xnu-4903.241.1.tar.gz

[apple/xnu.git] / osfmk / arm / locks_arm.c

/*
 * Copyright (c) 2007-2017 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
 */

#define ATOMIC_PRIVATE 1
#define LOCK_PRIVATE 1

#include <mach_ldebug.h>

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

#include <arm/cpu_data_internal.h>
#include <arm/proc_reg.h>
#include <arm/smp.h>
#include <machine/atomic.h>
#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>

#define DTRACE_RW_SHARED        0x0     //reader
#define DTRACE_RW_EXCL          0x1     //writer
#define DTRACE_NO_FLAG          0x0     //not applicable

#endif  /* CONFIG_DTRACE */

#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 ANY_LOCK_DEBUG  (USLOCK_DEBUG || LOCK_DEBUG || MUTEX_DEBUG)

// Panic in tests that check lock usage correctness
// These are undesirable when in a panic or a debugger is runnning.
#define LOCK_CORRECTNESS_PANIC() (kernel_debugger_entry_count == 0)

unsigned int    LcksOpts = 0;

#if CONFIG_DTRACE && __SMP__
extern uint64_t dtrace_spin_threshold;
#endif

/* Forwards */


#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 */

extern unsigned int not_in_kdp;

/*
 *      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)

#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 */


/*
 *      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, const char *);
#else                           /* USLOCK_DEBUG */
#define USLDBG(stmt)
#endif                          /* USLOCK_DEBUG */

/*
 * Owner thread pointer when lock held in spin mode
 */
#define LCK_MTX_SPIN_TAG  0xfffffff0


#define interlock_lock(lock)    hw_lock_bit    ((hw_lock_bit_t*)(&(lock)->lck_mtx_data), LCK_ILOCK_BIT)
#define interlock_try(lock)             hw_lock_bit_try((hw_lock_bit_t*)(&(lock)->lck_mtx_data), LCK_ILOCK_BIT)
#define interlock_unlock(lock)  hw_unlock_bit  ((hw_lock_bit_t*)(&(lock)->lck_mtx_data), LCK_ILOCK_BIT)
#define lck_rw_ilk_lock(lock)   hw_lock_bit  ((hw_lock_bit_t*)(&(lock)->lck_rw_tag), LCK_RW_INTERLOCK_BIT)
#define lck_rw_ilk_unlock(lock) hw_unlock_bit((hw_lock_bit_t*)(&(lock)->lck_rw_tag), LCK_RW_INTERLOCK_BIT)

#define memory_barrier()        __c11_atomic_thread_fence(memory_order_acq_rel_smp)
#define load_memory_barrier()   __c11_atomic_thread_fence(memory_order_acquire_smp)
#define store_memory_barrier()  __c11_atomic_thread_fence(memory_order_release_smp)

// Enforce program order of loads and stores.
#define ordered_load(target, type) \
                __c11_atomic_load((_Atomic type *)(target), memory_order_relaxed)
#define ordered_store(target, type, value) \
                __c11_atomic_store((_Atomic type *)(target), value, memory_order_relaxed)

#define ordered_load_mtx(lock)                  ordered_load(&(lock)->lck_mtx_data, uintptr_t)
#define ordered_store_mtx(lock, value)  ordered_store(&(lock)->lck_mtx_data, uintptr_t, (value))
#define ordered_load_rw(lock)                   ordered_load(&(lock)->lck_rw_data, uint32_t)
#define ordered_store_rw(lock, value)   ordered_store(&(lock)->lck_rw_data, uint32_t, (value))
#define ordered_load_rw_owner(lock)             ordered_load(&(lock)->lck_rw_owner, thread_t)
#define ordered_store_rw_owner(lock, value)     ordered_store(&(lock)->lck_rw_owner, thread_t, (value))
#define ordered_load_hw(lock)                   ordered_load(&(lock)->lock_data, uintptr_t)
#define ordered_store_hw(lock, value)   ordered_store(&(lock)->lock_data, uintptr_t, (value))
#define ordered_load_bit(lock)                  ordered_load((lock), uint32_t)
#define ordered_store_bit(lock, value)  ordered_store((lock), uint32_t, (value))


// Prevent the compiler from reordering memory operations around this
#define compiler_memory_fence() __asm__ volatile ("" ::: "memory")

#define LOCK_PANIC_TIMEOUT      0xc00000
#define NOINLINE                __attribute__((noinline))


#if __arm__
#define interrupts_disabled(mask) (mask & PSR_INTMASK)
#else
#define interrupts_disabled(mask) (mask & DAIF_IRQF)
#endif


#if __arm__
#define enable_fiq()            __asm__ volatile ("cpsie  f" ::: "memory");
#define enable_interrupts()     __asm__ volatile ("cpsie if" ::: "memory");
#endif

/*
 * Forward declarations
 */

static void lck_rw_lock_shared_gen(lck_rw_t *lck);
static void lck_rw_lock_exclusive_gen(lck_rw_t *lck);
static boolean_t lck_rw_lock_shared_to_exclusive_success(lck_rw_t *lck);
static boolean_t lck_rw_lock_shared_to_exclusive_failure(lck_rw_t *lck, uint32_t prior_lock_state);
static void lck_rw_lock_exclusive_to_shared_gen(lck_rw_t *lck, uint32_t prior_lock_state);
static lck_rw_type_t lck_rw_done_gen(lck_rw_t *lck, uint32_t prior_lock_state);
static boolean_t lck_rw_grab(lck_rw_t *lock, int mode, boolean_t wait);

/*
 * atomic exchange API is a low level abstraction of the operations
 * to atomically read, modify, and write a pointer.  This abstraction works
 * for both Intel and ARMv8.1 compare and exchange atomic instructions as
 * well as the ARM exclusive instructions.
 *
 * atomic_exchange_begin() - begin exchange and retrieve current value
 * atomic_exchange_complete() - conclude an exchange
 * atomic_exchange_abort() - cancel an exchange started with atomic_exchange_begin()
 */
static uint32_t
atomic_exchange_begin32(uint32_t *target, uint32_t *previous, enum memory_order ord)
{
        uint32_t        val;

        val = load_exclusive32(target, ord);
        *previous = val;
        return val;
}

static boolean_t
atomic_exchange_complete32(uint32_t *target, uint32_t previous, uint32_t newval, enum memory_order ord)
{
        (void)previous;         // Previous not needed, monitor is held
        return store_exclusive32(target, newval, ord);
}

static void
atomic_exchange_abort(void)
{
        clear_exclusive();
}

static boolean_t
atomic_test_and_set32(uint32_t *target, uint32_t test_mask, uint32_t set_mask, enum memory_order ord, boolean_t wait)
{
        uint32_t                value, prev;

        for ( ; ; ) {
                value = atomic_exchange_begin32(target, &prev, ord);
                if (value & test_mask) {
                        if (wait)
                                wait_for_event();       // Wait with monitor held
                        else
                                atomic_exchange_abort();        // Clear exclusive monitor
                        return FALSE;
                }
                value |= set_mask;
                if (atomic_exchange_complete32(target, prev, value, ord))
                        return TRUE;
        }
}

void _disable_preemption(void)
{
        thread_t        thread = current_thread();
        unsigned int    count;

        count = thread->machine.preemption_count + 1;
        ordered_store(&thread->machine.preemption_count, unsigned int, count);
}

void _enable_preemption(void)
{
        thread_t        thread = current_thread();
        long            state;
        unsigned int    count;
#if __arm__
#define INTERRUPT_MASK PSR_IRQF
#else   // __arm__
#define INTERRUPT_MASK DAIF_IRQF
#endif  // __arm__

        count = thread->machine.preemption_count;
        if (count == 0)
                panic("Preemption count negative");     // Count will go negative when released
        count--;
        if (count > 0)
                goto update_count;                      // Preemption is still disabled, just update
        state = get_interrupts();                       // Get interrupt state
        if (state & INTERRUPT_MASK)
                goto update_count;                      // Interrupts are already masked, can't take AST here

        disable_interrupts_noread();                    // Disable interrupts
        ordered_store(&thread->machine.preemption_count, unsigned int, count);
        if (thread->machine.CpuDatap->cpu_pending_ast & AST_URGENT) {
#if __arm__
#if __ARM_USER_PROTECT__
        uintptr_t up = arm_user_protect_begin(thread);
#endif  // __ARM_USER_PROTECT__
                enable_fiq();
#endif  // __arm__
                ast_taken_kernel();                     // Handle urgent AST
#if __arm__
#if __ARM_USER_PROTECT__
                arm_user_protect_end(thread, up, TRUE);
#endif  // __ARM_USER_PROTECT__
                enable_interrupts();
                return;                                 // Return early on arm only due to FIQ enabling
#endif  // __arm__
        }
        restore_interrupts(state);                      // Enable interrupts
        return;

update_count:
        ordered_store(&thread->machine.preemption_count, unsigned int, count);
        return;
}

int get_preemption_level(void)
{
        return current_thread()->machine.preemption_count;
}

