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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 "misc.h"
12#include "ctree.h"
13#include "extent_io.h"
14#include "locking.h"
15
16#ifdef CONFIG_BTRFS_DEBUG
17static void btrfs_assert_spinning_writers_get(struct extent_buffer *eb)
18{
19 WARN_ON(eb->spinning_writers);
20 eb->spinning_writers++;
21}
22
23static void btrfs_assert_spinning_writers_put(struct extent_buffer *eb)
24{
25 WARN_ON(eb->spinning_writers != 1);
26 eb->spinning_writers--;
27}
28
29static void btrfs_assert_no_spinning_writers(struct extent_buffer *eb)
30{
31 WARN_ON(eb->spinning_writers);
32}
33
34static void btrfs_assert_spinning_readers_get(struct extent_buffer *eb)
35{
36 atomic_inc(&eb->spinning_readers);
37}
38
39static void btrfs_assert_spinning_readers_put(struct extent_buffer *eb)
40{
41 WARN_ON(atomic_read(&eb->spinning_readers) == 0);
42 atomic_dec(&eb->spinning_readers);
43}
44
45static void btrfs_assert_tree_read_locks_get(struct extent_buffer *eb)
46{
47 atomic_inc(&eb->read_locks);
48}
49
50static void btrfs_assert_tree_read_locks_put(struct extent_buffer *eb)
51{
52 atomic_dec(&eb->read_locks);
53}
54
55static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
56{
57 BUG_ON(!atomic_read(&eb->read_locks));
58}
59
60static void btrfs_assert_tree_write_locks_get(struct extent_buffer *eb)
61{
62 eb->write_locks++;
63}
64
65static void btrfs_assert_tree_write_locks_put(struct extent_buffer *eb)
66{
67 eb->write_locks--;
68}
69
70void btrfs_assert_tree_locked(struct extent_buffer *eb)
71{
72 BUG_ON(!eb->write_locks);
73}
74
75#else
76static void btrfs_assert_spinning_writers_get(struct extent_buffer *eb) { }
77static void btrfs_assert_spinning_writers_put(struct extent_buffer *eb) { }
78static void btrfs_assert_no_spinning_writers(struct extent_buffer *eb) { }
79static void btrfs_assert_spinning_readers_put(struct extent_buffer *eb) { }
80static void btrfs_assert_spinning_readers_get(struct extent_buffer *eb) { }
81static void btrfs_assert_tree_read_locked(struct extent_buffer *eb) { }
82static void btrfs_assert_tree_read_locks_get(struct extent_buffer *eb) { }
83static void btrfs_assert_tree_read_locks_put(struct extent_buffer *eb) { }
84void btrfs_assert_tree_locked(struct extent_buffer *eb) { }
85static void btrfs_assert_tree_write_locks_get(struct extent_buffer *eb) { }
86static void btrfs_assert_tree_write_locks_put(struct extent_buffer *eb) { }
87#endif
88
89void btrfs_set_lock_blocking_read(struct extent_buffer *eb)
90{
91 trace_btrfs_set_lock_blocking_read(eb);
92 /*
93 * No lock is required. The lock owner may change if we have a read
94 * lock, but it won't change to or away from us. If we have the write
95 * lock, we are the owner and it'll never change.
96 */
97 if (eb->lock_nested && current->pid == eb->lock_owner)
98 return;
99 btrfs_assert_tree_read_locked(eb);
100 atomic_inc(&eb->blocking_readers);
101 btrfs_assert_spinning_readers_put(eb);
102 read_unlock(&eb->lock);
103}
104
105void btrfs_set_lock_blocking_write(struct extent_buffer *eb)
106{
107 trace_btrfs_set_lock_blocking_write(eb);
108 /*
109 * No lock is required. The lock owner may change if we have a read
110 * lock, but it won't change to or away from us. If we have the write
111 * lock, we are the owner and it'll never change.
