Re: [Xen-devel] qeustion: a panic in __do_update_va_mapping()

["Xuquan (Quan Xu)" <xuquan8@xxxxxxxxxx>]

On November 01, 2016 9:21 PM, Andrew Cooper wrote:
>On 01/11/16 12:07, Xuquan (Quan Xu) wrote:
>> On November 01, 2016 8:00 PM, Andrew Cooper wrote:
>>> On 01/11/16 11:57, Xuquan (Quan Xu) wrote:
>>>> On November 01, 2016 7:41 PM, Andrew Cooper
>>> <andrew.cooper3@xxxxxxxxxx > wrote:
>>>>> On 01/11/16 11:23, Xuquan (Quan Xu) wrote:
>>>>>> On November 01, 2016 7:16 PM, Andrew Cooper <
>>>>> andrew.cooper3@xxxxxxxxxx > wrote:
>>>>>>> On 01/11/16 11:01, Xuquan (Quan Xu) wrote:
>>>>>>>> Hi Andrew,
>>>>>>>>
>>>>>>>> When I run some application with Xen, I encounter a Panic with
>>>>>>>> log as the
>>>>>>> bottom of this email.
>>>>>>>> I find this panic is as similar as your fix e4e9d2d4e76bd8fe22
>>> 'x86/p2m-ept:
>>>>>>> don't unmap the EPT pagetable while it is still in use'.
>>>>>>>
>>>>>>> Its not the same.  My fix was for a pagefault.  Your crash is
>>>>>>> hitting a
>>>>>>> BUG()
>>>>>>>
>>>>>>> You need to investigate which BUG() is being hit (you are clearly
>>>>>>> not using staging, as page_alloc.c:429 is outside of a function), and 
>>>>>>> why.
>>>>>>>
>>>>>> It is not using staging, a internal version, but the
>>>>>> __do_update_va_mapping() is
>>>>> the same..
>>>>>> So I think it is similar to staging.
>>>>> __do_update_va_mapping() is not relevant.  Your problem is in
>>>>> alloc_heap_pages(), not __do_update_va_mapping().
>>>>>
>>>> Andrew, thanks for your help..
>>>>
>>>> Check it,
>>>> the BUG() is from
>>>> do_memory_op() -- alloc_domheap_pages() -- alloc_heap_pages()..
>>>> , not from  __do_update_va_mapping().
>>>>
>>>> If so, I think the information is too limited to debug..
>>>>
>>>> the BUG() is being hit at:
>>>> ...
>>>> alloc_heap_pages()
>>>>     for ( i = 0; i < (1 << order); i++ )
>>>>     {
>>>>         /* Reference count must continuously be zero for free pages. */
>>>>         BUG_ON(pg[i].count_info != PGC_state_free); ...
>>>>
>>>>
>>>> I guess I hit a 'count_info == -1', more put_page() is called to return the
>page..
>>> Yes.  This means that you have a reference counting error elsewhere
>>> in the hypervisor, and something is dropping too many references.
>>>
>> :(:(..
>> Any method to address it?
>
>Not specifically.  It is similar to chasing a double free bug.
>
>You should review whatever local additions you have in your tree extra 
>carefully.
>It might be that there is a setup path which doesn't take a ref, or a buggy 
>error
>path which cleans up too many refs.
>

Andrew, thank you very much!!
I think it is likely a buggy error of local additions..

Quan

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