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btrfs: introduce BTRFS_NESTING_SPLIT for split blocks

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If we are splitting a leaf/node, we could do something like the
following

lock(leaf)  BTRFS_NESTING_NORMAL
  lock(left) BTRFS_NESTING_LEFT + BTRFS_NESTING_COW
    push from leaf -> left
      reset path to point to left
        split left
          allocate new block, lock block BTRFS_NESTING_SPLIT

at the new block point we need to have a different nesting level,
because we have already used either BTRFS_NESTING_LEFT or
BTRFS_NESTING_RIGHT when pushing items from the original leaf into the
adjacent leaves.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2020-08-20 11:46:06 -04:00 committed by David Sterba
parent bf59a5a216
commit 4dff97e690
2 changed files with 11 additions and 2 deletions
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4
fs/btrfs/ctree.c
View file

@ -3537,7 +3537,7 @@ static noinline int split_node(struct btrfs_trans_handle *trans,
btrfs_node_key(c, &disk_key, mid);
split = alloc_tree_block_no_bg_flush(trans, root, 0, &disk_key, level,
c->start, 0, BTRFS_NESTING_NORMAL);
c->start, 0, BTRFS_NESTING_SPLIT);
if (IS_ERR(split))
return PTR_ERR(split);
@ -4324,7 +4324,7 @@ static noinline int split_leaf(struct btrfs_trans_handle *trans,
btrfs_item_key(l, &disk_key, mid);
right = alloc_tree_block_no_bg_flush(trans, root, 0, &disk_key, 0,
l->start, 0, BTRFS_NESTING_NORMAL);
l->start, 0, BTRFS_NESTING_SPLIT);
if (IS_ERR(right))
return PTR_ERR(right);

9
fs/btrfs/locking.h
View file

@ -52,6 +52,15 @@ enum btrfs_lock_nesting {
BTRFS_NESTING_LEFT_COW,
BTRFS_NESTING_RIGHT_COW,
/*
* When splitting we may push nodes to the left or right, but still use
* the subsequent nodes in our path, keeping our locks on those adjacent
* blocks. Thus when we go to allocate a new split block we've already
* used up all of our available subclasses, so this subclass exists to
* handle this case where we need to allocate a new split block.
*/
BTRFS_NESTING_SPLIT,
/*
* We are limited to MAX_LOCKDEP_SUBLCLASSES number of subclasses, so
* add this in here and add a static_assert to keep us from going over