112 */
113 if (eb->lock_nested && current->pid == eb->lock_owner)
114 return;
115 if (eb->blocking_writers == 0) {
116 btrfs_assert_spinning_writers_put(eb);
117 btrfs_assert_tree_locked(eb);
118 eb->blocking_writers++;
119 write_unlock(&eb->lock);
120 }
121}
122
123/*
124 * take a spinning read lock. This will wait for any blocking
125 * writers
126 */
127void btrfs_tree_read_lock(struct extent_buffer *eb)
128{
129 u64 start_ns = 0;
130
131 if (trace_btrfs_tree_read_lock_enabled())
132 start_ns = ktime_get_ns();
133again:
134 read_lock(&eb->lock);
135 BUG_ON(eb->blocking_writers == 0 &&
136 current->pid == eb->lock_owner);
137 if (eb->blocking_writers && current->pid == eb->lock_owner) {
138 /*
139 * This extent is already write-locked by our thread. We allow
140 * an additional read lock to be added because it's for the same
141 * thread. btrfs_find_all_roots() depends on this as it may be
142 * called on a partly (write-)locked tree.
143 */
144 BUG_ON(eb->lock_nested);
145 eb->lock_nested = true;
146 read_unlock(&eb->lock);
147 trace_btrfs_tree_read_lock(eb, start_ns);
148 return;
149 }
150 if (eb->blocking_writers) {
151 read_unlock(&eb->lock);
152 wait_event(eb->write_lock_wq,
153 eb->blocking_writers == 0);
154 goto again;
155 }
156 btrfs_assert_tree_read_locks_get(eb);
157 btrfs_assert_spinning_readers_get(eb);
158 trace_btrfs_tree_read_lock(eb, start_ns);
159}
160
161/*
162 * take a spinning read lock.
163 * returns 1 if we get the read lock and 0 if we don't
164 * this won't wait for blocking writers
165 */
166int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
167{
168 if (eb->blocking_writers)
169 return 0;
170
171 read_lock(&eb->lock);
172 if (eb->blocking_writers) {
173 read_unlock(&eb->lock);
174 return 0;
175 }
176 btrfs_assert_tree_read_locks_get(eb);
177 btrfs_assert_spinning_readers_get(eb);
178 trace_btrfs_tree_read_lock_atomic(eb);
179 return 1;
180}
181
182/*
183 * returns 1 if we get the read lock and 0 if we don't
184 * this won't wait for blocking writers
185 */
186int btrfs_try_tree_read_lock(struct extent_buffer *eb)
187{
188 if (eb->blocking_writers)
189 return 0;
190
191 if (!read_trylock(&eb->lock))
192 return 0;
193
194 if (eb->blocking_writers) {
195 read_unlock(&eb->lock);
196 return 0;
197 }
198 btrfs_assert_tree_read_locks_get(eb);
199 btrfs_assert_spinning_readers_get(eb);
200 trace_btrfs_try_tree_read_lock(eb);
201 return 1;
202}
203
204/*
205 * returns 1 if we get the read lock and 0 if we don't
206 * this won't wait for blocking writers or readers
207 */
208int btrfs_try_tree_write_lock(struct extent_buffer *eb)
209{
210 if (eb->blocking_writers || atomic_read(&eb->blocking_readers))
211 return 0;
212
213 write_lock(&eb->lock);
214 if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) {
215 write_unlock(&eb->lock);
216 return 0;
217 }
218 btrfs_assert_tree_write_locks_get(eb);
219 btrfs_assert_spinning_writers_get(eb);
220 eb->lock_owner = current->pid;
221 trace_btrfs_try_tree_write_lock(eb);
222 return 1;
223}
224
225/*
226 * drop a spinning read lock
227 */
228void btrfs_tree_read_unlock(struct extent_buffer *eb)
229{
230 trace_btrfs_tree_read_unlock(eb);
231 /*
232 * if we're nested, we have the write lock. No new locking
233 * is needed as long as we are the lock owner.
234 * The write unlock will do a barrier for us, and the lock_nested
235 * field only matters to the lock owner.
236 */
237 if (eb->lock_nested && current->pid == eb->lock_owner) {
238 eb->lock_nested = false;
239 return;
240 }
241 btrfs_assert_tree_read_locked(eb);
242 btrfs_assert_spinning_readers_put(eb);
243 btrfs_assert_tree_read_locks_put(eb);
244 read_unlock(&eb->lock);
245}
246
247/*
248 * drop a blocking read lock
249 */
250void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
251{
252 trace_btrfs_tree_read_unlock_blocking(eb);
253 /*
254 * if we're nested, we have the write lock. No new locking
255 * is needed as long as we are the lock owner.
