2.5.64-mm8 breaks MASQ

2.5.64-mm8 breaks MASQ

[Tom Sightler]

I have been attempting to test the -mm kernels.  I was having problems
with the anticipatory scheduler up causing the machine to hang during
loading of the USB driver.  The recent fixes that went into -mm8 seem to
have corrected this problem, unfortunately I'm now hitting another
issue.

It seems that -mm8 breaks MASQ support in iptables.  Actually I can't
get any MASQ/NAT to work at all.  The same exact config works fine with
vanilla 2.5.64 and 2.5.64-ac4.

Backing out the brlock patches returns everything to normal operation so
there's something happening with those.  I'll try to look at them
individually if I get a chance but I know practically nothing about that
code so somebody will probably spot a problem quicker.

Later,
Tom

Re: 2.5.64-mm8 breaks MASQ

[Shawn]

This actually broke in -mm7, but I don't know what causes it.

I have to admit, I haven't even looked at the patch to see what changed.
Oh well, I suspect good ol' 65-mm1 will fix things up. If so, my TiVo
could stop holding it's breath. ;)

Anyone else seeing this?

On Mon, 2003-03-17 at 11:29, Tom Sightler wrote:
> I have been attempting to test the -mm kernels.  I was having problems
> with the anticipatory scheduler up causing the machine to hang during
> loading of the USB driver.  The recent fixes that went into -mm8 seem to
> have corrected this problem, unfortunately I'm now hitting another
> issue.
> 
> It seems that -mm8 breaks MASQ support in iptables.  Actually I can't
> get any MASQ/NAT to work at all.  The same exact config works fine with
> vanilla 2.5.64 and 2.5.64-ac4.
> 
> Backing out the brlock patches returns everything to normal operation so
> there's something happening with those.  I'll try to look at them
> individually if I get a chance but I know practically nothing about that
> code so somebody will probably spot a problem quicker.
> 
> Later,
> Tom
> 
> 
> -
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Re: 2.5.64-mm8 breaks MASQ

[Andrew Morton]

Shawn <core@enodev.com> wrote:
>
> This actually broke in -mm7, but I don't know what causes it.
> 
> I have to admit, I haven't even looked at the patch to see what changed.
> Oh well, I suspect good ol' 65-mm1 will fix things up. If so, my TiVo
> could stop holding it's breath. ;)
> 
> Anyone else seeing this?

Stephen is looking into it.  Please send him your iptables
configuration info. 

Re: 2.5.64-mm8 breaks MASQ

[Tom Sightler]

On Tue, 2003-03-18 at 05:55, Andrew Morton wrote:
> Shawn <core@enodev.com> wrote:
> >
> > This actually broke in -mm7, but I don't know what causes it.
> > 
> > I have to admit, I haven't even looked at the patch to see what changed.
> > Oh well, I suspect good ol' 65-mm1 will fix things up. If so, my TiVo
> > could stop holding it's breath. ;)
> > 
> > Anyone else seeing this?
> 
> Stephen is looking into it.  Please send him your iptables
> configuration info. 

My iptables config is just a simple one-liner as follows:

iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE

eth1 is an Aironet PCCARD wireless adapter connected to my corporate
network

eth0 is 3c556 (3c59x driver) Mini-PCI 10/100 with various systems
connected to it.

I also regularly NAT my VMware virtual machine (normally configured for
host only networking) which sits on vmnet1.

I've tried several variations of the iptables option, such as:

iptables -t nat -A POSTROUTING -s 192.168.4.1/24 -j MASQUERADE

iptables -t nat -A POSTROUTING -o ! eth0 -j MASQUERADE

All of these variations work without the brlock patches backed out. 
Actually, I haven't been able to get any MASQ/NAT options to work with
the brlock removal patches.

Let me know if you need more info.

