Re: [PATCH 07/20] btrfs: handle chunk tree lookup error in btrfs_relocate_sys_chunks()

Qu Wenruo
2024-01-25T04:08:21Z

On 2024/1/25 07:48, David Sterba wrote:
> The unhandled case in btrfs_relocate_sys_chunks() loop is a corruption,
> as it could be caused only by two impossible conditions:
>
> - at first the search key is set up to look for a chunk tree item, with
> offset -1, this is an inexact search and the key->offset will contain
> the correct offset upon a successful search, a valid chunk tree item
> cannot have an offset -1
>
> - after first successful search, the found_key corresponds to a chunk
> item, the offset is decremented by 1 before the next loop, it's
> impossible to find a chunk item there due to alignment and size
> constraints
>
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
> fs/btrfs/volumes.c | 12 +++++++++++-
> 1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index d67785be2c77..6aae92e4b424 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -3393,7 +3393,17 @@ static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info)
> mutex_unlock(&fs_info->reclaim_bgs_lock);
> goto error;
> }
> - BUG_ON(ret == 0); /* Corruption */
> + if (ret == 0) {
> + /*
> + * On the first search we would find chunk tree with
> + * offset -1, which is not possible. On subsequent
> + * loops this would find an existing item on an invalid
> + * offset (one less than the previous one, wrong
> + * alignment and size).
> + */
> + ret = -EUCLEAN;
> + goto error;

This can be handled by adding new root item offset key check in
tree-checker, then converting to an ASSERT().

Thanks,
Qu
> + }
>
> ret = btrfs_previous_item(chunk_root, path, key.objectid,
> key.type);