linux-kernel - Re: [pmem_attach_disk] WARNING: CPU: 46 PID: 518 at kernel/memremap.c:363 devm_memremap

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Date:   Mon, 30 Oct 2017 08:59:46 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Fengguang Wu <fengguang.wu@...el.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vishal Verma <vishal.l.verma@...el.com>
Subject: Re: [pmem_attach_disk] WARNING: CPU: 46 PID: 518 at
 kernel/memremap.c:363 devm_memremap_pages+0x350/0x4b0

On Mon, Oct 30, 2017 at 12:40 AM, Fengguang Wu <fengguang.wu@...el.com> wrote:
>
> CC nvdimm maintainers.
>
> On Sun, Oct 29, 2017 at 11:51:55PM +0100, Fengguang Wu wrote:
>>
>> Hi Linus,
>>
>> Up to now we see the below boot error/warnings when testing v4.14-rc6.
>>
>> They hit the RC release mainly due to various imperfections in 0day's
>> auto bisection. So I manually list them here and CC the likely easy to
>> debug ones to the corresponding maintainers in the followup emails.
>>
>> boot_successes: 4700
>> boot_failures: 247
>
>
> [...]
>
>> WARNING:at_kernel/memremap.c:#devm_memremap_pages: 1
>
>
> Bisect failed, hope it's not hard to debug:
>
>         Start
> [   18.989316] devm_memremap_pages attempted on mixed region [mem 0x680000000-0x103dffffff flags 0x200]


This appears to be a problem in the test environment. "Persistent
Memory" can only be specified on a minimum of a 128MB boundary if it
intersects "System RAM". Assuming I did my math right this appears to
end on 16MB boundary. Fixing this problem in the kernel would require
this patch set:

    "mm: sub-section memory hotplug support": https://lwn.net/Articles/707908/

...but I have abandoned / pushed that to the back of my queue since
BIOS induced version of this problem does not appear to trigger in
practice. I assume this test is using memmap=ss!nn?