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Commit 83a27052 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
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virtio-net: fix a race on 32bit arches 



commit 3fa2a1df (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: default avatarEric Dumazet <edumazet@google.com>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Acked-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7dbb4918

drivers/net/virtio_net.c

+12 −7
Original line number Diff line number Diff line
@@ -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;