From 6056415d3a513846f774e7bbee0de0460b1c15df Mon Sep 17 00:00:00 2001 From: Kirill Tkhai Date: Tue, 13 Mar 2018 13:55:55 +0300 Subject: net: Add comment about pernet_operations methods and synchronization Make locking scheme be visible for users, and provide a comment what for we are need exit_batch() methods, and when it should be used. Signed-off-by: Kirill Tkhai Signed-off-by: David S. Miller --- include/net/net_namespace.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/net/net_namespace.h') diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h index d4417495773a..71abc8d79178 100644 --- a/include/net/net_namespace.h +++ b/include/net/net_namespace.h @@ -312,6 +312,20 @@ struct net *get_net_ns_by_id(struct net *net, int id); struct pernet_operations { struct list_head list; + /* + * Below methods are called without any exclusive locks. + * More than one net may be constructed and destructed + * in parallel on several cpus. Every pernet_operations + * have to keep in mind all other pernet_operations and + * to introduce a locking, if they share common resources. + * + * Exit methods using blocking RCU primitives, such as + * synchronize_rcu(), should be implemented via exit_batch. + * Then, destruction of a group of net requires single + * synchronize_rcu() related to these pernet_operations, + * instead of separate synchronize_rcu() for every net. + * Please, avoid synchronize_rcu() at all, where it's possible. + */ int (*init)(struct net *net); void (*exit)(struct net *net); void (*exit_batch)(struct list_head *net_exit_list); -- cgit v1.2.3-59-g8ed1b