[PATCH][NETNS] fix net released by rcu callback

[Daniel Lezcano <dlezcano@fr.ibm.com>]

When a network namespace reference is held by a network subsystem,
and when this reference is decremented in a rcu update callback, we
must ensure that there is no more outstanding rcu update before
trying to free the network namespace.

In the normal case, the rcu_barrier is called when the network namespace
is exiting in the cleanup_net function.

But when a network namespace creation fails, and the subsystems are
undone (like the cleanup), the rcu_barrier is missing.

This patch adds the missing rcu_barrier.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
---
  net/core/net_namespace.c |    2 ++
  1 file changed, 2 insertions(+)

Index: net-2.6/net/core/net_namespace.c
===================================================================
--- net-2.6.orig/net/core/net_namespace.c
+++ net-2.6/net/core/net_namespace.c
@@ -112,6 +112,8 @@ out_undo:
                 if (ops->exit)
                         ops->exit(net);
         }
+
+       rcu_barrier();
         goto out;
  }