xnu-1456.1.26.tar.gz

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

/*
 * Copyright (c) 2000-2008 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>

#include <i386/mp.h> /* mp_recent_debugger_activity() */
#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 <machine/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_RW_LCK_EX_WRITER_SPIN_CODE	0x106
#define LCK_RW_LCK_EX_WRITER_WAIT_CODE	0x107
#define LCK_RW_LCK_EX_READER_SPIN_CODE	0x108
#define LCK_RW_LCK_EX_READER_WAIT_CODE	0x109
#define LCK_RW_LCK_SHARED_SPIN_CODE	0x110
#define LCK_RW_LCK_SHARED_WAIT_CODE	0x111
#define LCK_RW_LCK_SH_TO_EX_SPIN_CODE	0x112
#define LCK_RW_LCK_SH_TO_EX_WAIT_CODE	0x113


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

unsigned int LcksOpts=0;

/* Forwards */

#if	MACH_KDB
void	db_print_simple_lock(
			simple_lock_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)
#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)	((pc) = GET_RETURN_PC())
#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)	++pc
#else	/* lint */
#define	OBTAIN_PC(pc)
#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 */


extern int lck_rw_grab_want(lck_rw_t *lck);
extern int lck_rw_grab_shared(lck_rw_t *lck);
extern int lck_rw_held_read_or_upgrade(lck_rw_t *lck);


/*
 * Forward definitions
 */

void lck_rw_lock_shared_gen(
	lck_rw_t	*lck);

void lck_rw_lock_exclusive_gen(
	lck_rw_t	*lck);

boolean_t lck_rw_lock_shared_to_exclusive_success(
	lck_rw_t	*lck);

boolean_t lck_rw_lock_shared_to_exclusive_failure(
	lck_rw_t	*lck,
	int		prior_lock_state);

void lck_rw_lock_exclusive_to_shared_gen(
	lck_rw_t	*lck,
	int		prior_lock_state);

lck_rw_type_t lck_rw_done_gen(
	lck_rw_t	*lck,
	int		prior_lock_state);


/*
 *      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->interlock == LCK_SPIN_TAG_DESTROYED)
		return;
	lck->interlock = 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);
	USLDBG(usld_lock_pre(l, pc));

	if(!hw_lock_to(&l->interlock, LockTimeOutTSC))	{/* Try to get the lock
							  * with a timeout */
		boolean_t uslock_acquired = FALSE;
		while (mp_recent_debugger_activity() &&
		    !(uslock_acquired = hw_lock_to(&l->interlock, LockTimeOutTSC)));
		if (uslock_acquired == FALSE)
			panic("Spinlock acquisition timed out: lock=%p, lock owner thread=0x%lx, current_thread: %p", l, (uintptr_t)l->interlock.lock_data, current_thread());
	}
	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);
	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);
	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%p is not a usimple lock", caller, l);
	if (!(l->debug.state & USLOCK_INIT))
		panic("%s:  %p is not an initialized lock",
		      caller, 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 %p became uninitialized",
		      caller, l);
	if ((l->debug.state & USLOCK_TAKEN))
		panic("%s:  lock 0x%p became TAKEN by someone else",
		      caller, 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%p hasn't been taken",
		      caller, l);
	if (l->debug.lock_thread != (void *) current_thread())
		panic("%s:  unlocking lock 0x%p, owned by thread %p",
		      caller, l, l->debug.lock_thread);
	if (l->debug.lock_cpu != mycpu) {
		printf("%s:  unlocking lock 0x%p on cpu 0x%x",
		       caller, 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%p became uninitialized",
		      caller, l);
	if ((l->debug.state & USLOCK_TAKEN))
		panic("%s:  lock 0x%p became TAKEN by someone else",
		      caller, 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",
		    (uintptr_t) lock_seq, (uintptr_t) mycpu,
		    (uintptr_t) op_name, (uintptr_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;
	l->lck_r_waiting = l->lck_w_waiting = 0;
}


/*
 *	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) {
		bzero(lck, sizeof(lck_rw_t));
		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_r_waiting = lck->lck_w_waiting = 0;
	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();
}


