:
 *              Tries to get a write lock.
 *
 *              Returns FALSE if the lock is not held on return.
 */

boolean_t
lck_rw_try_lock_exclusive(
        lck_rw_t        *lck)
{
        boolean_t       istate;

        istate = lck_interlock_lock(lck);

        if (lck->lck_rw_want_write || lck->lck_rw_want_upgrade || lck->lck_rw_shared_count) {
                /*
                 *      Can't get lock.
                 */
                lck_interlock_unlock(lck, istate);
                return(FALSE);
        }

        /*
         *      Have lock.
         */

        lck->lck_rw_want_write = TRUE;

        lck_interlock_unlock(lck, istate);

#if CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_TRY_LOCK_EXCL_ACQUIRE, lck, 1);
#endif
        return(TRUE);
}

/*
 *      Routine:        lck_rw_try_lock_shared
 *      Function:
 *              Tries to get a read lock.
 *
 *              Returns FALSE if the lock is not held on return.
 */

boolean_t
lck_rw_try_lock_shared(
        lck_rw_t        *lck)
{
        boolean_t       istate;

        istate = lck_interlock_lock(lck);
/* No reader priority check here... */
        if (lck->lck_rw_want_write || lck->lck_rw_want_upgrade) {
                lck_interlock_unlock(lck, istate);
                return(FALSE);
        }

        lck->lck_rw_shared_count++;

        lck_interlock_unlock(lck, istate);

#if CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_TRY_LOCK_SHARED_ACQUIRE, lck, 0);
#endif
        return(TRUE);
}

void
lck_rw_assert(
        lck_rw_t        *lck,
        unsigned int    type)
{
        switch (type) {
        case LCK_RW_ASSERT_SHARED:
                if (lck->lck_rw_shared_count != 0) {
                        return;
                }
                break;
        case LCK_RW_ASSERT_EXCLUSIVE:
                if ((lck->lck_rw_want_write ||
                     lck->lck_rw_want_upgrade) &&
                    lck->lck_rw_shared_count == 0) {
                        return;
                }
                break;
        case LCK_RW_ASSERT_HELD:
                if (lck->lck_rw_want_write ||
                    lck->lck_rw_want_upgrade ||
                    lck->lck_rw_shared_count != 0) {
                        return;
                }
                break;
        default:
                break;
        }

        panic("rw lock (%p) not held (mode=%u)\n", lck, type);
}

/*
 *      Routine:        lck_mtx_alloc_init
 */
lck_mtx_t *
lck_mtx_alloc_init(
        lck_grp_t       *grp,
        lck_attr_t      *attr)
{
        lck_mtx_t       *lck;

        if ((lck = (lck_mtx_t *)kalloc(sizeof(lck_mtx_t))) != 0)
                lck_mtx_init(lck, grp, attr);
                
        return(lck);
}

/*
 *      Routine:        lck_mtx_free
 */
void
lck_mtx_free(
        lck_mtx_t       *lck,
        lck_grp_t       *grp)
{
        lck_mtx_destroy(lck, grp);
        kfree(lck, sizeof(lck_mtx_t));
}

/*
 *      Routine:        lck_mtx_ext_init
 */
static void
lck_mtx_ext_init(
        lck_mtx_ext_t   *lck,
        lck_grp_t       *grp,
        lck_attr_t      *attr)
{
        bzero((void *)lck, sizeof(lck_mtx_ext_t));

        if ((attr->lck_attr_val) & LCK_ATTR_DEBUG) {
                lck->lck_mtx_deb.type = MUTEX_TAG;
                lck->lck_mtx_attr |= LCK_MTX_ATTR_DEBUG;
        }

        lck->lck_mtx_grp = grp;

        if (grp->lck_grp_attr & LCK_GRP_ATTR_STAT)
                 lck->lck_mtx_attr |= LCK_MTX_ATTR_STAT;
}

/*
 *      Routine:        lck_mtx_init
 */
void
lck_mtx_init(
        lck_mtx_t       *lck,
        lck_grp_t       *grp,
        lck_attr_t      *attr)
{
        lck_mtx_ext_t   *lck_ext;
        lck_attr_t      *lck_attr;

        if (attr != LCK_ATTR_NULL)
                lck_attr = attr;
        else
                lck_attr = &LockDefaultLckAttr;

        if ((lck_attr->lck_attr_val) & LCK_ATTR_DEBUG) {
                if ((lck_ext = (lck_mtx_ext_t *)kalloc(sizeof(lck_mtx_ext_t))) != 0) {
                        lck_mtx_ext_init(lck_ext, grp, lck_attr);       
                        lck->lck_mtx_tag = LCK_MTX_TAG_INDIRECT;
                        lck->lck_mtx_ptr = lck_ext;
                }
        } else {
                lck->lck_mtx_ilk = 0;
                lck->lck_mtx_locked = 0;
                lck->lck_mtx_waiters = 0;
                lck->lck_mtx_pri = 0;
        }
        lck_grp_reference(grp);
        lck_grp_lckcnt_incr(grp, LCK_TYPE_MTX);
}

