Branch data Line data Source code
1 : : /*
2 : : * Copyright (C) 2008 Oracle. All rights reserved.
3 : : *
4 : : * This program is free software; you can redistribute it and/or
5 : : * modify it under the terms of the GNU General Public
6 : : * License v2 as published by the Free Software Foundation.
7 : : *
8 : : * This program is distributed in the hope that it will be useful,
9 : : * but WITHOUT ANY WARRANTY; without even the implied warranty of
10 : : * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
11 : : * General Public License for more details.
12 : : *
13 : : * You should have received a copy of the GNU General Public
14 : : * License along with this program; if not, write to the
15 : : * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
16 : : * Boston, MA 021110-1307, USA.
17 : : */
18 : : #include <linux/sched.h>
19 : : #include <linux/pagemap.h>
20 : : #include <linux/spinlock.h>
21 : : #include <linux/page-flags.h>
22 : : #include <asm/bug.h>
23 : : #include "ctree.h"
24 : : #include "extent_io.h"
25 : : #include "locking.h"
26 : :
27 : : static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
28 : :
29 : : /*
30 : : * if we currently have a spinning reader or writer lock
31 : : * (indicated by the rw flag) this will bump the count
32 : : * of blocking holders and drop the spinlock.
33 : : */
34 : 0 : void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
35 : : {
36 [ # # ]: 0 : if (eb->lock_nested) {
37 : 0 : read_lock(&eb->lock);
38 [ # # ][ # # ]: 0 : if (eb->lock_nested && current->pid == eb->lock_owner) {
39 : : read_unlock(&eb->lock);
40 : : return;
41 : : }
42 : : read_unlock(&eb->lock);
43 : : }
44 [ # # ]: 0 : if (rw == BTRFS_WRITE_LOCK) {
45 [ # # ]: 0 : if (atomic_read(&eb->blocking_writers) == 0) {
46 [ # # ]: 0 : WARN_ON(atomic_read(&eb->spinning_writers) != 1);
47 : 0 : atomic_dec(&eb->spinning_writers);
48 : : btrfs_assert_tree_locked(eb);
49 : 0 : atomic_inc(&eb->blocking_writers);
50 : : write_unlock(&eb->lock);
51 : : }
52 [ # # ]: 0 : } else if (rw == BTRFS_READ_LOCK) {
53 : : btrfs_assert_tree_read_locked(eb);
54 : 0 : atomic_inc(&eb->blocking_readers);
55 [ # # ]: 0 : WARN_ON(atomic_read(&eb->spinning_readers) == 0);
56 : 0 : atomic_dec(&eb->spinning_readers);
57 : : read_unlock(&eb->lock);
58 : : }
59 : : return;
60 : : }
61 : :
62 : : /*
63 : : * if we currently have a blocking lock, take the spinlock
64 : : * and drop our blocking count
65 : : */
66 : 0 : void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
67 : : {
68 [ # # ]: 0 : if (eb->lock_nested) {
69 : 0 : read_lock(&eb->lock);
70 [ # # ][ # # ]: 0 : if (eb->lock_nested && current->pid == eb->lock_owner) {
71 : : read_unlock(&eb->lock);
72 : : return;
73 : : }
74 : : read_unlock(&eb->lock);
75 : : }
76 [ # # ]: 0 : if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
77 [ # # ]: 0 : BUG_ON(atomic_read(&eb->blocking_writers) != 1);
78 : 0 : write_lock(&eb->lock);
79 [ # # ]: 0 : WARN_ON(atomic_read(&eb->spinning_writers));
80 : 0 : atomic_inc(&eb->spinning_writers);
81 [ # # ][ # # ]: 0 : if (atomic_dec_and_test(&eb->blocking_writers) &&
82 : : waitqueue_active(&eb->write_lock_wq))
83 : 0 : wake_up(&eb->write_lock_wq);
84 [ # # ]: 0 : } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
85 [ # # ]: 0 : BUG_ON(atomic_read(&eb->blocking_readers) == 0);
86 : 0 : read_lock(&eb->lock);
87 : 0 : atomic_inc(&eb->spinning_readers);
88 [ # # ][ # # ]: 0 : if (atomic_dec_and_test(&eb->blocking_readers) &&
89 : : waitqueue_active(&eb->read_lock_wq))
90 : 0 : wake_up(&eb->read_lock_wq);
91 : : }
92 : : return;
93 : : }
94 : :
95 : : /*
96 : : * take a spinning read lock. This will wait for any blocking
97 : : * writers
98 : : */
99 : 0 : void btrfs_tree_read_lock(struct extent_buffer *eb)
100 : : {
101 : : again:
102 : 0 : read_lock(&eb->lock);
103 [ # # ][ # # ]: 0 : if (atomic_read(&eb->blocking_writers) &&
104 : 0 : current->pid == eb->lock_owner) {
105 : : /*
106 : : * This extent is already write-locked by our thread. We allow
107 : : * an additional read lock to be added because it's for the same
108 : : * thread. btrfs_find_all_roots() depends on this as it may be
109 : : * called on a partly (write-)locked tree.
110 : : */
111 [ # # ]: 0 : BUG_ON(eb->lock_nested);
112 : 0 : eb->lock_nested = 1;
113 : : read_unlock(&eb->lock);
114 : 0 : return;
115 : : }
116 [ # # ]: 0 : if (atomic_read(&eb->blocking_writers)) {
117 : : read_unlock(&eb->lock);
118 [ # # ][ # # ]: 0 : wait_event(eb->write_lock_wq,
119 : : atomic_read(&eb->blocking_writers) == 0);
120 : : goto again;
121 : : }
122 : 0 : atomic_inc(&eb->read_locks);
123 : 0 : atomic_inc(&eb->spinning_readers);
124 : : }
125 : :
126 : : /*
127 : : * returns 1 if we get the read lock and 0 if we don't
128 : : * this won't wait for blocking writers
129 : : */
130 : 0 : int btrfs_try_tree_read_lock(struct extent_buffer *eb)
131 : : {
132 [ # # ]: 0 : if (atomic_read(&eb->blocking_writers))
133 : : return 0;
134 : :
135 : 0 : read_lock(&eb->lock);
136 [ # # ]: 0 : if (atomic_read(&eb->blocking_writers)) {
137 : : read_unlock(&eb->lock);
138 : 0 : return 0;
139 : : }
140 : 0 : atomic_inc(&eb->read_locks);
141 : 0 : atomic_inc(&eb->spinning_readers);
142 : 0 : return 1;
143 : : }
144 : :
145 : : /*
146 : : * returns 1 if we get the read lock and 0 if we don't
147 : : * this won't wait for blocking writers or readers
148 : : */
149 : 0 : int btrfs_try_tree_write_lock(struct extent_buffer *eb)
150 : : {
151 [ # # ][ # # ]: 0 : if (atomic_read(&eb->blocking_writers) ||
152 : 0 : atomic_read(&eb->blocking_readers))
153 : : return 0;
154 : 0 : write_lock(&eb->lock);
155 [ # # ][ # # ]: 0 : if (atomic_read(&eb->blocking_writers) ||
156 : 0 : atomic_read(&eb->blocking_readers)) {
157 : : write_unlock(&eb->lock);
158 : 0 : return 0;
159 : : }
160 : 0 : atomic_inc(&eb->write_locks);
161 : 0 : atomic_inc(&eb->spinning_writers);
162 : 0 : eb->lock_owner = current->pid;
163 : 0 : return 1;
164 : : }
165 : :
166 : : /*
167 : : * drop a spinning read lock
168 : : */
169 : 0 : void btrfs_tree_read_unlock(struct extent_buffer *eb)
170 : : {
171 [ # # ]: 0 : if (eb->lock_nested) {
172 : 0 : read_lock(&eb->lock);
173 [ # # ][ # # ]: 0 : if (eb->lock_nested && current->pid == eb->lock_owner) {
174 : 0 : eb->lock_nested = 0;
175 : : read_unlock(&eb->lock);
176 : 0 : return;
177 : : }
178 : : read_unlock(&eb->lock);
179 : : }
180 : : btrfs_assert_tree_read_locked(eb);
181 [ # # ]: 0 : WARN_ON(atomic_read(&eb->spinning_readers) == 0);
182 : 0 : atomic_dec(&eb->spinning_readers);
183 : 0 : atomic_dec(&eb->read_locks);
184 : : read_unlock(&eb->lock);
185 : : }
186 : :
187 : : /*
188 : : * drop a blocking read lock
189 : : */
190 : 0 : void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
191 : : {
192 [ # # ]: 0 : if (eb->lock_nested) {
193 : 0 : read_lock(&eb->lock);
194 [ # # ][ # # ]: 0 : if (eb->lock_nested && current->pid == eb->lock_owner) {