/*
 * compute the deadline to spin against when
 * waiting for a change of state on a lck_rw_t
 */
static inline uint64_t
lck_rw_deadline_for_spin(lck_rw_t *lck)
{
	if (lck->lck_rw_can_sleep) {
		if (lck->lck_r_waiting || lck->lck_w_waiting || lck->lck_rw_shared_count > machine_info.max_cpus) {
			/*
			 * there are already threads waiting on this lock... this
			 * implies that they have spun beyond their deadlines waiting for 
			 * the desired state to show up so we will not bother spinning at this time...
			 *   or
			 * the current number of threads sharing this lock exceeds our capacity to run them
			 * concurrently and since all states we're going to spin for require the rw_shared_count
			 * to be at 0, we'll not bother spinning since the latency for this to happen is
			 * unpredictable...
			 */
			return (mach_absolute_time());
		}
		return (mach_absolute_time() + MutexSpin);
	} else
		return (mach_absolute_time() + (100000LL * 1000000000LL));
}


/*
 *      Routine:        lck_rw_lock_exclusive
 */
void
lck_rw_lock_exclusive_gen(
	lck_rw_t	*lck)
{
	uint64_t	deadline = 0;
	int		slept = 0;
	int		gotlock = 0;
	int		lockheld = 0;
	wait_result_t	res = 0;
	boolean_t	istate = -1;

#if	CONFIG_DTRACE
	boolean_t dtrace_ls_initialized = FALSE;
	boolean_t dtrace_rwl_excl_spin, dtrace_rwl_excl_block, dtrace_ls_enabled= FALSE;
	uint64_t wait_interval = 0;
	int readers_at_sleep = 0;
#endif

	/*
	 *	Try to acquire the lck_rw_want_write bit.
	 */
	while ( !lck_rw_grab_want(lck)) {

#if	CONFIG_DTRACE
		if (dtrace_ls_initialized == FALSE) {
			dtrace_ls_initialized = TRUE;
			dtrace_rwl_excl_spin = (lockstat_probemap[LS_LCK_RW_LOCK_EXCL_SPIN] != 0);
			dtrace_rwl_excl_block = (lockstat_probemap[LS_LCK_RW_LOCK_EXCL_BLOCK] != 0);
			dtrace_ls_enabled = dtrace_rwl_excl_spin || dtrace_rwl_excl_block;
			if (dtrace_ls_enabled) {
				/*
				 * Either sleeping or spinning is happening,
				 *  start a timing of our delay interval now.
				 */
				readers_at_sleep = lck->lck_rw_shared_count;
				wait_interval = mach_absolute_time();
			}
		}
#endif
		if (istate == -1)
			istate = ml_get_interrupts_enabled();

		deadline = lck_rw_deadline_for_spin(lck);

		KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_WRITER_SPIN_CODE) | DBG_FUNC_START, (int)lck, 0, 0, 0, 0);
		
		while (((gotlock = lck_rw_grab_want(lck)) == 0) && mach_absolute_time() < deadline)
			lck_rw_lock_pause(istate);

		KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_WRITER_SPIN_CODE) | DBG_FUNC_END, (int)lck, 0, 0, gotlock, 0);

		if (gotlock)
			break;
		/*
		 * if we get here, the deadline has expired w/o us
		 * being able to grab the lock exclusively
		 * check to see if we're allowed to do a thread_block
		 */
		if (lck->lck_rw_can_sleep) {

			istate = lck_interlock_lock(lck);

			if (lck->lck_rw_want_write) {

				KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_WRITER_WAIT_CODE) | DBG_FUNC_START, (int)lck, 0, 0, 0, 0);

				lck->lck_w_waiting = TRUE;

				res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
				lck_interlock_unlock(lck, istate);

