There was a race between ll_unlink and ll_create_node: notably,

There was a race between ll_unlink and ll_create_node: notably,
ll_unlink would make the inode available on the MDS before the local
dentry/inode on the client was put away.  This could lead to re-using
inode numbers with a concurrent create going on.

We fixed this using the generation number.  We also added the
inode/generation to unlink as a sanity check.