Re: [PATCH] btrfs: fix backref walking not returning all inode refs

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

> From: Filipe Manana <fdmanana@suse.com>
> 
> When using the logical to ino ioctl v2, if the flag to ignore offsets of
> file extent items (BTRFS_LOGICAL_INO_ARGS_IGNORE_OFFSET) is given, the
> backref walking code ends up not returning references for all file offsets
> of an inode that point to the given logical bytenr. This happens since
> kernel 6.2, commit 6ce6ba534418 ("btrfs: use a single argument for extent
> offset in backref walking functions"), as it mistakenly skipped the search
> for file extent items in a leaf that point to the target extent if that
> flag is given. Instead it should only skip the filtering done by
> check_extent_in_eb() - that is, it should not avoid the calls to that
> function.
> 
> So fix this by always calling check_extent_in_eb() and have this function
> do the filtering only if an extent offset is given and the flag to ignore
> offsets is not set.
> Fixes: 6ce6ba534418 ("btrfs: use a single argument for extent offset in backref walking functions")
> Reported-by: Vladimir Panteleev <git@vladimir.panteleev.md>
> Link: https://lore.kernel.org/linux-btrfs/CAHhfkvwo=nmzrJSqZ2qMfF-rZB-ab6ahHnCD_sq9h4o8v+M7QQ@mail.gmail.com/
> Tested-by: Vladimir Panteleev <git@vladimir.panteleev.md>
> CC: stable@vger.kernel.org # 6.2+
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

fstests(btrfs/299) will fail with this patch.

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2023/05/04

> ---
>  fs/btrfs/backref.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/btrfs/backref.c b/fs/btrfs/backref.c
> index e54f0884802a..8e61be3fe9a8 100644
> --- a/fs/btrfs/backref.c
> +++ b/fs/btrfs/backref.c
> @@ -45,7 +45,9 @@ static int check_extent_in_eb(struct btrfs_backref_walk_ctx *ctx,
>  	int root_count;
>  	bool cached;
>  
> -	if (!btrfs_file_extent_compression(eb, fi) &&
> +	if (!ctx->ignore_extent_item_pos &&
> +	    ctx->extent_item_pos > 0 &&
> +	    !btrfs_file_extent_compression(eb, fi) &&
>  	    !btrfs_file_extent_encryption(eb, fi) &&
>  	    !btrfs_file_extent_other_encoding(eb, fi)) {
>  		u64 data_offset;
> @@ -552,13 +554,10 @@ static int add_all_parents(struct btrfs_backref_walk_ctx *ctx,
>  				count++;
>  			else
>  				goto next;
> -			if (!ctx->ignore_extent_item_pos) {
> -				ret = check_extent_in_eb(ctx, &key, eb, fi, &eie);
> -				if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP ||
> -				    ret < 0)
> -					break;
> -			}
> -			if (ret > 0)
> +			ret = check_extent_in_eb(ctx, &key, eb, fi, &eie);
> +			if (ret == BTRFS_ITERATE_EXTENT_INODES_STOP || ret < 0)
> +				break;
> +			else if (ret > 0)
>  				goto next;
>  			ret = ulist_add_merge_ptr(parents, eb->start,
>  						  eie, (void **)&old, GFP_NOFS);
> -- 
> 2.35.1