256 * The write unlock will do a barrier for us, and the lock_nested
257 * field only matters to the lock owner.
258 */
259 if (eb->lock_nested && current->pid == eb->lock_owner) {
260 eb->lock_nested = false;
261 return;
262 }
263 btrfs_assert_tree_read_locked(eb);
264 WARN_ON(atomic_read(&eb->blocking_readers) == 0);
265 /* atomic_dec_and_test implies a barrier */
266 if (atomic_dec_and_test(&eb->blocking_readers))
267 cond_wake_up_nomb(&eb->read_lock_wq);
268 btrfs_assert_tree_read_locks_put(eb);
269}
270
271/*
272 * take a spinning write lock. This will wait for both
273 * blocking readers or writers
274 */
275void btrfs_tree_lock(struct extent_buffer *eb)
276{
277 u64 start_ns = 0;
278
279 if (trace_btrfs_tree_lock_enabled())
280 start_ns = ktime_get_ns();
281
282 WARN_ON(eb->lock_owner == current->pid);
283again:
284 wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
285 wait_event(eb->write_lock_wq, eb->blocking_writers == 0);
286 write_lock(&eb->lock);
287 if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) {
288 write_unlock(&eb->lock);
289 goto again;
290 }
291 btrfs_assert_spinning_writers_get(eb);
292 btrfs_assert_tree_write_locks_get(eb);
293 eb->lock_owner = current->pid;
294 trace_btrfs_tree_lock(eb, start_ns);
295}
296
297/*
298 * drop a spinning or a blocking write lock.
299 */
300void btrfs_tree_unlock(struct extent_buffer *eb)
301{
302 int blockers = eb->blocking_writers;
303
304 BUG_ON(blockers > 1);
305
306 btrfs_assert_tree_locked(eb);
307 trace_btrfs_tree_unlock(eb);
308 eb->lock_owner = 0;
309 btrfs_assert_tree_write_locks_put(eb);
310
311 if (blockers) {
312 btrfs_assert_no_spinning_writers(eb);
313 eb->blocking_writers--;
314 /*
315 * We need to order modifying blocking_writers above with
316 * actually waking up the sleepers to ensure they see the
317 * updated value of blocking_writers
318 */
319 cond_wake_up(&eb->write_lock_wq);
320 } else {
321 btrfs_assert_spinning_writers_put(eb);
322 write_unlock(&eb->lock);
323 }
324}
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 (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 wake_up(&eb->write_lock_wq);
83 } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
84 BUG_ON(atomic_read(&eb->blocking_readers) == 0);
85 read_lock(&eb->lock);
86 atomic_inc(&eb->spinning_readers);
87 if (atomic_dec_and_test(&eb->blocking_readers))
88 wake_up(&eb->read_lock_wq);
89 }
90 return;
91}
92
93/*
94 * take a spinning read lock. This will wait for any blocking
95 * writers
96 */
97void btrfs_tree_read_lock(struct extent_buffer *eb)
98{
99again:
100 read_lock(&eb->lock);
101 if (atomic_read(&eb->blocking_writers) &&
102 current->pid == eb->lock_owner) {
103 /*
104 * This extent is already write-locked by our thread. We allow
105 * an additional read lock to be added because it's for the same
106 * thread. btrfs_find_all_roots() depends on this as it may be
107 * called on a partly (write-)locked tree.
