fs/btrfs/locking.h

   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/lockdep.h>
  12 #include <linux/percpu_counter.h>
  13 #include "extent_io.h"
  14
  15 struct extent_buffer;
  16 struct btrfs_path;
  17 struct btrfs_root;
  18
  19 #define BTRFS_WRITE_LOCK 1
  20 #define BTRFS_READ_LOCK 2
  21
  22 /*
  23  * We are limited in number of subclasses by MAX_LOCKDEP_SUBCLASSES, which at
  24  * the time of this patch is 8, which is how many we use.  Keep this in mind if
  25  * you decide you want to add another subclass.
  26  */
  27 enum btrfs_lock_nesting {
  28         BTRFS_NESTING_NORMAL,
  29
  30         /*
  31          * When we COW a block we are holding the lock on the original block,
  32          * and since our lockdep maps are rootid+level, this confuses lockdep
  33          * when we lock the newly allocated COW'd block.  Handle this by having
  34          * a subclass for COW'ed blocks so that lockdep doesn't complain.
  35          */
  36         BTRFS_NESTING_COW,
  37
  38         /*
  39          * Oftentimes we need to lock adjacent nodes on the same level while
  40          * still holding the lock on the original node we searched to, such as
  41          * for searching forward or for split/balance.
  42          *
  43          * Because of this we need to indicate to lockdep that this is
  44          * acceptable by having a different subclass for each of these
  45          * operations.
  46          */
  47         BTRFS_NESTING_LEFT,
  48         BTRFS_NESTING_RIGHT,
  49
  50         /*
  51          * When splitting we will be holding a lock on the left/right node when
  52          * we need to cow that node, thus we need a new set of subclasses for
  53          * these two operations.
  54          */
  55         BTRFS_NESTING_LEFT_COW,
  56         BTRFS_NESTING_RIGHT_COW,
  57
  58         /*
  59          * When splitting we may push nodes to the left or right, but still use
  60          * the subsequent nodes in our path, keeping our locks on those adjacent
  61          * blocks.  Thus when we go to allocate a new split block we've already
  62          * used up all of our available subclasses, so this subclass exists to
  63          * handle this case where we need to allocate a new split block.
  64          */
  65         BTRFS_NESTING_SPLIT,
  66
  67         /*
  68          * When promoting a new block to a root we need to have a special
  69          * subclass so we don't confuse lockdep, as it will appear that we are
  70          * locking a higher level node before a lower level one.  Copying also
  71          * has this problem as it appears we're locking the same block again
  72          * when we make a snapshot of an existing root.
  73          */
  74         BTRFS_NESTING_NEW_ROOT,
  75
  76         /*
  77          * We are limited to MAX_LOCKDEP_SUBLCLASSES number of subclasses, so
  78          * add this in here and add a static_assert to keep us from going over
  79          * the limit.  As of this writing we're limited to 8, and we're
  80          * definitely using 8, hence this check to keep us from messing up in
  81          * the future.
  82          */
  83         BTRFS_NESTING_MAX,
  84 };
  85
  86 enum btrfs_lockdep_trans_states {
  87         BTRFS_LOCKDEP_TRANS_COMMIT_PREP,
  88         BTRFS_LOCKDEP_TRANS_UNBLOCKED,
  89         BTRFS_LOCKDEP_TRANS_SUPER_COMMITTED,
  90         BTRFS_LOCKDEP_TRANS_COMPLETED,
  91 };
  92
  93 /*
  94  * Lockdep annotation for wait events.
  95  *
  96  * @owner:  The struct where the lockdep map is defined
  97  * @lock:   The lockdep map corresponding to a wait event
  98  *
  99  * This macro is used to annotate a wait event. In this case a thread acquires
 100  * the lockdep map as writer (exclusive lock) because it has to block until all
 101  * the threads that hold the lock as readers signal the condition for the wait
 102  * event and release their locks.
 103  */
 104 #define btrfs_might_wait_for_event(owner, lock)                                 \
 105         do {                                                                    \
 106                 rwsem_acquire(&owner->lock##_map, 0, 0, _THIS_IP_);             \
 107                 rwsem_release(&owner->lock##_map, _THIS_IP_);                   \
 108         } while (0)
 109
 110 /*
 111  * Protection for the resource/condition of a wait event.
 112  *
 113  * @owner:  The struct where the lockdep map is defined
 114  * @lock:   The lockdep map corresponding to a wait event
 115  *
 116  * Many threads can modify the condition for the wait event at the same time
 117  * and signal the threads that block on the wait event. The threads that modify
 118  * the condition and do the signaling acquire the lock as readers (shared
 119  * lock).
