linux-kernel - Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG

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Message-ID: <CAPcyv4h6HO6fs6k7QMD77jkz2djCeWCtWomCdNb0-1Q4VKanqw@mail.gmail.com>
Date:   Tue, 26 Jun 2018 12:07:40 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Mike Snitzer <snitzer@...hat.com>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Toshi Kani <toshi.kani@....com>,
        device-mapper development <dm-devel@...hat.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode

On Tue, Jun 26, 2018 at 11:58 AM, Mike Snitzer <snitzer@...hat.com> wrote:
> On Tue, Jun 26 2018 at  2:52pm -0400,
> Dan Williams <dan.j.williams@...el.com> wrote:
>
>> On Tue, Jun 26, 2018 at 10:59 AM, Ross Zwisler
>> <ross.zwisler@...ux.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@...ux.intel.com>
>> > Suggested-by: Mike Snitzer <snitzer@...hat.com>
>> > Cc: stable@...r.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.