Hi,
I was debugging an issue caused by a bad usage of dpdk.
That is fixed in the meantime and I'll backport that into our code as well.
But along debugging that, I found a potential hang in virtnet_send_command
that my case ran into.
The following code can become an infinite loop:
/* Spin for a response, the kick causes an ioport write, trapping
* into the hypervisor, so the request should be handled immediately.
*/
while (!virtqueue_get_buf(vi->cvq, &tmp) &&
!virtqueue_is_broken(vi->cvq))
cpu_relax();
In my case dpdk broke something - not exactly clear what - and due to that
following calls through virtnet_send_command ran into this hang.
Effectively it seems that the buffers didn't get refreshed at all anymore.
That said the dpdk issue to touch devices that belong to a kernel owned
driver is fixed, so one could leave the code as is for now.
Yet I wanted to make you aware in case you would vote for a time or retry
based upper limit on that loop to avoid hangs - who knows what else might
bring it in this broken state in a different case.
Kind Regards,
Christian Ehrhardt
P.S.
Steps to reproduce, backtraces and more data can be found in:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1570195
A general setup howto for DPDK in KVM guests which is a prereq is at:
https://help.ubuntu.com/16.04/serverguide/DPDK.html#dpdk-in-guest
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