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

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Message-ID: <20171031070819.favx7xdsxqzsmuoc@wfg-t540p.sh.intel.com>
Date:   Tue, 31 Oct 2017 08:08:19 +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>,
        Huang Ying <ying.huang@...el.com>,
        Aaron Lu <aaron.lu@...el.com>
Subject: Re: [pmem_attach_disk] WARNING: CPU: 46 PID: 518 at
 kernel/memremap.c:363 devm_memremap_pages+0x350/0x4b0

CC Ying and Aaron for Dan's tips on nvdimm testing.

On Mon, Oct 30, 2017 at 05:24:42PM -0700, Dan Williams wrote:
>On Mon, Oct 30, 2017 at 5:00 PM, Fengguang Wu <fengguang.wu@...el.com> wrote:
>> 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.
>>
>
>Something is going wrong with memmap= because you are not getting 1G
>aligned address ranges. I think you would have better luck switching
>to the official nvdimm emulation in qemu-kvm rather than relying on
>memmap= which is just a fragile / unreliable interface. In fact we
>should look to deprecate it and point everyone to use the standard
>methods. We just have a problem of legacy pre-ACPI6 platforms that
>have no other way than a kernel command line to identify persistent
>memory ranges.

Got it. Thank you for the tips!

Thanks,
Fengguang