1 /* SPDX-License-Identifier: GPL-2.0 */
2 /*
3 * Copyright (C) 2008 Oracle. All rights reserved.
4 */
5
6 #ifndef BTRFS_LOCKING_H
7 #define BTRFS_LOCKING_H
8
9 #include <linux/atomic.h>
10 #include <linux/wait.h>
11 #include <linux/lockdep.h>
12 #include <linux/percpu_counter.h>
13 #include "extent_io.h"
14
15 struct extent_buffer;
16 struct btrfs_path;
17 struct btrfs_root;
18
19 #define BTRFS_WRITE_LOCK 1
20 #define BTRFS_READ_LOCK 2
21
22 /*
23 * We are limited in number of subclasses by MAX_LOCKDEP_SUBCLASSES, which at
24 * the time of this patch is 8, which is how many we use. Keep this in mind if
25 * you decide you want to add another subclass.
26 */
27 enum btrfs_lock_nesting {
28 BTRFS_NESTING_NORMAL,
29
30 /*
31 * When we COW a block we are holding the lock on the original block,
32 * and since our lockdep maps are rootid+level, this confuses lockdep
33 * when we lock the newly allocated COW'd block. Handle this by having
34 * a subclass for COW'ed blocks so that lockdep doesn't complain.
35 */
36 BTRFS_NESTING_COW,
37
38 /*
39 * Oftentimes we need to lock adjacent nodes on the same level while
40 * still holding the lock on the original node we searched to, such as
41 * for searching forward or for split/balance.
42 *
43 * Because of this we need to indicate to lockdep that this is
44 * acceptable by having a different subclass for each of these
45 * operations.
46 */
47 BTRFS_NESTING_LEFT,
48 BTRFS_NESTING_RIGHT,
49
50 /*
51 * When splitting we will be holding a lock on the left/right node when
52 * we need to cow that node, thus we need a new set of subclasses for
53 * these two operations.
54 */
55 BTRFS_NESTING_LEFT_COW,
56 BTRFS_NESTING_RIGHT_COW,
57
58 /*
59 * When splitting we may push nodes to the left or right, but still use
60 * the subsequent nodes in our path, keeping our locks on those adjacent
61 * blocks. Thus when we go to allocate a new split block we've already
62 * used up all of our available subclasses, so this subclass exists to
63 * handle this case where we need to allocate a new split block.
64 */
65 BTRFS_NESTING_SPLIT,
66
67 /*
68 * When promoting a new block to a root we need to have a special
69 * subclass so we don't confuse lockdep, as it will appear that we are
70 * locking a higher level node before a lower level one. Copying also
71 * has this problem as it appears we're locking the same block again
72 * when we make a snapshot of an existing root.
73 */
74 BTRFS_NESTING_NEW_ROOT,
75
76 /*
77 * We are limited to MAX_LOCKDEP_SUBLCLASSES number of subclasses, so
78 * add this in here and add a static_assert to keep us from going over
79 * the limit. As of this writing we're limited to 8, and we're
80 * definitely using 8, hence this check to keep us from messing up in
81 * the future.
82 */
83 BTRFS_NESTING_MAX,
84 };
85
86 enum btrfs_lockdep_trans_states {
87 BTRFS_LOCKDEP_TRANS_COMMIT_PREP,
88 BTRFS_LOCKDEP_TRANS_UNBLOCKED,
89 BTRFS_LOCKDEP_TRANS_SUPER_COMMITTED,
90 BTRFS_LOCKDEP_TRANS_COMPLETED,
91 };
92
93 /*
94 * Lockdep annotation for wait events.
95 *
96 * @owner: The struct where the lockdep map is defined
97 * @lock: The lockdep map corresponding to a wait event
98 *
99 * This macro is used to annotate a wait event. In this case a thread acquires
100 * the lockdep map as writer (exclusive lock) because it has to block until all
101 * the threads that hold the lock as readers signal the condition for the wait
102 * event and release their locks.
103 */
104 #define btrfs_might_wait_for_event(owner, lock) \
105 do { \
106 rwsem_acquire(&owner->lock##_map, 0, 0, _THIS_IP_); \
107 rwsem_release(&owner->lock##_map, _THIS_IP_); \
108 } while (0)
109
110 /*
111 * Protection for the resource/condition of a wait event.
