Re: [Xen-devel][PV-ops][PATCH] Netback: Fix PV network issue for netback multiple threads patchset

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 07/01/2010 05:47 PM, Ian Campbell wrote:
>> Hm, I hadn't meant to commit that properly.  I had it locally and
>> accidentally pushed it out.
>>
>> I only did that patch as an RFC in response to an issue alluded to by
>> Dongxiao (or was it you?) about things not being fully initialized by
>> the time the async code starts.  Is this a real issue, and if so, what's
>> the correct fix?
>>     
> I don't think there is an actual current issue, just a potential one
> since we are relying on data structures being zeroed rather than
> properly initialised to keep the async code from running off into the
> weeds, it just seemed a little fragile this way.
>
> Originally I said:
>   
>>> The crash is in one of the calls to list_move_tail and I think it is
>>> because netbk->pending_inuse_head not being initialised until after
>>> the 
>>> threads and/or tasklets are created (I was running in threaded mode).
>>> Perhaps even though we are now zeroing the netbk struct those fields
>>> should still be initialised before kicking off any potentially
>>> asynchronous tasks?
>>>       
> this specific issue was fixed by zeroing the netbk array as it is
> allocated, I just thought we could make things more robust by not
> triggering the async code until everything was fully setup.
>   

It would only affect system startup time, not domain creation?

I was looking at it because Stefano was having fairly consistent crashes
on domain creation, and it looked like sort-of-racy symptoms.

    J

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