[NETNS]: Simplify the network namespace list locking rules.

Denis V. Lunev <den@sw.ru> noticed that the locking rules
for the network namespace list are over complicated and broken.

In particular the current register_netdev_notifier currently
does not take any lock making the for_each_net iteration racy
with network namespace creation and destruction. Oops.

The fact that we need to use for_each_net in rtnl_unlock() when
the rtnetlink support becomes per network namespace makes designing
the proper locking tricky.  In addition we need to be able to call
rtnl_lock() and rtnl_unlock() when we have the net_mutex held.

After thinking about it and looking at the alternatives carefully
it looks like the simplest and most maintainable solution is
to remove net_list_mutex altogether, and to use the rtnl_mutex instead.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 17 deletions

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index e478e353ea6b..0e0ca6d06fa5 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -15,7 +15,6 @@ static LIST_HEAD(pernet_list);
 static struct list_head *first_device = &pernet_list;
 static DEFINE_MUTEX(net_mutex);
 
-static DEFINE_MUTEX(net_list_mutex);
 LIST_HEAD(net_namespace_list);
 
 static struct kmem_cache *net_cachep;
@@ -23,16 +22,6 @@ static struct kmem_cache *net_cachep;
 struct net init_net;
 EXPORT_SYMBOL_GPL(init_net);
 
-void net_lock(void)
-{
-        mutex_lock(&net_list_mutex);
-}
-
-void net_unlock(void)
-{
-        mutex_unlock(&net_list_mutex);
-}
-
 static struct net *net_alloc(void)
 {
         return kmem_cache_alloc(net_cachep, GFP_KERNEL);
@@ -62,9 +51,9 @@ static void cleanup_net(struct work_struct *work)
         mutex_lock(&net_mutex);
 
         /* Don't let anyone else find us. */
-        net_lock();
+        rtnl_lock();
         list_del(&net->list);
-        net_unlock();
+        rtnl_unlock();
 
         /* Run all of the network namespace exit methods */
         list_for_each_entry_reverse(ops, &pernet_list, list) {
@@ -151,9 +140,9 @@ struct net *copy_net_ns(unsigned long flags, struct net *old_net)
         if (err)
                 goto out_unlock;
 
-        net_lock();
+        rtnl_lock();
         list_add_tail(&new_net->list, &net_namespace_list);
-        net_unlock();
+        rtnl_unlock();
 
 
 out_unlock:
@@ -178,9 +167,9 @@ static int __init net_ns_init(void)
         mutex_lock(&net_mutex);
         err = setup_net(&init_net);
 
-        net_lock();
+        rtnl_lock();
         list_add_tail(&init_net.list, &net_namespace_list);
-        net_unlock();
+        rtnl_unlock();
 
         mutex_unlock(&net_mutex);
         if (err)