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

[Jason Wang <jasowang@redhat.com>]

On 11/06/2013 07:17 PM, Michael S. Tsirkin wrote:
> 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?
>

Nope, it was introduced in the multiqueue virito-net, since the bh were
created conditionally from that commit.

commit fed699f9ca6ae8a0fb62803334cf46fa64d1eb91
Author: Jason Wang <jasowang@redhat.com>
Date:   Wed Jan 30 19:12:39 2013 +0800

    virtio-net: multiqueue support
>
>> ---
>>  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