net: make namespace iteration possible under RCU

All we need to take care of is using proper RCU list
add/del primitives and inserting a synchronize_rcu()
at one place to make sure the exit notifiers are run
after everybody has stopped iterating the list.

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 11 insertions, 3 deletions

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index b7292a2719dc..5cd0b22e649d 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -6,6 +6,7 @@
 #include <linux/delay.h>
 #include <linux/sched.h>
 #include <linux/idr.h>
+#include <linux/rculist.h>
 #include <net/net_namespace.h>
 #include <net/netns/generic.h>
 
@@ -127,7 +128,7 @@ static struct net *net_create(void)
         rv = setup_net(net);
         if (rv == 0) {
                 rtnl_lock();
-                list_add_tail(&net->list, &net_namespace_list);
+                list_add_tail_rcu(&net->list, &net_namespace_list);
                 rtnl_unlock();
         }
         mutex_unlock(&net_mutex);
@@ -156,9 +157,16 @@ static void cleanup_net(struct work_struct *work)
 
         /* Don't let anyone else find us. */
         rtnl_lock();
-        list_del(&net->list);
+        list_del_rcu(&net->list);
         rtnl_unlock();
 
+        /*
+         * 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.
+         */
+        synchronize_rcu();
+
         /* Run all of the network namespace exit methods */
         list_for_each_entry_reverse(ops, &pernet_list, list) {
                 if (ops->exit)
@@ -219,7 +227,7 @@ static int __init net_ns_init(void)
                 panic("Could not setup the initial network namespace");
 
         rtnl_lock();
-        list_add_tail(&init_net.list, &net_namespace_list);
+        list_add_tail_rcu(&init_net.list, &net_namespace_list);
         rtnl_unlock();
 
         mutex_unlock(&net_mutex);