Re: [PATCH v2 6/6] xfs: assert the reservation covers each da fork growth

[Darrick J. Wong]

On Mon, Aug 10, 2026 at 10:43:19AM -0600, Javier Tia wrote:
> xfs_da_grow_inode_int() subtracts the blocks it just allocated from
> args->total, the caller's remaining block reservation.  The subtraction
> is unsigned, so a caller that reaches it with too small a total wraps
> the field instead of failing, and every allocation afterwards runs with
> a bogus reservation.  Assert the remaining reservation still covers the
> step, so an under-reserved or uninitialised total trips in debug builds
> instead of silently wrapping.
> 
> Suggested-by: Darrick J. Wong <djwong@xxxxxxxxxx>
> Signed-off-by: Javier Tia <floss@xxxxxxx>

Looks good,
Reviewed-by: "Darrick J. Wong" <djwong@xxxxxxxxxx>

--D

> ---
>  fs/xfs/libxfs/xfs_da_btree.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_da_btree.c b/fs/xfs/libxfs/xfs_da_btree.c
> index ad801b7bd2dd..9be407affc6e 100644
> --- a/fs/xfs/libxfs/xfs_da_btree.c
> +++ b/fs/xfs/libxfs/xfs_da_btree.c
> @@ -2385,6 +2385,7 @@ xfs_da_grow_inode_int(
>  	}
>  
>  	/* account for newly allocated blocks in reserved blocks total */
> +	ASSERT(args->total >= dp->i_nblocks - nblks);
>  	args->total -= dp->i_nblocks - nblks;
>  
>  out_free_map:
> -- 
> Javier Tia
> 
>