Re: [PATCH v2 4/6] btrfs-progs: check/lowmem: Repair bad imode early

[Nikolay Borisov <nborisov@suse.com>]

On 5.09.19 г. 10:57 ч., Qu Wenruo wrote:
> For lowmem mode, if we hit a bad inode mode, normally it is reported
> when we checking the DIR_INDEX/DIR_ITEM of the parent inode.
> 
> If we didn't repair at that timing, the error will be recorded even we
> fixed it later.
> 
> So this patch will check for INODE_ITEM_MISMATCH error type, and if it's
> really caused by invalid imode, repair it and clear the error.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  check/mode-lowmem.c | 39 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c
> index 5f7f101daab1..5d0c520217fa 100644
> --- a/check/mode-lowmem.c
> +++ b/check/mode-lowmem.c
> @@ -1550,6 +1550,35 @@ static int lowmem_delete_corrupted_dir_item(struct btrfs_root *root,
>  	return ret;
>  }
>  
> +static int try_repair_imode(struct btrfs_root *root, u64 ino)
> +{
> +	struct btrfs_inode_item *iitem;
> +	struct btrfs_path path;
> +	struct btrfs_key key;
> +	int ret;
> +
> +	key.objectid = ino;
> +	key.type = BTRFS_INODE_ITEM_KEY;
> +	key.offset = 0;
> +	btrfs_init_path(&path);
> +
> +	ret = btrfs_search_slot(NULL, root, &key, &path, 0, 0);
> +	if (ret > 0)
> +		ret = -ENOENT;
> +	if (ret < 0)
> +		goto out;
> +	iitem = btrfs_item_ptr(path.nodes[0], path.slots[0],
> +			       struct btrfs_inode_item);
> +	if (!is_valid_imode(btrfs_inode_mode(path.nodes[0], iitem))) {

INODE_ITEM_MISMATCH is only set if:

1. The first inode item is not a directory (it should always be)
2. There is a mismatch between the filetype in the inode item and in the
dir/index item pointing to it.

By using this check you could possibly miss case 1 above, if the first
inode has a valid type e.g. regular whereas it should really be a
directory.

I'm not entirely sure whether it makes sense to handle this situation,
since admittedly, it would require a perfect storm to get such a
corruption.


<snip>