Commit 4dff97e6 authored Aug 20, 2020 by Josef Bacik Committed by David Sterba Oct 07, 2020

btrfs: introduce BTRFS_NESTING_SPLIT for split blocks



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>

parent bf59a5a2

fs/btrfs/ctree.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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);

fs/btrfs/locking.h

+9 −0

Original line number	Diff line number	Diff line
		@@ -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