On Wed, Jun 06, 2012 at 10:35:24AM +0200, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@xxxxxxxxxx>
>
> commit 3fa2a1df909 (virtio-net: per cpu 64 bit stats (v2)) added a race
> on 32bit arches.
>
> We must use separate syncp for rx and tx path as they can be run at the
> same time on different cpus. Thus one sequence increment can be lost and
> readers spin forever.
>
> Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
> Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
> Cc: Jason Wang <jasowang@xxxxxxxxxx>
I'm still thinking about moving tx to take a xmit lock long term,
meanwhile this fix appears appropriate for 3.5.
Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
Dave, can you pick this up pls?
> ---
> drivers/net/virtio_net.c | 19 ++++++++++++-------
> 1 file changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 5214b1e..f18149a 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -42,7 +42,8 @@ module_param(gso, bool, 0444);
> #define VIRTNET_DRIVER_VERSION "1.0.0"
>
> struct virtnet_stats {
> - struct u64_stats_sync syncp;
> + struct u64_stats_sync tx_syncp;
> + struct u64_stats_sync rx_syncp;
> u64 tx_bytes;
> u64 tx_packets;
>
> @@ -300,10 +301,10 @@ static void receive_buf(struct net_device *dev, void *buf, unsigned int len)
>
> hdr = skb_vnet_hdr(skb);
>
> - u64_stats_update_begin(&stats->syncp);
> + u64_stats_update_begin(&stats->rx_syncp);
> stats->rx_bytes += skb->len;
> stats->rx_packets++;
> - u64_stats_update_end(&stats->syncp);
> + u64_stats_update_end(&stats->rx_syncp);
>
> if (hdr->hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> pr_debug("Needs csum!\n");
> @@ -565,10 +566,10 @@ static unsigned int free_old_xmit_skbs(struct virtnet_info *vi)
> while ((skb = virtqueue_get_buf(vi->svq, &len)) != NULL) {
> pr_debug("Sent skb %p\n", skb);
>
> - u64_stats_update_begin(&stats->syncp);
> + u64_stats_update_begin(&stats->tx_syncp);
> stats->tx_bytes += skb->len;
> stats->tx_packets++;
> - u64_stats_update_end(&stats->syncp);
> + u64_stats_update_end(&stats->tx_syncp);
>
> tot_sgs += skb_vnet_hdr(skb)->num_sg;
> dev_kfree_skb_any(skb);
> @@ -703,12 +704,16 @@ static struct rtnl_link_stats64 *virtnet_stats(struct net_device *dev,
> u64 tpackets, tbytes, rpackets, rbytes;
>
> do {
> - start = u64_stats_fetch_begin(&stats->syncp);
> + start = u64_stats_fetch_begin(&stats->tx_syncp);
> tpackets = stats->tx_packets;
> tbytes = stats->tx_bytes;
> + } while (u64_stats_fetch_retry(&stats->tx_syncp, start));
> +
> + do {
> + start = u64_stats_fetch_begin(&stats->rx_syncp);
> rpackets = stats->rx_packets;
> rbytes = stats->rx_bytes;
> - } while (u64_stats_fetch_retry(&stats->syncp, start));
> + } while (u64_stats_fetch_retry(&stats->rx_syncp, start));
>
> tot->rx_packets += rpackets;
> tot->tx_packets += tpackets;
>
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