[Xen-devel] High Net and Disk Use == stuck domain

["Christopher S. Aker" <caker@xxxxxxxxxxxx>]

For the past year or so we've been seeing a bug whereby a domU's CPU 
would spin up to a steady 100, 200, 300 or 400% (4 vcpus), console would 
freeze, and some or all of the network-facing services within the domU 
would connect but block without any output.  Disk IO would flatline. 
The domU would never recover and required rebooting.
Since pv_ops hasn't always been around, we previously had only seen this 
behavior with xen-patched domUs (2.6.18.x), but now we're seeing it with 
pv_ops.  Identical symptoms.  And, I have a user that is able to 
reliable reproduce it on 2.6.27.4!
His recipe is downloading an ISO from a very fast and close-by news 
server using nzbget.  The trigger appears to be a combination of high 
network use and high disk use (like download from a very fast mirror) -- 
because we weren't able to reproduce the problem when saving to a tmpfs 
mount.
I was able to grab the output of sysrq t while it was in the bad state:

http://theshore.net/~caker/xen/BUGS/D-state/console.log

The number of processes in D state (39) is quite suspicious.

Let me know if there's anything else I can provide.

-Chris


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