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      1 /*	$NetBSD: kref.h,v 1.14 2023/02/24 11:02:06 riastradh Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2013 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Taylor R. Campbell.
      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 #ifndef _LINUX_KREF_H_
     33 #define _LINUX_KREF_H_
     34 
     35 #include <sys/types.h>
     36 #include <sys/atomic.h>
     37 #include <sys/systm.h>
     38 
     39 #include <linux/atomic.h>
     40 #include <linux/refcount.h>
     41 #include <linux/mutex.h>
     42 #include <linux/spinlock.h>
     43 
     44 struct kref {
     45 	unsigned int kr_count;
     46 };
     47 
     48 static inline void
     49 kref_init(struct kref *kref)
     50 {
     51 	atomic_store_relaxed(&kref->kr_count, 1);
     52 }
     53 
     54 static inline void
     55 kref_get(struct kref *kref)
     56 {
     57 	const unsigned int count __unused =
     58 	    atomic_inc_uint_nv(&kref->kr_count);
     59 
     60 	KASSERTMSG((count > 1), "getting released kref");
     61 }
     62 
     63 static inline bool
     64 kref_get_unless_zero(struct kref *kref)
     65 {
     66 	unsigned count;
     67 
     68 	do {
     69 		count = atomic_load_relaxed(&kref->kr_count);
     70 		if ((count == 0) || (count == UINT_MAX))
     71 			return false;
     72 	} while (atomic_cas_uint(&kref->kr_count, count, (count + 1)) !=
     73 	    count);
     74 
     75 	return true;
     76 }
     77 
     78 static inline int
     79 kref_sub(struct kref *kref, unsigned int count, void (*release)(struct kref *))
     80 {
     81 	unsigned int old, new;
     82 
     83 	membar_release();
     84 
     85 	do {
     86 		old = atomic_load_relaxed(&kref->kr_count);
     87 		KASSERTMSG((count <= old), "overreleasing kref: %u - %u",
     88 		    old, count);
     89 		new = (old - count);
     90 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
     91 
     92 	if (new == 0) {
     93 		membar_acquire();
     94 		(*release)(kref);
     95 		return 1;
     96 	}
     97 
     98 	return 0;
     99 }
    100 
    101 static inline int
    102 kref_put_lock(struct kref *kref, void (*release)(struct kref *),
    103     spinlock_t *interlock)
    104 {
    105 	unsigned int old, new;
    106 
    107 	membar_release();
    108 
    109 	do {
    110 		old = atomic_load_relaxed(&kref->kr_count);
    111 		KASSERT(old > 0);
    112 		if (old == 1) {
    113 			spin_lock(interlock);
    114 			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
    115 				membar_acquire();
    116 				(*release)(kref);
    117 				return 1;
    118 			}
    119 			spin_unlock(interlock);
    120 			return 0;
    121 		}
    122 		new = (old - 1);
    123 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
    124 
    125 	return 0;
    126 }
    127 
    128 static inline int
    129 kref_put(struct kref *kref, void (*release)(struct kref *))
    130 {
    131 
    132 	return kref_sub(kref, 1, release);
    133 }
    134 
    135 static inline int
    136 kref_put_mutex(struct kref *kref, void (*release)(struct kref *),
    137     struct mutex *interlock)
    138 {
    139 	unsigned int old, new;
    140 
    141 	membar_release();
    142 
    143 	do {
    144 		old = atomic_load_relaxed(&kref->kr_count);
    145 		KASSERT(old > 0);
    146 		if (old == 1) {
    147 			mutex_lock(interlock);
    148 			if (atomic_add_int_nv(&kref->kr_count, -1) == 0) {
    149 				membar_acquire();
    150 				(*release)(kref);
    151 				return 1;
    152 			}
    153 			mutex_unlock(interlock);
    154 			return 0;
    155 		}
    156 		new = (old - 1);
    157 	} while (atomic_cas_uint(&kref->kr_count, old, new) != old);
    158 
    159 	return 0;
    160 }
    161 
    162 static inline unsigned
    163 kref_read(const struct kref *kref)
    164 {
    165 
    166 	return atomic_load_relaxed(&kref->kr_count);
    167 }
    168 
    169 /*
    170  * Not native to Linux.  Mostly used for assertions...
    171  */
    172 
    173 static inline bool
    174 kref_referenced_p(struct kref *kref)
    175 {
    176 
    177 	return (0 < kref->kr_count);
    178 }
    179 
    180 static inline bool
    181 kref_exclusive_p(struct kref *kref)
    182 {
    183 
    184 	KASSERT(0 < kref->kr_count);
    185 	return (kref->kr_count == 1);
    186 }
    187 
    188 #endif  /* _LINUX_KREF_H_ */
    189