/* Forward declarations for unexported functions that are used externally */
void hw_lock_bit(hw_lock_bit_t *lock, unsigned int bit);
void hw_unlock_bit(hw_lock_bit_t *lock, unsigned int bit);

#if     __SMP__
static unsigned int
hw_lock_bit_to_contended(hw_lock_bit_t *lock, uint32_t mask, uint32_t timeout);
#endif

static inline unsigned int
hw_lock_bit_to_internal(hw_lock_bit_t *lock, unsigned int bit, uint32_t timeout)
{
        unsigned int success = 0;
        uint32_t        mask = (1 << bit);
#if     !__SMP__
        uint32_t        state;
#endif

#if     __SMP__
        if (__improbable(!atomic_test_and_set32(lock, mask, mask, memory_order_acquire, FALSE)))
                success = hw_lock_bit_to_contended(lock, mask, timeout);
        else
                success = 1;
#else   // __SMP__
        (void)timeout;
        state = ordered_load_bit(lock);
        if (!(mask & state)) {
                ordered_store_bit(lock, state | mask);
                success = 1;
        }
#endif  // __SMP__

#if CONFIG_DTRACE
        if (success)
                LOCKSTAT_RECORD(LS_LCK_SPIN_LOCK_ACQUIRE, lock, bit);
#endif

        return success;
}

unsigned int
hw_lock_bit_to(hw_lock_bit_t *lock, unsigned int bit, uint32_t timeout)
{
        _disable_preemption();
        return hw_lock_bit_to_internal(lock, bit, timeout);
}

#if     __SMP__
static unsigned int NOINLINE
hw_lock_bit_to_contended(hw_lock_bit_t *lock, uint32_t mask, uint32_t timeout)
{
        uint64_t        end = 0;
        int             i;
#if CONFIG_DTRACE
        uint64_t begin;
        boolean_t dtrace_enabled = lockstat_probemap[LS_LCK_SPIN_LOCK_SPIN] != 0;
        if (__improbable(dtrace_enabled))
                begin = mach_absolute_time();
#endif
        for ( ; ; ) {   
                for (i = 0; i < LOCK_SNOOP_SPINS; i++) {
                        // Always load-exclusive before wfe
                        // This grabs the monitor and wakes up on a release event
                        if (atomic_test_and_set32(lock, mask, mask, memory_order_acquire, TRUE)) {
                                goto end;
                        }
                }
                if (end == 0)
                        end = ml_get_timebase() + timeout;
                else if (ml_get_timebase() >= end)
                        break;
        }
        return 0;
end:
#if CONFIG_DTRACE
        if (__improbable(dtrace_enabled)) {
                uint64_t spintime = mach_absolute_time() - begin;
                if (spintime > dtrace_spin_threshold)
                        LOCKSTAT_RECORD2(LS_LCK_SPIN_LOCK_SPIN, lock, spintime, mask);
        }
#endif
        return 1;
}
#endif  // __SMP__

void
hw_lock_bit(hw_lock_bit_t *lock, unsigned int bit)
{
        if (hw_lock_bit_to(lock, bit, LOCK_PANIC_TIMEOUT))
                return;
#if     __SMP__
        panic("hw_lock_bit(): timed out (%p)", lock);
#else
        panic("hw_lock_bit(): interlock held (%p)", lock);
#endif
}

void
hw_lock_bit_nopreempt(hw_lock_bit_t *lock, unsigned int bit)
{
        if (__improbable(get_preemption_level() == 0))
                panic("Attempt to take no-preempt bitlock %p in preemptible context", lock);
        if (hw_lock_bit_to_internal(lock, bit, LOCK_PANIC_TIMEOUT))
                return;
#if     __SMP__
        panic("hw_lock_bit_nopreempt(): timed out (%p)", lock);
#else
        panic("hw_lock_bit_nopreempt(): interlock held (%p)", lock);
#endif
}

unsigned int
hw_lock_bit_try(hw_lock_bit_t *lock, unsigned int bit)
{
        uint32_t        mask = (1 << bit);
#if     !__SMP__
        uint32_t        state;
#endif
        boolean_t       success = FALSE;

        _disable_preemption();
#if     __SMP__
        // TODO: consider weak (non-looping) atomic test-and-set
        success = atomic_test_and_set32(lock, mask, mask, memory_order_acquire, FALSE);
#else
        state = ordered_load_bit(lock);
        if (!(mask & state)) {
                ordered_store_bit(lock, state | mask);
                success = TRUE;
        }
#endif  // __SMP__
        if (!success)
                _enable_preemption();

#if CONFIG_DTRACE
        if (success)
                LOCKSTAT_RECORD(LS_LCK_SPIN_LOCK_ACQUIRE, lock, bit);
#endif

        return success;
}

static inline void
hw_unlock_bit_internal(hw_lock_bit_t *lock, unsigned int bit)
{
        uint32_t        mask = (1 << bit);
#if     !__SMP__
        uint32_t        state;
#endif

#if     __SMP__
        __c11_atomic_fetch_and((_Atomic uint32_t *)lock, ~mask, memory_order_release);
        set_event();
#else   // __SMP__
        state = ordered_load_bit(lock);
        ordered_store_bit(lock, state & ~mask);
#endif  // __SMP__
#if CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_SPIN_UNLOCK_RELEASE, lock, bit);
#endif
}

/*
 *      Routine:        hw_unlock_bit
 *
 *              Release spin-lock. The second parameter is the bit number to test and set.
 *              Decrement the preemption level.
 */
void
hw_unlock_bit(hw_lock_bit_t *lock, unsigned int bit)
{
        hw_unlock_bit_internal(lock, bit);
        _enable_preemption();
}

void
hw_unlock_bit_nopreempt(hw_lock_bit_t *lock, unsigned int bit)
{
        if (__improbable(get_preemption_level() == 0))
                panic("Attempt to release no-preempt bitlock %p in preemptible context", lock);
        hw_unlock_bit_internal(lock, bit);
}

/*
 *      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((void *) 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)
{
        hw_lock_init(&lck->hwlock);
        lck->type = LCK_SPIN_TYPE;
        lck_grp_reference(grp);
        lck_grp_lckcnt_incr(grp, LCK_TYPE_SPIN);
        store_memory_barrier();
}

/*
 * arm_usimple_lock is a lck_spin_t without a group or attributes
 */
void inline
arm_usimple_lock_init(simple_lock_t lck, __unused unsigned short initial_value)
{
        lck->type = LCK_SPIN_TYPE;
        hw_lock_init(&lck->hwlock);
        store_memory_barrier();
}


/*
 *      Routine:        lck_spin_lock
 */
void
lck_spin_lock(lck_spin_t *lock)
{
#if     DEVELOPMENT || DEBUG
        if (lock->type != LCK_SPIN_TYPE)
                panic("Invalid spinlock %p", lock);
#endif  // DEVELOPMENT || DEBUG
        hw_lock_lock(&lock->hwlock);
}

/*
 *      Routine:        lck_spin_lock_nopreempt
 */
void
lck_spin_lock_nopreempt(lck_spin_t *lock)
{
#if     DEVELOPMENT || DEBUG
        if (lock->type != LCK_SPIN_TYPE)
                panic("Invalid spinlock %p", lock);
#endif  // DEVELOPMENT || DEBUG
        hw_lock_lock_nopreempt(&lock->hwlock);
}

/*
 *      Routine:        lck_spin_try_lock
 */
int
lck_spin_try_lock(lck_spin_t *lock)
{
        return hw_lock_try(&lock->hwlock);
}

/*
 *      Routine:        lck_spin_try_lock_nopreempt
 */
int
lck_spin_try_lock_nopreempt(lck_spin_t *lock)
{
        return hw_lock_try_nopreempt(&lock->hwlock);
}

/*
 *      Routine:        lck_spin_unlock
 */
void
lck_spin_unlock(lck_spin_t *lock)
{
#if     DEVELOPMENT || DEBUG
        if ((LCK_MTX_STATE_TO_THREAD(lock->lck_spin_data) != current_thread()) && LOCK_CORRECTNESS_PANIC())
                panic("Spinlock not owned by thread %p = %lx", lock, lock->lck_spin_data);
        if (lock->type != LCK_SPIN_TYPE)
                panic("Invalid spinlock type %p", lock);
#endif  // DEVELOPMENT || DEBUG
        hw_lock_unlock(&lock->hwlock);
}

/*
 *      Routine:        lck_spin_unlock_nopreempt
 */
void
lck_spin_unlock_nopreempt(lck_spin_t *lock)
{
#if     DEVELOPMENT || DEBUG
        if ((LCK_MTX_STATE_TO_THREAD(lock->lck_spin_data) != current_thread()) && LOCK_CORRECTNESS_PANIC())
                panic("Spinlock not owned by thread %p = %lx", lock, lock->lck_spin_data);
        if (lock->type != LCK_SPIN_TYPE)
                panic("Invalid spinlock type %p", lock);
#endif  // DEVELOPMENT || DEBUG
        hw_lock_unlock_nopreempt(&lock->hwlock);
}

