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/percpu_counter.h>
12 #include "extent_io.h"
13
14 #define BTRFS_WRITE_LOCK 1
15 #define BTRFS_READ_LOCK 2
16 #define BTRFS_WRITE_LOCK_BLOCKING 3
17 #define BTRFS_READ_LOCK_BLOCKING 4
18
19 /*
20 * We are limited in number of subclasses by MAX_LOCKDEP_SUBCLASSES, which at
21 * the time of this patch is 8, which is how many we use. Keep this in mind if
22 * you decide you want to add another subclass.
23 */
24 enum btrfs_lock_nesting {
25 BTRFS_NESTING_NORMAL,
26
27 /*
28 * When we COW a block we are holding the lock on the original block,
29 * and since our lockdep maps are rootid+level, this confuses lockdep
30 * when we lock the newly allocated COW'd block. Handle this by having
31 * a subclass for COW'ed blocks so that lockdep doesn't complain.
32 */
33 BTRFS_NESTING_COW,
34
35 /*
36 * Oftentimes we need to lock adjacent nodes on the same level while
37 * still holding the lock on the original node we searched to, such as
38 * for searching forward or for split/balance.
39 *
40 * Because of this we need to indicate to lockdep that this is
41 * acceptable by having a different subclass for each of these
42 * operations.
43 */
44 BTRFS_NESTING_LEFT,
45 BTRFS_NESTING_RIGHT,
46
47 /*
48 * When splitting we will be holding a lock on the left/right node when
49 * we need to cow that node, thus we need a new set of subclasses for
50 * these two operations.
51 */
52 BTRFS_NESTING_LEFT_COW,
53 BTRFS_NESTING_RIGHT_COW,
54
55 /*
56 * When splitting we may push nodes to the left or right, but still use
57 * the subsequent nodes in our path, keeping our locks on those adjacent
58 * blocks. Thus when we go to allocate a new split block we've already
59 * used up all of our available subclasses, so this subclass exists to
60 * handle this case where we need to allocate a new split block.
61 */
62 BTRFS_NESTING_SPLIT,
63
64 /*
65 * When promoting a new block to a root we need to have a special
66 * subclass so we don't confuse lockdep, as it will appear that we are
67 * locking a higher level node before a lower level one. Copying also
68 * has this problem as it appears we're locking the same block again
69 * when we make a snapshot of an existing root.
70 */
71 BTRFS_NESTING_NEW_ROOT,
72
73 /*
74 * We are limited to MAX_LOCKDEP_SUBLCLASSES number of subclasses, so
75 * add this in here and add a static_assert to keep us from going over
76 * the limit. As of this writing we're limited to 8, and we're
77 * definitely using 8, hence this check to keep us from messing up in
78 * the future.
79 */
80 BTRFS_NESTING_MAX,
81 };
82
83 static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
84 "too many lock subclasses defined");
85
86 struct btrfs_path;
87
88 void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
89 void btrfs_tree_lock(struct extent_buffer *eb);
90 void btrfs_tree_unlock(struct extent_buffer *eb);
91
92 void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest,
93 bool recurse);
94 void btrfs_tree_read_lock(struct extent_buffer *eb);
95 void btrfs_tree_read_unlock(struct extent_buffer *eb);
96 void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb);
97 void btrfs_set_lock_blocking_read(struct extent_buffer *eb);
98 void btrfs_set_lock_blocking_write(struct extent_buffer *eb);
99 int btrfs_try_tree_read_lock(struct extent_buffer *eb);
100 int btrfs_try_tree_write_lock(struct extent_buffer *eb);
101 int btrfs_tree_read_lock_atomic(struct extent_buffer *eb);
102 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root);
103 struct extent_buffer *__btrfs_read_lock_root_node(struct btrfs_root *root,
104 bool recurse);
105
btrfs_read_lock_root_node(struct btrfs_root * root)106 static inline struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
107 {
108 return __btrfs_read_lock_root_node(root, false);
109 }
110
111 #ifdef CONFIG_BTRFS_DEBUG
btrfs_assert_tree_locked(struct extent_buffer * eb)112 static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) {
113 BUG_ON(!eb->write_locks);
114 }
115 #else
btrfs_assert_tree_locked(struct extent_buffer * eb)116 static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) { }
117 #endif
118
119 void btrfs_set_path_blocking(struct btrfs_path *p);
120 void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
121
btrfs_tree_unlock_rw(struct extent_buffer * eb,int rw)122 static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
123 {
124 if (rw == BTRFS_WRITE_LOCK || rw == BTRFS_WRITE_LOCK_BLOCKING)
125 btrfs_tree_unlock(eb);
126 else if (rw == BTRFS_READ_LOCK_BLOCKING)
127 btrfs_tree_read_unlock_blocking(eb);
128 else if (rw == BTRFS_READ_LOCK)
129 btrfs_tree_read_unlock(eb);
130 else
131 BUG();
132 }
133
134 struct btrfs_drew_lock {
135 atomic_t readers;
136 struct percpu_counter writers;
137 wait_queue_head_t pending_writers;
138 wait_queue_head_t pending_readers;
139 };
140
141 int btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
142 void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock);
143 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
144 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
145 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
146 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
147 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
148
149 #endif
150
