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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 (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}
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 /*
37 * no lock is required. The lock owner may change if
38 * we have a read lock, but it won't change to or away
39 * from us. If we have the write lock, we are the owner
40 * and it'll never change.
41 */
42 if (eb->lock_nested && current->pid == eb->lock_owner)
43 return;
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}
60
61/*
62 * if we currently have a blocking lock, take the spinlock
63 * and drop our blocking count
64 */
65void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw)
66{
67 /*
68 * no lock is required. The lock owner may change if
69 * we have a read lock, but it won't change to or away
70 * from us. If we have the write lock, we are the owner
71 * and it'll never change.
72 */
73 if (eb->lock_nested && current->pid == eb->lock_owner)
74 return;
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 /*
82 * atomic_dec_and_test implies a barrier for waitqueue_active
83 */
84 if (atomic_dec_and_test(&eb->blocking_writers) &&
85 waitqueue_active(&eb->write_lock_wq))
86 wake_up(&eb->write_lock_wq);
87 } else if (rw == BTRFS_READ_LOCK_BLOCKING) {
88 BUG_ON(atomic_read(&eb->blocking_readers) == 0);
89 read_lock(&eb->lock);
90 atomic_inc(&eb->spinning_readers);
91 /*
92 * atomic_dec_and_test implies a barrier for waitqueue_active
93 */
94 if (atomic_dec_and_test(&eb->blocking_readers) &&
95 waitqueue_active(&eb->read_lock_wq))
96 wake_up(&eb->read_lock_wq);
97 }
98}
99
100/*
101 * take a spinning read lock. This will wait for any blocking
102 * writers
103 */
104void btrfs_tree_read_lock(struct extent_buffer *eb)
105{
106again:
107 BUG_ON(!atomic_read(&eb->blocking_writers) &&
108 current->pid == eb->lock_owner);
109
110 read_lock(&eb->lock);
111 if (atomic_read(&eb->blocking_writers) &&
112 current->pid == eb->lock_owner) {
113 /*
114 * This extent is already write-locked by our thread. We allow
115 * an additional read lock to be added because it's for the same
116 * thread. btrfs_find_all_roots() depends on this as it may be
117 * called on a partly (write-)locked tree.
118 */
119 BUG_ON(eb->lock_nested);
120 eb->lock_nested = 1;
121 read_unlock(&eb->lock);
122 return;
123 }
124 if (atomic_read(&eb->blocking_writers)) {
125 read_unlock(&eb->lock);
126 wait_event(eb->write_lock_wq,
127 atomic_read(&eb->blocking_writers) == 0);
128 goto again;
129 }
130 atomic_inc(&eb->read_locks);
131 atomic_inc(&eb->spinning_readers);
132}
133
134/*
135 * take a spinning read lock.
136 * returns 1 if we get the read lock and 0 if we don't
137 * this won't wait for blocking writers
138 */
139int btrfs_tree_read_lock_atomic(struct extent_buffer *eb)
140{
141 if (atomic_read(&eb->blocking_writers))
142 return 0;
143
144 read_lock(&eb->lock);
145 if (atomic_read(&eb->blocking_writers)) {
146 read_unlock(&eb->lock);
147 return 0;
148 }
149 atomic_inc(&eb->read_locks);
150 atomic_inc(&eb->spinning_readers);
151 return 1;
152}
153
154/*
155 * returns 1 if we get the read lock and 0 if we don't
156 * this won't wait for blocking writers
157 */
158int btrfs_try_tree_read_lock(struct extent_buffer *eb)
159{
160 if (atomic_read(&eb->blocking_writers))
161 return 0;
162
163 if (!read_trylock(&eb->lock))
164 return 0;
165
166 if (atomic_read(&eb->blocking_writers)) {
167 read_unlock(&eb->lock);
168 return 0;
169 }
170 atomic_inc(&eb->read_locks);
171 atomic_inc(&eb->spinning_readers);
172 return 1;
173}
174
175/*
176 * returns 1 if we get the read lock and 0 if we don't
177 * this won't wait for blocking writers or readers
178 */
179int btrfs_try_tree_write_lock(struct extent_buffer *eb)
180{
181 if (atomic_read(&eb->blocking_writers) ||
182 atomic_read(&eb->blocking_readers))
183 return 0;
184
185 write_lock(&eb->lock);
186 if (atomic_read(&eb->blocking_writers) ||
187 atomic_read(&eb->blocking_readers)) {
188 write_unlock(&eb->lock);
189 return 0;
190 }
191 atomic_inc(&eb->write_locks);
192 atomic_inc(&eb->spinning_writers);
193 eb->lock_owner = current->pid;
194 return 1;
195}
196
197/*
198 * drop a spinning read lock
199 */
200void btrfs_tree_read_unlock(struct extent_buffer *eb)
201{
202 /*
203 * if we're nested, we have the write lock. No new locking
204 * is needed as long as we are the lock owner.
