Re: [Xen-devel] libxl: cannot start guest

[Christoph Egger <Christoph.Egger@xxxxxxx>]

On 05/22/12 16:20, Ian Campbell wrote:

> On Tue, 2012-05-22 at 15:03 +0100, Christoph Egger wrote:
>> On 05/22/12 15:21, Ian Campbell wrote:
>>
>>> On Tue, 2012-05-22 at 14:18 +0100, Christoph Egger wrote:
>>>> I thinkIn xs_talkv() something must fail.
>>>>
>>>>> The only thing which springs to mind is that it may generate an
>>>>> @IntroduceDomain watch event. However xl is single threaded so we won't
>>>>> process that event until we unwind to whichever point we do an event
>>>>> loop iteration, in which case the corruption would have to happen later
>>>>> than right after xs_introduce_domain().
>>>>>
>>>>> Did you manage to determine if "Bad file descriptor" was due to it being
>>>>> closed vs. the value being corrupted?
>>>>
>>>> My suspicion is that
>>>>
>>>>    if (msg.type != type)
>>>>
>>>> in xs_talkv() is true.
>>>>
>>>
>>> Yes, that definitely seems worth investigating.
>>
>>
>> Ok, I got it.
>>
>> xenstored crashes due to dereferencing NULL pointer.
> 
> Huh, xenstore has materially changed for quite a while (since February).
> 
>> In xenstored_domain.c, map_interface()  *xcg_handle is NULL
>> and in xc_gnttab.c, xc_gnttab_map_grant_ref() it is dereferenced.
> 
> This comes from 24757:aae516b78fce. Diego and Alex aren't around any
> more but CCing Daniel in case he remembers anything.
> 
> I guess the original xc_gnttab_open which sets *xcg_handle is failing
> for you, I suppose that is to be expected on NetBSD? Either way it
> should still work after this has failed.
> 
> All the >= checks on *xcg_handle seem wrong to me. Really they should be
> checking != NULL, since otherwise they don't actually discriminate the
> two cases! Does making that change help?

Yes, that helps! I can start guests again.

Christoph

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