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