Re: [PATCH 1/2] btrfs: tree-checker: introduce checks for FREE_SPACE_INFO

[David Sterba <dsterba@suse.cz>]

On Tue, Mar 10, 2026 at 08:49:25AM +1030, Qu Wenruo wrote:
> Introduce checks for FREE_SPACE_INFO item, which include:
> 
> - Key alignment check
>   The objectid is the logical bytenr of the chunk/bg, and offset is the
>   length of the chunk/bg, thus they should all be aligned to the fs
>   block size.
> 
> - Item size check
>   The FREE_SPACE_INFO should a fix size.
> 
> - Flags check
>   The flags member should has no other flags than
>   BTRFS_FREE_SPACE_USING_BITMAPS.
> 
>   For future expansion, introduce a new macro
>   BTRFS_FREE_SPACE_FLAGS_MASK for such checks.
> 
>   And since we're here, the BTRFS_FREE_SPACE_USING_BITMAPS should not
>   use unsigned long long, as the flags is only 32 bits wide.
>   So fix that to use unsigned long.
> 
> - Extent count check
>   That member shows how many free space bitmap/extent items there are
>   inside the chunk/bg.
> 
>   And we know the chunk size (from key->offset), thus there should be at
>   most (key->offset >> sectorsize_bits) blocks inside the chunk.
>   Use that value as the upper limit and if that counter is larger than
>   that, there is a high chance it's a bitflip in high bits.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>  fs/btrfs/tree-checker.c         | 45 +++++++++++++++++++++++++++++++++
>  include/uapi/linux/btrfs_tree.h |  3 ++-
>  2 files changed, 47 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
> index ac4c4573ee39..980e4d52061f 100644
> --- a/fs/btrfs/tree-checker.c
> +++ b/fs/btrfs/tree-checker.c
> @@ -1928,6 +1928,48 @@ static int check_dev_extent_item(const struct extent_buffer *leaf,
>  	return 0;
>  }
>  
> +static int check_free_space_info(struct extent_buffer *leaf, struct btrfs_key *key,
> +				 int slot)
> +{
> +	struct btrfs_fs_info *fs_info = leaf->fs_info;
> +	struct btrfs_free_space_info *fsi;
> +	const u32 blocksize = fs_info->sectorsize;
> +	u32 flags;
> +
> +	if (unlikely(!IS_ALIGNED(key->objectid, blocksize) ||
> +		     !IS_ALIGNED(key->offset, blocksize))) {
> +		generic_err(leaf, slot,
> +		"free space info key range is not aligned to %u, has (%llu %u %llu)",

Please use the BTRFS_KEY_FMT macro for key specifier, I'll fix it in
git, thanks.