loopback: Implement 64bit stats on 32bit arches

Uses a seqcount_t to synchronize stat producer and consumer, for packets
and bytes counter, now u64 types.

(dropped counter being rarely used, stay a native "unsigned long" type)

No noticeable performance impact on x86, as it only adds two increments
per frame. It might be more expensive on arches where smp_wmb() is not
free.

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

1 files changed, 51 insertions, 10 deletions

diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
index 72b7949c91b1..09334f8f148b 100644
--- a/drivers/net/loopback.c
+++ b/drivers/net/loopback.c
@@ -60,11 +60,51 @@
 #include <net/net_namespace.h>
 
 struct pcpu_lstats {
-        unsigned long packets;
-        unsigned long bytes;
+        u64 packets;
+        u64 bytes;
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+        seqcount_t seq;
+#endif
         unsigned long drops;
 };
 
+#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
+static void inline lstats_update_begin(struct pcpu_lstats *lstats)
+{
+        write_seqcount_begin(&lstats->seq);
+}
+static void inline lstats_update_end(struct pcpu_lstats *lstats)
+{
+        write_seqcount_end(&lstats->seq);
+}
+static void inline lstats_fetch_and_add(u64 *packets, u64 *bytes, const struct pcpu_lstats *lstats)
+{
+        u64 tpackets, tbytes;
+        unsigned int seq;
+
+        do {
+                seq = read_seqcount_begin(&lstats->seq);
+                tpackets = lstats->packets;
+                tbytes = lstats->bytes;
+        } while (read_seqcount_retry(&lstats->seq, seq));
+
+        *packets += tpackets;
+        *bytes += tbytes;
+}
+#else
+static void inline lstats_update_begin(struct pcpu_lstats *lstats)
+{
+}
+static void inline lstats_update_end(struct pcpu_lstats *lstats)
+{
+}
+static void inline lstats_fetch_and_add(u64 *packets, u64 *bytes, const struct pcpu_lstats *lstats)
+{
+        *packets += lstats->packets;
+        *bytes += lstats->bytes;
+}
+#endif
+
 /*
  * The higher levels take care of making this non-reentrant (it's
  * called with bh's disabled).
@@ -86,21 +126,23 @@ static netdev_tx_t loopback_xmit(struct sk_buff *skb,
 
         len = skb->len;
         if (likely(netif_rx(skb) == NET_RX_SUCCESS)) {
+                lstats_update_begin(lb_stats);
                 lb_stats->bytes += len;
                 lb_stats->packets++;
+                lstats_update_end(lb_stats);
         } else
                 lb_stats->drops++;
 
         return NETDEV_TX_OK;
 }
 
-static struct net_device_stats *loopback_get_stats(struct net_device *dev)
+static struct rtnl_link_stats64 *loopback_get_stats64(struct net_device *dev)
 {
         const struct pcpu_lstats __percpu *pcpu_lstats;
-        struct net_device_stats *stats = &dev->stats;
-        unsigned long bytes = 0;
-        unsigned long packets = 0;
-        unsigned long drops = 0;
+        struct rtnl_link_stats64 *stats = &dev->stats64;
+        u64 bytes = 0;
+        u64 packets = 0;
+        u64 drops = 0;
         int i;
 
         pcpu_lstats = (void __percpu __force *)dev->ml_priv;
@@ -108,8 +150,7 @@ static struct net_device_stats *loopback_get_stats(struct net_device *dev)
                 const struct pcpu_lstats *lb_stats;
 
                 lb_stats = per_cpu_ptr(pcpu_lstats, i);
-                bytes   += lb_stats->bytes;
-                packets += lb_stats->packets;
+                lstats_fetch_and_add(&packets, &bytes, lb_stats);
                 drops   += lb_stats->drops;
         }
         stats->rx_packets = packets;
@@ -158,7 +199,7 @@ static void loopback_dev_free(struct net_device *dev)
 static const struct net_device_ops loopback_ops = {
         .ndo_init      = loopback_dev_init,
         .ndo_start_xmit= loopback_xmit,
-        .ndo_get_stats = loopback_get_stats,
+        .ndo_get_stats64 = loopback_get_stats64,
 };
 
 /*