1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
|
/*
* CDDL HEADER START
*
* The contents of this file are subject to the terms of the
* Common Development and Distribution License (the "License").
* You may not use this file except in compliance with the License.
*
* You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
* or http://www.opensolaris.org/os/licensing.
* See the License for the specific language governing permissions
* and limitations under the License.
*
* When distributing Covered Code, include this CDDL HEADER in each
* file and include the License file at usr/src/OPENSOLARIS.LICENSE.
* If applicable, add the following below this CDDL HEADER, with the
* fields enclosed by brackets "[]" replaced with your own identifying
* information: Portions Copyright [yyyy] [name of copyright owner]
*
* CDDL HEADER END
*/
/*
* Copyright (c) 2010, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2014, 2015 by Delphix. All rights reserved.
* Copyright 2016 The MathWorks, Inc. All rights reserved.
*/
/*
* A Zero Reference Lock (ZRL) is a reference count that can lock out new
* references only when the count is zero and only without waiting if the count
* is not already zero. It is similar to a read-write lock in that it allows
* multiple readers and only a single writer, but it does not allow a writer to
* block while waiting for readers to exit, and therefore the question of
* reader/writer priority is moot (no WRWANT bit). Since the equivalent of
* rw_enter(&lock, RW_WRITER) is disallowed and only tryenter() is allowed, it
* is perfectly safe for the same reader to acquire the same lock multiple
* times. The fact that a ZRL is reentrant for readers (through multiple calls
* to zrl_add()) makes it convenient for determining whether something is
* actively referenced without the fuss of flagging lock ownership across
* function calls.
*/
#include <sys/zrlock.h>
#include <sys/trace_defs.h>
/*
* A ZRL can be locked only while there are zero references, so ZRL_LOCKED is
* treated as zero references.
*/
#define ZRL_LOCKED -1
#define ZRL_DESTROYED -2
void
zrl_init(zrlock_t *zrl)
{
mutex_init(&zrl->zr_mtx, NULL, MUTEX_DEFAULT, NULL);
zrl->zr_refcount = 0;
cv_init(&zrl->zr_cv, NULL, CV_DEFAULT, NULL);
#ifdef ZFS_DEBUG
zrl->zr_owner = NULL;
zrl->zr_caller = NULL;
#endif
}
void
zrl_destroy(zrlock_t *zrl)
{
ASSERT0(zrl->zr_refcount);
mutex_destroy(&zrl->zr_mtx);
zrl->zr_refcount = ZRL_DESTROYED;
cv_destroy(&zrl->zr_cv);
}
void
zrl_add_impl(zrlock_t *zrl, const char *zc)
{
for (;;) {
uint32_t n = (uint32_t)zrl->zr_refcount;
while (n != ZRL_LOCKED) {
uint32_t cas = atomic_cas_32(
(uint32_t *)&zrl->zr_refcount, n, n + 1);
if (cas == n) {
ASSERT3S((int32_t)n, >=, 0);
#ifdef ZFS_DEBUG
if (zrl->zr_owner == curthread) {
DTRACE_PROBE3(zrlock__reentry,
zrlock_t *, zrl,
kthread_t *, curthread,
uint32_t, n);
}
zrl->zr_owner = curthread;
zrl->zr_caller = zc;
#endif
return;
}
n = cas;
}
mutex_enter(&zrl->zr_mtx);
while (zrl->zr_refcount == ZRL_LOCKED) {
cv_wait(&zrl->zr_cv, &zrl->zr_mtx);
}
mutex_exit(&zrl->zr_mtx);
}
}
void
zrl_remove(zrlock_t *zrl)
{
uint32_t n;
#ifdef ZFS_DEBUG
if (zrl->zr_owner == curthread) {
zrl->zr_owner = NULL;
zrl->zr_caller = NULL;
}
#endif
n = atomic_dec_32_nv((uint32_t *)&zrl->zr_refcount);
ASSERT3S((int32_t)n, >=, 0);
}
int
zrl_tryenter(zrlock_t *zrl)
{
uint32_t n = (uint32_t)zrl->zr_refcount;
if (n == 0) {
uint32_t cas = atomic_cas_32(
(uint32_t *)&zrl->zr_refcount, 0, ZRL_LOCKED);
if (cas == 0) {
#ifdef ZFS_DEBUG
ASSERT3P(zrl->zr_owner, ==, NULL);
zrl->zr_owner = curthread;
#endif
return (1);
}
}
ASSERT3S((int32_t)n, >, ZRL_DESTROYED);
return (0);
}
void
zrl_exit(zrlock_t *zrl)
{
ASSERT3S(zrl->zr_refcount, ==, ZRL_LOCKED);
mutex_enter(&zrl->zr_mtx);
#ifdef ZFS_DEBUG
ASSERT3P(zrl->zr_owner, ==, curthread);
zrl->zr_owner = NULL;
membar_producer(); /* make sure the owner store happens first */
#endif
zrl->zr_refcount = 0;
cv_broadcast(&zrl->zr_cv);
mutex_exit(&zrl->zr_mtx);
}
int
zrl_refcount(zrlock_t *zrl)
{
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
int n = (int)zrl->zr_refcount;
return (n <= 0 ? 0 : n);
}
int
zrl_is_zero(zrlock_t *zrl)
{
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
return (zrl->zr_refcount <= 0);
}
int
zrl_is_locked(zrlock_t *zrl)
{
ASSERT3S(zrl->zr_refcount, >, ZRL_DESTROYED);
return (zrl->zr_refcount == ZRL_LOCKED);
}
#ifdef ZFS_DEBUG
kthread_t *
zrl_owner(zrlock_t *zrl)
{
return (zrl->zr_owner);
}
#endif
#if defined(_KERNEL)
EXPORT_SYMBOL(zrl_add_impl);
EXPORT_SYMBOL(zrl_remove);
#endif
|