 120  */
 121 #define btrfs_lockdep_acquire(owner, lock)                                      \
 122         rwsem_acquire_read(&owner->lock##_map, 0, 0, _THIS_IP_)
 123
 124 /*
 125  * Used after signaling the condition for a wait event to release the lockdep
 126  * map held by a reader thread.
 127  */
 128 #define btrfs_lockdep_release(owner, lock)                                      \
 129         rwsem_release(&owner->lock##_map, _THIS_IP_)
 130
 131 /*
 132  * Macros for the transaction states wait events, similar to the generic wait
 133  * event macros.
 134  */
 135 #define btrfs_might_wait_for_state(owner, i)                                    \
 136         do {                                                                    \
 137                 rwsem_acquire(&owner->btrfs_state_change_map[i], 0, 0, _THIS_IP_); \
 138                 rwsem_release(&owner->btrfs_state_change_map[i], _THIS_IP_);    \
 139         } while (0)
 140
 141 #define btrfs_trans_state_lockdep_acquire(owner, i)                             \
 142         rwsem_acquire_read(&owner->btrfs_state_change_map[i], 0, 0, _THIS_IP_)
 143
 144 #define btrfs_trans_state_lockdep_release(owner, i)                             \
 145         rwsem_release(&owner->btrfs_state_change_map[i], _THIS_IP_)
 146
 147 /* Initialization of the lockdep map */
 148 #define btrfs_lockdep_init_map(owner, lock)                                     \
 149         do {                                                                    \
 150                 static struct lock_class_key lock##_key;                        \
 151                 lockdep_init_map(&owner->lock##_map, #lock, &lock##_key, 0);    \
 152         } while (0)
 153
 154 /* Initialization of the transaction states lockdep maps. */
 155 #define btrfs_state_lockdep_init_map(owner, lock, state)                        \
 156         do {                                                                    \
 157                 static struct lock_class_key lock##_key;                        \
 158                 lockdep_init_map(&owner->btrfs_state_change_map[state], #lock,  \
 159                                  &lock##_key, 0);                               \
 160         } while (0)
 161
 162 static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
 163               "too many lock subclasses defined");
 164
 165 void btrfs_tree_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
 166
 167 static inline void btrfs_tree_lock(struct extent_buffer *eb)
 168 {
 169         btrfs_tree_lock_nested(eb, BTRFS_NESTING_NORMAL);
 170 }
 171
 172 void btrfs_tree_unlock(struct extent_buffer *eb);
 173
 174 void btrfs_tree_read_lock_nested(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
 175
 176 static inline void btrfs_tree_read_lock(struct extent_buffer *eb)
 177 {
 178         btrfs_tree_read_lock_nested(eb, BTRFS_NESTING_NORMAL);
 179 }
 180
 181 void btrfs_tree_read_unlock(struct extent_buffer *eb);
 182 int btrfs_try_tree_read_lock(struct extent_buffer *eb);
 183 int btrfs_try_tree_write_lock(struct extent_buffer *eb);
 184 struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root);
 185 struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root);
 186 struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root);
 187
 188 #ifdef CONFIG_BTRFS_DEBUG
 189 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb)
 190 {
 191         lockdep_assert_held_write(&eb->lock);
 192 }
 193 #else
 194 static inline void btrfs_assert_tree_write_locked(struct extent_buffer *eb) { }
 195 #endif
 196
 197 void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
 198
 199 static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
 200 {
 201         if (rw == BTRFS_WRITE_LOCK)
 202                 btrfs_tree_unlock(eb);
 203         else if (rw == BTRFS_READ_LOCK)
 204                 btrfs_tree_read_unlock(eb);
 205         else
 206                 BUG();
 207 }
 208
 209 struct btrfs_drew_lock {
 210         atomic_t readers;
 211         atomic_t writers;
 212         wait_queue_head_t pending_writers;
 213         wait_queue_head_t pending_readers;
 214 };
 215
 216 void btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
 217 void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
 218 bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
 219 void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
 220 void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
 221 void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
 222
 223 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 224 void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level);
 225 void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb);
 226 #else
 227 static inline void btrfs_set_buffer_lockdep_class(u64 objectid,
 228                                         struct extent_buffer *eb, int level)
 229 {
 230 }
 231 static inline void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root,
 232                                                    struct extent_buffer *eb)
 233 {
 234 }
 235 #endif
 236
 237 #endif