108 */
109 BUG_ON(eb->lock_nested);
110 eb->lock_nested = 1;
111 read_unlock(&eb->lock);
112 return;
113 }
114 read_unlock(&eb->lock);
115 wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
116 read_lock(&eb->lock);
117 if (atomic_read(&eb->blocking_writers)) {
118 read_unlock(&eb->lock);
119 goto again;
120 }
121 atomic_inc(&eb->read_locks);
122 atomic_inc(&eb->spinning_readers);
123}
124
125/*
126 * returns 1 if we get the read lock and 0 if we don't
127 * this won't wait for blocking writers
128 */
129int btrfs_try_tree_read_lock(struct extent_buffer *eb)
130{
131 if (atomic_read(&eb->blocking_writers))
132 return 0;
133
134 read_lock(&eb->lock);
135 if (atomic_read(&eb->blocking_writers)) {
136 read_unlock(&eb->lock);
137 return 0;
138 }
139 atomic_inc(&eb->read_locks);
140 atomic_inc(&eb->spinning_readers);
141 return 1;
142}
143
144/*
145 * returns 1 if we get the read lock and 0 if we don't
146 * this won't wait for blocking writers or readers
147 */
148int btrfs_try_tree_write_lock(struct extent_buffer *eb)
149{
150 if (atomic_read(&eb->blocking_writers) ||
151 atomic_read(&eb->blocking_readers))
152 return 0;
153 write_lock(&eb->lock);
154 if (atomic_read(&eb->blocking_writers) ||
155 atomic_read(&eb->blocking_readers)) {
156 write_unlock(&eb->lock);
157 return 0;
158 }
159 atomic_inc(&eb->write_locks);
160 atomic_inc(&eb->spinning_writers);
161 eb->lock_owner = current->pid;
162 return 1;
163}
164
165/*
166 * drop a spinning read lock
167 */
168void btrfs_tree_read_unlock(struct extent_buffer *eb)
169{
170 if (eb->lock_nested) {
171 read_lock(&eb->lock);
172 if (eb->lock_nested && current->pid == eb->lock_owner) {
173 eb->lock_nested = 0;
174 read_unlock(&eb->lock);
175 return;
176 }
177 read_unlock(&eb->lock);
178 }
179 btrfs_assert_tree_read_locked(eb);
180 WARN_ON(atomic_read(&eb->spinning_readers) == 0);
181 atomic_dec(&eb->spinning_readers);
182 atomic_dec(&eb->read_locks);
183 read_unlock(&eb->lock);
184}
185
186/*
187 * drop a blocking read lock
188 */
189void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
190{
191 if (eb->lock_nested) {
192 read_lock(&eb->lock);
193 if (eb->lock_nested && current->pid == eb->lock_owner) {
194 eb->lock_nested = 0;
195 read_unlock(&eb->lock);
196 return;
197 }
198 read_unlock(&eb->lock);
199 }
200 btrfs_assert_tree_read_locked(eb);
201 WARN_ON(atomic_read(&eb->blocking_readers) == 0);
202 if (atomic_dec_and_test(&eb->blocking_readers))
203 wake_up(&eb->read_lock_wq);
204 atomic_dec(&eb->read_locks);
205}
206
207/*
208 * take a spinning write lock. This will wait for both
209 * blocking readers or writers
210 */
211void btrfs_tree_lock(struct extent_buffer *eb)
212{
213again:
214 wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
215 wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
216 write_lock(&eb->lock);
217 if (atomic_read(&eb->blocking_readers)) {
218 write_unlock(&eb->lock);
219 wait_event(eb->read_lock_wq,
220 atomic_read(&eb->blocking_readers) == 0);
221 goto again;
222 }
223 if (atomic_read(&eb->blocking_writers)) {
224 write_unlock(&eb->lock);
225 wait_event(eb->write_lock_wq,
226 atomic_read(&eb->blocking_writers) == 0);
227 goto again;
228 }
229 WARN_ON(atomic_read(&eb->spinning_writers));
230 atomic_inc(&eb->spinning_writers);
231 atomic_inc(&eb->write_locks);
232 eb->lock_owner = current->pid;
233}
234
235/*
236 * drop a spinning or a blocking write lock.
237 */
238void btrfs_tree_unlock(struct extent_buffer *eb)
239{
240 int blockers = atomic_read(&eb->blocking_writers);
241
242 BUG_ON(blockers > 1);
243
244 btrfs_assert_tree_locked(eb);
245 atomic_dec(&eb->write_locks);
246
247 if (blockers) {
248 WARN_ON(atomic_read(&eb->spinning_writers));
249 atomic_dec(&eb->blocking_writers);
250 smp_wmb();
251 wake_up(&eb->write_lock_wq);
252 } else {
253 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
254 atomic_dec(&eb->spinning_writers);
255 write_unlock(&eb->lock);
256 }
257}
258
259void btrfs_assert_tree_locked(struct extent_buffer *eb)
260{
261 BUG_ON(!atomic_read(&eb->write_locks));
262}
263
264void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
265{
266 BUG_ON(!atomic_read(&eb->read_locks));
267}