Later,
Tom

Re: 2.5.64-mm8 breaks MASQ

[jjs]

Shawn wrote:

>This actually broke in -mm7, but I don't know what causes it.
>
>I have to admit, I haven't even looked at the patch to see what changed.
>Oh well, I suspect good ol' 65-mm1 will fix things up. If so, my TiVo
>could stop holding it's breath. ;)
>
>Anyone else seeing this?
>  
>

I'm seeing a weird problem with later 2.5.64-mm,
probably related - when the problem hits, I have
to "make things work" quickly, so there is not a
lot of time to analyze (booting back into the 
latest -ac kernel makes everyone happy)

The box in question, running RH 8.0, is set up
as a dhcp server, iptables firewall, and squid
proxy for a small network of 6 systems (3 linux,
3 ms windows)

After booting up, it all works initially, but after
some time, the windows/dhcp users complain
that they can't get out to the internet anymore.

Very odd, since my internet access via a linux
workstation seems fine - I could just say "wow,
it sure sucks to be a win doze user" and move
on, but I can't quite get away with that...

So the problem is rather interesting, and multi-
faceted - I'm not sure at this point whether the
problems follow the ms windows users, or the
dhcp users, or those not plugged into the same
switch that's in my office... but I'm willing to 
try possible fixes through a brute force trial
and error approach.

Joe

Re: 2.5.64-mm8 breaks MASQ

[Stephen Hemminger]

Fixed (at least for me), the problem with netfilter/iptables.

Here is a replacement for the brlock-removal-1 patch.  The changes to
fix the bug are all in the netfilter.c part.

---------------------------------------------------------------------
diff -urN -X dontdiff linux-2.5/include/linux/netdevice.h linux-2.5-nobrlock/include/linux/netdevice.h
--- linux-2.5/include/linux/netdevice.h	2003-03-11 09:08:00.000000000 -0800
+++ linux-2.5-nobrlock/include/linux/netdevice.h	2003-03-12 14:52:22.000000000 -0800
@@ -452,7 +452,7 @@
 	int			(*func) (struct sk_buff *, struct net_device *,
 					 struct packet_type *);
 	void			*data;	/* Private to the packet type		*/
-	struct packet_type	*next;
+	struct list_head	packet_list;
 };
 
 
diff -urN -X dontdiff linux-2.5/net/core/dev.c linux-2.5-nobrlock/net/core/dev.c
--- linux-2.5/net/core/dev.c	2003-03-11 09:08:01.000000000 -0800
+++ linux-2.5-nobrlock/net/core/dev.c	2003-03-17 10:50:43.000000000 -0800
@@ -90,7 +90,6 @@
 #include <linux/etherdevice.h>
 #include <linux/notifier.h>
 #include <linux/skbuff.h>
-#include <linux/brlock.h>
 #include <net/sock.h>
 #include <linux/rtnetlink.h>
 #include <linux/proc_fs.h>
@@ -117,6 +116,7 @@
 
 #include <asm/current.h>
 
+
 /* This define, if set, will randomly drop a packet when congestion
  * is more than moderate.  It helps fairness in the multi-interface
  * case when one of them is a hog, but it kills performance for the
@@ -170,8 +170,11 @@
  *		86DD	IPv6
  */
 
-static struct packet_type *ptype_base[16];	/* 16 way hashed list */
-static struct packet_type *ptype_all;		/* Taps */
+static spinlock_t ptype_lock = SPIN_LOCK_UNLOCKED;
+static struct list_head ptype_base[16];	/* 16 way hashed list */
+static struct list_head ptype_all;	/* Taps */
+
+static spinlock_t master_lock = SPIN_LOCK_UNLOCKED;
 
 #ifdef OFFLINE_SAMPLE
 static void sample_queue(unsigned long dummy);
@@ -203,7 +206,6 @@
 
 static struct subsystem net_subsys;
 
-
 /*******************************************************************************
 
 		Protocol management and registration routines
@@ -245,8 +247,7 @@
 {
 	int hash;
 
