Re: [Xen-devel] [ 3009.778974] mcelog:16842 map pfn expected mapping type write-back for [mem 0x0009f000-0x000a0fff], got uncached-minus

["Liu, Jinsong" <jinsong.liu@xxxxxxxxx>]

Konrad Rzeszutek Wilk wrote:
> On Fri, Nov 16, 2012 at 05:47:54PM +0100, Sander Eikelenboom wrote:
>> 
>> Friday, November 16, 2012, 5:07:33 PM, you wrote:
>> 
>>> On Fri, Nov 16, 2012 at 01:40:56PM +0100, Sander Eikelenboom wrote:
>>>> Hi Konrad,
>>>> 
>>>> Sometime ago i reported this one at boot up:
>>>> 
>>>> [ 3009.778974] mcelog:16842 map pfn expected mapping type
>>>> write-back for [mem 0x0009f000-0x000a0fff], got uncached-minus [
>>>> 3009.788570] ------------[ cut here ]------------ [ 3009.798175]
>>>> WARNING: at arch/x86/mm/pat.c:774 untrack_pfn+0xa1/0xb0() [
>>>> 3009.807966] Hardware name: MS-7640 [ 3009.817677] Modules linked
>>>> in: [ 3009.827524] Pid: 16842, comm: mcelog Tainted: G        W   
>>>> 3.7.0-rc5-20121116-reverted-persistent-warn-patwarn #1 [
>>>> 3009.837415] Call Trace: [ 3009.847110]  [<ffffffff810674fa>]
>>>> warn_slowpath_common+0x7a/0xb0 [ 3009.856857] 
>>>> [<ffffffff81067545>] warn_slowpath_null+0x15/0x20 [ 3009.866562] 
>>>> [<ffffffff81042041>] untrack_pfn+0xa1/0xb0 [ 3009.876201] 
>>>> [<ffffffff8111a59b>] unmap_single_vma+0x86b/0x8e0 [ 3009.885895] 
>>>> [<ffffffff81100f16>] ? release_pages+0x196/0x1f0 [ 3009.895488] 
>>>> [<ffffffff8111a65c>] unmap_vmas+0x4c/0xa0 [ 3009.905134] 
>>>> [<ffffffff8111c8fa>] exit_mmap+0x9a/0x180 [ 3009.914706] 
>>>> [<ffffffff81064e72>] mmput+0x52/0xd0 [ 3009.924252] 
>>>> [<ffffffff810652b7>] dup_mm+0x3c7/0x510 [ 3009.933839] 
>>>> [<ffffffff81065fd5>] copy_process+0xac5/0x14a0 [ 3009.943430] 
>>>> [<ffffffff81066af3>] do_fork+0x53/0x360 [ 3009.952843] 
>>>> [<ffffffff810b25c7>] ? lock_release+0x117/0x250 [ 3009.962283] 
>>>> [<ffffffff817d26c0>] ? _raw_spin_unlock+0x30/0x60 [ 3009.971532] 
>>>> [<ffffffff817d3495>] ? sysret_check+0x22/0x5d [ 3009.980820] 
>>>> [<ffffffff81017523>] sys_clone+0x23/0x30 [ 3009.990046] 
>>>> [<ffffffff817d37f3>] stub_clone+0x13/0x20 [ 3009.999335] 
>>>> [<ffffffff817d3469>] ? system_call_fastpath+0x16/0x1b [
>>>> 3010.008667] ---[ end trace 2d9694c2c0a24da8 ]---  
>>>> 
>>>> 
>>>> It seems to be due to the "mcelog" userspace tool provided with
>>>> Debian Squeeze (mcelog 1.0~pre3-3  x86-64 Machine Check Exceptions
>>>> collector and decoder). I can trigger this warning easily by
>>>> restarting the mcelog tool with /etc/init.d/mcelog restart  
>>>> 
>>>> Should that one also function with the xen mcelog driver, or is a
>>>> newer version required ? 
>> 
>>> The reason we get is b/c I had to disable the PAT functionality in
>>> the Linux kernel for Xen. This is b/c it only worked one way -
>>> meaning you could convert a page from 
>>> WriteBack to WriteCombine or WriteBack to Uncached. But you could
>>> not 
>>> do WriteCombine back to WriteBack - due to one of the functions that
>>> changes the bits was using an "unfiltered" way to identify the bits
>>> on the 
>>> page.
>> 
>>> Anyhow, we had a disaster b/c some of these pages that used to
>>> WriteBack (WB) 
>>> got converted to WriteCombine (WC) and then were returned back as
>>> such 
>>> to the page pool. And if they were re-used by filesystem invariably
>>> we got 
>>> corruptions.
>> 
>>> So until the PAT table lookup thing that Peter H. Anvin suggested
>>> gets implemented this splat gotta show up :-(
>> 
>> Not a big problem for me, i was just wondering :-)
>> I'm more interested in the netfront troubles, since it's already rc5.
>> 
>>> Does mcelog still work even with this warning?
>> 
>> Not the daemon:
>> 
>> serveerstertje:~# sh /etc/init.d/mcelog start
>> Starting Machine Check Exceptions decoder: daemon: Cannot allocate
>> memory 
>> 
> Ugh.
> CC-ing Liu here.
> 

How to reproduce it (sorry I miss the history of this thread)?
I have a try at Xen side, w/ kernel 3.6.0-rc7+, no problem at my side.

Thanks,
Jinsong

>> 
>>>> 
>>>> --
>>>> Sander


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