In dm_create_persistent(), when setting up an existing snapshot, if the valid bit from the snapshot header is not set, refuse to activate the snapshot. --- linux-2.4.20a/drivers/md/dm-exception-store.c 2003/02/26 14:50:56 +++ linux-2.4.20b/drivers/md/dm-exception-store.c 2003/03/25 19:02:24 @@ -590,6 +590,12 @@ /* * Sanity checks. */ + if (!ps->valid) { + DMWARN("snapshot is marked invalid"); + r = -EINVAL; + goto bad; + } + if (ps->chunk_size != chunk_size) { DMWARN("chunk size for existing snapshot different " "from that requested");