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925baedd CM |
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> | |
925baedd CM |
19 | #include <linux/pagemap.h> |
20 | #include <linux/spinlock.h> | |
21 | #include <linux/page-flags.h> | |
4881ee5a | 22 | #include <asm/bug.h> |
925baedd CM |
23 | #include "ctree.h" |
24 | #include "extent_io.h" | |
25 | #include "locking.h" | |
26 | ||
48a3b636 | 27 | static void btrfs_assert_tree_read_locked(struct extent_buffer *eb); |
d397712b | 28 | |
b4ce94de | 29 | /* |
bd681513 CM |
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. | |
b4ce94de | 33 | */ |
bd681513 | 34 | void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) |
925baedd | 35 | { |
ea4ebde0 CM |
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; | |
bd681513 CM |
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); | |
b4ce94de | 58 | } |
bd681513 | 59 | return; |
b4ce94de | 60 | } |
f9efa9c7 | 61 | |
b4ce94de | 62 | /* |
bd681513 CM |
63 | * if we currently have a blocking lock, take the spinlock |
64 | * and drop our blocking count | |
b4ce94de | 65 | */ |
bd681513 | 66 | void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) |
b4ce94de | 67 | { |
ea4ebde0 CM |
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 | ||
bd681513 CM |
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); | |
ee863954 DS |
82 | /* |
83 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
84 | */ | |
cbea5ac1 CM |
85 | if (atomic_dec_and_test(&eb->blocking_writers) && |
86 | waitqueue_active(&eb->write_lock_wq)) | |
bd681513 CM |
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); | |
ee863954 DS |
92 | /* |
93 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
94 | */ | |
cbea5ac1 CM |
95 | if (atomic_dec_and_test(&eb->blocking_readers) && |
96 | waitqueue_active(&eb->read_lock_wq)) | |
bd681513 | 97 | wake_up(&eb->read_lock_wq); |
b4ce94de | 98 | } |
bd681513 | 99 | return; |
b4ce94de CM |
100 | } |
101 | ||
102 | /* | |
bd681513 CM |
103 | * take a spinning read lock. This will wait for any blocking |
104 | * writers | |
b4ce94de | 105 | */ |
bd681513 | 106 | void btrfs_tree_read_lock(struct extent_buffer *eb) |
b4ce94de | 107 | { |
bd681513 | 108 | again: |
ea4ebde0 CM |
109 | BUG_ON(!atomic_read(&eb->blocking_writers) && |
110 | current->pid == eb->lock_owner); | |
111 | ||
5b25f70f AJ |
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 | } | |
bd681513 CM |
126 | if (atomic_read(&eb->blocking_writers)) { |
127 | read_unlock(&eb->lock); | |
39f9d028 LB |
128 | wait_event(eb->write_lock_wq, |
129 | atomic_read(&eb->blocking_writers) == 0); | |
bd681513 | 130 | goto again; |
b4ce94de | 131 | } |
bd681513 CM |
132 | atomic_inc(&eb->read_locks); |
133 | atomic_inc(&eb->spinning_readers); | |
b4ce94de CM |
134 | } |
135 | ||
f82c458a CM |
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 | ||
b4ce94de | 156 | /* |
bd681513 CM |
157 | * returns 1 if we get the read lock and 0 if we don't |
158 | * this won't wait for blocking writers | |
b4ce94de | 159 | */ |
bd681513 | 160 | int btrfs_try_tree_read_lock(struct extent_buffer *eb) |
b4ce94de | 161 | { |
bd681513 CM |
162 | if (atomic_read(&eb->blocking_writers)) |
163 | return 0; | |
b4ce94de | 164 | |
ea4ebde0 CM |
165 | if (!read_trylock(&eb->lock)) |
166 | return 0; | |
167 | ||
bd681513 CM |
168 | if (atomic_read(&eb->blocking_writers)) { |
