Re: mm, something wring in page_lock_anon_vma_read()?

From: Vlastimil Babka
Date: Thu Jun 08 2017 - 09:59:32 EST


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
>>>>>
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>>>> .
>>>>
>>>
>>>
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>>
>>
>> .
>>
>
>
>