netdev - Re: [PATCH] net: make namespace iteration possible under RCU

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Date:	Thu, 18 Jun 2009 14:15:04 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	Netdev <netdev@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...stanetworks.com>
Subject: Re: [PATCH] net: make namespace iteration possible under RCU

On Thu, 2009-06-18 at 13:45 +0200, Jiri Pirko wrote:
> Thu, Jun 18, 2009 at 01:08:23PM CEST, johannes@...solutions.net wrote:
> >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@...solutions.net>
> >---
> > 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 <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>
> > 
> >@@ -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();
> 
> IMHO you do not need to call synchronize_rcu() here since rcu_barrier() is
> called later just before net_free(net). Seems redundant.

Heh, well, I discussed that earlier with Eric and we do not want anyone
to have a reference to the struct net while the pernet->exit calls are
run, and thus we do need it here.

johannes

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