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
  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 */
  22enum 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
  81static_assert(BTRFS_NESTING_MAX <= MAX_LOCKDEP_SUBCLASSES,
  82              "too many lock subclasses defined");
  83
  84struct btrfs_path;
  85
  86void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
  87void btrfs_tree_lock(struct extent_buffer *eb);
  88void btrfs_tree_unlock(struct extent_buffer *eb);
  89
  90void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest);
  91void btrfs_tree_read_lock(struct extent_buffer *eb);
  92void btrfs_tree_read_unlock(struct extent_buffer *eb);
  93int btrfs_try_tree_read_lock(struct extent_buffer *eb);
  94int btrfs_try_tree_write_lock(struct extent_buffer *eb);
  95struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root);
  96struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root);
  97
  98#ifdef CONFIG_BTRFS_DEBUG
  99static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) {
 100        lockdep_assert_held(&eb->lock);
 101}
 102#else
 103static inline void btrfs_assert_tree_locked(struct extent_buffer *eb) { }
 104#endif
 105
 106void btrfs_unlock_up_safe(struct btrfs_path *path, int level);
 107
 108static 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
 118struct 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
 125int btrfs_drew_lock_init(struct btrfs_drew_lock *lock);
 126void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock);
 127void btrfs_drew_write_lock(struct btrfs_drew_lock *lock);
 128bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock);
 129void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock);
 130void btrfs_drew_read_lock(struct btrfs_drew_lock *lock);
 131void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock);
 132
 133#endif
 134