Re: [PATCH] xfs: fail dax mount if reflink is enabled on a partition

Darrick J. Wong
2022-08-04T00:51:28Z

On Wed, Aug 03, 2022 at 06:47:24AM +0000, ruansy.fnst@fujitsu.com wrote:
>
>
> 在 2022/7/29 12:54, Darrick J. Wong 写道:
> > On Fri, Jul 29, 2022 at 03:55:24AM +0000, ruansy.fnst@fujitsu.com wrote:
> >>
> >>
> >> 在 2022/7/22 0:16, Darrick J. Wong 写道:
> >>> On Thu, Jul 21, 2022 at 02:06:10PM +0000, ruansy.fnst@fujitsu.com wrote:
> >>>> 在 2022/7/1 8:31, Darrick J. Wong 写道:
> >>>>> On Thu, Jun 09, 2022 at 10:34:35PM +0800, Shiyang Ruan wrote:
> >>>>>> Failure notification is not supported on partitions. So, when we mount
> >>>>>> a reflink enabled xfs on a partition with dax option, let it fail with
> >>>>>> -EINVAL code.
> >>>>>>
> >>>>>> Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> >>>>>
> >>>>> Looks good to me, though I think this patch applies to ... wherever all
> >>>>> those rmap+reflink+dax patches went. I think that's akpm's tree, right?
> >>>>>
> >>>>> Ideally this would go in through there to keep the pieces together, but
> >>>>> I don't mind tossing this in at the end of the 5.20 merge window if akpm
> >>>>> is unwilling.
> >>>>
> >>>> BTW, since these patches (dax&reflink&rmap + THIS + pmem-unbind) are
> >>>> waiting to be merged, is it time to think about "removing the
> >>>> experimental tag" again? :)
> >>>
> >>> It's probably time to take up that question again.
> >>>
> >>> Yesterday I tried running generic/470 (aka the MAP_SYNC test) and it
> >>> didn't succeed because it sets up dmlogwrites atop dmthinp atop pmem,
> >>> and at least one of those dm layers no longer allows fsdax pass-through,
> >>> so XFS silently turned mount -o dax into -o dax=never. :(
> >>
> >> Hi Darrick,
> >>
> >> I tried generic/470 but it didn't run:
> >> [not run] Cannot use thin-pool devices on DAX capable block devices.
> >>
> >> Did you modify the _require_dm_target() in common/rc? I added thin-pool
> >> to not to check dax capability:
> >>
> >> case $target in
> >> stripe|linear|log-writes|thin-pool) # add thin-pool here
> >> ;;
> >>
> >> then the case finally ran and it silently turned off dax as you said.
> >>
> >> Are the steps for reproduction correct? If so, I will continue to
> >> investigate this problem.
> >
> > Ah, yes, I did add thin-pool to that case statement. Sorry I forgot to
> > mention that. I suspect that the removal of dm support for pmem is
> > going to force us to completely redesign this test. I can't really
> > think of how, though, since there's no good way that I know of to gain a
> > point-in-time snapshot of a pmem device.
>
> Hi Darrick,
>
> > removal of dm support for pmem
> I think here we are saying about xfstest who removed the support, not
> kernel?
>
> I found some xfstests commits:
> fc7b3903894a6213c765d64df91847f4460336a2 # common/rc: add the restriction.
> fc5870da485aec0f9196a0f2bed32f73f6b2c664 # generic/470: use thin-pool
>
> So, this case was never able to run since the second commit? (I didn't
> notice the not run case. I thought it was expected to be not run.)
>
> And according to the first commit, the restriction was added because
> some of dm devices don't support dax. So my understanding is: we should
> redesign the case to make the it work, and firstly, we should add dax
> support for dm devices in kernel.

dm devices used to have fsdax support; I think Christoph is actively
removing (or already has removed) all that support.

> In addition, is there any other testcase has the same problem? so that
> we can deal with them together.

The last I checked, there aren't any that require MAP_SYNC or pmem aside
from g/470 and the three poison notification tests that you sent a few
days ago.

--D

>
> --
> Thanks,
> Ruan
>
>
> >
> > --D
> >
> >>
> >> --
> >> Thanks,
> >> Ruan.
> >>
> >>
> >>
> >>>
> >>> I'm not sure how to fix that...
> >>>
> >>> --D
> >>>
> >>>>
> >>>> --
> >>>> Thanks,
> >>>> Ruan.
> >>>>
> >>>>>
> >>>>> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> >>>>>
> >>>>> --D
> >>>>>
> >>>>>> ---
> >>>>>> fs/xfs/xfs_super.c | 6 ++++--
> >>>>>> 1 file changed, 4 insertions(+), 2 deletions(-)
> >>>>>>
> >>>>>> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> >>>>>> index 8495ef076ffc..a3c221841fa6 100644
> >>>>>> --- a/fs/xfs/xfs_super.c
> >>>>>> +++ b/fs/xfs/xfs_super.c
> >>>>>> @@ -348,8 +348,10 @@ xfs_setup_dax_always(
> >>>>>> goto disable_dax;
> >>>>>> }
> >>>>>>
> >>>>>> - if (xfs_has_reflink(mp)) {
> >>>>>> - xfs_alert(mp, "DAX and reflink cannot be used together!");
> >>>>>> + if (xfs_has_reflink(mp) &&
> >>>>>> + bdev_is_partition(mp->m_ddev_targp->bt_bdev)) {
> >>>>>> + xfs_alert(mp,
> >>>>>> + "DAX and reflink cannot work with multi-partitions!");
> >>>>>> return -EINVAL;
> >>>>>> }
> >>>>>>
> >>>>>> --
> >>>>>> 2.36.1
> >>>>>>
> >>>>>>
> >>>>>>