-	br_write_lock_bh(BR_NETPROTO_LOCK);
-
+	spin_lock_bh(&ptype_lock);
 #ifdef CONFIG_NET_FASTROUTE
 	/* Hack to detect packet socket */
 	if (pt->data && (long)(pt->data) != 1) {
@@ -256,14 +257,12 @@
 #endif
 	if (pt->type == htons(ETH_P_ALL)) {
 		netdev_nit++;
-		pt->next  = ptype_all;
-		ptype_all = pt;
+		list_add_rcu(&pt->packet_list, &ptype_all);
 	} else {
 		hash = ntohs(pt->type) & 15;
-		pt->next = ptype_base[hash];
-		ptype_base[hash] = pt;
+		list_add_rcu(&pt->packet_list, &ptype_base[hash]);
 	}
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
+	spin_unlock_bh(&ptype_lock);
 }
 
 extern void linkwatch_run_queue(void);
@@ -279,29 +278,30 @@
  */
 void dev_remove_pack(struct packet_type *pt)
 {
-	struct packet_type **pt1;
-
-	br_write_lock_bh(BR_NETPROTO_LOCK);
+	struct list_head *head, *pelem;
 
-	if (pt->type == htons(ETH_P_ALL)) {
-		netdev_nit--;
-		pt1 = &ptype_all;
-	} else
-		pt1 = &ptype_base[ntohs(pt->type) & 15];
-
-	for (; *pt1; pt1 = &((*pt1)->next)) {
-		if (pt == *pt1) {
-			*pt1 = pt->next;
+	if (pt->type == htons(ETH_P_ALL))
+		head = &ptype_all;
+	else 
+		head =  &ptype_base[ntohs(pt->type) & 15];
+	
+	spin_lock_bh(&ptype_lock);
+	list_for_each(pelem, head) {
+		if (list_entry(pelem, struct packet_type, packet_list) == pt) {
+			list_del(pelem);
 #ifdef CONFIG_NET_FASTROUTE
 			if (pt->data)
 				netdev_fastroute_obstacles--;
 #endif
+			if (pt->type == htons(ETH_P_ALL)) 
+				netdev_nit--;
 			goto out;
 		}
 	}
 	printk(KERN_WARNING "dev_remove_pack: %p not found.\n", pt);
-out:
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
+
+ out:
+	spin_unlock_bh(&ptype_lock);
 }
 
 /******************************************************************************
@@ -896,11 +896,13 @@
 
 void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev)
 {
-	struct packet_type *ptype;
+	struct list_head *plist;
 	do_gettimeofday(&skb->stamp);
 
-	br_read_lock(BR_NETPROTO_LOCK);
-	for (ptype = ptype_all; ptype; ptype = ptype->next) {
+	rcu_read_lock();
+	list_for_each_rcu(plist, &ptype_all) {
+		struct packet_type *ptype
+			= list_entry(plist, struct packet_type, packet_list);
 		/* Never send packets back to the socket
 		 * they originated from - MvS (miquels@drinkel.ow.org)
 		 */
@@ -930,7 +932,7 @@
 			ptype->func(skb2, skb->dev, ptype);
 		}
 	}
-	br_read_unlock(BR_NETPROTO_LOCK);
+	rcu_read_unlock();
 }
 
 /* Calculate csum in the case, when packet is misrouted.
@@ -1423,6 +1425,7 @@
 
 int netif_receive_skb(struct sk_buff *skb)
 {
+	struct list_head *pcur;
 	struct packet_type *ptype, *pt_prev;
 	int ret = NET_RX_DROP;
 	unsigned short type = skb->protocol;
@@ -1443,8 +1446,10 @@
 
 	skb->h.raw = skb->nh.raw = skb->data;
 
+	rcu_read_lock();
 	pt_prev = NULL;
-	for (ptype = ptype_all; ptype; ptype = ptype->next) {
+	list_for_each_rcu(pcur, &ptype_all) {
+		ptype = list_entry(pcur, struct packet_type, packet_list);
 		if (!ptype->dev || ptype->dev == skb->dev) {
 			if (pt_prev) {
 				if (!pt_prev->data) {
@@ -1466,17 +1471,23 @@
 #endif /* CONFIG_NET_DIVERT */
 
