[NET]: Fix race condition about network device name allocation.

Kenji Kaneshige found this race between device removal and
registration.  On unregister it is possible for the old device to
exist, because sysfs file is still open.  A new device with 'eth%d'
will select the same name, but sysfs kobject register will fial.

The following changes the shutdown order slightly. It hold a removes
the sysfs entries earlier (on unregister_netdevice), but holds a
kobject reference.  Then when todo runs the actual last put free
happens.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 7 insertions, 1 deletions

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index b21307b15b82..5c19b0646d7a 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -456,9 +456,15 @@ static struct class net_class = {
 #endif
 };
 
+/* Delete sysfs entries but hold kobject reference until after all
+ * netdev references are gone.
+ */
 void netdev_unregister_sysfs(struct net_device * net)
 {
-        device_del(&(net->dev));
+        struct device *dev = &(net->dev);
+
+        kobject_get(&dev->kobj);
+        device_del(dev);
 }
 
 /* Create sysfs entries for network device. */