Re: [Xen-devel] [PATCH v3 0/3] map grant refs at pfn = mfn

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Aug 06, 2014 at 02:39:34PM +0100, Thomas Leonard wrote:
[...]
> >> >> Checkout the branch grant_map_identity_4.4_2
> >> >
> >> > Thanks - it's working now!
> >>
> >> Update: if my VM uses the network and then exits quickly, dom0 gets
> >> stuck.
> >
> > What do you mean by exit quickly? xl destroy domain?
> 
> The guest starts, sends a few packets and then exits (possibly before
> the packets have been transmitted). This happens before "xl create"
> manages to attach to the console.
> 

Are you using mirage DomU? I guess it takes much shorter time to bootup
/ shutdown than a normal Linux guest?

The packets definite hit backend at that time, otherwise you would not
have seen that error message.

Using console attach to determine what state guest is in is inacurate as
it's asynchronised.

My preliminary analysis is as followed:
  1. DomU transmit a packet
  2. packet received and mapped in Dom0
  3. packet goes into Dom0 stack
  4. DomU exits, xenbus thread in Dom0 stops processing threads
  5. packet processed in Dom0 stack, netback puts grefs of
     that packets in dealloc_ring
  6. Dom0 waits for all grefs to be unmapped before freeing up
     resources
As the thread to unmap grefs is stopped in step 4, now Dom0 waits
forever in step 6. :-(

Normally a DomU won't exit this fast so the sequence is actually 123564.

Wei.

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