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/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
  99 static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) {
 100         lockdep_assert_held(&eb->lock);
 101 }
 102 #else
 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
 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