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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Copyright (C) 2008 Oracle. All rights reserved.
4 */
5
6#include <linux/sched.h>
7#include <linux/pagemap.h>
8#include <linux/spinlock.h>
9#include <linux/page-flags.h>
10#include <asm/bug.h>
11#include "ctree.h"
12#include "extent_io.h"
13#include "locking.h"
14
15static void btrfs_assert_tree_read_locked(struct extent_buffer *eb);
16
17/*
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.
21 */
22void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
23{
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;
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);
46 }
47}
48
49/*
50 * if we currently have a blocking lock, take the spinlock
51 * and drop our blocking count
52 */
53void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
54{
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
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);
69 /*
70 * atomic_dec_and_test implies a barrier for waitqueue_active
71 */
72 if (atomic_dec_and_test(&eb->blocking_writers) &&
73 waitqueue_active(&eb->write_lock_wq))
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);
79 /*
80 * atomic_dec_and_test implies a barrier for waitqueue_active
81 */
82 if (atomic_dec_and_test(&eb->blocking_readers) &&
83 waitqueue_active(&eb->read_lock_wq))
84 wake_up(&eb->read_lock_wq);
85 }
86}
87
88/*
89 * take a spinning read lock. This will wait for any blocking
90 * writers
91 */
92void btrfs_tree_read_lock(struct extent_buffer *eb)
93{
94again:
95 BUG_ON(!atomic_read(&eb->blocking_writers) &&
96 current->pid == eb->lock_owner);
97
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 }
112 if (atomic_read(&eb->blocking_writers)) {
113 read_unlock(&eb->lock);
114 wait_event(eb->write_lock_wq,
115 atomic_read(&eb->blocking_writers) == 0);
116 goto again;
117 }
118 atomic_inc(&eb->read_locks);
119 atomic_inc(&eb->spinning_readers);
120}
121
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 */
127int 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
142/*
143 * returns 1 if we get the read lock and 0 if we don't
144 * this won't wait for blocking writers
145 */
146int btrfs_try_tree_read_lock(struct extent_buffer *eb)
147{
148 if (atomic_read(&eb->blocking_writers))
149 return 0;
150
151 if (!read_trylock(&eb->lock))
152 return 0;
153
154 if (atomic_read(&eb->blocking_writers)) {
155 read_unlock(&eb->lock);
156 return 0;
157 }
158 atomic_inc(&eb->read_locks);
159 atomic_inc(&eb->spinning_readers);
160 return 1;
161}
162
163/*
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
166 */
167int btrfs_try_tree_write_lock(struct extent_buffer *eb)
168{
169 if (atomic_read(&eb->blocking_writers) ||
170 atomic_read(&eb->blocking_readers))
171 return 0;
172
173 write_lock(&eb->lock);
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);
181 eb->lock_owner = current->pid;
182 return 1;
183}
184
185/*
186 * drop a spinning read lock
187 */
188void btrfs_tree_read_unlock(struct extent_buffer *eb)
189{
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;
199 }
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 */
210void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
211{
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;
221 }
222 btrfs_assert_tree_read_locked(eb);
223 WARN_ON(atomic_read(&eb->blocking_readers) == 0);
224 /*
225 * atomic_dec_and_test implies a barrier for waitqueue_active
226 */
227 if (atomic_dec_and_test(&eb->blocking_readers) &&
228 waitqueue_active(&eb->read_lock_wq))
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
236 */
237void btrfs_tree_lock(struct extent_buffer *eb)
238{
239 WARN_ON(eb->lock_owner == current->pid);
240again:
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;
249 }
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);
259 eb->lock_owner = current->pid;
260}
261
262/*
263 * drop a spinning or a blocking write lock.
264 */
265void btrfs_tree_unlock(struct extent_buffer *eb)
266{
267 int blockers = atomic_read(&eb->blocking_writers);
268
269 BUG_ON(blockers > 1);
270
271 btrfs_assert_tree_locked(eb);
272 eb->lock_owner = 0;
273 atomic_dec(&eb->write_locks);
274
275 if (blockers) {
276 WARN_ON(atomic_read(&eb->spinning_writers));
277 atomic_dec(&eb->blocking_writers);
278 /*
279 * Make sure counter is updated before we wake up waiters.
