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 <ktkhai@virtuozzo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index d441749..71abc8d 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -312,6 +312,20 @@
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);