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Commit f4618d39 authored by Eric W. Biederman's avatar Eric W. Biederman Committed by David S. Miller
Browse files

[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: default avatarEric W. Biederman <ebiederm@xmission.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 32db9276

include/net/net_namespace.h

+0 −3
Original line number Diff line number Diff line
@@ -96,9 +96,6 @@ static inline void release_net(struct net *net) 
#endif

}



extern void net_lock(void);

extern void net_unlock(void);



#define for_each_net(VAR)				\

	list_for_each_entry(VAR, &net_namespace_list, list)

net/core/net_namespace.c

+6 −17
Original line number Diff line number Diff line
@@ -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)