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

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Date:   Thu, 8 Jun 2017 15:59:15 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Xishi Qiu <qiuxishi@...wei.com>,
        "'Kirill A . Shutemov'" <kirill.shutemov@...ux.intel.com>
Cc:     zhong jiang <zhongjiang@...wei.com>,
        Hugh Dickins <hughd@...gle.com>,
        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>,
        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>
Subject: Re: mm, something wring in page_lock_anon_vma_read()?

On 06/08/2017 03:44 PM, Xishi Qiu wrote:
> On 2017/5/23 17:33, Vlastimil Babka wrote:
> 
>> On 05/23/2017 11:21 AM, zhong jiang wrote:
>>> On 2017/5/23 0:51, Vlastimil Babka wrote:
>>>> On 05/20/2017 05:01 AM, zhong jiang wrote:
>>>>> 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
>>>>>> in Red Hat's kernel-3.10.0-229.4.2.el7 that might happen.
>>>>>>
>>>>>> Hugh
>>>>>>
>>>>>> .
>>>>>>
>>>>> Hi, Hugh
>>>>>
>>>>> I find the following message from the dmesg.
>>>>>
>>>>> [26068.316592] BUG: Bad rss-counter state mm:ffff8800a7de2d80 idx:1 val:1
>>>>>
>>>>> I can prove that the __mapcount is misaccount.  when task is exited. the rmap
>>>>> still exist.
>>>> Check if the kernel in question contains this commit: ad33bb04b2a6 ("mm:
>>>> thp: fix SMP race condition between THP page fault and MADV_DONTNEED")
>>>   HI, Vlastimil
>>>  
>>>   I miss the patch.
>>
>> Try applying it then, there's good chance the error and crash will go
>> away. Even if your workload doesn't actually run any madvise(MADV_DONTNEED).
>>
> 
> Hi Vlastimil,
> 
> I find this error was reported by Kirill as following, right?
> https://patchwork.kernel.org/patch/7550401/

That was reported by Minchan.

> The call trace is quite like the same as ours.

In that thread, the error seems just disappeared in the end.

So, did you apply the patch I suggested? Did it help?

> Thanks,
> Xishi Qiu
> 
>>> when I read the patch. I find the following issue. but I am sure it is right.
>>>
>>>       if (unlikely(pmd_trans_unstable(pmd)))
>>>         return 0;
>>>     /*
>>>      * A regular pmd is established and it can't morph into a huge pmd
>>>      * from under us anymore at this point because we hold the mmap_sem
>>>      * read mode and khugepaged takes it in write mode. So now it's
>>>      * safe to run pte_offset_map().
>>>      */
>>>     pte = pte_offset_map(pmd, address);
>>>
>>>   after pmd_trans_unstable call,  without any protect method.  by the comments,
>>>   it think the pte_offset_map is safe.    before pte_offset_map call, it still may be
>>>   unstable. it is possible?
>>
>> IIRC it's "unstable" wrt possible none->huge->none transition. But once
>> we've seen it's a regular pmd via pmd_trans_unstable(), we're safe as a
>> transition from regular pmd can't happen.
>>
>>>   Thanks
>>> zhongjiang
>>>>> Thanks
>>>>> zhongjiang
>>>>>
>>>>> --
>>>>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
>>>>> the body to majordomo@...ck.org.  For more info on Linux MM,
>>>>> see: http://www.linux-mm.org/ .
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>>>>>
>>>>
>>>> .
>>>>
>>>
>>>
>>> --
>>> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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>>>
>>
>>
>> .
>>
> 
> 
>