linux-kernel - Re: [PATCH 2/5] mm, devm_memremap_pages: handle errors allocating final devres action

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Message-Id: <20180521161026.709d5f2876e44f151da3d179@linux-foundation.org>
Date:   Mon, 21 May 2018 16:10:26 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     stable@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Jérôme Glisse <jglisse@...hat.com>,
        Logan Gunthorpe <logang@...tatee.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] mm, devm_memremap_pages: handle errors allocating
 final devres action

On Mon, 21 May 2018 15:35:24 -0700 Dan Williams <dan.j.williams@...el.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.
> 
> 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.
> 
> Cc: <stable@...r.kernel.org>
> Fixes: e8d513483300 ("memremap: change devm_memremap_pages interface...")
> Cc: Christoph Hellwig <hch@....de>
> Cc: "Jérôme Glisse" <jglisse@...hat.com>
> Cc: Logan Gunthorpe <logang@...tatee.com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.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 :(