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From: Dan Williams <dan.j.williams@intel.com>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: stable <stable@vger.kernel.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Paul Mackerras <paulus@samba.org>, Christoph Hellwig <hch@lst.de>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	linux-nvdimm <linux-nvdimm@lists.01.org>
Subject: Re: [5.4-stable PATCH 0/7] libnvdimm: Cross-arch compatible namespace alignment
Date: Tue, 26 May 2020 13:42:44 -0700	[thread overview]
Message-ID: <CAPcyv4jW9P2FP2p6OiLoN+e_wzZY9-c8C-mMMoDqohuTekF7WQ@mail.gmail.com> (raw)
In-Reply-To: <20200522120009.GA1456052@kroah.com>

On Fri, May 22, 2020 at 5:00 AM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> On Fri, May 22, 2020 at 01:58:00PM +0200, Greg KH wrote:
> > On Thu, May 21, 2020 at 04:37:43PM -0700, Dan Williams wrote:
> > > Hello stable team,
> > >
> > > These patches have been shipping in mainline since v5.7-rc1 with no
> > > reported issues. They address long standing problems in libnvdimm's
> > > handling of namespace provisioning relative to alignment constraints
> > > including crashes trying to even load the driver on some PowerPC
> > > configurations.
> > >
> > > I did fold one build fix [1] into "libnvdimm/region: Introduce an 'align'
> > > attribute" so as to not convey the bisection breakage to -stable.
> > >
> > > Please consider them for v5.4-stable. They do pass the latest
> > > version of the ndctl unit tests.
> >
> > What about 5.6.y?  Any user upgrading from 5.4-stable to 5.6-stable
> > would hit a regression, right?
> >
> > So can we get a series backported to 5.6.y as well?  I need that before
> > I can take this series.

Yes, should be the exact same set, but I will run the regression suite
to be sure.

> Also, I really don't see the "bug" that this is fixing here.  If this
> didn't work on PowerPC before, it can continue to just "not work" until
> 5.7, right?

There's a mix of "never worked" and "used to work" in this set. The
PowerPC case is indeed a "never worked", but I highlighted it as it
was the simplest to understand.

> What problems with 5.4.y and 5.6.y is this series fixing
> that used to work before?

The "used to work" bug fixed by this set is the fact that the kernel
used to force a 128MB (memory hotplug section size) alignment padding
on all persistent memory namespaces to enable DAX operation. The
support for sub-sections (2MB) dropped forced alignment padding, but
unfortunately introduced a regression for the case of trying to create
multiple unaligned namespaces. When that bug triggers namespace
creation for the region is disabled, iirc, previously that lockout
scenario was prevented.

Jeff, can you corroborate this?

I otherwise agree, if the above never worked then this can all wait
for v5.7 upgrades.
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  reply	other threads:[~2020-05-26 20:43 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-21 23:37 [5.4-stable PATCH 0/7] libnvdimm: Cross-arch compatible namespace alignment Dan Williams
2020-05-21 23:37 ` [5.4-stable PATCH 1/7] mm/memremap_pages: Kill unused __devm_memremap_pages() Dan Williams
2020-05-21 23:37 ` [5.4-stable PATCH 2/7] mm/memremap_pages: Introduce memremap_compat_align() Dan Williams
2020-05-21 23:37 ` [5.4-stable PATCH 3/7] libnvdimm/pfn: Prevent raw mode fallback if pfn-infoblock valid Dan Williams
2020-05-21 23:38 ` [5.4-stable PATCH 4/7] libnvdimm/pfn_dev: Don't clear device memmap area during generic namespace probe Dan Williams
2020-05-21 23:38 ` [5.4-stable PATCH 5/7] libnvdimm/namespace: Enforce memremap_compat_align() Dan Williams
2020-05-21 23:38 ` [5.4-stable PATCH 6/7] libnvdimm/region: Introduce NDD_LABELING Dan Williams
2020-05-21 23:38 ` [5.4-stable PATCH 7/7] libnvdimm/region: Introduce an 'align' attribute Dan Williams
2020-05-22 11:58 ` [5.4-stable PATCH 0/7] libnvdimm: Cross-arch compatible namespace alignment Greg KH
2020-05-22 12:00   ` Greg KH
2020-05-26 20:42     ` Dan Williams [this message]
2020-05-26 20:49       ` Jeff Moyer
2020-05-26 20:52         ` Dan Williams
2020-06-01 11:07           ` Greg KH

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