]>
Commit | Line | Data |
---|---|---|
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 | void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) | |
35 | { | |
36 | /* | |
37 | * no lock is required. The lock owner may change if | |
38 | * we have a read lock, but it won't change to or away | |
39 | * from us. If we have the write lock, we are the owner | |
40 | * and it'll never change. | |
41 | */ | |
42 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
43 | return; | |
44 | if (rw == BTRFS_WRITE_LOCK) { | |
45 | if (atomic_read(&eb->blocking_writers) == 0) { | |
46 | WARN_ON(atomic_read(&eb->spinning_writers) != 1); | |
47 | atomic_dec(&eb->spinning_writers); | |
48 | btrfs_assert_tree_locked(eb); | |
49 | atomic_inc(&eb->blocking_writers); | |
50 | write_unlock(&eb->lock); | |
51 | } | |
52 | } else if (rw == BTRFS_READ_LOCK) { | |
53 | btrfs_assert_tree_read_locked(eb); | |
54 | atomic_inc(&eb->blocking_readers); | |
55 | WARN_ON(atomic_read(&eb->spinning_readers) == 0); | |
56 | 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 | void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) | |
67 | { | |
68 | /* | |
69 | * no lock is required. The lock owner may change if | |
70 | * we have a read lock, but it won't change to or away | |
71 | * from us. If we have the write lock, we are the owner | |
72 | * and it'll never change. | |
73 | */ | |
74 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
75 | return; | |
76 | ||
77 | if (rw == BTRFS_WRITE_LOCK_BLOCKING) { | |
78 | BUG_ON(atomic_read(&eb->blocking_writers) != 1); | |
79 | write_lock(&eb->lock); | |
80 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
81 | atomic_inc(&eb->spinning_writers); | |
82 | /* | |
83 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
84 | */ | |
85 | if (atomic_dec_and_test(&eb->blocking_writers) && | |
86 | waitqueue_active(&eb->write_lock_wq)) | |
87 | wake_up(&eb->write_lock_wq); | |
88 | } else if (rw == BTRFS_READ_LOCK_BLOCKING) { | |
89 | BUG_ON(atomic_read(&eb->blocking_readers) == 0); | |
90 | read_lock(&eb->lock); | |
91 | atomic_inc(&eb->spinning_readers); | |
92 | /* | |
93 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
94 | */ | |
95 | if (atomic_dec_and_test(&eb->blocking_readers) && | |
96 | waitqueue_active(&eb->read_lock_wq)) | |
97 | wake_up(&eb->read_lock_wq); | |
98 | } | |
99 | return; | |
100 | } | |
101 | ||
102 | /* | |
103 | * take a spinning read lock. This will wait for any blocking | |
104 | * writers | |
105 | */ | |
106 | void btrfs_tree_read_lock(struct extent_buffer *eb) | |
107 | { | |
108 | again: | |
109 | BUG_ON(!atomic_read(&eb->blocking_writers) && | |
110 | current->pid == eb->lock_owner); | |
111 | ||
112 | read_lock(&eb->lock); | |
113 | if (atomic_read(&eb->blocking_writers) && | |
114 | current->pid == eb->lock_owner) { | |
115 | /* | |
116 | * This extent is already write-locked by our thread. We allow | |
117 | * an additional read lock to be added because it's for the same | |
118 | * thread. btrfs_find_all_roots() depends on this as it may be | |
119 | * called on a partly (write-)locked tree. | |
120 | */ | |
121 | BUG_ON(eb->lock_nested); | |
122 | eb->lock_nested = 1; | |
123 | read_unlock(&eb->lock); | |
124 | return; | |
125 | } | |
126 | if (atomic_read(&eb->blocking_writers)) { | |
127 | read_unlock(&eb->lock); | |
128 | wait_event(eb->write_lock_wq, | |
129 | atomic_read(&eb->blocking_writers) == 0); | |
130 | goto again; | |
131 | } | |
132 | atomic_inc(&eb->read_locks); | |
133 | atomic_inc(&eb->spinning_readers); | |
134 | } | |
135 | ||
136 | /* | |
137 | * take a spinning read lock. | |
138 | * returns 1 if we get the read lock and 0 if we don't | |
139 | * this won't wait for blocking writers | |
140 | */ | |
141 | int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) | |
142 | { | |
143 | if (atomic_read(&eb->blocking_writers)) | |
144 | return 0; | |
145 | ||
146 | read_lock(&eb->lock); | |
147 | if (atomic_read(&eb->blocking_writers)) { | |
148 | read_unlock(&eb->lock); | |
149 | return 0; | |
150 | } | |
151 | atomic_inc(&eb->read_locks); | |
152 | atomic_inc(&eb->spinning_readers); | |
153 | return 1; | |
154 | } | |
155 | ||
156 | /* | |
157 | * returns 1 if we get the read lock and 0 if we don't | |
158 | * this won't wait for blocking writers | |
159 | */ | |
160 | int btrfs_try_tree_read_lock(struct extent_buffer *eb) | |
161 | { | |
162 | if (atomic_read(&eb->blocking_writers)) | |
163 | return 0; | |
164 | ||
165 | if (!read_trylock(&eb->lock)) | |
166 | return 0; | |
167 | ||
168 | if (atomic_read(&eb->blocking_writers)) { | |
169 | read_unlock(&eb->lock); | |
170 | return 0; | |
171 | } | |
172 | atomic_inc(&eb->read_locks); | |
173 | atomic_inc(&eb->spinning_readers); | |
