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Commit d7d99872 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

netns: add pre_exit method to struct pernet_operations 



Current struct pernet_operations exit() handlers are highly
discouraged to call synchronize_rcu().

There are cases where we need them, and exit_batch() does
not help the common case where a single netns is dismantled.

This patch leverages the existing synchronize_rcu() call
in cleanup_net()

Calling optional ->pre_exit() method before ->exit() or
->exit_batch() allows to benefit from a single synchronize_rcu()
call.

Note that the synchronize_rcu() calls added in this patch
are only in error paths or slow paths.

Tested:

$ time for i in {1..1000}; do unshare -n /bin/false;done

real	0m2.612s
user	0m0.171s
sys	0m2.216s

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2a54003e

include/net/net_namespace.h

+5 −0
Original line number Diff line number Diff line
@@ -355,8 +355,13 @@ struct pernet_operations { 
	 * 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.

	 *

	 * Note that a combination of pre_exit() and exit() can

	 * be used, since a synchronize_rcu() is guaranteed between

	 * the calls.

	 */

	int (*init)(struct net *net);

	void (*pre_exit)(struct net *net);

	void (*exit)(struct net *net);

	void (*exit_batch)(struct list_head *net_exit_list);

	unsigned int *id;

net/core/net_namespace.c

+28 −0
Original line number Diff line number Diff line
@@ -145,6 +145,17 @@ static void ops_free(const struct pernet_operations *ops, struct net *net) 
	}

}



static void ops_pre_exit_list(const struct pernet_operations *ops,

			      struct list_head *net_exit_list)

{

	struct net *net;



	if (ops->pre_exit) {

		list_for_each_entry(net, net_exit_list, exit_list)

			ops->pre_exit(net);

	}

}



static void ops_exit_list(const struct pernet_operations *ops,

			  struct list_head *net_exit_list)

{
@@ -328,6 +339,12 @@ static __net_init int setup_net(struct net *net, struct user_namespace *user_ns) 
	 * for the pernet modules whose init functions did not fail.

	 */

	list_add(&net->exit_list, &net_exit_list);

	saved_ops = ops;

	list_for_each_entry_continue_reverse(ops, &pernet_list, list)

		ops_pre_exit_list(ops, &net_exit_list);



	synchronize_rcu();



	saved_ops = ops;

	list_for_each_entry_continue_reverse(ops, &pernet_list, list)

		ops_exit_list(ops, &net_exit_list);
@@ -541,10 +558,15 @@ static void cleanup_net(struct work_struct *work) 
		list_add_tail(&net->exit_list, &net_exit_list);

	}



	/* Run all of the network namespace pre_exit methods */

	list_for_each_entry_reverse(ops, &pernet_list, list)

		ops_pre_exit_list(ops, &net_exit_list);



	/*

	 * Another CPU might be rcu-iterating the list, wait for it.

	 * This needs to be before calling the exit() notifiers, so

	 * the rcu_barrier() below isn't sufficient alone.

	 * Also the pre_exit() and exit() methods need this barrier.

	 */

	synchronize_rcu();
@@ -1101,6 +1123,8 @@ static int __register_pernet_operations(struct list_head *list, 
out_undo:

	/* If I have an error cleanup all namespaces I initialized */

	list_del(&ops->list);

	ops_pre_exit_list(ops, &net_exit_list);

	synchronize_rcu();

	ops_exit_list(ops, &net_exit_list);

	ops_free_list(ops, &net_exit_list);

	return error;
@@ -1115,6 +1139,8 @@ static void __unregister_pernet_operations(struct pernet_operations *ops) 
	/* See comment in __register_pernet_operations() */

	for_each_net(net)

		list_add_tail(&net->exit_list, &net_exit_list);

	ops_pre_exit_list(ops, &net_exit_list);

	synchronize_rcu();

	ops_exit_list(ops, &net_exit_list);

	ops_free_list(ops, &net_exit_list);

}
@@ -1139,6 +1165,8 @@ static void __unregister_pernet_operations(struct pernet_operations *ops) 
	} else {

		LIST_HEAD(net_exit_list);

		list_add(&init_net.exit_list, &net_exit_list);

		ops_pre_exit_list(ops, &net_exit_list);

		synchronize_rcu();

		ops_exit_list(ops, &net_exit_list);

		ops_free_list(ops, &net_exit_list);

	}