linux-kernel - Re: [3.15rc1] BUG at mm/filemap.c:202!

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Message-ID: <5366A9D9.8000100@nod.at>
Date:	Sun, 04 May 2014 22:58:01 +0200
From:	Richard Weinberger <richard@....at>
To:	Hugh Dickins <hughd@...gle.com>
CC:	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [3.15rc1] BUG at mm/filemap.c:202!

Am 04.05.2014 22:37, schrieb Hugh Dickins:
> On Sat, 3 May 2014, Richard Weinberger wrote:
>> On Thu, May 1, 2014 at 6:20 PM, Richard Weinberger
>> <richard.weinberger@...il.com> wrote:
>>> On Wed, Apr 16, 2014 at 10:40 PM, Hugh Dickins <hughd@...gle.com> wrote:
>>>>
>>>> Help!
>>>
>>> Using a trinity as of today I'm able to trigger this bug on UML within seconds.
>>> If you want me to test patch, I can help.
>>>
>>> I'm also observing one strange fact, I can trigger this on any kernel version.
>>> So far I've managed UML to crash on 3.0 to 3.15-rc...
>>
>> After digging deeper into UML's mmu and tlb code I've found issues and
>> fixed them.
>>
>> But I'm still facing this issue. Although triggering the BUG_ON() is
>> not so easy as before
>> I can trigger "BUG: Bad rss-counter ..." very easily.
>> Now the interesting fact, with my UML mmu and flb fixes applied it
>> happens only on kernels >= 3.14.
>> If it helps I can try to bisect it.
> 
> Thanks a lot for trying, but from other mail it looks like your
> bisection got blown off course ;(

Yeah, looks like the issue I'm facing on UML is a completely different
story. Although the symptoms are identical. :-(

> I expect for the moment you'll want to concentrate on getting UML's
> TLB flushing back on track with 3.15-rc.

This is what I'm currently doing. But it might take some time
as I'm a mm novice.

> Once you have that sorted out, I wouldn't be surprised if the same
> changes turn out to fix your "Bad rss-counter"s on 3.14 also.
> 
> If not, and if you do still have time to bisect back between 3.13 and
> 3.14 to find where things went wrong, it will be a bit tedious in that
> you would probably have to apply
> 
> 887843961c4b "mm: fix bad rss-counter if remap_file_pages raced migration"
> 7e09e738afd2 "mm: fix swapops.h:131 bug if remap_file_pages raced migration"
> 
> at each stage, to avoid those now-known bugs which trinity became rather
> good at triggering.  Perhaps other fixes needed, those the two I remember.
> 
> Please don't worry if you don't have time for this, that's understandable.
> 
> Or is UML so contrary that one of those commits actually brings on the
> problem for you?

Hehe, no. I gave it a quick try, both 887843961c4b and 7e09e738afd2
seem to be unrelated to the issues I see.

Thanks,
//richard
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