Loading...
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
27void 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 (rw == BTRFS_WRITE_LOCK) {
37 if (atomic_read(&eb->blocking_writers) == 0) {
38 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
39 atomic_dec(&eb->spinning_writers);
40 btrfs_assert_tree_locked(eb);
41 atomic_inc(&eb->blocking_writers);
42 write_unlock(&eb->lock);
43 }
44 } else if (rw == BTRFS_READ_LOCK) {
45 btrfs_assert_tree_read_locked(eb);
46 atomic_inc(&eb->blocking_readers);
47 WARN_ON(atomic_read(&eb->spinning_readers) == 0);
48 atomic_dec(&eb->spinning_readers);
49 read_unlock(&eb->lock);
50 }
51 return;
52}
53
54/*
55 * if we currently have a blocking lock, take the spinlock
56 * and drop our blocking count
57 */
58void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
59{
60 if (rw == BTRFS_WRITE_LOCK_BLOCKING) {
61 BUG_ON(atomic_read(&eb->blocking_writers) != 1);
62 write_lock(&eb->lock);
63 WARN_ON(atomic_read(&eb->spinning_writers));
64 atomic_inc(&eb->spinning_writers);
65 if (atomic_dec_and_test(&eb->blocking_writers))
66 wake_up(&eb->write_lock_wq);
67 } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
68 BUG_ON(atomic_read(&eb->blocking_readers) == 0);
69 read_lock(&eb->lock);
70 atomic_inc(&eb->spinning_readers);
71 if (atomic_dec_and_test(&eb->blocking_readers))
72 wake_up(&eb->read_lock_wq);
73 }
74 return;
75}
76
77/*
78 * take a spinning read lock. This will wait for any blocking
79 * writers
80 */
81void btrfs_tree_read_lock(struct extent_buffer *eb)
82{
83again:
84 wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
85 read_lock(&eb->lock);
86 if (atomic_read(&eb->blocking_writers)) {
87 read_unlock(&eb->lock);
88 wait_event(eb->write_lock_wq,
89 atomic_read(&eb->blocking_writers) == 0);
90 goto again;
91 }
92 atomic_inc(&eb->read_locks);
93 atomic_inc(&eb->spinning_readers);
94}
95
96/*
97 * returns 1 if we get the read lock and 0 if we don't
98 * this won't wait for blocking writers
99 */
100int btrfs_try_tree_read_lock(struct extent_buffer *eb)
101{
102 if (atomic_read(&eb->blocking_writers))
103 return 0;
104
105 read_lock(&eb->lock);
106 if (atomic_read(&eb->blocking_writers)) {
107 read_unlock(&eb->lock);
108 return 0;
109 }
110 atomic_inc(&eb->read_locks);
111 atomic_inc(&eb->spinning_readers);
112 return 1;
113}
114
115/*
116 * returns 1 if we get the read lock and 0 if we don't
117 * this won't wait for blocking writers or readers
118 */
119int btrfs_try_tree_write_lock(struct extent_buffer *eb)
120{
121 if (atomic_read(&eb->blocking_writers) ||
122 atomic_read(&eb->blocking_readers))
123 return 0;
124 write_lock(&eb->lock);
125 if (atomic_read(&eb->blocking_writers) ||
126 atomic_read(&eb->blocking_readers)) {
127 write_unlock(&eb->lock);
128 return 0;
129 }
130 atomic_inc(&eb->write_locks);
131 atomic_inc(&eb->spinning_writers);
132 return 1;
133}
134
135/*
136 * drop a spinning read lock
137 */
138void btrfs_tree_read_unlock(struct extent_buffer *eb)
139{
140 btrfs_assert_tree_read_locked(eb);
141 WARN_ON(atomic_read(&eb->spinning_readers) == 0);
142 atomic_dec(&eb->spinning_readers);
143 atomic_dec(&eb->read_locks);
144 read_unlock(&eb->lock);
145}
146
147/*
148 * drop a blocking read lock
149 */
150void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
151{
152 btrfs_assert_tree_read_locked(eb);
153 WARN_ON(atomic_read(&eb->blocking_readers) == 0);
154 if (atomic_dec_and_test(&eb->blocking_readers))
155 wake_up(&eb->read_lock_wq);
156 atomic_dec(&eb->read_locks);
157}
158
159/*
160 * take a spinning write lock. This will wait for both
161 * blocking readers or writers
162 */
163int btrfs_tree_lock(struct extent_buffer *eb)
164{
165again:
166 wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
167 wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
168 write_lock(&eb->lock);
169 if (atomic_read(&eb->blocking_readers)) {
170 write_unlock(&eb->lock);
171 wait_event(eb->read_lock_wq,
172 atomic_read(&eb->blocking_readers) == 0);
173 goto again;
174 }
175 if (atomic_read(&eb->blocking_writers)) {
176 write_unlock(&eb->lock);
177 wait_event(eb->write_lock_wq,
178 atomic_read(&eb->blocking_writers) == 0);
179 goto again;
180 }
181 WARN_ON(atomic_read(&eb->spinning_writers));
182 atomic_inc(&eb->spinning_writers);
183 atomic_inc(&eb->write_locks);
184 return 0;
185}
186
187/*
188 * drop a spinning or a blocking write lock.
189 */
190int btrfs_tree_unlock(struct extent_buffer *eb)
191{
192 int blockers = atomic_read(&eb->blocking_writers);
193
194 BUG_ON(blockers > 1);
195
196 btrfs_assert_tree_locked(eb);
197 atomic_dec(&eb->write_locks);
198
199 if (blockers) {
200 WARN_ON(atomic_read(&eb->spinning_writers));
201 atomic_dec(&eb->blocking_writers);
202 smp_wmb();
203 wake_up(&eb->write_lock_wq);
204 } else {
205 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
206 atomic_dec(&eb->spinning_writers);
207 write_unlock(&eb->lock);
208 }
209 return 0;
210}
211
212void btrfs_assert_tree_locked(struct extent_buffer *eb)
213{
214 BUG_ON(!atomic_read(&eb->write_locks));
215}
216
217void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
218{
219 BUG_ON(!atomic_read(&eb->read_locks));
220}
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}