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From: Dan Williams <dan.j.williams@intel.com>
To: Logan Gunthorpe <logang@deltatee.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
	stable <stable@vger.kernel.org>, "Christoph Hellwig" <hch@lst.de>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Linux MM" <linux-mm@kvack.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/5] mm, devm_memremap_pages: handle errors allocating final devres action
Date: Tue, 22 May 2018 10:25:13 -0700	[thread overview]
Message-ID: <CAPcyv4ga3e0WSe4LeGbzpwj2QNU-XMezYDh54TPon6UKbhpP0Q@mail.gmail.com> (raw)
In-Reply-To: <b636aa5e-205b-4d67-09f8-230755de31b6@deltatee.com>

On Tue, May 22, 2018 at 10:03 AM, Logan Gunthorpe <logang@deltatee.com> wrote:
>
>
> On 22/05/18 10:56 AM, Dan Williams wrote:
>> On Tue, May 22, 2018 at 9:42 AM, Logan Gunthorpe <logang@deltatee.com> wrote:
>>> 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?
>>
>> devm_add_action() does not call the release function,
>> devm_add_action_or_reset() does.
>
> Oh, yes. Thanks I see that now.
>
>> Ah, true, good catch!
>>
>> We should manually kill in the !registered case. I think this means we
>> need to pass in the custom kill routine, because for the pmem driver
>> it's blk_freeze_queue_start().
>
> It may be cleaner to just have the caller call the specific kill
> function if devm_memremap_pages fails...

As far as I can see by then it's too late, or we need to expose
release details to the caller which defeats the purpose of devm
semantics.

> Though, I don't fully
> understand how the nvdimm pmem driver cleans up the percpu counter.

The dev_pagemap setup for pmem is entirely too subtle and arguably a
layering violation as it reuses the block layer q_usage_counter
percpu_ref. We arrange for that counter to be shutdown before the
blk_cleanup_queue() does the same.

  reply	other threads:[~2018-05-22 17:25 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-21 22:35 [PATCH 0/5] mm: rework hmm to use devm_memremap_pages Dan Williams
2018-05-21 22:35 ` [PATCH 1/5] mm, devm_memremap_pages: mark devm_memremap_pages() EXPORT_SYMBOL_GPL Dan Williams
2018-05-22  6:29   ` Christoph Hellwig
2018-05-21 22:35 ` [PATCH 2/5] mm, devm_memremap_pages: handle errors allocating final devres action Dan Williams
2018-05-21 23:10   ` Andrew Morton
2018-05-22  0:07     ` Dan Williams
2018-05-22 16:42       ` Logan Gunthorpe
2018-05-22 16:56         ` Dan Williams
2018-05-22 17:03           ` Logan Gunthorpe
2018-05-22 17:25             ` Dan Williams [this message]
2018-05-22 17:36               ` Logan Gunthorpe
2018-05-22  6:30   ` Christoph Hellwig
2018-05-21 22:35 ` [PATCH 3/5] mm, hmm: use devm semantics for hmm_devmem_{add, remove} Dan Williams
2018-05-22  6:30   ` Christoph Hellwig
2018-05-21 22:35 ` [PATCH 4/5] mm, hmm: replace hmm_devmem_pages_create() with devm_memremap_pages() Dan Williams
2018-05-22  6:31   ` Christoph Hellwig
2018-05-22 17:13   ` Logan Gunthorpe
2018-05-22 21:38     ` Dan Williams
2018-05-21 22:35 ` [PATCH 5/5] mm, hmm: mark hmm_devmem_{add, add_resource} EXPORT_SYMBOL_GPL Dan Williams
2018-05-22  6:32   ` Christoph Hellwig
2018-05-22 21:31     ` Andrew Morton
2018-06-05 18:24       ` Jerome Glisse
2018-05-24  0:10 ` [PATCH 0/5] mm: rework hmm to use devm_memremap_pages Jerome Glisse
2018-05-24  3:18   ` Dan Williams
2018-05-24  6:35     ` Christoph Hellwig
2018-05-29 22:22     ` Dave Airlie
2018-05-29 22:31       ` Dan Williams
2018-05-29 23:00         ` Dave Airlie
2018-05-29 23:33           ` Dan Williams
2018-06-05 18:48             ` Jerome Glisse
2018-06-05 22:19               ` Dave Airlie
2018-06-05 23:06                 ` Dan Williams
2018-06-06  0:08                   ` Jerome Glisse
2018-06-06  1:33                     ` Dan Williams
2018-06-06  7:14                       ` Christoph Hellwig
2018-06-07 14:16                       ` Jerome Glisse
2018-06-07 18:39                         ` Dan Williams

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