net: permanent NUD pins ethernet interfaces when ATM is compiled in.

When ATM and Ethernet are compiled in, ATM and Ethernet create their
NEIGH/ARP tables, they are both assigned to family AF_INET.

int neigh_add(....) {

 ...
        for (tbl=neigh_tables; tbl; tbl = tbl->next) {
                if (tbl->family != ndm->ndm_family)
                        continue;
  ...
}

As ATM table is created before Ethernet(main?) table,
net/core/neighbour.c::neigh_add() function add all permanent IP ARP
Ethernet NUD to the IP ATM table, which is wrong.

Therefore, when net/core/neighbour.c::neigh_ifdown() is called ARP
entries are not cleared, leaving dev->refcnt to a value that will never
be able to reach 0 anymore.

So, when net/core/dev.c::unregister_netdevice() is called it stalls
without being able to destroy the interface leaving the system with no
network tools working anymore.

This is really easy to reproduce:

openvpn --mktun --dev tap10
ip addr add 10.20.30.20/24 dev tap10
ip link set up dev tap10
ip neighbour add 10.20.30.40 lladdr 01:02:03:04:05:06 nud permanent dev tap10
ip link set down dev tap10
openvpn --rmtun --dev tap10

and then kernel log starts being filled by:

unregister_netdevice: waiting for tap10 to become free. Usage count = 2
unregister_netdevice: waiting for tap10 to become free. Usage count = 2
unregister_netdevice: waiting for tap10 to become free. Usage count = 2
unregister_netdevice: waiting for tap10 to become free. Usage count = 2

Finally made a patch that follows what Linux 2.6 does, which consists of
having "netlink" and "no-netlink" tables.

Diagnosed-by: Sylvain Rochet <gradator@gradator.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>

3 files changed, 22 insertions, 4 deletions

diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 7ee3810cb68857..f05cc2169fc44d 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -192,6 +192,7 @@ struct neigh_table
 };
 
 extern void			neigh_table_init(struct neigh_table *tbl);
+extern void			neigh_table_init_no_netlink(struct neigh_table *tbl);
 extern int			neigh_table_clear(struct neigh_table *tbl);
 extern struct neighbour *	neigh_lookup(struct neigh_table *tbl,
 					     const void *pkey,
diff --git a/net/atm/clip.c b/net/atm/clip.c
index 5905d30034d38c..977649410753a4 100644
--- a/net/atm/clip.c
+++ b/net/atm/clip.c
@@ -752,7 +752,7 @@ static struct atm_clip_ops __atm_clip_ops = {
 
 static int __init atm_clip_init(void)
 {
-	neigh_table_init(&clip_tbl);
+	neigh_table_init_no_netlink(&clip_tbl);
 
 	clip_tbl_hook = &clip_tbl;
 	atm_clip_ops_set(&__atm_clip_ops);
diff --git a/net/core/neighbour.c b/net/core/neighbour.c
index 7630a627a2904a..27cf5b491f4538 100644
--- a/net/core/neighbour.c
+++ b/net/core/neighbour.c
@@ -1248,7 +1248,7 @@ void neigh_parms_release(struct neigh_table *tbl, struct neigh_parms *parms)
 }
 
 
-void neigh_table_init(struct neigh_table *tbl)
+void neigh_table_init_no_netlink(struct neigh_table *tbl)
 {
 	unsigned long now = jiffies;
 	unsigned long phsize;
@@ -1302,10 +1302,27 @@ void neigh_table_init(struct neigh_table *tbl)
 
 	tbl->last_flush = now;
 	tbl->last_rand = now + tbl->parms.reachable_time*20;
+}
+
+void neigh_table_init(struct neigh_table *tbl)
+{
+	struct neigh_table *tmp;
+
+	neigh_table_init_no_netlink(tbl);
 	write_lock(&neigh_tbl_lock);
-	tbl->next = neigh_tables;
-	neigh_tables = tbl;
+	for (tmp = neigh_tables; tmp; tmp = tmp->next) {
+		if (tmp->family == tbl->family)
+		break;
+	}
+	tbl->next       = neigh_tables;
+	neigh_tables    = tbl;
 	write_unlock(&neigh_tbl_lock);
+
+	if (unlikely(tmp)) {
+		printk(KERN_ERR "NEIGH: Registering multiple tables for "
+			"family %d\n", tbl->family);
+		dump_stack();
+	}
 }
 
 int neigh_table_clear(struct neigh_table *tbl)