				if (res == THREAD_WAITING) {
					res = thread_block(THREAD_CONTINUE_NULL);
					slept++;
				}
				KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_WRITER_WAIT_CODE) | DBG_FUNC_END, (int)lck, res, slept, 0, 0);
			} else {
				lck->lck_rw_want_write = TRUE;
				lck_interlock_unlock(lck, istate);
				break;
			}
		}
	}
	/*
	 * Wait for readers (and upgrades) to finish...
	 * the test for these conditions must be done simultaneously with
	 * a check of the interlock not being held since
	 * the rw_shared_count will drop to 0 first and then want_upgrade
	 * will be set to 1 in the shared_to_exclusive scenario... those
	 * adjustments are done behind the interlock and represent an
	 * atomic change in state and must be considered as such
	 * however, once we see the read count at 0, the want_upgrade not set
	 * and the interlock not held, we are safe to proceed
	 */
	while (lck_rw_held_read_or_upgrade(lck)) {

#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 (dtrace_ls_initialized == FALSE) {
			dtrace_ls_initialized = TRUE;
			dtrace_rwl_excl_spin = (lockstat_probemap[LS_LCK_RW_LOCK_EXCL_SPIN] != 0);
			dtrace_rwl_excl_block = (lockstat_probemap[LS_LCK_RW_LOCK_EXCL_BLOCK] != 0);
			dtrace_ls_enabled = dtrace_rwl_excl_spin || dtrace_rwl_excl_block;
			if (dtrace_ls_enabled) {
				/*
				 * Either sleeping or spinning is happening,
				 *  start a timing of our delay interval now.
				 */
				readers_at_sleep = lck->lck_rw_shared_count;
				wait_interval = mach_absolute_time();
			}
		}
#endif
		if (istate == -1)
			istate = ml_get_interrupts_enabled();

		deadline = lck_rw_deadline_for_spin(lck);

		KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_READER_SPIN_CODE) | DBG_FUNC_START, (int)lck, 0, 0, 0, 0);

		while ((lockheld = lck_rw_held_read_or_upgrade(lck)) && mach_absolute_time() < deadline)
			lck_rw_lock_pause(istate);

		KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_READER_SPIN_CODE) | DBG_FUNC_END, (int)lck, 0, 0, lockheld, 0);

		if ( !lockheld)
			break;
		/*
		 * if we get here, the deadline has expired w/o us
		 * being able to grab the lock exclusively
		 * check to see if we're allowed to do a thread_block
		 */
		if (lck->lck_rw_can_sleep) {

			istate = lck_interlock_lock(lck);

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

				lck->lck_w_waiting = TRUE;

				res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
				lck_interlock_unlock(lck, istate);

				if (res == THREAD_WAITING) {
					res = thread_block(THREAD_CONTINUE_NULL);
					slept++;
				}
				KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_READER_WAIT_CODE) | DBG_FUNC_END, (int)lck, res, slept, 0, 0);
			} else {
				lck_interlock_unlock(lck, istate);
				/*
				 * must own the lock now, since we checked for
				 * readers or upgrade owner behind the interlock
				 * no need for a call to 'lck_rw_held_read_or_upgrade'
				 */
				break;
			}
		}
	}

#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 (dtrace_ls_enabled == TRUE) {
		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
 *
 *	called from the assembly language wrapper...
 *	prior_lock_state is the value in the 1st
 * 	word of the lock at the time of a successful
 *	atomic compare and exchange with the new value...
 * 	it represents the state of the lock before we
 *	decremented the rw_shared_count or cleared either
 * 	rw_want_upgrade or rw_want_write and
 *	the lck_x_waiting bits...  since the wrapper
 * 	routine has already changed the state atomically, 
 *	we just need to decide if we should
 *	wake up anyone and what value to return... we do
 *	this by examining the state of the lock before
 *	we changed it
 */
lck_rw_type_t
lck_rw_done_gen(
	lck_rw_t	*lck,
	int		prior_lock_state)
{
	lck_rw_t	*fake_lck;
	lck_rw_type_t	lock_type;