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

/*
 * Routine: kdp_lck_spin_is_acquired
 * NOT SAFE: To be used only by kernel debugger to avoid deadlock.
 */
boolean_t
kdp_lck_spin_is_acquired(lck_spin_t *lck) {
        if (not_in_kdp) {
                panic("panic: spinlock acquired check done outside of kernel debugger");
        }
        return ((lck->lck_spin_data & ~LCK_SPIN_TAG_DESTROYED) != 0) ? TRUE:FALSE;
}

/*
 *      Initialize a usimple_lock.
 *
 *      No change in preemption state.
 */
void
usimple_lock_init(
                  usimple_lock_t l,
                  unsigned short tag)
{
#ifndef MACHINE_SIMPLE_LOCK
        USLDBG(usld_lock_init(l, tag));
        hw_lock_init(&l->lck_spin_data);
#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
        pc_t            pc;

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

        if (!hw_lock_to(&l->lck_spin_data, LockTimeOut))        /* Try to get the lock
                                                         * with a timeout */
                panic("simple lock deadlock detection - l=%p, cpu=%d, ret=%p", &l, cpu_number(), pc);

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


extern void     sync(void);

/*
 *      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
        pc_t            pc;

        OBTAIN_PC(pc, l);
        USLDBG(usld_unlock(l, pc));
        sync();
        hw_lock_unlock(&l->lck_spin_data);
#else
        simple_unlock((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
        pc_t            pc;
        unsigned int    success;

        OBTAIN_PC(pc, l);
        USLDBG(usld_lock_try_pre(l, pc));
        if ((success = hw_lock_try(&l->lck_spin_data))) {
                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,
                        const 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)
{
        const 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 0x%x already locked (at %p) by",
                       caller, (integer_t) 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)
{
        int             mycpu;
        const 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)
{
        int             mycpu;
        const 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)
{
        const 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)
{
        int             mycpu;
        const 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 */

/*
 * The C portion of the shared/exclusive locks package.
 */

/*
 * compute the deadline to spin against when
 * waiting for a change of state on a lck_rw_t
 */
#if     __SMP__
static inline uint64_t
lck_rw_deadline_for_spin(lck_rw_t *lck)
{
        lck_rw_word_t   word;

        word.data = ordered_load_rw(lck);
        if (word.can_sleep) {
                if (word.r_waiting || word.w_waiting || (word.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));
}
#endif  // __SMP__

static boolean_t
lck_rw_drain_status(lck_rw_t *lock, uint32_t status_mask, boolean_t wait __unused)
{
#if     __SMP__
        uint64_t        deadline = 0;
        uint32_t        data;

        if (wait)
                deadline = lck_rw_deadline_for_spin(lock);

        for ( ; ; ) {
                data = load_exclusive32(&lock->lck_rw_data, memory_order_acquire_smp);
                if ((data & status_mask) == 0)
                        break;
                if (wait)
                        wait_for_event();
                else
                        clear_exclusive();
                if (!wait || (mach_absolute_time() >= deadline))
                        return FALSE;
        }
        clear_exclusive();
        return TRUE;
#else
        uint32_t        data;

        data = ordered_load_rw(lock);
        if ((data & status_mask) == 0)
                return TRUE;
        else
                return FALSE;
#endif  // __SMP__
}

/*
 * Spin while interlock is held.
 */
static inline void
lck_rw_interlock_spin(lck_rw_t *lock)
{
#if __SMP__
        uint32_t        data;

        for ( ; ; ) {
                data = load_exclusive32(&lock->lck_rw_data, memory_order_relaxed);
                if (data & LCK_RW_INTERLOCK)
                        wait_for_event();
                else {
                        clear_exclusive();
                        return;
                }
        }
#else
        panic("lck_rw_interlock_spin(): Interlock locked %p %x", lock, lock->lck_rw_data);
#endif
}

/*
 * We disable interrupts while holding the RW interlock to prevent an
 * interrupt from exacerbating hold time.
 * Hence, local helper functions lck_interlock_lock()/lck_interlock_unlock().
 */
static inline boolean_t
lck_interlock_lock(lck_rw_t *lck)
{
        boolean_t       istate;

        istate = ml_set_interrupts_enabled(FALSE);      
        lck_rw_ilk_lock(lck);
        return istate;
}

static inline void
lck_interlock_unlock(lck_rw_t *lck, boolean_t istate)
{
        lck_rw_ilk_unlock(lck);
        ml_set_interrupts_enabled(istate);
}


#define LCK_RW_GRAB_WANT        0
#define LCK_RW_GRAB_SHARED      1

static boolean_t
lck_rw_grab(lck_rw_t *lock, int mode, boolean_t wait)
{
        uint64_t        deadline = 0;
        uint32_t        data, prev;
        boolean_t       do_exch;

#if __SMP__
        if (wait)
                deadline = lck_rw_deadline_for_spin(lock);
#else
        wait = FALSE;   // Don't spin on UP systems
#endif

        for ( ; ; ) {
                data = atomic_exchange_begin32(&lock->lck_rw_data, &prev, memory_order_acquire_smp);
                if (data & LCK_RW_INTERLOCK) {
                        atomic_exchange_abort();
                        lck_rw_interlock_spin(lock);
                        continue;
                }
                do_exch = FALSE;
                if (mode == LCK_RW_GRAB_WANT) {
                        if ((data & LCK_RW_WANT_EXCL) == 0) {
                                data |= LCK_RW_WANT_EXCL;
                                do_exch = TRUE;
                        }
                } else {        // LCK_RW_GRAB_SHARED
                        if (((data & (LCK_RW_WANT_EXCL | LCK_RW_WANT_UPGRADE)) == 0) ||
                                (((data & LCK_RW_SHARED_MASK)) && ((data & LCK_RW_PRIV_EXCL) == 0))) {
                                data += LCK_RW_SHARED_READER;
                                do_exch = TRUE;
                        }
                }
                if (do_exch) {
                        if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_acquire_smp))
                                return TRUE;
                } else {
                        if (wait)                                               // Non-waiting
                                wait_for_event();
                        else
                                atomic_exchange_abort();
                        if (!wait || (mach_absolute_time() >= deadline))
                                return FALSE;
                }
        }
}


/*
 *      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)
{
        if (attr == LCK_ATTR_NULL)
                attr = &LockDefaultLckAttr;
        memset(lck, 0, sizeof(lck_rw_t));
        lck->lck_rw_can_sleep = TRUE;
        if ((attr->lck_attr_val & LCK_ATTR_RW_SHARED_PRIORITY) == 0)
                lck->lck_rw_priv_excl = TRUE;

        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;
#if MACH_LDEBUG
        lck_rw_assert(lck, LCK_RW_ASSERT_NOTHELD);
#endif
        lck->lck_rw_tag = LCK_RW_TAG_DESTROYED;
        lck_grp_lckcnt_decr(grp, LCK_TYPE_RW);
        lck_grp_deallocate(grp);
        return;
}

/*
 *      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", lck_rw_type);
}

/*
 *      Routine:        lck_rw_lock_exclusive
 */
void
lck_rw_lock_exclusive(lck_rw_t *lock)
{
        thread_t        thread = current_thread();

        thread->rwlock_count++;
        if (atomic_test_and_set32(&lock->lck_rw_data,
                (LCK_RW_SHARED_MASK | LCK_RW_WANT_EXCL | LCK_RW_WANT_UPGRADE | LCK_RW_INTERLOCK),
                LCK_RW_WANT_EXCL, memory_order_acquire_smp, FALSE)) {
#if     CONFIG_DTRACE
                LOCKSTAT_RECORD(LS_LCK_RW_LOCK_EXCL_ACQUIRE, lock, DTRACE_RW_EXCL);
#endif  /* CONFIG_DTRACE */
        } else
                lck_rw_lock_exclusive_gen(lock);
#if MACH_ASSERT
        thread_t owner = ordered_load_rw_owner(lock);
        assertf(owner == THREAD_NULL, "state=0x%x, owner=%p", ordered_load_rw(lock), owner);
#endif
        ordered_store_rw_owner(lock, thread);
}

/*
 *      Routine:        lck_rw_lock_shared
 */
void
lck_rw_lock_shared(lck_rw_t *lock)
{
        uint32_t        data, prev;

        current_thread()->rwlock_count++;
        for ( ; ; ) {
                data = atomic_exchange_begin32(&lock->lck_rw_data, &prev, memory_order_acquire_smp);
                if (data & (LCK_RW_WANT_EXCL | LCK_RW_WANT_UPGRADE | LCK_RW_INTERLOCK)) {
                        atomic_exchange_abort();
                        lck_rw_lock_shared_gen(lock);
                        break;
                }
                data += LCK_RW_SHARED_READER;
                if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_acquire_smp))
                        break;
                cpu_pause();
        }
#if MACH_ASSERT
        thread_t owner = ordered_load_rw_owner(lock);
        assertf(owner == THREAD_NULL, "state=0x%x, owner=%p", ordered_load_rw(lock), owner);
#endif
#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_LOCK_SHARED_ACQUIRE, lock, DTRACE_RW_SHARED);
#endif  /* CONFIG_DTRACE */
        return;
}