205 * The write unlock will do a barrier for us, and the lock_nested
206 * field only matters to the lock owner.
207 */
208 if (eb->lock_nested && current->pid == eb->lock_owner) {
209 eb->lock_nested = 0;
210 return;
211 }
212 btrfs_assert_tree_read_locked(eb);
213 WARN_ON(atomic_read(&eb->spinning_readers) == 0);
214 atomic_dec(&eb->spinning_readers);
215 atomic_dec(&eb->read_locks);
216 read_unlock(&eb->lock);
217}
218
219/*
220 * drop a blocking read lock
221 */
222void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb)
223{
224 /*
225 * if we're nested, we have the write lock. No new locking
226 * is needed as long as we are the lock owner.
227 * The write unlock will do a barrier for us, and the lock_nested
228 * field only matters to the lock owner.
229 */
230 if (eb->lock_nested && current->pid == eb->lock_owner) {
231 eb->lock_nested = 0;
232 return;
233 }
234 btrfs_assert_tree_read_locked(eb);
235 WARN_ON(atomic_read(&eb->blocking_readers) == 0);
236 /*
237 * atomic_dec_and_test implies a barrier for waitqueue_active
238 */
239 if (atomic_dec_and_test(&eb->blocking_readers) &&
240 waitqueue_active(&eb->read_lock_wq))
241 wake_up(&eb->read_lock_wq);
242 atomic_dec(&eb->read_locks);
243}
244
245/*
246 * take a spinning write lock. This will wait for both
247 * blocking readers or writers
248 */
249void btrfs_tree_lock(struct extent_buffer *eb)
250{
251 WARN_ON(eb->lock_owner == current->pid);
252again:
253 wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0);
254 wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0);
255 write_lock(&eb->lock);
256 if (atomic_read(&eb->blocking_readers)) {
257 write_unlock(&eb->lock);
258 wait_event(eb->read_lock_wq,
259 atomic_read(&eb->blocking_readers) == 0);
260 goto again;
261 }
262 if (atomic_read(&eb->blocking_writers)) {
263 write_unlock(&eb->lock);
264 wait_event(eb->write_lock_wq,
265 atomic_read(&eb->blocking_writers) == 0);
266 goto again;
267 }
268 WARN_ON(atomic_read(&eb->spinning_writers));
269 atomic_inc(&eb->spinning_writers);
270 atomic_inc(&eb->write_locks);
271 eb->lock_owner = current->pid;
272}
273
274/*
275 * drop a spinning or a blocking write lock.
276 */
277void btrfs_tree_unlock(struct extent_buffer *eb)
278{
279 int blockers = atomic_read(&eb->blocking_writers);
280
281 BUG_ON(blockers > 1);
282
283 btrfs_assert_tree_locked(eb);
284 eb->lock_owner = 0;
285 atomic_dec(&eb->write_locks);
286
287 if (blockers) {
288 WARN_ON(atomic_read(&eb->spinning_writers));
289 atomic_dec(&eb->blocking_writers);
290 /*
291 * Make sure counter is updated before we wake up waiters.
292 */
293 smp_mb();
294 if (waitqueue_active(&eb->write_lock_wq))
295 wake_up(&eb->write_lock_wq);
296 } else {
297 WARN_ON(atomic_read(&eb->spinning_writers) != 1);
298 atomic_dec(&eb->spinning_writers);
299 write_unlock(&eb->lock);
300 }
301}
302
303void btrfs_assert_tree_locked(struct extent_buffer *eb)
304{
305 BUG_ON(!atomic_read(&eb->write_locks));
306}
307
308static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
309{
310 BUG_ON(!atomic_read(&eb->read_locks));
311}