/*      $NetBSD: kern_mutex_obj.c,v 1.15 2023/10/02 21:03:55 ad Exp $   */

/*-
* Copyright (c) 2008, 2019, 2023 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Andrew Doran.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: kern_mutex_obj.c,v 1.15 2023/10/02 21:03:55 ad Exp $");

#include <sys/param.h>
#include <sys/atomic.h>
#include <sys/mutex.h>
#include <sys/kmem.h>

/* Mutex cache */
#define MUTEX_OBJ_MAGIC 0x5aa3c85d
struct kmutexobj {
       kmutex_t        mo_lock;
       u_int           mo_magic;
       u_int           mo_refcnt;
       uint8_t         mo_pad[COHERENCY_UNIT - sizeof(kmutex_t) -
           sizeof(u_int) * 2];
};

/*
* mutex_obj_alloc:
*
*      Allocate a single lock object, waiting for memory if needed.
*/
kmutex_t *
mutex_obj_alloc(kmutex_type_t type, int ipl)
{
       struct kmutexobj *mo;

       mo = kmem_intr_alloc(sizeof(*mo), KM_SLEEP);
       KASSERT(ALIGNED_POINTER(mo, coherency_unit));
       _mutex_init(&mo->mo_lock, type, ipl,
           (uintptr_t)__builtin_return_address(0));
       mo->mo_magic = MUTEX_OBJ_MAGIC;
       mo->mo_refcnt = 1;

       return (kmutex_t *)mo;
}

/*
* mutex_obj_alloc:
*
*      Allocate a single lock object, failing if no memory available.
*/
kmutex_t *
mutex_obj_tryalloc(kmutex_type_t type, int ipl)
{
       struct kmutexobj *mo;

       mo = kmem_intr_alloc(sizeof(*mo), KM_NOSLEEP);
       KASSERT(ALIGNED_POINTER(mo, coherency_unit));
       if (__predict_true(mo != NULL)) {
               _mutex_init(&mo->mo_lock, type, ipl,
                   (uintptr_t)__builtin_return_address(0));
               mo->mo_magic = MUTEX_OBJ_MAGIC;
               mo->mo_refcnt = 1;
       }

       return (kmutex_t *)mo;
}

/*
* mutex_obj_hold:
*
*      Add a single reference to a lock object.  A reference to the object
*      must already be held, and must be held across this call.
*/
void
mutex_obj_hold(kmutex_t *lock)
{
       struct kmutexobj *mo = (struct kmutexobj *)lock;

       KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
           "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
            __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
       KASSERTMSG(mo->mo_refcnt > 0,
           "%s: lock %p: mo->mo_refcnt (%#x) == 0",
            __func__, mo, mo->mo_refcnt);

       atomic_inc_uint(&mo->mo_refcnt);
}

/*
* mutex_obj_free:
*
*      Drop a reference from a lock object.  If the last reference is being
*      dropped, free the object and return true.  Otherwise, return false.
*/
bool
mutex_obj_free(kmutex_t *lock)
{
       struct kmutexobj *mo = (struct kmutexobj *)lock;

       KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
           "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
            __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
       KASSERTMSG(mo->mo_refcnt > 0,
           "%s: lock %p: mo->mo_refcnt (%#x) == 0",
            __func__, mo, mo->mo_refcnt);

       membar_release();
       if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
               return false;
       }
       membar_acquire();
       mutex_destroy(&mo->mo_lock);
       kmem_intr_free(mo, sizeof(*mo));
       return true;
}

/*
* mutex_obj_refcnt:
*
*      Return the reference count on a lock object.
*/
u_int
mutex_obj_refcnt(kmutex_t *lock)
{
       struct kmutexobj *mo = (struct kmutexobj *)lock;

       return mo->mo_refcnt;
}