Re: [PATCH nf-next 3/3] netfilter: replace list_head with single linked list

On Sat, Jul 09, 2016 at 01:30:38AM +0200, Florian Westphal wrote:

Aaron Conole [off-list ref] wrote:

quoted

--- a/net/netfilter/core.c
+++ b/net/netfilter/core

[..]

quoted

+#define nf_entry_dereference(e) \
+	rcu_dereference_protected(e, lockdep_is_held(&nf_hook_mutex))
 
-static struct list_head *nf_find_hook_list(struct net *net,
-					   const struct nf_hook_ops *reg)
+static struct nf_hook_entry *nf_find_hook_list(struct net *net,
+					       const struct nf_hook_ops *reg)
 {
-	struct list_head *hook_list = NULL;
+	struct nf_hook_entry *hook_list = NULL;
 
 	if (reg->pf != NFPROTO_NETDEV)
-		hook_list = &net->nf.hooks[reg->pf][reg->hooknum];
+		hook_list = rcu_dereference(net->nf.hooks[reg->pf]
+					    [reg->hooknum]);
 	else if (reg->hooknum == NF_NETDEV_INGRESS) {
 #ifdef CONFIG_NETFILTER_INGRESS
 		if (reg->dev && dev_net(reg->dev) == net)
-			hook_list = &reg->dev->nf_hooks_ingress;
+			hook_list =
+				rcu_dereference(reg->dev->nf_hooks_ingress);

Both of these should use nf_entry_dereference() to avoid the lockdep
splat reported by kbuild robot:

net/netfilter/core.c:75 suspicious rcu_dereference_check() usage!
2 locks held by swapper/1:
#0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff81c2e567>] rtnl_lock+0x17/0x20
#1:  (nf_hook_mutex){+.+...}, at: [<ffffffff81c58fcb>] nf_register_net_hook+0xcb/0x240

Aaron, please, send a v2.

I have a patchset that changes the footprint of the hook function as
it was discussed during the last Netfilter Workshop that clashes with
this.

Thanks!