169 | read_unlock(&eb->lock); | |
170 | return 0; | |
b9473439 | 171 | } |
bd681513 CM |
172 | atomic_inc(&eb->read_locks); |
173 | atomic_inc(&eb->spinning_readers); | |
174 | return 1; | |
b4ce94de CM |
175 | } |
176 | ||
177 | /* | |
bd681513 CM |
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 | |
b4ce94de | 180 | */ |
bd681513 | 181 | int btrfs_try_tree_write_lock(struct extent_buffer *eb) |
b4ce94de | 182 | { |
bd681513 CM |
183 | if (atomic_read(&eb->blocking_writers) || |
184 | atomic_read(&eb->blocking_readers)) | |
185 | return 0; | |
ea4ebde0 | 186 | |
f82c458a | 187 | write_lock(&eb->lock); |
bd681513 CM |
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); | |
5b25f70f | 195 | eb->lock_owner = current->pid; |
b4ce94de CM |
196 | return 1; |
197 | } | |
198 | ||
199 | /* | |
bd681513 CM |
200 | * drop a spinning read lock |
201 | */ | |
202 | void btrfs_tree_read_unlock(struct extent_buffer *eb) | |
203 | { | |
ea4ebde0 CM |
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; | |
5b25f70f | 213 | } |
bd681513 CM |
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 | { | |
ea4ebde0 CM |
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; | |
5b25f70f | 235 | } |
bd681513 CM |
236 | btrfs_assert_tree_read_locked(eb); |
237 | WARN_ON(atomic_read(&eb->blocking_readers) == 0); | |
ee863954 DS |
238 | /* |
239 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
240 | */ | |
cbea5ac1 CM |
241 | if (atomic_dec_and_test(&eb->blocking_readers) && |
242 | waitqueue_active(&eb->read_lock_wq)) | |
bd681513 CM |
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 | |
b4ce94de | 250 | */ |
143bede5 | 251 | void btrfs_tree_lock(struct extent_buffer *eb) |
b4ce94de | 252 | { |
166f66d0 | 253 | WARN_ON(eb->lock_owner == current->pid); |
bd681513 CM |
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; | |
f9efa9c7 | 263 | } |
bd681513 CM |
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); | |
5b25f70f | 273 | eb->lock_owner = current->pid; |
925baedd CM |
274 | } |
275 | ||
bd681513 CM |
276 | /* |
277 | * drop a spinning or a blocking write lock. | |
278 | */ | |
143bede5 | 279 | void btrfs_tree_unlock(struct extent_buffer *eb) |
925baedd | 280 | { |
bd681513 CM |
281 | int blockers = atomic_read(&eb->blocking_writers); |
282 | ||
283 | BUG_ON(blockers > 1); | |
284 | ||
285 | btrfs_assert_tree_locked(eb); | |
ea4ebde0 | 286 | eb->lock_owner = 0; |
bd681513 CM |
287 | atomic_dec(&eb->write_locks); |
288 | ||
289 | if (blockers) { | |
290 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
291 | atomic_dec(&eb->blocking_writers); | |
a83342aa DS |
292 | /* |
293 | * Make sure counter is updated before we wake up waiters. | |
294 | */ | |
cbea5ac1 CM |
295 | smp_mb(); |
296 | if (waitqueue_active(&eb->write_lock_wq)) | |
297 | wake_up(&eb->write_lock_wq); | |
bd681513 CM |
298 | } else { |
299 | WARN_ON(atomic_read(&eb->spinning_writers) != 1); | |
300 | atomic_dec(&eb->spinning_writers); | |
301 | write_unlock(&eb->lock); | |
302 | } | |
925baedd CM |
303 | } |
304 | ||
b9447ef8 | 305 | void btrfs_assert_tree_locked(struct extent_buffer *eb) |
925baedd | 306 | { |
bd681513 CM |
307 | BUG_ON(!atomic_read(&eb->write_locks)); |
308 | } | |
309 | ||
48a3b636 | 310 | static void btrfs_assert_tree_read_locked(struct extent_buffer *eb) |
bd681513 CM |
311 | { |
312 | BUG_ON(!atomic_read(&eb->read_locks)); | |
925baedd | 313 | } |