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c1d7c514 | 1 | // SPDX-License-Identifier: GPL-2.0 |
925baedd CM |
2 | /* |
3 | * Copyright (C) 2008 Oracle. All rights reserved. | |
925baedd | 4 | */ |
c1d7c514 | 5 | |
925baedd | 6 | #include <linux/sched.h> |
925baedd CM |
7 | #include <linux/pagemap.h> |
8 | #include <linux/spinlock.h> | |
9 | #include <linux/page-flags.h> | |
4881ee5a | 10 | #include <asm/bug.h> |
925baedd CM |
11 | #include "ctree.h" |
12 | #include "extent_io.h" | |
13 | #include "locking.h" | |
14 | ||
48a3b636 | 15 | static void btrfs_assert_tree_read_locked(struct extent_buffer *eb); |
d397712b | 16 | |
b4ce94de | 17 | /* |
bd681513 CM |
18 | * if we currently have a spinning reader or writer lock |
19 | * (indicated by the rw flag) this will bump the count | |
20 | * of blocking holders and drop the spinlock. | |
b4ce94de | 21 | */ |
bd681513 | 22 | void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) |
925baedd | 23 | { |
ea4ebde0 CM |
24 | /* |
25 | * no lock is required. The lock owner may change if | |
26 | * we have a read lock, but it won't change to or away | |
27 | * from us. If we have the write lock, we are the owner | |
28 | * and it'll never change. | |
29 | */ | |
30 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
31 | return; | |
bd681513 CM |
32 | if (rw == BTRFS_WRITE_LOCK) { |
33 | if (atomic_read(&eb->blocking_writers) == 0) { | |
34 | WARN_ON(atomic_read(&eb->spinning_writers) != 1); | |
35 | atomic_dec(&eb->spinning_writers); | |
36 | btrfs_assert_tree_locked(eb); | |
37 | atomic_inc(&eb->blocking_writers); | |
38 | write_unlock(&eb->lock); | |
39 | } | |
40 | } else if (rw == BTRFS_READ_LOCK) { | |
41 | btrfs_assert_tree_read_locked(eb); | |
42 | atomic_inc(&eb->blocking_readers); | |
43 | WARN_ON(atomic_read(&eb->spinning_readers) == 0); | |
44 | atomic_dec(&eb->spinning_readers); | |
45 | read_unlock(&eb->lock); | |
b4ce94de | 46 | } |
b4ce94de | 47 | } |
f9efa9c7 | 48 | |
b4ce94de | 49 | /* |
bd681513 CM |
50 | * if we currently have a blocking lock, take the spinlock |
51 | * and drop our blocking count | |
b4ce94de | 52 | */ |
bd681513 | 53 | void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) |
b4ce94de | 54 | { |
ea4ebde0 CM |
55 | /* |
56 | * no lock is required. The lock owner may change if | |
57 | * we have a read lock, but it won't change to or away | |
58 | * from us. If we have the write lock, we are the owner | |
59 | * and it'll never change. | |
60 | */ | |
61 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
62 | return; | |
63 | ||
bd681513 CM |
64 | if (rw == BTRFS_WRITE_LOCK_BLOCKING) { |
65 | BUG_ON(atomic_read(&eb->blocking_writers) != 1); | |
66 | write_lock(&eb->lock); | |
67 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
68 | atomic_inc(&eb->spinning_writers); | |
ee863954 DS |
69 | /* |
70 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
71 | */ | |
cbea5ac1 CM |
72 | if (atomic_dec_and_test(&eb->blocking_writers) && |
73 | waitqueue_active(&eb->write_lock_wq)) | |
bd681513 CM |
74 | wake_up(&eb->write_lock_wq); |
75 | } else if (rw == BTRFS_READ_LOCK_BLOCKING) { | |
76 | BUG_ON(atomic_read(&eb->blocking_readers) == 0); | |
77 | read_lock(&eb->lock); | |
78 | atomic_inc(&eb->spinning_readers); | |
ee863954 DS |
79 | /* |
80 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
81 | */ | |
cbea5ac1 CM |
82 | if (atomic_dec_and_test(&eb->blocking_readers) && |
83 | waitqueue_active(&eb->read_lock_wq)) | |
bd681513 | 84 | wake_up(&eb->read_lock_wq); |
b4ce94de | 85 | } |
b4ce94de CM |
86 | } |
87 | ||
88 | /* | |
bd681513 CM |
89 | * take a spinning read lock. This will wait for any blocking |
90 | * writers | |
b4ce94de | 91 | */ |
bd681513 | 92 | void btrfs_tree_read_lock(struct extent_buffer *eb) |
b4ce94de | 93 | { |
bd681513 | 94 | again: |