/*
 *      Routine:        lck_mtx_init_ext
 */
void
lck_mtx_init_ext(
        lck_mtx_t       *lck,
        lck_mtx_ext_t   *lck_ext,
        lck_grp_t       *grp,
        lck_attr_t      *attr)
{
        lck_attr_t      *lck_attr;

        if (attr != LCK_ATTR_NULL)
                lck_attr = attr;
        else
                lck_attr = &LockDefaultLckAttr;

        if ((lck_attr->lck_attr_val) & LCK_ATTR_DEBUG) {
                lck_mtx_ext_init(lck_ext, grp, lck_attr);
                lck->lck_mtx_tag = LCK_MTX_TAG_INDIRECT;
                lck->lck_mtx_ptr = lck_ext;
        } else {
                lck->lck_mtx_ilk = 0;
                lck->lck_mtx_locked = 0;
                lck->lck_mtx_waiters = 0;
                lck->lck_mtx_pri = 0;
        }
        lck_grp_reference(grp);
        lck_grp_lckcnt_incr(grp, LCK_TYPE_MTX);
}

/*
 *      Routine:        lck_mtx_destroy
 */
void
lck_mtx_destroy(
        lck_mtx_t       *lck,
        lck_grp_t       *grp)
{
        boolean_t lck_is_indirect;
        
        if (lck->lck_mtx_tag == LCK_MTX_TAG_DESTROYED)
                return;
        lck_is_indirect = (lck->lck_mtx_tag == LCK_MTX_TAG_INDIRECT);
        lck->lck_mtx_tag = LCK_MTX_TAG_DESTROYED;
        if (lck_is_indirect)
                kfree(lck->lck_mtx_ptr, sizeof(lck_mtx_ext_t));
        lck_grp_lckcnt_decr(grp, LCK_TYPE_MTX);
        lck_grp_deallocate(grp);
        return;
}

/*
 * Routine:     lck_mtx_lock_spinwait
 *
 * Invoked trying to acquire a mutex when there is contention but
 * the holder is running on another processor. We spin for up to a maximum
 * time waiting for the lock to be released.
 *
 * Called with the interlock unlocked.
 */
void
lck_mtx_lock_spinwait(
        lck_mtx_t               *lck)
{
        thread_t                holder;
        volatile lck_mtx_t      *mutex;
        uint64_t                deadline;

        if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT)
                mutex = lck;
        else
                mutex = &lck->lck_mtx_ptr->lck_mtx;

        KERNEL_DEBUG(
                MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_SPIN) | DBG_FUNC_NONE,
                (int)lck, (int)mutex->lck_mtx_locked, 0, 0, 0);

        deadline = mach_absolute_time() + MutexSpin;
        /*
         * Spin while:
         *   - mutex is locked, and
         *   - its locked as a spin lock, or
         *   - owner is running on another processor, and
         *   - owner (processor) is not idling, and
         *   - we haven't spun for long enough.
         */
        while ((holder = (thread_t) mutex->lck_mtx_locked) != NULL) {
                if ((holder == (thread_t)MUTEX_LOCKED_AS_SPIN) ||
                    ((holder->machine.specFlags & OnProc) != 0 &&
                     (holder->state & TH_IDLE) == 0 &&
                     mach_absolute_time() < deadline)) {
                        cpu_pause();
                        continue;
                }
                break;
        }
#if     CONFIG_DTRACE
        /*
         * We've already kept a count via deadline of how long we spun.
         * If dtrace is active, then we compute backwards to decide how
         * long we spun.
         *
         * Note that we record a different probe id depending on whether
         * this is a direct or indirect mutex.  This allows us to 
         * penalize only lock groups that have debug/stats enabled
         * with dtrace processing if desired.
         */
        if (lck->lck_mtx_tag != LCK_MTX_TAG_INDIRECT) {
                LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_SPIN, lck,
                    mach_absolute_time() - (deadline - MutexSpin));
        } else {
                LOCKSTAT_RECORD(LS_LCK_MTX_EXT_LOCK_SPIN, lck,
                    mach_absolute_time() - (deadline - MutexSpin));
        }
        /* The lockstat acquire event is recorded by the assembly code beneath us. */
#endif
}