 #if defined(CONFIG_BRIDGE) || defined(CONFIG_BRIDGE_MODULE)
-	if (skb->dev->br_port && br_handle_frame_hook) {
-		int ret;
+	if (skb->dev->br_port) {
+		int (*curhook)(struct sk_buff *) = br_handle_frame_hook;
 
-		ret = handle_bridge(skb, pt_prev);
-		if (br_handle_frame_hook(skb) == 0)
-			return ret;
-		pt_prev = NULL;
+		barrier();	/* prevent compiler RCU problems */
+		if (curhook) {
+			int ret;
+			ret = handle_bridge(skb, pt_prev);
+			if (curhook(skb) == 0)
+				return ret;
+			pt_prev = NULL;
+		}
 	}
 #endif
 
-	for (ptype = ptype_base[ntohs(type) & 15]; ptype; ptype = ptype->next) {
+	list_for_each_rcu(pcur, &ptype_base[ntohs(type) & 15]) {
+		ptype = list_entry(pcur, struct packet_type, packet_list);
+
 		if (ptype->type == type &&
 		    (!ptype->dev || ptype->dev == skb->dev)) {
 			if (pt_prev) {
@@ -1506,6 +1517,7 @@
 		 */
 		ret = NET_RX_DROP;
 	}
+	rcu_read_unlock();
 
 	return ret;
 }
@@ -1580,7 +1592,7 @@
 	unsigned long start_time = jiffies;
 	int budget = netdev_max_backlog;
 
-	br_read_lock(BR_NETPROTO_LOCK);
+	preempt_disable();
 	local_irq_disable();
 
 	while (!list_empty(&queue->poll_list)) {
@@ -1609,7 +1621,7 @@
 	}
 out:
 	local_irq_enable();
-	br_read_unlock(BR_NETPROTO_LOCK);
+	preempt_enable();
 	return;
 
 softnet_break:
@@ -1925,7 +1937,6 @@
 #define dev_proc_init() 0
 #endif	/* CONFIG_PROC_FS */
 
-
 /**
  *	netdev_set_master	-	set up master/slave pair
  *	@slave: slave device
@@ -1943,18 +1954,23 @@
 
 	ASSERT_RTNL();
 
+	spin_lock_bh(&master_lock);
 	if (master) {
-		if (old)
+		if (old) {
+			spin_unlock_bh(&master_lock);
 			return -EBUSY;
+		}
 		dev_hold(master);
 	}
 
-	br_write_lock_bh(BR_NETPROTO_LOCK);
 	slave->master = master;
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
+	spin_unlock_bh(&master_lock);
 
-	if (old)
+	if (old) {
+		/* wait for all BH */
+		synchronize_kernel();
 		dev_put(old);
+	}
 
 	if (master)
 		slave->flags |= IFF_SLAVE;
@@ -1962,6 +1978,7 @@
 		slave->flags &= ~IFF_SLAVE;
 
 	rtmsg_ifinfo(RTM_NEWLINK, slave, IFF_SLAVE);
+
 	return 0;
 }
 
@@ -2623,6 +2640,7 @@
 	struct net_device *d, **dp;
 
 	BUG_ON(dev_boot_phase);
+	might_sleep();
 
 	/* If device is running, close it first. */
 	if (dev->flags & IFF_UP)
@@ -2646,10 +2664,8 @@
 		return -ENODEV;
 	}
 
-	/* Synchronize to net_rx_action. */
-	br_write_lock_bh(BR_NETPROTO_LOCK);
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
-
+	/* wait for RCU */
+	synchronize_kernel();
 
 #ifdef CONFIG_NET_FASTROUTE
 	dev_clear_fastroute(dev);
@@ -2755,7 +2771,6 @@
 	return 0;
 }
 
