Re: [PATCH 8/8] xfs: ensure post-EOF zeroing happens after zeroing part of a file

[Allison Henderson <allison.henderson@oracle.com>]

Looks ok to me. Thx!

Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

On 06/21/2018 11:31 AM, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> If a user asks us to zero_range part of a file, the end of the range is
> EOF, and not aligned to a page boundary, invoke writeback of the EOF
> page to ensure that the post-EOF part of the page is zeroed.  This
> ensures that we don't expose stale memory contents via mmap, if in a
> clumsy manner.
> 
> Found by running generic/127 when it runs zero_range and mapread at EOF
> one after the other.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>   fs/xfs/xfs_bmap_util.c |   15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> 
> diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> index abc37b0899c0..c94d376e4152 100644
> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -1208,7 +1208,20 @@ xfs_free_file_space(
>   		return 0;
>   	if (offset + len > XFS_ISIZE(ip))
>   		len = XFS_ISIZE(ip) - offset;
> -	return iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops);
> +	error = iomap_zero_range(VFS_I(ip), offset, len, NULL, &xfs_iomap_ops);
> +	if (error)
> +		return error;
> +
> +	/*
> +	 * If we zeroed right up to EOF and EOF straddles a page boundary we
> +	 * must make sure that the post-EOF area is also zeroed because the
> +	 * page could be mmap'd and iomap_zero_range doesn't do that for us.
> +	 * Writeback of the eof page will do this, albeit clumsily.
> +	 */
> +	if (offset + len < XFS_ISIZE(ip) || ((offset + len) & PAGE_MASK) == 0)
> +		return 0;
> +	return filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
> +			(offset + len) & ~PAGE_MASK, LLONG_MAX);
>   }
>   
>   /*
> 
> --
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