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

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Date:   Tue, 31 Oct 2017 01:00:53 +0100
From:   Fengguang Wu <fengguang.wu@...el.com>
To:     Dan Williams <dan.j.williams@...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

Hi Dan,

On Mon, Oct 30, 2017 at 08:59:46AM -0700, Dan Williams wrote:
>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/

Good to know that!

>...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?

Yes, we used

        memmap=104G!26G memmap=104G!154G 

The warning showed up only once -- attached is the full dmesg.

Thanks,
Fengguang

View attachment "dmesg-ivb44:20171026090137:x86_64-rhel-7.2:gcc-6:4.14.0-rc6:1" of type "text/plain" (130693 bytes)