[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>

diff --git a/net/core/dev.c b/net/core/dev.c
index f2b61111e26d5c5c16d621e548065a8fed15dfcd..5a7f20f7857468aeab6ba56ba391c228a59efc91 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3314,7 +3314,6 @@ void netdev_run_todo(void)
                        continue;
                }
 
-               netdev_unregister_sysfs(dev);
                dev->reg_state = NETREG_UNREGISTERED;
 
                netdev_wait_allrefs(dev);
@@ -3325,11 +3324,11 @@ void netdev_run_todo(void)
                BUG_TRAP(!dev->ip6_ptr);
                BUG_TRAP(!dev->dn_ptr);
 
-               /* It must be the very last action,
-                * after this 'dev' may point to freed up memory.
-                */
                if (dev->destructor)
                        dev->destructor(dev);
+
+               /* Free network device */
+               kobject_put(&dev->dev.kobj);
        }
 
 out:
@@ -3480,6 +3479,9 @@ void unregister_netdevice(struct net_device *dev)
        /* Notifier chain MUST detach us from master device. */
        BUG_TRAP(!dev->master);
 
+       /* Remove entries from sysfs */
+       netdev_unregister_sysfs(dev);
+
        /* Finish processing unregister after unlock */
        net_set_todo(dev);
 

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index b21307b15b82d7e09d34101180d9f7131bf1f418..5c19b0646d7a3e09c0284a93686c2d738fc92fd1 100644 (file)
--- 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. */