Re: [PATCH v2] btrfs: improve error reporting in lookup_inline_extent_backref

[Filipe Manana <fdmanana@kernel.org>]

On Wed, Apr 27, 2022 at 01:03:44PM +0300, Nikolay Borisov wrote:
> When iterating the backrefs in an extent item if the ptr to the
> 'current' backref record goes beyond the extent item a warning is
> generated and -ENOENT is returned. However what's more appropriate to
> debug such cases would be to return EUCLEAN and also print identifying
> information about the performed search as well as the current content of
> the leaf containing the possibly corrupted extent item.
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
> V2:
>  * Removed WARN_ON and instead introduced btrfs_crit as an error printing
>  mechanism
>  * Now prints a proper error message with information about the searched reference
>  fs/btrfs/extent-tree.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 963160a0c393..5e29c2cee46e 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -895,7 +895,14 @@ int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
>  	err = -ENOENT;
>  	while (1) {
>  		if (ptr >= end) {
> -			WARN_ON(ptr > end);
> +			if (ptr > end) {
> +				err = -EUCLEAN;
> +				btrfs_crit(fs_info,
> +"overrun extent record at slot %lu [%llu BTRFS_EXTENT_ITEM_KEY %llu] while looking for inline extent for root %llu owner %llu offset %llu",
> +				path->slots[0], bytenr, num_bytes,
> +				root_objectid, root_objectid, owner, offset);

Printing 'parent' is also needed in order to figure out what type of reference
we were looking for.

Also, %d can be used to print the slot, as path->slots is an int array.

> +				btrfs_print_leaf(path->nodes[0]);

The leaf should be dumped before printing the message, see:

https://btrfs.wiki.kernel.org/index.php/Development_notes#Output

Other than that, it looks fine.

Thanks.

> +			}
>  			break;
>  		}
>  		iref = (struct btrfs_extent_inline_ref *)ptr;
> --
> 2.25.1
>