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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Thu, 6 Jun 2019 15:06:26 -0700
Message-ID: <CAPcyv4hHs75hYs+Ye+NHHiU31C6CnBqCFdo=2c5seN7kvxKOrw@mail.gmail.com>
Subject: Re: [PATCH v9 11/12] libnvdimm/pfn: Fix fsdax-mode namespace
 info-block zero-fields
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     stable <stable@vger.kernel.org>, Linux MM <linux-mm@kvack.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Oscar Salvador <osalvador@suse.de>,
        Michal Hocko <mhocko@suse.com>
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On Thu, Jun 6, 2019 at 2:46 PM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Wed, 05 Jun 2019 14:58:58 -0700 Dan Williams <dan.j.williams@intel.com> wrote:
>
> > At namespace creation time there is the potential for the "expected to
> > be zero" fields of a 'pfn' info-block to be filled with indeterminate
> > data. While the kernel buffer is zeroed on allocation it is immediately
> > overwritten by nd_pfn_validate() filling it with the current contents of
> > the on-media info-block location. For fields like, 'flags' and the
> > 'padding' it potentially means that future implementations can not rely
> > on those fields being zero.
> >
> > In preparation to stop using the 'start_pad' and 'end_trunc' fields for
> > section alignment, arrange for fields that are not explicitly
> > initialized to be guaranteed zero. Bump the minor version to indicate it
> > is safe to assume the 'padding' and 'flags' are zero. Otherwise, this
> > corruption is expected to benign since all other critical fields are
> > explicitly initialized.
> >
> > Fixes: 32ab0a3f5170 ("libnvdimm, pmem: 'struct page' for pmem")
> > Cc: <stable@vger.kernel.org>
> > Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>
> The cc:stable in [11/12] seems odd.  Is this independent of the other
> patches?  If so, shouldn't it be a standalone thing which can be
> prioritized?
>

The cc: stable is about spreading this new policy to as many kernels
as possible not fixing an issue in those kernels. It's not until patch
12 "libnvdimm/pfn: Stop padding pmem namespaces to section alignment"
as all previous kernel do initialize all fields.

I'd be ok to drop that cc: stable, my concern is distros that somehow
pickup and backport patch 12 and miss patch 11.