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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
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}
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}