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net: Add comment about pernet_operations methods and synchronization

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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>
This commit is contained in:
Kirill Tkhai 2018-03-13 13:55:55 +03:00 committed by David S. Miller
parent 8b4e6b3ca2
commit 6056415d3a
1 changed files with 14 additions and 0 deletions
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14
include/net/net_namespace.h
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@ -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);