112 *
113 * @owner: The struct where the lockdep map is defined
114 * @lock: The lockdep map corresponding to a wait event
115 *
116 * Many threads can modify the condition for the wait event at the same time
117 * and signal the threads that block on the wait event. The threads that modify
118 * the condition and do the signaling acquire the lock as readers (shared
119 * lock).
120 */
121 #define btrfs_lockdep_acquire(owner, lock) \
122 rwsem_acquire_read(&owner->lock##_map, 0, 0, _THIS_IP_)
123
124 /*
125 * Used after signaling the condition for a wait event to release the lockdep
126 * map held by a reader thread.
127 */
128 #define btrfs_lockdep_release(owner, lock) \
129 rwsem_release(&owner->lock##_map, _THIS_IP_)
130
131 /*
132 * Macros for the transaction states wait events, similar to the generic wait
133 * event macros.
134 */
135 #define btrfs_might_wait_for_state(owner, i) \
136 do { \
137 rwsem_acquire(&owner->btrfs_state_change_map[i], 0, 0, _THIS_IP_); \
138 rwsem_release(&owner->btrfs_state_change_map[i], _THIS_IP_); \
139 } while (0)
140
141 #define btrfs_trans_state_lockdep_acquire(owner, i) \
142 rwsem_acquire_read(&owner->btrfs_state_change_map[i], 0, 0, _THIS_IP_)
143
144 #define btrfs_trans_state_lockdep_release(owner, i) \
145 rwsem_release(&owner->btrfs_state_change_map[i], _THIS_IP_)
146
147 /* Initialization of the lockdep map */
148 #define btrfs_lockdep_init_map(owner, lock) \
149 do { \
150 static struct lock_class_key lock##_key; \
151 lockdep_init_map(&owner->lock##_map, #lock, &lock##_key, 0); \
152 } while (0)
153
154 /* Initialization of the transaction states lockdep maps. */
155 #define btrfs_state_lockdep_init_map(owner, lock, state) \
156 do { \
157 static struct lock_class_key lock##_key; \
158 lockdep_init_map(&owner->btrfs_state_change_map[state], #lock, \
159 &lock##_key, 0); \
160 } while (0)
161
162 static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
163 "too many lock subclasses defined");
164
165 void btrfs_tree_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
166
167 static inline void btrfs_tree_lock(struct extent_buffer *eb)
168 {
169 btrfs_tree_lock_nested(eb, BTRFS_NESTING_NORMAL);
170 }
171
172 void btrfs_tree_unlock(struct extent_buffer *eb);
173
174 void btrfs_tree_read_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
175
176 static inline void btrfs_tree_read_lock(struct extent_buffer *eb)
177 {
178 btrfs_tree_read_lock_nested(eb, BTRFS_NESTING_NORMAL);
179 }
180
181 void btrfs_tree_read_unlock(struct extent_buffer *eb);
182 int btrfs_try_tree_read_lock(struct extent_buffer *eb);
183 int btrfs_try_tree_write_lock(struct extent_buffer *eb);
184 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root);
185 struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root);
186 struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root);
187
188 #ifdef CONFIG_BTRFS_DEBUG
189 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb)
190 {
191 lockdep_assert_held_write(&eb->lock);
192 }
193 #else
194 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb) { }
195 #endif
196
197 void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
198
199 static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
200 {
201 if (rw == BTRFS_WRITE_LOCK)
202 btrfs_tree_unlock(eb);
203 else if (rw == BTRFS_READ_LOCK)
204 btrfs_tree_read_unlock(eb);
205 else
206 BUG();
207 }
208
209 struct btrfs_drew_lock {
210 atomic_t readers;
211 atomic_t writers;
212 wait_queue_head_t pending_writers;
213 wait_queue_head_t pending_readers;
214 };
215
216 void btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
217 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
218 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
219 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
220 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
221 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
222
223 #ifdef CONFIG_DEBUG_LOCK_ALLOC
224 void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level);
225 void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb);
226 #else
227 static inline void btrfs_set_buffer_lockdep_class(u64 objectid,
228 struct extent_buffer *eb, int level)
229 {
230 }
231 static inline void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root,
232 struct extent_buffer *eb)
233 {
234 }
235 #endif
236
237 #endif
238
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