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 --- include/net/net_namespace.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/net/net_namespace.h') diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h index 1ab4f920f109..47e35cce3b64 100644 --- a/include/net/net_namespace.h +++ b/include/net/net_namespace.h @@ -291,6 +291,7 @@ static inline struct net *read_pnet(const possible_net_t *pnet) #endif } +/* Protected by net_rwsem */ #define for_each_net(VAR) \ list_for_each_entry(VAR, &net_namespace_list, list) -- cgit v1.2.3