Re: [PATCH 0/6] Support DAX for device-mapper dm-linear devices

[Dan Williams]

On Tue, Jun 21, 2016 at 8:44 AM, Kani, Toshimitsu <toshi.kani@xxxxxxx> wrote:
> On Tue, 2016-06-21 at 09:41 -0400, Mike Snitzer wrote:
>> On Mon, Jun 20 2016 at  6:22pm -0400,
>> Mike Snitzer <snitzer@xxxxxxxxxx> wrote:
>> >
>> > On Mon, Jun 20 2016 at  5:28pm -0400,
>> > Kani, Toshimitsu <toshi.kani@xxxxxxx> wrote:
>> >
>  :
>> > Looks good, I folded it in and tested it to work.  Pushed to my 'wip'
>> > branch.
>> >
>> > No longer seeing any corruption in my test that was using partitions to
>> > span pmem devices with a dm-linear device.
>> >
>> > Jens, any chance you'd be open to picking up the first 2 patches in this
>> > series?  Or would you like to see them folded or something different?
>>
>> I'm now wondering if we'd be better off setting a new QUEUE_FLAG_DAX
>> rather than establish GENHD_FL_DAX on the genhd?
>>
>> It'd be quite a bit easier to allow upper layers (e.g. XFS and ext4) to
>> check for a queue flag.
>
> I think GENHD_FL_DAX is more appropriate since DAX does not use a request
> queue, except for protecting the underlining device being disabled while
> direct_access() is called (b2e0d1625e19).
>
> About protecting direct_access, this patch assumes that the underlining
> device cannot be disabled until dtr() is called.  Is this correct?  If not,
> I will need to call dax_map_atomic().

Kernel internal usages of dax should be using dax_map_atomic() to
safely resolve device removal races.