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Date: Tue, 26 Jun 2018 15:13:46 -0400
From: Mike Snitzer <snitzer@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
        Toshi Kani <toshi.kani@hpe.com>,
        device-mapper development <dm-devel@redhat.com>,
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Subject: Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode
Message-ID: <20180626191346.GA7233@redhat.com>
References: <20180626175932.8899-1-ross.zwisler@linux.intel.com>
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On Tue, Jun 26 2018 at  3:07pm -0400,
Dan Williams <dan.j.williams@intel.com> wrote:

> On Tue, Jun 26, 2018 at 11:58 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> > On Tue, Jun 26 2018 at  2:52pm -0400,
> > Dan Williams <dan.j.williams@intel.com> wrote:
> >
> >> On Tue, Jun 26, 2018 at 10:59 AM, Ross Zwisler
> >> <ross.zwisler@linux.intel.com> wrote:
> >> > QUEUE_FLAG_DAX is an indication that a given block device supports
> >> > filesystem DAX and should not be set for PMEM namespaces which are in "raw"
> >> > or "sector" modes.  These namespaces lack struct page and are prevented
> >> > from participating in filesystem DAX.
> >> >
> >> > Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
> >> > Suggested-by: Mike Snitzer <snitzer@redhat.com>
> >> > Cc: stable@vger.kernel.org
> >>
> >> Why is this cc: stable? What is the user visible impact of this change
> >> especially given the requirement to validate QUEUE_FLAG_DAX with
> >> bdev_dax_supported()? Patch looks good, but it's just a cosmetic fixup
> >> afaics.
> >
> > This isn't cosmetic when you consider that stacking up a DM device is
> > looking at this flag to determine whether a table does or does _not_
> > support DAX.
> >
> > So this patch, in conjunction with the other changes in the series, is
> > certainly something I'd consider appropriate for stable.
> 
> I think this classifies as something that never worked correctly and
> is not a regression. It does not identify which commit it is repairing
> or the user visible failure mode.

So you're taking issue with making stacked dax configs work in older
kernels?  That's fine.  We can drop the stable cc if you like.

But I mean we intended for this to work.. so the Fixes commit references
can easily be added, e.g.: 545ed20e6df68a4d2584a29a2a28ee8b2f7e9547
("dm: add infrastructure for DAX support")