Re: [PATCH] btrfs: Improve error reporting in lookup_inline_extent_backref

[David Sterba <dsterba@suse.cz>]

On Wed, Apr 20, 2022 at 02:54:00PM +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 the in-memory
> state of the offending leaf.
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/extent-tree.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 963160a0c393..5a53bcfdca83 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -895,7 +895,10 @@ int lookup_inline_extent_backref(struct btrfs_trans_handle *trans,
>  	err = -ENOENT;
>  	while (1) {
>  		if (ptr >= end) {
> -			WARN_ON(ptr > end);
> +			if (WARN_ON(ptr > end)) {
> +				err = -EUCLEAN;
> +				btrfs_print_leaf(path->slots[0]);

This gives a warning, the slots array does not contain the extent buffer
pointer so this should have been path->nodes[0] but this is already in
'leaf', fixed.