Re: [Qemu-devel] Qemu-KVM 0.12.3 and Multipath -> Assertion

[Kevin Wolf <kwolf@redhat.com>]

Am 04.05.2010 15:42, schrieb Peter Lieven:
> hi kevin,
> 
> you did it *g*
> 
> looks promising. applied this patched and was not able to reproduce yet :-)
> 
> secure way to reproduce was to shut down all multipath paths, then 
> initiate i/o
> in the vm (e.g. start an application). of course, everything hangs at 
> this point.
> 
> after reenabling one path, vm crashed. now it seems to behave correctly and
> just report an DMA timeout and continues normally afterwards.

Great, I'm going to submit it as a proper patch then.

Christoph, by now I'm pretty sure it's right, but can you have another
look if this is correct, anyway?

> can you imagine of any way preventing the vm to consume 100% cpu in
> that waiting state?
> my current approach is to run all vms with nice 1, which helped to keep the
> machine responsible if all vms (in my test case 64 on a box) have hanging
> i/o at the same time.

I don't have anything particular in mind, but you could just attach gdb
and get another backtrace while it consumes 100% CPU (you'll need to use
"thread apply all bt" to catch everything). Then we should see where
it's hanging.

Kevin