net: sched: act_skbmod: remove dependency on rtnl lock

Move read of skbmod_p rcu pointer to be protected by tcf spinlock. Use tcf
spinlock to protect private skbmod data from concurrent modification during
dump.
Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/act_skbmod.c

@@ -156,7 +156,6 @@ static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
 
 	d = to_skbmod(*a);
 
-	ASSERT_RTNL();
 	p = kzalloc(sizeof(struct tcf_skbmod_params), GFP_KERNEL);
 	if (unlikely(!p)) {
 		tcf_idr_release(*a, bind);
@@ -166,10 +165,10 @@ static int tcf_skbmod_init(struct net *net, struct nlattr *nla,
 	p->flags = lflags;
 	d->tcf_action = parm->action;
 
-	p_old = rtnl_dereference(d->skbmod_p);
-
 	if (ovr)
 		spin_lock_bh(&d->tcf_lock);
+	/* Protected by tcf_lock if overwriting existing action. */
+	p_old = rcu_dereference_protected(d->skbmod_p, 1);
 
 	if (lflags & SKBMOD_F_DMAC)
 		ether_addr_copy(p->eth_dst, daddr);
@@ -205,15 +204,18 @@ static int tcf_skbmod_dump(struct sk_buff *skb, struct tc_action *a,
 {
 	struct tcf_skbmod *d = to_skbmod(a);
 	unsigned char *b = skb_tail_pointer(skb);
-	struct tcf_skbmod_params  *p = rtnl_dereference(d->skbmod_p);
+	struct tcf_skbmod_params  *p;
 	struct tc_skbmod opt = {
 		.index   = d->tcf_index,
 		.refcnt  = refcount_read(&d->tcf_refcnt) - ref,
 		.bindcnt = atomic_read(&d->tcf_bindcnt) - bind,
-		.action  = d->tcf_action,
 	};
 	struct tcf_t t;
 
+	spin_lock_bh(&d->tcf_lock);
+	opt.action = d->tcf_action;
+	p = rcu_dereference_protected(d->skbmod_p,
+				      lockdep_is_held(&d->tcf_lock));
 	opt.flags  = p->flags;
 	if (nla_put(skb, TCA_SKBMOD_PARMS, sizeof(opt), &opt))
 		goto nla_put_failure;
@@ -231,8 +233,10 @@ static int tcf_skbmod_dump(struct sk_buff *skb, struct tc_action *a,
 	if (nla_put_64bit(skb, TCA_SKBMOD_TM, sizeof(t), &t, TCA_SKBMOD_PAD))
 		goto nla_put_failure;
 
+	spin_unlock_bh(&d->tcf_lock);
 	return skb->len;
 nla_put_failure:
+	spin_unlock_bh(&d->tcf_lock);
 	nlmsg_trim(skb, b);
 	return -1;
 }