This patch moves the rcu_barrier from rollback_registered_many
(inside the rtnl_lock) into netdev_run_todo (just outside the rtnl_lock).
This allows us to gain the full benefit of sychronize_net calling
synchronize_rcu_expedited when the rtnl_lock is held.
The rcu_barrier in rollback_registered_many was originally a synchronize_net
but was promoted to be a rcu_barrier() when it was found that people were
unnecessarily hitting the 250ms wait in netdev_wait_allrefs(). Changing
the rcu_barrier back to a synchronize_net is therefore safe.
Since we only care about waiting for the rcu callbacks before we get
to netdev_wait_allrefs() it is also safe to move the wait into
netdev_run_todo.
This was tested by creating and destroying 1000 tap devices and observing
/proc/lock_stat. /proc/lock_stat reports this change reduces the hold
times of the rtnl_lock by a factor of 10. There was no observable
difference in the amount of time it takes to destroy a network device.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
dev = list_first_entry(head, struct net_device, unreg_list);
call_netdevice_notifiers(NETDEV_UNREGISTER_BATCH, dev);
- rcu_barrier();
+ synchronize_net();
list_for_each_entry(dev, head, unreg_list)
dev_put(dev);
__rtnl_unlock();
+ /* Wait for rcu callbacks to finish before attempting to drain
+ * the device list. This usually avoids a 250ms wait.
+ */
+ if (!list_empty(&list))
+ rcu_barrier();
+
while (!list_empty(&list)) {
struct net_device *dev
= list_first_entry(&list, struct net_device, todo_list);