/*
 *      Routine:        lck_rw_lock_shared_to_exclusive
 */
boolean_t
lck_rw_lock_shared_to_exclusive(lck_rw_t *lock)
{
        uint32_t        data, prev;

        for ( ; ; ) {
                data = atomic_exchange_begin32(&lock->lck_rw_data, &prev, memory_order_acquire_smp);
                if (data & LCK_RW_INTERLOCK) {
                        atomic_exchange_abort();
                        lck_rw_interlock_spin(lock);
                        continue;
                }
                if (data & LCK_RW_WANT_UPGRADE) {
                        data -= LCK_RW_SHARED_READER;
                        if ((data & LCK_RW_SHARED_MASK) == 0)           /* we were the last reader */
                                data &= ~(LCK_RW_W_WAITING);            /* so clear the wait indicator */
                        if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_acquire_smp))
                                return lck_rw_lock_shared_to_exclusive_failure(lock, prev);
                } else {
                        data |= LCK_RW_WANT_UPGRADE;            /* ask for WANT_UPGRADE */
                        data -= LCK_RW_SHARED_READER;           /* and shed our read count */
                        if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_acquire_smp))
                                break;
                }
                cpu_pause();
        }
                                                                                /* we now own the WANT_UPGRADE */
        if (data & LCK_RW_SHARED_MASK)          /* check to see if all of the readers are drained */
                lck_rw_lock_shared_to_exclusive_success(lock);  /* if not, we need to go wait */
#if MACH_ASSERT
        thread_t owner = ordered_load_rw_owner(lock);
        assertf(owner == THREAD_NULL, "state=0x%x, owner=%p", ordered_load_rw(lock), owner);
#endif
        ordered_store_rw_owner(lock, current_thread());
#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_LOCK_SHARED_TO_EXCL_UPGRADE, lock, 0);
#endif  /* CONFIG_DTRACE */
        return TRUE;
}


/*
 *      Routine:        lck_rw_lock_shared_to_exclusive_failure
 *      Function:
 *              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
 */
static boolean_t
lck_rw_lock_shared_to_exclusive_failure(
        lck_rw_t        *lck,
        uint32_t        prior_lock_state)
{
        thread_t        thread = current_thread();
        uint32_t        rwlock_count;

        /* Check if dropping the lock means that we need to unpromote */
        rwlock_count = thread->rwlock_count--;
#if MACH_LDEBUG
        if (rwlock_count == 0) {
                panic("rw lock count underflow for thread %p", thread);
        }
#endif
        if ((prior_lock_state & LCK_RW_W_WAITING) &&
                ((prior_lock_state & LCK_RW_SHARED_MASK) == LCK_RW_SHARED_READER)) {
                /*
                 *      Someone else has requested upgrade.
                 *      Since we've released the read lock, wake
                 *      him up if he's blocked waiting
                 */
                thread_wakeup(LCK_RW_WRITER_EVENT(lck));
        }

        if ((rwlock_count == 1 /* field now 0 */) && (thread->sched_flags & TH_SFLAG_RW_PROMOTED)) {
                /* sched_flags checked without lock, but will be rechecked while clearing */
                lck_rw_clear_promotion(thread, unslide_for_kdebug(lck));
        }

        KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_CODE) | DBG_FUNC_NONE,
                     VM_KERNEL_UNSLIDE_OR_PERM(lck), lck->lck_rw_shared_count, lck->lck_rw_want_upgrade, 0, 0);

        return (FALSE);
}

/*
 *      Routine:        lck_rw_lock_shared_to_exclusive_success
 *      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
 */
static boolean_t
lck_rw_lock_shared_to_exclusive_success(
        lck_rw_t        *lock)
{
        __kdebug_only uintptr_t trace_lck = VM_KERNEL_UNSLIDE_OR_PERM(lock);
        int                     slept = 0;
        lck_rw_word_t           word;
        wait_result_t           res;
        boolean_t               istate;
        boolean_t               not_shared;

#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_rw_drain_status(lock, LCK_RW_SHARED_MASK, FALSE)) {

                word.data = ordered_load_rw(lock);
#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 = word.shared_count;
                                wait_interval = mach_absolute_time();
                        }
                }
#endif

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_SPIN_CODE) | DBG_FUNC_START,
                             trace_lck, word.shared_count, 0, 0, 0);

                not_shared = lck_rw_drain_status(lock, LCK_RW_SHARED_MASK, TRUE);

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_SPIN_CODE) | DBG_FUNC_END,
                             trace_lck, lock->lck_rw_shared_count, 0, 0, 0);

                if (not_shared)
                        break;

                /*
                 * if we get here, the spin deadline in lck_rw_wait_on_status()
                 * 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 (word.can_sleep) {
                        
                        istate = lck_interlock_lock(lock);
                        
                        word.data = ordered_load_rw(lock);
                        if (word.shared_count != 0) {
                                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SH_TO_EX_WAIT_CODE) | DBG_FUNC_START,
                                             trace_lck, word.shared_count, 0, 0, 0);

                                word.w_waiting = 1;
                                ordered_store_rw(lock, word.data);

                                thread_set_pending_block_hint(current_thread(), kThreadWaitKernelRWLockUpgrade);
                                res = assert_wait(LCK_RW_WRITER_EVENT(lock),
                                                THREAD_UNINT | THREAD_WAIT_NOREPORT_USER);
                                lck_interlock_unlock(lock, 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,
                                             trace_lck, res, slept, 0, 0);
                        } else {
                                lck_interlock_unlock(lock, 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, lock, mach_absolute_time() - wait_interval, 0);
                } else {
                        LOCKSTAT_RECORD4(LS_LCK_RW_LOCK_SHARED_TO_EXCL_BLOCK, lock,
                            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, lock, 1);
#endif
        return (TRUE);
}


/*
 *      Routine:        lck_rw_lock_exclusive_to_shared
 */

void lck_rw_lock_exclusive_to_shared(lck_rw_t *lock)
{
        uint32_t        data, prev;

        assertf(lock->lck_rw_owner == current_thread(), "state=0x%x, owner=%p", lock->lck_rw_data, lock->lck_rw_owner);
        ordered_store_rw_owner(lock, THREAD_NULL);
        for ( ; ; ) {
                data = atomic_exchange_begin32(&lock->lck_rw_data, &prev, memory_order_release_smp);
                if (data & LCK_RW_INTERLOCK) {
#if __SMP__
                        atomic_exchange_abort();
                        lck_rw_interlock_spin(lock);    /* wait for interlock to clear */
                        continue;
#else
                        panic("lck_rw_lock_exclusive_to_shared(): Interlock locked (%p): %x", lock, data);
#endif // __SMP__
                }
                data += LCK_RW_SHARED_READER;
                if (data & LCK_RW_WANT_UPGRADE)
                        data &= ~(LCK_RW_WANT_UPGRADE);
                else
                        data &= ~(LCK_RW_WANT_EXCL);
                if (!((prev & LCK_RW_W_WAITING) && (prev & LCK_RW_PRIV_EXCL)))
                        data &= ~(LCK_RW_W_WAITING);
                if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_release_smp))
                        break;
                cpu_pause();
        }
        return lck_rw_lock_exclusive_to_shared_gen(lock, prev);
}

/*
 *      Routine:        lck_rw_lock_exclusive_to_shared_gen
 *      Function:
 *              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.
 */
static void
lck_rw_lock_exclusive_to_shared_gen(
        lck_rw_t        *lck,
        uint32_t        prior_lock_state)
{
        __kdebug_only uintptr_t trace_lck = VM_KERNEL_UNSLIDE_OR_PERM(lck);
        lck_rw_word_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.data = prior_lock_state;

        KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_TO_SH_CODE) | DBG_FUNC_START,
                             trace_lck, fake_lck->want_excl, fake_lck->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.priv_excl && fake_lck.w_waiting) && fake_lck.r_waiting)
                thread_wakeup(LCK_RW_READER_EVENT(lck));

        KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_TO_SH_CODE) | DBG_FUNC_END,
                             trace_lck, lck->lck_rw_want_excl, 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", lck_rw_type);
        return FALSE;
}

