Re: [PATCH v2 1/5] ext4: prevent data corruption with inline data + DAX

["Theodore Ts'o" <tytso@mit.edu>]

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 <ross.zwisler@linux.intel.com>
> CC: stable@vger.kernel.org

Thanks, applied.

					- Ted