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Date: Mon, 21 May 2018 16:10:26 -0700
From: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/5] mm, devm_memremap_pages: handle errors allocating
 final devres action
Message-Id: <20180521161026.709d5f2876e44f151da3d179@linux-foundation.org>
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To: Dan Williams <dan.j.williams@intel.com>
Cc: stable@vger.kernel.org, Christoph Hellwig <hch@lst.de>, =?ISO-8859-1?Q?J=E9r=F4me?= Glisse <jglisse@redhat.com>, Logan Gunthorpe <logang@deltatee.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On Mon, 21 May 2018 15:35:24 -0700 Dan Williams <dan.j.williams@intel.com> =
wrote:

> The last step before devm_memremap_pages() returns success is to
> allocate a release action to tear the entire setup down. However, the
> result from devm_add_action() is not checked.
>=20
> Checking the error also means that we need to handle the fact that the
> percpu_ref may not be killed by the time devm_memremap_pages_release()
> runs. Add a new state flag for this case.
>=20
> Cc: <stable@vger.kernel.org>
> Fixes: e8d513483300 ("memremap: change devm_memremap_pages interface...")
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: "J=E9r=F4me Glisse" <jglisse@redhat.com>
> Cc: Logan Gunthorpe <logang@deltatee.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Why the cc:stable?  The changelog doesn't describe the end-user-visible
impact of the bug (it always should, for this reason).

AFAICT we only go wrong when a small GFP_KERNEL allocation fails
(basically never happens), with undescribed results :(