[PATCH] Fix race condition about network device name allocation

Stephen Hemminger
2007-05-14T15:59:18Z

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>

---
net/core/dev.c | 10 ++++++----
net/core/net-sysfs.c | 8 +++++++-
2 files changed, 13 insertions(+), 5 deletions(-)

--- 2.6.21-rc1.orig/net/core/dev.c 2007-05-11 11:02:55.000000000 -0700
+++ 2.6.21-rc1/net/core/dev.c 2007-05-14 08:44:52.000000000 -0700
@@ -3245,7 +3245,6 @@ void netdev_run_todo(void)
continue;
}

- netdev_unregister_sysfs(dev);
dev->reg_state = NETREG_UNREGISTERED;

netdev_wait_allrefs(dev);
@@ -3256,11 +3255,11 @@ 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:
@@ -3411,6 +3410,9 @@ void unregister_netdevice(struct net_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);

--- 2.6.21-rc1.orig/net/core/net-sysfs.c 2007-05-11 11:02:55.000000000 -0700
+++ 2.6.21-rc1/net/core/net-sysfs.c 2007-05-14 08:44:52.000000000 -0700
@@ -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. */