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virtio-net: fix a race on 32bit arches
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commit 3fa2a1d (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@google.com>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Acked-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Eric Dumazet authored and David S. Miller committed Jun 11, 2012
1 parent 7dbb491 commit 83a2705
Showing 1 changed file with 12 additions and 7 deletions.
19 changes: 12 additions & 7 deletions drivers/net/virtio_net.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;

Expand Down Expand Up @@ -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");
Expand Down Expand Up @@ -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);
Expand Down Expand Up @@ -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;
Expand Down

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