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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 | |
b95be2d9 DS |
17 | void btrfs_set_lock_blocking_read(struct extent_buffer *eb) |
18 | { | |
19 | /* | |
20 | * No lock is required. The lock owner may change if we have a read | |
21 | * lock, but it won't change to or away from us. If we have the write | |
22 | * lock, we are the owner and it'll never change. | |
23 | */ | |
24 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
25 | return; | |
26 | btrfs_assert_tree_read_locked(eb); | |
27 | atomic_inc(&eb->blocking_readers); | |
28 | WARN_ON(atomic_read(&eb->spinning_readers) == 0); | |
29 | atomic_dec(&eb->spinning_readers); | |
30 | read_unlock(&eb->lock); | |
31 | } | |
32 | ||
33 | void btrfs_set_lock_blocking_write(struct extent_buffer *eb) | |
925baedd | 34 | { |
ea4ebde0 | 35 | /* |
b95be2d9 DS |
36 | * No lock is required. The lock owner may change if we have a read |
37 | * lock, but it won't change to or away from us. If we have the write | |
38 | * lock, we are the owner and it'll never change. | |
ea4ebde0 CM |
39 | */ |
40 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
41 | return; | |
b95be2d9 DS |
42 | if (atomic_read(&eb->blocking_writers) == 0) { |
43 | WARN_ON(atomic_read(&eb->spinning_writers) != 1); | |
44 | atomic_dec(&eb->spinning_writers); | |
45 | btrfs_assert_tree_locked(eb); | |
46 | atomic_inc(&eb->blocking_writers); | |
47 | write_unlock(&eb->lock); | |
b4ce94de | 48 | } |
b4ce94de | 49 | } |
f9efa9c7 | 50 | |
aa12c027 DS |
51 | void btrfs_clear_lock_blocking_read(struct extent_buffer *eb) |
52 | { | |
53 | /* | |
54 | * No lock is required. The lock owner may change if we have a read | |
55 | * lock, but it won't change to or away from us. If we have the write | |
56 | * lock, we are the owner and it'll never change. | |
57 | */ | |
58 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
59 | return; | |
60 | BUG_ON(atomic_read(&eb->blocking_readers) == 0); | |
61 | read_lock(&eb->lock); | |
62 | atomic_inc(&eb->spinning_readers); | |
63 | /* atomic_dec_and_test implies a barrier */ | |
64 | if (atomic_dec_and_test(&eb->blocking_readers)) | |
65 | cond_wake_up_nomb(&eb->read_lock_wq); | |
66 | } | |
67 | ||
68 | void btrfs_clear_lock_blocking_write(struct extent_buffer *eb) | |
b4ce94de | 69 | { |
ea4ebde0 CM |
70 | /* |
71 | * no lock is required. The lock owner may change if | |
72 | * we have a read lock, but it won't change to or away | |
73 | * from us. If we have the write lock, we are the owner | |
74 | * and it'll never change. | |
75 | */ | |
76 | if (eb->lock_nested && current->pid == eb->lock_owner) | |
77 | return; | |
aa12c027 DS |
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 | /* atomic_dec_and_test implies a barrier */ | |
83 | if (atomic_dec_and_test(&eb->blocking_writers)) | |
84 | cond_wake_up_nomb(&eb->write_lock_wq); | |
b4ce94de CM |
85 | } |
86 | ||
87 | /* | |
bd681513 CM |
88 | * take a spinning read lock. This will wait for any blocking |
89 | * writers | |
b4ce94de | 90 | */ |
bd681513 | 91 | void btrfs_tree_read_lock(struct extent_buffer *eb) |
b4ce94de | 92 | { |
bd681513 | 93 | again: |
ea4ebde0 CM |
94 | BUG_ON(!atomic_read(&eb->blocking_writers) && |
95 | current->pid == eb->lock_owner); | |
96 | ||
5b25f70f AJ |
97 | read_lock(&eb->lock); |
98 | if (atomic_read(&eb->blocking_writers) && | |
99 | current->pid == eb->lock_owner) { | |
100 | /* | |
