ixgb: fix race on rx_buffer_len in mtu change

some random coverage testing found that when changing mtu
under heavy traffic load, NAPI would use the rx_buffer_len variable
after it had been changed by change_mtu.

Similar to e1000 bugs found long ago.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 7 insertions, 3 deletions

diff --git a/drivers/net/ixgb/ixgb_main.c b/drivers/net/ixgb/ixgb_main.c
index 4bf6bbc65822..c3234c451043 100644
--- a/drivers/net/ixgb/ixgb_main.c
+++ b/drivers/net/ixgb/ixgb_main.c
@@ -1573,14 +1573,18 @@ ixgb_change_mtu(struct net_device *netdev, int new_mtu)
                 return -EINVAL;
         }
 
+        if (old_max_frame == max_frame)
+                return 0;
+
+        if (netif_running(netdev))
+                ixgb_down(adapter, true);
+
         adapter->rx_buffer_len = max_frame + 8; /* + 8 for errata */
 
         netdev->mtu = new_mtu;
 
-        if ((old_max_frame != max_frame) && netif_running(netdev)) {
-                ixgb_down(adapter, true);
+        if (netif_running(netdev))
                 ixgb_up(adapter);
-        }
 
         return 0;
 }