linux-kernel - Re: mm, something wring in page_lock_anon_vma

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Date:   Mon, 22 May 2017 17:48:04 +0800
From:   Xishi Qiu <qiuxishi@...wei.com>
To:     Hugh Dickins <hughd@...gle.com>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...nel.org>,
        Johannes Weiner <hannes@...xchg.org>,
        "Mel Gorman" <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Minchan Kim <minchan@...nel.org>,
        "David Rientjes" <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, <aarcange@...hat.com>,
        <sumeet.keswani@....com>, Rik van Riel <riel@...hat.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        zhong jiang <zhongjiang@...wei.com>
Subject: Re: mm, something wring in page_lock_anon_vma_read()?

On 2017/5/20 10:40, Hugh Dickins wrote:

> On Sat, 20 May 2017, Xishi Qiu wrote:
>>
>> Here is a bug report form redhat: https://bugzilla.redhat.com/show_bug.cgi?id=1305620
>> And I meet the bug too. However it is hard to reproduce, and 
>> 624483f3ea82598("mm: rmap: fix use-after-free in __put_anon_vma") is not help.
>>
>> From the vmcore, it seems that the page is still mapped(_mapcount=0 and _count=2),
>> and the value of mapping is a valid address(mapping = 0xffff8801b3e2a101),
>> but anon_vma has been corrupted.
>>
>> Any ideas?
> 
> Sorry, no.  I assume that _mapcount has been misaccounted, for example
> a pte mapped in on top of another pte; but cannot begin tell you where

Hi Hugh,

What does "a pte mapped in on top of another pte" mean? Could you give more info?

Thanks,
Xishi Qiu

> in Red Hat's kernel-3.10.0-229.4.2.el7 that might happen.
> 
> Hugh
> 
> .
>