From f0b07bb151b098d291fd1fd71ef7a2df56fb124a Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Thu, 29 Mar 2018 19:20:32 +0300 Subject: net: Introduce net_rwsem to protect net_namespace_list rtnl_lock() is used everywhere, and contention is very high. When someone wants to iterate over alive net namespaces, he/she has no a possibility to do that without exclusive lock. But the exclusive rtnl_lock() in such places is overkill, and it just increases the contention. Yes, there is already for_each_net_rcu() in kernel, but it requires rcu_read_lock(), and this can't be sleepable. Also, sometimes it may be need really prevent net_namespace_list growth, so for_each_net_rcu() is not fit there. This patch introduces new rw_semaphore, which will be used instead of rtnl_mutex to protect net_namespace_list. It is sleepable and allows not-exclusive iterations over net namespaces list. It allows to stop using rtnl_lock() in several places (what is made in next patches) and makes less the time, we keep rtnl_mutex. Here we just add new lock, while the explanation of we can remove rtnl_lock() there are in next patches. Fine grained locks generally are better, then one big lock, so let's do that with net_namespace_list, while the situation allows that. Signed-off-by: Kirill Tkhai Signed-off-by: David S. Miller --- net/core/net_namespace.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'net/core/net_namespace.c') diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c index b5796d17a302..7fdf321d4997 100644 --- a/net/core/net_namespace.c +++ b/net/core/net_namespace.c @@ -33,6 +33,10 @@ static struct list_head *first_device = &pernet_list; LIST_HEAD(net_namespace_list); EXPORT_SYMBOL_GPL(net_namespace_list); +/* Protects net_namespace_list. Nests iside rtnl_lock() */ +DECLARE_RWSEM(net_rwsem); +EXPORT_SYMBOL_GPL(net_rwsem); + struct net init_net = { .count = REFCOUNT_INIT(1), .dev_base_head = LIST_HEAD_INIT(init_net.dev_base_head), @@ -309,9 +313,9 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns) if (error < 0) goto out_undo; } - rtnl_lock(); + down_write(&net_rwsem); list_add_tail_rcu(&net->list, &net_namespace_list); - rtnl_unlock(); + up_write(&net_rwsem); out: return error; @@ -450,7 +454,7 @@ static void unhash_nsid(struct net *net, struct net *last) * and this work is the only process, that may delete * a net from net_namespace_list. So, when the below * is executing, the list may only grow. Thus, we do not - * use for_each_net_rcu() or rtnl_lock(). + * use for_each_net_rcu() or net_rwsem. */ for_each_net(tmp) { int id; @@ -485,7 +489,7 @@ static void cleanup_net(struct work_struct *work) down_read(&pernet_ops_rwsem); /* Don't let anyone else find us. */ - rtnl_lock(); + down_write(&net_rwsem); llist_for_each_entry(net, net_kill_list, cleanup_list) list_del_rcu(&net->list); /* Cache last net. After we unlock rtnl, no one new net @@ -499,7 +503,7 @@ static void cleanup_net(struct work_struct *work) * useless anyway, as netns_ids are destroyed there. */ last = list_last_entry(&net_namespace_list, struct net, list); - rtnl_unlock(); + up_write(&net_rwsem); llist_for_each_entry(net, net_kill_list, cleanup_list) { unhash_nsid(net, last); @@ -900,6 +904,9 @@ static int __register_pernet_operations(struct list_head *list, list_add_tail(&ops->list, list); if (ops->init || (ops->id && ops->size)) { + /* We held write locked pernet_ops_rwsem, and parallel + * setup_net() and cleanup_net() are not possible. + */ for_each_net(net) { error = ops_init(ops, net); if (error) @@ -923,6 +930,7 @@ static void __unregister_pernet_operations(struct pernet_operations *ops) LIST_HEAD(net_exit_list); list_del(&ops->list); + /* See comment in __register_pernet_operations() */ for_each_net(net) list_add_tail(&net->exit_list, &net_exit_list); ops_exit_list(ops, &net_exit_list); -- cgit