Btrfs: release both paths before logging dir/changed extents
[firefly-linux-kernel-4.4.55.git] / fs / btrfs / locking.c
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
27 static 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  */
34 void 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  */
66 void 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  */
99 void btrfs_tree_read_lock(struct extent_buffer *eb)
100 {
101 again:
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  */
130 int 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  */
149 int 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  */
169 void 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  */
190 void 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  */
213 void btrfs_tree_lock(struct extent_buffer *eb)
214 {
215 again:
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  */
240 void 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
262 void btrfs_assert_tree_locked(struct extent_buffer *eb)
263 {
264         BUG_ON(!atomic_read(&eb->write_locks));
265 }
266
267 static void btrfs_assert_tree_read_locked(struct extent_buffer *eb)
268 {
269         BUG_ON(!atomic_read(&eb->read_locks));
270 }