Re: Re: [Xen-devel] tap:qcow causes dom-U to hang in 3.0.3

[Roland Paterson-Jones <roland@rolandpj.com>]

Julian Chesterfield wrote:

> Roland,
>
> Can you also verify whether there's an active tapdisk process running 
> in Dom0 for each tap:{aio,qcow} vbd. We are aware of a bug with the 
> qcow implementation that we hope to submit a fix for very soon. It's 
> likely that you are seeing the same issue.

To answer your question, yes, it does appear that a tapdisk process is 
still running (this is after the dom-U has hung):

[root@dom0-0-50-45-5d-6a-bc ~]# ps -aef | grep tapdisk
root      4135     1  0 15:42 ?        00:00:01 tapdisk 
/dev/xen/tapctrlwrite1 /dev/xen/tapctrlread1

There is only one tap device, and the pid is the same as the single 
candidate while the dom-U was still reachable.

The hand seems to occur on the first (significant?) disk write inside 
the dom-U. For example:

-bash-3.00# dd if=/dev/zero of=./test-10MB bs=1k count=$((10*1024))

Has hung the dom-U, and I can no longer console or ssh into the dom-U.

Interestingly, on the dom-U, the qcow file has shrunk from its pervious 
peak of > 1TB, and is now appearing modestly as:

[root@dom0-0-50-45-5d-6a-bc ~]# ls -als /mnt/instance_image_store_0/
total 1564432
      4 drwxr-xr-x  2 root root       4096 Nov 10 15:42 .
      8 drwxr-xr-x  8 root root       4096 Nov  7 17:56 ..
1563132 -rw-r--r--  1 root root 1599078400 Nov 10 15:42 2
   1288 -rw-r--r--  1 root root    2466816 Nov 10 16:09 2.qcow

It's all very confusing. I'd love it to work, of course. Let me know 
what I can do to help with a diagnosis.

I'm running on the (binary) PAE-enabled 3.0.3 release.

Thanks and kind regards
Roland