	/*
	 * prior_lock state is a snapshot of the 1st word of the
	 * lock in question... we'll fake up a pointer to it
	 * and carefully not access anything beyond whats defined
	 * in the first word of a lck_rw_t
	 */
	fake_lck = (lck_rw_t *)&prior_lock_state;

	if (fake_lck->lck_rw_shared_count <= 1) {
		if (fake_lck->lck_w_waiting)
			thread_wakeup(RW_LOCK_WRITER_EVENT(lck));

		if (!(fake_lck->lck_rw_priv_excl && fake_lck->lck_w_waiting) && fake_lck->lck_r_waiting)
			thread_wakeup(RW_LOCK_READER_EVENT(lck));
	}
	if (fake_lck->lck_rw_shared_count)
		lock_type = LCK_RW_TYPE_SHARED;
	else
		lock_type = LCK_RW_TYPE_EXCLUSIVE;

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

	return(lock_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
 *	Function:
 *		assembly fast path code has determined that this lock
 *		is held exclusively... this is where we spin/block
 *		until we can acquire the lock in the shared mode
 */
void
lck_rw_lock_shared_gen(
	lck_rw_t	*lck)
{
	uint64_t	deadline = 0;
	int		gotlock = 0;
	int		slept = 0;
	wait_result_t	res = 0;
	boolean_t	istate = -1;
	
#if	CONFIG_DTRACE
	uint64_t wait_interval = 0;
	int readers_at_sleep = 0;
	boolean_t dtrace_ls_initialized = FALSE;
	boolean_t dtrace_rwl_shared_spin, dtrace_rwl_shared_block, dtrace_ls_enabled = FALSE;
#endif

	while ( !lck_rw_grab_shared(lck)) {

#if	CONFIG_DTRACE
		if (dtrace_ls_initialized == FALSE) {
			dtrace_ls_initialized = TRUE;
			dtrace_rwl_shared_spin = (lockstat_probemap[LS_LCK_RW_LOCK_SHARED_SPIN] != 0);
			dtrace_rwl_shared_block = (lockstat_probemap[LS_LCK_RW_LOCK_SHARED_BLOCK] != 0);
			dtrace_ls_enabled = dtrace_rwl_shared_spin || dtrace_rwl_shared_block;
			if (dtrace_ls_enabled) {
				/*
				 * Either sleeping or spinning is happening,
				 *  start a timing of our delay interval now.
				 */
				readers_at_sleep = lck->lck_rw_shared_count;
				wait_interval = mach_absolute_time();
			}
		}
#endif
		if (istate == -1)
			istate = ml_get_interrupts_enabled();

		deadline = lck_rw_deadline_for_spin(lck);

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

		while (((gotlock = lck_rw_grab_shared(lck)) == 0) && mach_absolute_time() < deadline)
			lck_rw_lock_pause(istate);

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

		if (gotlock)
			break;
		/*
		 * if we get here, the deadline has expired w/o us
		 * being able to grab the lock for read
		 * check to see if we're allowed to do a thread_block
		 */
		if (lck->lck_rw_can_sleep) {

			istate = lck_interlock_lock(lck);

			if ((lck->lck_rw_want_write || lck->lck_rw_want_upgrade) &&
			    ((lck->lck_rw_shared_count == 0) || lck->lck_rw_priv_excl)) {

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

				lck->lck_r_waiting = TRUE;

				res = assert_wait(RW_LOCK_READER_EVENT(lck), THREAD_UNINT);
				lck_interlock_unlock(lck, istate);

				if (res == THREAD_WAITING) {
					res = thread_block(THREAD_CONTINUE_NULL);
					slept++;
				}
				KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_WAIT_CODE) | DBG_FUNC_END,
					     (int)lck, res, slept, 0, 0);
			} else {
				lck->lck_rw_shared_count++;
				lck_interlock_unlock(lck, istate);
				break;
			}
		}
	}

#if	CONFIG_DTRACE
	if (dtrace_ls_enabled == TRUE) {
		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_failure
 *	Function:
 *		assembly fast path code has already dropped our read
 *		count and determined that someone else owns 'lck_rw_want_upgrade'
 *		if 'lck_rw_shared_count' == 0, its also already dropped 'lck_w_waiting'
 *		all we need to do here is determine if a wakeup is needed
 */
boolean_t
lck_rw_lock_shared_to_exclusive_failure(
	lck_rw_t	*lck,
	int		prior_lock_state)
{
	lck_rw_t	*fake_lck;

