linux-kernel - Re: kernel BUG in munlock_vma_pages

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Message-ID: <52A6275F.4040007@oracle.com>
Date:	Mon, 09 Dec 2013 15:26:07 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Vlastimil Babka <vbabka@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>
CC:	joern@...fs.org, mgorman@...e.de,
	Michel Lespinasse <walken@...gle.com>, riel@...hat.com,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: kernel BUG in munlock_vma_pages_range

On 12/09/2013 12:12 PM, Vlastimil Babka wrote:
> On 12/09/2013 06:05 PM, Sasha Levin wrote:
>> On 12/09/2013 04:34 AM, Vlastimil Babka wrote:
>>> Hello, I will look at it, thanks.
>>> Do you have specific reproduction instructions?
>>
>> Not really, the fuzzer hit it once and I've been unable to trigger it again. Looking at
>> the piece of code involved it might have had something to do with hugetlbfs, so I'll crank
>> up testing on that part.
>
> Thanks. Do you have trinity log and the .config file? I'm currently unable to even boot linux-next
> with my config/setup due to a GPF.
> Looking at code I wouldn't expect that it could encounter a tail page, without first encountering a
> head page and skipping the whole huge page. At least in THP case, as TLB pages should be split when
> a vma is split. As for hugetlbfs, it should be skipped for mlock/munlock operations completely. One
> of these assumptions is probably failing here...

If it helps, I've added a dump_page() in case we hit a tail page there and got:

[  980.172299] page:ffffea003e5e8040 count:0 mapcount:1 mapping:          (null) index:0
x0
[  980.173412] page flags: 0x2fffff80008000(tail)

I can also add anything else in there to get other debug output if you think of something else useful.


Thanks,
Sasha

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