netdev - [PATCH] virtio_net: Fix stalled inbound traffic on early packets

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Message-Id: <200712061659.44803.borntraeger@de.ibm.com>
Date:	Thu, 6 Dec 2007 16:59:44 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org,
	Anthony Liguori <aliguori@...ibm.com>
Subject: [PATCH] virtio_net: Fix stalled inbound traffic on early packets

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@...ibm.com>
---
 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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