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Date:	Wed, 26 Sep 2007 21:54:47 -0600
From: (Eric W. Biederman)
To:	David Miller <>
Cc:	Daniel Lezcano <>,
	Benjamin Thery <>,
	Kirill Korotaev <>, "Denis V. Lunev" <>,
	Linux Containers <>,
Subject: [PATCH] netns:  Simplify the network namespace list locking rules.

Denis V. Lunev <> 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 <>
 include/net/net_namespace.h |    3 ---
 net/core/net_namespace.c    |   23 ++++++-----------------
 2 files changed, 6 insertions(+), 20 deletions(-)

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index 13b0e3b..934c840 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -96,9 +96,6 @@ static inline void release_net(struct net *net)
-extern void net_lock(void);
-extern void net_unlock(void);
 #define for_each_net(VAR)				\
 	list_for_each_entry(VAR, &net_namespace_list, list)
diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index e478e35..0e0ca6d 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);
 static struct kmem_cache *net_cachep;
@@ -23,16 +22,6 @@ static struct kmem_cache *net_cachep;
 struct net 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)
 	/* Don't let anyone else find us. */
-	net_lock();
+	rtnl_lock();
-	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();
@@ -178,9 +167,9 @@ static int __init net_ns_init(void)
 	err = setup_net(&init_net);
-	net_lock();
+	rtnl_lock();
 	list_add_tail(&init_net.list, &net_namespace_list);
-	net_unlock();
+	rtnl_unlock();
 	if (err)

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