ea4ebde0 CM |
95 | BUG_ON(!atomic_read(&eb->blocking_writers) && |
96 | current->pid == eb->lock_owner); | |
97 | ||
5b25f70f AJ |
98 | read_lock(&eb->lock); |
99 | if (atomic_read(&eb->blocking_writers) && | |
100 | current->pid == eb->lock_owner) { | |
101 | /* | |
102 | * This extent is already write-locked by our thread. We allow | |
103 | * an additional read lock to be added because it's for the same | |
104 | * thread. btrfs_find_all_roots() depends on this as it may be | |
105 | * called on a partly (write-)locked tree. | |
106 | */ | |
107 | BUG_ON(eb->lock_nested); | |
108 | eb->lock_nested = 1; | |
109 | read_unlock(&eb->lock); | |
110 | return; | |
111 | } | |
bd681513 CM |
112 | if (atomic_read(&eb->blocking_writers)) { |
113 | read_unlock(&eb->lock); | |
39f9d028 LB |
114 | wait_event(eb->write_lock_wq, |
115 | atomic_read(&eb->blocking_writers) == 0); | |
bd681513 | 116 | goto again; |
b4ce94de | 117 | } |
bd681513 CM |
118 | atomic_inc(&eb->read_locks); |
119 | atomic_inc(&eb->spinning_readers); | |
b4ce94de CM |
120 | } |
121 | ||
f82c458a CM |
122 | /* |
123 | * take a spinning read lock. | |
124 | * returns 1 if we get the read lock and 0 if we don't | |
125 | * this won't wait for blocking writers | |
126 | */ | |
127 | int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) | |
128 | { | |
129 | if (atomic_read(&eb->blocking_writers)) | |
130 | return 0; | |
131 | ||
132 | read_lock(&eb->lock); | |
133 | if (atomic_read(&eb->blocking_writers)) { | |
134 | read_unlock(&eb->lock); | |
135 | return 0; | |
136 | } | |
137 | atomic_inc(&eb->read_locks); | |
138 | atomic_inc(&eb->spinning_readers); | |
139 | return 1; | |
140 | } | |
141 | ||
b4ce94de | 142 | /* |
bd681513 CM |
143 | * returns 1 if we get the read lock and 0 if we don't |
144 | * this won't wait for blocking writers | |
b4ce94de | 145 | */ |
bd681513 | 146 | int btrfs_try_tree_read_lock(struct extent_buffer *eb) |
b4ce94de | 147 | { |
bd681513 CM |
148 | if (atomic_read(&eb->blocking_writers)) |
149 | return 0; | |
b4ce94de | 150 | |
ea4ebde0 CM |
151 | if (!read_trylock(&eb->lock)) |
152 | return 0; | |
153 | ||
bd681513 CM |
154 | if (atomic_read(&eb->blocking_writers)) { |
155 | read_unlock(&eb->lock); | |
156 | return 0; | |
b9473439 | 157 | } |
bd681513 CM |
158 | atomic_inc(&eb->read_locks); |
159 | atomic_inc(&eb->spinning_readers); | |
160 | return 1; | |
b4ce94de CM |
161 | } |
162 | ||
163 | /* | |
bd681513 CM |
164 | * returns 1 if we get the read lock and 0 if we don't |
165 | * this won't wait for blocking writers or readers | |
b4ce94de | 166 | */ |
bd681513 | 167 | int btrfs_try_tree_write_lock(struct extent_buffer *eb) |
b4ce94de | 168 | { |
bd681513 CM |
169 | if (atomic_read(&eb->blocking_writers) || |
170 | atomic_read(&eb->blocking_readers)) | |
171 | return 0; | |
ea4ebde0 | 172 | |
f82c458a | 173 | write_lock(&eb->lock); |
bd681513 CM |
174 | if (atomic_read(&eb->blocking_writers) || |
175 | atomic_read(&eb->blocking_readers)) { | |
176 | write_unlock(&eb->lock); | |
177 | return 0; | |
178 | } | |
179 | atomic_inc(&eb->write_locks); | |
180 | atomic_inc(&eb->spinning_writers); | |
5b25f70f | 181 | eb->lock_owner = current->pid; |
b4ce94de CM |
182 | return 1; |
183 | } | |
184 | ||
185 | /* | |
bd681513 CM |
186 | * drop a spinning read lock |
187 | */ | |
188 | void btrfs_tree_read_unlock(struct extent_buffer *eb) | |
189 | { | |
ea4ebde0 CM |
190 | /* |
191 | * if we're nested, we have the write lock. No new locking | |
192 | * is needed as long as we are the lock owner. | |
193 | * The write unlock will do a barrier for us, and the lock_nested | |
194 | * field only matters to the lock owner. | |
195 | */ | |
196 | if (eb->lock_nested && current->pid == eb->lock_owner) { | |
197 | eb->lock_nested = 0; | |
198 | return; | |
5b25f70f | 199 | } |
bd681513 CM |
