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_write_locked(struct extent_buffer * eb)99 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb)
100 {
101 	lockdep_assert_held_write(&eb->lock);
102 }
103 #else
btrfs_assert_tree_write_locked(struct extent_buffer * eb)104 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb) { }
105 #endif
106 
107 void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
108 
btrfs_tree_unlock_rw(struct extent_buffer * eb,int rw)109 static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
110 {
111 	if (rw == BTRFS_WRITE_LOCK)
112 		btrfs_tree_unlock(eb);
113 	else if (rw == BTRFS_READ_LOCK)
114 		btrfs_tree_read_unlock(eb);
115 	else
116 		BUG();
117 }
118 
119 struct btrfs_drew_lock {
120 	atomic_t readers;
121 	struct percpu_counter writers;
122 	wait_queue_head_t pending_writers;
123 	wait_queue_head_t pending_readers;
124 };
125 
126 int btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
127 void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock);
128 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
129 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
130 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
131 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
132 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
133 
134 #ifdef CONFIG_DEBUG_LOCK_ALLOC
135 void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level);
136 void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb);
137 #else
btrfs_set_buffer_lockdep_class(u64 objectid,struct extent_buffer * eb,int level)138 static inline void btrfs_set_buffer_lockdep_class(u64 objectid,
139 					struct extent_buffer *eb, int level)
140 {
141 }
btrfs_maybe_reset_lockdep_class(struct btrfs_root * root,struct extent_buffer * eb)142 static inline void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root,
143 						   struct extent_buffer *eb)
144 {
145 }
146 #endif
147 
148 #endif
149