/*
 *      Routine:        lck_rw_try_lock_shared
 */

boolean_t lck_rw_try_lock_shared(lck_rw_t *lock)
{
        uint32_t        data, prev;

        for ( ; ; ) {
                data = atomic_exchange_begin32(&lock->lck_rw_data, &prev, memory_order_acquire_smp);
                if (data & LCK_RW_INTERLOCK) {
#if __SMP__
                        atomic_exchange_abort();
                        lck_rw_interlock_spin(lock);
                        continue;
#else
                        panic("lck_rw_try_lock_shared(): Interlock locked (%p): %x", lock, data);
#endif
                }
                if (data & (LCK_RW_WANT_EXCL | LCK_RW_WANT_UPGRADE)) {
                        atomic_exchange_abort();
                        return FALSE;                                           /* lock is busy */
                }
                data += LCK_RW_SHARED_READER;                   /* Increment reader refcount */
                if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_acquire_smp))
                        break;
                cpu_pause();
        }
#if MACH_ASSERT
        thread_t owner = ordered_load_rw_owner(lock);
        assertf(owner == THREAD_NULL, "state=0x%x, owner=%p", ordered_load_rw(lock), owner);
#endif
        current_thread()->rwlock_count++;
#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_TRY_LOCK_SHARED_ACQUIRE, lock, DTRACE_RW_SHARED);
#endif  /* CONFIG_DTRACE */
        return TRUE;
}


/*
 *      Routine:        lck_rw_try_lock_exclusive
 */

boolean_t lck_rw_try_lock_exclusive(lck_rw_t *lock)
{
        uint32_t        data, prev;
        thread_t        thread;

        for ( ; ; ) {
                data = atomic_exchange_begin32(&lock->lck_rw_data, &prev, memory_order_acquire_smp);
                if (data & LCK_RW_INTERLOCK) {
#if __SMP__
                        atomic_exchange_abort();
                        lck_rw_interlock_spin(lock);
                        continue;
#else
                        panic("lck_rw_try_lock_exclusive(): Interlock locked (%p): %x", lock, data);
#endif
                }
                if (data & (LCK_RW_SHARED_MASK | LCK_RW_WANT_EXCL | LCK_RW_WANT_UPGRADE)) {
                        atomic_exchange_abort();
                        return FALSE;
                }
                data |= LCK_RW_WANT_EXCL;
                if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_acquire_smp))
                        break;
                cpu_pause();
        }
        thread = current_thread();
        thread->rwlock_count++;
#if MACH_ASSERT
        thread_t owner = ordered_load_rw_owner(lock);
        assertf(owner == THREAD_NULL, "state=0x%x, owner=%p", ordered_load_rw(lock), owner);
#endif
        ordered_store_rw_owner(lock, thread);
#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_RW_TRY_LOCK_EXCL_ACQUIRE, lock, DTRACE_RW_EXCL);
#endif  /* CONFIG_DTRACE */
        return TRUE;
}


/*
 *      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", lck_rw_type);
}


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

        assertf(lck->lck_rw_owner == THREAD_NULL, "state=0x%x, owner=%p", lck->lck_rw_data, lck->lck_rw_owner);
        assertf(lck->lck_rw_shared_count > 0, "shared_count=0x%x", lck->lck_rw_shared_count);
        ret = lck_rw_done(lck);

        if (ret != LCK_RW_TYPE_SHARED)
                panic("lck_rw_unlock_shared(): lock %p held in mode: %d", lck, ret);
}


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

        assertf(lck->lck_rw_owner == current_thread(), "state=0x%x, owner=%p", lck->lck_rw_data, lck->lck_rw_owner);
        ret = lck_rw_done(lck);

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


/*
 *      Routine:        lck_rw_lock_exclusive_gen
 */
static void
lck_rw_lock_exclusive_gen(
        lck_rw_t        *lock)
{
        __kdebug_only uintptr_t trace_lck = VM_KERNEL_UNSLIDE_OR_PERM(lock);
        lck_rw_word_t           word;
        int                     slept = 0;
        boolean_t               gotlock = 0;
        boolean_t               not_shared_or_upgrade = 0;
        wait_result_t           res = 0;
        boolean_t               istate;

#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_excl bit.
         */
        while (!lck_rw_grab(lock, LCK_RW_GRAB_WANT, FALSE)) {

#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 = lock->lck_rw_shared_count;
                                wait_interval = mach_absolute_time();
                        }
                }
#endif

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_WRITER_SPIN_CODE) | DBG_FUNC_START, trace_lck, 0, 0, 0, 0);

                gotlock = lck_rw_grab(lock, LCK_RW_GRAB_WANT, TRUE);

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_WRITER_SPIN_CODE) | DBG_FUNC_END, trace_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
                 */
                word.data = ordered_load_rw(lock);
                if (word.can_sleep) {

                        istate = lck_interlock_lock(lock);
                        word.data = ordered_load_rw(lock);

                        if (word.want_excl) {

                                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_WRITER_WAIT_CODE) | DBG_FUNC_START, trace_lck, 0, 0, 0, 0);

                                word.w_waiting = 1;
                                ordered_store_rw(lock, word.data);

                                thread_set_pending_block_hint(current_thread(), kThreadWaitKernelRWLockWrite);
                                res = assert_wait(LCK_RW_WRITER_EVENT(lock),
                                                THREAD_UNINT | THREAD_WAIT_NOREPORT_USER);
                                lck_interlock_unlock(lock, 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, trace_lck, res, slept, 0, 0);
                        } else {
                                word.want_excl = 1;
                                ordered_store_rw(lock, word.data);
                                lck_interlock_unlock(lock, istate);
                                break;
                        }
                }
        }
        /*
         * Wait for readers (and upgrades) to finish...
         */
        while (!lck_rw_drain_status(lock, LCK_RW_SHARED_MASK | LCK_RW_WANT_UPGRADE, FALSE)) {

#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 = lock->lck_rw_shared_count;
                                wait_interval = mach_absolute_time();
                        }
                }
#endif

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_READER_SPIN_CODE) | DBG_FUNC_START, trace_lck, 0, 0, 0, 0);

                not_shared_or_upgrade = lck_rw_drain_status(lock, LCK_RW_SHARED_MASK | LCK_RW_WANT_UPGRADE, TRUE);

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_READER_SPIN_CODE) | DBG_FUNC_END, trace_lck, 0, 0, not_shared_or_upgrade, 0);

                if (not_shared_or_upgrade)
                        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
                 */
                word.data = ordered_load_rw(lock);
                if (word.can_sleep) {

                        istate = lck_interlock_lock(lock);
                        word.data = ordered_load_rw(lock);

                        if (word.shared_count != 0 || word.want_upgrade) {
                                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_EX_READER_WAIT_CODE) | DBG_FUNC_START, trace_lck, 0, 0, 0, 0);

                                word.w_waiting = 1;
                                ordered_store_rw(lock, word.data);

                                thread_set_pending_block_hint(current_thread(), kThreadWaitKernelRWLockWrite);
                                res = assert_wait(LCK_RW_WRITER_EVENT(lock),
                                                THREAD_UNINT | THREAD_WAIT_NOREPORT_USER);
                                lck_interlock_unlock(lock, 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, trace_lck, res, slept, 0, 0);
                        } else {
                                lck_interlock_unlock(lock, 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_drain_status'
                                 */
                                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, lock,
                            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, lock,
                            mach_absolute_time() - wait_interval, 1,
                            (readers_at_sleep == 0 ? 1 : 0), readers_at_sleep);
                }
        }
        LOCKSTAT_RECORD(LS_LCK_RW_LOCK_EXCL_ACQUIRE, lock, 1);
#endif  /* CONFIG_DTRACE */
}

/*
 *      Routine:        lck_rw_done
 */

lck_rw_type_t lck_rw_done(lck_rw_t *lock)
{
        uint32_t        data, prev;
        boolean_t       once = FALSE;

        for ( ; ; ) {
                data = atomic_exchange_begin32(&lock->lck_rw_data, &prev, memory_order_release_smp);
                if (data & LCK_RW_INTERLOCK) {          /* wait for interlock to clear */
#if __SMP__
                        atomic_exchange_abort();
                        lck_rw_interlock_spin(lock);
                        continue;
#else
                        panic("lck_rw_done(): Interlock locked (%p): %x", lock, data);
#endif // __SMP__
                }
                if (data & LCK_RW_SHARED_MASK) {        /* lock is held shared */
                        assertf(lock->lck_rw_owner == THREAD_NULL, "state=0x%x, owner=%p", lock->lck_rw_data, lock->lck_rw_owner);
                        data -= LCK_RW_SHARED_READER;
                        if ((data & LCK_RW_SHARED_MASK) == 0)   /* if reader count has now gone to 0, check for waiters */
                                goto check_waiters;
                } else {                                        /* if reader count == 0, must be exclusive lock */
                        if (data & LCK_RW_WANT_UPGRADE) {
                                data &= ~(LCK_RW_WANT_UPGRADE);
                        } else {
                                if (data & LCK_RW_WANT_EXCL)
                                        data &= ~(LCK_RW_WANT_EXCL);
                                else                                    /* lock is not 'owned', panic */
                                        panic("Releasing non-exclusive RW lock without a reader refcount!");
                        }
                        if (!once) {
                                // Only check for holder and clear it once
                                assertf(lock->lck_rw_owner == current_thread(), "state=0x%x, owner=%p", lock->lck_rw_data, lock->lck_rw_owner);
                                ordered_store_rw_owner(lock, THREAD_NULL);
                                once = TRUE;
                        }
check_waiters:
                        /*
                         * test the original values to match what
                         * lck_rw_done_gen is going to do to determine
                         * which wakeups need to happen...
                         *
                         * if !(fake_lck->lck_rw_priv_excl && fake_lck->lck_w_waiting)
                         */
                        if (prev & LCK_RW_W_WAITING) {
                                data &= ~(LCK_RW_W_WAITING);
                                if ((prev & LCK_RW_PRIV_EXCL) == 0)
                                        data &= ~(LCK_RW_R_WAITING);
                        } else
                                data &= ~(LCK_RW_R_WAITING);
                }
                if (atomic_exchange_complete32(&lock->lck_rw_data, prev, data, memory_order_release_smp))
                        break;
                cpu_pause();
        }
        return lck_rw_done_gen(lock, prev);
}