	/*
	 * prior_lock state is a snapshot of the 1st word of the
	 * lock in question... we'll fake up a pointer to it
	 * and carefully not access anything beyond whats defined
	 * in the first word of a lck_rw_t
	 */
	fake_lck = (lck_rw_t *)&prior_lock_state;

	if (fake_lck->lck_w_waiting && fake_lck->lck_rw_shared_count == 1) {
		/*
		 *	Someone else has requested upgrade.
		 *	Since we've released the read lock, wake
		 *	him up if he's blocked waiting
		 */
		thread_wakeup(RW_LOCK_WRITER_EVENT(lck));
	}
	KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_CODE) | DBG_FUNC_NONE,
		     (int)lck, lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, 0, 0);

	return (FALSE);
}


/*
 *	Routine:	lck_rw_lock_shared_to_exclusive_failure
 *	Function:
 *		assembly fast path code has already dropped our read
 *		count and successfully acquired 'lck_rw_want_upgrade'
 *		we just need to wait for the rest of the readers to drain
 *		and then we can return as the exclusive holder of this lock
 */
boolean_t
lck_rw_lock_shared_to_exclusive_success(
	lck_rw_t	*lck)
{
	uint64_t	deadline = 0;
	int		slept = 0;
	int		still_shared = 0;
	wait_result_t	res;
	boolean_t	istate = -1;

#if	CONFIG_DTRACE
	uint64_t wait_interval = 0;
	int readers_at_sleep = 0;
	boolean_t dtrace_ls_initialized = FALSE;
	boolean_t dtrace_rwl_shared_to_excl_spin, dtrace_rwl_shared_to_excl_block, dtrace_ls_enabled = FALSE;
#endif

	while (lck->lck_rw_shared_count != 0) {

#if	CONFIG_DTRACE
		if (dtrace_ls_initialized == FALSE) {
			dtrace_ls_initialized = TRUE;
			dtrace_rwl_shared_to_excl_spin = (lockstat_probemap[LS_LCK_RW_LOCK_SHARED_TO_EXCL_SPIN] != 0);
			dtrace_rwl_shared_to_excl_block = (lockstat_probemap[LS_LCK_RW_LOCK_SHARED_TO_EXCL_BLOCK] != 0);
			dtrace_ls_enabled = dtrace_rwl_shared_to_excl_spin || dtrace_rwl_shared_to_excl_block;
			if (dtrace_ls_enabled) {
				/*
				 * Either sleeping or spinning is happening,
				 *  start a timing of our delay interval now.
				 */
				readers_at_sleep = lck->lck_rw_shared_count;
				wait_interval = mach_absolute_time();
			}
		}
#endif
		if (istate == -1)
			istate = ml_get_interrupts_enabled();

		deadline = lck_rw_deadline_for_spin(lck);

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

		while ((still_shared = lck->lck_rw_shared_count) && mach_absolute_time() < deadline)
			lck_rw_lock_pause(istate);

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

		if ( !still_shared)
			break;
		/*
		 * if we get here, the deadline has expired w/o
		 * the rw_shared_count having drained to 0
		 * check to see if we're allowed to do a thread_block
		 */
		if (lck->lck_rw_can_sleep) {
			
			istate = lck_interlock_lock(lck);
			
			if (lck->lck_rw_shared_count != 0) {
				KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_WAIT_CODE) | DBG_FUNC_START,
					     (int)lck, lck->lck_rw_shared_count, 0, 0, 0);

				lck->lck_w_waiting = TRUE;

				res = assert_wait(RW_LOCK_WRITER_EVENT(lck), THREAD_UNINT);
				lck_interlock_unlock(lck, istate);

