LXR linux/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#define BTRFS_WRITE_LOCK_BLOCKING 3
  17#define BTRFS_READ_LOCK_BLOCKING 4
  18
  19/*
  20 * We are limited in number of subclasses by MAX_LOCKDEP_SUBCLASSES, which at
  21 * the time of this patch is 8, which is how many we use.  Keep this in mind if
  22 * you decide you want to add another subclass.
  23 */
  24enum btrfs_lock_nesting {
  25        BTRFS_NESTING_NORMAL,
  26
  27        /*
  28         * When we COW a block we are holding the lock on the original block,
  29         * and since our lockdep maps are rootid+level, this confuses lockdep
  30         * when we lock the newly allocated COW'd block.  Handle this by having
  31         * a subclass for COW'ed blocks so that lockdep doesn't complain.
  32         */
  33        BTRFS_NESTING_COW,
  34
  35        /*
  36         * Oftentimes we need to lock adjacent nodes on the same level while
  37         * still holding the lock on the original node we searched to, such as
  38         * for searching forward or for split/balance.
  39         *
  40         * Because of this we need to indicate to lockdep that this is
  41         * acceptable by having a different subclass for each of these
  42         * operations.
  43         */
  44        BTRFS_NESTING_LEFT,
  45        BTRFS_NESTING_RIGHT,
  46
  47        /*
  48         * When splitting we will be holding a lock on the left/right node when
  49         * we need to cow that node, thus we need a new set of subclasses for
  50         * these two operations.
  51         */
  52        BTRFS_NESTING_LEFT_COW,
  53        BTRFS_NESTING_RIGHT_COW,
  54
  55        /*
  56         * When splitting we may push nodes to the left or right, but still use
  57         * the subsequent nodes in our path, keeping our locks on those adjacent
  58         * blocks.  Thus when we go to allocate a new split block we've already
  59         * used up all of our available subclasses, so this subclass exists to
  60         * handle this case where we need to allocate a new split block.
  61         */
  62        BTRFS_NESTING_SPLIT,
  63
  64        /*
  65         * When promoting a new block to a root we need to have a special
  66         * subclass so we don't confuse lockdep, as it will appear that we are
  67         * locking a higher level node before a lower level one.  Copying also
  68         * has this problem as it appears we're locking the same block again
  69         * when we make a snapshot of an existing root.
  70         */
  71        BTRFS_NESTING_NEW_ROOT,
  72
  73        /*
  74         * We are limited to MAX_LOCKDEP_SUBLCLASSES number of subclasses, so
  75         * add this in here and add a static_assert to keep us from going over
  76         * the limit.  As of this writing we're limited to 8, and we're
  77         * definitely using 8, hence this check to keep us from messing up in
  78         * the future.
  79         */
  80        BTRFS_NESTING_MAX,
  81};
  82
  83static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
  84              "too many lock subclasses defined");
  85
  86struct btrfs_path;
  87
  88void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
  89void btrfs_tree_lock(struct extent_buffer *eb);
  90void btrfs_tree_unlock(struct extent_buffer *eb);
  91
  92void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest,
  93                            bool recurse);
  94void btrfs_tree_read_lock(struct extent_buffer *eb);
  95void btrfs_tree_read_unlock(struct extent_buffer *eb);
  96void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb);
  97void btrfs_set_lock_blocking_read(struct extent_buffer *eb);
  98void btrfs_set_lock_blocking_write(struct extent_buffer *eb);
  99int btrfs_try_tree_read_lock(struct extent_buffer *eb);
 100int btrfs_try_tree_write_lock(struct extent_buffer *eb);
 101int btrfs_tree_read_lock_atomic(struct extent_buffer *eb);
 102struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root);
 103struct extent_buffer *__btrfs_read_lock_root_node(struct btrfs_root *root,
 104                                                  bool recurse);
 105
 106static inline struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root)
 107{
 108        return __btrfs_read_lock_root_node(root, false);
 109}
 110
 111#ifdef CONFIG_BTRFS_DEBUG
 112static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) {
 113        BUG_ON(!eb->write_locks);
 114}
 115#else
 116static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) { }
 117#endif
 118
 119void btrfs_set_path_blocking(struct btrfs_path *p);
 120void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
 121
 122static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw)
 123{
 124        if (rw == BTRFS_WRITE_LOCK || rw == BTRFS_WRITE_LOCK_BLOCKING)
 125                btrfs_tree_unlock(eb);
 126        else if (rw == BTRFS_READ_LOCK_BLOCKING)
 127                btrfs_tree_read_unlock_blocking(eb);
 128        else if (rw == BTRFS_READ_LOCK)
 129                btrfs_tree_read_unlock(eb);
 130        else
 131                BUG();
 132}
 133
 134struct btrfs_drew_lock {
 135        atomic_t readers;
 136        struct percpu_counter writers;
 137        wait_queue_head_t pending_writers;
 138        wait_queue_head_t pending_readers;
 139};
 140
 141int btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
 142void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock);
 143void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
 144bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
 145void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
 146void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
 147void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
 148
 149#endif
 150