/*
 *      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
 */
static lck_rw_type_t
lck_rw_done_gen(
        lck_rw_t        *lck,
        uint32_t        prior_lock_state)
{
        lck_rw_word_t   fake_lck;
        lck_rw_type_t   lock_type;
        thread_t                thread;
        uint32_t                rwlock_count;

        /*
         * 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.data = prior_lock_state;

        if (fake_lck.shared_count <= 1) {
                if (fake_lck.w_waiting)
                        thread_wakeup(LCK_RW_WRITER_EVENT(lck));

                if (!(fake_lck.priv_excl && fake_lck.w_waiting) && fake_lck.r_waiting)
                        thread_wakeup(LCK_RW_READER_EVENT(lck));
        }
        if (fake_lck.shared_count)
                lock_type = LCK_RW_TYPE_SHARED;
        else
                lock_type = LCK_RW_TYPE_EXCLUSIVE;

        /* Check if dropping the lock means that we need to unpromote */
        thread = current_thread();
        rwlock_count = thread->rwlock_count--;
#if MACH_LDEBUG
        if (rwlock_count == 0)
                panic("rw lock count underflow for thread %p", thread);
#endif
        if ((rwlock_count == 1 /* field now 0 */) && (thread->sched_flags & TH_SFLAG_RW_PROMOTED)) {
                /* sched_flags checked without lock, but will be rechecked while clearing */
                lck_rw_clear_promotion(thread, unslide_for_kdebug(lck));
        }
#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_lock_shared_gen
 *      Function:
 *              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
 */
static void
lck_rw_lock_shared_gen(
        lck_rw_t        *lck)
{
        __kdebug_only uintptr_t trace_lck = VM_KERNEL_UNSLIDE_OR_PERM(lck);
        lck_rw_word_t           word;
        boolean_t               gotlock = 0;
        int                     slept = 0;
        wait_result_t           res = 0;
        boolean_t               istate;

#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 /* CONFIG_DTRACE */

        while ( !lck_rw_grab(lck, LCK_RW_GRAB_SHARED, FALSE)) {

#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

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_SPIN_CODE) | DBG_FUNC_START,
                             trace_lck, lck->lck_rw_want_excl, lck->lck_rw_want_upgrade, 0, 0);

                gotlock = lck_rw_grab(lck, LCK_RW_GRAB_SHARED, TRUE);

                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_SPIN_CODE) | DBG_FUNC_END,
                             trace_lck, lck->lck_rw_want_excl, 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);

                        word.data = ordered_load_rw(lck);
                        if ((word.want_excl || word.want_upgrade) &&
                            ((word.shared_count == 0) || word.priv_excl)) {

                                KERNEL_DEBUG(MACHDBG_CODE(DBG_MACH_LOCKS, LCK_RW_LCK_SHARED_WAIT_CODE) | DBG_FUNC_START,
                                             trace_lck, word.want_excl, word.want_upgrade, 0, 0);

                                word.r_waiting = 1;
                                ordered_store_rw(lck, word.data);

                                thread_set_pending_block_hint(current_thread(), kThreadWaitKernelRWLockRead);
                                res = assert_wait(LCK_RW_READER_EVENT(lck),
                                                THREAD_UNINT | THREAD_WAIT_NOREPORT_USER);
                                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,
                                             trace_lck, res, slept, 0, 0);
                        } else {
                                word.shared_count++;
                                ordered_store_rw(lck, word.data);
                                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  /* CONFIG_DTRACE */
}


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) &&
                    (lck->lck_rw_owner == THREAD_NULL)) {
                        return;
                }
                break;
        case LCK_RW_ASSERT_EXCLUSIVE:
                if ((lck->lck_rw_want_excl || lck->lck_rw_want_upgrade) &&
                        (lck->lck_rw_shared_count == 0) &&
                    (lck->lck_rw_owner == current_thread())) {
                        return;
                }
                break;
        case LCK_RW_ASSERT_HELD:
                if (lck->lck_rw_shared_count != 0)
                        return;         // Held shared
                if ((lck->lck_rw_want_excl || lck->lck_rw_want_upgrade) &&
                    (lck->lck_rw_owner == current_thread())) {
                        return;         // Held exclusive
                }
                break;
        case LCK_RW_ASSERT_NOTHELD:
                if ((lck->lck_rw_shared_count == 0) &&
                   !(lck->lck_rw_want_excl || lck->lck_rw_want_upgrade) &&
                    (lck->lck_rw_owner == THREAD_NULL)) {
                        return;
                }
                break;
        default:
                break;
        }
        panic("rw lock (%p)%s held (mode=%u)", lck, (type == LCK_RW_ASSERT_NOTHELD ? "" : " not"), type);
}


/*
 * Routine: kdp_lck_rw_lock_is_acquired_exclusive
 * NOT SAFE: To be used only by kernel debugger to avoid deadlock.
 */
boolean_t
kdp_lck_rw_lock_is_acquired_exclusive(lck_rw_t *lck) {
        if (not_in_kdp) {
                panic("panic: rw lock exclusive check done outside of kernel debugger");
        }
        return ((lck->lck_rw_want_upgrade || lck->lck_rw_want_excl) && (lck->lck_rw_shared_count == 0)) ? TRUE : FALSE;
}

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

/*
 * Forward declaration
 */

void 
lck_mtx_ext_init(
                 lck_mtx_ext_t * lck,
                 lck_grp_t * grp,
                 lck_attr_t * attr);

/*
 *      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((void *) lck, sizeof(lck_mtx_t));
}

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

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

#ifdef  BER_XXX
        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_type = LCK_MTX_TYPE;
                }
        } else
#endif
        {
                lck->lck_mtx_ptr = NULL;                // Clear any padding in the union fields below
                lck->lck_mtx_waiters = 0;
                lck->lck_mtx_pri = 0;
                lck->lck_mtx_type = LCK_MTX_TYPE;
                ordered_store_mtx(lck, 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_type = LCK_MTX_TYPE;
        } else {
                lck->lck_mtx_waiters = 0;
                lck->lck_mtx_pri = 0;
                lck->lck_mtx_type = LCK_MTX_TYPE;
                ordered_store_mtx(lck, 0);
        }
        lck_grp_reference(grp);
        lck_grp_lckcnt_incr(grp, LCK_TYPE_MTX);
}

/*
 *      Routine:        lck_mtx_ext_init
 */
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));

        lck->lck_mtx.lck_mtx_type = LCK_MTX_TYPE;

        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;
}

/* The slow versions */
static void lck_mtx_lock_contended(lck_mtx_t *lock, thread_t thread, boolean_t interlocked);
static boolean_t lck_mtx_try_lock_contended(lck_mtx_t *lock, thread_t thread);
static void lck_mtx_unlock_contended(lck_mtx_t *lock, thread_t thread, boolean_t interlocked);

/*
 *      Routine:        lck_mtx_verify
 *
 *      Verify if a mutex is valid
 */
static inline void
lck_mtx_verify(lck_mtx_t *lock)
{
        if (lock->lck_mtx_type != LCK_MTX_TYPE)
                panic("Invalid mutex %p", lock);
#if     DEVELOPMENT || DEBUG
        if (lock->lck_mtx_tag == LCK_MTX_TAG_DESTROYED)
                panic("Mutex destroyed %p", lock);
#endif  /* DEVELOPMENT || DEBUG */
}

/*
 *      Routine:        lck_mtx_check_preemption
 *
 *      Verify preemption is enabled when attempting to acquire a mutex.
 */

static inline void
lck_mtx_check_preemption(lck_mtx_t *lock)
{
#if     DEVELOPMENT || DEBUG
        int pl = get_preemption_level();

        if (pl != 0)
                panic("Attempt to take mutex with preemption disabled. Lock=%p, level=%d", lock, pl);
#else
        (void)lock;
#endif
}

