net: Get rid of rtnl_link_stats64 / net_device_stats union

In commit be1f3c2c027cc5ad735df6a45a542ed1db7ec48b "net: Enable 64-bit
net device statistics on 32-bit architectures" I redefined struct
net_device_stats so that it could be used in a union with struct
rtnl_link_stats64, avoiding the need for explicit copying or
conversion between the two.  However, this is unsafe because there is
no locking required and no lock consistently held around calls to
dev_get_stats() and use of the statistics structure it returns.

In commit 28172739f0a276eb8d6ca917b3974c2edb036da3 "net: fix 64 bit
counters on 32 bit arches" Eric Dumazet dealt with that problem by
requiring callers of dev_get_stats() to provide storage for the
result.  This means that the net_device::stats64 field and the padding
in struct net_device_stats are now redundant, so remove them.

Update the comment on net_device_ops::ndo_get_stats64 to reflect its
new usage.

Change dev_txq_stats_fold() to use struct rtnl_link_stats64, since
that is what all its callers are really using and it is no longer
going to be compatible with struct net_device_stats.

Eric Dumazet suggested the separate function for the structure
conversion.

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

1 files changed, 28 insertions, 42 deletions

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 8018f6bf3051..17e95e37aed9 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -162,42 +162,32 @@ static inline bool dev_xmit_complete(int rc)
 /*
  *      Old network device statistics. Fields are native words
  *      (unsigned long) so they can be read and written atomically.
- *      Each field is padded to 64 bits for compatibility with
- *      rtnl_link_stats64.
  */
 
-#if BITS_PER_LONG == 64
-#define NET_DEVICE_STATS_DEFINE(name)   unsigned long name
-#elif defined(__LITTLE_ENDIAN)
-#define NET_DEVICE_STATS_DEFINE(name)   unsigned long name, pad_ ## name
-#else
-#define NET_DEVICE_STATS_DEFINE(name)   unsigned long pad_ ## name, name
-#endif
-
 struct net_device_stats {
-        NET_DEVICE_STATS_DEFINE(rx_packets);
-        NET_DEVICE_STATS_DEFINE(tx_packets);
-        NET_DEVICE_STATS_DEFINE(rx_bytes);
-        NET_DEVICE_STATS_DEFINE(tx_bytes);
-        NET_DEVICE_STATS_DEFINE(rx_errors);
-        NET_DEVICE_STATS_DEFINE(tx_errors);
-        NET_DEVICE_STATS_DEFINE(rx_dropped);
-        NET_DEVICE_STATS_DEFINE(tx_dropped);
-        NET_DEVICE_STATS_DEFINE(multicast);
-        NET_DEVICE_STATS_DEFINE(collisions);
-        NET_DEVICE_STATS_DEFINE(rx_length_errors);
-        NET_DEVICE_STATS_DEFINE(rx_over_errors);
-        NET_DEVICE_STATS_DEFINE(rx_crc_errors);
-        NET_DEVICE_STATS_DEFINE(rx_frame_errors);
-        NET_DEVICE_STATS_DEFINE(rx_fifo_errors);
-        NET_DEVICE_STATS_DEFINE(rx_missed_errors);
-        NET_DEVICE_STATS_DEFINE(tx_aborted_errors);
-        NET_DEVICE_STATS_DEFINE(tx_carrier_errors);
-        NET_DEVICE_STATS_DEFINE(tx_fifo_errors);
-        NET_DEVICE_STATS_DEFINE(tx_heartbeat_errors);
-        NET_DEVICE_STATS_DEFINE(tx_window_errors);
-        NET_DEVICE_STATS_DEFINE(rx_compressed);
-        NET_DEVICE_STATS_DEFINE(tx_compressed);
+        unsigned long   rx_packets;
+        unsigned long   tx_packets;
+        unsigned long   rx_bytes;
+        unsigned long   tx_bytes;
+        unsigned long   rx_errors;
+        unsigned long   tx_errors;
+        unsigned long   rx_dropped;
+        unsigned long   tx_dropped;
+        unsigned long   multicast;
+        unsigned long   collisions;
+        unsigned long   rx_length_errors;
+        unsigned long   rx_over_errors;
+        unsigned long   rx_crc_errors;
+        unsigned long   rx_frame_errors;
+        unsigned long   rx_fifo_errors;
+        unsigned long   rx_missed_errors;
+        unsigned long   tx_aborted_errors;
+        unsigned long   tx_carrier_errors;
+        unsigned long   tx_fifo_errors;
+        unsigned long   tx_heartbeat_errors;
+        unsigned long   tx_window_errors;
+        unsigned long   rx_compressed;
+        unsigned long   tx_compressed;
 };
 
 #endif  /*  __KERNEL__  */
@@ -666,14 +656,13 @@ struct netdev_rx_queue {
  *      Callback uses when the transmitter has not made any progress
  *      for dev->watchdog ticks.
  *
- * struct rtnl_link_stats64* (*ndo_get_stats64)(struct net_device *dev
+ * struct rtnl_link_stats64* (*ndo_get_stats64)(struct net_device *dev,
  *                      struct rtnl_link_stats64 *storage);
  * struct net_device_stats* (*ndo_get_stats)(struct net_device *dev);
  *      Called when a user wants to get the network device usage
  *      statistics. Drivers must do one of the following:
- *      1. Define @ndo_get_stats64 to update a rtnl_link_stats64 structure
- *         (which should normally be dev->stats64) and return a ponter to
- *         it. The structure must not be changed asynchronously.
+ *      1. Define @ndo_get_stats64 to fill in a zero-initialised
+ *         rtnl_link_stats64 structure passed by the caller.
  *      2. Define @ndo_get_stats to update a net_device_stats structure
  *         (which should normally be dev->stats) and return a pointer to
  *         it. The structure may be changed asynchronously only if each
@@ -888,10 +877,7 @@ struct net_device {
         int                     ifindex;
         int                     iflink;
 
-        union {
-                struct rtnl_link_stats64 stats64;
-                struct net_device_stats stats;
-        };
+        struct net_device_stats stats;
 
 #ifdef CONFIG_WIRELESS_EXT
         /* List of functions to handle Wireless Extensions (instead of ioctl).
@@ -2147,7 +2133,7 @@ extern void		dev_mcast_init(void);
 extern const struct rtnl_link_stats64 *dev_get_stats(struct net_device *dev,
                                                      struct rtnl_link_stats64 *storage);
 extern void             dev_txq_stats_fold(const struct net_device *dev,
-                                           struct net_device_stats *stats);
+                                           struct rtnl_link_stats64 *stats);
 
 extern int              netdev_max_backlog;
 extern int              netdev_tstamp_prequeue;