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From: Logan Gunthorpe <logang@deltatee.com>
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Date: Tue, 22 May 2018 10:42:33 -0600
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Subject: Re: [PATCH 2/5] mm, devm_memremap_pages: handle errors allocating
 final devres action
Sender: owner-linux-mm@kvack.org
List-ID: <linux-mm.kvack.org>
To: Dan Williams <dan.j.williams@intel.com>, Andrew Morton <akpm@linux-foundation.org>
Cc: stable <stable@vger.kernel.org>, Christoph Hellwig <hch@lst.de>, =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= <jglisse@redhat.com>, Linux MM <linux-mm@kvack.org>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>

Hey Dan,

On 21/05/18 06:07 PM, Dan Williams wrote:
> Without this change we could fail to register the teardown of
> devm_memremap_pages(). The likelihood of hitting this failure is tiny
> as small memory allocations almost always succeed. However, the impact
> of the failure is large given any future reconfiguration, or
> disable/enable, of an nvdimm namespace will fail forever as subsequent
> calls to devm_memremap_pages() will fail to setup the pgmap_radix
> since there will be stale entries for the physical address range.

Sorry, I don't follow this. The change only seems to prevent a warning
from occurring in this situation. Won't pgmap_radix_release() still be
called regardless of whether this patch is applied?

But it looks to me like this patch doesn't quite solve the issue -- at
least when looking at dax/pmem.c: If devm_add_action_or_reset() fails,
then dax_pmem_percpu_kill() won't be registered as an action and the
percpu_ref will never get killed. Thus, dax_pmem_percpu_release() would
not get called and dax_pmem_percpu_exit() will hang waiting for a
completion that will never occur. So we probably need to add a kill call
somewhere on the failing path...


Logan