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 enum btrfs_lockdep_trans_states {
82 	BTRFS_LOCKDEP_TRANS_COMMIT_PREP,
83 	BTRFS_LOCKDEP_TRANS_UNBLOCKED,
84 	BTRFS_LOCKDEP_TRANS_SUPER_COMMITTED,
85 	BTRFS_LOCKDEP_TRANS_COMPLETED,
86 };
87 
88 /*
89  * Lockdep annotation for wait events.
90  *
91  * @owner:  The struct where the lockdep map is defined
92  * @lock:   The lockdep map corresponding to a wait event
93  *
94  * This macro is used to annotate a wait event. In this case a thread acquires
95  * the lockdep map as writer (exclusive lock) because it has to block until all
96  * the threads that hold the lock as readers signal the condition for the wait
97  * event and release their locks.
98  */
99 #define btrfs_might_wait_for_event(owner, lock)					\
100 	do {									\
101 		rwsem_acquire(&owner->lock##_map, 0, 0, _THIS_IP_);		\
102 		rwsem_release(&owner->lock##_map, _THIS_IP_);			\
103 	} while (0)
104 
105 /*
106  * Protection for the resource/condition of a wait event.
107  *
108  * @owner:  The struct where the lockdep map is defined
109  * @lock:   The lockdep map corresponding to a wait event
110  *
111  * Many threads can modify the condition for the wait event at the same time
112  * and signal the threads that block on the wait event. The threads that modify
113  * the condition and do the signaling acquire the lock as readers (shared
114  * lock).
115  */
116 #define btrfs_lockdep_acquire(owner, lock)					\
117 	rwsem_acquire_read(&owner->lock##_map, 0, 0, _THIS_IP_)
118 
119 /*
120  * Used after signaling the condition for a wait event to release the lockdep
121  * map held by a reader thread.
122  */
123 #define btrfs_lockdep_release(owner, lock)					\
124 	rwsem_release(&owner->lock##_map, _THIS_IP_)
125 
126 /*
127  * Macros for the transaction states wait events, similar to the generic wait
128  * event macros.
129  */
130 #define btrfs_might_wait_for_state(owner, i)					\
131 	do {									\
132 		rwsem_acquire(&owner->btrfs_state_change_map[i], 0, 0, _THIS_IP_); \
133 		rwsem_release(&owner->btrfs_state_change_map[i], _THIS_IP_);	\
134 	} while (0)
135 
136 #define btrfs_trans_state_lockdep_acquire(owner, i)				\
137 	rwsem_acquire_read(&owner->btrfs_state_change_map[i], 0, 0, _THIS_IP_)
138 
139 #define btrfs_trans_state_lockdep_release(owner, i)				\
140 	rwsem_release(&owner->btrfs_state_change_map[i], _THIS_IP_)
141 
142 /* Initialization of the lockdep map */
143 #define btrfs_lockdep_init_map(owner, lock)					\
144 	do {									\
145 		static struct lock_class_key lock##_key;			\
146 		lockdep_init_map(&owner->lock##_map, #lock, &lock##_key, 0);	\
147 	} while (0)
148 
149 /* Initialization of the transaction states lockdep maps. */
150 #define btrfs_state_lockdep_init_map(owner, lock, state)			\
151 	do {									\
152 		static struct lock_class_key lock##_key;			\
153 		lockdep_init_map(&owner->btrfs_state_change_map[state], #lock,	\
154 				 &lock##_key, 0);				\
155 	} while (0)
156 
157 static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
158 	      "too many lock subclasses defined");
159 
160 struct btrfs_path;
161 
162 void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
163 void btrfs_tree_lock(struct extent_buffer *eb);
164 void btrfs_tree_unlock(struct extent_buffer *eb);
165 
166 void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
167 void btrfs_tree_read_lock(struct extent_buffer *eb);
168 void btrfs_tree_read_unlock(struct extent_buffer *eb);
169 int btrfs_try_tree_read_lock(struct extent_buffer *eb);
170 int btrfs_try_tree_write_lock(struct extent_buffer *eb);
171 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root);
172 struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root);
173 struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root);
174 
175 #ifdef CONFIG_BTRFS_DEBUG
btrfs_assert_tree_write_locked(struct extent_buffer * eb)176 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb)
177 {
178 	lockdep_assert_held_write(&eb->lock);
179 }
180 #else
btrfs_assert_tree_write_locked(struct extent_buffer * eb)181 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb) { }
182 #endif
183 
184 void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
185 
btrfs_tree_unlock_rw(struct extent_buffer * eb,int rw)186 static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
187 {
188 	if (rw == BTRFS_WRITE_LOCK)
189 		btrfs_tree_unlock(eb);
190 	else if (rw == BTRFS_READ_LOCK)
191 		btrfs_tree_read_unlock(eb);
192 	else
193 		BUG();
194 }
195 
196 struct btrfs_drew_lock {
197 	atomic_t readers;
198 	atomic_t writers;
199 	wait_queue_head_t pending_writers;
200 	wait_queue_head_t pending_readers;
201 };
202 
203 void btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
204 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
205 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
206 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
207 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
208 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
209 
210 #ifdef CONFIG_DEBUG_LOCK_ALLOC
211 void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level);
212 void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb);
213 #else
btrfs_set_buffer_lockdep_class(u64 objectid,struct extent_buffer * eb,int level)214 static inline void btrfs_set_buffer_lockdep_class(u64 objectid,
215 					struct extent_buffer *eb, int level)
216 {
217 }
btrfs_maybe_reset_lockdep_class(struct btrfs_root * root,struct extent_buffer * eb)218 static inline void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root,
219 						   struct extent_buffer *eb)
220 {
221 }
222 #endif
223 
224 #endif
225