Re: [Xen-devel] network hang trigger

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> When I was thinking about this problem, I was imagining a deadlock
> condition where rapid back to back packets (eg a fragmented icmp packet
> from ping or a fragmented udp packet from nfs) was causing a hang until
> part of the deadlock timed itself out and the packets started flowing
> again. I couldn't see 1 packet causing a buffer exhaustion unless it got
> itself into a loop where it kept retrying to send the second fragment
> and didn't free the buffer each time, but even then the buffer bug would
> be a side effect.
> 
> The deadlock would have to be caused in the transmit from xenU to xen0,
> and something about the difference between sending a ping and responding
> to a ping is the difference between always causing a lockup and only
> sometimes causing a lockup.

Try tcpdumping each end of teh connecttion.

I find that for ping 0->U, the 'seizure' is entirely within DOM0 --
ping responses are still received, but for some reason they don't make
it up to the ping application.

For ping U->0, it does look as though the network seizes up -- I see
no packets in either direction.

 -- Keir


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