Re: [PATCH 1/2] xfs: don't free rt blocks when we're doing a REMAP bunmapi call

[Christoph Hellwig <hch@infradead.org>]

On Wed, Sep 16, 2020 at 08:28:33PM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> When callers pass XFS_BMAPI_REMAP into xfs_bunmapi, they want the extent
> to be unmapped from the given file fork without the extent being freed.
> We do this for non-rt files, but we forgot to do this for realtime
> files.  So far this isn't a big deal since nobody makes a bunmapi call
> to a rt file with the REMAP flag set, but don't leave a logic bomb.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/libxfs/xfs_bmap.c |    9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 1b0a01b06a05..e8cd0012a017 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -5057,9 +5057,12 @@ xfs_bmap_del_extent_real(
>  				  &mod);
>  		ASSERT(mod == 0);
>  
> -		error = xfs_rtfree_extent(tp, bno, (xfs_extlen_t)len);
> -		if (error)
> -			goto done;
> +		if (!(bflags & XFS_BMAPI_REMAP)) {
> +			error = xfs_rtfree_extent(tp, bno, (xfs_extlen_t)len);
> +			if (error)
> +				goto done;
> +		}
> +
>  		do_fx = 0;
>  		nblks = len * mp->m_sb.sb_rextsize;
>  		qfield = XFS_TRANS_DQ_RTBCOUNT;

We also don't need to calculate bno for this case.