Re: [Qemu-devel] [PATCH] virtio-net: only delete bh that existed

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Nov 06, 2013 at 04:58:08PM +0800, Jason Wang wrote:
> We delete without check whether it existed during exit. This will lead NULL
> pointer deference since it was created conditionally depends on guest driver
> status and features. So add a check of existence before trying to delete it.
> 
> Cc: qemu-stable@nongnu.org
> Signed-off-by: Jason Wang <jasowang@redhat.com>

Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

Looks like the bug was introduced by:
	commit 17ec5a8686143da66208273d355f2eeb09807614
	Author: KONRAD Frederic <fred.konrad@greensocs.com>
	Date:   Thu Apr 11 16:29:57 2013 +0200
	    virtio-net: add the virtio-net device.

Before that we had a single bh and created/destroyed
that unconditionally.
Is this a correct analysis?



> ---
>  hw/net/virtio-net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 22dbd05..ae51d96 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1601,7 +1601,7 @@ static int virtio_net_device_exit(DeviceState *qdev)
>          if (q->tx_timer) {
>              timer_del(q->tx_timer);
>              timer_free(q->tx_timer);
> -        } else {
> +        } else if (q->tx_bh) {
>              qemu_bh_delete(q->tx_bh);
>          }
>      }
> -- 
> 1.8.3.2