200 | btrfs_assert_tree_read_locked(eb); |
201 | WARN_ON(atomic_read(&eb->spinning_readers) == 0); | |
202 | atomic_dec(&eb->spinning_readers); | |
203 | atomic_dec(&eb->read_locks); | |
204 | read_unlock(&eb->lock); | |
205 | } | |
206 | ||
207 | /* | |
208 | * drop a blocking read lock | |
209 | */ | |
210 | void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb) | |
211 | { | |
ea4ebde0 CM |
212 | /* |
213 | * if we're nested, we have the write lock. No new locking | |
214 | * is needed as long as we are the lock owner. | |
215 | * The write unlock will do a barrier for us, and the lock_nested | |
216 | * field only matters to the lock owner. | |
217 | */ | |
218 | if (eb->lock_nested && current->pid == eb->lock_owner) { | |
219 | eb->lock_nested = 0; | |
220 | return; | |
5b25f70f | 221 | } |
bd681513 CM |
222 | btrfs_assert_tree_read_locked(eb); |
223 | WARN_ON(atomic_read(&eb->blocking_readers) == 0); | |
ee863954 DS |
224 | /* |
225 | * atomic_dec_and_test implies a barrier for waitqueue_active | |
226 | */ | |
cbea5ac1 CM |
227 | if (atomic_dec_and_test(&eb->blocking_readers) && |
228 | waitqueue_active(&eb->read_lock_wq)) | |
bd681513 CM |
229 | wake_up(&eb->read_lock_wq); |
230 | atomic_dec(&eb->read_locks); | |
231 | } | |
232 | ||
233 | /* | |
234 | * take a spinning write lock. This will wait for both | |
235 | * blocking readers or writers | |
b4ce94de | 236 | */ |
143bede5 | 237 | void btrfs_tree_lock(struct extent_buffer *eb) |
b4ce94de | 238 | { |
166f66d0 | 239 | WARN_ON(eb->lock_owner == current->pid); |
bd681513 CM |
240 | again: |
241 | wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0); | |
242 | wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); | |
243 | write_lock(&eb->lock); | |
244 | if (atomic_read(&eb->blocking_readers)) { | |
245 | write_unlock(&eb->lock); | |
246 | wait_event(eb->read_lock_wq, | |
247 | atomic_read(&eb->blocking_readers) == 0); | |
248 | goto again; | |
f9efa9c7 | 249 | } |
bd681513 CM |
250 | if (atomic_read(&eb->blocking_writers)) { |
251 | write_unlock(&eb->lock); | |
252 | wait_event(eb->write_lock_wq, | |
253 | atomic_read(&eb->blocking_writers) == 0); | |
254 | goto again; | |
255 | } | |
256 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
257 | atomic_inc(&eb->spinning_writers); | |
258 | atomic_inc(&eb->write_locks); | |
5b25f70f | 259 | eb->lock_owner = current->pid; |
925baedd CM |
260 | } |
261 | ||
bd681513 CM |
262 | /* |
263 | * drop a spinning or a blocking write lock. | |
264 | */ | |
143bede5 | 265 | void btrfs_tree_unlock(struct extent_buffer *eb) |
925baedd | 266 | { |
bd681513 CM |
267 | int blockers = atomic_read(&eb->blocking_writers); |
268 | ||
269 | BUG_ON(blockers > 1); | |
270 | ||
271 | btrfs_assert_tree_locked(eb); | |
ea4ebde0 | 272 | eb->lock_owner = 0; |
bd681513 CM |
273 | atomic_dec(&eb->write_locks); |
274 | ||
275 | if (blockers) { | |
276 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
277 | atomic_dec(&eb->blocking_writers); | |
a83342aa DS |
278 | /* |
279 | * Make sure counter is updated before we wake up waiters. | |
280 | */ | |
2e32ef87 | 281 | smp_mb__after_atomic(); |
cbea5ac1 CM |
282 | if (waitqueue_active(&eb->write_lock_wq)) |
283 | wake_up(&eb->write_lock_wq); | |
bd681513 CM |
284 | } else { |
285 | WARN_ON(atomic_read(&eb->spinning_writers) != 1); | |
286 | atomic_dec(&eb->spinning_writers); | |
287 | write_unlock(&eb->lock); | |
288 | } | |
925baedd CM |
289 | } |
290 | ||
b9447ef8 | 291 | void btrfs_assert_tree_locked(struct extent_buffer *eb) |
925baedd | 292 | { |
bd681513 CM |
293 | BUG_ON(!atomic_read(&eb->write_locks)); |
294 | } | |
295 | ||
48a3b636 | 296 | static void btrfs_assert_tree_read_locked(struct extent_buffer *eb) |
bd681513 CM |
297 | { |
298 | BUG_ON(!atomic_read(&eb->read_locks)); | |
925baedd | 299 | } |