101 | * This extent is already write-locked by our thread. We allow | |
102 | * an additional read lock to be added because it's for the same | |
103 | * thread. btrfs_find_all_roots() depends on this as it may be | |
104 | * called on a partly (write-)locked tree. | |
105 | */ | |
106 | BUG_ON(eb->lock_nested); | |
107 | eb->lock_nested = 1; | |
108 | read_unlock(&eb->lock); | |
109 | return; | |
110 | } | |
bd681513 CM |
111 | if (atomic_read(&eb->blocking_writers)) { |
112 | read_unlock(&eb->lock); | |
39f9d028 LB |
113 | wait_event(eb->write_lock_wq, |
114 | atomic_read(&eb->blocking_writers) == 0); | |
bd681513 | 115 | goto again; |
b4ce94de | 116 | } |
bd681513 CM |
117 | atomic_inc(&eb->read_locks); |
118 | atomic_inc(&eb->spinning_readers); | |
b4ce94de CM |
119 | } |
120 | ||
f82c458a CM |
121 | /* |
122 | * take a spinning read lock. | |
123 | * returns 1 if we get the read lock and 0 if we don't | |
124 | * this won't wait for blocking writers | |
125 | */ | |
126 | int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) | |
127 | { | |
128 | if (atomic_read(&eb->blocking_writers)) | |
129 | return 0; | |
130 | ||
131 | read_lock(&eb->lock); | |
132 | if (atomic_read(&eb->blocking_writers)) { | |
133 | read_unlock(&eb->lock); | |
134 | return 0; | |
135 | } | |
136 | atomic_inc(&eb->read_locks); | |
137 | atomic_inc(&eb->spinning_readers); | |
138 | return 1; | |
139 | } | |
140 | ||
b4ce94de | 141 | /* |
bd681513 CM |
142 | * returns 1 if we get the read lock and 0 if we don't |
143 | * this won't wait for blocking writers | |
b4ce94de | 144 | */ |
bd681513 | 145 | int btrfs_try_tree_read_lock(struct extent_buffer *eb) |
b4ce94de | 146 | { |
bd681513 CM |
147 | if (atomic_read(&eb->blocking_writers)) |
148 | return 0; | |
b4ce94de | 149 | |
ea4ebde0 CM |
150 | if (!read_trylock(&eb->lock)) |
151 | return 0; | |
152 | ||
bd681513 CM |
153 | if (atomic_read(&eb->blocking_writers)) { |
154 | read_unlock(&eb->lock); | |
155 | return 0; | |
b9473439 | 156 | } |
bd681513 CM |
157 | atomic_inc(&eb->read_locks); |
158 | atomic_inc(&eb->spinning_readers); | |
159 | return 1; | |
b4ce94de CM |
160 | } |
161 | ||
162 | /* | |
bd681513 CM |
163 | * returns 1 if we get the read lock and 0 if we don't |
164 | * this won't wait for blocking writers or readers | |
b4ce94de | 165 | */ |
bd681513 | 166 | int btrfs_try_tree_write_lock(struct extent_buffer *eb) |
b4ce94de | 167 | { |
bd681513 CM |
168 | if (atomic_read(&eb->blocking_writers) || |
169 | atomic_read(&eb->blocking_readers)) | |
170 | return 0; | |
ea4ebde0 | 171 | |
f82c458a | 172 | write_lock(&eb->lock); |
bd681513 CM |
173 | if (atomic_read(&eb->blocking_writers) || |
174 | atomic_read(&eb->blocking_readers)) { | |
175 | write_unlock(&eb->lock); | |
176 | return 0; | |
177 | } | |
178 | atomic_inc(&eb->write_locks); | |
179 | atomic_inc(&eb->spinning_writers); | |
5b25f70f | 180 | eb->lock_owner = current->pid; |
b4ce94de CM |
181 | return 1; |
182 | } | |
183 | ||
184 | /* | |
bd681513 CM |
185 | * drop a spinning read lock |
186 | */ | |
187 | void btrfs_tree_read_unlock(struct extent_buffer *eb) | |
188 | { | |
ea4ebde0 CM |
189 | /* |
190 | * if we're nested, we have the write lock. No new locking | |
191 | * is needed as long as we are the lock owner. | |
192 | * The write unlock will do a barrier for us, and the lock_nested | |
193 | * field only matters to the lock owner. | |
194 | */ | |
195 | if (eb->lock_nested && current->pid == eb->lock_owner) { | |
