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kern_mutex_obj.c revision 1.5 
      1 /*	$NetBSD: kern_mutex_obj.c,v 1.5 2011/09/27 01:02:38 jym Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2008 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Andrew Doran.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 #include <sys/cdefs.h>
     33 __KERNEL_RCSID(0, "$NetBSD: kern_mutex_obj.c,v 1.5 2011/09/27 01:02:38 jym Exp $");
     34 
     35 #include <sys/param.h>
     36 #include <sys/atomic.h>
     37 #include <sys/mutex.h>
     38 #include <sys/pool.h>
     39 
     40 /* Mutex cache */
     41 #define	MUTEX_OBJ_MAGIC	0x5aa3c85d
     42 struct kmutexobj {
     43 	kmutex_t	mo_lock;
     44 	u_int		mo_magic;
     45 	u_int		mo_refcnt;
     46 };
     47 
     48 static int	mutex_obj_ctor(void *, void *, int);
     49 
     50 static pool_cache_t	mutex_obj_cache		__read_mostly;
     51 
     52 /*
     53  * mutex_obj_init:
     54  *
     55  *	Initialize the mutex object store.
     56  */
     57 void
     58 mutex_obj_init(void)
     59 {
     60 
     61 	mutex_obj_cache = pool_cache_init(sizeof(struct kmutexobj),
     62 	    coherency_unit, 0, 0, "mutex", NULL, IPL_NONE, mutex_obj_ctor,
     63 	    NULL, NULL);
     64 }
     65 
     66 /*
     67  * mutex_obj_ctor:
     68  *
     69  *	Initialize a new lock for the cache.
     70  */
     71 static int
     72 mutex_obj_ctor(void *arg, void *obj, int flags)
     73 {
     74 	struct kmutexobj * mo = obj;
     75 
     76 	mo->mo_magic = MUTEX_OBJ_MAGIC;
     77 
     78 	return 0;
     79 }
     80 
     81 /*
     82  * mutex_obj_alloc:
     83  *
     84  *	Allocate a single lock object.
     85  */
     86 kmutex_t *
     87 mutex_obj_alloc(kmutex_type_t type, int ipl)
     88 {
     89 	struct kmutexobj *mo;
     90 
     91 	mo = pool_cache_get(mutex_obj_cache, PR_WAITOK);
     92 	mutex_init(&mo->mo_lock, type, ipl);
     93 	mo->mo_refcnt = 1;
     94 
     95 	return (kmutex_t *)mo;
     96 }
     97 
     98 /*
     99  * mutex_obj_hold:
    100  *
    101  *	Add a single reference to a lock object.  A reference to the object
    102  *	must already be held, and must be held across this call.
    103  */
    104 void
    105 mutex_obj_hold(kmutex_t *lock)
    106 {
    107 	struct kmutexobj *mo = (struct kmutexobj *)lock;
    108 
    109 	KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
    110 	    "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
    111 	     __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
    112 	KASSERTMSG(mo->mo_refcnt > 0,
    113 	    "%s: lock %p: mo->mo_refcnt (%#x) == 0",
    114 	     __func__, mo, mo->mo_refcnt);
    115 
    116 	atomic_inc_uint(&mo->mo_refcnt);
    117 }
    118 
    119 /*
    120  * mutex_obj_free:
    121  *
    122  *	Drop a reference from a lock object.  If the last reference is being
    123  *	dropped, free the object and return true.  Otherwise, return false.
    124  */
    125 bool
    126 mutex_obj_free(kmutex_t *lock)
    127 {
    128 	struct kmutexobj *mo = (struct kmutexobj *)lock;
    129 
    130 	KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
    131 	    "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
    132 	     __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
    133 	KASSERTMSG(mo->mo_refcnt > 0,
    134 	    "%s: lock %p: mo->mo_refcnt (%#x) == 0",
    135 	     __func__, mo, mo->mo_refcnt);
    136 
    137 	if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
    138 		return false;
    139 	}
    140 	mutex_destroy(&mo->mo_lock);
    141 	pool_cache_put(mutex_obj_cache, mo);
    142 	return true;
    143 }
    144