4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <edumazet@xxxxxxxxxx>
commit d7d99872c144a2c2f5d9c9d83627fa833836cba5 upstream.
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: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/net/net_namespace.h | 5 +++++
net/core/net_namespace.c | 28 ++++++++++++++++++++++++++++
2 files changed, 33 insertions(+)
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -353,8 +353,13 @@ 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;
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -154,6 +154,17 @@ static void ops_free(const struct pernet
}
}
+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)
{
@@ -342,6 +353,12 @@ out_undo:
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);
ops = saved_ops;
@@ -554,10 +571,15 @@ static void cleanup_net(struct work_stru
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();
@@ -977,6 +999,8 @@ static int __register_pernet_operations(
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;
@@ -991,6 +1015,8 @@ static void __unregister_pernet_operatio
/* 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);
}
@@ -1015,6 +1041,8 @@ static void __unregister_pernet_operatio
} 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);
}
