linux-kernel - Re: [PATCH] memremap: Fix NULL pointer BUG in get_zone_device

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Message-ID: <CAPcyv4gJtTj8chX_eTNhs1PJ=D3X7USuDXwFSWSEZt1cUAXpUw@mail.gmail.com>
Date:   Tue, 23 Aug 2016 17:34:55 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     "Kani, Toshimitsu" <toshi.kani@....com>
Cc:     "Mulumudi, Abhilash Kumar" <m.abhilash-kumar@....com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "ard.biesheuvel@...aro.org" <ard.biesheuvel@...aro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "brian.starkey@....com" <brian.starkey@....com>
Subject: Re: [PATCH] memremap: Fix NULL pointer BUG in get_zone_device_page()

On Tue, Aug 23, 2016 at 4:47 PM, Kani, Toshimitsu <toshi.kani@....com> wrote:
> On Tue, 2016-08-23 at 15:32 -0700, Dan Williams wrote:
>> On Tue, Aug 23, 2016 at 11:43 AM, Toshi Kani <toshi.kani@....com>
>> wrote:
>  :
>> I'm not sure about this fix.  The point of honoring
>> vmem_altmap_offset() is because a portion of the resource that is
>> passed to devm_memremap_pages() also contains the metadata info block
>> for the device.  The offset says "use everything past this point for
>> pages".  This may work for avoiding a crash, but it may corrupt info
>> block metadata in the process.  Can you provide more information
>> about the failing scenario to be sure that we are not triggering a
>> fault on an address that is not meant to have a page mapping?  I.e.
>> what is the host physical address of the page that caused this fault,
>> and is it valid?
>
> The fault address in question was the 2nd page of an NVDIMM range.  I
> assumed this fault address was valid and needed to be handled.  Here is
> some info about the base and patched cases.  Let me know if you need
> more info.
>
> Base
> ====
>
> The following NVDIMM range was set to /dev/dax.

With ndctl create-namespace or manually via sysfs?  Specifically I'm
looking for what the 'align' attribute was set to when the
configuration was established.  Can you provide a dump of the sysfs
attributes for the /dev/dax parent device?