On Mon, Sep 11, 2017 at 11:05:22PM -0600, Ross Zwisler wrote:
> If an inode has inline data it is currently prevented from using DAX by a
> check in ext4_set_inode_flags(). When the inode grows inline data via
> ext4_create_inline_data() or removes its inline data via
> ext4_destroy_inline_data_nolock(), the value of S_DAX can change.
>
> Currently these changes are unsafe because we don't hold off page faults
> and I/O, write back dirty radix tree entries and invalidate all mappings.
> There are also issues with mm-level races when changing the value of S_DAX,
> as well as issues with the VM_MIXEDMAP flag:
>
> https://www.spinics.net/lists/linux-xfs/msg09859.html
>
> The unsafe transition of S_DAX can reliably cause data corruption, as shown
> by the following fstest:
>
> https://patchwork.kernel.org/patch/9948381/
>
> Fix this issue by preventing the DAX mount option from being used on
> filesystems that were created to support inline data. Inline data is an
> option given to mkfs.ext4.
>
> Signed-off-by: Ross Zwisler <[email protected]>
> CC: [email protected]
Thanks, applied.
- Ted