195 : 0 : eb->lock_nested = 0;
196 : : read_unlock(&eb->lock);
197 : 0 : return;
198 : : }
199 : : read_unlock(&eb->lock);
200 : : }
201 : : btrfs_assert_tree_read_locked(eb);
202 [ # # ]: 0 : WARN_ON(atomic_read(&eb->blocking_readers) == 0);
203 [ # # ][ # # ]: 0 : if (atomic_dec_and_test(&eb->blocking_readers) &&
204 : : waitqueue_active(&eb->read_lock_wq))
205 : 0 : wake_up(&eb->read_lock_wq);
206 : 0 : atomic_dec(&eb->read_locks);
207 : : }
208 : :
209 : : /*
210 : : * take a spinning write lock. This will wait for both
211 : : * blocking readers or writers
212 : : */
213 : 0 : void btrfs_tree_lock(struct extent_buffer *eb)
214 : : {
215 : : again:
216 [ # # ][ # # ]: 0 : wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
217 [ # # ][ # # ]: 0 : wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
218 : 0 : write_lock(&eb->lock);
219 [ # # ]: 0 : if (atomic_read(&eb->blocking_readers)) {
220 : : write_unlock(&eb->lock);
221 [ # # ][ # # ]: 0 : wait_event(eb->read_lock_wq,
222 : : atomic_read(&eb->blocking_readers) == 0);
223 : : goto again;
224 : : }
225 [ # # ]: 0 : if (atomic_read(&eb->blocking_writers)) {
226 : : write_unlock(&eb->lock);
227 [ # # ][ # # ]: 0 : wait_event(eb->write_lock_wq,
228 : : atomic_read(&eb->blocking_writers) == 0);
229 : : goto again;
230 : : }
231 [ # # ]: 0 : WARN_ON(atomic_read(&eb->spinning_writers));
232 : 0 : atomic_inc(&eb->spinning_writers);
233 : 0 : atomic_inc(&eb->write_locks);
234 : 0 : eb->lock_owner = current->pid;
235 : 0 : }
236 : :
237 : : /*
238 : : * drop a spinning or a blocking write lock.
239 : : */
240 : 0 : void btrfs_tree_unlock(struct extent_buffer *eb)
241 : : {
242 : 0 : int blockers = atomic_read(&eb->blocking_writers);
243 : :
244 [ # # ]: 0 : BUG_ON(blockers > 1);
245 : :
246 : : btrfs_assert_tree_locked(eb);
247 : 0 : atomic_dec(&eb->write_locks);
248 : :
249 [ # # ]: 0 : if (blockers) {
250 [ # # ]: 0 : WARN_ON(atomic_read(&eb->spinning_writers));
251 : 0 : atomic_dec(&eb->blocking_writers);
252 : 0 : smp_mb();
253 [ # # ]: 0 : if (waitqueue_active(&eb->write_lock_wq))
254 : 0 : wake_up(&eb->write_lock_wq);
255 : : } else {
256 [ # # ]: 0 : WARN_ON(atomic_read(&eb->spinning_writers) != 1);
257 : 0 : atomic_dec(&eb->spinning_writers);
258 : : write_unlock(&eb->lock);
259 : : }
260 : 0 : }
261 : :
262 : 0 : void btrfs_assert_tree_locked(struct extent_buffer *eb)
263 : : {
264 [ # # ][ # # ]: 0 : BUG_ON(!atomic_read(&eb->write_locks));
[ # # ]
265 : 0 : }
266 : :
267 : : static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
268 : : {
269 [ # # ][ # # ]: 0 : BUG_ON(!atomic_read(&eb->read_locks));
[ # # ]
270 : : }
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