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>

diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index ded434b032a44ec406a0fa8bcb11d688d95b7efa..b34a6ee73754c857fac757d0fd65aefa4675b699 100644 (file)
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -208,6 +208,9 @@ static inline struct net *read_pnet(struct net * const *pnet)
 #define for_each_net(VAR)                              \
        list_for_each_entry(VAR, &net_namespace_list, list)
 
+#define for_each_net_rcu(VAR)                          \
+       list_for_each_entry_rcu(VAR, &net_namespace_list, list)
+
 #ifdef CONFIG_NET_NS
 #define __net_init
 #define __net_exit

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index b7292a2719dc046bd6772cbd8ee4926e811d0254..5cd0b22e649d0967c536522c20451c476e8fd1a6 100644 (file)
--- 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);