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      1 /*	$NetBSD: kern_mutex_obj.c,v 1.15 2023/10/02 21:03:55 ad Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2008, 2019, 2023 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 1.15 2023/10/02 21:03:55 ad Exp $");
     34 
     35 #include <sys/param.h>
     36 #include <sys/atomic.h>
     37 #include <sys/mutex.h>
     38 #include <sys/kmem.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 	uint8_t		mo_pad[COHERENCY_UNIT - sizeof(kmutex_t) -
     47 	    sizeof(u_int) * 2];
     48 };
     49 
     50 /*
     51  * mutex_obj_alloc:
     52  *
     53  *	Allocate a single lock object, waiting for memory if needed.
     54  */
     55 kmutex_t *
     56 mutex_obj_alloc(kmutex_type_t type, int ipl)
     57 {
     58 	struct kmutexobj *mo;
     59 
     60 	mo = kmem_intr_alloc(sizeof(*mo), KM_SLEEP);
     61 	KASSERT(ALIGNED_POINTER(mo, coherency_unit));
     62 	_mutex_init(&mo->mo_lock, type, ipl,
     63 	    (uintptr_t)__builtin_return_address(0));
     64 	mo->mo_magic = MUTEX_OBJ_MAGIC;
     65 	mo->mo_refcnt = 1;
     66 
     67 	return (kmutex_t *)mo;
     68 }
     69 
     70 /*
     71  * mutex_obj_alloc:
     72  *
     73  *	Allocate a single lock object, failing if no memory available.
     74  */
     75 kmutex_t *
     76 mutex_obj_tryalloc(kmutex_type_t type, int ipl)
     77 {
     78 	struct kmutexobj *mo;
     79 
     80 	mo = kmem_intr_alloc(sizeof(*mo), KM_NOSLEEP);
     81 	KASSERT(ALIGNED_POINTER(mo, coherency_unit));
     82 	if (__predict_true(mo != NULL)) {
     83 		_mutex_init(&mo->mo_lock, type, ipl,
     84 		    (uintptr_t)__builtin_return_address(0));
     85 		mo->mo_magic = MUTEX_OBJ_MAGIC;
     86 		mo->mo_refcnt = 1;
     87 	}
     88 
     89 	return (kmutex_t *)mo;
     90 }
     91 
     92 /*
     93  * mutex_obj_hold:
     94  *
     95  *	Add a single reference to a lock object.  A reference to the object
     96  *	must already be held, and must be held across this call.
     97  */
     98 void
     99 mutex_obj_hold(kmutex_t *lock)
    100 {
    101 	struct kmutexobj *mo = (struct kmutexobj *)lock;
    102 
    103 	KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
    104 	    "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
    105 	     __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
    106 	KASSERTMSG(mo->mo_refcnt > 0,
    107 	    "%s: lock %p: mo->mo_refcnt (%#x) == 0",
    108 	     __func__, mo, mo->mo_refcnt);
    109 
    110 	atomic_inc_uint(&mo->mo_refcnt);
    111 }
    112 
    113 /*
    114  * mutex_obj_free:
    115  *
    116  *	Drop a reference from a lock object.  If the last reference is being
    117  *	dropped, free the object and return true.  Otherwise, return false.
    118  */
    119 bool
    120 mutex_obj_free(kmutex_t *lock)
    121 {
    122 	struct kmutexobj *mo = (struct kmutexobj *)lock;
    123 
    124 	KASSERTMSG(mo->mo_magic == MUTEX_OBJ_MAGIC,
    125 	    "%s: lock %p: mo->mo_magic (%#x) != MUTEX_OBJ_MAGIC (%#x)",
    126 	     __func__, mo, mo->mo_magic, MUTEX_OBJ_MAGIC);
    127 	KASSERTMSG(mo->mo_refcnt > 0,
    128 	    "%s: lock %p: mo->mo_refcnt (%#x) == 0",
    129 	     __func__, mo, mo->mo_refcnt);
    130 
    131 	membar_release();
    132 	if (atomic_dec_uint_nv(&mo->mo_refcnt) > 0) {
    133 		return false;
    134 	}
    135 	membar_acquire();
    136 	mutex_destroy(&mo->mo_lock);
    137 	kmem_intr_free(mo, sizeof(*mo));
    138 	return true;
    139 }
    140 
    141 /*
    142  * mutex_obj_refcnt:
    143  *
    144  *	Return the reference count on a lock object.
    145  */
    146 u_int
    147 mutex_obj_refcnt(kmutex_t *lock)
    148 {
    149 	struct kmutexobj *mo = (struct kmutexobj *)lock;
    150 
    151 	return mo->mo_refcnt;
    152 }
    153