-
 /*
  *	Initialize the DEV module. At boot time this walks the device list and
  *	unhooks any devices that fail to initialise (normally hardware not
@@ -2786,6 +2801,11 @@
 	if (dev_proc_init())
 		goto out;
 
+	/* Initialize packet type chains */
+	INIT_LIST_HEAD(&ptype_all);
+	for (i = 0; i < ARRAY_SIZE(ptype_base); i++) 
+	        INIT_LIST_HEAD(&ptype_base[i]);
+
 	subsystem_register(&net_subsys);
 
 #ifdef CONFIG_NET_DIVERT
diff -urN -X dontdiff linux-2.5/net/core/netfilter.c linux-2.5-nobrlock/net/core/netfilter.c
--- linux-2.5/net/core/netfilter.c	2003-03-11 09:08:01.000000000 -0800
+++ linux-2.5-nobrlock/net/core/netfilter.c	2003-03-18 14:10:14.000000000 -0800
@@ -19,7 +19,6 @@
 #include <linux/interrupt.h>
 #include <linux/if.h>
 #include <linux/netdevice.h>
-#include <linux/brlock.h>
 #include <linux/inetdevice.h>
 #include <net/sock.h>
 #include <net/route.h>
@@ -44,8 +43,12 @@
    sleep. */
 static DECLARE_MUTEX(nf_sockopt_mutex);
 
+/*
+ * nf_hooks are protected by using read-copy-update
+ */
 struct list_head nf_hooks[NPROTO][NF_MAX_HOOKS];
 static LIST_HEAD(nf_sockopts);
+static spinlock_t nf_hook_lock = SPIN_LOCK_UNLOCKED;
 
 /* 
  * A queue handler may be registered for each protocol.  Each is protected by
@@ -56,28 +59,34 @@
 	nf_queue_outfn_t outfn;
 	void *data;
 } queue_handler[NPROTO];
+static rwlock_t queue_handler_lock = RW_LOCK_UNLOCKED;
 
 int nf_register_hook(struct nf_hook_ops *reg)
 {
 	struct list_head *i;
 
-	br_write_lock_bh(BR_NETPROTO_LOCK);
+	spin_lock_bh(&nf_hook_lock);
 	for (i = nf_hooks[reg->pf][reg->hooknum].next; 
 	     i != &nf_hooks[reg->pf][reg->hooknum]; 
 	     i = i->next) {
 		if (reg->priority < ((struct nf_hook_ops *)i)->priority)
 			break;
 	}
-	list_add(&reg->list, i->prev);
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
+	list_add_rcu(&reg->list, i->prev);
+	spin_unlock_bh(&nf_hook_lock);
+
+	synchronize_kernel();
 	return 0;
 }
 
 void nf_unregister_hook(struct nf_hook_ops *reg)
 {
-	br_write_lock_bh(BR_NETPROTO_LOCK);
-	list_del(&reg->list);
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
+	spin_lock_bh(&nf_hook_lock);
+	list_del_rcu(&reg->list);
+	spin_unlock_bh(&nf_hook_lock);
+
+	/* wait for all receivers that may still be using hook */
+	synchronize_kernel();
 }
 
 /* Do exclusive ranges overlap? */
@@ -335,72 +344,30 @@
 	return nf_sockopt(sk, pf, val, opt, len, 1);
 }
 
-static unsigned int nf_iterate(struct list_head *head,
-			       struct sk_buff **skb,
-			       int hook,
-			       const struct net_device *indev,
-			       const struct net_device *outdev,
-			       struct list_head **i,
-			       int (*okfn)(struct sk_buff *),
-			       int hook_thresh)
-{
-	for (*i = (*i)->next; *i != head; *i = (*i)->next) {
-		struct nf_hook_ops *elem = (struct nf_hook_ops *)*i;
-
-		if (hook_thresh > elem->priority)
-			continue;
-
-		switch (elem->hook(hook, skb, indev, outdev, okfn)) {
-		case NF_QUEUE:
-			return NF_QUEUE;
-
-		case NF_STOLEN:
-			return NF_STOLEN;
-
-		case NF_DROP:
-			return NF_DROP;
-
-		case NF_REPEAT:
-			*i = (*i)->prev;
-			break;
-
-#ifdef CONFIG_NETFILTER_DEBUG
-		case NF_ACCEPT:
-			break;
-
-		default:
-			NFDEBUG("Evil return from %p(%u).\n", 
-				elem->hook, hook);
-#endif
-		}
-	}
-	return NF_ACCEPT;
-}
-
 int nf_register_queue_handler(int pf, nf_queue_outfn_t outfn, void *data)
 {      
 	int ret;
 
