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[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>
hifive-unleashed-5.1
Eric W. Biederman 2007-09-26 22:40:08 -07:00 committed by David S. Miller
parent 32db927686
commit f4618d39a3
2 changed files with 6 additions and 20 deletions
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3
include/net/net_namespace.h
View File

@ -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)

23
net/core/net_namespace.c
View File

@ -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)