/*
 * Called from assembly code when a destroyed mutex is detected
 * during a lock/unlock/try/convert
 */

void
lck_mtx_interlock_panic(
                        lck_mtx_t               *lck)
{
        panic("trying to interlock destroyed mutex %p", lck);
}


#if     MACH_KDB

void
db_show_one_lock(
        lock_t  *lock)
{
        db_printf("Read_count = 0x%x, %swant_upgrade, %swant_write, ",
                  lock->lck_rw_shared_count,
                  lock->lck_rw_want_upgrade ? "" : "!",
                  lock->lck_rw_want_write ? "" : "!");
        db_printf("%swaiting, %scan_sleep\n", 
                  (lock->lck_r_waiting || lock->lck_w_waiting) ? "" : "!", 
                  lock->lck_rw_can_sleep ? "" : "!");
        db_printf("Interlock:\n");
        db_show_one_simple_lock((db_expr_t) ((vm_offset_t)simple_lock_addr(lock->lck_rw_interlock)),
                        TRUE, (db_expr_t)0, (char *)0);
}

#endif  /* MACH_KDB */

/*
 * The C portion of the mutex package.  These routines are only invoked
 * if the optimized assembler routines can't do the work.
 */

/*
 *      Routine:        lock_alloc
 *      Function:
 *              Allocate a mutex for external users who cannot
 *              hard-code the structure definition into their
 *              objects.
 *              For now just use kalloc, but a zone is probably
 *              warranted.
 */
mutex_t *
mutex_alloc(
        unsigned short  tag)
{
        mutex_t         *m;

        if ((m = (mutex_t *)kalloc(sizeof(mutex_t))) != 0)
          mutex_init(m, tag);
        return(m);
}

/*
 *      Routine:        mutex_free
 *      Function:
 *              Free a mutex allocated for external users.
 *              For now just use kfree, but a zone is probably
 *              warranted.
 */
void
mutex_free(
        mutex_t         *m)
{
        kfree(m, sizeof(mutex_t));
}


#if     MACH_KDB
/*
 * Routines to print out simple_locks and mutexes in a nicely-formatted
 * fashion.
 */

const char *simple_lock_labels =        "ENTRY    ILK THREAD   DURATION CALLER";
const char *mutex_labels =              "ENTRY    LOCKED WAITERS   THREAD CALLER";

void
db_show_one_simple_lock (
        db_expr_t       addr,
        boolean_t       have_addr,
        __unused db_expr_t      count,
        __unused char           * modif)
{
        simple_lock_t   saddr = (simple_lock_t) ((vm_offset_t) addr);

        if (saddr == (simple_lock_t)0 || !have_addr) {
                db_error ("No simple_lock\n");
        }
#if     USLOCK_DEBUG
        else if (saddr->lock_type != USLOCK_TAG)
                db_error ("Not a simple_lock\n");
#endif  /* USLOCK_DEBUG */

        db_printf ("%s\n", simple_lock_labels);
        db_print_simple_lock (saddr);
}

void
db_print_simple_lock (
        simple_lock_t   addr)
{

        db_printf ("%08x %3d", addr, *hw_lock_addr(addr->interlock));
#if     USLOCK_DEBUG
        db_printf (" %08x", addr->debug.lock_thread);
        db_printf (" %08x ", addr->debug.duration[1]);
        db_printsym ((int)addr->debug.lock_pc, DB_STGY_ANY);
#endif  /* USLOCK_DEBUG */
        db_printf ("\n");
}

void
db_show_one_mutex (
        db_expr_t       addr,
        boolean_t       have_addr,
        __unused db_expr_t      count,
        __unused char           * modif)
{
        mutex_t         * maddr = (mutex_t *)((vm_offset_t) addr);

        if (maddr == (mutex_t *)0 || !have_addr)
                db_error ("No mutex\n");
#if     MACH_LDEBUG
        else if (maddr->type != MUTEX_TAG)
                db_error ("Not a mutex\n");
#endif  /* MACH_LDEBUG */

        db_printf ("%s\n", mutex_labels);
        db_print_mutex (maddr);
}

void
db_print_mutex (
        mutex_t         * addr)
{
        db_printf ("%08x %6d %7d",
                   addr, *addr, addr->lck_mtx.lck_mtx_waiters);
#if     MACH_LDEBUG
        db_printf (" %08x ", addr->thread);
        db_printsym (addr->pc, DB_STGY_ANY);
#endif  /* MACH_LDEBUG */
        db_printf ("\n");
}

#endif  /* MACH_KDB */