196 | eb->lock_nested = 0; | |
197 | return; | |
5b25f70f | 198 | } |
bd681513 CM |
199 | btrfs_assert_tree_read_locked(eb); |
200 | WARN_ON(atomic_read(&eb->spinning_readers) == 0); | |
201 | atomic_dec(&eb->spinning_readers); | |
202 | atomic_dec(&eb->read_locks); | |
203 | read_unlock(&eb->lock); | |
204 | } | |
205 | ||
206 | /* | |
207 | * drop a blocking read lock | |
208 | */ | |
209 | void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb) | |
210 | { | |
ea4ebde0 CM |
211 | /* |
212 | * if we're nested, we have the write lock. No new locking | |
213 | * is needed as long as we are the lock owner. | |
214 | * The write unlock will do a barrier for us, and the lock_nested | |
215 | * field only matters to the lock owner. | |
216 | */ | |
217 | if (eb->lock_nested && current->pid == eb->lock_owner) { | |
218 | eb->lock_nested = 0; | |
219 | return; | |
5b25f70f | 220 | } |
bd681513 CM |
221 | btrfs_assert_tree_read_locked(eb); |
222 | WARN_ON(atomic_read(&eb->blocking_readers) == 0); | |
093258e6 DS |
223 | /* atomic_dec_and_test implies a barrier */ |
224 | if (atomic_dec_and_test(&eb->blocking_readers)) | |
225 | cond_wake_up_nomb(&eb->read_lock_wq); | |
bd681513 CM |
226 | atomic_dec(&eb->read_locks); |
227 | } | |
228 | ||
229 | /* | |
230 | * take a spinning write lock. This will wait for both | |
231 | * blocking readers or writers | |
b4ce94de | 232 | */ |
143bede5 | 233 | void btrfs_tree_lock(struct extent_buffer *eb) |
b4ce94de | 234 | { |
166f66d0 | 235 | WARN_ON(eb->lock_owner == current->pid); |
bd681513 CM |
236 | again: |
237 | wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0); | |
238 | wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); | |
239 | write_lock(&eb->lock); | |
970e74d9 DS |
240 | if (atomic_read(&eb->blocking_readers) || |
241 | atomic_read(&eb->blocking_writers)) { | |
bd681513 | 242 | write_unlock(&eb->lock); |
bd681513 CM |
243 | goto again; |
244 | } | |
245 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
246 | atomic_inc(&eb->spinning_writers); | |
247 | atomic_inc(&eb->write_locks); | |
5b25f70f | 248 | eb->lock_owner = current->pid; |
925baedd CM |
249 | } |
250 | ||
bd681513 CM |
251 | /* |
252 | * drop a spinning or a blocking write lock. | |
253 | */ | |
143bede5 | 254 | void btrfs_tree_unlock(struct extent_buffer *eb) |
925baedd | 255 | { |
bd681513 CM |
256 | int blockers = atomic_read(&eb->blocking_writers); |
257 | ||
258 | BUG_ON(blockers > 1); | |
259 | ||
260 | btrfs_assert_tree_locked(eb); | |
ea4ebde0 | 261 | eb->lock_owner = 0; |
bd681513 CM |
262 | atomic_dec(&eb->write_locks); |
263 | ||
264 | if (blockers) { | |
265 | WARN_ON(atomic_read(&eb->spinning_writers)); | |
266 | atomic_dec(&eb->blocking_writers); | |
093258e6 | 267 | /* Use the lighter barrier after atomic */ |
2e32ef87 | 268 | smp_mb__after_atomic(); |
093258e6 | 269 | cond_wake_up_nomb(&eb->write_lock_wq); |
bd681513 CM |
270 | } else { |
271 | WARN_ON(atomic_read(&eb->spinning_writers) != 1); | |
272 | atomic_dec(&eb->spinning_writers); | |
273 | write_unlock(&eb->lock); | |
274 | } | |
925baedd CM |
275 | } |
276 | ||
b9447ef8 | 277 | void btrfs_assert_tree_locked(struct extent_buffer *eb) |
925baedd | 278 | { |
bd681513 CM |
279 | BUG_ON(!atomic_read(&eb->write_locks)); |
280 | } | |
281 | ||
48a3b636 | 282 | static void btrfs_assert_tree_read_locked(struct extent_buffer *eb) |
bd681513 CM |
283 | { |
284 | BUG_ON(!atomic_read(&eb->read_locks)); | |
925baedd | 285 | } |