Re: [PATCH 0/5] Introduce 'yank' oob qmp command to recover from hanging qemu

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Paolo Bonzini (pbonzini@redhat.com) wrote:
> On 13/05/20 13:26, Daniel P. Berrangé wrote:
> > Are you referring to the in-kernel NFS client hangs here ?  AFAIK, it is
> > impossible to do anything to get out of those hangs from userspace, because
> > the thread is stuck in an uninterruptable sleep in kernel space.
> > 
> > If using the in-QEMU NFS client, then there is a network connection that
> > can be yanked just like the NBD client.
> 
> But it's a bad idea to yank it (and also the NBD client) because you're
> not sure which wites have made it to the server (and to the medium) and
> which haven't.

No, that's OK - if you look at the COLO case, and some other cases,
you've got a dead storage device but your redundant pair might be OK;
so it's OK to yank it.
Other similar storage cases are trying to migrate a VM that has one dead
disk, even if you know and accept it's dead and unresponding, you often
can't kill it off if the device is hung.

> Effectively, the in-QEMU NFS client and NBD client are always operating
> in "soft" mode, but we should always treat that as a bug (which cannot
> be fixed) and not a feature for read-write images.
Dave

> 
> Paolo
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK