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      1 /*	$NetBSD: kern_rwlock_obj.c,v 1.13 2023/10/02 21:03:55 ad Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 2008, 2009, 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_rwlock_obj.c,v 1.13 2023/10/02 21:03:55 ad Exp $");
     34 
     35 #include <sys/param.h>
     36 #include <sys/atomic.h>
     37 #include <sys/kmem.h>
     38 #include <sys/rwlock.h>
     39 
     40 /* Mutex cache */
     41 #define	RW_OBJ_MAGIC	0x85d3c85d
     42 struct krwobj {
     43 	krwlock_t	ro_lock;
     44 	u_int		ro_magic;
     45 	u_int		ro_refcnt;
     46 	uint8_t		mo_pad[COHERENCY_UNIT - sizeof(krwlock_t) -
     47 	    sizeof(u_int) * 2];
     48 };
     49 
     50 /*
     51  * rw_obj_alloc:
     52  *
     53  *	Allocate a single lock object, waiting for memory if needed.
     54  */
     55 krwlock_t *
     56 rw_obj_alloc(void)
     57 {
     58 	struct krwobj *ro;
     59 
     60 	ro = kmem_intr_alloc(sizeof(*ro), KM_SLEEP);
     61 	KASSERT(ALIGNED_POINTER(ro, coherency_unit));
     62 	_rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0));
     63 	ro->ro_magic = RW_OBJ_MAGIC;
     64 	ro->ro_refcnt = 1;
     65 
     66 	return (krwlock_t *)ro;
     67 }
     68 
     69 /*
     70  * rw_obj_tryalloc:
     71  *
     72  *	Allocate a single lock object, but fail if no memory is available.
     73  */
     74 krwlock_t *
     75 rw_obj_tryalloc(void)
     76 {
     77 	struct krwobj *ro;
     78 
     79 	ro = kmem_intr_alloc(sizeof(*ro), KM_NOSLEEP);
     80 	KASSERT(ALIGNED_POINTER(ro, coherency_unit));
     81 	if (__predict_true(ro != NULL)) {
     82 		_rw_init(&ro->ro_lock, (uintptr_t)__builtin_return_address(0));
     83 		ro->ro_magic = RW_OBJ_MAGIC;
     84 		ro->ro_refcnt = 1;
     85 	}
     86 
     87 	return (krwlock_t *)ro;
     88 }
     89 
     90 /*
     91  * rw_obj_hold:
     92  *
     93  *	Add a single reference to a lock object.  A reference to the object
     94  *	must already be held, and must be held across this call.
     95  */
     96 void
     97 rw_obj_hold(krwlock_t *lock)
     98 {
     99 	struct krwobj *ro = (struct krwobj *)lock;
    100 
    101 	KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
    102 	KASSERT(ro->ro_refcnt > 0);
    103 
    104 	atomic_inc_uint(&ro->ro_refcnt);
    105 }
    106 
    107 /*
    108  * rw_obj_free:
    109  *
    110  *	Drop a reference from a lock object.  If the last reference is being
    111  *	dropped, free the object and return true.  Otherwise, return false.
    112  */
    113 bool
    114 rw_obj_free(krwlock_t *lock)
    115 {
    116 	struct krwobj *ro = (struct krwobj *)lock;
    117 
    118 	KASSERT(ro->ro_magic == RW_OBJ_MAGIC);
    119 	KASSERT(ro->ro_refcnt > 0);
    120 
    121 	membar_release();
    122 	if (atomic_dec_uint_nv(&ro->ro_refcnt) > 0) {
    123 		return false;
    124 	}
    125 	membar_acquire();
    126 	rw_destroy(&ro->ro_lock);
    127 	kmem_intr_free(ro, sizeof(*ro));
    128 	return true;
    129 }
    130 
    131 /*
    132  * rw_obj_refcnt:
    133  *
    134  *	Return the reference count for a lock object.
    135  */
    136 u_int
    137 rw_obj_refcnt(krwlock_t *lock)
    138 {
    139 	struct krwobj *ro = (struct krwobj *)lock;
    140 
    141 	return ro->ro_refcnt;
    142 }
    143