/*
 *      Routine:        lck_mtx_lock
 */
void
lck_mtx_lock(lck_mtx_t *lock)
{
        thread_t        thread;

        lck_mtx_verify(lock);
        lck_mtx_check_preemption(lock);
        thread = current_thread();
        if (atomic_compare_exchange(&lock->lck_mtx_data, 0, LCK_MTX_THREAD_TO_STATE(thread),
                                        memory_order_acquire_smp, FALSE)) {
#if     CONFIG_DTRACE
                LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_ACQUIRE, lock, 0);
#endif /* CONFIG_DTRACE */
                return;
        }
        lck_mtx_lock_contended(lock, thread, FALSE);
}

/*
        This is the slow version of mutex locking.
 */
static void NOINLINE
lck_mtx_lock_contended(lck_mtx_t *lock, thread_t thread, boolean_t interlocked)
{
        thread_t        holding_thread;
        uintptr_t       state;
        int             waiters;

        if (interlocked)
                goto interlock_held;

        /* TODO: short-duration spin for on-core contention <rdar://problem/10234625> */

        /* Loop waiting until I see that the mutex is unowned */
        for ( ; ; ) {
                interlock_lock(lock);
interlock_held:
                state = ordered_load_mtx(lock);
                holding_thread = LCK_MTX_STATE_TO_THREAD(state);
                if (holding_thread == NULL)
                        break;
                ordered_store_mtx(lock, (state | LCK_ILOCK | ARM_LCK_WAITERS)); // Set waiters bit and wait
                lck_mtx_lock_wait(lock, holding_thread);
                /* returns interlock unlocked */
        }

        /* Hooray, I'm the new owner! */
        waiters = lck_mtx_lock_acquire(lock);
        state = LCK_MTX_THREAD_TO_STATE(thread);
        if (waiters != 0)
                state |= ARM_LCK_WAITERS;
#if __SMP__
        state |= LCK_ILOCK;                             // Preserve interlock
        ordered_store_mtx(lock, state); // Set ownership
        interlock_unlock(lock);                 // Release interlock, enable preemption
#else
        ordered_store_mtx(lock, state); // Set ownership
        enable_preemption();
#endif
        load_memory_barrier();

#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_ACQUIRE, lock, 0);
#endif /* CONFIG_DTRACE */
}

/*
 *      Common code for mutex locking as spinlock
 */
static inline void
lck_mtx_lock_spin_internal(lck_mtx_t *lock, boolean_t allow_held_as_mutex)
{
        uintptr_t       state;

        interlock_lock(lock);
        state = ordered_load_mtx(lock);
        if (LCK_MTX_STATE_TO_THREAD(state)) {
                if (allow_held_as_mutex)
                        lck_mtx_lock_contended(lock, current_thread(), TRUE);
                else
                        // "Always" variants can never block. If the lock is held and blocking is not allowed
                        // then someone is mixing always and non-always calls on the same lock, which is
                        // forbidden.
                        panic("Attempting to block on a lock taken as spin-always %p", lock);
                return;
        }
        state &= ARM_LCK_WAITERS;                                               // Preserve waiters bit
        state |= (LCK_MTX_SPIN_TAG | LCK_ILOCK);        // Add spin tag and maintain interlock
        ordered_store_mtx(lock, state);
        load_memory_barrier();

#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_MTX_LOCK_SPIN_ACQUIRE, lock, 0);
#endif /* CONFIG_DTRACE */
}

/*
 *      Routine:        lck_mtx_lock_spin
 */
void
lck_mtx_lock_spin(lck_mtx_t *lock)
{
        lck_mtx_check_preemption(lock);
        lck_mtx_lock_spin_internal(lock, TRUE);
}

/*
 *      Routine:        lck_mtx_lock_spin_always
 */
void
lck_mtx_lock_spin_always(lck_mtx_t *lock)
{
        lck_mtx_lock_spin_internal(lock, FALSE);
}

/*
 *      Routine:        lck_mtx_try_lock
 */
boolean_t
lck_mtx_try_lock(lck_mtx_t *lock)
{
        thread_t        thread = current_thread();

        lck_mtx_verify(lock);
        if (atomic_compare_exchange(&lock->lck_mtx_data, 0, LCK_MTX_THREAD_TO_STATE(thread),
                                        memory_order_acquire_smp, FALSE)) {
#if     CONFIG_DTRACE
                LOCKSTAT_RECORD(LS_LCK_MTX_TRY_LOCK_ACQUIRE, lock, 0);
#endif /* CONFIG_DTRACE */
                return TRUE;
        }
        return lck_mtx_try_lock_contended(lock, thread);
}

static boolean_t NOINLINE
lck_mtx_try_lock_contended(lck_mtx_t *lock, thread_t thread)
{
        thread_t        holding_thread;
        uintptr_t       state;
        int             waiters;

#if     __SMP__
        interlock_lock(lock);
        state = ordered_load_mtx(lock);
        holding_thread = LCK_MTX_STATE_TO_THREAD(state);
        if (holding_thread) {
                interlock_unlock(lock);
                return FALSE;
        }
#else
        disable_preemption_for_thread(thread);
        state = ordered_load_mtx(lock);
        if (state & LCK_ILOCK)
                panic("Unexpected interlock set (%p)", lock);
        holding_thread = LCK_MTX_STATE_TO_THREAD(state);
        if (holding_thread) {
                enable_preemption();
                return FALSE;
        }
        state |= LCK_ILOCK;
        ordered_store_mtx(lock, state);
#endif  // __SMP__
        waiters = lck_mtx_lock_acquire(lock);
        state = LCK_MTX_THREAD_TO_STATE(thread);
        if (waiters != 0)
                state |= ARM_LCK_WAITERS;
#if __SMP__
        state |= LCK_ILOCK;                             // Preserve interlock
        ordered_store_mtx(lock, state); // Set ownership
        interlock_unlock(lock);                 // Release interlock, enable preemption
#else
        ordered_store_mtx(lock, state); // Set ownership
        enable_preemption();
#endif
        load_memory_barrier();
        return TRUE;
}

static inline boolean_t
lck_mtx_try_lock_spin_internal(lck_mtx_t *lock, boolean_t allow_held_as_mutex)
{
        uintptr_t       state;

        if (!interlock_try(lock))
                return FALSE;
        state = ordered_load_mtx(lock);
        if(LCK_MTX_STATE_TO_THREAD(state)) {
                // Lock is held as mutex
                if (allow_held_as_mutex)
                        interlock_unlock(lock);
                else
                        // "Always" variants can never block. If the lock is held as a normal mutex
                        // then someone is mixing always and non-always calls on the same lock, which is
                        // forbidden.
                        panic("Spin-mutex held as full mutex %p", lock);
                return FALSE;
        }
        state &= ARM_LCK_WAITERS;                                               // Preserve waiters bit
        state |= (LCK_MTX_SPIN_TAG | LCK_ILOCK);        // Add spin tag and maintain interlock
        ordered_store_mtx(lock, state);
        load_memory_barrier();

#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_MTX_TRY_SPIN_LOCK_ACQUIRE, lock, 0);
#endif /* CONFIG_DTRACE */
        return TRUE;
}

/*
 *      Routine: lck_mtx_try_lock_spin
 */
boolean_t
lck_mtx_try_lock_spin(lck_mtx_t *lock)
{
        return lck_mtx_try_lock_spin_internal(lock, TRUE);
}

/*
 *      Routine: lck_mtx_try_lock_spin_always
 */
boolean_t
lck_mtx_try_lock_spin_always(lck_mtx_t *lock)
{
        return lck_mtx_try_lock_spin_internal(lock, FALSE);
}



/*
 *      Routine:        lck_mtx_unlock
 */
void
lck_mtx_unlock(lck_mtx_t *lock)
{
        thread_t        thread = current_thread();
        uintptr_t       state;
        boolean_t       ilk_held = FALSE;

        lck_mtx_verify(lock);

        state = ordered_load_mtx(lock);
        if (state & LCK_ILOCK) {
                if(LCK_MTX_STATE_TO_THREAD(state) == (thread_t)LCK_MTX_SPIN_TAG)
                        ilk_held = TRUE;        // Interlock is held by (presumably) this thread
                goto slow_case;
        }
        // Locked as a mutex
        if (atomic_compare_exchange(&lock->lck_mtx_data, LCK_MTX_THREAD_TO_STATE(thread), 0,
                                        memory_order_release_smp, FALSE)) {
#if     CONFIG_DTRACE
                LOCKSTAT_RECORD(LS_LCK_MTX_UNLOCK_RELEASE, lock, 0);
#endif /* CONFIG_DTRACE */
                return;
        }
slow_case:
        lck_mtx_unlock_contended(lock, thread, ilk_held);
}

static void NOINLINE
lck_mtx_unlock_contended(lck_mtx_t *lock, thread_t thread, boolean_t ilk_held)
{
        uintptr_t       state;

        if (ilk_held) {
                state = ordered_load_mtx(lock);
        } else {
#if     __SMP__
                interlock_lock(lock);
                state = ordered_load_mtx(lock);
                if (thread != LCK_MTX_STATE_TO_THREAD(state))
                        panic("lck_mtx_unlock(): Attempt to release lock not owned by thread (%p)", lock);
#else
                disable_preemption_for_thread(thread);
                state = ordered_load_mtx(lock);
                if (state & LCK_ILOCK)
                        panic("lck_mtx_unlock(): Unexpected interlock set (%p)", lock);
                if (thread != LCK_MTX_STATE_TO_THREAD(state))
                        panic("lck_mtx_unlock(): Attempt to release lock not owned by thread (%p)", lock);
                state |= LCK_ILOCK;
                ordered_store_mtx(lock, state);
#endif
                if (state & ARM_LCK_WAITERS) {
                        lck_mtx_unlock_wakeup(lock, thread);
                        state = ordered_load_mtx(lock);
                } else {
            assertf(lock->lck_mtx_pri == 0, "pri=0x%x", lock->lck_mtx_pri);
                }
        }
        state &= ARM_LCK_WAITERS;   /* Clear state, retain waiters bit */
#if __SMP__
        state |= LCK_ILOCK;
        ordered_store_mtx(lock, state);
        interlock_unlock(lock);
#else
        ordered_store_mtx(lock, state);
        enable_preemption();
#endif

