[PATCH net] virtio-net: add a missing synchronize_net()

[Eric Dumazet]

From: Eric Dumazet <eduma...@google.com>

It seems many drivers do not respect napi_hash_del() contract.

When napi_hash_del() is used before netif_napi_del(), an RCU grace
period is needed before freeing NAPI object.

Fixes: 91815639d880 ("virtio-net: rx busy polling support")
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Jason Wang <jasow...@redhat.com>
Cc: Michael S. Tsirkin <m...@redhat.com>
---
 drivers/net/virtio_net.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fd8b1e62301f..7276d5a95bd0 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1497,6 +1497,11 @@ static void virtnet_free_queues(struct virtnet_info *vi)
                netif_napi_del(&vi->rq[i].napi);
        }
 
+       /* We called napi_hash_del() before netif_napi_del(),
+        * we need to respect an RCU grace period before freeing vi->rq
+        */
+       synchronize_net();
+
        kfree(vi->rq);
        kfree(vi->sq);
 }