Re: [PATCH 0/2] virtio: console: add locking around control out-vq

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

On (Fri) 29 Mar 2013 [08:38:49], Asias He wrote:
> On Thu, Mar 28, 2013 at 04:58:31PM +0530, Amit Shah wrote:
> > The in-vq operations were protected by a lock, but the out-vq
> > operations were not.  This caused panics / errors as described in
> > patch 2.  Fix that.
> 
> BTW, this looks suspicious. Why no lock here?
> 
>    static void remove_controlq_data(struct ports_device *portdev)
>    {
>            struct port_buffer *buf;
>            unsigned int len;
>    
>            if (!use_multiport(portdev))
>                    return;
>    
>            while ((buf = virtqueue_get_buf(portdev->c_ivq, &len)))
>                    free_buf(buf, true);
>    
>            while ((buf = virtqueue_detach_unused_buf(portdev->c_ivq)))
>                    free_buf(buf, true);
>    }

Since this is c_ivq, you mean why can't the host be queueing up data
in the vq while we're removing the buffers from the vq.

This function is called from two places, virtcons_remove() and
virtcons_freeze(). In both the cases, everything is set up so the host
can't send anything: vdev->config->reset() ensures that.

Is there something else that can be happening?

		Amit