On 2018/10/18 0:09, Michael S. Tsirkin wrote:

On Wed, Oct 17, 2018 at 07:44:12PM +0900, Ake Koomsin wrote:

quoted

Commit 713a98d90c5e ("virtio-net: serialize tx routine during reset")
introduces netif_tx_disable() after netif_device_detach() in order to
avoid use-after-free of tx queues. However, there are two issues.

1) Its operation is redundant with netif_device_detach() in case the
   interface is running.
2) In case of the interface is not running before suspending and
   resuming, the tx does not get resumed by netif_device_attach().
   This results in losing network connectivity.

It is better to use netif_tx_lock_bh()/netif_tx_unlock_bh() instead for
serializing tx routine during reset. This also preserves the symmetry
of netif_device_detach() and netif_device_attach().

Fixes commit 713a98d90c5e ("virtio-net: serialize tx routine during reset")
Signed-off-by: Ake Koomsin <redacted>

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

Thanks a lot for debugging!
Seems like stable material to me, right?

Yes. With this patch, we can avoid network connectivity lost
because of tx not get re-enabled under some situation. Plus, it avoids
redundant operation between netif_device_detach() and
netif_tx_disable().

I tested the patch on Linux net-next and QEMU master by suspending/
resuming the virtual machine repeatedly. The network looks no problem
and has no connectivity lost so far. I tested with both user-mode
networking and tap interface.

Best Regards

quoted

---
 drivers/net/virtio_net.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 3f5aa59c37b7..3e2c041d76ac 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -2267,8 +2267,9 @@ static void virtnet_freeze_down(struct virtio_device *vdev)
 	/* Make sure no work handler is accessing the device */
 	flush_work(&vi->config_work);
 
+	netif_tx_lock_bh(vi->dev);
 	netif_device_detach(vi->dev);
-	netif_tx_disable(vi->dev);
+	netif_tx_unlock_bh(vi->dev);
 	cancel_delayed_work_sync(&vi->refill);
 
 	if (netif_running(vi->dev)) {

@@ -2304,7 +2305,9 @@ static int virtnet_restore_up(struct virtio_device *vdev)
 		}
 	}
 
+	netif_tx_lock_bh(vi->dev);
 	netif_device_attach(vi->dev);
+	netif_tx_unlock_bh(vi->dev);
 	return err;
 }
 

-- 
2.19.1