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 struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root); 98 99 #ifdef CONFIG_BTRFS_DEBUG 100 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb) 101 { 102 lockdep_assert_held_write(&eb->lock); 103 } 104 #else 105 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb) { } 106 #endif 107 108 void btrfs_unlock_up_safe(struct btrfs_path *path, int level); 109 110 static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw) 111 { 112 if (rw == BTRFS_WRITE_LOCK) 113 btrfs_tree_unlock(eb); 114 else if (rw == BTRFS_READ_LOCK) 115 btrfs_tree_read_unlock(eb); 116 else 117 BUG(); 118 } 119 120 struct btrfs_drew_lock { 121 atomic_t readers; 122 struct percpu_counter writers; 123 wait_queue_head_t pending_writers; 124 wait_queue_head_t pending_readers; 125 }; 126 127 int btrfs_drew_lock_init(struct btrfs_drew_lock *lock); 128 void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock); 129 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock); 130 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock); 131 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock); 132 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock); 133 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock); 134 135 #ifdef CONFIG_DEBUG_LOCK_ALLOC 136 void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level); 137 void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb); 138 #else 139 static inline void btrfs_set_buffer_lockdep_class(u64 objectid, 140 struct extent_buffer *eb, int level) 141 { 142 } 143 static inline void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, 144 struct extent_buffer *eb) 145 { 146 } 147 #endif 148 149 #endif 150