				if (res == THREAD_WAITING) {
					res = thread_block(THREAD_CONTINUE_NULL);
					slept++;
				}
				KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_WAIT_CODE) | DBG_FUNC_END,
					     (int)lck, res, slept, 0, 0);
			} else {
				lck_interlock_unlock(lck, istate);
				break;
			}
		}
	}
#if	CONFIG_DTRACE
	/*
	 * We infer whether we took the sleep/spin path above by checking readers_at_sleep.
	 */
	if (dtrace_ls_enabled == TRUE) {
		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
 * 	Function:
 *		assembly fast path has already dropped
 *		our exclusive state and bumped lck_rw_shared_count
 *		all we need to do here is determine if anyone
 *		needs to be awakened.
 */
void
lck_rw_lock_exclusive_to_shared_gen(
	lck_rw_t	*lck,
	int		prior_lock_state)
{
	lck_rw_t	*fake_lck;

	/*
	 * prior_lock state is a snapshot of the 1st word of the
	 * lock in question... we'll fake up a pointer to it
	 * and carefully not access anything beyond whats defined
	 * in the first word of a lck_rw_t
	 */
	fake_lck = (lck_rw_t *)&prior_lock_state;

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

	/*
	 * don't wake up anyone waiting to take the lock exclusively
	 * since we hold a read count... when the read count drops to 0,
	 * the writers will be woken.
	 *
	 * wake up any waiting readers if we don't have any writers waiting,
	 * or the lock is NOT marked as rw_priv_excl (writers have privilege)
	 */
	if (!(fake_lck->lck_rw_priv_excl && fake_lck->lck_w_waiting) && fake_lck->lck_r_waiting)
		thread_wakeup(RW_LOCK_READER_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);
}


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), first word %08x\n", lck, type, *(uint32_t *)lck);
}

/*
 *      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;

	lck->lck_mtx.lck_mtx_ptr = (void *)LCK_MTX_PTR_EXTENDED;
}

/*
 *      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;
			lck->lck_mtx_ilocked = 1;
		}
	} else {
		lck->lck_mtx_owner = 0;
		lck->lck_mtx_ptr = 0;
		lck->lck_mtx_waiters = 0;
		lck->lck_mtx_pri = 0;
		lck->lck_mtx_ilocked = 0;
		lck->lck_mtx_mlocked = 0;
		lck->lck_mtx_promoted = 0;
		lck->lck_mtx_spin = 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;
		lck->lck_mtx_ilocked = 1;
	} else {
		lck->lck_mtx_owner = 0;
		lck->lck_mtx_ptr = 0;
		lck->lck_mtx_waiters = 0;
		lck->lck_mtx_pri = 0;
		lck->lck_mtx_ilocked = 0;
		lck->lck_mtx_mlocked = 0;
		lck->lck_mtx_promoted = 0;
		lck->lck_mtx_spin = 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_mtx_lock_mark_destroyed(lck);

	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;
}


#define	LCK_MTX_LCK_WAIT_CODE		0x20
#define	LCK_MTX_LCK_WAKEUP_CODE		0x21
#define	LCK_MTX_LCK_SPIN_CODE		0x22
#define	LCK_MTX_LCK_ACQUIRE_CODE	0x23
#define LCK_MTX_LCK_DEMOTE_CODE		0x24


/*
 * Routine: 	lck_mtx_unlock_wakeup_x86
 *
 * Invoked on unlock when there is contention.
 *
 */
void
lck_mtx_unlock_wakeup_x86 (
	lck_mtx_t	*mutex,
	int		owner_was_promoted)
{

	KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAKEUP_CODE) | DBG_FUNC_START, (int)mutex, owner_was_promoted, mutex->lck_mtx_waiters, 0, 0);

	if (lck_mtx_lock_decr_waiter(mutex))
		thread_wakeup_one((event_t)(((unsigned int*)mutex)+(sizeof(lck_mtx_t)-1)/sizeof(unsigned int)));

	if (owner_was_promoted) {
		thread_t	thread = current_thread();


		KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_DEMOTE_CODE) | DBG_FUNC_NONE, (uintptr_t)thread_tid(thread), thread->promotions,
			     thread->sched_mode & TH_MODE_PROMOTED, 0, 0);

		if (thread->promotions > 0) {
			spl_t	s = splsched();

			thread_lock(thread);

			if (--thread->promotions == 0 && (thread->sched_mode & TH_MODE_PROMOTED)) {

				thread->sched_mode &= ~TH_MODE_PROMOTED;

				if (thread->sched_mode & TH_MODE_ISDEPRESSED) {
					KERNEL_DEBUG_CONSTANT(
						MACHDBG_CODE(DBG_MACH_SCHED,MACH_DEMOTE) | DBG_FUNC_NONE,
						thread->sched_pri, DEPRESSPRI, 0, mutex, 0);

					set_sched_pri(thread, DEPRESSPRI);
				}
				else {
					if (thread->priority < thread->sched_pri) {
						KERNEL_DEBUG_CONSTANT(
							MACHDBG_CODE(DBG_MACH_SCHED,MACH_DEMOTE) | DBG_FUNC_NONE,
							thread->sched_pri, thread->priority, 0, mutex, 0);

						compute_priority(thread, FALSE);
					}
				}
			}
			thread_unlock(thread);
			splx(s);
		}
	}
	KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAKEUP_CODE) | DBG_FUNC_END, (int)mutex, 0, mutex->lck_mtx_waiters, 0, 0);
}


/*
 * Routine: 	lck_mtx_lock_acquire_x86
 *
 * Invoked on acquiring the mutex when there is
 * contention.
 * mutex is owned...  interlock is not held
 */
void
lck_mtx_lock_acquire_x86(
	lck_mtx_t	*mutex)
{
	thread_t	thread = current_thread();
	integer_t	priority;

	KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_ACQUIRE_CODE) | DBG_FUNC_START, (int)mutex, 0, mutex->lck_mtx_waiters, 0, 0);

	priority = lck_mtx_lock_get_pri(mutex);

	if (thread->sched_pri < priority) {

		if (lck_mtx_lock_mark_promoted(mutex)) {
			spl_t	s = splsched();

			thread_lock(thread);

			if (thread->sched_pri < priority) {

				KERNEL_DEBUG_CONSTANT(
					MACHDBG_CODE(DBG_MACH_SCHED,MACH_PROMOTE) | DBG_FUNC_NONE,
					thread->sched_pri, priority, 0, mutex, 0);

				set_sched_pri(thread, priority);
			}
			thread->promotions++;
			thread->sched_mode |= TH_MODE_PROMOTED;

			thread_unlock(thread);
			splx(s);
		}
	}
	KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_ACQUIRE_CODE) | DBG_FUNC_END, (int)mutex, 0, mutex->lck_mtx_waiters, 0, 0);
}



/*
 * Routine: 	lck_mtx_lock_spinwait_x86
 *
 * 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.
 */
int
lck_mtx_lock_spinwait_x86(
	lck_mtx_t	*mutex)
{
	thread_t	holder;
	uint64_t	deadline;
	int		retval = 1;
	int		loopcount = 0;

	KERNEL_DEBUG(
		MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_SPIN_CODE) | DBG_FUNC_START,
		(int)mutex, (int)mutex->lck_mtx_owner, mutex->lck_mtx_waiters, 0, 0);

	deadline = mach_absolute_time() + MutexSpin;

	/*
	 * Spin while:
	 *   - mutex is locked, and
	 *   - its locked as a spin lock, and
	 *   - owner is running on another processor, and
	 *   - owner (processor) is not idling, and
	 *   - we haven't spun for long enough.
	 */
	do {
		if (lck_mtx_lock_grab_mutex(mutex)) {
			retval = 0;
			break;
		}
		if ((holder = (thread_t) mutex->lck_mtx_owner) != NULL) {

			if ( !(holder->machine.specFlags & OnProc) ||
			     (holder->state & TH_IDLE)) {
				if (loopcount == 0)
					retval = 2;
				break;
			}
		}
		cpu_pause();

		loopcount++;

	} while (mach_absolute_time() < deadline);


