Re: [PATCH v3 3/6] ext4: Online defrag not supported with DAX

Jan Kara
2016-02-17T21:34:38Z

On Tue 16-02-16 20:34:16, Ross Zwisler wrote:
> Online defrag operations for ext4 are hard coded to use the page cache.
> See ext4_ioctl() -> ext4_move_extents() -> move_extent_per_page()
>
> When combined with DAX I/O, which circumvents the page cache, this can
> result in data corruption. This was observed with xfstests ext4/307 and
> ext4/308.
>
> Fix this by only allowing online defrag for non-DAX files.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>

We need to handle this eventually but for now we are fine. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> fs/ext4/ioctl.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 0f6c369..e32c86f 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -583,6 +583,11 @@ group_extend_out:
> "Online defrag not supported with bigalloc");
> err = -EOPNOTSUPP;
> goto mext_out;
> + } else if (IS_DAX(inode)) {
> + ext4_msg(sb, KERN_ERR,
> + "Online defrag not supported with DAX");
> + err = -EOPNOTSUPP;
> + goto mext_out;
> }
>
> err = mnt_want_write_file(filp);
> --
> 2.5.0
>
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR