Re: [PATCH 2/2] virtio: console: add locking around c_ovq operations

[Amit Shah <amit.shah@redhat.com>]

On (Fri) 29 Mar 2013 [08:29:01], Asias He wrote:
> On Thu, Mar 28, 2013 at 04:58:33PM +0530, Amit Shah wrote:
> > When multiple ovq operations are being performed (lots of open/close
> > operations on virtio_console fds), the __send_control_msg() function can
> > get confused without locking.
> > 
> > A simple recipe to cause badness is:
> > * create a QEMU VM with two virtio-serial ports
> > * in the guest, do
> >   while true;do echo abc >/dev/vport0p1;done
> >   while true;do echo edf >/dev/vport0p2;done
> > 
> > In one run, this caused a panic in __send_control_msg().  In another, I
> > got
> > 
> >    virtio_console virtio0: control-o:id 0 is not a head!
> > 
> > This also results repeated messages similar to these on the host:
> > 
> >   qemu-kvm: virtio-serial-bus: Unexpected port id 478762112 for device virtio-serial-bus.0
> >   qemu-kvm: virtio-serial-bus: Unexpected port id 478762368 for device virtio-serial-bus.0
> > 
> > Reported-by: FuXiangChun <xfu@redhat.com>
> > Signed-off-by: Amit Shah <amit.shah@redhat.com>
> 
> So, probably this will not apply on virtio-next because of the
> virtqueue_add_outbuf change.

Yes, one-line context change.

> Anyway,  Reviewed-by: Asias He <asias@redhat.com>

Thanks!

		Amit