#if     CONFIG_DTRACE
        LOCKSTAT_RECORD(LS_LCK_MTX_UNLOCK_RELEASE, lock, 0);
#endif /* CONFIG_DTRACE */
}

/*
 *      Routine:        lck_mtx_assert
 */
void
lck_mtx_assert(lck_mtx_t *lock, unsigned int type)
{
        thread_t        thread, holder;
        uintptr_t       state;

        state = ordered_load_mtx(lock);
        holder = LCK_MTX_STATE_TO_THREAD(state);
        if (holder == (thread_t)LCK_MTX_SPIN_TAG) {
                        // Lock is held in spin mode, owner is unknown.
                return; // Punt
        }
        thread = current_thread();
        if (type == LCK_MTX_ASSERT_OWNED) {
                if (thread != holder)
                        panic("lck_mtx_assert(): mutex (%p) owned", lock);
        } else if (type == LCK_MTX_ASSERT_NOTOWNED) {
                if (thread == holder)
                        panic("lck_mtx_assert(): mutex (%p) not owned", lock);
        } else
                panic("lck_mtx_assert(): invalid arg (%u)", type);
}

/*
 *      Routine:        lck_mtx_ilk_unlock
 */
boolean_t
lck_mtx_ilk_unlock(lck_mtx_t *lock)
{
        interlock_unlock(lock);
        return TRUE;
}

/*
 *      Routine:        lck_mtx_convert_spin
 *
 *      Convert a mutex held for spin into a held full mutex
 */
void
lck_mtx_convert_spin(lck_mtx_t *lock)
{
        thread_t        thread = current_thread();
        uintptr_t       state;
        int                     waiters;

        state = ordered_load_mtx(lock);
        if (LCK_MTX_STATE_TO_THREAD(state) == thread)
                return;         // Already owned as mutex, return
        if ((state & LCK_ILOCK) == 0 || (LCK_MTX_STATE_TO_THREAD(state) != (thread_t)LCK_MTX_SPIN_TAG))
                panic("lck_mtx_convert_spin: Not held as spinlock (%p)", lock);
        state &= ~(LCK_MTX_THREAD_MASK);                // Clear the spin tag
        ordered_store_mtx(lock, state);
        waiters = lck_mtx_lock_acquire(lock);   // Acquire to manage priority boosts
        state = LCK_MTX_THREAD_TO_STATE(thread);
        if (waiters != 0)
                state |= ARM_LCK_WAITERS;
#if __SMP__
        state |= LCK_ILOCK;
        ordered_store_mtx(lock, state);                 // Set ownership
        interlock_unlock(lock);                                 // Release interlock, enable preemption
#else
        ordered_store_mtx(lock, state);                 // Set ownership
        enable_preemption();
#endif
}


/*
 *      Routine:        lck_mtx_destroy
 */
void
lck_mtx_destroy(
                lck_mtx_t * lck,
                lck_grp_t * grp)
{
        if (lck->lck_mtx_type != LCK_MTX_TYPE)
                panic("Destroying invalid mutex %p", lck);
        if (lck->lck_mtx_tag == LCK_MTX_TAG_DESTROYED)
                panic("Destroying previously destroyed lock %p", lck);
        lck_mtx_assert(lck, LCK_MTX_ASSERT_NOTOWNED);
        lck->lck_mtx_tag = LCK_MTX_TAG_DESTROYED;
        lck_grp_lckcnt_decr(grp, LCK_TYPE_MTX);
        lck_grp_deallocate(grp);
        return;
}

/*
 *      Routine:        lck_spin_assert
 */
void
lck_spin_assert(lck_spin_t *lock, unsigned int type)
{
        thread_t        thread, holder;
        uintptr_t       state;

        if (lock->type != LCK_SPIN_TYPE)
                panic("Invalid spinlock %p", lock);

        state = lock->lck_spin_data;
        holder = (thread_t)(state & ~LCK_ILOCK);
        thread = current_thread();
        if (type == LCK_ASSERT_OWNED) {
                if (holder == 0)
                        panic("Lock not owned %p = %lx", lock, state);
                if (holder != thread)
                        panic("Lock not owned by current thread %p = %lx", lock, state);
                if ((state & LCK_ILOCK) == 0)
                        panic("Lock bit not set %p = %lx", lock, state);
        } else if (type == LCK_ASSERT_NOTOWNED) {
                if (holder != 0) {
                        if (holder == thread)
                                panic("Lock owned by current thread %p = %lx", lock, state);
                        else
                                panic("Lock %p owned by thread %p", lock, holder);
                }
                if (state & LCK_ILOCK)
                        panic("Lock bit set %p = %lx", lock, state);
        } else
                panic("lck_spin_assert(): invalid arg (%u)", type);
}

boolean_t
lck_rw_lock_yield_shared(lck_rw_t *lck, boolean_t force_yield)
{
        lck_rw_word_t   word;

        lck_rw_assert(lck, LCK_RW_ASSERT_SHARED);

        word.data = ordered_load_rw(lck);
        if (word.want_excl || word.want_upgrade || force_yield) {
                lck_rw_unlock_shared(lck);
                mutex_pause(2);
                lck_rw_lock_shared(lck);
                return TRUE;
        }

        return FALSE;
}

/*
 * Routine: kdp_lck_mtx_lock_spin_is_acquired
 * NOT SAFE: To be used only by kernel debugger to avoid deadlock.
 */
boolean_t
kdp_lck_mtx_lock_spin_is_acquired(lck_mtx_t *lck)
{
        uintptr_t       state;

        if (not_in_kdp) {
                panic("panic: spinlock acquired check done outside of kernel debugger");
        }
        state = ordered_load_mtx(lck);
        if (state == LCK_MTX_TAG_DESTROYED)
                return FALSE;
        if (LCK_MTX_STATE_TO_THREAD(state) || (state & LCK_ILOCK))
                return TRUE;
        return FALSE;
}

void
kdp_lck_mtx_find_owner(__unused struct waitq * waitq, event64_t event, thread_waitinfo_t * waitinfo)
{
        lck_mtx_t * mutex = LCK_EVENT_TO_MUTEX(event);
        waitinfo->context = VM_KERNEL_UNSLIDE_OR_PERM(mutex);
        uintptr_t state   = ordered_load_mtx(mutex);
        thread_t holder   = LCK_MTX_STATE_TO_THREAD(state);
        if ((uintptr_t)holder == (uintptr_t)LCK_MTX_SPIN_TAG) {
                waitinfo->owner = STACKSHOT_WAITOWNER_MTXSPIN;
        } else {
                assertf(state != (uintptr_t)LCK_MTX_TAG_DESTROYED, "state=0x%llx", (uint64_t)state);
                assertf(state != (uintptr_t)LCK_MTX_TAG_INDIRECT, "state=0x%llx", (uint64_t)state);
                waitinfo->owner = thread_tid(holder);
        }
}

void
kdp_rwlck_find_owner(__unused struct waitq * waitq, event64_t event, thread_waitinfo_t * waitinfo)
{
        lck_rw_t        *rwlck = NULL;
        switch(waitinfo->wait_type) {
                case kThreadWaitKernelRWLockRead:
                        rwlck = READ_EVENT_TO_RWLOCK(event);
                        break;
                case kThreadWaitKernelRWLockWrite:
                case kThreadWaitKernelRWLockUpgrade:
                        rwlck = WRITE_EVENT_TO_RWLOCK(event);
                        break;
                default:
                        panic("%s was called with an invalid blocking type", __FUNCTION__);
                        break;
        }
        waitinfo->context = VM_KERNEL_UNSLIDE_OR_PERM(rwlck);
        waitinfo->owner = thread_tid(rwlck->lck_rw_owner);
}