280 */
281 smp_mb__after_atomic();
282 if (waitqueue_active(&eb->write_lock_wq))
283 wake_up(&eb->write_lock_wq);
284 } else {
285 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
286 atomic_dec(&eb->spinning_writers);
287 write_unlock(&eb->lock);
288 }
289}
290
291void btrfs_assert_tree_locked(struct extent_buffer *eb)
292{
293 BUG_ON(!atomic_read(&eb->write_locks));
294}
295
296static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
297{
298 BUG_ON(!atomic_read(&eb->read_locks));
299}
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
27static 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 */
34void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw)
35{
36 if (eb->lock_nested) {
37 read_lock(&eb->lock);
38 if (eb->lock_nested && current->pid == eb->lock_owner) {
39 read_unlock(&eb->lock);
40 return;
41 }
42 read_unlock(&eb->lock);
43 }
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 */
66void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
67{
68 if (eb->lock_nested) {
69 read_lock(&eb->lock);
70 if (eb->lock_nested && current->pid == eb->lock_owner) {
71 read_unlock(&eb->lock);
72 return;
73 }
74 read_unlock(&eb->lock);
75 }
76 if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
77 BUG_ON(atomic_read(&eb->blocking_writers) != 1);
78 write_lock(&eb->lock);
79 WARN_ON(atomic_read(&eb->spinning_writers));
80 atomic_inc(&eb->spinning_writers);
81 if (atomic_dec_and_test(&eb->blocking_writers) &&
82 waitqueue_active(&eb->write_lock_wq))
83 wake_up(&eb->write_lock_wq);
84 } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
85 BUG_ON(atomic_read(&eb->blocking_readers) == 0);
86 read_lock(&eb->lock);
87 atomic_inc(&eb->spinning_readers);
88 if (atomic_dec_and_test(&eb->blocking_readers) &&
89 waitqueue_active(&eb->read_lock_wq))
90 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 */
99void btrfs_tree_read_lock(struct extent_buffer *eb)
100{
101again:
102 read_lock(&eb->lock);
103 if (atomic_read(&eb->blocking_writers) &&
104 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 BUG_ON(eb->lock_nested);
112 eb->lock_nested = 1;
113 read_unlock(&eb->lock);
114 return;
115 }
116 if (atomic_read(&eb->blocking_writers)) {
117 read_unlock(&eb->lock);
118 wait_event(eb->write_lock_wq,
119 atomic_read(&eb->blocking_writers) == 0);
120 goto again;
121 }
122 atomic_inc(&eb->read_locks);
123 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 */
130int btrfs_try_tree_read_lock(struct extent_buffer *eb)
131{
132 if (atomic_read(&eb->blocking_writers))
133 return 0;
134
135 read_lock(&eb->lock);
136 if (atomic_read(&eb->blocking_writers)) {
137 read_unlock(&eb->lock);
138 return 0;
139 }
140 atomic_inc(&eb->read_locks);
141 atomic_inc(&eb->spinning_readers);
142 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 */
149int btrfs_try_tree_write_lock(struct extent_buffer *eb)
150{
151 if (atomic_read(&eb->blocking_writers) ||
152 atomic_read(&eb->blocking_readers))
153 return 0;
154 write_lock(&eb->lock);
155 if (atomic_read(&eb->blocking_writers) ||
156 atomic_read(&eb->blocking_readers)) {
157 write_unlock(&eb->lock);
158 return 0;
159 }
160 atomic_inc(&eb->write_locks);
161 atomic_inc(&eb->spinning_writers);
162 eb->lock_owner = current->pid;
163 return 1;
164}
165
166/*
167 * drop a spinning read lock
168 */
169void btrfs_tree_read_unlock(struct extent_buffer *eb)
170{
171 if (eb->lock_nested) {
172 read_lock(&eb->lock);
173 if (eb->lock_nested && current->pid == eb->lock_owner) {
174 eb->lock_nested = 0;
175 read_unlock(&eb->lock);
176 return;
177 }
178 read_unlock(&eb->lock);
179 }
180 btrfs_assert_tree_read_locked(eb);
181 WARN_ON(atomic_read(&eb->spinning_readers) == 0);
182 atomic_dec(&eb->spinning_readers);
183 atomic_dec(&eb->read_locks);
184 read_unlock(&eb->lock);
185}
186
187/*
188 * drop a blocking read lock
189 */
190void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
191{
192 if (eb->lock_nested) {
193 read_lock(&eb->lock);
194 if (eb->lock_nested && current->pid == eb->lock_owner) {
195 eb->lock_nested = 0;
196 read_unlock(&eb->lock);
197 return;
198 }
199 read_unlock(&eb->lock);
200 }
201 btrfs_assert_tree_read_locked(eb);
202 WARN_ON(atomic_read(&eb->blocking_readers) == 0);
203 if (atomic_dec_and_test(&eb->blocking_readers) &&
204 waitqueue_active(&eb->read_lock_wq))
205 wake_up(&eb->read_lock_wq);
206 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 */
213void btrfs_tree_lock(struct extent_buffer *eb)
214{
215again:
216 wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
217 wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
218 write_lock(&eb->lock);
219 if (atomic_read(&eb->blocking_readers)) {
220 write_unlock(&eb->lock);
221 wait_event(eb->read_lock_wq,
222 atomic_read(&eb->blocking_readers) == 0);
223 goto again;
224 }
225 if (atomic_read(&eb->blocking_writers)) {
226 write_unlock(&eb->lock);
227 wait_event(eb->write_lock_wq,
228 atomic_read(&eb->blocking_writers) == 0);
229 goto again;
230 }
231 WARN_ON(atomic_read(&eb->spinning_writers));
232 atomic_inc(&eb->spinning_writers);
233 atomic_inc(&eb->write_locks);
234 eb->lock_owner = current->pid;
235}
236
237/*
238 * drop a spinning or a blocking write lock.
239 */
240void btrfs_tree_unlock(struct extent_buffer *eb)
241{
242 int blockers = atomic_read(&eb->blocking_writers);
243
244 BUG_ON(blockers > 1);
245
246 btrfs_assert_tree_locked(eb);
247 atomic_dec(&eb->write_locks);
248
249 if (blockers) {
250 WARN_ON(atomic_read(&eb->spinning_writers));
251 atomic_dec(&eb->blocking_writers);
252 smp_mb();
253 if (waitqueue_active(&eb->write_lock_wq))
254 wake_up(&eb->write_lock_wq);
255 } else {
256 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
257 atomic_dec(&eb->spinning_writers);
258 write_unlock(&eb->lock);
259 }
260}
261
262void btrfs_assert_tree_locked(struct extent_buffer *eb)
263{
264 BUG_ON(!atomic_read(&eb->write_locks));
265}
266
267static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
268{
269 BUG_ON(!atomic_read(&eb->read_locks));
270}