174 | return 1; | |
175 | } | |
176 | ||
177 | /* | |
178 | * returns 1 if we get the read lock and 0 if we don't | |
179 | * this won't wait for blocking writers or readers | |
180 | */ | |
181 | int btrfs_try_tree_write_lock(struct extent_buffer *eb) | |
182 | { | |
183 | if (atomic_read(&eb->blocking_writers) || | |
184 | atomic_read(&eb->blocking_readers)) | |
185 | return 0; | |
186 | ||
187 | write_lock(&eb->lock); | |
188 | if (atomic_read(&eb->blocking_writers) || | |
189 | atomic_read(&eb->blocking_readers)) { | |
190 | write_unlock(&eb->lock); | |
191 | return 0; | |
192 | } | |
193 | atomic_inc(&eb->write_locks); | |
194 | atomic_inc(&eb->spinning_writers); | |
195 | eb->lock_owner = current->pid; | |
196 | return 1; | |
197 | } | |
198 | ||
199 | /* | |
200 | * drop a spinning read lock | |
201 | */ | |
202 | void btrfs_tree_read_unlock(struct extent_buffer *eb) | |
203 | { | |
204 | /* | |
205 | * if we're nested, we have the write lock. No new locking | |
206 | * is needed as long as we are the lock owner. | |
207 | * The write unlock will do a barrier for us, and the lock_nested | |
208 | * field only matters to the lock owner. | |
209 | */ | |
210 | if (eb->lock_nested && current->pid == eb->lock_owner) { | |
211 | eb->lock_nested = 0; | |
212 | return; | |
213 | } | |
214 | btrfs_assert_tree_read_locked(eb); | |
215 | WARN_ON(atomic_read(&eb->spinning_readers) == 0); | |
216 | atomic_dec(&eb->spinning_readers); | |
217 | atomic_dec(&eb->read_locks); | |
218 | read_unlock(&eb->lock); | |
219 | } | |
220 | ||
221 | /* | |
222 | * drop a blocking read lock | |
223 | */ | |
224 | void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb) | |
225 | { | |
226 | /* | |
227 | * if we're nested, we have the write lock. No new locking | |
228 | * is needed as long as we are the lock owner. | |
229 | * The write unlock will do a barrier for us, and the lock_nested | |
230 | * field only matters to the lock owner. | |
231 | */ | |
232 | if (eb->lock_nested && current->pid == eb->lock_owner) { | |
233 | eb->lock_nested = 0; | |
234 | return; | |
235 | } | |
236 | btrfs_assert_tree_read_locked(eb); | |
237 | WARN_ON(atomic_read(&eb->blocking_readers) == 0); | |
238 | /* | |
239 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
240 | */ | |
241 | if (atomic_dec_and_test(&eb->blocking_readers) && | |
242 | waitqueue_active(&eb->read_lock_wq)) | |
243 | wake_up(&eb->read_lock_wq); | |
244 | atomic_dec(&eb->read_locks); | |
245 | } | |
246 | ||
247 | /* | |
248 | * take a spinning write lock. This will wait for both | |
249 | * blocking readers or writers | |
250 | */ | |
251 | void btrfs_tree_lock(struct extent_buffer *eb) | |
252 | { | |
253 | WARN_ON(eb->lock_owner == current->pid); | |
254 | again: | |
255 | wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0); | |
256 | wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); | |
257 | write_lock(&eb->lock); | |
258 | if (atomic_read(&eb->blocking_readers)) { | |
259 | write_unlock(&eb->lock); | |
260 | wait_event(eb->read_lock_wq, | |
261 | atomic_read(&eb->blocking_readers) == 0); | |
262 | goto again; | |
263 | } | |
264 | if (atomic_read(&eb->blocking_writers)) { | |
265 | write_unlock(&eb->lock); | |
266 | wait_event(eb->write_lock_wq, | |
267 | atomic_read(&eb->blocking_writers) == 0); | |
268 | goto again; | |
269 | } | |
270 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
271 | atomic_inc(&eb->spinning_writers); | |
272 | atomic_inc(&eb->write_locks); | |
273 | eb->lock_owner = current->pid; | |
274 | } | |
275 | ||
276 | /* | |
277 | * drop a spinning or a blocking write lock. | |
278 | */ | |
279 | void btrfs_tree_unlock(struct extent_buffer *eb) | |
280 | { | |
281 | int blockers = atomic_read(&eb->blocking_writers); | |
282 | ||
283 | BUG_ON(blockers > 1); | |
284 | ||
285 | btrfs_assert_tree_locked(eb); | |
286 | eb->lock_owner = 0; | |
287 | atomic_dec(&eb->write_locks); | |
288 | ||
289 | if (blockers) { | |
290 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
291 | atomic_dec(&eb->blocking_writers); | |
292 | /* | |
293 | * Make sure counter is updated before we wake up waiters. | |
294 | */ | |
295 | smp_mb(); | |
296 | if (waitqueue_active(&eb->write_lock_wq)) | |
297 | wake_up(&eb->write_lock_wq); | |
298 | } else { | |
299 | WARN_ON(atomic_read(&eb->spinning_writers) != 1); | |
300 | atomic_dec(&eb->spinning_writers); | |
301 | write_unlock(&eb->lock); | |
302 | } | |
303 | } | |
304 | ||
305 | void btrfs_assert_tree_locked(struct extent_buffer *eb) | |
306 | { | |
307 | BUG_ON(!atomic_read(&eb->write_locks)); | |
308 | } | |
309 | ||
310 | static void btrfs_assert_tree_read_locked(struct extent_buffer *eb) | |
311 | { | |
312 | BUG_ON(!atomic_read(&eb->read_locks)); | |
313 | } |