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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew

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