-	br_write_lock_bh(BR_NETPROTO_LOCK);
+	write_lock_bh(&queue_handler_lock);
 	if (queue_handler[pf].outfn)
 		ret = -EBUSY;
 	else {
-		queue_handler[pf].outfn = outfn;
 		queue_handler[pf].data = data;
+		queue_handler[pf].outfn = outfn;
 		ret = 0;
 	}
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
-
+	write_unlock_bh(&queue_handler_lock);
 	return ret;
 }
 
 /* The caller must flush their queue before this */
 int nf_unregister_queue_handler(int pf)
 {
-	br_write_lock_bh(BR_NETPROTO_LOCK);
+	write_lock_bh(&queue_handler_lock);
 	queue_handler[pf].outfn = NULL;
 	queue_handler[pf].data = NULL;
-	br_write_unlock_bh(BR_NETPROTO_LOCK);
+	write_unlock_bh(&queue_handler_lock);
+
 	return 0;
 }
 
@@ -422,9 +389,10 @@
 	struct net_device *physoutdev = NULL;
 #endif
 
+	read_lock(&queue_handler_lock);
 	if (!queue_handler[pf].outfn) {
 		kfree_skb(skb);
-		return;
+		goto out;
 	}
 
 	info = kmalloc(sizeof(*info), GFP_ATOMIC);
@@ -433,7 +401,7 @@
 			printk(KERN_ERR "OOM queueing packet %p\n",
 			       skb);
 		kfree_skb(skb);
-		return;
+		goto out;
 	}
 
 	*info = (struct nf_info) { 
@@ -463,8 +431,9 @@
 #endif
 		kfree(info);
 		kfree_skb(skb);
-		return;
 	}
+ out:
+	read_unlock(&queue_handler_lock);
 }
 
 int nf_hook_slow(int pf, unsigned int hook, struct sk_buff *skb,
@@ -474,6 +443,7 @@
 		 int hook_thresh)
 {
 	struct list_head *elem;
+	const struct nf_hook_ops *ops = NULL;
 	unsigned int verdict;
 	int ret = 0;
 
@@ -490,9 +460,7 @@
 		}
 	}
 
-	/* We may already have this, but read-locks nest anyway */
-	br_read_lock_bh(BR_NETPROTO_LOCK);
-
+	rcu_read_lock();
 #ifdef CONFIG_NETFILTER_DEBUG
 	if (skb->nf_debug & (1 << hook)) {
 		printk("nf_hook: hook %i already set.\n", hook);
@@ -501,15 +469,26 @@
 	skb->nf_debug |= (1 << hook);
 #endif
 
-	elem = &nf_hooks[pf][hook];
-	verdict = nf_iterate(&nf_hooks[pf][hook], &skb, hook, indev,
-			     outdev, &elem, okfn, hook_thresh);
-	if (verdict == NF_QUEUE) {
-		NFDEBUG("nf_hook: Verdict = QUEUE.\n");
-		nf_queue(skb, elem, pf, hook, indev, outdev, okfn);
+	verdict = NF_ACCEPT;
+	list_for_each_rcu(elem, &nf_hooks[pf][hook]) {
+		ops = list_entry(elem, const struct nf_hook_ops, list);
+
+		if (hook_thresh > ops->priority)
+			continue;
+
+		verdict = ops->hook(hook, &skb, indev, outdev, okfn);
+		if (verdict != NF_ACCEPT)
+			goto out;
+
 	}
 
