Hello Rusty,
while implementing and testing virtio on s390 I found a problem in
virtio_net: The current virtio_net driver has a startup race, which
prevents any incoming traffic:
If try_fill_recv submits buffers to the host system data might be
filled in and an interrupt is sent, before napi_enable finishes.
In that case the interrupt will kick skb_recv_done which will then
call netif_rx_schedule. netif_rx_schedule checks, if NAPI_STATE_SCHED
is set - which is not as we did not run napi_enable. No poll routine
is scheduled. Furthermore, skb_recv_done returns false, we disables
interrupts for this device.
One solution is the enable napi before inbound buffer are available.
Signed-off-by: Christian Borntraeger <borntraeger@xxxxxxxxxx>
---
drivers/net/virtio_net.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
Index: kvm/drivers/net/virtio_net.c
===================================================================
--- kvm.orig/drivers/net/virtio_net.c
+++ kvm/drivers/net/virtio_net.c
@@ -285,13 +285,15 @@ static int virtnet_open(struct net_devic
{
struct virtnet_info *vi = netdev_priv(dev);
+ napi_enable(&vi->napi);
try_fill_recv(vi);
/* If we didn't even get one input buffer, we're useless. */
- if (vi->num == 0)
+ if (vi->num == 0) {
+ napi_disable(&vi->napi);
return -ENOMEM;
+ }
- napi_enable(&vi->napi);
return 0;
}
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