#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 (mutex->lck_mtx_ptr != (void *)LCK_MTX_PTR_EXTENDED) {
		LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_SPIN, mutex,
		    mach_absolute_time() - (deadline - MutexSpin));
	} else {
		LOCKSTAT_RECORD(LS_LCK_MTX_EXT_LOCK_SPIN, mutex,
		    mach_absolute_time() - (deadline - MutexSpin));
	}
	/* The lockstat acquire event is recorded by the assembly code beneath us. */
#endif

	KERNEL_DEBUG(
		MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_SPIN_CODE) | DBG_FUNC_END,
		(int)mutex, (int)mutex->lck_mtx_owner, mutex->lck_mtx_waiters, retval, 0);

	return retval;
}



/*
 * Routine: 	lck_mtx_lock_wait_x86
 *
 * Invoked in order to wait on contention.
 *
 * Called with the interlock locked and
 * returns it unlocked.
 */
void
lck_mtx_lock_wait_x86 (
	lck_mtx_t	*mutex)
{
	thread_t	self = current_thread();
	thread_t	holder;
	integer_t	priority;
	integer_t	old_lck_mtx_pri;
	spl_t		s;
#if	CONFIG_DTRACE
	uint64_t	sleep_start = 0;

	if (lockstat_probemap[LS_LCK_MTX_LOCK_BLOCK] || lockstat_probemap[LS_LCK_MTX_EXT_LOCK_BLOCK]) {
		sleep_start = mach_absolute_time();
	}
#endif
	KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAIT_CODE) | DBG_FUNC_START, (int)mutex, (int)mutex->lck_mtx_owner, mutex->lck_mtx_waiters, 0, 0);

	priority = self->sched_pri;

	if (priority < self->priority)
		priority = self->priority;
	if (priority < BASEPRI_DEFAULT)
		priority = BASEPRI_DEFAULT;

	if (mutex->lck_mtx_waiters == 0)
		old_lck_mtx_pri = 0;
	else
		old_lck_mtx_pri = mutex->lck_mtx_pri;

	if (old_lck_mtx_pri < priority)
		mutex->lck_mtx_pri = priority;

	if ( (holder = (thread_t)mutex->lck_mtx_owner) ) {

		s = splsched();
		thread_lock(holder);

		if (holder->sched_pri < priority) {
			KERNEL_DEBUG_CONSTANT(
				MACHDBG_CODE(DBG_MACH_SCHED, MACH_PROMOTE) | DBG_FUNC_NONE,
				holder->sched_pri, priority, holder, mutex, 0);

			set_sched_pri(holder, priority);
			
			if (mutex->lck_mtx_promoted == 0) {
				holder->promotions++;
				holder->sched_mode |= TH_MODE_PROMOTED;

				mutex->lck_mtx_promoted = 1;
			}
		}
		thread_unlock(holder);
		splx(s);
	}
	mutex->lck_mtx_waiters++;

	assert_wait((event_t)(((unsigned int*)mutex)+((sizeof(lck_mtx_t)-1)/sizeof(unsigned int))), THREAD_UNINT);

	lck_mtx_ilk_unlock(mutex);

	thread_block(THREAD_CONTINUE_NULL);

	KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_MTX_LCK_WAIT_CODE) | DBG_FUNC_END, (int)mutex, (int)mutex->lck_mtx_owner, mutex->lck_mtx_waiters, 0, 0);

#if	CONFIG_DTRACE
	/*
	 * Record the Dtrace lockstat probe for blocking, block time
	 * measured from when we were entered.
	 */
	if (sleep_start) {
		if (mutex->lck_mtx_ptr != (void *)LCK_MTX_PTR_EXTENDED) {
			LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_BLOCK, mutex,
			    mach_absolute_time() - sleep_start);
		} else {
			LOCKSTAT_RECORD(LS_LCK_MTX_EXT_LOCK_BLOCK, mutex,
			    mach_absolute_time() - sleep_start);
		}
	}
#endif
}


#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);
}

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

const char *simple_lock_labels =	"ENTRY    ILK THREAD   DURATION 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");
}

#endif	/* MACH_KDB */