veth: fix 64bit stats on 32bit arches

Using 64bit stats on 32bit arches must use a synchronization or readers
can get transient values.

Fixes bug introduced in commit 6311cc44a2 (veth: convert to 64 bit
statistics)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 37 insertions, 18 deletions

diff --git a/drivers/net/veth.c b/drivers/net/veth.c
index 8730d6494633..4b6db3b6c5d5 100644
--- a/drivers/net/veth.c
+++ b/drivers/net/veth.c
@@ -12,6 +12,7 @@
 #include <linux/slab.h>
 #include <linux/ethtool.h>
 #include <linux/etherdevice.h>
+#include <linux/u64_stats_sync.h>
 
 #include <net/dst.h>
 #include <net/xfrm.h>
@@ -24,12 +25,13 @@
 #define MAX_MTU 65535           /* Max L3 MTU (arbitrary) */
 
 struct veth_net_stats {
-        u64     rx_packets;
-        u64     tx_packets;
-        u64     rx_bytes;
-        u64     tx_bytes;
-        u64     tx_dropped;
-        u64     rx_dropped;
+        u64                     rx_packets;
+        u64                     tx_packets;
+        u64                     rx_bytes;
+        u64                     tx_bytes;
+        u64                     rx_dropped;
+        u64                     tx_dropped;
+        struct u64_stats_sync   syncp;
 };
 
 struct veth_priv {
@@ -137,21 +139,29 @@ static netdev_tx_t veth_xmit(struct sk_buff *skb, struct net_device *dev)
         if (dev_forward_skb(rcv, skb) != NET_RX_SUCCESS)
                 goto rx_drop;
 
+        u64_stats_update_begin(&stats->syncp);
         stats->tx_bytes += length;
         stats->tx_packets++;
+        u64_stats_update_end(&stats->syncp);
 
+        u64_stats_update_begin(&rcv_stats->syncp);
         rcv_stats->rx_bytes += length;
         rcv_stats->rx_packets++;
+        u64_stats_update_end(&rcv_stats->syncp);
 
         return NETDEV_TX_OK;
 
 tx_drop:
         kfree_skb(skb);
+        u64_stats_update_begin(&stats->syncp);
         stats->tx_dropped++;
+        u64_stats_update_end(&stats->syncp);
         return NETDEV_TX_OK;
 
 rx_drop:
+        u64_stats_update_begin(&rcv_stats->syncp);
         rcv_stats->rx_dropped++;
+        u64_stats_update_end(&rcv_stats->syncp);
         return NETDEV_TX_OK;
 }
 
@@ -162,21 +172,30 @@ rx_drop:
 static struct rtnl_link_stats64 *veth_get_stats64(struct net_device *dev,
                                                   struct rtnl_link_stats64 *tot)
 {
-        struct veth_priv *priv;
+        struct veth_priv *priv = netdev_priv(dev);
         int cpu;
-        struct veth_net_stats *stats;
-
-        priv = netdev_priv(dev);
 
         for_each_possible_cpu(cpu) {
-                stats = per_cpu_ptr(priv->stats, cpu);
-
-                tot->rx_packets += stats->rx_packets;
-                tot->tx_packets += stats->tx_packets;
-                tot->rx_bytes   += stats->rx_bytes;
-                tot->tx_bytes   += stats->tx_bytes;
-                tot->tx_dropped += stats->tx_dropped;
-                tot->rx_dropped += stats->rx_dropped;
+                struct veth_net_stats *stats = per_cpu_ptr(priv->stats, cpu);
+                u64 rx_packets, rx_bytes, rx_dropped;
+                u64 tx_packets, tx_bytes, tx_dropped;
+                unsigned int start;
+
+                do {
+                        start = u64_stats_fetch_begin_bh(&stats->syncp);
+                        rx_packets = stats->rx_packets;
+                        tx_packets = stats->tx_packets;
+                        rx_bytes = stats->rx_bytes;
+                        tx_bytes = stats->tx_bytes;
+                        rx_dropped = stats->rx_dropped;
+                        tx_dropped = stats->tx_dropped;
+                } while (u64_stats_fetch_retry_bh(&stats->syncp, start));
+                tot->rx_packets += rx_packets;
+                tot->tx_packets += tx_packets;
+                tot->rx_bytes   += rx_bytes;
+                tot->tx_bytes   += tx_bytes;
+                tot->rx_dropped += rx_dropped;
+                tot->tx_dropped += tx_dropped;
         }
 
         return tot;