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

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Date:	Wed, 17 Feb 2016 22:34:50 +0100
From:	Jan Kara <jack@...e.cz>
To:	Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc:	linux-kernel@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Theodore Ts'o <tytso@....edu>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
	Jeff Layton <jlayton@...chiereds.net>,
	Jens Axboe <axboe@...nel.dk>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-block@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	linux-nvdimm@...ts.01.org, xfs@....sgi.com
Subject: Re: [PATCH v3 3/6] ext4: Online defrag not supported with DAX

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@...ux.intel.com>

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

Reviewed-by: Jan Kara <jack@...e.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@...e.com>
SUSE Labs, CR