sfc: Hold efx_nic::stats_lock while reading efx_nic::mac_stats

efx_nic::stats_lock is used to serialise stats updates, but each
reader was dropping it before it finished reading efx_nic::mac_stats.

If there were concurrent stats reads using procfs, or one using procfs
and one using ethtool, an update could race with a read.  On a 32-bit
system, the reader could see word-tearing of 64-bit stats (32 bits of
the old value and 32 bits of the new).

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/drivers/net/ethernet/sfc/ethtool.c b/drivers/net/ethernet/sfc/ethtool.c
index 52c9ee4c8aa3..55a25b14d304 100644
--- a/drivers/net/ethernet/sfc/ethtool.c
+++ b/drivers/net/ethernet/sfc/ethtool.c
@@ -489,13 +489,14 @@ static void efx_ethtool_get_stats(struct net_device *net_dev,
         const struct efx_ethtool_stat *stat;
         struct efx_channel *channel;
         struct efx_tx_queue *tx_queue;
-        struct rtnl_link_stats64 temp;
         int i;
 
         EFX_BUG_ON_PARANOID(stats->n_stats != EFX_ETHTOOL_NUM_STATS);
 
+        spin_lock_bh(&efx->stats_lock);
+
         /* Update MAC and NIC statistics */
-        dev_get_stats(net_dev, &temp);
+        efx->type->update_stats(efx);
 
         /* Fill detailed statistics buffer */
         for (i = 0; i < EFX_ETHTOOL_NUM_STATS; i++) {
@@ -525,6 +526,8 @@ static void efx_ethtool_get_stats(struct net_device *net_dev,
                         break;
                 }
         }
+
+        spin_unlock_bh(&efx->stats_lock);
 }
 
 static void efx_ethtool_self_test(struct net_device *net_dev,