Call btrfs_cow_block while lowering tree level.

When freeing root block of a tree,  btrfs_free_extent' parameter
'ref_generation' is from root block itseft.  When freeing non-root
block,  'ref_generation' is from its parent. so when converting a
non-root block to root block, we must guarantee its generation is
equal to its parent's generation.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index cf32651876bf..ef8809c1e69c 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -720,6 +720,9 @@ static int balance_level(struct btrfs_trans_handle *trans,
                 /* promote the child to a root */
                 child = read_node_slot(root, mid, 0);
                 BUG_ON(!child);
+                ret = btrfs_cow_block(trans, root, child, mid, 0, &child);
+                BUG_ON(ret);
+
                 root->node = child;
                 path->nodes[level] = NULL;
                 clean_tree_block(trans, root, mid);