From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Berg Subject: Re: [PATCH] wireless extensions: play with netns Date: Thu, 18 Jun 2009 02:39:01 +0200 Message-ID: <1245285541.31588.79.camel@johannes.local> References: <1245263058.31588.38.camel@johannes.local> <1245276899.31588.57.camel@johannes.local> <1245282099.31588.69.camel@johannes.local> <1245283327.31588.74.camel@johannes.local> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: John Linville , Netdev , linux-wireless , "Eric W. Biederman" , Alexey Dobriyan To: "Eric W. Biederman" Return-path: In-Reply-To: Sender: linux-wireless-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org On Wed, 2009-06-17 at 17:30 -0700, Eric W. Biederman wrote: > >> This of course gives you a network namespace that can be found by for_each_net rcu > >> while the per net exit functions are running. I think that opens up to races > >> that I don't want to think about. > > > > Indeed. Can we move the rcu_barrier() up? Or we could insert a > > synchronize_rcu() (which is sufficient for rcu_read_lock) before the > > exit functions are run? > > I don't think we can move the barrier. But adding an extra synchronize_rcu > should be fine. We are talking about the slowest of the slow paths here. > It is so slow it even gets it's own kernel thread. Ok :) New patch below. Yes, you're right, we can't move it, it might still be used from exit for net_assign_generic or so. johannes Subject: net: make namespace iteration possible under RCU We already call rcu_barrier(), so all we need to take care of is using proper RCU list add/del primitives. Signed-off-by: Johannes Berg --- include/net/net_namespace.h | 3 +++ net/core/net_namespace.c | 10 +++++++--- 2 files changed, 10 insertions(+), 3 deletions(-) --- wireless-testing.orig/include/net/net_namespace.h 2009-06-18 01:36:26.000000000 +0200 +++ wireless-testing/include/net/net_namespace.h 2009-06-18 02:17:14.000000000 +0200 @@ -211,6 +211,9 @@ static inline struct net *read_pnet(stru #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 --- wireless-testing.orig/net/core/net_namespace.c 2009-06-18 01:36:39.000000000 +0200 +++ wireless-testing/net/core/net_namespace.c 2009-06-18 02:03:06.000000000 +0200 @@ -6,6 +6,7 @@ #include #include #include +#include #include #include @@ -134,7 +135,7 @@ struct net *copy_net_ns(unsigned long fl err = setup_net(new_net); if (!err) { rtnl_lock(); - list_add_tail(&new_net->list, &net_namespace_list); + list_add_tail_rcu(&new_net->list, &net_namespace_list); rtnl_unlock(); } mutex_unlock(&net_mutex); @@ -163,9 +164,12 @@ static void cleanup_net(struct work_stru /* Don't let anyone else find us. */ rtnl_lock(); - list_del(&net->list); + list_del_rcu(&net->list); rtnl_unlock(); + /* if somebody is rcu-iterating the list, wait */ + synchronize_rcu(); + /* Run all of the network namespace exit methods */ list_for_each_entry_reverse(ops, &pernet_list, list) { if (ops->exit) @@ -227,7 +231,7 @@ static int __init net_ns_init(void) err = setup_net(&init_net); 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); -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html