+ out:;
 	switch (verdict) {
+	case NF_QUEUE:
+		NFDEBUG("nf_hook: Verdict = QUEUE.\n");
+		nf_queue(skb, elem, pf, hook, indev, outdev, okfn);
+		break;
+
 	case NF_ACCEPT:
 		ret = okfn(skb);
 		break;
@@ -518,9 +497,14 @@
 		kfree_skb(skb);
 		ret = -EPERM;
 		break;
+#ifdef CONFIG_NETFILTER_DEBUG
+	default:
+		NFDEBUG("Evil return %d from %p(%u).\n", verdict,
+			ops->hook, hook);
+#endif
 	}
 
-	br_read_unlock_bh(BR_NETPROTO_LOCK);
+	rcu_read_unlock();
 	return ret;
 }
 
@@ -528,48 +512,61 @@
 		 unsigned int verdict)
 {
 	struct list_head *elem = &info->elem->list;
-	struct list_head *i;
+	const struct list_head *head = &nf_hooks[info->pf][info->hook];
+	const struct list_head *i;
 
-	/* We don't have BR_NETPROTO_LOCK here */
-	br_read_lock_bh(BR_NETPROTO_LOCK);
-	for (i = nf_hooks[info->pf][info->hook].next; i != elem; i = i->next) {
-		if (i == &nf_hooks[info->pf][info->hook]) {
-			/* The module which sent it to userspace is gone. */
-			NFDEBUG("%s: module disappeared, dropping packet.\n",
-			         __FUNCTION__);
-			verdict = NF_DROP;
-			break;
+	rcu_read_lock();
+	list_for_each_rcu(i, head) {
+		/* traverse loop until we find elem */
+		if (elem) {
+			if (i != elem) 
+				continue;
+
+			elem = NULL;
+			/* Continue and process next element */
+			if (verdict == NF_ACCEPT) 
+				continue;
+
+			/* Process this element again */
+			if (verdict == NF_REPEAT) 
+				verdict = NF_ACCEPT;
 		}
-	}
 
-	/* Continue traversal iff userspace said ok... */
-	if (verdict == NF_REPEAT) {
-		elem = elem->prev;
-		verdict = NF_ACCEPT;
-	}
+		if (verdict == NF_ACCEPT) {
+			const struct nf_hook_ops *ops
+				= list_entry(elem, typeof(*ops), list);
 
-	if (verdict == NF_ACCEPT) {
-		verdict = nf_iterate(&nf_hooks[info->pf][info->hook],
-				     &skb, info->hook, 
-				     info->indev, info->outdev, &elem,
-				     info->okfn, INT_MIN);
-	}
+			verdict = ops->hook(info->hook, &skb, 
+					    info->indev, info->outdev, 
+					    info->okfn);
+		}
 
-	switch (verdict) {
-	case NF_ACCEPT:
-		info->okfn(skb);
-		break;
+		switch (verdict) {
+		case NF_ACCEPT:
+			info->okfn(skb);
+			break;
 
-	case NF_QUEUE:
-		nf_queue(skb, elem, info->pf, info->hook, 
-			 info->indev, info->outdev, info->okfn);
+		case NF_QUEUE:
+			nf_queue(skb, elem, info->pf, info->hook, 
+				 info->indev, info->outdev, info->okfn);
+			break;
+
+		case NF_DROP:
+			kfree_skb(skb);
+			break;
+		}
 		break;
+	}
 
-	case NF_DROP:
+	if (elem) {
+		/* The module which sent it to userspace is gone. */
+		NFDEBUG("%s: module disappeared, dropping packet.\n",
+			__FUNCTION__);
 		kfree_skb(skb);
-		break;
 	}
-	br_read_unlock_bh(BR_NETPROTO_LOCK);
+
+
+	rcu_read_unlock();
 
 	/* Release those devices we held, or Alexey will kill me. */
 	if (info->indev) dev_put(info->indev);



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