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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 "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}