Re: [Qemu-devel] [PATCH V4] net: Forbid dealing with packets when VM is not running

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

On Wed, Aug 27, 2014 at 01:53:21PM +0200, Michael S. Tsirkin wrote:
> On Tue, Aug 26, 2014 at 04:06:17PM +0800, zhanghailiang wrote:
> > For all NICs(except virtio-net) emulated by qemu,
> > Such as e1000, rtl8139, pcnet and ne2k_pci,
> > Qemu can still receive packets when VM is not running.
> > 
> > If this happened in *migration's* last PAUSE VM stage, but
> > before the end of the migration, the new receiving packets will possibly dirty
> > parts of RAM which has been cached in *iovec*(will be sent asynchronously) and
> > dirty parts of new RAM which will be missed.
> > This will lead serious network fault in VM.
> > 
> > To avoid this, we forbid receiving packets in generic net code when
> > VM is not running.
> > 
> > Bug reproduction steps:
> > (1) Start a VM which configured at least one NIC
> > (2) In VM, open several Terminal and do *Ping IP -i 0.1*
> > (3) Migrate the VM repeatedly between two Hosts
> > And the *PING* command in VM will very likely fail with message:
> > 'Destination HOST Unreachable', the NIC in VM will stay unavailable unless you
> > run 'service network restart'
> > 
> > Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
> 
> Reviewed-by: Michael S. Tsirkin <mst@redhat.com>

Please add:
Cc: qemu-stable@nongnu.org

when applying this.

Thanks!


> > ---
> >  v4:
> > - The action of flush queued packets is unnecessary, remove this.
> >   (Thanks for the help of Jason Wang and Stefan). 
> > 
> >  v3:
> > - change the 'vmstate' to 'vm_running'
> > 
> >  v2:
> > - remove the superfluous check of nc->received_disabled 
> > ---
> > 
> >  net/net.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/net/net.c b/net/net.c
> > index 6d930ea..4cb92c0 100644
> > --- a/net/net.c
> > +++ b/net/net.c
> > @@ -41,6 +41,7 @@
> >  #include "qapi-visit.h"
> >  #include "qapi/opts-visitor.h"
> >  #include "qapi/dealloc-visitor.h"
> > +#include "sysemu/sysemu.h"
> >  
> >  /* Net bridge is currently not supported for W32. */
> >  #if !defined(_WIN32)
> > @@ -452,6 +453,12 @@ void qemu_set_vnet_hdr_len(NetClientState *nc, int len)
> >  
> >  int qemu_can_send_packet(NetClientState *sender)
> >  {
> > +    int vm_running = runstate_is_running();
> > +
> > +    if (!vm_running) {
> > +        return 0;
> > +    }
> > +
> >      if (!sender->peer) {
> >          return 1;
> >      }
> > -- 
> > 1.7.12.4
> >